Midterm 1 Notes - Merged - PSYC 304B - Brain and Behaviour - Lecture 1 - 2024

PSYC 304B: Brain and Behaviour September 12, 2024 Lecture 1: ‘Seeing’ Neurons Objectives 1. Appreciate that neurons and circuits are the foundational units of brain function. 2. Be able to label and differentiate between different types of neurons. 3. Be...

PSYC 304B: Brain and Behaviour September 12, 2024 Lecture 1: ‘Seeing’ Neurons Objectives 1. Appreciate that neurons and circuits are the foundational units of brain function. 2. Be able to label and differentiate between different types of neurons. 3. Be able to evaluate methods for identifying neurons as anatomical building blocks, including Golgi, dye injection, genetically encoded fluorescent proteins, immunohistochemistry, electron microscopy and brain clearing 4. Understand research applications for different visualization techniques. Key Milestones in Neuroscience - Cell theory – 1830’s o Theodor Schwann and Matthias Jakob Schleiden o Idea that all living organisms are made up of cells - Reticular Theory – 1873 o Camillo Golgi o Developed the silver stain/Golgi stain technique to visualize neurons o Idea that nervous system is a continuous network - Neuron Doctrine – 1889 o Santiago Ramón Y Cajal o Neurons are independent units ▪ Structurally and functionally distinct o Information is transmitted via synapses (gaps) - Electron Microscopy – 1950’s o Confirmed the neuron doctrine Neuron Anatomy Types of Neurons Region and Functions - Shape of neuron is related to its specific function o More dendrites = integrates more information o Less dendrites = more specialized Challenges of Visualizing Neurons and Circuits - Connectome: the wiring/synaptic connectivity of all neurons o Allows us to infer the function of a neural circuit o Prediction of the flow of information o Understanding dysfunction + guide potential treatments - Visualizing a single neuron is simple, but mapping an entire circuit or connectome is not o There are so many neurons in the brain! o Mapping all of them at once → information overload Methods of Visualization Method 1: The Golgi Stain - Chemical process that causes silver impregnation in neurons - Small % of neurons labelled o Unknown why some are labelled and not others - Can be used on dead tissue, including humans - Tried and true technique; relatively easy - Reveals changes in synaptic density o Result of synaptic pruning during early development o Excessive pruning → schizophrenia (can be seen on Golgi stain with fewer dendritic spines) Method 2: Dye Filling Neurons - Dye injection o Dye spreads throughout the entire cell via diffusion → allows us to see full structure o Difficult to pinpoint neuron + inject dye without damaging it - Can be done on live or dead tissue - Useful for studying specific neurons - Ex. Dye filling purkinje neurons o Large complex neurons critical for motor control o Studied in detail using dye injection to map their dendritic structure and connections Method 3: Immunohistochemistry - Targets/identifies any specific protein (antigen) – biomarker localization o Uses antibodies to locate specific proteins (biomarkers) o Helps map out protein presence and function in neurons - Combines multiple antibodies o Multiple antibodies allow visualization of different proteins simultaneously o Different colours can be used for multiple proteins in one tissue sample. - Dead tissue, can be used on human tissue - Has been used to show that one of the first pathological signs of Alzheimer’s is a loss of synaptic proteins - Reasonably cheap and feasible - Examples: Method 4: Genetically-encoded fluorescent proteins - All cells share same DNA, but differential transcription causes different genes to be expressed in different cells → distinct neuron types, tissues, regions, etc. - Certain promoters are only active in specific cell types  o Therefore, by artificially expressing genes under the control of a cell-specific promoter, you can get cell-specific gene expression - Green Fluorescent Protein (GFP) o Isolated from jellyfish ▪ Can be mutated to have all colours of the rainbow Can be done to other fluorescent proteins as well - Critical choice – what promoter to use o Promoter determines specificity - Create genetic construct → piece of DNA that contains the fluorescent gene o Transgenic animal lines ▪ Modifying the DNA of an animal so all cells carry GFP gene o Viral transduction ▪ Using a virus to deliver GFP gene into cells - Costly set up, cheap and efficient once you have the transgenic animal or virus - Can label genetically-identified cells o Promoters rely on cells’ gene expression o Can verify successful gene manipulation - Choosing the right promoter: o CAG promoter ▪ Active in all cells o Thy 1 promoter ▪ Active in a fraction of all types of neurons  o L7 promoter ▪ Active in cerebellar Purkinje neurons o Doublecortin promoter ▪ Active in immature neurons o Iba1 promoter ▪ Active in microglia o GFAP promoter ▪ Active in astrocytes Disadvantages of Traditional Visualization Techniques - Brain tissue must be cut to visualize neurons - Anything that is translucent scatters light o Thick brain tissue is challenging ▪ Light gets scattered, reducing resolution and clarity - The solution?... CLARITY Technique – Brain Clearing - This preparation technique involves brain clearing o Lipids, fats, membranes removed so less light is scattered - Light can penetrate deeper, emitted light will be captured without scattering - Antibodies can also penetrate more easily (immunohistochemistry) o Allowing for thicker tissue samples - Allows imaging of FPs in larger blocks of tissue - Can track axons over long distances, identify networks/coarse neuroanatomy - Can only be done on dead tissue Visualizing FPs with Confocal Microscopy - Fluorescent microscope o All light from tissue is reflected to the eye piece - Confocal microscope o Pinhole eliminates out-of-focus light, allowing visualization of a single focal plane o Reconstruct images from different focal planes 2 Photon Microscopes - Must image living tissue to see changes over time o 2 photon microscopes ▪ Image deep into tissue through dura (100s um) Dura – brain’s protective covering Method 5: Electron Microscopy - Can be used with immunohistochemistry, FPS, or on its own - Method: - Best resolution - Expensive! o Microscope itself is expensive, requires employing a technician - Requires stable environment o Needs to be in a vacuum - Time consuming o Took 12+ years to map connectivity of 302 neurons of the C-elgans (worm) NS PSYC 304B: Brain and Behaviour September 19, 2024 Lecture 2: Neurophysiology Objectives 1. Be able to describe how different ions contribute to the resting membrane potential of neurons and glial cells. 2. Explain how the distribution of ions results in a negative charge inside neurons. 3. List the sequence of ion flows that underlies an important neuronal signal called an action potential. 4. Describe how specialized ion channels propagate the action potential from the start of an axon to the tips of its every branch. 5. Contrast the way the action potentials spread down myelinated versus unmyelinated axons. Neurophysiology - Study of electrical and chemical processes in neurons. - Electrochemical signaling o Information flows within a neuron via electrical signals; information passes between neurons through chemical signals. - Two fundamental neuronal signals o Action potentials + synaptic transmission ▪ Dependant on electrical properties of neurons ▪ Determine how information is processed and “decisions” are made The Membrane Potential Electrical Signals: Vocabulary - All living cells have an electrical charge—more negative on the inside than outside the cell o Proteins, which are the bulk of the cell, are negatively charged - Ions: Electrically charged molecules o Anions are negatively charged o Cations are positively charged - Common ions involved in electrical signaling: o Potassium ions (K+) o Sodium ions (Na+) o Chlorine (Cl-) o Calcium (Ca 2+) o Magnesium (Mg 2+) - Diffusion: ions flow from areas of high concentration to low concentration - Electrostatic Pressure: like charges repel, opposite charges attract Lipid Bilayer - Separation of two conducting solutions o Cytoplasm & extracellular fluid - Charged ions o Difference in the relative concentrations o Creates a voltage difference Membrane Potential - Voltage difference across the membrane - Flow of anion/cations = change in membrane potential - Charged particles always travel through the past of least resistance - Vm = Vin – Vout - Measure with a voltmeter o Typically, a cell sits around -65 mV o Negative inside the cell Resting Membrane Potential of Glial Cells - [K+] inside = 400 mM - [K+] outside = 20 mM - Only permeable to K+ at rest - Chemical/concentration gradient o K+ diffuses out of cell o Creates an electrical gradient - Equilibrium potential o Chemical driving force = electrical driving force o Calculated using the Nernst Equation o Concentration forces K+ out, negative Vm pulls K+ in o Result = -75 mV resting membrane potential Resting Membrane Potential of Neurons - Neurons o 3 major ions: K+, Na+, Cl- o Also, slight permeability to Na+ (sodium ions) - Nernst for sodium o Small Na+ conductance depolarizes the cell a little o Sodium equilibrium potential is +55mV → cell is -65mV Na/K ATPase Pump (Sodium-Potassium Pump) - Actively transports 3 Na+ ions out and 2 K+ ions in using ATP (energy) o Against their electrochemical gradients - Maintains the concentration gradients for Na+ and K+ - Result: The inside remains negatively charged compared to the outside, establishing the resting potential. Chloride ions - Concentration o [Cl-] in = 52mM o [Cl-] out = 560 mM - Concentration gradient o Drives Cl- in - Electrical gradient o Pushes Cl- out - Equilibrium potential o -70mV Resting membrane potential is dependent on relative permeabilities - Goldman Equation - At rest PK: PNa : PCl = 1.0 : 0.04 : 0.45 The Action Potential - The starting point of an electrical signal o Hyperpolarized Vm ▪ “Further from 0” Ex. -65 mV o We can think of voltage as force that pushes ions in/out of cell - Action potential regenerates signal so it makes it to the end of the cell Voltage-gated ion channels 1. Resting o VG channel closed o Positively charged extracellular side o Negatively charged cytoplasmic side 2. Activated o Caused by potential change o VG channel open o Activation gate open o Inactivation gate closing (but is a little slow) 3. Inactivated o Channel closed by the activation gate o When inactivated, the cell cannot fire another action potential – Refractory Period  - VG Na Channels o At rest: -70 mV o Activated: -55 mV o Inactivated: +40 mV - VG K+ Channels o The opening and closing of VG K+ channels rapidly bring the vicinity back to a hyperpolarized state o Positive charge inside the cell and high [K+] forces K+ out o Slow closing of VG K+ channels causes hyperpolarization AP conduction down the ion - One way train due to refractory period o Current passively flows in both directions o Only VG channels downstream are at rest and can open o Local depolarization opens those VG Na+ channels o Which opens adjacent VG Na+ channels. Etc, etc… Conducting an electrophysiological experiment - Needs o Healthy cells o Microscope, fine electrodes, noise reduction o Signal acquisition device: amplifier, digitizer, computer software - Consideration of Ohms Law o V = Voltage (volts) o I = Current (amperes)  o R = Resistance (ohms) o G = Conductance (Siemens) ▪ G = 1/R o Insulators – separate electrical conductors, are really good resistors - Experimental set-up: AP – Key Characteristics - Summary o Action potentials are produced by movement of Na+ ions into the cell. o At the peak of an action potential, the concentration gradient pushing Na+ ions into the cell equals the positive charge driving them out. o Membrane shifts briefly from a resting state to an active state and back ▪ Ex. the membrane suddenly and briefly becomes permeable to Na+ ions - Steps o Voltage-gated Na+ channels open in response to depolarization, and Na+ ions enter; more channels open and more Na+ enters; o Continues as membrane potential reaches the Na+ equilibrium potential of +55 mV o As cell interior becomes more positive, voltage-gated K+ channels open o K+ moves out and the resting potential is restored  - Key Points o Action potentials are regenerated along the axon—each adjacent section is depolarized, and a new action potential occurs. o Action potentials travel in one direction because of the refractory state of the membrane after a depolarization. o Action potentials are an all or none process – when threshold is reached an action potential will occur at the same strength every time. Myelinated axons - Saltatory conduction – rapid conduction occurring in myelinated axons - Action potential occurs at nodes of Ranvier o Myelinated portions in between are “skipped over” - Importance of myelin… o Multiple Sclerosis (MS) ▪ Disorder that occurs when body’s immune system produces antibodies that attack myelin, and thus conduction of action potentials ▪ Wide variety of symptoms that affect sensory and/or motor systems, depending on which axons are attacked PSYC 304B: Brain and Behaviour September 26, 2024 Lecture 3: Synaptic Transmission Objectives 1. Be able to list the stages of chemical synaptic transmission 2. Be able to describe the mechanism by which excitatory and inhibitory neurotransmitters function 3. Distinguish between action potentials and post synaptic potentials. 4. Distinguish between temporal and spatial summation 5. Apply basic neurophysiology principles to the knee jerk reflex neural chain 6. Describe the strengths and weaknesses of two visualization techniques for viewings neuronal circuits History of Understanding Synaptic Transmission - Charles Scott Sherrington (1904) o Coined the term ‘synapse’ - Thomas Renton Elliot (1904) o Hypothesized that adrenaline (EPI) is a chemical released at nerve endings to transmit signals to target organs o Applied adrenaline directly to an animal heart and saw the heart beat faster o “Adrenalin might then be the chemical stimulant liberated on each occasion when the impulse arrives at the periphery.” o Discovery was dismissed by his supervisor - Henry Dale (1914/1933) o Discovered neurotransmitter acetylcholine (Ach) ▪ Found that it had a slowing effect on parasympathetic nervous system o Won Nobel Prize - Otto Loewi (1921) o Dreamed of an experiment  1. Stimulate vagus nerve of donor heart 2. Heart rate slows down 3. Remove fluid sample 4. Add fluid to recipient heart 5. Heart rate slows down! o Vagusstoff o Accelerans-stoff - John Eccles (1951) o Eccles, coombs & brock o Depolarized a cell, following cell hyperpolarized instead of depolarized as expected by an electrical signal Visualizing vesicles and receptors with EM (electron microscopy) - Typical CNS synapse o Vesicles, mitochondria, 2 active zones (dark fuzzy bands indicated by arrows = regions of dense synaptic machinery) o Slower, complex, can be excitatory or inhibitory - The neuromuscular junction o Acetylcholine receptors darkly labelled, seen at postsynaptic membrane immediately across from synaptic vesicles o Insane number of vesicles → Muscles need to regenerate signals frequently. o Faster, less adaptable but more synchronous Types of Synapses - Chemical synapses o Injected current causes an action potential in the presynaptic cell, release of neurotransmitters and a change in potential of the postsynaptic cell - Electrical synapses o Transmit signals between neurons o Current enters the post synaptic cell through a gap junction channel Synaptic Transmission Part A: - Vesicles dock near the plasma membrane - Presynaptic terminal depolarization - Arriving AP causes opening of VG Ca2+ channels Part B: - Ca2+ entry triggers vesicle fusion with presynaptic membrane - Neurotransmitter ligands spills into synaptic cleft o Ligands: bind specific receptors Part C: - NT’s bind to post synaptic membrane receptors - Ionotropic receptors have associated ion channels that open when bound o Depending on receptor ▪ EPSP or IPSP Terminology - Post synaptic potential: A brief change from resting potential in the post synaptic cell - Excitatory post synaptic potential (EPSP): When the post synaptic cell becomes depolarized (excited) and therefore more likely to fire an action potential  - Inhibitory post synaptic potential (IPSP): When the post synaptic cell becomes hyperpolarized and therefore less likely to fire action potential - Synaptic delay: delay between the presynaptic AP reaching the axon terminal and creating a post synaptic potential Visualizing vesicles during synaptic transmission Experiment using freeze-fracture electron microscopy: - At rest… o Vesicles docked and ready to be released o Stimulate a depolarization and freeze the tissue - Exo and endocytosis… o 5ms later – can see fusion with the presynaptic membrane (exocytosis) o 10s later – endocytosis of vesicles is visible ▪ Vesicle membranes are recycled to form new vesicles Recording post synaptic potentials - In red – excitatory connection - In blue – inhibitory connection Excitatory Neurotransmitters - Glutamate o Primary excitatory NT in the brain o Binds to AMPA receptors to allow passage of cations ▪ Ex. Na+, K+, etc. - AMPA Receptors o Glutamate ionotropic receptors o Ligand-gated o Depolarizing o Non-selective cation Integration of inputs - Excitatory inputs push the neuron towards firing by making the inside more positive - Inhibitory inputs push the neuron away from firing by making the inside more negative - The neuron only fires an action potential if the summed effects of all inputs depolarize the cell enough to reach the threshold at the axon hillock Spatial vs. Temporal Summation A) Spatial summation: multiple inputs from different locations summate B) Temporal summation: repeated inputs from a single synapse overtime summate - These summation mechanisms are crucial for determining whether a neuron will generate action potential based on the overall balance of excitation and inhibition Types of Synapses Neuronal Circuitry - Neurons and synapses combine to make circuits. - Neural chain: o A simple series of neurons ▪ Ex. the knee-jerk reflex consists of a sensory neuron, a synapse, and a motor neuron. ▪ Extremely fast: large, myelinated axons, sensory cells synapse directly onto motor neurons, ionotropic synapses Knee-Jerk Reflex: Visualizing Circuits Mapping Circuit Connectivity With Brainbow – See reading Mapping Circuit Connectivity with GRASP - GFP reconstitution across synaptic partners o Fluorescent labelling of “synaptically-connected” neurons o Based on spatial proximity o Promoters are key! ▪ Label pre-machinery/post synaptic machinery with complimenting “halves” of GFP - mGRASP – Mammalian GFP Reconstitution Across Synaptic Partners o Video showing an application of mGRASP combined with 3D modeling imaging in the hippocampus Mapping Circuit Connectivity with Rabies Virus - In nature o Rabies virus has the ability to infect cells and travel retrogradely (to the presynaptic neuron) - Engineering the virus o Be less virulent (not cause disease) o Express a fluorescent protein o Infect specific cells - Method o Infect starter cells o Virus will travel backwards across the 1 synapse o View connection via fluorescent microscope PSYC 304B: Brain and Behaviour October 3, 2024 Lecture 4: Neuroanatomy (Human Nervous System) Objectives 1. Define and differentiate each aspect of the human nervous system. 2. Recognize the various functions and neurophysiology impacts of each aspect of the human nervous system. 3. Describe the basic developmental stages of the human brain. 4. Describe major historical contributions to our understanding of the brain’s structure and function The Nervous System - Gross neuroanatomy o Visible to the naked eye - Central nervous system (CNS) o Brain + spinal cord - Peripheral nervous system (PNS) o All parts of nervous system outside of skull/spinal column Somatic nervous system - Interacts with the environment - Efferent neurons: carry motor signals to the periphery o ‘E’ for exit - Afferent neurons: carry sensory info to the CNS o ‘A’ for arrive - Consists of cranial nerves and spinal nerves o Cranial nerves: enters the periphery through a hole in the skull ▪ 12 pairs; some are sensory, some are motor, some have both functions— separate axons in the nerve carry the sensory and motor signals ▪ CN XI (Accessory) – Is an imposter, because it comes from the spinal cord (but is considered a cranial nerve because it exits through a second hole in the skull) The Spine - Spinal nerves – 31 pairs o Each spinal nerve is the fusion of two distinct branches, or roots: ▪ Dorsal root—carries sensory information from the body to the spinal cord ▪ Ventral root—carries motor information from the spinal cord to the muscles Autonomic Nervous System - Regulation of the internal environment - Efferent neurons: carry motor signals to internal organs - Afferent neurons: carry sensory info to the CNS  - Splits into sympathetic nervous system (fight or flight) and… o Main neurotransmitter: norepinephrine (noradrenaline) - … Parasympathetic nervous system (rest or digest) o Neurotransmitter: acetylcholine (Ach) Sympathetic Parasympathetic Increase heartbeat Decrease heartbeat Dilate pupils Constrict pupils Stimulate secretion by sweat glands Contract bladder Dilate blood vessels in the digestive system - The autonomic nervous system spans the central and peripheral nervous systems - Autonomic ganglia o Are groups of neurons (cell bodies) located outside the CNS o Side note: in the CNS, the groupings are called nuclei o Preganglionic neurons run from the CNS to the autonomic ganglia o Postganglionic neurons run from the autonomic ganglia to targets in the body. The History of Research on the Brain - Early Egyptians and Greeks (Aristotle) o 1300 – 300 BCE o Mental capacities came from the heart o Egyptians preserved liver, lungs, stomach, intestines, and heart in Pharoah’s tombs (important to ensure continued existence in the afterlife) - Herophilus (300 BCE) o “Father of anatomy” o Performed dissections on humans and animals - Galen (~100) o Greco-Roman physician o Reported behavioral changes to gladiators with injuries to the head o Animal spirits passed along nerves to all regions of the body  - Leonardo da Vinci o Cross sections - Rene Descartes (1956-1650) o Animal and human behaviour is like the workings of a machine o Proposed the concept of a spinal reflex and neural pathways o Proposed the pineal gland as the junction between the body and the mind o Dualism – Humans have a non-material soul as well as a material body - Phrenology (19th century) o Assigned separate functions to different cortical areas o Bumps on skull – causes by enlarged brain regions – matched to certain behaviours o Opponents – stated the brain works as a whole - Paul Broca (1824-1880) o Language ability restricted to a small area of the brain o Assessed the brain of a man who was unable to produce speech for several years before death o Lesions only is a small area of the frontal left lobe. o Region is now called Broca’s area - William James (1890) – Principles of psychology o Consciousness an aspect of the human nervous system The Brain – Basics - The brain has two cerebral hemispheres - Cerebral cortex: folded outermost layer of the cerebral hemispheres, comprised mostly of neuron cell bodies, dendrites, and axons. - Folds (gyri and sulci) increase amount of cortex that can fit into the skull, and are grouped together into lobes Anatomical Conventions - Horizontal o Divides the brain into an upper and lower part - Sagittal o Divides the body into left and right halves - Coronal o Divides the body into front (anterior) and back (posterior) regions Two Colours of Brain Tissue - Grey matter o Contains neuronal cell bodies o Involved in information processing - White matter o Composed of myelinated axons o Serves as “information highways” ▪ Connecting different brain regions Four Lobes of the Cortex - Frontal o Movement o High-level cognition - Parietal o Spatial cognition o Sensory processing - Occipital o Visual processing - Temporal o Auditory processing o Sense of smell o Aspects of learning Parts of the Human Brain The Postcentral Gyrus - Located in the parietal lobe - Processes sensory information such as touch and pain - The sensory homunculus represents different body parts according to their sensory significance The Precentral Gyrus - Located in the frontal lobe - Controls voluntary movements - The motor homunculus represents different body parts according to the degree of motor control required Brain Development - 25 Days o Forebrain o Midbrain o Hindbrain - 50 Days o Forebrain ▪ Telencephalon ▪ Diencephalon o Midbrain ▪ Mesencephalon o Hindbrain ▪ Metencephalon ▪ Myelencephalon The Adult Brain Forebrain Structures - Telencephalon (Tel – “far off, distant) o Cerebral cortex ▪ Responsible for higher cortical functioning - Diencephalon (Di – “two”) o Thalamus ▪ Acts as a relay station for all incoming sensory information ▪ Processes sensory signals before they reach the cerebral cortex o Hypothalamus ▪ Located below the thalamus and involved in regulating vital functions ▪ Controls the pituitary gland, which has widespread effects on the endocrine system Midbrain Structures - Mesencephalon (Mes – “middle) o Midbrain ▪ Composed of tectum (important for sensory and motor functions) ▪ Contains the reticular formation, which regulates sleep, arousal, temperature control, and motor control Hindbrain Structures - Metencephalon (Met – “beside, after”) o Pons (part of brainstem) ▪ Functions as a “bridge” connecting the medulla to the midbrain ▪ Plays a role in relaying signals between the cerebellum and the forebrain o Cerebellum ▪ Responsible for balance, coordination, and fine-tuning motor movements - Myelencephalon (Myel – “marrow, spinal cord”) o Medulla (part of brainstem) ▪ Regulates breathing and heartbeat ▪ Serves as pathway for all neurons passing from the brain to the spinal cord Brain Imaging Techniques Computerized Axial Tomography (CAT or CT) - A measure of X-ray absorption with ionizing radiation at several positions around the head; maps tissue density - Great for imaging bones, detecting tumours, bleeds (best for solid structures) Magnetic Resonance Imaging (MRI) - Produces high-resolution images using radio frequency energy - Better for detailed images of softer tissue Diffusion Tensor Imaging (DTI) - Uses MRI technology to study white matter tracts; based on fractional anisotropy (FA)— fancy way of saying water diffusing along the length of white matter tracts - Used to study MS, strokes, TBI, Alzheimer’s, plan surgery, study development… Positron Emission Tomography (PET) - Produces images of brain activity; identifies brain regions that contribute to specific functions - Involves a radioactive tracer (glucose) - Metabolically active tissue will use more glucose - Tracer emits gamma waves as it breaks down - Detects cancer, observe heart damage, study brain function Functional MRI (fMRI) - Detects small changes in brain metabolism, such as oxygen use, in active brain areas - fMRI can show how networks of brain structures collaborate Using Brain Imaging to Assess Consciousness - Brain Imaging can overcome limitations of other assessment methods - It can complement traditional studies of brain lesions - Imaging can address the state of consciousness in individuals in a coma o Study example: Researchers prompted brain activity in a comatose patient by asking them to imagine specific tasks. Supplementary motor area (SMA) and premotor cortex (PMC) showed activation, indicating consciousness. Using Brain Imaging in Social Neuroscience - Social neuroscience: aims to understand brain activity as it relates to our interactions with others - Dyadic functional MRI: employs an MRI scanner that is fitted with dual head coils o Ex. Study showed that as a pair of friends looked at each other’s faces, BOLD signal was found in the temporoparietal junction, FFA, and frontal cortex. PSYC 304B: Brain and Behaviour October 10, 2024 Lecture 5: Neuroendocrinology Objectives 1. Contrast the different chemical signaling systems within the body and between individuals 2. Classify the major classes of hormones and describe how they affect target cells. 3. Describe the structure and function of neuroendocrine cells. 4. Contrast the receptors and mechanisms of action of peptide and amine hormones versus steroid hormones. 5. Compare the genomic versus nongenomic actions of steroid hormones. 6. Understand how the brain regulates hormone production and secretion 7. Distinguish the mechanisms of hormone secretion in the posterior versus anterior pituitary gland. 8. Describe neurobehavioral functions of hormones secreted from the adrenal, thyroid, and pineal glands. 9. Understand how gonadal steroids activate mating behavior in male and female vertebrates 10. Describe how hormones play a role in pair-bonding in monogamous species of voles 11. Appreciate the reciprocal nature of hormonal effects on behaviour—that behaviours affect hormone release too A Brief History Ancient Greeks & The Body’s Humors - Phlegm – phlegmatic (impassive) - Black bile – bilious (irritable) - Blood – sanguine (cheerful) - Yellow bile (choler) – choleric (hot-tempered) Aristotle - Accurately described effects of castration in birds, and compared the effects to those observed in eunuchs (castrated men) Behavioral Endocrinology (1849) - Arnold Adolf Berthold (after John Hunter) - Observed behaviour and development of castrated, uncastrated, and reimplanted roosters Hormones - Hormones: chemicals secreted by cells in one part of the body that travel through the bloodstream to act on targets in other parts of the body. - Endocrine glands: release hormones within the body. - Exocrine glands: use ducts to secrete fluids such as tears and sweat outside the body. Chemical Communication Forms of Chemical Communication - Endocrine – a hormone is released into the bloodstream to act on target tissues - Synaptic (neurocrine)—chemical release and diffusion across a synapse - Autocrine—released chemical acts on the releasing cell - Paracrine—the released chemical diffuses to nearby target cells - Pheromone—hormones used to communicate between individuals of the same species; pheromones are released into the environment. - Allomone communication—allomones are chemicals released by one species to affect the behaviour of another species. Hormone Action General Principles of Hormone Action 1. Hormones act in a gradual fashion. 2. Hormones act by changing the probability or intensity of a behaviour. 3. The relationship between behaviour and hormones is reciprocal. 4. A hormone may have multiple effects, and one behaviour can be affected by several hormones. 5. Hormones often have a pulsatile secretion pattern—in bursts. 6. Some hormones are controlled by circadian clocks in the brain. 7. Hormones can interact with other hormones and change their effects. 8. Hormones can only affect cells with a receptor protein for that hormone. Neuroendocrine and Neurochemical Signaling - Cells—Neuroendocrine cells o Are neurons that release hormones into the blood. - Neuropeptides o (Peptides used by neurons) can act as neuromodulators and alter sensitivity to transmitters. - Neuromodulators o Can modify the reactivity of cells to specific transmitters—they act more slowly than neurotransmitters and have longer lasting effects. Hormone Types → Classification via Chemical Structure - Peptide—Short string of amino acids - Amine—Modified amino acid - Steroid—Four rings of carbon atoms o Derivatives of cholesterol Main Modes of Action - Protein and amine hormones bind to receptors on the cell surface, which causes release of a second messenger, which brings about changes in cellular function - Steroid hormones pass through the cell membrane and bind to receptors inside the cell. Protein and Amine Hormone Action - Rapid - When they bind to the extracellular part of a receptor, the receptor changes shape - The intracellular part then activates a second messenger o Secondary messengers: ▪ Cyclic adenosine monophosphate (cAMP) ▪ Cyclic guanosine monophosphate (cGMP) Steroid Hormone Action - Slow - Receptors are within target cells - When steroid-receptor complexes form, they alter protein production, producing long-lasting effects - The steroid-receptor complex binds to DNA and acts as a transcription factor—controlling gene expression - Steroid receptor cofactors may be necessary for the cell to respond to the steroid-receptor complexes - Some steroids act on more than one receptor—called receptor isoforms—with functional differences. - Other effects of steroids: o Estradiol can have a nongenomic effect—a rapid, brief effect involving neuronal membrane receptors ▪ Promote cell growth  ▪ Alter metabolism ▪ Influence NT release ▪ Modulate ion channels (like Ca2+, K+, Na+, and Cl-) ▪ Provide neuroprotection by preventing apoptosis ▪ Promote vasodilation o Testosterone has rapid effects on receptors located in axons and other sites distant from the nucleus ▪ Similar to estradiol effects Neuro-steroids - Steroids made in the brain - Progesterone-like neurosteroids, reduce anxiety (non-competitive agonist to GABA receptors) - The brain also produces an enzyme, aromatase, that can convert testosterone entering the brain into estrogens. o Aromatase abundant in hypothalamus o Testosterone is the major precursor for making estrogens. Ovaries have a lot of aromatase, thus release a lot of estrogen (testes very little). - No steroid hormone is found exclusively in one sex Hormone Regulation Feedback Systems - Negative feedback: output feeds back and inhibits further secretion - Autocrine feedback loop: endocrine cells release a hormone whose presence feeds back on the endocrine cells to inhibit further secretion  - Target cell feedback: hormone acts on its target cells; the biological effect is detected by the endocrine gland and further release is inhibited. HPA Axis (Hypothalamic-Pituitary-Adrenal Axis) Hypothalamus - Brain regulation involves the hypothalamus which can direct hormone release from endocrine glands o Uses releasing hormones to regulate the pituitary’s release of tropic hormones - The brain detects the hormone’s effects and exerts negative feedback on the hypothalamus o Negative feedback goes to both the pituitary gland and the hypothalamus Anterior Pituitary Gland - Releases tropic hormones that affect other endocrine glands Behavioural Endocrinology Example Study: Testosterone and Mating Behaviour in Mice - Step 1 o Observe several individuals (a representative sample) o Results: most male adult rats will try to mount and copulate with a receptive female in their cage - Step 2 o Remove endocrine gland (testes) and observe behaviour o Results: the male rat will stop its copulatory behaviour - Conclusion o Testosterone loss leads to reduction in copulatory behaviour - Are you happy with this conclusion? o Did you eliminate alternate explanations? - Next steps – building evidence o Return of behaviour with return of hormone ▪ Inject castrated mice with testosterone → return of behaviour o Eliminate functionality of the hormone in a different approach ▪ Make a knock-out organism—knock out the gene that encodes the testosterone receptor - Next question… o We have established a relationship between copulatory behaviour and testosterone. But what is it? o Does copulatory behaviour frequency correlate with levels of testosterone? o Technique—Observe behaviour and measure circulating testosterone: ▪ Autoimmunoassay: label hormone of interest (testosterone) with an antibody - Turns out… o Copulatory behaviour does not correlate with circulating testosterone behaviour o Testosterone permits the behaviour, but does not determine how much of the behaviour the individual exhibits  - More Questions: o How does testosterone permit sexual behaviour? o Where in the brain does testosterone have an effect? Techniques to Study Testosterone in the Brain - Autoradiography o Identifies where testosterone binds o Steps: ▪ Injection: the rat is injected with radioactively labeled testosterone molecules ▪ Accumulation: these labeled testosterone molecules enter the bloodstream and accumulation cells that have androgen receptors ▪ Brain removal: brain is removed and frozen ▪ Slicing and film application: the brain tissue is thinly sliced, and a film is placed on top of the slices. The radioactively labeled testosterone molecules emit particles that “expose the film.” ▪ Film development: when the film is developed, black dots form in areas where testosterone has accumulated, allowing visualization - Immunohistochemistry o Shows which cells have the receptors for testosterone - In-situ hybridization o Shows where the receptors are being produced by detecting mRNA, which helps determine which cells are prepared to respond to testosterone Summary by technique: Endocrine Glands The Pituitary Gland (hypophysis) - Anterior pituitary (adenohypophysis) - Posterior pituitary (neurohypophysis) - The two parts are separate in function The Pituitary Stalk (infundibulum) - Connects the pituitary to the hypothalamus; contains many axons that extend only to the posterior pituitary - Blood vessels carry information only to the anterior pituitary Posterior Pituitary - Secretes oxytocin and vasopressin o Oxytocin is involved in reproductive and parenting behaviour, uterine contraction, and the milk letdown reflex ▪ Reflex can be conditioned to a baby’s cries o Vasopressin ▪ Increases blood pressure and inhibits urine formation o Oxytocin and vasopressin can also serve as neurotransmitters - Neurons in the supraoptic nuclei and paraventricular nuclei of the hypothalamus synthesize these hormones and transport them along the axons in the stalk Hypothalamic Neurons - Synthesize releasing hormones o Releasing hormones are responsible for regulating the release of other hormones from the anterior pituitary gland - Axons from these cells converge on the median eminence, above the pituitary stalk - Releasing hormones are secreted into blood vessels called the hypophyseal portal system, and are carried to the anterior pituitary, which then releases tropic hormones Hypothalamic Neuroendocrine Cells - Influenced by circulating messages, such as other hormones, blood sugar, and immune system products - Synaptic inputs from other brain areas The Anterior Pituitary Releases 6 tropic hormones… 1. Adrenocorticotropic hormone (ACTH): controls release of adrenal cortex steroid hormones 2. Thyroid-stimulating hormone (TSH): increases thyroid hormone release Gonadotropins (FSH, LH): 3. Follicle-stimulating hormone (FSH): stimulates egg-containing follicles Influence the in ovaries or sperm production in males gonads (testis/ovaries) 4. Luteinizing hormone (LH): stimulates follicles to form the corpora lutea in ovaries and testosterone production by the testes 5. Prolactin: stimulates lactation in females and is involved in parental behaviour. 6. Growth hormone (GH/somatotropin): influences growth, mostly during sleep. The stomach hormone ghrelin also evokes GH release. Major Endocrine Glands Adrenal Glands - Located on top of each kidney - Adrenal cortex o Secretes steroid hormones (adrenocorticoids) o Glucocorticoids → involved with glucose metabolism ▪ Cortisol: stress hormone that increases blood glucose and breaks down protein o Mineralocorticoids → regulates ion balance ▪ Aldosterone: acts on kidneys to retain sodium o Androgens (sex hormones) → involved in reproduction/secondary sexual characteristics ▪ Androstenedione: contributes to adult pattern of body hair in men and women - Adrenal medulla o Releases the amine hormones epinephrine (adrenaline) and norepinephrine (noradrenaline) ▪ Controlled by sympathetic nervous system Pituitary Gland (continued from prev. pages) - Thyroid-stimulating hormone (TSH): release is controlled by negative feedback from blood levels and by thyrotropin-releasing hormone (TRH) from hypothalamus o Produces calcitonin → promotes calcium deposition in bones o Produces thyroid hormones ▪ Thyroxine (tetraiodothyronine)/ Triiodothyronine ▪ Contain/rely on iodine Iodine deficiency → Swelling of gland, known as Goiter  Early thyroid deficiency can result in cretinism (congenital hypothyroidism + intellectual disability) Pineal Gland - Produces melatonin → regulates sleep o Works with circadian rhythms Gonads—Ovaries and Testes - Produce sex steroids - The hypothalamus controls gonadal hormone production by releasing gonadotropin releasing-hormone (GnRH) o GnRH stimulates the anterior pituitary to release FSH or LH - Testes o Produce and secrete testosterone (which is an androgen) ▪ Regulated by LH (regulated by GnRH) o Sperm production → regulated by FSH - Ovaries o Produce hormones in cycles ▪ Progestins (ex. progesterone) ▪ Estrogens (ex. 17B-estradiol) o Hormone release controlled by LH and FSH → controlled by GnRH New Research Oxytocinergic neurons - Research question: How do various oxytocin circuits in the brain contribute to social behaviour? - Methods (using mice) o Magnocellular neurons: large cell-bodied neurons in hypothalamus ▪ Project to the posterior pituitary to release oxytocin  o Parvocellular neurons: small cell-bodied neurons in hypothalamus that synapse on magnocellular cells ▪ Activated by specific social stimuli, such as the gentle touch of a mouse - Experimental Methods o Scientists used designer receptors exclusively activated by designer drugs (DREADDs) to manipulate parvocellular cells ▪ Allowed for activation/disabling neurons using specific drugs - Findings o When disabled: significant reduction in interaction times between female mice o When activated: prolonged interactions between female mice - Conclusion o Oxytocinergic circuits play a crucial role in modulating social behaviour ▪ Gentle touch → activates parvocellular neurons → activates magnocellular neurons → release of oxytocin → social behaviour Psychosocial Dwarfism - Growth failure due to stress and neglect in early childhood - Mediated through CNS + its endocrine functions - Removal of stress → normal growth resumes - Growth impairments appear to be mediated by… o Cortisol o GH o Somatomedins (Released by liver in response to GH) Courtship in ringdoves - Sensory information o Visual information from the environment elicits activity in the sensory pathway ▪ Ex. Male ringdove sees attractive female o Information projected to various parts of the brain for interpretation/processing ▪ Cortex, cerebellum, hypothalamus… - …Neural-neural link: o The perception of an attractive female is processed as a neural-neural link, meaning it will further neuroendocrine actions - Perception of an available mate o Activates neurosecretory cells in the hypothalamus ▪ Secretes GnRH → released into hypothalamic-pituitary portal system - …Neuro-endocrine link: o Process involves converting a neural signal into an endocrine response - Hormonal cascade o The anterior pituitary releases gonadotropins such as LH and FSH o Testes produces testosterone - …Endocrine-endocrine link: o The release of gonadotropins and testosterone - +…Endocrine-neuro link: o Testosterone alters excitability of specific brain neurons → courtship display behaviour (ex., bowing coos) - Female response o Female dove responds to the courtship behaviour of the male, which provides new visual information… triggering another neural-to-neural interaction - Feedback cycle → neural and hormonal signals continue to interact Integrated Reponses – Conclusions - Hormonal and neural systems interact to produce responses o The milk letdown reflex o Ringdove courtship o Etc… - Communication signals can be o Neural-to-neural o Neural-to-endocrine o Endocrine-to-endocrine o Endocrine-to-neural - The hormonal and neural systems exert reciprocal influences on each other - Experience affects hormone secretion, hormones affect behaviour, and behaviour affects future experiences