Neurotransmitters and Mental Health

Prayer Request

• A prayer request was given, asking Allah to make learning beneficial and to increase knowledge.

Learning Objectives

• Students will be able to define neurotransmitters.
• Students will be able to list types of neurotransmitter receptors.
• Students will be able to classify neurotransmitters by function and chemistry.
• Students will be able to identify sites of neurotransmitters in the brain.
• Students will be able to explain the implications of neurotransmitter imbalance on mental health.
• Students will be able to list diagnostic methods for neurotransmitter imbalance.

Neurotransmitter Definition

• The criteria for a substance to be considered a neurotransmitter are:
  • The substance must be present within the presynaptic neuron.
  • The substance must be released in response to presynaptic depolarization, and the release must be calcium-dependent.
  • Specific receptors for the substance must be present on the postsynaptic cell.

Neurotransmitter Action Localization

• Neurotransmitters act either locally or more diffusely.
  • Local action involves altering the excitability of a single or a few postsynaptic cells.
  • Diffuse action involves long axons that locally release neurotransmitters onto distant targets.

Classification of Neurotransmitters

• Neurotransmitters can be classified as excitatory or inhibitory.
  • Examples of excitatory neurotransmitters include glutamate, acetylcholine, histamine, dopamine, norepinephrine, and epinephrine.
  • Examples of inhibitory neurotransmitters include GABA and serotonin.
  • Dopamine is both excitatory and inhibitory.

Neurotransmitter Receptors

• Whether a neurotransmitter is excitatory or inhibitory depends on the receptor type it acts on.
• Inhibitory postsynaptic potential decreases firing and propagation of the action potential due to chloride ion influx.
• Neurotransmitter receptors include ionotropic and G-protein-coupled receptors.

Types of Receptors Detailed

• Ionotropic Receptors (Ligand-Activated Ion Channels):
  • Allow ions (sodium, potassium, or calcium) to pass through.
  • Act quickly.
  • Example: NMDA receptors, involved in learning and memory.
  • Example: AMPA receptors, mediate fast excitatory transmission.
• G-Protein-Coupled Receptors:
  • Activate intracellular signaling pathways via G-proteins.
  • Lead to changes in gene expression, enzyme activity, or ion channel behavior.
  • Slower but have longer-lasting effects.
  • Example: Dopamine D2 receptors, associated with reward and motivation.
  • Example: Acetylcholine receptors (muscarinic), found in the heart and brain.
  • Example: GABA receptors (GABA-B), modulate neuronal activity.
  • Example: Serotonin receptors (5-HT1A), related to anxiety and depression.

Neurotransmitter Examples

• Acetylcholine (ACh):

  • Excitatory (usually), except in the heart (inhibitory).
  • Released from motor neurons.
  • Regulates sleep cycle and muscle functioning.

• Norepinephrine:

• Epinephrine:

  • Excitatory.
  • Released from chromaffin cells.
  • Responsible for the "fight-or-flight" response.

• Dopamine:

  • Both excitatory and inhibitory.
  • Released from the substantia nigra.
  • Inhibits unnecessary movements, inhibits prolactin, and stimulates growth hormone.

• Gamma-Aminobutyric acid (GABA):

  • Inhibitory.
  • Released from various brain regions.
  • Reduces neuronal excitability.

• Glutamate (Glu):

  • Excitatory.
  • Released from sensory neurons and the cerebral cortex.
  • Regulates central nervous system excitability, learning, and memory.

• Serotonin (5-HT):

  • Inhibitory.
  • Released from brain stem neurons and other locations.
  • Regulates body temperature, pain, emotions, and the sleep cycle.

• Histamine:

  • Excitatory.
  • Released from various sites (hypothalamus, stomach cells, etc.).
  • Regulates wakefulness, blood pressure, pain, sexual behavior, and inflammatory responses.

Neuromodulators

• Neuromodulation differs from neurotransmission by the duration of action at the synapse.
• Neuromodulators spend a significant time in cerebrospinal fluid modulating the activity of many neurons.
• Examples of neuromodulators are dopamine, serotonin, acetylcholine, histamine, and norepinephrine.

Neurotransmitter Imbalance-Related Disorders

• Related disorders include Alzheimer's disease, depression, schizophrenia, Parkinson's disease, epilepsy, Huntington's disease, and myasthenia gravis.

Diagnosis of Neurotransmitter Imbalance

• Identifying causes and symptoms.
• Diagnostic tests.
  • Neurotransmitter testing, often analyzed from urine samples.
  • Brain scans.
  • Brain tissue assays.

Summary of Neurotransmitters

• Neurotransmitters are small molecule transmitters and neuropeptides.
• Primarily biogenic amines that modulate ongoing activity in the brain and peripheral tissues in a gradual manner.
• Drugs influencing transmitter actions are crucial in treating neurological and mental health disorders.