Chemical Communications: Neurotransmitters and Hormones PDF

**Chemical Communications:** **Neurotransmitters and Hormones** Cells Communicate in Many Ways, three principal types of molecules for communications: **Receptors** - protein molecules that bind to ligands and effect some type of change. **Chemical messengers** - also called ligands, interact w...

**Chemical Communications:** **Neurotransmitters and Hormones** Cells Communicate in Many Ways, three principal types of molecules for communications: **Receptors** - protein molecules that bind to ligands and effect some type of change. **Chemical messengers** - also called ligands, interact with the receptors. Can transform other cells or tissues by interacting with receptors. **Secondary messengers** - carry the message from the receptor to the inside of the cell and amplify the message. **Neurons or nerve cells --** where signals are transmitted by specific compounds. **Neurotransmitters -** adjacent neurons of a specific compounds that carries signal at the end of the neuron. Communication between the eyes and the brain, is by **neural transmission.** **Neurotransmitters** carry the necessary messages from the neurons to the muscle cells and the endocrine glands. **Hormone** is secreted into the bloodstream. **Adrenaline** is a hormone that binds to specific receptors in muscle and liver cells. Second messenger, **cyclic AMP (cAMP),** second messenger leads to modification of several enzymes involved in carbohydrate metabolism. **Neurotransmitters** Chemical messengers between a neuron and another target cell: neuron, muscle cell, or cell of a gland. **Hormone** A chemical messenger released by an endocrine gland into the bloodstream and transported in the blood to reach its target cell. **Receptors** -- of three basic parts of cell communication this is always protein-based. **Synapse** An aqueous small space between the tip of a neuron and its target cell. A long, fiber-like part called an **axon.** Hair-like structures called **dendrites** If chemical signal travels, say, from axon to dendrite, we call the nerve ends on the axon the **presynaptic** site. **Vesicles -** neurotransmitters are stored at the presynaptic site, small, membrane-enclosed packages. Receptors are located on the **postsynaptic** site of the cell body or the dendrite **Hormone** A chemical messenger released by an endocrine gland into the bloodstream and transported in the blood to reach its target cell. The distinction between hormones and neurotransmitters is **physiological**, not chemical. Pituitary gland is suspended from the hypothalamus by a stalk of neural tissue. -Chemical messengers with their messenger type \(a) Glutamate - amino acid \(b) Oxytocin - peptidergic \(c) Testosterone - steroid **Cholinergic Messenger** **A. Cholinergic Receptors** main cholinergic neurotransmitter is **acetylcholine** **Receptor** - is a transmembrane protein B. **Storage of Messengers** **C. Calcium as a Signaling Agent (Secondary Messenger)** \- The receptor protein has five subunits. \- Calcium ions control our heartbeats; our movements through the action of skeletal muscles; and through the release of neurotransmitters in our neurons, learning and memory **D. The Action of Messengers** **E. The Removal of Messengers** Acetylcholine is removed rapidly from the receptor site by the enzyme **acetylcholinesterase**, which hydrolyzes it. (Alzheimer's disease) Three pathological hallmarks in the brain: (1) buildup of protein deposits known as amyloid plaques outside the nerve cells, (2) neurofibrillar tangles composed of tau proteins, and (3) brain shrinkage. **F. Control of Neurotransmission** Succinylcholine and decamethonium bromide resemble the choline end of acetylcholine and therefore act as competitive inhibitors of acetylcholinesterase. Ligand-gated ion channeling - where acetylcholine enables the ion channels to open and propagate signals. **Amino Acid Neurotransmitters** **A. Messengers** -Amino acids are distributed throughout the neurons individually or as parts of peptides and proteins. -glutamic acid, aspartic acid, and cysteine, act as excitatory neurotransmitters -(GABA), are inhibitory neurotransmitters **B. Receptors** -Phencyclidine (PCP), an antagonist of this receptor, induces hallucination. PCP, known by the street name "angel dust," is a controlled substance; it causes bizarre psychotic behavior and long-term psychological problems. **C. Removal of Messengers** **Transporter** A protein molecule that carries small molecules, such as glucose or glutamic acid, across a membrane **A. Monoamine Messengers** **B. Signal Transduction** process by which the initial signal is spread and amplified throughout the cell is called signal transduction. A cascade of events through which the signal of a neurotransmitter or hormone delivered to its receptor is carried inside the target cell and amplified into many signals that can cause protein modifications, enzyme activation, and the opening of membrane channels. **C. Secondary Messengers** Adenylate cyclase produces a secondary messenger inside the cell, cyclic AMP (cAMP) The activation of adenylate cyclase accomplishes two important goals: 1. It converts an event occurring at the outer surface of the target cell (adsorption onto receptor site) to a change inside the target cell (formation of cAMP). 2. It amplifies the signal **D. Removal of Signal** The cAMP already produced is destroyed by the enzyme phosphodiesterase, which catalyzes the hydrolysis of the phosphoric ester bond, yielding AMP. **E. Control of Neurotransmission** The G-protein--adenylate cyclase cascade in transduction signaling is not limited to monoamine messengers **F. Removal of Neurotransmitters** The body inactivates monoamines by oxidizing them to aldehydes. **G. Histamines** The neurotransmitter histamine is present in mammalian brains. two kinds of receptors for histamine: H(sub)1 - can be blocked by antihistamines such as dimenhydrinate and can be found in the respirstory tract. H(sub)2 - can be blocked by ranitidine and can be found mainly in the stomach Helicobacter pylori - main culprit in the formation of most ulcers. **Peptides in Chemical Communications** **A. Messengers** first brain peptides isolated were the **enkephalins -** ind to specific pain receptors and seem to control pain perception. **neuropeptide Y -** affects the hypothalamus, a region that integrates the body's hormonal and nervous systems. When its receptors are blocked (for example, by leptin, the "thin" protein), appetite is suppressed. **Leptin** is an anorexic agent **substance P** (P for "pain") - involved in transmission of pain signals. **B. Secondary Messengers and Control of Metabolism** All peptidergic messengers, hormones, and neurotransmitters act through secondary messengers. Glucagon is a peptide hormone that is critical for maintaining blood glucose levels. By turning on gluconeogenesis and turning off glycolysis, the liver produces more glucose for the blood. \- Glucagon increase the level of blood glucose. \- Insulin lowers the level of blood glucose. **Steroid Hormone Messengers** Steroid hormones, including sex hormones, are hydrophobic and can pass through cell membranes by passive diffusion. Once inside the cell, they bind to protein receptors, which help transport them through the cytoplasm. These receptors are mostly in the nucleus, where the steroid-receptor complex can bind to DNA or work with transcription factors to influence gene expression and protein synthesis. This process is slow, taking hours. However, steroids can also act quickly by affecting cell membrane ion channels, as seen in the rapid release of enzymes during fertilization. Additionally, steroid hormones, or neurosteroids, can function as neurotransmitters in the brain, affecting sleep, pain, and other neural functions. **Drugs Affect Chemical Communications** -An **antagonist** drug blocks the receptor and prevents its stimulation. -An **agonist** drug competes with the natural messenger for the receptor site. Once there, it stimulates the receptor.  Five principal ways that drugs control chemical communications? 1\. An antagonist drug blocks the receptor and prevents its stimulation. 2\. An agonist drug competes with the natural messenger for the receptor site. Once there, it stimulates the receptor. 3\. Other drugs decrease the concentration of the messenger by controlling the release of messengers from their storage. 4\. Other drugs increase the concentration of the messenger by inhibiting its removal from the receptors. 5. Still others act to inhibit or activate specific enzymes inside the cells. **- Selective Serotonin Reuptake Inhibitors (SSRIs)** are currently one of the most popular antidepressants. **Norepinephrine Reuptake Inhibitors (NRIs)** block the reuptake of this important neurotransmitter **Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)** block both serotonin and norepinephrine reuptake, and represent another modern important class of antidepressant **Monoamine Oxidase Inhibitors (MAOIs)** were an early class of antidepressant.