6.13 Neurotransmitters and Neuromodulators

Acetylcholine

Synthesized from choline + coenzyme A, cholinergic neurons release __, which are primarily responsible for muscle contractions

[ when bound to | it helps ]

• Nicotinic __ receptors | cognitive functions and behavior

  • agonist: nicotine, plant alkaloid compound in tobacco products

• Muscarinic __ receptors | innervate salivary glands, smooth muscle cells, and heart

  • agonist: muscarine, poison found in some mushrooms

  • antagonist: atropine

Atropine

Naturally occurring antagonist of muscarinic receptors → relax smooth muscles

Found in eyedrops with dilation of pupils

Acetylcholinesterase

Enzyme responsible for the degradation of ACh

Sarin

Nerve gas that inhibits aceylcholinesterase, causing build up of ACh in synaptic cleft

beta-amyloid protein

Mutations of chromosomes 1, 14, 21 lead to __ production associated with neuronal cell death in a severe version of Alzheimer’s Disease, as early 30 years old

Biogenic Amines

Small charged ions synthesized from amino acids + amino groups (NH2)

• catecholamines [dopamine, norepinephrine, epinephrine*]

• serotonin

• histamine

(*) = not a neurotransmitter, but is a major hormone

Catecholamine

A subclass of biogenic amines, __ have a catechol ring and an amine group. They are formed from amino acid tyrosine via:

• uptake of tyrosine → L-dopa

  • conversion by tyrosine hydroxylase

• continual synthesis (in the following order), depending which enzymes are present:

  • 1. dopamine

  • 2. Norepinephrine

  • 3. Epinephrine

Essential for mood, motivation, directed attention, movement, blood pressure regulation, and hormone release

Note: all of their receptors are metabotropic

Monoamine oxidase

Enzyme that breaks down catecholamine neurotransmitters in extracellular fluid and axon terminal

Monoamine oxidase inhibitors

Drugs that increase amount of norepinephrine and dopamine via slowing down their metabolic degradation

Adrenergic

__ is used to describe neurons and receptors that release/bind norepinephine or epinephrine

• alpha-__ receptors

  • A2 = presynaptically inhibits norepinephine

  • A1 = stimulates/inhibits K+ channels

• beta-__ receptors

  • work via Gs proteins

  • B1, B2, B3

Serotonin

Also known as 5-HT, it is produced from tryptophan (essential amino acid)

• excites muscles and inhibits pathways mediating sensation

• regulates food intake, reproductive behavior, mood + anxiety

Paxil

__ and Lexapro are drugs that inactivates 5-HT reuptake → increases serotonin in synapses → aid treatment of depression

LSD

Lyseric acid diethylamide. Stimulates 5-HT2A receptor in brain → hallucinations

Glutamate

Major neurotransmitter in CNS (interacts with 50% of excitatory synapses)

• AMPA = depolarizes w/ Na+ influx

when reaches certain potential

• NMDA = increased Ca+ uptake

• Plays important role in Long Term Potential

GABA

Major inhibitory neurotransmitter in brain. Modified form of glutamate (amino acid)

• Inc. Cl- influx → polarizes cell

• has ionotropic and metabotropic receptors

Xanax

__ (alprazolam) alongside Valium (diazepam) acts as agonists to GABA receptors and increase Cl- influx → reduces anxiety and induces sleep