Chemistry of Behavior: Neurotransmitters and Neural Pathways

Vocabulary practice flashcards generated from lecture notes on neurotransmitter chemistry, catecholaminergic and cholinergic pathways, receptor mechanisms, and chemogenetic tools.

Catecholamines

A class of organic compounds containing a catechol group and an amine, synthesized from the amino acid precursor tyrosine; includes dopamine, norepinephrine, and epinephrine.

Tyrosine Hydroxylase (TH)

The rate-limiting enzyme in catecholamine synthesis that converts tyrosine to L-dopa; inhibited by high cytosolic catecholamine levels when release rate is low, and stimulated by high release rates or increased $\text{Ca}^{2+}$ concentration.

Substantia Nigra Pars Compacta

A midbrain region containing dopaminergic neurons that degenerate and die in Parkinson's disease.

Mesolimbocortical Pathway

A dopaminergic pathway originating in the ventral tegmental area (VTA) and projecting to the nucleus accumbens, cortex (including insula), and hippocampus; involved in motivation, reward processing, and decision-making.

Mesostriatal Pathway

A dopaminergic pathway projecting from the substantia nigra to the striatum (caudate and putamen) that plays a critical role in activating goal-directed motor actions.

D1-like Receptors

A family of metabotropic dopamine receptors (including D1 and D5) that stimulate adenylyl cyclase, increasing cAMP and PKA levels to enhance the $\text{Ca}^{2+}$ influx necessary for neurotransmitter release.

D2-like Receptors

A family of metabotropic dopamine receptors (including D2, D3, and D4) that inhibit adenylyl cyclase, decreasing cAMP production from ATP and lowering overall cellular activity.

Dopamine Transporter (DAT)

A presynaptic membrane protein responsible for clearing dopamine from the synaptic cleft via reuptake, dictating synaptic dopamine availability.

Locus Coeruleus

A brainstem nucleus located in the rostral area of the pons that serves as the primary site for norepinephrine synthesis in the central nervous system.

Adrenergic Receptors

G-protein coupled receptors bound by norepinephrine and epinephrine, categorized into excitatory $\alpha_1$, inhibitory $\alpha_2$, and excitatory $\beta$ subtypes.

Epinephrine

A catecholamine converted from norepinephrine that acts in the periphery (cannot cross the blood-brain barrier) to increase arousal, elevate blood glucose, redirect blood flow to muscles, stop digestion, and raise cardiac output via $\beta$ receptors.

Choline Acetyltransferase (ChAT)

An enzyme specific to cholinergic neurons that synthesizes acetylcholine (ACh) from choline and acetyl CoA.

Acetylcholinesterase (AChE)

A non-cell-specific enzyme located in the synaptic cleft that breaks down acetylcholine into choline and acetic acid; its inhibition reduces heart rate and blood pressure, and irreversible inhibition causes death by respiratory paralysis.

Nicotinic Acetylcholine Receptors (nAChRs)

Ionotropic ligand-gated ion channels that open upon binding ACh or nicotine, allowing $\text{Na}^+$ influx into the postsynaptic cell for rapid excitatory signaling.

Muscarinic Acetylcholine Receptors (mAChRs)

Metabotropic G-protein coupled receptors activated by ACh or muscarine that produce slow excitatory or inhibitory postsynaptic effects, typically by altering $\text{K}^+$ and $\text{Ca}^{2+}$ channel conductance.

Diphenhydramine

An antihistamine (brand name Benadryl) that exhibits anticholinergic side effects such as slowing digestion and inducing memory loss at higher doses.

Scopolamine

A motion sickness drug that acts as a strong muscarinic ACh receptor antagonist; high doses produce delirium, hallucinations, memory loss, and tachycardia.

DREADDs

Designer Receptors Exclusively Activated by Designer Drugs; a chemogenetic technique using engineered mutant cholinergic receptors that remain dormant until selectively activated by clozapine-N-oxide (CNO).

hM3Dq

An excitatory DREADD variant that couples to the $G_q$ signaling pathway, causing neuronal activation and depolarization upon CNO binding.

hM4Di

An inhibitory DREADD variant that couples to the $G_i$ signaling pathway, causing neuronal inhibition and hyperpolarization upon CNO binding.

Cre-recombinase Technology

A genetic system combining transgenic animals expressing Cre enzyme under cell-type-specific promoters with Cre-dependent adeno-associated viruses (AAVs) carrying loxP sequences to target gene expression exclusively to specific cell types.

Otto Loewi's Experiment

A landmark physiological study demonstrating chemical neurotransmission by showing that fluid transferred from a stimulated frog heart slowed the contraction rate of a second heart, identifying the substance as acetylcholine.