Synthesized from precursor tryptophan.

Synthesized in axon terminal (bouton).

Cell bodies mainly in median and dorsal raphe nuclei.

The rate-limiting factor is availability of tryptophan.

Precursors are presynaptic glucose and glutamine.

Synaptic action is terminated through reuptake.

Glutamate release is stimulated by nicotine.

Dopamine and norepinephrine are deactivated in the same pathways: Either through reuptake or synaptic metabolism by monoamine oxidase-A (MAO-A) or catecholamine O-methyl transferase (COMT).

Dopamine is metabolized into homovanillic acid (HVA) by MAO-A in the synaptic cleft, or by COMT in the presynaptic neuron after reuptake.

COMT inhibitors such as entacapone are used to increase bioavailability of levodopa in the treatment of Parkinson disease.

Reuptake or MAO-A metabolism.

Metabolite is 5-hydroxyindoleacetic acid (5-HIAA).

Locus ceruleus in the upper pons.

Receptors that when activated, can cause depolarization and increase the likelihood of an action potential.

Examples include: Dopamine (D1, D5), cholinergic receptors, norepinephrine (NE-α1, NE-β), serotonin (5-HT1c, 5-HT2, 5-HT3), glutamate receptors, and substance P-NK.

A membrane anchored receptor with a single unit.

A single peptide forms seven transmembrane domains.

They use a second messenger system, therefore are slow in response.

Examples of G-protein coupled receptors: All 5-HT receptors except 5-HT3, most dopamine receptors, all opioid receptors, norepinephrine receptors.

Receptors that when activated, can cause hyperpolarization and decrease the likelihood of an action potential.

Examples include: Dopamine D2, D3, D4, NE-α2, 5-HT1A, γ-aminobutyric acid (GABA-A), opioid μ and δ.

Ion channels connected to a receptor. The binding of ligands to the receptor changes the opening of the ion channels, and therefore regulates the ion channels.

Substantia nigra, supplies nigrostriatal pathway, associated with extrapyramidal syndrome;

Ventral tegmental area (VTA), supplies mesolimbic pathway and mesocortical pathway, associated with antipsychotic effects and reward system;

Hypothalamus, supplies tuberoinfundibular pathway, associated with prolactin regulation.

It is generally assumed that the mesolimbic pathway is associated with positive symptoms, and the mesocortical pathway is associated with negative symptoms.

Endogenous opioids (enkephalins, endorphins, and dynorphins).

Substance P.

Neurotensin.

Somatostatin.

Vasopressin.

Oxytocin.

Neuropeptide Y.

All peptide neurotransmitters are synthesized in the soma (cell body).