Small molecules involved in the propagation of a nerve signal across the synapses.
Classes of neurotransmitters include:
- Amino acid and derivatives: Glutamate, Glycine, GABA, Epinephrine, Dopamine, Serotonin, etc.
- Opioids: Endorphin, Enkephalin
- Peptides: Neuropeptide-Y, Oxytocin, Vasopressin, etc.
- Cannabinoid: Anandamide
- Gaseous: Nitric Oxide
Neurotransmitters are not repressive or activating per-se as their effects on the postsynaptic cell are due to different receptors.
Neurotransmitter receptors are of two types:
- Ionotropic: Ligand-gated ion channels that open up or close upon binding to neurotransmitter.
- Metabotropic: Receptors that transduce the signal through secondary messengers upon neurotransmitter binding