Classes of neurotransmitters include:
- Amino acid and its derivatives: Glutamate, Glycine, GABA, Epinephrine, Dopamine, Serotonin etc
- Opioids: Endorphin, Enkephalin
- Peptides: Neuropeptide-Y, Oxytocin, Vasopressin etc
- Cannabinoid: Anandamide
- Gaseous: Nitric Oxide
Neurotransmitters per-se are not repressive or activating and their effects on the postsynaptic cell is because of the 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