Glutamate (neurotransmitter)
In neuroscience, glutamate refers to the anion of glutamic acid in its role as a neurotransmitter: a chemical that nerve cells use to send signals to other cells. It is by a wide margin the most abundant excitatory neurotransmitter in the vertebrate nervous system. It is used by every major excitatory function in the vertebrate brain, accounting in total for well over 90% of the synaptic connections in the human brain. It also serves as the primary neurotransmitter for some localized brain regions, such as cerebellum granule cells.
Endocannabinoid system
Cannabinoid binding sites exist throughout the central and peripheral nervous systems. The two most relevant receptors for cannabinoids are the CB and CB receptors, which are expressed predominantly in the brain and immune system respectively. Density of expression varies based on species and correlates with the efficacy that cannabinoids will have in modulating specific aspects of behavior related to the site of expression. For example, in rodents, the highest concentration of cannabinoid binding sites are in the basal ganglia and cerebellum, regions of the brain involved in the initiation and coordination of movement. In humans, cannabinoid receptors exist in much lower concentration in these regions, which helps explain why cannabinoids possess a greater efficacy in altering rodent motor movements than they do in humans.