In vivo neurochemical effects induced by changes in endocannabinoid neurotransmission.

Neurotropic effects of endo- and exo-cannabinoids are largely caused by their effects on classical neurotransmitter signaling. Pharmacological and molecular tools have been used to selectively target the endocannabinoid system. Endocannabinoids mostly act as retrograde messengers and, upon release from postsynaptic neurons, they modulate neurotransmitter release by activating presynaptic cannabinoid receptors. Generally, increased and decreased endocannabinoid neurotransmission results in decreases and increases in neurotransmitter release, respectively. However, net effects are often pleiotropic, probably owing to the level of regional endogenous tone, transsynaptic mechanisms and cumulative actions. Changes in classical neurotransmitter function can, in turn, modulate endocannabinoid signaling. Importantly, the endocannabinoid system can be altered in response to physiological and pathogenic events and targeted for therapeutic intervention.