During early brain development hippocampal activity is driven by two excitatory neurotransmitters, glutamate and GABA. Because GABA does not have the usual inhibitory function it has in the mature brain, other systems need to be in place to stabilize the activity of neuronal networks and prevent the potential danger of runaway excitation that may lead, for example, to epileptic activity. Potential candidates for such a system are the endocannabinoids: endogenously produced metabolites capable of activating the brain's cannabinoid (CB) receptors. Bernard et al. investigated endocannabinoid signaling during the first postnatal week in the rat hippocampus, an age that corresponds, in terms of brain development and physiological activity, to the last trimester of pregnancy in humans. Endocannabinoids were released by both interneurons and pyramidal cells in the CA1 region of the hippocampus, activating CB1 receptors and reducing GABA release. Interfering with endocannabinoid signaling during pregnancy either by smoking cannabis or by using recently developed CB1 receptor antagonists may thus affect the normal brain development of the fetus and the newborn child. — PRS
Proc. Natl. Acad. Sci. U.S.A. 102, 9388 (2005).