Science Cannabis

102 THE SCIENCE OF MARIJUANAand catalepsy produced by cannabinoids. It is noteworthy that dogs exhibita prominent ataxia/catalepsy response to cannabinoids, and dog cerebellumis particularly enriched in CB-1 receptors, relative to othermammalian species.In the hippocampus, CB-1 sites are concentrated on the cell bodiesand apical dendrites of pyramidal cells, and these receptors are thoughtto play an important role in mediating some of the effects of marijuanaon short-term memory. There are high densities of CB-1 receptors in theolfactory bulb but these are not clearly associated with any particularaspect of the drug's actions. Receptors are present in some regions ofhypothalamus, and these may account for the effects of marijuana oncardiovascular function and the control of body temperature. The relativeabsence of CB-1 receptors from brainstem structures is undoubtedlyrelated to the low toxicity of the cannabinoids, as they do not directlyaffect the key brainstem nuclei involved in the control of respiration orblood pressure. Although the density of sites is relatively low, CB-1 receptorbinding is present at all levels in the spinal cord, and is enriched indorsal horn. These sites may be of importance in mediating the analgesicactions of cannabinoids, and in the synergistic interaction of cannabinoidswith opioid analgesics.What Can Animal Behavior Experiments Tell Us?Studying the actions of psychotropic drugs in animals is inherently difficult—theanimals cannot tell us what they are experiencing. The applicationof ingenious behavioral tests, however, can tell us a great dealabout how a drug "feels" to an animal. One technique that is widely usedassesses the discriminative stimulus effects of CNS drugs. In this test theanimals, usually rats, are trained to press a lever in their cage in order toobtain a food reward, usually a small attractively flavored food pellet, andthe reward is given automatically after a certain number of lever presses.The animals are then presented with two alternative levers and mustlearn to press one (the saline lever) if they had received a saline injectionjust before the test session, or the other (the drug lever) if they had been