The cannabinoid receptor/transmitter system is under intense investigation as to the delineation of its many roles in modulating and controlling neural processes which range from analgesia to memory (Howlett 1998). The research proposed in this application is a continuation of an ongoing program to study the electrophysiological and neurobiological factors responsible for cannabinoid receptor mediated effects in the CNS and in particular in the hippocampus. The current research program is investigating three major areas of cannabinoid receptor function, 1) which specific subtypes of potassium channels are responsible for the types of currents previously shown to be modulated by cannabinoid receptor-G-protein coupling to different cellular signaling processes, 2) to determine the interaction between GABAergic mechanisms and cannabinoid receptor activation in culture and in slices of hippocampus and 3) to investigate in further detail the protective effect of cannabinoids with respect to NMDA and mitochondrial models of neurotoxicity. Each of the above aims is directly related to a fourth objective of the program which is to evaluate and characterize the electrophysiological consequences that occur from tolerance to cannabinoids following chronic exposure. In prior studies this laboratory it was shown that repeated administration of cannabinoid agonists resulted in desensitization of the cannabinoid receptor-to-G-protein coupling as evidenced by decreased receptor stimulated GTP-gamma-S binding (Sim et al., 1996). In this project we propose to examine the changes in the above cannabinoid mediated processes (K-channel and GABA-B receptor modulation) in a cellular model of tolerance using primary cultures of hippocampal neurons. These effects will then be compared with recordings made in hippocampal slices obtained from tolerant animals. Information obtained from those studies will be applied to investigations of the protective actions of cannabinoids in cellular models of neurotoxicity in which hippocampal cells in culture are protected if exposed to 2 different cannabinoid receptor agonists (WIN 55,212-2, CP55940).