The goal of this project is to examine the nature and mechanisms of nicotine-cannabinoid interaction in the modulation of synaptic transmission, with the ultimate hope of furthering our understanding of how these drugs of abuse exert their wide range of behavioral and cognitive effects. Such studies may reveal insights on the cellular substrate underlying predisposition to drug abuse in people smoking in their early age (Kandel et al., 1994). In spite of extensive studies of neuronal nicotinic receptors (nAChRs), their role in CNS function remains only partially understood. The effects of exogenously administered nicotine presumably mimics the normal control of synaptic transmission exerted by the endogenous nicotinic agonist, acetylcholine. Emergent studies from the sponsor lab in conjunction with works of Wannacott, Collins, Collier, Clark and many others indicated that a major function of nAChRs is to modulate the extent and duration of neurotransmitter release at a variety of synapses throughout the CNS. The addictive properties of nicotine are amply supported by behavioral studies demonstrating self administration. The cellular substrates and molecular mechanisms underlying nicotine addiction are not known, but the confluence of data strongly implicates nicotine induced enhancement of synaptic transmission in the dopaminergic mesolimbic pathway as critically involved in behavioral reinforcement. Furthermore, the possibility that presynaptic nAChRs might be involved in aspects of memory function is suggested by recent studies in hippocampus demonstrating potent synaptic facilitation by nicotine. Another drug of abuse (although of debatable addiction potency) that, like nicotine, mimics the action of an endogenous regulator, is terahydrocannabinol. Both plant derived and endogenous cannabinoids (e.g.anandamide) have been shown to depress neurotransmission. The ability of nicotinic agonists to facilitate, and cannabinoids to inhibit, neurotransmission suggests that these agents may interact directly or indirectly in modulating synaptic functions. To test for possible interaction of cannabinoids and nicotine, I conducted preliminary experiments examining the effects of these drugs on mouse ventral tegmental area (VTA) neurons in vitro and find that anandamide potently inhibits the nAChR-mediated activation of these neurons. The goal of my proposal is to investigate these phenomena in detail. The overall approach will be to record evoked currents (EPSCs) and spontaneous synaptic currents (SSCs) at mice VTA-nucleus accumbens (NA) and hippocampal synapses in vitro. As a first step, modulation of neurotransmission by nicotine and anandamide applied singly will be assayed by measuring nicotine-induced changes of the amplitude, time course and frequency of the SSCs, as well as in changes of the amplitude, time course and failure rate of evoked currents. Next, using the same approach, interaction at the presynaptic terminals to modulate secretion will be investigated by applying both agents together. Finally, pharmacological experiments will be conducted to dissect the molecular mechanism(s) underlying the interaction between anandamide and nicotine. These studies should better our understanding of the cellular substrates and physiological mechanisms that may underlie nicotine and cannabinoids effects on behavior and cognition. Moreover, they will provide essential information toward the evaluation of the use of nicotine and cannabinoids as therapeutic agents.
