Objectives: To characterize the mechanism by which cannabinoids dynamically regulate synaptic transmission in the neocortex. Plan: Specific Aim 1: Determine how cannabinoids change spontaneous synaptic transmission Using the patch-clamp technique we will record from neuronal wild-type and null cannabinoid receptor 1 (CB1) mutants and examine how endogenous and exogenous cannabinoids stimulate spontaneous release. Specific Aim 2: Determine how cannabinoids change evoked synaptic transmission Using the patch-clamp technique we will make paired recordings from neocortical neurons and test how synaptic transmission is affected by the CB1 mutants. Using single terminal recordings we will test if presynaptic ion channel modulation accounts for the cannabinoid actions. Specific Aim 3: Determine how cannabinoids shape calcium signaling at excitatory synapses CaSR affects synaptic transmission in a number of ways, impacting spontaneous and evoked, and inhibitory and excitatory forms differently. Based on preliminary data we will test to determine if there are functional interactions between CaSR and CB1 Methods: Using pharmacological and genetic approaches we will determine how cannabinoids affect synaptic transmission. Clinical Relevance: Endogenous cannabinoid signaling is vital for important brain functions. Exogenous cannabinoids have been used as recreational drugs and therapeutically to treat pain, epilepsy, and posttraumatic stress disorder. CB1 has been identified as a receptor that may be mediating many of these actions but recent data suggests that CB1 is only partially responsible. We will perform experiments to determine if CB1 is working alone or with other G-protein coupled receptors as heterodimers to mediate these effects. These experiments will provide us with preclinical data that characterize the mechanism by which cannabinoids operate at various sites in the brain. Since the pharmacological characteristics for CB1 will be different when working alone or as a heterodimers completion of our specific aims will allow us to identify more specific pharmacological targets. Enhanced understanding of these mechanisms may lead to the refinement of therapeutic cannabinoids that retain therapeutic effects but have fewer unwanted side effects. The goal is to improve control of pain, seizures, and posttraumatic stress disorder experienced by Veterans. Relevance to VA’s Mission: We have experienced a large increase in cannabinoid use in Veterans in association with its legalization and its promise as therapy for post traumatic disorder, chronic pain, and epilepsy. These diseases are prevalent in the Veteran population. Unfortunately, the large incidence of side effects with cannabinoids underlines the need for more effective and less toxic medications. By increasing understanding of the neural pathways used by endogenous cannabinoids we will identify targets for safer and more effective can nabinoids.