CaV2.2 splice variants in the hippocampus: function and pharmacology

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The effects of cannabinoids are diverse and dose dependent. For instance, low doses produce anxiolysis whereas high doses induce anxiety; similar effects have been seen on memory and cognition. However, the reasons for this are not clear. At the synapse level, the cannabinoid receptor 1 (CB1R) is known to impact transmitter release through inhibition of presynaptic calcium channels, including the N-type (CaV2.2) channels that are paramount in coupling neuronal activity to transmitter release in the hippocampus (HPC). This brain area is important for emotional processing and learning, and CaV2.2 channels are essential in one of the best-studied circuits in the brain. Our long-term goal is to decipher the regulation and function of CaV2.2 channels at specific HPC synapses to inform basic mechanisms of HPC activity, and enable novel therapies based on CB1R signaling. Alternative splicing is a cell-specific mechanism that impacts the function and regulation of CaV2.2 channels. Splicing of exon 18a generates the +18a-CaV2.2 and D18a-CaV2.2 splice variants. Neurotransmission in synapses that express +18a-CaV2.2 variants exhibit enhanced probability of transmitter release, and reduced modulation by CB1R agonists compared to those that express the +18a-CaV2.2 variants, but the underlying mechanisms are unknown. +18-CaV2.2 splice variants contain a 21 aminoacid insertion in the region that interacts with the release machinery. Our central hypothesis is +18a-CaV2.2 splice variants enhance transmitter release and prevent CB1R inhibition of neurotransmission via differential interaction with SNARE proteins. To test this, we will use validated mouse models with restricted splice choice (+18a-only or 18a-only) and recombinase-based labeling of specific neurons in HPC for electrophysiology in acute slices, and biochemical assays to evaluate protein interaction. The specific aims of the project are: 1) To determine the functional impact of +18a-CaV2.2 and D18a-CaV2.2 splice variants on transmitter release in HPC, and 2) To determine the role of +18a-CaV2.2 and D18a-CaV2.2 splice variants on CB1R modulation of transmitter release in HPC. The results of this project are expected to provide insights into the basic mechanisms underlying hippocampal function, as well for the contradictory effects of cannabinoids. Novel cell-specific effectors of CB1R signaling could positively impact development of cannabinoid-based therapeutics