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

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

Grant Number: 5R01MH124811-05
NIH Institute/Center: NIH
Principal Investigator: Arturo Andrade