Prenatal Cannabinoid Exposure Mediated Cognitive Deficits in the Offspring: Elucidation of the Mechanism and Identifying Therapeutic Targets

Abstract

Cannabinoid is currently one of the most commonly used recreational drugs in the world with an approximate user of 22.2 million. As more and more states in the US are legalizing the use of cannabinoid, the rate of cannabinoid use is increasing specially in pregnant women. The active ingredient of cannabis is delta‐9‐tetrahydrocannabinol (THC) which can cross blood placental barrier and may cause enduring alterations in synaptic circuitry of the fetal brain. The aim of our study is to investigate the mechanism of learning and memory deficits in case of prenatal cannabinoid exposure (PCE) in the adolescent offspring. An osmotic pump filled with either vehicle or the cannabinoid receptor full agonist WIN55,212‐2 (2 mg/kg body weight/day) was implanted subcutaneously in Gestational Day‐3 to deliver the drug at a constant rate until the pups were born. Open field test was performed to see the effect of PCE on locomotor activity which revealed no abnormality in the general motor activity. Contextual fear conditioning test indicated a significantly reduced freezing behavior in the PCE group compared to the vehicle exposed group. Hippocampus based spatial memory test Morris water maze showed that during the trial period, PCE animals exhibit no preference for any particular quadrant while control animals had an increased preference for the quadrant where the hidden platform was present during the training period. Electrophysiological experiments were performed on the Schaffer collateral pathway of acute hippocampal slices to measure synaptic plasticity. Impairment in both long term potentiation (LTP) and long‐term depression (LTD), which are important parameters of synaptic plasticity, were observed. These impairments were associated with downstream changes in the glutamatergic signaling. An increase in cannabinoid receptor type 1(CB1) expression followed by reduced neural cell adhesion molecule (NCAM) and its active form polysialylated NCAM (PSA‐NCAM) expression have been observed in the hippocampus of PCE animals. Interestingly, restoration of PSA‐NCAM activity restored the LTP deficits observed in PCE animals. Thus, based on the previous studies and our current data, it can be postulated that, the observed cognitive deficits in the PCE animals might be partly due to an imbalance in glutamate receptors mediated neurotransmission influenced by NCAM/PSA NCAM. Understanding this specific NCAM/PSA‐NCAM interdependent signaling cascade will lead to an identification of a specific therapeutic target to improve gestational cannabinoid exposure mediated memory deficits.