Astroglial CB1 Cannabinoid Receptors Mediate CP 55,940-Induced Conditioned Place Aversion Through Cyclooxygenase-2 Signaling in Mice

Cannabinoids (CBs), such as phytocannabinoids, synthetic CBs, and endogenous CBs, can be neuroprotective, rewarding, or aversive. The aversive effects of CBs may hinder their medical and recreational applications. It is unknown which type of CB receptors mediates the direct aversive effects of synthetic CB CP 55,940 which is an analog of Δ9-tetrahydrocannabinol, the major psychoactive component of marijuana. In this study, we address this question by taking the advantage of systematic type 1 CB receptor (CB1R) knockout mice and conditional reinstatement of this receptor only in astrocytes. We show that CP 55,940 at a concentration of 1 mg/kg induces conditioned place aversion (CPA) and the CPA effect of CP 55,940 is mediated by the astroglial CB1Rs. Inhibiting cyclooxygenase-2 (COX-2) eliminates CP 55,940-induced CPA in mice that only express CB1Rs in astrocytes. These findings conclude that CPA effect of CP 55,940 is mediated by the astroglial CB1Rs through COX-2 signaling, suggesting that selective COX-2 inhibition or precise isolation of astroglial CB1R activity may be the strategy for treating aversive response of medical and recreational administrations of marijuana.

Cannabinoids Exacerbate Alcohol Teratogenesis by a CB1-Hedgehog Interaction

We tested whether cannabinoids (CBs) potentiate alcohol-induced birth defects in mice and zebrafish, and explored the underlying pathogenic mechanisms on Sonic Hedgehog (Shh) signaling. The CBs, Δ9-THC, cannabidiol, HU-210, and CP 55,940 caused alcohol-like effects on craniofacial and brain development, phenocopying Shh mutations. Combined exposure to even low doses of alcohol with THC, HU-210, or CP 55,940 caused a greater incidence of birth defects, particularly of the eyes, than did either treatment alone. Consistent with the hypothesis that these defects are caused by deficient Shh, we found that CBs reduced Shh signaling by inhibiting Smoothened (Smo), while Shh mRNA or a CB1 receptor antagonist attenuated CB-induced birth defects. Proximity ligation experiments identified novel CB1-Smo heteromers, suggesting allosteric CB1-Smo interactions. In addition to raising concerns about the safety of cannabinoid and alcohol exposure during early embryonic development, this study establishes a novel link between two distinct signaling pathways and has widespread implications for development, as well as diseases such as addiction and cancer.

Effects of the cannabinoid receptor agonist CP-55,940 on incentive salience attribution

Pavlovian conditioned approach paradigms are used to characterize the nature of motivational behaviors in response to stimuli as either directed toward the cue (i.e., sign-tracking) or the site of reward delivery (i.e., goal-tracking). Recent evidence has shown that activity of the endocannabinoid system increases dopaminergic activity in the mesocorticolimbic system, and other studies have shown that sign-tracking behaviors are dependent on dopamine. Therefore, we hypothesized that administration of a cannabinoid agonist would increase sign-tracking and decrease goal-tracking behaviors. Forty-seven adult male Sprague Dawley rats were given a low, medium, or high dose of the cannabinoid agonist CP-55,940 (N=12 per group) or saline (N=11) before Pavlovian conditioned approach training. A separate group of rats (N=32) were sacrificed after PCA training for measurement of cannabinoid receptor type 1 (CB1) and fatty acid amide hydrolase (FAAH) using in situ hybridization. Contrary to our initial hypothesis, CP-55,940 dose-dependently decreased sign-tracking and increased goal-tracking behavior. CB1 expression was higher in sign-trackers compared to goal-trackers in the prelimbic cortex, but there were no significant differences in CB1 or FAAH expression in the infralimbic cortex, dCA1, dCA3, dorsal dentate gyrus, or amygdala. These results demonstrate that cannabinoid signaling can specifically influence behavioral biases toward sign- or goal-tracking. Pre-existing differences in CB1 expression patterns, particularly in the prelimbic cortex, could contribute to individual differences in the tendency to attribute incentive salience to reward cues.