Differential response to acute and repeated stress in cannabinoid CB1 receptor knockout newborn and adult mice.

Previous studies have suggested that the endocannabinoid CB1 receptor (ECBR) system is involved in stress. However, the nature of this association is complex. Here, we investigated the role of CB1 receptors in the response to stress by comparing the effects of various stress modalities in CB1-/- receptor deficient and wild-type mice, at adulthood and during early development. Response to acute stress was assayed by plasma corticosterone (CS) and adrenocorticotrophic hormone (ACTH), USVs and motor inhibition. The response to repeated stress was assessed by USVs and motor inhibition. Since repeated bell stress seemed to cause a cumulative fear in CB1 receptor knockout mice, these behavioral responses were also compared to those observed after a single severe stress (forced swimming). In wild-type, but not in CB1 receptor knockout mice, bell stress-induced elevations of ACTH and CS were significant. The first exposure to bell stress had no significant effect on USVs or mobility. Upon repeated exposures, significant suppression of USVs, together with behavioral inhibition, were observed in CB1 knockout but not in wild-type mice. Swim stress inhibited USVs in the knockout animals, and the profound motor inhibition displayed by all animals was greater and more prolonged in the CB1-/- mice. Since the knockout mice lack the CB1 receptor throughout pre- and postnatal life, the stress response in pups was also assayed (by separation-induced USVs). Wild-type pups displayed the characteristic developmental peak in USV emissions; it was completely lacking in knockout pups. We conclude that acutely, the absence of CB1 receptors reduces the neuroendocrine response and does not affect the behavioral response to moderate stress. However, upon repeated stress or acute severe stress, CB1 receptor deficiency causes persistent behavioral inhibition. Finally, the CB1 receptor plays a role in modulating the stress response from an early age. These observations suggest that CB1 receptors participate in the mediation of the stress response and that the absence of these receptors results in a greater vulnerability to stress. We suggest that the stress-induced endocrine and behavioral suppression in CB1 receptor deficient mice may serve as a model for some forms of post-traumatic stress disorder (PTSD). Further, the role of CB1 receptors in coping with stress is a lifelong function. Finally, although equivalent research has not been performed in human infants, the postnatal suppression of the stress response in CB1 receptor knockout pups may have implications when cannabinoid-based therapy is considered for children.

Up-regulation of the endocannabinoid system in the uterus of leptin knockout (ob/ob) mice and implications for fertility.

The levels of the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) are under the negative control of leptin in the rodent hypothalamus. As leptin and endocannabinoids play opposite roles in the control of reproduction, we have investigated whether the impaired fertility typical of leptin-defective ob/ob mice is due, in part, to enhanced uterine endocannabinoid levels. We found that levels of both anandamide and 2-AG in the uterus of ob/ob mice are significantly elevated with respect to wild-type littermates, due to reduced hydrolase activity in the case of anandamide, and to reduced monoacylglycerol lipase and enhanced diacylglycerol lipase activity in the case of 2-AG. Furthermore, the process mediating endocannabinoid cellular uptake was also impaired in ob/ob mice, whereas the levels of cannabinoid and anandamide receptors were not modified. Although ineffective in wild-type mice, treatment of ob/ob mice with leptin re-established endocannabinoid levels and enzyme activities back to the values observed in wild-type littermates. Finally, treatment of ob/ob females with the CB1 receptor antagonist SR141716A did not improve their fertility, and inhibition of endocannabinoid inactivation with the endocannabinoid uptake inhibitor OMDM-1 in wild-type females did not result in impaired fertility.