Increased mortality, hypoactivity, and hypoalgesia in cannabinoid CB1 receptor knockout mice

Delta(9)-Tetrahyhrocannabinol (Delta(9)-THC), the major psychoactive ingredient in preparations of Cannabis sativa (marijuana, hashish), elicits central nervous system (CNS) responses, including cognitive alterations and euphoria. These responses account for the abuse potential of cannabis, while other effects such as analgesia suggest potential medicinal applications. To study the role of the major known target of cannabinoids in the CNS, the CBI cannabinoid receptor, we have produced a mouse strain with a disrupted CB1 gene. CB1 knockout mice appeared healthy and fertile, but they had a significantly increased mortality rate. They also displayed reduced locomotor activity, increased ring catalepsy, and hypoalgesia in hotplate and formalin tests. Delta(9)-THC-induced ring-catalepsy, hypomobility, and hypothermia were completely absent in CBI mutant mice. In contrast, rye still found Delta(9)-THC-induced analgesia in the tail-flick test and other behavioral (licking of the abdomen) and physiological (diarrhea) responses after Delta(9)-THC administration. Thus, most, but not all, CNS effects of Delta(9)-THC are mediated by the CB1 receptor.