Cannabinoid modulation of rat pup ultrasonic vocalizations.

The present study investigated the effects of the cannabinoid receptor agonist CP 55,940 (1-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl) phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol) and the cannabinoid receptor antagonist SR 141716A (N-(piperidin-l-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1 H-pyrazole-3-carboxamide hydrochloride) on ultrasonic vocalizations, body temperature and activity in 11-13-day-old rat pups. Testing occurred in a 5-min session 30 min following drug administration. CP 55,940 produced a dose-dependent decrease in ultrasonic vocalizations, with a 1000-micrograms/kg dose causing an almost complete inhibition of calls. Doses of 100 and 1000 micrograms/kg of CP 55,940, but not 10 micrograms/kg, caused significant hypothermia in the pups and the 1000 micrograms/kg dose also inhibited activity. The cannabinoid receptor antagonist SR 141716A (20 mg/kg) reversed the effects of 1000 micrograms/kg CP 55,940 on ultrasonic vocalizations and body temperature, but the benzodiazepine receptor antagonist flumazenil (20 mg/kg), the dopamine D1 receptor antagonist SCH 23390 (0.5 mg/kg) and the opioid receptor antagonist naloxone (1 mg/kg) did not. When administered alone, SR 141716A (20 mg/kg) increased pup ultrasonic vocalizations without affecting body temperature or activity. These results indicate that cannabinoids modulate ultrasonic vocalization production in rat pups in a manner that is independent of hypothermia. The increase in ultrasonic vocalizations produced by SR 141716A is one of the first reported behavioural effects of this drug and suggests that the endogenous cannabinoid ligand anandamide may be involved in the regulation of ultrasonic vocalizations.