Age- and sex-related induction of excessive grooming and "wet-dog" shakes by the codeinone RX 336-M in the rat.

Peripheral administration of the dihydrocodeinone RX 336-M (6 mg/kg) stimulated vigorous "wet-dog" shakes and excessive grooming in young drug-naive rats. The effects of RX 336-M were greater in younger than in older animals of both sexes, and were greater in 39-day-old male rats than in female rats of the same age. In a second experiment, female rats were pretreated with testosterone benzoate (1 mg/kg/day) for 1 week prior to testing the effects of RX 336-M at 39 days of age. The sex hormone pretreatment enhanced the ability to RX 336-M to induce "wet-dog" shakes and excessive grooming in female rats. The results suggest that both sex- and hormone-dependent developmental status are critical in the display of the so-called "quasi-morphine withdrawal syndrome." The results imply, and are consistent with previous studies which suggest, that different neural mechanisms underlie the behavioral responses induced by ACTH and RX 336-M.