Weanling female and male rats were exposed to either pups or pup-sized toys for 10 days beginning at 22 days of age in order to assess differences between pup-directed and toy-directed behaviors and to determine whether exposure to pups at this time increases susceptibility to maternal sensitization in adulthood. Adult sensitization involved exposing each subject to pups for 10 days beginning at 78 days of age. The principal results were as follows: (a) Weanlings retrieved, licked, and lay over pups, but not toys, and chewed on toys, but not pups, (b) Weanling males snowed more pup retrieval than weanling females, (c) Females and males preexposed to pups during "weanlinghood" showed more retrieval and licking of pups in adulthood than those not preexposed to pups, (d) Adult females were more fully maternal or nonmaternal than were adult males or weanlings of either sex, as indicated by their lower "partial retrieval" and "inconsistent retrieval" scores, their tendency to retrieve rapidly or not at all, and their greater correlation between retrieval and nest construction.

No abstract

Behavioral and neurochemical evidence indicates links between the opioid and GABA neurotransmitter systems. To assess effects of chronic opiates on the major site of postsynaptic GABAergic activity, the GABAA receptor, we administered chronic morphine and naltrexone to mice and evaluated binding at the benzodiazepine and t-butylbicyclophosphorothionate (TBPS) sites and GABA-dependent chloride uptake. After morphine (3 days), benzodiazepine receptor binding in vivo but not in vitro was increased in cortex compared to placebo-treated mice. TBPS binding was unchanged in cortex, but muscimol-stimulated chloride uptake was increased at low doses of muscimol. Benzodiazepine and TBPS binding and muscimol-stimulated chloride uptake were unchanged in naltrexone-(8 days) compared to placebo-treated mice. When naltrexone was administered previously to block opiate sites, the increases in benzodiazepine binding and chloride uptake observed with chronic morphine were reversed. These results indicate that chronic morphine but not naltrexone enhances benzodiazepine binding and GABAA receptor function, perhaps by an action at opioid receptors.