Differential role of cholecystokinin receptor subtypes in opioid modulation of ongoing maternal behavior

Cholecystokinin (CCK) can have effects opposite those of opioids. The prese nt study was undertaken to determine whether peripheral injections of antag onists of the CCK1 receptor (lorglumide) and the CCK2 receptor (L-365,260) can influence the effects of morphine on maternal behavior during lactation . A total of 110 female Wistar rats were tested on days 5 and 6 postpartum. Groups were randomly assigned to morphine vehicle (MV-SC) + saline (S-IP), MV + lorglumide (LDR: 1.0 or 10.0 mg/kg), MV + L- 365,260 (10 mg/kg), morp hine chlorhydrate (MC: 7.0 mg/kg) + S, MC + LOR (1.0 or 10.0 mg/kg), and MC + L-365,260 (1.0 or 10 mg/kg). Maternal behavior testing was started 30 mi n after the injections, at which time pups were placed in the home cage of their mother. Latencies for retrieval, grouping, and crouching responses we re scored. The results show that both lorglumide and L-365,260 potentiated the MC-induced inhibition of maternal behavior. In addition L-365,260 treat ment alone inhibited maternal behavior. Blockade of both the CCK1 and CCK2 receptors potentiated the morphine-induced disruption of maternal behavior, while CCK2 antagonism alone also inhibited this behavior. The results sugg est that CCK2 antagonism of opioid-induced disruption of maternal behavior occurs due to the action of CCK on both CCK1 and CCK2 receptor subtypes. (C ) 1999 Elsevier Science Inc.