Anxiety, motor activation, and maternal-infant interactions in 5HT(1B) knockout mice

This study describes the development of anxiety and motor activation in mic e lacking the serotonin (5HT) 1B receptor and in wild type controls and cha racterizes their early mother-infant interactions. In the isolation-induced ultrasonic vocalization paradigm, 5HT(1B) knockout pups vocalized less and were hyperactive, rearing, jumping, and rolling more often than wild type pups. One week postpartum, 5HT(1B) knockout mothers spent 20% more of their time outside the nest and were also hyperactive, rearing and climbing to t he edge of the cage more often than the wild type mothers. There were no ge notype effects on pup retrieval. Knockout adults were less anxious in the e levated plus-maze, defecated less, and head-dipped more, although none of t he standard measures of anxiety (time and entries in the open arms) were di fferent. 5HT(1B) knockout mice of both sexes were hyperactive during both t he light and the dark phases of the 24-hr cycle. Thus, 5HT(1B) knockout mic e show reduced anxiety and are hyperactive throughout their life.