Decreased in vivo binding to brain benzodiazepine receptors during social isolation.

Pharmacologic studies have demonstrated that benzodiazepines can modulate the ultrasonic vocalizations (USV) associated with social separation of rat pups. In this study, in vivo receptor autoradiography was used to determine if brain benzodiazepine receptors were functionally less available to bind an exogenous ligand during social separation. The labelled benzodiazepine receptor antagonist 3H-RO 15-1788 was given to 10-day-old rat pups during 25 minutes of social separation. In autoradiographic studies of brains from separated pups, the binding of 3H-RO 15-1788 was decreased in neocortex (frontal, motor, and somatosensory), hippocampus, and superior and inferior colliculi. As these same regions showed no alteration of in vitro binding of 3H-RO 15-1788, these in vivo binding decreases do not reflect changes in receptor number. The interpretation of decreased in vivo binding and implications of these results for defining the neural substrates of separation behavior are discussed.