Changes in brain opiate receptors in rats with isolation syndrome

Prolonged social isolation of Wistar rats produces various neurochemical, neuroendocrine and behavioral changes. Some of isolated rats exhibit interspecies aggressive behavior (mouse-killing). It is suggested that social isolation leads to a stress-like state of rats. On the other hand, the participation of endogenous opioid mechanisms in stress is well known. We found that social isolation induced a decrease in the number of opiate receptors in rat frontal cortex, striatum, hippocampus and periaqueductal grey matter. The decrease was most pronounced in isolated aggressive rats. The affinity of opiate receptors in striatum and hippocampus was increased and in frontal cortex was decreased, these changes being more distinct in isolated aggressive than in isolated non-aggressive rats. These data suggest that social isolation of rats induces great changes in brain opiate receptor functions.