High sensitivity of brain octopamine levels to stress.

Rats were submitted to unsignalled and uncontrolled electrical shocks. When re-exposed to the same situation but not shocked, 24 h later, their locomotor activity was significantly reduced compared to that of controls. This conditioned suppression was associated with a significant decrease in p-octopamine (OA) in brain stem and hypothalamus. Shocks delivered just before brain fixation produced an even larger decrease in cerebral OA. Heart levels of OA were not affected. Cerebral and peripheral levels of dopamine and noradrenaline were not significantly or reliably affected. These results, as those of previous experiments, suggest that octopamine is involved in emotional, neurovegetative responses to stress.