Long-term effects of behavioral testing on serum hormones and brain weight

The effects of prior behavioral testing on endocrine function, brain weight, and neurotransmitter receptors were examined. Rats with a history of behavioral testing were significantly different from comparatively naive animals. Prior tested male and females had lower prolactin levels than nontested animals, and serum luteinizing hormone and corticosterone levels were elevated in males. In both sexes, hippocampal brain weight was greater in previously tested animals. However, estimates of brain membrane protein content and neurotransmitter receptors were unaffected by prior testing. These data suggest that prior tested animals respond as if they had experienced a history of chronic stress. Therefore, past history of the organism must be considered in studies designed to evaluate any agent's effect on neuroendocrine or neurochemical parameters.