Neuroendocrine changes following habituation of animal hypnosis in male rabbits

Neuroendocrine changes have been studied in male rabbits during daily repeated inductions of animal hypnosis. All the animals attained the habituation but after different times, showing a different individual sensitivity to the treatment. Once habituation was reached, further treatment did not elicit any recovery. Corticosterone plasma levels gradually increased during treatment, reached a peak at habituation and did not change afterwards. Because corticosterone was not modified after habituation was established, despite further manipulation of the animals, it can be assumed that the increase of corticosterone is due to hypnosis. ACTH did not follow the same pattern of variation as corticosterone: an increase was found at habituation, but this was not statistically significant. Estradiol decreased and the testosterone/estradiol (T/E) ratio increased on the final day with respect to Day 1, whereas testosterone plasma levels were not modified by the treatment. However, there was a general increase of testosterone metabolites (dihydrotestosterone, estradiol) studied in vitro in the anterior hypothalamus of rabbits sacrificed at the end of the treatment. Thus the different responsiveness associated with repeated induction of animal hypnosis changes basal levels of ACTH, steroid hormones and central testosterone metabolism.