Relationship between the thymus and neurochemical changes in the hypothalamus–preoptic area and prefrontal cortex in female rats with delayed puberty

Abstract

In female rats, aged 55–58 days with delayed puberty due to deficient growth and environmental stress, 5-hydroxyindoleacetic acid levels and serotonin turnover rate in the hypothalamus–preoptic area as well as body weight, body weight gain and relative weight of ovaries, uterus, adrenals and preputial glands were lower while serotonin and 5-hydroxyindoleacetic acid levels in the prefrontal cortex were higher when compared to normal rats with the latest onset of puberty aged 42–52 days. In rats with delayed puberty, multiple regression analysis revealed a significant negative dependence on dopamine turnover in the hypothalamus–preoptic area for body weight gain and, of all organs, for the relative weight of the thymus. A similar negative significant dependence on serotonin turnover rate in the prefrontal cortex was also found for the relative weight of thymus and spleen. The same analysis in the opposite direction revealed a significant negative dependence of 3,4-dihydroxyphenylacetic acid levels and dopamine turnover rate in the hypothalamus–preoptic area as well as serotonin turnover rate in the prefrontal cortex only on thymus weight. After separation of delayed pubertal rats into two groups, based on absolute ovarian weight, the rats in the low ovarian weight range and no signs of puberty exhibited: lower body weight gain, lower body weight, and lower relative weight only of thymus, ovaries and preputial glands in parallel with an increased dopamine turnover rate in the hypothalamus–preoptic area and serotonin turnover rate in the prefrontal cortex compared to the delayed pubertal rats in the high ovarian weight range and early signs of puberty. The results suggest that in rats with delayed puberty: (1) serotonergic activation in the hypothalamus–preoptic area is lower compared to normal puberty rats; (2) dopaminergic activation in the hypothalamus–preoptic area negatively affects body weight gain, thymus weight and initiation of puberty and (3) thymus weight is negatively implicated in dopaminergic activation in the hypothalamus–preoptic area and serotonergic activation in the prefrontal cortex and positively related to ovarian weight and early signs of puberty.