Activity Changes of the Hypothalamus-Pituitary Hormonal Axis in Peripubertal Female Rats

Little is known about the regulation of gene expression related to the hypothalamus-pituitary (HP) axis around the onset of normal puberty. In the present study, we examined the expression profiles of genes in HP hormone circuit on every other day from postnatal day (PND) 29 to PND 43. Average vaginal opening (VO) date was PND 37 (66%), and the weight of reproductive organs increased significantly from PND 37. Serum steroid hormone levels significantly increased on PND 39. The appearance of a number of Graafian follicles and corpora lutea on PND 37. Generally, our polymerase chain reactions (PCR) results showed that most of the expression of hypothalamus and pituitary factors tended to increase after VO, and the patterns were rather unstable and no significant peak pattern such as LH surge shown in proestrus adults. The mRNA levels of gonadotropin-inhibitory hormone (GnIH)-GPR147 and neurokinin B(Tac)-TacR3 mostly reached a peak in the last period of the experimental schedule. In pituitary, mRNA level of gonadotropin subunits (Cgα, LH-β and FSH-β) also significantly increased on later experimental period. In conclusion, we could confirm the rapid growth and maturation of reproductive organs immediately after VO, and dynamic changes in gene expression of the HP axis factors. The gene expression patterns at peripubertal period were incomplete and unstable without showing the preovulatory LH surge-related gene expression pattern in adults. The present study on neuroendocrine control of peripubertal sexual maturation may offer a basis for understanding normo- and/or patho-physiological status of puberty.