Pro-gonadotropin-releasing hormone (ProGnRH) and GnRH content in the preoptic area and the basal hypothalamus of anterior medial preoptic nucleus/suprachiasmatic nucleus-lesioned persistent estrous rats

Abstract

The content of GnRH and its precursor peptide were quantified in female rats bearing lesions in the anterior medial preoptic nucleus (AMPO) and the suprachiasmatic nucleus (SCN), and the effects of the lesions on the synthetic activity of the GnRH neurons were evaluated. Electrolytic lesions which induced persistent estrous (PE), or irregular estrous cycles, were produced by passing 5-10 microA of direct current into the AMPO or the SCN of female rats which exhibited regular 4 days estrous cycles before the lesions. Approximately 5 weeks after lesion placement, blood samples were withdrawn from catheterized, freely moving animals and plasma LH, PRL, estrogen, and progesterone were determined by RIA. The preovulatory surges of LH and PRL were eliminated in AMPO- or SCN-lesioned PE rats. Moreover, the LH surge was eliminated and the PRL surge significantly attenuated after estrogen and progesterone treatment of rats bearing complete lesions, irrespective of the presence of ovaries. Irregular cycling animals with incomplete AMPO or SCN lesions, exhibited attenuated LH surge and PRL surge similar to proestrous controls. In one incidence this occurred spontaneously, and could also be induced by sequential estrogen and progesterone injections. After ovariectomy, plasma LH levels were significantly lower in the lesioned animals as compared to sham operated rats (P less than 0.05). Similar secretory patterns of LH and PRL were obtained from a second series of sham-operated rats during the different stages of the estrous cycle or from AMPO- or SCN-lesioned rats during persistent estrus. After 2 months the animals were killed between 0830 and 0930 h, and the preoptic area and the basal hypothalamus were microdissected from the brain sections. After extraction and purification, proGnRH and GnRH levels were measured by RIA. ProGnRH levels in the preoptic area were significantly reduced in AMPO- or in SCN-lesioned rats, compared to proestrous controls (P less than 0.01). In contrast, GnRH levels in either area did not differ in AMPO- or in SCN-lesioned animals compared to sham-operated, proestrous controls. Therefore, lesions of the AMPO or the SCN produce PE and reduce proGnRH without reducing GnRH levels. These data would suggest that the AMPO and the SCN participate in the control of the estrous cycle and are necessary for preovulatory surges of PRL and LH to occur and that the AMPO and the SCN form part of the neural circuit that regulates GnRH synthesis and/or release.