The release of pituitary LH and sprouting of LH-releasing hormone (LHRH)-containing neurons after anterior hypothalamic deafferentation

History of the Development of Knowledge about the Neuroendocrine Control of Ovulation-Recent Knowledge on the Molecular Background

The physiology of reproduction has been of interest to researchers for centuries. The purpose of this work is to review the development of our knowledge on the neuroendocrine background of the regulation of ovulation. We first describe the development of the pituitary gland, the structure of the median eminence (ME), the connection between the hypothalamus and the pituitary gland, the ovarian and pituitary hormones involved in ovulation, and the pituitary cell composition. We recall the pioneer physiological and morphological investigations that drove development forward. The description of the supraoptic-paraventricular magnocellular and tuberoinfundibular parvocellular systems and recognizing the role of the hypophysiotropic area were major milestones in understanding the anatomical and physiological basis of reproduction. The discovery of releasing and inhibiting hormones, the significance of pulse and surge generators, the pulsatile secretion of the gonadotropin-releasing hormone (GnRH), and the subsequent pulsatility of luteinizing (LH) and follicle-stimulating hormones (FSH) in the human reproductive physiology were truly transformative. The roles of three critical neuropeptides, kisspeptin (KP), neurokinin B (NKB), and dynorphin (Dy), were also identified. This review also touches on the endocrine background of human infertility and assisted fertilization.

Circadian locomotor rhythms, but not photoperiodic responses, survive surgical isolation of the SCN in hamsters

Surgical isolation of the suprachiasmatic nuclei (SCN) within a hypothalamic island is reported to produce loss of circadian rhythmicity. The results have been interpreted to indicate that SCN efferents are necessary for the expression of circadian rhythms. It is not clear, however, whether the loss of circadian rhythms in behavioral responses following SCN isolation is attributable to transection of efferents, to loss of cells within the island, or to gliosis produced by the knife cut. To explore this issue, we examined locomotor activity and gonadal state of male golden hamsters housed in constant darkness (DD, with a dim red light for maintenance) for at least 10 weeks following isolation of the SCN from the rest of the brain by cuts by means of a Halasz wire microknife. Brain sections were immunocytochemically stained for the peptides vasoactive intestinal polypeptide (VIP), vasopressin (VP) or neurophysin II (NP II), and neuropeptide Y (NPY) to localize the SCN and to assess its viability, and for glial fibrillary acidic protein (GFAP) to delimit the border of the knife cut. Experimental animals with VIP and VP/NP II immunoreactivity in the SCN within the island retained free-running locomotor rhythms following transection of SCN efferents. Animals with cuts that failed to sever SCN efferents, and sham-operated animals (in which the Halasz knife was lowered but not rotated), also maintained circadian rhythmicity. Hamsters sustaining severe damage to the SCN showed disrupted locomotor activity. In those hamsters that retained circadian locomotor rhythmicity following SCN isolation, gonads failed to regress in DD, demonstrating the absence of an appropriate photoperiodic response. The results suggest a multiplicity of SCN coupling mechanisms in the control of circadian rhythms.

Catecholamine reinnervation of supraoptic nucleus after deafferenting mechanical lesions and superior cervical ganglionectomy: histofluorescence and functional assessments in young adult and aged rats

Catecholaminergic innervation of the hypothalamic vasopressin (VP)-secreting supraoptic nucleus (SON) was examined at selected intervals after deafferenting neurosurgical lesions, with respect to potential contribution of peripheral vascular sympathetic fibers. Young adult (3 months) and aged (20 months) male F344 rats were subjected to mechanical knife-cut lesion just caudal and medial to the SON, superior cervical ganglionectomy (SCGx), or both surgeries. SON and lesion sites were assessed at 4, 14, 30 or 45 days after surgery, by CA histofluorescence. Functional evaluation in rats subjected to chronic lesions consisted of monitoring water balance (water consumption and urine volumes, and urine osmolality and VP content) in individual rats for presurgical and postsurgical intervals. Histofluorescence evaluation showed that SCGx did not affect the overall SON fluorescence pattern, although a minor sympathetic contribution to that pattern was discerned by comparing SON in rats subjected to lesion alone vs SCGx + lesion. Morphological reinnervation of SON was accomplished at 30 days in young rats, and 45 days in aged rats, after both lesion and SCGx. In young rats, histofluorescence density 30 days after deafferentation was denser than the innervation pattern seen in intact (sham-lesioned) animals, while reinnervation at 45 days postsurgically in aged rats only approximated the presurgical pattern. Vasopressin excretion and corresponding water conservation measures were compromised by SON deafferentation at both ages; excreted VP levels and water balance did not rebound to presurgical values at chronic postsurgical intervals in either young or aged rats.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of prior surgical disconnection of the anterior mediobasal hypothalamus on LHRH release in vitro

The degenerative responses of luteinizing hormone-releasing hormone (LHRH)-containing neurons within the mediobasal hypothalamus (MBH) after knife cut lesions (FC) made in the frontal plane of the retrochiasmatic hypothalamus include a reduced number of LHRH-immunoreactive (ir) nerve terminals in the median eminence, reduction in LHRH content of the MBH and growth of novel irLHRH-containing neural processes into FC scar tissue. We have now investigated basal and secretogogue-evoked LHRH release in vitro from the preoptic area-MBH (POA-MBH) of adult male rats at 10 or 60 days after FC. Basal LHRH release rate (P less than 0.05) and total (P less than 0.01) amount released 60 days after FC were reduced when compared to control (CONT) hypothalami, but not shams. A 30 min pulse of naloxone (NAL, 1 mg/ml) stimulated greater than 2-fold relative increase in LHRH release for all groups; however, the total amount of LHRH released by FC hypothalami was less (P less than 0.05) than that of CONT, but not sham POA-MBHs. Although exposure to elevated KCl significantly increased (P less than 0.01) LHRH release for all 3 groups, the FC secretory response was less than that of both CONT (P less than 0.05) and sham (P less than 0.01) groups. In the second experiment single POA-MBH were perifused at 10 days (sham and FC) or 60 days (CONT, sham and FC) after surgery.(ABSTRACT TRUNCATED AT 250 WORDS)