Peptidergic neurohormonal systems in the basal hypothalamus of the ferret and the mink: Immunocytochemical study of variations during the annual reproductive cycle

Abstract

The hypothalamic systems secreting corticotropin-releasing hormone (CRF), somatostatin, oxytocin, vasopressin and luteinizing hormone-releasing hormone (LHRH) were characterized using immunochemistry, and variations were studied in relation to the recrudescence of testicular activity in the ferret and the mink, two species with opposite photoregulation of their annual reproductive cycles. Under the present conditions of study, the immunoreactivity of the CRF, somatostatin, and oxytocin systems showed no significant variation in either species. In contrast, in these two species, the immunoreactivity of the LHRH system varied considerably depending on the date of observation. The increase in the number and immunoreactivity of the LHRH-secreting neurons that occurred in November in the mink and in January in the ferret, is in agreement with previous results showing that the photoperiod plays an essential role in regulating the annual activity of the testis and that the photoperiodic environmental conditions required for the activation of the LHRH system differ between the species. Similarly, correlations could be found between an increase in immunoreactivity of the vasopressinergic axons projecting to the external median eminence and the recrudescence of testicular activity.

Suprachiasmatic Nucleus Lesions Abolish Photoperiod-Induced Changes in the Testis Function and GnRH Immunoreactivity in the Mink, a Short-Day Breeder

“…Brains of intact and SCNx minks were fixed for the immunocytochemical study of the GnRH neurohormonal system as previously de scribed [5,24]. After deep equi-thesin anesthesia, animals were per fused through the heart with PBS followed by a fresh solution o f 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.2) containing 0.2% picric acid.…”

“…Brains were then removed from the skull, carefully dissected and the hypothalamus was immersed in the perfusion fixative at 4°C for the next 24-48 h. They were then rinsed for 18 h in PBS containing 10% sucrose and frozen in liquid nitrogen. Ten-micron-thick frontal sections were cut in a cryostat and serially thaw-mounted on gelatincoated histological slides before being treated for indirect immunof luorescence microscopy as previously described [5,24]. Sections were incubated for 18 h with a primary antibody diluted 1:200, GnRH rabbit antiserum raised in our laboratory [24] and for 3 h with a secondary antibody conjugated with fluorescein isothyocyanate diluted 1:100.…”

“…Ten-micron-thick frontal sections were cut in a cryostat and serially thaw-mounted on gelatincoated histological slides before being treated for indirect immunof luorescence microscopy as previously described [5,24]. Sections were incubated for 18 h with a primary antibody diluted 1:200, GnRH rabbit antiserum raised in our laboratory [24] and for 3 h with a secondary antibody conjugated with fluorescein isothyocyanate diluted 1:100. For each brain, immunostained perikarya were localized in 240-260 pm of tissue consisting of serial 10-urn sections (mean, 25 sections/animal).…”

“…Minks were anesthetized and perfused through the heart with phosphate-buffered saline (PBS) followed by 4% paraformalde hyde as previously described [24]. 30 pm serial frontal sections were cut throughout the suprachiasmatic area and stained with cresyl violet.…”

Morphofunctional Evidence for the Involvement of Hypothalamic Dopaminergic and GABAergic Neurons in the Mechanisms of Photoperiod-Dependent Prolactin Release in the Mink

“…Briefly, sections were incubated for 18 h in a humid atmosphere with primary antibody diluted to 1/1,000 and for 3 h with a secondary antibody conjugated with fluorescein isothiocyanate diluted to 1/100. Sections were carefully rinsed in PBS between the primary and sec ondary antibodies [22].…”