Differential Photoperiodic Control of Seasonal Variations in Pulsatile Luteinizing Hormone Release in Long-Day (Ferret) and Short-Day (Mink) Mammals

Abstract

The aim of this study was to elucidate the pituitary adjustments implicated in photoperiodic control of reproduction in two mammalian species, the ferret and the mink. In the ferret, which displays renewed testicular activity when the days lengthen, we observed a stimulation of the pulsatile liberation of luteinizing hormone (LH) reflecting the pulsatile activity of the gonadotropin-releasing hormone (GnRH) system when daylight was equal to or in excess of LD 8:16. This photoperiod coincides precisely with the phase of photosensitivity known to be essential for gonadal stimulation in this species. In the mink, which displays renewed testicular activity when the days shorten, pituitary stimulation was activated when daylight was reduced to LD 11:13, and gonadal stimulation occurred only when daylight was further reduced to LD 10:14. In addition to requiring different photoperiodic stimuli to trigger the seasonal reproductive process, the two species display variations in the "timing" of pituitary control of renewed gonadal activity.

Effects of Superior Cervical Ganglionectomy and Melatonin Replacement on Intra-hypothalamic LHRH Content and Pulsatile Luteinizing Hormone Release in the Mink

“…In contrast with this, it has been previously shown in intact minks reared in natural conditions that the main parameters statistically affected during seasonal variations were pulse frequency and the correlated mean plasma LH concentration, while no significant variations in amplitude and peak length were detected (Jallageas et al, 1994b). One possibility to explain the different results obtained from intact and melatonin treated ganglionectomized mink, is that slight discrepancies in synchronization between intact animals can exist when they are maintained under natural environmental photoperiod (Jallageas et al, 1994a).…”

“…Concerning pituitary activity, we have previously observed in control mink a reasonably good correlation between mean plasma LH levels and LH pulse frequencies. At the onset of testicular rest, for instance, the pattern of LH secretion is characterized by a decrease in pulse frequency combined with a decrease of the mean plasma LH concentration (Jallageas et al, 1994b). In this study, however, the result of pineal deafferentation in untreated mink is a lack of a detectable pulsatile pattern of LH release, even though the mean plasma LH level is similar to that recorded at the onset of testicular regression in controls.…”

Dynamics of Connexin 43 Levels and Distribution in the Mink (Mustela vison) Anterior Pituitary Are Associated with Seasonal Changes in Anterior Pituitary Prolactin Content1

“…In the mink, a short-day seasonal breeder, blood prolactin (PRL) concentration has been reported highest in spring and the lactation period and lowest in autumn and winter [19][20][21][22]. Gonadotropin serum levels are low in spring and high in winter [23][24][25]. Our results indicate that mink anterior pituitary expresses Cx43 and that both the levels of the protein and the number of Cx43-positive gap junctions increase during periods of increased anterior pituitary PRL content.…”

Photoperiod Affects the Gonadotropin- Releasing Hormone Neuronal System of Male Prairie Voles <bolditalic>(Microtus ochrogaster)</bolditalic>

“…summer) breeding mammals [4, 6, 7]. Reduced secretion of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) leads to suppressed gametogenesis and steroidogenesis, and eventual regression of the reproductive system [1, 3, 8, 9].…”