Superior cervical ganglionectomy prevents gonadal regression and increased plasma prolactin concentrations induced by long days in goats

Abstract

The effects of the abolition of the diurnal change in melatonin secretion on the photoperiodic response of the gonadal axis and prolactin secretion to long days were examined in female goats. Female Saanen goats, reared under short-day conditions (8 h light: 16 h darkness; lights on at 05.00 h) at 22 +/- 2 degrees C for 5 months, were bilaterally superior cervical ganglionectomized (SCGX). One month after surgery, both SCGX and intact control goats were divided into two groups. Animals in group 1 were maintained under short days and those in group 2 moved to long days (16 h light: 8 h darkness; lights on at 05.00 h). In group 1, both SCGX and intact goats ovulated periodically and basal plasma prolactin levels were maintained throughout the day. In intact controls, exposure to long days suppressed ovulation and increased prolactin secretion for the first 150-200 days of exposure. The animals became photorefractory after this time; ovulation recurred and prolactin secretion returned to basal levels. Superior cervical ganglionectomy abolished or weakened the suppression of gonadal function and eliminated the increase in prolactin secretion induced by exposure to long days in the intact controls. These results suggest that the pattern of melatonin secretion under long days is necessary to induce the photoperiodic response of gonadal function and prolactin secretion to long days and that, under natural conditions, melatonin regulates the seasonal changes in gonadal function and prolactin secretion by mediating the effect of long days.

Effects of 5-Hydroxytryptophan and Melatonin on Plasma Prolactin Concentration in Intact and Cervical Ganglionectomized Goats

“…It has been reported that the dissection of epiphysis or ganglion cervicale craniale in sheep and goats reduces the plasma PRL concentration 6,7,13,14). This was partly verified in the present experiment, because the plasma PRL concentrations in 2 of the 4 GCCX-goats during the light hours were reduced and did not increase after the lights-off.…”

Presence of a Distinct 24‐Hour Melatonin Rhythm in the Ventricular Cerebrospinal Fluid of the Goat

“…The goat is, like sheep, a short-day breeder, and the female's ovarian cyclicity is under photoperiodic control [Mori et al, 19841. Involvement of the pineal gland as well as the role of melatonin have also been demonstrated in this species [Maeda et al, 1986;Mori and Okamura, 19861. The mechanism underlying melatonin's action, however, remains yet to be clarified in any species.…”

Sensitivity of Goats to a Light Pulse During the Night as Assessed by Suppression of Melatonin Concentrations in the Plasma

“…26 and 0.68 pW/cm2 (0.87 and 2.3 lux). Previous workers using goats have exposed them to light intensities of 120-150 pW/cm3 (400-500 lux) during experiments involving manipulation of artifical photoperiods and melatonin assessment [Maeda et al, 1984[Maeda et al, , 1986Mori and Okamura, 1986;Chemineau et al, 19861. According to our results, and following the relationship between percent suppression and light intensity, this would be sufficient to acutely suppress melatonin concentrations in the goat by at least 80-85%, as shown by Maeda et al [ 19841 with Saanen and Shiba goats. Goats seem to be slightly less sensitive to light at night than sheep, as assessed by melatonin assay.…”