Effect of frontal hypothalamic deafferentation on photoperiod-induced changes of luteinizing hormone secretion in the ewe.

These experiments were conducted sequentially in two parts. In the first, we examined the effect of frontal hypothalamic deafferentation (FHD) on photoperiod-induced changes in luteinizing hormone (LH) concentration in ovariectomized ewes ('steroid-independent' changes). In the second we placed Silastic implants of estradiol-17 beta in these same ewes and examined the effect of FHD on photoperiod-induced changes in the LH concentration in the presence of estradiol ('steroid-dependent' changes). 15 ovariectomized Suffolk ewes were subjected either to FHD (n = 10) or sham FHD (n = 5). They were placed in a photochamber and exposed to the following lighting regimens. In the first part, two trials of alternating lighting periods were used: trial 1 = 120 days of 8 h light (L):16 h dark (D) followed by 90 days of 16L:8D; trial 2 = 90 days of 8L:16D followed by 60 days of 16L:8D. In the second part, three lighting periods of alternating daylengths were used: 65 days of 16L:8D, followed by 60 days of 8L:16D and by 60 days of 16L:8D. Blood samples were collected from the jugular vein at 20-min intervals for 3 or 4 h during the last day of each lighting period. Data on mean LH concentrations were obtained. The location of the FHD was verified histologically. In the absence of gonadal steroids, 16L:8D increased, whereas 8L:16D decreased the LH concentration (p less than 0.001) in both sham FHD and FHD ewes.(ABSTRACT TRUNCATED AT 250 WORDS)