Effects of Frontal Hypothalamic Deafferentation on Seasonal Breeding and Secretion of Luteinizing Hormone, Prolactin and Melatonin in the Ewe

242 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.The neural pathway(s) by which photoperiodic signals reach the hypothalamo-hypophyseal (H-H) system to regulate reproductive function in the ewe was studied. This was done by subjecting ewes to frontal hypothalamic deafferentation (FHD) and then to either natural or artificial lighting environments and monitoring changes in hormone secretion. FHD did not alter melatonin secretion, but prevented the onset of normal anestrous season. Moreover, FHD did not alter photoperiod-induced, estrogen independent changes in luteinizing hormone (LH) secretion, but hampered photoperiod-induced, estrogen dependent changes in LH concentrations. This suggests that photoperiod signals, which regulate changes in the sensitivity of the H-H system to the negative feedback effect of estrogen and finally seasonal breeding, are mediated by the direct neural connections between the anterior and mediobasal hypothalamus (AH-MBH neural connections) rather than the indirect neurohumoral pathway through the pineal. Basal LH secretion and ovulation were not disrupted by FHD, but the estrogen-induced LH surges were modified. This suggests that the anterior hypothalamus is required for the mediobasal hypothalamus to maintain normal LH surges, but not basal LH secretion and ovulation. FHD did not alter basal prolactin secretion. Neither seasonal nor photoperiod-induced changes in prolactin concentrations were abolished by FHD. The pattern of the diurnal prolactin rhythm during either the nonbreeding season or under 16L:8D also was not disrupted by FHD. The peak value of the diurnal prolactin rhythm during the nonbreeding season, but not under 16L:8D, was reduced by FHD. This suggests that basal prolactin secretion and photoperiodic regulation of prolactin rhythms remained effective, but high temperature-stimulated prolactin release was impaired, in the absence of the direct AH-MBH neural connections. In conclusion, the direct AH-MBH neural connections are indispensible for photoperiodic control of either changes in the sensitivity of the H-H system to the negative feedback effect of estrogen or seasonal breeding. On the other hand, photoperiod signals which regulate circannual and diurnal rhythms of prolactin secretion are mediated by pathways other than, or in addition to, the direct AH-MBH neural connections.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD