OLFACTORY-BULB REMOVAL DOES NOT PREVENT GONADOTROPIN OR PROLACTIN RESPONSES TO CHANGING PHOTOPERIOD IN THE EWE

The purpose of this study was to determine if bilateral olfactory bulb removal (Bulbx) alters photoperiod-induced changes of gonadotropin and prolactin secretion in the ewe. Ovariectomized (group 1; n = 12) or ovariectomized estradiol-treated (group 2; n = 12) Suffolk ewes underwent Bulbx (7 per group) or sham operations (5 per group). All ewes subsequently were placed into photochambers and exposed to a photoregimen of alternating 16 h light/8 h dark and 10 h light/ 14 h dark photoperiods. Plasma concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin were determined in blood samples taken twice weekly from group 2 ewes. At the end of each 90-day photoregimen blood samples from all ewes in both groups were taken at frequent intervals for 4 h to determine LH pulse parameters. During the initial 16 h light/8 h dark photoperiod, plasma melatonin concentrations were determined for group 2 ewes during a 24-hour period. The completeness of Bulbx was determined at time of necropsy for all Bulbx ewes. In addition, the functional completeness of Bulbx was determined in group 2 ewes by exposing them to ram's wool and measuring changes in LH secretion. Bulbx did not affect either basal or photoperiod-induced changes in LH, FSH and prolactin in group 2 ewes. LH pulse parameters varied with photoperiod but were not significantly (p > 0.05) affected by Bulbx in either group 1 or group 2 ewes. The normal nocturnal elevation in plasma melatonin concentrations was unaffected by Bulbx. Bulbx prevented the rapid elevation of LH in 6 of 7 ewes following exposure to ram's wool (p < 0.01 vs. sham). Olfactory bulb removal was greater than 90% complete in all ewes. These results indicate that Bulbx of ewes does not detectably alter the secretion of melatonin, LH, FSH or prolactin, an effect markedly different than that reported for the hamster. We conclude that the olfactory bulbs of the ewe do not tonically influence gonadotropin or prolactin secretion nor do they affect photoresponsiveness.