lhrh--his(5)-trp(7)-tyr(8)- and Body-Weight

GnRH-II is the most evolutionarily conserved member of the GnRH peptide family. In mammals, GnRH-II has been shown to regulate reproductive and feeding behaviors. In female musk shrews, GnRH-II treatment increases mating behaviors and decreases food intake. Although GnRH-II-containing neurons are known to reside in the midbrain, the neural sites of GnRH-II action are undetermined, as is the degree to which GnRH-II is regulated by energy availability. To determine whether GnRH-II function is affected by changes in food intake, we analyzed the levels of GnRH-II mRNA in the midbrain and GnRH-II protein in numerous target regions. Adult musk shrews were ad libitum fed, food restricted, or food restricted and refed for varying durations. Compared with ad libitum levels, food restriction decreased, and 90 min of refeeding reinstated, GnRH-II mRNA levels in midbrain and GnRH-II peptide in several target areas including the medial habenula and ventromedial nucleus. Refeeding for 90 min also reinstated female sexual behavior in underfed shrews. In male shrews, abundant GnRH-II peptide was present in all sites assayed, including the preoptic area, a region with only low GnRH-II in females. In contrast to females, food restriction did not affect GnRH-II protein in male brains or inhibit their mating behavior. Our results further define the relationship between GnRH-II, energy balance, and reproduction, and suggest that food restriction may inhibit female reproduction by reducing GnRH-II output to several brain nuclei. We postulate that this highly conserved neuropeptide functions similarly in other mammals, including humans, to fine-tune reproductive efforts with periods of sufficient energy resources.

Topics: Animals; Body Weight; Brain; Eating; Energy Metabolism; Female; Gonadotropin-Releasing Hormone; Male; Preoptic Area; RNA, Messenger; Sexual Behavior, Animal; Shrews

GnRH is an evolutionarily conserved peptide of which there are multiple structural variants. One form, GnRH II, is the most widespread in vertebrates, but its primary function remains unclear. In female musk shrews, administration of GnRH II, but not GnRH I, reinstates mating behavior previously inhibited by food restriction. Because this finding suggests that the function of GnRH II may be linked to energetic status, we tested whether GnRH II directly affects food intake. Adult female musk shrews were maintained on ad libitum feeding or food restricted for 48 h, after which they were infused centrally with GnRH I (1 microg), GnRH II (1 microg), or saline. Food intake was recorded 90 min, and 3, 6, 24, and 48 h after infusion. GnRH II administration, but not saline or GnRH I, reduced 24-h food intake in ad libitum animals. Short-term food intake (90 min and 3 h) of both ad libitum and underfed shrews receiving GnRH II was also reduced by as much as 33%, relative to the food intake of saline-infused controls. GnRH I infusion did not affect short-term food intake differently than saline infusion in shrews fed ad libitum. In underfed females, GnRH I had an effect on short-term food intake that was intermediate to saline and GnRH II. We conclude that, in addition to its permissive role in regulating reproduction, GnRH II may also modulate food intake in mammals. Because GnRH II is present in primate brain, it may also serve a similar function in humans.

Topics: Animals; Body Weight; Circadian Rhythm; Conserved Sequence; Eating; Evolution, Molecular; Feeding Behavior; Female; Food Deprivation; Gonadotropin-Releasing Hormone; Shrews

The importance of late winter pairing activity on the neuroendocrinology of wild waterfowl is unknown. In this study, we examined the sex-related differences in the roles of late winter pairing activity and seasonal influences on neuroendocrine and reproductive physiology in both male and female mallards. Our main goals were to determine (1) which physiological responses were influenced by pairing status or by seasonal changes and (2) whether responses differed between the sexes. Thus, physiological responses of mallards in different pairing status categories were assessed at two times: January 28 to February 5 and February 24 to March 3. Ducks were assigned to one of the following pairing status categories: strong pairs, temporary pairs, unpaired or lone birds within the flock, or birds isolated in same-sex groups. Seasonal changes correlated with increases in both gonadal mass and hypothalamic content of vasoactive intestinal peptide in both sexes, whereas only pairing status correlated with changes in body mass in both sexes. The main sex-related differences were the following: (1) Seasonal decreases in hypothalamic gonadotrophin releasing hormone II content occurred only in females. (2) Seasonal increases in serum prolactin occurred only in males, whereas levels in females were low throughout the study. (3) Both male and female gonadal masses increased seasonally, but male gonadal mass was initially twice that of females. (4) Body mass of both sexes was influenced by pairing status correlations (i.e., all paired or lone birds were heavier than isolated birds), but body mass in males decreased seasonally. No sex-related differences occurred in hypothalamic gonadotrophin releasing hormone I content or circulating serum luteinizing hormone. Taken together, these results indicate that seasonal reproduction in mallards is regulated not only by seasonal but also by social cues, and differences occur between the sexes, months in advance of actual breeding.

Topics: Animals; Body Weight; Female; Gonadotropin-Releasing Hormone; Gonads; Hypothalamus; Luteinizing Hormone; Male; Neurosecretory Systems; Prolactin; Pyrrolidonecarboxylic Acid; Reproduction; Seasons; Sex Characteristics; Sexual Behavior, Animal; Vasoactive Intestinal Peptide