No abstract

In the present study, we tested the hypothesis that short-term fasting would reduce leptin gene expression, circulating leptin, and LH pulsatility in prepubertal heifers in association with a decrease in circulating concentrations of insulin and insulin-like growth factor I (IGF-I). Twelve prepubertal crossbred heifers (mean +/- SD = 315 +/- 5 kg body weight) were assigned randomly to one of two treatments in two replicates: 1) control; normal feed consumption (n = 6) and 2) fasted; 48 h of total feed restriction (n = 6). Blood samples were collected at 15-min intervals for 8 h on Days 0 and 2 of the experiment and twice on Day 1. Subcutaneous fat samples were collected before treatment onset (Day -1) and at the end of the intensive blood sampling on Day 2. Acute feed restriction markedly reduced leptin mRNA in adipose tissue (P < 0.01) and circulating concentrations of leptin (P < 0.05), IGF-I (P < 0.01), and insulin (P = 0.05) as compared with controls on Day 2. Moreover, the treatment x day interaction (P < 0.076) and within-day contrasts (expressed as a percentage of Day 0 values) revealed that the mean frequency of LH pulses in the fasted group was lower (P < 0.06) than in controls on Day 2. Neither mean concentrations of growth hormone (GH) nor GH secretory dynamics were affected by acute feed restriction. Fasting-mediated decreases in leptin gene expression and circulating leptin, in association with reductions in secretion of IGF-I, insulin, and LH, provide a basis for investigating leptin as a hormone signaling energy status to the central reproductive axis in cattle.

Among eutherian mammals, only primates possess trichromatic color vision. In Old World primates, trichromacy was made possible by a visual pigment gene duplication. In most New World primates, trichromacy is based on polymorphic variation in a single X-linked gene that produces, by random X inactivation, a patchy mosaic of spectrally distinct cone photoreceptors in heterozygous females. In the present work, we have modeled the latter strategy in a nonprimate by replacing the X-linked mouse green pigment gene with one encoding the human red pigment. In the mouse retina, the human red pigment seems to function normally, and heterozygous female mice express the human red and mouse green pigments at levels that vary between animals. Multielectrode array recordings from heterozygous female retinas reveal significant variation in the chromatic sensitivities of retinal ganglion cells. The data are consistent with a model in which these retinal ganglion cells draw their inputs indiscriminately from a coarse-grained mosaic of red and green cones. These observations support the ideas that (i) chromatic signals could arise from stochastic variation in inputs drawn nonselectively from red and green cones and (ii) tissue mosaicism due to X chromosome inactivation could be one mechanism for driving the evolution of CNS diversity.trichromacy ͉ mouse genetics ͉ retinal ganglion cells ͉ cone visual pigments

The working hypothesis was that dietary fats differing in fatty acid composition would differentially influence ovarian follicular growth. Cows (n = 27) were fed isoenergetic, isonitrogenous, and isofibrous diets containing no added fat (control; CT, n = 7) or diets supplemented with fats containing primarily saturated (SAT, n = 7), polyunsaturated (PU, n = 7), or highly polyunsaturated (HPU, n = 6) fatty acids. Coincident changes in serum lipid metabolites, insulin, and GH and the concentration of IGF-I in large and medium-sized follicles also were examined. Body weights and body condition scores remained similar for all groups throughout the study. Polyunsaturated fat increased (diet x day, P = .06) the number of medium-sized follicles on d 5 through 9 of a synchronized estrous cycle within 3 wk of onset of feeding and maximized (P < .001) this to a fourfold difference at ovariectomy after 7 wk. Fats with predominantly SAT and HPU tended (P < .10) to produce these effects after 7 wk. All fat-supplemented diets increased serum concentrations of total cholesterol (P < .05), GH (P < .05), and follicular fluid IGF-I in large follicles (P < .065) compared to CT but differentially influenced serum concentrations of insulin. Polyunsaturated fat stimulated a marked increase (P < .001) in serum insulin relative to controls within 3 wk, whereas SAT and HPU increased (P < .05) serum insulin only after 6 to 7 wk. We conclude that consumption of PU fatty acids stimulates a greater rate of ovarian follicular growth in cattle compared to CT, AT, and HPU. Future research should investigate the potential role of insulin in mediating PU effects on follicular growth.

Objectives of the current studies were to characterize the pattern of GnRH secretion in the cerebrospinal fluid of the bovine third ventricle, determine its correspondence with the tonic and surge release of LH in ovariectomized cows, and examine the dynamics of GnRH pulse generator activity in response to known modulators of LH release (suckling; neuropeptide Y [NPY]). In ovariectomized cows, both tonic release patterns and estradiol-induced surges of GnRH and LH were highly correlated (0.95; p < 0.01). Collectively, LH pulses at the baseline began coincident with (84%) or within one sampling point after (100%) the onset of a GnRH pulse, and all estradiol-induced LH surges were accompanied by corresponding surges of GnRH. A 500- microg dose of NPY caused immediate cessation of LH pulses and lowered (p < 0.001) plasma concentrations of LH for at least 4 h. This corresponded with declines (p < 0.05) in both GnRH pulse amplitude and frequency, but GnRH pulses were completely inhibited for only 1.5-3 h. In intact, anestrous cows, GnRH pulse frequency did not differ before and 48-54 h after weaning on Day 18 postpartum, but concentrations of GnRH (p < 0.05) and amplitudes of GnRH pulses (4 of 7 cows) increased in association with weaning and heightened secretion of LH. We conclude that the study of GnRH secretory dynamics in third-ventricle CSF provides a reasonable approach for examining the activity and regulation of the hypothalamic pulse generator in adult cattle. However, data generated using this approach must be interpreted in their broadest context. Although strong neurally mediated inhibitors of LH pulsatility (suckling; NPY) had robust effects on one or more GnRH secretory characteristics in CSF, only high doses of NPY briefly abolished GnRH pulses. This implies that the GnRH signal received at the hypophyseal portal vessels under these conditions may differ quantitatively or qualitatively from those in CSF, and theoretically would be undetectable or below a biologically effective threshold when LH pulses are absent.

No abstract

The onset of puberty in mammals involves an increase in the pulsatile release of GNRH and LH. The KISS1 gene is essential for pubertal development, and its product, kisspeptin, stimulates the release of LH. The objective of this study was to determine the effects of kisspeptin in the hypothalamic-adenohypophyseal-gonadal axis of prepubertal ewe lambs. Ewe lambs (28 weeks of age) were treated intravenously with saline (control, nZ6) or kisspeptin (20 mg kisspeptin; nZ6) every hour for 24 h. Kisspeptin stimulated pulse-like release of LH within 15 min following injections, and increased the frequency and amplitude of LH pulses, and mean circulating concentrations of LH and estradiol. A surge-like release of LH was observed in four kisspeptin-treated lambs beginning 17 h after the onset of treatment, and all four lambs had elevated circulating concentrations of progesterone within 5 days post-treatment. However, circulating concentrations of progesterone decreased within 2 days after the initial rise in three of the four ewe lambs, indicating that induced luteal activity was of short duration. The proportion of lambs that were pubertal (defined by circulating concentrations of progesterone above 1 ng/ml for at least 7 days) by 35 weeks of age (8/11) and the mean age at puberty (32G1 weeks) for those reaching puberty within the experimental period did not differ between treatments. Results support a role for kisspeptin in the activation of the hypothalamic-adenohypophyseal axis leading to the onset of puberty in ewe lambs.

Onset of puberty is characterised by a marked increase in the frequency of release of gonadotrophin-releasing hormone (GnRH) and luteinising hormone (LH). The Kiss1 gene plays a critical role in pubertal development, and its product, kisspeptin, stimulates GnRH and LH release. In the present study, we tested the hypothesis that Kiss1 gene expression in the preoptic area (POA) and hypothalamus increases during maturation of the reproductive neuroendocrine axis in association with increased LH pulsatility. Ovariectomised, oestradiol-replaced lambs were euthanised at 25, 30 and 35 weeks of age. Blood samples were collected before euthanasia to characterise the pattern of LH release. Kiss1 mRNA was detected in coronal sections of the POA and hypothalamus and Kiss1-expressing cells were identified on the basis of silver grain density. The mean number of Kiss1-expressing cells in the POA/periventricular (PeV) areas increased from 25 to 30 weeks of age. No further increase at 35 weeks of age was observed, and the changes in Kiss1 expression in the POA/PeV were independent of changes in LH pulse frequency. The mean number of Kiss1-expressing cells in the arcuate (ARC) nucleus did not differ among age groups, although it was greater in the middle ARC of lambs exhibiting increased frequency of LH release. The density of silver grains per cell did not differ among groups in any of the areas studied. The results obtained indicate that the Kiss1 gene is activated in the POA/PeV and ARC of ewe lambs during juvenile development, and that kisspeptin neurones in the middle ARC, in particular, are involved in the acceleration of pulsatile LH release during maturation of the reproductive neuroendocrine axis in ewe lambs.