Neuropeptide Y Gene Expression in Male Sheep: Influence of Photoperiod and Testosterone

Abstract

The frequency of pulsatile release of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) is high in the breeding season and low in the nonbreeding season. These alterations in the patterns of GnRH and LH release are due to an interaction of daylength and gonadal steroid negative feedback. A vast amount of data indicates that steroid-responsive neural systems may play a role in regulating seasonal changes in GnRH release. One candidate system is neuropeptide Y (NPY). To determine the independent and interactive influences of photoperiod and steroid exposure on NPY mRNA levels, we used hypothalamic tissue from four groups (n = 4 per group) of castrated male sheep that were simultaneously housed in photochambers and exposed to: (1) a 16L:8D photoperiod (LD); (2) LD and implanted with testosterone (LD + T); (3) a 10L:14D photoperiod (SD), and (4) SD + T. Circulating levels of T averaged 2.8 ± 0.2 ng/ml in implanted animals, but were undetectable in nonimplanted males. Mean LH levels were significantly reduced (p < 0.01) in the LD + T group as compared with the other groups which did not differ from each other. The silver grain area per NPY neuron in the arcuate nucleus, as assessed by in situ hybridization, was inversely related to mean LH values, with the grain area per cell being significantly greater (p < 0.05) for LD + T males than for all other groups which did not differ from each other. NPY cell numbers were not significantly different (p > 0.10) among the treatment groups. These results show that NPY mRNA expression is increased in male sheep during a LD photoperiod in a T-dependent manner. Our data are consistent with the idea that NPY is involved in the seasonal regulation of GnRH and LH release in the male sheep.

Selected hormonal and neurotransmitter mechanisms regulating feed intake in sheep

“…Finally, short-day photoperiod exposure in ovariectomized ewes or in rams reduced the number of cells positive for NPY mRNA (by in situ hybridization) as well as the number of silver grains per cell, suggesting reduced NPY expression during a period that corresponds to reduced voluntary feed intake . Similar effects were observed with wethers (Dobbins et al, 2004). By contrast, the effect of fasting to increase NPY expression appeared to be restricted to long-day photoperiod exposed sheep (Archer et al, 2004).…”

Reproduction phase‐related variations in neuropeptide Y immunoreactivity in the olfactory system, forebrain, and pituitary of the female catfish, Clarias batrachus (Linn.)

“…Dufourny et al (2005) suggested that NPY-containing neurons in the arcuate nucleus (ARC) coexpress progesterone receptors, innervate GnRH neurons, and may be involved in progesterone-mediated inhibition of GnRH secretion. Although castration decreased NPY gene expression in the ARC, testosterone replacement restored castrationinduced attenuation in the NPY levels (Gruenewald et al, 1994;Sohn et al, 2002;Dobbins et al, 2004). NPYcontaining neurons in the ARC of ewe concentrate estrogen (Sar et al, 1990) and show seasonal variation in the cell population (Skinner and Herbison, 1997).…”

“…The hypothalamic neuropeptide Y (NPY)-containing system in mammals is believed to be involved in the steroidal modulation of gonadotropin-releasing hormone (GnRH; Urban et al, 1996;Dobbins et al, 2004). Dufourny et al (2005) suggested that NPY-containing neurons in the arcuate nucleus (ARC) coexpress progesterone receptors, innervate GnRH neurons, and may be involved in progesterone-mediated inhibition of GnRH secretion.…”

Variations in Peptide YY and Y2 Receptor Genes Are Associated With Severe Obesity in Pima Indian Men

“…Therefore, it is possible that PYY or Y2R, or a different gene in the pathway that is activated by their interaction, is hormonally controlled. For example, NPY (a family member of PYY) expression is increased in male sheep in a testosterone-dependent manner (14), and testosterone also contributes to age-related changes of NPY expression (15). Since PYY belongs to the same family as NPY, it is possible that PYY also has a sex hormone-regulated element or other indirect hormone-controlled factor regulatory sites.…”