Severe inflammatory challenges are frequently coupled to decreased food intake and disruption of reproductive function, the latter via deregulation of different signaling pathways that impinge onto GnRH neurons. Recently, the hypothalamic Kiss1 system, a major gatekeeper of GnRH function, was suggested as potential target for transmitting immune-mediated repression of the gonadotropic axis during acute inflammation, and yet key facets of such a phenomenon remain ill defined. Using lipopolysaccharide S (LPS)-treated male rats as model of inflammation, we document herein the pattern of hypothalamic kisspeptin immunoreactivity (IR) and hormonal responses to kisspeptin during the acute inflammatory phase. LPS injections induced a dramatic but transient drop of serum LH and testosterone levels. Suppression of gonadotropic function was associated with a significant decrease in kisspeptin-IR in the arcuate nucleus (ARC) that was not observed under conditions of metabolic stress induced by 48-h fasting. In addition, absolute responses to kisspeptin-10 (Kp-10), in terms of LH and testosterone secretion, were significantly attenuated in LPS-treated males that also displayed a decrease in food intake and body weight. Yet pair-fed males did not show similar alterations in LH and testosterone secretory responses to Kp-10, whose magnitude was preserved, if not augmented, during food restriction. In summary, our data document the impact of acute inflammation on kisspeptin content at the ARC as key center for the neuroendocrine control of reproduction. Our results also suggest that suppressed gonadotropic function following inflammatory challenges might involve a reduction in absolute responsiveness to kisspeptin that is independent of the anorectic effects of inflammation.
The Suprachiasmatic Nucleus Changes the Daily Activity of the Arcuate Nucleus α-MSH Neurons in Male Rats
