Heat stress induces physiological, behavioral, and hypothalamic alterations in female mice

Extreme variations of environmental factors can affect physiology and behavior. The aim was to examine the impact of heat stress on general physiology and reproductive neuroendocrinology. Adult female mice were exposed to a heat wave of 8 hours of heat/day, with 33°C maximum and 28°C minimum, for one week (HS group). Control animals (CTL) were maintained at room temperature (21±1°C). At the end of the protocol, animals were classified according to their estrous cycle as Estrus or Diestrus (N=5/group). Significant changes (p<0.05) were observed in physiological parameters of HS vs. CTL, including decreased food and increased water intake, and increased body temperature from day 4 of heat exposure onward. In addition, HS showed difficults in nest-building behavior compared to CTL. Differences in the estrous cycling were not observed between HS and CTL. In the arcuate nucleus (ARC) of the hypothalamus, a significant reduction in the number of blood vessels was observed in HS regardless of estrous cycle. Finally, gonadotropin-releasing hormone (GnRH) immunoreactive neurons were detected in the ARC of CTL Estrus animals, with a significant reduction (p<0.05) in HS Estrus group, whereas GnRH neurons were not detected in Diestrus animals. The physiological and behavioral alterations, together with hypothalamic changes, indicate that the exposure to a heat wave may induce both physiological adaptive mechanisms and modifications in hypothalamic circuits associated with reproduction.