Analysis of gonadotrophin‐releasing hormone‐1 and kisspeptin neuronal systems in the nonphotoregulated seasonally breeding eastern rock elephant‐shrew (Elephantulus myurus)

Abstract

Of the 18 sub‐Saharan elephant‐shrew species, only eastern rock elephant‐shrews reproduce seasonally throughout their distribution, a process seemingly independent of photoperiod. The present study characterizes gonadal status and location/intensity of gonadotrophin‐releasing hormone‐1 (GnRH‐1) and kisspeptin immunoreactivities in this polyovulating species in the breeding and nonbreeding seasons. GnRH‐1‐immunoreactive (ir) cell bodies are predominantly in the medial septum, diagonal band, and medial preoptic area; processes are generally sparse except in the external median eminence. Kisspeptin‐ir cell bodies are detected only within the arcuate nucleus; the density of processes is generally low, except in the septohypothalamic nucleus, ventromedial bed nucleus of the stria terminalis, arcuate nucleus, and internal and external median eminence. Kisspeptin‐ir processes are negligible at locations containing GnRH‐1‐ir cell bodies. The external median eminence is the only site with conspicuously overlapping distributions of the respective immunoreactivities and, accordingly, a putative site for kisspeptin's regulation of GnRH‐1 release in this species. In the nonbreeding season in males, there is an increase in the rostral population of GnRH‐1‐ir cell bodies and density of GnRH‐1‐ir processes in the median eminence. In both sexes, the breeding season is associated with increased kisspeptin‐ir process density in the rostral periventricular area of the third ventricle and arcuate nucleus; at the latter site, this is positively correlated with gonadal mass. Cross‐species comparisons lead us to hypothesize differential mechanisms within these peptidergic systems: that increased GnRH‐1 immunoreactivity during the nonbreeding season reflects increased accumulation with reduced release; that increased kisspeptin immunoreactivity during the breeding season reflects increased synthesis with increased release.