Mating induces gonadotropin-releasing hormone neuronal activation in anosmic female ferrets

In females of both spontaneously and induced ovulating species, pheromones from male conspecifics can directly stimulate GnRH neuronal activity, there by inducing pituitary LH secretion and stimulating the onset of estrus. How ever, whether pheromones contribute to the steroid- or mating-induced preov ulatory activation of GnRH neurons is less clear. Previous studies in the f erret, an induced ovulator, raised the possibility that olfactory cues cont ribute to the ability of genital-somatosensory stimulation to activate GnRH neurons in the mediobasal hypothalamus (MBH). In the present study the per centage of GnRH neurons colabeled with Fos-immunoreactivity (IR), used as a marker for neuronal activation, was investigated in the MBH of mated gonad ectomized, estradiol-treated female ferrets in which both nares were occlud ed. In addition, the percentage of GnRH neurons colabeled with Fos-IR was e xamined in the MBH of gonadectomized, estradiol-treated female ferrets expo sed to male bedding. Bilateral nares occlusion successfully blocked mating or odor-induced increments in Fos-IR in central olfactory regions, includin g the cortical and medial amygdala. By contrast, the percentage of GnRH neu rons expressing Fos-IR did not differ between mated nares- and sham-occlude d females. Exposure to male bedding alone failed to induce Fos-IR in MBH Gn RH neurons. Thus, the mating-induced preovulatory activation of GnRH neuron s in the female ferret's MBH appears to rely solely on genital-somatosensor y as opposed to olfactory inputs.