Diminished baroreflex function following ovariectomy is a consequence of the reduced excitability of a sex specific population of low threshold myelinated baroreceptor afferents in the rat

Abstract

Concomitant with menopause there is a significant reduction in the capacity of the baroreflex (BRx). Loss of so‐called sex hormones is but one factor. Our previous in situ BRx studies have validated and quantified the contribution of a sex specific subpopulation of low‐threshold myelinated aortic baroreceptor afferents (Ah‐type) in eliciting depressor dynamics not observed in male rats. Ovariectomy greatly reduces the excitability of these Ah‐type afferents while the excitability of low threshold myelinated A‐type and high threshold unmyelinated C‐type afferents is unchanged.OBJECTIVEDetermine if the ovariectomy‐mediated loss in excitability of Ah‐type afferents alters the depressor response evoked by this sex specific baroreceptor afferent pathway. Age‐matched, normal (NF) and ovariectomized (OVX) female rats were prepared for selective, bipolar electrical stimulation of the left aortic depressor nerve. The OVX (n = 9) presented with a significantly diminished parasympathetic mediated reduction in mean arterial pressure in comparison to the NF (n = 16). Interestingly, the most significant changes in depressor dynamics occurs at electrical thresholds and frequencies most closely aligned with Ah‐type baroreceptor fibers. We conclude that these sex specific afferents may provide a neuromodulatory pathway uniquely associated with the hormonal regulation of BRx function. HL072012, HL081819