Variations in afferent conduction and axonal morphometrics of aortic depressive nerve imply wider baroreflex function of low-threshold and sex-specific myelinated Ah-type baroreceptor neurons in rats

Unique Expression of Angiotensin Type-2 Receptor in Sex-Specific Distribution of Myelinated Ah-Type Baroreceptor Neuron Contributing to Sex-Dimorphic Neurocontrol of Circulation

“…Although a sex difference in AT 2 R expression is identified at first order BRNs, we still do not know the neuron-specific distribution of this receptor simply because vagal ganglion is composed of multiple cell types, including the low-threshold and sex-specific distribution of myelinated Ah-type BRNs, 13,15,17,21 and traditionally classified myelinated A-and unmyelinated C-types. 14,29,40 Thus, it would be extremely important for us to evaluate the AT 2 R expression in identified single cells to understand the cell-specific function in sexual dimorphism of baroreflex.…”

“…The sex differences in neurocontrol of circulation at baroreflex level have almost been neglected although AT 1 R or AT 2 R has been identified in nodose ganglia (NG) or nucleus of tractus solitary (NTS). a female-specific subpopulation of low-threshold myelinated Ah-type baroreceptor neurons (BRNs), which presented not only in NG [13][14][15][16][17][18] but also in NTS. 19,20 Ah-type BRNs were rarely found in adult male rats and exhibited an excitability profile that was strongly influenced by circulating sex hormones 3,18,21 and neurotransmitters.…”

Spontaneous activities in baroreflex afferent pathway contribute dominant role in parasympathetic neurocontrol of blood pressure regulation

“…According to measured conduction velocity (CV) at cell‐attached configuration using vagus‐nodose slice, those neurons showing fast CV > 10 m/s without the repolarization hump were classified as myelinated A‐types, those showing faster CV > 4 m/s with repolarization hump were classified as myelinated Ah‐types, while, those neurons showing slow CV < 1/s with significant repolarization hump at room temperature were classified as unmyelinated C‐types . The baroreflex modality of the first‐order neurons were also verified by the fluorescence at cell body with Dil transported along with the afferent fibers.…”

“…Baroreceptor neurons in intact vagus‐nodose slice and the location of NTS in the horizontal brainstem slices were determined as previously described . Spontaneous and evoked discharges of AP were recorded using intact vagus‐nodose slices . The spontaneous synaptic currents were recorded using horizontal brainstem slice .…”

“…Despite the close association of the baroreflex function with parasympathetic activation and having the extensive studies on baroreflex at both afferent and efferent pathways, the underlying mechanism at cellular and physiological level is still largely unknown due to the difficulties in handling these tissues for proper physiological measurements. Over the years, we have developed a highly reliable approaches for electrophysiological recording using vagus‐nodose slice, which allows us demonstrating a critical female‐specific Ah‐type neurons in the nodose and their potential role in neurocontrol of blood pressure …”