KCa1.1 is potential marker for distinguishing Ah-type baroreceptor neurons in NTS and contributes to sex-specific presynaptic neurotransmission in baroreflex afferent pathway

Sexual-dimorphic neurocontrol of circulation has been described in baroreflex due largely to the function of myelinated Ah-type baroreceptor neurons (BRNs, 1st-order) in nodose. However, it remains unclear if sex- and afferent-specific neurotransmission could also be observed in the central synapses within nucleus of solitary track (NTS, 2nd-order). According to the principle of no mixed neurotransmission among afferents and differentiation of Ah- and A-types to iberiotoxin (IbTX) observed in nodose, the 2nd-order Ah-type BRNs are highly expected. To test this hypothesis, the excitatory post-synaptic currents (EPSCs) were recorded in identified 2nd-order BRNs before and after IbTX using brain slice and whole-cell patch. These results showed that, in male rats, the dynamics of EPSCs in capsaicin-sensitive C-types were dramatically altered by IbTX, but not in capsaicin-insensitive A-types. Interestingly, near 50% capsaicin-insensitive neurons in females showed similar effects to C-types, suggesting the existence of Ah-types in NTS, which may be the likely reason why the females had lower blood pressure and higher sensitivity to aortic depressor nerve stimulation via KCa1.1-mediated presynaptic glutamate release from Ah-type afferent terminals.