title: Electrophysiological and neuroanatomical evidence of sexual dimorphism in aortic baroreceptor and vagal afferents in rat.
abstract: Evidence for sexual dimorphism in autonomic control of cardiovascular function is both compelling and confounding. Across healthy and disease populations sex-associated differences in neurocirculatory hemodynamics are far too complex to be entirely related to sex hormones. As an initial step toward identifying additional physiological mechanisms, we investigated whether there is a sex bias in the relative expression of low-threshold-myelinated and high-threshold-unmyelinated aortic baroreceptor afferents in rats. These two types of afferent fibers have markedly different reflexogenic effects upon heart rate and blood pressure and thus the potential impact upon baroreflex dynamics could be substantial. Our results, using a combination of a patch-clamp study of fluorescently identified aortic baroreceptor neurons (ABN) and morphometric analysis of aortic baroreceptor nerve fibers, demonstrate that females exhibit a greater percentage of myelinated baroreceptor fibers (24.8% vs. 18.7% of total baroreceptor fiber population, P < 0.01) and express a functional subtype of myelinated ABN rarely found in age-matched males (11% vs. 2.3%, n = 107, P < 0.01). Interestingly, this neuronal phenotype is more prevalent in the general population of female vagal afferent neurons (17.7% vs. 3.8%, n = 169, P < 0.01), and ovariectomy does not alter its expression but does lessen neuronal excitability. These data suggest there are fundamental neuroanatomical and electrophysiological differences between aortic baroreceptor afferents of female and male rats. Possible explanations are presented as to how such a greater prevalence of low-threshold myelinated afferents could be a contributing factor to the altered baroreflex sensitivity and vagal tone of females compared with males.
authors.affiliation: Department of Pharmacology, Harbin Medical University, Harbin, China.
authors.forename: Bai-Yan
authors.initials: BY
authors.lastname: Li
authors.forename: Guo-Fen
authors.initials: GF
authors.lastname: Qiao
authors.forename: Bin
authors.initials: B
authors.lastname: Feng
authors.forename: Rui-Bo
authors.initials: RB
authors.lastname: Zhao
authors.forename: Yan-Jie
authors.initials: YJ
authors.lastname: Lu
authors.forename: John H
authors.initials: JH
authors.lastname: Schild
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000344:Afferent Pathways / Q000033:anatomy & histology / Q000502:physiology*; D000818:Animals; D001011:Aorta / Q000294:innervation / Q000502:physiology; D002211:Capsaicin / Q000494:pharmacology; D016000:Cluster Analysis; D004594:Electrophysiology; D005260:Female; D008297:Male; D008854:Microscopy, Electron; D009413:Nerve Fibers, Myelinated / Q000502:physiology / Q000648:ultrastructure; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D010052:Ovariectomy; D018408:Patch-Clamp Techniques; D011311:Pressoreceptors / Q000033:anatomy & histology / Q000502:physiology*; D058910:Purinergic P2 Receptor Agonists; D051381:Rats; D017207:Rats, Sprague-Dawley; D012737:Sex Factors; D014630:Vagus Nerve / Q000033:anatomy & histology / Q000502:physiology*
chemical_list: D058910:Purinergic P2 Receptor Agonists; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002211:Capsaicin