title: An afferent explanation for sexual dimorphism in the aortic baroreflex of rat.
abstract: Sex differences in baroreflex (BRx) function are well documented. Hormones likely contribute to this dimorphism, but many functional aspects remain unresolved. Our lab has been investigating a subset of vagal sensory neurons that constitute nearly 50% of the total population of myelinated aortic baroreceptors (BR) in female rats but less than 2% in male rats. Termed "Ah," this unique phenotype has many of the nonoverlapping electrophysiological properties and chemical sensitivities of both myelinated A-type and unmyelinated C-type BR afferents. In this study, we utilize three distinct experimental protocols to determine if Ah-type barosensory afferents underlie, at least in part, the sex-related differences in BRx function. Electron microscopy of the aortic depressor nerve (ADN) revealed that female rats have less myelin (P < 0.03) and a smaller fiber cross-sectional area (P < 0.05) per BR fiber than male rats. Electrical stimulation of the ADN evoked compound action potentials and nerve conduction profiles that were markedly different (P < 0.01, n = 7 females and n = 9 males). Selective activation of ADN myelinated fibers evoked a BRx-mediated depressor response that was 3-7 times greater in female (n = 16) than in male (n = 17) rats. Interestingly, the most striking hemodynamic difference was functionally dependent upon the rate of myelinated barosensory fiber activation. Only 5-10 Hz of stimulation evoked a rapid, 20- to 30-mmHg reduction in arterial pressure of female rats, whereas rates of 50 Hz or higher were required to elicit a comparable depressor response from male rats. Collectively, our experimental results are suggestive of an alternative myelinated baroreceptor afferent pathway in females that may account for, at least in part, the noted sex-related differences in autonomic control of cardiovascular function.
authors.affiliation: Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana; Department of Biomedical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indiana;
authors.forename: Grace C
authors.initials: GC
authors.lastname: Santa Cruz Chavez
authors.affiliation: Department of Biomedical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indiana;
authors.forename: Bai-Yan
authors.initials: BY
authors.lastname: Li
authors.affiliation: Rammelkamp Center for Education and Research, MetroHealth Campus, Cleveland, Ohio; and.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Glazebrook
authors.affiliation: Rammelkamp Center for Education and Research, MetroHealth Campus, Cleveland, Ohio; and Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio.
authors.forename: Diana L
authors.initials: DL
authors.lastname: Kunze
authors.affiliation: Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana; Department of Biomedical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indiana; jschild@iupui.edu.
authors.forename: John H
authors.initials: JH
authors.lastname: Schild
mesh_terms: D000200:Action Potentials; D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001011:Aorta / Q000294:innervation*; D017704:Baroreflex; D004558:Electric Stimulation; D005260:Female; D006439:Hemodynamics; D008297:Male; D040542:Mechanotransduction, Cellular; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D009431:Neural Conduction; D010275:Parasympathetic Nervous System / Q000166:cytology / Q000502:physiology*; D010641:Phenotype; D011311:Pressoreceptors / Q000502:physiology*; D051381:Rats; D012727:Sex Characteristics; D012737:Sex Factors; D013997:Time Factors
keywords: autonomic nervous system; baroreceptor; cardiovascular; vagal; visceral