title: Regulation of cardiac innervation and function via the p75 neurotrophin receptor.
abstract: Homeostatic regulation of cardiac function is dependent on the balance of inputs from the sympathetic and parasympathetic nervous systems. We investigated whether the p75 neurotrophin receptor plays a developmental role in cardiac innervation by analyzing sympathetic and parasympathetic fibers in the atria of p75 knockout and wildtype mice at several stages of postnatal development, and examining the effect on control of heart rate. We found that parasympathetic innervation of the atria in p75-/- mice was similar to wildtype at all time points, but that the density of sympathetic innervation was dynamically regulated. Compared to wildtype mice, the p75-/- mice had less innervation at postnatal day 4, an increase at day 28, and decreased innervation in adult mice. These changes reflect defects in initial fiber in-growth and the timing of the normal developmental decrease in sympathetic innervation density in the atria. Thus, p75 regulates both the growth and stability of cardiac sympathetic fibers. The distribution of sympathetic fibers was also altered, so that many regions lacked innervation. Basal heart rate was depressed in adult p75-/- mice, and these mice exhibited a diminished heart rate response to restraint stress. This resulted from the lack of sympathetic innervation rather than increased parasympathetic transmission or a direct effect of p75 in cardiac cells. Norepinephrine was elevated in p75-/- atria, but stimulating norepinephrine release with tyramine produced less tachycardia in p75-/- mice than wild type mice. This suggests that altered density and distribution of sympathetic fibers in p75-/- atria impairs the control of heart rate.
authors.affiliation: Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, United States.
authors.forename: Beth A
authors.initials: BA
authors.lastname: Habecker
authors.forename: Parizad
authors.initials: P
authors.lastname: Bilimoria
authors.forename: Camille
authors.initials: C
authors.lastname: Linick
authors.forename: Kurt
authors.initials: K
authors.lastname: Gritman
authors.forename: Christina U
authors.initials: CU
authors.lastname: Lorentz
authors.forename: William
authors.initials: W
authors.lastname: Woodward
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Birren
mesh_terms: D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology; D000375:Aging / Q000502:physiology; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D020439:Growth Cones / Q000378:metabolism / Q000648:ultrastructure; D006321:Heart / Q000254:growth & development / Q000294:innervation* / Q000502:physiology; D006325:Heart Atria / Q000254:growth & development / Q000294:innervation; D006339:Heart Rate / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020932:Nerve Growth Factor / Q000378:metabolism; D020933:Neurotrophin 3 / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D010275:Parasympathetic Nervous System / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism; D020800:Receptor, Nerve Growth Factor / Q000235:genetics / Q000378:metabolism*; D013315:Stress, Psychological / Q000235:genetics / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D009435:Synaptic Transmission / Q000235:genetics; D013610:Tachycardia / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D014439:Tyramine / Q000494:pharmacology
chemical_list: D018759:Adrenergic Uptake Inhibitors; D020933:Neurotrophin 3; D020800:Receptor, Nerve Growth Factor; D020932:Nerve Growth Factor; D009638:Norepinephrine; D014439:Tyramine