title: Hindlimb unloading elicits anhedonia and sympathovagal imbalance.
abstract: The hindlimb-unloaded (HU) rat model elicits cardiovascular deconditioning and simulates the physiological adaptations to microgravity or prolonged bed rest in humans. Although psychological deficits have been documented following bed rest and spaceflight in humans, few studies have explored the psychological effects of cardiovascular deconditioning in animal models. Given the bidirectional link established between cardiac autonomic imbalance and psychological depression in both humans and in animal models, we hypothesized that hindlimb unloading would elicit an alteration in sympathovagal tone and behavioral indexes of psychological depression. Male, Sprague-Dawley rats confined to 14 days of HU displayed anhedonia (a core feature of human depression) compared with casted control (CC) animals evidenced by reduced sucrose preference (CC: 81 +/- 2.9% baseline vs. HU: 58 +/- 4.5% baseline) and reduced (rightward shift) operant responding for rewarding electrical brain stimulation (CC: 4.4 +/- 0.3 muA vs. 7.3 +/- 1.0 muA). Cardiac autonomic blockade revealed elevated sympathetic [CC: -54 +/- 14.1 change in (Delta) beats/min vs. HU: -118 +/- 7.6 Delta beats/min] and reduced parasympathetic (CC: 45 +/- 11.8 Delta beats/min vs. HU: 8 +/- 7.3 Delta beats/min) cardiac tone in HU rats. Heart rate variability was reduced (CC: 10 +/- 1.4 ms vs. HU: 7 +/- 0.7 ms), and spectral analysis of blood pressure indicated loss of total, low-, and high-frequency power, consistent with attenuated baroreflex function. These data indicate that cardiovascular deconditioning results in sympathovagal imbalance and behavioral signs consistent with psychological depression. These findings further elucidate the pathophysiological link between cardiovascular diseases and affective disorders.
authors.affiliation: Department of Psychology, The University of Iowa, Iowa City, IA 52242-1407, USA. alan-johnson@uiowa.edu
authors.forename: Julia A
authors.initials: JA
authors.lastname: Moffitt
authors.forename: Angela J
authors.initials: AJ
authors.lastname: Grippo
authors.forename: Terry G
authors.initials: TG
authors.lastname: Beltz
authors.forename: Alan Kim
authors.initials: AK
authors.lastname: Johnson
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D017704:Baroreflex; D001522:Behavior, Animal / Q000187:drug effects; D001794:Blood Pressure; D018493:Cardiovascular Deconditioning / Q000187:drug effects; D002319:Cardiovascular System / Q000294:innervation*; D003216:Conditioning, Operant; D003345:Corticosterone / Q000097:blood; D003863:Depression / Q000209:etiology* / Q000503:physiopathology / Q000523:psychology; D019422:Dietary Sucrose / Q000008:administration & dosage; D004558:Electric Stimulation; D005518:Food Preferences; D005583:Fourier Analysis; D006339:Heart Rate; D019417:Hindlimb Suspension / Q000009:adverse effects*; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000503:physiopathology*; D014630:Vagus Nerve / Q000187:drug effects / Q000503:physiopathology*
chemical_list: D000319:Adrenergic beta-Antagonists; D019422:Dietary Sucrose; D018727:Muscarinic Antagonists; D003345:Corticosterone