Behavioral and cardiac responses to mild stress in young and aged rats: effects of amphetamine and vasopressin.
Young (3-month-old) male Wistar rats showed a relative decrease in heart rate to a sudden silence superimposed on low intensity background noise. This bradycardia was accompanied by immobility behavior. In 26-month-old rats the magnitude of the heart rate response was reduced while immobility behavior remained in the same order of magnitude as in young controls. In the aged rats a shift in autonomic regulation of heart rate in the direction of increased sympathetic influence was indicated by the results obtained by blocking the autonomic input with atropine methyl-nitrate (0.5 mg/kg) or atenolol (1 mg/kg) given subcutaneously (SC) 30 min prior to testing. Pretest (30 min) administration of amphetamine (0.5 mg/kg SC) reinstated the bradycardiac response in aged rats to a level seen in young ones. Arginine-vasopressin (AVP, 10 micrograms/kg SC), administered 60 min before the experiment, markedly facilitated the cardiac response in young animals but failed to restore cardiac responses in aged ones. The immobility behavior in the peptide-treated aged rats was also absent. The present findings suggest that a diminished central aminergic drive in aged rats is causing a reduction of the parasympathetic cardiac response to stress of sudden silence. The results also indicate an age-related vasopressinergic modulation of behavioral and cardiac responses to mild stress.
Buwalda
B
B
Department of Animal Physiology, University of Groningen, Haren, The Netherlands.
Koolhaas
J M
JM
Bohus
B
B
D000375:Aging / Q000502:physiology*; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D001143:Arousal / Q000187:drug effects* / Q000502:physiology; D001341:Autonomic Nervous System / Q000187:drug effects* / Q000502:physiology; D001522:Behavior, Animal / Q000187:drug effects* / Q000502:physiology; D003913:Dextroamphetamine / Q000494:pharmacology*; D004562:Electrocardiography / Q000187:drug effects; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D013315:Stress, Psychological / Q000150:complications*; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology
D001127:Arginine Vasopressin; D003913:Dextroamphetamine