The effect of the stress of forcible submergence on the diving response in muskrats (Ondatra zibethica)

Publisher Website
Google Scholar
Abstract
The effect of the stress of forced submergence in the laboratory on a number of cardiovascular adjustments to diving was examined. Free muskrats, diving in large holding tanks, always displayed bradycardia and heart rate fell from a predive rate of 320 ± 6 to 34 ± 3 beats∙min−1 after 20 s submergence. In the laboratory this degree of bradycardia was only seen during whole-body submergence of anesthetized animals; restrained unanesthetized muskrats showed significantly less bradycardia. Forced submergence of only the head caused about half the bradycardia seen during whole-body submergence in both unanesthetized restrained and anesthetized muskrats. Decerebrated animals gave identical responses to those of anesthetized muskrats. Cardiac output was redistributed in forced diving to favour the heart and brain even when diving heart rate was three times that in free dives. However, many other tissues still received a significant proportion of cardiac output and must have placed a drain on the blood oxygen store which restricted apnoeic tolerance. Struggling during forced submergence was frequent and has a reflex or unconscious component since even decerebrated animals struggled during a dive. The present data suggest that the additional stresses imposed on muskrats during forcible submergence in the laboratory reduce rather than potentiate the cardiovascular adjustments to diving.

This publication has 2 references indexed in Scilit: