Differential sensitivity to morphine in nervous and normal pointer dogs

The effects of morphine and pentobarbital on body temperature and heart rate were studied in a line of pointer dogs characterized as genetically nervous. Intravenous administration of cumulative doses of morphine to the conscious, restrained, nervous dogs produced less tachycardia and hypothermia than were observed in control dogs. Nervous and control dogs did not differ in their responses to pentobarbital. These data are consistent with recent findings that nervous dogs have a lower density of opioid receptors in the brain than do control dogs.