Effects of combined carotid sinus and aortic depressor nerve denervations in neonatal rat pups.

Denervation of the major peripheral chemo- and barosensory organs of neonatal mammals is known to produce age-dependent effects on mortality and on respiratory and cardiovascular functions. In the current series of experiments, these phenomena were more fully characterized in the young rat. 8- to 9-day-old rats showed few effects of combined carotid sinus and aortic depressor nerve (CSAD) denervation. During the days following surgery, these animals maintained normal body temperatures, had relatively normal weight gain, little cardiorespiratory disruption, and none died. Denervation at earlier ages (postnatal days 3-4 or 0-1) resulted in considerable mortality, 24 and 59%, respectively. In addition, body temperatures were lower, and the weight gain was impaired in the denervated pups as compared with controls, and these effects were more severe in the CSAD nonsurvivors than in the survivors. Also, nonsurvivors had much more severe disruptions of cardiorespiratory patterns measured 24-96 h after surgery than did CSAD survivors. Twenty-four hours after surgery, pups that later died could be identified based on low heart rates and long inspiratory times. CSAD survivors maintained a pattern of moderate cardiorespiratory disruption as compared with controls. Finally, our results indicate that the additional stress of subcutaneous electrocardiography lead implantation and/or daily maternal separation for cardiorespiratory recording increased the mortality in the 3- to 4-day-old CSAD pups from 11 to 40%.