The goal of this study was to identify the source of baroreceptor-related noradrenergic innervation of the diagonal band of Broca (DBB). Male Sprague-Dawley rats underwent sinoaortic denervation (SAD, n = 13) or sham SAD surgery (n = 13). We examined Fos expression produced by baroreceptor activation and dopamine-beta-hydroxylase immunofluorescence in hindbrain regions that contain noradrenergic neurons. Baroreceptors were stimulated by increasing blood pressure >40 mmHg with phenylephrine (10 microgram. kg(-1). min(-1) iv) in sham SAD and SAD rats. Controls were infused with 0.9% saline. Only the locus ceruleus (LC) demonstrated a baroreceptor-dependent increase in Fos immunoreactivity in dopamine-beta-hydroxylase-positive neurons. In a second experiment, normal rats received rhodamine-labeled microsphere injections in the DBB (n = 12) before phenylephrine or vehicle infusion. In these experiments, only the LC consistently contained Fos-positive cells after phenylephrine infusion that were retrogradely labeled from the DBB. Finally, we lesioned the LC with ibotenic acid and obtained extracellular recordings from identified vasopressin neurons in the supraoptic nucleus. LC lesions significantly reduced the number of vasopressin neurons that were inhibited by acute baroreceptor stimulation. Together, these results suggest that noradrenergic neurons in the LC participate in the baroreflex activation of the DBB and may thus be important in the baroreflex inhibition of vasopressin-releasing neurons in the supraoptic nucleus.

No abstract

A small balloon placed at the junction of the superior vena cava and right atrium was used to stimulate cardiac volume receptors in pentobarbital sodium-anesthetized male rats. Extracellular recordings were obtained from antidromically identified vasopressinergic and oxytocinergic neurosecretory cells of the supraoptic nucleus. Cells were considered sensitive to the stimulus if balloon inflation resulted in a 30% change in firing frequency. Balloon inflation that did not stretch the caval-atrial junction had no significant effect on vasopressin neurons (n = 51, P > 0.05). Stretch of the caval-atrial junction decreased the firing activity in 64 of 83 putative vasopressin neurons (P < 0.01 compared with control). Stretch of the caval-atrial junction influenced the firing activity of only 3 of 26 antidromically activated oxytocinergic neurons, an effect not statistically different from control (P > 0. 05). When bilateral vagotomy was performed while recording from vasopressin neurons (n = 5), sensitivity to stretch of the caval-atrial junction was eliminated. Cardiac receptors located at the junction of the superior vena cava and right atrium may be important in regulating the activity of vasopressinergic but not oxytocinergic neurons of the supraoptic nucleus.

The bispectral index (BIS) monitor is an electroencephalographic recording device that generates a single numeric value. It has traditionally been used to measure anesthetic depth and avoid awareness in the operating room setting. In this report, the authors present different scenarios in the pediatric intensive care unit that demonstrate the potential applications of the BIS monitor outside of the operating room setting. The scenarios presented include use of the BIS monitor during titration of barbiturate coma, procedural sedation, sedation assessment during mechanical ventilation, and sedation while administering potentially confounding medications. Previous reports regarding the use of the BIS monitor in such scenarios and potential future applications are reviewed

Bispectral index (BIS) values were prospectively recorded in pediatric intensive care unit patients receiving continuous infusion of a neuromuscular blocking agent. Sedation was provided by a continuous infusion of midazolam or propofol. The BIS number was recorded by a bedside computer every 10 seconds but was concealed from health care workers. BIS values were recorded for 476 hours (161 893 BIS values) in 12 patients. The BIS number was 50 to 70, 57% of the time; < or =49, 35% of the time; and > or =71, 8% of the time. When supplemental doses of sedatives were administered, the BIS number was >70, 64% of the time; 50 to 70, 31% of the time; and < or =49, 5% of the time. Oversedation was more likely with propofol than midazolam. During the use of neuromuscular blocking agents, oversedation is a common occurrence. Physiologic parameters are not an accurate means of assessing the depth of sedation.