The importance of baroreceptor afferents for the decrease in brain glucose utilization during stimulation of the rostroventrolateral medulla of the rat

Abstract

The rostroventrolateral medulla (RVLM) is the main integration center for the regulation of the sympathetic outflow. The present study had the aim of investigating the effects of stimulation of the RVLM on the glucose utilization of the brain. Local cerebral glucose utilization (LCGU) can be regarded as an indicator of the brain functional activity. In anesthetized (chloralose-urethan), paralyzed (pancuronium) and ventilated rats, the medulla was exposed by a ventral craniotomy. The RVLM was stimulated by microinjection of 100 nl of 0.5 M sodium glutamate ( n = 6). The effective stimulation was verified by the increase in arterial blood pressure. In a control group ( n = 7), an identical volume of saline was injected into the RVLM. Local cerebral glucose utilization was measured in both groups using the 2-[ 14C]deoxyglucose method. The results showed a significant decrease in LCGU in the stimulated group in 33 of 39 brain structures examined. In order to investigate whether the decrease in brain glucose utilization is secondary to the stimulation of baroreceptor afferents by the increase in arterial blood pressure the carotid sinus nerves and both vagal nerves were cut. In this denervated group ( n = 5) the decrease in LCGU was abolished in all brain structures although blood pressure was increased to a degree comparable to the innervated group. It is concluded that cerebral glucose metabolism is decreased during stimulation of the RVLM and that this decrease is secondary to the activation of baroreceptor afferents by the increase in blood pressure.