Glucose utilization, blood flow and capillary density in the ventrolateral medulla of the rat

A specific population of neurons in the ventrolateral medulla (VLM) acts as the main integration center for the regulation of the sympathetic outflow to the cardiovascular system. In order to investigate whether this nucleus can be distinguished from its surroundings in the reticular formation of the medulla with respect to functional and morphological variables, the present study investigates several of such variables in this area on a quantitative basis. Local medullary glucose utilization was measured by the 2-[14C]deoxyglucose method; local medullary blood flow was quantified using iodo[14C]-antipyrine, and the local density of perfused capillaries was calculated by counting the number of intravascular fluorescent spots in brain sections after i.v. infusion of a globulin-coupled fluorescent dye. The values obtained from the VLM were compared with the respective values found in a reference area of the same brain section (gigantocellular nucleus). The values for glucose utilization, blood flow and capillary density were significantly (P less than 0.05) higher in the VLM than in the reference area (gigantocellular nucleus). This difference was 44.7% for glucose utilization, 34.1% for blood flow and 19.7% for capillary density. These data support the hypothesis that neurons in the VLM are specifically well supplied for being directly regulated in their activity by the PCO2 and pH in the arterial blood.