Autoradiographic determination of local cerebral blood flow and local cerebral glucose utilization during chemical stimulation of the nucleus tractus solitarii of anesthetized rats

Abstract

This study was conducted to determine whether the decrease in cerebral blood flow (CBF) observed during chemical stimulation of the nucleus tractus solitarius (NTS) can be explained by a decrease in cerebral metabolism. In anesthetized (urethane and chloralose), paralyzed and artificially ventilated rats, neurons in the NTS were chemically stimulated by microinjection of l-glutamate. Local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) were quantified in 43 brain structures by quantitative autoradiographic techniques using [ 14 C] iodoantipyrine and 2- [ 14 C] deoxyglucose, respectively. During chemical stimulation of the NTS ( n=6), LCBF decreased significantly in 32 of the 43 structures investigated when compared to either a control group with artificial cerebrospinal fluid injection ( n=6), or a controlled hemorrhage group ( n=5). In the controlled hemorrhage group, blood pressure was decreased to a degree comparable to that induced by microinjection of l-glutamate into the NTS. Mean blood flow of all structures investigated was significantly ( P<0.01) lower in the stimulation group than that in the control group and in the hemorrhage group. No significant differences in LCGU were observed between the three investigated groups in all structures examined except for an increase in LCGU in the chemically stimulated NTS site. It is concluded that the decrease in LCBF measured in most brain structures during chemical stimulation of the NTS is not caused by a decrease in LCGU in these structures and may therefore be explained by neurogenic influences on brain vessels.