DIFFERENCE IN TOPOLOGY AND NUMBERS OF BAROSENSITIVE CATECHOLAMINERGICAND CHOLINERGIC NEURONS IN THE MEDULLA BETWEEN SHR AND WKY RATS

We hypothesized that there may be a significant difference in the neur onal composition of the baroreceptor reflex pathway between normotensi ve Wistar Kyoto (WKY) and spontaneously hypertensive SHR rats. Using t he double-immunoreactive (IR) method, the topology and numbers of baro sensitive neurons that contain glutamate (Glu), glutamic acid decarbox ylase (GAD), tyrosine hydroxylase (TH), phenylethanolamine N-methyltra nsferase (PNMT) and choline acetyltransferase (ChAT) were compared bet ween the two strains. The control rats were sham-operated only for can nulation of the trachea and femoral artery/vein. The test rats were in jected with the presser agent phenylephrine to raise blood pressure an d stimulate arterial baroreceptors. In both the control and test exper iments, the c-Fos/Glu-, GAD-, TH- and PNMT-IR neurons were found in th e nucleus tractus solitarii (NTS) and ventrolateral medulla (VLM), whi le the FosB/ChAT-IR neurons were found in the NTS, dorsal motor nucleu s of the vagus (DMX) and nucleus ambiguus (AMB). In the control experi ment, no significant difference in numbers was recognized in any of th e double-IR neurons between the two strains. In the test experiment, t he numbers of FosB/ChAT-IR neurons in the NTS, DMX and AMB were signif icantly smaller in SHR than in WKY. The numbers of c-Fos/TH-IR neurons in the caudal VLM were significantly larger in SHR than in WKY. These results suggest that a smaller number of barosensitive cholinergic ne urons in the DMX and AMB in SHR causes the weaker baroreceptor-cardiac vagal reflex in SHR, and that a larger number of barosensitive catech olaminergic neurons in the caudal VLM in SHR are involved in the stron ger baroreceptor-vasopressin reflex in SHR. (C) 1998 Elsevier Science B.V. All rights reserved.