Functional Topography in the Rat Rostral Ventrolateral Medulla (RVLM): Distribution of C1 Neurons that Respond to Cardiovascular versus Metabolic Stimuli

Abstract

Neurons controlling cardiovascular responses and glucose counter regulation are co‐located within the RVLM, with activated neurons lying almost exclusively caudal to the caudal pole of the facial nucleus (FN). However, it is unclear whether the same neurons are involved in triggering both cardiovascular and metabolic responses. We compared the distributions of RVLM C1 neurons activated by cardiovascular or metabolic stimuli using Fos to identify activated neurons. To conscious male or female rats, we administered insulin (10 U/kg ip) or 2‐deoxyglucose (2DG; 400 mg/kg sc) to induce hypoglycaemia or nitroprusside (NP; 1 mg/ml iv), hydralazine (HDZ; 10 mg/kg iv) or diazoxide (DZX; 50 mg/kg iv) to cause hypotension. Rats were transcardially perfused with formaldehyde 90 or 120 minutes later. Coronal 30‐micrometer thick sections of medulla (1:4 series) from the spinomedullary junction to mid‐FN were immunoperoxidase‐stained to show Fos‐immunoreactivity plus phenylethanolamine N‐methyl transferase (PNMT)‐immunoreactivity to identify C1 neurons. The 6 sections containing the 600 micrometers caudal to the caudal pole of FN (sections FN0 to FN‐5) were each divided into 3 equal segments (medial, middle, lateral) and the total numbers of PNMT neurons with Fos nuclei (Fos+PNMT neurons) were counted. The numbers of Fos+PNMT neurons were greater in the medial and middle thirds than in the lateral third of the C1 cell column in insulin‐ and 2DG‐treated rats. In NP‐, DZX‐or HDZ‐treated rats, the numbers of Fos+PNMT neurons were greater in the middle and lateral two thirds of the C1 cell column. Two‐way ANOVA showed a very strong interaction between stimulus and laterality (p<0.0001), both for number of Fos+PNMT neurons and for percentage of PNMT neurons with Fos nuclei. These results reveal that the extent of Fos expression in PNMT neurons in the medial versus lateral zones depends on the type of stimulus. Post‐hoc analysis confirmed that, in the medial zone, the metabolic stimuli activated more PNMT neurons than cardiovascular stimuli, while it was the opposite in the lateral zone (p<0.0001 in both cases). These results show that hypoglycaemia‐responsive RVLM C1 neurons are concentrated in the medial and middle thirds of the C1 cell column whereas hypotension‐responsive RVLM C1 neurons are concentrated in the middle and lateral two thirds of the column. Hence, within the rat RVLM, C1 neurons are distributed topographically according to their function.Support or Funding InformationNHMRC 1025031; NIH HL096787 & HL130577This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.