Adrenaline Synthesizing Nerve Cells in The Medulla Of Normotensive and Hypertensive Rats

1. We have studied the number and distribution of adrenaline synthesizing nerve cells in the medulla oblongata of the rat, using a combination of immunofluorescence to visualize the enzyme phenylethanolamine‐N‐methyltransferase (PNMT) and catecholamine fluorescence to detect central catecholamines. 2. The distribution of adrenaline synthesizing nerve cells was similar in normo‐tensive (Wistar Kyoto) rats, spontaneous hypertensive rats, and stroke‐prone rats. Few of the cells visualized by PNMT immunofluorescence were detected by the Faglu fluorescence method for catecholamines. The CI (ventrolateral) and C2 (dorsomedial) groups of PNMT cells were anatomically distinct from the Al and A2 groups of catecholamine fluorescent cells and lay rostral to these cells within the medulla. There was a third group of adrenaline synthesizing cells close to the midline in the rostral medulla, and we have called this the C3 group. 3. There was a 32% increase in the number of PNMT cells in the medulla of 4‐week‐old stroke‐prone rats. 4. PNMT enzyme activity in a cross‐segment of the medulla containing the adrenaline synthesizing cells was also increased by 30% in both spontaneous hypertensive rats and stroke‐prone rats.