Catecholaminergic activity of the baroreceptor areas of the brain in response to bilateral dorsolateral transection of medulla oblongata in rats.

Central catecholaminergic activity was studied by measurement of norepinephrine (NE), epinephrine (EPI), their metabolites: total 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol in brain nuclei in response to bilateral dorsomedullary knife-cut (DMK-cut) in rats. In saline-pretreated conscious rats DMK-cut caused a marked hypertension, tachycardia and increases in plasma NE, EPI and vasopressin. Chlorisondamine (CHL) prevented the rise in plasma catecholamines and the tachycardia but failed to prevent the hypertension and the increment in plasma vasopressin. DMK-cut decreased NE and EPI in the nucleus tractus solitari (NTS) and A2 area; there were no catecholamine changes in A1 area or the periventricular nucleus but an increase in the paraventricular nucleus (PVN), the latter effect reversed by CHL. CHL alone or combined with DMK-cut had no effect on catecholamine concentrations in NTS-A2 area but lowered MHPG content. It is suggested that DMK-cut decreases the activity of the catecholaminergic system originating in A1 and terminating in PVN, where it causes catecholamine accumulation and may be involved in vasopressin release and thereby contribute to hypertension. In NTS-A2 area, however, the DMK-cut appears to increase catecholaminergic activity since catecholamines are depleted. Central effects of DMK-cut differ from those of ganglionic blockade-induced inhibition of the baroflex presumably due to sectioning of other pathways in addition to the primary baroreceptor input.