EFFECTS OF LATERAL PARABRACHIAL NUCLEUS LESIONS IN CHRONIC RENAL HYPERTENSIVE RATS

Neuroanatomic studies describing forebrain projections to the lateral parabrachial nucleus suggest a central integrative role in cardiovascu lar regulation. We performed this study to examine the role of this po ntine nucleus in the maintenance of one-kidney, figure-8 renal-wrap hy pertension. Bilateral ibotenic acid ablation of the lateral parabrachi al nucleus was performed 4 weeks after induction of hypertension or sh am operation. In hypertensive rats, ablation produced a significant re duction in mean arterial pressure from 160 +/- 4 to 118 +/- 2 mm Hg an d a transient but significant increase in heart rate from 381 +/- 5 to 408 +/- 8 beats per minute on the first day after ablation; arterial pressure returned to preablation values by day 5 after ablation. In sh am-operated, normotensive animals, arterial pressure was not altered b y ablation, and a transient but significant increase in heart rate fro m 384 +/- 8 to 419 +/- 7 beats per minute was again observed. Before a blation, trimethaphan administration produced a significantly greater drop in arterial pressure in hypertensive (Delta-72.8 +/- 4.6 mm Hg) v ersus normotensive (Delta-55.7 +/- 4.1 mm Hg) animals. This effect was eliminated on day 1 after ablation yet returned on day 4 after ablati on. In blood samples obtained before ablation and on days 1 and 4 afte r ablation, circulating plasma catecholamine concentrations in both gr oups remained unchanged. These observations suggest that, because of p ossible alternate neural compensatory mechanisms, lateral parabrachial nucleus ablation produces a significant yet transient reversal of ren al-wrap hypertension. Thus, the lateral parabrachial nucleus may contr ibute to the increased sympathetic nervous system function associated with this model.