Pressor, dipsogenic, natriuretic and kaliuretic response to central carbachol in rats with lesion of the medial septal area.

In the present study we investigated the effect of electrolytic lesion of the medial septal area (MSA) on the dipsogenic, natriuretic, kaliuretic and pressor responses elicited by intracerebroventricular (i.c.v.) injection of the cholinergic agonist carbachol. Freely moving rats with sham or MSA lesion (1-7 days and 14-18 days) and a stainless steel cannula implanted into the lateral ventricle were studied. In sham rats, i.c.v. injection of carbachol (7.5 nmol) produced an increase in water intake (10.2 +/- 1.5 ml/h), mean arterial pressure (MAP) (35 +/- 5 mmHg) and urinary Na+ and K+ excretion (551 +/- 83 and 170 +/- 17 muEq/120 min, resp.). The pressor (18 +/- 3 and 14 +/- 4 mmHg, resp.) and natriuretic responses (178 +/- 58 and 172 +/- 38 muEq/120 min) produced by i.c.v. carbachol in acute or chronic MSA-lesioned rats were reduced. No change was observed in urinary K+ excretion and a reduced water intake (5 +/- 1.3 ml/h) was observed only in acute MSA-lesioned rats. These results suggest that the MSA plays an important role for the pressor and natriuretic responses induced by central cholinergic activation in rats. A small influence of this structure on water intake may also be suggested.