Pressor effects of acetylcholine microinjected into forebrain nuclei of unanesthetized rats

1. The injection of 13.5-54 nmol/500 nl of acetylcholine (ACH) into different brain areas of unanesthetized freely-moving 200-250 g male Wistar rats caused only pressor responses. 2. In the prosencephalon, the lateral septal area was the site at which ACH was more effective, whereas injections into surrounding areas, such as the accumbens/bed nucleus striae terminalis, the medial septal area or the lateral ventricle were less effective. No blood pressure effects were observed after injection into the anterior amygdala. 3. In the diencephalon, the ventromedial hypothalamic nucleus was the most sensitive site, whereas injection of ACH into surrounding areas, such as the posterior and lateral hypothalamic or the dorsal and ventral premammillary nuclei was less effective. 4. At all sites tested, the local pretreatment with 138-276 nmol atropine abolished the pressor response to ACH, suggesting a mediation through muscarinic receptors. 5. The sites of injection were confirmed histologically. 6. The present data indicate the existence of a cholinergic-sensitive site involved in the control of blood pressure at the level of the lateral septal area.