Cholinergic mechanisms within the caudate nucleus mediate changes in blood pressure

Microinjections of 10 micrograms of carbachol into the caudate nucleus induced changes in the blood pressure of cats anesthetized locally, paralyzed and artificially respired. These responses were dependent on the site of injection. Carbachol, microinjected at rostral levels of the caudate nucleus, elicited pressor responses while a decrease in blood pressure was observed following injections at caudal levels. Both of these effects were blocked by prior microinjection of atropine. Microinjections of carbachol outside the caudate did not affect the resting blood pressure. However, injections of carbachol into the lateral ventricle always produced pressor responses independent of the site of injection along the antero-posterior extension of the ventricle. On the other hand, microinjections of dopamine (20 micrograms) into the caudate nucleus failed to modify blood pressure. From this study, it is concluded that within the caudate nucleus there are two different muscarinic mechanisms, which when activated, mediate changes in blood pressure, possibly through the sympathetic nervous system.