Comparative distribution and cardiovascular actions of substance P and substance K within the nucleus tractus solitarius of rats

Abstract

An investigation has been made into the comparative distribution and cardiovascular actions of Substance P (SP) and Substance K (SK) in the nucleus tractus solitarius (NTS) of rats. The two tachykinins were similarly distributed in the NTS region, as determined by radioimmunoassay of microdissected brain nuclei, although SP was present in an approximately 10 fold higher concentration than SK. Unilateral nodose ganglionectomy resulted in a non-significant reduction of tachykinin immunoreactivity in the ipsilateral NTS. Microinjection of synthetic SP into the NTS of urethane anaesthetised rats did not cause any significant changes in mean arterial pressure or heart rate. In contrast, SK (18 pmol) elicited a significant bradycardia which was maximal at 2 min after the injection. The bradycardic response was blocked in rats pre-treated with atropine. These results extend previous studies in which contrasting functional activities of SP and SK were demonstrated in peripheral systems, to indicate that tachykinins may exhibit different functional roles in the brain. SK, unlike SP, may be involved in central cardiovascular control via an action within the NTS.