Multiple inhibitory actions of the paramedian reticular nucleus--effects on blood pressure and motor activities in rats.

The paramedian reticular nucleus (PRN) is a triangle midline structure located in the caudal medulla. Electrophysiological and biochemical evidence has suggested that PRN is an important depressor area, and it regulates various cardiovascular functions. The present results have demonstrated that PRN also plays an inhibitory role in a variety of behavioral functions. Lesions of this nucleus produced augmentations of many behavioral measures including: locomotor activity, clockwise and anti-clockwise turnings, as well as stereotyped behavior in rats. It also produced an increased and a more randomized pattern of locomotion. Destructions of the area of nucleus of solitary tract, which affects bradycardia and sometimes hypotension; as well as the midbrain reticular formation, which does not show any cardiovascular responses, yielded much less significant effects. These results confirm previous physiological findings from our laboratory and further suggest that PRN is a unique and independent area which exerts multiple inhibitory actions upon various physiological and behavioral functions in animals.