Electrophysiological, pharmacological and behavioral studies of different physiological roles of the nucleus paragigantocellularis

The nucleus paragigantocellularis (PGI) is located in the rostral ventrolateral medulla and has noticeable connections with some other brain nuclei, such as locus ceruleus, nucleus raphe magnus and periaqueductal gray. In rats it is 3 mm in rostrocaudal and 1 mm in mediolateral and 1 mm in the dorsolateral aspect. Anatomically and functionally, PGI has been divided into two subnuclei, retrofacial and juxtafacial paragigantocellularis. PGI is consisted of small- (8-20 µm) and medium- (21-35 µm) sized neurons, which are adrenergic, serotonergic, and peptidergic. More recent cytochemical studies have also shown enkephalinergic, cholinergic and glutaminergic neurons in this brain structure. PGI's functions involve the regulation of blood pressure, heart rate, respiration, and pain sensation and control. In these series of studies, which has been conducted in our lab, we have evaluated different roles of PGI in blood pressure, nociception, and morphine tolerance and dependence through electrophysiological recordings, specific chemical and electrical lesioning techniques, pharmacological approaches and behavioral techniques.