Developmental analysis of raphe dorsalis unit activity in the rat

Unit activity of raphe dorsalis neurons was recorded in rats between 3 and 24 days of age. Both a regular discharge pattern and a slow firing rate were observed as early as day 3. The frequency of discharge was not statistically different at any age from the mean discharge rate in the adult rat. It was concluded that the electrophysiological activity of 5-HT neurons develops early in the process of maturation, prior to that of the biochemistry and anatomy of these neurons.