Fig. 3.

Circulating corticosteroid concentrations were elevated in mildly stressed rats and in aged rats. There was a significant increase in circulating corticosteroids in 22-month-old compared with 4-month-old rats (p < 0.05, Student’s t test) and similarly in rats that had been housed in isolation, i.e., mildly stressed rats, compared with the control rats that had been housed as a group (p < 0.01, Student’s ttest). Analysis was made in samples obtained from rats at the end of electrophysiological recording in all cases. The number of observations is given in parentheses.