Baseline 24-Hour Plasma Corticosterone Rhythm in Normal, Sham-Operated and Septally-Lesioned Rats

In order to test whether septal ablation alters the resting 24-hour plasma corticosterone rhythm or increases sensitivity to stimulation, baseline 24-hour plasma corticosterone values were measured in normal, sham-operated and septally-lesioned rats under ‘standard’ and ‘rigorous’ environmental conditions. Mapping the rhythm at 4-hour intervals in 24 h confirmed that there is an elevation in the rhythm around trough time following septal damage under the standard environmental condition, as previously reported. In contrast, an 8-point map of the rhythm, determined under rigorously controlled environmental conditions, demonstrated that following septal ablation in rats, the 24-h baseline rhythm in plasma corticosterone is identical to that seen in normal and sham-operated animals. Thus, the hypothesis is borne out that although the baseline adrenal function is normal in septally-lesioned rats, adrenal responses to stimulation are enhanced.