Effects of Septal Lesions on Fear-potentiated Startle, and on the Anxiolytic Effects of Buspirone and Diazepam

The present study evaluated the effect of septal lesions on baseline startle amplitude, potentiated startle (a measure of conditioned fear), and the ability of either buspirone or diazepam to block potentiated startle. Baseline responding to an acoustic stimulus was obtained for all rats, followed by potentiated startle training (ten light-shock pairings on each of two days). Rats were then given bilateral electrolytic lesions of the septum or sham surgery. Four and seven days following surgery all rats were tested again for baseline startle amplitude. Ten days postsurgery, rats were injected with either 5.0 mg/kg buspirone or vehicle and tested for potentiated startle (increased acoustic startle in the presence of a light previously paired with shock). Five days later septal-lesioned animals were injected with either 5.0 mg/kg of diazepam or vehicle and again tested for potentiated startle. Septal lesions increased baseline startle amplitude significantly, but did not alter the magnitude of potentiated startle or impair the ability of buspirone or diazepam to block potentiated startle. In Experiment 2 rats were trained using the above procedures, and were subsequently given discrete bilateral lesions of the lateral septum or sham surgery. Lateral septal lesions again had no effect on the magnitude of potentiated startle. These findings do not support an involvement of the septum in the inhibition of fear, or in the mediation of the anxiolytic effects of buspirone or diazepam.