Raphe-septal neurons changes in sensitivity to desipramine following an early septal lesion in the rat

Abstract

1. 1. The ekctrophysiological responsivity to desipramine (DMI) applied by systemic or local route was tested in Wistar female rats submitted to a wide lesion in the lateral septal area on the 8th day after birth. 2. 2. One year after a septal lesion, the dorsal raphe nucleus (DRN) stimulation produced an initial brief response in lateral septal and CA1/CA3 neurons. In the control and sham-lesion groups, most recordings showed only this initial brief response (non-late responding neurons); however, in the lesion group most of the recorded neurons showed an aftenh'scharge. 3. 3. DMI (2.14 mg/kg, 21 days, i.p.) increased the firing rate in septal and CA1/CA3 non-late responding neurons. In the equivalent septal neurons from lesion group, DMI produced the inverse effect, i.e., a decreased firing rate. 4. 4. In septal non-late responding neurons, DMI (2 mM; 10–15 nAmps, 0.5 sec) applied by microkmtopnoresis increased the firing rate only after long-term systemic DMI impregnation. The response to locally applied DMI did not occur in the lesion group even after long-term DMI treatment. 5. 5. In conclusion, an early lateral septal lesion canceled the response of intermediate-dorsal septal neurons to DMI applied by systemic and local routes.