Anxiogenic-like effect induced by substance P injected into the lateral septal nucleus.

The lateral septal nucleus is known to modulate aversive reactions and to receive a strikingly dense substance P (SP) innervation. In the present study, after determining the optimal intracerebroventricular dose (10 pmol) to induce aversive responses, we applied SP directly into the lateral septal nucleus, and quantified anxiogenic responses using the elevated plus-maze (EPM) test. Notably, when placed in the EPM these animals presented clear aversive behaviors expressed either as jumps and bursts of running (darting responses) or freezing. However, we observed an effective increase in the anxiogenic responses evaluated in the EPM test uniquely in the animals that presented freezing. Animals expressing darting responses, in turn, were likely to have a stronger aversive condition, in which anxiogenic-like responses were hindered when measured in the EPM test. Overall, the present results support the idea that SP may have an important modulatory role on anxiogenic responses mediated by the lateral septal nucleus.