Separation of septal influences on lordosis, ultrasound production, and body weight.

Previous results suggest that septal fibers inhibit lordosis, ultrasound production, and bodily growth (rate of weight gain) in female hamsters. To determine if the systems responsible for these effects can be dissociated, septal connections with or through the preoptic area (POA) were disrupted by horizontal cuts across the interface between these areas. Some subjects received cuts that were centered medially and extended across most of the interface. Others received cuts that were offset laterally and disrupted just the lateral half of this region. Each response was affected by at least one of these cuts. However, the patterns of effects differed across measures. Lordosis was facilitated equally by medial and lateral cuts, suggesting its dependence on fibers that are concentrated where the cuts overlapped, i.e., laterally along the septal-POA interface. In contrast, ultrasound rate was increased just by the more medial cuts, suggesting its dependence on relatively medial fibers. Finally, body weight was increased by both lesions but consistently responded more to the more medial cuts. This suggests that the relevant fibers are distributed across much of the septal-POA interface but are concentrated in its medial half. Taken together, these results suggest that septal connections affecting lordosis, ultrasound production, and body weight follow different trajectories as they enter or leave the ventral septum. In turn, this strengthens the case for the mediation of these effects by distinct populations of septal cells.