SEPARATION OF SEPTAL INFLUENCES ON LORDOSIS, ULTRASOUND PRODUCTION, AND BODY-WEIGHT

Previous results suggest that septal fibers inhibit lordosis, ultrasou nd production, and bodily growth (rate of weight gain) in female hamst ers. 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 ex tended across most of the interface. Others received cuts that were of fset laterally and disrupted just the lateral half of this region. Eac h response was affected by at least one of these cuts. However, the pa tterns of effects differed across measures. Lordosis was facilitated e qually by medial and lateral cuts, suggesting its dependence on fibers that are concentrated where the cuts overlapped, i.e., laterally alon g 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 th at the relevant fibers are distributed across much of the septal-POA i nterface but are concentrated in its medial half. Taken together, thes e results suggest that septal connections affecting lordosis, ultrasou nd production, and body weight follow different trajectories as they e nter or leave the ventral septum. In rum, this strengthens the case fo r the mediation of these effects by distinct populations of septal cel ls. (C) 1998 Elsevier Science Inc.