The distribution of anterogradely-labeled fibers and retrogradely-labeled cell bodies in the interpeduncular nucleus (IPN) was mapped after injections of wheat-germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into various structures of the basal forebrain in adult rats. WGA-HRP injections into the medial septum/vertical limb of the diagonal band nucleus resulted in: 1) dense anterograde labeling in the rostral, intermediate, and central subnuclei; and 2) retrograde labeling in the apical and central subnuclei. Injections into the lateral septum produced: 1) no anterograde labeling in the IPN; and 2) retrograde labeling which was dense in the apical subnucleus, moderate in the central and lateral subnuclei, and light in the intermediate subnucleus. Injections into the horizontal limb of the diagonal band nucleus resulted in: 1) anterograde labeling which was most pronounced in the central, rostral, and intermediate subnuclei; and 2) retrograde labeling which was strongest in the apical, central, and lateral subnuclei. After injections into the substantia innominata-magnocellular preoptic nucleus, there was: 1) dense anterograde labeling in the rostral and central subnuclei and moderate anterograde labeling in the intermediate subnucleus; and 2) essentially no retrograde cell labeling in the IPN. These findings demonstrate that the IPN receives inputs from, and projects to specific portions of the basal forebrain. The rostral and central subnuclei are the primary targets of inputs from the basal forebrain to the IPN, and the apical subnucleus is the primary source of IPN projections to the basal forebrain.
Recent findings suggest that exogenous gangliosides improve recovery of a learned behavior (alternation in a T-maze) which is thought to be related to sprouting after lesions of the entorhinal cortex. In the present investigation, we studied an unlearned behavior (the open-field hyperactivity resulting from bilateral entorhinal lesions) to evaluate whether ganglioside treatments reduce the severity of initial postlesion impairments or improve recovery. We also examined whether the treatments enhance the sprouting of septodenate fibers which parallels the recovery of open-field activity. The typical behavioral changes induced by bilateral entorhinal lesions include hyperactivity, reduced habituation of activity, and a gradual time-dependent return toward control levels. We found that rats treated with total brain gangliosides (30 mg/kg) showed a smaller lesion-induced increase, consistently lower levels, and greater within-session habituation of activity than did saline-treated counterparts. Control rats treated with gangliosides did not exhibit a reduction in activity, suggesting that the effect was on lesion-induced hyperactivity rather than on activity, per se. Ganglioside-treated rats showed a slight, but consistently smaller lesion-induced sprouting response by the septodentate pathway than did untreated counterparts at all postlesion intervals examined (3, 5, 7, and 10 days). The present findings indicate that ganglioside treatments reduce the severity of the initial behavioral effects after entorhinal lesions without enhancing the sprouting by septodentate fibers.
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