Mossy fiber distribution in four lines of rats: A correlative study with avoidance abilities and excitability thresholds

Abstract

The distribution of the mossy fiber terminals in the hippocampal regio inferior was studied by the histochemical sulfide silver Timm method in four lines of rats selected for high (HAS) or low (LAS) avoidance scores and for high (HET) or low (LET) excitability thresholds of the neuromuscular apparatus. The results showed that HAS subjects, which have been found to exhibit the absolute lower excitability threshold, have significantly fewer mossy fibers in the infrapyramidal layers—that is, on the basal dendrites of the CA3 pyramidal cells—than did the three other groups. This observation confirms previous findings indicating a negative correlation between the density of mossy fiber terminals in these layers and active avoidance abilities. Since, however, HET subjects exhibit both high avoidance scores and high excitability thresholds but also present a large density of mossy fiber terminals in the infrapyramidal layer, the hypothesis of a direct relationship between few mossy fiber projections on basal dendrites of pyramidal cells and high avoidance scores must probably be revised.