ABSTRACT
Abstract .................................................................................................................. 389 26.1 Introduction................................................................................................. 390 26.2 The Hippocampal Mossy Fiber Projection ................................................ 391 26.3 Selectively Bred Strains as Tools for Testing Brain-Behavior
Relations ..................................................................................................... 392 26.4 Verifying Association between Traits: Genetic and
Phenotypic Correlations ............................................................................. 393 26.5 Solutions for the Linkage Problem............................................................ 394 26.6 Extending the Behavioral Analysis: Correlations with Other
Hippocampus-Dependent Tasks ................................................................. 396 26.7 Searching for “Non Hippocampal” Behavioral Correlates ....................... 399 26.8 Conflicting Data ......................................................................................... 401 26.9 Emerging Hypotheses................................................................................. 402 26.10 Some More Problems................................................................................. 403 26.11 The Real World Test for Genetic Brain-Behavior Relations: Natural
Selection and Evolution ............................................................................. 403 26.12 Conclusions and Outlook ........................................................................... 406 Acknowledgments.................................................................................................. 407 References.............................................................................................................. 408 List of Abbreviations in Text ................................................................................ 410
This chapter analyzes the natural genetic variability of the so-called intra/infrapyramidal mossy fiber (IIP-MF) projection in mice and rats, which terminates upon the basal dendrites of hippocampal pyramidal cells, and its relations to behavior. The analysis included thus far the following steps: (i) identification of structural traits sensitive to selective breeding for extremes in two-way avoidance, (ii) testing
the robustness of the associations found by studying individual and genetic correlations between hippocampal traits and behavior, (iii) confirming causal relationships by manipulating the structural variable in inbred (isogenic) strains, thereby eliminating the possibility of genetic linkage, (iv) further ruling out the possibility of spurious associations by studying the correlations between the hippocampal trait and other behaviors known to depend on hippocampal functioning, (v) searching for behavioral correlates of the IIP-MF variation in behaviors thought to be unrelated to hippocampal function, (vi) testing the effects of natural selection on differential IIP-MF distributions in naturalistic environments, and (vii), studying the variability of the IIP-MF distribution in small mammals with differential lifestyles. Taken together, the data imply that the hippocampus mediates a considerable number of behaviorally distinct processes, a view in accordance with the connectivity of this structure. The common denominator may be that variations of the IIP-MF entail differences in the stability of parallel hippocampal processing.
