Dentate gyrus folding per brain hemispheres do not vary with habitat complexity in two octodontid rodents

LUIS EBENSPERGER; JORGE MPODOZIS; RAUL SOBRERO

CABA

Congreso; World Congress on Brain, Behavior and Emotions; 2016

CCM EVENTOS LTDA

Cortical folding scales uniformly across individuals and species of mammals. Mechanistic explanations to cortical folding focus either on forces external to the developing cortex or intrinsic, such us axonal tension, differential proliferation, or expansion of developing structures that are bonded to one another. However, the relative importance of habitat and social complexity (two external factors) on cortical folding and the extra-cortical folding in divided brain remains unexplored. We studied two natural populations of Octodon lunatus (Los Molles, LM) and O. degus (El Salitre, ES), two Chilean endemic rodent species that face contrasting vegetation cover of habitat used, but that also differ in the extent of sociality. We measured a dentate gyrus (DG) folding index per degu brain hemisphere (LM=3F+3M; ES=4F+3M). DG folding index was estimated by dividing the number of inward folds per hemisphere by the DG surface per hemisphere. We used General Lineal Models followed by best fit and supported model approaches to examine how degu sex, body mass, total group size, and range area within population predicted variation in the number of DG folding. The examination of how ecological and social factors predicted number of DG folding of O. lunatus revealed that the best fit model at LM was not well supported. Similarly, the best fit model at ES was not well supported, implying that number of DG folding of O. lunatus and O. degus were not well predicted by any of the predictors examined between species populations. This finding contrasts with previous studies on primates that support associations between hippocampal folding, brain asymmetry, and individual social cognitive skills. Within populations, asymmetry, number of DG folding of O. lunatus and O. degus were not well predicted by total group size, a structural aspect of group living. Funding: This study was partially supported by FONDECYT grant 3150306 to R.S., FONDECYT grants 1090302 and 1130091 to L.E.