Estimates of volumes and pyramidal cell numbers in the prelimbic subarea of the prefrontal cortex in experimental hypothyroid rats.

In previous quantitative studies we demonstrated that the volumes of the cerebellar and hippocampal granular layers, as well as their total number of cells, were reduced in 30 days old hypothyroid rats. We decided to extend these studies to the prelimbic subarea of the medial prefrontal cortex using the same morphometric procedures. The cortical volume and the total number of neurons of its Layer III were determined. After correcting for the tissue shrinkage factor, it was found that the volume of the entire prelimbic cortex and that of its Layer III was smaller in hypothyroid rats than in controls. Conversely, the number of neurons per unit volume of cortical Layer III was greater in hypothyroids. This indicates that there is a markedly increased cell packing density, probably related to the neuropil impoverishment, as was described by other authors almost forty years ago for the sensorimotor and visual cortices, applying inaccurate quantitative methods.