Lateral asymmetries in the trigeminal ganglion of the male rat

We have applied stereological methods to estimate the number and perikaryal size of primary sensory neurons in celloidin-embedded trigeminal ganglia of male albino rats, specifically looking for inter-individual and side variability. The mean total number of neurons per ganglion was 35,300, with a moderate variability among ganglia. On average, 66% of the neurons were classified as A-type and 34% as B-type. Although for individual cases there could be notable side differences in the number of neurons of each type, on a population basis these differences were not significant. Mean neuronal volume was four times larger for A- than for B-cells, and both populations exhibited a moderate variability among individuals. High intra-animal side differences were found for A-cells, which were on average a significant 23.5% larger in the right ganglia. B-cells did not show significant side differences. The distribution of individual volumes around the mean value was consistently skewed to the right, particularly in the case of A-cells, which partially overlapped with the largest B-cells. In the right ganglion the distribution of A-cells, but not of B-cells, showed a rightward bias, revealing the increase in bigger neurons. The existence of larger A-type neurons in the right trigeminal ganglion may provide a structural substrate fur some somesthetically based complex behaviors which are best performed by rats using their right vibrissae. (C) 2000 Elsevier Science B.V. All rights reserved.