A morphometric comparative study of the medial geniculate body of the rabbit and the fox.

Unbiased stereological methods were used to morphometrically examine and compare the medial geniculate body (MGB) of two species from different mammalian orders. The MGB had a similar nuclear pattern, and it was parcelled into three major cytoarchitectural areas: the dorsal nucleus (MGd), the ventral nucleus (MGv) and the medial nucleus (MGm). The MGd was predominant in the fox, where it contributed nearly 50% to the total MGB volume, while in the rabbit, the MGv was insignificantly larger than the MGd. In both species, the percentage contribution of the MGm was the lowest. The MGd in the fox was also characterized by twice as many neurons per mm(3) as in the rabbit, whereas a reverse proportion was observed in the MGm, although the numerical density in the MGv was very similar in both species. The total number of MGB neurons in the fox was over twice higher than that in the rabbit. The variability in the percentage contribution of the MGd, MGv and MGm cells to the total neuronal population of the MGB was different in both mammals. In the rabbit, there was a larger contribution from the MGv and MGm, while in the fox, the MGd was predominant. These data demonstrate that the main areas of the MGB complex differ in terms of the morphometric characteristics in both species. Our results also show that the negative correlation between the volume and numerical density in the sensory centres of the brain might not be as distinct as in the non-sensory brain structures.