A morphometric study of the amygdala in the common shrew

The characteristic features of the common shrew amygdala (CA), as shown by volumetric comparisons of the individual nuclei, are the poor development of the lateral (LA) and basomedial (BM) nuclei as well as the particularly strong formation of the basolateral (BL) and lateral olfactory tract (NLOT) nuclei. The central (CE), cortical (CO) and medial (ME) nuclei are also well organised in this species. All these features are even more distinctly visible when the total number of neurons in the nuclei referred to are compared. A comparison of the densities of neurons in the individual nuclei with the mean numerical density of cells in the CA indicates that there are the 3 different regions within the common shrew's CA. The densities of neurons in the LA, BL, and BM are significantly lower than the mean density of cells in the CA (p < 0.05). In the CE this value does not differ from the mean (p > 0.05). In the CO, ME and NLOT the density values are significantly higher than the mean (p < 0.05). Furthermore, a similar division of the shrew's CA can, to some extent, be performed using the size parameters of the amygdaloid neurons as a marker. Interestingly, the large neurons populate less densely organised CA areas like the LA, BL and BM, whereas the small cells populate the ME and NLOT, where the neurons are densely arranged. The CE and CO occupy intermediate positions, with the neurons similar in size to the mean for the shrew's CA.