A morphometric study of the amygdala in the guinea pig.

The characteristic features of guinea pig amygdala (CA), as shown by volumetric comparisons of the individual nuclei, are the poor development of the basolateral (BL) and lateral olfactory tract (NLOT) nuclei as well as the strong formation of the lateral (LA) and basomedial (BM) nuclei. The central (CE), cortical (CO) and medial (ME) nuclei also appear to be well represented in this species. All these features are even more pronounced when the total number of neurons in the nuclei referred to was taken into consideration. A comparison of the densities of neurons in the individual nuclei with the mean numerical density of cells in the guinea pig CA indicates that the densities of neurons in LA, BL, BM, CE and CO are significantly lower than the mean (p < 0.05), whereas in the ME and NLOT these values are significantly higher than the mean (p < 0.05). It is noteworthy, that the densities of the neurons in CE and CO do not differ statistically from each other (p > 0.05) and are significantly higher than the respective values in LA, BL and BM (p < 0.05). Furthermore, a similar division of the guinea pig CA may to some extent be made using the size parameters of the amygdaloid neurons as a marker. Interestingly, the large neurons populate organised CA areas like LA, BL and BM less densely, whereas the small cells create ME and NLOT, where the neurons are densely arranged. CE and CO occupy intermediate positions, with the neurons similar in size to the mean for the guinea pig CA.