Is there a structure equivalent to the mammalian basolateral amygdaloid complex in amphibians?

To the Editor:

RE: ‘Evolution of the amygdaloid complex in vertebrates, with special reference to the anamnio-amniotic transition’ by Moreno and Gonzalez. Journal of Anatomy, Vol. 211, pp. 151–163.

Moreno and González, in their review on the evolution of the amygdala, omitted to mention that their consideration of the amphibian ‘lateral’ amygdala as a multisensorial structure equivalent to the basolateral amygdaloid complex of mammals is controversial. We have proposed elsewhere that the absence of dorsal thalamic input to the lateral portions of the amygdala in amphibians precludes its role as a multisensory associative region, as is expected from parts of the basolateral complex (Laberge et al., 2006). In a study of sensory responses in the toad telencephalon, responses to sensory modalities other than olfaction were only found in the medial parts of the amygdala (Laberge & Roth, 2007). Our recent results further show that intracellularly labeled thalamic neurons do not send axon branches to the lateral parts of the amygdala in the toad Bombina orientalis (F. Laberge, S. Mühlenbrock-Lenter, U. Dicke and G. Roth unpublished data). Species differences could exist, but we feel that the assertion by Moreno and González that the lateral amygdala represents a structure equivalent to the basolateral amygdaloid complex of mammals is not yet supported by experimental observations of thalamic input and multimodal sensory responses in this region.