Reply

Comparing ‘equivalent’ or ‘homologous’ structures across vertebrates requires decisions to be made concerning the most relevant characteristics to be used or the different levels of homology that can be considered – molecular, ontogenetic, functional, etc. (Puelles & Medina, 2002). In our studies in amphibians we have chosen to rely on a variety of evidence to compare brain regions, e.g. their origin, organization, and function. In this scenario, we have tentatively proposed an organization of the anuran amygdaloid complex that can be readily compared to that of amniotes. Thus, in particular, we have defined the anuran lateral amygdala (LA) as a multimodal area in the ventral pallium that shares features with the amygdaloid ventropallial derivatives of the basolateral complex of amniotes (Moreno & González, 2004). This is far from considering the LA to be equivalent to the basolateral amygdala (BLA) of mammals. In amniotes (including mammals), the BLA includes ventropallial and lateropallial derivatives and what we have consistently observed is that the anuran ventropallial LA shares many features with the ventropallial regions of the BLA. These would include: (1) common gene expression patterns (Brox et al., 2003, 2004; Moreno et al., 2004); (2) connections with the hypothalamus (Bruce & Neary, 1995; Moreno & González, 2004, 2005); (3) afferents (although limited) from the thalamus and parabrachial area (Marín et al., 1997; Moreno & González, 2004); and (4) cholinergic connections from the subpallium (Marín et al., 1997; Moreno et al., 2004). Therefore the interpretation of Laberge et al. (2006) that amphibians would entirely lack a BLA equivalent, is not shared by us.

The organization of the anuran amygdaloid complex and the names given to its components are intended to facilitate the comparison with amniotes and in our review (Moreno & González, 2007) we provide evidence from several sources on which to base the comparison with amniotes. However, on the basis of connectivity and ‘functional’ properties a different scheme is being proposed in which a ‘medial amygdala’ in the subpallium is compared to the BLA of mammals (Roth et al. 2004; Mühlenbrock-Lenter et al. 2005). Again, it all depends on which characteristics are considered when comparing brain structures. We consider that the greater the number of shared features between two structures, the higher the possibility of equivalence.