Hodological characterization of the medial amygdala in anuran amphibians

Abstract

Early studies in anuran amphibians defined the amygdala as a single unit that only later could be subdivided into medial and lateral parts with the achievement of sensitive immunohistochemical and tracing techniques. However, the terminology used was often misleading when comparing with "homologous" amygdaloid nuclei in amniotes. Recently, the basal telencephalon of anurans has been demonstrated to be more complex than previously thought, and distinct amygdaloid nuclei were proposed on the basis of immunohistochemistry. Moreover, developmental data are increasing that support this notion. In the present study, we analyzed the patterns of afferent and efferent connections of the medial amygdala (MeA; formerly amygdala pars lateralis), considered as the main target of the vomeronasal information from the accessory olfactory bulb, as in other vertebrates. By means of axonal transport of dextran amines, the afferent and efferent connections of the MeA were traced in Rana perezi and Xenopus laevis under in vivo and in vitro conditions. Largely similar results were found in both species. The results showed abundant intratelencephalic and extratelencephalic connections that were readily comparable to those of other tetrapods. Most of these connections were reciprocal and, in particular, the strong relation of the MeA with the hypothalamus, via the stria terminalis, was demonstrated. Immunohistochemical techniques showed staining patterns that revealed abundant peptidergic afferents to the MeA, as well as minor inputs containing other neurotransmitters such as catecholamines. Double-labeling experiments demonstrated that the peptidergic fibers that reach the MeA originate in the ventral hypothalamus, whereas the catecholaminergic innervation of the MeA arises in the caudal extent of the posterior tubercle. Taken together, the results about connectivity in our study support the comparison of the MeA in anurans with its counterparts (and similarly named) amygdaloid nuclei in amniotes. Most of the hodological features of the medial amygdala seem to be shared by those tetrapods with well-developed vomeronasal systems.

The Vertebrate mesolimbic reward system and social behavior network: A comparative synthesis

“…The anuran meAMY also sends massive projections to the VMH (Moreno and González, 2003) and is developmentally derived from the subpallium, but also contains some cells originating from the ventral telencephalon (Moreno and González, 2007b). To our knowledge no lesion or stimulation studies have been done …”

Distribution of Neuropeptide FF-Like Immunoreactivity in the Brain of <i>Dermophis mexicanus</i> (Amphibia; Gymnophiona): Comparison with FMRFamide Immunoreactivity

“…Differently, the nucleus accumbens and the striatum proper, located in rostral and mid telencephalic levels , seem to be only moderately innervated by NPFF-ir fi bers in all amphibians studied, whereas distinct amygdaloid territories possess heavier innervation. In Dermophis , abundant NPFF-ir were located in the pars lateralis of the amygdala [according to Northcutt and Kicliter, 1980], but most likely this region would correspond with the recently re-named medial amygdala of anurans, which possesses the strongest NPFF-ir innervation [Crespo et al, 2003;Moreno and González, 2003].…”

Evolution of the Amygdala: New Insights from Studies in Amphibians

“…The dendrites course rostrally inside the dorsal striato-pallidal neuropil. To the left, clusters of two and four neurons illustrate neurons typical of the subpallial amygdala with small somata, smooth dendrites that arborize locally and axonal projec- Marín et al [1998] and Moreno and González [2003 Brox et al [2004] Main olfactory component (cortical Herrick [1948] termed the rostral part of the vomeronasal extended amygdala in salamander, the lateral cellular prominence, and the caudal part receiving strong AOB input, nucleus amygdalae.…”

“…Rostrally, it extends dorsal to the striato-pallidum, and caudally it merges with the dorsal preoptic region. Thus, the extended vomeronasal amygdala comprises both the amygdala pars lateralis of Northcutt and Kicliter [1980], also named medial amygdala by Moreno and González [2003], and the striato-pallial transition area [Marín et al, 1997a, b;Roth et al, 2004;Laberge and Roth, 2005], also named anterior amygdala by Marín and collaborators [1998] (see table 1 for a survey of the different nomenclatures describing the amphibian amygdaloid complex). The caudal component of the vomeronasal amygdala receives input from the AOB and projects strongly to the preoptic area and hypothalamus.…”