Anuran olfactory bulb organization: embryology, neurochemistry and hodology.
ABSTRACT In Xenopus laevis, we analyzed the origin of the projection neurons and interneurons in the developing olfactory bulbs by studying the expression patterns of the genes x-Eomes, x-Lhx5, x-Dll3 and x-Pax6. Olfactory bulb interneurons were characterized by using four conserved molecular markers for distinct subpopulations: gamma-aminobutyric acid, calretinin, calbindin, and tyrosine hydroxylase. Immunohistochemistry was combined with tract-tracing experiments to demonstrate the projection neurons and the interneurons of the olfactory bulbs simultaneously. Taken together, the results showed: (1) the pallial nature of the olfactory bulb and its projection neurons in Xenopus, like in mammals with comparable central projection areas, (2) the subpallial origin of the interneurons that, most likely, follow migratory pathways comparable to those described for mammals, (3) the different interneuron types possess neurochemical characteristics similar to mammals. Therefore, the present results show that the origin, chemoarchitecture and central connections of the olfactory bulbs are highly conserved in evolution.
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ABSTRACT: We used two developmental transcription factors, x-Eomes (T-box family) and x-Lhx5 (LIM-homeodomain family), to follow the origin and development of the olfactory bulbs in Xenopus. During embryonic and larval development, x-Eomes and x-Lhx5 were expressed in highly similar patterns, in the lateral and latero-ventral wall of the pallium. In adults, both markers were strongly and specifically expressed in mitral cells, i.e., in the projection neurons of the main and accessory olfactory bulbs. These results demonstrate the pallial origin of the olfactory projecting cells in Xenopus. Combined with previous results suggesting a subpallial origin for olfactory interneurons, these findings emphasize the dual origin of different neuronal populations in the bulbs of anamniotes, and suggest that this organization is a shared feature of tetrapods.Neuroreport 01/2004; 14(18):2355-8. · 1.40 Impact Factor
- Nature reviews. Neuroscience 12/2001; 2(11):780-90. · 31.67 Impact Factor
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ABSTRACT: A comparative analysis of LIM-homeodomain (LIM-hd) expression patterns in the developing stage 32 Xenopus brain is presented. x-Lhx2, x-Lhx7, and x-Lhx9 were isolated and their expression, together with that of x-Lhx1 and x-Lhx5, was analyzed in terms of prosomeric brain development and LIM-hd combinatorial code and compared with mouse expression data. The results show an almost complete conservation of expression patterns in the diencephalon. The Lhx1/5 and Lhx2/9 subgroups label the pretectum/ventral thalamus/zona limitans versus the dorsal thalamus, respectively, in alternating stripes of expression in both species. Conversely, strong divergences in expression patterns are observed between the telencephalon of the two species for Lhx1/5 and Lhx2/9. Lhx7 exhibits particularly conservative patterns and is proposed as a medial ganglionic eminence marker. The conservation of diencephalic segments is proposed to mirror the conservative nature of diencephalic structures across vertebrates. In contrast, the telencephalic divergences are proposed to reflect the emergence of significant novelty in the telencephalon (connectivity changes) at the anamniote/amniote transition. Moreover, the data allow the new delineation of pallial and subpallial domains in the developing frog telencephalon, which are compared with mouse subdivisions. In the pallium, the mouse combinatorial expression of LIM-hd is notably richer than in the frog, again possibly reflecting evolutionary changes in cortical connectivity.Journal of Neuroscience 11/2001; 21(19):7620-9. · 6.91 Impact Factor