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To better understand the formation and adult organization of the avian pallium, we studied
the expression patterns of gamma-aminobutyric acid (GABA), calbindin (CB), calretinin (CR),
and neuronal nitric oxide synthase (nNOS) in the hippocampal formation and hyperpallium of
developing and adult chicks. Each marker showed a specific spatiotemporal expression pattern
and was expressed in a region (area)-specific but dynamic manner during development. The
combinatorial expression of these markers was very useful for identifying and following the
development of subdivisions of the chicken hippocampal formation and hyperpallium. In the
hyperpallium, three separate radially arranged subdivisions were present since early development
showing distinct expression patterns: the apical hyperpallium (CB-rich); the intercalated
hyperpallium (nNOS-rich, CB-poor); the dorsal hyperpallium (nNOS-poor, CB-moderate). Furthermore,
a novel division was identified (CB-rich, CR-rich), interposed between hyper- and
mesopallium and related to the lamina separating both, termed laminar pallial nucleus. This
gave rise at its surface to part of the lateral hyperpallium. Later in development, the interstitial
nucleus of the apical hyperpallium became visible as a partition of the apical hyperpallium. In the
hippocampal formation, at least five radial divisions were observed, and these were compared
with the divisions proposed recently in adult pigeons. Of note, the corticoid dorsolateral area
(sometimes referred as caudolateral part of the parahippocampal area) contained CB immunoreactivity
patches coinciding with Nissl-stained cell aggregates, partially resembling the patches
described in the mammalian entorhinal cortex. Each neurochemical marker was present in
specific neuronal subpopulations and axonal networks, providing insights into the functional
maturation of the chicken pallium. J. Comp. Neurol. 497:751–771, 2006.
Grant sponsor: Spanish Direccio´n General de Investigacio´n-Fondo Europeo de Desarrollo Regional (FEDER); Grant number: BFI2003-06453-C02-01/02; Grant sponsor: Se´neca; Grant number: PB/50/FS/02; Grant sponsor: Red Centro de Investigacio´n de Enfermedades Neurolo´gicas-Nodo 318. |
