Abstract
Striatal projecting neurons, known as medium spiny neurons (MSNs), segregate into two compartments called matrix and striosome in the mammalian striatum. The matrix domain is characterized by the presence of calbindin immunopositive (CB+) MSNs, not observed in the striosome subdivision. The existence of a similar CB+ MSN population has recently been described in two striatal structures in male zebra finch (a vocal learner bird): the striatal capsule and the Area X, a nucleus implicated in song learning. Female zebra finches show a similar pattern of CB+ MSNs than males in the developing striatum but loose these cells in juveniles and adult stages. In the present work we analyzed the existence and allocation of CB+ MSNs in the striatal domain of the vocal learner bird budgerigar (representative of psittaciformes order) and the non-vocal learner bird quail (representative of galliformes order). We studied the co-localization of CB protein with FoxP1, a transcription factor expressed in vertebrate striatal MSNs. We observed CB+ MSNs in the medial striatal domain of adult male and female budgerigars, although this cell type was missing in the potentially homologous nucleus for Area X in budgerigar. In quail, we observed CB+ cells in the striatal domain at developmental and adult stages but they did not co-localize with the MSN marker FoxP1. We also described the existence of the CB+ striatal capsule in budgerigar and quail and compared these results with the CB+ striatal capsule observed in juvenile zebra finches. Together, these results point out important differences in CB+ MSN distribution between two representative species of vocal learner and non-vocal learner avian orders (respectively the budgerigar and the quail), but also between close vocal learner bird families.
Highlights
Medium spiny neurons integrate cortico-basal ganglia-thalamocortical circuits for motor learning in vertebrates (Graybiel et al, 1994; Packard and Knowlton, 2002; Fino and Venance, 2010; review of medium spiny neurons (MSNs) circuits in vertebrates in Reiner et al, 1998)
We studied the co-localization of CB with FoxP1, a marker for MSNs in vertebrates (Tamura et al, 2003; Haesler et al, 2004; Teramitsu et al, 2004) and analyzed the cellular distribution of CB+ cells in the striatal domain of male and female budgerigars to better characterize the gender differences that have been previously described in these birds (Brauth et al, 2005)
The most dorsal sector is close to the pallial /subpallial border and it contains the medial striatum (MSt) in the periventricular zone, and the lateral striatum (LSt) in the intermediate stratum
Summary
Medium spiny neurons integrate cortico-basal ganglia-thalamocortical circuits for motor learning in vertebrates (Graybiel et al, 1994; Packard and Knowlton, 2002; Fino and Venance, 2010; review of MSN circuits in vertebrates in Reiner et al, 1998). Vocal learner birds develop a special neural circuit for song learning and production, the song system. This so called song system depends on MSN function in its striatal subdivision (Nottebohm and Arnold, 1976; Nottebohm et al, 1976; Striedter, 1994; Durand et al, 1997; Gahr, 2000; Roberts et al, 2002). Like chickens or quails, only produce innate sounds and they do not develop a network of telencephalic nuclei for vocal learning (Konishi, 1963; Gahr, 2000; Puelles et al, 2007). Parrots, the proposed closest living relatives of passerines (Suh et al, 2011) are able of movement learning by imitation (Moore, 1992), which, like song learning, implicates striatal projecting neuron circuits
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