Change and Its Neural Mechanism of Volumes of Song Control Nuclei During Development in the Striated Mannikin (Lonchura striata swinhoei)

The present study investigated the changes of volumes of four vocal control nuclei:robust nucleus of the archistriatum (RA),lateral magnocellular nucleus of the anterior neostriatum(LMAN),Area X and high vocal center (HVC) during development in the songbird,Striated Mannikin (Lonchura striata swinhoei).By using of neural tract-tracing methods,the process of neural connectivity within the four nuclei was studied to further understand the neural mechanism of development and sexual differentiation of vocal control nuclei in songbirds.The results were as follows:1)Both male and female RA volumes most significantly changed around 20 or 30 days,and the sexual differences in volumes occurred around 20 or 30 days.Both male and female RA received efferent fibers from LMAN and HVC around 15 or 25 days respectively.2)Both male and female LMAN volumes experienced first increase and subsequent decrease.However,the peaks of changes of female LMAN volumes were 10-day delay compared to those of males.The LMAN volumes both in males and in females changed most rapidly in two periods:from 20 to 25 days age and from 30 to 40 days during the whole development.The neural connections between LMAN and RA established around 15 days age in both males and females.However,female LMAN received fewer connections than male LMAN.3)Area X volume changed most rapidly from 20 to 25 days.Area X received HVC efferent fibers around 15 days.Female Area X received fewer connections than male Area X.4)Both male and female HVC volumes changed significantly around 20 or 30 days.The establishment of neural connection between HVC and Area X or between HVC and RA was around 15 days or 25 days respectively.The present study suggested that the time when the volume of vocal control nuclei changed significantly was approximately corresponded to the time of establishment of neural connection(s) among the vocal control nuclei.Thus the neural development of vocal control nuclei or their sexual differences might be correlated to the establishment of their own neural connections.