Study On The Cytoarchitecture Of Tectal Layer â…  And Distribution Of Some Neuropeptides Within Its Related Nuclei In Chick

Approximately 90% of the retinal ganglion cells contribute to the tectofugal pathwayin chick. So the optic rectum is centrum of visual system. The avian optic tectum showsthe highly organized lamination. Some visual information is sent to the nucleus geniculatuslateralis ventralis (GLv) via the cells in layerⅠ(Ⅰcells) of the tectum in birds and is usedfor color vision, papillary reflex, and optomotor mechanisms. In the meanwhile, the optictectum receive input of GLv. The nucleus isthmi pars parvocellularis (Ipc), parsmagno-cellularis (Imc), and pars semilunaris (SLu), all of them receiving ipsilateral tectalinput in parallel. Ipc receives strong and topographically ordered input from tectal layer 10neurons and constitutes an inhibitory return projection onto the outer retinorecipient layers2-5. The depth of tectal layerⅠand the morphological characteristics of tectal cells in layerⅠwas investigated using Nissle staining, Golgi staining, and postmortem labeled with DiImethod. Most ofⅠcells appeared shuttle, others showed round, oval, pyramidal, triangular,and polygonal etc. The lateral region of layerⅠwas thicker than the ventral and the dorsalregions. According to the area of soma,Ⅰcells can be divided into four kinds: giant cells,large cells, medium cells and small cells. The medium cells were the most in the lateralregion of layerⅠ. The small cells were the most in the dorsal and the ventral regions. Thenumbers of giant cells were the least in all the regions of layerⅠ. There were 2～6 primarydendrites inⅠcells, most of which gave off two primary dendrites(60.7%, n=128). TheGABA, GnRH,β-EP, VIP and SP-like immunoreaction positive neurons within the nucleirelated to the tectal layerⅠwere observed in the different photoperiod. The photoperiodwas designed into four levels. They are 11L:13D, 13L:11D, 15L:9D, and 17L:7D. TheGABA-like immunoreaction positive neurons could be seen in Imc, Glv on 11L:13Dphotoperiod before laying; and in Imc, GLv on 11L:13D, 17L:7D photoperiod after laying.The GnRH-like immunoreaction positive neurons could be seen in Imc, Ipc on 11L:13Dphotoperiod before laying; in Imc, Ipc on 13L:11D photoperiod aider laying.β-EP-likeimmunoreaction positive neurons could be seen in GLv on 15L:9D photoperiod before laying; in Irne, GLv in 11L:13D photoperiod after laying. VIP-like immunoreactionpositive neurons could be seen in Imc, Ipc on 15L:9D and in GLv on 17L:7D photoperiodbefore laying; in Imc on 13L:11D and in GLv on 17L:7D photoperiod after laying. SP-likeimmunoreaction positive neurons could be seen in GLv on 15L:9D photoperiod beforelaying and in GLv on 17L:7D photoperiod after laying. The results indicated that GABAmay be the important inhibitory neuropeptides; VIP,β-EP, SP also involved in theregulation of the GnRH. Optical information may control the chicken productionperformance by adjusting the distribution of GABA, VIP andβ-EP neuropeptides withinthe nuclei related to the tectal layerⅠ.