ABSTRACT
Objective To study the morphological types of the retinal ganglion cells (RGCs) projecting to tectum in the chick. Methods The tectal projecting RGCs in the chick were identified by retrograde axonal transport of Fast blue and their dendrites were labeled by intracellular injection of Lucifer Yellow.The retinotectal projecting ganglion cells were classified according to somal areas,dendritic field sizes and dendritic branching pattern. Results Retinotectal projecting ganglion cells were divided into 3 groups and 5 subgroups,Group Ic/Is,Group IIc/IIs,Group IVc.Group I cells had small somal area and small dendritic field.They contained 2 subgroups of Is(simple)and Ic(complex).Group II cells had medium sized soma and dendritic field,and also included 2 subgroups of IIs and IIc.Group IV cells had large soma and dendritic field,and only contained a subgroup IVc.The proportion of each subgroup was 27.7%(Ic),33.6%(Is),2.5%(IIc),24.4%(IIs),and 11.8%(IVc),respectively. Conclusion The types of retinotectal projecting ganglion cell were prominently composed of small to medium sized neurons(88.2%)and some large neurons(11.8%).Ofthese,subgroup Ic cells which were very similar to ? cells were found in the chick and subgroup Is and IIs were not reported in the mammalin retina.The cells in group Ⅲ,which were found in the chick central retina,did not project to the tectum. [