THE THALAMO-HYPERSTRIATAL SYSTEM IS ESTABLISHED BY THE TIME OF HATCHING IN CHICKS (GALLUS-GALLUS) - A CHOLERA-TOXIN-B SUBUNIT STUDY

Connections of the thalamo-hyperstriatal system of hatching chicks wer e investigated using multiple injections of cholera toxin B subunit (C Tb) in the wulst. In the diencephalon, cells with CTb-like immunoreact ivity (CTb-LI), were seen bilaterally in n. dorsolateralis anterior th alami, pars lateralis dorsalis and ventralis, n. dorsolateralis anteri or thalami, pars magnocellularis, and pars lateralis rostralis. Within this complex, more CTb-LI cells were observed in the ventral portions of the ipsilateral side, whereas more labeled cells were found in the dorsolateral portions of the contralateral side. Moreover, CTb-LI cel ls were seen bilaterally in n. superficialis magnocellularis. In the n onvisual thalamic structures, numerous CTb-LI cells were seen in n. do rsolateralis anterior thalami, pars medialis and n. dorsolateralis pos terior thalami. In the ventral thalamus, intense CTb-LI fibers/termina ls were present in the external half of the external laminae of n. gen iculatus lateralis, pars ventralis. Moderate to minor concentrations o f fibrous labeling were found in n. intercalatus thalami and n. ventro lateral thalami. Moreover, efferent projections of the wulst were evid ent in the most ventral half of the optic tectum and the pretectal are as. The latter included n. pretectalis medialis, n. spiriformis medial is, n. principalis precommissuralis, n. lentiformis mesencephali, pars magnocellularis, and n. superficialis synecephali. Also, CTb-LI fiber s were seen in n. basal optic root. The present study provides strong evidence that neuronal connections of the thalamo-hyperstriatal system are well established by the time of hatching. Additionally, efferent projections from the wulst to the diencephalic, mesencephalic, and pre tectal structures are evident.