Some data on connections of neurons of nuclei isthmi of the chicken.

After PhA-L injection into the tectum opticum of chickens, column-like labelled terminal arborizations were found in tectum and also labelled neurons of Ipc and Imc in the corresponding sections. The PhA-L labele proved the projection from both Imc and Ipc neurons to tectum; their terminal axonarborizations were clearly discernible. Column-like terminal arborizations of different sizes were found both in PHA-L and Golgi impregnated preparations. GABA immunostaining displayed GABA positive neurons in Imc. The EM-Golgi study corroborated that the axon-terminals of Imc neurons established symmetrical synapses in the tectum. The results of the present study support the existence of an inhibitory feedback loop from Imc neurons to the tectum.