Etude topographique des interneurones ocellaires et de quelques uns de leurs prolongements chez Periplaneta americana

Abstract

The topography of the largest ocellar interneurons in the brain of the cockroach Periplaneta americana was shown with cobalt chloride. The ocellar interneurons coloured from one nerve are confined to the ipsilateral side of the pars intercerebralis; their number and their position vary along the ocellar tract. If two ocellar nerves colour from the ocelli, the interneurons show a bilateral symmetry. Only one interneuron runs through the brain between each ocellus and the contralateral connective to the mesothoracic ganglion. When the injection of cobalt chloride is done without any current from the ocellus, the second-order ocellar neurons only are coloured, but when it is done using a current the higher order interneurons are also coloured. Axonal iontophoresis from a cervical connective back into the brain, has revealed that the cellular body of the contralateral higher-order interneuron is situated in the postero-ventral part of the protocerebrum. This pericaryon with a long cellular process is the largest of the ocellar ones (Ø = 50–60 μm). These results are discussed in relation to the ocellar and visual pathways of Schistocerca.