ANATOMY OF NEURONS CROSSING THE TRITOCEREBRAL COMMISSURES OF THE COCKROACH PERIPLANETA-AMERICANA (BLATTARIA)

The neuronal connections of the tritocerebral commissures of Periplane ta americana were studied in the brain-suboesophageal ganglion complex and the stomatogastric nervous system by means of heavy metal iontoph oresis through cut nerve ends followed by silver intensification. The tritocerebral commissure 1 (Tc1) contains mainly the processes of the subpharyngeal nerve (Spn) whose neurons are located in both tritocereb ral lobes and in the frontal ganglion. Some neurons of the frontal gan glion project through the Tc1 to the contralateral tritocerebrum. A fe w fibers in this commissure were observed projecting to the protocereb rum and the suboesophageal ganglion. There are tritocerebral neurons w hich pass through the Tc1 or the tritocerebral commissure 2 (Tc2) and extend on into the stomatogastric nervous system. One axon of a descen ding giant neuron appears in the Tc2. This neuron lies in the tritocer ebrum and connects the brain to the contralateral side of the ventral nerve cord. In addition, sensory fibers of the labral nerve (Ln) trave rse both commissures to the opposite tritocerebrum. The anatomical and physiological relevance of the identified neuronal pathways is discus sed. (C) 1995 Wiley-Liss, Inc.