The functional organization of motor neurons in an insect ganglion

Abstract

The distribution of motor nerve cell bodies in the metathoracic ganglion of the cockroach Periplaneta americana was mapped and displayed in three dimensions. A dense ring of ribonucleic acid (RNA) appears in the perinuclear cytoplasm of a nerve cell body whose axon has been cut in a peripheral nerve trunk. Using this RNA ring as the primary marker, 5 cell maps of ganglia from different animals were constructed to indicate which motor nerve cell body sends its axon out a particular peripheral nerve trunk. We count about 3000 neurons in the ganglion, and of these about 230 are above 20 $\mu$ m in diameter. About 100 of these larger cells are generally arranged in bilaterally symmetrical pairs. These cell pairs have been assigned numbers and can be identified from one animal to another. Nerve cell bodies associated with nerves 3 through 6 send their axons out the ipsilateral nerve trunks. Cells associated with nerve 2 send their axons out the contralateral nerve trunk. This study may provide a basis for understanding the structural and metabolic organization responsible for the particular behavioural capacities of certain populations of neurons.