Unpaired Median Neurones in a Lepidopteran Larva (Antheraea Pernyi): I. Anatomy and Physiology

Abstract

The anatomy and physiology of two unpaired median neurones (MC1 and MC2) with bilaterally symmetrical axons in abdominal ganglia 3, 4, 5 and 6 of Antheraea pernyi larvae were studied. Intracellular dye filling of MC1 and MC2 revealed that they were distinguishable from all other neurones in the ganglia and that they both had axons projecting out of the ganglia in right and left nerves 1. The two cells were identical in their central anatomy and physiology, but could be distinguished from one another by their peripheral branching patterns. The significance of these patterns was investigated by detailed study of the neural and muscular anatomy of the proleg-bearing segments 3, 4, 5 and 6. The peripheral axons of MC1 and MC2 were exclusively associated with nerve trunks that could be traced to blocks of muscle. Intracellular recordings of the two median cells characteristically showed overshooting soma action potentials that were followed by a long afterhyperpolarization lasting many seconds. Simultaneous recordings from median cells in the same ganglion revealed that MC1 and MC2 shared an excitatory synaptic drive that largely determined their patterns of firing. Recordings from median cells in different ganglia showed that the common synaptic drive was also shared by median cells in different segments. Selective lesions of the ventral nerve cord indicated that the synaptic drive to MC1 and MC2 originated in the suboesophageal ganglion. These cells were similar in anatomy and physiology to the median cells in several other insects.