VARIATIONS IN LOCATION AND SIZE OF IDENTIFIED FLIGHT MOTONEURONS IN THE SILK MOTH, BOMBYX-MORI L (LEPIDOPTERA, BOMBYCIDAE)

Neurons are commonly identified by some specific features. However, recent studies showed variations in identified neurons, which casts doubt on the reliability of neuron identification. This paper tests the anatomical approach that groups of neurons. which look roughly the same in different preparations, really do contain the same neurons; it also tests the reliability of motor neuron identification by cell body size and position of flight motor neurons in the silk moth, Bombyx mori (Lepidoptera:Bombycidae). Soma size and position of 9 motor neurons, which innervate the mesothoracic dorsal longitudinal muscles (DLMs), were quantitatively measured in cobalt back-filled preparations. The neurons were classified into 5 subgroups by soma size and position, and muscle innervation, although neurons in the same subgroup could not be individually identified. The soma size was essentially constant for individual neuron subgroups, but the position varied somewhat. Two subgroups were generally distributed at one position in the ganglion, but others had 2 separate soma areas, and different animals showed different distributions in these 2 areas. These results show that DLM motor neurons can be identified by the soma size and position only when the variation of soma position is examined in advance.