The morphology of two groups of spiking local interneurons in the metathoracic ganglion of the locust.

Two bilaterally symmetrical groups of spiking local interneurons are described in a segmental ganglion of the locust. Interneurons in both groups are excited by specific sets of sensory receptors on one leg. The cell bodies of the anterior-lateral group lie amongst approximately 40 small cell bodies at the anterior of the ganglion, close to the lateral edge of an anterior connective. Interneurons in this group have primary neurites in Ventral Commissure I ( VCI ), and dorsoventral processes in the Oblique Tract, which divide the extensive neuropilar branches into distinct ventral and dorsal regions. Cell bodies of the midline group lie amongst a group of approximately 100 small cell bodies near the ventral midline. Interneurons in this group have primary neurites in Ventral Commissure II ( VCII ), and dorsoventral processes in the Perpendicular Tract, which divide the neuropilar branches into dorsal and ventral regions. The ventral branches of interneurons in both groups are numerous and of a uniform texture, whereas the dorsal branches are sparse and varicose. The ventral branches project to the same ventral areas of neuropil as the afferents from some hairs on a hind leg. The dorsal branches of a midline interneuron and the branches of a leg motor neuron that it affects project to the same dorsal area of neuropil. Some midline interneurons receive direct inputs from leg hair afferents and make direct connections with leg motor neurons.