The morphological diversity and receptive fields of spiking local interneurons in the locust metathoracic ganglion.

Twenty-one types of spiking local interneurons are described in a segmental ganglion of the locust. All have their cell bodies in a group at the ventral midline of the metathoracic ganglion. The interneurons are characterized by their shape as revealed by intracellular injection of dye, and by their physiology as revealed by intracellular recording. Each interneuron conforms to a basic plan, but the characteristic shape of each is derived from the elaboration of branches in some regions of the neuropil and by their absence in other regions. Some interneurons have ventral branches that extend over most of one-half of the metathoracic neuropil, whilst others have ventral branches restricted to a small region of neuropil. A few interneurons have dorsal branches that enter the first abdominal neuromere . Each type of interneuron is excited by a specific array of mechanoreceptors on the hind leg ipsilateral to its neuropilar branches. Some interneurons have a wide receptive field that encompasses most of the dorsal surfaces of the distal three parts of a leg, whilst others have a field limited to the spurs at the distal end of the tibia. The relationship between the shape of an interneuron and the size or orientation of its receptive field is discussed.