Morphology of a new population of spiking local interneurones in the locust metathoracic ganglion.

A new population of spiking local interneurones is described in the metathoracic ganglion of the locust. All have their cell bodies in a cluster at the ventral, anteromedial portion of the ganglion close to the inner edge of an anterior connective. Their branches are restricted to the same half of the ganglion as their cell bodies. Fifteen types of these unilateral interneurones have been characterized by their morphology, as revealed by intracellular injection of dye, and by their physiology, as revealed by intracellular recording. Each interneurone has a characteristic shape and physiological action, but they form three distinct subgroups according to their gross morphology and their mode of operation. Interneurones of the first subgroup have ventral branches that extend over most of one-half of the metathoracic neuropil and receive inputs mainly from exteroceptors on the ipsilateral hind leg. Typically, they have extensive and reciprocal receptive fields along the dorsoventral axis of the hind leg. Interneurones of the second subgroup have two main ventral branches which extend either medially or laterally and receive inputs mainly from proprioceptors of the hind leg. Interneurones of the third subgroup have few ventral branches and are inhibited by inputs anywhere on the hind leg.