Tiling of the body wall by multidendritic sensory neurons in Manduca sexta

A plexus of multidendritic sensory neurons, the dendritic arborization (da) neurons, innervates the epidermis of soft-bodied insects. Previous studies have indicated that the plexus may comprise distinct subtypes of da neuron s, which utilize diverse cyclic 3',5'-guanosine monophosphate signaling pat hways and could serve several functions. Here, we identify three distinct c lasses of da neurons in Manduca, which we term the alpha, beta, and gamma c lasses. These three classes differ in their sensory responses, branch compl exity, peripheral dendritic fields, and axonal projections. The two identif ied alpha neurons branch over defined regions of the body wall, which in so me cases correspond to specific natural folds of the cuticle. These cells p roject to an intermediate region of the neuropil and appear to function as proprioceptors. Three beta neurons are characterized by long, sinuous dendr itic branches and axons that terminate in the ventral neuropil. The functio n of this group of neurons is unknown. Four neurons belonging to the gamma class have the most complex peripheral dendrites. A representative gamma ne uron responds to forceful touch of the cuticle. Although the dendrites of d a neurons of different classes may overlap extensively, cells belonging to the same class show minimal dendritic overlap. As a result, the body wall i s independently tiled by the beta and gamma da neurons and partially innerv ated by the alpha neurons. These properties of the da system likely allow i nsects to discriminate the quality and location of several types of stimuli acting on the cuticle. J. Comp. Neurol. 440: 271-283,2001. (C) 2001 Wiley- Liss, Inc.