Transplantation of cricket sensory neurons to ectopic locations: arborizations and synaptic connections.

The cerci (abdominal sensory appendages) of crickets were transplanted to a leg stump after amputating the leg. Single identifiable cercal afferents were stained and found to regenerate into the host thoracic ganglia. A given neuron always arborizes in the same area of neuropil of the foreign ganglion and is distinctive in this property from other identified neurons. Taken as a whole, the results show that the afferents from the ectopic cercus are spatially ordered, the destination of a particular afferent within the ganglion being correlated with the location of its sensory cell body on the cercal surface. This is the case for the pro-, meso-, and metathoracic ganglion and the topography of these ectopic projections bears some resemblance to the normal projections found in the terminal ganglion. Thus the insect segmental ganglion seems to possess a set of markers which are interpretable by all afferent neurons, and this organization is repeated in each ganglion. The ectopic afferents make functional synaptic connections with intersegmental interneurons, one of which is described anatomically here. However, the ectopic afferents do not, as had previously been reported, make functional connections with the medial giant or lateral giant interneuron (the normal targets of cercal sensory neurons in the terminal ganglion).