The development of projections and connections from transplanted locust sensory neurons

Neurons innervating wind-sensitive hairs on the locust head form characteristic projections and connections within the CNS. These depend on intrinsic properties of the epidermis from which the hair and its neuron are formed (Anderson & Bacon, 1979; Bacon & Anderson, 1984). To investigate further these intrinsic properties and also extrinsic factors involved in guiding axon growth and determining synaptic connectivity, pieces of epidermis from the head were transplanted to the posterior head, prothorax, or mesothorax. Thus wind-sensitive neurons developing from the grafts were caused to grow into foreign parts of the CNS. The neuronal projections from the graft hairs were examined by filling the axons with cobalt, and their connectivity with an identified interneuron, the Tritocerebral Commissure Giant, was examined by recording electrophysiologically the activity of the interneuron during stimulation of the graft hairs. The results show that the neuronal projections are confined to one tract, the median ventral tract, and to one arborization area, the ventral association centre, in all ganglia; in all ganglia, neurons from different epidermal regions preserve their location-specific properties of forming ipsilateral or additional contralateral projections; the extent of their projection in the CNS is not interpretable in terms of intrinsic instructions only; in foreign ganglia, they fail to form connections with their normal target interneuron.