ACTIVITY-DEPENDENT STRUCTURAL DYNAMICS OF INSECT SENSORY FIBERS

This report analyses the role of neuronal activity in shaping the axon al arborizations of sensory neurons from individually identified filif orm hairs on the prosternum of locusts (Locusta migratoria), and their connections with a pair of identified interneurons (A4l1). Afferents from lateral filiform hairs terminate in the ipsilateral neuropil and connect only with the ipsilateral interneuron in all instars. Afferent s from ventral filiform hairs possess ipsi- and contralateral branches and make monosynaptic connections with both interneurons in first ins tars. In later instars, the ipsilateral branch, and its synaptic conne ction to the ipsilateral interneuron, is gradually reduced until it is lost in the adult, whereas the contralateral branch, and its synaptic connection with the contralateral interneuron, is strengthened. There fore, after an initial overgrowth of fibers and synapses, segregation of fibers occurs involving the loss of synaptic connections. This loss of branches and synapses was prevented by immobilizing a subpopulatio n of ventral and lateral filiform hairs, or each group independently, so that their normal activity was blocked. In such treated animals aff erents from ventral filiform hairs retain their ipsi- and contralatera l branches until adulthood. We therefore conclude that afferent activi ty plays an important role in shaping the final structure and connecti vity of afferents, as neither the peripheral position of the receptors nor the hormonal environment was changed by these manipulations.