Selective reinnervation of two cell populations in the adult pigeon ciliary ganglion.

1. Presynaptic fibres innervating the adult pigeon ciliary ganglion were cut 2 mm proximal to the ganglion. The modification of transmission in the ciliary and choroid cell populations was studied after periods of 6 hr-100 days.2. Transmission failed after 2 days and for the next 10 days there was no transmission through the ganglion. Long latency responses in both ciliary and choroid nerves were first observed at 13-15 days, and the latency decreased toward control values in 40 days. Electrical transmission reappeared in the ciliary population in about 26 days.3. Presynaptic fibres innervating the ciliary population have higher conduction velocities and lower electrical thresholds than those innervating the choroid group. This relation was maintained throughout the reinnervation process. Fibres innervating the extraocular muscles also regenerated and achieved conduction velocities similar to their control values.4. In two experiments out of seventeen, a few fast conducting, low threshold fibres, presumably stray ciliary fibres, innervated choroid cells and induced electrical transmission.5. It is concluded that each group of cells, ciliary and choroid, was reinnervated in a highly selective manner by its original class of presynaptic fibres, and that the presynaptic ciliary elements cause the specializations necessary for electrical transmission.