Chick ciliary ganglionic neurons require an interaction with their peripheral targets for survival during a critical period of their embryonic development in vivo. It has recently been shown that survival of these neurons in dissociated cell cultures is supported by extract from whole chick embryo. In this study, an assay system based on microwell cultures of ciliary ganglionic neurons was used to demonstrate that a very rich source of trophic factor for them is the intraocular target tissues they innervate. Out of 8000 trophic units present in a 12-day embryo, 2500 were contained in the eye. A subdissection of the eye showed its activity to be localized in a fraction containing the ciliary body and choroid coat, with a specific activity almost 20-fold higher than that of the whole embryo. This selective intraocular distribution at a time when survival or death of ciliary ganglionic neurons is decided in vivo suggests that this soluble factor may be involved in the normal development of the ciliary ganglion.

1. An approach is described for recording and characterizing giant nerve fibre activity in intact, freely moving earthworms. 2. Medial giant fibre (MGF) spikes were conducted in an anterior-posterior direction at a mean rate of 32.2 m/s; lateral giant fibre (LGF) spikes were conducted in a posterior-anterior direction at a mean rate of 12.5 m/s. 3. Rates of giant fibre spike conduction and maximal frequencies of firing (up to 500/s) in intact animals were higher than values previously reported in isolated preparations. 4. MGF spikes were followed 1:1 by presumed giant motor axon spikes and facilitating muscle potentials. 5. Single MGF or LGF spikes evoked by applying tactile stimulation were not accompanied by longitudinal contraction, but a series of two or more MGF spikes or three or more LGF spikes were accompanied by such contractions. 6. MGF and LGF spikes occurred infrequently during locomotory movements in the absence of any experimenter-applied stimulation, suggesting that sensory inputs associated with normal locomotion over an irregular substrate are sufficient to excite giant fibres.