Abstract:

The activity rearrangement of optic fibers during the formation of the retinotectal projection implies the existence of retrograde activity mediated signals affecting growing fibers. Since tranmitter release is a good candidate for this, the capacity of neurotransmitters to regulate axonal growth was tested. Retinal explants were made onto laminin-polylysine coated coverslips and the outgrowing neurites, which filled several criteria for being optic axons, were monitored by timelapse videomicroscopy.

A number of neurotransmitters (and agonists) including glutamate, serotonin and dopamine were added to the culture medium without noticeable effect. TTX also had no effect. Nicotine at 50um, however, rapidly and strongly inhibited filopodial movement and growth. This inhibition could be antagonized by curare and a-bungarotoxin.

Nicotine was equally effective when delivered locally to the growth cone with a micropipette. We speculate that nicotinic cholinergic receptors may be a component of a retrograde regulatory signal.

This work was supported by EY06746.