Formation and modulation of chemical connections: evoked acetylcholine release from growth cones and neurites of specific identified neurons.

The ability to release acetylcholine (ACh) from cultured neurons of Helisoma was assessed by micromanipulating ACh-sensitive somata into contact with presynaptic neurons. ACh release was reliably detected from neurites and growth cones of cholinergic neuron B5, but not neuron B19, as early as 3 s after contact with novel target neurons. The rapid onset of transmission correlates with the ability of neuron B5, but not neuron B19, to indiscriminately form chemical connections and may be related to the specificity of synaptogenesis. The neuropeptide FMRFamide reduces ACh release at early chemical connections. The rapid onset of functional transmission and the ability of FMRFamide to modulate chemical transmission at this early chemical connection suggest that neuron B5 acquires its presynaptic apparatus through an intrinsic program independently of target contact.