Autoradiographic measurement of tritiated agmatine as an indicator of physiologic activity inHermissenda visual and vestibular neurons

[3H]Agmatine (amino-4-guanidobutane) has been shown to be potentially useful for identifying and assessing the ACh sensitivity of specific neurons. Small cationic amines are able to permeate ACh-activated ion channels in sympathetic neurons and vertebrate endplates. Sensory neurons of the photic pathway in the nudibranch molluscHermissendacrassicornis are cholinergic and the synaptic interactions between the photic and vestibular systems have been well characterized electrophysiologically. We have therefore tested the feasibility of using autoradiography with [3H]agmatine, (a) to identify known ACh-responsive postsynaptic cells and (b) to examine its ability to serve as an indicator of physiologic activity within the photic and vestibular pathways under conditions of darkness and light stimulation.