Optical imaging of the spatiotemporal patterning of neural responses in the embryonic chick superior cervical ganglion

Multiple-site optical recording of transmembrane potential changes with a v oltage-sensitive dye was used to reveal the functional expression and devel opmental changes of the postsynaptic potentials in the early embryonic chic k superior cervical ganglion. The ganglia were isolated from five- to 12-da y-old chick embryos with preganglionic nerve fibres (vertebral and/or cervi cal carotic nerves) attached. The preparations were stained with a voltage- sensitive merocyanine-rhodanine dye (NK2761). Voltage-related optical (abso rbance) changes were recorded simultaneously from 127 contiguous loci in th e preparation, using a 12 x 12-element photodiode array. Optical changes ha ving two components were evoked by preganglionic nerve stimulation. One com ponent was the fast spike-like signal and another the delayed slow signal. The amplitude of the slow signal was decreased by repetitive stimulation, r educed by low external calcium ion concentrations and eliminated in the pre sence of manganese or cadmium ions. The slow signals were also eliminated i n the presence of D-tubocurarine. Accordingly, we concluded that the slow s ignal corresponds to cholinergic excitatory postsynaptic potentials. In the five- and six-day-old superior cervical ganglia, only the fast optical sig nals (referred to as the action potentials) were recorded. Slow optical sig nals (referred to as the excitatory postsynaptic potentials) were detected from preparations older than seven days. The amplitude of the slow optical signal gradually increased, together with an expansion of the response area , as the developmental stage proceeded from seven to 10 days. To compare th e distribution patterns of the neural responses evoked by stimuli applied t o the cervical carotic and vertebral nerves, we have mapped and imaged the spatial patterning of the synaptic responses. In the maps, the positions of the peak size regions of the slow signals were assessed, and we found that there were differences in the location of these areas for the cervical car otic vs vertebral nerves. From these experimental results, we conclude that synaptic function within the chick superior cervical ganglion is initiated at the seven-day-old embr yonic stage, and reaches a maximum level at 10 days. Synaptic transmission at these stages is mediated solely by nicotinic acetylcholine receptors. Th e spatial mapping of the synaptic responses reveals that the neural populat ions related synaptically to the cervical carotic and vertebral nerves are located separately within the ganglion, even at an early developmental stag e. (C) 1999 IBRO. Published by Elsevier Science Ltd.