Optical mapping of the early development of the response pattern to vagal stimulation in embryonic chick brain stem

1. In both intact and slice preparations of vagus-brain stem isolated from 3- to 8-day-old chick embryos, the spatial pattern of neural responses to vagal stimulation and its development were assessed by means of multiple-site optical recording of electrical activity, using a voltage-sensitive merocyanine-rhodanine dye (NK2761) and a 12 x 12-element photodiode array. 2. The first neural responses, viz. fast optical signals (related to the action potential), were recorded in the 4-day-old brain stem preparation, and slow optical signals (related to excitatory postsynaptic potentials) were detected from late 7- and 8-day-old brain stem preparations. 3. The evoked optical signals appeared to be concentrated longitudinally in the central region of the stimulated side of the intact brain stem preparation and in a limited dorsal area in the slice preparation. The signal size gradually increased and the response area expanded as development proceeded. 4. Based on the above results, we have constructed developmental maps of the spatial patterns of the fast and slow optical responses. In the maps, the positions of the peak-size regions of the fast and slow signals were assessed and we have found that there were differences in the location of these areas for the fast vs. the slow signals in the late 7- and 8-day-old embryonic brain stem preparations. 5. In the maps for the late 7- and 8-day-old embryonic brain stems, the fast signal response area seems to correspond to the dorsal motor nucleus of the vagus nerve and the slow response area to the nucleus tractus solitarii.