Functional development of the vagal and glossopharyngeal nerve-related nuclei in the embryonic rat brainstem: optical mapping with a voltage-sensitive dye

Abstract

We investigated functional organization of the vagus nerve (N. X)- and glossopharyngeal nerve (N. IX)-related nuclei in the embryonic rat brainstem and compared their development and spatial distribution patterns, using multiple-site optical recording with a fast voltage-sensitive dye, NK2761. Intact brainstem preparations with N. X and N. IX attached were dissected from E13-E16 rat embryos, and electrical responses evoked by N. X/N. IX stimulation were optically recorded from many loci of the stained preparations. We analyzed optical waveforms and separated fast and slow optical signals corresponding to the antidromic/orthodromic action potentials and the excitatory postsynaptic potentials (EPSPs), respectively. We constructed contour line maps of signal amplitudes and identified motor and sensory nuclei of N. X and N. IX. In the N. X-related motor nucleus (the dorsal motor nucleus of the vagus nerve: DMNV), the fast signals were distributed in multiple-peak patterns, suggesting that the neurons and/or their activity are not distributed uniformly within the motor nuclei at early developmental stages. In the sensory nucleus (the nucleus of the tractus solitarius: NTS), the EPSPs were first detected from E15 in normal physiological solution for both N. X and N. IX. The N. IX-related NTS partially overlapped with the N. X-related NTS, but the peak locations were different between these two nerves. The results obtained in this study suggest that functional organization of the N. X- and N. IX-related nuclei changes dynamically with development in the embryonic rat brainstem.