Optical Approaches to Functional Organization of Glossopharyngeal and Vagal Motor Nuclei in the Embryonic Chick Hindbrain

Abstract

We investigated the functional organization of the glossopharyngeal and vagal motor nuclei during embryogenesis using multiple-site optical recording with a fast voltage-sensitive dye. Intact brain stem preparations with glossopharyngeal and vagus nerves were dissected from 4- to 8-day-old chick embryos. Electrical responses evoked by glossopharyngeal/vagus nerve stimulation were optically recorded from many loci of the stained preparations. In 4- to 6-day-old preparations, action potential-related fast spikelike signals were detected from the nucleus of the glossopharyngeal nerve and the dorsal motor nucleus of the vagus nerve. Contour line maps of the signal amplitude showed multiple-peak patterns, suggesting that the neurons and/or their activity were not uniformly distributed within the nuclei at early developmental stages. As development proceeded from 4 to 6 days, the peaks fused with each other and the number of peaks decreased gradually. In most 7- and 8-day-old preparations, only a single peak was identified in the nuclei, and the distribution of the signal amplitude formed a layered pattern surrounding the peak-signal area. These results suggest that functional organization of the motor nuclei in the embryonic hindbrain changes dynamically with development, resulting in a rearrangement of functional nuclear cores from multiple-peaks to a single peak.

Switching of the transmitters that mediate hindbrain correlated activity in the chick embryo

“…These neurons become excitable around day 4 of incubation (Momose‐Sato et al. , 1991; Sato et al. , 2002), at which time the spontaneous depolarization wave first emerges.…”

Using voltage‐sensitive dye recording to image the functional development of neuronal circuits in vertebrate embryos

“…The vagal nucleus is one of the structures in which functional organization and development have been most extensively studied using voltage-sensitive dye recording. The functional development of vagal projections has been examined in intact brainstem preparations and in slice preparations from chicken and rat embryos following electrical stimulation of the vagus nerve (Kamino et al, 1989Komuro et al, 1991;Momose-Sato et al, 1991, 1994Sato et al, 1993Sato et al, , 1998Sato et al, , 2002. In both species, TTX-dependent fast optical signals associated with antidromically propagated action potentials in vagal motoneurons and orthodromically propagated action potentials in vagal afferents can be detected at very early stages, as the motor and sensory axons are extending out of and into the brain stem, respectively.…”

“…2(B); . In addition, a more detailed study of the developing glossopharyngeal motor nucleus and DMNV (Sato et al, 2002) shows an initial pattern of multiple small peaks of antidromic activation that eventually coalesce into a single large peak in each nucleus, suggesting spatial differences in the maturation of electrical excitability in these motor nuclei. Thus, voltage-sensitive dye recording can be used to assess detailed topographic relationships between and within brainstem nuclei with respect to functional differentiation and connectivity.…”

Optical Imaging Analysis of Neural Circuit Formation in the Embryonic Brain

“…The recordings were made in single sweeps and no off‐line filters were used. (Reproduced with permission of the American Physiological Society from Sato et al 33 ) (c) Summary of the sequence of events in the embryonic emergence of neural responses in the chick N. IX‐ and N. X‐related nuclei. The N. IX‐ and N. X‐related NTS are shown in light and dark green, respectively.…”

“…In the NTS, action potential‐related fast signals were initially evoked by N. IX/N. X stimulation from the E4 stage (Stage 24), 31–33 suggesting that excitability of the sensory nerve fibres is generated within the brainstem no later than E4. Conversely, in the Nuc IX and DMNV, the fast signals were observed from the E3.5 (Stage 23) and E4 stages, 31–34 suggesting that excitability of the glossopharyngeal and vagal motoneurons is generated within the brainstem no later than E3.5 and E4, respectively.…”