Search

One of the earliest activities expressed within the developing central nervous system is a widely propagating wave-like activity, which we referred to as the depolarization wave. Despite considerable consensus concerning the global features of the activity, its physiological role is yet to be clarified. The depolarization wave is expressed during a specific period of functional synaptogenesis, and this developmental profile has led to the hypothesis that the wave plays some roles in synaptic network organization. In the present study, we tested this hypothesis by inhibiting the depolarization wave in ovo and examining its effects on the development of functional synapses in vagus nerve-related brainstem nuclei of the chick embryo. Chronic inhibition of the depolarization wave had no significant effect on the developmental time course, amplitude, and spatial distribution of monosynaptic excitatory postsynaptic potentials in the first-order nuclei of the vagal sensory pathway (the nucleus of the tractus solitarius (NTS) and the contralateral non-NTS region), but reduced polysynaptic responses in the higher-order nucleus (the parabrachial nucleus). These results suggest that the depolarization wave plays an important role in the initial process of functional synaptic expression in the brainstem, especially in the higher-order nucleus of the cranial sensory pathway., (Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.)

The multiple-site optical recording technique with a voltage-sensitive dye, NK2761, was used to survey the functional organization of neuronal networks related to the vagus nerve (N.X) in the E16-stage rat brainstem. When we stimulated N.X, in addition to the responses in the vagal sensory nucleus (nucleus of the tractus solitarius (NTS)) on the stimulated side, other response areas were bilaterally detected. Characteristics of the optical signals in these areas suggested that they correspond to neural activity in the second/higher-ordered nucleus of the vagal pathway. The first area was located at the level of the pons. Based upon morphological information, we suggest that this area corresponds to the parabrachial nucleus (PBN), which receives inputs from the NTS. The second area was located between the NTS and the PBN. We suggest that this area is the A5 noradrenergic group. These results suggest that the N.X-related neural networks are established similarly to the adult pattern from an early developmental stage., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

Using voltage-sensitive dye recording, we traced the ontogenetic expression of neural excitability related to the glossopharyngeal nerve (N. IX) and the vagus nerve (N. X) in the embryonic chick brainstem. At the 3.5-day embryonic stage, by averaging optical signals, we succeeded in recording very small action potential-related optical responses (DeltaI/I<10(-4)) induced by N. IX stimulation in the nucleus of the glossopharyngeal nerve (motor nucleus). This suggests that glossopharyngeal excitability in the motor nucleus is first generated no later than this developmental stage. On the other hand, action potential-related optical responses induced by N. X stimulation were first detected at the 4-day embryonic stage. Comparison with morphogenesis indicated that glossopharyngeal and vagal motoneurons acquire their excitability and send their axons to the periphery soon after they leave the proliferative pool.

Multiple-site optical recording with a fast voltage-sensitive dye, absorption dye NK2761, was used to study the developmental organization of functional synaptic networks in the vagal pathway. Glutamatergic excitatory postsynaptic potentials (EPSPs) evoked by vagus nerve stimulation was first detected from the nucleus of the tractus solitarius (NTS) at embryonic day 7 (E7) in chick embryos and E15 in rat embryos, when morphological differentiation of pre- and postsynaptic neurons is incomplete. When extracellular Mg2+ was removed, small EPSPs were elicited at E6 in chick embryos and E14 in rat embryos. These results suggest that synaptic function mediated by N-methyl-D-aspartate (NMDA) receptors is latently generated 1 day before the expression of glutamatergic EPSP. Functional synapses related to the glossophyaryngeal nerve appear to be generated at the same time as the vagus nerve, but their spatial distribution was different from that of the vagus nerve. We further investigated the development of second synaptic pathways from the NTS to higher centers, and found that neuronal circuits from the NTS are already generated when the primary afferents form functional synapses with NTS neurons.

Abstract: To regulate the autonomic function, the vagus nerve transfers various sensory information from peripheral organs, and appropriate motor reflexes are produced in the neural circuit. The functional development of the vagal pathway during the early phase of embryonic development has long been unclear. Optical recording with voltage-sensitive dyes has provided a new approach to the analysis of the functional development of the embryonic central nervous system. In this review, we present recent progress in optical studies on the vagal pathway in the embryonic chick and rat brainstems. The topics include how neural excitability is initially expressed in the motor and sensory nuclei [e.g. the dorsal motor nucleus of the vagus nerve (DMNV) and the nucleus of the tractus solitarius (NTS)] and how synapse networks are formed in the primary and higher-ordered sensory nuclei [e.g. the parabrachial nucleus (PBN)]. We also refer to the functional development of the glossopharyngeal nuclei and compare the developmental steps with those of the vagal nuclei. [Copyright &y& Elsevier]

The multiple-site optical recording technique with a voltage-sensitive dye, NK2761, was used to survey functional organization of neural circuits related to the vagus nerve in the embryonic chick brainstem. When we stimulated the vagus nerve, in addition to the responses in the vagal sensory nucleus (nucleus of the tractus solitarius (NTS)) and motor nucleus (dorsal motor nucleus of the vagus nerve (DMNV)) on the stimulated side, another response area was discriminated at the level of the pons/rostral medulla on the contralateral side. Characteristics of the contralateral optical signals suggested that they correspond to the neural activity in the second/higher-ordered nucleus of the vagal pathway, possibly the parabrachial nucleus, which receives inputs from the NTS. Blockade of non-N-methyl- d-aspartate (NMDA) receptors abolished the responses on the contralateral side, together with the postsynaptic firing in the NTS, suggesting the significance of non-NMDA receptor function in sensory information transfer via the NTS. The responses on the contralateral side were first detected from the 7-day-old embryonic stage, when the glutamatergic excitatory postsynaptic potentials were first expressed in the NTS. The results suggest that the synaptic pathway from the NTS to the contralateral nucleus is already generated when the primary vagal afferents make functional synapses on NTS neurons. [ABSTRACT FROM AUTHOR]