Ultrastructure of the central subnucleus of the nucleus tractus solitarii and the esophageal afferent terminals in the rat

Abstract

The central subnucleus of the nucleus tractus solitarii (ceNTS) receives afferent projections from the esophageal wall and projects to the nucleus ambiguus, thus serving as a relay nucleus for peristalsis of the esophagus. Here we examine the synaptic organization of the ceNTS, and its esophageal afferents by using transganglionic anterograde transport of cholera toxin-conjugated horseradish peroxidase (CT-HRP). When CT-HRP was injected into the subdiaphragmatic esophagus, many anterogradely labeled terminals were found only in the ceNTS. The ceNTS was composed of round or oval-shaped, small neurons (14.7x8.7 micro m) containing sparse organelles and an irregularly shaped nucleus. The average number of axosomatic terminals was only 1.3 per section cut through the nucleolus. Most of them (92%) contained round vesicles and formed asymmetric synaptic contacts (Gray's type I), and a few (8%) contained pleomorphic vesicles and formed symmetric synaptic contacts (Gray's type II). All anterogradely labeled terminals contacted dendrites but not the neuronal somata. The labeled terminals were large (2.55+/-0.07 micro m) and exclusively Gray's type I. More than half of them (60%) contacted small dendrites (less than 1 micro m in diameter), and contained dense-cored vesicles. More than 40% of the labeled terminals contacted two to four dendrites, thus forming a synaptic glomerulus. Sometimes a labeled terminal that contacted an unlabeled terminal by an adherent junction was found within the glomerulus. The large terminals and these complex synaptic relations appeared to characterize the esophageal afferent projections in the ceNTS.

The ultrastructure of perisynaptic glia in the nucleus tractus solitarii of the adult rat: Comparison between single synapses and multisynaptic arrangements

“…Studies performed at the cerebellar mossy fiber to granule cells synapse indicate that glutamate spillover in divergent glomeruli enhances the efficacy of fast synaptic transmission by decreasing fluctuations resulting from probabilistic transmitter release (DiGregorio et al, 2002;Sargent et al, 2005). In the NTS, sensory afferent terminals are frequently involved in divergent arrangements (Chazal et al, 1991;Davis, 1998;Hayakawa et al, 2003;May et al, 2007;Whitehead, 1986). One may postulate that glutamate spillover within these synaptic clusters helps to insure reliable transmission of sensory information.…”

“…Scale bars: 500 nm (electron micrographs), 400 nm (three-dimensional reconstructions). Chazal et al, 1991;Davis, 1998;Hayakawa et al, 2003;May et al, 2007;Whitehead, 1986). Accordingly, about half of our reconstructed synapses were directly apposed to at least one other synapse without intervening glia.…”

“…Most NTS synapses are glutamatergic including those made by visceral primary afferents (Lachamp et al, 2006; see also Baude et al, 2009 for review). In addition to single synapses, the NTS contains numerous divergent and convergent multisynaptic arrangements (Brining and Smith, 1996;Chazal et al, 1991;Davis, 1998;Hayakawa et al, 2003;May et al, 2007;Whitehead, 1986). The present study was undertaken to quantitatively analyze and compare the ultrastructure of perisynaptic glia at single and complex NTS synapses.…”

Silent Synapses in Developing Rat Nucleus Tractus Solitarii Have AMPA Receptors

“…More specifically related to synaptic formation, spillover may recruit extrasynaptic NMDARs or activate distant NMDAR clusters floating in the dendritic membrane (Friedman et al, 2000;Washbourne et al, 2002). For the adult NTS, vagal afferent terminals are generally large, and most synapses are part of synaptic glomeruli (Mrini and Jean, 1995;Hayakawa et al, 2003). This peculiar organization may favor crosstalk between active synapses during development and contribute to synaptic processing as well as autonomic circuit formation.…”

Fine structural survey of the intermediate subnucleus of the nucleus tractus solitarii and its glossopharyngeal afferent terminals

“…Electron microscopic studies have revealed the ultrastructure and synaptic organization of the isNTS, the ceNTS, and the geNTS, which are composed of small neurons with few cell organelles and an irregularly shaped nucleus (Leslie et al 1982;Chazal et al 1991;Mrini and Jean 1995;Hayakawa et al 2003). The vagal afferent terminals from the esophagus were large, contained round synaptic vesicles and made asymmetric synaptic contacts (Gray's type I) that formed synaptic glomeruli (Hayakawa et al 2003).…”