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

Abstract

The intermediate subnucleus of the nucleus tractus solitarii (imNTS) receives somatosensory inputs from the soft palate and pharynx, and projects onto the nucleus ambiguus, thus serving as a relay nucleus for swallowing. The ultrastructure and synaptology of the rat imNTS, and its glossopharyngeal afferent terminals, have been examined with cholera toxin-conjugated horseradish peroxidase (CT-HRP) as an anterograde tracer. The imNTS contained oval or ellipsoid-shaped, small to medium-sized neurons (18.2 x 11.4 microm) with little cytoplasm, few cell organelles and an irregularly shaped nucleus. The cytoplasm often contained one or two nucleolus-like stigmoid bodies. The average number of axosomatic terminals was 1.8 per profile. About 83% of them contained round vesicles and formed asymmetric synaptic contacts (Gray's type I), while about 17% contained pleomorphic vesicles and formed symmetric synaptic contacts (Gray's type II). The neuropil contained small or large axodendritic terminals, and about 92% of them were Gray's type I. When CT-HRP was injected into the nodose ganglion, many labeled terminals were found in the imNTS. All anterogradely labeled terminals contacted dendrites but not somata. The labeled terminals were usually large (2.69+/-0.09 mum) and exclusively of Gray's type I. They often contacted more than two dendrites, were covered with glial processes, and formed synaptic glomeruli. A small unlabeled terminal occasionally made an asymmetric synaptic contact with a large labeled terminal. The large glossopharyngeal afferent terminals and the neurons containing stigmoid bodies characterized the imNTS neurons that received pharyngeal afferents.

Activation of Neurons in the Rat Medulla Following a Gag Reflex Stimulus

“…The location of many of the activated neurons correlated relatively well with our proposed model of gag reflex connectivity, including those in the NTS, dorsal motor 10, hypoglossal nucleus, and NA. The majority of vagal and glossopharyngeal afferent information from the posterior pharyngeal wall is carried to the NTS [17][18][19][20][21]. The NTS, in turn, excites neurons in the nucleus ambiguus (NA) which then activates the pharyngeal and velar muscles (CN X) and the muscles of the tongue (via CN XII) [14].…”

“…However, the pattern of activation that was observed in the NTS subnuclei seems logical based on the functional differences reported for each area. For example, SolVL has been linked to cessation of breathing [27], Sol M to baroreceptor reflexes with a decrease in parasympathetic innervations of the heart [28], and SolIM to laryngeal and pharyngeal sensation [21,29]. These are activities that take place during the gag motor response [1,[7][8][9]14].…”

Effects of stroke‐induced damage to swallow‐related areas in the brain on swallowing mechanics of elderly patients

“…As for the peripheral inputs, Hayakawa et al. 26 investigated the anatomical connections to the NTS of the glossopharyngeal nerve, which innervates the soft palate and pharynx, reporting that the intermediate subnucleus received direct afferent terminals. Jia et al.…”

A pharynx-to-brain axis controls pharyngeal inflammation–induced anxiety

“…The pharynx is densely innervated by the glossopharyngeal and vagal nerves ( 7 – 9 ). Previous murine studies using cholera toxin or wheat germ agglutinin conjugated horseradish peroxidase neural tracers discovered that glossopharyngeal and vagal sensory fibers in the pharynx arise from the pseudo-unipolar nodose/jugular/petrosal (NJP) sensory neurons, which then predominantly project to the nucleus of the solitary tract (NTS) ( 10 , 11 ). However, limitations in the tracing tools and strategies for targeted manipulation of ganglia-projecting neurons have prevented a clear understanding of the precise cell type–specific organization and function(s) of pathways between the pharynx and brain in pharyngitis-associated anxiety.…”