Gustatory solitary tract development: A role for neuropilins

Abstract

The rostral nucleus of the solitary tract (rNST) receives orosensory information from taste bud cells in the tongue and palate via cranial nerves VII and IX. These nerves enter the brainstem, form the solitary tract (ST) and synapse with neurons in the rNST, which then relay incoming sensory information to other brain areas to process external gustatory stimuli. Factors that direct or regulate the trajectory of the developing ST are largely unknown. We used DiI to identify ST projections originating from cells in the geniculate ganglia of embryonic rats from embryonic day 14 through 18 (E14-E18). After identifying the ST fibers, immunolabeling for and protein expression analysis of the axon guidance molecules neuropilin-1 (Npn-1) and neuropilin-2 (Npn-2) and their binding partners, semaphorin-3A (Sema-3A) and semaphorin-3F (Sema-3F) were performed. The results detail the formation of ST projections into the gustatory brainstem and their relationship to developing rNST neurons. DiI-labeled ST fibers were present in the brainstem as early as E14. Npn-1 was expressed in the ST and in the trigeminal tract at E14, but levels of the protein declined through E18. The expression levels of the binding partner of Npn-1, Sema-3A, increased from E14 to E18. Npn-2 was expressed in the ST and, additionally, in radially oriented, tuft-like structures within the brainstem at E14. Expression levels of Npn-2 also declined through E18, in contrast to the expression levels of its binding partner, Sema-3F, which increased during this time period. For the first time, the time course and particular molecular components involved in development of the ST have been identified. These results indicate that the neuropilin and semaphorin families of axon guidance molecules are potential molecular participants in ST formation.

Persistent Brainstem Dysfunction in Long-COVID: A Hypothesis

“…Importantly, the brainstem’s pons and medulla have the highest expression of ACE2 . More recently, neuropilin-1 has been confirmed as a co-receptor that facilitates SARS-CoV-2 infection into cells, especially in the olfactory epithelium where ACE2 expression is relatively low. , Interestingly, neuropilin-1 is also expressed in the brainstem of developing animal brains. , Thus, the mature brainstem may also express neuropilin-1 that promotes SARS-CoV-2 infection.…”

“… 51 , 52 Interestingly, neuropilin-1 is also expressed in the brainstem of developing animal brains. 53 , 54 Thus, the mature brainstem may also express neuropilin-1 that promotes SARS-CoV-2 infection.…”

Axonal Projection Patterns of the Dorsal Interneuron Populations in the Embryonic Hindbrain

“…The role of the neuropilin (Npn) receptors and their semaphorin (Sema) ligands in axonal growth is well known in various sensory and motor neural systems (Neufeld et al, 2002;Meléndez-Herrera and Varela-Echavarría, 2006;Pasterkamp, 2012). In the hindbrain, Nrp1 and Sema3A were found to form gradients across the projections of A1-derived pontine axons (Solowska et al, 2002), whereas Npn-1/2 were shown to be expressed in axons projecting from the NTS, which contain dA3-derived neurons (Corson et al, 2013). These spatiotemporal expression patterns indicate that the Npn and Sema families of axon guidance molecules are potential molecular regulators for dA1 and dA3 axonal trajectories.…”

Non-Instrumental Test for the Evaluation of Tongue Function

“…The XII nerve guides the muscle activity of most of the contractile districts, while the X nerve, in addition to giving parasympathetic fibers, is activated by the contraction of the palatoglossus muscle (an extrinsic muscle of the tongue) [ 7 , 8 ]. The lingual nerve innervates the anterior portion for gustatory and somatic sensitivity and anastomoses with afferent fibers of the cranial facial nerve or VII (cord of the eardrum) [ 9 ]. Sympathetic fibers arrive at the lingual musculature from the superior cervical ganglion [ 10 ].…”