Analysis of the distribution of vagal afferent projections from different peripheral organs to the nucleus of the solitary tract in rats

Abstract

Anatomical tracing studies examining the vagal system can conflate details of sensory afferent and motor efferent neurons. Here, we used a serotype of adeno-associated virus that transports retrogradely and exhibits selective tropism for vagal afferents, to map their soma location and central termination sites within the nucleus of the solitary tract (NTS). We examined the vagal sensory afferents innervating the trachea, duodenum, stomach, or heart, and in some animals, from two organs concurrently.We observed no obvious somatotopy in the somata distribution within the nodose ganglion. The central termination patterns of afferents from different organs within the NTS overlap substantially. Convergence of vagal afferent inputs from different organs onto single NTS neurons is observed. Abdominal and thoracic afferents terminate throughout the NTS, including in the rostral NTS, where the 7th cranial nerve inputs are known to synapse. To address whether the axonal labeling produced by viral transduction is so widespread because it fills axons traveling to their targets, and not just terminal fields, we labeled pre and postsynaptic elements of vagal afferents in the NTS . Vagal afferents form multiple putative synapses as they course through the NTS, with each vagal afferent neuron distributing sensory signals to multiple second-order NTS neurons. We observe little selectivity between vagal afferents from different visceral targets and NTS neurons with common neurochemical phenotypes, with afferents from different organs making close appositions with the same NTS neuron. We conclude that specific viscerosensory information is distributed widely within the NTS and that the coding of this input is probably determined by the intrinsic properties and projections of the second-order neuron.

Vagotomy blunts cardiorespiratory responses to vagal afferent stimulation via pre‐ and postsynaptic effects in the nucleus tractus solitarii

“…However, the nTS is the initial site for the integration and modulation of numerous viscerosensory inputs, and thus is critically involved in many cardiorespiratory reflexes. Vagal afferent terminal fields in the nTS overlap with glossopharyngeal terminals that carry baro‐ and chemoreceptor input (Loewy, 1990), and nTS neurons may receive multiple inputs from different sensory modalities (Bassi et al., 2022; Zagon et al., 1999). Furthermore, the nTS undergoes several forms of plasticity at the circuit level.…”

Selective transduction and photoinhibition of pre-Botzinger neurons that project to the facial nucleus in rats affect the nasofacial activity

“…Sections were placed directly into cryoprotectant in a 24-well plate and stored at −20°C until processing. Fluorescence immunohistochemistry was performed as previously described (Bassi et al, 2022; Menuet et al, 2020; Ngo et al, 2020). Primary antibodies used were chicken anti-GFP (1:5000, Aves Labs Inc, Davis, CA, USA, Cat#: GFP-1010), mouse anti-TH (1:5000, Merck-Millipore, Bayswater, VIC, Australia, Cat#: MAB318), rabbit anti-parvalbumin (1:5000, Abcam, Melbourne, VIC, Australia, Cat#: ab11427), Goat anti-ChAT: (1:1000, Chemicon-Merck, Bayswater, Australia, Cat#: AB144P), rabbit anti-dsRed: (1:5000, Takara Bio, Clontech, Australia, Cat#: 632496), goat anti-mCherry (1:5000, Sicgen, Cantanhede, Portugal; Cat#: AB0040-200).…”

“…Immediately following the RNAScope protocol, the immunofluorescence protocol for MuGFP was performed as previously described (Bassi et al, 2022) and nuclei DAPI stained. 4’,6-diamidine-2-phenylindole dihydrochloride And coverslipped using ProLong™ Gold Antifade Mountant (Invitrogen by Thermo Fisher Scientific).…”

“…Imaging was performed at the Biological and Optical Microscopy Platform, University of Melbourne as previously described (Bassi et al, 2022). Lower power images were taken using epifluorescence microscopy (Zeiss Axio Imager D1 microscope with a Zeiss AxioCam MR3 camera and EC Plan-NeoFuar 10x/0.3 air objective, Carl-Zeiss, North Ryde, NSW, Australia).…”

“…Whilst GtACR2-MuGFP expression was examined across all animals, the maps of the distribution were generated from 7 and 5 representative animals of non-selective and selective expression of GtACR2-MuGFP, respectively. To build the maps of distribution, the images containing GtACR2-MuGFP expression were selected and transformed in binary images according to a previously determined protocol (Bassi et al, 2022). The traced bitmap image was overlayed on the corresponding coronal preBötC schematic diagram (Paxinos and Watson, 2006) using the original fluorescence image as a guide.…”