Parainfluenza 3-Induced Cough Hypersensitivity in the Guinea Pig Airways.

The effect of respiratory tract viral infection on evoked cough in guinea pigs was evaluated. Guinea pigs were inoculated intranasally with either parainfluenza type 3 (PIV3) and cough was quantified in conscious animals. The guinea pigs infected with PIV3 (day 4) coughed nearly three times more than those treated with the viral growth medium in response to capsaicin, citric acid, and bradykinin. Since capsaicin, citric acid, and bradykinin evoked coughing in guinea pigs can be inhibited by drugs that antagonize the transient receptor potential cation channel, subfamily V, member 1 (TRPV1), it was reasoned that the virally-induced hypertussive state may involve alterations in TPRV1 activity. PIV3 infection caused a phenotypic switch in tracheal nodose Aδ "cough receptors" such that nearly 50% of neurons began to express, de novo, TRPV1 mRNA. There was also an increase TRPV1 expression in jugular C-fiber neurons as determined by qPCR. It has previously been reported that tracheal-specific nodose neurons express the BDNF receptor TrkB and jugular neurons express the NGF receptor TrkA. Jugular neurons also express the artemin receptor GFRα3. All these neurotrophic factors have been associated with increases in TRPV1 expression. In an ex vivo perfused guinea pig tracheal preparation, we demonstrated that within 8 h of PIV3 infusion there was no change in NGF mRNA expression, but there was nearly a 10-fold increase in BDNF mRNA in the tissue, and a small but significant elevation in the expression of artemin mRNA. In summary, PIV3 infection leads to elevations in TRPV1 expression in the two key cough evoking nerve subtypes in the guinea pig trachea, and this is associated with a hypertussive state with respect to various TRPV1 activating stimuli.

The vagus nerve is one route of transneural invasion for intranasally inoculated influenza a virus in mice.

Intranasally inoculated neurotropic influenza viruses in mice infect not only the respiratory tract but also the central nervous system (CNS), mainly the brain stem. Previous studies suggested that the route of invasion of virus into the CNS was via the peripheral nervous system, especially the vagus nerve. To evaluate the transvagal transmission of the virus, we intranasally inoculated unilaterally vagectomized mice with a virulent influenza virus (strain 24a5b) and examined the distribution of the viral protein and genome by immunohistochemistry and in situ hybridization over time. An asymmetric distribution of viral antigens was observed between vagal (nodose) ganglia: viral antigen was detected in the vagal ganglion of the vagectomized side 2 days later than in the vagal ganglion of the intact side. The virus was apparently transported from the respiratory mucosa to the CNS directly and decussately via the vagus nerve and centrifugally to the vagal ganglion of the vagectomized side. The results of this study, thus, demonstrate that neurotropic influenza virus travels to the CNS mainly via the vagus nerve.

Presence of VZV and HSV-1 DNA in human nodose and celiac ganglia.

Polymerase chain reaction (PCR) revealed herpes simplex virus (HSV) and varicella zoster virus (VZV) DNA in human nodose and celiac ganglia. This is the first detection of VZV DNA in ganglia of the human autonomic nervous system. The ability of reactivated VZV to produce serious, sometimes fatal neurological disease in the absence of rash, raises the possibility that VZV reactivation from autonomic ganglia might be involved in visceral disease.

Latent herpes simplex virus type 1 gene expression in ganglia innervating the human gastrointestinal tract.

Using in situ hybridization, we demonstrated that latent herpes simplex virus type 1 (HSV-1) gene expression is prevalent in human adult nodose ganglia. This suggests that infection of gastrointestinal sensory nerves, probably through swallowed virus-laden oral secretions, occurs commonly and that HSV-1 reactivating from this site may play a role in recurrent gastrointestinal disorders.

Oral inoculation of SCID mice with an attenuated herpes simplex virus-1 strain causes persistent enteric nervous system infection and gastric ulcers without direct mucosal infection.

BACKGROUND: After placement of herpes simplex virus type 1 (HSV-1) into the esophageal lumen of BALB/c mice, the virus replicated in enteric neurons within the esophagus and stomach and was transported to the sensory ganglia of the vagus nerve (nodose ganglia), where viral replication also occurs and where ultimately a long term latent infection is established. This described infection of immunocompetent mice primarily involved neuronal cells and associated satellite cells. EXPERIMENTAL DESIGN: Severe combined immunodeficient (SCID) mice were orally infected with an attenuated strain of HSV-1 to better identify sites of viral involvement in the gastrointestinal tract, particularly the mucosa. RESULTS: Three to five weeks after oral inoculation of SCID mice with HSV-1 strain in1814, a persistent viral infection of the gastrointestinal tract was established in most of the mice. Extensive viral replication was detected by immunohistochemistry throughout pathways of the vagus nerve and within the intrinsic enteric nervous system. Despite this ultimately fatal infection, viral replication in the gut occurred almost exclusively in enteric neurons and their processes; viral proteins were occasionally seen in smooth muscle cells immediately adjacent to heavily infected enteric ganglia. More than 50% of these persistently infected mice, when killed 18 to 31 days postinoculation, had gastric ulcers that were identified grossly and histologically. Only one of the 40 gastric ulcers was found to contain viral Ag. The remaining ulcers, although devoid of viral proteins, were found adjacent to virus-infected ganglia. CONCLUSIONS: HSV-1 can enter enteric neurons with minimal initial mucosal involvement, and once inside the nervous system, the virus is contained there despite the absence of a specific host immune response. Furthermore, chronically infected enteric neurons may provide an indirect mechanism for the pathogenesis of gastric ulcers in these immune-deficient mice.

Dendritic morphology of cardiac related medullary neurons defined by circuit-specific infection by a recombinant pseudorabies virus expressing beta-galactosidase.

The transneuronal herpesvirus tracer, pseudorabies virus (PRV) was used to determine the dendritic architecture of cardiac-related neurons. We constructed a derivative of the Bartha strain of PRV called PRV-BaBlu, that carries the lacZ gene of E. coli. Expression of beta-galactosidase by this recombinant virus enabled us to define the dendritic morphology of motoneurons and interneurons that innervate the heart. beta-galactosidase antigen filled dendritic processes that were clearly revealed by antibodies to beta-galactosidase. In contrast, the standard enzymatic reaction for detection of beta-galactosidase activity stained the cell soma well, but was inferior for labeling dendrites. Following PRV-BaBlu cardiac injection, infected neurons were clearly defined and labeled dendrites could be traced for long distances, sometimes greater than 800 microns from the cell body. Labeled dendrites of cardiomotor neurons primarily located in the nucleus ambiguus (NA) were extensive and sometimes intertwined with dendrites from other labeled motoneurons. Dendrites of labeled neurons in the dorsal motor nucleus of the vagus (DMV) typically extended in the mediolateral direction in the transverse plane. Transynaptically labeled interneurons interposed between the cardiorespiratory region of the nucleus tractus solitarius (NTS) and the NA were primarily located in the NA region and the reticular arc, the area between the DMV and NA. These interneurons had long dendrites extending along the reticular arc in the transverse plane. The dendritic arborizations of infected cardiac-related neurons in the NTS were variable in extent. We conclude that antibody detection of beta-galactosidase expressed by PRV-BaBlu after infection of neural cardiac circuits provides a superior method to define the dendrites and dendritic fields of cardiac-related motoneurons and interneurons.