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Equine ileocolonic aganglionosis, which is also called lethal white foal syndrome (LWFS), is a severe congenital condition characterized by the unsuccessful colonization of neural crest progenitors in the caudal part of the small intestine and the entire large intestine. LWFS, which is attributable to a mutation in the endothelin receptor B gene, is the horse equivalent of Hirschsprung's disease in humans. Affected foals suffer from aganglionosis or hypoganglionosis of the enteric ganglia resulting in intestinal akinesia and colic. In other species with aganglionosis, fibers of extrinsic origin show an abnormal distribution pattern within the gut wall, but we have no information to date regarding this occurrence in horses. Our present aim is to investigate the distribution of extrinsic sympathetic and sensory neural fibers in LWFS, focusing on ileum and the pelvic flexure of the colon of two LWFS foals compared with a control subject. The sympathetic fibers were immunohistochemically identified with the markers tyrosine hydroxylase and dopamine beta-hydroxylase. The extrinsic sensory fibers were identified with the markers Substance P (SP) and calcitonin gene-related peptide (CGRP). Since SP and CGRP are also synthesized by subclasses of horse intramural neurons, LWFS represents a good model for the selective study of extrinsic fiber distribution. Affected foals showed large bundles of extrinsic fibers, compared with the control, as observed in Hirschsprung's disease. Furthermore, altered adrenergic pathways were observed, prominently in the pelvic flexure. The numbers of SP- and CGRP-immunoreactive fibers in the muscle, a target of enteric neurons, were dramatically reduced, whereas fibers deduced to be extrinsic sensory axons persisted around submucosal blood vessels. Fiber numbers in the mucosa were reduced. Thus, extrinsic innervation, contributing to modulate enteric functions, might also be affected during LWFS.

Atypical and classical scrapie-infected sheep brain tissue was monolaterally injected into the tonsils of lambs to investigate their role as a prion entry point. We first detected classical PrP Sc within the inoculated tonsil and in the ipsilateral retropharyngeal lymph node at 3 months postinoculation (p.i.). At 7 months p.i., PrP Sc colonized other lymphoid tissues bilaterally, including ileal Peyer's patches. The earliest PrP Sc deposition within the brain was ipsilaterally observed at 9 months p.i. in the substantia reticularis of the medulla oblongata. At 12 months p.i., PrP Sc deposition was present bilaterally in the nucleus parasympathicus nervi vagi, as well as in the intermediolateral cell column of the thoracolumbar spinal cord. No PrP Sc was detected in the lambs inoculated with atypical scrapie. These findings suggest that neuroinvasion may naturally occur from the tonsil after a widespread prion replication within the lymphoid tissues during classical scrapie only, thus mimicking the pathogenesis after oral ingestion.

The lower esophageal sphincter (LES) is a specialized, thickened muscle region with a high resting tone mediated by myogenic and neurogenic mechanisms. During swallowing or belching, the LES undergoes strong inhibitory innervation. In the horse, the LES seems to be organized as a “one-way” structure, enabling only the oral-anal progression of food. We characterized the esophageal and gastric pericardial inhibitory and excitatory intramural neurons immunoreactive (IR) for the enzymes neuronal nitric oxide synthase (nNOS) and choline acetyltransferase. Large percentages of myenteric plexus (MP) and submucosal (SMP) plexus nNOS-IR neurons were observed in the esophagus (72 ± 9 and 69 ± 8 %, respectively) and stomach (57 ± 17 and 45 ± 3 %, respectively). In the esophagus, cholinergic MP and SMP neurons were 29 ± 14 and 65 ± 24 vs. 36 ± 8 and 38 ± 20 % in the stomach, respectively. The high percentage of nitrergic inhibitory motor neurons observed in the caudal esophagus reinforces the role of the enteric nervous system in the horse LES relaxation. These findings might allow an evaluation of whether selective groups of enteric neurons are involved in horse neurological disorders such as megaesophagus, equine dysautonomia, and white lethal foal syndrome.

European eels live most of their lives in freshwater until spawning migration to the Sargasso Sea. During seawater adaptation, eels modify their physiology, and their digestive system adapts to the new environment, drinking salt water to compensate for the continuous water loss. In that period, eels stop feeding until spawning. Thus, the eel represents a unique model to understand the adaptive changes of the enteric nervous system (ENS) to modified salinity and starvation. To this purpose, we assessed and compared the enteric neuronal density in the cranial portion of the intestine of freshwater eels (control), lagoon eels captured in brackish water before their migration to the Sargasso Sea (T0), and starved seawater eels hormonally induced to sexual maturity (T18; 18 weeks of starvation and treatment with standardized carp pituitary extract). Furthermore, we analyzed the modification of intestinal neuronal density of hormonally untreated eels during prolonged starvation (10 weeks) in seawater and freshwater. The density of myenteric (MP) and submucosal plexus (SMP) HuC/D-immunoreactive (Hu-IR) neurons was assessed in wholemount preparations and cryosections. The number of MP and SMP HuC/D-IR neurons progressively increased from the freshwater to the salty water habitat (control > T0 > T18; P < 0.05). Compared with freshwater eels, the number of MP and SMP HuC/ D-IR neurons significantly increased (P < 0.05) in the intestine of starved untreated salt water eels. In conclusion, high salinity evokes enteric neuroplasticity as indicated by the increasing number of HuC/D-IR MP and SMP neurons, a mechanism likely contributing to maintaining the body homeostasis of this fish in extreme conditions.

The neurochemistry of enteric neurons differs among species of small laboratory rodents (guinea-pig, mouse, rat). In this study we characterized the phenotype of ileal myenteric plexus (MP) neuronal cells and fibers of the bank vole (Myodes glareolus), a common rodent living in Europe and in Northern Asia which is also employed in prion experimental transmission studies. Six neuronal markers were tested: choline acetyltransferase (ChAT), neuronal nitric oxide synthase (nNOS), calbindin (CALB), calcitonin gene-related peptide (CGRP) and substance P (SP), along with HuC/D as a pan-neuronal marker. Neurons expressing ChAT- and nNOS-immunoreactivity (IR) were 36 ± 12% and 24 ± 5%, respectively. Those expressing CGRP-, SP- and CALB-IR were 3 ± 3%, 21 ± 5% and 6 ± 2%, respectively. Therefore, bank vole MPs differ consistently from murine MPs in neurons expressing CGRP-, SP- and CALB-IR. These data may contribute to define the prion susceptibility of neuron cell populations residing within ileal MPs from bank voles, along with their morpho-functional alterations following oral experimental prion challenge.

Sympathetic trunk ganglia (STG) neurons projecting to the urinary bladder trigone of the boar were studied by coupling retrograde tracing Fast Blue (FB) and double-labeling immunofluorescence methods. FB-positive neurons were localized in the L1-S3 STG. Immunohistochemical staining revealed the catecholaminergic (tyrosine hydroxylase-/dopamine beta hydroxylase immunoreactivity) phenotype of the majority of FB-positive neurons, which also preferentially expressed neuropeptide Y. In addition, some of the FB-positive dopaminergic perikarya were immunoreactive for calcitonin gene-related peptide, substance P, vasoactive intestinal peptide, vesicular acetylcholine-transporter, neuronal nitric oxide synthase, somatostatin, and leu-enkephalin. Functional hypotheses have been formulated.

Gastritis and gastric ulcerations occur frequently in neonatal foals. The relationship between cytokines expressed by gastric mucosa and gastric histopathology in healthy or sick foals has never been investigated. The aim of this study was to compare the histological diagnosis and endoscopic view with cytokine expression (TNF-α, IL-1β, IL-4, IL-8, IL-13, and IFN-γ) of gastric mucosa. Twenty-two foals were definitively enrolled in the study: 19 were critically ill, and 3 were healthy foals. Gastric biopsy specimens were collected for histological examination and for cytokine mRNA qualitative real-time PCR analysis. This study shows that there is a substantial agreement between histology and endoscopy and that foals with evidence of gastritis and gastric ulcerations have higher probability of expressing TNF-α. Moreover, the overall profile of cytokines expression, with a low percentage of IFN-γ, a high percentage of IL-4, and the absence of IL-13, suggests a down-regulation of the Th1 cell-mediated immune response and an impaired Th2 response in the gastric wall in the neonatal period.