Mesenteric neurons in the adult rat are responsive to ileal treatment with benzalkonium chloride

A piglet model of iatrogenic rectosigmoid hypoganglionosis reveals the impact of the enteric nervous system on gut barrier function and microbiota postnatal development

BACKGROUND

Hirschsprung-associated enterocolitis physiopathology likely involves disturbed interactions between gut microbes and the host during the early neonatal period. Our objective was to create a neonatal porcine model of iatrogenic aganglionosis to evaluate the impact of the enteric nervous system (ENS) on microbiota and intestinal barrier postnatal development.

METHODS

Under general anesthesia, the rectosigmoid serosa of 5-day-old suckling piglets was exposed to 0.5% benzalkonium chloride solution (BAC, n = 7) or saline (SHAM, n = 5) for 1 h. After surgery, animals returned to their home-cage with the sow and littermates and were studied 21 days later.

RESULTS

BAC treatment induced partial aganglionosis with absence of myenteric plexus and reduced surface area of submucosal plexus ganglia (-58%, P < 0.05) in one third of the rectosigmoid circumference. Epithelial permeability of this zone was increased (conductance +63%, FITC-dextran flux +386%, horseradish-peroxidase flux +563%, P < 0.05). Tight junction protein remodeling was observed with decreased ZO-1 (-95%, P < 0.05) and increased claudin-3 and e-cadherin expressions (+197% and 61%, P < 0.05 and P = 0.06, respectively). BAC piglets harbored greater abundance of proinflammatory bacteria (Bilophila, Fusobacterium) compared to SHAM in the rectosigmoid lumen.

CONCLUSIONS

This large animal model demonstrates that hypoganglionosis is associated with dramatic defects of gut barrier function and establishment of proinflammatory bacteria.

A Time-Limited and Partially Reversible Model of Hypoganglionosis Induced by Benzalkonium Chloride Treatment

Serosal application of benzalkonium chloride (BAC) has been previously applied to produce a model of aganglionosis; however, confusion remains regarding the extent of chemical ablation of enteric myenteric plexus after BAC treatment. The time sequence of BAC-induced effects on the myenteric plexus of the rat colon was determined and followed the morphologic changes. After sacrifice of animals 7, 14, 28, 56, 84 or 168 days postintervention, colonic tissue samples were removed, fixed in formalin, and cut into 5-μm longitudinal sections for histological analysis. The neural analysis was used to re-evaluate BAC treatments for the appropriate model. Compared with rats in sham groups, rats in 0.1 %-30-min BAC group maintained only 15.27 ± 4.80 % of ganglia per section in a 1-cm/5-μm slice and 11.76 ± 2.30 % of ganglionic cells after 28 days, the lower and stable number of ganglionic cells between Day 7 and 84 (from 11.67 ± 2.10 to 19.05 ± 5.10 %). Although an increase, ganglionic cell numbers did not recover at Day168 when compared with the numbers in sham groups. The results showed that characteristics of rats in the 0.1 %-30-min BAC group between Day 7 and 84 most closely kept in stable state, suggesting that these treatment parameters are ideal for producing a hypoganglia model of hypoganglionosis.

Neurogenesis in the adult peripheral nervous system

Most researchers believe that neurogenesis in mature mammals is restricted only to the subgranular zone of the dentate gyrus and the subventricular zone of the lateral ventricle in the central nervous system. In the peripheral nervous system, neurogenesis is thought to be active only during prenatal development, with the exception of the olfactory neuroepithelium. However, sensory ganglia in the adult peripheral nervous system have been reported to contain precursor cells that can proliferate in vitro and be induced to differentiate into neurons. The occurrence of insult-induced neurogenesis, which has been reported by several investigators in the brain, is limited to a few recent reports for the peripheral nervous system. These reports suggest that damage to the adult nervous system induces mechanisms similar to those that control the generation of new neurons during prenatal development. Understanding conditions under which neurogenesis can be induced in physiologically non-neurogenic regions in adults is one of the major challenges for developing therapeutic strategies to repair neurological damage. However, the induced neurogenesis in the peripheral nervous system is still largely unexplored. This review presents the history of research on adult neurogenesis in the peripheral nervous system, which dates back more than 100 years and reveals the evidence on the under estimated potential for generation of new neurons in the adult peripheral nervous system.

Enteric glia are multipotent in culture but primarily form glia in the adult rodent gut

It is unclear whether neurogenesis occurs in the adult mammalian enteric nervous system (ENS). Neural crest-derived cells capable of forming multilineage colonies in culture, and neurons and glia upon transplantation into chick embryos, persist throughout adult life in the mammalian ENS. In this study we sought to determine the physiological function of these cells. We discovered that these cells could be identified based on CD49b expression and that they had characteristics of enteric glia, including p75, GFAP, S100B, and SOX10 expression. To test whether new neurons or glia arise in the adult gut under physiological conditions, we marked dividing progenitors with a thymidine analog in rodents under steady-state conditions, or during aging, pregnancy, dietary changes, hyperglycemia, or exercise. We also tested gut injuries including inflammation, irradiation, benzalkonium chloride treatment, partial gut stenosis, and glial ablation. We readily observed neurogenesis in a neurogenic region of the central nervous system, but not reproducibly in the adult ENS. Lineage tracing of glial cells with GFAP-Cre and GFAP-CreERT2 also detected little or no adult ENS neurogenesis. Neurogenesis in the adult gut is therefore very limited under the conditions we studied. In contrast, ENS gliogenesis was readily observed under steady-state conditions and after injury. Adult enteric glia thus have the potential to form neurons and glia in culture but are fated to form mainly glia under physiological conditions and after the injuries we studied.

No reduction with ageing of the number of myenteric neurons in benzalkonium chloride treated rats

The number of myenteric neurons may be reduced by topical serosal application of benzalkonium chloride (BAC). We studied the effects of ageing in the population of neurons that survive after the application of BAC. Ten treated and ten control animals were killed at intervals of 2, 6, 12 and 18 months after the surgery. We performed myenteric neurons counting in serially cut histological preparations of the descending colon. The control animals revealed a continuous loss of myenteric neurons number with increasing of age. Interestingly, contrary to control animals, the BAC-treated rats presented no neuron loss with ageing at any experimental time. The reasons for their survival with ageing could be related to a neuroplasticity phenomenon.

Postnatal histogenesis in the peripheral nervous system

The issue of postnatal neurogenesis has gained great importance over the last few years and the recent amazing scientific advancements, changing our viewpoint on the long-lasting "no new neurons" dogma, have opened promising new perspectives on the treatment of the damaged nervous system. While most of the researchers have focused on the central nervous system, the peripheral nervous system has received little attention so far with respect to postnatal histogenesis. To attract scientific attention on this issue, the present article was written with the aim of reviewing the body of literature on postnatal histogenesis in the various districts of the peripheral nervous system, from the historical roots to the most recent reports.

Morphological and functional changes after benzalkonium chloride treatment of the small intestinal Thiry-Vella loop in rats

The aim of this work was to study the effects of benzalkonium chloride (BAC) treatment on the small intestine and its functioning in rats surgically prepared with Thiry-Vella intestinal loop. The loops were treated with either BAC, which ablated much of the myenteric plexus and extrinsic innervation, or with physiological saline (SAL). In vivo drinking experiments were performed to examine the effect on fluid intake and behavioral indices of distending the loop with a balloon. Spontaneous motility and its changes induced by acetylcholine (ACh) and histamine (His) were studied on isolated stripes in vitro. Finally, samples from the loops were examined histologically. Though reduction of the cell number was less than expected and no differences of the thickness of the muscular layer between the two groups was observed, BAC treatment altered the pattern of spontaneous activity and also the sensitivity to ACh and His in isolated stripes. In vivo distension of the SAL-treated loops reduced fluid intake and produced signs of aversivity; these effects were absent in the BAC-treated group. Our results show that despite the differences in the degree of ablation from those obtained by others, BAC treatment can be used to study the mechanisms underlying the effects of the enteral stimuli on the behavior.

NADPH-diaphorase-positive ganglion cells of the rat adrenal gland: age- and sex-related changes in their number, size, and distribution

The rat adrenal gland contains ganglion cells able to synthesize nitric oxide (NO). This messenger molecule controls and modulates adrenal secretory activity and blood flow. The present study analyzed the number, size, and distribution of NO-producing adrenal neurons in adulthood and during postnatal development by means of beta-nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry. This method reliably visualizes the enzyme responsible for NO generation. The reactive neurons per adrenal gland were 350-400 in both male and female adult rats. The positive nerve cell bodies were mostly located in the medulla, few being detected within the cortex and the subcapsular region. Dual labeling with anti-microtubule-associated protein 2 antibody, specific for neuronal elements, confirmed this distribution. Anti-microtubule-associated protein 1b antibody identified a subset of NADPH-d-positive neurons, displaying different degrees of maturation according to their position within the adrenal gland. At birth, there were about 220 NADPH-d-labeled neurons per adrenal gland in both sexes. As confirmed by dual immunocytochemical labeling, their great majority was evenly distributed between the cortex and the subcapsular region, the medulla being practically devoid of stained neurons. After birth, the number of adrenal NADPH-d-positive ganglion cells displayed a strong postnatal increase and reached the adult-like distribution after 1-2 months. During the period of increase, there was a transient difference in the numbers of these cells in the two sexes. Thus we present here evidence of plasticity in the number, size, and distribution of NADPH-d-positive adrenal neurons between birth and adulthood; in addition, we describe transient sex-related differences in their number and distribution during the 2nd postnatal week, which are possibly related to the epigenetic action of gonadal hormones during this period.

Myenteric denervation of rat jejunum alters calcium responsiveness of intestinal smooth muscle

BACKGROUND/AIMS

Long-term myenteric and extrinsic denervation of a segment of rat jejunum results in increased stress generation by the longitudinal muscle layer of the denervated segment 15 days after denervation. This study examined whether alterations in the properties of either cell membrane calcium channels and/or sarcoplasmic reticular Ca(2+)-adenosine triphosphatase (ATPase) contribute to the increased stress development.

METHODS

The effects of the calcium channel blocker nifedipine and the sarcoplasmic reticular Ca(2+)-ATPase inhibitor cyclopiazonic acid on the contractile activity of denervated and control smooth muscle were determined.

RESULTS

The ability of nifedipine to inhibit KCl-induced contractions was significantly increased in denervated tissues; however, there was no difference in the potency of nifedipine when tissues were stimulated with carbachol. Calcium concentration-response curves obtained in the presence of either KCl or carbachol were determined in tissues previously depleted of calcium. Long-term denervated tissues showed an increased sensitivity to calcium and a decreased maximum contractile response after stimulation with carbachol. Cyclopiazonic acid inhibited repletion of intracellular calcium stores of control muscle but had no effect in denervated tissue.

CONCLUSIONS

Long-term denervation of a segment of rat small intestine results in profound alterations in calcium metabolism at the cell membrane and, to a lesser extent, at the sarcoplasmic reticulum of smooth muscle cells of the longitudinal muscle layer.

Conjunctiva and subconjunctival tissue in primary open-angle glaucoma after long-term topical treatment: an immunohistochemical and ultrastructural study

BACKGROUND

Primary open-angle glaucoma is commonly treated with long-term hypotensive medical therapy. When this approach becomes inadequate, therapy proceeds with surgery. The present study investigates morphological changes in the conjunctival and subconjunctival tissues induced by short- and long-term topical medical therapy of primary open-angle glaucoma.

METHODS

Comparisons were made between biopsy specimens from glaucomatous patients, who received specific eyedrop therapy (timolol and pilocarpine) for various periods of time, and control patients with no conjunctival pathology or topical treatment. Histological, immunohistochemical and ultrastructural parameters were investigated.

RESULTS

The morphometric analysis of histological sections and immunohistochemistry (anti-fibronectin antibody) in medium- and long-term therapy patients showed: (a) significant increases in the thickness and number of epithelial cell layers; (b) significant increases in the fibroblast density in both subepithelial and deep connective tissue; and (c) a more compact connective tissue, richer in collagen fibers arranged in whirls, with some inflammatory elements. These findings were confirmed by the ultrastructural analysis. In the same patients, the other immunohistochemical parameters investigated (anti-HLA-DR, anti-CD1a, anti-CD4, anti-CD8, anti-IL2 and C3b antibodies) revealed a tendency to chronic inflammation. Following specific surgery, this tendency manifested itself in a diffuse immune response, especially in those patients who underwent medium- and long-term medical therapy.

CONCLUSION

According to these results, antiglaucomatous surgery should be rehabilitated and considered as an alternative to long-term medical therapy in the first-instance treatment of primary open-angle glaucoma.

Effects of eye enucleation on NADPH-diaphorase positive neurons in the superficial layers of the rat superior colliculus

Dihydronicotinamide adenine-dinucleotide phosphate diaphorase (NADPH-d) positive neurons in the superficial layers of superior colliculus (SC) were studied in the adult rat after eye enucleation at postnatal day 5 (P5). Bilaterally, NADPH-d histochemistry revealed either weakly or intensely labeled neurons. In the SC contralateral to the enucleation, the volume of superficial layers decreased significantly, whereas the total number of NADPH-d positive neurons was only slightly reduced, thus resulting in an increased cell density. Bilaterally, the number of NADPH-d positive neurons was around 20% of Nissl-stained neurons. While the number of neurons which were weakly positive for NADPH-d was unchanged contralateral to the enucleation (thus resulting in a significant increase in their percentage on the overall NADPH-d population), the number of intensely labeled neurons decreased by 30%. Intensely labeled neurons were classified with respect to cell size and dendritic distribution. Some (126) were reconstructed and analyzed on the computer, in order to quantitate morphological differences in dendritic distribution in the denervated and control SC. The percent of neurons which could be assigned to some classes (marginal, stellate, narrow field vertical and wide field vertical) was reduced contralateral to the enucleation. In addition, vertically-oriented neurons (narrow field vertical, wide field vertical and pyriform) showed a significant decrease in soma size, dendritic length and number of branch points. And finally, the overall orientation of dendrites on narrow and wide field vertical neurons was more dispersed, when compared to the control colliculus. Thus, P5 eye enucleation affects the adult morphology of NADPH-d positive neurons in the superficial layers of the rat SC, resulting in increased cell density, changed relative number of cells in each morphological type, and altered soma size, dendritic length and orientation in specific neurons.

Quantitative study of the NADPH-diaphorase-positive myenteric neurons of the rat ileum

The subpopulation of myenteric neurons able to synthesize nitric oxide was studied quantitatively in the adult rat, using the NADPH-diaphorase histochemical method on whole-mount preparations of distended distal ileum. The spatial density of NADPH-diaphorase-positive myenteric neurons was 2388 +/- 193/cm2 (S.D.; five rats), comprising about 27% of the nerve cell bodies per ganglion. Most neurons were intensely stained and displayed predominantly a Dogiel type I morphology; about 8% of the labelled nerve cells were ovoid neurons, exhibiting a pale cytoplasmic reaction product. The mean somatic size of all NADPH-diaphorase-positive myenteric neurons was 446 +/- 40 microns2, with a mean nuclear size of 96 +/- 18 microns2 (mean values +/- S.D.; five rats). Such values fell exactly within the range of neuronal sizes of the total myenteric population, marked by means of NADH-diaphorase histochemistry. Therefore, the morphometric analysis did not identify any peculiar cell size feature, characterizing this specific nerve cell subpopulation. Thus, the present study provides quantitative data on the size, density and proportion of those myenteric neurons that may synthesize nitric oxide in the distal ileum of the rat.