Louise Pontell

University of Melbourne, Melbourne, Victoria, Australia

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Publications (19)63.7 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Recent investigation of the intestine following ischemia and reperfusion (I/R) has revealed that nitric oxide synthase (NOS) neurons are more strongly affected than other neuron types. This implies that NO originating from NOS neurons contributes to neuronal damage. However, there is also evidence of the neuroprotective effects of NO. In this study, we compared the effects of I/R on the intestines of neuronal NOS knockout (nNOS(-/-)) mice and wild-type mice. I/R caused histological damage to the mucosa and muscle and infiltration of neutrophils into the external muscle layers. Damage to the mucosa and muscle was more severe and greater infiltration by neutrophils occurred in the first 24 h in nNOS(-/-) mice. Immunohistochemistry for the contractile protein, α-smooth muscle actin, was used to evaluate muscle damage. Smooth muscle actin occurred in the majority of smooth muscle cells in the external musculature of normal mice but was absent from most cells and was reduced in the cytoplasm of other cells following I/R. The loss was greater in nNOS(-/-) mice. Basal contractile activity of the longitudinal muscle and contractile responses to nerve stimulation or a muscarinic agonist were reduced in regions subjected to I/R and the effects were greater in nNOS(-/-) mice. Reductions in responsiveness also occurred in regions of operated mice not subjected to I/R. This is attributed to post-operative ileus that is not significantly affected by knockout of nNOS. The results indicate that deleterious effects are greater in regions subjected to I/R in mice lacking nNOS compared with normal mice, implying that NO produced by nNOS has protective effects that outweigh any damaging effect of this free radical produced by enteric neurons.
    Cell and Tissue Research 06/2012; 349(2):565-76. · 3.68 Impact Factor
  • Autonomic Neuroscience. 09/2011; 163(s 1–2):58–59.
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    ABSTRACT: Periods of ischemia followed by restoration of blood flow cause ischemia/reperfusion (I/R) injury. In the intestine, I/R damage to the mucosa and neurons is prominent. Functionally, abnormalities occur in motility, most conspicuously a slowing of transit, possibly as a consequence of damage to neurons and/or muscle. Here, we describe degenerative and regenerative changes that have not been previously reported in intestinal muscle. The mouse small intestine was made ischemic for 1 h, followed by re-perfusion for 1 h to 7 days. The tissues were examined histologically, after hematoxylin/eosin and Masson's trichrome staining, and by myeloperoxidase histochemistry to detect inflammatory reactions to I/R. Histological analysis revealed changes in the mucosa, muscle, and neurons. The mucosa was severely but transiently damaged. The mucosal surface was sloughed off at 1-3 h, but re-epithelialization occurred by 12 h, and the epithelium appeared healthy by 1-2 days. Longitudinal muscle degeneration was followed by regeneration, but little effect on the circular muscle was noted. The first signs of muscle change were apparent at 3-12 h, and by 1 and 2 days, extensive degeneration within the muscle was observed, which included clear cytoplasm, pyknotic nuclei, and apoptotic bodies. The muscle recovered quickly and appeared normal at 7 days. Histological evidence of neuronal damage was apparent at 1-7 days. Neutrophils were not present in the muscle layers and were infrequent in the mucosa. However, they were often seen in the longitudinal muscle at 1-3 days and were also present in the circular muscle. Neutrophil numbers increased in the mucosa in both I/R and sham-operated animals and remained elevated from 1 h to 7 days. We conclude that I/R causes severe longitudinal muscle damage, which might contribute to the long-term motility deficits observed after I/R injury to the intestine.
    Cell and Tissue Research 02/2011; 343(2):411-9. · 3.68 Impact Factor
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    ABSTRACT: Changes in intestinal function, notably impaired transit, following ischemia/reperfusion (I/R) injury are likely to derive, at least in part, from damage to the enteric nervous system. Currently, there is a lack of quantitative data and methods on which to base quantitation of changes that occur in enteric neurons. In the present work, we have investigated quantifiable changes in response to ischemia of the mouse small intestine followed by reperfusion from 1 h to 7 days. I/R caused distortion of nitric oxide synthase (NOS)-containing neurons, the appearance of a TUNEL reaction in neurons, protein nitrosylation and translocation of Hu protein. Protein nitrosylation was detected after 1 h and was detectable in 10% of neurons by 6 h in the ischemic region, indicating that reactive peroxynitrites are rapidly produced and can interact with proteins soon after reperfusion. Apoptosis, revealed by TUNEL staining, was apparent at 6 h. The profile sizes of NOS neurons were increased by 60% at 2 days and neurons were still swollen at 7 days, both in the ischemic region and proximal to the ischemia. The distribution of the enteric neuron marker and oligonucleotide binding protein, Hu, was significantly changed in both regions. Hu protein translocation to the nucleus was apparent by 3 h and persisted for up to 7 days. Particulate Hu immunoreactivity was observed in the ganglia 3 h after I/R but was never observed in control. Our observations indicate that effects of I/R injury can be detected after 1 h and that neuronal changes persist to at least 7 days. Involvement of NO and reactive oxygen species in the changes is indicated by the accumulation of nitrosylated protein aggregates and the swelling and distortion of nitrergic neurons. It is concluded that damage to the enteric nervous system, which is likely to contribute to functional deficits following ischemia and re-oxygenation in the intestine, can be quantified by Hu protein translocation, protein nitrosylation, swelling of nitrergic neurons and apoptosis.
    Cell and Tissue Research 02/2011; 344(1):111-23. · 3.68 Impact Factor
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    ABSTRACT: A number of methods to augment the resistance of the outlet of the urinary bladder and to improve continence have been developed, including the artificial urinary sphincter and the placement of skeletal muscle around the urethra. It has been recently shown in a rabbit model that transplantation of smooth muscle around the proximal urethra reduces incontinence caused by internal sphincter deficiency. In the present work we have investigated the re-innervation of a peri-urethral smooth muscle transplant, and whether re-innervating axons have an appropriate effect when they are stimulated. Detrusor muscle from the dome of the bladder was transplanted to encircle the proximal urethras of rats. Rats tolerated the surgery and transplantation without any signs of compromised health. At 8 weeks the new sphincter was intact and easily recognised. The transplant contracted in response to transmural stimulation (1-5Hz for up to 5min) in a similar way to freshly removed detrusor strips. Contractions were graded with stimulus frequency, they peaked at about 10s and faded to a lower tension that was maintained. The amplitudes of sustained contractions of the transplants were reduced to about 10% by hyoscine and were almost abolished by tetrodotoxin. Histological examination revealed healthy, vascularised smooth muscle in the transplants, similar in appearance to freshly dissected detrusor. Re-innervation was confirmed immunohistochemically for transplanted detrusor muscle and transplants of dartos muscle. We conclude that smooth muscle transplanted to form a new sphincter around the urethra becomes functionally re-innervated and has potential to be used for sphincter augmentation.
    Autonomic neuroscience: basic & clinical 01/2011; 159(1-2):71-6. · 1.82 Impact Factor
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    ABSTRACT: In the present study the relationship between tissue damage and changed electro-physiological properties of Dogiel type II myenteric neurons within the first 24 hours after induction of inflammation with trinitrobenzene sulfonate (TNBS) in the guinea-pig ileum was investigated. Treatment with TNBS causes damage to the mucosa, inflammatory responses in the mucosa and enteric ganglia and changes in myenteric neuron properties. Thus we hypothesise that the physiological changes in the myenteric neurons could be due to damage to their mucosal processes or inflammation in the vicinity of cell bodies or the processes. We found an association between hyperexcitability of myenteric Dogiel type II neurons and damage to the mucosa and its innervation at 3 and 24 h, times when there was also an inflammatory reaction. The lack of hyperexcitability in neurons from control tissues in which axons projecting to the mucosa were severed suggests that inflammation may be an important contributing factor to the neuronal hyperexcitability at the acute stage of inflammation. Despite mucosal repair and re-innervation of the mucosa before 7 days after induction of inflammation, neuronal hyperexcitability persists. Although the mechanisms underlying neuronal hyperexcitability at the acute stage of inflammation might be different from those underlying long-term changes in the absence of active inflammation in the ganglia, the persistent changes in neuronal excitability may contribute to post-inflammatory gut dysfunctions.
    The Journal of Physiology 01/2011; 589(Pt 2):325-39. · 4.38 Impact Factor
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    ABSTRACT: The intestine is recognised to play a key role in the transmission of prion diseases. These diseases are associated with pathological isoforms (PrP(Sc)) of the normal cellular prion protein (PrP(C)) and can be transmitted between individuals or arise spontaneously. The brain, as the primary site of prion replication, could provide infectious prions to peripheral tissues. Here, we examine whether the brain is a source of intestinal prion accumulation. Following intracerebral inoculation with human origin prions the ileums of BalbC mice with clinical prion disease were assessed by Western immunoblot and immunohistochemical analysis for the presence of PrP(Sc) and the survival of enteric glial cells (EGCs) and specific neuronal subpopulations in the myenteric and submucosal plexus. PrP(Sc) was detected in the ileum of 13/13 mice following intracerebral inoculation with prions and 0/4 saline-inoculated mice. PrP(Sc) was localised at detectable levels in the Peyer's patches of infected mice. Investigation of neuronal subpopulations revealed a significant decrease in neurofilament reactive neurons (11±8%, p<0.05, n=5) compared with saline-inoculated mice (23±5%, n=3). Neuronal nitric oxide synthase (nNOS) and tyrosine hydroxylase reactive neurons were decreased in some (2 of 4 and 1 of 3, respectively) but not all prion-infected mice, whereas calretinin and vasoactive intestinal peptide reactive neurons were unaffected. EGCs were highly distorted in circumscribed ganglia of the myenteric plexus. In areas of glial derangement, the neurons showed undefined outlines and faint cytoplasmic immunoreactivity for the pan-neuronal marker Hu and loss of nNOS reactivity. The present work shows that PrP(Sc) can be transmitted from the brain to the intestine. This causes pathological changes in enteric glia and neurons. We conclude that PrP(Sc) of brain origin finds a substrate in the naturally occurring PrP(C) of EGCs and neurons. This results in a reservoir of PrP(Sc) in the intestine, which may represent a source of prion disease transmission through surgical procedures and environmental contamination.
    Gut 12/2010; 59(12):1643-51. · 10.73 Impact Factor
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    ABSTRACT: The family of two-pore domain potassium (K(₂P)) channels is important in setting and controlling the background potassium current of excitable cells. This study examines the localisation of the acid-sensitive channel, K(₂P)9.1 (TASK3), in cells of the gastric mucosa. We observed K(₂P)9.1 immunoreactivity in endocrine cells of the mucosal glands of the guinea-pig, rat and mouse but the channels were not detected in parietal, chief, or mucous cells. K(₂P)9.1 channel immunoreactivity was consistently co-localised with histidine decarboxylase immunopositive enterochromaffin-like (ECL) cells, and with the majority of ghrelin immunoreactive X/A cells. Localisation in somatostatin immunoreactive D cells was rare in the guinea-pig, and did not occur in the stomach of rat, but, in the mouse, K(₂P)9.1 channels were observed in the majority of somatostatin-immunoreactive D cells. Conversely, sections taken from the guinea-pig and mouse stomachs, but not rat stomach, revealed K(₂P)9.1 in gastrin-containing G cells. These results demonstrate the presence of K(₂P)9.1 channels in the entero-endocrine ECL, G and D cell populations of the stomach that regulate acid secretion through the release of histamine, gastrin and somatostatin. K(₂P)9.1 channels were located in the ghrelin X/A cells that regulate food intake.
    Journal of molecular histology 12/2010; 41(6):403-9. · 1.75 Impact Factor
  • Gastroenterology 01/2010; 138(5). · 12.82 Impact Factor
  • Gastroenterology 01/2010; 138(5). · 12.82 Impact Factor
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    ABSTRACT: We investigated the effect of inflammation on slow synaptic transmission in myenteric neurons in the guinea pig ileum. Inflammation was induced by the intraluminal injection of trinitrobenzene sulfonate, and tissues were taken for in vitro investigation 6-7 days later. Brief tetanic stimulation of synaptic inputs (20 Hz, 1 s) induced slow excitatory postsynaptic potentials (EPSPs) in 49% and maintained postsynaptic excitation that lasted from 27 min to 3 h in 13% of neurons from the inflamed ileum. These neurons were classified electrophysiologically as AH neurons; 10 were morphological type II neurons, and one was type I. Such long-term hyperexcitability after a brief stimulus is not encountered in enteric neurons of normal intestine. Electrophysiological properties of neurons with maintained postsynaptic excitation were similar to those of neurons with slow EPSPs. Another form of prolonged excitation, sustained slow postsynaptic excitation (SSPE), induced by 1-Hz, 4-min stimulation, in type II neurons from the inflamed ileum reached its peak earlier but had lower amplitude than that in control. Unlike slow EPSPs and similar to SSPEs, maintained excitation was not inhibited by neurokinin-1 or neurokinin-3 receptor antagonists. Maintained postsynaptic excitation was not influenced by PKC inhibitors, but the PKA inhibitor, H-89, caused further increase in neuronal excitability. In conclusion, maintained excitation, observed only in neurons from the inflamed ileum, may contribute to the dysmotility, pain, and discomfort associated with intestinal inflammation.
    AJP Gastrointestinal and Liver Physiology 07/2009; 297(3):G582-93. · 3.65 Impact Factor
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    ABSTRACT: An acute enteritis is commonly followed by intestinal neuromuscular dysfunction, including prolonged hyperexcitability of enteric neurons. Such motility disorders are associated with maintained increases in immune cells adjacent to enteric ganglia and in the mucosa. However, whether the commonly used animal model, trinitrobenzene sulphonate (TNBS)-induced enteritis, causes histological and immune cell changes similar to human enteric neuropathies is not clear. We have made a detailed study of the mucosal damage and repair and immune cell invasion following intralumenal administration of TNBS. Intestines from untreated, sham-operated and TNBS-treated animals were examined at 3 h to 56 days. At 3 h, the mucosal surface was completely ablated, by 6 h an epithelial covering was substantially restored and by 1 day there was full re-epithelialisation. The lumenal epithelium developed from a squamous cell covering to a fully differentiated columnar epithelium with mature villi at about 7 days. Prominent phagocytic activity of enterocytes occurred at 1-7 days. A surge of eosinophils and T lymphocytes associated with the enteric nerve ganglia occurred at 3 h to 3 days. However, elevated immune cell numbers occurred in the lamina propria of the mucosa until 56 days, when eosinophils were still three times normal. We conclude that the disruption of the mucosal surface that causes TNBS-induced ileitis is brief, a little more than 6 h, and causes a transient immune cell surge adjacent to enteric ganglia. This is much briefer than the enteric neuropathy that ensues. Ongoing mucosal inflammatory reaction may contribute to the persistence of enteric neuropathy.
    Archiv für Pathologische Anatomie und Physiologie und für Klinische Medicin 07/2009; 455(1):55-65. · 2.68 Impact Factor
  • Autonomic Neuroscience-basic & Clinical - AUTON NEUROSCI-BASIC CLIN. 01/2009; 149(1):27-28.
  • Autonomic Neuroscience-basic & Clinical - AUTON NEUROSCI-BASIC CLIN. 01/2009; 149(1):97-98.
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    ABSTRACT: The consequences of inflammation of a short region of the guinea-pig ileum on the properties of neurons in the celiac ganglia were investigated. Inflammation (ileitis) was induced in 5-8 cm of intestine by the intralumenal injection of trinitrobenzene sulfonate, 6-7 days before tissue was taken. Celiac ganglion neurons were investigated using intracellular microelectrodes and the cells were filled with dye from the recording electrode, to determine their morphologies. Tonic and phasic neurons were identified. In ganglia from normal guinea-pigs and from guinea-pigs with ileitis, cell bodies of tonic neurons were larger and their dendrites were longer and more numerous than those of phasic neurons. Tonic neurons were selectively affected by intestinal inflammation. The number of action potentials elicited by the same intensity of depolarizing current for neurons after ileal inflammation was twice that of neurons from control animals, the threshold current to evoke action potentials was about half, and some of the neurons were spontaneously active. Neurons from untreated or sham-operated animals were never spontaneously active. Many more neurons were affected than project to the 5-8 cm of intestine that was inflamed. We conclude that inflammation of a segment of the ileum causes a selective, humorally mediated, increase in excitability of tonic neurons in the celiac ganglion that control motility and secretion, but not of phasic neurons that project to the intestinal vasculature and other targets.
    Neuroscience Letters 09/2008; 444(3):231-5. · 2.03 Impact Factor
  • Autonomic Neuroscience-basic & Clinical - AUTON NEUROSCI-BASIC CLIN. 01/2007; 135(1):84-85.
  • Autonomic Neuroscience-basic & Clinical - AUTON NEUROSCI-BASIC CLIN. 01/2007; 135(1):84-84.
  • Autonomic Neuroscience-basic & Clinical - AUTON NEUROSCI-BASIC CLIN. 01/2007; 135(1):24-25.
  • Autonomic Neuroscience-basic & Clinical - AUTON NEUROSCI-BASIC CLIN. 01/2007; 135(1):86-86.

Publication Stats

48 Citations
63.70 Total Impact Points

Institutions

  • 2009–2012
    • University of Melbourne
      • Department of Anatomy and Neuroscience
      Melbourne, Victoria, Australia
  • 2007–2011
    • Victoria University Melbourne
      Melbourne, Victoria, Australia