Electrophysiological and morphological changes in colonic myenteric neurons from chemotherapy-treated patients: A pilot study

BACKGROUND: Patients receiving anticancer chemotherapy experience a multitude of gastrointestinal side‐effects. However, the causes of these symptoms are uncertain and whether these therapeutics directly affect the enteric nervous system is unknown. Our aim was to determine whether the function and morphology of myenteric neurons are altered in specimens of the colon from chemotherapy‐treated patients. METHODS: Colon specimens were compared from chemotherapy‐treated and non‐treated patients following colorectal resections for removal of carcinoma. Intracellular electrophysiological recordings from myenteric neurons and immunohistochemistry were performed in whole mount preparations. KEY RESULTS: Myenteric S neurons from chemotherapy‐treated patients were hyperexcitable; more action potentials (11.4 ± 9.4, p < 0.05) were fired in response to depolarising current pulses than in non‐treated patients (1.4 ± 0.5). The rheobase and the threshold to evoke action potentials were significantly lower for neurons from chemotherapy‐treated patients compared to neurons from non‐treated patients (p < 0.01). Fast excitatory postsynaptic potential reversal potential was more positive in neurons from chemotherapy‐treated patients (p < 0.05). An increase in the number of neurons with translocation of Hu protein from the cytoplasm to the nucleus was observed in specimens from chemotherapy‐treated patients (103 ± 25 neurons/mm(2), 37.2 ± 7.0%, n = 8) compared to non‐treated (26 ± 5 neurons/mm(2), 11.9 ± 2.7%, n = 12, p < 0.01). An increase in the soma size of neuronal nitric oxide synthase‐immunoreactive neurons was also observed in these specimens. CONCLUSIONS & INFERENCES: This is the first study suggesting functional and structural changes in human myenteric neurons in specimens of colon from patients receiving anticancer chemotherapy. These changes may contribute to the causation of gastrointestinal symptoms experienced by chemotherapy‐treated patients

Human enteric neurons: morphological, electrophysiological, and neurochemical identification

BACKGROUND: Access to tissue, difficulties with dissection, and poor visibility of enteric ganglia have hampered electrophysiological recordings of human enteric neurons. Here, we report a method to combine intracellular recording with simultaneous morphological identification of neurons in the intact myenteric plexus of human colon ex vivo. METHODS: Specimens of human colon were dissected into flat-sheet preparations with the myenteric plexus exposed. Myenteric neurons were impaled with conventional microelectrodes containing 5% 5,6-carboxyfluorescein in 20 mM Tris buffer and 1 M KC. KEY RESULTS: Electrophysiological recordings identified myenteric neurons with S and AH type properties (n = 13, N = 7) which were dye filled and classified during the recording as Dogiel type I (n = 10), Dogiel type II (n = 2), or filamentous (n = 1) cells. This classification was confirmed after fixation, in combination with immunohistochemical characterization. CONCLUSIONS & INFERENCES: This method allows electrophysiological characterization with simultaneous identification of morphology. It can be used to identify recorded cells immediately after impalement and greatly facilitates recordings of human myenteric neurons in freshly dissected specimens of tissue. It can also be combined with immunohistochemical labeling of recorded cells

Characterization of the colonic response to bisacodyl in children with treatment-refractory constipation

Background: Colonic manometry with intraluminal bisacodyl infusion can be used to assess colonic neuromuscular function in children with treatment‐refractory constipation. If bisacodyl does not induce high‐amplitude propagating contractions (HAPCs), this can be an indication for surgical intervention. A detailed characterization of the colonic response to intraluminal bisacodyl in children with constipation may help to inform clinical interpretation of colonic manometry studies. / Methods: Studies were performed in five pediatric hospitals. Analysis included identification of HAPCs, reporting HAPCs characteristics, and an area under the curve (AUC) analysis. Comparisons were performed between hospitals, catheter type, placement techniques, and site of bisacodyl infusion. / Results: One hundred and sixty‐five children were included (median age 10, range 1‐17 years; n = 96 girls). One thousand eight hundred and ninety‐three HAPCs were identified in 154 children (12.3 ± 8.8 HAPCs per child, 0.32 ± 0.21 HAPCs per min; amplitude 113.6 ± 31.5 mm Hg; velocity 8.6 ± 3.8 mm/s, propagation length 368 ± 175 mm). The mean time to first HAPC following bisacodyl was 553 ± 669 s. Prior to the first HAPC, there was no change in AUC when comparing pre‐ vs post‐bisacodyl (Z = −0.53, P = .60). The majority of HAPCs terminated in a synchronous pressurization in the rectosigmoid. Defecation was associated with HAPCs (χ 2(1)=7.04, P < .01). Site of bisacodyl administration, catheter type, and hospital location did not alter the response. / Conclusions and Inferences: Intraluminal bisacodyl induced HAPCs in 93% of children with treatment‐refractory constipation. The bisacodyl response is characterized by ≥1 HAPC within 12 minutes of infusion. The majority of HAPCs terminate in a synchronous pressurization in the rectosigmoid. Optimal clinical management based upon colonic manometry findings is yet to be determined

Extrinsic primary afferent signalling in the gut

Visceral sensory neurons activate reflex pathways that control gut function and also give rise to important sensations, such as fullness, bloating, nausea, discomfort, urgency and pain. Sensory neurons are organised into three distinct anatomical pathways to the central nervous system (vagal, thoracolumbar and lumbosacral). Although remarkable progress has been made in characterizing the roles of many ion channels, receptors and second messengers in visceral sensory neurons, the basic aim of understanding how many classes there are, and how they differ, has proven difficult to achieve. We suggest that just five structurally distinct types of sensory endings are present in the gut wall that account for essentially all of the primary afferent neurons in the three pathways. Each of these five major structural types of endings seems to show distinctive combinations of physiological responses. These types are: 'intraganglionic laminar' endings in myenteric ganglia; 'mucosal' endings located in the subepithelial layer; 'muscular–mucosal' afferents, with mechanosensitive endings close to the muscularis mucosae; 'intramuscular' endings, with endings within the smooth muscle layers; and 'vascular' afferents, with sensitive endings primarily on blood vessels. 'Silent' afferents might be a subset of inexcitable 'vascular' afferents, which can be switched on by inflammatory mediators. Extrinsic sensory neurons comprise an attractive focus for targeted therapeutic intervention in a range of gastrointestinal disorders.Australian National Health and Medical Research Counci

For whom and under what circumstances do school-based energy balance behavior interventions work? Systematic review on moderators

The aim of this review was to systematically review the results and quality of studies investigating the moderators of school-based interventions aimed at energy balance-related behaviors. We systematically searched the electronic databases of Pubmed, EMBASE, Cochrane, PsycInfo, ERIC and Sportdiscus. In total 61 articles were included. Gender, ethnicity, age, baseline values of outcomes, initial weight status and socioeconomic status were the most frequently studied potential moderators. The moderator with the most convincing evidence was gender. School-based interventions appear to work better for girls than for boys. Due to the inconsistent results, many studies reporting non-significant moderating effects, and the moderate methodological quality of most studies, no further consistent results were found. Consequently, there is lack of insight into what interventions work for whom. Future studies should apply stronger methodology to test moderating effects of important potential target group segmentations

Functional GABAB receptors are present in guinea pig nodose ganglion cell bodies but not in peripheral mechanosensitive endings

The effects of the GABAB-selective agonist baclofen were studied on guinea pig nodose ganglion neurones using grease gap and intracellular recording techniques, and on peripheral mechanosensitive endings in the guinea pig oesophagus and stomach with extracellular recordings. GABA dose-dependently reduced the amplitude of the compound action potential of C-type neurones (C spikes, EC50 = 30.9 microM), which was prevented by the GABAA antagonist bicuculline (10 microM). The GABAB agonist baclofen (1-300 microM) did not produce any significant effect on the amplitude of C spikes. In microelectrode studies, baclofen (100 microM) evoked hyperpolarisation (by 2.53 +/- 0.51 mV, n = 6, N = 5) in a subset of nodose neurones (6 out of 26, N = 18). In seven out of eight neurones (N = 8) with a slow after-hyperpolarisation following action potentials, baclofen significantly inhibited its amplitude by 19 +/- 4% (n = 7, p < 0.05). GABA (100 microM) evoked a depolarisation of 9.3 +/- 2.4 mV (10 nodose neurones, N = 9, p < 0.05) associated with a decrease in input impedance of 49 +/- 12% (N = 4, p < 0.05). Baclofen (100-200 microM) did not affect either spontaneous or stretch-evoked firing of distension-sensitive vagal mechanoreceptors of the guinea pig oesophagus and stomach but did inhibit mechanoreceptors in the ferret oesophagus. Antibodies to GABAB receptor 1a splice variants labelled most of the neurones and numerous fibres in the guinea pig nodose ganglion while antibodies to GABAB receptor 1b splice variants stained only nerve cell bodies. There were numerous nerve fibres showing GABAB receptor 1a- and 1b-like immunoreactivity in the myenteric plexus in the guinea pig oesophagus and stomach but not in anterogradely labelled extrinsic vagal nerve fibres. The result indicates that most guinea pig C-type nodose ganglion neurones have GABAB receptors on their cell bodies but their density on distension-sensitive peripheral endings is too low to allow modulation of mechanotransduction. There is a significant species-dependent difference in the expression of GABAB receptors on peripheral vagal mechanosensitive endings