Three-Dimensional-Printed Electrochemical Sensor for Simultaneous Dual Monitoring of Serotonin Overflow and Circular Muscle Contraction.

Serotonin (5-HT) is a key signaling molecule within the mucosal epithelium of the intestinal wall and has been shown to be an important modulator of motility. At present, no single approach has been established for simultaneous dual measurement of 5-HT overflow and circular muscle contraction. We developed a 3D-printed carbon black/polylactic acid (PLA) electrochemical sensor, which had a geometry suitable for ex vivo measurement in the anorectum. The device was characterized for sensitivity and stability for 5-HT measurements as well as suitability for accurate tracking of anorectal contractions. The 3D-printed electrochemical sensor had a linear range in physiological concentrations of 5-HT (1-10 µM) present within the intestinal tract and a limit of detection of 540 nM. The sensor was stable for 5-HT measurement following ex vivo tissue measurements. There was a signficant correlation in the amplitude and duration of individual contractions when comparing the measurements using an isometric force transducer and 3D-printed electrochemical sensor. Finally, in the presence of 1 µM fluoxetine, the sensor was able to monitor a reduction in contractility as well as an increase in 5-HT overflow as predicted. Overall, the 3D-printed sensor has the ability to conduct dual simultaneous measurements of 5-HT overflow and contractility. This single device will have significant potential for clinical measurements of anorectum function and signaling that can direct therapeutic management of patients with bowel disorders.

Elucidating the genetic basis of crystalline biofilm formation in Proteus mirabilis.

Proteus mirabilis forms extensive crystalline biofilms on urethral catheters that occlude urine flow and frequently complicate the management of long-term-catheterized patients. Here, using random transposon mutagenesis in conjunction with in vitro models of the catheterized urinary tract, we elucidate the mechanisms underpinning the formation of crystalline biofilms by P. mirabilis. Mutants identified as defective in blockage of urethral catheters had disruptions in genes involved in nitrogen metabolism and efflux systems but were unaffected in general growth, survival in bladder model systems, or the ability to elevate urinary pH. Imaging of biofilms directly on catheter surfaces, along with quantification of levels of encrustation and biomass, confirmed that the mutants were attenuated specifically in the ability to form crystalline biofilms compared with that of the wild type. However, the biofilm-deficient phenotype of these mutants was not due to deficiencies in attachment to catheter biomaterials, and defects in later stages of biofilm development were indicated. For one blocking-deficient mutant, the disrupted gene (encoding a putative multidrug efflux pump) was also found to be associated with susceptibility to fosfomycin, and loss of this system or general inhibition of efflux pumps increased sensitivity to this antibiotic. Furthermore, homologues of this system were found to be widely distributed among other common pathogens of the catheterized urinary tract. Overall, our findings provide fundamental new insight into crystalline biofilm formation by P. mirabilis, including the link between biofilm formation and antibiotic resistance in this organism, and indicate a potential role for efflux pump inhibitors in the treatment or prevention of P. mirabilis crystalline biofilms.

Lessons Learnt from Managing Orthopaedic Trauma During the First Wave of the COVID-19 Pandemic at a UK District General Hospital.

Background: The Coronavirus disease (COVID-19) pandemic has contributed to over 1,000,000 deaths worldwide. Hospitals responded by expanding services to accommodate the forecasted rise in COVID-19-related admissions. We describe the effects these changes had on management of orthopaedic trauma and patient outcomes at a district general hospital in Southern England. Methods: Data were extrapolated retrospectively from two separate 6-week periods in 2019 and 2020 (1st April-13th May) using electronic records of patients referred to the orthopaedic team. Soft tissue injuries were included where a confirmed diagnosis was made with radiological evidence. Patients were excluded if no orthopaedic intervention was required. Data were compared between the two time periods. Results: There were fewer attendances to hospital in 2020 compared with 2019 (178 vs. 328), but time from presentation to surgery significantly increased in 2020 (2.94 days vs. 4.91 days, p = 0.009). There were fewer operative complications in 2020 (36/145 vs. 11/88, p < 0.001). However, ordinal logistic regression analysis found a significantly greater complication severity in 2020 including death (p = 0.039). Complication severity was unrelated to COVID-19 status. Conclusions: Restructuring of orthopaedic services in response to the COVID-19 pandemic has been associated with significant delays to surgery and higher post-operative complication severity. Our results demonstrate the need for fast-track emergency operative orthopaedic services in UK district general hospitals whilst the COVID-19 pandemic continues.

Effect of colchicine on the uptake of prolactin and insulin into Golgi fractions of rat liver.

In previous studies we have shown that 125I-labeled prolactin is taken up by a receptor-dependent process and concentrated in an intact form in Golgi elements from female rat liver (J. Biol. Chem., 1979, 254:209-214). In this study we have examined the effect of colchicine on this uptake process into Golgi elements. Colchicine [25 mumol (10 mg)/100 gm body wt] was injected intraperitoneally in adult female rats, and hepatic Golgi fractions were prepared at 1, 2, and 3 h postinjection. The enzyme recoveries and morphological appearance of fractions from colchicine-treated and control (alcohol alone) animals were similar. At times greater than 1 h after colchicine there was a marked (greater than 60%) inhibition of uptake of 125I-ovine prolactin (125I-oPRL) into Golgi light and intermediate fractions but no inhibition of uptake into Golgi heavy and plasmalemma elements. At times from 2 to 45 min postinjection, 125I-oPRL was extracted from Golgi elements and found to be largely intact as judged by rebinding to receptors. The inhibitory effect of colchicine was seen at doses ranging from 0.25 mumol to 25 mumol/100 g body wt. Vincristine also inhibited 125I-oPRL uptake into the Golgi light and intermediate fractions but lumicolchicine had no inhibitory effect. There was a smaller effect of colchicine both at early (1 h) and later (3 h) times on the extent and pattern of 125I-insulin uptake. Colchicine treatment did not produce a significant change in lactogen receptor levels in the Golgi fractions. These results demonstrate that colchicine treatment inhibited the transfer of prolactin into Golgi vesicular elements. The much smaller effect on insulin uptake suggests that there may be differences in the manner in which the two hormones are handled in the course of internalization.

Effect of colchicine on internalization of prolactin in female rat liver: an in vivo radioautographic study.

Binding and internalization of 125I-ovine prolactin into hepatocytes of female rats was visualized by the in vivo radioautographic method (Bergeron, J. J. M., G. Levine, R. Sikstrom, D. O'Shaughnessey, B. Kopriwa, N. J. Nadler, and B. I. Posner, 1977, Proc. Natl. Acad. Sci. USA, 745:051-5055). Receptor-mediated internalization of label was observed into lipoprotein-filled vesicles in the Golgi/bile canalicular region of the hepatocyte. Colchicine treatment had no effect on the internalization of label into the lipoprotein-filled vesicles. However, the location of the radio-labeled lipoprotein-filled vesicles was altered from the Golgi/bile canalicular region to subsinusoidal. Radioactive content of hepatocytes decreased as a function of time after injection of 125I-prolactin; however, colchicine treatment markedly retarded this loss of label. Subcellular fractionation experiments indicated that colchicine treatment led to decreased levels of 125I-prolactin accumulation in microsomes but augmented the accumulation of label in the L fraction. It is concluded that in normal female rats prolactin is internalized into lipoprotein-filled vesicles in the Golgi region before degradation of the hormone. Colchicine treatment accumulates labeled lipoprotein-containing vesicles in a subsinusoidal region and retards hormone catabolism. The labeled vesicles observed after colchicine treatment may correspond to the unique vesicles previously observed in the L fraction and found to be enriched in prolactin receptors (Khan, M. N., B. I. Posner, A. K. Verma, R. J. Khan, and J. J. M. Bergeron, 1981, Proc. Natl. Acad. Sci. USA, 78:4980-4981).

Changes in murine anorectum signaling across the life course.

BACKGROUND: Increasing age is associated with an increase in the incidence of chronic constipation and fecal impaction. The contribution of the natural aging process to these conditions is not fully understood. This study examined the effects of increasing age on the function of the murine anorectum. METHODS: The effects of increasing age on cholinergic, nitrergic, and purinergic signaling pathways in the murine anorectum were examined using classical organ bath assays to examine tissue function and electrochemical sensing to determine age-related changes in nitric oxide and acetylcholine release. KEY RESULTS: Nitrergic relaxation increased between 3 and 6 months, peaked at 12 months and declined in the 18 and 24 months groups. These changes were in part explained by an age-related decrease in nitric oxide (NO) release. Cholinergic signaling was maintained with age by an increase in acetylcholine (ACh) release and a compensatory decrease in cholinesterase activity. Age-related changes in purinergic relaxation were qualitatively similar to nitrergic relaxation although the relaxations were much smaller. Increasing age did not alter the response of the anorectum smooth muscle to exogenously applied ACh, ATP, sodium nitroprusside or KCl. Similarly, there was no change in basal tension developed by the anorectum. CONCLUSIONS AND INFERENCES: The decrease in nitrergic signaling with increasing age may contribute to the age-related fecal impaction and constipation previously described in this model by partially obstructing defecation.

Mucosal serotonin overflow is associated with colonic stretch rather than phasic contractions.

BACKGROUND: Many studies have shown that mucosal serotonin (5-HT) is associated with motility, however, recently there have been some questions to the precise role of this transmitter. The majority of studies have focused on understanding the role of mucosal 5-HT on colonic migratory motor complexes, but very few studies have been carried out to understand how 5-HT release may be associated with other motility patterns. METHODS: Using distal colon segments from C57BL/6J mice, mucosal 5-HT overflow was monitored using amperometry while applying tension in longitudinal or circular directions to stretch the tissue. KEY RESULTS: Phasic and basal 5-HT levels were not associated with the strength of phasic contractions, while being altered using scopolamine and L-NNA. There was a significant increase in mucosal 5-HT with longitudinal and circular muscle stretch. A greater applied force was needed to activate 5-HT release in the circular muscle. In the longitudinal muscle, 5-HT levels increased with stretch until 3 mN, after which the levels returned back to baseline. This stretch-evoked 5-HT overflow was inhibited by transient receptor potential A1 (TRPA1) agonist, 30 µM ruthenium red in both circular and longitudinal muscle preparations. The decreased 5-HT overflow after 3 mN of tension was reversed using a 5-HT4 antagonist 100 nM GR113808. CONCLUSIONS & INFERENCES: Our findings show a relationship between colonic stretch and mucosal 5-HT overflow, while no relationship is observed with phasic colonic contractions. Such findings provide more insight into the role of mucosal 5-HT in influencing the pattern of colonic motility to diversify fecal propulsion.

Electrochemical sensor for the detection of multiple reactive oxygen and nitrogen species from ageing central nervous system homogenates.

Reactive oxygen and nitrogen species (ROS/RNS) have been widely implicated in the ageing process and various approaches exist for monitoring these species in biological tissues. These approaches at present are limited to monitoring either a single pro-oxidant species or total pro-oxidant levels and therefore provide limited insight into the range of pro-oxidant species and their relative proportions in the ageing process. We have utilised a sensor that allows us to simultaneously monitor hydrogen peroxide, peroxynitrite, nitric oxide and nitrite. Using CNS homogenates from the pond snail, Lymnaea, we were able to show that levels of these ROS/RNS increased between young and old CNS homogenates and were different in various aged CNS regions.

Management of root-knot nematode (Meloidogyne incognita) in bottle gourd using different botanicals in pots.

A pot experiment was conducted to study the efficacy of different botanicals in varying doses for management of root-knot nematode, M. incognita in bottle gourd. The results exhibited that madar (Calotropis procera) and neem (Azadirachta indica) leaves application proved to be more effective in improving plant growth characters and reducing root-knot index and final nematode population. Among the doses tested, higher dose of 1.5 % (w/w) was more effective than lower ones.

Insulin-like growth factor-binding proteins in hypophysectomized rat liver: characterization and subcellular localization.

We have characterized binding proteins for insulin-like growth factors (IGFs) in hepatic subcellular fractions and in the washed supernatants of these fractions in normal and hypophysectomized (hypox) rats. In the course of assessing IGF-II-binding sites on rat liver microsomes, we observed that [125I] IGF-II binding to the microsomal membranes of hypox rats was much lower than that in normal rats. Paradoxically, binding increased in hypox animals at low concentrations (0.5-5 ng/ml) of unlabeled IGF-II. After resuspension and centrifugation (washing) of the microsomes, no difference was found in [125I]IGF-II binding to hypox vs. normal microsomes. However, the binding of [125I]IGF-II to the washing supernatant (SN) from hypox rat microsomes was greater than binding to that from normal animals. Binding to SN was inhibited by unlabeled IGF-II in a dose-dependent manner. Scatchard analyses indicated that the affinity constant for binding by hypox SN was higher than that of normal SN and the microsomal fractions of both hypox and normal rats. After further subfractionation of the liver, no binding activity was found in SN from plasmalemma, whereas it was about 20% of input counts per min of [125I]IGF-II in SN from combined Golgi-endosome fractions of hypox rat liver. We next compared IGF-binding moieties in microsomal SN with those in plasma using cross-linking of [125I]IGF-II followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In normal rat plasma, we observed the presence of 42K, 39K, 31K, and 27K binding complexes. In hypox rat plasma only a 42-39K doublet was found. In the SN of normal rat microsomes, the predominant complex migrated at 39K and was distinguishable only after acidification. In the SN of hypox rat microsomes, the 42K complex was predominant, with a minor 34K complex. These studies have identified IGF-binding moieties in hepatic tissues, particularly in hepatic vesicular elements, which interfere in the binding of IGF-II to membrane receptors. Their presence in these receptor-rich elements may influence IGF binding to intracellular receptors and, hence, the biological activity of the peptide.

Pharmacokinetics and saturable renal tubular secretion of zidovudine in rats.

The purpose of this study was to assess the effects of dose on the pharmacokinetics of zidovudine (3'-azido-3'-deoxythymidine; AZT) in rats. Zidovudine (AZT) was administered intravenously at doses of 10, 50, 100, and 250 mg/kg. Plasma and urine AZT concentrations were determined by HPLC. Plasma AZT concentrations declined rapidly with a terminal half-life ranging from 0.76 h at a dose of 10 mg/kg to 1.58 h at 250 mg/kg. Total clearance (CLT) was similar at the doses of 10 and 50 mg/kg, with values of 2.80 and 2.73 L/h/kg, respectively. However, there was a trend toward nonlinearity at the dose of 100 mg/kg (CLT = 2.13 L/h/kg) and a significant decrease in CLT (1.22 L/h/kg) at the dose of 250 mg/kg. Nonrenal clearance remained unaffected by dose with a mean value of 0.98 L/h/kg. Renal clearance (CLR) was similar at the doses of 10 and 50 mg/kg, with values of 1.89 and 1.37 L/h/kg, respectively. However, significant decreases in CLR were observed at the doses of 100 (CLR = 1.30 L/h/kg) and 250 mg/kg (CLR = 0.57 L/h/kg). The maximum transport capacity (Tmax) and the Michaelis-Menten constant (Km) for renal tubular secretion obtained after simultaneously fitting plasma concentration-time profiles at the four doses to a renal clearance model were 215.5 +/- 82.1 mg/h and 119.3 +/- 80.5 mg/L, respectively, thereby yielding an unbound secretory intrinsic clearance (CLus,int) of 1.81 L/h. The high Tmax and Km values account for the high CLR of AZT and explain the linearity of CLR over a wide range of AZT plasma concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of CCK cholescintigraphy to differentiate choledochal cyst from gallbladder.

A 17-year-old girl presented with right upper quadrant pain and was found to have a subhepatic cyst by ultrasound and CT. A DISIDA scan showed prompt filling of both the gallbladder and a very dilated common bile duct consistent with a choledochal cyst. Following intravenous administration of cholecystokinin, there was immediate emptying of the gallbladder into the cyst. Quantitative cholecystokinin cholescintigraphy may be a useful adjunct in the differentiation of choledochal cyst from gallbladder activity.

Mucosal adenosine triphosphate mediates serotonin release from ileal but not colonic guinea pig enterochromaffin cells.

BACKGROUND: Mechanical stimulation of the mucosal epithelium results in increased serotonin (5-HT) release from enterochromaffin (EC) cells. Little is known about how this process varies in different regions of the intestinal tract; however, purines are felt to play a role. We studied the relationship between mechanical stimulation, adenosine triphosphate (ATP), and 5-HT release from ileal and colonic mucosal tissue. METHODS: Amperometric recordings of ATP and 5-HT were carried out using an ATP biosensor and boron-doped diamond microelectrode. Levels of extracellular ATP and 5-HT were monitored using high performance liquid chromatography. KEY RESULTS: Under basal conditions, 5-HT levels were significantly decreased in the ileum (p < 0.001) but not the colon in the presence of the P2 antagonist suramin (100 µM). Ecto-ATPase inhibitor ARL67156 (10 µM) elevated ATP levels in the ileum and colon (both p < 0.001), but only 5-HT levels in the ileum (p < 0.001). Exogenous ATP increased 5-HT release in the presence of tetrodotoxin in the ileum (p < 0.001), but had not effect in the colon. Mechanical stimulation increased levels of 5-HT in the ileum (p < 0.001) and colon (p < 0.01), but levels returned to baseline in the presence of suramin and MRS2179 in the ileum. The onset of 5-HT release was delayed following mechanical stimulation. The rise time of the ATP response was quicker than that of 5-HT during mechanical stimulation. CONCLUSIONS & INFERENCES: During mechanical stimulation of the mucosal epithelium, ATP mediates 5-HT release from EC cells in the ileum, but not the colon. Mucosal 5-HT signaling following mechanical stimulation is varied in different regions of the intestinal tract.

Myenteric neuron numbers are maintained in aging mouse distal colon.

BACKGROUND Age-associated myenteric neuronal loss has been described in several species. In some studies,cholinergic neurons have been reported to be selectively vulnerable, whereas nitrergic neurons are spared. Aging of the mouse enteric nervous system(ENS) and the subtypes of mouse myenteric neurons that may be lost have been little studied. We therefore investigated changes in the numbers of total neurons and two neuronal subpopulations in the mouse distal colon during aging. METHODS Wholemount preparations from 3­4-, 12­13-, 18­19-, and 24­25-month-old C57BL/6 mice were double immunolabeled with HuC/D antibody to identify the total neuronal population and antisera to either calbindin or neuronal nitric oxide synthase (nNOS) to identify myenteric neuronal subpopulations. Samples were analyzed by confocal microscopy. New procedures were employed to ensure unbiased counting and to correct for changes in gut dimensions with age and stretch during sample preparation. The density of nerve fibers in the tertiary plexus was also studied. KEY RESULTS No significant change in numbers of total neurons or of either subpopulation with age was measured, but because of gut growth, the density of myenteric neurons decreased between 3­4 and 12­13 months. The density of nNOS-immunoreactive nerve fibers in the tertiary plexus increased significantly with age, up to 18­19 months. Numerous swollen processes of CB and nNOS-immunoreactive neurons were observed in 18­19- and 24­25-month-old animals. Conclusions &Inferences These results indicate that aging does not result in a loss of myenteric neurons in mouse distal colon at the ages studied, although neurodegenerative changes, which may impact on neuronal function, do occur.

Visceral hypersensitivity in female but not in male serotonin transporter knockout rats.

BACKGROUND: Visceral hypersensitivity occurs in irritable bowel syndrome (IBS), particularly in women. Serotonin signaling, including reduced serotonin transporter (SERT) expression, may be disrupted in IBS patients. We studied SERT gene knockout (KO) rats to determine if they exhibited sex-related alterations in visceral sensitivity. METHODS: We measured serotonin in the colonic mucosa using HPLC and amperometric microelectrode techniques. Visceral sensitivity was assessed using the electromyographic visceromotor response (VMR) in response to colorectal balloon distention (CRD). We studied the electrophysiologic properties of colon projecting sensory neurons in vitro using whole-cell recordings. KEY RESULTS: Mucosal serotonin levels were not different among male and female WT and SERT KO rats. Serotonin oxidation currents in vitro were larger (P < 0.05) in tissues from male and female SERT KO compared with WT rats. Oxidation currents in male and female WT, but not SERT KO, rats were increased (P < 0.05) by the SERT inhibitor fluoxetine (1 µmol L(-1) ). The VMR to CRD was increased in female but not in male SERT KO rats (P < 0.05); this response varied with the estrous cycle. Colon projecting sensory neurons from female SERT KO rats fired more action potentials compared with neurons from female WT rats. There were no differences in action potential firing in neurons from male WT and SERT KO rats. CONCLUSIONS & INFERENCES: Increased colonic extracellular serotonin in female SERT KO rats is associated with visceral hypersensitivity and hyperexcitability of colon projecting sensory neurons. The SERT KO rat is a model for studying interactions between serotonin, sex and visceral sensation.

Changes in the innervation of the mouse internal anal sphincter during aging.

BACKGROUND: The innervation of the mouse internal anal sphincter (IAS) has been little studied, and how it changes during aging has not previously been investigated. The aim of this study was therefore to characterize the distribution and density of subtypes of nerve fibers in the IAS and underlying mucosa in 3-, 12- to 13-, 18- and 24- to 25-month-old male C57BL/6 mice. METHODS: Nerve fibers were immunolabeled with antibodies against protein gene product 9.5 (PGP9.5), neuronal nitric oxide synthase (nNOS), vasoactive intestinal polypeptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP), and calretinin (CR). Immunoreactivity in nerve fibers in the circular muscle and mucosa was quantified using Image J software. KEY RESULTS: In young adult (3 month) mice, nNOS-immunoreactive (IR) nerve fibers were densely distributed in the circular muscle, but relatively few in the mucosa; VIP-IR nerve fibers were abundant in the circular muscle and common in the mucosa; SP-IR nerve fibers were common in circular muscle and mucosa; CGRP- and CR-IR nerve fibers were dense in mucosa and sparse in circular muscle. The density of PGP9.5 immunoreactivity (IRY) was not significantly reduced with age, but a significant reduction in nNOS-IRY and SP-IRY with age was found in the IAS circular muscle. Neuronal nitric oxide synthase-, VIP-, and SP-IRY in the anal mucosa were significantly reduced with age. CGRP-IRY in both circular muscle and mucosa was increased in 18-month-old animals. CONCLUSIONS & INFERENCES: The density of immunoreactivity of markers for some types of IAS nerve fibers decreases during aging, which may contribute to age-related ano-rectal dysfunction.

Electroanalytical approaches to study signaling mechanisms in the gastrointestinal tract.

Electroanalytical techniques over the past few years have been applied to study real-time release of various signaling molecules in the GI tract. These approaches have become highly attractive as they provide dynamic spatial information on the amount of signaling molecules released. Although these approaches are relatively new to the field, the studies to date have provided useful insights into the alterations in signaling mechanisms during maturation, obesity and in a model of colitis. New methods and techniques have also allowed the possibility to obtain information on the signaling process and future developments will provide a wide diverse array of information that will be of benefit to all researchers in the field of gastroenterology. This review focuses on the types of techniques utilized, the information they can provide, their potential advantages and disadvantages in monitoring signaling processes in the gastrointestinal tract, the existing scientific studies that have utilized electroanalytical methods to date and the future potential impact of such approaches.

Translation of flecainide- and mexiletine-induced cardiac sodium channel inhibition and ventricular conduction slowing from nonclinical models to clinical.

INTRODUCTION: Nonclinical in vivo models used for cardiovascular safety testing have not previously been studied for their sensitivity for detection of conduction slowing resulting from cardiac sodium channel block. The goal of this study was to examine the sensitivity of in vivo models to cardiac sodium channel block, and translation of the effect from in vitro to in vivo models using sodium channel inhibitors flecainide and mexiletine; flecainide, but not mexiletine is commonly associated with QRS complex prolongation in humans. METHODS: Inhibition of cloned cardiac sodium channels (hNav1.5) was studied using the IonWorks platform. Conduction slowing was measured in vitro in the rabbit isolated ventricular wedge (RVW) and in vivo in the conscious telemetered rat and dog, and anaesthetised dog. RESULTS: Flecainide and mexiletine inhibited hNav1.5 channels with IC50 values of 10.7 and 67.2 µM respectively. In the RVW, QRS was increased by flecainide at 60 bpm, and at 120bpm, there was an increased effect of both drugs. In conscious rats, flecainide significantly increased QRS complex duration; mexiletine had no significant effect, but there was an increase at the highest dose in 4/6 animals. QRS complex was increased by flecainide and mexiletine in anaesthetised dogs but this was not statistically significant; in conscious dog, only flecainide produced a significant increase in QRS complex. DISCUSSION: When compared to clinical data, effects of flecainide and mexiletine in RVW and conscious dog compared well with effects in patients and healthy volunteers in terms of sensitivity. The anaesthetised dog was least sensitive for detection of changes in QRS. All assays showed some differentiation between the expected conduction slowing activity of flecainide and mexiletine. Based on these data, RVW and conscious dog were most predictive for effects of compounds on QRS complex and cardiac conduction.

Inhibitory neuromuscular transmission to ileal longitudinal muscle predominates in neonatal guinea pigs.

BACKGROUND: Inhibitory neurotransmission to the longitudinal muscle is more prominent in the neonatal than in the adult guinea pig ileum. METHODS: Inhibitory neuromuscular transmission was investigated using in vitro ileal longitudinal muscle myenteric plexus (LMMP) preparations made from neonatal (< or =48 h postnatal) and adult ( approximately 4 weeks postnatal) guinea pigs. KEY RESULTS: Amperometric measurements of nicotine-induced nitric oxide (NO) release (measured as an oxidation current) from myenteric ganglia revealed larger currents in neonatal (379 +/- 24 pA) vs adult (119 +/- 39 pA, P < 0.05) tissues. Nicotine-induced oxidation currents were blocked by the nitric oxide synthase (NOS) inhibitor, nitro-l-arginine (NLA, 100 micromol L(-1)). Nicotine-induced, NLA-sensitive oxidation currents could be detected in the tertiary plexus of neonatal but not adult tissues. Immunohistochemistry demonstrated stronger NOS immunoreactivity in neonatal compared with adult myenteric ganglia. Western blot studies revealed higher levels of NOS in neonatal compared with adult LMMP. Cell counts revealed that the total number of myenteric neurons in the small intestine was greater in adults than in neonatal guinea pigs, however, the ratio of NOS : Calbindin neurons was significantly higher in neonatal compared with adult tissues. CONCLUSIONS & INFERENCES: Nitric oxide signaling to the longitudinal muscle is stronger in neonatal compared with adult guinea pig ileum. Nitric oxide synthase-containing neurons are diluted postnatally by cholinergic and other, as yet unidentified neuronal subtypes.

Electrochemical monitoring of nitric oxide released by myenteric neurons of the guinea pig ileum.

Nitric oxide (NO) released by myenteric neurons in isolated segments of guinea pig ileum was monitored in vitro using continuous amperometry. NO was detected as an oxidation current recorded with a boron-doped diamond microelectrode held at 1 V vs a Ag|AgCl reference electrode. This potential was sufficient to oxidize NO. Longitudinal muscle-myenteric plexus (LMMP) and circular muscle strip preparations were used. In the LMMP preparation, NO release was evoked by superfusion of 1 mumol L(-1) nicotine, which activates nicotinic acetylcholine receptors expressed by myenteric neurons and myenteric nerve endings. The oxidation current was ascribed to NO based on the following observations: (i) no response was detected at less positive potentials (0.75 V) at which only catecholamines and biogenic amines are oxidized, (ii) the current was abolished in the presence of the nitric oxide synthase antagonist, N-nitro-l-arginine (l-NNA) and (iii) oxidation currents were attenuated by addition of the NO scavenger, myoglobin, to the superfusing solution. In the LMMP preparation, stimulated release produced a maximum current that corresponded nominally to 46 nmol L(-1) of NO. The oxidation currents decreased to 10 and 2 nmol L(-1), respectively, when the tissue was perfused with tetrodotoxin and l-NNA. Oxidation currents recorded from circular muscle strips (stimulated using nicotine) were threefold larger than those recorded from the LMMP. This study shows that NO release can be detected from various in vitro preparations of the guinea pig ileum using real-time electroanalytical techniques.