Kim Nichols

Nitric oxide synthase distribution in the rat intestine: A histochemical analysis

BACKGROUND Nitric oxide is an inhibitory transmitter of nonadrenergic, noncholinergic neurons and is purported to be an endothelium-derived relaxant-type factor in the mammalian gut. This study aimed to provide a complete report on the distribution of NO synthase in the rat small and large intestine. METHODS NO synthase was visualized histochemically through this enzymes reduced nicotinamide adenine dinucleotide phosphate diaphorase activity and the distribution of staining within the gut wall. RESULTS The presence of NO synthase activity in myenteric neurons and their efferents to the circular muscle was confirmed. The largest proportion of stained cells per ganglion was found in the ileum, and the smallest proportion was in the colon. Stained neural elements were also found within the submucosa throughout the intestine. Stained cells within the myenteric and submucous nerve plexi displayed both type I and type II morphologies, with the latter being more numerous. In addition to neural staining, submucosal arterioles showed a regular pattern of small patches of staining unrelated to any perivascular innervation. CONCLUSIONS These findings indicate an extensive neural and vascular localization of NO generation potential throughout the wall of the rat intestine, thus providing a structural basis for the functional diversity of NO.

Strategies to reduce medication errors with reference to older adults.

Background  In Australia, around 59% of the general population uses prescription medication with this number increasing to about 86% in those aged 65 and over and 83% of the population over 85 using two or more medications simultaneously. A recent report suggests that between 2% and 3% of all hospital admissions in Australia may be medication related with older Australians at higher risk because of higher levels of medicine intake and increased likelihood of being admitted to hospital. The most common medication errors encountered in hospitals in Australia are prescription/medication ordering errors, dispensing, administration and medication recording errors. Contributing factors to these errors have largely not been reported in the hospital environment. In the community, inappropriate drugs, prescribing errors, administration errors, and inappropriate dose errors are most common. Objectives  To present the best available evidence for strategies to prevent or reduce the incidence of medication errors associated with the prescribing, dispensing and administration of medicines in the older persons in the acute, subacute and residential care settings, with specific attention to persons aged 65 years and over. Search strategy  Bibliographic databases PubMed, Embase, Current contents, The Cochrane Library and others were searched from 1986 to present along with existing health technology websites. The reference lists of included studies and reviews were searched for any additional literature. Selection criteria  Systematic reviews, randomised controlled trials and other research methods such as non-randomised controlled trials, longitudinal studies, cohort or case-control studies, or descriptive studies that evaluate strategies to identify and manage medication incidents. Those people who are involved in the prescribing, dispensing or administering of medication to the older persons (aged 65 years and older) in the acute, subacute or residential care settings were included. Where these studies were limited, evidence available on the general patient population was used. Data collection and analysis  Study design and quality were tabulated and relative risks, odds ratios, mean differences and associated 95% confidence intervals were calculated from individual comparative studies containing count data where possible. All other data were presented in a narrative summary. Results  Strategies that have some evidence for reducing medication incidents are: •  computerised physician ordering entry systems combined with clinical decision support systems; •  individual medication supply systems when compared with other dispensing systems such as ward stock approaches; •  use of clinical pharmacists in the inpatient setting; •  checking of medication orders by two nurses before dispensing medication; •  a Medication Administration Review and Safety committee; and •  providing bedside glucose monitors and educating nurses on importance of timely insulin administration. In general, the evidence for the effectiveness of intervention strategies to reduce the incidence of medication errors is weak and high-quality controlled trials are needed in all areas of medication prescription and delivery.

Histochemical localization of nitric oxide-synthesizing neurons and vascular sites in the guinea-pig intestine

Laminar preparations of fixed segments of the guinea-pig intestine were examined for nitric oxide synthase activity using reduced nicotinamide adenine dinucleotide phosphate and nitroblue tetrazolium salt as substrates. Under conditions specific for detecting nitric oxide synthase-related diaphorase activity, a subpopulation of neural elements in the myenteric plexus, deep muscular plexus and submucosa were intensely stained. Intensely stained nerve fibres were distributed throughout the meshworks of the myenteric plexus and its innervation of the circular muscle, and in the submucosa within Henles plexus. Intensely stained nerve cells and their processes were evident in most myenteric ganglia but were rare in ganglia of Henles plexus. Stained ganglion cells comprised types I, II and VI of the morphologically defined enteric nerve cells. Stained neural elements were increasingly prevalent within successively more caudal segments of the intestine. In addition to neuronal staining, arterioles of the submucosal vascular network displayed distinct, punctate patches of staining distributed over their surface. Perivascular nerve fibre staining was absent. These results show nitric oxide synthase activity to be present within neurons and fibres of the major enteric nerve layers and within submucosal blood vessels throughout the guinea-pig small and large intestine.

Neural mechanisms underlying migrating motor complex formation in mouse isolated colon

Little is known about the intrinsic enteric reflex pathways associated with migrating motor complex (MMC) formation. Acetylcholine (ACh) mediates the rapid component of the MMC, however a non‐cholinergic component also exists. The present study investigated the possible role of endogenous tachykinins (TKs) in the formation of colonic MMCs and the relative roles of excitatory and inhibitory pathways. MMCs were recorded from the circular muscle at four sites (proximal, proximal‐mid, mid‐distal and distal) along the mouse colon using force transducers. The tachykinin (NK1 and NK2) receptor antagonists SR‐140 333 (250 nM) and SR‐48 968 (250 nM) reduced the amplitude of MMCs at all recording sites, preferentially abolishing the long duration contraction. Residual MMCs were abolished by the subsequent addition of atropine (1 μM). The neuronal nitric oxide synthase inhibitor, Nωnitro‐L‐arginine (L‐NOARG, 100 μM), increased MMC amplitude in the distal region, whilst reducing the amplitude in the proximal region. In preparations where MMCs did not migrate to the distal colon, addition of L‐NOARG resulted in the formation of MMCs. Subsequent addition of apamin (250 nM) or suramin (100 μM) further increased MMC amplitude in the distal region, whilst suramin increased MMC amplitude in the mid‐distal region. Apamin but not suramin reduced MMC amplitude in the proximal region. Subsequent addition of SR‐140 333 and SR‐48 968 reduced MMC amplitude at all sites. Residual MMCs were abolished by atropine (1 μM). In conclusion, TKs, ACh, nitric oxide (NO) and ATP are involved in the neural mechanisms underlying the formation of MMCs in the mouse colon. Tachykinins mediate the long duration component of the MMC via NK1 and NK2 receptors. Inhibitory pathways may be involved in determining whether MMCs are formed.

Productive Pedagogies: A Redefined Methodology for Analysing Quality Teacher Practice.

This paper identifies the ways in which the Productive Pedagogies framework has been refined as a research tool for evaluating classroom practice within a current study into issues of school reform in Queensland. Initially emerging from the landmark Queensland School Reform Longitudinal Study (1998–2001), the Productive Pedagogies has been taken up widely in Australia and internationally as both a research tool and metalanguage to support teachers to critically reflect on their practice. In this paper, following a brief description of the model’s four dimensions, we detail how we have addressed some methodological concerns in using and modifying the framework for the present study. In response to critiques by other researchers and debates within our own research team, we justify our use of the framework. To these ends, we present a refined methodology that addresses the importance of pedagogical process, substantiates the inclusion of particular items within the framework, supports a critical approach to issues of difference, includes students’ perspectives and recognises the significance of content knowledge in the assessment of quality pedagogy.

Immunopositive GABAergic neural sites display nitric oxide synthase-related NADPH diaphorase activity in the human colon

In the enteric nervous system, gamma-aminobutyric acid (GABA) is a transmitter of interneurons which are proposed to innervate excitatory and inhibitory motor neurons. Nitric oxide (NO) is a putative transmitter of enteric inhibitory motor nerves targeted by GABA. In addition, NO is synthesized by a variety of enteric nerves throughout the gut wall indicative of its potential to be a transmitter of other nerve types, including interneurons. We sought to determine if some populations of nitrergic neurons are interneurons in human infant colon. As enteric neural GABA is exclusive to interneurons, colocalization with NO synthase-related NADPH diaphorase was examined. GABA-transaminase (GABA-T) immunohistochemistry was used to identify GABAergic neurons and a histochemical protocol was used as a marker of neuronal NO synthase-related NADPH diaphorase activity in enteric layers. GABA-T immunoreactive neurons were seen in the ganglionated nerve networks of the myenteric and submucosal layers. GABA-T immunoreactive fibres were also present in the longitudinal and circular muscle layers. A subpopulation of GABA-T immunoreactive neurons within both the myenteric and submucosal ganglia express NO synthase-related activity. This colocalization extends further to a subpopulation of fibers within the muscle layers. These findings strongly suggest that in addition to its role in inhibitory motor neurons, NO may also be a transmitter of enteric interneurons.

Neurochemical characterization and distribution of enteric GABAergic neurons and nerve fibres in the human colon

GABA, somatostatin and enkephalin are neurotransmitters of enteric interneurons and comprise part of the intrinsic neural circuits regulating peristalsis. Within the relaxation phase of reflex peristalsis, nitric oxide (NO) is released by inhibitory motor neurons and perhaps enteric interneurons as well. Previously, we identified by GABA transaminase (GABA-T) immunohistochemistry, a subpopulation of GABAergic interneurons in the human colon which also contain NO synthase activity and hence produce NO. In this study, we have examined further the capacity for cotransmission within the GABAergic innervation in human colon. The expression of two important neuropeptides within GABAergic neurons was determined by combined double-labelled immunocytochemistry using antibodies for GABA-T, enkephalin and somatostatin, together with the demonstration of NO synthase-related NADPH diaphorase staining in cryosectioned colon. Both neuropeptides were found in GABAergic neurons of the colon. The evidence presented herein confirms the colocalization of NO synthase activity and GABA-T immunoreactivity in subpopulations of enteric neurons and further allows the neurochemical classification of GABAergic neurons of the human colon into three subsets: (i) neurons colocalizing somatostatin-like immunoreactivity representing about 40% of the GABAergic neurons, (ii) neurons colocalizing enkephalin-like immunoreactivity, about 9% of the GABAergic neurons and (iii) neurons colocalizing NO synthase activity, about 23% of the GABAergic neurons. This division of GABAergic interneurons into distinct subpopulations of neuropeptide or NO synthase containing cells is consistent with and provides an anatomical correlate for the pharmacology of these transmitters and the pattern of transmitter release during reflex peristalsis.

Neural sites of the human colon colocalize nitric oxide synthase-related NADPH diaphorase activity and neuropeptide Y

BACKGROUND/AIMS Nitric oxide and neuropeptide Y (NPY) exert similar biological actions in the mammalian intestine including modulation of food intake, blood flow, motility, and secretion. In addition, these substances coexist in submucosal secretomotor neurons of the rodent intestine. The aim of this study was to determine the relative disposition of elements displaying NPY immunoreactivity and NO synthase-related nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activity in the nerve networks of the human infant colon. METHODS Transverse and longitudinal sections, treated for immunohistofluorescent detection of NPY and then processed for NO synthase-related NADPH diaphorase histochemistry, were examined. RESULTS Neural elements containing NPY immunoreactivity and NO synthase-related activity were identified in the external muscle layers, myenteric plexus, and all nerve layers of the submucosa, including Henles plexus, the intermediate nerve layer, and Meissners plexus. Perivascular NPY-immunoreactive nerve fibers did not contain NO synthase activity. There were no nitrergic perivascular nerve fibers. NPY-immunoreactive endocrine cells in the mucosa did not display NO synthase-related activity. CONCLUSIONS These findings provide anatomical data indicating that NPY immunoreactivity and NO synthase-related activity are extensively colocalized in all layers of the human infant gut wall.

Representational Classroom Practices that Contribute to Students’ Conceptual and Representational Understanding of Chemical Bonding

Understanding bonding is fundamental to success in chemistry. A number of alternative conceptions related to chemical bonding have been reported in the literature. Research suggests that many alternative conceptions held by chemistry students result from previous teaching; if teachers are explicit in the use of representations and explain their content-specific forms and functions, this might be avoided. The development of an understanding of and ability to use multiple representations is crucial to students’ understanding of chemical bonding. This paper draws on data from a larger study involving two Year 11 chemistry classes (n = 27, n = 22). It explores the contribution of explicit instruction about multiple representations to students’ understanding and representation of chemical bonding. The instructional strategies were documented using audio-recordings and the teacher-researcher’s reflection journal. Pre-test–post-test comparisons showed an improvement in conceptual understanding and representational competence. Analysis of the students’ texts provided further evidence of the students’ ability to use multiple representations to explain macroscopic phenomena on the molecular level. The findings suggest that explicit instruction about representational form and function contributes to the enhancement of representational competence and conceptual understanding of bonding in chemistry. However, the scaffolding strategies employed by the teacher play an important role in the learning process. This research has implications for professional development enhancing teachers’ approaches to these aspects of instruction around chemical bonding.

[3H]GABA uptake and GABA localization in mucosal endocrine cells of the rat stomach and colon.

The aim of this study was to characterize the distribution of GABAergic cells in the rat gut mucosa. Thin and/or thick serial sections of segments of rat antrum and distal colon were treated for autoradiographic localization of sites of [3H]GABA (50 nM) high-affinity uptake, or GABA immunoreactivity. Dense accumulations of silver grains were localized to a discrete population of granulated mucosal cells. These appeared to be D-type endocrine cells. These gut regions also displayed strongly GABA-immunoreactive mucosal cells. These results confirm the presence of GABAergic cells in the rat antral mucosa, and reveal that [3H]GABA is accumulated by mucosal endocrine cells in the rat colon.