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M J Neal

Publications and source records attributed to M J Neal.

At least 37 records · Page 2Linked to original sources
PubMed1997

Inhibition by nociceptin of the light-evoked release of ACh from retinal cholinergic neurones.

The retina possesses cholinergic amacrine cells which release acetylcholine (ACh) in response to flickering light. Using an eye-cup preparation in anaesthetized rabbits we found that when the retina was exposed to nociceptin, the light-evoked release of ACh was reduced in a concentration-dependent manner (IC50 = 100 nM), the maximum effect being 60% inhibition. Opioid receptors were not involved in the inhibitory effect of nociceptin because its action was not blocked by naloxone (1 microM) and furthermore mu-opioids enhanced the light-evoked release of ACh. Using rabbit retina homogenates we found that the retina possessed a substantial number of high-affinity binding sites for [3H]-nociceptin indicating the presence of ORL1-receptors. Since [des-Phe1]-nociceptin, which has no affinity for the ORL1-receptor, had no effect on the light-evoked release of ACh it is unlikely that the action of nociceptin was simply non-specific. We conclude that the inhibitory effect of nociceptin on retinal ACh release involves activation of the ORL1 receptors.

Acetylcholine↗
PubMed1997

Rescue of photoreceptor function by AAV-mediated gene transfer in a mouse model of inherited retinal degeneration.

Knowledge of the mutations leading to inherited retinal degenerations provides a foundation for the development of somatic gene therapy in which potentially corrective genes are transferred to the target photoreceptor cells. Towards this end, we have evaluated the efficacy of a recombinant adeno-associated virus (AAV) vector to deliver and express the correct form of the cGMP phosphodiesterase-beta (PDE-beta) gene in the retinas of rd mice, which suffer rapid retinal degeneration due to recessive mutation in the endogenous gene. A truncated murine opsin promoter was used to drive expression of the PDE-beta cDNA. Following intraocular injection of AAV. PDE-beta, increased retinal expression of immunoreactive PDE protein was observed, including within photoreceptor cell bodies. Compared with age-matched controls, treated eyes showed increased numbers of photoreceptors and a two-fold increase in sensitivity to light as measured by in vitro electroretinography. These findings provide evidence that rescue of functional photoreceptor neurons can be achieved by somatic gene therapy.

Animals↗
PubMed1996

Sub-species discrimination, using pyrolysis mass spectrometry and self-organising neural networks, of Propionibacterium acnes isolated from normal human skin.

Curie-point pyrolysis mass spectra were obtained from 30 Propionibacterium acnes strains isolated from the foreheads of six healthy humans. Multivariate analyses and Kohonen artificial neural networks (KANNs), employing unsupervised learning, were used successfully to discriminate between the P.acnes isolates from different individual hosts. The classification of the isolates by KANNs was compared with the more classical multivariate techniques of canonical variates analysis and hierarchical cluster analysis and found to give similar groupings. The combination of pyrolysis mass spectrometry with these numerical methods also showed that more than one strain of P.acnes had been isolated from three of the human hosts.

Adult↗
PubMed1996

Quantitative analysis of multivariate data using artificial neural networks: a tutorial review and applications to the deconvolution of pyrolysis mass spectra.

The implementation of artificial neural networks (ANNs) to the analysis of multivariate data is reviewed, with particular reference to the analysis of pyrolysis mass spectra. The need for and benefits of multivariate data analysis are explained followed by a discussion of ANNs and their optimisation. Finally, an example of the use of ANNs for the quantitative deconvolution of the pyrolysis mass spectra of Staphylococcus aureus mixed with Escherichia coli is demonstrated.

Escherichia coli↗
PubMed1995

Nitric oxide inhibits depolarization-induced release of endogenous dopamine in the rabbit retina.

The effect of nitric oxide donor compounds (sodium nitroprusside, hydroxylamine and S-nitroso-N-acetyl-D,L-penicillamine) on depolarization-induced release of endogenous dopamine in the light-adapted, isolated retina of the rabbit was studied by HPLC. All three compounds had the same effect, reducing the amount of dopamine released by up to 90%. The effect was concentration dependent, saturating at 300 microM; it was blocked by the nitric oxide scavenger, mannitol (50 mM), which by itself had no effect on the basal release of dopamine. GABAA receptors were not involved. Possible cellular mechanisms underlying the findings are discussed. It is suggested that the inhibitory interaction between dopamine and nitric oxide could represent a higher order function in the light adaptation process in the retina.

Animals↗
PubMed1995

Baclofen enhancement of acetylcholine release from amacrine cells in the rabbit retina by reduction of glycinergic inhibition.

1. The mechanism by which the GABAB-receptor agonist, baclofen, enhances the light-evoked release of [3H]acetylcholine (ACh) from cholinergic amacrine cells was studied using an eye-cup preparation in anaesthetized rabbits and isolated retinas. 2. When applied locally to the rabbit retina, baclofen increased the release of ACh evoked by a flickering light (3 Hz) by over 40%. 3. In isolated retinas, baclofen strikingly inhibited the K(+)-evoked release of glycine but had no effect on GABA release. 4. In the rabbit eye cup, strychnine enhanced the light-evoked release of ACh to a similar degree to that produced by baclofen. The effects of baclofen and strychnine on the light-evoked release of ACh were not additive. In contrast, bicuculline did not affect the enhancing action of baclofen on the light-evoked release of ACh. 5. In order to see whether the glycinergic amacrine cells might be stimulated by ACh, isolated rat and rabbit retinas were exposed to muscarine. This cholinergic agonist potentiated the K(+)-evoked release of glycine by 54%. 6. We suggest that baclofen enhances the light-evoked release of ACh from amacrine cells by inhibiting glycine release from glycinergic amacrine cells which are stimulated by ACh and form an inhibitory feedback loop to the cholinergic neurones.

Acetylcholine↗
PubMed1995

Spatio-temporal pattern of ocular clusterin mRNA expression in the rd mouse.

To define the relationship between progressive photoreceptor degeneration and clusterin upregulation, we analysed the spatio-temporal distribution and level of clusterin mRNA in the retinal degeneration (rd) mouse. Expression was increased in the retinal pigment epithelium and inner retina, but not detected in the photoreceptors. These results indicate that increased clusterin mRNA is not causally involved in apoptotic mechanisms of photoreceptor death but may relate to lipid-recycling or cytoprotective functions.

Aging↗
PubMed1995

Increased expression of retinal TIMP3 mRNA in simplex retinitis pigmentosa is localized to photoreceptor-retaining regions.

The human tissue inhibitor of metalloproteinases-3 (TIMP3) gene is the most recently characterized member of a family of genes whose products are implicated in extracellular matrix (ECM) remodelling. We previously described an increase in expression of TIMP3 mRNA in retinas affected by the progressive photoreceptor degenerative disease, simplex retinitis pigmentosa (RP). To gain further insight into the association between TIMP3 overexpression and retinal degeneration, we have analyzed the cellular localization of TIMP3 mRNA in control and simplex RP retinas using in situ hybridization. No TIMP3 mRNA expression was detectable in control neural retina. IN RP-affected retinas, overexpression of TIMP3 mRNA was observed in photoreceptor inner segments and in the ganglion cell layer only in those regions retaining relatively nondystrophic retinal architecture. Modulation of TIMP3 expression in these regions, possibly in association with matrix metalloproteinases, may reflect remodelling of the retinal ECM and concomitant reorganization of neuronal connectivity.

Aged↗
PubMed1994

Expression of TIMP3 mRNA is elevated in retinas affected by simplex retinitis pigmentosa.

To explore the molecular and cellular mechanisms associated with photoreceptor death in retinitis pigmentosa (RP), we have investigated altered transcriptional activity in RP retinas by a differential cDNA screening approach. We identified a clone (K222) showing over-expression in simplex RP retinas compared with controls. K222 encodes a partial cDNA of the human tissue inhibitor of metalloproteinases-3 (TIMP3) gene, a member of a family of genes implicated in extracellular matrix (ECM) remodelling. Increased expression of TIMP3 in degenerating RP retinas may reflect restructuring of the ECM architecture, and disruption of photoreceptor-matrix interactions could contribute to activation of apoptotic cell death processes.

Adult↗
PubMed1994

Adenovirus-mediated gene transfer to murine retinal cells in vitro and in vivo.

Adenovirus-mediated gene transfer to retinal cells was evaluated using the replication-defective recombinant adenovirus vector Ad2/CMVlacZ-1 (coding for beta-galactosidase) both in an in vitro murine culture model and in vivo in adult mice. In vitro, no difference in infectability of neuronal and glial cells was observed, and 50% of neurons expressed the exogenous gene at low viral concentration (10 pfu/cell). In vivo, intraocular injection of 3 x 10(6) pfu Ad2/CMVlacZ-1 resulted in expression of the transferred beta-galactosidase gene in retinal pigment epithelium and ganglion cells. These results demonstrate that Ad2/CMVlacZ-1 is an effective vector for gene transfer into retinal cells.

Adenoviridae↗
PubMed1994

Effects of ischaemia on neurotransmitter release from the isolated retina.

The effects of "ischaemia" (glucose-free Krebs-bicarbonate medium gassed with N2/CO2) on the release of glutamate and other major neurotransmitters in the retina were examined using the isolated rat and rabbit retina. Amino acid transmitters, acetylcholine, and dopamine were measured by HPLC. The release of glutamate, aspartate, GABA, and glycine from ischaemic retinas was more than doubled after 30 min, and after 90 min of ischaemia the release of amino acids was approximately 15-20-fold that of control values. Ischaemia also produced large increases in the release of dopamine from both the rat and especially the rabbit retina. In contrast, the release of acetylcholine from the rat retina was significantly decreased by ischaemia, although the release of choline was increased. Because the ischaemia-induced release of glutamate, aspartate, and GABA from the rat retina was completely Ca independent, and exposure of the retina to high K (50 mM) did not stimulate amino acid release, it is concluded that the mechanisms underlying the ischaemia-induced release do not involve an initial release of K or an influx of calcium.

Acetylcholine↗
PubMed1994

Rapid identification using pyrolysis mass spectrometry and artificial neural networks of Propionibacterium acnes isolated from dogs.

Curie-point pyrolysis mass spectra were obtained from reference Propionibacterium strains and canine isolates. Artificial neural networks (ANNs) were trained by supervised learning (with the back-propagation algorithm) to recognize these strains from their pyrolysis mass spectra; all the strains isolated from dogs were identified as human wild type P. acnes. This is an important nosological discovery, and demonstrates that the combination of pyrolysis mass spectrometry and ANNs provides an objective, rapid and accurate identification technique. Bacteria isolated from different biopsy specimens from the same dog were found to be separate strains of P. acnes, demonstrating a within-animal variation in microflora. The classification of the canine isolates by Kohonen artificial neural networks (KANNs) was compared with the classical multivariate techniques of canonical variates analysis and hierarchical cluster analysis, and found to give similar results. This is the first demonstration, within microbiology, of KANNs as an unsupervised clustering technique which has the potential to group pyrolysis mass spectra both automatically and relatively objectively.

Animals↗
PubMed1994

Enhancement of retinal acetylcholine release by DAMGO: possibly a direct opioid receptor-mediated excitatory effect.

1. An eye-cup preparation in anaesthetized rabbits was used to examine opioid modulation of acetylcholine (ACh) release from cholinergic neurones in the retina. 2. The mu-opioid receptor agonist, [D-Ala2, MePhe4, Gly-ol5]-enkephalin (DAMGO), when applied locally to the retina at concentrations between 1-30 microM significantly increased the light-evoked release of ACh. The effect of DAMGO was completely blocked by the selective mu-receptor antagonist CTOP but the kappa-receptor antagonist nor-binaltorphimine (norBNI) did not affect the action of DAMGO on ACh release indicating that the opioid produced its effect by activation of mu-receptors (the rabbit retina has negligible delta-receptors). 3. Blockade with bicuculline and strychnine of GABAergic and glycinergic inputs to the cholinergic neurones did not affect the action of DAMGO on ACh release. Also DAMGO did not reduce the potassium-evoked release of either GABA or glycine from rat isolated retinas. 4. Exposure of the rabbit retina to a combination of an A1-adenosine receptor antagonist, 8-cyclopentyl-1,3 dipropylxanthine (DPCPX), and adenosine deaminase did not affect the enhancing action of DAMGO on the light-evoked release of ACh. 5. When the retina in the rabbit eye-cup was exposed to kainate, the release of ACh was increased by approximately three times the resting release. In the presence of DAMGO the kainate-evoked release of ACh was enhanced by 44%. 6. These experiments show that activation of mu-opioid receptors by DAMGO increases the release of ACh elicited by physiological stimulation (flickering light). Since we could find no evidence thatDAMGO reduces inhibitory inputs to the cholinergic neurones, it seems that the enhancing action ofDAMGO on the light-evoked release of ACh involves a direct excitatory effect rather than disinhibition.This conclusion is supported by the enhancing action of DAMGO on the kainate-evoked release of ACh because kainate is thought to act directly on the cholinergic neurones.

Acetylcholine↗
PubMed1994

Assessment of liposomal transfection of ocular tissues in vivo.

A possible route to the treatment of inherited retinal degenerations such as retinitis pigmentosa (RP) is the application of somatic gene therapy by the transfer and expression of corrective functional genes in ocular tissue. Cationic liposomes are established vehicles for the delivery and expression of exogenous genes in mammalian cells both in vitro and in vivo1. We report here a preliminary assessment of liposome-mediated transfer of a plasmid carrying the reporter gene lacZ (encoding the enzyme beta-galactosidase) into tissues of the adult rabbit eye.

Animals↗
PubMed1993

Abnormal distribution of retinal clusterin in retinitis pigmentosa.

Increased expression of clusterin mRNA is associated with neurodegenerative states, including retinas affected by retinitis pigmentosa (RP). We have investigated the distribution of immunoreactive clusterin in normal and RP-affected retinas. Reactivity at the inner limiting membrane, plexiform layers, and photoreceptors in normal retina accords well with clusterin's postulated role as a membrane protective agent. In RP-affected retina the organized distribution is lost and overall reactivity appears decreased. The changes in this case may reflect increased turnover or removal of clusterin, perhaps via interaction with components of the immune system.

Adult↗
PubMed1993

Comparison of clusterin gene expression in normal and dystrophic human retinas.

To gain insight into the mechanisms underlying altered clusterin expression in retinal degeneration, the cellular distribution of clusterin mRNA in normal and in retinitis pigmentosa-affected retinas was compared using in situ hybridization. In contrast to the normal retina, where clusterin mRNA is localized in the inner nuclear and ganglion cell layers, a clustered distribution is observed throughout the dystrophic retina. The results indicate an expression of clusterin gene in normal retinal neurons and suggest that its altered regulation in neurodegeneration is not purely a glial cell phenomenon.

Adult↗