A case of xanthogranulomatous appendicitis in the female pelvis

Xanthogranulomatous inflammation is an uncommon form of chronic inflammatory process. Only a few isolated case reports of xanthogranulomatous appendicitis (XA) have been published. XA has nonspecific imaging findings and cannot be reliably differentiated on imaging from locally advanced malignancy. XA however follows a benign course and can potentially be treated with surgical resection.

Working memory impairment and its associated sleep-related respiratory parameters in children with obstructive sleep apnea

STUDY OBJECTIVE

Working memory deficits in children with obstructive sleep apnea (OSA) have been reported in previous studies, but the results were inconclusive. This study tried to address this issue by delineating working memory functions into executive processes and storage/maintenance components based on Baddeley's working memory model.

METHODS

Working memory and basic attention tasks were administered on 23 OSA children aged 8-12 years and 22 age-, education-, and general cognitive functioning-matched controls. Data on overnight polysomnographic sleep study and working memory functions were compared between the two groups. Associations between respiratory-related parameters and cognitive performance were explored in the OSA group.

RESULTS

Compared with controls, children with OSA had poorer performance on both tasks of basic storage and central executive components in the verbal domain of working memory, above and beyond basic attention and processing speed impairments; such differences were not significant in the visuo-spatial domain. Moreover, correlational analyses and hierarchical regression analyses further suggested that obstructive apnea-hypopnea index (OAHI) and oxygen saturation (SpO2) nadir were associated with verbal working memory performance, highlighting the potential pathophysiological mechanisms of OSA-induced cognitive deficits.

CONCLUSIONS

Verbal working memory impairments associated with OSA may compromise children's learning potentials and neurocognitive development. Early identification of OSA and assessment of the associated neurocognitive deficits are of paramount importance. Reversibility of cognitive deficits after treatment would be a critical outcome indicator.

Green pit viper antivenom from Thailand and Agkistrodon halys antivenom from China compared in treating Cryptelytrops albolabris envenomation of mice

OBJECTIVE

To compare the relative efficacy of the green pit viper antivenom from Thailand and Agkistrodon halys antivenom from China. DESIGN. In-vivo experimental study.

SETTING

A wildlife conservation organisation, a university, a poison information centre, and a regional hospital in Hong Kong.

MAIN OUTCOME MEASURES

Pre- and post-antivenom lethal dose 50 (LD50) of the Cryptelytrops albolabris venom, median effective dose (ED50) of green pit viper antivenom and Agkistrodon halys antivenom against a lethal dose of the venom. SUBJECTS. Adult mice.

RESULTS

The intraperitoneal LD50 of the venom from locally caught Cryptelytrops albolabris was 0.14 microL. After post-exposure treatment with 10 microL of antivenom, it was elevated to 0.36 microL and 0.52 microL by the green pit viper antivenom and the Agkistrodon halys antivenom, respectively. The ED50 was 32.02 microL for green pit viper antivenom and 6.98 microL for Agkistrodon halys antivenom. Both green pit viper antivenom and Agkistrodon halys antivenom ameliorated the lethality of Cryptelytrops albolabris venom in mice.

CONCLUSION

The overall superior neutralisation capacity of Agkistrodon halys antivenom over green pit viper antivenom may be related to the geographic proximity of the venoms used for antivenom preparation. The results point towards the need for further comparison of the two antivenoms on protein or immunoglobulin weight basis, and with respect to non-lethal clinically significant toxicities.

Ceftriaxone ameliorates motor deficits and protects dopaminergic neurons in 6-hydroxydopamine-lesioned rats

Parkinson's disease is caused by the degeneration of dopaminergic neurons in substantia nigra. There is no current promising treatment for neuroprotection of dopaminergic neurons. Ceftriaxone is a beta-lactam antibiotic and has been reported to offer neuroprotective effects (Rothstein, J.-D., Patel, S., Regan, M.-R., Haenggeli, C., Huang, Y.-H., Bergles, D.-E., Jin, L., Dykes, H.-M., Vidensky, S., Chung, D.-S., Toan, S.-V., Bruijn, L.-I., Su, Z.-Z., Gupta, P., and Fisher, P.-B. (2005) Beta-lactam antibiotics offer neuroprotection by increasing glutamate transporter expression Nature433, 73-77). In the present study, efficacy of ceftriaxone in neuroprotection of dopaminergic neurons and amelioration of motor deficits in a rat model of Parkinson's disease were investigated. Ceftriaxone was administrated in 6-hydroxydopamine-lesioned rats. Using behavioral tests, grip strength and numbers of apomorphine-induced contralateral rotation were declined in the ceftriaxone-treated group. More importantly, cell death of dopaminergic neurons was found to decrease. In addition, both the protein expression and immunoreactivity for GLT-1 were up-regulated. The present results strongly indicate that ceftriaxone is a potential agent in the treatment of Parkinson's disease.

Secretin as a neurohypophysial factor regulating body water homeostasis

Hypothalamic magnocellular neurons express either one of the neurohypophysial hormones, vasopressin or oxytocin, along with different neuropeptides or neuromodulators. Axonal terminals of these neurons are generally accepted to release solely the two hormones but not others into the circulation. Here, we show that secretin, originally isolated from upper intestinal mucosal extract, is present throughout the hypothalamo-neurohypophysial axis and that it is released from the posterior pituitary under plasma hyperosmolality conditions. In the hypothalamus, it stimulates vasopressin expression and release. Considering these findings together with our previous findings that show a direct effect of secretin on renal water reabsorption, we propose here that secretin works at multiple levels in the hypothalamus, pituitary, and kidney to regulate water homeostasis. Findings presented here challenge previous understanding regarding the neurohypophysis and could provide new concepts in treating disorders related to osmoregulation.

5-HT excites globus pallidus neurons by multiple receptor mechanisms

Anatomical and neurochemical studies indicated that the globus pallidus receives serotonergic innervation from raphe nuclei but the membrane effects of 5-HT on globus pallidus neurons are not entirely clear. We address this question by applying whole-cell patch-clamp recordings on globus pallidus neurons in immature rat brain slices. Under current-clamp recording, 5-HT depolarized globus pallidus neurons and increased their firing rate, an action blocked by both 5-HT(4) and 5-HT(7) receptor antagonists and attributable to an increase in cation conductance(s). Further experiments indicated that 5-HT enhanced the hyperpolarization-activated inward conductance which is blocked by 5-HT(7) receptor antagonist. To determine if 5-HT exerts any presynaptic effects on GABAergic and glutamatergic inputs, the actions of 5-HT on synaptic currents were studied. At 10 microM, 5-HT increased the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) but had no effect on both the frequency and amplitude of miniature inhibitory postsynaptic currents (mIPSCs). However, 5-HT at a higher concentration (50 microM) decreased the frequency but not the amplitude of the mIPSCs, indicating an inhibition of GABA release from the presynaptic terminals. This effect was sensitive to 5-HT(1B) receptor antagonist. In addition to the presynaptic effects on GABAergic neurotransmission, 5-HT at 50 microM had no consistent effects on glutamatergic neurotransmission, significantly increased the frequency of miniature excitatory postsynaptic currents (mEPSCs) in 4 of 11 neurons and decreased the frequency of mEPSCs in 3 of 11 neurons. In conclusion, we found that 5-HT could modulate the excitability of globus pallidus neurons by both pre- and post-synaptic mechanisms. In view of the extensive innervation by globus pallidus neurons on other basal ganglia nuclei, this action of 5-HT originated from the raphe may have a profound effect on the operation of the entire basal ganglia network.

Endogenous release of secretin from the hypothalamus

Previous studies demonstrated that secretin could be released from the cerebellum, where it exerts a facilitatory action on the GABAergic inputs into the Purkinje neurons. In the present article, we provide evidence of the endogenous release of secretin in the hypothalamus and the mechanisms underlying this release. Incubation of the hypothalamic explants with KCl induces the release of secretin to 4.35 +/- 0.45-fold of the basal level. This K+-induced release was tetrodotoxin and cadmium sensitive, suggesting the involvement of voltage-gated sodium and calcium channels. The use of specific blockers further revealed the involvement of L-, N-, and P-type high voltage-activated (HVA) calcium channels. Results present in the current article provide further and more solid evidence of the role of secretin as a neuropeptide in the mammalian central nervous system.

Ablation of gene expression of N-methyl-D-aspartate receptor one by antisense oligonucleotides in striatal neurons in culture

In the present study, a twenty-mer antisense oligonucleotide specific for N-methyl-D-aspartate receptor one (ANR1) was applied to striatal neurons in primary cell culture. The ANR1 was found to be specific and nontoxic. Significant reductions in expression of NR1 mRNA and proteins were resulted after a single dose of ANR1 transcripts. Interestingly, there were reductions in total NR1 proteins but two phosphorylated forms of NR1 proteins at serine 896 and 897 residues were not reduced. There was also no change in the pattern of distribution of NR1 immunoreactivity in the striatal neurons. In addition, significant reductions of NMDA-mediated peak inward current were found after application of a higher concentration of ANR1 (20-100 microM) by patch clamp recordings. The present results indicate that ANR1 is a useful agent in reducing NMDA receptor functions. The present data thus provide detailed cellular and molecular mechanisms to explain our previous findings of amelioration of motor symptoms in a rat model of Parkinson's disease. More importantly, application of ANR1 was also found to display neuroprotective effects of striatal neurons against NMDA-induced excitotoxic cell death. The findings have implications in development of new approach in prevention of cell death in neurodegenerative diseases and new treatments for these diseases.

Neurotensin selectively facilitates glutamatergic transmission in globus pallidus

The tridecapeptide neurotensin has been demonstrated to modulate neurotransmission in a number of brain regions. There is evidence that neurotensin receptors exist in globus pallidus presynaptically and postsynaptically. Whole-cell patch-clamp recordings were used to investigate the modulatory effects of neurotensin on glutamate and GABA transmission in this basal ganglia nucleus in rats. Neurotensin at 1 microM significantly increased the frequency of glutamate receptor-mediated miniature excitatory postsynaptic currents. In contrast, neurotensin had no effect on GABA(A) receptor-mediated miniature inhibitory postsynaptic currents. The presynaptic facilitation of neurotensin on glutamatergic transmission could be mimicked by the C-terminal fragment, neurotensin (8-13), but not by the N-terminal fragment, neurotensin (1-8). The selective neurotensin type-1 receptor antagonist, SR48692 {2-[(1-(7-chloro-4-quinolinyl)-5-2(2,6-dimethoxyphenyl)pyrazol-3-yl)carbonylamino]-tricyclo(3.3.1.1.(3.7))-decan-2-carboxylic acid}, blocked this facilitatory effect of neurotensin, and which itself had no effect on miniature excitatory postsynaptic currents. The specific phospholipase C inhibitor, U73122 {1-[6-[[17beta-3-methoyyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione}, significantly inhibit neurotensin-induced facilitation on glutamate release. Taken together with the reported postsynaptic depolarization of neurotensin in globus pallidus, it is suggested that neurotensin excites the globus pallidus neurons by multiple mechanisms which may provide a rationale for further investigations into its involvement in motor disorders originating from the basal ganglia.

Secretin: A Pleiotrophic Hormone

Secretin holds a unique place in the history of endocrinology and gastrointestinal physiology, as it is the first peptide designated as a hormone. During the last century since its first discovery, the hormonal effects of secretin in the gastrointestinal tract were extensively studied, and its principal role in the periphery was found to stimulate exocrine secretion from the pancreas. Recently, a functional role of secretin in the brain has also been substantiated, with evidence suggesting a possible role of secretin in embryonic brain development. Given that secretin and its receptors are widely expressed in multiple tissues, this peptide should therefore exhibit pleiotrophic functions throughout the body. The present article reviews the current knowledge on the central and peripheral effects of secretin as well as its therapeutic uses.

Endogenous release and multiple actions of secretin in the rat cerebellum

Previous studies demonstrated that secretin could modulate synaptic transmission in the rat cerebellum. In the present report, we provide evidence for the endogenous release of secretin in the cerebellum and further characterize the actions of secretin in this brain area. First, to show that secretin is released endogenously, blocks of freshly dissected cerebella were challenged with a high concentration of KCl. Incubation with KCl almost doubled the rate of secretin release. This KCl-induced release was sensitive to tetrodotoxin and cadmium suggesting the involvement of voltage-gated sodium and calcium channels. The use of specific channel blockers further revealed that L-type and P/Q-type calcium channels underlie both basal and KCl-evoked secretin release. In support of this, depolarization of Purkinje neurons in the presence of NMDA, group II mGluR and cannabinoid CB1 receptor blockers resulted in increased inhibitory postsynaptic current frequency. Second, we found that the previously reported facilitatory action of secretin on GABAergic inputs to Purkinje neurons is partly dependent on the release of endogenous glutamate. In the presence of CNQX, an AMPA/kainate receptor antagonist, the facilitatory effect of secretin on GABA release was significantly reduced. In support of this idea, application of AMPA, but not kainate receptor agonist, facilitated GABA release from inhibitory terminals, an action that was sensitive to AMPA receptor antagonists. These data indicate that a direct and an indirect pathway mediate the action of secretin in the basket cell-Purkinje neuron synapse. The results provide further and more solid evidence for the role of secretin as a neuropeptide in the mammalian CNS.

Expression and spatial distribution of secretin and secretin receptor in human cerebellum

The expression and spatial distribution of secretin and its receptor in human cerebellum were investigated by in situ hybridization and immunohistochemical techniques. Secretin mRNAs are found in Purkinje cells whereas secretin receptor transcripts are present in Purkinje cells and basket cells in the molecular cell layer. In addition, secretin-immunoreactivities are localized in both the soma and dendrites of Purkinje cells. These data are the first demonstration of the spatial distribution of secretin and its receptor in distinct neurons within the human cerebellum. The cellular localizations of this ligand-receptor pair are consistent with the proposed actions of secretin in the cerebellum of rodents and hence suggest that secretin also serves specific neural functions in the human cerebellum.

Evaluation of Scanning Resolution on Retinal Nerve Fiber Layer Measurement Using Optical Coherence Tomography in Normal and Glaucomatous Eyes

PURPOSE

To evaluate the effect of varying the scanning resolution of optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) measurement on diagnostic sensitivity and functional correlation in glaucoma.

PATIENTS AND METHODS

314 eyes from 182 subjects including 107 normal eyes, 83 glaucoma suspect eyes, and 124 glaucoma eyes were included in this cross-sectional study. Standard automated perimetry and OCT measurement of RNFL thickness were performed. Each individual underwent two scanning protocols: (1) fast RNFL thickness (3.4) scan (with resolution of 256 scan points) and (2) RNFL thickness (3.4) scan (with resolution of 512 scan points). RNFL thickness was compared among the groups. Diagnostic sensitivity was evaluated with Receiver Operating Characteristic (ROC) Curve. Relationship between RNFL thickness and visual field mean deviation was examined using linear regression analysis.

RESULTS

Measured RNFL thickness using fast RNFL thickness (3.4) scan was significantly higher compared with RNFL thickness (3.4) scan in average, superior, nasal and inferior RNFL in all diagnostic groups. Comparing normal and glaucoma groups, RNFL thickness (3.4) scan produced the largest area under the ROC curve (0.912) based on average RNFL thickness. A stronger correlation between average RNFL and visual field mean deviation was found in RNFL thickness (3.4) scan (R = 0.75, R = 0.56).

CONCLUSIONS

Higher resolution RNFL scan provides better diagnostic sensitivity in glaucoma detection and a stronger correlation with visual function.

Neurotensin depolarizes globus pallidus neurons in rats via neurotensin type-1 receptor

The globus pallidus is a major component in the indirect pathway of the basal ganglia. There is evidence that neurotensin receptors exist in this nucleus. To determine the electrophysiological effects of neurotensin on pallidal neurons, whole-cell patch-clamp recordings were performed in the acutely prepared brain slices. Under current-clamp recordings, neurotensin at 1 microM depolarized pallidal neurons. Voltage-clamp recordings also showed an inward current induced by neurotensin. The depolarizing effect of neurotensin could be mimicked by the C-terminal fragment, neurotensin (8-13), but not by the N-terminal fragment, neurotensin (1-8). Both SR 142948A, a non-selective neurotensin receptor type-1 and type-2 antagonist, and SR 48692, a selective type-1 receptor antagonist, blocked the depolarizing effect of neurotensin, and which themselves had no effect on membrane potential. Thus, neurotensin type-1 receptors appear to mediate the effect of neurotensin. The depolarization evoked by neurotensin persisted in the presence of tetrodotoxin, ionotropic and metabotropic glutamate and GABA receptor antagonists, indicating that neurotensin excited the pallidal neurons by activating the receptor expressed on the neurons recorded. Current-voltage relationship revealed that both the suppression of a potassium conductance and the activation of a cationic conductance are involved in the neurotensin-induced depolarization. Based on the action of neurotensin in the globus pallidus we hypothesize that alterations of the striatopallidal neurotensin system contribute to symptoms of basal ganglia motor disorders.

Striatal neurons but not nigral dopaminergic neurons in neonatal primary cell culture express endogenous functional N-methyl-d-aspartate receptors

Developmental expression of N-methyl-D-aspartate (NMDA) receptor subunits were determined and compared in striatal and nigral neurons in neonatal primary cell cultures. In striatal neurons, NR1, NR2A and NR2B mRNAs and immunoreactivity, and NR2D mRNA were found and the maximal levels of NR1 mRNA and immunoreactivity expression were found at 6 day-in-vitro (DIV). NMDA receptors found at this stage in striatal neurons are likely to contain NR1 plus NR2A, NR2B and NR2D subunits. In nigral neurons, NR1 and NR2B mRNAs and immunoreactivity, and NR2D mRNA were found and the maximal level of NR1 immunoreactivity expression was found at 10 DIV. Unlike striatal neurons, NMDA receptors found in nigral neurons are likely to contain NR1 plus NR2B and NR2D subunits only. NMDA-induced toxicity assays showed that striatal neurons were most susceptible to cell death at around 10 DIV but nigral neurons were not susceptible to NMDA-induced cell death at all stages. In addition, patch clamp analysis revealed that functional NMDA receptors could only be found in striatal neurons but not in nigral dopaminergic neurons in vitro. The present results indicate that striatal and nigral neurons are programmed to express distinct NMDA receptor subunits during their endogenous development in cell cultures. Despite dopaminergic neurons in culture display NMDA receptor subunits, functional NMDA receptors are not assembled. The present findings have demonstrated that dopaminergic neurons in vitro may behave very differently to their counterparts in vivo in terms of NMDA receptor-mediated responses. Our results also have implications in transplantations using dopaminergic neurons in vitro in treatments of Parkinson's disease.

Rotational behavior and electrophysiological effects induced by GABA(B) receptor activation in rat globus pallidus

GABA is the major neurotransmitter used in the globus pallidus and there is evidence that GABA(B) receptors exist in this nucleus. Here we show that unilateral microinjection of baclofen, a GABA(B) receptor agonist, induced ipsilateral turning in Sprague-Dawley rats. This effect was prevented by preinjection of the GABA(B) receptor antagonist CGP55845A, which itself did not cause rotation. Thus, activation of GABA(B) receptor may suppress the activity of globus pallidus neurons, which is in line with the finding that the glutamate receptor antagonists (+/-)-2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitroquinoxaline-2,3-dione also caused similar ipsilateral turning when injected into globus pallidus. Furthermore, in the presence of these glutamate receptor antagonists, injection of baclofen resulted in fewer rotations. To test the possibility that baclofen reduced glutamate release onto globus pallidus neurons, the effects of baclofen on miniature excitatory postsynaptic currents were studied in rat brain slices. Patch-clamp recordings showed that baclofen at 30 microM significantly reduced the frequency of the miniature excitatory postsynaptic currents. However, baclofen induced a weak outward current only in a minority of globus pallidus neurons. These pre- and postsynaptic effects of baclofen were reversed or prevented by CGP55845A. These results suggest that GABA(B) receptor in globus pallidus plays an important role in the regulation of movement by modulating glutamatergic inputs at a presynaptic site.

Secretin as a neuropeptide

The role of secretin as a classical hormone in the gastrointestinal system is well-established. The recent debate on the use of secretin as a potential therapeutic treatment for autistic patients urges a better understanding of the neuroactive functions of secretin. Indeed, there is an increasing body of evidence pointing to the direction that, in addition to other peptides in the secretin/glucagon superfamily, secretin is also a neuropeptide. The purpose of this review is to discuss the recent data for supporting the neurocrine roles of secretin in rodents. By in situ hybridization and immunostaining, secretin was found to be expressed in distinct neuronal populations within the cerebellum and cerebral cortex, whereas the receptor transcript was found throughout the brain. In the rat cerebellum, secretin functions as a retrograde messenger to facilitate GABA transmission, indicating that it can modulate motor and other functions. In summary, the recent data support strongly the neuropeptide role of secretin, although the secretin-autism link remains to be clarified in the future.

Secretin facilitates GABA transmission in the cerebellum

Secretin was the first hormone discovered in human history, and yet, its function as a neuropeptide has been overlooked in the past. The recent discovery of the potential use of secretin in treating autistic patients, together with the conflicting reports on its effectiveness, urges an in-depth investigation of this issue. We show here that in the rat cerebellar cortex, mRNAs encoding secretin are localized in the Purkinje cells, whereas those of its receptor are found in both Purkinje cells and GABAergic interneurons. Immunoreactivity for secretin is localized in the soma and dendrites of Purkinje cells. In addition, secretin facilitates evoked, spontaneous, and miniature IPSCs recorded from Purkinje cells. We propose that secretin is released from the somatodendritic region of Purkinje cells and serves as a retrograde messenger modulating GABAergic afferent activity.

In situ model for studying potassium currents in various growth plate chondrocyte subpopulations

A new in situ model of partially digested growth plate cartilage suitable for patch clamp study of membrane currents of chondrocytes from various differentiation stages was developed. Thin sections of growth plate were enzyme digested to expose intact membranes of chondrocytes previously covered by extracellular matrix. This treatment dramatically increased the success rate of tight-seal formation from virtually 0% up to 40%. Whole-cell patch clamp recording revealed a delayed outward rectifying current as the major macroscopic current in chondrocytes of all differentiation stages. This current was sensitive to tetraethylammonium chloride and reversed polarity at a membrane potential close to the equilibrium potential of K+. Chondrocytes at resting stage expressed a much smaller K+ current than the proliferative and hypertrophic chondrocytes. When the current amplitudes were normalized for the cell membrane area, proliferative cells expressed a significantly higher outward current density.

Real-time analysis of the activities of GnRH and GnRH analogs in alphaT3-1 cells by the Cytosensor microphysiometer

Gonadotropin-releasing hormone (GnRH), acting via the GnRH receptor, elicited rapid extracellular acidification responses in mouse gonadotrope-derived alphaT3-1 cells as measured by the Cytosensor microphysiometer, which indirectly monitors cellular metabolic rates. GnRH increased the extracellular acidification rate of the cells in a dose-dependent manner (EC(50) = 1.81 +/- 0.24 nM). The GnRH-stimulated acidification rate could be attenuated by protein kinase C (PKC) down-regulation, extracellular Ca2+ depletion, and the voltage-sensitive Ca2+ channel (VSCC) blocker nifedipine, indicating that the acidification response is activated by both Ca2+ and PKC-mediated pathways. Upon continuous exposure to 100 nM GnRH or periodic stimulation by 10 nM GnRH at 40 min intervals, homologous desensitization was more pronounced in the absence of extracellular Ca2+, suggesting that desensitization of GnRH activity may be mediated via depletion of intracellular Ca2+ stores. We have also compared the potency of eight GnRH analogs on alphaT3-1 cells. No acidification response was detected for GnRH free acid, consistent with the idea that the C-terminal amide is a critical structural determinant for GnRH activity. Replacement of Gly-NH(2) at the C-terminus by N-ethylamide dramatically reduced the EC(50) value, suggesting that substitution of the Gly-NH(2) moiety by N-ethylamide increases the potency of GnRH analogs. Substitution of Gly at position 6 by D-Trp significantly reduced the EC(50) value, whereas D-Lys at the same position slightly increased the EC(50) value, implying that either an aromatic amino acid or a non-basic amino acid at position 6 may be essential for potent GnRH agonists. In summary, our results demonstrate that the Cytosensor microphysiometer can be used to evaluate the actions of GnRH and GnRH analogs in alphaT3-1 cells in a real-time and noninvasive manner. This silicon-based microphysiometric system should provide new information on the structure-function studies of GnRH and is an invaluable tool for the screening of new GnRH agonists and antagonists in the future.

Inhibitory postsynaptic currents of rat substantia nigra pars reticulata neurons: role of GABA receptors and GABA uptake

Whole-cell patch-clamp recordings were made from substantia nigra pars reticulata neurons in midbrain slices of young rats to study the characteristics of spontaneous and evoked inhibitory postsynaptic currents and factors which govern their decay kinetics. In the presence of the glutamate receptor antagonists D, L-2-amino-5-phosphonopentanoic acid (20 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (20 microM), bicuculline-sensitive spontaneous inward inhibitory postsynaptic currents were often observed using high Cl(-) electrodes. Application of the selective GABA(B) receptor antagonist CGP55845A (2 microM) did not alter the half decay time of these inhibitory postsynaptic currents, which however was prolonged by the potent GABA uptake blocker tiagabine (1 microM). In addition, the frequencies and amplitudes of the inhibitory postsynaptic currents were significantly reduced by tiagabine but these effects were prevented by CGP55845A. Inhibitory postsynaptic currents with similar sensitivity to bicuculline could also be evoked intranigrally. Similar to the spontaneous currents, the decay time of evoked inhibitory postsynaptic currents was not affected by 2 microM CGP55845A. However, in the absence of CGP55845A, tiagabine shortened the IPSC decay time but had an opposite effect if CGP55845A was present. These data suggest that the spontaneous and evoked inhibitory postsynaptic currents recorded from substantia nigra pars reticulata neurons are mediated mainly by GABA(A) receptors. Uptake of GABA helps to terminate these currents. When the uptake mechanism is blocked, accumulation of GABA would lead to activation of presynaptic GABA(B) receptors and reduction in GABA release. The role of postsynaptic GABA(B) receptors in substantia nigra pars reticulata of young rats seems to be minimal.

Changes in morphology and behaviour of retinal growth cones before and after crossing the midline of the mouse chiasm - a confocal microscopy study

The growth of retinal axons was investigated in different regions of the optic chiasm in C57 pigmented mouse embryos aged embryonic day 13 (E13) to E15. Individual retinal axons and their growth cones were labelled anterogradely by DiI and imaged using a confocal imaging system. In aldehyde-fixed embryos, retinal growth cones display a simple form in the optic nerve and become more complex in morphology in the chiasm. The complex form is particularly prominent in those axons that turn to the ipsilateral tract in the premidline region of chiasm. Moreover, complex growth cones are also commonly found in axons in the postmidline chiasm, which are markedly different in morphology from those axons in the premidline region, suggesting that the postmidline chiasm contains a novel environment for the pathfinding of retinal axons. In another experiment, the dynamic growth of retinal axons is studied in a brain slice preparation of the living retinofugal pathway. Retinal axons show an intermittent growth across the premidline and postmidline chiasm. Extensive remodelling of growth cone form followed by a shift in growth direction is commonly seen during the pause periods, indicating that signals that guide axon growth across the chiasm are not restricted to the midline, but are laid down throughout the chiasm. Moreover, dramatic changes in axon trajectory are noted first at the premidline chiasm where the uncrossed axons segregate from the crossed axons, and second at the postmidline chiasm where specific sorting of retinal axons according to their position in the dorsal ventral retinal axis and their ages are known to take place. These results show that there are two distinct environments, separated by the midline in the chiasm, where axons show different responses to local guidance cues and develop the distinct fibre orders.

Occlusion of the presynaptic action of cannabinoids in rat substantia nigra pars reticulata by cadmium

Whole-cell patch-clamp recordings were made from substantia nigra pars reticulata (SNR) neurones in rat midbrain slices to characterise the presynaptic action of cannabinoids on GABA neurotransmission and to study the involvement of calcium channels. The cannabinoid agonist WIN55212-2 at 10 microM reduced the amplitudes of GABA(A) receptor mediated spontaneous postsynaptic currents (IPSCs). This effect was fully reversed by the selective cannabinoid CB1 receptor antagonist SR141716A (20 microM). WIN55212-2 also caused a reduction in the evoked IPSC amplitude, which was associated with a significant increase in the paired pulse ratio over a 50 ms interval. In addition, the reduction in spontaneous IPSC amplitude by WIN55212-2 could be largely occluded by the presence of extracellular Cd2+ (200 microM). These observations suggest that cannabinoids exert a presynaptic inhibition on GABAergic transmission to SNR neurones via CB1 receptor, an action which involves inhibition of Cd2+-sensitive presynaptic Ca2+ channels.

Differential expression of pre- and postsynaptic GABA(B) receptors in rat substantia nigra pars reticulata neurones

Whole-cell recordings were made from substantia nigra pars reticulata in rat midbrain slices to study the functional expression of pre- and postsynaptic GABA(B) receptors in GABA output neurones. Baclofen (up to 300 microM) dose-dependently activated a weak current which was insensitive to tetrodotoxin and Ca2+-free solution but blocked by Ba2+ and 2-OH-saclofen. The maximum current activated by baclofen (30 microM) was 43.0 +/- 4.5 pA (n = 27), representing only 23% of that in dopamine neurones. Baclofen (1-30 microM) also reduced the frequency of the GABA(A) receptor-mediated miniature inhibitory postsynaptic currents while the distribution of their amplitudes was unaffected. This presynaptic effect of baclofen, prominent at a concentration as low as 1 microM, was sensitive to 2-OH-saclofen and occluded by Cd2+, but was unaffected by Ba2+. The results suggest a predominant role of the presynaptic GABA(B) receptors in substantia nigra pars reticulata. The relative abundance of pre- and postsynaptic GABA(B) receptor subtypes in this brain region may also be important in mediating the anticonvulsant effect of baclofen in rats.

Presynaptic inhibition of GABAergic inputs to rat substantia nigra pars reticulata neurones by a cannabinoid agonist

Whole-cell patch-clamp recordings were made from substantia nigra pars reticulata (SNR) neurones in rat midbrain slices to investigate the electrophysiological effects of cannabinoids. The cannabinoid receptor agonist WIN 55212-2 (10 microM) significantly reduced intranigrally evoked and spontaneous inhibitory post-synaptic currents (IPSCs) which were mediated by GABA(A) receptors. The postsynaptic current induced by bath application of GABA was not affected by the presence of WIN 55212-2. The actions of WIN 55212-2 were not mimicked by the inactive enantiomer WIN 55212-3. WIN 55212-2 also hyperpolarized the membrane of SNR neurones in a tetrodotoxin/0-Ca2+-insensitive manner. These data suggest that cannabinoids modulate the activity of SNR neurones by presynaptic inhibition of GABA inputs. They may also exert a direct post-synaptic inhibition on these neurones.

Pre-synaptic effect of the ATP-sensitive potassium channel opener diazoxide on rat substantia nigra pars reticulata neurons

Spontaneous synaptic currents were recorded from visually identified substantia nigra pars reticulata (SNR) neurons in the rat brain slice preparation by whole-cell patch clamp technique. GABA neurons were distinguished from dopamine neurons by their electrophysiological characteristics. In the presence of 20 microM AP5 and CNQX, the spontaneous synaptic currents recorded from GABA neurons were sensitive to bicuculline and reversed polarity at a potential close to the equilibrium potential of Cl-, indicating that they were mediated by GABA(A) receptors. TTX at 1 microM eliminated action potential-dependent release of GABA from nerve terminals, revealing the miniature inhibitory post-synaptic currents (mIPSCs). The ATP-sensitive potassium channel (K(ATP) channel) opener diazoxide (30-300 microM) significantly reduced the frequency of the mIPSCs in a dose-dependent manner. However, diazoxide did not affect the average value and the distribution of the mIPSC amplitudes. Thus, this effect of diazoxide was pre-synaptic in nature. The K(ATP) channel blocker glibenclamide (300 microM) was able to restore the frequency of the mIPSCs. These data suggest that the striatonigral projection, which represents the major inhibitory input controlling SNR GABA neuron activities, possesses presynaptic K(ATP) channels on the nerve terminals.

Sulphonylureas reverse hypoxia induced K(+)-conductance increase in substantia nigra pars reticulata neurones

Membrane potentials were recorded from neuronal somata in the substantia nigra pars reticulata of the rat midbrain slice using the whole-cell patch-clamp technique. Hypoxia induced a consistent decrease in input resistance often accompanied by membrane hyperpolarization and cessation of firing. The membrane hyperpolarization was mediated by K+ as indicated by its reversal potential at -88 +/- 9 mV, which is close to the equilibrium potential of K+. The hypoxic response was not sensitive to 1 microM tetrodotoxin or superfusion with Ca2(+)-free medium. While glibenclamide at 30 microM and tolbutamide at 300 microM had no effect on the resting membrane properties of the neurones, these sulphonylureas reversed the hypoxia-induced membrane hyperpolarization and restored firing. Inclusion of 2 mM of ATP in the recording pipette also prevented the hyperpolarization. These observations suggest that post-synaptic ATP-sensitive potassium channels exist on the GABA neurones of SNR and that these channels are activated in energy-depleting conditions exemplified by hypoxia.

An isolated rat vibrissal preparation with stable responses of slowly adapting mechanoreceptors

Sinus hairs were isolated from rats and examined in an isolated organ bath while superfused with oxygenated synthetic interstitial fluid. The distal end of the deep vibrissal nerve was teased for single unit recordings of responses from slowly adapting mechanoreceptors to standard bending of the hair. Sinus hair type I and type II receptors could be clearly identified by their respective characteristic firing pattern. Their responses were stable for at least 5 h even if the sinus hair had been stored at 4 degrees C for 24 h beforehand. Electron microscopic examination of these hairs at the end of experiments showed well preserved ultrastructure without abnormalities. The short diffusion distances in this preparation make it well suited for studying drug effects with the aim of investigating the mechanoelectric transduction process in these receptors.

Cytoplasmic Ca2+ concentrations in intact Merkel cells of an isolated, functioning rat sinus hair preparation

An isolated, functioning sinus hair preparation was developed to investigate cytoplasmic Ca2+ concentrations in intact Merkel cells using microfluorimetric techniques. Intracellular Ca2+ levels were monitored by means of photon counters in small groups of Merkel cells loaded with the calcium fluorescent indicators fura-2 or fluo-3. Mechanical stimulation of Merkel cells with fine glass rods resulted in small transient increases in intracellular Ca2+ levels (by about 20%) in the group of Merkel cells around the stimulating probe. A rise in Ca2+ is presumed to be essential for the postulated synaptic transmission to the afferent nerve terminal. Depolarization with a high concentration of potassium chloride (100 mM) caused increases in intracellular Ca2+ concentrations in Merkel cells (by about 70%) only in the presence of extracellular Ca2+, indicating an influx of Ca2+ through voltage-gated channels. The Ca2+ response was abolished neither by (+)-BayK8644 nor omega-conotoxin, suggesting that the Ca2+ channels are different from the classical L- or N-type channels. Extracellular application of ATP (10 microM to 5 mM) caused dose-dependent increases in intracellular Ca2+ levels in Merkel cells of up to sevenfold from the basal level of about 100 nM. Similar responses to ATP were also measured during superfusion with Ca(2+)-free medium, suggesting intracellular stores as the main Ca2+ source. Pre-incubation of Merkel cells with the purinoceptor antagonist suramin (100 microM) for 30 min reduced the Ca2+ responses to ATP by about 50% compared with control conditions. In conclusion, the results have demonstrated that a rise in intracellular Ca2+ in Merkel cells can be evoked by mechanical stimulation, membrane depolarization and chemical stimulation by ATP. These observations strongly suggest a possible contribution of Ca2+ to the normal responsiveness of Merkel cell mechanoreceptors, in turn supporting the hypothesis that Merkel cells are involved in the mechano-electric transduction process in sinus hair type I mechanoreceptors.

Inhibitory synaptic potentials in guinea-pig substantia nigra dopamine neurones in vitro

1. The properties of stimulus-evoked and spontaneous inhibitory synaptic potentials were examined in guinea-pig substantia nigra dopamine neurones in sagittal and coronal midbrain slices in the presence of glutamate receptor antagonists. 2. Focal electrical stimulation within the substantia nigra, cerebral peduncle, internal capsule or the striatum evoked a biphasic IPSP consisting of a fast and a slow component, with peak latencies of about 30 and 250 ms, respectively. The fast component was sensitive to chloride injection, reversed polarity at -79.4 +/- 1.1 mV and was blocked by the GABAA receptor antagonists picrotoxin and bicuculline. The slow IPSP reversed at -99.3 +/- 5.4 mV and was blocked by the GABAB receptor antagonists 2-hydroxysaclofen and CGP 35348. 3. Spontaneous IPSPs were observed in many neurones. These events reversed polarity at -77.5 +/- 2.6 mV and were completely blocked by bicuculline and/or picrotoxin. In the presence of TTX, small spontaneous events remained which probably represent miniature IPSPs. In coronal slices, application of 4-aminopyridine raised the frequency of spontaneous IPSPs, presumably by activating nigral interneurones, but failed to reveal spontaneous biphasic IPSPs or spontaneous pure slow IPSPs. 4. The amplitude of the fast IPSPs fluctuated from trial to trial. Amplitude histograms of minimal fast IPSPs displayed evenly spaced peaks, suggesting that synaptic transmission is quantal at these synapses. The measured peak spacing depended on the driving force for Cl-. 5. The fast IPSP showed little or no paired-pulse depression, and in the presence of 2-hydroxysaclofen (400-600 microM) showed paired-pulse facilitation. The GABAB agonist baclofen inhibited the fast IPSP via a presynaptic mechanism. The pharmacologically isolated slow IPSP showed marked paired-pulse facilitation. 6. It is concluded that synaptic inhibition in the substantia nigra is mediated by GABA, is relatively resistant to frequency-dependent depression and is regulated by presynaptic GABAB autoreceptors. Striatonigral and pallidonigral fibres activate both GABAA and GABAB receptors, while intranigral pathways appear to activate predominantly GABAA receptors.

Taurine and glycine activate the same Cl- conductance in substantia nigra dopamine neurones

Intracellular recordings were made from substantia nigra dopamine neurones in a rat brain slice preparation. Spontaneous firing in these cells was reversibly inhibited by taurine applied by superfusion (300 microM-20 mM) or by focal pressure ejection. Neurones recorded with electrodes filled with KCl were depolarised at resting potential by taurine; the taurine depolarisation reversed polarity at -36.6 +/- 1.0 mV (7 cells). When electrodes filled with K-acetate or K-methyl sulphate were used, taurine caused a hyperpolarisation which reversed at -74.2 +/- 3.8 mV (9 cells). These effects of taurine were accompanied by a fall in input resistance or, in voltage clamp, an increase in conductance. Taurine thus appeared to increase membrane chloride conductance. The effect of taurine persisted in tetrodotoxin, 0-Ca2+/10 mM Mg2+, and bicuculline, but was blocked by strychnine (10 microM). Maximal responses to either taurine or glycine occluded responses to the other amino acid. Taurine therefore acts directly on dopamine neurones in the substantia nigra to increase the same membrane Cl- conductance as that mediating the action of glycine. Taurine may also act at the same recognition site as glycine in these cells.

The use of routine wound swabs and Kardex review for the surveillance of surgical wound infections

Prospective post-operative wound surveillance was carried out in two phases on 1285 patients. A total of 120 infections were documented. In phase I a review of routine swabs and Kardex was conducted in parallel with continuous surveillance. In this phase continuous surveillance detected 31/35 infections and routine swabs and Kardex methods picked up 28/35 infections. In phase 2 continuous surveillance was not carried out and routine swab and Kardex review detected 78/85 infections. Overall II infections were documented following discharge. Continuous surveillance is sensitive but laborious. The method described here would enable infection control nurses to visit patients in whom infections are more likely to occur, and still provide reliable and accurate rates of infections.

Electrophysiology of dopaminergic and non-dopaminergic neurones of the guinea-pig substantia nigra pars compacta in vitro

1. The membrane properties of substantia nigra pars compacta neurones were studied using an in vitro slice preparation of guinea-pig midbrain. 2. Neurones were divided into two classes based on their electrophysiological properties: bursting neurones displayed a burst of several rapidly accommodating action potentials in response to relaxation of hyperpolarizing current injected through the microelectrode, while non-bursting neurones produced regularly spaced action potentials. These neuronal types were found to be electrophysiologically distinct from those recorded in the substantia nigra pars reticulata and the subthalamic nucleus. 3. Non-bursting neurones, which comprised ca 85% of the sampled cells, were characterized by a slow, pacemaker pattern of firing at rest, broad action potentials, a pronounced spike after-hyperpolarization, long membrane time constants, and strong transient outward and time-dependent inward rectification. 4. Bursting neurones, comprising ca 15% of the sample, displayed rapid firing rates at rest, fast action potentials, a shallow spike after-hyperpolarization and briefer membrane time constants. All of these parameters were significantly different from those of the non-bursting type. Bursting neurones lacked transient outward or time-dependent inward rectification. 5. Both types of cells were capable of generating pronounced calcium-dependent, low-threshold spikes in the presence of tetrodotoxin (TTX). However, only the non-bursting type displayed calcium-dependent rhythmic oscillations in membrane potential near resting potential in the presence of TTX. The firing rate, action potential shape and after-hyperpolarization of non-bursting neurones were strongly influenced by calcium-dependent currents. 6. The majority of cells were injected with biocytin, which allowed morphological reconstruction of the neurones and confirmation of their location within the pars compacta. Non-bursting neurones had variable soma shapes and their dendrites were mostly directed in a medio-lateral direction. Many cells extended some of their dendrites into the pars reticulata. Bursting neurones were mainly fusiform in shape with their dendrites oriented in a medio-lateral direction; a few had dendrites extending into the pars reticulata. 7. Thirty-six neurones were also double labelled using a combination of biocytin or Lucifer Yellow injection with tyrosine hydroxylase (TH) immunohistochemistry. Non-bursting neurones all displayed TH immunofluorescence, while none of the bursting neurones were TH positive.(ABSTRACT TRUNCATED AT 400 WORDS)

Contractile response of the isolated dorsal aorta of the snake to angiotensin II and norepinephrine

Vasopressor action is a phylogenetically old function of angiotensin (ANG) II. The action can be ascribed to both direct activation of vascular ANG II receptors and through catecholamine release. In the Rat snake, Ptyas korros, the possible presence of common adrenergic-ANG receptors and their involvement in this action have been proposed. In order to elucidate the vasopressor mechanism of ANG II in the snake, and to test the presence of common adrenergic-ANG receptors, the contractile response of isolated snake dorsal aorta to [Val5]ANG II and norepinephrine (NE) was studied using the cobra, Naja naja and the Rat snake, Ptyas korros. Both ANG II (3 X 10(-11) to 10(-6) M) and NE (10(-8) to 10(-5) M) produced a dose-dependent increase in tension in the aortic strips of Naja, which were more sensitive to ANG II. Phenotolamine, an alpha-adrenergic antagonist, competitively inhibited NE without altering the response to ANG II. [Sar1, Ala8]ANG II inhibited ANG II but did not affect the response to NE. A similar dose-dependent increase in tension in the aortic strips of Ptyas was seen with NE (10(-8) to 10(-5) M) but these strips did not respond to ANG II. These results suggest that functionally separate receptors for ANG II and NE exist in the dorsal aorta of the cobra and that local liberation of catecholamines from the adrenergic nerve terminals do not play a role in the expression of ANG II action. There also exist differences in the nature of ANG II action/receptors among different species of snakes and different vascular beds in the same species.