Activation of Rod Input in a Model of Retinal Degeneration Reverses Retinal Remodeling and Induces Formation of Functional Synapses and Recovery of Visual Signaling in the Adult Retina.

A major cause of human blindness is the death of rod photoreceptors. As rods degenerate, synaptic structures between rod and rod bipolar cells disappear and the rod bipolar cells extend their dendrites and occasionally make aberrant contacts. Such changes are broadly observed in blinding disorders caused by photoreceptor cell death and are thought to occur in response to deafferentation. How the remodeled retinal circuit affects visual processing following rod rescue is not known. To address this question, we generated male and female transgenic mice wherein a disrupted cGMP-gated channel (CNG) gene can be repaired at the endogenous locus and at different stages of degeneration by tamoxifen-inducible cre-mediated recombination. In normal rods, light-induced closure of CNG channels leads to hyperpolarization of the cell, reducing neurotransmitter release at the synapse. Similarly, rods lacking CNG channels exhibit a resting membrane potential that was ~10 mV hyperpolarized compared to WT rods, indicating diminished glutamate release. Retinas from these mice undergo stereotypic retinal remodeling as a consequence of rod malfunction and degeneration. Upon tamoxifen-induced expression of CNG channels, rods recovered their structure and exhibited normal light responses. Moreover, we show that the adult mouse retina displays a surprising degree of plasticity upon activation of rod input. Wayward bipolar cell dendrites establish contact with rods to support normal synaptic transmission, which is propagated to the retinal ganglion cells. These findings demonstrate remarkable plasticity extending beyond the developmental period and support efforts to repair or replace defective rods in patients blinded by rod degeneration.SIGNIFICANCE STATEMENT Current strategies for treatment of neurodegenerative disorders are focused on the repair of the primary affected cell type. However, the defective neurons function within a complex neural circuitry, which also becomes degraded during disease. It is not known whether rescued neurons and the remodeled circuit will establish communication to regain normal function. We show that the adult mammalian neural retina exhibits a surprising degree of plasticity following rescue of rod photoreceptors. The wayward dendrites of rod bipolar cells re-establish contact with rods to support normal synaptic transmission, which is propagated to the retinal ganglion cells. These findings support efforts to repair or replace defective rods in patients blinded by rod cell loss.

The impact of seasonality on the dynamics and control of Ascaris lumbricoides infections.

Intestinal nematode infections affect a huge proportion of the world's population. Increasingly these infections, particularly amongst the poorest communities, are controlled through mass drug treatment programs. Seasonal variations of climate and behaviour in these regions can be significant, but their impact on the dynamics of infection and implications for the effectiveness of any mass drug treatment program (a pulsed reduction in worm burden in hosts) is not clearly understood. Here the effect of seasonality on the dynamics of the soil-based helminth, Ascaris lumbricoides, is investigated using a reformulated version of the Anderson-May model for macro-parasitic infections. Explicit analytical expressions are obtained for the stable oscillatory solution over the annual cycle, which provides a means of relating times of peak numbers of eggs, larvae and mature worms to seasonal variations. Numerical and analytical techniques are then used to consider the impact of seasonality on the optimal timing of drug treatment. Our results show that there is a relatively large window for the timing of optimal treatment, and the impact of repeated annual mass drug treatments can be substantially improved if they are timed to coincide with the months when the number of eggs and larvae are at their lowest - minimising reinfection. In terms of a more measurable quantity, in our example this corresponds to the months when the seasonal temperature is highest. Multiple annual treatments at (or close to) the optimal time each year are predicted to achieve local elimination in the community, whereas treatment at other times has a more limited impact. A key finding is that even for pronounced seasonality, perturbations in mean worm burden, and hence seasonal variation in observed egg output, may be small, potentially explaining why seasonal effects have been overlooked. Taken together these results suggest that seasonality of soil-transmitted helminths requires further experimental, field and mathematical study if the impact for mass drug administration programs is to be exploited.

The descriptive epidemiology of accelerometer-measured physical activity in older adults.

BACKGROUND: Objectively measured physical activity between older individuals and between populations has been poorly described. We aimed to describe and compare the variation in accelerometry data in older UK (EPIC-Norfolk) and American (NHANES) adults. METHODS: Physical activity was measured by uniaxial accelerometry in 4,052 UK (49-91 years) and 3459 US older adults (49-85 years). We summarized physical activity as volume (average counts/minute), its underlying intensity distribution, and as time spent <100counts/minute, ≥809counts/minute and ≥2020counts/minute both for total activity and that undertaken in ≥10-min bouts. RESULTS: In EPIC-Norfolk 65% of wear-time was spent at <100 counts/minute and 20% spent in the range 100-500 counts/minute. Only 4.1% of this cohort accumulated more than 30 min/day of activity above 2020 counts/minute in 10-min bouts. If a cut-point of >809 counts/minute is used 18.7% of people reached the 30 min/day threshold. By comparison, 2.5% and 9.5% of American older adults accumulated activity at these levels, respectively. CONCLUSION: As assessed by objectively measured physical activity, the majority of older adults in this UK study did not meet current activity guidelines. Older adults in the UK were more active overall, but also spent more time being sedentary than US adults.

Frequency of undiagnosed psoriatic arthritis among psoriasis patients in Australian dermatology practice.

BACKGROUND: Psoriatic arthritis commonly develops in psoriasis patients and, if undiagnosed, can lead to potentially avoidable joint damage and an increased risk of comorbidity and mortality. Increased awareness of PsA symptoms among dermatologists provides an opportunity for earlier diagnosis, more timely therapy and prevention of disability. OBJECTIVE: To provide Australian epidemiological data on the frequency of undiagnosed PsA among psoriasis patients in dermatology practice, and to investigate the impact of psoriasis on quality of life and work productivity. METHODS: Nine tertiary centre dermatology practices enrolled patients presenting with plaque psoriasis and no prior rheumatologist-confirmed PsA diagnosis. Patients were screened using the Psoriatic Arthritis Screening and Evaluation (PASE) questionnaire and were referred to a rheumatologist for assessment of PsA status using CASPAR criteria if they had a PASE score ≥44. RESULTS: Based on the composite and sequential application of PASE and CASPAR criteria, undiagnosed PsA among psoriasis patients in this study is 9% [95% CI: 6, 12]. The PPV of PASE in this setting is 26% [95% CI: 19, 34]. Nail involvement and chronic large plaque psoriasis were identified as independent positive predictors of PsA, whereas scalp psoriasis was an independent negative predictor of PsA. Patients with moderate-to-severe psoriasis (PASI ≥15) had lower quality of life scores than patients with less severe psoriasis. CONCLUSION: In this study, the frequency of undiagnosed PsA in Australian dermatology practice was 9% among plaque psoriasis patients with no prior PsA diagnosis. Compared with psoriasis alone, the impact of undiagnosed PsA on health-related quality of life of psoriasis patients is substantial.

Variant innervation of the mylohyoid muscle by the lingual nerve.

The nerve to mylohyoid muscle supplies the mylohyoid and the anterior belly of the digastric muscles, with terminal sensory branches that might innervate the submental skin and mandibular teeth. The nerve to mylohyoid muscle typically originates from the posterior surface of the inferior alveolar nerve right before entering the mandibular foramen. In rare cases, the nerve to mylohyoid muscle arises from the lingual nerve. The variations of the nerve to mylohyoid muscle might have led to failure of an inferior alveolar nerve blockade. During the routine dissection of a cadaveric head, a rare case was identified where the nerve to mylohyoid muscle had origins from both the inferior alveolar and lingual nerves. This case is reviewed and salient literature reviewed.

Combining etanercept with traditional agents in the treatment of psoriasis: a review of the clinical evidence.

Psoriasis is a chronic, systemic inflammatory disorder manifesting primarily in skin and potentially in joints, frequently necessitating treatment with conventional systemic therapies, phototherapy or biological agents. Patients with moderate to severe disease suffer a diminished quality of life, experience significant comorbidities and have a higher mortality. Although traditional treatments are effective in the short-term, their use is often limited by concerns over long-term toxicity, including end-organ damage and risk of malignancy. Combination therapy is a commonly used approach and is often more effective than any single agent. Lower doses of two treatments in combination can also minimize potential side effects from a single agent at higher doses. Etanercept is a recombinant human tumour necrosis factor (TNF)α receptor (p75) protein fused with the Fc portion of IgG1 that binds to TNFα. This article reviews the evidence on the efficacy and safety of etanercept in combination with methotrexate, acitretin, narrowband UVB and cyclosporin. The largest body of evidence assesses the combination with methotrexate, although evidence is available for the other combinations. Data suggest that although highly effective as monotherapy, etanercept in combination with a conventional systemic agent can enhance efficacy and allow drug sparing. Potentially, the combination may also result in faster treatment responses and permit safe transitioning from one systemic agent to another. Evidence to date suggests that these benefits can be achieved without significant additional toxicity, although long-term data on the efficacy and safety of the combination in psoriatic populations is limited and further evaluation is warranted.

Honey promotes angiogeneic activity in the rat aortic ring assay.

OBJECTIVE: To investigate possible effects of honey on angiogenesis, using in vitro analogues of angiogenesis and an endothelial proliferation assay. METHOD: Using an in vitro rat aortic ring assay we compared pseudotubule formation by medicinal honey (Activon), supermarket honey (Rowse) and a honey-based ointment (Mesitran), with that of artificial honey (70% w/w sugar glucose/fructose). Pseudotubules were analysed using TCS Cellworks AngioSys software. The Angiokit sytem was used to validate the results. Using the MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium. Bromide] assay, toxicity was also assessed on human umbilical vein endothelial cells (HUVEC) directly adherent to plastic. RESULTS: All honey preparations stimulated pseudotubule formation, maximal at around 0.2% honey. Medicinal honeys were more active than Rowse. The effect was not attributable to the sugar content. Among the honeys tested, the Manuka-based Activon preparation reduced residual viable biomass compared with a sugar control at > 0.32% v/v concentration. Rowse had a similar effect only at 2.5%, the highest dose tested. CONCLUSION: The influence of honey constituents on angiogenesis in a wound dressing context is likely to be positive, but would depend on the effective dilution of the honey and the penetration of the active constituents against an osmotic gradient. The extent to which this occurs has yet to be established. CONFLICT OF INTEREST: This work was conceived, designed and executed by the authors. Medical honey preparations were supplied unconditionally but free of charge by the distributors.

Basic compatibility of Albugo candida in Arabidopsis thaliana and Brassica juncea causes broad-spectrum suppression of innate immunity.

A biotrophic parasite often depends on an intrinsic ability to suppress host defenses in a manner that will enable it to infect and successfully colonize a susceptible host. If the suppressed defenses otherwise would have been effective against alternative pathogens, it follows that primary infection by the "suppressive" biotroph potentially could enhance susceptibility of the host to secondary infection by avirulent pathogens. This phenomenon previously has been attributed to true fungi such as rust (basidiomycete) and powdery mildew (ascomycete) pathogens. In our study, we observed broad-spectrum suppression of host defense by the oomycete Albugo candida (white blister rust) in the wild crucifer Arabidopsis thaliana and a domesticated relative, Brassica juncea. A. candida subsp. arabidopsis suppressed the "runaway cell death" phenotype of the lesion mimic mutant lsd1 in Arabidopsis thaliana in a sustained manner even after subsequent inoculation with avirulent Hyaloperonospora arabidopsis (Arabidopsis thaliana downy mildew). In sequential inoculation experiments, we show that preinfection by virulent Albugo candida can suppress disease resistance in cotyledons to several downy mildew pathogens, including contrasting examples of genotype resistance to H. arabidopsis in Arabidopsis thaliana that differ in the R protein and modes of defense signaling used to confer the resistance; genotype specific resistance in B. juncea to H. parasitica (Brassica downy mildew; isolates derived from B. juncea); species level (nonhost) resistance in both crucifers to Bremia lactucae (lettuce downy mildew) and an isolate of the H. parasitica race derived from Brassica oleracea; and nonhost resistance in B. juncea to H. arabidopsis. Broad-spectrum powdery mildew resistance conferred by RPW8 also was suppressed in Arabidopsis thaliana to two morphotypes of Erysiphe spp. following pre-infection with A. candida subsp. arabidopsis.

[Diagnosis and treatment of infectious pharyngeal inflammation].

Symptoms of viral and/or streptococcal infectious pharyngitis are of interest in the context of different therapeutic strategies. This study involved 3 family medicine clinics, one emergency service department, and 694 patients. Streptococcal pharyngitis occurred in 24% of the adult patients and in 29% of all the patients. The remaining ones had acute viral pharyngitis or a mixed viral/bacterial infection. Medicamentous therapy given to 98% of the patients included local antibiotics (42%), systemic antibacterial monotherapy (12%), and combined antibiotic therapy (44%). Lysozime-containing preparations (larypront, dequalar, etc.) recommended for pathogenetic therapy had the active ingredient in the form of a dequalinium complex to deliver lysozime to pharyngeal mucosa. The frequency of streptococcal infection in patients with secondary sore throat receiving the combined treatment was twice lower (12%) than in the general group. The strategy of therapy was the same as in primary sore throat.

The impact of morphine treatment on bladder cancer cell proliferation and apoptosis: in vitro studies.

AIM: The aim of this study was to determine the effect of morphine on bladder cancer cell proliferation and apoptosis in vitro. MATERIALS AND METHODS: MTT assay was used to measure percentage growth of RT-112 human bladder cancer cells after 72 hours of morphine/morphine + naloxone treatment. Expression of µ-opioid receptors was assessed by Western blot and finally, apoptotic assay with CellEvent Caspase-3/7 Green Detection Reagent was carried out using confocal microscopy. RESULTS: The MTT assays showed that morphine increased RT-112 cell growth. Naloxone inhibited this growth enhancing effect. Western blot analysis regarding µ-opioid receptor expression in RT-112 cells remains inconclusive. Morphine was also found to decrease the rate of apoptosis of RT-112 cells, an effect which naloxone inhibited. CONCLUSIONS: This study provides evidence that morphine, at clinically relevant doses, causes RT-112 bladder cancer cell proliferation, possibly opioid receptor mediated and at least some of this effect might be due to decreased apoptosis. Clinically, this suggests that in patients with bladder cancer, managing pain with morphine might have detrimental consequences on patient outcomes and alternative pain relief should be considered if possible.

Stable and specific association between the yeast recombination and DNA repair proteins RAD1 and RAD10 in vitro.

The RAD1 and RAD10 genes of Saccharomyces cerevisiae are two of at least seven genes which are known to be required for damage-specific recognition and/or damage-specific incision of DNA during nucleotide excision repair. RAD1 and RAD10 are also involved in a specialized mitotic recombination pathway. We have previously reported the purification of the RAD10 protein to homogeneity (L. Bardwell, H. Burtscher, W. A. Weiss, C. M. Nicolet, and E. C. Friedberg, Biochemistry 29:3119-3126, 1990). In the present studies we show that the RAD1 protein, produced by in vitro transcription and translation of the cloned gene, specifically coimmunoprecipitates with the RAD10 protein translated in vitro or purified from yeast. Conversely, in vitro-translated RAD10 protein specifically coimmunoprecipitates with the RAD1 protein. The sites of this stable and specific interaction have been mapped to the C-terminal regions of both polypeptides. This portion of RAD10 protein is evolutionarily conserved. These results are the first biochemical evidence of a specific association between any eukaryotic proteins genetically identified as belonging to a recombination or DNA repair pathway and suggest that the RAD1 and RAD10 proteins act at the same or consecutive biochemical steps in both nucleotide excision repair and mitotic recombination.

Fruit and vegetable intake and cardiovascular risk factors in people with newly diagnosed type 2 diabetes.

BACKGROUND/OBJECTIVES: The cardiovascular benefit of increasing fruit and vegetable (F&V) intake following diagnosis of diabetes remains unknown. We aimed to describe how quantity and variety of F&V intake, and plasma vitamin C, change after diagnosis of type 2 diabetes and examine whether these changes are associated with improvements in cardiovascular risk factors. SUBJECTS/METHODS: A total of 401 individuals with screen-detected diabetes from the ADDITION-Cambridge study were followed up over 5 years. F&V intake was assessed by food frequency questionnaire and plasma vitamin C at baseline, at 1 year and at 5 years. Linear mixed models were used to estimate associations of changes in quantity and variety of F&V intake, and plasma vitamin C, with cardiovascular risk factors and a clustered cardiometabolic risk score (CCMR), where a higher score indicates higher risk. RESULTS: F&V intake increased in year 1 but decreased by year 5, whereas variety remained unchanged. Plasma vitamin C increased at 1 year and at 5 years. Each s.d. increase (250g between baseline and 1 year and 270g between 1 and 5 years) in F&V intake was associated with lower waist circumference (-0.92 (95% CI: -1.57, -0.27) cm), HbA1c (-0.11 (-0.20, -0.03) %) and CCMR (-0.04 (-0.08, -0.01)) at 1 year and higher high-density lipoprotein (HDL)-cholesterol (0.04 (0.01, 0.06) mmol/l) at 5 years. Increased plasma vitamin C (per s.d., 22.5 µmol/l) was associated with higher HDL-cholesterol (0.04 (0.01, 0.06) mmol/l) and lower CCMR (-0.07 (-0.12, -0.03)) between 1 and 5 years. CONCLUSIONS: Increases in F&V quantity following diagnosis of diabetes are associated with lower cardiovascular risk factors. Health promotion interventions might highlight the importance of increasing, and maintaining increases in, F&V intake for improved cardiometabolic health in patients with diabetes.

The descriptive epidemiology of the diurnal profile of bouts and breaks in sedentary time in older English adults.

Background: High sedentary time is associated with adverse metabolic health outcomes and mortality in older adults. It has been suggested that breaking up sedentary time may be beneficial for metabolic health; however, population prevalence data are lacking on the patterns of sedentary behaviour which would identify opportunities for intervention. Methods: We used data of adults aged ≥ 60 years (n = 3705) from the population-based EPIC-Norfolk cohort, to characterize the patterns of total sedentary time, breaks in sedentary time and sedentary bouts across the day and assess their associations with participant characteristics, using multi-level regression. Sedentary time was measured objectively by a hip-mounted accelerometer (ActigraphTM GT1M) worn for 7 days during waking time. Results: More than 50% of every waking hour was spent sedentary, increasing to a peak of 83% in the evening. On average fewer breaks were accrued in the evenings compared with earlier in the day. Marginally more sedentary time was accrued on weekend days compared with weekdays (difference 7.4 min, 95% confidence interval 5.0-9.7). Large proportions of this sedentary time appear to be accrued in short bouts (bouts of < 10 min for 32% of the time). Older age, being male, being retired, not being in paid employment and having a higher body mass index were associated with greater sedentary time and fewer breaks. Conclusion: Sedentary time is common throughout the day but peaks in the evenings with fewer breaks and longer bouts. We identified a number of characteristics associated with sedentary time and additionally inversely associated with sedentary breaks, which should inform the development and targeting of strategies to reduce sedentary time among older adults.

Furosemide reverses multidrug resistance status in bladder cancer cells in vitro.

BACKGROUND: Multidrug resistance (MDR) has a potentially serious influence on cancer treatment and should be taken into consideration in the design and application of therapeutic regimens. It is mediated through the activity of cellular pumps. AIM: To investigate whether furosemide, itself a pump-blocker, reverses MDR in an in vitro model. MATERIALS AND METHODS: An MDR bladder cancer cell line (MGH-u 1R) and its parental (drug sensitive) clone were exposed to epirubicin and furosemide, with the concentration of one drug fixed and that of the other serially diluted in a 96-well plate format. Both drugs formed the variable component in separate experiments. After a 1-h exposure, the cells were washed and replenished with fresh medium. To examine the toxicity of epirubicin and furosemide separately and in combination, monotetrazolium-based assays were carried out. Intracellular epirubicin distribution was assessed by confocal microscopy as a second index of resistance status after in vitro exposure. RESULTS: MGH-u 1R cells incubated with furosemide showed distribution of drug similar to that in the parental cells (MGH-u 1 sensitive). Controls (without furosemide) continued to show a resistant pattern of fluorescence. In cytotoxicity assays furosemide appeared substantially non-toxic. Resistant cells in the toxicity titration experiments showed increased resistance to levels of furosemide over 500 mug/ml. Parental cells were made only marginally more sensitive against increased background toxicity. CONCLUSION: Furosemide is effective in reversing MDR status in bladder cancer cell lines in vitro. It may also have an increment of intrinsic cytotoxicity, but only at higher concentrations. We propose a potential for further investigation of furosemide as an adjunct to chemotherapy for superficial bladder cancer.

Meglumine Eicosapentaenoic acid (MeEPA) a new soluble omega-3 fatty acid formulation: in vitro bladder cancer cytotoxicity tests in combination with epirubicin and mitomycin.

OBJECTIVE: To determine if Meglumine-Eicosapentaenoic Acid (MeEPA) acts synergistically with epirubicin and mitomycin to enhance cytotoxicity towards bladder cancer cell lines in vitro. MATERIALS AND METHODS: Bladder cancer cells were exposed to MeEPA in combination with epirubicin or mitomycin. Residual viable cell biomass was estimated with the methyl-thiazoldiphenyl tetrazolium (MTT) assay following drug exposure. Drug interaction was analysed using median effect analysis to determine levels of synergism. RESULTS: Most combinations of MeEPA with both epirubicin and mitomycin showed a high-level of synergism. At high doses, drug precipitation adversely affected MTT assay analysis suggesting antagonism of action. However, the predominant pattern was of synergism for most dose combinations tested. CONCLUSION: Bladder cancer treated by endoscopic resection alone is subject to high recurrence rates. Post-operative intravesical instillation of epirubicin and mitomycin can halve recurrence rates, but there is no evidence that disease progression to invasive bladder cancer is altered. Thus, optimisation of current treatment strategies is required. The anti-tumour activity of fatty acids is well established and MeEPA is a new, soluble formulation with the potential to enhance intravesical drug efficacy.

Seminal prostasomes inhibit the angiogenesis activity of rat aortic rings.

Prostasomes are organelles secreted by prostatic epithelial cells, and are believed to have a role in fertility and prostatic disease. They are known to influence sperm motility and the acrosome reaction, and are thought to have a role in cell transformation, immunosuppression, proliferation, facilitation of local invasion, and angiogenesis. Previously, we have demonstrated the inhibitory effect of prostasomes derived from human semen on angiogenesis using HUVEC cells grown on matrigel. In this study, we use the rat aortic ring assay system, arguably a closer reflection of the in vivo situation. Quantification was by a spectrophotometric method, and underlying mechanisms assessed. Prostasomes demonstrated a clear inhibition of angiogenesis, and this effect persisted after heat treatment of prostasomes to denature protein. This fits with other known effects of prostasomes known to be due to the membrane lipid component, which is unusually high in sphingomyelin and cholesterol.

The selective vulnerability of striatopallidal neurons.

The different types of striatal neuron show a range of vulnerabilities to a variety of insults. This can be clearly seen in Huntington's disease where a well mapped pattern of pathological events occurs. Medium spiny projection (MSP) neurons are the first striatal cells to be affected as the disease progresses whilst interneurons, in particular the NADPH diaphorase positive ones, are spared even in the late stages of the disease. The MSP neurons themselves are also differentially affected. The death of MSP neurons in the patch compartment of the striatum precedes that in the matrix compartment and the MSP neurons of the dorsomedial caudate nucleus degenerate before those in the ventral lateral putamen. The enkephalin positive striatopallidal MSP neurons are also more vulnerable than the substance P/dynorphin MSP neurons. We review the potential causes of this selective vulnerability of striatopallidal neurons and discuss the roles of endogenous glutamate, nitric oxide and calcium binding proteins. It is concluded that MSP neurons in general are especially susceptible to disruptions of cellular respiration due to the enormous amount of energy they expend on maintaining unusually high transmembrane potentials. We go on to consider a subpopulation of enkephalinergic striatopallidal neurons in the rat which are particularly vulnerable. This subpopulation of neurons readily undergo apoptosis in response to experimental manipulations which affect dopamine and/or corticosteroid levels. We speculate that the cellular mechanisms underlying this cell death may also operate in degenerative disorders such as Huntington's disease thereby imposing an additional level of selectivity on the pattern of degeneration. The possible contribution of the selective death of striatopallidal neurons to a number of clinically important psychiatric conditions including obsessive compulsive disorders and Tourette's syndrome is also discussed.

Short-term metabolic fate of L-[13N]glutamate in the Walker 256 carcinosarcoma in vivo.

In vivo studies with L-[13N]glutamate in the Walker 256 carcinosarcoma implanted under the renal capsule of female Sprague-Dawley rats demonstrate that uptake of glutamate and the rate of incorporation of the nitrogen label from this amino acid into metabolites is slower in the tumor than in nontumorous kidney tissue. Glutamate dehydrogenase, glutaminase, and alanine aminotransferase activities are significantly lower within the tumor than within the adjoining kidney. However, the tumor expresses high levels of aspartate aminotransferase, attesting to the importance of this enzyme in the metabolism of glutamate. Indeed, high performance liquid chromatographic analysis showed that the principal metabolic fate of label derived from L-[13N]glutamate in the tumor is incorporation into aspartate. Measurement of specific activity ratios of glutamate to aspartate shows that the transfer of nitrogen from glutamate to aspartate is rapid and that equilibration of label among components of the aspartate aminotransferase reaction is attained within minutes after tumor uptake. Analyses of the nontumorous portion of the implanted kidney also showed that aspartate is the major recipient of glutamate nitrogen. However, high performance liquid chromatographic analyses of deproteinized tissue revealed that glutamine and ammonia are also significant 13N-labeled metabolites formed from L-[13N]glutamate within the kidney. Proportionately lower amounts of these labeled metabolites were found in the tumor.

Presynaptic mu and delta opioid receptor modulation of GABAA IPSCs in the rat globus pallidus in vitro.

The role of enkephalin and the opioid receptors in modulating GABA release within the rat globus pallidus (GP) was investigated using whole-cell patch recordings made from visually identified neurons. Two major GP neuronal subtypes were classified on the basis of intrinsic membrane properties, action potential characteristics, the presence of the anomalous inward rectifier (Ih), and anode break depolarizations. The mu opioid receptor agonist [D-Ala2-N-Me-Phe4-Glycol5]-enkephalin (DAMGO) (1 microM) reduced GABAA receptor-mediated IPSCs evoked by stimulation within the striatum. DAMGO also increased paired-pulse facilitation, indicative of presynaptic mu opioid receptor modulation of striatopallidal input. In contrast, the delta opioid agonist D-Pen-[D-Pen2, 5]-enkephalin (DPDPE) (1 microM) was without effect. IPSCs evoked by stimulation within the GP were depressed by application of [methionine 5']-enkephalin (met-enkephalin) (30 microM). Met-enkephalin also reduced the frequency, but not the amplitude, of miniature IPSCs (mIPSCs) and increased paired-pulse facilitation of evoked IPSCs, indicative of a presynaptic action. Both DAMGO and DPDPE reduced evoked IPSCs and the frequency, but not amplitude, of mIPSCs. However, spontaneous action potential-driven IPSCs were reduced in frequency by met-enkephalin and DAMGO, whereas DPDPE was without effect. Overall, these results indicate that presynaptic mu opioid receptors are located on striatopallidal terminals and pallidopallidal terminals of spontaneously firing GP neurons, whereas presynaptic delta opioid receptors are preferentially located on terminals of quiescent GP cells. Enkephalin, acting at both of these receptor subtypes, serves to reduce GABA release in the GP and may therefore act as an adaptive mechanism, maintaining the inhibitory function of the GP in basal ganglia circuitry.