Pb2+ modulates the NMDA-receptor-channel complex

Summary The actions of Pb²⁺ on NMDA channel currents of acutely dissociated hippocampal CA1- and CA3-neurones from adult rats activated by aspartate plus glycine (asp/gly) were examined. A fast reversible and a slow irreversible response to Pb²⁺ were found. Pb²⁺ applied simultaneously with asp/gly decreased an inward current. The threshold concentration was below 2 M, the current was reduced > 90% at concentrations over 100 M, The decrease of the asp/gly activated current showed no voltage dependence. Opening of NMDA channels was not necessary for Pb²⁺-action, as preincubation in 50 M Pb²⁺-containing external solution for several seconds dramatically reduced the response to asp/gly/Pb²⁺. This effect was reversed within 2 to 5 s of wash. Presence of Pb²⁺ or asp/Pb²⁺ or glycine/Pb²⁺ in the external solution did not prevent recovery of the NMDA receptor/channel complex from desensitization. Prolonged perfusion of a cell with the asp/gly/Pb²⁺-containing external solution resulted in an irreversible decrease of the asp/gly current, whereas the amplitude of the asp/gly/Pb²⁺ response did not change over the duration of an experiment. We conclude that Pb²⁺ modulates NMDA channel activity via interaction with the NMDA/glycine receptor: as a result the channel current decreases.Abbreviations NMDA N-methyl-D-aspartate - LTP long-term potentiation - AP5 2-amino-5-phosphonovalerate - EGTA ethylene glycol bis(-aminoethylether)-N,N,N,N-tetraacetic acid - HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid Correspondence to H. L. Haas at the above address     

Efficacy of various dithiol compounds in acute As2O3 poisoning in mice

The efficacy ofdl-dimercaptopropanol (British Anti-Lewisite, BAL),dl-dimercaptopropanesulfonate (DMPS), and meso-dimercaptosuccinic acid (DMS A) was compared in reducing the acute As₂O₃ toxicity in mice. Mice were treated with a single equimolar dose of a dithiol compound (0.7 mmol/kg i.p.) 0.5 or 30 min after the s.c. injection of various doses of As₂O₃. Both DMPS and DMSA were significantly (p<0.05) more effective in mice treated 0.5 min after the poisoning if compared to BAL on an equimolar level. The highest potency ratio (PR) (LD50 with treatment/LD5o without treatment) was found in animals injected with DMSA (PR=8.6). The corresponding value for DMPS was 4.2, and for BAL 2.1, respectively. In animals treated 30 min after poisoning the efficacy of DMPS (PR = 2.6) was similar to the efficacy of DMSA 2.4, both being only slightly superior to BAL 2.O. DMPS and DMSA were found to be much less toxic than BAL. The LD₅₀ of arsenic was 0.057 mmol/kg. The efficacy of BAL, DMPS, and DMSA in reducing the tissue content of arsenic following acute As₂O₃ poisoning was investigated in mice (n=6/group) and guinea pigs (n=3-4/group). The animals were injected s.c. with 0.043 mmol/kg As₂O₃ (containing a tracer dose of⁷⁴As(III)). Thirty minutes later the antidotes were administered A were more effective in reducing the arsenic content of tissues than BAL. Moreover, BAL caused accumulation of the toxicant in the brain. It is concluded that the recommendation of BAL as drug of choice in acute arsenic poisoning needs to be carefully re-evaluated.     

Hippocampal loss of the GABAA receptor α1 subunit in patients with chronic pharmacoresistant epilepsies

Alterations of gamma aminobutyric acid (GABA)-mediated neurotransmission have been implicated in the pathogenesis of epilepsies. Here we examine the distribution of the GABA_A receptor in the hippocampus of 78 surgical specimens from patients with chronic pharmacoresistant focal epilepsies. The receptor was localized immunohistochemically with the monoclonal antibody bd-24 which selectively recognizes the ₁ subunit of the GABA_A receptor. The results were compared with the receptor distribution of 28 normal hippocampal specimens obtained at autopsy. In the great majority of the surgical specimens a loss of GABA_A receptor immunoreactivity was present in CA1 (92.3%), CA4 (78.2%), the dentate granular cell layer (70.5%) and the molecular layer of the dentate gyrus (65.4%). The subiculum revealed a normal staining pattern in all but 4 cases. In no instance did we observe an increase of immunoreactivity in any region or cell population. The decrease of GABA_A receptor immunoreactivity was closely related to neuronal loss in the respective specimen and to Ammon's horn sclerosis. There was no correlation between GABA_A receptor loss and the patient's age at surgery, duration of seizures, age at onset of seizures and to the presence or absence of secondary generalized tonic clonic seizures. The data suggest that the observed loss of GABA_A receptor immunoreactivity is a secondary phenomenon rather than an event that is relevant for the pathogenesis of epileptic seizures.     

Kainate activates Ca2+-permeable glutamate receptors and blocks voltage-gated K+ currents in glial cells of mouse hippocampal slices

Glial cells in the CA1 stratum radiatum of the hippocampus of 9- to 12-day-old mice show intrinsic responses to glutamate due to the activation of -amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/ kainate receptors. In the present study we have focused on a subpopulation of the hippocampal glial cells, the complex cells, characterized by voltage-gated Na⁺ and K⁺ channels. Activation of glutamate receptors in these cells led to two types of responses, the activation of a cationic conductance, and a longer-lasting blockade of voltage-gated K⁺ channels. In particular, the transient (inactivating) component of the outwardly rectifying K⁺ current was diminished by kainate. Concomitantly, as described in Bergmann glial cells, kainate also elevated cytosolic Ca²⁺. This increase was due to an influx via the glutamate receptor itself. In contrast to Bergmann glial cells, the cytosolic Ca²⁺ increase was not a link to the K⁺ channel blockade, since the blockade occurred in the absence of the Ca²⁺ signal and, vice versa, an increase in cytosolic Ca²⁺ induced by ionomycin did not block the transient K⁺ current. We conclude that glutamate receptor activation leads to complex and variable changes in different types of glial cells; the functional importance of these changes is as yet unresolved.     

L-701,324, a selective antagonist at the glycine site of the NMDA receptor, counteracts haloperidol-induced muscle rigidity in rats

  Rationale: It has recently been suggested that the overactivity of glutamatergic neurotransmission may contribute to the pathophysiology of Parkinson’s disease. Therefore, a search for new compounds which block glutamatergic receptors and show antiparkinsonian properties in animal models of this disease seems to be justified. Objective: The aim of this study was to determine whether L-701,324 [7-chloro-4-hydroxy-3(3-phenoxy) phenylquinoline-2-(H)-one], a selective and full antagonist at the glycine site of the NMDA receptor, counteracts parkinsonian-like muscle rigidity and catalepsy induced by haloperidol in rats. Methods: The muscle tone was measured as the resistance developed to passive flexion and extension of the hind limb. Electromyographic (EMG) activity was additionally recorded in the gastrocnemius and tibialis anterior muscles. Results: L-701,324 (2.5–40 mg/kg IP) dose-dependently decreased the muscle tone enhanced by haloperidol (1–5 mg/kg IP). Likewise, the haloperidol-enhanced resting EMG activity and the EMG reflex response to passive movements were diminished by lower and almost abolished by higher doses of L-701,324. However, up to a dose of 20 mg/kg IP, L-701,324 did not influence haloperidol (0.5 mg/kg IP)-induced catalepsy. Moreover, L-701,324 (1.25–5 mg/kg IP) given alone or together with haloperidol (0.5–1 mg/kg IP) disturbed rotarod performance. Gross observation of behaviour indicated that rats injected with L-701,324 in doses equal to or higher than 5 mg/kg, alone or in combination with haloperidol, were markedly ataxic, i.e. rats showed signs of disturbed balance and loss of control over their hind limbs. Conclusions: The present study suggests that L-701,324 exhibits a beneficial action in the animal model of parkinsonian rigidity, but not that of parkinsonian akinesia. Nonetheless, this compound is not devoid of motor side-effects. Received: 1 February 1998 / Final version: 20 October 1998     

Motor activity of rats following intracerebral injections of drugs influencing GABA mechanisms

Summary Motor activity of rats was recorded following bilateral injections of GABA and the two GABA analogues gammahydroxybutyric acid (GHBA) and baclofen into the nucleus accumbens. GABA produced a shortlasting hypoactivity and this effect was potentiated by the GABA transaminase inhibitor aminooxyacetic acid (AOAA). More pronounced hypoactivities were caused by GHBA and baclofen. The hypoactivity was followed by hyperactivity after GHBA, baclofen and, to a small extent, after AOAA plus GABA. Systemic treatment with GHBA and GABA also suppressed motor activity and GHBA caused a subsequent hyperactivity. Small doses of GABA and particularly GHBA injected into the nucleus accumbens caused an increase in motor activity without the preceding decrease, especially when the rats were habituated to the environment. The effects appeared specific since no or only small changes in motor activity were induced by carnitine and betahydroxybutyric acid, structurally related to GABA and GHBA, respectively. Furthermore, the motor activity was stimulated by local treatment with the GABA receptor blocking agent picrotoxin, but not by strychnine or pentylenetetrazole. GHBA and GABA inhibited the apomorphine-induced activity of reserpine-treated rats indicating that these compounds stimulate GABA receptors beyond the dopamine synapses. The motor activity was depressed by GHBA and GABA given into the rostral and intermediate neostriatum and into the globus pallidus and, to a smaller extent, when given into the caudal neostriatum. The stimulatory effect of GHBA or picrotoxin was less, pronounced after local application to the globus pallidus or the neostriatum than when applied to the nucleus accumbens. The increased motor activity by GHBA, baclofen and GABA might be due to stimulation of GABA autoreceptors in the nucleus accumbens. The decreased motor activity might be evoked by stimulation of postsynaptic GABA receptors in the nucleus accumbens but a similar action in the corpus striatum might contribute.Part of the data was presented at the symposium on Interactions Among Putative Transmitters in the Brain held at the Mario Negri Institute, Milan, Italy on October 26–28, 1976     

Proliferation kinetics of the dermal infiltrate in cutaneous malignant lymphomas

Summary To obtain information about the role of local proliferation in the pathogenesis of dermal infiltrate in malignant cutaneous lymphomas, we determined the percentage of ³H-thymidine-labeled infiltrating cells (³H-index).A linear correlation was found between proliferative activity and clinical stage in mycosis fungoides, i.e., the ³H-index is moderately elevated in stage I and high in stage III.The ³H-index is within normal range in dermal infiltrate of Sézary syndrome, diffuse lymphocytic lymphoma, as well as in lymphocytoma benigna cutis.In parapsoriasis en plaques two groups can be distinguished: in the smallplaque variant (chronic superficial dermatitis) the ³H-index is low, whereas the large-plaque variant (prereticulotic poikiloderma) shows strong proliferative activity.Thus, determination of proliferative activity seems to give new insights into the pathogenesis of dermal infiltrate in cutaneous lymphomas.Zusammenfassung Um die Bedeutung der lokalen Zellproliferation im dermalen Infiltrat bei cutanen malignen Lymphomen zu untersuchen, bestimmten wir den Prozentsatz der ³H-Thymidin-markierten Infiltratzellen (³H-Index.Zwischen dem klinischen Stadium der Mycosis fungoides und der Proliferationsaktivität des dermalen Infiltrats besteht eine lineare Beziehung; im Stadium I ist die Proliferation niedrig, im Stadium III sehr hoch.Nicht erhöht ist der ³H-Index im dermalen Infiltrat beim Sézary-Syndrom, diffusen lymphocytischen Lymphom sowie bei Lymphocytoma benigna cutis.Bei der Parapsoriasis en plaques müssen zwei Formen unterschieden werden: bei der kleinfleckigen Form (chronic superficial dermatitis) ist der ³H-Index niedrig, während die großfleckige Form (Präretikulotisches Poikiloderm) eine starke Proliferationsaktivität aufweist.Die Untersuchung des Proliferationsverhaltens gibt neue Einblicke in die Pathogenese des dermalen Infiltrats cutaner Lymphome.     

Contribution of thallium-201-SPECT to the grading of tumorous alterations of the brain

Single photon emission computed tomography (SPECT) with thallium-201-chloride (²⁰¹TI) was used in 22 patients to assess the grade of malignancy of brain tumors.Low- and high-grade malignant gliomas could be well differentiated by calculating the Grade Index (GI), i.e., ²⁰¹TI uptake in the tumor area relative to a contralateral brain region. Low-grade gliomas (WHO-grade I–II) usually showed a GI of <1.5. Tumors classified histologically as high-grade malignant (WHO-grade III–IV) had GI values greater than 1.42 and a mean value of 1.89.Until labelled amino-acid tracers for gamma-cameras become commercially available, thallium-201 brain-SPECT can provide an independent and complementary method to CT/MRI for the differential diagnosis of grading of brain tumors. This simple technique can help to reduce sampling errors during needle biopsies of brain tumors, particularly of high-grade lesions incorrectly graded as low-grade tumors due to inadequate biopsy material. In addition, pre- and post-therapy studies can influence the strategy of therapy itself and allow an early detection of recurrences.     

Kluger's “Fixateur interne” for spinal instability

Kluger's Fixateur Interne proved to be an excellent tool not only in spinal trauma for repositioning of impacted fractures and transpedicular stabilization of the dorsal column but also in other forms of thoracic or lumbar instability.After spinal tumor excision from a dorsal approach and vertebral replacement with methylmethacrylate additional stability through dorsal fixation was achieved with this device.Spondylodiscitis, symptomatic spondylolisthesis, spinal instability from degenerative disc disease as well as nonunion following previous surgery could be cured using Kluger's internal fixation. Rare complications, i.e. from broken screws or rods (5%) caused no problems, but some patients required a second operation for readjustment of malpositioned screws which were causing pain or neurological deficit.     

Effects of molsidomine and dopamine infusion on the size of canine experimental myocardial infarct

Summary The effects of i.v. molsidomine and dopamine infusion on mean haemodynamic changes, myocardial oxygen consumption (pressure-rate-product), and ultimate infarct size were studied in pentobarbital-anaesthetized, open-chest dogs and compared to those occurring in dogs receiving saline infusion. Either agent was administered in a separate setting. Haemodynamic variables and oxygen consumption were determined during a 6-h period after ligation of the left anterior descending coronary artery and collected at 1-h intervals. Infarct size was determined by post-mortem nitroblue tetrazolium stain of intracellular lactic dehydrogenase enzymes. Coronary artery ligation during saline infusion (n=8) resulted in decreased blood pressure and cardiac output, whereas heart rate, systemic peripheral resistance, end-diastolic filling pressure and myocardial oxygen consumption increased. Infarct size amounted to 24.2±3.2% (i. e., 23.8±3.1 g) of left ventricular mass. Infusion of 1.4 g/kg/min molsidomine (n=8) produced significant fall of blood pressure, cardiac output, filling pressure and oxygen consumption while heart rate and peripheral resistance were unaffected. The infarct volume was reduced to 49% (P<0.01) of that observed in saline controls. The administration of 3 g/kg/min dopamine (n=8) elevated blood pressure and cardiac output initially with a subsequent reduction of either parameter. Arteriolar vascular resistance and oxygen consumption increased but filling pressure remained unchanged. Infarct size was not different from saline controls. Infusion of 6 g/kg/min dopamine, however, significantly increased blood pressure, heart rate, and peripheral resistance. Cardiac output and filling pressure fell and myocardial oxygen consumption rose. The histochemically measured final infarct was reduced to 13.5±1.8% of left ventricle (i. e., 16.2±2.2 g, P<0.05 vs saline control), but the hearts were edematous and haemorrhagic. Therapy with molsidomine appears promising in the treatment of clinical myocardial infarction with haemodynamic sequellae. The safe use of therapy with higher dopamine doses in patients with acute myocardial infarction, however, awaits further investigation.Part of the dopamine experiments were done at Bayer AG, Institut für Pharmakologie