The neuroprotective action of dizocilpine (MK-801) in the rat middle cerebral artery occlusion model of focal ischaemia

1. An acute model of focal ischaemia, which involves permanent occlusion of the middle cerebral artery of the rat with 4 h survival, was used to find the minimum effective plasma concentration of dizocilpine (MK-801) and to determine its dose-effect relationship. 2. MK-801 was administered at the time of occlusion and was given as an i.v. bolus followed by an infusion for 4 h to maintain a steady state plasma concentration of the drug throughout the study. MK-801 was given at 3 dose levels; 0.04 mg kg-1 i.v. bolus + 0.6 micrograms kg-1 min-1 infusion; 0.12 mg kg-1 i.v. bolus + 1.8 micrograms kg-1 min-1 infusion; 0.4 mg kg-1 i.v. bolus + 6 micrograms kg-1 min-1 infusion, which gave mean plasma levels over the 4 h of 8.0 ng ml-1, 18.9 ng ml-1 and 113.2 ng ml-1 respectively. 3. MK-801 at 8.0 ng ml-1 gave 10% reduction in the volume of ischaemic brain damage in the cerebral cortex which just reached significance. The middle dose of MK-801 (18.9 ng ml-1) gave a highly significant reduction in the volume of ischaemic brain damage in the cerebral cortex and hemisphere, volumes of ischaemic tissue being reduced by 60% and 50% compared to saline-treated animals, respectively. The highest plasma concentration of MK-801 (113.2 ng ml-1) resulted in a 35% reduction in the volume of hemispheric damage and a 40% reduction in the volume of cortical damage, which were significant.4. The reduction in the amount of protection afforded by the highest dose of MK-801 may be due to the hypotensive effect of this dose. There was no protection against the volume of damage in the caudate nucleus for any of the doses of MK-801 tested.5. Therefore the minimum effective plasma concentration of MK-801 was 8.0 ngml1, although the greatest protection was seen with a plasma level of 18.9 ng ml- 1. This correlates well with the concentration of MK-801 required to block N-methyl-D-aspartate (NMDA) receptors and prevent NMDA receptor mediated neurotoxicity in vitro.

Multiple K-ras codon 12 mutations in cholangiocarcinomas demonstrated with a sensitive polymerase chain reaction technique

By using a modified polymerase chain reaction strategy, we have devised an approach to detect a K-ras oncogene mutated at codon 12 in the presence of 1000 normal alleles. This is a considerable improvement in sensitivity on previous assays. Application of this assay to 15 cholangiocarcinomas showed that all contained a K-ras mutation to codon 12 and that nine of the tumors contained two or more mutations. In 11 cases, mutations were present in less than 10% of the cells in the sample. In common with pancreatic adenocarcinomas, in which 75 to 95% of cases contain a mutation in K-ras, cholangiocarcinomas show a very high frequency of ras gene mutation, but within a tumor only a fraction of cells contain a ras mutation. The presence of multiple mutations and the low frequency of mutant alleles in the samples argue against K-ras mutations being the initiating genetic lesion in this tumor, but suggest that ras gene mutation is involved in the stepwise progression of neoplastic cells to full malignancy.

Analysis of ras gene mutations in childhood myeloid leukaemia

Previous studies have shown that approximately 30% of adult acute myeloid leukaemias and 20% of adult acute lymphoid leukaemias contain point mutated ras oncogenes. In order to assess whether ras oncogenes are also involved in childhood leukaemias, we have used polymerase chain reaction (PCR) amplification and synthetic oligonucleotide probes to study the nature and frequency of ras gene mutations in childhood leukaemias, concentrating largely on the acute myeloid leukaemias (AML). Thirty-four childhood presentation AML DNAs were screened for mutations in and around codons 12, 61 and 117 of N-, K- and H-ras. Eight of these samples (24%) contained ras mutations. As in the adult disease, the gene predominantly involved was N-ras (6/8), with occasional activation of K-ras (2/6). The most common base change was a G----A transition at codon 12 or 13 (4/8). Of the patients with mutant ras, 4/8 were diagnosed as AML FAB subtype M5. Five of the 34 childhood AMLs analysed displayed abnormalities of chromosome 7. However, none of these cases contained a mutant ras gene. One AML patient was studied at relapse, 14 months after initial presentation. The presentation mutation (N61p3) was not detectable, although a new mutation (N13Cys) was readily identified. This observation extends our original finding with presentation and relapse samples of adult AML, in which it was uncommon for the relapse sample to contain the same ras mutation as the presentation DNA. In addition, two out of five patients diagnosed as juvenile CML, were found to harbour mutant ras.

Striatal A2 receptor regulates apomorphine-induced turning in rats with unilateral dopamine denervation

The effect of the purine agonist N-ethylcarboxamido-adenosine (NECA) on apomorphine-induced rotation was investigated in rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway. Intrastriatal administration of NECA on the denervated side caused a dose-dependent inhibition of contralateral rotation. This inhibition was prevented by prior intrastriatal injection of theophylline. The adenosine A1 receptor antagonist 8-cyclopentyltheophylline was ineffective at concentrations which block this receptor, but effective in preventing the action of NECA at concentrations which block the adenosine A2 receptor. In the absence of apomorphine, NECA had no effect on behaviour. It is concluded that A2 receptor activation counteracts apomorphine effects in the striatum. Since the A2 receptor may be localized to striatal cholinergic neurones, the possible role of these neurones in purine-induced behaviours is discussed.

Economics of mastitis control

The frequency of use and the effects of mastitis control practices on SCC and milk yield were investigated. A survey of current management practices was combined with DHI production information to determine the relationship between milk yield, SCC, management practices, and production and producer characteristics under field conditions. The expected negative relationship between SCC and milk, fat, and protein yield was substantiated. The SCC for an individual cow was a better indicator of milk loss than was a bulk tank SCC. Most recommended mastitis control practices were estimated to be economically beneficial; however, using a sanitizer in the washing solution and having a company change the milking machine inflations were not economical. Questions were raised about the economic efficiency and efficacy of treating all cows as opposed to selected cows at drying off.

The neuroprotective actions of kynurenic acid and MK-801 in gerbils are synergistic and not related to hypothermia

The broad spectrum excitatory amino acid antagonist, kynurenic acid was evaluated in a transient forebrain ischaemia model in gerbils. When administered i.p., 15 min prior to a 5 min period of ischaemia, a dose-related neuroprotective effect was seen with 800 mg/kg of kynurenic acid showing very good protection. A combination of kynurenic acid (200 or 400 mg/kg) and MK-801 (0.1 mg/kg) gave a synergistic neuroprotective effect. Neither kynurenic acid (200 or 400 mg/kg) nor MK-801 (0.3 mg/kg) was neuroprotective when administered by itself 30 min post-ischaemically, but when co-administered significant protection of the CA1 pyramidal neurones of the hippocampus was seen. In addition, we examined the effect of maintaining core body temperature on the neuroprotective action of MK-801 and kynurenic acid following the suggestion that it was a hypothermic effect of MK-801 which resulted in neuroprotection in gerbils. When the body temperature of the gerbils was maintained at 37 degrees C for a period of 24 h it did not affect the neuroprotective action of MK-801 (0.1 or 10 mg/kg) or kynurenic acid (200 mg/kg).

Protection of CA1 pyramidal cell function by MK-801 following ischaemia in the gerbil

Electrophysiological recordings were made from hippocampal slices of gerbils which had undergone a 5 min period of bilateral carotid occlusion. Normal CA1 population spikes, field potentials and synaptic responses were obtained from slices of gerbils pretreated with the N-methyl-D-aspartate antagonist, MK-801 (10 mg/kg, i.p., 1 h before the occlusion). In contrast, no CA1 population spike could be obtained from slices of untreated gerbils, although field potentials and population spikes were obtained from the dentate granule cell region of these slices in response to perforant path stimulation. These studies indicate that the CA1 pyramidal cells identified histologically as protected by MK-801 from selective neuronal degeneration produced by a 5 min period of global ischaemia, are also functionally protected and retain their normal synaptic responsiveness.

Molecular mechanism for the inhibitory action of interferon on hematopoiesis

Spleen cell suspensions obtained from adult mice were separated by Ficoll/Hypaque and Percoll density gradient centrifugation. The enriched erythroblast populations were maintained in liquid culture medium for 8 hours with 10,000 units of murine interferon (IFN) alpha and beta. Exposure of these cell cultures to murine IFN alpha and beta resulted in a 48% to 70% increase in 2-5adenylate synthetase (2-5AS) activity. In parallel studies, adult mice were injected daily for 1 or 2 weeks with recombinant human IFN alpha A/D (rHuIFN alpha A/D) at a dose of 10(6) or 10(7) units/kg body weight. This treatment did not significantly affect body weight but did produce a mean 70% increase in spleen wet weight and a mean 46% increase in number of nucleated cells per spleen. This increase in number of splenic hematopoietic cells did not result in a corresponding increase in number of circulating cells. In fact, during this 1 to 2 week period the hematocrit dropped from 45% to 38% in mice injected with high dose rHuIFN alpha A/D. From these findings we propose that IFN induces an early 2-5AS activity in erythroblasts and megakaryocytes. This 2-5AS activity, which is known to inhibit protein synthesis in other cell systems, is thought to be responsible for the block or prolongation in blood cell maturation observed in the present studies.

Enhancement of transformation rates in higher plants by low-dose irradiation: Are DNA repair systems involved in the incorporation of exogenous DNA into the plant genome?

Irradiation (X-ray; 5-15 Gy) of protoplasts treated with plasmid-DNA and PEG yielded higher transformation rates in comparison to non-irradiated protoplasts transformed by the same method. This could be demonstrated for four plant species. The irradiation doses used did not affect the total number of colonies regenerated without selection pressure, but resulted in 3-6-fold enhancement of hygromycin- or kanamycin-resistant colonies. Plant regeneration frequencies of transformed colonies derived from irradiated and non-irradiated protoplasts were similar in tobacco as well as in Petunia. Higher integration rates of foreign DNA as a consequence of an increased recombination machinery in irradiated cells may be responsible for the enhancement of the number of stably transformed colonies.

International collaborative study of the retention reproducibility of basic drugs in high-performance liquid chromatography on a silica column with a methanol-ammonium nitrate eluent

An international collaborative study between 10 laboratories has been carried out to study the reproducibility of the separation of basic drugs on silica columns. The laboratories used common solutions of drugs on both a common batch of packing material and different batches of the same brand of packing material. These were also compared with separations on other brands of packing material. Variations within-batch, within-brand and between brands have been compared. The retentions of the drugs were compared using retention times, capacity factors and relative capacity factors compared with an internal standard. The last method was found to give the most reproducible results. Considerable variations were found between the different brands of silica with a smaller variation between the batches of a single silica brand. However, unlike earlier studies, significant variations were found for separations on a single batch of silica which were partly attributed to differences in eluent preparation and column temperature.

Neuroprotective effects of MK-801 in vivo: selectivity and evidence for delayed degeneration mediated by NMDA receptor activation

The ability of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 to prevent neuronal degeneration in the rat striatum and hippocampus caused by intracerebral injection of excitotoxins has been examined. Excitotoxic damage was assessed after 7 d, using histological and biochemical [choline acetyltransferase (ChAT) glutamate decarboxylase (GAD)] measurements. Systemically administered MK-801 was found to protect against neurodegeneration caused by NMDA (200 nmol) and the naturally occurring NMDA receptor agonist quinolinate (120-600 nmol) but not against that induced by kainate (5 nmol) or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA; 50 nmol), indicating a selectivity for NMDA receptor-mediated neuronal loss. Neurotoxicity caused by NMDA (200 nmol) or quinolinate (200 nmol) was prevented by MK-801 (1-10 mg/kg, i.p.) administered in a single dose after excitotoxin injection. In the striatum, significant protection of cholinergic neurons (assessed by ChAT measurements) was observed when MK-801 was given up to 5 hr after injection of NMDA or quinolinate, whereas protection of GABAergic neurons (assessed by GAD measurements) was obtained up to 2 hr. The results suggest that GABAergic neurons degenerate more rapidly than cholinergic neurons. The competitive NMDA receptor antagonist 3-[(+/-)-2-carboxypiperazin-4-yl]-propyl-1-phosphonate (100 mg/kg, i.p.) gave partial protection of striatal neurons when administered 1 hr after quinolinate injection. In the rat hippocampus, administration of 10 mg/kg MK-801 i.p. 1 hr after quinolinate injection caused almost complete protection of pyramidal and granule neurons, whereas the degeneration of CA3/CA4 pyramidal neurons caused by kainate injection was unaffected. These observations indicate that neurons in rat striatum and hippocampus do not die as an immediate consequence of exposure to high concentrations of NMDA agonists but that a delayed process is involved that requires NMDA receptor activation. In this respect, intracerebral injections of NMDA agonists may mimic the pathological changes that are thought to occur in the brain following periods of cerebral ischemia, where delayed neuronal degeneration occurs.

Retention reproducibility of basic drugs in high-performance liquid chromatography on a silica column with a methanol-ammonium nitrate eluent. Batch-to-batch reproducibility of the stationary phase

The effect of changing the brand and batches of the silica stationary phase used with a methanol-aqueous ammonium nitrate eluent for the high-performance liquid chromatographic separation of basic drugs has been studied. Considerable care had to be taken to obtain a reproducible eluent and the effect of small changes in the concentration of the ammonia solution were examined closely. Large differences in both the capacity factor and relative capacity factors were found for separations on columns packed with four different brands of silica. Significant differences were also observed with columns containing eighteen different batches of Spherisorb S5W, which had been manufactured over a period of several years.

Characterisation of acid dyes in forensic fibre analysis by high-performance liquid chromatography using narrow-bore columns and diode array detection

A gradient elution high-performance liquid chromatographic (HPLC) system with a diode array detector and a short narrow-bore (40 x 1 mm I.D.) column has been used to characterise a number of acid dyes. The resolution and reproducibility of the HPLC system have been evaluated and the detection limits for various dyes have been estimated. Comparisons are made with current methods of fibre dyestuff examination used in forensic science. The system has been applied to the analysis of dye extracted from single fibres. Using diode array detection, both chromatographic and spectral data can be produced in a single operation from casework sized samples.

MK-801 is neuroprotective in gerbils when administered during the post-ischaemic period

The neuroprotective effects of the non-competitive N-methyl-D-aspartate receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) have been evaluated in the gerbil hippocampus when the drug was administered i.p. at various times during and after a 5 min period of transient forebrain ischaemia, induced by bilateral common carotid artery occlusion. A single dose of 1, 3 or 10 mg/kg of MK-801 gave significant protection of hippocampal CA1 and CA2 pyramidal neurons when administered during the occlusion and up to 24 h following the period of ischaemia. A dose of 0.3 mg/kg was effective when administered during the occlusion period but gave no protection at 30 min or 2 h post-ischaemia. Experiments in which MK-801 was administered in repeated doses indicated that significant protection was achieved with 1 mg/kg of MK-801 repeated post-ischaemically and with 1 mg/kg MK-801 supplemented with repeated doses of 0.3 mg/kg of MK-801. However 0.3 mg/kg of MK-801 followed by repeated doses of 0.03 mg/kg administered post-ischaemically was not neuroprotective. These results indicate that MK-801 can protect hippocampal neurons from ischaemia-induced neuronal degeneration when it is administered up to 24 h after the insult. These data provide further evidence that therapeutic intervention in the post-ischaemic period can successfully prevent neurodegenerative events, and that the delayed degeneration of hippocampal neurons following an ischaemic insult occurs by an N-methyl-D-aspartate receptor-mediated process.

Sample handling and storage for the quantitative analysis of volatile compounds in blood: the determination of toluene by headspace gas chromatography

The problems associated with the handling and storage of blood samples for the analysis of toluene in toxicological casework using headspace gas chromatography have been investigated. Significant losses of toluene and the internal standard, ethylbenzene, from solution may be observed during handling. Toluene may be lost into the headspace above the blood in a storage container while such headspaces can also be detrimental, leading to the formation of n-hexanal, a possible interference with the assay. Large differences in the stability of toluene were seen for blood samples in different types of storage container. Storage containers in which the sample was only in contact with glass, teflon, or aluminum foil were most satisfactory. It is recommended that blood samples should be stored in appropriate containers with minimum headspace under cold conditions (4 degrees C). Transfers of blood should also be made at cold temperatures. The applicability of these guidelines to the analysis of other volatile compounds is discussed.

A semiautomated system for measurement of 96 simultaneous spectrophotometric enzyme assays

A semiautomated system for spectrophotometric measurement of enzyme activity is described. In comparison to a 1-ml reaction volume monitored continuously by a conventional spectrophotometer, this system requires 1/10 to 1/100 the volume of sample, and 1/8 to 1/4 the time for measurement and computation of 96 enzyme assays. The system hardware consists of a 96-well platereader interfaced to a personal computer. Absorbances of 96 reactions are measured at timed intervals. These data are transmitted electronically from the platereader to the computer through the modem port using a modem program. The reaction rates are computed from the timed absorbance readings using a spreadsheet program. Three enzyme assays are presented, but the method has been used for several other assays and is applicable to many spectrophotometric rate assays. Many laboratories currently possess one or both of the two major components of the relatively inexpensive system described.

Systemic administration of MK-801 protects against ischemia-induced hippocampal neurodegeneration in the gerbil

The neuroprotective effects of MK-801, a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors, were evaluated in models of cerebral ischemia using Mongolian gerbils. Bilateral occlusion of the carotid arteries for a period of 5 min resulted in a consistent pattern of degeneration of hippocampal CA1 and CA2 pyramidal neurons, which was quantified using an image analyzer. Systemic administration of MK-801 (0.01-10 mg/kg, i.p.) 1 hr prior to the occlusion caused a dose-dependent protection of the CA1 and CA2 neurons. The ED50 value for neuroprotection by MK-801 was calculated to be 0.3 mg/kg, and at doses greater than or equal to 3 mg/kg the majority of animals were completely protected against the ischemic insult. Systemic administration of MK-801 (1 or 10 mg/kg, i.p.) 1 hr prior to unilateral occlusion of the right carotid artery resulted in significant protection against hippocampal neurodegeneration following 10 min of occlusion, and increased the survival rate after 30 min of occlusion. The potent neuroprotective effects of MK-801 in these cerebral ischemia models add further weight to the evidence that NMDA receptors are involved in the mechanism of ischemia-induced neuronal degeneration.

Retention reproducibility of basic drugs in high-performance liquid chromatography on a silica column with a methanol-ammonium nitrate eluent. The effect of the mobile phase and the operating conditions

The reproducibility of capacity factors and relative capacity factors are compared as methods for recording retentions for the high-performance liquid chromatography of basic drugs on a silica column with methanol-aqueous ammonium nitrate as the eluent. The effects of changing the column temperature and the ionic strength, pH and proportion of organic modifier in the eluent on the retentions and selectivity have been studied. The results suggest that the mobile phase and operating conditions must be closely defined in order to obtain results of adequate reproducibility to develop a data base of retention values for interlaboratory comparisons and/or for the identification of basic drugs.

The interaction between MK-801 and receptors for N-methyl-D-aspartate: functional consequences

Electrophysiological studies using a cortical slice preparation revealed that MK-801 is a potent, non-competitive, antagonist of N-methyl-D-aspartate (NMDA)-induced depolarisations. Also, MK-801 was a highly selective antagonist, exhibiting a high degree of use-dependency. It completely blocked responses to NMDA and quinolinic acid but had no effect on responses produced by kainic acid or quisqualic acid. Using [3H]MK-801, high affinity binding sites for MK-801 were detected in membranes of the rat brain. The pharmacological specificity and regional distribution of binding sites for MK-801 were consistent with an action of the compound at the level of the NMDA receptor-associated ion channel. Administered parenterally, MK-801 had a remarkable neuroprotective role. It caused essentially complete protection against loss of neurones produced by injection of neurotoxic doses of NMDA or quinolinic acid into the striatum or hippocampus. Furthermore, MK-801 was highly effective in preventing loss of hippocampal neurones following bilateral occlusion of the common carotid arteries in the gerbil.

Systemic administration of MK-801 prevents N-methyl-D-aspartate-induced neuronal degeneration in rat brain

MK-801 is a novel, potent and selective non-competitive antagonist of the N-methyl-D-aspartate (NMDA) subtype of excitatory amino acid receptors. Pretreatment of rats with MK-801 (1-10 mg/kg, i.p.) prevented neuronal degeneration in the hippocampus and striatum caused by direct intracranial injections of NMDA (20-120 nmol), but did not protect against the loss of neurones induced by kainate (2.5 nmol) injected into the striatum. Thus, MK-801 is a selective antagonist of neuronal degeneration caused by excessive stimulation of NMDA receptors in vivo.