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L Ritchie

Publications and source records attributed to L Ritchie.

15 recordsLinked to original sources
PubMed1997

Association of c-fos mRNA expression and excitotoxicity in primary cultures of mouse neocortical and cerebellar neurons.

The effect of excitatory amino acids (EAAs) on c-fos mRNA expression was studied in primary cultures of mouse cerebellar granule cells and in neocortical neurons after 2 and 7 days in vitro (div). In cultured granule cells at 2 and 7 div, and in cortical neurons at 2 div, exposure to low levels (< or = 10 microM) of a variety of EAAs (viz. glutamate [Glu], S-sulpho-L-cysteine [SC], N-methyl-D-aspartate [NMDA], alpha-amino-3-hydroxy-5-methyl-4-isoxazole [AMPA], and kainate [KA]) resulted in a transient increase in the level of c-fos mRNA which peaked at 30 min but returned to a basal level by 120 min. However, exposure of granule cells (7 div) to high levels (250 microM) of Glu, NMDA, KA, SC and of cortical neurons (7 div) to high levels (250 microM) of Glu, NMDA, KA, SC, or AMPA and to low levels (< or = 10 microM) of Glu and AMPA resulted in a delay in c-fos mRNA induction but a subsequent, progressive increase that was sustained for at least 240 min. Furthermore, this effect was accompanied by a dose-related increase in the release of the cytosolic enzyme, lactate dehydrogenase, used as an indicator of excitotoxicity. A ratio (Q240/30) for the steady-state levels of c-fos mRNA after 30 min and 240 min of exposure to EAAs was determined which showed that Q240/30 >2 correlated reproducibly with excitotoxic cell death, whereas a ratio of < or = 1 correlated with a nonexcitotoxic event. In both cell types at 7 div, coadministration of the selective NMDA receptor antagonist, DL(+/-)-2-amino-5-phosphonopentanoic acid (APV) with cytotoxic levels of Glu 1) protected against EAA-induced neurotoxicity and 2) exhibited a transient c-fos mRNA expression (Q240/30 values approximately 1). In contrast, the AMPA/KA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), provided no protection against excitotoxicity and had no significant effect on the Glu-induced delay in c-fos mRNA expression. These results suggest that the Q240/30 c-fos mRNA ratio may 1) be used as a predictive index for excitotoxic neuronal death, 2) provide information on the identity of the receptor subtype mediating excitotoxicity in different brain cell types, and 3) aid in establishing the role of excitotoxicity during the development of neurons in vitro.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1996

NMDA receptor-mediated cGMP synthesis in primary cultures of mouse cerebellar granule cells appears to involve neuron-astrocyte communication with NO operating as the intercellular messenger.

The possibility that neuron-astrocyte communication may be responsible for glutamate (Glu)-stimulated cGMP formation even in relatively homogeneous primary cultures of mouse cerebellar granule cells (7 days in vitro) was investigated. Pharmacological analysis using selective excitatory amino acid (EAA) receptor antagonists showed that cGMP production, stimulated in these cultures by Glu and a variety of endogenous EAAs structurally-related to Glu (namely, L-aspartate, L-cysteine sulphinate, L-homocysteate, S-sulpho-L-cysteine), was mediated wholly by N-methyl-D-aspartate (NMDA) receptor activation. Moreover, EAA-induced responses were dependent on the presence of extracellular calcium but unaffected by addition of the L-type voltage-sensitive calcium channel blockers nifedipine (10 microM) or verapamil (5 microM). The mode of calcium entry was also shown to be important since the calcium ionophore, A23187 (10 microM), was unable to stimulate cGMP levels above basal. cGMP formation was blocked by the competitive nitric oxide synthase inhibitor, L-NG-nitroarginine (100 microM), consistent with a role of nitric oxide (NO) in this signalling pathway. In the presence of added haemoglobin (1 microM), acting as a membrane-impermeable NO scavenger, Glu-stimulated cGMP formation was abolished implying that NO must act as an intercellular messenger. When the neuronal population was destroyed following a 24 hr exposure to the excitotoxin, S-sulpho-L-cysteine (200 microM), Glu-stimulated cGMP formation was abolished; whereas responses to the NO donor, sodium nitroprusside (SNP), although markedly reduced were still double that stimulated by Glu in the absence of the excitotoxin, suggesting the presence of non-neuronal cells that can generate cGMP if supplied directly with NO. Consistent with this suggestion, low levels of the glial specific enzyme, glutamine synthetase, were detected in granule cell cultures. Furthermore, omission or delayed addition of the antimitotic agent, cytosine arabinoside (20 microM), to the growth medium caused a significant increase in the level of Glu-stimulated cGMP formation.

Animals↗
PubMed1996

Glutamate toxicity in primary cerebellar cultures from mouse brain is unaffected by changes in cGMP levels.

During evaluation of potential end-points for in vitro neurotoxicity screening we investigated what influence changes in cyclic GMP (cGMP) levels might exert on the degree of glutamate (Glu)-induced neurotoxicity in primary cultures of mouse cerebellar granule cells. Depletion of Glu-stimulated cGMP levels by N-methyl-D-aspartate receptor antagonists fully protected against Glu-induced toxicity. However, when Glu-stimulated cGMP levels were either depleted or elevated by the use of a variety of pharmacological agents acting intracellularly at various points of the NO/cGMP signalling pathway the degree of cytotoxicity exerted by Glu was unaltered. These results imply that cGMP and NO do not modulate the toxic effects of Glu and are therefore unsuitable as biomarkers of excitotoxicity in these cells.

Animals↗
PubMed1996

A prototypic intracellular calcium antagonist, TMB-8, protects cultured cerebellar granule cells against the delayed, calcium-dependent component of glutamate neurotoxicity.

The effect(s) of a prototypic intracellular Ca2+ antagonist, 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8), on glutamate-induced neurotoxicity was investigated in primary cultures of mouse cerebellar granule cells. Glutamate evoked an increase in cytosolic free-Ca2+ levels ([Ca2+]i) that was dependent on the extracellular concentration of Ca2+ ([Ca2+]o). In addition, this increase in [Ca2+]i correlated with a decrease in cell viability that was also dependent on [Ca2+]o. Glutamate-induced toxicity, quantified by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) staining, was shown to comprise two distinct components, an "early" Na+/Cl(-)-dependent component observed within minutes of glutamate exposure, and a "delayed" Ca(2+)-dependent component (ED50 approximately 50 microM) that coincided with progressive degeneration of granule cells 4-24 h after a brief (5-15 min) exposure to 100 microM glutamate. Quantitative analysis of cell viability and morphological observations identify a "window" in which TMB-8 (at > 100 microM) protects granule cells from the Ca(2+)-dependent, but not the Na+/Cl(-) -dependent, component of glutamate-induced neurotoxic damage, and furthermore, where TMB-8 inhibits glutamate-evoked increases in [Ca2+]i. These findings suggest that Ca2+ release from a TMB-8-sensitive intracellular store may be a necessary step in the onset of glutamate-induced excitotoxicity in granule cells. However, these conclusions are compromised by additional observations that show that TMB-8 (1) exhibits intrinsic toxicity and (2) is able to reverse its initial inhibitory action on glutamate-evoked increases in [Ca2+]i and subsequently effect a pronounced time-dependent potentiation of glutamate responses. Dantrolene, another putative intracellular Ca2+ antagonist, was completely without effect in this system with regard to both glutamate-evoked increases in [Ca2+]i and glutamate-induced neurotoxicity.

Animals↗
PubMed1995

Stroke units.

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Cerebrovascular Disorders↗
PubMed1995

Is Bell's palsy a reactivation of varicella zoster virus?

Despite various pointers to an infectious aetiology, the cause of Bell's palsy remains obscure. We examined paired sera from 62 patients with facial palsy and 50 age and sex matched contemporaneous controls. Significantly more patients than controls had IgM antibodies by ELISA to varicella zoster virus (56.5% vs. 20%, P = 0.0001) and herpes simplex virus (41.9% vs. 18%, P = 0.006). Additionally, significantly more patients than controls were positive for CF antibody to varicella zoster virus (14.5% vs. 0%, P = 0.004) but not to herpes simplex or cytomegalovirus. Significantly more controls than patients (54% vs. 25.8%, P = 0.002) had no evidence of antigenic stimulation by any of the herpesvirus group. No significant difference between patients and controls in seropositivity by IgM ELISA to cytomegalovirus. Epstein-Barr virus and IFA for human herpes virus 6 was found. Furthermore, there was no significant difference between the two groups as to evidence of recent infection by the following agents: rubella virus and Borrelia burgdorferi by IgM ELISA, influenza A. influenza B, adenovirus, respiratory syncytial virus, mumps and measles. Mycoplasma pneumoniae, Coxiella burnetii and chlamydia spp. by complement fixation test. The first reported case of clinically and serologically proven Mycoplasma pneumoniae pneumonia associated with Bell's palsy is described. The rate of complete recovery at 6-8 weeks after onset was not significantly different in patients who were given steroids compared to those who were not. Ear related symptoms were the most common, occurring in 12 of 65 cases, but only three (4.6%) had clinical shingles (vesicles in ear).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Bovine spongiform encephalopathy: a scrapie-like disease of British cattle.

Scrapie is a CNS degenerative infection of sheep and goats, which is invariably fatal after incubation periods of several months to years. Related disorders are found naturally in man and other species. There is a impairment of protein catabolism in scrapie and related diseases which leads to the accumulation of sparingly-soluble protein deposits in brain. These protein aggregates may share with the amyloid of Alzheimer's disease (AD) some common stage in the biochemical pathways of their formation, although different proteins are affected in scrapie (the PrP protein) and AD (the A4-precursor protein). Recently, cattle with the clinical signs and brain pathology of a neurodegenerative disease have been reported, and this cattle disorder has been called bovine spongiform encephalopathy (BSE). BSE-affected brains contain abnormal forms of the bovine homologue of PrP. This provides biochemical evidence that BSE is cattle scrapie rather than cattle AD.

Animals↗
PubMed1988

A mutation in the DNA adenine methylase gene (dam) of Salmonella typhimurium decreases susceptibility to 9-aminoacridine-induced frameshift mutagenesis.

A mutant of Salmonella typhimurium with a reduced response to mutation induction by 9-aminoacridine (9AA) has been isolated. The mutation (dam-2) is located in the DNA adenine methylase gene. The dam-2 mutant strain exhibits a level of sensitivity to 2-aminopurine (2AP) intermediate between that of the dam+ and the DNA adenine methylation-deficit dam-1 strain, and 2AP sensitivity was reversed by introduction of a mutH mutation or of the plasmid pMQ148 (which carries a functional Escherichia coli dam+ gene). However, the dam-2 strain is not grossly defective in DNA adenine methylase activity. Whole cell DNA appears full methylated at -GATC- sites. The levels of 9AA required to induce equivalent levels of frameshift mutagenesis in the dam-2 strain were approximately 2-fold higher than for the dam+ strain. Introduction of pMQ148 dam+ reduced the level of 9AA required for induction of frameshift mutations 4-fold in the dam-2 strain and 2-fold in the dam+ strain. The dam-2 mutation had no effect on the levels of ICR191 required for induction of frameshift mutations, but introduction of pMQ148 reduced the ICR191-induced mutagenesis 2-fold. The dam+/pMQ148, dam-2/pMQ148 and dam-1/pMQ148 strains showed identical dose-response curves for both 9AA and ICR191. These results are consistent with a slightly reduced (dam-2) or increased (pMQ148) rate of methylation at the replication fork. The 2AP sensitivity of the dam-2 strain cannot be simply explained. Furthermore, addition of methionine to the assay medium reverses the 2AP sensitivity of the dam-2 strain, but has no effect on 9AA mutagenesis.

Aminacrine↗
PubMed1983

Changes in resistance in mixed infections of susceptible and benzimidazole resistant strains of Haemonchus contortus and Trichostrongylus colubriformis passaged in sheep.

Benzimidazole resistant strains of Haemonchus contortus and Trichostrongylus colubriformis were each diluted with equal numbers of their respective susceptible genotypes and passaged in separate worm-free sheep. The progeny of the mixed susceptible and resistant infections were diluted with equal numbers of susceptible genotypes before passaging on two further consecutive occasions in worm-free sheep. In H contortus the amount of thiabendazole required to prevent a 50 per cent egg hatching (LC50) was reduced at each generation, but the reduction was significant (P less than 0.05) only at the third passage. In T colubriformis the LC50 for thiabendazole was reduced only at the first passage and thereafter remained constant. The reduction was not significant. In another experiment, the dilution with susceptible genotypes was made only at the first passage. Thereafter for two further generations the progeny produced from the mixed infection were passaged in worm-free sheep. In H contortus a reduced amount of thiabendazole was required to prevent a 50 per cent egg hatching at each generation, but did not reach a level of significance. The result for T colubriformis was identical to the continuous dilution experiment.

Animals↗
PubMed1981

Investigations for anthelmintic resistance in gastrointestinal nematodes from goats.

Field results from a commercial goat herd, based on egg counts and larval differentiation, suggested that anthelmintic resistance was present to albendazole, fenbendazole, levamisole, morantel, naphthalophos and phenothiazine. When the isolate was tested in sheep, using levamisole or oxfendazole, a possible resistance was shown for Trichostrongylus sp but no resistance was demonstrated in Haemonchus or Ostertagia spp. Ivermectin at a dose rate of 100 micrograms/kg was more than 98 per cent efficient in removing the adults of each of the three species of nematode. The phenomenon relating to the influence of the host on anthelmintic resistance is discussed.

Animals↗
PubMed1981

Prolonged anthelmintic effect of closantel and disophenol against a thiabendazole selected resistant strain of Haemonchus contortus in sheep.

Two long-acting anthelmintics, closantel and disophenol, were tested by treatment 90, 60 and 30 days before challenge with a thiabendazole selected laboratory strain of Haemonchus contortus. The sheep were slaughtered 28 days after infection for total worm counts. A significant reduction in the number of adults remaining at autopsy was recorded after treatment with both anthelmintics 30 and 60 days before challenge but there was zero efficacy when the animals were treated 90 days before challenge. No significant difference was exhibited between the two compounds. Variability in response was recorded between animals on the 60 day period of treatment, which for disophenol may be dose related because animals receiving the lower volumes showed higher worm counts. For both anthelmintics a variability in the rate of metabolism may be responsible. The possibility offered by both anthelmintics for treating benzimidazole resistant strains of H contortus is discussed.

Animals↗
PubMed1976

Effects of cerebellar lesions on saccadic eye movements.

1. Areas of cerebellar cortex related to saccadic eye movements were ablated in three Macaca mulatta monkeys trained to fixate visual targets. There followed a postoperative dysmetria of saccadic eye movements which appeared to be the result of an impairment specifically within the saccadic system. 2. Convergent evidence from two experimental paradigms indicated that the saccadic deficit was a function of the position of the eye in the orbit and did not involve retinal error processing. 3. The pattern of this position-dependent dysmetria suggests that the eye was no longer fully compensating for the elastic restoring forces imposed by the orbital medium and antagonist muscle(s). 4. The similarity of these data to saccadic eye movements of human cerebellar patients and arm movements of rhesus monkeys with cerebellar lesions indicates that the inability to compensate for the differential loads placed on motor systems by the mechanics of those systems may explain several cerebellar symptoms.

Animals↗