PubMed Health⌕ Search

Biomedical subjects

G A Pritchard

Publications and source records attributed to G A Pritchard.

At least 19 recordsLinked to original sources
PubMed1999

Lorazepam attenuates the behavioral effects of dizocilpine.

To characterize the potential interaction between the excitatory and inhibitory neurotransmitter systems, the effects of dizocilpine, CPP, and lorazepam on open-field behavior and pentylenetetrazol-induced seizures were evaluated in mice. Dizocilpine (0.01-0.1 mg/kg), CPP (1-10 mg/kg), or vehicle was administered intraperitoneally 15 min prior to lorazepam (0.2-2 mg/kg) or vehicle. Behavioral monitoring began 25 min after the lorazepam injection. Upon completion of testing, unrestrained mice were infused intravenously with pentylenetetrazole until the onset of a full tonic-clonic seizure. The highest dose of dizocilpine by itself significantly increased the average distance traveled, the number of rears, and the number of stereotypies during the test period. Lorazepam alone dose dependently decreased activity on all behavioral parameters. Lorazepam also completely antagonized the hyperactivity produced by dizocilpine when the two compounds were coadministered. This antagonism is most likely due to an interaction in the regulation of dopaminergic tone which underlies motor activity. Lorazepam exerted a dose-dependent anticonvulsant effect. Dizocilpine alone had no effect on seizure induction and did not potentiate the anticonvulsive effect of lorazepam when coadministered with lorazepam. CPP reduced the number of rears and the number of stereotypies during the test period. CPP did not alter the pentylenetetrazol-induced seizure threshold and did not influence the anticonvulsant effect of lorazepam.

Animals↗
PubMed1999

In situ hybridization histochemistry as a method to assess GABA(A) receptor subunit mRNA expression following chronic alprazolam administration.

Previous work in our laboratory has demonstrated region-specific effects for chronic alprazolam on binding and function at the GABA(A) receptor. The present study evaluated regional changes in mRNA expression of several subunits of the GABA(A) receptor following chronic alprazolam administration that might underlie these effects. Mice received alprazolam (2 mg/kg/day) or vehicle via subcutaneously implanted osmotic pumps for 1, 7, 14 or 28 days. In situ hybridization histochemistry was performed on tissue sections using [35S]dATP oligonucleotide probes corresponding to the alpha1 and gamma2 subunits of the GABA(A) receptor. Specific hybridization was clearly demonstrated and alpha1 subunit mRNA expression in frontoparietal cortex (layers II-IV) on day 1 of infusion was reduced in animals receiving alprazolam compared to vehicle. On subsequent days, there were no alterations in the levels of alpha1 subunit mRNA in the frontoparietal cortex, hippocampus or dentate gyrus. Expression of gamma2 subunit mRNA was increased on day 1 in the frontoparietal cortex (layer VI), hippocampus and dentate gyrus. mRNA expression was also increased in the dentate gyrus on day 28 of infusion. Comparison of the present study with the results of chronic treatment with other benzodiazepines clearly demonstrates that the pattern of mRNA subunit alterations obtained is both treatment- and region-specific. This makes a definitive conclusion regarding benzodiazepines and their interactions with GABA(A) receptors difficult at best.

Alprazolam↗
PubMed1998

Effects of ketoconazole on triazolam pharmacokinetics, pharmacodynamics and benzodiazepine receptor binding in mice.

We previously demonstrated that ketoconazole is a potent inhibitor of triazolam biotransformation in vitro and in vivo. Despite significant elevations in triazolam plasma levels with coadministration of ketoconazole, the pharmacodynamic enhancement was lower than predicted based on plasma levels of triazolam. The present study examines the effects of ketoconazole on benzodiazepine receptor binding in vitro as well as on open-field behavior in male CD-1 mice. Triazolam alone inhibited [3H]flunitrazepam binding with an IC50 value of 0.85 nM and a Ki value of 0.50 nM. Ketoconazole alone also competitively antagonized [3H]flunitrazepam binding in a concentration-dependent manner with an IC50 value of 1.56 microM and a Ki value of 1.17 microM. In the presence of 1, 3 or 9 microM ketoconazole, the IC50 value of triazolam was increased to 1.11, 1. 58 and 5.73 nM, respectively, whereas maximal binding was reduced by 36%, 69% and 89%. Coadministration of 50 mg/kg ketoconazole and triazolam (0.1-0.3 mg/kg) to intact animals significantly elevated plasma and brain triazolam levels. Ketoconazole could be measured in mouse brain at levels averaging 31% of those in plasma. Ketoconazole alone had minimal or no effect on open field activity, but it significantly potentiated the decreased activity seen with triazolam administration. The ability of ketoconazole to inhibit triazolam displacement of [3H]flunitrazepam binding may explain the muted pharmacodynamic effect of this benzodiazepine in the presence of ketoconazole. Based on these results, it is likely that ketoconazole acts as a neutral ligand at the benzodiazepine receptor.

Animals↗
PubMed1997

The NMDA receptor competitive antagonist CPP modulates benzodiazepine tolerance and discontinuation.

Benzodiazepine discontinuation is characterized by a syndrome of increased activity and reduced seizure threshold that is similar to effects mediated by the glutamatergic system. To elucidate the involvement of the glutamatergic system in benzodiazepine tolerance and discontinuation, we administered lorazepam, the NMDA antagonist CPP, and the combination of these compounds either concomitantly or consecutively to mice via osmotic pumps and evaluated pentylenetetrazole-induced seizure threshold, open-field activity, and benzodiazepine receptor binding during and after chronic administration. Animals receiving lorazepam alone developed partial tolerance at 7 days and complete tolerance at 14 days to the anticonvulsant effects of lorazepam. This effect was partly attenuated by CPP coadministration with lorazepam. This combination produced only partial tolerance. A reduction in seizure threshold was observed 4 days after discontinuation of lorazepam alone. This effect was abolished by coadministration of CPP with lorazepam and by CPP administration during the withdrawal period. Benzodiazepine binding in most structures examined was significantly reduced at 14 days during chronic lorazepam administration (versus 1 day), and coadministration of CPP did not alter this decrement. After lorazepam discontinuation, binding was increased at 4 and 7 days versus chronically treated animals and versus vehicle within the cerebral cortex. This effect was abolished by coadministration of CPP as well as by CPP administration during the lorazepam withdrawal period. These data support the involvement of the glutamatergic system in benzodiazepine tolerance and discontinuation.

Animals↗
PubMed1996

Triazolam biotransformation by human liver microsomes in vitro: effects of metabolic inhibitors and clinical confirmation of a predicted interaction with ketoconazole.

Biotransformation of the triazolobenzodiazepine triazolam to its hydroxylated metabolites, alpha-hydroxy (OH)- and 4-OH-triazolam, was studied in vitro using microsomal preparations of human liver. Mean values of Vmax (10.3 nM/min/mg of protein) and Km (304 microM) for the 4-OH pathway exceeded values for the alpha-OH pathway (2.4 and 74, respectively). However the mean Vmax/Km ratios for the two pathways were nearly identical, indicating that both contribute approximately equally to intrinsic clearance. Ketoconazole was a powerful inhibitor of triazolam biotransformation, having mean competitive Ki values of 0.006 and 0.023 microM for the alpha-OH and 4-OH pathways. This is consistent with the role of P450-3A isoforms in mediating triazolam biotransformation. The serotonin2 antagonist antidepressant nefazodone inhibited the alpha-OH and 4-OH pathways (Ki = 0.6 and 1.7 microM, respectively), but with considerably less activity than ketoconazole. Among six selective serotonin reuptake-inhibitor antidepressants, norfluoxetine was the most potent inhibitor (Ki = 2.7 and 8.0 microM) and fluoxetine itself was the weakest (Ki = 7.0 and 44.3 microM). In a double-blind clinical pharmacokinetic-pharmacodynamic study, administration of triazolam (0.125 mg) preceded by ketoconazole, compared to triazolam preceded by placebo, produced a nearly 9-fold reduction in apparent oral clearance of triazolam (41 vs. 337 ml/min) and a 4-fold prolongation of half-life (13.5 vs. 3.4 hr). Pharmacodynamic testing indicated enhancement of electroencephalographic beta activity, and enhanced decrements in digit-symbol substitution test performance, attributable to coadministration of ketoconazole. Plasma ketoconazole concentrations measured in the clinical study ranged from 0.02 microgram/ml (projected minimum) to 4.95 micrograms/ml (maximum). An in vitro-in vivo scaling model, using these plasma ketoconazole concentrations together with liver partition ratios and the in vitro Ki values, predicted a decrement of triazolam clearance due to ketoconazole coadministration that was consistent with the 88% decrement in clearance actually observed in vivo.

Adult↗
PubMed1995

Pregnenolone sulfate potentiation of NMDA-mediated increases in intracellular calcium in cultured chick cortical neurons.

Pregnenolone sulfate (PS) has been reported to selectively augment glutamate-induced depolarizations mediated by the NMDA subtype of the glutamate receptor. The present study examines the ability of this neuroactive steroid to potentiate NMDA-mediated increases in intracellular calcium in cultured chick cortical neurons using the fluorescent dye Fura2. PS, in the absence of NMDA and glycine, significantly elevated intracellular calcium at 250 and 500 microM. This increase in free calcium was significantly attenuated at 250 microM PS by the prior addition of 50 microM CNQX, 10 microM dizocilpine or 1 microM nimodipine. NMDA and glycine, when added to the cells in saturating concentrations of 500 and 50 microM, respectively, consistently increased intracellular free calcium over baseline levels. In the presence of NMDA and glycine, both 50 and 100 microM PS produced a further significant rise in intracellular free calcium. The prior addition of CNQX, dizocilpine or both compounds together significantly inhibited this elevation in free calcium. The application of the endogenous polyamine spermine (250 microM) significantly potentiated the response of chick cortical neuronal cells to NMDA and glycine. PS, in the presence of NMDA, glycine and spermine, produced a further increase in intracellular free calcium at concentrations of 50 and 100 microM. The prior application of CNQX, dizocilpine or both compounds together significantly attenuated this rise in free calcium. These data confirm that PS is a positive allosteric modulator of the NMDA receptor and provide evidence that this neurosteroid does not interact with the polyamine modulatory site.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1994

Polyamine potentiation and inhibition of NMDA-mediated increases of intracellular free Ca2+ in cultured chick cortical neurons.

Polyamine potentiation and inhibition of N-methyl-D-aspartate (NMDA) receptor-mediated Ca2+ changes was studied in cultured chick cortical neurons. Spermidine and spermine potentiated the effect of saturating concentrations of NMDA and glycine. No effect of spermidine or spermine was observed in the absence of NMDA or in the presence of either kainate or quisqualate. Similarly, antagonism of the NMDA receptor complex with dizocilpine (an open channel blocker), or with competitive antagonists to the NMDA or glycine binding sites greatly attenuated or completely abolished the combined effects of polyamines plus NMDA and glycine. N-Acetylspermine and N-acetylspermidine, in the presence or absence of NMDA and glycine, were without effect. These data strongly suggest that spermidine and spermine are potent and selective agonists at the polyamine binding site. Putrescine and diethylenetriamine were ineffective as antagonists of NMDA-mediated intracellular free Ca2+ increases in the presence or absence of added spermine or spermidine. Arcaine and 1,10-diaminodecane, however, antagonized NMDA-mediated intracellular free Ca2+ increases in the presence and absence of spermine and spermidine, and therefore appear to act either as inverse agonists at the polyamine binding site or as open channel blockers of the NMDA receptor.

Animals↗
PubMed1994

Isolation and characterization of the promoter of the human GABAA receptor alpha 1 subunit gene.

The GABAA receptor, as assessed by ligand binding and chloride flux measurement in vivo and in vitro, is down-regulated in response to chronic benzodiazepine exposure. The mRNA levels of the alpha 1 and gamma 2 subunits of the receptor are also reduced. We have isolated the promoter of the gene encoding the alpha 1 subunit of the GABAA receptor to elucidate the regulatory mechanism of its expression. A DNA segment 650 bp long has been isolated that includes 151 bp of untranslated 5' end of the cDNA sequence and 500 bp of potential promoter-enhancer region. The transcriptional activity of this DNA segment linked to the firefly luciferase gene showed a strong orientation specificity. The promoter activity was localized to a 60-bp segment by deletion mapping. Mobility shift binding assay results suggest that this segment may interact with one or more factors in HeLa cell nuclear extracts to form a transcriptional complex. Primary cultures of embryonic chick cortical cells transfected with the promoter-luciferase construct were treated chronically with lorazepam. Transcriptional activity of this promoter construct was strongly repressed by chronic administration of lorazepam.

Animals↗
PubMed1993

Polyamine neurotoxicity is antagonized by dizocilpine in cultured chick cortical neurons.

Release of endogenous polyamines may contribute to neuronal loss in ischemia and related conditions. Primary cortical neurons were exposed to spermine and spermidine and subsequently assayed for [3H]ouabain binding to quantify neuronal loss. Neuronal survival was significantly decreased in the presence of spermine at 24 h (500 microM), 48 h (250 microM and 500 microM) and 72 h (10-500 microM) relative to controls. Co-application of 250 microM spermine and 10 microM dizocilpine for 48 h completely inhibited the effect of spermine alone. Spermidine exposure (10-500 microM) did not alter neuronal survival at any of the time points. These data indicate that the polyamine spermine is toxic to neurons in vitro and that toxicity is prevented by the NMDA-associated channel antagonist dizocilpine.

Animals↗
PubMed1993

Prenatal cocaine exposure: decreased sensitization to cocaine and decreased striatal dopamine transporter binding in offspring.

Pregnant mice were treated with cocaine, 10 mg/kg/day, during days 13 to 20 of gestation. Cocaine sensitization and dopamine transporter binding were evaluated in offspring at 6 weeks of age. Sensitization, defined as the increase in activity after 5 injections of cocaine compared to 1 injection, was reduced in cocaine-exposed mice. Dopamine transporter binding in striatum was also significantly reduced in cocaine-exposed mice compared to controls.

Animals↗
PubMed1992

Plasma fatty acid profiles in benign breast disorders.

Breast pain (mastalgia) and macroscopic breast cysts present commonly. Mastalgia may be improved by dietary manipulation to reduce saturated fat or supplement essential fatty acid intake. Fatty acid profiles were measured in women with mastalgia and breast cysts, before and during treatment with evening primrose oil, a rich source of essential fatty acids. The fatty acid profiles of both groups of patients were abnormal, with increased proportions of saturated fatty acids and reduced proportions of essential fatty acids. Treatment with evening primrose oil improved the fatty acid profiles towards normal, but this was not necessarily associated with a clinical response.

Breast Diseases↗
PubMed1991

Chronic benzodiazepine administration. VIII. Receptor upregulation produced by chronic exposure to the inverse agonist FG-7142.

Treatment with benzodiazepine agonists is associated with the development of behavioral tolerance and receptor downregulation, whereas antagonist administration has been reported to lead to increased activity and receptor upregulation. To determine the effects of chronic inverse agonist administration, mice were treated with FG-7142 (20 mg/kg/day) by implanted s.c. osmotic pumps for 1 to 14 days. No seizures were observed in FG-7142-exposed animals. Open-field activity was unchanged as compared to controls at days 1 and 2, but was elevated significantly at days 4 and 7. Activity was reduced below control values at day 14. Benzodiazepine receptor binding determined in vivo was unchanged for days 1, 4 and 7 within the hippocampus but was elevated at day 14. Binding remained unchanged in the cortex, cerebellum, hypothalamus and pons-medulla for the duration of drug exposure. Cortical benzodiazepine binding assessed in vitro was unchanged at days 1 and 2 but increased at days 4, 7 and 14 vs. vehicle treated controls. Binding at the gamma-aminobutyric acid site was increased at day 7 whereas binding of t-[35S]butylbicyclophosphoro-thionate was increased at days 7 and 14 of FG-7142 exposure. Maximal muscimol-slimulated [36Cl-] uptake was elevated at days 4, 7 and 14 compared to day 1 of exposure. These results demonstrate that chronic continuous exposure to FG-7142 is associated with an absence of kindled seizures and with behavioral and neurochemical changes indicative of gamma-aminobutyric acidA receptor upregulation.

Animals↗
PubMed1990

Characterization of Ca2(+)-mobilizing excitatory amino acid receptors in cultured chick cortical cells.

The effects of glutamate and other more selective excitatory amino acid (EAA) analogs on intracellular free calcium concentration ( [Ca2+]i) were examined in Fura 2-loaded cultured chick embryo cortical cells (90% neuronal). Four EAA receptors were evident in these studies: an N-methyl-D-aspartate (NMDA) receptor, a kainate receptor, and two quisqualate receptors. The [Ca2+]i response to NMDA was blocked or reversed by selective antagonists such as 2-amino-5-phosphonovalerate (APV), MK801 and ketamine, as well as by desmethylimipramine and dextromethorphan. Glycine potentiated the [Ca2+]i response to NMDA, and high concentrations of glycine selectively overcame blockade by kynurenic acid, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and cis-piperidine-2,3-dicarboxylic acid (PDA). The [(Ca2+]i response to kainate was generally larger than the NMDA response, and the kainate response desensitized slightly over the first minute. CNQX was more potent as an antagonist of the kainate response than of the NMDA response, even in the absence of added glycine; kynurenic acid and PDA conversely had little effect on the kainate response in these cells at concentrations which blocked the NMDA response. The desensitization of the [Ca2+]i response to kainate was greatly augmented by quisqualate and by the putative ionotropic quisqualate receptor agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). In the absence of kainate, both quisqualate and AMPA increased [Ca2+]i though less so than did NMDA or kainate. Quisqualate (and AMPA and glutamate) were not acting as partial agonists at the kainate receptor, since the potency of these agonists in reversing the kainate [Ca2+]i response was independent of kainate concentration. Quisqualate, but not AMPA, also produced a small increase in [Ca2+]i which preceded the negative effect of this agonist on the kainate response. This increase in [Ca2+]i could also be evoked by quisqualate or glutamate after inhibition of the kainate response by AMPA. Quisqualate and glutamate, but not the other EAA agonists, also increased [Ca2+]i after chelation of extracellular calcium with EGTA. This effect appears to be mediated by the metabotropic quisqualate receptor. These cells should provide a useful system for studying regulation and interactions of EAA receptors, and for screening drugs which might act at these receptors.

Animals↗
PubMed1989

Lipids in breast carcinogenesis.

Excess dietary fat has been identified as a risk factor in the development of human breast carcinoma. However, the quality of fat may be more important than the overall quantity. We have studied the growth of human MCF7 breast carcinoma xenografts in athymic mice treated with dietary supplements of N-6 and N-3 series essential fatty acids given as natural preparations of evening primrose oil and fish oil. Olive oil and normal laboratory diet lacking the essential fatty acids served as controls. Animals treated with essential fatty acids developed tumours which were significantly smaller than both control groups (Mann-Whitney U test, P less than 0.001). Median tumour weights according to diet were: evening primrose oil, 133 mg; fish oil, 70 mg; olive oil, 212 mg; and control, 270 mg. Nutritional intervention to increase the proportion of essential fatty acids in the diet may have a role in the management of breast carcinoma.

Animals↗
PubMed1989

Cytophotometric assessment of T-2 toxin induced alterations in azure B-RNA and Coomassie-protein in supraoptic-magnocellular neurons of rat hypothalami.

Quantitative cytophotometry was used to monitor T-2 toxin-induced alterations in azure B-RNA and Coomassie-total cell protein in supraoptic-magnocellular neurons of rat hypothalami. Thirty male Sprague-Dawley rats (200-220g) were given a single i.p. injection of T-2 toxin (0.5, 0.75, 1.00 and 1.50 x LD50), a trichothecene mycotoxin; rats were decapitated 8 hours post-dosing. After stoichiometric azure B-RNA and Coomassie-protein staining of brain sections, scanning-integrating microdensitometry was used to quantify toxin-induced alterations in these well established indices of neuronal toxicity. Within the magnocellular neurons of the supraoptic nuclei, significant reductions in azure B-RNA reactivity were observed in the 0.75, 1.00 and 1.50 x LD50 groups (i.e. 11%, 13% and 8%, respectively); no differences in RNA levels were observed between controls and the 0.50 x LD50 group. In addition, a decrease in Coomassie-total cell protein was seen in animals receiving 0.50, 0.75 and 1.50 x LD50 T-2 toxin (i.e. 33%, 21% and 12%, respectively); however, toxin administration did not alter protein levels in the 1.00 x LD50 group. Furthermore, a dose-dependent decrease in systolic blood pressure was observed at 8 hr. post-injections (i.e., approximately -39%, -52%, -66% and -64% for the 0.50, 0.75, 1.00 and 1.50 x LD50 groups, respectively). Additional observations include pronounced polydipsia, ascites, abdominal and subdural hemorrhage, and horripilation (piloerection) in experimental groups. It is postulated that the T-2 toxin-induced reductions in azure B-RNA and Coomassie-protein represent an early indication of impaired metabolic activity. Since these neurons are important sites of vasopressin (antidiuretic hormone) synthesis, these data suggest an impaired osmoregulatory ability. The pronounced polydipsia which occurred shortly after intoxication is further evidence of this impairment. Although these findings do not provide insight relating to the mechanism of osmoregulatory disruption, it is advanced that the supraoptic-magnocellular compartment represents an important site in T-2 toxin mycotoxicosis. Moreover, these findings support previous claims that T-2 toxin intoxication may critically impair the vasopressinergic response to toxin-induced cardiovascular collapse.

Animals↗
PubMed1989

Cytophotometric analysis of T-2 toxin induced alterations in chromatin condensation and neuronal nuclear volume of rat supraoptic-magnocellular neurons.

Quantitative cytophotometry and ocular filar micrometry were used to monitor T-2 toxin induced alterations in chromatin and neuronal nuclear volume in supraoptic-magnocellular neurons of rat hypo-thalami. Thirty male Sprague-Dawley rats (200-220g) were given a single i.p. injection of T-2 toxin (0.5, 0.75, 1.0 and 1.5 X LD50), a trichothecene mycotoxin; rats were decapitated 8 hours post-dosing. After stoichiometric Feulgen-DNA staining of brain sections, scanning-integrating microdensitometry was used to quantify changes in the susceptibility of chromatin to Feulgen acid hydrolysis. Changes in neuronal nuclear volumes were also determined histometrically. Within the magnocellular neurons of the supraoptic nuclei, significant reductions in F-DNA reactivity were observed in the 0.5, 0.75, and 1.0 X LD50 groups (i.e. 3.7%, 4.4% and 2.5%, respectively); however, rats receiving 1.5 X LD50 T-2 toxin showed no difference in F-DNA reactivity compared to controls. In addition, ocular filar micrometry demonstrated increased neuronal nuclear volumes in all groups receiving T-2 toxin, and following an inverse trend to that seen with F-DNA stainability. Additional observations included pronounced polydipsia, polyphagia and horripilation in the experimental groups, independent of the dosages employed; these changes were evident within 1 hour post-injection. It is postulated that the T-2 toxin induced reduction in the susceptibility of chromatin to Feulgen acid hydrolysis and concomitant increases in neuronal nuclear volumes represent an early indication of impaired metabolic activity. Since these neurons are important sites of vasopressin (antidiuretic hormone) synthesis, these data suggest an impaired osmoregulatory ability. The pronounced polydipsia which occurred shortly after intoxication is further evidence of this impairment. Although these findings do not provide insight relating to the mechanism of osmoregulatory disruption, it is evident that an impaired ability to osmoregulate is among the earliest indications of acute T-2 toxin mycotoxicosis.

Animals↗