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Results for “Drug Collateral Sensitivity”

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PubMed1984

The effect of vinca alkaloids in enhancing the sensitivity of a methotrexate-resistant (L1210/R7A) line, studied by flow cytometric and chromosome number analysis.

Two L1210 murine lymphoma cell lines sensitive and resistant to methotrexate (L1210 and L1210/ R7A , respectively) and previously shown to exhibit collateral sensitivity to the vinca alkaloids have been studied by flow cytofluorimetric techniques following propidium iodide staining of the DNA. Following treatment with a range of concentrations of vincristine, both cell lines showed a build-up of fluorescence in the 4n position. However, the methotrexate-resistant cell line exhibited this effect at lower doses of vincristine. On an equimolar basis, the vinca alkaloids ranked for intensity of this effect in the order vinblastine greater than vindesine greater than vincristine. DNA fluorescent histograms following various times of continuous exposure to vincristine showed an accumulation of material at the 8n position, which was shown by chromosome analysis to be due to polyploidy. It was concluded that methotrexate-resistant cells (L1210/ R7A ) experience difficulty in traversing mitosis and this difficulty is enhanced by the vinca alkaloids.

Animals↗

PubMed1993

Interstitial PCO2 and pH in rat hippocampal slices measured by means of a novel fast CO2/H(+)-sensitive microelectrode based on a PVC-gelled membrane.

We describe here the construction and properties of a double-barrelled microelectrode (tip diameter 4-10 microns) which permits simultaneous measurements of PCO2 and pH, and which has a 90% response time of only one or a few seconds for a step change in PCO2. The fast response of the CO2-sensitive barrel is due to (i) the use of a PVC-gelled (tridodecylamine-containing) membrane solution which enables the construction of extremely short (> or = 4 microns), yet mechanically stable, membrane columns, and (ii) the presence of carbonic anhydrase in the filling solution. Recordings made in the pyramidal layer of area CA1 in rat hippocampal slices showed that the deviation in the acid direction of the basal interstitial pH (pH0) from that of the perfusion solution was attributable to a higher PCO2 level within the tissue. Most of the late acid shift evoked by stimulation of the Schaffer collaterals (5- to 20-s trains at 10 Hz) could also be explained on the basis of an accumulation of interstitial CO2 at a constant HCO3- concentration. This conclusion was supported by the finding that inhibition of extracellular carbonic anhydrase activity by 10 microM benzolamide completely abolished the activity-induced fall in pH0, but not the increase in PCO2. The initial stimulus-induced alkalosis was accompanied by a slight decrease in PCO2 only, implying a parallel increase in the interstitial HCO3- concentration. Benzolamide produced a dramatic enhancement of the early alkaline shift as well as of the simultaneous fall in PCO2. The latter effect of the drug unmasks a cellular CO2 sink that is induced by neuronal activity.

Animals↗

PubMed2005

Use of a force-plate actometer for detecting and quantifying vertical leaping induced by amphetamine in BALB/cJ mice, but not in C57BL/6J, DBA/2J, 129X1/SvJ, C3H/HeJ, and CD-1 mice.

The force-plate actometer is a relatively new computer-based instrument with high temporal and spatial resolution that has been used to measure the behavioral effects of genetic restriction (e.g., inbred mice) and drugs (e.g., dopaminergic agonists and antagonists) on a variety of behaviors in rodents, including locomotor activity, stereotypies, tremor, and wall rearing. In the present study, the force-plate actometer was used to measure the differential effects of amphetamine-induced (10.0mg/kg) vertical leaping in five inbred mouse strains (BALB/cJ, C57BL/6J, DBA/2J, 129X1/SvJ, and C3H/HeJ) and one outbred stock (CD-1). Across a 13-day, five-injection procedure, mice of the BALB/cJ strain leaped an average of 82 times per 60-min session; the C57BL/6J, DBA/2J, 129X1/SvJ, C3H/HeJ strains and CD-1 stock always showed zero or near zero levels of vertical leaping following amphetamine treatment. The quantitative precision afforded by the force-plate actometer revealed that the mean duration of the leaps by the BALB/cJ strain was 0.18 second, and the corresponding peak force averaged 87.4 gram per leap, which was more than 400% of the average body weight of this strain. Although no evidence of behavioral sensitization was indicated for amphetamine's effects on vertical leaping, sensitization to amphetamine's effects on spatial confinement (i.e., bouts of low mobility) was observed in all mouse types. Results indicate that the force-plate actometer is an instrument well suited for detecting and quantifying both vertical leaping and collateral behaviors induced by amphetamine in mice.

Amphetamine↗

PubMed2000

Clustering of mutations in the first transmembrane domain of the human reduced folate carrier in GW1843U89-resistant leukemia cells with impaired antifolate transport and augmented folate uptake.

We have studied the molecular basis for the resistance of human CEM leukemia cells to GW1843, a thymidylate synthase inhibitor. GW1843-resistant cells displayed a approximately 100-fold resistance to GW1843 and methotrexate but were collaterally sensitive to the lipophilic antifolates trimetrexate and AG337, which enter cells by diffusion. These cells exhibited a 12-fold decreased methotrexate influx but surprisingly had a 2-fold decreased folic acid growth requirement. This was associated with a 4-fold increased influx of folic acid, a 3.5-fold increased steady-state level of folic acid, and a 2.3-fold expansion of the cellular folate pool. Characterization of the transport kinetic properties revealed that GW1843-resistant cells had the following alterations: (a) 11-fold decreased transport K(m) for folic acid; (b) 6-fold increased transport K(m) for GW1843; and (c) a slightly increased transport V(max) for folic acid. Sequence analysis showed that GW1843-resistant cells contained the mutations Val-29 --> Leu, Glu-45 --> Lys, and Ser-46 --> Ile in the first transmembrane domain of the reduced folate carrier. Transfection of the mutant-reduced folate carrier cDNA into methotrexate transport null cells conferred resistance to GW1843. This is the first demonstration of multiple mutations in a confined region of the human reduced folate carrier in an antifolate-resistant mutant. We conclude that certain amino acid residues in the first transmembrane domain play a key role in (anti)folate binding and in the conferring of drug resistance.

Antimetabolites, Antineoplastic↗

PubMed1987

Effects of phencyclidine, SKF 10,047 and related psychotomimetic agents on N-methyl-D-aspartate receptor mediated synaptic responses in rat hippocampal slices.

The effects of representative drugs from three classes of psychotomimetic compounds (arylcyclohexylamines, benzomorphan opioids and dioxolanes) have been examined on synaptic transmission at an identified monosynaptic pathway in rat hippocampal slices. The compounds tested were phencyclidine (PCP) and ketamine, the racemate and isomers of SKF 10,047 (N-allylnormetazocine), and the isomers of dioxadrol (dexoxadrol and levoxadrol). In the absence of added magnesium ions (Mg) in the perfusion medium low frequency stimulation of the Schaffer collateral-commissural pathway evoked a burst of population spikes in the CA1 cell body region. The secondary components of this response could be abolished by the selective N-methyl-D-aspartate (NMDA) antagonist D-2-amino-5-phosphonovalerate (APV). PCP (1 microM) or ketamine (10 microM) selectively blocked the secondary components of the synaptic response. The effect of PCP was neither mimicked nor prevented by hexamethonium and atropine, phentolamine and propranolol, or clonidine and was therefore unlikely to involve cholinergic or adrenergic neurotransmitter systems. The sigma opiate, (+/-)-SKF 10,047 (10 microM) also abolished selectively the secondary components of the synaptic response. There was no apparent difference between the potency of the stereoisomers of this compound. The action of (+/-)-SKF 10,047 was not affected by either naloxone or haloperidol, indicating that this effect did not involve opioid receptors or the haloperidol-sensitive sigma site. Dexoxadrol (10 microM), but not levoxadrol (10 microM), also selectively blocked the secondary components of the synaptic response. It is concluded that these psychotomimetic agents can block an NMDA receptor-mediated component of synaptic transmission in the hippocampus and that this effect is mediated by a specific PCP/sigma site.

Analgesics↗

PubMed1993

Severe depletion of cellular thiols and glutathione-related enzymes of a carmustine-resistant L1210 strain associates with collateral sensitivity to cyclophosphamide.

Cyclophosphamide (CPA) increased the life span of both carmustine (BCNU)-resistant (L1210/BCNU) and BCNU-sensitive L1210 (L1210/0) leukaemic mice; their sensitivity to CPA, however, was extremely different. The BCNU-resistant strain was much more sensitive (collaterally) to CPA than was its sensitive counterpart. The collateral sensitivity was accompanied by a severe reduction in the activity of glutathione-related enzymes and in protein thiol (SH) and non-protein SH levels in BCNU-resistant cells. The activity of glutathione reductase (GSSG-R) was 2 times higher in the L1210/0 cells than in the L1210/BCNU cells. Glutathione-S-transferase (GST) was also almost 2 times more active in the sensitive cells than in the resistant strain. To develop resistance against CPA with a single treatment (60 mg/kg) per passage, the L1210/BCNU strain needed 26 passages, whereas the L1210/0 strain required significantly fewer. The resistance developed against CPA was associated with a moderate elevation of thiols in the L1210/CPA cells, whereas this elevation was approximately 3 times more pronounced in the L1210/BCNU/CPA cells. The severely reduced activity of GST in the L1210/BCNU strain was markedly increased when these cells were made resistant to CPA; the GSSG-R activity, however, remained low, suggesting an irreversible injury of this enzyme by BCNU.

Animals↗

PubMed2003

Anesthetic sensitivities to propofol and halothane in mice lacking the R-type (Cav2.3) Ca2+ channel.

UNLABELLED: Because inhibition of voltage-dependent Ca(2+) channels can be a mechanism underlying general anesthesia, we examined sensitivities to propofol and halothane in mice lacking the R-type (Ca(v)2.3) channel widely expressed in neurons. Sleep time after propofol injection (26 mg/kg IV) and halothane MAC(RR) and MAC (50% effective concentrations for the loss of the righting reflex and for the tail pinch/withdrawal response, respectively) were determined. Significantly shorter propofol-induced sleep time (291.6 +/- 16.8 s versus 344.4 +/- 12.1 s) and larger halothane MAC(RR) (1.11% +/- 0.04% versus 0.98% +/- 0.03%) were observed in Ca(v)2.3 channel knockouts (Ca(v)2.3(-/-)) than in wild-type (Ca(v)2.3(+/+)) litter mates. To investigate the basis of the decreased anesthetic sensitivities in vivo, field excitatory postsynaptic potentials and population spikes (PSs) were recorded from Schaffer collateral CA1 synapses in hippocampal slices. Propofol (10-30 micro M) inhibited PSs by potentiating gamma-aminobutyric acid-ergic inhibition, and this potentiation was markedly smaller at 30 micro M in Ca(v)2.3(-/-) mice, possibly accounting for the decreased propofol sensitivity in vivo. Halothane (1.4%-2.2%) inhibited field excitatory postsynaptic potentials similarly in both genotypes, whereas 1%-2% halothane depressed PSs more in Ca(v)2.3(-/-) mice, suggesting the postsynaptic role of the R-type channel in the propagation of excitation and other mechanisms underlying the increased halothane MAC(RR) in Ca(v)2.3(-/-) mice. IMPLICATIONS: Because inhibition of neuronal Ca(2+) currents can be a mechanism underlying general anesthesia, we examined anesthetic sensitivities in mice lacking the R-type (Ca(v)2.3) Ca(2+) channels both in vivo and in hippocampal slices. Decreased sensitivities in mutant mice imply a possibility that agents blocking this channel may increase the requirements of anesthetics/hypnotics.

Anesthetics, Inhalation↗

PubMed2003

Transection of intrinsic polysynaptic pathways reduces N-methyl-D-aspartate neurotoxicity in hippocampal slice cultures.

Hippocampal CA1 neurons have been shown to be highly susceptible to excitotoxicity produced by various forms of insult. CA1 neurotoxicity is partly dependent on over activity of N-methyl-D-aspartate (NMDA) receptors. It is unclear, however, if sensitivity of this region to excitotoxicity is related to inherent properties of CA1 neurons and/or network activation of polysynaptic pathways. The present studies examined the role of mossy fiber and Schaffer collateral function in promoting NMDA-induced neurodegeneration. Organotypic hippocampal cultures were subjected to transection of mossy fibers, Schaffer collaterals, or CA1 efferent fibers and then exposed to NMDA (20 microM) for 1 h. Hippocampal damage was assessed 24 h later via fluorescent microscopy. NMDA exposure produced significant excitotoxicity in all regions (160-500% of control), particularly in the CA1. In each region, toxicity was reduced by co-exposure to NMDA with MK-801 (20 microM), to near-control levels. Surgical transection of mossy fibers and Schaffer collaterals significantly reduced NMDA-induced neurotoxicity in the CA1 ( approximately 20%), and to a lesser extent, the CA3 and dentate regions. Conversely, transection of CA1 efferent fibers did not reduce the neurotoxicity in these regions. These data indicate that CA1 neurotoxicity caused by excitotoxic insult depends, in part, on 'network activation' of intrinsic polysynaptic pathways.

Animals↗

PubMed2004

Expression of vanilloid receptor TRPV1 in the rat trigeminal sensory nuclei.

Little is known about the central projection patterns of trigeminal afferent neurons expressing the vanilloid receptor TRPV1 and their coexpression of neuromodulatory peptides. To address these issues, we examined the distribution of TRPV1-positive neurons in the trigeminal ganglion (TG) and trigeminal sensory nuclei principalis (Vp), oralis (Vo), interpolaris (Vi), and caudalis (Vc) in the rat via light and electron microscopy. In addition, we studied the colocalization of TRPV1-positive neurons with substance P (SP) and calcitonin gene-related peptide (CGRP) via confocal microscopy. In TG, only small and medium-sized neurons were immunopositive for TRPV1. The staining for TRPV1 was found in axon collaterals in the dorsal parts of Vp, Vo, and Vi and in terminals and fibers throughout lamina I and the outer zone of lamina II (IIo) of Vc. With electron microscopy, TRPV1-positive fibers in the ascending and descending trigeminal tracts were found to be unmyelinated. Almost all TRPV1-positive terminals in Vc contained numerous large dense-core vesicles and formed synaptic contacts with single small dendrites. Multiple immunofluorescence revealed a high degree of colocalization of TRPV1 with SP and CGRP in TG neurons as well as in fibers and terminals confined to laminae I and IIo of Vc. These results suggest that the central projections of unmyelinated (C) afferents sensitive to noxious heat and capsaicin are organized differently between Vc and the rostral trigeminal nuclei and that Vc may play a role in the development of hyperalgesia.

Afferent Pathways↗

PubMed1990

Changes in glutathione content and resistance to anticancer agents in human stomach cancer cells induced by treatments with melphalan in vitro.

A clone of a human gastric carcinoma cell line was used to determine whether cells which had survived a treatment with Melphalan would express altered survival responses when treated again with this agent 1 week or more later. Cells were treated for 1 h each week with 2 micrograms/ml (99% lethal dose). After the first Melphalan treatment, the cells exhibited a 10-fold reduction in sensitivity to Melphalan. This was preceded by a 2-fold increase in intracellular glutathione content. By the end of 10 weekly treatments, the cells were 50 times more resistant than controls (based on changes in survival fractions). They also demonstrated collateral resistance to Actinomycin D, 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea, galactitol, and X-rays, but showed no change in sensitivity to 5-fluorouracil, bleomycin, and Adriamycin. The resistance to Melphalan was not reversible when treatment was withheld for 4 weeks on two different occasions. The results suggest that treatment with a high dose of Melphalan either selects an existing population of cells with a high GSH content or induces mutations leading to increased GSH content or both, and this results in the expression of greater Melphalan resistance at the time of other treatments. Furthermore, Melphalan treatment stimulates a 50% increase in GSH content in resistant cells in just 6 h, an 85% increase in 36 h, and a 150% increase in 72 h. L-Buthionine sulfoximine partially reversed the expression of resistance to Melphalan by inducing a 60% reduction in intracellular glutathione content.

Buthionine Sulfoximine↗

PubMed1996

Separation of resistance to antitumor diarylsulfonylurea agents from collateral sensitivity to mitochondrial toxins.

Compared with parental GC3/c1 human colon adenocarcinoma cells, which are diarylsulfonylurea (DSU)-sensitive cells, the DSU-resistant clone LYC5 demonstrates 4.2-, 12.8-, and 5.3- fold increase in sensitivity to the mitochondrial toxins rotenone, antimycin, and oligomycin, respectively. Studies with hybrids formed by fusion of parental GC3/c1 cells with LYC5 cells have indicated that resistance to antitumor DSUs and collateral sensitivity to mitochondrial toxins are recessive and therefore potentially linked. To examine this, we transfected a cDNA library from GC3/c1 cells, constructed in pcDNA3, into LYC5 cells. G418-resistant colonies were selected and further selected in a single step for resistance to rotenone (100 nm). Individual colonies (designated T5LR) were expanded and tested for sensitivity to mitochondrial toxins, antitumor DSU agents (LY195779 and LY186391) that demonstrate a 45-50-fold differential potency against GC3/c1, LYC5 cells, and the antimitotic agent vincristine. Results demonstrate that resistance to mitochondrial toxins rotenone, antimycin, and oligomycin can be transferred without conferring a DSU-sensitive phenotype. Furthermore, in T5LR clones, resistance to mitochondrial toxins was not associated with increased resistance to vincristine or increased P-glycoprotein expression, supporting the contention that resistance to these agents is independent of P-glycoprotein. Southern blot analysis of T5LR clones demonstrated unique integration sites for the neomycin phosphotransferase gene into genomic DNA in clones 4 and 9, indicating independent derivation. Analysis of clones 4, 6, and 9 with use of polymerase chain reaction demonstrated a cDNA insert of approximately 1.0 kilobase.

Antimycin A↗

PubMed2005

Cholinergic modulation of the spatiotemporal pattern of hippocampal activity in vitro.

The aim of this study was to use optical imaging with voltage-sensitive dyes (Di-4-ANEPPS), to examine the cholinergic modulation of CA1 network responses to Schaffer collateral input. By comparing responses recorded with optical imaging and field recordings across the proximodistal axis of CA1, it was initially demonstrated that voltage-sensitive dyes could report reliably both the pattern of activation and cholinergic modulation. The higher spatial resolution of optical imaging was used to explore the somatodendritic profile of cholinergic modulation. It was found that activation of muscarinic acetylcholine receptors (mAChR) (1-10 microM carbachol), inhibited evoked responses across all layers of CA1. This was accompanied by an increase in paired-pulse facilitation in the apical and distal dendritic layers (40 ms inter-stimulus interval), but not in perisomatic regions. The mAChR antagonist, 20 microM atropine, alone increased facilitation at perisomatic sites, suggesting that muscarinic signalling pathways actively suppress perisomatic responses to repetitive stimulation. In contrast, the activation of nicotinic acetylcholine receptors (10 microM nicotine) had no significant effect on single evoked responses, but selectively increased facilitation at perisomatic sites. These results suggest that cholinergic modulation of the hippocampal CA1 network has multiple differential effects on the somatodendritic processing of the Schaffer collateral input.

Acetylcholine↗

PubMed1994

GABA synapses formed in vitro by local axon collaterals of nucleus accumbens neurons.

GABAergic medium-spiny neuron axons not only form the principal projections of the nucleus accumbens (nAcc) but also branch locally in a dense network overlapping their own dendrites, suggesting that their recurrent synapses mediate the major information processing functions of the nAcc. We used postnatal nAcc cultures to study these synapses individually. In culture, as in the intact nAcc, medium-spiny neurons account for over 95% of the cells and are GABAergic. Strikingly, these neurons showed a spike afterhyperpolarization (AHP) that was largely blocked by the GABAA antagonist bicuculline. The bicuculline-sensitive AHP occurred without or with latency, and met criteria for monosynapticity; consistent with this, dye fills showed the presence of recurrent axons and a low incidence of dye coupling. Blockade of Ca2+ influx eliminated this autaptic PSP, while TTX almost completely eliminated it, indicating that it is due to exocytic GABA release principally at axodendritic contacts. While blocking GABAB receptors had no direct effect on the autaptic PSP, activating these receptors with baclofen produced presynaptic inhibition, as well as directly mediated hyperpolarization; together, these actions increased the signal-to-noise ratio in the cellular response to synaptic inputs. Bicuculline also increased the signal-to-noise ratio; in addition, it induced burst firing and depolarization inactivation. In contrast, the indirect GABA agonist flurazepam and the GABA uptake blocker nipecotic acid each enhanced autaptic PSPs. Since autapses formed in vitro appear to be functionally equivalent to synapses between neighboring medium-spiny neurons that receive similar inputs, these results bear on the function of intrinsic GABA synapses in the intact nAcc. Thus, intrinsic GABA synapses are likely to regulate the signal-to-noise ratio in nAcc information processing and may be important targets for the modulatory actions of endogenous neurotransmitters and drugs.

Animals↗

PubMed1980

Behavior-dependent evoked potentials in the hippocampal CA1 region of the rat. II. Effect of eserine, atropine, ether and pentobarbital.

The correlations of the rat's behaviors and the hippocampal EEG with the averaged evoked potentials (AEPs) evoked by the Schaffer collaterals in the hippocampal CA1 region of the rat were studied after intraperitoneal injections of several drugs known to affect hippocampal EEG. Ether and eserine induced continuous train of rhythmical slow activity (RSA) of 5-6/sec in the hippocampal EEG, during which the AEPs showed waveforms intermediate between those elicited during large irregular activity (LIA) in the awake, immobile control and those elicited during walking in the control. Low dose nembutal and atropine induced high amplitude LIA during immobility, resembling EEG during slow-wave sleep (SWS). The AEPs during these LIA states, and that during LIA of wake-immobility were of similar waveforms. The AEP waveforms are proposed to form a continuum which corresponds to the continuum of EEG from high amplitude LIA to RSA of increasing frequency. AEP waveforms do not depend only on walking or similar movements which correlate with high frequency RSA. Atropine sulfate (25-50 mg/kg i.p.) severely dampened the oscillations in the AEPs of rats during walking or similar movements, even though the high frequency RSA was essentially unaffected. The difference between AEPs during immobility and those during walking was markedly reduced after atropine, even though the EEG-behavior relationship persisted. The effect of atropine on AEPs may be interpreted as a direct effect on the hippocampus which is apparently inconsistent with present knowledge. If the effect was on inputs from the brain stem or the septum to the hippocampus, the hypothesis that there are two pharmacological types of RSA (atropine-sensitive and -resistant) requires re-definition and re-examination.

Animals↗

PubMed2001

Taxotere resistance in SUIT Taxotere resistance in pancreatic carcinoma cell line SUIT 2 and its sublines.

AIM: To investigate the specific mechanisms of intrinsic and acquired resistance to taxotere (TXT) in pancreatic adenocarcinoma (PAC). METHODS: MTT assay was used to detect the sensitivity of PAC cell line SUIT-2 and its sublines (S-007, S-013, S-020, S-028 and TXT selected SUIT-2 cell line, S2/TXT) to TXT. Mdr1 (P-gp), multidrug resistance associated protein (MRP), lung resistance protein (LRP) and beta-tubulin isotype gene expressions were detected by RT-PCR. The functionality of P-gp and MRP was tested using their specific blocker verapamil (Ver) and indomethacin (IMC), respectively. The transporter activity of P-gp was also confirmed by Rhodamine 123 accumulation assay. RESULTS: S-020 and S2/TXT were found to be significantly resistant to TXT(19 and 9.5-fold to their parental cell line SUIT-2, respectively). RT-PCR demonstrated strong expression of Mdr1 in these two cell lines, but weaker expression or no expression in other cells lines. MRP and LRP expressions were found in most of these cell lines. The TXT-resistance in S2-020 and S2/TXT could be reversed almost completely by Ver, but not by IMC. Flow cytometry showed that Ver increased the accumulation of Rhodamine-123 in these two cell lines. Compared with S-020 and SUIT-2, the levels of beta-tubulin isotype II, III expressions in S-2/TXT were increased remarkably. CONCLUSION: The both intrinsic and acquired TXT-related drug resistance in these PAC cell lines is mainly mediated by P-gp, but had no relationship to MRP and LRP expressions. The increases of beta-tubulin isotype II, III might be collateral changes that occur when the SUIT-2 cells are treated with TXT.

Antineoplastic Agents, Phytogenic↗

PubMed1997

Effects of acute, chronic ethanol and withdrawal on dorsal raphe neurons: electrophysiological studies.

The effect of a single intravenous administration of ethanol (0.25-1.0 g/kg) on the spontaneous activity of putative serotonin neurons of the dorsal raphe nucleus was studied in unanesthetized rats. Ethanol produced a slight but progressive decline in neuronal activity in 67% (six of nine) of all neurons tested. The remaining 33% (three of nine) were unresponsive. Upon withdrawal of chronic ethanol treatment (1-5 g/kg every 6 h for six consecutive days, 12 h from last ethanol administration), the mean firine rate of dorsal raphe neurons was found to be significantly reduced, by about 30% (n=71), as compared with the control group (n=83), whereas the cells/track index was unaltered. Under these conditions, ethanol administration further reduced firing rate in 67% (four of six) of all the neurons tested. In the remaining 33% (two of six), no response was observed. At 72 h after the last ethanol administration, the mean firing rate of dorsal raphe neurons was found to be within control values (n=90). Further, to evaluate the functional status of the autoreceptors under control conditions and after withdrawal from chronic ethanol, the selective serotonin-1A receptor agonist 8-hydroxy-(2-di-n-propylamino)tetralin was administered intravenously in cumulative doses (1-16 microg/kg) and dose-response curves were generated for both groups. Autoreceptor sensitivity of dorsal raphe neurons was found to be not statistically different in control and ethanol withdrawn rats (n=6 for both groups) as indexed by a similar potency displayed by 8-hydroxy-(2-di-n-propylamino)tetralin in reducing the spontaneous activity of dorsal raphe neurons. The results indicate that, in spite of the widespread use of serotonin transmission potentiating agents in the treatment of alcoholism, neither acute nor withdrawal from chronic ethanol administration produces drastic effects on dorsal raphe neurons. However, the inhibition of dorsal raphe neuronal activity after acute ethanol may be due to the reported ability of ethanol to increase serotonin release from terminal areas. This increased serotonin tone could, at the level of recurrent axon collaterals in the dorsal raphe nucleus, reduce the spontaneous activity of the cells. On the other hand, a similar reduction in spontaneous activity after withdrawal from ethanol correlates well with the reduction in serotonin levels observed under these conditions in microdialysis studies.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1975

Modification and inheritance of pleiotropic cross resistance and collateral sensitivity in Saccharomyces cerevisiae.

A meiotic segregant (oliPR1) was isolated with a phenotype of multiple cross resistance and collateral sensitivity. Strain oliPR1 has increased sensitivity to ethidium bromide, dequalinium chloride, acriflavin, paromomycin and neomycin, and increased resistance to oligomycin, rutamycin, venturicidin, triethyltin bromide, antimycin, carbonylcynamide-m-chlorophenylhydrazone, tetra-N-butylammonium bromide, dibenzyldimethylammonium chloride, triphenylmethlphosphonium bromide, chloramphenicol, carbomycin, tetracycline, triton X-165 and cycloheximide. Single gene inheritance of the cross resistance and collateral sensitivity was shown by 2:2 parental ditype segregation and reversion of the complete phenotype by a spontaneous revertant. The locus conferring the oliPR1 phenotype was mapped 11.7 units from an unspecified centromere. Antibiotic resistance showed incomplete dominance, with the level of hybrid resistance dependent upon the inhibitor tested. Resistant diploids that produced four resistant ascospores were the result of mitotic recombination prior to meiosis. A partial revertant phenotype (sensitive to all inhibitors except oligomycin, antimycin and carbonylcyanide-m-chlorophenylhydrazone) was shown to be due to a single nuclear gene causing partial suppression of oliPR1. Anaerobic pretreatment, 37degrees and 0.5 MKC1 were observed to reduce the growth of oliPR1 when challenged with seven diverse inhibitors (antimycin, carbonylcyanide-m-chlorophenylhydrazone,-chloramphenicol, cycloheximide, oligomycin, triethyltin bromide, and triphenylmethylphosphonium bromide). Resistance to cycloheximide was not altered by the [rho--] state. A revertant of oliPR1 (sensitive to the above inhibitors but resistant to ethidium bromide, paromycin and neomycin) showed anaerobic and temperature sensitization to ethidium bromide, paromomycin and neomycin. Continuous monitoring of oxygen uptake by the revertant afteranaerobic pretreatment revealed that anaerbiosis sensitized respiratory adaptation of the revertant to neomycin. It is proposed that oliPR1 is a mutation resulting in the alteration of plasma membrane permeability to many diverse inhibitors.

Antimycin A↗

PubMed1992

Human lymphoblastoid cells with acquired resistance to C2-desamino-C2-methyl-N10-propargyl-5,8-dideazafolic acid: a novel folate-based thymidylate synthase inhibitor.

We describe the characterization of human lymphoblastoid cell lines with acquired resistance (greater than 20,000-fold) to a novel folate-based thymidylate synthase (TS) (EC 2.1.1.45) inhibitor, C2-desamino-C2-methyl-N10-propargyl-5,8-dideazafolic acid (ICI198583). This acquired resistance was associated with a 64-fold amplification of the TS gene, a similar elevation in the corresponding mRNA, and an approximately 200-fold increase in both TS activity and TS protein. This amplification was maintained when the cells were grown in the absence of the selective agent, ICI198583, for 340 generations. TS isolated from one of the resistant cell lines, W1-L2:C1, displayed inhibition kinetic parameters similar to those of TS isolated from the parent W1-L2 cell line. It thus appears unlikely that resistance is due to an altered TS enzyme having a lower affinity for ICI198583. The resistant cell line, W1-L2:C1, was cross-resistant to other folate-based TS inhibitors but was as sensitive as the parent cell line, W1-L2, to 5-fluorodeoxyuridine. The W1-L2:C1 cell line was collaterally sensitive to the classical dihydrofolate reductase (EC 1.5.1.3) inhibitor methotrexate as well as to the lipophilic dihydrofolate reductase inhibitors metoprine and 2,4-diamino-5-methyl-6-[(3,4,5-trimethoxyanilino)methyl]quinazolin e glucuronic acid salt (also called trimetrexate). When the W1-L2 and W1-L2:C1 cell lines were exposed to 1 microM ICI198583 for 24 h they accumulated the same concentration of total cellular ICI198583 polyglutamates despite the fact that the latter cell line accumulated a 300-fold greater concentration of ICI198583 monoglutamate. As polyglutamates, the tetra- and pentaglutamate forms predominated in the W1-L2 cell line, whereas the diglutamate form predominated in the W1-L2:C1 cell line, with few higher polyglutamates being detected. The lack of tri- and higher polyglutamates of ICI198583 (i.e., the more active species) in the W1-L2:C1 cell line may also contribute to the observed resistance. These findings may have important implications in light of the rapid onset of resistance to antifolates in the clinic.

Antineoplastic Agents↗