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Clonal analysis of helper and effector T-cell function in neonatal transplantation tolerance: clonal deletion of helper cells determines lack of in vitro responsiveness.

Mice rendered tolerant at birth of H-2 alloantigens display concordant in vivo and in vitro phenotypes: they fail to reject skin grafts bearing the tolerated antigens, and their lymphoid cells fail to participate in tolerogenspecific mixed lymphocyte reactions (MLRs) and cell-mediated lympholysis (CML). Tolerant animals normally reject third-party skin allografts and develop positive MLRs and CML to third-party antigens. It has been suggested that clonal deletion of antigen reactive cells is the basis for this spectrum of responses. To investigate further the basis for the lack of in vitro alloreactivity, we conducted limiting dilution studies with lymph node cells from adult mice tolerant of various H-2 disparities. When the frequencies of (a) cells responding to the tolerogen in MLR and (b) interleukin-2-producing cells against the tolerogen were determined, it appeared that both types of cells were functionally deleted, that is, the frequency of cells responding to tolerogen-bearing stimulator cells was identical with that of cells stimulated with syngeneic cells. On the assumption that cells from H-2 tolerant mice are deficient in helper cell activity toward the tolerogen, we performed CML cultures under conditions in which exogenous help was provided in the form of supernatants derived from concanavalin A stimulated rat spleen cell cultures. Lymphoid cells from H-2 tolerant mice generated significant cytotoxicity toward the tolerogen under these conditions, although the absolute level of killing was reduced compared with that of cells from normal mice. Limiting dilution assays confirmed that Tc precursors were present in tolerant mice, and that they were reduced to less than 10% of normal numbers; however, tolerogen-specific Tc precursors were present in frequencies significantly greater than self-reactive Tc precursors. These data indicate that a deletion mechanism operates in neonatal transplantation tolerance to reduce the clone size of all three categories of functional T cells assayed, but that its efficiency is greatest among cells destined to provide specific T-cell help. The absolute functional deletion of helper cells determines the in vitro CML unresponsiveness of lymphoid cells from tolerant mice, and may be a crucial factor in promoting the in vivo phenotype of skin allograft tolerance.

Animals↗

Associative control of tolerance to the sedative and hypothermic effects of chlordiazepoxide.

Pavlovian control of tolerance to the sedative and hypothermic effects of chlordiazepoxide (CDP) was demonstrated in two experiments. In Experiment I, drug-experienced rats were repeatedly treated with CDP (30 mg/kg) in one environment (CS+); on alternate days, they were given saline injections in a different environment (CS-). Duration of sleeping and inactivity were used as measures of sedation. A comparable conditioning procedure was used in Experiment II, but tolerance to the hypothermic effect of CDP was the dependent measure. During tolerance testing, rats from both Experiments I and II were given CDP in one of three environments, CS+, CS-, or a novel environment (CSnov). In Experiment I, rats were equally tolerant in all three test environments when duration of sleep was assessed. However, when inactivity was used as the measure of tolerance, rats showed tolerance in CS+ and CS-, and significantly less tolerance in CSnov. Drug-naive controls showed similar nontolerant responses to CDP in all environments, thus ruling out the possibility that the effect of sedation was mediated nonassociatively. In Experiment II, drug-experienced rats showed tolerance to CDP-induced hypothermia in CS+ and CS- but less tolerance in CSnov. A compensatory hyperthermia was observed when these rats were given saline in CS+. There was some evidence for a generalization gradient in the conditional control of tolerance in both experiments.

Analysis of Variance↗

Morphine and delta 9-tetrahydrocannabinol: two-way cross tolerance for antinociceptive and heart-rate responses in the rat.

Tail-flick analgesic responses and heart-rate changes were measured in male Sprague-Dawley rats challenged with an acute IP morphine sulfate (MS) or delta 9-THC injection after receiving daily injections of delta 9-THC or morphine, respectively. Degree of tolerance development to each agent was determined before the cross-tolerance challenge was administered. Cross tolerance occurred to analgesic and bradycardic effects of a 10 mg/kg THC challenge in rats receiving 50 mg/kg MS injections over a 23-day period. Cross tolerance to the bradycardic effects of a 20 mg/kg MS challenge occurred in rats receiving seven daily 10 mg/kg delta 9-THC injections and to MS tail-flick analgesia after 14 days. Although rapid tolerance occurred during administration of both agents, cross tolerance to THC bradycardia occurred only in groups exhibiting complete tolerance to MS injections; cross tolerance to MS bradycardia was observed in animals that were only partially tolerant to THC injections. The data extend earlier cross tolerance data in the mouse to the rat, and provide new information using heart rate, a response that may mirror aversive internal states induced by drugs.

Analgesia↗

Absence of environment-specificity in morphine tolerance acquired in non-distinctive environments: habituation or stimulus overshadowing?

The experiments reported here investigated the mechanisms of drug tolerance acquisition in environments differing in distinctiveness. Specifically, they examined the hypothesis that tolerance acquired in non-distinctive environments might involve habituation while tolerance acquired in distinctive environments involves a classical conditioning or associative learning mechanism. In Experiment 1, rats pre-exposed to injection-ritual cues (placebo injections) prior to acquisition of tolerance to morphine analgesia in distinctive or non-distinctive environments showed a typically attenuated tolerance response on an environment-change test. The magnitude of the attenuation was not affected by the distinctiveness of the acquisition environment. In Experiment 2, rats acquiring tolerance in distinctive or non-distinctive environments, but without prior injection-ritual pre-exposure, did not demonstrate an attenuation of tolerance on an environment-change test. Tolerance acquired in either environment was unaffected by a subsequent rest period in the colony room, but was attenuated by a subsequent period of daily placebo injections in the colony room. It is argued that failure to observe environment-specific tolerance, as in Experiment 2 and in previous reports in the literature, may reflect overshadowing of environmental stimuli by injection-ritual stimuli, and are not indicative of a fundamental difference between the mechanisms of tolerance acquisition in environments varying in distinctiveness.

Analysis of Variance↗

The contribution of environmental cues to cross-tolerance between ethanol and pentobarbital.

The contribution of Pavlovian conditioning of environmental cues has been studied in relation to tolerance to ethanol-induced hypothermia and cross-tolerance to pentobarbital. Two groups of 12 male Sprague-Dawley rats were exposed every other day to a distinctive set of environmental cues paired with an IP injection of either ethanol 2.5 g/kg or an equivalent volume of isotonic saline. On alternating non-drug days, both groups received saline in the animal room. When they were tested for tolerance to the hypothermic effect of ethanol 2.5 g/kg and cross-tolerance to pentobarbital 25 mg/kg in each environment, tolerance and cross-tolerance in the ethanol-treated group were significantly more pronounced in the ethanol-paired environment than in the saline-paired environment. This indicates the importance of a conditional factor in tolerance and cross-tolerance in this paradigm. Determination of blood levels of ethanol and pentobarbital at various times after injection indicated that conditioned tolerance and cross-tolerance can be explained in part by dispositional factors.

Animals↗

Similarities and differences between D-ALA2 MET5 enkephalin amide and morphine in the induction of tolerance to their effects on catalepsy and on dopamine metabolism in the rat brain.

Rats were made tolerant to morphine or to DALA, a synthetic analogue of met-enkephalin, by prolonged exposure to these compounds. Tolerance was assessed by evaluating the resistance of the treated rats to present catalepsy after an acute dose of the opiates. Both morphine and DALA induced tolerance and cross-tolerance to the cataleptic effect. Acute administration of morphine and DALA increased the concentration of DOPAC in striatum, limbic area and s.nigra of control rats. This increase was not present when morphine was given acutely to chronically morphine-treated rats, indicating that these animals were tolerant to this effect. Chronically morphine-treated rats given DALA presented partial tolerance to the biochemical effect of the peptide in limbic area and in s.nigra but not in striatum, indicating that only in certain areas was cross-tolerance produced by chronic morphine. When DALA was administered at different doses to chronically DALA treated rats, the peptide induced rise in DA catabolite was similar to that produced in control animals, so clearly there was no tolerance to this biochemical effect. In these animals cross tolerance to morphine's effect on DA metabolism was present in s.nigra but not in the other two areas, indicating that s.nigra is particularly sensitive to opiate-induced tolerance on DA metabolism.

3,4-Dihydroxyphenylacetic Acid↗

Degree and stability of tolerance to penicillin in Streptococcus pyogenes.

The degree of antibiotic tolerance may be assessed by determining the tolerance percentage of a bacterial strain, defined as the surviving fraction of an inoculum that has been exposed for 24 hours to a high concentration of a beta-lactam antibiotic. In 61 clinical isolates of Streptococcus pyogenes, tolerance percentages ranged from 0 to 0.43. From the slopes of the killing curves it can be deduced that killing starts to be delayed at a tolerance percentage of 0.1. Although a tolerance percentage exceeding 0.1 was observed in 41.4% of the strains, the incidence of clinically relevant forms of tolerance is expected to occur in a smaller fraction of the strains. Tolerance percentages of two strains stored at 20 degrees C, 4 degrees C or -70 degrees C (tolerance percentages 0.43 and 0.36) decreased to 0.03 or less in six weeks. Tolerance percentages could be completely restored in these strains, but not in sensitive strains, by successive selection for this property on penicillin gradients of increasing concentration. In four strains isolated from a family outbreak, identical levels of tolerance percentage could be selected for with the same technique.

Adult↗

The NMDA receptor antagonist dizocilpine differentially affects environment-dependent and environment-independent ethanol tolerance.

Antagonists of the N-methyl-D-aspartate subtype of glutamate receptor have been reported to block the development of tolerance to various effects of ethanol and opiates, using paradigms in which tolerance is believed to be governed by learning. There is considerable evidence to implicate the N-methyl-D-aspartate receptor in learning processes, and therefore the ability of the antagonists to block tolerance has been attributed to their effects on learning. To evaluate this hypothesis, we compared, in C57BL/6 mice, the effect of the uncompetitive N-methyl-D-aspartate receptor antagonist, dizocilpine, on environment-dependent (associative) tolerance to ethanol, which is governed by learning, and on environment-independent (nonassociative) ethanol tolerance, in which learning plays a minimal role. Environment-dependent tolerance was induced by repeated ethanol injections, and dizocilpine blocked the development of this type of tolerance to the hypothermic and incoordinating effects of ethanol. In contrast, when environment-independent ethanol tolerance was induced by feeding the mice an ethanol-containing liquid diet, dizocilpine treatment had no effect on the development of tolerance to the hypothermic, incoordinating or hypnotic effects of ethanol. The results support the hypothesis that the effect of N-methyl-D-aspartate receptor antagonists on ethanol tolerance reflects the more general role of this receptor in processes involving learning and memory.

Animals↗

Contribution of visceral obesity to the deterioration of the metabolic risk profile in men with impaired glucose tolerance.

AIMS/HYPOTHESIS: Impaired glucose tolerance is associated with metabolic alterations which increase cardiovascular disease risk. The contribution of hyperglycaemia to this increased risk is, however, not clear. Abdominal obesity is often observed in subjects with impaired glucose tolerance; our objective was therefore to find the contribution of visceral adipose tissue to the deterioration of the metabolic risk profile noted in subjects with impaired glucose tolerance. METHODS: We studied 284 men with a normal glucose tolerance and 66 men with impaired glucose tolerance which was defined as a glycaemia between 7.8 and 11.1 mmol/l 2 h after a 75-g glucose load. RESULTS: Men with impaired glucose tolerance had more visceral adipose tissue and higher concentrations of plasma glucose and insulin in the fasting state and following a 75-g oral glucose load than men with a normal glucose tolerance. They also had higher concentrations of plasma cholesterol, triglycerides, apolipoprotein B and lower concentrations of HDL-cholesterol as well as higher cholesterol:HDL-cholesterol ratios than men with a normal glucose tolerance. The two groups of men were then compared after a statistical adjustment for the amount of visceral adipose tissue. Although men with impaired glucose tolerance still had higher fasting plasma glucose and insulin concentrations after the adjustment for visceral adipose tissue, differences in all the variables of the lipid-lipoprotein profile were eliminated. CONCLUSION/INTERPRETATION: Visceral adipose tissue accumulation is an important factor in the deterioration of the plasma lipid-lipoprotein noted in men with impaired glucose tolerance.

Abdomen↗

Tolerance with low dose intravenous nitroglycerin therapy in acute myocardial infarction.

The question of vascular tolerance was examined in 154 patients with acute myocardial infarction (64 anterior, 90 inferior) who were treated with prolonged low dose intravenous nitroglycerin in a recent randomized placebo-controlled study. The dose of nitroglycerin was carefully titrated to decrease mean blood pressure by 10% in normotensive patients and 30% in hypertensive (blood pressure greater than 140/90 mm Hg) patients, but not less than 80 mm Hg. Tolerance was defined as the need to increase the dose to maintain this hemodynamic effect. It was labelled "true" if chest pain was absent and "apparent" if chest pain was present. Group analysis of dose, pain scores, hemodynamic, 2-dimensional echocardiographic and clinical parameters monitored serially before and after therapy indicated benefit with nitroglycerin over placebo despite equalizing of blood pressures after 10 hours. Reversal of blood pressures and volumes after discontinuing nitroglycerin suggested lack of significant tolerance. However, detailed individual analysis suggested significant hemodynamic tolerance in 37 patients (24%), both in the true tolerance (12%) and apparent tolerance (12%) subgroups. Tolerance appeared early, requiring the dose to be increased by 30 +/- 39 micrograms/min within 11 +/- 9 hours. The dose was greater (p less than 0.001) in the tolerance than in the no tolerance subgroup, both before (60 vs 27 micrograms/min) and after (90 vs 38 micrograms/min) 10 hours. Tolerance blunted the beneficial effect on infarct size, but positive effects on function, topography and complications persisted.

Blood Pressure↗

The development of tolerance to antilipolytic agents in rats.

The development of tolerance to the action of certain antilipolytic agents has been investigated in vivo in rats. Tolerance to oral nicotinic acid developed during twice daily dosing for 4 days at 100 and 250 mg/kg but not at 10, 25 or 50 mg/kg. Tolerance induced by high doses of nicotinic acid was no longer detectable after a further week without treatment. Tolerance developed to a dose of 10 mg/kg nicotinic acid when dosing was repeated at hourly intervals for up to 6 hr. Rats made tolerant to nicotinic acid also became tolerant to both 5-methylpyrazole-3-carboxylic acid and to pyridyl-3-tetrazole and rats made tolerant to these antilipolytic agents were also tolerant to nicotinic acid. Rats made tolerant to nicotinic acid still responded to the antilipolytic activity of the prostaglandin analogue, sulprostone. These results suggest that nicotinic acid, pyridyl-3-tetrazole and 5-methylpyrazole-3-carboxylic acid act through a common mechanism or receptor and that the development of tolerance is associated with this receptor or the mechanism by which it is linked to adenylate cyclase.

Animals↗

Development of tolerance to respiratory depression in morphine- and etorphine-pellet-implanted mice.

Tolerance to opiate-induced depression of respiratory rate was studied in unanesthetized mice following chronic treatment with morphine or etorphine. Mice implanted subcutaneously (s.c.) with morphine pellets showed development of tolerance to morphine administered both s.c. and intracerebroventricularly (i.c.v.) and to s.c. etorphine and heroin. However, no cross-tolerance to i.c.v. etorphine or heroin was observed. In contrast, mice implanted with etorphine pellets demonstrated development of tolerance to all 3 agents given either s.c. or i.c.v. These findings on development of tolerance to opiate-induced respiratory depression differ from our previous studies measuring analgesia in which mice tolerant to s.c. morphine did not demonstrate development of tolerance to s.c. etorphine or heroin (unidirectional non-cross-tolerance). To investigate a possible mechanism for this difference in development of tolerance, apparent pA2 values for respiratory rate depression were determined for s.c. morphine-naloxone and etorphine-naloxone. The apparent pA2 values for these two opiates were similar, in contrast to the dissimilar apparent pA2 values previously found when analgesia was measured. The apparent pA2 values demonstrated differences between the respiratory depressant and analgesic effects of these opiates, but there was no obvious relationship between apparent pA2 values and the absence of unidirectional non-cross-tolerance observed for respiratory depression.

Animals↗

The NMDA receptor antagonist MK-801 prevents long-lasting non-associative morphine tolerance in the rat.

Several studies have demonstrated that the N-methyl-D-aspartate (NMDA) antagonist MK-801 attenuates the development of morphine tolerance and withdrawal. These studies employed repeated morphine injections to induce tolerance, a procedure in which learning has been suggested to play a significant role in tolerance development. MK-801 has been reported to block some types of learning, and it is unclear, therefore, whether the effect of MK-801 on tolerance development is due to its antagonism of associative (learning) or non-associative factors. Moreover, previous studies have tested the effects of MK-801 on morphine tolerance only up to 48 h after its induction; yet morphine tolerance can persist for many months, and it is not known whether MK-801 can block long-lasting tolerance. In the present study, therefore, we adopted a model of morphine tolerance in which the involvement of learning is minimized by using a single injection of morphine in a sustained-release preparation, and we tested tolerance for up to 56 days. In the first experiment, simultaneously administering MK-801 (0.2 mg/kg, s.c.) and morphine (60 mg/kg, s.c.), each in a sustained-release preparation, abolished tolerance that lasted at least 12 days. Analgesia was measured in the hot-plate test following a test dose of morphine (15 mg/kg, i.p.). In the second experiment, delivering MK-801 and morphine as before, the duration of morphine-induced catalepsy and analgesia was prolonged. Nevertheless, 24 h later one symptom of naloxone-precipitated withdrawal was significantly attenuated in these same animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesia↗

Interference with tolerance induction of primed B cells by the Fc fragment of immunoglobulin.

The capacity to interfere with tolerance induction in primed B cells was examined. Previous work had shown that TNP-specific splenic B cells from mice primed and boosted with TNP-KLH are highly susceptible to in vitro tolerization upon a brief exposure to TNP on a carrier unrelated to KLH. In the present work it was found that tolerance induction in these primed B cells could be partially disrupted by addition of the Fc fragment of immunoglobulin, a B-cell mitogen, and adjuvant, during exposure of the B cells to tolerogen. Addition of Fc fragments prepared by papain digestion of human IgG interfered with tolerization routinely in approximately 30-60% of the spleen cells susceptible to tolerogen. Addition of whole IgG or Fab fragments had no effect on tolerance induction. As little as 5 micrograms/ml of the Fc fragment preparation significantly interfered with tolerization and 32-64 micrograms/ml was optimal. Disruption of tolerization was most effective when the Fc fragment was added to the spleen cells either 4 hr prior to tolerogen or simultaneously with tolerogen; addition of the Fc fragment 4 hr after exposure to tolerogen was significantly less effective. Disruption of tolerization by the Fc fragment was not through polyclonal activation of B cells, as antigen was required for generation of significant numbers of PFC to TNP. Also, disruption was not through expansion of low avidity clones of B cells insusceptible to tolerogen, as the avidity of the antibody produced with and without Fc fragments present was approximately the same. These results show that the Fc fragment of IgG can partially interfere with tolerization of primed B cells. The manner in which Fc fragments may function to prevent tolerization through its lymphoid cell stimulatory capacities is discussed.

Animals↗

Defective B-cell tolerance in New Zealand black mice. Fc receptor-independence of resistance to low-epitope-density tolerogens.

Trinitrophenyl (TNP) human gamma-globulin with low-epitope-density tolerizes B cells from normal BDF1 mice in a Fc gamma receptor-dependent manner but does not tolerize B cells from preautoimmune NZB mice. In order to investigate the relationships between tolerance induction and epitope density independently of Fc gamma receptor function in these two strains, TNP conjugates of two additional thymic-independent tolerogenic carriers, D-glutamic acid-D-lysine (D-GL) and carboxymethyl cellulose (CMC), were tested. A brief pulse with low-epitope-density conjugates such as TNP4.4-D-GL rendered unfractionated or T-cell-depleted spleen cells from BDF1 but not NZB mice tolerant in a hapten-specific manner. Spleen cells from NZB mice, however, were susceptible to tolerization with TNP13.5-D-GL. NZB mice were also resistant to tolerance induction in vivo with TNP5.5-D-GL, TNP3-CMC, and TNP6-CMC, all of which tolerize BDF1 mice in vivo. Both strains were tolerized with TNP13.5-D-GL and TNP13-CMC in vivo. NZB mice were also significantly less susceptible to tolerance induction with TNP3-CMC when TNP-Ficoll was substituted for TNP Brucella abortus as the challenge antigen. These findings militate against the possibility that an Fc gamma receptor defect is the principal mechanism of resistance of NZB B cells to tolerance induction with-low-epitope density conjugates.

Animals↗

Cross-tolerance to centrally injected barbiturates.

Hypnotic responses to intracerebroventricular (i.c.v) injections of either barbital, pentobarbital, R(-) and S(+) mephorbarbital, or racemic metharbital were compared to those produced by phenobarbital. Dose--response relationships were obtained for all except S(+) mephorbarbital and metharbital. Chronic i.c.v. phenobarbital administration resulted in tolerance to the drug's hypnotic effects. However, chronic barbital administration using an identical regimen did not produce tolerance, nor were phenobarbital tolerant rats cross-tolerant to barbital. Chronic i.c.v pentobarbital resulted in an irreversible decrease in responsiveness to its own effects and to those of other barbiturates. This was attributed to the high alkalinity of the solution (pH 9.6) since i.c.v. injection of saline adjusted to the same pH also reduced responsiveness to i.c.v. barbiturates. However, rats tolerant to i.c.v. phenobarbital were tolerant to acute i.c.v. injection of pentobarbital. Similar cross-tolerance was observed on systemic administration of the barbiturates. The efflux rates of i.c.v. phenobarbital or barbital and their distribution to different brain areas were identical in tolerant and nontolerant rats. Awakening phenobarbital brain levels of the tolerant rats were approximately three times higher than those in nontolerant controls. The conclusion is reached that central administration of phenobarbital provides a valid model for studying functional tolerance.

Animals↗

Change in hypothermia and catalepsy induced by cannabinoids or morphine in mice tolerant to these substances.

delta 8-Tetrahydrocannabinol (THC)- and 8 beta, 9 beta-epoxyhexahydrocannabinol (EHHC)-tolerant mice were tolerant to the hypothermia produced by morphine while 8 alpha, 9 alpha-EHHC-tolerant mice were not. Morphine-tolerant mice acquired partial tolerance to the hypothermic effect of 8 alpha,9 alpha-EHHC, but not to the effect of delta 8-THC and 8 beta,9 beta-EHHC. Cataleptogenic effects of all cannabinoids were enhanced in morphine-tolerant mice as compared to non-tolerant animals. It seems that morphine-tolerant mice exhibited hypersensitivity to the cataleptogenic effect of the cannabinoids without potentiation of the hypothermia. These results suggest that the morphine-tolerant mouse may acquire 'latent' cross-tolerance to the hypothermic effect of the cannabinoids.

Animals↗

Tolerance to anticonvulsant effects of the partial benzodiazepine receptor agonist abecarnil in kindled rats involves learning.

The effects of chronic treatment with the beta-carboline, abecarnil, a novel partial and/or subtype-specific agonist at central benzodiazepine receptors, were studied on fully kindled amygdaloid seizures in rats. Two different experimental protocols were used to differentiate between "pharmacologic tolerance', i.e. tolerance as a function of drug exposure, and "contingent tolerance, i.e. tolerance contingent upon the repeated occurrence of the criterion effect, i.e. the anticonvulsant effect. When kindled seizures were repeatedly initiated during chronic treatment of rats with abecarnil (5 mg/kg i.p. three times daily), marked tolerance developed to its anticonvulsant effect, although plasma levels of abecarnil even increased during the 2 weeks of treatment. When the same treatment protocol was used, but seizures were initiated only at the start and end of the treatment period, almost no tolerance to the anticonvulsant effect of abecarnil was measured, indicating an important role of learning processes for the development of tolerance. In contrast to the differences in anticonvulsant tolerance between the two protocols, the motor impairment induced by abecarnil was similarly attenuated during chronic treatment according to both protocols. The data indicate that, because of the response contingency in abecarnil tolerance, development of tolerance to anticonvulsant effects of this compound depends critically on seizure frequency during drug administration, while adverse effects of this compound are reduced independently of seizure frequency.

Animals↗