Endometriosis in Rhesus Monkeys (Macaca mulatta) Following Chronic Exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin

Endometriosis in Rhesus Monkeys (Macaca mulatta) Following ChronicExposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin. RIER, S. E.,MARTIN, D. C., BOWMAN, R. E., DMOWSKI, W. P., AND BECKER, J.L. (1993). Fundam. Appl. Toxicol. 21, 433–441. The incidence of the reproductive disease endometriosis wasdetermined in a colony of rhesus monkeys chronically exposedto 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin) fora period of 4 years. Ten years after termination of dioxin treatment,the presence of endometriosis was documented by surgical laparoscopyand the severity of disease was assessed. The incidence of endometriosiswas directly correlated with dioxin exposure and the severityof disease was dependent upon the dose administered (p <0.001). Three of 7 animals exposed to 5 ppt dioxin (43%) and5 of 7 animals exposed to 25 ppt dioxin (71%) had moderate tosevere endometriosis. In contrast, the frequency of diseasein the control group was 33%, similar to an overall prevalenceof 30% in 304 rhesus monkeys housed at The Harlow Primate Centerwith no dioxin exposure. This 15-year study indicates that latentfemale reproductive abnormalities may be associated with dioxinexposure in the rhesus. Therefore, the effects of this toxinmay be more diverse than previously recognized.     

Prevalence of Endometriosis in Rhesus (Macaca mulatta) Monkeys Ingesting PCB (Aroclor 1254): Review and Evaluation

A total of 80 menstruating rhesus monkeys (Macaca mulatta) wereequally and randomly divided among groups receiving 0, 5, 20,40, or 80 µg of Aroclor 1254/kg body weight/day duringa 6-year toxicological-reproduction study. During the first3 years of the study, 4 of the treated monkeys became moribundand were euthanized; 3 had endometriosis. This finding suggesteda possible link between the PCB treatment and the occurrenceof endometriosis. However, neither a laparoscopic examinationof the control and high-dose monkeys nor the necropsy data providedevidence for a possible link between the PCB treatment and theobserved incidence (37% (6/16) of controls; 25% (16/64) of treatedmonkeys and/or the severity of the endometrial lesions. Additionalclinical and historical data not contained in previous reportsare presented to facilitate independent evaluation of the relationshipbetween PCB ingestion and endometriosis. We conclude that theincidence and severity of the endometriosis lesions observedin the rhesus monkeys utilized in this study did not have anyrelationship with the dosages of Aroclor 1254 they ingested.     

13-Week Inhalation Toxicity Study of Dimethylformamide (DMF) in Cynomolgus Monkeys

This study was conducted to assess the subchronic inhalationtoxicity of dimethylformamide (DMF) in the cynomolgus monkey.Particular attention was paid to the liver since DMF has beenshown to produce liver damage in rodents, dogs, and humans.Groups of three cynomolgus monkeys/sex/group received whole-bodyexposures for 6 hr/day, 5 days/week for 13 weeks to0, 30, 100,or 500 ppm DMF. Evaluations for toxicity included body and organweights, clinical observations, hematology, serum chemistry,urinalysis, and gross and microscopic examinations. Clinicallaboratory evaluations were conducted twice prior to the startof the study at exposure weeks 2, 4, 8, and 12 and at necropsy.Semen, collected from male monkeys three times prior to thestart of the study and weekly during the course of the study,was analyzed for sample volume, sperm count, motility, and morphology.In addition, daily vaginal swabs were obtained from all femalesprior to exposure to determine mean menses cycle length. Althoughthere was a slight trend toward increased cycle length, thistrend could not be definitely attributed to compound exposure.Based on extensive monitoring of the monkeys' clinical condition,semen quantity and quality, and clinical and pathological evaluations,no exposure-related adverse health effects were detected followingexposure to concentrations of DMF ranging from 30 to 500 ppmfor 13 weeks.     

One-Year Study in Dogs of the Toxicity of HFA-134a by Inhalation

Abstract

HFA-134a, a chlorine-free hydrofluoroalkane, was administered for 1 h daily to beagle dogs by means of a system for inhalation by face mask. In this 1-yr study, animals received atmospheric air, air containing an additional 12% nitrogen, or air containing a nominal 12% HFA-134a for 376 or 377 days. HFA-134a was rapidly absorbed into and cleared from the blood. There were no treatment-related clinical signs or effects on body weight, food consumption, ophthalmoscopy, heart function, respiratory rate, pulse rate, haematology, blood biochemistry, urine analysis, or postmortem findings. HFA-134a was considered to be nontoxic and to provide a safe alternative to chlorofluorocarbons for use in pharmaceutical metered-dose inhaler formulations.     

Toxicity and disposition of 2,3,4,7,8-pentachlorodibenzofuran (4PeCDF) in the rhesus monkey (Macaca mulatta)

The toxicity and disposition of 2,3,4,7,8-pentachlorodibenzofuran (4PeCDF), a ubiquitous and acutely toxic environmental contaminant, was examined in three adult male Rhesus monkeys administered a single iv dose of 34 micrograms (0.1 mumol)/kg. Within 20 min, 4PeCDF was eliminated from the blood and was distributed to the liver, skin, adipose, and muscle tissues. Excretion occurred primarily via the feces with a minimum whole body half-life approximately 38 days. Within 7-14 days after administration, the packed cell volume and serum triglyceride and bile acid concentrations were significantly increased while serum cholesterol, protein, and albumin concentrations were decreased relative to pretreatment levels. Thyroid hormone levels were also altered with an increase in TSH and a decrease in T3 and T4 concentrations. After 28 days, two monkeys began exhibiting alopecia, hyperkeratinization of the toe and finger nails, facial chloracne-like lesions, and loss of body weight. They subsequently died 40 and 48 days after treatment. Similar symptoms of toxicity were observed in the third animal 58 days after 4PeCDF administration, but this animal appeared to fully recover and was administered 4PeCDF orally and [3H]1,2,3,7,8-pentachloro-dibenzofuran (1PeCDF) dermally 238 days after the initial iv dose. In this animal, approximately 2% of an oral dose of [14C]-4PeCDF was absorbed from the stomach and small intestine in 6 hr and was distributed mainly to the muscle and skin and less than 99% of a dermal dose of 1PeCDF remained at the site of application. Pathological findings in the monkeys that died indicated hyperplastic and metaplastic changes in the gastric mucosa, the Meibomian glands of the eyelid, and the ceruminous glands of the ear. Regression of these lesions was present in the surviving animal. Therefore, 4PeCDF produces dioxin-like toxicity in the monkey similar to that reported for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and in the same dose range.     

三硝基甲苯对恒河猴血液系统毒性研究

用60mg/kg和120mg/kg三硝基甲苯给恒河猴灌胃3个月。结果表明,血液中形成高铁血红蛋白,出现变性珠蛋白小体,网织红细胞升高。高铁血蛋白形成快、恢复快;与血中TNT及2、6-二硝基-4-氨基甲苯含量密切相关。骨髓象呈增生性贫血,脾脏则呈贫血性病理改变。     

Effect of Chronic Exposure of PCB (Aroclor 1254) on Specific and Nonspecific Immune Parameters in the Rhesus (Macaca mulatta) Monkey

Effects of Chronic Exposure of PCB (Aroclor 1254) on Specificand Nonspecific Immune Parameters in the Rhesus (Macaca mulatta)Monkey. Tryphonas, H., Luster, M. I., Schiffman, G., Dawson,L.-L., Hodgen, M., Germolec, D., Hayward, S., Bryce, F., Loo,J. C. K., Mandy, F., and Arnold, D. L. (1991). Fundam. Appl.Toxicol. 16, 773–786. The immunomodulatory effects oflow-level, chronic polychlorinated biphenyl PCB; (Aroclor 1254)exposure were investigated in female rhesus (Macaca mulatta)monkeys. Five groups of monkeys (initially 16 monkeyS/group)were orally administered PCB at levels of 0, 5, 20, 40, or 80µg/kg body wt/day. Tests for immunomodulation were initiatedafter 55 months of exposure to PCBs. Statistically significantobserved immune changes included a dose-related decrease inthe anamnestic (IgM and IgG) response to sheep red blood cells.Conversely, the antibody response to pneumococcus antigen didnot differ significantly across the test groups. A statisticallysignificant dose-related decrease in lymphoproliferation wasnoted with increasing doses of PCBs when phytohemagglutininand Concanavalin A, but not when pokeweed mitogen, were usedas mitogens. A trend toward reduced peak chemiluminescence (mV/min)was observed in zymosan-activated peripheral blood monocytes.The time to peak chemiluminescence of phorbol myristate acetateactivation was statistically increased in a dose-response fashion.Flow cytometric analysis results of peripheral blood lymphocytesusing the markers CD4, CD8, and CD20 were similar across thetest groups. The mean percentage levels for the CD2 marker inthe treated groups were statistically lower than the mean inthe control, while absolute numbers for CD2 were similar acrossthe test groups. Serum hydrocortisone levels did not differamong the test groups. Taken together these results indicatethat low-level, chronic PCB exposure alters a number of rhesusmonkey immune system components and that these effects may bedue to altered T-cell and/or macrophage function. These datamay be of use in extrapolating potential human health effectsfollowing chronic PCB exposure.     

Effects of Inhalation Exposures to an M1-Receptor Agonist on Ventilation in Rhesus Monkeys

ABSTRACT

Information was needed on effects of possible occupational inhalation exposure to an M]-receptor agonist (xanomeline) such as might occur during the manufacturing process. Both acute and repeated inhalation exposures to xanomeline were carried out in six male rhesus monkeys using a head-dome exposure system. Exposure concentrations ranged from 0.3 to 10 mg/m³. The exposure durations were up to 2 weeks. Decreases in tidal volume and increases in respiratory frequency were both time and concentration related during acute exposures. These effects were blocked with atropine pre-treatment. Correlation with pulmonary resistance measurements in two monkeys suggested that these were bronchoconstrictive changes that increased with severity with time at a given concentration and with concentration when measured after a constant exposure time. The dose-response was relatively steep with 10 mg/m³ becoming intolerable to the monkeys after approximately 15 minutes, but no measurable effects were observed at 0.3 mg/m³ after up to 4 hours of exposure. To investigate the effects of repeated exposures, monkeys were exposed for 4 hr/day, 5 days/wk for 2 weeks to 0.0 (air only), 0.3, and 1.2 mg xanomeline/m³ of air. When compared to the air-only exposure, 0.3 mg/m³ caused no significant changes in tidal volume. in contrast, 1.2 mg/m³ caused a rapid and significant decrease in tidal volume that was sustained throughout the 4-hr exposure. A slower rise in breathing frequency also occurred. Repeated exposures did not alter the effects seen after a single exposure. It is concluded that xanomeline, a M₁ - receptor agonist, can acutely alter normal ventilation in non-human primates at airborne concentrations ≥0.6 mg/m³ and should be carefully controlled in a manufacturing environment. The no-observed-effect concentration was 0.3 mg/m³.     

Antipyrine plasma half-life. In vivo indicator of oxidative metabolic capability in Rhesus monkeys (Macaca mulatta).

Antipyrine plasma half-life (APH) has been used as an indicator of hepatic oxidase activity in rhesus monkeys (Macaca mulatta). Plasma disappearance of 14CH3-N-antipyrine (AP) was measured radiometrically. AP and 3 metabolites were detected using high pressure liquid chromatography. APH was assessed during a 300-day control period and following phenobarbital (PB) pretreatments. Significant interindividual variability was observed requiring that animals be used as their own controls. PB (15 mg/kg i.m., 2/day X 4 days) reduced mean APH values from 81 +/- 12 to 41 +/- 2 min. PB treatment also increased monooxygenase catalyzed aldrin epoxidation, dihydroisodrin hydroxylation and benzo(a)pyrene oxidation measured using liver biopsy homogenates. These parameters permit 'continual' assessment of HMO activity in rhesus monkeys under a variety of experimental conditions.     

Effect of dietary chronic cadmium exposure on cell-mediated immune response in Rhesus monkeys (Macaca mulatta): role of calcium deficiency

The role of Ca deficiency on the immunomodulatory effects of chronic Cd exposure for a period of 10 weeks in male Rhesus monkeys were assessed by the blastogenic capacity of peripheral blood lymphocytes (PBL) in response to T-cell mitogens, phytohemagglutinin (PHA), and concanavalin A (Con A). Calcium deficiency significantly decreased the blastogenic response to PHA (P<0.01) and Con A (P<0.05). Although Cd exposure in normal monkeys significantly increased the blastogenic response to Con A (P<0.05), Cd exposure in Ca-deficient monkeys produced a further significant decrease in the blastogenic response to Con A (P<0.001). Total and ionic Ca were also significantly decreased in plasma of Ca deficient monkeys exposed to Cd. It is possible that these two observations may be related to each other. Thus, it is important to assess the nutritional status of the host while evaluating the immunotoxicological effects of an environmental pollutant.     

Pharmacokinetics of Methylmercury in the Blood of Monkeys (Macaca fascicularis)

Pharmacokinetics of Methylmercury in the Blood of Monkeys (Macacafascicularis). RICE, D. C., KREWSKI, D., COLLINS, B. T., ANDW1LLES, R. F. (1989). Fundam. Appl Toxicol. 12, 23–33.Statistical analysis of the blood mercury profiles of groupsof two and four adult female cynomolgus monkeys (Macaca fascicularis)given single oral doses of 500 µg and 50 µCi (25.3µg) methylmercury/kg body wt, respectively, indicatesthat a two-compartment model best describes the absorption andelimination of methylmercury in blood. Absorption was largelycomplete within 6 hr, and the half-time of methylmercury duringthe terminal elimination phase ranged from 10 to 15 days. Inaddition, three groups of five adult female cynomolgus monkeyswere dosed with methylmercury every Monday, Wednesday, and Fridayfor periods up to 2 years at effective doses of 10, 25, or 50µg methylmercury/kg body wt/day. The average blood levelsat steady state were estimated to be 0.27 ± 0.02, 0.69± 0.03, and 1.51 ± 0.08 ppm, respectively, withaverage time taken to achieve 95% of the steady-state bloodlevel being about 92 days. The steady-state blood levels obtainedvia extrapolation of the results from the two single-dose experimentswere significantly different from those actually achieved, indicatingthat the average steady-state blood levels under chronic dosingconditions may not be accurately estimated on the basis of short-termexperiments. The data were also used to examine the impact ofdifferent dosing intervals on variation in blood mercury levels.     

Teratologic evaluation of metaproterenol in the rhesus monkey (Macaca mulatta)

In order to further evaluate the teratologic potential of metaproterenol (Alupent), an experiment was conducted in timed pregnant rhesus monkeys (Macaca mulatta). Pregnancy was established by bioassay of serum for chorionic gonadotropin according to the method of Tullner and Hertz using the uterine weight of immature mice. Metaproterenol as a 1 mg/ml solution in water was administered by stomach tube at a dose of 5 mg/kg (approximately 3 times the human dose) for 11 consecutive days beginning on days 18–23 of gestation in a total of 12 animals. At approximately day 100 of gestation, the fetus was removed from each monkey by cesarean section. Each fetus was examined for extermal abnormalities, the viscera for any deviations from normal, and the skeletons, after clearing and staining with Alizarin Red S, for any structural deviations. No changes were observed that could be attributed to the administration of metaproterenol. Four concurrently untreated pregnant animals were included.     

Flow Cytometric Analysis of Micronuclei in Peripheral Blood Reticulocytes IV: An Index of Chromosomal Damage in the Rhesus Monkey (Macaca mulatta)

We report evaluation in rhesus monkeys of a flow cytometricprocedure (MicroFlow) that has previously been shown to allowassessment of micronucleated reticulocytes (MN-RETs) in theperipheral blood of rats and dogs. Reticulocytes (RETs) werelabeled with anti-CD71-fluorescein isothiocyanate, DNA was stainedwith propidium iodide using RNase treatment, and anti-CD61-phycoerythrinwas used to reduce interference from platelets. Flow cytometricdata were compared with microscopic scores of peripheral bloodand bone marrow using standard acridine orange staining. A singleiv administration of cyclophosphamide (CP, 5 mg/kg) inducedan approximately 10-fold increase in blood MN-RET frequency,with the peak occurring 2 days after administration. After dailyCP treatment to approximate a steady-state condition, the frequencyof MN-RETs in peripheral blood was approximately 25% of thatin bone marrow, indicating strong selection against MN-RETs.Nonetheless, CP-treated animals exhibited markedly elevatedblood MN-RET values (2.45–3.99%, n = 3; compared to amean baseline of 0.12%, n = 6). These measurements closely reflectedthe increased frequencies observed in the bone marrow compartment(Spearman correlation coefficient = 0.9856, n = 6). These datasuggest that MN-RET measurements in blood are suitable for assessingchemical-induced chromosomal damage and can be readily integratedinto routine toxicity tests, allowing genotoxicity data to beobtained as an integral part of toxicity evaluations. Microscopy-basedscoring is challenging due to the low frequency of RETs andMN-RET in monkeys, but sufficient numbers of cells are easilyscored with the flow cytometric procedure.     

One-Year Dietary Toxicity Study with Methidathion in Beagle Dogs

The purpose of this study was to determine the chronic toxicityof methidathion, an organophosphate insecticide, in dogs. Groupsof beagle dogs, four/sex/dose, were fed methidathion at constantdietary concentrations of 0, 0.5, 2, 4, 40, or 140 ppm for 1year. The equivalent daily dosages were approximately 0, 0.02,0.07, 0.15, 1.4, and 4.7 mg/kg. There were no deaths or adverseclinical signs associated with the treatment. Weekly body weightsand weight gains were not affected. Mean daily food consumptionwas reduced in male dogs given the 140-ppm diet. Major treatment-relatedeffects were cholestasis, chronic inflammation in the liver,and cholinesterase (ChE) inhibition. The liver effects wereindicated by gross and microscopic pathologic findings as wellas moderate increases in serum bile acids and enzyme activities(alanine aminotransferase, aspartate aminotransferase, sorbitoldehydrogenase, and alkaline phosphatase) in all dogs receiving40 ppm. RBC ChE was inhibited in males at 40 ppm and in femalesat 140 ppm. Brain ChE was inhibited in both sexes at 140 ppm;the magnitude of inhibition relative to control was slightlygreater with the cerebellar fraction than with the cerebralfraction. Serum ChE was not affected at any dose level. In conclusion,liver was the target organ in beagle dogs given 40 ppm (equivalentto 1.4 mg/kg/day) methidathion in diet for 1 year. The no-observable-effectlevel was 4 ppm (0.15 mg/kg/day) for both liver cholestasisand ChE inhibition.     

Subchronic Toxicity, Metabolism, and Pharmacokinetics of the Aminobenzamide Anticonvulsant Ameltolide (LY2O1 116) in Rhesus Monkeys

Studies were undertaken to define the subchronic toxicologicprofile of ameltolide, an aminobenzamide anticonvulsant, inyoung adult rhesus monkeys. Daily doses of ameltolide, dissolvedin 10% aqueous acacia, were administered orally via nasogastricintubation at dosages of 5, 10, 20, 45, and 100 mg/kg. Deathsoccurred in two monkeys, one each at 45 and 100 mg/kg, whichwere directly attributable to the effects of the compound. Theexact cause of death in these monkeys was not readily apparent.A third monkey (100 mg/kg) was killed moribund on Day 82 ofthe study due to conditions not directly related to treatment.Clinical signs in monkeys treated with 100 mg/kg included convulsions, diarrhea, weakness, inappetance, vomition, and ataxia.Plasma concentrations of the N-acetyl metabolite of ameltolidewere greater than parent drug concentrations by one to two ordersof magnitude. Mean area under the plasma-time curve (AUC) valuesfor ameltolide were larger than expected at doses of 20 mg/kgor greater, while AUC values for the metabolite were less thanexpected at 45 and 100 mg/kg. These findings suggest a saturationof metabolism and/or excretion at the two higher doses. Similarnonlinearity was seen with mean peak concentrations for bothparent and metabolite. No specific target organ toxicity wasfound on histological evaluation of tissue sections. Methemoglobinconcentration was increased in monkeys given 45 or 100 mg ameltolide/kg.This change was not considered to be toxicologically importantas there were no corroborative clinical, gross, or histopathologicalfindings. A meltolide administered by nasogastric intubationat doses up to 20 mg/kg/day for 3 months did not cause any toxicologicallyimportant alterations in rhesus monkeys.     

Social hierarchy in monkeys (Macaca mulatta) modified by chlordiazepoxide hydrochloride

The effects of intramuscular injection of chlordiazepoxide hydrochloride (Librium) on individual and social behaviour was tested on a colony formed by four rhesus monkeys. Spontaneous mobility of each animal was continuously recorded by telemetry. Behaviour was quantified during three periods of 15 min each: first control (C I), delivery of pellets to an elevated feeder (CP) and second control (C II). Results were as follows:Administration of 5 mg/kg to the dominant monkey produced a 50 % reduction of spontaneous mobility which lasted for several hours. In addition there was some decrease of walking, a reduction of feeding, increase in lying and complete absence of grooming.The number of attacks increased significantly during C I, was not modified during CP and diminished during C II. It is postulated that chlordiazepoxide produced a decrease of normal signs of dominance and increased the challenge and replacement of the non-drugged animal against the authority of the leader of the group.Increasing the dose injected into the dominant animal to 10 mg/kg produced a greater and more lasting reduction of spontaneous mobility, with some cumulative effects, a reduction of walking during C I and C II, an absence of mounting and grooming and an increase of lying. Attacks also increased during C I and CP. while disappearing during C II. After the fifth injection there was a change in the hierarchical structure of the colony, with the dominant drugged animal dropping position, and the leadership of the group being taken by the monkey which was number 2.Injection of 10 mg/kg of chlordiazepoxide into the lowest ranking monkey, did not modify his hierarchical position, nor did it produce any signs of hostility. His behaviour was. however, modilied, decreasing spontaneous mobility and walking, abolishing grooming and increasing lying down.In the investigation of psychoactive drugs the social status of the experimental animal should be taken into consideration as an important factor in the interpretation of results.     

Inhalation Toxicity Study of Formamide in Rats

Formamide is a widely used solvent for the manufacture and processingof plastics, and the possibility for inhalation exposure existsfor workers. To assess the toxicity of repeated inhalation ofsublethal concentrations of formamide, three groups of 10 maleCrl:CD BR rats each were exposed nose-only for 6 hr/day, 5 days/weekfor 2 weeks to design concentrations of 100, 500, or 1500 ppmof formamide vapor in air. A control group of 10 male rats wasexposed simultaneously to air only. At the end of the exposureperiod, blood and urine samples were collected for clinicalanalyses, and 5 rats per group were killed for pathologic examination.The remaining 5 rats per group were retained for a 14-day postexposureobservation (recovery) period and then subjected to the sameclinical and pathologic examinations. Male rats exposed to 1500ppm had significantly depressed body weights and body weightgains during the exposure and recovery periods compared to controls.Clinical pathologic examinations revealed that decreased plateletand/or lymphocyte counts were observed in rats exposed to 500or 1500 ppm of formamide. Pathologic examinations revealed compound-relatedmicroscopic changes in the kidneys of rats exposed to 1500 ppmformamide. Minimal to severe necrosis and regeneration of renaltubular epithelial cells were observed principally in the outerstripe of the outer medulla and in cortical medullary rays.Based upon the hematologic and clinical chemical parametersmeasured, the no-observed-effect exposure concentration forrepeated inhalation of formamide was considered to be 100 ppm,under the conditions of this study. The findings of treatment-relatedmicroscopic lesions in the kidneys as well as increases in meanabsolute kidney weights and kidney-to-body weight ratios reflectthe target organ toxicity.     

Retention of functional tolerance to ethanol in rhesus monkeys (Macaca mulatta)

Tolerance to ethanol (3 g/kg 90 min prior to testing) was assessed in a group of 4 rhesus monkeys in which tolerance development had been observed using the same behavioral task one year prior to the present study. Although some decrements in performance on a two-choice discrimination-reversal learning task were observed, these changes were transient and statistically insignificant. Results indicate that functional tolerance persisted throughout a one year abstinence period.     

Development of functional tolerance to ethanol in rhesus monkeys (Macaca mulatta)

Four rhesus monkeys were extensively trained until performance reached asymptote on a two-choice discrimination-reversal task. Doses of ethanol (3 g/kg) or placebo (aqueous lactose solutions isocaloric to 3 g/kg of ethanol) were then administered by gavage 90 min prior to testing. Following an initial decrement when ethanol was first administered, performance gradually returned on subsequent days to levels which were equivalent to those found under placebo conditions despite continued drug administration. Ethanol treatment affected accuracy of responding during both the acquisition and reversal phases of the task as well as the quantity of behavior emitted by the animals. Changes in performance levels were independent of fluctuations in blood ethanol concentrations. Functional tolerance developed within approximately 18 days as indicated by the recovery of performance on the discrimination-reversal task. Furthermore, this tolerance was retained during a 24 day period during which no ethanol was administered.