Hugh L. Evans

Effects of aniracetam on delayed matching-to-sample performance of monkeys and pigeons

A 3-choice, variable-delay, matching-to-sample procedure was used to evaluate drugs in both pigeons and monkeys while tested under nearly-identical conditions. Aniracetam (Roche 13-5057) improved accuracy of matching at all retention intervals following oral administration (12.5, 25 and 50 mg/kg) to macaque monkeys, with a maximal effect at 25 mg/kg. Aniracetam also antagonized scopolamine-induced impairment of the monkeys performance. Intramuscular administration of these same doses of aniracetam produced a similar, but not significant trend toward improved matching accuracy in pigeons.

Effects of DDAVP, a vasopressin analog, on delayed matching behavior in the pigeon

Five pigeons were tested in a delayed matching-to-sample task after receiving an acute injection of DDAVP (1-desamino-8-D-arginine), scopolamine or d-amphetamine. A feeding test also was used to document non-specific drug effects. Scopolamine produced a marked dose-related decrement in accuracy of matching, regardless of delay, indicating that scopolamine impairs both discrimination and short-term memory. Neither DDAVP nor d-amphetamine produced consistent changes in delayed matching. Thus, an experimental model of short-term memory with pigeons did not confirm the findings of others of a positive effect of DDAVP upon cognitive performance in humans.

The temporal relationship between behavioral and hematological effects of inhaled benzene

The time-effect relationship of the behavioral and hematological changes caused by inhaled benzene was investigated in C57BL mice. Mice were exposed to air, or 100, 300, 1000, or 3000 ppm benzene in standard inhalation chambers employing dynamic vapor exposure techniques. Mice were exposed for 6 hr/day for the number of days necessary to achieve a minimum concentration X time (Ct) product of 3000 ppm-days. The intermittent exposure regimen of 6 hr/day was employed to simulate occupational exposure. The most sensitive behavioral index (milk-licking) was affected by the lowest concentration tested (100 ppm), while homecage food intake, hindlimb grip strength, and body weight were reduced only at 1000 and 3000 ppm. Some of these previously undocumented behavioral changes occurred as rapidly as hematological changes that have been considered hallmarks of benzene toxicity. A significant decrease in circulating lymphocytes occurred after exposure to all concentrations. Circulating red blood cells were variably affected by benzene, in that anemia resulted after 10 days exposure to 100 ppm and after 3 days exposure to 300 ppm but not after 3 days exposure to 1000 ppm or a single exposure of 3000 ppm. The data indicate a departure from Ct relationships, and suggest that exposure duration as well as daily dose may be an important factor in benzene toxicity.

Effects of toluene inhalation on behavior and expired carbon dioxide in macaque monkeys

Cynomolgus macaque monkeys received head-only exposure to 0, 100, 200, 500, 1000, 2000, 3000, and 4500 ppm toluene for 50 min while simultaneously tested for delayed matching-to-sample behavior, a test of cognitive functions. Response time increased and accuracy of matching decreased at 2000 ppm or more of toluene, indicating an attentional deficit but not specific memory effects. Behavioral indices exhibited monotonic concentration-related changes. Expired carbon dioxide (CO2), the most sensitive index, displayed an inverted U-shaped concentration-effect curve, which increased at 100 ppm (the TLV) and decreased at 4500 ppm toluene. Changes in expired CO2 provide new evidence of physiological changes at very low levels of toluene. These changes may indicate combined behavioral, respiratory, sensory, and metabolic effects. No behavioral measure exhibited either cumulative effects or tolerance to 4500 ppm during two 3-day exposures. However, both response time and expired CO2 exhibited an acute, within-session tolerance. The results indicate that brief inhalation exposure to toluene impairs cognitive and motor abilities at concentrations below those causing overt signs, such as ataxia and intention tremoring.

Effects of Toluene Inhalation on Carbon Dioxide Production and Locomotor Activity in Mice

Rapid and noninvasive tests of locomotor activity (LA) and carbon dioxide production (minute volume expired CO2, or VECO2) in mice were sensitive to the effects of inhaled toluene. Compared to sham exposures, toluene at 100 ppm had no effect on LA or VECO2; at 1000 and 3000 ppm, LA increased during exposure, while VECO2 was suppressed for 6 to 24 min at the beginning of exposure. In a nominal 10,000-ppm exposure, toluene levels were increased from 1000 to 10,500 ppm in 60 min. At these levels, toluene abolished LA at concentrations above 8000 ppm, and suppressed VECO2 throughout exposure. During recovery from toluene-induced narcosis, both LA and VECO2 were elevated above control. In other studies, groups of mice inhaled toluene daily at 0, 100, 1000, or 3000 ppm, 5 hr/day for 8 or 90 days, and were tested individually 30 to 90 min after termination of exposure. Under these conditions, toluene decreased postexposure VECO2 for 1-2 weeks, altered the weekly pattern of change in VECO2, and did not affect LA. No effects of repeated, daily exposure to toluene were observed on body weight. These results demonstrate the utility of the present method to detect changes in LA and metabolic rate resulting from toluene inhalation, and suggest that different mechanisms are involved in the behavioral and metabolic responses to toluene inhalation.

Effects of trimethyltin on homecage behavior of rats

Diurnal patterns of feeding, drinking, locomotor activity, and rearing in male Fischer-344 rats were examined for 2 weeks after a single oral dose of trimethyltin chloride (TMT) at 0, 3, 5, or 7 mg/kg. Body weights and feeding and drinking efficiency ratios (ratios of amount of food or water consumed per unit effort) were also determined daily. TMT caused a dose- and time-related drop in body weight; two of five rats in the 7 mg/kg group were killed moribund on 15 days after dosing. Feed consumption fell to 25% of control within 5 days after 7 mg/kg TMT, and to 50% of control for Days 2 and 3 after 5 mg/kg TMT. Water consumption doubled within 2 days after 7 mg/kg TMT and remained elevated for 2 weeks. Feeding efficiency dropped to 40% of control after 7 mg/kg, but drinking efficiency was unchanged. The diurnal patterns of drinking and of rearing were disrupted at all doses of TMT; a normal peak in rearing activity, occurring immediately prior to light onset, was markedly attenuated after all doses on Day 3, and at 5 and 7 mg/kg on Days 5 and 7 post-TMT. These results suggest (1) that the regulation of feed and water intake is severely compromised after a high dose of TMT, and (2) that the rats cyclical patterns of homecage behavior are sensitive to TMT doses as low as 3 mg/kg.

Animal models of environmentally induced memory impairment.

Cognitive dysfunction has been reported as a consequence of occupational exposure to chemicals such as metals and solvents.”’ It is difficult to identify the causative agent in these clinical cases because of ethical restrictions on performing experiments with humans and because of numerous confounding variables in occupationally exposed populations (e.g., alcohol and drug use, health status, and exposure to a wide variety of industrial chemicals). In spite of the obvious impact of industrial products upon the nervous system, toxicologists have only begun to measure and interpret cognitive function in animals. Pharmacologists, on the other hand, have relied heavily upon single-response, one-trial tests (e.g. passive avoidance), which are not effective in separating the non-specific effects of drugs and toxicants measured as rate and speed from specific effects upon cognition. More suitable are operant, multiple-choice measures of accuracy, a less ambiguous index of cognitive function than speed. These issues were reviewed more fully by Evans and Daniel.’ We therefore developed experimental models of cognitive dysfunction with the macaque monkey, which closely resembles the human in both cognitive function and in response to drugs and toxicant^.^.^ Also, pigeons were used as an alternative model because they are economical and yet capable of complex cognitive

Nonhuman primates in behavioral toxicology: Issues of validity, ethics and public health

The small, but vital, niche of nonhuman primates in neurotoxicology is examined. Several models of sensory and cognitive function have been especially useful with primates. Their sensitivity to low doses is clear. The validity of data from these models is indicated by their high correlation with data from intoxicated and normal humans, by the degree to which they approximate job functions and other vital human performances, and by their ability to document specific changes in behavioral function which correlate well with morphological and biochemical effects. The use of primates for this research is justified by the absence of adequate alternatives using nonprimate species, in vitro tests or computer programs. A series of experiments on the effects of methylmercury is used to illustrate ethical and scientific issues concerning research with primates. Recent trends are illustrated by data with trimethyltin.

Behavioral effects of acrylamide in the mouse

Abstract The behavioral toxicity of acrylamide was characterized in the mouse by comparing standard measures of toxicity such as body weight loss and mortality with measures of hindlimb grip strength, locomotor activity, and appetitive behaviors including episodic milk-licking. In the latter test, the mouse received 15-min access daily to a highly palatable, nonessential food substance (10% sweetened milk) that was not available in the maintenance diet. Two strains of mice, CD-1 and C57BL 6J , were injected ip five times weekly with either saline, 20, 60, or 100 mg/kg of acrylamide. Subchronic, but not acute, administration of 100 mg/kg produced weight loss, a severe neuropathy within 3 days, and 100% mortality within 2 weeks. Mice receiving 60 mg/kg subchronically had only a slight loss of body weight but developed a neuropathy within 3 weeks of dosing at which time there was a 50% mortality. Preceding these signs of toxicity, there was a highly significant increase in episodic milk-licking; this increase was significant in both strains of mice by Day 2 and remained elevated throughout the dosing period. The 20 mg/kg dose of acrylamide decreased hindlimb grip strength after 5 weeks of dosing but did not affect milk-licking or body weight even after 7 weeks of dosing. The new use of this test of appetitive behavior has documented a robust effect of acrylamide which preceded other signs of toxicity. The appearance of the various toxic signs was better predicted by the magnitude of the daily dose than the cumulative dose. This study also demonstrated the feasibility of using the mouse in behavioral toxicology.

Behaviors in the Home Cage Reveal Toxicity: Recent Findings and Proposals for the Future

Nervous system impairment is prominent among signs of chemical toxicity in humans and animals, yet evaluation of behavioral and neurologic responses is seldom included in premarket screening. The sensitivity and validity of automatically recorded rodent locomotor activity, whether inside or outside of the home cage, justifies its inclusion in first-tier testing. Home cage behaviors are studied in the toxicologic laboratory using quantitative techniques from behavioral neuroscience. A practical, noninvasive, automated system was developed and validated at New York University, in accord with Federal guidelines for testing neurotoxicity. Effects of neurotoxicants on motor activity, eating, drinking, and the daily cycle of rest-activity indicate sensitivity to a variety of chemicals as well as new avenues to the understanding of mechanisms of toxicity. The rats pattern of nocturnal activity is particularly sensitive to neurotoxicants and thus deserves additional attention. The coefficient of variability of various end points did not correlate with sensitivity to toxicants. This underscores the need for behavioral data to supplement theoretical considerations in test selection. The systems advantages are economy, high data capacity, humaneness, accessible and well-known end points, widely available equipment, automation, and the potential for direct comparisons of several different animal species.