Effect of chronic MK-801 and/or phenytoin on the acquisition of complex behaviors in rats.

The purpose of the present experiment was to assess the effects of chronic MK-801 (an N-methyl-D-aspartate receptor antagonist) and/or phenytoin (a sodium channel blocker) treatment on behavioral acquisition and performance in rats. Learning, audio/visual discrimination and motivation were modeled using incremental repeated acquisition (IRA), audio/visual discrimination (AVD) and progressive ratio (PR) tasks, respectively. MK-801 and/or phenytoin were administered daily, 7 days/week by orogastric gavage beginning just after weaning on postnatal day (PND) 23 and continuing until PND 306. Monday through Friday behavioral assessments began on PND 27 and continued until PND 430. Throughout treatment, subjects in the high dose MK-801 (1.0 mg/kg/day) and the high dose drug combination (1.0 mg/kg/day MK-801+150 mg/kg/day phenytoin) groups exhibited decreased body weight gains compared to control subjects. For these two affected groups, response rates were also decreased in all tasks. Task acquisition, as evidenced by an increase in response accuracy, was decreased for both these groups in the AVD task, but only for the high dose MK-801 group in the IRA task. The data suggest that chronic MK-801 treatment adversely affects the acquisition of IRA and AVD task performance and that the inclusion of phenytoin in the MK-801 dosing regimen blocks some of the adverse effects of chronic MK-801 treatment on IRA task acquisition. These findings are in marked contrast with those observed in nonhuman primates and suggest important species differences associated with chronic exposure to compounds that block NMDA receptors and/or sodium channels.

Beamline Performance Simulations for the Fundamental Neutron Physics Beamline at the Spallation Neutron Source.

Monte Carlo simulations are being performed to design and characterize the neutron optics components for the two fundamental neutron physics beamlines at the Spallation Neutron Source. Optimization of the cold beamline includes characterization of the guides and benders, the neutron transmission through the 0.89 nm monochromator, and the expected performance of the four time-of-flight choppers. The locations and opening angles of the choppers have been studied using a simple spreadsheet-based analysis that was developed for other SNS chopper instruments. The spreadsheet parameters are then optimized using Monte Carlo techniques to obtain the results presented in this paper. Optimization of the 0.89 nm beamline includes characterizing the double crystal monochromator and the downstream guides. The simulations continue to be refined as components are ordered and their exact size and performance specifications are determined.

Commissural myelotomy for intractable cancer pain: report of two cases.

PATIENTS: We describe two patients with cancer-related low back and bilateral lower extremity pain that failed pharmacologic treatment. RESULTS: In both cases, commissural myelotomy provided significant pain relief. The role of myelotomy in the management of cancer pain is discussed.

Neuropathic pain in the cancer patient.

Cancer presents itself in numerous ways, adding to the complexity of any pain syndrome with which it is associated. Neuropathic pain, unlike many other pain syndromes, is difficult to treat even in the absence of cancer. The combination results in a heterogeneous group of patients with a complex set of symptoms. This makes the assessment of pain, classification of syndromes, and clinical study a challenge. If the disease is nonprogressive, general principles of care are essentially the same as in those without cancer. In patients with progressive disease and more refractory painful conditions, spinal anesthetic and neurosurgical therapies must often be considered. Under such circumstances, caregivers are forced to carefully balance uncertain benefits and risks, often without the luxury of time. More careful observation and controlled trials in these patients help facilitate this challenging process.

Acute effects of caffeine on several operant behaviors in rhesus monkeys.

The acute effects of 1,3-trimethylxanthine (caffeine) were assessed using an operant test battery (OTB) of complex food-reinforced tasks that are thought to depend upon relatively specific brain functions, such as motivation to work for food (progressive ratio, PR), learning (incremental repeated acquisition, IRA), color and position discrimination (conditioned position responding, CPR), time estimation (temporal response differentiation, TRD), and short-term memory and attention (delayed matching-to-sample, DMTS). Endpoints included response rates (RR), accuracies (ACC), and percent task completed (PTC). Caffeine sulfate (0.175-20.0 mg/kg, IV), given 15 min pretesting, produced significant dose-dependent decreases in TRD percent task completed and accuracy at doses > or = 5.6 mg/kg. Caffeine produced no systematic effects on either DMTS or PR responding, but low doses tended to enhance performance in both IRA and CPR tasks. Thus, in monkeys, performance of an operant task designed to model time estimation is more sensitive to the disruptive effects of caffeine than is performance of the other tasks in the OTB.

Acute behavioral effects of phencyclidine on rhesus monkey performance in an operant test battery.

The effects of phencyclidine (PCP; a noncompetitive NMDA antagonist) were assessed in rhesus monkeys using performance in an operant test battery (OTB) consisting of five food-reinforced tasks thought to engender responses dependent upon aspects of time estimation, short-term memory, motivation, learning, and color and position discrimination. End-points included percent task completed (PTC), response rate or latency, and response accuracy. Testing occurred 15 min after IV injections of PCP (0.00, 0.003, 0.01, 0.03, 0.1, 0.13, 0.18, and 0.3 mg/kg). PCP disrupted performance of all tasks at 0.30 mg/kg. PTC was significantly decreased in the time estimation, motivation, and learning tasks at doses > or = 0.13 mg/kg. PTC for the short-term memory and color and position discrimination tasks was significantly decreased at 0.18 mg/kg and above. Response rate was significantly decreased at 0.13 mg/kg and above in the motivation and learning tasks and at 0.18 mg/kg and above in the time estimation, short-term memory, and color and position discrimination tasks. Response accuracy was significantly decreased in the time estimation, short-term memory, and learning tasks at doses > or = 0.13 mg/kg, while accuracy in the color and position discrimination task was decreased only at 0.30 mg/kg. PCP's effects on OTB performance were generally nonspecific, in that the time estimation, short-term memory, learning, and motivation tasks were all equally sensitive, with the color and position discrimination task being the least sensitive. These results are different than those obtained from earlier studies on the effects of MK-801, a more selective noncompetitive NMDA antagonist.

Acute effects of methylenedioxymethamphetamine (MDMA) on several complex brain functions in monkeys.

The effects of MDMA were assessed in rhesus macaques using behavior in an operant test battery (OTB) consisting of five food-reinforced tasks designed to model aspects of time estimation, short-term memory, and attention, motivation, learning, and color and position discrimination. Testing occurred 30 min after intramuscular, injections of MDMA (0.0, 0.1, 0.3, and 1.0 mg/kg). The behavioral endpoints monitored included percent task completed, response rate or latency, and response accuracy. Percent task completed was significantly decreased in the time estimation, learning, and motivation tasks at 1.0 mg/kg as compared to saline controls. Response accuracies in the time estimation and learning tasks were also decreased at 1.0 mg/kg. Response rate was decreased at 1.0 mg/kg in the motivation task but was not significantly affected in any other tasks. No behavioral endpoints were significantly affected in the short-term memory and attention and color and position discrimination tasks at any dose tested. Results indicate that time estimation, motivation, and learning are more sensitive to the acute effects of MDMA than are short-term memory and attention and color and position discrimination.

Acute behavioral effects of MK-801 in rhesus monkeys: assessment using an operant test battery.

The acute effects of MK-801, a selective, noncompetitive NMDA receptor antagonist, were assessed using an operant test battery (OTB) of complex food-reinforced tasks that are thought to depend upon relatively specific brain functions such as motivation to work for food (progressive ratio, PR), learning (incremental repeated acquisition, IRA), color and position discrimination (conditioned position responding, CPR), time estimation (temporal response differentiation, TRD), and short-term memory and attention (delayed matching-to-sample, DMTS). Endpoints included response rates (RR), accuracies (ACC), and percent task completed (PTC). MK-801 (0.003-0.075 mg/kg, IV), given 15 min pretesting, produced significant dose-dependent decreases in measures of IRA and TRD performance at doses > or = 0.03 mg/kg. In both tasks, MK-801 produced significant decreases in accuracy at doses lower than those required to affect response rate. MK-801 also produced statistically significant decreases in PR, CPR, and DMTS measures, but only at higher doses (> or = 0.056 mg/kg) that caused significant decreases in both response rates and accuracies. These results indicate that, in monkeys, performance of operant tasks designed to model learning and time estimation is more sensitive to the disruptive effects of MK-801 than performance of tasks that model motivation, color, and position discrimination, and short-term memory and attention.

Repeated measures designs in behavioral toxicology: application to chronic marijuana smoke exposure.

This paper discusses the application of repeated measures methods in the statistical analysis of an experiment in behavioral toxicology. The chronic marijuana smoke exposure study conducted at the National Center for Toxicological Research is used for an example of the types of problems that one encounters in analyzing these types of studies. In particular, the standard univariate analysis most frequently used for repeated measures analyses has some very restrictive assumptions on the form of the covariance matrices. These assumptions are not met in the example discussed and are rarely met in many other problems. Other possible models for analyzing repeated measures when these assumptions are not met are presented and discussed. Other problems specific to the chronic marijuana smoke exposure study that may occur in similar type studies are presented. These include pooling the experimental units into groups with comparable baselines, choosing a function of the measures to be analyzed, dealing with a large data set with many observation times and missing data, unequal group sizes and different designs for different subsets of the experimental animals. The standard univariate repeated measures analysis was chosen to analyze the data even though the violations of the covariance assumptions may lead to finding differences that do not exist (Type I or false-positive errors), since the other methods presented also had covariance assumptions that were not met or had low power. Use of Bonferroni-type multiple comparisons on the single degree of freedom contrasts of interest hopefully reduced the chances of these false-positive results.

The effect of chronic cocaine exposure during pregnancy on the acquisition of operant behaviors by rhesus monkey offspring.

To explore possible long-term effects of gestational cocaine exposure in a nonhuman primate model, pregnant rhesus monkeys were treated from about 1 month of gestation until term with either 0 (N = 3), 0.3 (N = 3), 1.0 (N = 3), or escalating doses up to 8.5 (N = 3) mg/kg (IM), three times per day, 5 consecutive days per week. Despite these differences in cocaine exposure, the experimental groups did not differ significantly with respect to the postnatal growth of offspring over an 18-month period following birth. Beginning at 6 months of age, the behavior of offspring was monitored using an operant test battery that included five food-reinforced tasks designed to model aspects of learning, color and position discrimination, time estimation, short-term memory and attention, and motivation. Although the acquisition of each operant behavior by offspring progressed significantly during training between 6 and 18 months of age, this acquisition was not differentially affected by gestational cocaine exposure. It was concluded that, in a rhesus monkey model, chronic cocaine exposure during pregnancy had no significant effect on the offsprings' acquisition of operant behaviors.

Prenatal ethanol exposure in rats: long-lasting effects on learning.

Pregnant Sprague-Dawley rats were fed a liquid diet containing either 0% (group C), 18% (group L), or 36% (group H) ethanol-derived calories (EDC) from gestational day 1 to 20. Male offspring were assessed under a conditioned taste aversion paradigm (PND 35-45), in a complex maze (PND 68-80), and for operant behavior (temporal response differentiation and motivation to work for food, PND 140-198). Although conditioned taste aversion was fully acquired by all groups, retention of the conditioned taste aversion response was impaired in group H animals. Importantly, deficits in the acquisition of timing behavior were found in group H (group L not tested), confirming that this operant task is quite sensitive in detecting prenatal drug effects and demonstrating that neurological effects of prenatal ethanol exposure persist into late adulthood.

Differential effects of two NMDA receptor antagonists on cognitive-behavioral development in nonhuman primates I.

The present experiment examined effects of chronic exposure to remacemide (an N-methyl-D-aspartate [NMDA] antagonist which also blocks fast sodium channels) or MK-801 (which blocks NMDA receptors, exclusively) on learning and motivation in young rhesus monkeys. Remacemide (20 or 50 mg/kg/day) or MK-801 (0.1 or 1.0 mg/kg/day) was administered every day to separate groups of animals via orogastric gavage for up to 2 years. Immediately prior to dosing, 5 days per week (M--F), throughout the 2-year dosing period, an incremental repeated acquisition (IRA) task was used to assess learning and a progressive ratio (PR) task was used to assess motivation. The results indicate an effect of 50 mg/kg/day remacemide to impair learning (IRA) which persisted even after drug treatment was discontinued. MK-801 had no effect on learning but transiently increased motivation. Because the effects of remacemide occurred independently of changes in motivation or response rates, they are likely due to specific cognitive impairments and are not due to an inability of subjects to fulfill the motoric requirements of the task. The fact that MK-801 did not alter learning suggests that NMDA antagonism alone may be insufficient to produce learning deficits in young monkeys and that such deficits may rely on the ancillary blockade of fast sodium channels.

Differential effects of two NMDA receptor antagonists on cognitive--behavioral performance in young nonhuman primates II.

The present experiment examined the effects of chronic exposure to remacemide (an NMDA antagonist that also blocks fast sodium channels) or MK-801 (which blocks NMDA receptors more selectively) on the acquisition of color and position discrimination and short-term memory behavior in juvenile rhesus monkeys. Throughout the 2-year dosing period, a conditioned position responding (CPR) task was used to assess color and position discrimination and a delayed matching-to-sample (DMTS) task was used to assess memory. Chronic exposure to high doses of either drug delayed the acquisition of accurate color and position discrimination without altering response rates. In the case of MK-801, these effects abated within 6 months of the start of treatment. In the case of remacemide, the effects persisted for 17 months of dosing. Neither compound significantly altered performance of the short-term memory task at any time point or at any dose tested. The fact that the effects of remacemide on behavioral performance were more persistent than those seen for MK-801 suggests that tolerance may develop to the behavioral effects of MK-801, which does not develop to the effects of remacemide. Alternatively, these results may suggest that the concurrent antagonism of NMDA receptors and fast sodium channels may have more profound consequences for behavior than does the antagonism of NMDA receptors alone.

Monkey versus human performance in the NCTR Operant Test Battery.

A battery of operant behavioral tasks, designed to monitor complex "cognitive" functions in monkeys, was adapted for use in children. Adaptations were then incorporated into the monkey battery so that monkeys and children performed exactly the same tasks. Food pellets served as reinforcers for monkeys; nickels for children. Correct responding in a task is thought to depend upon relatively specific brain functions including short-term memory and attention, learning, time perception, motivation, and color and position discrimination. Eight 4-year-old rhesus monkeys served as subjects, and groups (n = 10 to 20) of 4- to 8-year-old children were recruited if they were not known to have any neurological, academic or behavioral problems. In performance of only the learning task was there any significant difference between monkeys and children. This difference was in response rate (not accuracy), with the monkeys responding faster than children. This lone difference in operant responding between monkeys and children was likely due to the fact that monkeys generally use all four appendages to respond whereas children generally do not.

Behavioral and neurochemical effects of chronic methylenedioxymethamphetamine (MDMA) treatment in rhesus monkeys.

Effects of chronic treatment with the putative serotonergic neurotoxicant MDMA were assessed in rhesus macaques using behavior in an operant test battery (OTB) designed to model aspects of time estimation, short-term memory, motivation, learning, and color and position discrimination. After an initial acute dose-response assessment, escalating doses of MDMA (0.10-20.0 mg/kg, im, twice daily, for 14 consecutive days at each dose) were administered, followed by three additional acute dose-response assessments. In general, tolerance to MDMA's acute effects was evident in all OTB tasks by the second week of repeated exposure to each individual MDMA dose and as doses escalated. Baseline OTB performance after chronic treatment was not significantly altered. Residual behavioral tolerance to MDMA's acute effects, however, was evident in all OTB tasks but was least pronounced in the motivation task. Monkeys were sacrificed (21 months after chronic treatment) and brains were dissected into several regions for neurochemical analyses. Serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) were analyzed via HPLC. Although MDMA-treated monkeys tended to have lower 5-HT concentrations in the frontal cortex, chronic MDMA treatment had no significant effects on 5-HT concentrations in any brain area sampled. Hippocampal 5-HIAA concentration, 5-HT uptake sites, and turnover of 5-HT of MDMA-treated monkeys were significantly lower than control values. DA concentrations in the CN of MDMA-treated monkeys were significantly greater than control values. No significant effects on DA concentrations were noted in any other brain area sampled. The absence of significant decreases in 5-HT and the general increase in DA concentrations are dissimilar to neurochemical effects reported after a short course of MDMA treatment at relatively high doses. These data suggest that chronic administration of gradually increasing doses of MDMA results in long-lasting tolerance to the drugs acute effects on the complex brain functions modeled in the OTB. It is uncertain, however, if such tolerance is related to the observed decreases in uptake sites and turnover of 5-HT in the hippocampus of these monkeys.

Assessing the potential toxicity of MK-801 and remacemide: chronic exposure in juvenile rhesus monkeys.

The present experiment examined the effects of chronic exposure to either 0.1 or 1.0 mg/kg MK-801 [a selective N-methyl-D-aspartate (NMDA) receptor antagonist] or 20.0 or 50.0 mg/kg remacemide (an NMDA receptor antagonist which also blocks fast sodium channels) in juvenile rhesus monkeys. Endpoints were monitored to provide a general index of subjects' health and included measures of clinical chemistry, hematology, ophthalmology, spontaneous home-cage behavior, and peak drug plasma levels. In general, both drugs were well tolerated and produced no treatment-related effects during 2 years of dosing and assessment. Periodic plasma drug level determinations provided limited evidence that both compounds may induce their own metabolism. The present results contrast sharply with previously reported effects of long-lasting impairments in the acquisition of incremental learning and in the development of color and position discrimination in these same subjects. These observations highlight the importance of collecting a broad range of toxicology data, including tests of cognitive function, to make comprehensive assessments of new drug safety. In the present case, the less obvious effects of these drugs on cognition defined the toxicologic response.

Study of sodium saccharin co-carcinogenicity in the rat.

A co-carcinogenicity experiment was conducted with female Sprague-Dawley rats in which the effects of short-term sodium saccharin dosing and initiation with a direct-acting carcinogen were examined in the urinary bladder. All initiated animals were administered 0.5 mg N-methyl-N-nitrosourea (MNU) by instillation into the bladder at 8 wk of age. The animals were also given saccharin at one of four levels in the diet (0, 1.0, 2.5 or 5%) for 4 wk either (1) just before treatment with MNU (4-8 wk of age), (2) centred on treatment with MNU (6-10 wk of age) or (3) after MNU treatment (8-12 wk of age). Additionally, a group of animals was exposed to saccharin through the milk for 3 wk by dosing the mothers, starting on the day of parturition. The animals were held on control diet until interim killing of 20 animals per group at about 590 days of age, removal for morbidity, or terminal killing of the remainder of 60 animals per treatment around 780 days of age. A histopathological examination was made of the urinary tract and the relationship of saccharin dose to bladder tumour prevalence analysed statistically. A consistent increase (with very weak statistical significance) in tumour rate at interim killing, and for the pathology data overall, was shown by the 2.5% dose group given saccharin from 8 to 12 wk of age. Tumour prevalences of 47.6 and 40.7% v. control prevalences of 21.1 and 25.4% were observed for the two time periods (P values < 0.076 and < 0.0853, respectively). All groups given saccharin neonatally showed increased tumour prevalence for both time periods, but none of the differences was statistically significant at the 95% confidence level. No consistent increase in tumour prevalence was seen in the groups given saccharin from 4 to 8 or 6 to 10 wk of age; thus, these data suggest that saccharin does not act as a strong co-carcinogen in the MNU-treated rat bladder.

Chronic toxicity/carcinogenicity studies of gentian violet in Fischer 344 rats: two-generation exposure.

A chronic feeding study was carried out in the F1a generation of dosed Fischer 344 rats of both sexes with gentian violet (GV). The test substance was administered in the diet to 570 male and 570 female rats at dose levels of 0 (control), 100, 300 and 600 ppm for 24 months. Rats were killed and necropsied after 12, 18 and 24 months of continuous dosing. Measurements of body weights, food consumption (and dose rate) and mortality and the results of histopathological examination were analysed statistically. Male and female rats fed 600 ppm GV for 24 months showed a decrease in body weights. Average food consumption based on g food/kg average body weight was essentially equal in all groups. Mortality at the end of the study (24 months) was approximately 33% in the controls for both males and females and approximately 66% in females of the high-dose group and 48 and 39% in males of the mid- and high-dose groups, respectively. All dose-related neoplastic pathology was noted at the final necropsy. Following 24 months of dosing, there was a significant difference from the controls in the incidence of follicular cell adenocarcinoma of the thyroid gland for both males (600 ppm GV) and females (300 and 600 ppm GV). Although the incidences were very low, statistical analysis showed a significant difference from the controls for hepatocellular adenomas in the mid-dose group of the females and the mid- and high-dose groups of the males. A dose-time-related incidence of mononuclear cell leukaemia was also noted in the females. There was high background incidence of the leukaemia. Several non-neoplastic dose-related lesions were observed in both males and females, principally in the 18- and 24-month necropsies. Almost all of these lesions were focal changes in the liver, many of which were probably related to the mononuclear cell leukaemia.

Carcinogenicity study of 3,3'-dimethylbenzidine dihydrochloride in BALB/c mice.

BALB/c mice (120/sex/dose) were given 0, 5, 9, 18, 35, 70 or 140 ppm of 3,3'-dimethylbenzidine dihydrochloride in their drinking-water and killed after 13, 26, 39, 52, 78 or 116 wk. Full histopathological evaluations were performed on all animals that were found dead or moribund, or that were killed on schedule. Fatal lung alveolar cell neoplasms began to appear in males receiving 140 ppm at 78 wk and there was a significant dose-related decrease in the time-to-death from this cause. There were no significant dose-related trends for this neoplasm in females, nor were there treatment-related effects on body weight, water consumption or other lesions in either sex. This is the first report of a neoplastic response to 3,3'-dimethylbenzidine dihydrochloride in mice.

Chronic toxicity/carcinogenicity studies of sulphamethazine in B6C3F1 mice.

A chronic feeding study was carried out in B6C3F1 mice with sulphamethazine (SMZ). The test substance was administered in the diet at dose levels of 0 (control), 300, 600, 1200, 2400 and 4800 ppm for 24 months. Mice were killed after 12, 18 and 24 months of continuous dosing. Body weights and food consumption were measured weekly, and mortality was recorded daily. All animals received a complete necropsy and histopathological examination, the results of which were analysed statistically. A slight decrease in body-weight gain was noted for mice of all dose groups with females showing the greater effect. Food consumption based on g food/g average body weight was relatively constant among the controls and various dose groups. The mortality rate for males and females of the control groups (8 and 8%, respectively) was higher than that for males and females of some of the higher dose groups. Neoplastic lesions associated with the ingestion of SMZ in the diet included follicular cell adenomas of the thyroid gland. At the 24-month necropsy, the incidence of this lesion for males and females of the 4800-ppm dose groups was 33 and 26%, respectively. Non-neoplastic dose-related lesions observed in both males and females included follicular cell hyperplasia (diffuse and focal) of the thyroid gland, haematopoietic cell proliferation of the spleen and pigmentation of the spleen. In females, pigmentation of the lymph nodes and hyperplasia of the mammary gland were also noted.