Neuroinflammation After Stereotactic Radiosurgery-Induced Brain Tumor Disintegration Is Linked to Persistent Cognitive Decline in a Mouse Model of Metastatic Disease

PURPOSE

Improved efficacy of anticancer therapy and a growing pool of survivors give rise to a question about their quality of life and return to premorbid status. Radiation is effective in brain metastasis eradication, although the optimal approach and long-term effects on brain function are largely unknown. We studied the effects of radiosurgery on brain function.

METHODS AND MATERIALS

Adult C57BL/6J mice with or without brain metastases (rat 9L gliosarcoma) were treated with cone beam single-arc stereotactic radiosurgery (SRS; 40 Gy). Tumor growth was monitored using bioluminescence, whereas longitudinal magnetic resonance imaging, behavioral studies, and histologic analysis were performed to evaluate brain response to the treatment for up to 18 months.

RESULTS

Stereotactic radiosurgery (SRS) resulted in 9L metastases eradication within 4 weeks with subsequent long-term survival of all treated animals, whereas all nontreated animals succumbed to the brain tumor. Behavioral impairment, as measured with a recognition memory test, was observed earlier in mice subjected to radiosurgery of tumors (6 weeks) in comparison to SRS of healthy brain tissue (10 weeks). Notably, the deficit resolved by 18 weeks only in mice not bearing a tumor, whereas tumor eradication was complicated by the persistent cognitive deficits. In addition, the results of magnetic resonance imaging were unremarkable in both groups, and histopathology revealed changes. SRS-induced tumor eradication triggered long-lasting and exacerbated neuroinflammatory response. No demyelination, neuronal loss, or hemorrhage was detected in any of the groups.

CONCLUSIONS

Tumor disintegration by SRS leads to exacerbated neuroinflammation and persistent cognitive deficits; therefore, methods aiming at reducing inflammation after tumor eradication or other therapeutic methods should be sought.

Modeling Space Radiation Induced Bone Changes in Rat Femurs through Finite Element Analysis

As the duration of manned missions outside of the Earth's protective shielding increase, astronauts are at risk for exposure to space radiation. Various organ systems may be damaged due to exposure. This study investigates the bone strength changes using finite element modeling of Long Evans rats (n=85) subjected to graded, head-only proton (0, 10, 25, and 100 cGy, 150 MeV/n) and ²⁸silicon (0, 10, 25, and 50 cGy, 300 MeV/n) radiation. The strength of the femoral neck will be examined due its clinical relevance to hip fractures. It has been shown in previous studies that bone mineral density was not reduced at the site of fracture. These findings question whether measurements of bone mineral density may be used to assess risk of hip fracture. The mechanisms leading to the irregular relationship between bone density and strength are still uncertain within literature and investigated to greater extent in clinical applications. Finite element analysis within this study simulated physiological loading of the femoral neck. No significant changes in femoral neck strength were found across doses of proton or ²⁸silicon head-only radiation. Future work includes performing mechanical testing of the bone samples. Moving from mouse to larger animal models may also provide the increased lifespan for assessing the long-term outcomes of radiation exposure.

The Rodent Psychomotor Vigilance Test (rPVT): A Method for Assessing Neurobehavioral Performance in Rats and Mice

The human Psychomotor Vigilance Test (PVT) is a widely used procedure for measuring changes in fatigue and sustained attention. The present article describes a rodent version of the PVT-termed the "rPVT"-that measures similar aspects of attention (i.e., performance accuracy, motor speed, premature responding, and lapses in attention). Data are presented that demonstrate both the short- and long-term usefulness of the rPVT when employed with laboratory rats. Rats easily learn the rPVT, and learning to perform the basic procedure takes less than two weeks of training. Once acquired, rat performances in the rPVT show a high degree of similarity to these same performance measures in the human PVT, including similarities in, lapses in attention, reaction times, vigilance decrements across session time (i.e., the human "time-on-task" effects), and the response-stimulus interval (RSI) effect described for humans. Thus the rPVT can be an extremely valuable tool for assessing the effects of a wide range of variables on sustained attention quite similar to human PVT performances, and thus can be useful for developing novel treatments for neurobehavioral dysfunctions.

A rodent model of the human psychomotor vigilance test: Performance comparisons

BACKGROUND

The human Psychomotor Vigilance Test (PVT) is commonly utilized as an objective risk assessment tool to quantify fatigue and sustained attention in laboratory, clinical, and operational settings.

NEW METHOD

Recent studies have employed a rodent version of the PVT (rPVT) to measure various aspects of attention (lapses in attention, reaction times) under varying experimental conditions.

RESULTS

Data are presented here to evaluate the short- and long-term utility of the rPVT adapted for laboratory rats designed to track the same types of performance variables as the human PVT-i.e., motor speed, inhibitory control ("impulsivity"), and attention/inattention. Results indicate that the rPVT is readily learned by rats and requires less than two weeks of training to acquire the basic procedure. Additional data are also presented on the effects of radiation exposure on these performance measures that indicate the utility of the procedure for assessing changes in neurobehavioral function in rodents across their lifespans.

COMPARISON WITH EXISTING METHOD(S)

Once stable performances are obtained, rats evidence a high degree of similarity to human performance measures, and include similarities in terms of lapses and reaction times, in addition to percent correct and premature responding. Similar to humans, rats display both a vigilance decrement across time on task and a response-stimulus interval effect.

CONCLUSIONS

The rPVT is a useful tool in the investigation of the effects of a wide range of variables on vigilance performance that compares favorably to the human PVT and for developing potential prophylactics, countermeasures, and treatments for neurobehavioral dysfunctions.

Effects of X-ray radiation on complex visual discrimination learning and social recognition memory in rats

The present report describes an animal model for examining the effects of radiation on a range of neurocognitive functions in rodents that are similar to a number of basic human cognitive functions. Fourteen male Long-Evans rats were trained to perform an automated intra-dimensional set shifting task that consisted of their learning a basic discrimination between two stimulus shapes followed by more complex discrimination stages (e.g., a discrimination reversal, a compound discrimination, a compound reversal, a new shape discrimination, and an intra-dimensional stimulus discrimination reversal). One group of rats was exposed to head-only X-ray radiation (2.3 Gy at a dose rate of 1.9 Gy/min), while a second group received a sham-radiation exposure using the same anesthesia protocol. The irradiated group responded less, had elevated numbers of omitted trials, increased errors, and greater response latencies compared to the sham-irradiated control group. Additionally, social odor recognition memory was tested after radiation exposure by assessing the degree to which rats explored wooden beads impregnated with either their own odors or with the odors of novel, unfamiliar rats; however, no significant effects of radiation on social odor recognition memory were observed. These data suggest that rodent tasks assessing higher-level human cognitive domains are useful in examining the effects of radiation on the CNS, and may be applicable in approximating CNS risks from radiation exposure in clinical populations receiving whole brain irradiation.

Latency and frequency of responding under discrete-trial fixed-interval schedules of reinforcement

Pigeons' key pecking was studied under a number of discrete-trial fixed-interval schedules of food reinforcement. Discrete trials were presented by briefly illuminating the keylight repetitively throughout the interreinforcement interval. A response latency counterpart to the fixed-interval scallop was found, latency showing a gradual, negatively accelerated decrease across the interval. This latency pattern was largely invariant across changes in fixed-interval length, number of trials per interval, and maximum trial duration. Frequency of responding during early trials in the intervals varied, however, with different schedule parameters, being directly related to fixed-interval length, inversely related to number of trials, and complexly affected by conjoint variations of fixed-interval length and number of trials. Response latency thus was found to be simply related to elapsed time during the interval while response frequency was complexly determined by other factors as well.

Neurobehavioral effects of head-only gamma-radiation exposure in rats

The present report describes initial steps in the development of an animal model for assessing the effects of low levels of radiation encountered in the space environment on human cognitive function by examining the effects of radiation on a range of neurobehavioral functions in rodents that are similar to a number of basic human cognitive functions. The present report presents baseline data on the effects of gamma radiation on neurobehavioral functions in rodents (psychomotor speed, discrimination accuracy and inhibitory control) that are similar to those in humans. Two groups of eight Long-Evans rats were trained to perform a reaction-time task that required them to depress a lever for 1-3 s and to release the lever within 1.5 s of a release stimulus (correct trial) to receive a reward. Releasing the lever prior to the release stimulus (error) terminated the trial. One group was exposed to head-only gamma radiation (5 Gy at a dose rate of 1 Gy/min), while the second group was sham-irradiated using the same anesthesia protocol. The irradiated group showed significant deficits in both performance accuracy (percentage correct scores) and performance reliability (false alarm scores) from 1 to 4 months after irradiation, indicating clear performance impairments. The increase in false alarm scores is consistent with reduced inhibitory control and a shift toward increased anticipatory responses at the cost of decreased accuracy. The nonirradiated group showed no such changes over the same period.

Consistent, high-level ethanol consumption in pig-tailed macaques via a multiple-session, limited-intake, oral self-dosing procedure

BACKGROUND

Alcohol abuse is a major public health burden that can lead to many adverse health effects such as impaired hepatic, gastrointestinal, central nervous system and immune system function. Preclinical animal models of alcohol abuse allow for experimental control over variables often difficult to control in human clinical studies (e.g., ethanol exposure before or during the study, history of other drug use, access to medical care, nutritional status, etc). Nonhuman primate models in particular provide increased genetic, anatomic and physiologic similarity to humans, relative to rodent models. A small percentage of macaques will spontaneously consume large quantities of ethanol; however, most nonhuman primate models of "voluntary" ethanol intake produce relatively low daily ethanol intake in the majority of monkeys.

METHODS

To facilitate study of chronic exposure to high levels of ethanol intake, a macaque model has been developed that induces consistent, daily high-level ethanol consumption. This multiple-session procedure employed 4 drinking sessions per day, with sessions occurring once every 6 hours.

RESULTS

The group average alcohol consumption was 4.6 g/kg/d (SEM 0.4), roughly twice the group average consumption of previous reports. Ethanol drinking sessions produced group mean blood ethanol levels of 95 mg/dl after 60 minutes, and fine motor control was impaired up to 90 minutes after a drinking session.

CONCLUSION

This model of multiple-session, limited access, oral ethanol self-dosing produced consistent, high-level ethanol consumption with each session qualifying as a "binge" drinking session using the definition of "binge" provided by the NIAAA (>80 mg/dl/session). This model of ethanol drinking in macaques will be of great utility in the study of immunological, physiological and behavioral effects of ethanol in nonhuman primates.

Environmental cues, alcohol seeking, and consumption in baboons: effects of response requirement and duration of alcohol abstinence

BACKGROUND

Environmental stimuli (cues) that have been paired with alcohol drinking may evoke classically conditioned states that in turn influence alcohol consumption and relapse to heavy drinking. Animal models using chained schedules of alcohol reinforcement may be useful for examining such complex interactions.

METHODS

Alcohol drinking was established in 4 baboons. A sequence of lights and tones was presented during daily 3-hour sessions. First, cues were presented alone and no programmed contingencies were in effect. Second, cues were paired with 3 linked components consisting of different behavioral contingencies leading to and concluding with access to alcohol for self-administration in the last component (i.e., a chained schedule of alcohol reinforcement). Third, the effects of withholding alcohol access (i.e., forced abstinence) and increasing the number of lever responses required per drink were evaluated.

RESULTS

Cues paired with a chained schedule of alcohol reinforcement engendered behaviors that brought baboons into contact with alcohol-related cues and occasioned operant responding that facilitated access to alcohol (alcohol seeking) during components that preceded alcohol access. Increasing the response requirement for each drink decreased the number of drinks and volume of alcohol consumed, but did not alter alcohol seeking. On the first session after 14 days of alcohol abstinence, latency to complete the operant requirement that produced alcohol access was decreased while both alcohol self-administration and volume of alcohol consumed were increased.

CONCLUSIONS

Alcohol self-administration and consumption were sensitive to increases in response requirement and duration of alcohol abstinence, while seeking was only enhanced by duration of alcohol abstinence. This animal model may be useful to further examine the interactions between environmental cues and behaviors associated with seeking and consumption of alcohol and to evaluate the efficacy of potential alcohol treatment drugs on these behaviors.

Morphine withdrawal dramatically reduces lymphocytes in morphine-dependent macaques

The immune effects of chronic opiate exposure and/or opiate withdrawal are not well understood. The results of human studies with opiate abusers are variable and may not be able to control for important factors such as subjects' drug histories, health and nutritional status. Nonhuman primate models are necessary to control these important factors. A model of opiate dependence in macaques was developed to study the effects of opiate dependence and withdrawal on measures of immune function. Four pigtailed macaques drank a mixture of morphine (20 mg/kg/session) and orange-flavored drink every 6 h for several months. During stable morphine dependence, absolute numbers of neutrophils, monocytes and lymphocytes did not change relative to pre-morphine levels. However, there was a significant decrease in the absolute number and percentage of natural killer (NK) cells in morphine dependence. Either precipitated withdrawal or abstinence for 24 h resulted in behavioral withdrawal signs in all animals. Absolute lymphocyte counts decreased and absolute netrophil counts increased significantly in withdrawal, relative to levels during morphine dependence. Lymphocyte subset (CD4+, CD8+, CD20+) cells were also decreased in absolute numbers with little change in their percentage distributions. There was, however, a significant increase in the percentage of NK cells in withdrawal relative to levels during morphine dependence. This study demonstrates the usefulness of voluntary oral self-dosing procedures for maintaining morphine dependence in nonhuman primates and demonstrates that the morphine withdrawal syndrome includes large alterations in blood parameters of immune system function, including nearly 50% reduction in numbers of CD4+, CD8+ and CD20+ cells.

Effects of morphine on circadian rhythms of motor activity and body temperature in pig-tailed macaques

Previous studies of the effects of opiates on motor activity and body temperature in nonhuman primates have been limited in scope and typically only conducted with restrained animals. The present study used radio-telemetry devices to continuously measure activity and temperature in unrestrained pig-tailed macaques for 24 h following morphine administration. Two dose-response functions (0.56 to 5.6 mg/kg, i.m.) were determined, one with morphine administered at 9 a.m. and one with morphine administrated at 3 p.m. Under both the 9 a.m. or 3 p.m. administration schedules, body temperature and activity were increased acutely. Activity was also reduced the following morning after morphine administered at either time. In other regards, morphine's effects on both temperature and activity differed between 9 a.m. and 3 p.m. injection, including periods of decreased activity immediately after the acute increases after 9 a.m. but not 3 p.m. administration. Surprisingly, motor activity also increased 9-12 h post-injection following morphine administered at 9 a.m., but not at 3 p.m. These results clearly show an interaction between timing of morphine administration and effects on temperature and activity. These results also underscore the fact that single injections of drugs may have multiple and delayed effects on circadian rhythms in macaques.

Crewmember performance before, during, and after spaceflight

The development of technologies for monitoring the welfare of crewmembers is a critical requirement for extended spaceflight. Behavior analytic methodologies provide a framework for studying the performance of individuals and groups, and brief computerized tests have been used successfully to examine the impairing effects of sleep, drug, and nutrition manipulations on human behavior. The purpose of the present study was to evaluate the feasibility and sensitivity of repeated performance testing during spaceflight. Four National Aeronautics and Space Administration crewmembers were trained to complete computerized questionnaires and performance tasks at repeated regular intervals before and after a 10-day shuttle mission and at times that interfered minimally with other mission activities during spaceflight. Two types of performance, Digit-Symbol Substitution trial completion rates and response times during the most complex Number Recognition trials, were altered slightly during spaceflight. All other dimensions of the performance tasks remained essentially unchanged over the course of the study. Verbal ratings of Fatigue increased slightly during spaceflight and decreased during the postflight test sessions. Arousal ratings increased during spaceflight and decreased postflight. No other consistent changes in rating-scale measures were observed over the course of the study. Crewmembers completed all mission requirements in an efficient manner with no indication of clinically significant behavioral impairment during the 10-day spaceflight. These results support the feasibility and utility of computerized task performances and questionnaire rating scales for repeated measurement of behavior during spaceflight.

Cocaine's effects on the perception of socially significant vocalizations in baboons

The effects of cocaine on the ability of baboons to discriminate among their natural affiliative 'grunt' vocalizations were examined to determine whether cocaine would produce discrimination impairments similar to those observed previously with acoustically-similar human vowel sounds , or whether differences in cocaine's effects might occur associated with the social significance of the calls. The task employed digitized calls of actual vocalizations recorded in the wild . Baboons pressed a lever to produce a repeating 'standard' grunt, and released the lever only when one of four other 'target' grunts was selected to occur in place of the standard grunt. Cocaine (0.01-.56 mg/kg, i.m.) impaired call perception, and these impairments were more pronounced than those observed previously for acoustically-similar human vowel sounds. Cocaine also elevated reaction times as a function of dose. The results demonstrate that cocaine impairs perceptual discriminations of the natural grunt vocalizations of baboons, and suggest that cocaine may have more pronounced effects on the perception of biologically-relevant as opposed to non-relevant communication signals.

Distributed communication and psychosocial performance in simulated space dwelling groups

The present report describes the development and application of a distributed interactive multi-person simulation in a computer-generated planetary environment as an experimental test bed for modeling the human performance effects of variations in the types of communication modes available, and in the types of stress and incentive conditions underlying the completion of mission goals. The results demonstrated a high degree of interchangeability between communication modes(audio, text) when one mode was not available. Additionally, the addition of time pressure stress to complete tasks resulted in a reduction in performance effectiveness, and these performance reductions were ameliorated via the introduction of positive incentives contingent upon improved performances. The results obtained confirmed that cooperative and productive psychosocial interactions can be maintained between individually isolated and dispersed members of simulated spaceflight crews communicating and problem-solving effectively over extended time intervals without the benefit of one another's physical presence.

The discrimination of baboon grunt calls and human vowel sounds by baboons

The ability of baboons to discriminate changes in the formant structures of a synthetic baboon grunt call and an acoustically similar human vowel (/epsilon/) was examined to determine how comparable baboons are to humans in discriminating small changes in vowel sounds, and whether or not any species-specific advantage in discriminability might exist when baboons discriminate their own vocalizations. Baboons were trained to press and hold down a lever to produce a pulsed train of a standard sound (e.g., /epsilon/ or a baboon grunt call), and to release the lever only when a variant of the sound occurred. Synthetic variants of each sound had the same first and third through fifth formants (F1 and F3-5), but varied in the location of the second formant (F2). Thresholds for F2 frequency changes were 55 and 67 Hz for the grunt and vowel stimuli, respectively, and were not statistically different from one another. Baboons discriminated changes in vowel formant structures comparable to those discriminated by humans. No distinct advantages in discrimination performances were observed when the baboons discriminated these synthetic grunt vocalizations.

Distributed interactive communication in simulated space-dwelling groups

This report describes the development and preliminary application of an experimental test bed for modeling human behavior in the context of a computer generated environment to analyze the effects of variations in communication modalities, incentives and stressful conditions. In addition to detailing the methodological development of a simulated task environment that provides for electronic monitoring and recording of individual and group behavior, the initial substantive findings from an experimental analysis of distributed interactive communication in simulated space dwelling groups are described. Crews of three members each (male and female) participated in simulated "planetary missions" based upon a synthetic scenario task that required identification, collection, and analysis of geologic specimens with a range of grade values. The results of these preliminary studies showed clearly that cooperative and productive interactions were maintained between individually isolated and distributed individuals communicating and problem-solving effectively in a computer-generated "planetary" environment over extended time intervals without benefit of one another's physical presence. Studies on communication channel constraints confirmed the functional interchangeability between available modalities with the highest degree of interchangeability occurring between Audio and Text modes of communication. The effects of task-related incentives were determined by the conditions under which they were available with Positive Incentives effectively attenuating decrements in performance under stressful time pressure.

Sex differences in the acoustic structure of vowel-like grunt vocalizations in baboons and their perceptual discrimination by baboon listeners

This study quantifies sex differences in the acoustic structure of vowel-like grunt vocalizations in baboons (Papio spp.) and tests the basic perceptual discriminability of these differences to baboon listeners. Acoustic analyses were performed on 1028 grunts recorded from 27 adult baboons (11 males and 16 females) in southern Africa, focusing specifically on the fundamental frequency (F0) and formant frequencies. The mean F0 and the mean frequencies of the first three formants were all significantly lower in males than they were in females, more dramatically so for F0. Experiments using standard psychophysical procedures subsequently tested the discriminability of adult male and adult female grunts. After learning to discriminate the grunt of one male from that of one female, five baboon subjects subsequently generalized this discrimination both to new call tokens from the same individuals and to grunts from novel males and females. These results are discussed in the context of both the possible vocal anatomical basis for sex differences in call structure and the potential perceptual mechanisms involved in their processing by listeners, particularly as these relate to analogous issues in human speech production and perception.

Central nervous system correlates of behavioral deficits following simian immunodeficiency virus infection

Despite the high incidence of cognitive and motor impairment in acquired immunodeficiency syndrome (AIDS) patients, the mechanisms of AIDS-related central nervous system (CNS) pathology are not completely understood. Infection with simian immunodeficiency virus (SIV) in macaques provides an excellent model of AIDS, including human immunodeficiency virus (HIV)-induced CNS pathology and cognitive/behavioral impairment. Co-inoculation with two SIV strains, SIV/17E-Fr and SIV/DeltaB670, accelerates SIV CNS disease, producing SIV encephalitis in over 90% of pig-tailed macaques within 3 months. In the present study, this SIV model was employed to identify cellular and viral correlates of behavioral impairment following SIV infection. Measures of psychomotor speed (simple reaction time), fine motor control (bimanual motor task), and general motor activity (home cage movement) were all adversely affected by SIV disease. Prior to euthanasia, performance was significantly impaired in both a simple reaction time task in 6 of 12 monkeys and a bimanual motor task in 5 of 6 monkeys. All monkeys evaluated (11 of 11) showed significant reductions in spontaneous motor activity. Significant correlations were found between impaired performance on the bimanual motor test and axonal damage (accumulation of beta-amyloid precursor protein in the corpus callosum) as well as increased microglial activation and macrophage infiltration (levels of CD68 and Ham56 immunostaining). These results suggest that axonal damage is related to the behavioral impairment induced by infection with SIV. The axonal damage may result from neuroimmune responses, including microglial and macrophage activation. Therefore, axonal damage may be a morphologic manifestation of neuronal dysfunction that underlies development of behavioral impairment in HIV/SIV CNS infection.

Cocaine's effects on detection, discrimination, and identification of auditory stimuli by baboons

The perceptual effects of cocaine were examined under conditions that required baboons to detect the presence of tones as well as to identify tones of different pitches, and the results compared to the results of prior studies on cocaine's effects on the detection of tones, the discrimination of different tone pitches, and the discrimination of different human vowel sounds of similar pitch. A reaction time procedure was employed in which baboons were trained to press a lever in the presence of a visual "ready" signal, and release the lever only when one tone pitch occurred, but not release the lever when a second, different tone pitch occurred. Changes in the percentage of correct detections and median reaction times for each tone were measured following intramuscular administration of cocaine (0.01-1.0 mg/kg). Cocaine impaired tone identification and shortened reaction times to the tones in all baboons. Cocaine's effects on accuracy, however, were primarily due to elevations in false alarm rates, as opposed to detection of the stimuli themselves. The results demonstrate that cocaine impairs the discriminability of tone pitches in baboons, and that such impairments can depend upon the type of stimuli employed (tones vs. speech sounds) and the type of procedure employed (discrimination vs. identification).

Cocaine's effects on the discrimination of simple and complex auditory stimuli by baboons

The effects of cocaine on tone frequency discriminations by baboons were examined and compared with previous data for more complex acoustic stimuli (speech sounds) to see if cocaine's perceptual effects on these discriminations depends upon the type of stimulus employed (i.e., tones vs. speech sounds). Baboons pressed a lever to produce one repeating "standard" tone and released the lever only when one of four other "comparison" tones occasionally occurred in place of the standard tone. Cocaine's effects were assessed once or twice weekly by giving an intramuscular injection of cocaine hydrochloride (0.01-0.56 mg/kg) immediately prior to performing the task and by examining correct detections and reaction times for each tone following drug administration. Cocaine impaired tone discriminability, with greater impairments occurring for those tones that were more similar in frequency to the standard tone. Cocaine's perceptual effects occurred within 20-70 min following drug administration. Cocaine also impaired or facilitated the speed of responding to auditory stimuli, depending upon the drug dose and subject. The results demonstrate that cocaine can impair auditory discriminations involving simple tones, as well as speech sounds, and further supports the suggestion that cocaine's effects are focused on CNS mechanisms related to the use of pitch cues.

Perceptual and motor effects of morphine and buprenorphine in baboons

The effects of morphine and buprenorphine on auditory perceptual discriminations and response latency ("reaction time") in baboons are compared. The task employed synthetic human vowel sounds that are readily generated in the laboratory, and closely approximate natural baboon "grunt" vocalizations [J. Acoust. Soc. Am. 101 (1997) 2951]. Baboons pressed a lever to produce one repeating "standard" vowel, and released the lever only when one of four other "comparison" vowels occasionally occurred in place of the standard vowel. The percentage of correct detections and median reaction time for each comparison were measured following intramuscular drug administrations of morphine (0.01-1.8 mg/kg) and buprenorphine (0.00032-0.032 mg/kg). Both morphine and buprenorphine impaired vowel discriminability, and greater impairments occurred for those comparison vowels that were more similar in formant structure to the standard vowel. Morphine increased reaction time in all baboons, and buprenorphine increased reaction time in two of three baboons. Morphine's perceptual effects occurred within 20-40 min following drug administration; buprenorphine's perceptual effects occurred 50-100 min following drug administration. Morphine and buprenorphine did not differ in the time course of their maximal reaction time effects. The results demonstrate that both morphine and buprenorphine can impair auditory discriminations involving human vowel sounds in baboons, as well as lengthen reaction times to the stimuli.

Effects of bilateral olivocochlear lesions on vowel formant discrimination in cats

Operant conditioning procedures were used to measure the effects of bilateral olivocochlear lesions on the cat's discrimination thresholds for changes in the second formant frequency (deltaF2) of the vowel /epsilon/. Three cats were tested with the formant discrimination task under quiet conditions and in the presence of continuous broadband noise at signal-to-noise ratios (S/Ns) of 23, 13, and 3 dB. In quiet, vowel levels of 50 and 70 dB produced average deltaF2s of 42 and 47 Hz, respectively, and these thresholds did not change significantly in low levels of background noise (S/Ns = 23 and 13 dB). Average deltaF2s increased to 94 and 97 Hz for vowel levels of 50 and 70 dB in the loudest level of background noise (S/N = 3 dB). Average deltaF2 thresholds in quiet and in lower noise levels were only slightly affected when the olivocochlear bundle was lesioned by making bilateral cuts into the floor of the IVth ventricle. In contrast, post-lesion deltaF2 thresholds in the highest noise level were significantly larger than pre-lesion values; the most severely affected subject showed post-lesion discrimination thresholds well over 200 Hz for both 50 and 70 dB vowels. These results suggest that olivocochlear feedback may enhance speech processing in high levels of ambient noise.

Effects of cocaine and quinpirole on perceptual and motor functions in baboons

The effects of cocaine and quinpirole were studied in baboons to determine whether quinpirole, a relatively selective D2/D3 dopamine agonist, produced effects similar to those of cocaine on perceptual and motor processes. To measure perceptual and motor function, three baboons were trained to discriminate differences between a standard vowel and four other synthetic vowels: response accuracy as well as response latencies, or "reaction times", were measured following drug administrations. Cocaine reduced reaction times in two baboons, and did not affect reaction times in a third; on the other hand, quinpirole lengthened reaction times in a dose-dependent manner in all baboons. Cocaine and quinpirole also differed in the time course to produce the maximal reaction time effect following drug administration. Cocaine and quinpirole did not differ consistently in their perceptual effects, as indicated by similar changes in d', a signal-detection index of discriminability. These distinct profiles of effects for cocaine and quinpirole suggest differing neurochemical actions for these two drugs.

Vowel discrimination in cats: thresholds for the detection of second formant changes in the vowel /epsilon/

The ability of cats to discriminate changes in the second formant of the vowel /epsilon/ was examined across a range of stimulus levels. Cats were trained to press and hold down a lever to produce a pulsed train of the standard vowel /epsilon/, and to release the lever only when a variant of [epsilon] occurred. Six synthetic variants of /epsilon/ had the same first and third formants (F1 and F3), but with the second formant (F2) located between 1700 and 2000 Hz. All stimuli were tested at levels of 10, 30, 50, and 70 dB SPL. Average difference thresholds for changes in F2 (delta F2) of the vowel /epsilon/ ranged from 87 to 36 Hz across levels of 10 to 70 dB SPL, and were only slightly above those of humans. Further, the delta F2 values were lower than pure-tone delta F values in the same frequency range, whereas humans exhibit higher delta F2 values than pure-tone delta F values in the same frequency range. Changes in the second formant in a negative direction (downward F2 shifts) were also found to be more difficult to detect than upward F2 shifts. These results suggest that, compared to pure tones, cats are better able to discriminate small changes in more complex, vowel-like stimuli.

Vowel discrimination in cats: acquisition, effects of stimulus level, and performance in noise

The ability of cats to discriminate accurately among different synthetic, steady-state vowels was examined across a range of stimulus levels and in background noise. Cats were trained to press and hold down a lever to produce a pulsed train of a standard vowel stimulus, and to release the lever only when a different vowel sound occurred. Five synthetic vowels were tested (/e/, /ae/, /a/, /o/, and /u/) at levels of 30, 50, 70, and 90 dB SPL. In separate experiments, each of these vowels served in turn as the standard vowel. All cats discriminated among the vowels accurately, and in general performed at least as well at high stimulus levels as at low levels. Where differences in vowel discriminability occurred, they were correlated with the relative changes in first and second formant peaks. Cats appear to predominantly utilize upward frequency changes in either the first or second formants of the vowels to make the discriminations; downward formant changes produced considerably lower discrimination performances. In background noise, high vowel discriminability was still maintained at an average signal/noise ratio of -12.3 dB. Thus cats can discriminate among vowels at high signal levels and in background noise, despite the fact that the neural representations of vowels based on rate responses in the auditory nerve can be severely degraded under these conditions.

Cocaine's effects on speech sound identification and reaction times in baboons

The effects of cocaine on speech sound discriminations was examined to determine whether cocaine's previously demonstrated effect in reducing speech sound discriminability was dependent upon either the type of stimuli employed (simple tones versus complex speech) or the procedure (stimulus detection versus stimulus discrimination). Because of demonstrated similarities in the way that baboons and humans discriminate speech, and in the way the CNS is thought to encode and process speech sounds in these two species, baboons were trained to perform a choice procedure to identify the occurrence of different synthetic vowel sounds (see text). Animals held down a lever and released the lever only when one of four target vowels sounded, and not when a fifth, standard vowel sounded. Acute IM administration of cocaine (0.0032-1.0 mg/kg) produced dose-dependent decreases in vowel discriminability that were mostly due to elevations in false alarms (i.e., releases to the standard vowel) following cocaine. Cocaine also shortened reaction times to the stimuli in two of three baboons, but to a much lesser extent than observed previously. These results suggest that cocaine may interfere with the ability of the CNS to process the acoustic cues in speech sounds, and that the effects of cocaine on reaction times may depend upon the complexity of the reaction time procedure employed.

Cocaine's effects on speech sound discriminations and reaction times in baboons

Three adult baboons were trained using a psychophysical procedure to discriminate between different synthetic vowel sounds [symbol: see text]. Baboons pressed and held a lever down to produce a pulsed train of a single reference vowel that served as the standard stimulus. Animals were trained to release the lever only when this standard vowel sound changed to one of the four remaining comparison vowels. A lever release within 1.5 s of this change in vowel sounds was defined as a correct detection of the change from the standard vowel to one of the comparison vowels, and was reinforced. All baboons readily learned the vowel discriminations and detected vowel changes at the 90-100% correct performance level. Acute IM administration of cocaine prior to test sessions (0.00032-3.2 mg/kg) produced dose-dependent decrements in vowel discriminability. At the same time, cocaine shortened lever release latencies (reaction times) to the vowel stimuli in two of three baboons. The cocaine-induced decrements in vowel discriminability were correlated with the degree to which frequency differences occurred among the different vowels in that lower vowel discriminability scores were found for those vowels with smaller spectral differences from the standard vowel. Further, false alarm rates were not systematically affected by cocaine, indicating that the cocaine-induced decrements in vowel discrimination accuracy occurred in the absence of systematic changes in the reliability of the baboons' discrimination performances.

Effects of cocaine on simple reaction times and sensory thresholds in baboons

The effects of chronic, daily administration of cocaine on auditory and visual reaction times and thresholds were studied in baboons. Single intramuscular injections of cocaine hydrochloride (0.1 to 5.6 mg/kg) were given once daily for periods of 10 to 25 days, and were followed immediately by psychophysical tests designed to assess cocaine's effects on simple reaction times as on auditory and visual threshold functions. Consistent reductions in reaction times were frequently observed over the cocaine dose range of 0.32 to 1.0 mg/kg; at higher doses, either decreases or increases in reaction times were observed, depending upon the animal. Lowered reaction times generally occurred immediately following the 1st day's cocaine injection, and continued through all subsequent days during the dose administration period, suggesting little development of tolerance or sensitivity to these reaction-time effects. Reaction-time decreases showed a U-shaped dose-effect function. The greatest decreases in reaction times occurred from 0.32 to 1.0 mg/kg, and produced an average reaction-time decrease of 10 to 12%. Concurrently measured auditory and visual thresholds showed no systematic changes as a function of cocaine dose. Pausing was observed during performance of the psychophysical tasks, with the length of total session pause times being directly related to cocaine dose.

Effects of cocaine on sensory motor function in baboons

The effects of cocaine on auditory and visual threshold functions and reaction times were studied in baboons. Single IM injections of cocaine HCl (0.001-1.0 mg/kg) were administered once or twice weekly and were followed immediately by psychophysical tests designed to assess cocaine's effects on sensory thresholds and reaction times. Consistent reductions in reaction times were observed in the cocaine dose range of 0.032-0.32 mg/kg. Reaction times were decreased by 5-8% at the more effective cocaine doses. Concurrently measured auditory and visual threshold sensitivities showed no systematic changes at any of the cocaine doses studied.

Frequency discrimination in noise: comparison of cat performances with auditory-nerve models

Pure-tone frequency discrimination (delta F) performances were measured in cats and compared to neural models of these delta F performances based on auditory-nerve data in cats. Animal psychophysical techniques were used to train cats to discriminate frequency changes for pulsed pure tones in background noise at both 1.0 and 3.0 kHz. A go-left, go-right procedure was employed, and delta F's were measured in noise as a function of signal level at a constant signal-to-noise ratio. In contrast to human listeners, cats showed increases in delta F at 1.0 kHz with increasing signal level. Model estimates of delta F's based on rate responses in the cat auditory nerve predict increasing delta F with increasing signal level, the trend observed in the cat psychophysical data. Model estimates of delta F's based on temporal (phase-locking) properties in cat auditory nerve, on the other hand, predict decreases in delta F that have been observed in previous data from human listeners [Dye and Hafter, J. Acoust. Soc. Am. 67, 1746-1753 (1980)]. These results suggest that for cats, average rate, rather than phase-locking, may be used by the central nervous system in performing frequency discrimination in background noise at 1.0 kHz. At 3.0 kHz cats showed little change in delta F as a function of signal level, a result similar to the trend for human listeners to show no change or slight increases in delta F with increases in signal level for tones in the 2- to 3-kHz range.

Beta-blocker effects on 24-h activity in normotensive and renovascular hypertensive baboons

Spontaneous motor activity of normotensive and renovascular hypertensive baboons was measured during oral dosing with the beta-adrenergic antagonists atenolol HCl (2.6 mg/kg/day) and d,l-propranolol HCl (6.8 mg/kg twice daily) in separate studies. Each study administered active drug for 21 consecutive days. Piezoelectric monitors sensitive to movement were worn continuously by the baboons. Propranolol decreased overall 24-h average activity during the third week of dosing in normotensive baboons but not in renovascular hypertensive baboons. The greatest reductions in activity averaged 20% at those times of day corresponding to the second daily drug dose both in normotensive baboons and, at this time of day only, in the majority of hypertensive baboons. Activity decreases reversed to baseline levels when propranolol was discontinued. For atenolol, most normotensive but no hypertensive baboons showed decreases in activity at the time of day corresponding to the daily drug dose.

General activity in baboons measured with a computerized, lightweight piezoelectric motion sensor: effects of drugs

A small, 1-oz activity-monitoring device is described for measuring motor activity continuously for periods of up to 42 days. The monitor employs a piezoelectric sensor that detects extremely small accelerations induced by movements. The monitor can be placed on collars or harnesses (e.g., for rabbits, cats, dogs, nonhuman primates, etc.). The use of the monitor is described within numerous laboratories studying the behavioral pharmacology of drugs in individually caged laboratory baboons. Patterns of daily activity were reliably recorded over periods of several months, and reflected the normal activity patterns of animals. The activity monitor recorded reliable, drug-induced changes in general activity that paralleled the known effects of the same drugs on learned behaviors. Low doses of the stimulants cocaine and d-amphetamine both increased general activity. Marked reductions in general activity were observed following both the administration of delta-9-tetrahydrocannabinol and an antihypertensive drug combination of diuretic and verapamil.

Behavioral performance effects of verapamil in normotensive and renovascular hypertensive baboons

Behavioral performances of normotensive and hypertensive adult male baboons were tested before, during, and following chronic oral dosing with verapamil. Performances during a five-color simultaneous match-to-sample task were measured for two doses (2.0, and 3.2 mg/kg/day) and vehicle. Each dose was administered for 21 consecutive days preceded and followed by 14-day baseline and recovery periods, respectively. Choice reaction times increased by 9% during the lower dose of verapamil, compared to vehicle; choice reaction times were unchanged at the higher dose. At baseline and during vehicle administration, the yellow and white stimuli were the most difficult to discriminate correctly; discrimination of these colors was slightly impaired by the lower, but not the higher dose of verapamil. Verapamil's behavioral effects were not modulated by blood pressure changes since both baboon groups showed equivalent changes in behavioral performance, but only renovascular hypertensive baboons showed blood pressure decreases. Verapamil appears to be an effective hypotensive and does not produce profound psychomotor impairment at clinically used doses during the first weeks of treatment.

Acute ethanol effects on sensory/motor function in baboons with a history of chronic ethanol ingestion

Baboons with a history of chronic, daily ethanol ingestion were subsequently studied under conditions that assessed the effects of acute oral self-administration of ethanol on auditory and visual threshold functions and reaction times. During the post-chronic experiment reported herein, the animals consumed specific amounts of ethanol twice weekly (0.1, 0.32, 1.0 or 1.3 g/kg), following which they immediately performed psychophysical tests designed to assess ethanol's effects on sensory thresholds and reaction times. Clear, dose-related increases in reaction times were observed following ethanol doses greater than 0.32 g/kg. Trends within individual threshold functions were consistent with systematic changes in auditory and visual threshold sensitivities of 1-3 dB at the high ethanol doses. Reaction time increases ranged from 25 to 180 ms above baseline levels at the highest dose (a 15% average increase). These general findings however, were in contrast to data obtained in the same animals under conditions of daily, chronic ethanol administration which characteristically showed greater sensory/motor effects of up to twice the magnitude of those observed with single doses.

Chronic hydrochlorothiazide and verapamil effects on motor activity in hypertensive baboons

Spontaneous motor activity was measured in six baboons during chronic oral dosing with a diuretic (hydrochlorothiazide/triamterene), a calcium channel blocker (verapamil), and a combination of the two drugs. Piezoelectric monitors sensitive to movement were attached to leather collars and were worn continuously by the baboons throughout the protocol. Baboons were made hypertensive during a preexperimental period by either 1) chronic administration of deoxycorticosterone acetate (DOCA)-salt or 2) surgical renal artery stenosis. Total inactive periods/day increased over baseline levels during diuretic alone and increased further during diuretic + verapamil combined. The total number of inactive periods/day returned toward baseline levels in the subsequent conditions of verapamil alone and baseline recovery. Activity levels decreased during combination dosing mainly during morning hours (0700-1100 h). Overall changes in activity occurred in the second week of dosing; this time period was found earlier to maximally decrease blood pressure and to impair behavioral performances.

Performance of baboons under a repeated acquisition procedure during chronic oral exposure to atenolol and propranolol

Repeated acquisition behavioral performances of normotensive and renovascular hypertensive baboons were tested before, during, and following chronic oral dosing with the beta-adrenergic antagonists atenolol HCl (2.6 mg/kg/day PO), and d,l propranolol HCl (6.8 mg/kg twice daily PO) in separate studies. Each study administered active drug for 21 consecutive days preceded and followed by 14-day baseline and recovery periods, respectively. Animals pressed five keys in sequence for food reinforcement during daily experimental sessions which consisted of alternating acquisition (new sequence learning) and performance (previously learned) task components. Atenolol increased response latencies during acquisition in comparison to performance components, and during early portions of sessions. Propranolol also increased response latencies during acquisition components in early periods of sessions, but fewer dependent measures were affected, and the magnitude of increases in response latencies was smaller (12% +/- 5 SEM) as compared with atenolol (47% +/- 13). Test doses of phencyclidine HCl (PCP) increased latencies to the same degree as atenolol. PCP markedly reduced accuracy, while atenolol or propranolol did not. Blood pressures remained stable under atenolol, and decreased by approximately 10-15 mmHg under propranolol. No differences between renovascular hypertensive and normotensive baboons were found as a function of drug conditions. Drug effects were not dependent on plasma propranolol concentration.

Behavioral effects of chronic, orally administered diuretic and verapamil in baboons

Behavioral performances of six baboons were tested during chronic oral dosing with diuretic (hydrochlorothiazide/triamterene), a calcium channel blocker (verapamil), and a combination of the two drugs. Reaction times and color matching-to-sample performances as well as physiological measures were obtained in deoxycorticosterone acetate (DOCA)-salt baboons and in renovascular hypertensive baboons. Combined diuretic and verapamil impaired color matching to a small degree in comparison to baseline performance, while drug administered alone had no effect. Weekly systolic and diastolic blood pressures decreased maximally from baseline during the drug combination period, and were accompanied by maximal increases in serum sodium. The largest behavioral impairments during combination dosing were observed for colors that were most difficult to discriminate during baseline. Significant positive correlations were found between systolic blood pressure and color matching accuracy. No differences between the animal hypertension groups were found as a function of drug condition either in physiological or behavioral responses. Only the combination of diuretic and verapamil produced a deleterious effect on color discrimination, which suggests further study of commonly administered drug combination therapies in hypertension.

Behavioral performance effects of nifedipine in normotensive and renovascular hypertensive baboons

Behavioral performances of normotensive and hypertensive adult male baboons were tested before, during, and following chronic oral dosing with nifedipine. Performances during a five-color simultaneous match-to-sample task were measured during three dosing schedules (0.20, 0.68, and 1.14 mg/kg/day) and vehicle. Each dose was administered for 21 consecutive days preceded and followed by 14-day baseline and recovery periods, respectively. Choice reaction times increased by 191 ms over baseline at the 0.68 mg/kg dose. Choice reaction times above the 95th percentile (i.e., the slowest reaction times) were the most slowed by nifedipine. Accuracy of color matching was decreased at 0.20 and 0.68 mg/kg by an average range of 2-4%. The yellow and white stimuli were the most difficult to discriminate correctly, and were also the most impaired by nifedipine. Nifedipine's behavioral effects were not modulated by blood pressure changes because daily changes in choice reaction time and systolic blood pressure were not correlated, and hypertensive status did not determine the behavioral effects. Potential sources of nifedipine's behavioral performance effects are discussed, with blood pressure changes excluded as a probable mechanism.

Ethanol's effects on auditory thresholds and reaction times during the acquisition of chronic ethanol self-administration in baboons

Baboons were trained to ingest ethanol at successively higher ethanol concentrations using oral self-administration techniques. Concurrently, animal psychophysical procedures were employed to determine auditory thresholds and reaction times daily. Maximal consumption of ethanol occurred at concentrations of 6-8% (w/v). During the initial period of ethanol self-administration, both auditory reaction times and auditory thresholds became elevated as animals consumed larger amounts of ethanol. For both the threshold and reaction time measures, the degree of elevation was correlated with the amount of ethanol consumed. These correlations decreased, however, with continued ethanol consumption. The elevations in sensory and motor function recovered to near-baseline levels when ethanol was no longer available.

Matching to sample, blood pressure and hormonal effects of chronic enalapril in baboons

Sensory and behavioral performance of three normotensive and one renovascular hypertensive baboon was tested before, during and following chronic oral dosing with the angiotensin converting enzyme (ACE) inhibitor enalapril. Performance measurements during a five-color simultaneous matching to sample task were obtained during enalapril dosing of 0.18 and 0.61 mg/kg/day, and vehicle. Each dose was administered for 21 consecutive days preceded and followed by 14 baseline and recovery periods, respectively. BP from awake animals as well as serum ACE activity were measured. Systolic BPs decreased by a maximum of 6-8% (8 mmHg). ACE activity was decreased in a dose-dependent fashion by 54.01% and 81.63% for 0.18 mg/kg and 0.61 mg/kg doses, respectively. At 0.61 mg/kg, the duration of simple key-press motor behavior increased by 15% in the first week and then progressively returned to baseline levels. Systematic changes in choice reaction times or color discrimination accuracy were not observed. Although the renovascular hypertensive baboon displayed greater hypotension and ACE inhibition, behavioral effects were not significantly different from normotensive baboons. The present study extends to sensory functions the lack of adverse behavioral side-effects of enalapril.

Behavioral performance effects of nifedipine in normotensive baboons: single dosing

The effects of single oral doses of the calcium channel blocker nifedipine were assessed on performance of a simultaneous color match-to-sample task in three normotensive baboons. Both accuracy of color matching, and speed and latency of response were measured 30 min after administration of 0.10, 0.34, 0.57, and 1.7 mg/kg and vehicle, with each dose tested on three occasions in randomized order. Systolic and diastolic blood pressures also were measured after testing sessions. Maximal decreases in systolic blood pressures (mean of three subjects = -4.56 mmHg) were obtained after ingestion of the 0.57 mg/kg dose. Nifedipine produced dose-related changes in choice reaction times with a trend toward increased reaction times of approximately 5% obtained at 0.34 and 1.7 mg/kg. A reversal of effect was noted at 0.57 mg/kg such that smaller changes in reaction times were obtained, suggesting a lack of correlation between blood pressure and behavioral performance changes. These results indicate that nifedipine administered in single doses to patients with hypertensive crisis is unlikely to produce large impairments in these aspects of sensory and motor functioning.

Diazepam and delta-9-THC: contrasting effects on the discrimination of speech sounds in nonhuman primates

The adult male baboons were trained on a psychophysical procedure to discriminate five synthetic, steady-state vowel sounds (/a/, /ae/, /e/, /U/, and /c/) from one another. A pulsed train of one vowel comprised the reference stimulus during a session. Animals were trained to press a lever and release the lever only when this reference vowel sound changed to one of the comparison vowels. All animals learned the vowel discriminations rapidly and, once learned, performed the discriminations at the 95-100% correct level. The IM administration of diazepam (0.32, 1.0, 3.2, and 10.0 mg/kg) produced dose-dependent decrements in vowel discriminability. The diazepam-induced decrements in vowel discriminability were correlated with the degree of spectral frequency differences found among the different vowels, with lower vowel discriminability scores found for those vowels with smaller spectral differences from the reference vowel. In contrast, oral administration of delta-9-THC (0.32, 1.0, 3.2, and 5.6 mg/kg) produced no decrements in vowel discriminability.