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Biomedical subjects

W Isaac

Publications and source records attributed to W Isaac.

11 recordsLinked to original sources
PubMed1991

The effects of occipital ablation on a conditioned visual avoidance learning task in young and old rats.

Previous data indicate that learning of a conditioned visual avoidance task following simultaneous complete bilateral occipital ablations is affected by the age of the organism as well as the postoperative recovery period. The present study investigated the performance of the avoidance task, following complete occipital ablations, in young and older rats given two different recovery intervals. Young rats given 10 days to recover performed more poorly than the young control animals; given 20 days to recover, young rats performed comparable to controls. Older rats given 10 days to recover performed significantly better than the controls; given 20 days to recover, older rats did not show a decrease in performance. The present finding is consistent with previous data which show that the occipital cortex exerted an inhibitory effect on the learning ability of the avoidance task in older rats, which, upon removal, enhanced the performance of these rats on the task.

Aging↗
PubMed1979

Effects of d-amphetamine and methylphenidate upon auditory threshold in the squirrel monkey.

The effects of d-amphetamine sulfate and methylphenidate hydrochloride on auditory thresholds in ten squirrel monkeys were examined using a 4.2 kHz stimulus in a free field. The results indicated that d-amphetamine raised auditory thresholds but methylphenidate did not alter the thresholds. The elevation of sensory thresholds by d-amphetamine was in agreement with previous studies suggesting that the drug acts as a behavioral depressant in diurnal animals.

Animals↗
PubMed1977

Effects of amphetamine and methylphenidate on fixed-interval responding in the squirrel monkey.

The effects of oral doses of d-amphetamine and methylphenidate on a fixed-interval operant response were studied in four young male squirrel monkeys. A fixed-interval of 80 sec with a limited hold of 20 sec was used. Methylphenidate produced no observable changes in behavior, while d-amphetamine produced dose related changes in both the rate of responding and the temporal patterning of responses. Since dose levels used included, and exceeded, human clinical dosages, the present findings may have implications for future research involving the clinical use of these drugs.

Animals↗
PubMed1977

Differences in placebo effects.

Constant volume injections of water and saline were evaluated in terms of their effects upon locomotor activity in the rat. Both solutions produced an overall decrease in activity and were found to be nonequivalent in their effect.

Animals↗
PubMed1977

Altering arousal in humans by varying ambient sensory conditions.

Reaction times of 6 male and 6 female college students were used as a measure of arousal under different levels of ambient sensory stimulation. Subjects were tested under conditions of light-quiet, light-noise, dark-quiet and dark-noise with a non-signalled reaction-time task using a tactile stimulus. All sensory conditions were presented to each subject in a counterbalanced order and replicated in a second session 3 to 8 wk. later. Significant main effects were noise and replication. Improvement in performance across replication was related to the sex of the subject. White noise and level of illumination interacted to produce the typical U-shaped function. Results are discussed in terms of their relevance for research using behavioral and physiological measures of arousal.

Acoustic Stimulation↗
PubMed1976

The effects of d-amphetamine and illumination on behaviors of the squirrel monkey.

A behavioral classification and scoring procedure was developed for observing specific responses of squirrel monkeys. The observational procedure along with the photocell method of measuring general activity were then employed to examine the effects of illumination and d-amphetamine on the behavior of squirrel monkeys. It was found that d-amphetamine decreased the incidence of those behaviors seen normally under light conditions while it increased the frequency of behaviors normally seen in the dark.

Animals↗
PubMed1975

The effects of age and illumination on the dose-response curves for three stimulants.

The dose-response relationships for three stimulants have been explored. These drugs have been shown to differ in potency and, with successive doubling of doses, have been found to have dose-response curves of differing slopes. In addition, the relationship between dose and activity level was not the same for younger and older rats. The relationship between dosage of both d-amphetamine and methylphenidate and locomotor activity was not the same in the light and the dark. The latter finding suggests a difference between these two stimulants and the third stimulant studied, caffeine, whose effects where unaltered by ambient illumination level.

Adaptation, Psychological↗
PubMed1975

Behavioral effects of d-amphetamine and caffeine in the squirrel monkey.

Four Squirrel monkeys were trianed on a bar-press response with reinforcement available every 80 sec. The effects of d-amphetamine and caffeine upon this response were studied in both light and dark. In addition to differential drug effects it was found that both illumination and sex of the subjects were important variables.

Analysis of Variance↗
PubMed1975

Stimulants and lesions of the substantia nigra and red nucleus.

The interaction of altered activity levels by stimulants and brainstem lesions was examined. Lesions of the substantia nigra and red nucleus significantly increased activity over control levels in albino rats. The stimulant action of d-amphetamine and methylphenidate was additive with lesion effects. In addition, stimulants disrupted the normal light-dark relationship with activity while the lesions did not. It is suggested that there are two functionally separate systems regulating locomotor activity.

Animals↗