Age differences in augmenting/reducing of occipital visually evoked potentials.
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Adolescent↗
Biomedical subjects
E W Snyder
Publications and source records attributed to E W Snyder.
Pattern reversal evoked potential amplitudes: life span changes.
Pattern reversal evoked potentials (PREPs) were recorded from people whose ages ranged from 4 to 90 years. Dramatic reductions in PREP amplitudes occurred between childhood and adolescence. These changes were most evident in females. Following adolescence there were no significant changes in amplitudes, even to old age. Latencies, on the other hand, have been shown to change most dramatically between adulthood and old age. PREP amplitudes and latencies, therefore, appear to provide different and unique information regarding development and aging. One cannot ignore PREP amplitudes without sacrificing information regarding early development.
Adolescent↗
Phencyclidine-induced alterations of rat electrophysiology.
Phencyclidine (PCP) at high doses causes both excitation and depression in the rat. The visual evoked potential (VEP) was measured in rats following PCP administration in doses ranging from 1 mg/kg to 56 mg/kg. Consistent lengthening of VEP latencies suggests that PCP has an unusual inhibitory effect on visual function in the presence of the excitatory signs of bilaterally synchronous cortical spiking. The epileptogenic properties of PCP are quite evident in rats.
Animals↗
Methadone-induced changes in the visual evoked response recorded from multiple sites in the cat brain.
Visual evoked responses (VERs) and EEG were recorded following the i.p. administration of five doses of methadone (0.5--4 mg/kg) to 12 adult cats, which were implanted with cortical and subcortical electrodes. Additional cats, subjected to the same drug regimen, were used to evaluate plasma methadone concentrations. Doses of methadone that produced plasma concentrations between 80 and 190 ng/ml differentially affected VERs recorded from cortical and subcortical sites. Of the subcortical structures evaluated, the limbic system, specifically the hippocampus, was the most sensitive to the effects of the drug. These effects appeared to be primarily depressant. Responses recorded from the reticular formation and centromedian were affected only by the highest dose of methadone, while VERs recorded from cortical sites were reliably altered following the two highest doses and appeared to reflect both excitation and depression. Behavioral changes, however, were clearly evidenced in some cats at lower doses of methadone. Therefore, the data suggest (1) that those structures evaluated electrophysiologically did not reflect the full force of the drug's action as evidenced by its effect on behavior, (2) that cortical and subcortical recording sites have differential sensitivities, and (3) that one clearly defined, principal size of action of methadone is absent in the cat.
Animals↗
Ontogeny of the visual evoked response in the stump-tailed macaque.
Visual evoked responses (VER's) of stump-tailed macaques were studied from birth to 80 weeks in an attempt to establish the utility of this species as a model of human neurophysiological development. Although human subjects and monkeys share a unique complexity of the VER at birth, the postnatal development of their VER's does not appear to follow a parallel sequence. The relatively dynamic nature of the VER during the 1st few weeks in a monkey's life may limit the usefulness of this species as a model of human development. The rapid changes in the VER of the developing monkey and the observation that these changes continue beyond 2 years of age should be considered in studies of the VER in which repeated measures are obtained over a prolonged period of time.
Animals↗
Visual evoked potentials in monkeys.
Visual evoked potentials (VEPs) were recorded from 2 cortical sites in stump-tailed macaques. VEPs recorded from striate cortex were basically consistent between animals (especially at low light intensity), remained remarkably stable over time, and compared favorably to VEPs reported by other investigators. We concluded that the VEP recorded from the striate cortex of day-active monkeys consists of 5 major peaks within the first 250 msec. The potentials recorded from post-central gyrus were simpler and more individualized and did not show intensity-related latency changes or increases in inter-subject variability. However, amplitudes of potentials recorded from both electrode placements increased with light intensity apparently reflecting the amplitude of individual potentials rather than the variability of these potentials from which the average VEPs were derived.
Animals↗
Sustained ingestion of methadone and the sleep of monkeys.
Methadone HCl was administered daily to four stump-tailed macaques. The animals' sleep was periodically examined throughtout a year of methadone maintenance and, in two animals, during eight months of withdrawal. REM sleep was substantially decreased by methadone treatment and gradually returned to predrug values over a 6- to 8-month period of maintenance. Measures of non-REM sleep and awakenings showed similar disruption with no return to predrug values. These changes were not correlated with alterations in plasma-methadone concentrations. REM sleep rebound occurred temporarily upon drug withdrawal in two animals, but no consistent sleep disruption was apparent during the subsequent eight months. Contrary to some suggestions, therefore, tolerance to the sleep-disruptive effects of the drug may be specific and incomplete, and extended REM rebound upon withdrawal is not a universal response.
Animals↗
Sawtooth waves: concomitants of rapid eye movement sleep in monkeys.
Sawtooth waves, 2--3 c/sec activity of at least 40 micro V, occurred primarily during clusters of REMs in stump-tailed macaques. On the average the activity began well after the onset of REMs but occasionally occurred soon before or immediately after a cluster of REMs. The activity was clearly defined but occupied less than 0.6% of an 8-h sleep record. A sawtooth burst was, on the average, 7.5 sec in duration.
Animals↗
Sudden toxicity of methadone in monkeys: behavioral and electrophysiological evidence.
A sudden and potentially lethal toxic reaction to a previously well-tolerated maintenance dose of methadone occurred in 4 of 6 monkeys. The reaction was characterized by gross behavioral and respiratory depression and a marked attenuation of both early and late components of the visual evoked response with an increase in most latencies. The nature of the evoked response alteration suggests a widespread central nervous system depressant effect of the drug during toxicity. Concomitant with the toxic reactions were dramatic increases in plasma methadone concentrations. Therefore the observed changes in sensitivity to methadone would appear to be the consequence of a sudden shift in pharmacokinetics resulting in toxic plasma concentrations.
Animals↗
Visual evoked response and behavioral correlates of plasma methadone concentrations in cats.
Twelve cats were implanted with cortical and depth electrodes. After they recovered from the operation, visual evoked responses (VERs) were recorded at 20 min following saline and methadone (0.5, 1, 2, 3, 4 mg/kg) administered IP in a semi-random order to each cat. Four other cats were similarly drugged and plasma was obtained for radioimmunoassay of methadone content. At the three lowest dose levels behavioral excitation and salivation were evident in some cats, while their VER configuration remained essentially unaltered and plasma methadone was barely measurable. Following the 3 and 4 mg/kg doses plasma methadone concentration increased dramatically, behavioral excitation and salivation were evident in most cats and VERs were reliably altered. The VER alterations, consisting of amplitude attenuation and a decrease in some latencies, were restricted to secondary VER components occurring between 50 and 100 msec despite the animals' extreme behavioral excitation. These results suggest that the reticular formation is not a principal site of the drug's effect.
Animals↗
Effects of chronic oral methadone on hepatic microsomal drug metabolism in monkeys.
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Animals↗
A miniature, readily available electrode pedestal for recording cerebral and other electrophysiological activity from several species.
A miniature, commercially available electrode pedestal with prewired and prenumbered leads was designed. It possesses long-term electrical reliability and can be applied to a wide range of animal species. It can be easily modified to record electroencephalograms, evoked responses, and related physiological measurements. The device is relatively small, with keyed and lock-down parts, and is resistant to damage.
Animals↗
Sustained ingestion of delta 9-tetrahydrocannabinol and the operant behavior of stump-tailed macaques.
Three stump-tailed macaques were trained to press a lever for liquid reinforcement on a tandem schedule which required the animal to delay responding for at least 30 sec after each reinforcer. If the animal responded during that interval, a clock was reset thus re-establishing the delay requirement. If he delayed responding appropriately, the monkey was shifted to a fixed-interval schedule of 135 sec duration. The FI component was terminated with a drop of flavored liquid at which point the delay requirement began anew. Following a stable baseline performance, two monkeys received 2 mg/kg of THC orally every third day for 90 days with the placebo administered on intervening days. The third animal received the placebo throughout testing. Each monkey's performance was described in terms of response rate and response patterning between reinforcers. Despite the sustained ingestion of THC neither animal showed appreciable change in test behavior attributable to tolerance to the drug. Although the drug continued to have a powerful effect throughout testing on the days it was administered, there was no evidence of any consistent or cumulative drug effect on placebo-day performance.
Animals↗