Biomedical subjects

Z M Nagy

Publications and source records attributed to Z M Nagy.

At least 19 recordsLinked to original sources

PubMed1979

The relationship between dendritic growth of cortical neurons and the ontogeny of conditioned and unconditioned reflex control.

Suppression of an infantile reflex (circling behavior) to electric shock in a straight-alley escape problem increased as a function of age and trials in male Swiss-Webster mice trained at 7, 9, or 11 days of age and retested 24 h later. Twenty-four hours retention of prior training, indicated by the superior performance of trained subjects relative to yoked-shock and age controls, was not evident until 9 days of age. Analyses of Golgi--Cox preparations of parieto-temporo-preoccipital cortices, taken immediately following testing, revealed that behavioral development was paralleled by age-related changes in apical, oblique, and basilar dendritic networks and number of apical dendritic spines of layer V pyramidal cells. Correlations between behavioral and histological measures, indicated no consistent association of retention capacity with any of the physiological measures. However, basilar dendritic growth was significantly correlated with unconditioned reflex control as well as initial learning ability.

Age Factors↗

PubMed1979

GABA-mediated behavioral inhibition during ontogeny in the mouse.

Although immature rats and mice generally demonstrate poor behavioral inhibitory capacities, some recent evidence may indicate the presence of substantial inhibitory control. The present experiment investigated the possibility that gamma-aminobutyric acid (GABA) systems may mediate some behavioral inhibition during early development. Mice 9-100 days old were injected with the GABA-elevating agent amino-oxyacetic acid (AOAA) and tested for behavioral activity. High levels of locomotor activity characteristic of immature control mice were attenuated following AOAA injection, whereas AOAA had little effect on the activity of adult mice. Moreover, AOAA produced a period of rebound hyperactivity for young but not for adult mice. These findings suggest that although GABA systems may mediate early behavioral inhibition, coordination between excitatory and inhibitory capacities matures slowly. In a second experiment the dopamine-beta-hydroxylase inhibitor FLA-63 prevented rebound hyperactivity in young mice pretreated with AOAA, suggesting that the excitatory component may be mediated by noradrenergic systems.

Aminooxyacetic Acid↗

PubMed1978

Relative aversion thresholds for shock in infant mice.

Using a spatial-preference technique, we tested separate groups of mice, 5, 7, 9, 11, 13, and 15 days of age, for escape and avoidance of a range of shock intensities administered from AC contant current and fixed impedance shock sources. With intensities ranging from 0 to .2 mA and 0 to 70 V for the respective sources, near asymptotic escape and avoidance were obtained at .1 mA and at 50 V for ages tested. Although few differences in the relative aversiveness of particular shock intensities were noted across ages with each source, the fixed impedance source produced more consistent avoidance than did the constant source. The findings suggest that the motivational properties of shock remain relatively constant throughout the early development of the mouse and that the technique employed in this study should prove useful in assessing possible age-related alterations in sensitivity to shock as a result of physiological or pharmacological manipulations.

Age Factors↗

PubMed1978

Emerging cholinergic mechanisms and ontogeny of response inhibition in the mouse.

Mice, 7, 11, 15, 19, and 85-115 (adult) days of age, served as subjects in experiments assessing effects of anticholinergics on the development of behavioral inhibition. The centrally active anticholinergic scopolamine produced a dose-dependent elevation in locomotor activity in 19-day-old and adult mice. Acquisition and retention of a step-off passive avoidance response (PAR) was initially studied in nondrugged subjects. Mice as young as 7 days of age learned and retained the PAR for 1 hr. Twenty-four-hour savings, however, were not observed until 19 days of age. Simple PAR performance deficits following scopolamine injection were first seen at 15 days of age. Mice in those age groups exhibiting 24-hr retention (19-day-olds and adults) were used to assess carry-over effects of scopolamine on retest. Only in the case of juveniles did scopolamine, injected prior to training, disrupt 24-hr retest performance. Since methylscopolamine, a peripherally active anticholinergic, had no effect on activity and PAR performance, it is assumed that scopolamine's effects were of central origin. The results suggest that behavioral suppression comes under cholinergic control during the second and third postnatal weeks but that cholinergic mechanisms may not mediate response inhibition uniformly throughout development.

Age Factors↗

PubMed1977

Development of learning and memory in mice genetically selected for differences in brain weight.

Mice selected for high (H), medium (M), and low (L) brain weight were trained to the goal arm opposite their preference in a shock-escape T-maze at 7, 9, 11, or 13 days of age. Twenty-four hours later, half of the trained groups at each age received additional training to the original goal, whereas the other half was trained to the opposite goal. Maturational control groups without prior training were trained on the selected retest days for the previously trained groups. Improvement in correct choice-point turns during training was suggested for the H-line by 9 days of age and by 11 days of age for the M- and L-lines. During retraining, H-line mice demonstrated 24-hr retention effects by 10 days of age, whereas 24-hr memory was not indicated for M- and L-lines at any of the ages investigated. These results indicate that the onsets of learning and memory were influenced by genes affecting brain weight, in that H-line mice demonstrated more rapid brain growth as well as heavier brain weights at every age studied as compared with M- and L-line mice which showed similar brain growth functions.

Age Factors↗

PubMed1977

Acquisition and retention of a passive-avoidance task as a function of age in mice.

In Experiment I groups of mice between 16 to 100 days of age were tested for retention of a passive-avoidance response between 1 min and 96 hr following a single training trial at 2 shock intensities. In general, although almost all age groups displayed reliable retention at all retest intervals, some retention losses were found among the youngest age groups at the longer retention intervals. Higher shock intensity resulted in longer retest latencies, primarily among the youngest mice. In Experiment II mice 16, 25, and 100 days of age were trained to criterion on the passive-avoidance task and retested on a single trial following retention intervals of 24, 96, 192, and 384 hr. Young mice exhibited severe retention losses relative to 100-day-old mice at the longer intervals, even though they did not show deficiencies in acquisition. Neurological maturity at the time of original training appears to account for the age-related memory differences.

Age Factors↗

PubMed1977

Cycloheximide produces adult-like retention deficits of prior learning in infant mice.

Utilizing a dosage of cycloheximide which was found to inhibit cerebral protein synthesis by almost 90% after injection, separate groups of 13-day-old mice received either cycloheximide or saline followed by 0 (control), 15, or 25 training trials in a discriminated shock-escape T-maze. Twenty-four hr later, each mouse was treated with cycloheximide or saline and tested for retention by an additional 25 trails in the T-maze. As reflected by correct choice-point turns, the results suggest that whereas salinetreated mice demonstrated reliable retention of prior learning, cycloheximide treated mice exhibited memory impairment; cycloheximide per se had no effect on performance during either original training or retest. A final experiment indicated that this memory impairment was not due to cycloheximide's general debilitating side effects at the time of retention testing. Taken together, these data suggest that protein synthesis inhibition during training impaired consolidation and/or retrieval processes involved in memory. The biochemical and behavioral effects following cycloheximide injection in 13-14-day-old mice in the present study parallel those reported with adult animals and lend indirect support to the hypothesis that the 24-hr memory capacity exhibited by these young mice reflects the early functioning of those processes involved in adult long-term memory.

Amnesia↗

PubMed1977

Undernutrition by rearing in large litters delays the development of reflexive, locomotor, and memory processes in mice.

In three experiments, the effects of early postnatal undernutrition on the ontogeny of several behavioral capacities of varying complexity were investigated in the mouse. Following birth, mouse pups in all experiments were reared in either "normally nourished" or "undernourished" conditions by maintaining litter sizes at 6 or 16, respectively. Experiments 1 and 2 examined the development of adultlike patterns of swimming behaviors and spontaneous locomotor activity, respectively, as a function of litter size. The maturation of both behavior patterns was delayed by about 2 days in the 16-litter mice. In Experiment 3, normally nourished and undernourished mice received 25 trials in a shock-escape T-maze at 9, 11, and 13 days of age, followed by similar retention tests 24 hr later. Although litter size had little effect upon correct turns at each age during training, mice reared in litters of six exhibited significant retention of prior training by 12 days of age, whereas comparable retention was not noted for the large litter mice until 14 days of age. Overall, these results suggest that nutritional deficits, imposed by rearing in large litters during the postnatal period of rapid central nervous system maturation, retard the development of behavioral capacities involving both unlearned and learned responses.

Age Factors↗

PubMed1976

Escape learning in infant mice as a function of drive level and drive shifts during acquisition.

Separate groups of 9-day-old Swiss-Webster mice began straight-alley escape training at .1 or .4 mA. After 12 trials, half of the mice in each group were shifted to .4 or .1 mA, respectively, whereas the remaining half continued at their original level for an additional 12 trials. Twenty-four hours later, half of each of the 4 shock-level groups were retested at .1 mA, half at .4 mA. The results indicated that those groups which made a large number of competing responses during early trials and showed a gradual reduction over training trials (.1-.1 and .1-.4) emitted the fewest number during retest at either shock level. In contrast, those groups with either limited (.4-.1) or no (.4-.4) opportunity to decrease competing responses during training showed evidence of poor (.4-.1) and no (.4-.4) retention of learned inhibition of that response. Running speed was clearly a performance measure, as it only reflected existing shock levels during both training and retention trials.

Age Factors↗

PubMed1976

Hypothermia causes adult-like retention deficits of prior learning in infant mice.

Nine-day-old S-W mice receiving deep body hypothermia or hyperthermia immediately after escape training were retested 1 or 24 hr later. Results indicated that hypothermia impaired 24-hr retention but had no effect upon 1-hr memory. Hyperthermia had no effect, with the mice demonstrating retention of the escape response at both retest intervals. In Experiment 2, administration of hypothermia or hyperthermia 23 hr after original training had no effect upon memory nor did either treatment produce motoric deficits upon retest 1 hr following thermal exposure. Experiment 3 indicated that hypothermia administered immediately after training produced retention deficits directly related to amount of body temperature reduction following hypothermia. These data are similar to those obtained with adult mice and suggest that memory processes occurring in 9-day-old mice may represent the onset of functioning of processes underlying adult long-term memory.

Age Factors↗

PubMed1976

Development of cholinergic inhibitory capacities in the hyperthyroid mouse.

The ontogeny of behavioral arousal and inhibition, as measured by spontaneous locomotor activity, was compared in four experiments for controls and mice injected with thyroxine as neonates. Mice treated with thyroxine at 1-3 days of age had higher activity levels at 10-15 days of age than controls, suggesting potentiation of arousal systems by the hormone treatment. Although thyroxine-accelerated development had no reliable effect upon the age at which peak activity occurred, scopolamine injections increased activity as early as 15 days of age in thyroxine-treated mice, whereas saline-treated or unhandled controls did not show a similar increase until 16-17 days of age. The findings were interpreted as indicating both a potentiation of arousal and a compensatory acceleration of cholinergic inhibitory capacities as a result of the neonatal hyperthyroidism. In addition, the importance of the behaviorally suppressive effects of a novel injection experience in the neonatal mouse was demonstrated.

Aging↗

PubMed1976

Neonatal thyroxine stimulation accelerates the maturation of both locomotor and memory processes in mice.

In two experiments mice were injected with thyroxine on Postnatal Days 1, 2, and 3, and the subsequent effects upon the development of the swimming reflex and the emergence of instrumental learning/memory processes were examined. In agreement with past studies, early thyroxine treatment accelerated the maturation of swimming capacities and general physical development compared with littermate controls receiving saline injections. In the second study, thyroxine- and saline-treated mice received 25 training trials on a shock-escape T-maze taks at 7, 9, 11, or 13 days of age with a retention test 24 hr later. The results indicated that while learning was equivalent within each of the ages between the treatment groups, onset of 24-hr retention capacity occurred approximately 2 days earlier in the thyroxine-treated mice than in controls. In addition, a performance deficit was observed in the thyroxine mice at the oldest age tested, in agreement with previous reports. The results of these experiments suggest that early hyperthyroidism results in earlier maturation of both locomotor and memory processes, followed by later performance deficits.

Age Factors↗

PubMed1976