Differential effects of l-amphetamine on ontogeny of active avoidance, intertrial responses, and locomotor activity

Cognitive training during infancy and adolescence accelerates adult associative learning: critical impact of age, stimulus contingency and training intensity

A growing body of evidence supports the hypothesis that juvenile cognitive training shapes neural networks and behavior, and thereby determines the adult's capacity for learning and memory. In particular, we have shown that infant rats, even though they do not develop an active avoidance strategy in a two-way active avoidance task, show as adults accelerated learning in the same learning task. This indicates that a memory trace was formed in the infant rats, which most likely is recruited during adult training. To identify the learning conditions, which are essential prerequisites to form this memory trace in infancy or adolescence, we investigated the critical impact of: (i) age, (ii) CS-UCS contingency, and (iii) pre-training intensity on this facilitating effect. We observed: (i) an age-dependent improvement of avoidance learning, (ii) that the beneficial impact of infant or adolescent pre-training on adult learning increases with the age at pre-training, (iii) that CS-UCS contingency during infant pre-training was most efficient to accelerate adult learning, (iv) that pre-training intensity (i.e. number of pre-training trials) was positively correlated with the pre-training induced acceleration of adult learning, and (v) that infant rats, compared to adolescent rats, need a higher training intensity to show learning improvement as adults. These results indicate that infant rats develop a goal-oriented escape strategy, which during adult training is replaced by an avoidance strategy, facilitated by the recruitment of the CS-UCS association, which has been learned during infant training. Based on these results the future challenge will be to identify the specific contribution of prefronto-limbic circuits in infant and adult learning in relation to their functional maturation.

A differential sex effect of amphetamine on exploratory behavior in maturing mice

The effects of amphetamine (5-20 mg/kg) were studied 60 min after injection in mice aged 2, 3, 4 and 6 weeks postpartum. Exploratory behavior as indicated by the "head poke" test was depressed at all ages, but appeared to be relatively uncomplicated by other effects at the 5 mg/kg dose. At 4 and 6 weeks control females showed significantly greater activity than males, and amphetamine produced a greater reduction for control levels than in males.

Behavioral effects of D-amphetamine in developing cats

The development of the behavioral effects of amphetamine was assessed in kittens of 1-53 days of age. Amphetamine-induced increases in locomotion occurred when animals were beyond 35 days of age. Stereotypic behavior was induced at all ages tested but the predominant type of stereotypy was age-related. From 1 to 14 days amphetamine induced licking. Pendular head movements occurred when animals were under 35 days. At 14 days of age darting, a response consisting of rapid pacing and turning began to occur. Tracking, a series of horizontal and vertical head movements also began to occur after 14 days. The adult response of vertical and horizontal head movements became most prominent after 35 days.

Differential effects of d-amphetamine and scopolamine on the ontogeny of rearing

Although rearing is ontogenetically an important behavior, very little is known about the neural bases of rearing. The role development of catecholaminergic and cholinergic neurons play in the ontogeny of rearing was investigated by examining rearing in infant, adolescent, and adult rats following various doses of d-amphetamine (an indirectly acting catecholaminergic agonist) and scopolamine (a cholinergic muscarinic receptor antagonist). d-Amphetamine increased rearing in infants but not in adolescents and adults. These findings suggest that activation of catecholaminergic neurons increases rearing in infants but not in adolescents or adults. Scopolamine increased rearing in adolescents and adults but not in infants, indicating that blocking transmission of cholinergic neurons increases rearing in only older rats.