The adolescent brain and age-related behavioral manifestations

Objective: Epidemiological studies indicate that experimentation with addictive drugs and onset of addictive disorders is primarily concentrated in adolescence and young adulthood. The authors describe basic and clinical data supporting adolescent neurodevelopment as a biologically critical period of greater vulnerability for experimentation with substances and acquisition of substance use disorders. Method: The authors reviewed recent literature regarding neurocircuitry underlying motivation, impulsivity, and addiction, with a focus on studies investigating adolescent neurodevelopment. Results: Adolescent neurodevelopment occurs in brain regions associated with motivation, impulsivity, and addiction. Adolescent impulsivity and/or novelty seeking as a transitional trait behavior can be explained in part by maturational changes in frontal cortical and subcortical monoaminergic systems. These developmental processes may advantageously promote learning drives for adaptation to adult roles but may also confer greater vulnerability to the addictive actions of drugs. Conclusions: An exploration of developmental changes in neurocircuitry involved in impulse control has significant implications for understanding adolescent behavior, addiction vulnerability, and the prevention of addiction in adolescence and adulthood.

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Developmental Neurocircuitry of Motivation in Adolescence: A Critical Period of Addiction Vulnerability

http://vaccinepapers.org/wp-content/uploads/Brain-development-in-rodents-and-humans1.pdf

Brain development in rodents and humans: Identifying benchmarks of maturation and vulnerability to injury across species

http://www.arts.uwaterloo.ca/%7eraha/CogSci600_web/Readings/wainwright4.pdf

Trajectories of brain development: point of vulnerability or window of opportunity?

Pubertal transitions in health.

The behavior and psychopharmacological sensitivity of periadolescent rats are examined in this review. Periadolescent rats are hyperactive and engage in more conspecific play behavior than younger or older rats. When compared with other-aged rats, periadolescents exhibit enhanced performance in simple active-avoidance learning tasks, but perform poorly in more complex appetitive and avoidance learning tasks in which increases in locomotor activity do not improve performance, perhaps as a result of age-specific alterations in selective attention or stimulus processing. Such behavioral "anomalies" of periadolescent animals observed in traditional laboratory situations may be in some way adaptive when considered in the context of the animals' natural habitat. In terms of psychopharmacological responsiveness, periadolescent rats, when compared with younger or older animals, are less sensitive to catecholaminergic agonists but are more responsive to the catecholaminergic antagonist haloperidol. This pattern of psychopharmacological sensitivity suggests that the catecholaminergic systems may be temporarily hyposensitive during the periadolescent period. Evidence is presented that a negative feedback system in the form of dopamine autoreceptors may become functionally mature in mesolimbic brain regions during the periadolescent period. The possibility is presented that maturation of these self-inhibitory autoreceptors might result in a temporary decrease in the efficacy of mesolimbic dopamine projections, perhaps contributing to the psychopharmacological and behavioral characteristics of periadolescent animals. In support of this suggestion, evidence is reviewed indicating that the behavior of adult animals with lesions of the ventral tegmental area, a region containing cell bodies from which these mesolimbic dopaminergic projections originate, resembles that of periadolescent rats.

Periadolescence: Age-dependent behavior and psychopharmacological responsivity in rats

Nutritive deprivation, suckling deprivation, gastronintestinal fill, and milk availability contribute to the control of sucking (as measured by jaw-muscle electromyograph) and ingestion of milk (provided via a tongue cannula) in 11-13-day-old rat pups. Depriving pups of the opportunity to suckle reliably increases subsequent sucking and milk intake. Intraoral delivery of milk also increases sucking, regardless of whether or not pups are suckling-deprived. Gastrointestinal preloads have no effect on sucking if pups are not receiving milk, but reliably block the increase in sucking which accompanies milk delivery. Finally, milk delivered to the pup's mouth prior to a suckling opportunity can either enhance or attenuate subsequent sucking depending on whether pups are allowed to consume milk while suckling. In all cases, a particular mode of sucking ("rhythmic" sucking) is most affected by experimental manipulation, and appears to be an important component of the pup's ingestive behavior.

The role of intraoral and gastrointestinal cues in the control of sucking and milk consumption in rat pups.

Electromyographic patterns associated with nonnutritive sucking in 11-13-day-old rat pups.

Electrophysiological recordings showed that 2-wk-old rats are actually asleep 66% of the time while suckling on the dam. The pups are no more likely to be awake while on the nipple than between nursing bouts. Sucking behavior, recorded electromyographically, occurred during sleep as well as during wakefulness. Pups were found to be asleep just prior to the dam's periodic milk ejections (ME) in 100% of 33 recorded instances and were briefly awakened by the ME, but 60% were asleep again within 30 s. These studies demonstrate the embedding of a vital early behavior pattern in the states of sleep.

Suckling in the rat: evidence for patterned behavior during sleep.

This study describes differences in feeding interactions in preterm and full-term infants shortly after birth (T1) and again at one month of age (T2). A group of “healthy” preterm infants (M GA=35 weeks) and a group of full-term infants were observed during a bottle-feed with their mothers. The Nursing Child Assessment of Feeding Scale (NCAFS) was administered, and mothers were asked to complete the Neonatal Perception Inventories (NPI) to assess perceptions of their infants. At T1 both preterm infants and their mothers had lower interactive scores on the NCAFS than full-term infants. One month later (T2), preterm mothers' scores had improved and were no longer significantly different from those of fullterm mothers, while differences between preterm and full-term infants, although diminished, remained significant. On the NPI, mothers of preterm and full-term infants showed few differences in preception of their infants. It is suggested that preterm and full-term dyads may face different tasks in their mutual adaptations during the first month of life.

Stephen C. Brake

Papers

Periadolescence: Age-dependent behavior and psychopharmacological responsivity in rats

The role of intraoral and gastrointestinal cues in the control of sucking and milk consumption in rat pups.

Electromyographic patterns associated with nonnutritive sucking in 11-13-day-old rat pups.

Suckling in the rat: evidence for patterned behavior during sleep.

Mother-infant feeding interactions in preterm and full-term infants