Stress effects in the hippocampus: synaptic plasticity and memory

It is now well-documented that exposures to uncontrollable (inescapable and unpredictable) stress in adulthood can have profound effects on brain and behavior. Converging lines of evidence from human and animal studies indicate that stress interferes with subsequent performances on a variety of hippocampal-dependent memory tasks. Animal studies further revealed that stress impedes ensuing induction of long-term potentiation (LTP) in the hippocampus. Because the hippocampus is important for key aspects of memory formation and because LTP has qualities congruent to an information storage mechanism, it is hypothesized that stress-induced modifications in hippocampal plasticity contribute to memory impairments associated with stress. Recent studies provide evidence that the amygdala, a structure important in stress- and emotion-related behaviors, plays a necessary role in the emergence of stress-associated changes in hippocampal LTP and memory. Early life stress also alters hippocampal plasticity and memory in a manner largely consistent with effects of adult stress exposure. This review focuses on endocrine-system-level mechanisms of stress effects in the hippocampus, and how stress, by altering the property of hippocampal plasticity, can subsequently influence hippocampal memory.     

The lntergenerational transmission of family violence: The long-term effects of aggressive behavior

This paper examines the contention that family violence is passed down from generation to generation. The sample was primarily nonclinical and was composed of 14 clients of community guidance clinics and 82 members of a randomly selected control group. The primary hypothesis that individuals who are exposed to a high degree of physical punishment as children are more likely to resort to family violence as adults was supported. Studies of the modeling of aggression were examined to suggest factors which may mediate the hypothesized relationship. It was found that respondents who had grown up in an environment characterized by either low family warmth or high stress in combination with exposure to a high degree of parental punishment were more likely to use physical punishment in their own families. Also, family violence was more likely to be transmitted in same-sex rather than cross-sex linkages.     

Intergenerational effects of cocaine on maternal aggressive behavior and brain oxytocin in rat dams

Gestational cocaine treatment results in significantly increased maternal aggression towards an intruder by postpartum day six, while acute postpartum treatment dose dependently decreases maternal aggressive (MA) behavior. Both increased and decreased aggression in the cocaine-treated dams are correlated with either decreased or increased levels of oxytocin in the amygdala, respectively. The current study was an effort to determine whether the effect of gestational cocaine on maternal aggression is transient or would continue into the postpartum period; whether an intermittent cocaine treatment regimen, which incorporates gestational and postpartum intermittent cocaine treatment, would differ from chronic daily gestational treatment; and finally, whether next generation female offspring of cocaine-treated or control dams would have altered MA behavior and oxytocin system changes attributable to either prenatal drug exposure, rearing condition or both. We now report no increase in maternal aggression following chronic gestational treatment and significantly lower levels of aggression in intermittently treated dams on postpartum day eight, with no significant effects in either group on postpartum day 12. Young adult female offspring of the cocaine-treated and control dams, who reared their own natural litters and were tested on postpartum day eight for maternal aggression, had higher levels of maternal aggression towards an intruder attributable to both prenatal cocaine exposure and rearing condition. Higher aggression in cocaine-reared next generation dams was associated with lower levels of oxytocin in the amygdala. Intergenerational effects of cocaine were apparent with respect to aggression and oxytocin system changes.     

Long-lasting effects of inescapable-predator stress on brain tryptophan metabolism and the behavior of juvenile mice

The kynurenine (KYN) pathway, which is initiated by indoleamine 2,3-dioxygenase, is the main tryptophan (TRP) metabolic pathway. It shares TRP with the serotonin (5-HT) pathway. We investigated the influence of inescapable-predator (rat) stress on behavior and brain TRP metabolism in mice. Male ICR mice (4W) were exposed to 20-min inescapable-predator stress. Behavior on an elevated plus-maze, and TRP, KYN, and 5-HT levels in the prefrontal cortex, hippocampus, amygdala, and dorsal raphe nuclei were measured 1 and 4 weeks after stress exposure. Predator stress increased the number of open-arm entries (NOA) 4 weeks after stress exposure without altering the number of closed-arm entries (NCA). Thus, the open/closed-arm entry ratio (NOA/NCA) increased after stress exposure. Predator stress increased KYN levels in the prefrontal cortex (until 4 weeks after stress exposure) and dorsal raphe nuclei (for 1 week after stress exposure), decreased 5-HT levels in all brain regions (until 4 weeks after stress exposure). Thus, predator stress increased the KYN/5-HT ratio in all regions, in particular in the prefrontal cortex and hippocampus until 4 weeks after stress exposure. Predator stress shifted the balance between the KYN and 5-HT pathways to the KYN pathway, and induced behavioral disinhibition.     

Progesterone regulation of synaptic transmission and plasticity in rodent hippocampus

Ovarian hormones influence memory formation by eliciting changes in neural activity. The effects of various concentrations of progesterone (P4) on synaptic transmission and plasticity associated with long-term potentiation (LTP) and long-term depression (LTD) were studied using in vitro hippocampal slices. Extracellular studies show that the highest concentration of P4 tested (10(-6) M) decreased the baseline synaptic transmission and magnitude of LTP, but did not affect LTD. Intracellular studies suggest the P4 effect to be mediated, at least in part, by GABA(A) activity. These results establish a general effect of P4 on synaptic transmission, multiple forms of synaptic plasticity, and a possible mechanism of P4 action in hippocampus.     

Strategy-dependent changes in memory: Effects on behavior and brain activity

In the present study, an implicit strategy manipulation was used to explore the contribution of memory strategy to brain activation and behavioral performance. Participants were biased to use either a short-term (maintenance-focused) or long-term (retrieval-focused) memory strategy within a single memory task through manipulation of task context. In comparing directly matched trials across the different task contexts, we observed clear changes in both behavioral performance and brain activity across a network of regions located primarily within lateral and medial frontal cortex. These effects of the memory strategy manipulation suggest that when a retrieval-focused strategy is induced, mnemonic processes are preferentially engaged during the encoding period. In contrast, when a maintenance-focused strategy is induced, mnemonic processes are preferentially engaged during the delay and response periods. Taken together, the results imply that covert cognitive strategies play an important role in modulating brain activation and behavior during memory tasks.     

Unfixed action patterns: social behavior and the brain

The 2000 Karger Workshop: ‘Social Modulation of Brain and Behavior’, New Orleans, LA, USA, 3 November 2000.     

Linked lives: the intergenerational transmission of antisocial behavior

There is a strong assumption of intergenerational continuity in behavior patterns, including antisocial behavior. Using a 3-generation, prospective study design, we examine the level of behavioral continuity between Generation 2 (G2) and Generation 3 (G3), and the role of economic disadvantage and parenting behaviors as mediating links. We estimate separate models for G2 fathers and G2 mothers. Data are drawn from the Rochester Youth Development Study, a longitudinal study begun in 1988 during G2's early adolescence (n = 1,000), which has collected prospective data on G2, their parents (G1), and now their G3 children. Results show that intergenerational continuity in antisocial behavior is evident, albeit somewhat modest. Parenting styles and financial stress do play a mediating role, although their effects vary by G2's gender. In general, adolescent delinquency plays a larger role in linking the generations for G2 fathers, whereas parenting behaviors and financial stress play a larger role for G2 mothers.     

Asymmetric frontal brain activity and parental rejection predict altruistic behavior: Moderation of oxytocin effects

Asymmetric frontal brain activity has been widely implicated in reactions to emotional stimuli and is thought to reflect individual differences in approach–withdrawal motivation. Here, we investigate whether asymmetric frontal activity, as a measure of approach–withdrawal motivation, also predicts charitable donations after a charity’s (emotion-eliciting) promotional video showing a child in need is viewed, in a sample of 47 young adult women. In addition, we explore possibilities for mediation and moderation, by asymmetric frontal activity, of the effects of intranasally administered oxytocin and parental love withdrawal on charitable donations. Greater relative left frontal activity was related to larger donations. In addition, we found evidence of moderation: Low levels of parental love withdrawal predicted larger donations in the oxytocin condition for participants showing greater relative right frontal activity. We suggest that when approach motivation is high (reflected in greater relative left frontal activity), individuals are generally inclined to take action upon seeing someone in need and, thus, to donate money to actively help out. Only when approach motivation is low (reflected in less relative left/greater relative right activity) do empathic concerns affected by oxytocin and experiences of love withdrawal play an important part in deciding about donations.     

From synaptic transmission to cognition: an intermediary role for dendritic spines

Dendritic spines are cytoplasmic protrusions that develop directly or indirectly from the filopodia of neurons. Dendritic spines mediate excitatory neurotransmission and they can isolate the electrical activity generated by synaptic impulses, enabling them to translate excitatory afferent information via several types of plastic changes, including neoformation, disappearance, redistribution and changes in geometric shape. The fine line between normal and abnormal excitatory neurotransmission is mediated by the concerted action of glutamate-mediated stimulation and calcium ion entry into spines. Moreover, within the range of normal excitatory activity, dendritic spines undergo specific plastic changes to regulate different forms of afferent information that are often related to distinct modes of cognition-related electrophysiological stimulation, such as long-term potentiation or long-term depression.     

Executive functions in adolescence: inferences from brain and behavior

Despite the advances in understanding cognitive improvements in executive function in adolescence, much less is known about the influence of affective and social modulators on executive function and the biological underpinnings of these functions and sensitivities. Here, recent behavioral and neuroscientific studies are summarized that have used different approaches (cognition, emotion, individual differences and training) in the study of adolescent executive functions. The combination of these different approaches gives new insight into this complex transitional phase in life, and marks adolescence as not only a period of vulnerabilities, but also great opportunities in terms of training possibilities and interventions.