Asymmetrical influence of mesocortical dopamine depletion on stress ulcer development and subcortical dopamine systems in rats: implications for psychopathology

Prenatal Exposure to Bisphenol A and/or Diethylhexyl Phthalate Impacts Brain Monoamine Levels in Rat Offspring

This study examines the sex-specific effects of gestational exposure (days 6-21) to endocrine-disrupting chemicals such as bisphenol A (BPA), diethylhexyl phthalate (DEHP), or their combination on brain monoamine levels that play an important role in regulating behavior. Pregnant Sprague-Dawley rats were orally administered saline, low doses (5 µg/kg BW/day) of BPA or DEHP, and their combination or a high dose (7.5 mg/kg BW/day) of DEHP alone or in combination with BPA during pregnancy. The offspring were subjected to a behavioral test and sacrificed in adulthood, and the brains were analyzed for neurotransmitter levels. In the paraventricular nucleus, there was a marked reduction in dopamine levels (p < 0.01) in male offspring from the BPA, DEHP, and B + D (HD) groups, which correlated well with their shock probe defensive burying times. Neurotransmitter changes in all brain regions examined were significant in female offspring, with DEHP (HD) females being affected the most, followed by the B + D groups. BPA and/or DEHP (LD) increased monoamine turnover in a region-specific manner in male offspring (p < 0.05). Overall, prenatal exposure to BPA, DEHP, or their combination alters monoamine levels in a brain region-specific, sex-specific, and dose-dependent manner, which could have implications for their behavioral and neuroendocrine effects.

Preventing prefrontal dysfunction by tDCS modulates stress-induced creativity impairment in women: an fNIRS study

Stress is a major external factor threatening creative activity. The study explored whether left-lateralized activation in the dorsolateral prefrontal cortex manipulated through transcranial direct current stimulation could alleviate stress-induced impairment in creativity. Functional near-infrared spectroscopy was used to explore the underlying neural mechanisms. Ninety female participants were randomly assigned to three groups that received stress induction with sham stimulation, stress induction with true stimulation (anode over the left and cathode over the right dorsolateral prefrontal cortex), and control manipulation with sham stimulation, respectively. Participants underwent the stress or control task after the transcranial direct current stimulation manipulation, and then completed the Alternative Uses Task to measure creativity. Behavioral results showed that transcranial direct current stimulation reduced stress responses in heart rate and anxiety. The functional near-infrared spectroscopy results revealed that transcranial direct current stimulation alleviated dysfunction of the prefrontal cortex under stress, as evidenced by higher activation of the dorsolateral prefrontal cortex and frontopolar cortex, as well as stronger inter-hemispheric and intra-hemispheric functional connectivity within the prefrontal cortex. Further analysis demonstrated that the cortical regulatory effect prevented creativity impairment induced by stress. The findings validated the hemispheric asymmetry hypothesis regarding stress and highlighted the potential for brain stimulation to alleviate stress-related mental disorders and enhance creativity.

Dopamine receptor activation elicits a possible stress-related coping behavior in a wild-caught songbird

Animals experience stress throughout their lives and exhibit both physiological and behavioral responses to cope with it. The stress response can become harmful when prolonged and increasing evidence suggests that dopamine plays a critical role in extinguishing the stress response. In particular, activation of the D2 dopamine receptor reduces glucocorticoids and increases coping behavior, i.e., behavioral responses to adverse stimuli that reduce the harmful effects of stress. However, few studies have examined the effects of dopamine on the stress responses of wild species. We therefore tested the hypothesis that activation of the D2 dopamine receptor influences coping-like behavior in a wild-caught species. We recorded behavior of house sparrows (Passer domesticus) before and after they received injections of D2 dopamine agonists, D2 dopamine antagonists, or saline. House sparrows are common in urban environments and understanding how they cope with stress may help us better understand how animals cope with urban stressors. We found that the birds significantly increased biting of inanimate objects after the agonist but there was no change following the antagonist or saline. The biting of inanimate objects may be a mechanism of behavioral coping. This change in biting behavior was not correlated with general movement. This study supports the hypothesis that D2 dopamine receptor activation is involved in the regulation of the stress response in a wild bird.

Functional lateralization in the prefrontal cortex of dopaminergic modulation of memory consolidation

There is increasing evidence of functional lateralization within the rat brain. Here, we have examined the lateralization of dopamine (DA) function in the medial prefrontal cortex (PFC) in relation to memory consolidation in the novel object recognition test (NOR). Male Wistar rats received single bilateral or unilateral injections into prelimbic-PFC of agonists (SKF81297; 0.2 µg, quinpirole; 1 µg, SB277,011; 0.5 µg) and antagonists (SCH23390; 3 µg, L-741,626; 1 µg, 7-OH-DPAT; 3 µg) at DA D1, D2, or D3 receptors, immediately following the exposure trial in the NOR, and were tested either 1 or 24 h later for discrimination between a novel and a familiar object. As previously reported, bilateral injection of a D1 antagonist (SCH23390, 3 µg/side), a D2 antagonist (L-741,626, 1 µg/side) or a D3 agonist (7-OH-DPAT, 3 µg/side) impaired NOR at 1 h, while a D1 agonist (SKF81297, 0.2 µg/side), a D2 agonist (quinpirole, 1 µg/side) or a D3 antagonist (SB277,011, 0.5 µg/side) improved NOR at 24 h. The same effects were seen with left-sided unilateral injections. No effects were seen with right-sided unilateral injections. Endogenous DA release in the prelimbic-PFC promotes memory consolidation in the NOR, but only on the left side of the brain.

Interhemispheric regulation of the rat medial prefrontal cortical glutamate stress response: role of local GABA- and dopamine-sensitive mechanisms

RATIONALE

We previously reported that stressors increase medial prefrontal cortex (PFC) glutamate (GLU) levels as a result of activating callosal neurons located in the opposite hemisphere and that this PFC GLU stress response is regulated by GLU-, dopamine- (DA-), and GABA-sensitive mechanisms (Lupinsky et al. 2010).

OBJECTIVES

Here, we examine the possibility that PFC DA regulates the stress responsivity of callosal neurons indirectly by acting at D₁ and D₂ receptors located on GABA interneurons.

METHODS

Microdialysis combined with drug perfusion (reverse dialysis) or microinjections was used in adult male Long-Evans rats to characterize D₁, D₂, and GABA_B receptor-mediated regulation of the PFC GABA response to tail-pinch (TP) stress.

RESULTS

We report that TP stress reliably elicited comparable increases in extracellular GABA in the left and right PFCs. SCH23390 (D₁ antagonist; 100 μM perfusate concentration) perfused by reverse microdialysis attenuated the local GABA stress responses equally in the left and right PFCs. Intra-PFC raclopride perfusion (D₂ antagonist; 100 μM) had the opposite effect, not only potentiating the local GABA stress response but also causing a transient elevation in basal (pre-stress) GABA. Moreover, unilateral PFC raclopride microinjection (6 nmol) attenuated the GLU response to TP stress in the contralateral PFC. Finally, intra-PFC baclofen perfusion (GABA_B agonist; 100 μM) inhibited the local GLU and GABA stress responses.

CONCLUSIONS

Taken together, these findings implicate PFC GABA interneurons in processing stressful stimuli, showing that local D₁, D₂, and GABA_B receptor-mediated changes in PFC GABA transmission play a crucial role in the interhemispheric regulation of GLU stress responsivity.

Hemispheric lateralization of resting-state functional connectivity of the ventral striatum: an exploratory study

Resting-state functional connectivity (rsFC) is widely used to examine cerebral functional organization. The ventral striatum (VS) is critical to motivated behavior, with extant studies suggesting functional hemispheric asymmetry. The current work investigated differences in rsFC between the left (L) and right (R) VS and explored gender differences in the extent of functional lateralization. In 106 adults, we computed a laterality index (fcLI) to query whether a target region shows greater or less connectivity to the L vs R VS. A total of 45 target regions with hemispheric masks were examined from the Automated Anatomic Labeling atlas. One-sample t test was performed to explore significant laterality in the whole sample and in men and women separately. Two-sample t test was performed to examine gender differences in fcLI. At a corrected threshold (p < 0.05/45 = 0.0011), the dorsomedial prefrontal cortex (dmPFC) and posterior cingulate cortex (pCC) showed L lateralization and the intraparietal sulcus (IPS) and supramarginal gyrus (SMG) showed R lateralization in VS connectivity. Except for the pCC, these findings were replicated in a different data set (n = 97) from the Human Connectome Project. Furthermore, the fcLI of VS-pCC was negatively correlated with a novelty seeking trait in women but not in men. Together, the findings may suggest a more important role of the L VS in linking saliency response to self control and other internally directed processes. Right lateralization of VS connectivity to the SMG and IPS may support attention and action directed to external behavioral contingencies.

Mastication as a Stress-Coping Behavior

Exposure to chronic stress induces various physical and mental effects that may ultimately lead to disease. Stress-related disease has become a global health problem. Mastication (chewing) is an effective behavior for coping with stress, likely due to the alterations chewing causes in the activity of the hypothalamic-pituitary-adrenal axis and autonomic nervous system. Mastication under stressful conditions attenuates stress-induced increases in plasma corticosterone and catecholamines, as well as the expression of stress-related substances, such as neurotrophic factors and nitric oxide. Further, chewing reduces stress-induced changes in central nervous system morphology, especially in the hippocampus and hypothalamus. In rodents, chewing or biting on wooden sticks during exposure to various stressors reduces stress-induced gastric ulcer formation and attenuates spatial cognitive dysfunction, anxiety-like behavior, and bone loss. In humans, some studies demonstrate that chewing gum during exposure to stress decreases plasma and salivary cortisol levels and reduces mental stress, although other studies report no such effect. Here, we discuss the neuronal mechanisms that underline the interactions between masticatory function and stress-coping behaviors in animals and humans.

Chronic stress alters the dendritic morphology of callosal neurons and the acute glutamate stress response in the rat medial prefrontal cortex

We have previously reported that interhemispheric regulation of medial prefrontal cortex (PFC)-mediated stress responses is subserved by glutamate (GLU)- containing callosal neurons. Evidence of chronic stress-induced dendritic and spine atrophy among PFC pyramidal neurons led us to examine how chronic restraint stress (CRS) might alter the apical dendritic morphology of callosal neurons and the acute GLU stress responses in the left versus right PFC. Morphometric analyses of retrogradely labeled, dye-filled PFC callosal neurons revealed hemisphere-specific CRS-induced dendritic retraction; whereas significant dendritic atrophy occurred primarily within the distal arbor of left PFC neurons, it was observed within both the proximal and distal arbor of right PFC neurons. Overall, CRS also significantly reduced spine densities in both hemispheres with the greatest loss occurring among left PFC neurons, mostly at the distal extent of the arbor. While much of the overall decrease in dendritic spine density was accounted by the loss of thin spines, the density of mushroom-shaped spines, despite being fewer in number, was halved. Using microdialysis we found that, compared to controls, basal PFC GLU levels were significantly reduced in both hemispheres of CRS animals and that their GLU response to 30 min of tail-pinch stress was significantly prolonged in the left, but not the right PFC. Together, these findings show that a history of chronic stress alters the dendritic morphology and spine density of PFC callosal neurons and suggest a mechanism by which this might disrupt the interhemispheric regulation of PFC-mediated responses to subsequent stressors.

Mesocortical dopamine depletion and anxiety-related behavior in the rat: sex and hemisphere differences

The mesocortical dopamine (DA) system of the rat plays an important role in prefrontal cortex (PFC) regulation of stress and emotion and exhibits functional hemispheric asymmetry for such processing. Since few studies examine sex differences in this context, we compared the effects of left vs. right unilateral PFC DA depletion in males and females in several behavioral situations associated with anxiety or aversion. Adult rats received unilateral injections of 6-hydroxydopamine (6-OHDA) or vehicle in the ventromedial (vm) PFC. Behavioral tests included a predator odor burying test, elevated plus maze and sucrose consumption with simple taste aversion. Tissue analysis confirmed that vmPFCs injected with 6-OHDA were depleted of DA (75-85%) compared to controls. Burying behavior and sucrose consumption were affected only by left lesions, similarly in both sexes. However, risk assessment behaviors were affected by right lesions in opposite directions in males and females. Behaviors modified preferentially by the left cortex thus showed less evidence of sex differences than those modulated by the right. While mesocortical DA depletion effects are lateralized, the nature of these effects can vary with sex and specific behavior. Such findings may be clinically significant, given the large gender differences in the incidence of mood and anxiety disorders, which also show many lateralized prefrontal abnormalities.

Hemispheric differences in the mesostriatal dopaminergic system

The mesostriatal dopaminergic system, which comprises the mesolimbic and the nigrostriatal pathways, plays a major role in neural processing underlying motor and limbic functions. Multiple reports suggest that these processes are influenced by hemispheric differences in striatal dopamine (DA) levels, DA turnover and its receptor activity. Here, we review studies which measured the concentration of DA and its metabolites to examine the relationship between DA imbalance and animal behavior under different conditions. Specifically, we assess evidence in support of endogenous, inter-hemispheric DA imbalance; determine whether the known anatomy provides a suitable substrate for this imbalance; examine the relationship between DA imbalance and animal behavior; and characterize the symmetry of the observed inter-hemispheric laterality in the nigrostriatal and the mesolimbic DA systems. We conclude that many studies provide supporting evidence for the occurrence of experience-dependent endogenous DA imbalance which is controlled by a dedicated regulatory/compensatory mechanism. Additionally, it seems that the link between DA imbalance and animal behavior is better characterized in the nigrostriatal than in the mesolimbic system. Nonetheless, a variety of brain and behavioral manipulations demonstrate that the nigrostriatal system displays symmetrical laterality whereas the mesolimbic system displays asymmetrical laterality which supports hemispheric specialization in rodents. The reciprocity of the relationship between DA imbalance and animal behavior (i.e., the capacity of animal training to alter DA imbalance for prolonged time periods) remains controversial, however, if confirmed, it may provide a valuable non-invasive therapeutic means for treating abnormal DA imbalance.

Diazepam potentiates the antidiabetic, antistress and anxiolytic activities of metformin in type-2 diabetes mellitus with cooccurring stress in experimental animals

Psychological stress is considered as one of the limiting factors in the management of type-2 diabetes mellitus (T2DM). Therefore, the basic objective of the present study was to evaluate the antidiabetic effect of metformin, diazepam, and their combination in cooccurring T2DM and stress condition (DMS). T2DM was induced in the male rats by administering streptozotocin (45 mg/kg, i.p.) and nicotinamide (110 mg/kg, i.p.) with time lag of 15 min. Rats were subjected to two sessions of cold restraint stress paradigm for one hour on the sixth and seventh day after streptozotocin injection. Administration of metformin (25 mg/kg, p.o.) and diazepam (1 mg/kg, p.o.) in combination from the seventh to thirteenth day after streptozotocin injection showed better improvement in glucose tolerance and insulin sensitivity compared to monotherapy of either drug. In addition, the combination significantly attenuated DMS-induced hyperglycemia, hypertriglyceridaemia, hypercorticosteronemia, anxiety-like behavior, and insulin resistance through modulating insulin signaling pathway in the liver compared to monotherapy. Further, improvement of mitochondrial function, integrity, and oxidative stress in hippocampus, hypothalamus, prefrontal cortex, striatum, amygdala, and nucleus accumbens was observed with the combination. Therefore, metformin in combination with diazepam may be a better therapeutic option in the management of T2DM with cooccurring stress condition.

Pre-gestational stress alters stress-response of pubertal offspring rat in sexually dimorphic and hemispherically asymmetric manner

Background

There is increasing evidence that maternal stress may have long-term effects on brain development in the offspring. In this study, we examined whether pre-gestational stress might affect offspring rats on the medial prefrontal cortical (mPFC) dopaminergic activity in response to acute stress in puberty and if so, whether such effects exhibited hemispheric asymmetry or sexual dimorphism.

Results

We used behavioral tests to assess the model of chronic unpredictable stress (CUS). We found that the activity in the open field test and sucrose intake test were lower for maternal rats in the CUS group than those in the control group. Offspring rats in the CUS group floated more and swam or climbed less as compared to the offsprings in the control group in the forced swimming test. The floating time was longer and swimming or climbing time was shorter in the female offspring rats than those in the males. Serum corticosterone and corticotrophin-releasing hormone levels were significantly higher for CUS maternal rats and their offsprings than the respective controls. The ratio of dihydroxy-phenyl acetic acid (DOPAC) to dopamine (DA), DA transporter (DAT), norepinephrine transporter (NET) were lower in the mPFC of offspring rats in the CUS group than the control group. Levels of catechol-O-methyltransferase (COMT) in the left mPFC of female offspring rats and in the right mPFC of both female and male offspring rats were lower in the CUS group than those in the controls, but there was no difference in the left mPFC of male offspring between the CUS and control groups. DOPAC, the ratio of DOPAC to DA, NET and COMT were lower in the right mPFC than in the left mPFC of offspring rats in the CUS group. The ratio of DOPAC to DA in the right mPFC was lower in the female offspring rats than male offspring rats in the CUS group. The NET and COMT levels in both left and right mPFC were lower in the female offspring rats than those of the male offsprings in the CUS group.

Conclusion

Our data provide evidence that the effect of pre-gestational stress on the mPFC dopaminergic activity in response to acute stress exhibited hemispheric asymmetry and sexual dimorphism in the pubertal offspring rats.

Lateralization of observational fear learning at the cortical but not thalamic level in mice

Major cognitive and emotional faculties are dominantly lateralized in the human cerebral cortex. The mechanism of this lateralization has remained elusive owing to the inaccessibility of human brains to many experimental manipulations. In this study we demonstrate the hemispheric lateralization of observational fear learning in mice. Using unilateral inactivation as well as electrical stimulation of the anterior cingulate cortex (ACC), we show that observational fear learning is controlled by the right but not the left ACC. In contrast to the cortex, inactivation of either left or right thalamic nuclei, both of which are in reciprocal connection to ACC, induced similar impairment of this behavior. The data suggest that lateralization of negative emotions is an evolutionarily conserved trait and mainly involves cortical operations. Lateralization of the observational fear learning behavior in a rodent model will allow detailed analysis of cortical asymmetry in cognitive functions.

Cerebral correlates of visual lateralization in Sepia

The common cuttlefish, Sepia officinalis (cephalopod mollusc) has recently become a relevant model for studying the setting-up of brain asymmetry among invertebrates. As the animals age from 3 to 30 days post hatching, they progressively develop a left-turning bias resulting from an eye-use preference. The aim of this study is to investigate whether anatomical (vertical, peduncle, inferior buccal, and optic lobes) or neurochemical (monoamines in optic lobes) brain asymmetries are present in the cuttlefish brain at 3 or at 30 post hatching days; and whether these correlate with side-turning preferences. We here find brain and behavioral asymmetry only at 30 post hatching days. Cuttlefish displayed a significant population bias towards a larger right peduncle lobe, and higher monoamine concentration in the left optic lobe (i.e. serotonin, dopamine and noradrenaline). None of these brain asymmetries were correlated to the studied side-turning bias. However, we found individual variation in the magnitude of the vertical and optic lobes asymmetry. A striking correlation was found with the behavioral results: the larger the right optic lobe and the right part of the vertical lobe, the stronger the bias to turn leftwards. To our knowledge, this is the first study to demonstrate a relationship at the individual level between brain and behavioral asymmetries in invertebrates.

Relationship between non-functional masticatory activity and central dopamine in stressed rats

  In humans, diurnal tooth-clenching and other oral stereotyped behaviour are associated with stress/anxiety. In rodents, gnawing/biting of objects is observed during exposure to stress. Both nigrostriatal and mesocortical dopaminergic systems are involved in the development of this coping behaviour. To clarify the relationship between central dopaminergic activity and stress-induced parafunctional masticatory behaviour, using microdialysis in vivo, we assessed the changes in extracellular dopamine concentrations in both prefrontal cortex and striatum of rats subjected to a mild tail pinch. The animals were divided into two groups according to the degree of non-functional masticatory activity (NFMA) displayed during exposure to tail pinch. In prefrontal cortex, rats which displayed severe NFMA showed a greater increase in extracellular dopamine concentration in relation to basal values (Emax=184±26%) than those which did not display this coping behaviour (Emax=139± 23%) (F(NFMA) [1,86]=3·97; P<0·05) (n=17). A positive association was also found between cortical dopamine maximal value from baseline and the degree of NFMA displayed (r=0·36; P<0·05) (n=17). There were no significant differences in the tail-pinch-induced striatal dopamine increase between both groups of rats (Emax=130±10%) (n=17). These results provide further evidence in support of prefrontal dopamine playing a relevant role in the expression of stress-induced masticatory coping behaviour.

Interhemispheric regulation of the medial prefrontal cortical glutamate stress response in rats

While stressors are known to increase medial prefrontal cortex (PFC) glutamate (GLU) levels, the mechanism(s) subserving this response remain to be elucidated. We used microdialysis and local drug applications to investigate, in male Long-Evans rats, whether the PFC GLU stress response might reflect increased interhemispheric communication by callosal projection neurons. We report here that tail-pinch stress (20 min) elicited comparable increases in GLU in the left and right PFC that were sodium and calcium dependent and insensitive to local glial cystine-GLU exchanger blockade. Unilateral ibotenate-induced PFC lesions abolished the GLU stress response in the opposite hemisphere, as did contralateral mGlu(2/3) receptor activation. Local dopamine (DA) D(1) receptor blockade in the left PFC potently enhanced the right PFC GLU stress response, whereas the same treatment applied to the right PFC had a much weaker effect on the left PFC GLU response. Finally, the PFC GLU stress response was attenuated and potentiated, respectively, following alpha(1)-adrenoreceptor blockade and GABA(B) receptor activation in the opposite hemisphere. These findings indicate that the PFC GLU stress response reflects, at least in part, activation of callosal neurons located in the opposite hemisphere and that stress-induced activation of these neurons is regulated by GLU-, DA-, norepinephrine-, and GABA-sensitive mechanisms. In the case of DA, this control is asymmetrical, with a marked regulatory bias of the left PFC DA input over the right PFC GLU stress response. Together, these findings suggest that callosal neurons and their afferentation play an important role in the hemispheric specialization of PFC-mediated responses to stressors.

Coping behavior causes asymmetric changes in neuronal activation in the prefrontal cortex and amygdala

When faced with an inescapable stressor, animals may engage in 'coping' behaviors, such as chewing inedible objects, that attenuate some physiological responses to the stressor. Previous evidence indicates that dopamine neurotransmission in the right prefrontal cortex is modulated by coping processes. Here we tested whether medial prefrontal cortical (mPFC) neuronal activation, as measured by Fos-immunoreactivity (Fos-ir), was altered in rats chewing inedible objects during exposure to novelty stress. We found that chewing caused an increase in Fos-ir that was selective for the right hemisphere of the mPFC along with a decrease in Fos-ir that was selective for the right central nucleus of the amygdala (CeA), a region that may regulate dopamine neurotransmission in mPFC. These observations suggest that coping during stress engages mPFC and CeA neuronal activity asymmetrically.

Sex differences in corticolimbic dopamine and serotonin systems in the rat and the effect of postnatal handling

Stress-related psychopathology is particularly prevalent in women, although the neurobiological reason(s) for this are unclear. Dopamine (DA) and serotonin (5-HT) systems however, are known to play important adaptive roles in stress and emotion regulation. The aims of the present study included examination of sex differences in stress-related behaviour and neuroendocrine function as well as post mortem neurochemistry, with the main hypothesis that corticolimbic DA and 5-HT systems would show greater functional activity in males than females. Long-Evans rats of both sexes were employed. Additional factors incorporated included differential postnatal experience (handled vs. nonhandled) and adult mild stress experience (acute vs. repeated (5) restraint). Regional neurochemistry measures were conducted separately for left and right hemispheres. Behaviourally, females showed more exploratory behaviour than males in the elevated plus maze and an openfield/holeboard apparatus. Females also exhibited significantly higher levels of adrenocorticotrophic hormone and corticosterone at all time points in response to restraint stress than males across treatment conditions, although both sexes showed similar habituation in stress-induced ACTH activation with repeated mild stress. Neurochemically, females had significantly higher levels of DA (in ventromedial prefrontal cortex (vmPFC), insular cortex and n. accumbens) and 5-HT (in vmPFC, amygdala, dorsal hippocampus and insula) than males. In contrast, males had higher levels of the DA metabolite DOPAC or DOPAC/DA ratios than females in all five regions and higher levels of the 5-HT metabolite 5-HIAA or 5-HIAA/5-HT ratios in vmPFC, amygdala and insula, suggesting greater neurotransmitter utilization in males. Moreover, handling treatment induced a significant male-specific upregulation of 5-HT metabolism in all regions except n. accumbens. Given the adaptive role of 5-HT and DAergic neurotransmission in stress and emotion regulation, the intrinsic sex differences we report in the functional status of these systems across conditions, may be highly relevant to the differential vulnerability to disorders of stress and emotion regulation.

Bipolar and major depressive disorder: neuroimaging the developmental-degenerative divide

Both major depressive disorder and bipolar disorder are the subject of a voluminous imaging and genetics literature. Here, we attempt a comprehensive review of MRI and metabolic PET studies conducted to date on these two disorders, and interpret our findings from the perspective of developmental and degenerative models of illness. Elevated activity and volume loss of the hippocampus, orbital and ventral prefrontal cortex are recurrent themes in the literature. In contrast, dorsal aspects of the PFC tend to display hypometabolism. Ventriculomegaly and white matter hyperintensities are intimately associated with depression in elderly populations and likely have a vascular origin. Important confounding influences are medication, phenotypic and genetic heterogeneity, and technological limitations. We suggest that environmental stress and genetic risk variants interact with each other in a complex manner to alter neural circuitry and precipitate illness. Imaging genetic approaches hold out promise for advancing our understanding of affective illness.

Early life programming of hemispheric lateralization and synchronization in the adult medial prefrontal cortex

Neonatal maternal separation (MS) in the rat increases the vulnerability to stressors later in life. In contrast, brief handling (H) in early life confers resilience to stressors in adulthood. Early life programming of stress reactivity may involve the medial prefrontal cortex (mPFC), a region which modulates various stress responses. Moreover, hemispheric specialization in mPFC may mediate adaptive coping responses to stress. In the present study, neuronal activity was examined simultaneously in left and right mPFC in adult rats previously subjected to MS, H or animal facility rearing (AFR). In vivo electrophysiology, under isoflurane anesthesia, was used to conduct acute recordings of unit and local field potential (LFP) activity in response to systemic administration of N-methyl-beta-carboline-3-carboxamide (FG-7142), a benzodiazepine receptor partial inverse agonist which mimics various stress responses. MS decreased basal unit activity selectively in right mPFC. Basal LFP activity was reduced with MS in left and right mPFC, compared to AFR and H, respectively. Hemispheric synchronization of basal LFP activity was also attenuated by MS at lower frequencies. FG-7142 elicited lateralized effects on mPFC activity with different early rearing conditions. Activity in left mPFC was greater with AFR and MS (AFR>MS), whereas activity was predominantly greater with H in right mPFC. Finally, compared to AFR, MS reduced and H enhanced hemispheric synchronization of LFP activity with FG-7142 treatment in a dose-dependent manner. These results indicate that functionally-relevant alterations in mPFC GABA transmission are programmed by the early rearing environment in a hemisphere-dependent manner. These findings may model the hemispheric specialization of mPFC function thought to mediate adaptive coping responses to stressors. They also suggest the possibility that early environmental programming of hemispheric functional coupling in mPFC is involved in conferring vulnerability or resilience to stressors later in life.

Unilateral hemispherectomy at adulthood asymmetrically affects immobile behavior of male Swiss mice

In order to test the hypothesis that behavioral coping with stressful situations is asymmetrically modulated by the hemispheres, we used the unilateral hemispherectomy procedure to assess the relative importance of each hemisphere in the determination of the immobility time during the forced swimming test. Under anesthesia, adult Swiss male mice were submitted to unilateral (right or left) hemispherectomy or sham surgery. Fifteen days after surgery, the immobile and turning behaviors of each mouse were measured during a 5-min forced swimming testing session. In general, while turning activity decreased significantly as the test progressed, an increase in immobility was observed. The unilateral hemispherectomy asymmetrically affected the immobility time in the forced swimming test. Particularly, the increase in immobility time of right-hemispherectomized mice was greater than that observed for sham-operated ones. In contrast, there were no differences in turning activity between the groups. The higher immobility time in males that had their right hemisphere removed supports the hypothesis that the two hemispheres contribute differentially to the behavioral response to stress.

Mesocortical dopamine and HPA axis regulation: Role of laterality and early environment

The infralimbic (IL) cortex is importantly involved in regulating behavioral and physiological responses to stress, including those of the hypothalamic-pituitary-adrenal (HPA) axis. The mesocortical dopamine (DA) system is an important afferent modulator of this region, is highly stress sensitive and frequently shows functional hemispheric asymmetry. Postnatal handling stimulation facilitates development of cortical asymmetry and is also associated with optimal HPA axis regulation. The present study examines the poorly understood role of the mesocortical DA system in regulating HPA axis function in adult rats which were handled (H) or nonhandled (NH) postnatally. In the first experiment, unilateral intra-IL cortex injection of the DA (D1/D2) antagonist alpha-flupenthixol into either hemisphere significantly exaggerated the restraint stress-induced increases in plasma adrenocorticotrophic hormone and corticosterone in NH rats. In H rats, the same effect was lateralized to the right IL cortex. In a second experiment, post mortem neurochemical analysis of DAergic measures in the IL cortex was conducted in H and NH animals following either acute or repeated (5 times) restraint stress. DAergic measures in the right IL cortex were significantly correlated with reduced stress hormone activation in both H and NH rats, especially in repeatedly restrained rats. However, while H rats showed a significant rightward shift in DA metabolism with repeated stress experience, NH rats shifted DA metabolism to the left. It is suggested that, during stress, mesocortical DA release normally acts in an adaptive, negative feedback capacity preventing excessive HPA activation and, with repeated stress, the right IL cortex is particularly important in this capacity. As well, the selective enhancement of DA metabolism in the right IL cortex of H rats may underlie, in part, their typically superior ability to adapt to stress and constrain HPA activity.

Influence of naturally occurring variations in maternal care on prepulse inhibition of acoustic startle and the medial prefrontal cortical dopamine response to stress in adult rats

In rats, naturally occurring variations in maternal care contribute to the development of individual differences in the behavioral and neuroendocrine responses to stress during adulthood. The dopamine (DA) projection to the medial prefrontal cortex (mPFC) plays an important role in mediating stress responsivity and is thought to be involved also in regulating sensorimotor gating. In the present study, we compared prepulse inhibition (PPI) of acoustic startle as well as the left and right mPFC DA stress responses in the adult offspring of high- and low-licking/grooming (LG) dams. Our data indicate that the offspring of low-LG animals are impaired on measures of PPI compared with high-LG animals. We also observed in low-LG animals a significant blunting of the mPFC DA stress responses that was lateralized to the right hemisphere, whereas in high-LG animals, the left and right mPFC DA stress responses were equally attenuated. Although mPFC levels of DA transporter did not differ between the two groups of animals, mPFC levels of catechol-O-methyl transferase immunoreactivity of low-LG animals were significantly lower than those of high-LG animals. These data provide evidence that variations in maternal care can lead to lasting changes in mPFC DA responsivity to stress and suggest the possibility that such changes in mesocorticolimbic DA function can also lead to deficits in sensorimotor gating.

Acute cortisol administration modulates EEG alpha asymmetry in volunteers: relevance to depression

The acute effects of cortisol (35mg) administration in 11 healthy male volunteers on resting frontal EEG asymmetry measured in the alpha band were investigated, using a within-subjects double-blind design. Results were indicative of a relative increase of right frontal activity with cortisol. This pattern of activity is similar to the deviant pattern that has been reported in patients suffering from depression, a condition often accompanied by elevated plasma cortisol levels. The significant effect on frontal asymmetry provides convergent support for our hypothesis, based upon previous results, that sustained (>30 minutes after stress termination) relative high levels of cortisol inhibit approach motivation.

Hemisphere-specific effects on serotonin but not dopamine innervation in the nucleus accumbens of gerbils caused by isolated rearing and a single early methamphetamine challenge

The aim of this study was twofold: We examined whether serotonin (5-HT) and dopamine (DA) innervations of the nucleus accumbens are lateralised and whether the environment or the combination with an early pharmacological impact might interfere with the postnatal maturation of the monoaminergic innervation. Male gerbils were assigned to either enriched rearing (ER) or isolated rearing (IR). Animals from both rearing conditions additionally received a single dose of either methamphetamine [MA (50 mg/kg ip)] or saline on postnatal day 14. DA and 5-HT fibres of the adult animals (postnatal day 90-110) were immunocytochemically stained and fibre densities were quantified in nucleus accumbens core and shell of both the left and right hemisphere. Our data demonstrate that the DA and 5-HT innervation is not lateralised in saline-treated animals of both rearing conditions. IR increases the DA fibre density in both hemispheres of saline controls, whereas an additional MA treatment reverses this effect. In both ER and IR groups, MA provokes an excessive 5-HT fibre in growth of only the right hemisphere. The combination of IR with MA induces right-side asymmetries of the 5-HT fibre density in both the core and shell. From the data obtained, we conclude that the maturation of the monoaminergic innervation of the nucleus accumbens is vulnerable to postnatal stimuli. The subtle "innervation imbalance" observed in our studies is consistent with previously reported effects in other brain regions of this animal model and may be causative for behavioural disturbances.

Low GSK-3beta in schizophrenia as a consequence of neurodevelopmental insult

Glycogen synthase kinase-3 (GSK-3) is a protein kinase highly abundant in brain and involved in signal transduction cascades, particularly neurodevelopment. Its activity and protein levels have been reported to be over 40% lower in postmortem frontal cortex of schizophrenic patients. GSK-3beta in occipital cortex of schizophrenic patients was not reduced, suggesting regional specificity. There was no reduction in GSK-3beta protein levels in fresh and immortalized lymphocytes and both GSK-3 activity and GSK-3beta mRNA levels in fresh lymphocytes from schizophrenic patients. In the schizophrenia-related neonatal ventral hippocampal lesion rat model, we measured GSK-3beta protein levels and GSK-3 activity in the frontal cortex. GSK-3beta protein levels in lesioned rats were significantly lower than in sham rats, favoring perinatal insult as a cause of low GSK-3beta in schizophrenia. Taken together, these studies suggest that low GSK-3 in postmortem brain of schizophrenic patients is a late consequence of perinatal neurodevelopmental insult in schizophrenia. In rats, acute or chronic cold restraint stress did not change GSK-3beta protein levels. Chronic treatment of rats with lithium, valproate, haloperidol or clozapine did not change rat cortical GSK-3beta protein levels ex vivo, supporting the concept that low GSK-3beta in schizophrenia is not secondary to stress or drug treatment. Our initial findings of low GSK-3beta protein levels in postmortem brain have been replicated by another group. Our own group has found additionally that GSK-3beta mRNA levels were 40% lower in postmortem dorsolateral prefrontal cortex (DLPFC) of schizophrenic patients, supporting our previous findings. Further studies will be aimed at determining whether nonspecific neonatal damage or only specific factors cause low GSK-3 as a late effect. We plan to study whether low GSK-3beta activity is associated with biochemical effects such as elevated beta-catenin levels.

Analysis of the cold-water restraint procedure in gastric ulceration and body temperature

Gastric mucosal injury induced by body restraint can be enhanced when combined with cold-water immersion. Based on this fact, the present study had two main purposes: (i) to examine the contribution of each of these two forms of stress on the development of gastric ulceration and regulation of body temperature and (ii) to investigate the importance of the animal's consciousness on gastric ulceration induced by the cold-water restraint. Independent groups of animals were exposed for 3 h to one of the following stressful treatments: body restraint plus cold-water (20+1 degrees C) immersion, body restraint alone or cold-water immersion alone. Control animals were not exposed to any form of stress. Half of the animals submitted to each of the four treatments were anesthetized with thionembutal (35 mg/kg), whereas the other half was injected with saline. Results indicated that body restraint alone was not sufficient to induce gastric ulceration or changes in body temperature. On the other hand, cold-water exposure, either alone or in conjunction with body restraint, induced the same amount of stomach erosions and hypothermia. Therefore, it appears that body restraint does not play an important role on gastric ulceration induced by the cold-water restraint procedure. Present results also indicated that conscious and anesthetized animals immersed in cold water presented robust gastric ulceration and a marked drop in body temperature. However, conscious animals developed more severe gastric damage in comparison to anesthetized animals although both groups presented the same degree of hypothermia. These findings suggest that hypothermia resulting from cold-water exposure has a deleterious effect on gastric ulceration but the animal's conscious activity during the cold-water immersion increases the severity of gastric mucosal damage. It is concluded that cold-water restraint is a useful procedure for the study of the underlying mechanisms involved in stress-induced ulceration.

Postnatal maturation of cortical serotonin lateral asymmetry in gerbils is vulnerable to both environmental and pharmacological epigenetic challenges

Long-term effects of postnatal differential rearing conditions and/or early methamphetamine (MA) application on serotonin (5-HT) fibre density were investigated in several cortical areas of both hemispheres of gerbils. The aim of this study was twofold: (1) Is the 5-HT fibre innervation of the cerebral cortex lateralised, and (2) if so, do postnatal environmental conditions and/or an early drug challenge interfere with development of 5-HT cerebral asymmetries? For that purpose, male gerbils were reared either under semi-natural or restricted environmental and social conditions, under both conditions once (on postnatal day 14) being treated with either a single dose of MA (50 mg/kg, i.p.) or saline. On postnatal day 110, 5-HT fibres were immunohistochemically stained and innervation densities quantified in prefrontal cortex, insular cortex, frontal cortex, parietal cortex, and entorhinal cortex. It was found that (1) 5-HT innervation in the cerebral cortex was clearly lateralised; (2) direction and extent of this asymmetry were not uniformly distributed over the different areas investigated; (3) both early methamphetamine challenge and rearing condition differentially interfered with adult 5-HT cerebral asymmetry; (4) combining MA challenge with subsequent restricted rearing tended to reverse the effects of MA on 5-HT cerebral asymmetry in some of the cortical areas investigated; and (5) significant responses in 5-HT cerebral asymmetry only occurred in prefrontal and entorhinal association cortices. The present findings suggest that the ontogenesis of cortical laterality is influenced by epigenetic factors and that disturbances of the postnatal maturation of lateralised functions may be associated with certain psychopathological behaviours.

Hemispheric asymmetry in stress processing in rat prefrontal cortex and the role of mesocortical dopamine

The prefrontal cortex (PFC) is known to play an important role not only in the regulation of emotion, but in the integration of affective states with appropriate modulation of autonomic and neuroendocrine stress regulatory systems. The present review highlights findings in the rat which helps to elucidate the complex nature of prefrontal involvement in emotion and stress regulation. The medial PFC is particularly important in this regard and while dorsomedial regions appear to play a suppressive role in such regulation, the ventromedial (particularly infralimbic) region appears to activate behavioral, neuroendocrine and sympathetic autonomic systems in response to stressful situations. This may be especially true of spontaneous stress-related behavior or physiological responses to relatively acute stressors. The role of the medial PFC is somewhat more complex in conditions involving learned adjustments to stressful situations, such as the extinction of conditioned fear responses, but it is clear that the medial PFC is important in incorporating stressful experience for future adaptive behavior. It is also suggested that mesocortical dopamine plays an important adaptive role in this region by preventing excessive behavioral and physiological stress reactivity. The rat brain shows substantial hemispheric specialization in many respects, and while the right PFC is normally dominant in the activation of stress-related systems, the left may play a role in countering this activation through processes of interhemispheric inhibition. This proposed basic template for the lateralization of stress regulatory systems is suggested to be associated with efficient stress and emotional self-regulation, and also to be shaped by both early postnatal experience and gender differences.

Effects of postnatal anoxia on striatal dopamine metabolism and prepulse inhibition in rats

Various evidence indicate that schizophrenia is a neurodevelopmental disorder. Epidemiological observations point to oxygen deficiencies during delivery as one of the early risk factors for developing schizophrenia. The aim of the present study was to examine the effect of postnatal anoxia in rats. Anoxia was experimentally induced by placing 9-day-old rat pups for 6 min in a chamber saturated with 100% nitrogen (N(2)). Exposure to anoxia on postnatal day (PND) 9 resulted in significantly reduced subcortical dopamine metabolism and turnover, as measured by striatal 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) concentrations. Furthermore, in the anoxic group only, striatal HVA concentrations were negatively correlated to prefrontal cortical N-acetylaspartate (NAA) levels. Similar findings of distorted prefrontal-subcortical interactions have recently been reported in schizophrenic patients. There was no effect of postnatal anoxia on either baseline or d-amphetamine-induced deficit in the prepulse inhibition (PPI) paradigm in adulthood. Accordingly, although oxygen deficiency early in life has been discussed as vulnerability factor in developing schizophrenia, exposure to postnatal anoxia in the rat does not show clear-cut phenomenological similarities with the disorder.

Participation of the substantia nigra dopaminergic neurons in the occurrence of gastric mucosal erosions

Previous reports indicate that dopaminergic systems play an important role on gastric mucosal erosions. In the present study, the participation of intrinsic neurons of the substantia nigra (SN) and ventral tegmental area (VTA) on the occurrence of stomach ulceration was investigated. It was found that bilateral microinfusions of a neurotoxic dose (20 microg/microl) of N-methyl-D-aspartate (NMDA) into the SN, but not in the VTA, lead to gastric erosions 24 h after the surgery. A decrease in dopamine levels in the caudate 24 h after the microinfusion of NMDA into the SN was also observed. Destruction of SN cell bodies with 6-hydroxydopamine (6-OHDA) did not induce gastric ulceration or changes in dopamine levels in the caudate nucleus 24 h after the lesioning procedure. NMDA neurotoxicity is mediated by the acute excitatory or activational effects, in contrast to 6-OHDA, suggesting that the occurrence of gastric ulceration after the infusion of NMDA into the SN is not due to the cell death per se but is related to an overactivation of these cells that precede their death. Taken together, these results suggest that modulation of dopaminergic levels by neurons located within the SN may play an important role for the development of gastric erosions.

What the rodent prefrontal cortex can teach us about attention-deficit/hyperactivity disorder: the critical role of early developmental events on prefrontal function

The present review surveys a broad range of findings on the functions of the rodent prefrontal cortex (PFC) in the context of the known pathophysiology of attention-deficit/hyperactivity disorder (ADHD). An overview of clinical findings concludes that dysfunction of the right PFC plays a critical role in ADHD and that a number of early developmental factors conspire to increase the risk of the disorder. Rodent studies are described which go far in explaining how the core processes which are deficient in ADHD are mediated by the PFC and that the mesocortical dopamine (DA) system plays a central role in modulating these functions. These studies also demonstrate a surprising degree of cerebral lateralization of prefrontal function in the rat. Importantly, the PFC is highly vulnerable to a wide variety of early developmental insults, which parallel the known risk factors for ADHD. It is suggested that the regulation of physiological and behavioral arousal is a fundamental role of the PFC, upon which many "higher" prefrontal functions are dependent or at least influenced. These right hemispheric arousal systems, of which the mesocortical DA system is a component, are greatly affected by early adverse events, both peri- and postnatally. Abnormal development, particularly of the right PFC and its DAergic afferents, is suggested to contribute directly to the core deficits of ADHD through dysregulation of the right frontostriatal system.

Effects of basolateral amygdala dopamine depletion on the nucleus accumbens and medial prefrontal cortical dopamine responses to stress

In vivo voltammetry was used to study the effects of basolateral amygdala dopamine depletion on stress-induced dopamine release in the nucleus accumbens and medial prefrontal cortex. Male Long-Evans rats received bilateral microinjections of 6-hydroxydopamine or vehicle into the basolateral amygdala. Changes in dopamine signal were monitored in the nucleus accumbens and in the right and left hemispheres of medial prefrontal cortex, in lesioned animals and shams. Animals were subjected to a physical stressor (tail pinch) and a species-typical threat (fox odour); each stressor was presented twice over four consecutive daily sessions. The results indicate that the nucleus accumbens dopamine responses to both stressors are significantly potentiated by dopamine-depleting lesions to basolateral amygdala. In contrast, while the dopamine stress response in the left medial prefrontal cortex did not differ between lesioned animals and shams, the right medial prefrontal cortical dopamine response to tail pinch, but not fox odour stress, was significantly attenuated in lesioned animals. Therefore, basolateral amygdala dopamine depletion had opposite effects on the nucleus accumbens and medial prefrontal cortical dopamine responses to stress, although the effect on the latter is lateralized to the right hemisphere in a stressor-specific manner. These data indicate that stress-induced activation of meso-amygdaloid dopamine exerts an inhibitory influence on the nucleus accumbens dopamine response to stress. They also suggest the possibility that meso-amygdaloid dopamine influences the nucleus accumbens dopamine response to stress indirectly by modulating stress-induced dopamine release in medial prefrontal cortex. These findings add to a growing body of evidence of a preferential involvement of right medial prefrontal cortical dopamine in a wide range of physiological responses to stress.

Excitotoxic lesions of the medial prefrontal cortex attenuate fear responses in the elevated-plus maze, social interaction and shock probe burying tests

Previous research investigating the effects of medial prefrontal cortex (MPFC) lesions on fear- and anxiety-related behavior has yielded an inconsistent body of findings. Behavioral studies have reported increases, decreases, and no effect on anxiety. In addition, many studies are complicated by the use of lesioning techniques that destroy fibers of passage, and the use of conditioned fear tests, which may introduce the confounding effects of learning and memory. Therefore, the present study examined the effects of ibotenic acid lesions of the MPFC (including prelimbic, infralimbic and anterior cingulate) on three wide-ranging and well-validated behavioral assays of anxiety: the elevated plus maze (EPM), social interaction (SI) and the shock-probe tests (SP). In the EPM test, lesioned rats showed a significantly higher percentage of open arm entries and open arm time than controls. In a version of the SI test sensitive to anxiolytic effects, lesioned rats were found to spend a significantly greater amount of time in active interaction with a conspecific; while another version of the SI test sensitive to anxiogenic effects did not show any differences between lesioned and non-lesioned controls. In the SP test, lesioned rats exhibited significantly lower rates of burying. In contrast, retention of shock probe avoidance was not affected. No effects of lesions on measures of locomotor activity or shock reactivity were found. The concordant anxiolytic-like effects found in the three behavioral assays strongly suggests a general reduction in fear responsiveness in MPFC lesioned rats.

Susceptibility of ascending dopamine projections to 6-hydroxydopamine in rats: effect of hypothermia

The aims of this study were to determine (1) whether mesolimbic and nigrostriatal DA cell bodies degenerate to different extents after 6-hydroxydopamine (6-OHDA) is administered into their respective terminal fields and (2) whether hypothermia, associated with sodium pentobarbital anesthesia, protects DA neurons from the toxic effects of 6-OHDA. To address these questions, 6-OHDA or vehicle was infused into either the ventral or dorsal striatum or into the medial forebrain bundle, under conditions of brain normothermia or hypothermia. Two weeks post-surgery, tyrosine hydroxylase-positive cell bodies were counted in the ventral tegmental area (VTA) and substantia nigra. In addition, autoradiographic labeling of tyrosine hydroxylase protein and dopamine transporter was quantified in dopamine terminal fields and cell body areas. Overall, DA cell bodies in the VTA were substantially less susceptible than those in the substantia nigra to depletion of dopaminergic markers. Hypothermia provided two types of neuroprotection. The first occurred when 6-OHDA was administered into the dorsal striatum, and was associated with a 30-50% increase in residual dopaminergic markers in the lateral portion of the VTA. The second neuroprotective effect of hypothermia occurred when 6-OHDA was given into the medial forebrain bundle. This was associated with a 200-300% increase in residual dopaminergic markers in the mesolimbic and nigrostriatal terminal fields; no significant protection occurred in the cell body regions.Collectively, these findings show that (1) the dopaminergic somata in the substantia nigra are more susceptible than those in the VTA to 6-OHDA-induced denervation, and (2) hypothermia can provide anatomically selective neuroprotection within the substantia nigra-VTA cell population. The continued survival of mesolimbic dopamine cell bodies after a 6-OHDA lesion may have functional implications relating to drugs of abuse, as somatodendritic release of dopamine in the VTA has been shown to play a role in the effectiveness of cocaine reward.

Acute cortisol effects on immediate free recall and recognition of nouns depend on stimulus valence

The present study investigated the acute effects of cortisol administration in normal healthy male volunteers on immediate free recall and recognition of pleasant, unpleasant, and neutral nouns using a between-subjects double-blind design. Two hours after cortisol (10 mg) or placebo administration, impaired recall and recognition of neutral and pleasant words was found in the treatment group, whereas recall and recognition of unpleasant words was similar in both groups. The interaction between treatment and stimulus valence was not mediated by "semantic cohesion," nor does it seem to have been mediated by stimulus arousal. Cortisol did not change mood. The changes with cortisol in recall and recognition of pleasant and unpleasant words parallel those found in depression, a condition that is often accompanied by elevated basal cortisol levels.

Lack of effect of acute, subchronic, or chronic stress on glycogen synthase kinase-3beta protein levels in rat frontal cortex

Glycogen synthase kinase (GSK)-3beta is a conserved serine/threonine protein kinase highly abundant in brain tissue. A dominant mechanism by which cells react to stress involves GSK-3beta. We studied the effect of stress on GSK-3beta levels ex vivo. We have previously found reduced GSK-3beta protein levels and GSK-3 activity in postmortem prefrontal cortex of schizophrenic patients. Since schizophrenic patients experience stress more severely than healthy people, we questioned whether their GSK-3beta reduction is stress-related using a rat model. Rats were exposed to acute, subchronic, or chronic stress using brief cold restraint. No effect was found on frontal cortex GSK-3beta protein levels. These results suggest that reduction in GSK-3beta levels in schizophrenic patients is not affected by cold restraint stress and supports the possibility that the changes observed in postmortem brains may be related to the disease.

Monoamine oxidase inhibitor-induced blockade of locomotor sensitization to quinpirole: role of striatal dopamine uptake inhibition

Previous studies have shown that the monoamine oxidase inhibitor (MAOI) clorgyline, blocks locomotor sensitization to the D(2)/D(3) dopamine agonist quinpirole and sensitizes self-directed mouthing behavior in rats by a mechanism independent of MAO inhibition. However, clorgyline is also an inhibitor of striatal dopamine uptake, and this mechanism could account for the effect of clorgyline on quinpirole sensitization. To investigate this possibility, the effects of clorgyline and pargyline were examined. Of these two MAOIs, only clorgyline inhibits dopamine uptake in the striatum. Rats received subcutaneous injections of clorgyline (1 mg/kg), pargyline (10 mg/kg) or vehicle 90 min prior to each injection of quinpirole (0.5 mg/kg, s.c., x8, twice weekly) or saline. Clorgyline and pargyline blocked the development of quinpirole-induced locomotor sensitization and sensitized self-directed mouthing behaviors in quinpirole rats. Thus, it is unlikely that clorgyline blocks locomotor sensitization to quinpirole via an inhibition of striatal dopamine uptake. Both MAOIs increased dopamine metabolism in the striatum, showed opposite effects in the prefrontal cortex, and eliminated the correlation between prefrontal dopamine and striatal DOPAC content found in quinpirole sensitized rats. We suggest that clorgyline and pargyline may affect the behavioral and neurochemical response to quinpirole via a previously reported MAOI-displaceable quinpirole binding site, a site which we hypothesize serves as a 'switch' to select what motor output becomes sensitized to repeated injections of quinpirole.

Behavioral effects of excitotoxic lesions of ventral medial prefrontal cortex in the rat are hemisphere-dependent

The ventral region of the medial prefrontal cortex (mPFC) is highly sensitive to stressful inputs and implicated in a variety of behaviors. Studies have also demonstrated numerous functional hemispheric asymmetries within this brain area of the rat. The present study examines the effects of ibotenic acid or sham lesions targeting the left, right or bilateral infralimbic cortex, on a variety of behaviors. Lesions (which destroyed infralimbic and ventral prelimbic cortex) were without effect on acquisition or reversal of a spatial learning task in the Morris water maze. Similarly unaffected were spontaneous and amphetamine-induced locomotor activity and sensitization, and prepulse inhibition of the acoustic startle response. In contrast, lesions significantly affected behavior in the elevated plus maze, as right-lesioned animals spent more time exploring the open arms of the maze than shams or left-lesioned rats, while not differing in closed arm entries. As well, in a simple taste aversion paradigm, right-lesioned rats drank significantly more of a sweetened milk/quinine solution than shams and left-lesioned rats, despite not differing in consumption of sweetened milk alone. The anxiolytic effects of right, but not left lesions of ventral mPFC, parallel the asymmetrical suppression of physiological stress responses previously reported for similar lesions. It is suggested that the right ventral mPFC plays a primary role in optimizing cautious and adaptive behavior in potentially threatening situations.

Frontal brain activation in anxious school children

BACKGROUND

An atypical EEG pattern of frontal brain activation has been found in infants and adults with emotional disorders. Eighty-two 8-year-old children and 56 11-year-old children were examined with regard to the following questions: 1. Do children who are diagnosed with anxiety disorder exhibit an atypical pattern of frontal brain activation? 2. Can this pattern be demonstrated in children of different ages? and 3. Are there gender differences in these patterns similar to those that have been demonstrated in adults? Baseline EEG activity was subjected to power spectral analysis.

RESULTS

In 8- and 11-year-old anxious girls, the well-known pattern of greater right than left frontal activation emerged that has been found previously in internalizing preschoolers. Healthy girls showed no frontal asymmetry at 8 years of age, and a greater left than right frontal brain activation at 11 years. In contrast, healthy boys demonstrated a significantly greater right than left frontal activation, whereas anxious boys displayed no frontal asymmetry at the age of 8, and a greater left than right frontal activation at the age of 11.

CONCLUSIONS

Children suffering from anxiety disorders exhibited a significantly different pattern of frontal brain activation than healthy children without any lifetime diagnosis of mental disorder. Distinct gender differences in frontal activation were found in anxious as well as in healthy children. This could be demonstrated in two samples of different ages.