Rand J. Gruen

Region-specific effects of acute and repeated restraint stress on the phosphorylation of mitogen-activated protein kinases

The mitogen-activated protein kinases (MAPKs) are a family of signal transduction mediators that regulate a host of cellular activities, including cell growth and proliferation, and differentiation and survival, via sequential phosphorylation and activation of a cassette of three protein kinases. MAPKs are also recruited when the brain undergoes synaptic plasticity and remodeling (e.g., during induction of long-term potentiation, learning and memory consolidation). The activities of some of these kinases are altered in response to various acute stimuli such as ischemic insult, visceral pain and electroconvulsive shock. In the present study we used immunoblotting techniques to examine the effects of acute and repeated restraint stress on the phosphorylation state of three MAPKs, the extracellular signal-regulated kinase Erk1/2, c-Jun-N-terminal kinase/stress-activated protein kinase (JNK/SAPK) and p38 MAPK, in different brain regions. A single exposure to 30 min of restraint stress-elevated phospho-Erk1/2 (P-Erk1/2) levels in all three brain regions examined (hippocampus, medial prefrontal cortex and cingulate cortex), but did not alter the phosphorylation pattern of the other two MAPKs in any region. In marked contrast, exposure to restraint for 11 days (30 min/day) reduced the levels of all three MAPKs, but only in the prefrontal cortex. The results are compared to the reported effects of acute and chronic stress on other biochemical and functional measures.

DO ENDOGENOUS EXCITATORY AMINO ACIDS INFLUENCE STRIATAL DOPAMINE RELEASE

In vivo microdialysis techniques were used to examine whether endogenous excitatory amino acids exert a tonic facilitatory influence on striatal dopamine release. Local application of NMDA and non-NMDA antagonists at 10 microM was without an effect on basal dopamine release while 100 microM and 1 mM of these drugs significantly enhanced the release. Our findings do not support the idea that excitatory amino acids have a tonic excitatory effect on striatal dopamine release.

Alterations in GABAA receptor binding in the prefrontal cortex following exposure to chronic stress

The present study was designed to examine the effects of chronic stress on GABAA receptor binding. Animals were randomly assigned to either a control, acute, or chronic stress condition and changes in specific binding were assessed using the GABAA receptor antagonist [3H]SR 95531. Exposure to chronic restraint stress led to a significant reduction in GABAA receptor binding in the prefrontal cortex. Alterations in specific binding were not observed in the cerebellum, caudate-putamen, hippocampus, or cingulate cortex however, suggesting that the effects of chronic stress may be regionally specific. Exposure to acute restraint did not lead to a significant alteration in [3H]SR 95531 binding in any brain region examined.

Tonic inhibition of striatal dopamine transmission: effects of benzodiazepine and GABAA receptor antagonists on extracellular dopamine levels

At present, it is unclear whether ligands which bind at the benzodiazepine/GABA receptor complex play a tonic modulatory role with regard to striatal dopamine (DA) transmission. The present study was designed to examine the effects of Ro15-1788, a benzodiazepine (BZ) receptor antagonist, and SR 95531, a GABAA receptor antagonist, on striatal extracellular DA (DA[e]) concentrations in anesthetized and awake rats using the technique of in vivo microdialysis. Local administration of Ro15-1788 resulted in a dose-dependent increase in DA[e] in both anesthetized and awake animals. The Ro15-1788-induced increase in DA[e] was blocked by coadministration of the BZ agonist diazepam, as well as GABA. Local administration of SR 95531 also resulted in a dose-dependent alteration in striatal DA levels in both anesthetized and awake animals. The SR 95531-induced increase in DA was blocked by coadministration of GABA. The results suggest that GABA may play a tonic inhibitory role with regard to striatal DA transmission.

The effects of perinatal diazepam exposure on stress-induced activation of the mesotelencephalic dopamine system.

The effects of perinatal diazepam exposure of rats on stress-induced metabolic activation of the mesotelencephalic dopamine (DA) system were examined. Footshock stress parameters were selected such that DA turnover was increased in the prefrontal cortex and certain mesolimbic dopaminergic regions; a stress-induced activation of striatum was not observed. Perinatal treatment with the anxiolytic benzodiazepine diazepam (days E8 through the first week after gestation) did not alter basal dopamine turnover in the prefrontal cortex or striatum, or in any of the mesolimbic sites examined except for the nucleus accumbens and ventral tegmental area (in which turnover was decreased). However, perinatal exposure to diazepam significantly reduced the magnitude of the stress-elicited increase in prefrontal cortical dopamine turnover, and conversely resulted in a stress-induced enhancement of turnover in the striatum. These data suggest that although perinatal exposure to diazepam may alter basal dopaminergic function in some regions, certain enduring changes in dopamine function in other mesotelencephalic DA sites are revealed only under conditions that result in perturbation of central dopamine neurons, such as environmental stress. These data also suggest that perinatal benzodiazepine exposure may be reflected in the adult in a decreased ability to cope with stress.

Perinatal diazepam exposure: Alterations in exploratory behavior and mesolimbic dopamine turnover

Perinatal exposure to diazepam has been shown to lead to alterations in motor activity and exploratory behavior in neonatal animals. Exploratory and locomotor behavior have been associated with changes in mesotelencephalic dopamine function. We have therefore examined the effects of perinatal diazepam administration on both exploratory behavior and mesotelencephalic dopamine turnover in the adult rat. Animals exposed to the benzodiazepine during the perinatal period engaged in significantly less exploratory behavior than did control subjects. The diazepam-induced alterations in behavior were developmentally specific: decreased exploratory behavior was observed at 90, but not 60, days of age. At 90 days of age, specific changes in dopamine turnover in diazepam-treated animals were restricted to mesolimbic (nucleus accumbens and ventral tegmental area) sites; alterations in dopamine turnover were not seen in other mesotelencephalic sites examined. The findings indicate that perinatal exposure to benzodiazepines leads to behavioral changes that are present in adulthood. These changes in exploratory behavior may be associated with alterations in mesolimbic dopamine function.

Regionally specific alterations in the low-affinity GABAA receptor following perinatal exposure to diazepam

Alterations in a low affinity form of the GABAA receptor were examined with [3H]bicuculline methylchloride in the adult rat following perinatal exposure to diazepam. Perinatal exposure resulted in a significant reduction in [3H]bicuculline binding in the cingulate cortex. A significant decrease in the ability of GABA to displace bound [3H]bicuculline was observed only in the hypothalamus. The results suggest that the effects of perinatal exposure to diazepam are regionally specific and that benzodiazepine receptors and low affinity GABAA receptors are functionally linked during the perinatal period.

Self-criticism, failure, and depressive affect: A test of personality-event congruence and symptom specificity

Diathesis-stress models of cognitive vulnerability to depression posit that personality factors (e.g., self-criticism) interact with congruent negative life events to produce distinct depressive symptom clusters. The present study employed a stress-induction procedure to assess whether self-criticism would interact with achievement-related failure to increase introjective depressive affect in a nonclinical sample. Hypotheses were generally supported with respect to introjective depressive affect reported immediately following the stress-induction procedure. However, self-criticism did not interact with achievement failure in predicting depressive affect reported 24 hours later.

Cognitive factors and stress-induced changes in catecholamine biochemistry.

The purpose of the present research was to determine whether dysfunctional attitudes, a cognitive attribute, predicted changes in catecholamine biochemistry. A cognitive task was used to induce stress in female subjects (n=21), and levels of plasma norepinephrine (NE) and homovanillic acid (HVA) were measured at three time points: at baseline (T1); immediately after stress exposure (T2); and 40 min later (T3). Dysfunctional attitudes were significantly and positively related to levels of plasma NE at T3, controlling for baseline levels. Dysfunctional attitudes were not significantly related to plasma HVA levels at any time point. Our findings provide initial support for the idea that dysfunctional attitudes, an attribute shown to play an important role in some forms of unipolar depression, predict stress-induced alterations in noradrenergic output.

Effects of repeated amphetamine treatment on regional GABAA receptor binding.

The present study examined the effects of repeated exposure to amphetamine on GABAA receptor binding in cortical and subcortical areas. The goal of the study was to determine whether changes in specific binding were related to behavioral sensitization. Animals were exposed to either saline (0.3 ml, s.c.; n=12) or d-amphetamine (2.5 mg/kg, s.c.; n=12) for 6 consecutive days and sacrificed after a 14-day withdrawal period. Differences in GABAA receptor binding in these two groups of animals were assessed using the GABAA receptor antagonist [3H]SR 95531. To verify that the preceding treatment regimen led to the development of behavioral sensitization, a separate set of animals (n=8/group) was exposed to the same regimen and challenged with d-amphetamine (2.5 mg/kg, s.c.) after the 14-day withdrawal period. As expected, preexposure to amphetamine led to the development of amphetamine sensitization. There were no differences in GABAA receptor binding in animals preexposed to saline and amphetamine in the prefrontal cortex, caudate-putamen, hypothalamus, or cerebellum. These findings do not provide support for the idea that changes in GABAA receptor binding in the medial prefrontal cortex or various subcortical areas are related to the development of behavioral sensitization.