Effects of psychological stress on monoamine systems in subregions of the frontal cortex and nucleus accumbens of the rat

Dopamine D1-like receptors in prelimbic, but not infralimbic, medial prefrontal cortex contribute to chronic stress-induced increases in cue-induced relapse to palatable food seeking during forced abstinence

Chronic stress exposure causes increased vulnerability to future relapse-like behavior in male, but not female, rats with a history of palatable food self-administration. These effects are mediated by dopamine D1-like receptors, but the anatomical location of chronic stress' dopaminergic mechanism is not known. Thus, male rats were trained to respond for palatable food pellets in daily sessions. During subsequent forced abstinence from food self-administration, stress was manipulated (0 or 3 h restraint/day for 7 days). Rats also received bilateral microinjections of the D1-like receptor antagonist SCH-23390 (0.25 μg/0.5 μl/side) or vehicle (0.5 μl/side) delivered to either prelimbic or infralimbic medial prefrontal cortex prior to daily treatments. Relapse tests in the presence of food-associated cues were conducted 7 days after the last treatment. Stress caused an increase and a decrease in responding during relapse tests in rats that received prelimbic vehicle and SCH-23390 infusions, respectively, relative to unstressed rats. In rats receiving IL infusions, however, stress caused an increase in responding regardless of whether the infusion was vehicle or SCH-23390. These results establish a specific role for prelimbic D1-like receptors in chronic stress-potentiated relapse.

Psychological stress-induced lower serum zinc and zinc redistribution in rats

In humans, long-term exposure to uncontrollable and unpredictable life stressors is a major precipitant in the development of depressive disorders. There are strong evidences that depression is accompanied by lower serum zinc. The aim of present study is to assess the effects of repeated psychological stress (PS) on the zinc metabolism in rat. The rats were divided into control group and PS group which were subdivided into three subgroups: 7-day group, 14-day group, and recovery group (ten rats in each subgroup). PS model was created by a communication box which contains room A and room B. Rats in room A were only exposed to the responses of rats which were randomly given electrical shock for 30 min in room B. PS was given to rats for 30 min every morning for 14 days. The serum corticosterone (CORT), zinc in serum and tissues, and zinc apparent absorption after PS exposure were investigated. The results showed that the serum CORT increased and serum zinc decreased after 7 and 14 days of PS treatment. The zinc concentration in the liver was increased by 14 days PS exposure, whereas its concentration in the hippocampus was decreased by 7 and 14 days of PS exposure. There were no significant changes in zinc concentration in the heart, spleen, kidney, duodenum, cortex, and cerebellum. A decrease in the zinc apparent absorption was observed in the 7- and 14-day PS groups. The increased serum CORT and liver zinc concentrations and decreased serum zinc and apparent absorption of zinc recovered to normal concentrations 7 days away from PS exposure. The results suggest that PS could induce lower serum zinc, which might be correlated with decreased zinc absorption in the small intestine and increased liver zinc accumulation after PS exposure. The consequent effects of decreased hippocampal and serum zinc and increased CORT concentration after PS exposure on stress-related diseases await further research.

Acute restraint stress prevents nicotine-induced mesolimbic dopaminergic activation via a corticosterone-mediated mechanism: a microdialysis study in the rat

BACKGROUND

Stress affects the responsiveness to nicotine (NIC), by increasing drug use, facilitating relapse and reinstating NIC self administration even after prolonged abstinence. In turn, high corticosterone (CORT) blood levels induced by stress may alter the neurobiological properties of NIC by acting on the dopamine (DA) mesolimbic system.

METHODS

In this study, we evaluated the effect of exposure to acute restraint stress on NIC-induced stimulation of the mesolimbic DA system of the rat, by studying extracellular DA levels in the nucleus accumbens shell (NAccs) with microdialysis.

RESULTS

NIC intravenous administration (130 μg/kg) increased DA levels in the NAccs in control rats but not in subjects exposed to stress; this latter phenomenon was prevented by blockade of CORT effects with the inhibitor of corticosterone synthesis metirapone (100 mg/kg) or the glucorticoid receptor antagonist mifepristone (150 μmol/kg).

CONCLUSIONS

These observations show that exposure to acute stress inhibits the stimulatory response of the mesolimbic DA system to NIC and suggest that this effect is mediated by circulating CORT acting on its receptors. These results may bear relevance in explaining the role played by stressful stimuli in NIC-seeking and taking behavior.

Prenatal exposure to MDMA alters noradrenergic neurodevelopment in the rat

3,4-methylenedioxymethamphetamine (MDMA; ecstasy) binds with high affinity to the norepinephrine transporter (NET), making the noradrenergic system a potential target during fetal exposure. Recent data indicate that adult rats that had been prenatally exposed to MDMA display persistent deficits in working memory and attention; behaviors consistent with abnormal noradrenergic signaling in the forebrain. The present study was designed to investigate whether prenatal exposure to MDMA from embryonic days 14-20 affects the structure and/or function of the noradrenergic system of the rat on postnatal day 21. Offspring that were prenatally exposed to MDMA exhibited an increase in noradrenergic fiber density in the prelimbic region of the prefrontal cortex and the CA1 region of the hippocampus that was not accompanied by an increase in the number of noradrenergic neurons in the locus coeruleus. Direct tissue autoradiography using tritiated nisoxetine demonstrated that while NET binding was not altered in the prelimbic cortex, the dentate gyrus, or the locus coeruleus, it was increased in the CA1, CA2, and CA3 regions of the hippocampus. Basal levels of norepinephrine were increased in the prefrontal cortex and the nucleus accumbens of MDMA-exposed rats, as compared to saline-treated controls. These findings indicate that prenatal exposure to MDMA results in structural changes in the noradrenergic system as well as functional alterations in NE neurotransmission in structures that are critical in attentional processing.

Dynamic regulation of dopamine and serotonin responses to salient stimuli during chronic haloperidol treatment

Antipsychotic drugs are the clinical standard for the treatment of schizophrenia. Although these drugs work initially, many compliant patients relapse due to treatment failure. The known biomarkers can not sufficiently explain antipsychotic treatment failure. We, therefore, enquired how the dynamic responses of the neurotransmitters, dopamine and serotonin, change in relation to treatment action and failure. Rats received either short-term (2-6 d) or long-term (12-14 d) treatment with haloperidol, which resembled human D2 receptor occupancy, using osmotic mini-pumps. Dopamine and serotonin basal levels and responses to novelty, appetitive food, and to an aversive tail pinch were measured in the prefrontal cortex, nucleus accumbens and caudate putamen using in-vivo microdialysis, and the behaviour was recorded. Subsequently, we used in-vivo voltammetry to measure dopamine overflow in the nucleus accumbens. Haloperidol decreased dopamine, but not serotonin baseline levels in a time-dependent way. Salient stimuli induced dopamine and serotonin responses. Short-term haloperidol treatment attenuated the mesolimbic dopamine responses to aversive stimulation, while the responses to appetitive stimulation were largely preserved. After long-term treatment, the initial response adaptations were reversed. Similar changes were also observed at the behavioural level. In-vivo voltammetry showed that nucleus accumbens dopamine adaptations and their reversal were mediated by changes in extracellular dopamine release. Chronic haloperidol treatment, which resembles human D2 receptor occupancy, modulates dopamine and behavioural responses to aversive and appetitive stimulation depending on the duration of treatment. Specific changes in dopamine response dynamics and their reversal may be a functional substrate of antipsychotic action and failure respectively.

Diet supplementation with iron augments brain oxidative stress status in a rat model of psychological stress

OBJECTIVE

We investigated the influence of iron supplementation on brain oxidative stress and antioxidase activity in psychologically stressed rats.

METHODS

Rats were maintained on diets with different iron doses for 1 wk, and all other constituents of the diet were equated exactly according to the AIN-93-G diet. At the end of the experimental period, rats were sacrificed and brains were collected. To evaluate the effect of iron consumption, serum iron, apparent iron absorption, levels of iron concentration, lipid peroxidation, reduced glutathione, and superoxide dismutase activities of brains were measured.

RESULTS

Iron overload significantly elevated the level of iron content and malonaldehyde in rat brain, especially in the psychologically stressed group. Apparent iron absorption was decreased by increased iron supplementation in rats treated with psychological stress more than in control rats. Similarly, iron overload decreased superoxide dismutase activity and apparent iron absorption more significantly in psychologically stressed rats than in controls. Reduced glutathione level varied with diet, increasing in rats on a moderately high-iron diet but decreasing in rats on a extremely high-level iron diet.

CONCLUSION

These results demonstrated that iron overload augments brain oxidative stress status and aggravates the decrease of apparent iron absorption in a rat model of psychological stress.

Pairing mild stress with increased serotonin-1B receptor expression in the nucleus accumbens increases susceptibility to amphetamine

Both serotonin-1B (5-HT(1B)) receptors and stress modulate the behavioral and neurobiological effects of psychostimulant drugs. In order to examine how these factors interact to influence the development of behaviors associated with addiction, we used viral-mediated gene transfer to transiently increase expression of 5-HT(1B) receptors in the nucleus accumbens (NAc) shell along with exposure to repeated mild stress (novelty + saline injection) in rats. Once the viral-mediated increases in gene expression had dissipated, the resulting effects of this 5-HT(1B)/stress pairing on the acute locomotor response to amphetamine and on the development of psychomotor sensitization were examined. We report that the increasing expression of 5-HT(1B) receptors on the terminals of NAc shell neurons that project to the ventral tegmental area and repeatedly exposing rats to mild stress subsequently enhance the acute locomotor-activating effects of amphetamine. In addition, the development of psychomotor sensitization (both locomotor activity and stereotypy components) is facilitated. These results suggest that serotonin signaling through NAc 5-HT(1B) heteroreceptors can interact with stress to increase susceptibility to the enduring forms of drug-induced plasticity that are associated with addiction.

Psychological stress induces dysregulation of iron metabolism in rat brain

Oxidative damage induced by abnormal iron accumulation in the brain is a primary cause of many neurodegenerative diseases, while the reason for iron deposition remains unclear. A previous study reported that various kinds of stress could cause a change in iron level and psychological stress (PS) was a risk factor for neuron death. In the present study we investigated the influence of PS on iron metabolism in rat brain. The results showed that both total iron and non-protein-bound-iron (NPBI) levels were higher in the cerebral cortex, hippocampus and striatum of PS rats. The levels of iron regulatory factors, including transferrin receptor 1 (TfR1), ferritin (Fn), and iron regulatory protein1 (IRP1), were all changed in the iron deposition regions of the PS-exposed rat brain, accompanied by intensified oxidative stress. It is concluded that PS can increase the intake of iron in some regions of brain and subsequently causes regional iron accumulation, indicating PS might be an important reason for iron deposition-caused neurodegenerative diseases.

Modulatory effect of environmental context and drug history on heroin-induced psychomotor activity and fos protein expression in the rat brain

The goal of the present study was to investigate the role of environmental context and drug history in modulating the effects of heroin on locomotor activity and Fos protein expression in the neocortex and striatal complex of the rat. It was found that (1) repeated i.p. administrations of a relatively low dose of heroin (1 mg/kg, i.p.) induced psychomotor sensitization only when the treatment was administered in a relatively 'novel' environment (ie, a unique test environment distinct from the home cage) but not when the same treatment was administered in the home cage; (2) environmental novelty facilitated heroin-induced Fos expression in the caudate, particularly in its most caudal regions; (3) environmental context also modulated heroin-induced Fos expression in the nucleus accumbens and in the neocortex; (4) repeated exposures to heroin dramatically altered its effects on Fos expression in the caudate and in the neocortex; and (5) Fos protein levels in the postero-dorsal caudate, in the shell of the nucleus accumbens, and in the barrel field cortex predicted most of the variance in heroin-induced activity scores, as shown by multiple regression analysis. The present report demonstrates that environment and drug history powerfully interact in shaping the neurobehavioral response to heroin, as previously shown for amphetamine and cocaine. Thus, a full understanding of the mechanisms responsible for the neurobehavioral adaptations produced by addictive drugs will also require taking into due consideration the environment in which drugs are experienced.

Behavioral response to emotional stress in rabbits: role of serotonin and serotonin2A receptors

Exposure to a novel environment is a stressor which modulates behavior, increases stress hormones and enhances the release of several neurotransmitters including serotonin (5-HT). Exposing rabbits to a novel environment significantly increases head-bob behavior but fails to alter either grooming or wet dog shakes compared with those observed in the home-cage. The goal of this study was to determine the role of 5-HT and its receptors in mediating novelty-elicited head-bob behavior. Reduction of central 5-HT levels after treatment with the serotonergic neurotoxin 5,7-DHT significantly decreased novelty-elicited head bobs by 40% compared with those in sham-lesioned rabbits, indicating that 5-HT mediates, in part, this behavior. Additionally, pretreatment with the 5-HT1A partial agonist and clinically used anxiolytic buspirone also significantly attenuated novelty-elicited head bobs. Pretreatment with the selective 5-HT2A antagonist M 100,907 significantly reduced novel environment-elicited head bobs by 40%. Furthermore, agonist-induced reduction of cortical 5-HT2A receptor density resulted in a significant 40% reduction in the number of head bobs elicited by the novel environment. These data demonstrate that rabbit head-bob behavior, an index of the response to novelty stress, is mediated, in part, by 5-HT activation of 5-HT2A receptors.

Specific personality traits and dopamine, serotonin genes in anxiety-depressive alcoholism among Han Chinese in Taiwan

BACKGROUND

Cloninger [Cloninger CR. 1987. Neurogenetic adaptive mechanisms in alcoholism. Science 236: 410-416.] had proposed a psychobiological model suggesting that three main personality dimensions distinguish the alcoholism into two subtypes (type I and type II). However, the classification was equivocal for clinical diagnosis. Recently, anxiety-depressive alcohol dependence (ANX/DEP ALC) has been posited as a genetically specific subtype of alcoholism. Its clinical characteristics were similar to individuals with type I alcoholism [Cloninger, C.R. 1987. Neurogenetic adaptive mechanisms in alcoholism. Science 236: 410-6.] such as having a high comorbidity with mood disorder, late-onset and more anxious/depressed traits. We attempted to investigate whether the dopamine D2 receptor (DRD2) and the serotonin transporter promoter region (5-HTTLPR) genes were involved in Novelty Seeking (NS) and Harm Avoidance (HA) of ANX/DEP ALC.

METHODS

We recruited 46 pure alcohol dependents (Pure ALC) and 87 anxiety-depression alcohol dependents (ANX/DEP ALC). All participants were diagnosed by DSM-IV criteria, genotyped by the PCR method and assessed with Tridimensional Personality Questionnaire (TPQ).

RESULTS

Both NS and HA were high in ANX/DEP ALC (p = 0.021; p = 0.001, respectively). The association between NS and ANX/DEP ALC only existed in subjects with DRD2 TaqI A1(+) allele (A1/A1 or A1/A2 genotypes) (p = 0.004) and in those with S/S genotype of 5-HTTLPR (p = 0.005). With the stratification of DRD2 TaqI A1(+) allele, high NS of ANX/DEP ALC existed only in carriers of 5-HTTLPR S/S genotype (p=0.001). Moreover, ANX/DEP ALC was related to high HA only in samples carrying 5-HTTLPR S/L or L/L genotype (p = 0.02).

CONCLUSIONS

These findings provided the empirical genetic characterization of the specific personality traits in ANX/DEP ALC among Han Chinese population in Taiwan.

Prenatal psychological stress causes higher emotionality, depression-like behavior, and elevated activity in the hypothalamo-pituitary-adrenal axis

In humans, stressful events during pregnancy may raise the risk of psychiatric disorders in offspring, and studies with rodents have found that physical prenatal stress can cause changes in the physiology, neurobiology, and behavior of offspring. In the present study, we examined whether psychological prenatal stress with little physical stress could cause changes in the neurobiology and behavior of offspring in Sprague-Dawley rats, as physical prenatal stress did. Dams received psychological stress by observing a rat being electrically shocked behind a transparent wall in the social communication box during the last trimester of gestation but were not exposed to any physical stress. Male offspring from the dams exposed to psychological stress showed enhanced emotionality in an open field test, depression-like behavior in a forced swim test, and enhanced activity in the hypothalamo-pituitary-adrenal axis, compared with rats from untreated dams. However, the prenatally stressed rats showed intact ability to acquire context conditioning. This is the first report that psychological prenatal stress in the communication box can cause changes in the neurobiology and behavior of offspring in rodents.

Differences in Cortical Serotonergic Innervation among Humans, Chimpanzees, and Macaque Monkeys: A Comparative Study

In this study, we assess the possibility that the evolution of human intellectual capacities was supported by changes in the supply of serotonin to the frontal cortex. To this end, quantitative comparative analyses were performed among humans, chimpanzees, and macaques. Immunohistochemical methods were used to visualize serotonin transporter-immunoreactive (SERT-ir) axons within the cerebral cortex. Areas 9 and 32 were chosen for evaluation due to their roles in working memory and theory of mind, respectively. Primary motor cortex was also evaluated because it is not associated with higher cognitive functions. The findings revealed that humans do not display a quantitative increase in serotonin innervation. However, the results indicated region- and layer-specific differences among species in serotonergic innervation pattern. Compared with macaques, humans and chimpanzees together displayed a greater density of SERT-ir axons relative to neuron density in layers V/VI. This change was detected in cortical areas 9 and 32, but not in primary motor cortex. Further, morphological specializations, coils of axons, were observed in humans and chimpanzees that were absent in macaques. These features may represent a greater capacity for cortical plasticity exclusive to hominoids. Taken together, these results indicate a significant reorganization of cortical serotonergic transmission in humans and chimpanzees.

Omega-3 fatty acid ethyl-eicosapentaenoate attenuates IL-1beta-induced changes in dopamine and metabolites in the shell of the nucleus accumbens: involved with PLA2 activity and corticosterone secretion

Previously, we have reported that interleukin-1 beta (IL-1) induces changes in dopaminergic (DA) and serotonergic systems in the core of the [corrected] nucleus accumbens (NAc). We have also demonstrated that n-3 fatty acid ethyl-eicosapentaenoate (EPA) can significantly reduce stress and anxiety-like behaviors, corticosterone concentrations [corrected] and peripheral inflammatory response induced by IL-1 administration. Compared to the core, the shell is involved more in emotion, stress and psychiatric diseases. However, the relationship between inflammation and the functions of DA system in the shell has not been studied. Since phospholipase (PL) A2 is a key enzyme in the [corrected] arachidonic acid-eicosanoids-prostaglandin [corrected] (PG)E2 pathway, and the change in NAc DA [corrected] system has been associated with glucocorticoid stimulation; [corrected] therefore, the hypotheses of this study are (1) that IL-1 induced changes in DA neurotransmission in the shell may be through PLA2-PGE2-corticosterone pathway; (2) EPA may attenuate IL-1 effects via inhibiting PLA2 activities, which blocks PGE2 stimulation of corticosterone. Using an in vivo microdialysis method, the present study showed that IL-1 administration significantly increased extracellular levels of DA, and its metabolites 3,4-dihydroxyphenylacetic acid, [corrected] and homovanillic acid [corrected] in the shell of the NAc. IL-1 also increased blood concentration of corticosterone and PGE2, and increased the activities of cytosolic and secretory [corrected] PLA2. IL-1-induced changes were significantly attenuated by EPA treatment. Furthermore, glucocorticoid [corrected] receptor antagonist mifepristone (RU486) pretreatment significantly blocked IL-1-induced changes in DA and metabolites. Quinacrine, [corrected] a PLA2 antagonist significantly blocked IL-1-induced [corrected] increase in PGE2 and corticosterone concentrations. These results demonstrated the hypotheses that IL-1 effects may be via PLA2-PGE2-corticosterone pathway and EPA attenuated IL-1 effects may be through the suppression of PLA2 expression, which then reduced PGE2 synthesis and corticosterone secretion.

Dopamine and monogamy

Social attachments play a central role in human society. In fact, such attachments are so important that deficits in the ability to form meaningful social bonds are associated with a variety of psychological disorders. Although mother-infant bonding has been studied for many years, we only recently have begun to examine the processes that underlie social bonds between adults. Over the past decade, central dopamine has become a focus of such research, especially its role in pair bonding between mates in species that display monogamous life strategies. Neuroanatomical and pharmacological studies in rodents have firmly established central dopamine systems, especially the mesocorticolimbic dopamine circuitry, in the formation, expression, and maintenance of monogamous pair bonds. As this research has progressed, it has become apparent that there is considerable overlap between the processes that underlie pair bonding and those that mediate responses to abused substances. This suggests that social bonding and substance abuse each may affect the other. Herein we review the current state of knowledge of central dopamine involvement in pair bond formation, expression, and maintenance. We first describe the neuroanatomical substrate within which dopamine exerts its effects on social bonding. We then describe dopamine receptor subtype-specific influences on pair bonding and how dopamine receptor activation may interact with activation of other neurochemical systems. Finally, we describe possible interactions between social bonding and substance abuse.

Regulation of anxiety and initiation of sexual behavior by CREB in the nucleus accumbens

Sexual deficits and other behavioral disturbances such as anxiety-like behaviors can be observed in animals that have undergone social isolation, especially in species having important social interactions. Using a model of protracted social isolation in adult rats, we observed increased anxiety-like behavior and deficits in both the latency to initiate sexual behavior and the latency to ejaculate. We show, using transgenic cAMP response element (CRE)-LacZ reporter mice, that protracted social isolation also reduces CRE-dependent transcription within the nucleus accumbens. This decrease in CRE-dependent transcription can be mimicked in nonisolated animals by local viral gene transfer of a dominant negative mutant of CRE-binding protein (CREB). We previously showed that this manipulation increases anxiety-like behavior. We show here that it also impairs initiation of sexual behavior in nonisolated animals, a deficit that can be corrected by anxiolytic drug treatment. This local reduction in CREB activity, however, has no influence on ejaculation parameters. Reciprocally, we used the viral transgenic approach to overexpress CREB in the nucleus accumbens of isolated animals. We show that this local increase in CREB activity completely rescued the anxiety phenotype of the isolated animals, as well as their deficit in initiating sexual behavior, but failed to rescue the deficit in ejaculation. Our data suggest a role for the nucleus accumbens in anxiety responses and in specific aspects of sexual behavior. The results also provide insight into the molecular mechanisms by which social interactions affect brain plasticity and behavior.

Pair-housing of male and female rats during chronic stress exposure results in gender-specific behavioral responses

Social support has a positive influence on the course of a depression and social housing of rats could provide an animal model for studying the neurobiological mechanisms of social support. Male and female rats were subjected to chronic footshock stress for 3 weeks and pair-housing of rats was used to mimic social support. Rats were isolated or housed with a partner of the opposite sex. A plastic tube was placed in each cage and subsequently used as a 'safe' area in an open field test. Time spent in the tube was used as a measurement of anxiety levels. Chronic stress increased adrenal weights in all groups, except for isolated females who showed adrenal hypertrophy in control conditions. In isolated males, chronic stress resulted in an increase in the time the animals spent in the tube. While stress did not affect this parameter in socially housed males, males with a stressed partner showed a similar response as isolated stressed males. Even though adrenal weights showed that isolated females were more affected by stress, after chronic stress exposure, they spent less time in the tube than socially housed females. Socially housed stressed females spent less time in the 'safe' tube compared to control counterparts, indicating that stress has a gender-specific behavioral effect.

IN CONCLUSION

pair-housing had a stress-reducing effect on behavior in males. Isolation of females was stressful by itself. Pair housing of females was not able to prevent stress-induced behavioral changes completely, but appeared to reduce the effects of chronic stress.

Molecular reactivity of mesocorticolimbic brain areas of high and low grooming rats after elevated plus maze exposure

High and low grooming rats (HG and LG), selected by extremities in stress-induced self-grooming on the elevated plus maze (EPM), display differences in stress coping style on the EPM, their motivation to self-administer cocaine, and differences in the reactivity of dopaminergic nerve terminals in mesocorticolimbic brain areas. This indicates a link between coping with a stressful/anxiogenic situation and drug intake. Here, we aimed to determine the molecular correlates of these differences by analyzing the reactivity of the mesocorticolimbic brain areas (the medial prefrontal cortex (mPFC) nucleus accumbens shell (NAS) and ventral tegmental area (VTA)) of HG and LG rats in response to EPM exposure. We report by measuring levels of immediate early gene (IEG) transcripts that EPM exposure-induced IEG expression was not significantly different between HG and LG rats. On the other hand, novel IEG expression patterns upon stress (EPM exposure) were apparent in all three areas including arc induction in the mPFC and NAS, CRH, BDNF, and Nr4a3 induction in the NAS, and serum glucocorticoid-regulated kinase (sgk) induction in the VTA. It is concluded that although the mPFC, NAS, and VTA play a role in modulating stress and grooming behavior, the neuronal reactivity in these regions measured by the IEG response is not related with behavioral extremities in stress coping style displayed on the EPM.

Benzodiazepine effect of 125I-iomazenil–benzodiazepine receptor binding and serum corticosterone level in a rat model

To test the change in free or unoccupied benzodiazepine receptor (BZR) density in response to diazepam, we investigated (125)I-iomazenil ((125)I-IMZ) binding and serum corticosterone levels in a rat model. Wistar male rats, which received psychological stress using a communication box for 5 days, were divided into two groups according to the amount of administered diazepam: no diazepam [D (0)] group and 10 mg/kg per day [D (10)] group of 12 rats each. The standardized uptake value (SUV) of (125)I-IMZ of the D (10) group were significantly lower (P < .05) than those of the D (0) group in the frontal, parietal and temporal cortices, globus pallidus, hippocampus, amygdala and hypothalamus. The serum corticosterone level ratio in the D (10) group was significantly lower than that in the D (0) group (P < .05). From the change in serum corticosterone levels, diazepam attenuated the psychological stress produced by the physical stress to animals in adjacent compartments. From the reduced binding of (125)I-IMZ, it is clear that diazepam competed with endogenous ligand for the free BZR sites, and the frontal, parietal and temporal cortices, globus pallidus, hippocampus, amygdala and hypothalamus are important areas in which (125)I-IMZ binding is strongly affected by administration of diazepam.

125I-iomazenil - benzodiazepine receptor binding and serum corticosterone level during psychological stress in a rat model

To test the hypothesis that benzodiazepine receptor density decreases in response to stress, we correlated (125)I-iomazenil ((125)I-IMZ) binding with serum corticosterone levels in a rat model. Wistar male rats were divided into four groups; control group (CON, 10 rats), no physical or psychological stress; and one-, three-, and five-day stress groups of 12 rats each (1-DAY, 3-DAY, and 5-DAY, respectively), receiving psychological stress for the given number of days. Psychological stress were given to rats with a communication box. The standardized uptake value (SUV) of (125)I-iomazenil of the 3-DAY and 5-DAY showed that (125)I-iomazenil-benzodiazepine receptor binding was significantly reduced in the cortices, accumbens nuclei, amygdala and caudate putamen (p<0.05). Serum corticosterone level ratio appeared to be slightly elevated in 3-DAY and 5-DAY, although this elevation was not significant. These data suggest that (125)I-IMZ is a useful radioligand to reflect received stress and its binding in the cortices, accumbens nuclei, amygdala and caudate putamen is strongly affected by psychological stress.

Opiate modulation of monoamines in the chick forebrain: Possible role in emotional regulation?

Numerous studies have shown that the opiate system is crucially involved in emotionally guided behavior. In the present study, we focussed on the medio-rostral neostriatum/hyperstriatum ventrale (MNH) of the chick forebrain. This avian prefrontal cortex analogue is critically involved in auditory filial imprinting, a well-characterized juvenile emotional learning event. The high density of mu-opiate receptors expressed in the MNH led to the hypothesis that mu-opiate receptor-mediated processes may modulate the glutamatergic, dopaminergic, and/or serotonergic neurotransmission within the MNH and thereby have a critical impact on filial imprinting. Using microdialysis and pharmaco-behavioral approaches in young chicks, we demonstrated that: the systemic application of the mu-opiate receptor antagonist naloxone (5, 50 mg/kg) significantly increased extracellular levels of 5-HIAA and HVA; the systemic application of the specific mu-opiate receptor agonist DAGO (5 mg/kg) increased the levels of HVA and taurine, an effect that was antagonized by simultaneously applied naloxone (5 mg/kg); the local application of DAGO (1 mM) had no effects on 5-HIAA, HVA, glutamate, and taurine, however, the effects of systemically injected naloxone (5 mg/kg) were abolished by simultaneously applied DAGO (1 mM); the systemic application of naloxone (5 mg/kg) increased distress behavior (measured as the duration of distress vocalization during separation from the peer group). These results are in line with our hypothesis that the mu-opiate receptor-mediated modulation of serotonergic and dopaminergic neurotransmission alters the emotional and motivational status of the animal and thereby may play a modulatory role during filial imprinting in the newborn animal.

Modulation of stress-induced dopamine release by excitotoxic damage of the entorhinal cortex in the rat

In the sham-operated rats, exposure to either footshock or psychological stress induced similar biphasic alterations of dopamine (DA) release (an initial increase followed by a decrease below baseline levels) in the amygdala 4 weeks after the surgery. On the other hand, the left entorhinal cortex lesions abolished the late decrement phase of DA release below baseline levels. These results suggest that entorhinal cortex lesions modulate stress-induced dopaminergic transmissions in the lateral amygdala.

Effect of immobilization stress on brain polyamine levels in spontaneously hypertensive and Wistar-Kyoto rats

The present study aimed to compare the basal brain polyamine levels and stress-induced brain polyamine level changes in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. For immobilization stress, both strains underwent acute (3 h per day immobilization for 2 days), chronic (3 h per day immobilization for 15 consecutive days), or no immobilization stress (control group). Basal putrescine (PU) levels in frontal cortex and hippocampus of SHR (11.03 +/- 0.81 and 11.36 +/- 0.33 nmol/g tissue, respectively) were significantly higher than WKY rats (6.90 +/- 1.44 and 7.82 +/- 0.71 nmol/g tissue, respectively). However, there were no strain differences in basal spermidine and spermine levels between the two. After acute stress, the PU levels in frontal cortex and hippocampus (15.99 +/- 0.45 and 14.10 +/- 0.95 nmol/g tissue, respectively) were significantly increased in SHR as compared to the non-stressed SHR (11.03 +/- 0.81 and 11.36 +/- 0.33 nmol/g tissue, respectively). In WKY rats, the PU level was significantly increased by acute stress in frontal cortex (11.68 +/- 1.12 nmol/g tissue) as compared to the non-stressed WKY (6.90 +/- 1.44 nmol/g tissue). After chronic stress, the PU levels in frontal cortex and hippocampus of SHR (12.44 +/- 0.54 and 11.34 +/- 0.66 nmol/g tissue, respectively) significantly decreased as compared to acute-stressed groups (15.99 +/- 0.45 and 14.01 +/- 0.95 nmol/g tissue, respectively). In WKY rats, after chronic stress, the PU level was significantly decreased in frontal cortex (5.73 +/- 0.36 nmol/g tissue) as compared to acute-stressed groups (11.68 +/- 1.12 nmol/g tissue). The PU levels in frontal cortex and hippocampus of acute-stressed (15.99 +/- 0.45 nmol/g tissue and 14.10 +/- 0.95 nmol/g tissue, respectively) and chronic-stressed (12.44 +/- 0.54 and 11.34 +/- 0.66 nmol/g tissue, respectively) SHR were significantly higher than acute-stressed (11.68 +/- 1.12 and 9.76 +/- 0.45 nmol/g tissue, respectively) and chronic-stressed (5.73 +/- 0.36 and 8.44 +/- 0.71 nmol/g tissue, respectively) WKY rats. The present study provides the higher basal PU level and stress-induced PU response in SHR as compared to WKY rats may be related to enhanced response of hypothalamic-pituitary-adrenocortical axis and sympathetic influence that may significantly contribute to the development of hypertension in SHR.