Stress-related activation of cerebral dopaminergic systems

Dopamine release during psychological stress in euthymic bipolar I disorder: a Positron Emission Tomography study with [11C]raclopride

BACKGROUND

Neurochemical mechanisms underlying stress induced relapse of mood episodes in Bipolar I Disorder (BD) remain unknown. This study investigated whether euthymic BD patients have a greater dopamine release in ventral striatum, caudate and putamen in response to psychological stress using Positron Emission Tomography (PET) scanning with the radiotracer [¹¹C]raclopride.

METHODS

Euthymic patients with BD (n = 10) and 10 matched healthy controls underwent two [¹¹C]raclopride PET scans, one during a "stress" and the other in a "no stress" condition separated by at least 24 h. Montreal Imaging Stress Test (MIST) was used to induce stress during stress condition. Participants received an injection of [¹¹C]raclopride over one minute followed by PET scan for 60 min. Participants were assessed for mood symptom severity at baseline, and before and after each scan. The reduction in [¹¹C]raclopride binding in stress condition compared with non-stress rest condition for each subject provided an estimate of dopamine release due to stress.

RESULTS

There was a significant effect of stress in reducing the [¹¹C]raclopride binding in the ventral striatum, caudate and putamen; however, no significant effects of group or condition x group interaction were found.

LIMITATIONS

Small sample size and recruitment of euthymic patients who may be less vulnerable to stress may limit the generalizability of findings.

CONCLUSIONS

Our findings showed that psychological stress led to dopamine release in the basal ganglia for all participants but the magnitude of dopamine release during a stress task was not different between euthymic BD patients and healthy controls.

The zebrafish tail immobilization (ZTI) test as a new tool to assess stress-related behavior and a potential screen for drugs affecting despair-like states

BACKGROUND

Affective disorders, especially depression and anxiety, are highly prevalent, debilitating mental illnesses. Animal experimental models are a valuable tool in translational affective neuroscience research. A hallmark phenotype of clinical and experimental depression, the learned helplessness, has become a key target for 'behavioral despair'-based animal models of depression. The zebrafish (Danio rerio) has recently emerged as a promising novel organism for affective disease modeling and CNS drug screening. Despite being widely used to assess stress and anxiety-like behaviors, there are presently no clear-cut despair-like models in zebrafish.

NEW METHOD

Here, we introduce a novel behavioral paradigm, the zebrafish tail immobilization (ZTI) test, as a potential tool to assess zebrafish despair-like behavior. Conceptually similar to rodent 'despair' models, the ZTI protocol involves immobilizing the caudal half of the fish body for 5 min, leaving the cranial part to move freely, suspended vertically in a small beaker with water.

RESULTS

To validate this model, we used exposure to low-voltage electric shock, alarm pheromone, selected antidepressants (sertraline and amitriptyline) and an anxiolytic drug benzodiazepine (phenazepam), assessing the number of mobility episodes, time spent 'moving', total distance moved and other activity measures of the cranial part of the body, using video-tracking. Both electric shock and alarm pheromone decreased zebrafish activity in this test, antidepressants increased it, and phenazepam was inactive. Furthermore, a 5-min ZTI exposure increased serotonin turnover, elevating the 5-hydroxyindoleacetic acid/serotonin ratio in zebrafish brain, while electric shock prior to ZTI elevated both this and the 3,4-dihydroxyphenylacetic acid/dopamine ratios. In contrast, preexposure to antidepressants sertraline and amitriptyline lowered both ratios, compared to the ZTI test-exposed fish.

COMPARISON WITH EXISTINGMETHOD(S)

The ZTI test is the first despair-like experimental model in zebrafish.

CONCLUSIONS

Collectively, this study suggests the ZTI test as a potentially useful protocol to assess stress-/despair-related behaviors, potentially relevant to CNS drug screening and behavioral phenotyping of zebrafish.

Dopaminergic Hyperactivity in Neurological Patients with Delirium

BACKGROUND

Delirium has important etiological, prognostic, and therapeutic implications. The study of neurochemical markers in this condition is relevant to the understanding of its pathophysiology. The assessment of the dopamine system is particularly relevant, as dopamine antagonists are the most used drugs in delirium.

AIM

To analyze neurotransmission markers in patients with delirium, focusing in the dopamine metabolite, homovanillic acid.

METHODS

A case-control study was performed at the National Institute of Neurology and Neurosurgery, Mexico, including hospitalized patients in which lumbar puncture was obtained for diagnostic purposes. Cases were selected if they fulfilled DSM-5 criteria for delirium. Age-paired controls were patients in which delirium was ruled out, selected at the same clinical scenario, during the same period. Neurological and systemic diagnoses were registered. Delirium was assessed using the DRS-98-R instrument. The dopamine metabolite, homovanillic acid (HVA), was measured by means of high-performance liquid chromatography. Other neurotransmission markers were also measured (5-hydroxyindoleacetic acid, glutamate, aspartate, GABA, glycine, arginine, citrulline, nitrites, and nitrates). A logistic regression model was used to determine pathogenic factors associated with the presence of delirium.

RESULTS

68 neurological patients with delirium and 68 patients without delirium were included. Higher homovanillic acid levels in cerebrospinal fluid were significantly associated with delirium. This result was significant after a subanalysis in patients without exposure to antipsychotics. Male gender and autoimmune limbic encephalitis were also associated with the presence of delirium.

CONCLUSIONS

In hospitalized neurological patients, dopaminergic hyperactivity and autoimmune limbic encephalitis are pathogenic factors associated with the presence of delirium.

Hypermethylation of Proopiomelanocortin and Period 2 Genes in Blood Are Associated with Greater Subjective and Behavioral Motivation for Alcohol in Humans

BACKGROUND

Epigenetic modifications of a gene have been shown to play a role in maintaining a long-lasting change in gene expression. We hypothesize that alcohol's modulating effect on DNA methylation on certain genes in blood is evident in binge and heavy alcohol drinkers and is associated with alcohol motivation.

METHODS

Methylation-specific polymerase chain reaction (PCR) assays were used to measure changes in gene methylation of period 2 (PER2) and proopiomelanocortin (POMC) genes in peripheral blood samples collected from nonsmoking moderate, nonbinging, binge, and heavy social drinkers who participated in a 3-day behavioral alcohol motivation experiment of imagery exposure to either stress, neutral, or alcohol-related cues, 1 per day, presented on consecutive days in counterbalanced order. Following imagery exposure on each day, subjects were exposed to discrete alcoholic beer cues followed by an alcohol taste test (ATT) to assess behavioral motivation. Quantitative real-time PCR was used to measure gene expression of PER2 and POMC gene levels in blood samples across samples.

RESULTS

In the sample of moderate, binge, and heavy drinkers, we found increased methylation of the PER2 and POMC DNA, reduced expression of these genes in the blood samples of the binge and heavy drinkers relative to the moderate, nonbinge drinkers. Increased PER2 and POMC DNA methylation was also significantly predictive of both increased levels of subjective alcohol craving immediately following imagery (p < 0.0001), and with presentation of the alcohol (2 beers) (p < 0.0001) prior to the ATT, as well as with alcohol amount consumed during the ATT (p < 0.003).

CONCLUSIONS

These data establish significant association between binge or heavy levels of alcohol drinking and elevated levels of methylation and reduced levels of expression of POMC and PER2 genes. Furthermore, elevated methylation of POMC and PER2 genes is associated with greater subjective and behavioral motivation for alcohol.

Reward and aversion processing in patients with post-traumatic stress disorder: functional neuroimaging with visual and thermal stimuli

In patients with post-traumatic stress disorder (PTSD), a decrease in the brain reward function was reported in behavioral- and in neuroimaging studies. While pathophysiological mechanisms underlying this response are unclear, there are several lines of evidence suggesting over-recruitment of the brain reward regions by aversive stimuli rendering them unavailable to respond to reward-related content. The purpose of this study was to juxtapose brain responses to functional neuroimaging probes that reliably produce rewarding and aversive experiences in PTSD subjects and in healthy controls. The stimuli used were pleasant, aversive and neutral images selected from the International Affective Picture System (IAPS) along with pain-inducing heat applied to the dorsum of the left hand; all were administered during 3 T functional magnetic resonance imaging. Analyses of IAPS responses for the pleasant images revealed significantly decreased subjective ratings and brain activations in PTSD subjects that included striatum and medial prefrontal-, parietal- and temporal cortices. For the aversive images, decreased activations were observed in the amygdala and in the thalamus. PTSD and healthy subjects provided similar subjective ratings of thermal sensory thresholds and each of the temperatures. When 46 °C (hot) and 42 °C (neutral) temperatures were contrasted, voxelwise between-group comparison revealed greater activations in the striatum, amygdala, hippocampus and medial prefrontal cortex in the PTSD subjects. These latter findings were for the most part mirrored by the 44 vs. 42 °C contrast. Our data suggest different brain alterations patterns in PTSD, namely relatively diminished corticolimbic response to pleasant and aversive psychosocial stimuli in the face of exaggerated response to heat-related pain. The present findings support the hypothesis that brain sensitization to pain in PTSD may interfere with the processing of psychosocial stimuli whether they are of rewarding or aversive valence.

Role of the orexin receptors within the nucleus accumbens in the drug priming-induced reinstatement of morphine seeking in the food deprived rats

Orexin plays a key role in mediating stress-induced drug relapse. However, the role of different types of orexinergic receptors that modulate stress-induced drug seeking remains unknown. The nucleus accumbens (NAc) has an important role in the reward system and receives orexinergic projections of the lateral hypothalamus. In addition, orexin interacts with other receptors that are involved in drug reinstatement. Therefore, in the present study, the role of orexin receptors in the NAc in morphine priming- induced reinstatement and the effect of food deprivation (FD) on drug reinstatement were examined. The extinguished morphine preference rats were tested for reinstatement following the 24-h FD condition after conditioning was induced. In the other groups, the animals were given intra-accumbal administration of SB334867 (01, 1 and 10 nM/0.5 μl DMSO) as an orexin-1 receptor antagonist and TCSOX229 (1, 5 and 25 nM/0.5 μl DMSO), as an orexin-2 receptor antagonist. The results showed that the blockade of two types of orexin receptors in the NAc remarkably attenuated the effect of FD on the drug reinstatement; however, they were more effective in FD condition. These findings indicate that the NAc is a brain area within which orexin has a fundamental role in the effect of stress on morphine-induced reinstatement and the effect of food deprivation- on the reinstatement of morphine.

1H NMR-Based Metabonomic Study of Functional Dyspepsia in Stressed Rats Treated with Chinese Medicine Weikangning

1H NMR-based metabolic profiling combined with multivariate data analysis was used to explore the metabolic phenotype of functional dyspepsia (FD) in stressed rats and evaluate the intervention effects of the Chinese medicine Weikangning (WKN). After a 7-day period of model establishment, a 14-day drug administration schedule was conducted in a WKN-treated group of rats, with the model and normal control groups serving as negative controls. Based on 1H NMR spectra of urine and serum from rats, PCA, PLS-DA, and OPLS-DA were performed to identify changing metabolic profiles. According to the key metabolites determined by OPLS-DA, alterations in energy metabolism, stress-related metabolism, and gut microbiota were found in FD model rats after stress stimulation, and these alterations were restored to normal after WKN administration. This study may provide new insights into the relationship between FD and psychological stress and assist in research into the metabolic mechanisms involved in Chinese medicine.

Compulsive methamphetamine taking in the presence of punishment is associated with increased oxytocin expression in the nucleus accumbens of rats

Methamphetamine addiction is mimicked in rats that self-administer the drug. However, these self-administration (SA) models do not include adverse consequences that are necessary to reach a diagnosis of addiction in humans. Herein, we measured genome-wide transcriptional consequences of methamphetamine SA and footshocks in the rat brain. We trained rats to self-administer methamphetamine for 20 days. Thereafter, lever-presses for methamphetamine were punished by mild footshocks for 5 days. Response-contingent punishment significantly reduced methamphetamine taking in some rats (shock-sensitive, SS) but not in others (shock-resistant, SR). Rats also underwent extinction test at one day and 30 days after the last shock session. Rats were euthanized one day after the second extinction test and the nucleus accumbens (NAc) and dorsal striatum were collected to measure gene expression with microarray analysis. In the NAc, there were changes in the expression of 13 genes in the SRvsControl and 9 genes in the SRvsSS comparison. In the striatum, there were 9 (6 up, 3 down) affected genes in the SRvsSS comparison. Among the upregulated genes was oxytocin in the NAc and CARTpt in the striatum of SR rats. These observations support a regional role of neuropeptides in the brain after a long withdrawal interval when animals show incubation of methamphetamine craving.

Dopamine dependent setting of a circadian oscillator underlying the memory for time of day

Animals learn and remember the time of day that significant conditions occur, and anticipate recurrence at 24-h intervals, even after only one exposure to the condition. On several place-conditioning tasks, animals show context avoidance or preference only near the time of day of the experience. The memory for time of day is registered by a circadian oscillator that is set at the time of the training. We show that manipulations of dopamine (DA) neurotransmission can set a time memory in place preference and avoidance tasks, indicating that time of day is part of the context that is learned. Single injections of the DA agonist, d-amphetamine sulfate given without further exposure to the conditioning apparatus, can reset the timing of anticipatory behavior evoked by previously acquired place-event associations. The data support a model for time memory in which DA signaling sets the phase of a circadian oscillator, which returns to the same state at regular 24-h intervals. The data also raise the possibility that some apparent impairments of memory formation or retention could reflect post-experience resetting of the optimal retrieval time rather than impairment of memory or retrieval per se.

The dopaminergic response to acute stress in health and psychopathology: A systematic review

Previous work in animals has shown that dopamine (DA) in cortex and striatum plays an essential role in stress processing. For the first time, we systematically reviewed the in vivo evidence for DAergic stress processing in health and psychopathology in humans. All studies included (n studies=25, n observations=324) utilized DA D2/3 positron emission tomography and measured DAergic activity during an acute stress challenge. The evidence in healthy volunteers (HV) suggests that physiological, but not psychological, stress consistently increases striatal DA release. Instead, increased medial prefrontal cortex (mPFC) DAergic activity in HV was observed during psychological stress. Across brain regions, stress-related DAergic activity was correlated with the physiological and psychological intensity of the stressor. The magnitude of stress-induced DA release was dependent on rearing conditions, personality traits and genetic variations in several SNPs. In psychopathology, preliminary evidence was found for stress-related dorsal striatal DAergic hyperactivity in psychosis spectrum and a blunted response in chronic cannabis use and pain-related disorders, but results were inconsistent. Physiological stress-induced DAergic activity in striatum in HV may reflect somatosensory properties of the stressor and readiness for active fight-or-flight behavior. DAergic activity in HV in the ventral striatum and mPFC may be more related to expectations about the stressor and threat evaluation, respectively. Future studies with increased sample size in HV and psychopathology assessing the functional relevance of stress-induced DAergic activity, the association between cortical and subcortical DAergic activity and the direct comparison of different stressors are necessary to conclusively elucidate the role of the DA system in the stress response.

Effects of SCH-23390 in combination with a low dose of 17β-estradiol on anxiety-like behavior in ovariectomized rats

The aim of this study was to explore effects on anxiety-like behavior of D₁ dopamine receptor agonist, SKF-38393, and of D₁ dopamine receptor antagonist, SCH-23390, given alone or in combination with a low dose of 17β-estradiol (17β-E₂) to ovariectomized (OVX) rats. Two weeks after surgery, OVX rats began 14 days of treatment with the vehicle, a low dose of 17β-E₂ (5.0 μg/rat, s.c.), SKF-38393 (0.1 mg/kg, i.p.), SCH-23390 (0.1 mg/kg, i.p.), SKF-38393 plus 17β-E₂, or SCH-23390 plus 17β-E₂. The animals were tested in the black and white model (BWM) and the open field test (OFT). SCH-23390 (0.1 mg/kg, i.p.) alone or in a combination with a low dose of 17β-E₂ (5.0 μg/rat, s.c.) resulted in anxiolytic-like effect in OVX rats in the BWM. Repeated treatment with SCH-23390 and 17β-E₂ profoundly increased anxiolytic-like effect of single substances exerted per se. Coadministration of SCH-23390 with 17β-E₂ increased frequency of rearing and grooming in OVX rats in OFT. SKF-38393 (0.1 mg/kg, i.p.) treatment failed to alter anxiety-like behavior in OVX rats in the BWM. The results of the present study suggest that 17β-E₂ and SCH-23390 interact to exert anxiolytic-like action and that each of these drugs can potentiate effects of each other.

Synergistic effects between CA1 mu opioid and dopamine D1-like receptors in impaired passive avoidance performance induced by hepatic encephalopathy in mice

BACKGROUND AND AIM

Numerous investigations have indicated that hepatic encephalopathy (HE) alters the levels of various neurotransmitters. However, comprehensive data regarding the effects of CA1 opioidergic and dopaminergic (DAergic) systems on HE-induced amnesia are still lacking.

METHODS

Following intra-dorsal hippocampal (CA1) injection of mu opioid and dopamine D1- and D2-like receptors antagonists in male mice, one-trial step-down and hole-board paradigms were used to assess memory and exploratory behaviors, respectively.

RESULTS

Our data demonstrated that HE impairs memory 24 days after bile duct ligation (BDL). Furthermore, while the higher dose of DA D1-like receptor antagonist (SCH23390, 0.5 μg/mouse) induced amnesia and anxiogenic-like behaviors, mu receptor antagonist (naloxone: 0.0125, 0.025 and 0.05 μg/mouse) and DA D2-like receptor antagonist (sulpiride: 0.0625, 0.125 and 0.25 μg/mouse) by themselves, could not exert an effect on memory performance in passive avoidance task. On the other hand, pre-test injection of all drugs reversed the HE-induced amnesia 24 days after BDL, while having no effect on exploratory behaviors. Pre-test co-administration of the subthreshold dose SCH23390 (0.25 μg/mouse) and sulpiride (0.0625 μg/mouse) or naloxone (0.0125 μg/mouse) could likewise reverse the BDL-induced amnesia. However, when the subthreshold sulpiride plus naloxone were co-administered, BDL-induced amnesia was not blocked.

CONCLUSIONS

Memory performance is impaired 24 days post BDL and CA1 mu opioid and DA D1-like receptors antagonist synergistic effects are likely involved in this phenomenon.

Ginsenoside rb1 modulates level of monoamine neurotransmitters in mice frontal cortex and cerebellum in response to immobilization stress

Cerebral monoamines play important roles as neurotransmitters that are associated with various stressful stimuli. Some components such as ginsenosides (triterpenoidal glycosides derived from the Ginseng Radix) may interact with monoamine systems. The aim of this study was to determine whether ginsenoside Rb1 can modulate levels of the monoamines such as dihydroxyphenylalanine (DOPA), dopamine (DA), norepinephrine (NE), epinephrine (EP), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydorxytryptamine (5-HT), 5-hydroxindole-3-acetic acid (5-HIAA), and 5-hydroxytryptophan (5-HTP) in mice frontal cortex and cerebellum in response to immobilization stress. Mice were treated with ginsenoside Rb1 (10 mg/kg, oral) before a single 30 min immobilization stress. Acute immobilization stress resulted in elevation of monoamine levels in frontal cortex and cerebellum. Pretreatment with ginsenoside Rb1 attenuated the stress-induced changes in the levels of monoamines in each region. The present findings showed the anti-stress potential of ginsenoside Rb1 in relation to regulation effects on the cerebral monoaminergic systems. Therefore, the ginsenoside Rb1 may be a useful candidate for treating several brain symptoms related with stress.

Adolescent rat circadian activity is modulated by psychostimulants

Circadian pattern of activity regulates many aspects of mammalian physiology and behavior to particular times of the day by entraining the circadian clocks to external environmental signals. Since circadian rhythms are sensitive to many pharmacological agents, it is important to understand if the repetitive use of psychostimulants such as amphetamine will alter the circadian rhythm behavioral activity pattern. The present study uses male Sprague-Dawley rats to study the long-term effects of amphetamine on the locomotor circadian rhythm activity pattern. Rats were randomly assigned to a testing cage that recorded their locomotor activity nonstop for eleven days using the open field assay, as follows: one day of baseline activity was recorded and then the experimental group was injected with amphetamine (0.6mg/kg) for 6days, no treatment for 3days (i.e., washout days) and then re-challenged with amphetamine for one more day while the control group was treated similarly with saline. The Cosine Curve Statistical Analysis (CCSA) test was used to fit a 24-hour curve to activity pattern. Results indicate that repetitive daily amphetamine injections cause behavioral sensitization and a significant change of circadian rhythm of locomotor activity pattern, and elicit behavioral expectation to receive the drug or expression of withdrawal during the washout days. The results suggest that either changes in circadian rhythm caused sensitization and withdrawal or sensitization and withdrawal caused the change in circadian rhythm activity.

Biological mechanisms underlying the relationship between stress and smoking: state of the science and directions for future work

Theories of addiction implicate stress as a crucial mechanism underlying initiation, maintenance, and relapse to cigarette smoking. Examinations of the biological stress systems, including functioning of the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system (ANS), have provided additional insights into the relationship between stress and smoking. To date, convergent data suggests that chronic cigarette smoking is associated with alterations in HPA and ANS functioning; however, less is known about the role of HPA and ANS functioning in smoking initiation and relapse following cessation. In order to organize existing findings and stimulate future research, the current paper summarizes the available literature on the roles of HPA axis and ANS functioning in the relationship between stress and cigarette smoking, highlights limitations within the existing literature, and suggests directions for future research to address unanswered questions in the extant literature on the biological mechanisms underlying the relationship between stress and smoking.

Stress decreases the ability to resist smoking and potentiates smoking intensity and reward

We have developed a novel human laboratory model to examine two primary aspects of stress-precipitated tobacco relapse: (1) Does stress reduce the ability to resist the first cigarette? (2) Once the first cigarette is initiated, does stress facilitate subsequent smoking? Using a within-subject design, daily smokers (n = 37) who were nicotine deprived overnight received a personalized imagery induction (stress or neutral) on two separate days, and then had the option of initiating a tobacco self-administration session or delaying initiation for up to 50 min in exchange for three levels of monetary reinforcement. Subsequently, the tobacco self-administration session entailed a 1-hour period in which subjects could choose to smoke using a smoking topography system. Following the stress induction, subjects were less able to resist smoking, smoked more intensely (increased puffs, shorter inter-puff interval, and greater peak puff velocity), and perceived greater satisfaction and reward from smoking. Stress significantly increased hypothalamus-pituitary-adrenal (HPA) axis reactivity, tobacco craving, negative emotion, and physiologic reactivity relative to the neutral condition. In addition, increased cortisol, ACTH, and tobacco craving were associated with reduced ability to resist smoking following stress. These findings have implications for understanding the impact of stress on smoking relapse and model development to assess smoking lapse behavior.

The effects of dopaminergic drugs in the dorsal hippocampus of mice in the nicotine-induced anxiogenic-like response

RATIONALE

Nicotine, an active alkaloid of tobacco has an acetylcholine property that alters anxiety-like behaviors in rodents. Moreover, several investigations suggest that the mesolimbic/cortical dopamine systems to be involved in the drugs affecting anxiety. The dopaminergic modulation of acetylcholine synaptic transmission has also been also suggested by different studies. Furthermore, modulation of such behaviors in rodents may be mediated through the dorsal hippocampus.

OBJECTIVES

In the present study, a possible role of the dorsal hippocampal acetylcholine receptor mechanism in nicotine's influence on anxiogenic-like responses has been investigated.

METHODS

During test sessions, the hole-board was used to investigate the effects of SCH23390, sulpiride, SKF38393 and quipirole on nicotine response in mice.

RESULTS

Intraperitoneal (i.p.) administration of nicotine (0.5 mg/kg) decreased the number of head dips but had no effect on other behaviors. Intra-dorsal hippocampal injections of ineffective doses of SCH23390 (SCH; 0.125 and 0.25 μg/mouse) or sulpiride (SUL; 0.5 and 0.75 μg/mouse) reversed head dips induced by nicotine but did not impact other exploratory behaviors. Furthermore, co-administration of ineffective doses of SKF38393 (SKF; 4 μg/mouse, dorsal hippocampus) or quipirole (QUI; 0.5 μg/mouse) in conjunction with an ineffective dose of nicotine (0.25 mg/kg, i.p.) decreased head dips induced by nicotine, but were otherwise ineffective.

CONCLUSION

These results may indicate a modulatory effect for the dorsal hippocampus dopamine receptors (D₁ and D₂) on an anxiogenic-like response induced by nicotine.

Anti-stress effect of ethyl acetate soluble fraction of Morus alba in chronic restraint stress

CONTEXT

Restraint stress is a well-known method to induce chronic stress which leads to alterations in various behavioral and biochemical parameters.

OBJECTIVE

The present work was designed to study anti-stress effects of Morus alba in chronic restraint stress (RS)-induced perturbations in behavioral, biochemical and brain oxidative stress status.

MATERIALS AND METHODS

The stress was produced by restraining the animals inside an adjustable cylindrical plastic tube for 3 h once daily for ten consecutive days. The ethyl acetate soluble fraction of Morus alba (EASF) 25, 50, 100 mg/kg and diazepam (1 mg/kg) per day was administered 60 min prior to the stress procedure. The behavioral and biochemical parameters such as open field, cognitive dysfunction; leucocytes count; blood glucose and corticosteroid levels were determined. On day 10, the rats were sacrificed and biochemical assessment of superoxide dismutase (SOD), lipid peroxidation (LPO), catalase (CAT), and glutathione reductase (GSH) in whole rat brain were performed.

RESULTS

Chronic restraint stress produced cognitive dysfunction, altered behavioral parameters, increased leucocytes count, SOD, LPO, glucose and corticosterone levels, with concomitant decrease in CAT and GSH activities. Gastric ulceration, adrenal gland and spleen weights were also used as the stress indices. All these RS induced perturbations were attenuated by EASF of Morus alba.

DISCUSSION

The results of the study suggest that in addition to its classically established pharmacological activities, the plant also has immense potential as an anti-stress agent of great therapeutic relevance.

CONCLUSION

This study indicates the beneficial role of Morus alba for the treatment of oxidative stress-induced disorders.

Mice lacking adenylyl cyclase-5 cope badly with repeated restraint stress

Physiological responses to acute stress proceed with the activation of the hypothalamus-pituitary-adrenal gland (HPA) system. Many brain regions are known to modulate the HPA axis activation in stress responses, but the detailed neural circuits and signaling system in the upstream of the HPA axis have to be explored further. Type 5 adenylyl cyclase (AC5) is highly concentrated in the dorsal striatum and nucleus accumbens, which are implicated in reward and stress-related behavior. AC5(-/-) mice exposed to daily 2-hr restraint stress for only 3-5 days showed poor stress-coping responses, including severe body weight loss, poor coat condition, respiratory difficulties, and freezing behavior. Plasma corticosterone levels during 2-hr stress sessions increased in AC5(-/-) mice compared with those of AC5(+/+) mice. However, neither the corticosterone receptor antagonist RU486 nor the CRH receptor antagonist NBI27914 blocked their poor stress coping, whereas the administration of the GABA(A) receptor allosteric modulator diazepam or the D1 dopamine receptor antagonist SCH23390 prior to restraint stress sessions changed their stress-coping response to the stressed AC5(+/+) mouse level. Stress-triggered c-Fos expression was completely blunted in the dorsal striatum of AC5(-/-). These results suggest that the AC5-associated signal system and neural network are involved in the regulation of anxiety and stress-coping response.

The role of dopamine in bipolar disorder

OBJECTIVE

Despite effective pharmacological treatments for bipolar disorder, we still lack a comprehensive pathophysiological model of the illness. Recent neurobiological research has implicated a number of key brain regions and neuronal components in the behavioural and cognitive manifestations of bipolar disorder. Dopamine has previously been investigated in some depth in bipolar disorder, but of late has not been a primary focus of attention. This article examines the role of dopamine in bipolar disorder, incorporating recent advances into established models where possible.

METHODS

A critical evaluation of the literature was undertaken, including a review of behavioural, neurochemical, receptor, and imaging studies, as well as genetic studies focusing on dopamine receptors and related metabolic pathways. In addition, pharmacologic manipulation of the central dopaminergic pathways and comparisons with other disease states such as schizophrenia were considered, principally as a means of exploring the hypothesised models.

RESULTS

Multiple lines of evidence, including data from pharmacological interventions and structural and functional magnetic resonance imaging studies, suggest that the dopaminergic system may play a central role in bipolar disorder.

CONCLUSION

Future research into the pathophysiological mechanisms of bipolar disorder and the development of new treatments for bipolar disorder should focus on the dopaminergic system.

Hypocretin/orexin in arousal and stress

Multiple lines of evidence indicate that hypocretin/orexin (HCRT) participates in the regulation of arousal and arousal-related process. For example, HCRT axons and receptors are found within a variety of arousal-related systems. Moreover, when administered centrally, HCRT exerts robust wake-promoting actions. Finally, a dysregulation of HCRT neurotransmission is associated with the sleep/arousal disorder, narcolepsy. Combined, these observations suggested that HCRT might be a key transmitter system in the regulation of waking. Nonetheless, subsequent evidence indicates that HCRT may not play a prominent role in the initiation of normal waking. Instead HCRT may participate in a variety of processes such as consolidation of waking and/or coupling metabolic state with behavioral state. Additionally, substantial evidence suggests a potential involvement of HCRT in high-arousal conditions, including stress. Thus, HCRT neurotransmission is closely linked to high-arousal conditions, including stress, and HCRT administration exerts a variety of stress-like physiological and behavioral effects that are superimposed on HCRT-induced increases in arousal. Combined, this evidence suggests the hypothesis that HCRT may participate in behavioral responding under high-arousal aversive conditions. Importantly, these actions of HCRT may not be limited to stress. Like stress, appetitive conditions are associated with elevated arousal levels and a stress-like activation of various physiological systems. These and other observations suggest that HCRT may, at least in part, exert affectively neutral actions that are important under high-arousal conditions associated with elevated motivation and/or need for action.

Chronic stress, drug use, and vulnerability to addiction

Stress is a well-known risk factor in the development of addiction and in addiction relapse vulnerability. A series of population-based and epidemiological studies have identified specific stressors and individual-level variables that are predictive of substance use and abuse. Preclinical research also shows that stress exposure enhances drug self-administration and reinstates drug seeking in drug-experienced animals. The deleterious effects of early life stress, child maltreatment, and accumulated adversity on alterations in the corticotropin releasing factor and hypothalamic-pituitary-adrenal axis (CRF/HPA), the extrahypothalamic CRF, the autonomic arousal, and the central noradrenergic systems are also presented. The effects of these alterations on the corticostriatal-limbic motivational, learning, and adaptation systems that include mesolimbic dopamine, glutamate, and gamma-amino-butyric acid (GABA) pathways are discussed as the underlying pathophysiology associated with stress-related risk of addiction. The effects of regular and chronic drug use on alterations in these stress and motivational systems are also reviewed, with specific attention to the impact of these adaptations on stress regulation, impulse control, and perpetuation of compulsive drug seeking and relapse susceptibility. Finally, research gaps in furthering our understanding of the association between stress and addiction are presented, with the hope that addressing these unanswered questions will significantly influence new prevention and treatment strategies to address vulnerability to addiction.

Developmental changes in stress adaptation in relation to psychopathology

As modern neuroscience seeks to understand the neural bases for mental illness, it is becoming increasingly important to define how and when complex neural circuits may be altered in individuals who carry the genetic vulnerability for psychopathology. One factor that could potentially play a contributory role in mental illness is the stress response. A variety of studies suggest that stress can alter the activity of several key cortical neurotransmitters, including glutamate, γ-aminobutyric acid, dopamine, and serotonin. Specifically, exposure to neurotoxic levels of adrenal steroid hormone, particularly if this occurs early in life, could potentially induce permanent changes of these transmitter systems in corticolimbic regions, such as the hippocampal formation and cingulate gyrus, that have a high density of glucocorticoid receptors. Overall, exposure to severe stress during the perinatal period could potentially induce alterations in the circuitry of the anterior cingulate cortex and hippocampal formation and interfere with the normal mechanisms underlying attention and learning.

Biological substrates of reward and aversion: a nucleus accumbens activity hypothesis

The nucleus accumbens (NAc) is a critical element of the mesocorticolimbic system, a brain circuit implicated in reward and motivation. This basal forebrain structure receives dopamine (DA) input from the ventral tegmental area (VTA) and glutamate (GLU) input from regions including the prefrontal cortex (PFC), amygdala (AMG), and hippocampus (HIP). As such, it integrates inputs from limbic and cortical regions, linking motivation with action. The NAc has a well-established role in mediating the rewarding effects of drugs of abuse and natural rewards such as food and sexual behavior. However, accumulating pharmacological, molecular, and electrophysiological evidence has raised the possibility that it also plays an important (and sometimes underappreciated) role in mediating aversive states. Here we review evidence that rewarding and aversive states are encoded in the activity of NAc medium spiny GABAergic neurons, which account for the vast majority of the neurons in this region. While admittedly simple, this working hypothesis is testable using combinations of available and emerging technologies, including electrophysiology, genetic engineering, and functional brain imaging. A deeper understanding of the basic neurobiology of mood states will facilitate the development of well-tolerated medications that treat and prevent addiction and other conditions (e.g., mood disorders) associated with dysregulation of brain motivation systems.

Long-chain polyunsaturated fatty acids modulate interleukin-1beta-induced changes in behavior, monoaminergic neurotransmitters, and brain inflammation in rats

Recent evidence has suggested that an imbalance between membrane (n-3) and (n-6) fatty acids may contribute to the etiology of autoimmune and neurodegenerative diseases. In this study, the mechanisms by which eicosapentaenoic acid (EPA), gamma-linolenic acid (GLA), and arachidonic acid (AA) modulate neurotransmitters, behavior, and brain inflammation were evaluated in rats that received central saline or interleukin-1beta (IL-1) administrations. In rats treated with saline, only the AA-enriched diet significantly increased anxiety-like behavior in the elevated plus maze, which was associated with increased corticosterone secretion. AA also increased the turnover of dopamine (DA), noradrenaline (NA), and serotonin (5-HT) in the amygdala and increased the prostaglandin (PG)E(2) level in the hippocampus. IL-1 administration slowed rat learning in the water maze and increased anxiety-like behavior, changes which were associated with increased homovanillic acid and 5-HT turnover, decreased NA in the hippocampus and amygdala, decreased DA in the frontal cortex, and decreased IL-10 in limbic brain regions. Increased corticosterone secretion following IL-1 administration was accompanied by increased NA turnover in the hippocampus (P < 0.05) and increased PGE(2) concentration (P < 0.01) in the limbic brain regions. Of the 3 diets tested, only EPA attenuated IL-1-induced behavioral changes (P < 0.05 or 0.01), which was associated with the modulation of EPA on the neuroendocrine and immune changes induced by IL-1. GLA reduced hippocampal PGE(2) concentration in rats given IL-1 (P < 0.01). AA did not counteract any of the changes induced by IL-1. These results suggest that EPA, GLA, and AA play different roles in the neuroendocrine-immune network.

Sex differences in the effects of two stress paradigms on dopaminergic neurotransmission

Sex differences in behavioral and neurobiological responses to stress are considered to modulate the prevalence of some psychiatric disorders, including major depression. In the present study, we compared dopaminergic neurotransmission and behavior in response to two different stress paradigms, the Forced Swim Test (FST) and the Chronic Mild Stress (CMS). Male and female rats were subjected to one session of swim stress for two consecutive days (FST) or to a variety of mild stressors alternating for six weeks (CMS). Subsequently, the tissue levels of dopamine (DA) and its metabolites (HVA and DOPAC) in the hippocampus, the hypothalamus, the prefrontal cortex and the striatum were measured using high-performance liquid chromatography (HPLC). The ratios HVA/DA and DOPAC/DA were also calculated as indices of the dopaminergic activity. Results from the FST determined that males exhibited lower immobility, higher climbing duration and increased dopaminergic activity in the prefrontal cortex and the hippocampus compared to females. CMS induced alterations in sucrose intake in both sexes, while it only decreased dopaminergic activity in the prefrontal cortex of females. These findings show that FST and CMS have different effects on the dopaminergic activity of discrete brain regions depending on the sex of the animal. These data support the growing evidence that females display a differential response and adaptation to stress than males.

Piplartine, an amide alkaloid from Piper tuberculatum, presents anxiolytic and antidepressant effects in mice

In the present work, we studied the effects of piplartine (PIP), an amide alkaloid isolated from the roots of Piper tuberculatum (Piperaceae), in the elevated plus maze, open field, rota rod, pentylenetetrazole (PTZ)-induced seizures, and forced swimming tests, in mice (Swiss, male, 25 g) to assess anxiolytic, sedative, muscle relaxant, anticonvulsant and antidepressant effects, respectively. Results showed that PIP (50 and 100 mg/kg, i.p.), similarly to diazepam, significantly increased not only the number of entrances (100% and 66%, respectively) but also the time of permanence in the open arms (104% and 199%, respectively), indicating that PIP presents an anxiolytic activity. Both effects were completely blocked by the previous administration of flumazenil what suggests the involvement of benzodiazepine type receptors. In the open field test, although PIP did not alter the number of crossings, it significantly increased grooming (103% and 119%) and rearing (60% and 23%), at the doses of 50 and 100 mg/kg respectively, as compared to controls. However, in the rota rod test, PIP was devoid of effect. Although in the PTZ-induced convulsion test, PIP did not alter the latency time for the onset of the first convulsion, as compared to controls, it significantly reduced in 58% and 60%, respectively, the animal's latency time to death. Furthermore, a significant and dose-dependent decrease in the immobility time, as evaluated by the forced swimming test, was observed after PIP administration (41% and 75% decrease, at the doses of 50 and 100 mg/kg, respectively), suggesting an antidepressant effect, similarly to that observed with imipramine, a classical antidepressant drug used as standard. In conclusion, we showed that PIP presents significant anxiolytic and antidepressant activities, making this drug potentially useful in anxiety and depression.

Comorbidity implications in brain disease: Neuronal substrates of symptom profiles

The neuronal substrates underlying aspects of comorbidity in brain disease states may be described over psychiatric and neurologic conditions that include affective disorders, cognitive disorders, schizophrenia, obsessive-compulsive disorder, substance abuse disorders as well as the neurodegenerative disorders. Regional and circuitry analyses of biogenic amine systems that are implicated in neural and behavioural pathologies are elucidated using neuroimaging, electrophysiological, neurochemical, neuropharmacological and neurobehavioural methods that present demonstrations of the neuropathological phenomena, such as behavioural sensitisation, cognitive impairments, maladaptive reactions to environmental stress and serious motor deficits. Considerations of neuronal alterations that may or may not be associated with behavioural abnormalities examine differentially the implications of discrete areas within brains that have been assigned functional significance; in the case of the frontal lobes, differential deficits of ventromedial and dorsolateral prefrontal cortex may be associated with different aspects of cognition, affect, remission or response to medication thereby imparting a varying aspect to any investigation of comorbidity.

Role of dopamine D1 and D2 receptors in CRF-induced disruption of sensorimotor gating

Corticotropin-releasing factor (CRF), a neuropeptide released during stress, has been reported to modulate startle behavior, including reducing the threshold for acoustic startle responding and reducing prepulse inhibition (PPI). The central mechanisms mediating CRF system regulation of startle and PPI are still unclear. Some antipsychotic drugs attenuate CRF-induced deficits in PPI in rats and mice. Here we tested the hypothesis that indirect activation of DA(1)-receptors (D(1)) and DA(2)-receptors (D(2)) contributes to the effects of CRF on PPI. We compared the effect of central administration of h/r-CRF (0.2-0.6 nmol) on PPI in mice with either a D(1) or D(2) receptor null mutation (knockout, KO) or in mice pretreated with D(1) or D(2) receptor antagonists SCH23390 (1 mg/kg) or haloperidol (1 mg/kg). D(1) and D(2) KO mice exhibited no significant differences in their sensitivity to CRF-induced disruptions of PPI. Similarly, neither SCH23390 nor haloperidol pretreatment altered the CRF-induced disruption in PPI, although both increased PPI at baseline. CRF-induced increases in startle also remained unchanged by any of the DA receptor manipulations. These results indicate that neither D(1)- nor D(2)-receptor activation is necessary for CRF to exert its effects on acoustic startle and PPI in mice.

Assessment of adolescent neurotoxicity: rationale and methodological considerations

This introduction to the special issue of Neurotoxicology and Teratology on "Risk of neurobehavioral toxicity in adolescence" begins by broadly considering the ontogeny and phylogeny of adolescence, and the potential value of animal models of adolescence. Major findings from the emerging neuroscience of adolescence are then highlighted to establish the importance of studies of adolescent neurotoxicity. A variety of methodological issues that are of particular relevance to adolescent exposures are then discussed. These include consideration of pharmacokinetic factors, inclusion of other-aged comparison group(s), and issues involving timing, route of administration, and exposure-induced alterations in growth rate. Despite such methodological challenges, research to determine whether adolescence is a time of increased vulnerability (or greater resiliency) to specific drugs and environmental toxicants is progressing rapidly, as exemplified by the work presented in the articles of this special issue.

Developmental psychopathology and neurobiology of aggression

The aim of this paper is to clarify how neural mechanisms at the molecular level, specifically the serotonergic (5-HT) system and the hypothalamic-pituitary-adrenal axis system (HPA) in conjunction with early life stress may contribute to the emergence of aggression, self-directed and otherwise, in borderline personality disorder (BPD). Chronic dysregulation of these biological systems, which function to regulate stress and emotion, may potentiate the development of impulsive aggression in borderline personality conditions. Our central premise in this paper is that brain development, stress regulation, and early pathonomic experience are interactive and cumulative in their mutual influence on the development of impulsive aggression in BPD. We review the parameters of impulsive aggression in BPD, followed by a discussion of the neurobiological and neuroendocrine correlates of impulsive aggression with and without BPD. We then focus on the developmental continuities in BPD with attention to brain maturation of 5-HT and HPA axis function during the life span and the influence of early adverse experiences on these systems. Finally, we comment on the data of the relative stability of aggression in BPD, adolescence as a developmental stage of potential vulnerability, and the course of aggressive behavior during the life span.

Disruption of cortical-limbic interaction as a substrate for comorbidity

The prefrontal cortex exerts a potent regulatory influence over subcortical systems that are involved in the regulation of affective states. In particular, the amygdala is a region that is known to play a prominent role in the expression of emotions, and this function is believed to be disrupted in affective disorders and drug abuse. In addition, dysfunction of the prefrontal cortex is believed to be a common element in many psychiatric disorders such as schizophrenia. Using electrophysiological recordings in rodents, we examined the interactions of the prefrontal cortex with the amygdala. Our studies showed that these areas are strongly interdependent, with the prefrontal cortex showing conditioned responses that depend on amygdala inputs, and in turn exerting a potent attenuation of activity within the amygdala. In particular, the ability of the prefrontal cortex to modulate amygdala activity is likely to play an important role in our ability to cope with stressors. We propose that a dysfunction within the prefrontal cortex disrupts the ability of this region to effectively modulate the amygdala, leaving the organism susceptible to detrimental effects of stressors. This would appear to be a common underlying process that may leave the individual susceptible to drug abuse and to the onset or exacerbation of psychiatric disorders such as schizophrenia and depression.

The effects of corticoptropin-releasing factor and the urocortins on striatal dopamine release induced by electrical stimulation-an in vitro superfusion study

The members of the CRF peptide family, corticotropin-releasing factor (CRF), urocortin I (Ucn I), urocortin II (Ucn II) and urocortin III (Ucn III) coordinate endocrine and behavioral responses to stress. CRF has also been demonstrated to stimulate dopamine (DA) synthesis. In our study, a superfusion system was used to investigate the effects of this peptide family on striatal DA release following electrical stimulation. The involvement of the CRF receptors was studied by pretreatment of rat striatal slices with selective CRF antagonists. CRF and Ucn I increased the release of [(3)H]DA while Ucn II and Ucn III were ineffective. The CRFR1 antagonist antalarmin inhibited the [(3)H]DA release induced by electrical stimulation and enhanced by CRF and Ucn I. The CRFR2 antagonist astressin-2B was ineffective. These results suggest that CRF and Ucn I mediate DA release through the activation of CRFR1. Ucn II and Ucn III are not involved in this process.

Hypocretin/orexin selectively increases dopamine efflux within the prefrontal cortex: involvement of the ventral tegmental area

Hypocretins (HCRTs) modulate a variety of behavioral and physiological processes, in part via interactions with multiple ascending modulatory systems. Further, HCRT efferents from the lateral hypothalamus innervate midbrain dopamine (DA) nuclei, and DA cell bodies express HCRT receptors. Combined, these observations suggest that HCRT may influence behavioral state and/or state-dependent processes via modulation of DA neurotransmission. The current studies used in vivo microdialysis in the unanesthetized rat to first characterize the effect of intracerebroventricular infusion of HCRT-1 (0.07, 0.7 nmol) on extracellular levels of DA within the prefrontal cortex (PFC) and nucleus accumbens (Acc). Electroencephalographic/electromyographic measures of sleep-wake state were collected along with select behavioral measures (eg locomotor activity, grooming). HCRT-1 dose-dependently increased PFC dialysate DA levels, and these increases were closely correlated with increases in time spent awake. In contrast, Acc DA levels were unaffected. Additional studies examined whether HCRT-1 acts directly within the ventral tegmental area (VTA) to selectively increase PFC DA efflux and modulate behavioral state. Unilateral infusion of HCRT-1 (0.1, 1.0 nmol) within the VTA increased PFC, but not Acc, DA levels. Importantly, intra-VTA infusion of HCRT-1 increased the time spent awake and grooming. Moreover, HCRT-induced increases in both time spent awake and time spent grooming were significantly correlated with post-infusion PFC DA levels. The current observations predict a prominent modulatory influence of HCRT on PFC-dependent cognitive and affective processes that results, in part, from actions within the VTA. Additionally, these observations suggest that the activation of VTA DA neurons contributes to the behavioral state-modulatory actions of HCRT.

Stress induces rapid changes in central catecholaminergic activity in Anolis carolinensis: Restraint and forced physical activity

Immobilization stress and physical activity separately influence monoaminergic function. In addition, it appears that stress and locomotion reciprocally modulate neuroendocrine responses, with forced exercise ameliorating stress-induced serotonergic activity in lizards. To investigate the interaction of forced physical activity and restraint stress on central dopamine (DA), norepinephrine (NE), and epinephrine (Epi), we measured these catecholamines and their metabolites in select brain regions of stressed and exercised male Anolis carolinensis lizards. Animals were handled briefly to elicit restraint stress, with some lizards additionally forced to run on a track until exhaustion, or half that time (50% of average time to exhaustion), compared to a control group that experienced no restraint or exercise. Norepinephrine concentrations in the hippocampus and locus ceruleus decreased with restraint stress, but returned to control levels following forced exhaustion. Levels of NE in the raphé nuclei and area postrema, and epinephrine in raphé became elevated following restraint stress, and returned to control levels following forced physical activity to 50% or 100% exhaustion. Striatal DA increased as animals were exercised to 50% of exhaustion, and returned to baseline with exhaustion. At exhaustion, striatal Epi levels were diminished, compared with controls. In the area postrema, exhaustion reversed a decline in epinephrine levels that followed forced physical activity. These results suggest that stress stimulates a rapid influence on central catecholamines. In addition, forced exercise, and even exhaustion, may alleviate the effects of restraint stress on central monoamines.

Age-dependent effects of maternal deprivation on oxidative stress in infant rat brain

Developing brain is much more sensitive to all kind of stressors than the developed brain. Early maternal deprivation causes some behavioural and physiological effects on rats. After the birth, there is no endocrinological response to stressors between post-natal 4 and 14th days, which is called stress-hyporesponsive period (SHRP) in rats. This hypo-responsiveness is time- and stressor-specific, as some more severe stressors have been shown to induce a stress response. The present study examined the effects of maternal deprivation on oxidative stress in the hippocampus, prefrontal cortex (PFC) and striatum regions of the brain both during and after SHRP of the infant rats. The results showed that maternal deprivation in SHRP increased antioxidant enzyme activities and reduced lipid peroxidation in infant rat brain. However, by the termination of SHRP, maternal deprivation reduced enzyme activities and increased lipid peroxidation. The results indicated that infant brain might be protected in SHRP from maternal deprivation-induced oxidative stress.

Role of angiotensin II and corticotropin-releasing hormone in hemodynamic responses to cocaine and stress

Cocaine produces characteristic behavioral and autonomic responses due to its unique pharmacological properties. Many of the autonomic responses resemble those to acute behavioral stress. Both cocaine and behavioral stress have been shown to evoke an increase in sympathetic nerve activity that is primarily responsible for the peripheral cardiovascular responses. We noted varying hemodynamic and sympathetic response patterns to cocaine administration and to acute behavioral stress in rats that correlate with the predisposition to develop both a sustained increase in arterial pressure and cardiomyopathies. Several lines of evidence suggest that the autonomic response patterns are dependent on the actions of central peptides including angiotensin II (Ang II) and corticotropin-releasing hormone (CRH). This is based on observations demonstrating that intracerebroventricular (icv) administration of receptor antagonists for Ang II or CRH attenuated the decrease in cardiac output (CO) and increase in vascular resistance noted in some animals after cocaine administration or startle. In contrast, icv Ang II enhances the cardiodepression associated with cocaine administration or startle. Based on this and other evidence, we propose that the autonomic response patterns to startle and to cocaine are closely related and dependent on central Ang II and CRH. Furthermore, we suggest that these central peptides may be responsible for varying predisposition to cardiovascular disease.