Involvement of the brain noradrenaline system in emotional changes caused by stress in rats

Noradrenergic tone mediates marble burying behavior after chronic stress and ethanol

RATIONALE

Stress plays a major role in the development of alcohol use disorder (AUD)-a history of chronic stress contributes to alcohol misuse, and withdrawal from alcohol elevates stress, perpetuating cycles of problematic drinking. Recent studies have shown that, in male mice, repeated chronic intermittent ethanol (CIE) and stress elevates alcohol use above either manipulation alone and impacts cognitive functions such as behavioral flexibility.

OBJECTIVE

Here, we investigated the impact of CIE and stress on anxiety in both sexes, and whether the norepinephrine (NE) system via locus coeruleus, which is implicated in both stress and alcohol motivation, is involved.

RESULTS

Male and female mice received multiple cycles of CIE and/or repeated forced swim stress (FSS), producing elevated drinking in both sexes. CIE/FSS treatment increased anxiety, which was blocked by treatment with the α1-AR inverse agonist prazosin. In contrast, administration of the corticotropin releasing factor receptor antagonist CP376395 into locus coeruleus did not reduce CIE/FSS-elevated anxiety. We also observed sex differences in behavioral responses to a history of CIE or FSS alone as well as differential behavioral consequences of prazosin treatment.

CONCLUSIONS

These data indicate that NE contributes to the development of anxiety following a history of alcohol and/or stress, and that the influence of both treatment history and NE signaling is sex dependent. These results argue for further investigation of the NE system in relation to disrupted behavior following chronic alcohol and stress, and support the assertion that treatments may differ across sex based on differential neural system engagement.

Neurobehavioral effects of alcohol in overcrowded male adolescent rats

Being a critical neurodevelopmental stage that is affected by social conditions, the period of adolescence was chosen as the age of examining possible modification of alcohol neurobehavioral effects by overcrowding. Adolescent male rats (postnatal day 35±1) were subjected to overcrowding and/or injected with ethanol, 2 g/kg, 20% w/v, (i.p.) for one week. 24 h after the last dose, motor, exploratory behavior, sociability and fear responses were assessed using open field, social interaction and defensive probe burying tests, respectively. Wet brain tissue nitric oxide and reduced glutathione contents as well as monoamine levels, namely dopamine, norepinephrine and serotonin, in addition to 5-HIAA were estimated. Overcrowding increased social play and freezing time. Alcohol administration under overcrowding condition impaired sociability and interfered with active fear response. Alcohol in normal or in under overcrowding condition, impaired motor and exploratory behavior and increased anxiety. These results indicate that concomitant exposure of male adolescent rats to overcrowding and alcohol induced adverse behavioral changes.

Effects of leisure activities at home on perceived care burden and the endocrine system of caregivers of dementia patients: a randomized controlled study

BACKGROUND

Psychological stress associated with caregiving is thought to underlie the high incidence of hypertension, ischemic heart disease, and mortality, as well as reduced immune function, among caregivers of dementia patients. Here, we examined the effects of periodic leisure activities performed by caregivers of dementia patients with care recipients at home on perceived care burden and levels of stress hormones.

METHODS

Participants were 42 caregivers aged ≥ 65 years of patients diagnosed with Alzheimer's dementia. They were randomly assigned to intervention and non-intervention groups. The intervention group underwent a leisure activity program (30 min/3 times/week for 24 weeks) with the care recipient, and the control group underwent normal care activities.

RESULTS

The Zarit Burden Interview (ZBI) score, a subjective indicator of care burden, significantly decreased after intervention in the intervention group (p < 0.05), whereas no difference was observed in the control group. No significant changes were observed in adrenaline, noradrenaline, dopamine, and cortisol levels in both groups.

CONCLUSIONS

The lack of changes in stress hormone levels despite a decrease in subjective care burden in the intervention group might be explained by the effects of the chosen leisure activity on the neuroendocrine system. Our findings suggest that periodic leisure activities can reduce perceived care burden among caregivers of dementia patients. However, in order to evaluate accurately the effects of leisure activities of the present study, long-term follow-up of both caregivers and care recipients is necessary. The Nagoya University Department of Medicine Ethics Committee Clinical Trials Registry Number is 1290.

Valeriana officinalis root extract suppresses physical stress by electric shock and psychological stress by nociceptive stimulation-evoked responses by decreasing the ratio of monoamine neurotransmitters to their metabolites

Background

In this study, we investigate the effects of valerian root extracts (VE) on physical and psychological stress responses by utilizing a communication box.

Methods

Eight-week-old ICR mice received oral administration of VE (100 mg/kg/0.5 ml) or equal volume of distilled water in every day for 3 weeks prior to being subjected to physical or psychological stress for 3 days, which are induced by communication box developed for physical electric shock and psychological stress by nociceptive stimulation-evoked responses. The stress condition was assessed by forced swimming test and serum corticosterone levels. In addition, norepinephrine (NE), serotonin (5-HT), and their metabolites such as 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO₄) and 5-hydroxyindoleacetic acid (5-HIAA) were measured in the hippocampus and amygdala at 1 h after final stress condition, respectively.

Results

Immobility time and corticosterone levels were significantly increased in both the physical and psychological stress groups compared to the control group. The administration of VE significantly reduced these parameters in both the physical and psychological stress groups. In addition, compared to the control group, physical and psychological stress groups showed significantly increased levels of MHPG-SO₄ and 5-HIAA in the hippocampus and amygdala, respectively. The administration of VE significantly suppressed the increase of MHPG-SO₄ and 5-HIAA in the two stress groups.

Conclusion

These results suggest that VE can suppress physical and psychological stress responses by modulating the changes in 5-HT and NE turnover in the hippocampus and amygdala.

Inactivation of the lateral habenula reduces anxiogenic behavior and cocaine seeking under conditions of heightened stress

Recent anatomical and functional studies have renewed interest in the lateral habenula (LHb), a critical brain region that works in an opponent manner to modulate aversive and appetitive processes. In particular, increased LHb activation is believed to drive anxiogenic states during stressful conditions. Here, we reversibly inactivated the LHb with GABA receptor agonists (baclofen/muscimol) in rats prior to testing in an open field, elevated plus maze, and defensive burying task in the presence or absence of yohimbine, a noradrenergic α2-receptor antagonist that acts as an anxiogenic stressor. In a second set of experiments using a cocaine self-administration and reinstatement model, we inactivated the LHb during extinction responding and cue-induced reinstatement of cocaine seeking in the presence or absence of yohimbine pretreatment. Inactivation of the LHb after yohimbine treatment attenuated anxiogenic behavior by increasing time spent in the open arms and reducing the time spent burying. Inactivation of the LHb also reduced cocaine seeking when cue-induced reinstatement occurred in the presence of yohimbine, but did not affect extinction responding or cue-induced reinstatement by itself. These data demonstrate that the LHb critically regulates states of heightened anxiety during both unconditioned behavior and conditioned appetitive processes.

Translational and reverse translational research on the role of stress in drug craving and relapse

RATIONALE AND BACKGROUND

High relapse rates during abstinence are a pervasive problem in drug addiction treatment. Relapse is often associated with stress exposure, which can provoke a subjective state of drug craving that can also be demonstrated under controlled laboratory conditions. Stress-induced relapse and craving in humans can be modeled in mice, rats, and monkeys using a reinstatement model in which drug-taking behaviors are extinguished and then reinstated by acute exposure to certain stressors. Studies using the reinstatement model in rats have identified the role of several neurotransmitters and brain sites in stress-induced reinstatement of drug seeking, but the degree to which these preclinical findings are relevant to the human condition is largely unknown.

OBJECTIVES AND HIGHLIGHTS

Here, we address this topic by discussing recent results on the effect of alpha-2 adrenoceptors and substance P-NK1 receptor antagonists on stress-induced reinstatement in mice and rats and stress-induced craving and potentially stress-induced relapse in humans. We also discuss brain sites and circuits involved in stress-induced reinstatement of drug seeking in rats and those activated during stress-induced craving in humans.

CONCLUSIONS

There is evidence that alpha-2 adrenoceptor agonists and NK1 receptor antagonists decrease stress-induced drug seeking in rats and stress-induced craving in humans. Whether these drugs would also prevent stress-induced drug relapse in humans and whether similar or different brain mechanisms are involved in stress-induced reinstatement in non-humans and stress-induced drug craving and relapse in humans are subjects for future research.

The neuropharmacology of relapse to food seeking: methodology, main findings, and comparison with relapse to drug seeking

Relapse to old, unhealthy eating habits is a major problem in human dietary treatments. The mechanisms underlying this relapse are unknown. Surprisingly, until recently this clinical problem has not been systematically studied in animal models. Here, we review results from recent studies in which a reinstatement model (commonly used to study relapse to abused drugs) was employed to characterize the effect of pharmacological agents on relapse to food seeking induced by either food priming (non-contingent exposure to small amounts of food), cues previously associated with food, or injections of the pharmacological stressor yohimbine. We also address methodological issues related to the use of the reinstatement model to study relapse to food seeking, similarities and differences in mechanisms underlying reinstatement of food seeking versus drug seeking, and the degree to which the reinstatement procedure provides a suitable model for studying relapse in humans. We conclude by discussing implications for medication development and future research. We offer three tentative conclusions: (1)The neuronal mechanisms of food-priming- and cue-induced reinstatement are likely different from those of reinstatement induced by the pharmacological stressor yohimbine. (2)The neuronal mechanisms of reinstatement of food seeking are possibly different from those of ongoing food-reinforced operant responding. (3)The neuronal mechanisms underlying reinstatement of food seeking overlap to some degree with those of reinstatement of drug seeking.

Hypothalamic projections to locus coeruleus neurons in rat brain

Locus coeruleus (LC) neurons respond to autonomic and visceral stimuli and discharge in parallel with peripheral sympathetic nerves. The present study characterized the synaptic organization of hypothalamic afferents with catecholaminergic neurons in the LC using electron microscopy. Peroxidase labeling of axon terminals that were anterogradely labeled from the paraventricular nucleus (PVN) was combined with gold-silver labeling of tyrosine hydroxylase in the LC. Approximately 19% of the anterogradely labeled axon terminals formed synaptic specializations with tyrosine hydroxylase-immunoreactive dendrites in the LC. Retrograde transport from the LC combined with immunocytochemical detection of enkephalin and corticotropin-releasing factor (CRF) suggested that most of the LC-projecting PVN neurons (30%) were CRF immunoreactive and few (2%) were enkephalin immunoreactive. Finally, dual retrograde tracing from the LC and median eminence revealed that PVN neurons that project to the LC are a population distinct from that projecting to the median eminence. The present data suggest that a population of hypothalamic neurons is poised to directly modulate the activity of LC neurons and may integrate autonomic responses in brain by influencing LC neurons. Moreover, PVN neurons that use CRF as a neurohormone are distinct from those that use CRF as a neuromodulator to impact on the LC.

Comparison of the effects of diazepam, the CRF1 antagonist CP-154,526 and the group II mGlu receptor agonist LY379268 on stress-evoked extracellular norepinephrine levels

The present study used an elevated platform procedure to investigate the effects of diazepam, a CRF1 antagonist CP-154,526 and a group II mGlu2/3 receptor agonist LY379268 on stress-evoked increase in extracellular norepinephrine (NE). Pretreatment with either diazepam (1 mg/kg, i.p.), CP-154,526 (20 mg/kg, i.p.) or LY379268 (1, 3 and 10 mg/kg, p.o.) significantly reduced platform stress-evoked NE. Interestingly, at the highest dose tested (10 mg/kg) LY379268 caused a marked increase in baseline NE levels. We tested whether this effect would diminish after repeated dosing. In contrast to acute administration, a challenge injection of LY379268 after repeated dosing (10 mg/kg x days) did not alter basal NE. Importantly, although less effective, LY379268 still significantly reduced stress-evoked NE. We further show that this increase in basal NE may involve mGlu2/3 receptor regulation of the GABAergic system. To this end, administration of the GABAB agonist, baclofen (4 mg/kg, i.p.), 2 h after dosing with LY379268, reversed the increase in baseline NE. These data suggest that, like diazepam and CP-154,526, group II mGlu2/3 receptor agonists can attenuate stress-evoked increase in extracellular NE in the rat prefrontal cortex. In addition they reveal a 'stress-like' increase in NE after high doses of LY379268 which may reflect mGlu3 receptor modulation of GABAergic transmission.

Group II mGlu receptor activation suppresses norepinephrine release in the ventral hippocampus and locomotor responses to acute ketamine challenge

Group II mGlu receptor agonists (eg LY379268 and LY354740) have been shown to reverse many of the behavioral responses to PCP as well as glutamate release elicited by PCP and ketamine. In the present set of experiments, we used in vivo microdialysis to show that, in addition to reversing PCP- and ketamine-evoked glutamate release, group II mGlu receptor stimulation also prevents ketamine-evoked norepinephrine (NE) release. Pretreating animals with the mixed 2/3 metabotropic glutamate (mGlu2/3) receptor agonist LY379268 (0.3-10 mg/kg) dose-dependently inhibited ketamine (25 mg/kg)-evoked NE release in the ventral hippocampus (VHipp). Ketamine hyperactivity was also reduced in a similar dose range. Following our initial observation on NE release, we conducted a series of microinjection experiments to reveal that the inhibitory effects of LY379268 on VHipp NE release may be linked to glutamate transmission within the medial prefrontal cortex. Finally, we were able to mimic the inhibitory effects of LY379268 on ketamine-evoked NE release by using a novel mGlu2 receptor selective positive modulator. (+/-) 2,2,2-Trifluoroethyl [3-(1-methyl-butoxy)-phenyl]-pyridin-3-ylmethyl-sulfonamide (2,2,2-TEMPS, characterized through in vitro GTPgammaS binding) at a dose of 100 mg/kg significantly reduced the NE response. Together, these results demonstrate a novel means to suppress noradrenergic neurotransmission (ie by activating mGlu2 receptors) and may, therefore, have important implications for neuropsychiatric disorders in which aberrant activation of the noradrenergic system is thought to be involved.

Psychological stress increases bilirubin metabolites in human urine

Some authors have suggested that psychological stress induces the production of reactive oxygen species (ROS). Some studies have supported that bilirubin exerts anti-oxidative effects in vivo. However, it is not known whether ROS induced by psychological stress provoke bilirubin oxidation in vivo. We investigated if the concentration of bilirubin oxidative metabolite (BOM), a bilirubin oxidative metabolite, increased in urine from subjects exposed to psychological stress. Sixty healthy male volunteers working in a pharmaceutical company were divided into a Group I which did not attend a conference, a Group II which attended a conference but did not deliver a speech, and a Group III which attended a conference and delivered speeches in the presence of the company executives. Subjective stress was scored (self-rating score) after subjects in Group III delivered their speeches at the conference. Urine was collected on the next day. The BOM concentrations, as measured by enzyme-linked immunosorbent assay, were normalized to the urinary concentration of creatinine. The concentration of BOM in Group III was significantly higher compared to that in Groups I and II (p<0.01 and p<0.05, respectively). Furthermore, in Group III, the concentration of BOM correlated with the self-rating stress score (r=0.53, p<0.01). These findings suggest that emotional stimuli are associated with an increase in the oxidative metabolites of bilirubin in human urine, and that BOMs could be useful markers of psychological stress.

Noradrenaline in the bed nucleus of the stria terminalis is critical for stress-induced reactivation of morphine-conditioned place preference in rats

The effect of noradrenaline in the bed nucleus of the stria terminalis and locus coeruleus on maintenance and reactivation of morphine-conditioned place preference induced by footshock stress was investigated in rats. After receiving alternate injection of morphine (10 mg/kg) and saline for 6 consecutive days, the rats spent more time in the drug-paired compartment (morphine-conditioned place preference) on day 7. These animals did not show morphine-conditioned place preference on day 37 following sham-footshock once every 3 days from days 8 to 36 (28 days drug-free). However, 15 min of intermittent footshock once every 3 days could induce the maintenance of morphine-conditioned place preference on day 37 with significantly more time spent in the drug-paired compartment than on day 0. Microinjection of the alpha(2)-adrenoceptor agonist, clonidine (0.1 or 1 microg), into the locus coeruleus 30 min before footshock did not affect stress-induced maintenance of conditioned place preference. However, infusions of clonidine (1 microg) into the bed nucleus of the stria terminalis significantly attenuated the maintenance of conditioned place preference induced by footshock stress. In another experiment, after a 21-day extinction of morphine-conditioned place preference, a single footshock could reactivate the morphine place preference that was significantly blocked by pretreatment with infusion of clonidine (0.1 or 1 microg) into the bed nucleus of the stria terminalis but not the locus coeruleus. Reactivation of morphine-conditioned place preference elicited by footshock stress was significantly inhibited by 6-hydroxydopamine-induced lesions in the ventral noradrenergic bundle, most of the norepinephrine input to the bed nucleus of the stria terminalis arising from caudal brain stem noradrenergic cell groups. In contrast, chemical lesions of the dorsal noradrenergic bundle that arises from the locus coeruleus had no such effects. These findings suggest that noradrenergic neurons in locus coeruleus are not involved in stress-induced reinstatement of drug-seeking and further clearly demonstrate that noradrenaline in the bed nucleus of the stria terminalis plays a critical role in mediating this effect. Comprehension of the neurochemical events underlying the stress-induced and the bed nucleus of the stria terminalis-mediated reinstatement of drug-seeking may, therefore, throw more light on the biological bases of drug dependence and addictive behavior

Dopamine and noradrenaline efflux in the rat prefrontal cortex after classical aversive conditioning to an auditory cue

We used bilateral microdialysis in the medial prefrontal cortex (PFC) of awake, freely moving rats to study aversive conditioning to an auditory cue in the controlled environment of the Skinner box. The presentation of the explicit conditioned stimuli (CS), previously associated with foot shocks, caused increased dopamine (DA) and noradrenaline (NA) efflux. This conditioned response was dependent on the immediate pairing of the two stimuli; in the pseudoconditioned group that received an equal number of both stimuli, but in an unpaired fashion, no conditioned increases in efflux were observed.

Selective corticotropin-releasing factor type 1 receptor antagonist blocks conditioned fear-induced release of noradrenaline in the hypothalamic paraventricular nucleus of rats

The effects of conditioned fear on the release of noradrenaline in the hypothalamic paraventricular nucleus (PVN) and the involvement of corticotropin-releasing factor (CRF) receptor type 1 (CRFR1) in conditioned fear-induced changes in noradrenaline release were examined by intracerebral microdialysis in rats. Conditioned fear was produced by placing animals into a box where they had previously been exposed to a 5-min period of electric footshock, 135 min prior to the start of experiment. Conditioned fear for 20 min produced a significant increase in the release of noradrenaline in the PVN. Intraperitoneal preadministration of a selective nonpeptidic CRFR1 antagonist, CRA1000, completely blocked the conditioned fear-induced release of noradrenaline. These results suggest that CRFR1 is involved in the release of noradrenaline in the hypothalamic PVN induced by conditioned fear.

Noradrenaline systems in the hypothalamus, amygdala and locus coeruleus are involved in the provocation of anxiety: basic studies

A variety of stressful events, including emotional stress, cause a marked increase in noradrenaline release in several brain regions, and especially in the hypothalamus, amygdala and locus coeruleus, in the rat brain. These findings suggest that an increased noradrenaline release could be closely related to the provocation of negative emotions such as anxiety and/or fear. In order to confirm this hypothesis, we carried out several studies. Diazepam, a typical benzodiazepine anxiolytic, significantly attenuated not only the immobilization stress-induced increase in noradrenaline release in the three rat brain regions but also the emotional changes of these animals, and these effects were antagonized by flumazenil, a benzodiazepine antagonist. Naloxone and opioid agents, such as morphine, beta-endorphin and [Met(5)]-enkephalin, significantly enhanced and attenuated the stress-induced increase in noradrenaline release in these regions and the stress-induced emotional change, respectively. Two stressful events which predominantly involve emotional factors, i.e., psychological stress and conditioned fear, caused significant increases in noradrenaline release selectively in these three brain regions and these increases were also significantly attenuated by pretreatment with diazepam in a flumazenil reversible manner. Yohimbine, an alpha(2)-adrenoceptor antagonist which caused a marked increase in noradrenaline release in the several brain regions, had an anxiolytic action in the two behavioral tests involving anxiety, i.e., the conditioned defensive burying test and the modified forced swim test. beta-Carbolines, which possess anxiogenic properties, significantly increased noradrenaline release in the hypothalamus, amygdala and locus coeruleus. Taken together, these findings suggest that the increased release of noradrenaline in the hypothalamus, amygdala and locus coeruleus is, in part, involved in the provocation of anxiety and/or fear in animals exposed to stress, and that the attenuation of this increase by benzodiazepine anxiolytics acting via the benzodiazepine receptor/GABAA receptor/chloride ionophore supramolecular complex may be the basic mechanism of action of these anxiolytic drugs.

Stress-induced relapse to heroin and cocaine seeking in rats: a review

Studies in humans suggest that exposure to stress increases the probability of relapse to drug use, but until recently there has been no animal model to study the mechanisms that mediate this effect. We have developed a reinstatement procedure that allows us to study the effect of stress on relapse to drug seeking in rats. Using this procedure, we have shown that exposure to intermittent footshock stress reliably reinstates heroin and cocaine seeking after prolonged drug-free periods. In the present paper, we summarize results from several studies on stress-induced reinstatement of heroin and cocaine seeking in rats. We first assess the degree to which the phenomenon of stress-induced relapse generalizes to other stressors, to behaviors controlled by other drugs of abuse, and to behaviors controlled by non-drug reinforcers. We then review evidence from studies concerned with the neurotransmitters, the brain sites, and the neural systems involved in stress-induced reinstatement of drug seeking. Finally, we consider the mechanisms that might underlie stress-induced relapse to drug seeking and the possible implications of the findings for the treatment of relapse to drug use in humans.

Catecholaminergic mechanisms underlying neurohypophysial hormone responses to unconditioned or conditioned aversive stimuli in rats

Oxytocin release from the neurohypophysis is facilitated by systemic cholecystokinin octapeptide (CCK) administration and noxious stimuli. Oxytocin release after CCK administration is mediated by A2 noradrenergic neurones while the release after noxious stimuli appears to be mediated by A1 noradrenergic neurones. On the other hand, facilitation of vasopressin release after noxious stimuli is not dependent upon noradrenergic neurones but on dopamine receptors. Environmental stimuli previously paired with noxious stimuli (conditioned fear stimuli) or novel environmental stimuli facilitate oxytocin release and suppress vasopressin release. These neuroendocrine responses to conditioned fear stimuli, but not to novel stimuli, are impaired by central noradrenaline depletion or i.c.v. adrenoceptor antagonists. These data suggest that there are at least two types of stress responses in neuroendocrine systems, one noradrenaline dependent, and one noradrenaline independent. It is also suggested that noradrenergic neurones are functionally heterogeneous in the control of oxytocin release.

Clonidine blocks stress-induced reinstatement of heroin seeking in rats: an effect independent of locus coeruleus noradrenergic neurons

Using a reinstatement procedure, it has been shown that intermittent footshock stress reliably reinstates extinguished drug-taking behaviour in rats. Here we studied the role of noradrenaline (NE), one of the main brain neurotransmitters involved in responses to stress, in reinstatement of heroin seeking. We first determined the effect of clonidine, an alpha-2 adrenergic receptor agonist that decreases NE cell firing and release, on stress-induced reinstatement of heroin seeking. Rats were trained to self-administer heroin (0.1 mg/kg per infusion, IV, three 3-h sessions per day) for 9-10 days. Extinction sessions were given for up to 11 days during which saline was substituted for the drug. Tests for reinstatement were then conducted after exposure to intermittent footshock (5, 15 and 30 min, 0.5 mA). During testing, clonidine was injected systemically (10-40 microgram/kg, i.p.) or directly into the lateral or fourth ventricles (1-3 microram). Clonidine (1-2 microgram per site) or its charged analogue, 2-[2, 6-diethylphenylamino]-2-imidazole (ST-91, 0.5-1 microgram per site), was also injected bilaterally into the locus coeruleus (LC), the main noradrenergic cell group in the brain. Clonidine blocked stress-induced reinstatement of drug seeking when injected systemically or into the cerebral ventricles. In contrast, neither clonidine nor ST-91 consistently altered stress-induced reinstatement when injected into the locus coeruleus. We therefore studied the effect of lesions of the lateral tegmental NE neurons on stress-induced reinstatement. 6-Hydroxydopamine (6-OHDA) lesions performed after training for heroin self-administration had no effect on extinction of heroin-taking behaviour, but significantly attenuated reinstatement induced by intermittent footshock. These data suggest that: (i) clonidine prevents stress-induced relapse to heroin seeking by its action on neurons other than those of the locus coeruleus; and (ii) activation of the lateral tegmental NE neurons contributes to stress-induced reinstatement of heroin seeking.

Involvement of central beta-adrenoceptors in the tachycardia induced by water immersion stress in rats

The purpose of the present study was to investigate whether central beta-adrenoceptors are involved in stress-induced cardiovascular responses in rats. Using a biotelemetry system, blood pressure and heart rate were measured at rest and during stress induced by immersion in 1 cm-deep water. Intracerebroventricular (i.c.v.) injections of a nonselective beta-adrenoceptor antagonist, DL-propranolol (5 or 50 microg), significantly and dose dependently attenuated the tachycardia induced by water immersion stress (drug-induced reduction of tachycardia at 5 min after the start of stress: 61.4 +/- 13.2% for 5 microg, 72.5 +/- 8.2% for 50 microg). The same doses of DL-propranolol had no effect on the resting heart rate. Injection (i.c.v.) of a lower dose (5 microg) of D-propranolol--which has a lower potency as a beta-adrenoceptor antagonist than DL-propranolol, but a similar local anesthetic, membrane-stabilizing activity--did not attenuate the stress-induced tachycardia, although a higher dose (50 microg) did. Intravenous administration of DL-propranolol (5 or 50 microg) significantly attenuated the stress-induced tachycardia (drug-induced reduction of tachycardia at 5 min after the start of stress: 20.0 +/- 7.5% for 5 microg, 42.4 +/- 3.4% for 50 microg). However, the attenuation was much smaller than in the i.c.v. DL-propranolol-injected group. The i.c.v. injection of the 50 microg dose of DL-propranolol significantly augmented both the resting blood pressure and the pressor response to water immersion stress, whereas the lower dose (5 microg) had no effect. The i.c.v. injection of 50 microg D-propranolol also augmented, although not significantly, the resting blood pressure and the pressor response to stress. These results suggest that central beta-adrenoceptors are involved in the tachycardia induced by water immersion stress in rats.

Role of adrenoceptors in vasopressin, oxytocin and prolactin responses to conditioned fear stimuli in the rat

Conditioned fear or novel environmental stimuli suppress vasopressin (VP) and augment oxytocin (OT) and prolactin (PRL) release in rats. We examined the effects of intracerebroventricular (i.c.v.) injections of adrenoceptor antagonists on these neuroendocrine responses to conditioned fear or novel environmental stimuli in male rats. A beta1 antagonist, metoprolol, blocked the VP but not the OT or PRL response to conditioned fear stimuli, but did not abolish neuroendocrine responses to novel environmental stimuli. A beta2 antagonist, ICI118551, impaired the PRL but not the VP or OT response to fear or novel environmental stimuli. In rats injected with a alpha1 adrenoceptor antagonist, benoxathian, conditioned fear stimuli did not significantly induce the VP, OT or PRL responses. The effects of benoxathian were not due to a general reduction of arousal, since benoxathian did not prevent the VP, OT or PRL response to novel environmental stimuli. These data suggest that beta1 adrenoceptors play a selective role in the VP response to conditioned fear stimuli, as do beta2 adrenoceptors in the prolactin response to conditioned fear and novel environmental stimuli. We conclude that alpha1 adrenoceptors play a facilitative role in VP, OT, PRL responses to conditioned fear stimuli.

Role of noradrenergic projections to the bed nucleus of the stria terminalis in neuroendocrine and behavioral responses to fear-related stimuli in rats

The bed nucleus of the stria terminalis (BNST) receives dense noradrenergic projections from the brainstem and has been claimed to play a role in expression of a variety of stress responses. Fear-related stimuli suppress vasopressin and facilitate oxytocin release from the neurohypophysis and induce behavioral suppression. Here we investigated in male rats whether conditioned fear stimuli increase noradrenergic activity in the BNST and whether depletion of epinephrine content in the BNST prevents neuroendocrine and behavioral responses to fear stimuli. Environmental stimuli previously paired with electric footshocks increased the ratio of 3-methoxy-4-hydroxyphenylglycol to norepinephrine contents in the BNST, suggesting that the stimuli activated noradrenergic projections to the BNST. 5-Amino-2, 4-dihydroxy-alpha-methylphenylethylamine, a neurotoxin relatively selective for noradrenergic fibers, when injected into the BNST 7 days before measurement, decreased the content of norepinephrine by 95% and that of dopamine or serotonin by about 50%. In the rats that received the neurotoxin, the suppressive vasopressin but not the augmentative oxytocin response to intermittent footshocks was abolished. In the experiments with conditioned fear stimuli, the neurotoxin given before training partially but significantly impaired the suppressive vasopressin and behavioral responses to testing stimuli. The neurotoxin given after training, however, did not prevent the vasopressin, oxytocin or behavioral responses. The results suggest that noradrenergic fibers in the BNST mediate the suppressive vasopressin but not the augmentative oxytocin response to nonassociatively applied fear stimuli and that they modulate, in a facilitative fashion, acquisition but not retention or recall of the emotional memory associated with the vasopressin and behavioral responses to conditioned fear stimuli.

Noradrenaline in basic models of depression

This review reports anatomical studies evaluating central and peripheral alpha 2- and beta-adrenoceptors. The results suggest abnormalities exist in the noradrenergic system in depressed patients. Most animal models involve the use of stress to simulate depression in man. All models that have been developed lead to differential changes in noradrenergic function. We have assessed the effects of reboxetine, a novel, selective noradrenaline-reuptake inhibitor (NARI) in olfactory bulbectomised rats, a procedure that induces significant changes in amygdala function. Reboxetine is an effective antidepressant in the forced swim test and open field test in bulbectomised rats. Unlike the tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs), reboxetine is ineffective in the 8-OH-DPAT hypothermia test, indicating that reboxetine is selective for the noradrenergic system. Owing to the abnormalities that occur in depression, it would seem sensible to target the noradrenergic system for treatment of this condition.

Use of animal models in peptic ulcer disease

Considerable progress has been made in the understanding of the formation of gastric erosions by the use of animals. The role of gastric acid secretion in their pathogenesis has been clarified. Gastric erosions are associated with the presence of acid in the stomach and slow gastric contractions. With several different experimental procedures, the animal's body temperature falls; preventing the fall averts erosions. A fall in body temperature or exposure to cold are associated with the secretion of thyrotropin-releasing hormone (TRH), and both increased and decreased concentration of corticotropin-releasing factor (CRH) in discrete regions of rat brains. Thyrotropin-releasing hormone when injected into specific sites in the brain produces gastric erosions and increases acid secretion and slow contractions, whereas CRH has the opposite effects. One of the major sites of interaction of the two peptides is in the dorsal motor complex of the vagus nerve. Thyrotropin-releasing hormone increases serotonin (5-HT) secretion into the stomach. Serotonin counter-regulates acid secretion and slow contractions. Many other peptides injected into discrete brain sites stimulate or inhibit gastric acid secretion.

Role of the amygdala in the coordination of behavioral, neuroendocrine, and prefrontal cortical monoamine responses to psychological stress in the rat

Exposure to mild stress is known to activate dopamine (DA), serotonin (5-HT), and norepinephrine (NE) metabolism in the anteromedial prefrontal cortex (m-PFC). Neuroanatomical site(s) providing afferent control of the stress activation of the m-PFC monoaminergic systems is at present unknown. The present study used a conditioned stress model in which rats were trained to fear a substartle-threshold tone paired previously with footshock and assessed for behavioral, neuroendocrine, and neurochemical stress responses. Bilateral NMDA-induced excitotoxic lesioning of the basolateral and central nuclei of the amygdala was performed before or after training. Pretraining amygdala lesions blocked stress-induced freezing behavior, ultrasonic vocalizations, adrenocortical activation, and dopaminergic metabolic activation in the m-PFC. Post-training amygdala lesions blocked stress-induced m-PFC DA, 5-HT, and NE metabolic activation. Post-training amygdala lesions also blocked stress-induced freezing and defecation, and greatly attenuated adrenocortical activation. These data provide evidence of amygdalar control of stress-induced metabolic activation of the monoaminergic systems in the m-PFC, as well as amygdalar integration of behavioral and neuroendocrine components of the rat stress response. These results are discussed in terms of possible relevance to stress-induced exacerbation of schizophrenic symptoms and the pathophysiology of posttraumatic stress disorder.

Input from central nucleus of the amygdala efferents to pericoerulear dendrites, some of which contain tyrosine hydroxylase immunoreactivity

Light microscopic anterograde tracing studies indicate that neurons in the central nucleus of the amygdala (CNA) project to a region of the dorsal pontine tegmentum ventral to the superior cerebellar peduncle which contains noradrenergic dendrites of the nucleus locus coeruleus (LC). However, it has not been established whether the efferent terminals from the CNA target catecholamine-containing dendrites of the LC or dendrites of neurons from neighboring nuclei which may extend into this region. To examine this question, we combined immunoperoxidase labeling of the anterograde tracer biotinylated dextran amine (BDA) from the CNA with immunogold-silver labeling of the catecholamine-synthesizing enzyme tryrosine hydroxylase (TH) in the rostrolateral LC region of adult rats. By light microscopy, BDA-labeled processes were dense in the dorsal pons within the parabrachial nuclei as well as in the pericoerulear region immediately ventral to the superior cerebellar peduncle. Higher magnification revealed that BDA-labeled varicose fibers overlapped TH-labeled processes in this pericoerulear region. By electron microscopy, anterogradely labeled axon terminals contained small, clear as well as some large dense core vesicles and were commonly apposed to astrocytic processes along some portion of their plasmalemma. BDA-labeled terminals mainly formed symmetric type synaptic contacts characteristic of inhibitory transmitters. Of 250 BDA-labeled axon terminals examined where TH immunoreactivity was present in the neuropil, 81% contacted unlabeled and 19% contacted TH-labeled dendrites. Additionally, amygdala efferents were often apposed to unlabeled axon terminals forming asymmetric (excitatory type) synapses. These results demonstrate that amygdaloid efferents may directly alter the activity of catecholaminergic and non-catecholaminergic neurons in this pericoerulear region of the rat brain. Furthermore, our study suggests that CNA efferents may indirectly affect the activity of pericoerulear neurons through modulation of excitatory afferents. Amygdaloid projections to noradrenergic neurons may help integrate behavioral and visceral responses to threatening stimuli by influencing the widespread noradrenergic projections from the LC.

Enkephalin terminals form inhibitory-type synapses on neurons in the rat nucleus locus coeruleus that project to the medial prefrontal cortex

Norepinephrine-containing fibres in the medial prefrontal cortex derive from the locus coeruleus, a brainstem nucleus which also receives a dense innervation of enkephalin-immunoreactive axon terminals. We combined immunogold-silver labelling of retrogradely transported FluoroGold from the medial prefrontal cortex with immunoperoxidase detection of leucine5-enkephalin in the same section of tissue through the locus coeruleus of adult rats. This dual-labelling experiment was conducted to determine whether axon terminals containing lecuine5-enkephalin target neurons in the locus coeruleus that project to the frontal cortex and, if so, what are their morphological characteristics. By light microscopy, enkephalin-labelled processes overlapped FluoroGold retrogradely labelled neurons in the locus coeruleus. By electron microscopy, retrogradely labelled perikarya and dendrites were commonly enveloped by astrocytic processes and received few afferents in the plane of section examined. However, at sites unoccupied by glial processes, abundant afferent input could be identified. In addition, some FluoroGold-labelled perikarya and dendrites lacked this glial ensheathment but were more frequently apposed by axon terminals. Of 163 FluoroGold-labelled perikarya and dendrites examined where enkephalin immunoreactivity was present in the neuropil, 42% were contacted by enkephalin-immunoreactive axon terminals. The peroxidase-labelled enkephalin terminals as well as the unlabelled terminals often contained both small, clear and large dense core vesicles. Both labelled and unlabelled terminals also formed primary symmetric synapses characteristic of inhibitory transmitters with retrogradely labelled perikarya and proximal dendrites. At times, more than one enkephalin-labelled terminal was found to converge on a common retrogradely labelled perikarya or dendrite. These results demonstrate cellular sites where enkephalin-containing afferents may directly modulate and most likely inhibit the activity of cortically projecting neurons in the locus coeruleus.

Forebrain pathways and their behavioural interactions with neuroendocrine and cardiovascular function in the rat

1. The forebrain is a major organizer of the complex behavioural, physiological and neuroendocrine responses to environmental challenges of a stressful nature. 2. Combined physiological and neuroanatomical studies suggest that a specific forebrain-brain stem network, composed of connections between the central nucleus of the amygdala, the paraventricular nucleus of the hypothalamus, the mesencephalic cuneiform nucleus, the parabrachial nucleus and the dorsal motor nucleus of the vagus nerve, may be important for integrating behavioural and physiological responses. 3. Based on studies using bilateral electrolytic lesions of the central nucleus of the amygdala, it has become clear that the central nucleus of the amygdala is one of the key structures involved in unconditioned responses to inescapable footshock. These responses include freezing behaviour, tachycardia and the release of adrenaline, noradrenaline, prolactin and corticosterone. However, this nucleus is involved only in the freezing behaviour and bradycardiac responses to conditioned emotional stress or to social defeat. 4. Both peptidergic (corticotropin releasing hormone and vasopressin/oxytocin) and aminergic (noradrenaline and dopamine) mechanisms in the central amygdala are involved in the regulation of integrated behavioural, physiological and neuroendocrine stress responses. This is indicated by studies with an infusion of an agonist and/or antagonist of the peptides or neurotransmitters into the central amygdala of freely moving rats. Sympathetic cardiac control is intensified by corticotropin releasing hormone and oxytocin, probably by inhibiting vagal output. In contrast, vagal activity is facilitated by vasopressin, noradrenaline and dopamine.

Ca(2+)-antagonistic action of bevantolol on hypothalamic neurons in vitro: its comparison with those of other beta-adrenoceptor antagonists, a local anesthetic and a Ca(2+)-antagonist

The Ca(2+)-antagonistic action of bevantolol, a beta 1-adrenoceptor antagonist, on high- and low-voltage activated Ca2+ currents (HVA- and LVA-ICa) was examined on neurons dissociated from rat brain. Bevantolol (10(-6) to 10(-4) M) inhibited concentration-dependently both ICa. The IC50 value of bevantolol for LVA-ICa was 4 x 10(-5) M, while bevantolol at 10(-4) M inhibited HVA-ICa by 28.5 +/- 7.7%. The potency of bevantolol in inhibiting both ICa was greater than those of propranolol, labetalol and lidocaine, while the inhibitory action of bevantolol on voltage-activated Na+ current was weakest among them. Bevantolol may possess Ca(2+)-antagonistic action that is independent from local anesthetic action.

Pattern and time course of immediate early gene expression in rat brain following acute stress

The pattern and time course of brain activation in response to acute swim and restraint stress were examined in the rat by in situ hybridization using complementary RNA probes specific for transcripts encoding the products of the immediate early genes c-fos, c-jun and zif/268. A widespread pattern of c-fos messenger RNA expression was detected in response to these stressors; surprisingly, the expression patterns were substantially similar following both swim and restraint stress. A dramatic induction of c-fos messenger RNA was observed in numerous neo- and allocortical regions, the lateral septal nucleus, the hypothalamic paraventricular and dorsomedial nuclei, the anterior hypothalamic area, the lateral portion of the retrochiasmatic area, the medial and cortical amygdaloid nuclei, the periaqueductal gray, and the locus coeruleus; however, a prominent induction of c-fos was also seen in numerous additional subcortical and brainstem regions. Although not as widely expressed in response to stress as c-fos, induction of zif/268 messenger RNA was also detected throughout many brain areas; these regions were largely similar to those in which c-fos was induced, although in a number of regions zif/268 was expressed in regions devoid of c-fos messenger RNA. Few brain areas showed increased expression of c-jun following stress; these regions also showed induction of c-fos and/or zif/268. The time courses of expression of all three immediate early genes were similar, with peak levels observed at the 30 or 60 min time point, and a markedly reduced signal evident at 120 min post-stress. However, in a number of cases a delayed and/or prolonged induction was noted that may be indicative of secondary neuronal activation. A number of recent studies have attempted to define neural pathways which convey stress-related information to the hypothalamic-pituitary-adrenal axis. The present results reveal a widespread pattern of neuronal activation in response to acute swim or restraint stress. These findings may aid in the identification of stress-specific neural circuits and are thus likely to have important implications for our understanding of neuronal regulation of the stress response.

Differential changes in rat brain noradrenaline turnover produced by continuous and intermittent restraint stress

This experiment was performed to investigate differential effects of continuous and intermittent restraint stress on noradrenaline (NA) turnover in brain regions of male Wistar rats by measuring levels of a major metabolite of NA, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) levels, as well as by measuring levels of plasma corticosterone and organ weights of the thymus, spleen, and adrenal glands. Rats in the 15-min and 30-min intermittently stressed groups showed significantly larger increases in MHPG-SO4 levels in most brain regions relative to those in the 90-min and 180-min continuously stressed groups, even though the total stress duration was equal or shorter. Body weight loss and loss of relative thymus weight in the 15-min intermittently stressed groups were the most marked among the five treatment groups. These findings suggest that stress-rest cyclicity is critical in determining the extent of stress-induced brain NA turnover and peripheral physiological responses.

Electric-foot-shock induced the suppression of fibrinolytic activity in rats

Electric-foot-shock was given to rats to initiate constant mental stress and its effect on fibrinolytic activity was analyzed. After the termination of electric-foot-shock which was given for an hour, euglobulin clot lysis time in the stressed group significantly prolonged than those in the control group. tissue plasminogen activator activity was also significantly lower in the stressed group. These effects lasted at least for an hour and returned to the control values 24 hours after the stress. Whole blood serotonin levels, which mainly show serotonin contents in platelets, were higher in the stressed group. A negative correlation between whole blood serotonin and tPA activity in the stressed group was obtained. These results suggest that prolonged mental stress impairs fibrinolysis by decreasing tPA activity with a concomitant increase of serotonin contents in platelets.

Amygdaloid noradrenaline is involved in the sensitization of the acoustic startle response in rats

The present study examined the role of noradrenaline (NA) in the central nucleus of the amygdala (cA) in the sensitization of the acoustic startle response (ASR) in rats. In the first experiment, local microinjections of 0, 0.5, 1, 2 nmol of the alpha 2-adrenergic antagonist yohimbine into the cA increased the magnitude of the ASR in a dose-dependent way. In the second experiment, foot shocks were applied to increase the ASR amplitude (sensitization). Local microinjections of 0, 4, 8, 16 nmol of the alpha 2-adrenergic agonist ST-91 into the cA dose dependently decreased the sensitizing effects of foot shocks on the amplitude of the ASR. It is conjectured that yohimbine increases and ST-91 decreases local NA release by acting at presynaptic autoreceptors. The present data suggest that the release of NA in the cA is involved in the mediation of the sensitizing effects of foot shocks on the ASR.

Psychological stress increases serotonin release in the rat amygdala and prefrontal cortex assessed by in vivo microdialysis

The effects of psychological stress on serotonin (5-HT) release were studied in the basolateral amygdaloid nucleus and the prefrontal cortex in conscious rats with in vivo microdialysis. Psychological stress, wherein emotional factors were predominantly involved, significantly increased extracellular 5-HT levels in these two areas. These findings suggest that activation of serotonergic neurons in these brain regions is involved in the emotional and/or cognitive states in animals.

A CRF antagonist attenuates stress-induced increases in NA turnover in extended brain regions in rats

We investigated the effects of intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) antagonist, alpha-helical CRF9-41 (ahCRF), on increases in noradrenaline (NA) turnover caused by immobilization stress in rat brain regions. Pretreatment with ahCRF (50 or 100 micrograms) significantly attenuated increases in levels of 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), the major metabolite of NA in rat brain, in the locus coeruleus (LC) region, and attenuated the MHPG-SO4/NA ratio after immobilization stress for 50 min in the cerebral cortex, hippocampus, amygdala, midbrain and hypothalamus. However, stress-induced increases in plasma corticosterone levels were not decreased significantly by pretreatment with ahCRF. These results suggest that CRF, released during stress, causes increases in NA release in extended brain regions of stressed rats.

Effects of bevantolol HCl on immobilization stress-induced hypertension and central beta-adrenoceptors in rats

Effects of chronic treatment with bevantolol, a beta-adrenoceptor blocker, and of repeated immobilization stress on blood pressure, body weight, and [3H]dihydroalprenolol ([3H]DHA) binding to the cerebral cortex were examined in rats. Systolic blood pressure increased to approximately 150 mmHg when stress was applied for 14 days (2 h day-1). This increase was inhibited by chronic treatment with bevantolol (250 mg kg-1 daily). However, bevantolol did not suppress the inhibition of body weight gain by stress. The maximum number of [3H]DHA binding sites (Bmax) in the cerebral cortex was decreased by stress without changing the affinity, and the decrease in Bmax mainly reflected the reduction of beta 1-adrenoceptors. Bevantolol treatment (250 mg kg-1) increased the Bmax to 137% and completely inhibited the downregulation of beta-adrenoceptors by stress. These results show that bevantolol can inhibit both the hypertension and downregulation of the central beta 1-adrenoceptors induced by stress.

Corticotropin-releasing factor activates the noradrenergic neuron system in the rat brain

The effect of corticotropin-releasing factor (CRF) on central noradrenaline (NA) metabolism was examined by measuring levels of the major metabolite of NA, 3-methoxy-4-hydroxy-phenylethyleneglycol sulfate (MHPG-SO4) in several rat brain regions. Various doses of CRF ranging from 0.5-10 micrograms injected ICV significantly increased MHPG-SO4 levels in several brain regions including the hypothalamus, amygdala, midbrain, locus coeruleus (LC) region, and pons + medulla oblongata excluding the LC region. Plasma corticosterone levels were also significantly increased after ICV CRF administration up to 0.5 micrograms. The present results that CRF not only elevates plasma corticosterone levels but also increases NA metabolism in many brain regions suggest its neurotransmitter and/or neuromodulator role exerting the excitatory action on central NA neurons.

Activation of brainstem catecholaminergic neurons by conditioned and unconditioned aversive stimuli as revealed by c-Fos immunoreactivity

In an attempt to define areas of the brain that respond to stressors and influence immune function, we have previously identified stress-induced, c-Fos-immunoreactive areas of the diencephalon. We found that c-Fos was strongly expressed in cells of the paraventricular nuclei (some of which contain corticotropin-releasing hormone (CRH)) and other hypothalamic areas directly associated with autonomic function. To further characterize the presumptive pathways mediating stress-induced immune alterations, including the assessment of brainstem catecholaminergic neuron involvement, the induction of c-Fos immunoreactivity was examined in the brainstem of rats exposed to conditioned and unconditioned, immunomodulating stimuli. In response to electric footshock (the unconditioned stimulus (US)), c-Fos immunoreactivity was strongly induced in the noradrenergic neurons of the locus ceruleus (A6), the nucleus of the solitary tract (A2/C2), the ventral lateral medulla (A1/C1), A5, and A7, as well as in unidentified neurons of the dorsal and ventral subdivisions of the periaqueductal gray (PAG), and in the serotonergic neurons of the dorsal raphe nuclei. Conditioned animals re-exposed to the conditioned stimulus showed c-Fos induction in these same areas but to a lesser degree. Control animals exposed only to the conditioning stimulus (CS) (electronic tone) in the absence of the US, expressed very little, if any, c-Fos activity in the above loci except for a small degree of baseline expression in the PAG. These results further confirm the role of autonomic and endocrine pathways as mediators of the stress response and will help to more fully characterize the pathways of stress-induced immune alteration.

Differential effects of tight and loose 2-hour restraint stress on extracellular concentrations of dopamine in nucleus accumbens and anteromedial frontal cortex

Changes in the extracellular dopamine (DA) concentrations were examined in the nucleus accumbens (NAS) and anteromedial frontal cortex (AMFCx) during either 2-hr loose or tight restraint stress by means of a microdialysis method. Loose restraint induced significant 100% and 30% increases in DA release in the AMFCx and NAS, respectively, and the increased DA levels returned to the control values despite continued stress. Tight restraint induced an almost constant 100-130% increase during stressing in the AMFCx and a 30% reduction in the NAS. Transient increases in DA release were observed in both regions soon after the cessation of loose, but not tight, restraint.

Regional differences in the regulation of dopamine and noradrenaline release in medial frontal cortex, nucleus accumbens and caudate-putamen: a microdialysis study in the rat

Dopamine (DA) and noradrenaline (NA) extracellular levels have been measured by microdialysis in the medial frontal cortex (MFC), nucleus accumbens (NAc) and caudate-putamen (CP) under baseline conditions in awake and halothane-anaesthetized rats, and after application of three types of stimuli which are likely to activate the brainstem catecholaminergic systems: mild stressors (handling and tail pinch), rewarded behavior (eating palatable food without prior food deprivation) and electrical stimulation of the lateral habenular nucleus. Changes were studied with and without uptake blockade (10 microM nomifensine in the perfusion fluid). The influence of calcium concentration (1.2 or 2.3 mM in the perfusion fluid) on DA and NA overflow was tested in some cases. Handling and tail pinch stimulated both DA and NA overflow in MFC, and enhanced NA overflow in NAc. By contrast, these mildly stressful stimuli had only marginal effects on DA overflow in NAc and no effects on either DA or NA overflow in CP. Eating behavior was accompanied by increased DA and NA overflow in MFC but had no effect in NAc. These regional differences were similar also when the manipulations were applied under uptake blockade, which indicates that the more pronounced changes seen in MFC did not simply reflect a more sparse innervation (i.e. lower density of uptake sites) in the MFC compared to the more densely innervated NAc and CP areas. Stimulation of the lateral habenula induced a 2-3-fold increase in NA overflow in both MFC, NAc and CP but had no consistent effect on DA overflow in any region. The effect on NA release was abolished by a transection of the ipsilateral fasciculus retroflexus (which carries the efferent output of the lateral habenula). The results show that the forebrain DA and NA projections to cortical and striatal targets are differentially regulated during ongoing behavior, that the mesocortical and mesostriatal DA systems respond quite differently to stressful and rewarding stimuli; and that the NA projection to MFC (like the dopaminergic one) is more responsive to stressful and rewarding stimuli than the ones innervating the striatum (NAc and CP). The results support the view that environmental stimuli evoking emotional arousal (whether aversive or non-aversive) are accompanied by increased DA and NA release above all in the MFC and only to a minor extent in limbic and striatal areas.

Effect of corticosterone on noradrenergic nuclei in the pons-medulla and [3H]NA release from terminals in hippocampal slices

The aim of the present study was to investigate possible membrane and genomic effects of corticosterone on the noradrenergic system of the rat brain. Corticosterone effects were studied in vivo by treating rats s.c. with 10 mg/kg corticosterone for 7 or 14 days. In the first two experiments corticosterone significantly decreased the noradrenaline (NA) and dopamine (DA) levels in the pons-medulla, an area which contains the A1-A7 noradrenergic cell groups, while the NA and DA levels in the dorsal hippocampus remained unchanged. In a third experiment where the locus coeruleus (LC) and the A1 and A2 nuclei (A1,A2) were analysed separately, NA levels were unchanged but total MHPG levels and the total MHPG/NA ratio were decreased in the A1,A2 area. Chronic corticosterone treatment (14 days) did not alter the alpha 2-adrenoceptor-mediated modulation of [3H]NA release from dorsal hippocampal slices. Neither the spontaneous outflow nor the electrically stimulated release of [3H]NA from dorsal hippocampal slices of untreated rats was affected by exposure of the slices to corticosterone (10(-7) M - 10(-4) M) in the superfusion buffer. Thus, chronic corticosterone treatment of rats altered the noradrenergic system of the pons-medulla, but did not change the alpha 2-adrenoceptor-mediated modulation of NA release in the dorsal hippocampus, a major terminal area of the LC neurons. Corticosterone also did not appear to have a direct membrane effect on the NA terminals in the dorsal hippocampus of the rat.

Psychological stress-induced increases in noradrenaline release in rat brain regions are attenuated by diazepam, but not by morphine

By measuring levels of noradrenaline (NA) and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) in the hypothalamus, amygdala and locus coeruleus region, we investigated the effects of diazepam 5.0 mg/kg, morphine 6.0 mg/kg, or naloxone at 5.0 or 10 mg/kg injected SC immediately before stress exposure, on increases in NA release caused by psychological stress. Psychological stress, wherein rats were exposed to emotional responses which were displayed by other electrically shocked rats, significantly increased MHPG-SO4 levels in the three brain regions examined and elevated plasma corticosterone levels. Both increases in brain MHPG-SO4 levels and elevations of plasma corticosterone levels induced by stress were attenuated significantly by diazepam but neither by morphine nor by naloxone. MHPG-SO4 levels in the hypothalamus and amygdala in the morphine-stress group were significantly higher than those in the saline-stress group. These findings suggest that psychological stress, in which an emotional factor is predominantly involved, causes increases in NA release in these brain regions examined and that these increases are attenuated only by diazepam, in contrast to the previous report, where increases in brain NA release caused by immobilization stress are attenuated not only by diazepam but also by morphine and are enhanced by naloxone.