Acceleration by stress of dopamine synthesis and metabolism in prefrontal cortex: antagonism by diazepam

Effects of beta-carboline on fear-related behavioral and neurohormonal responses in infant rhesus monkeys

We examined the effects of the inverse benzodiazepine agonist ethyl-beta-carboline-3-carboxylate (beta-CCE) on behavioral, hormonal, and neurochemical responses in infant rhesus monkeys exposed to fearful situations. Our paradigm elicits three distinct adaptive patterns of defensive behavior. From previous work, we hypothesized that behaviors induced by attachment bond disruption are predominantly mediated by opiate systems, whereas behaviors induced by the threat of attack are mediated by benzodiazepine systems. When beta-CCE (0, 125, 250, and 500 micrograms/kg) was administered immediately after maternal separation, the 500 micrograms/kg dose increased freezing and the 250 and 500 micrograms/kg doses reduced environmental exploration. Test conditions produced increased plasma ACTH and cortisol concentrations and increased cerebrospinal fluid (CSF) concentrations of MHPG and DOPAC; beta-CCE did not further affect these metabolites. A dose of 1000 micrograms/kg of beta-CCE increased CSF concentrations of DOPAC and MHPG in infants left with their mothers. During test conditions, it further increased CSF MHPG (but not DOPAC) concentrations, and reduced cooing while increasing freezing and barking and other hostile behaviors. Our results thus confirm that benzodiazepine systems mediate threat-related behaviors and suggest that coos, which were thought to predominantly reflect the degree of distress during separation, can be modulated by the infant's level of fear. beta-CCE also activated stress-related pituitary-adrenal hormonal systems and brain norepinephrine (NE) and dopamine (DA) systems. These effects occurred when animals remained undisturbed in their home cages with their mothers, suggesting that benzodiazepine receptors directly modulate brain NE and DA systems.

Effects of immobilization stress and of a benzodiazepine derivative on rat central dopamine system

The effects of a novel benzodiazepine derivative, Ro 16-6028 on rat brain dopamine system were examined under stress and non-stress conditions. Thirty minutes restraint stress increased dopamine synthesis in two dopamine neuron regions, prefrontal cortex and nucleus accumbence. Ro 16-6028 inhibited potently dopamine synthesis in prefrontal cortex, nucleus accumbens and striatum in dose dependent manner under non-stress condition. Furthermore, Ro 16-6028 reverses the stress-induced augmentation of the synthesis in prefrontal cortex. These findings indicate that Ro 16-6028 has an anxiolytic profile and that central dopamine system plays an important role in stress reaction.

Positron emission tomography and magnetic resonance imaging: a review and a local circuit neurons hypo(dys)function hypothesis of schizophrenia

A review of brain imaging (PET and MRI) studies on schizophrenia and recent data from neuroanatomy, neurophysiology, neuropathology, neurochemistry, neuropsychology, and cortical organization theory is integrated with the concept of local circuit neurons (LCNs) in a new hypothesis--the local circuit neurons hypo(dys)function hypothesis of schizophrenia--that attempts to explain the pathogenesis and pathophysiology of schizophrenia through a hypofunction (or dysfunction) of the local circuit neurons in prefrontal and limbic-temporal areas. This hypofunction (dysfunction) is then related to the neurocircuitry, neuropsychology, and psychopathology of schizophrenia.

Psychological stress increases dopamine turnover selectively in mesoprefrontal dopamine neurons of rats: reversal by diazepam

The effects of psychological stress on catecholamine and indoleamine metabolism were examined in various brain regions of rats. Psychologically stressed rats were exposed to emotional responses of foot-shocked rats, but were themselves prevented from receiving foot-shock. Psychological stress for 30 min resulted in significant increases of both 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels in the medial prefrontal cortex (MPFC), but not in other dopamine (DA) terminal fields. The levels of noradrenaline (NA), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were unaffected in all brain regions examined after 30 min of psychological stress. A small but significant increase of DOPAC levels in the ventral tegmental area (VTA) was observed after a shorter (10 min) duration of stress. Moreover, an increase of DOPAC levels in the MPFC 30 min after psychological stress was attenuated by diazepam (5 mg/kg), and this attenuating effect was antagonized by Ro 15-1788 (15 mg/kg). These results suggest that mesoprefrontal DA neurons are selectively activated by psychological stress, and that the activation of the A10 cell body site (VTA) may precede that of the terminal field (MPFC). Moreover, diazepam was found to possess an inhibitory effect on the activation of mesoprefrontal DA neurons induced by psychological stress, and this effect may be partly mediated by benzodiazepine (BZD) receptors and implicated in the specific anxiolytic action of BZDs.

Controllable and uncontrollable footshock and monoaminergic activity in the frontal cortex of male and female rats

Effects of controllable and uncontrollable footshock on monoaminergic activity in the frontal cortex and plasma corticosterone levels were studied in male and female rats. Subjects were exposed to a shuttle-box procedure for a period of either 30 min (60 shocks) or 90 min (180 shocks). A shuttle response ended shock presentation for escape subjects, whereas their yoked, same-sex, counterparts were unable to escape from shock presentation. A third group was exposed to the experimental environment, but did not receive any shocks. Concentrations of noradrenaline, serotonin and dopamine and their major metabolites were measured in the frontal cortex by high performance liquid chromatography with electrochemical detection. Plasma corticosterone was measured by radioimmunoassay. Results of this experiment show that: (1) exposure to the experimental environment without shock already increased the activity of all 3 transmitter systems. In particular, serotonin was very responsive to mere confinement to the shuttle-box. Changes induced by exposure to the experimental environment were similar for males and females. (2) Presentation of footshocks further increased transmitter activity. The activation of noradrenaline and dopamine was larger after uncontrollable shock than after controllable shock. Moreover, uncontrollable shock resulted in higher serotonin levels than controllable shock. (3) Sex-dependent effects of controllability were found for noradrenaline and dopamine, but not for serotonin. Differences in catecholaminergic activity between controllable and uncontrollable shock were larger in females than in males. (4) In both males and females, corticosterone levels in plasma were increased by exposure to the experimental environment. A further elevation was found in response to footshock presentation, which was independent of the controllability of shock.

The anxiogenic beta-carboline FG 7142 selectively increases dopamine release in rat prefrontal cortex as measured by microdialysis

The effect of the anxiogenic beta-carboline methyl-beta-carboline-3-carboxyamide (FG 7142) on dopamine release in prefrontal cortex and striatum in the awake freely moving rat was determined using the technique of microdialysis. FG 7142 (25 mg/kg, i.p.) caused a time-dependent increase in dopamine release in prefrontal cortex which was statistically significantly greater than the response to vehicle administration. Dopamine release in striatum was unaltered by FG 7142. Pretreatment of animals with the benzodiazepine antagonist Ro 15-1788 (30 mg/kg, i.p., 15 min prior to FG 7142 administration) completely abolished the increase in dopamine release caused by FG 7142 in prefrontal cortex. These data indicate that the anxiogenic benzodiazepine inverse agonist FG 7142 can selectively increase dopamine release in prefrontal cortex, and that this effect appears to be mediated via the gamma-aminobutyric acid/benzodiazepine receptor complex.

LY 171555-induced hyperdefensiveness in the mouse does not implicate benzodiazepine receptors

In naive mice the selective D2 agonist LY171555 dose-dependently (0.5-5 mg/kg) induces defensive responses toward non-aggressive conspecifics. In order to investigate possible anxiogenic properties of the D2 agonist, its behavioural effects were compared with those produced by the benzodiazepine receptor inverse agonist methyl-beta-carboline-3-carboxylate(beta-CCM) in the elevated plus maze and in social interactions with non-aggressive opponents. When tested in the elevated plus maze, mice injected with LY 171555 (0.005-1 mg/kg) showed no decrease either of the number of entries or of the time spent in the open arms. At 5 mg/kg an actual increase of these two measures was observed. By contrast, beta-CCM (1-3 mg/kg) dose-dependently decreased both the number of entries and the time spent in the open arms without altering locomotion. The effects of beta-CCM were antagonized by the benzodiazepine receptor antagonist RO 15-1788 (3 mg/kg) showing a selective involvement of benzodiazepine receptors in their modulation. On the other hand, beta-CCM, (1-3 mg/kg) did not produce significant effects on defensive behaviour of mice interacting with non-aggressive opponents and the defensive responses of mice treated with 1 mg/kg LY 171555 were not prevented by 5 mg/kg chlordiazepoxide. These results show that DA D2-mediated hyperdefensiveness and anxiety modulated by benzodiazepine receptors are unrelated phenomena and suggest that this behavioural response may represent a model of those forms of fear-related reaction that do not respond to benzodiazepine treatment.

Sex differences in the effects of inescapable footshock on central catecholaminergic and serotonergic activity

In two experiments sex differences in changes in central noradrenergic, dopaminergic and serotonergic activity were measured immediately after a 30-min session of inescapable footshocks. In Experiment 1 concentrations of noradrenaline, dopamine, serotonin and their major metabolites were determined in the frontal cortex, hypothalamus, amygdala, striatum, mesencephalon and the medulla-pons area. Inescapable shock increased the activity of all 3 transmitter systems, as evidence by increased metabolite concentrations in specific brain areas. Shock-induced increments in metabolite levels were larger in females than in males, especially for the serotonergic system. In addition, shock presentation resulted in a decrement in the noradrenaline content in most areas studied. In the frontal cortex, noradrenaline was reduced by inescapable shock in males but not in females. In Experiment 2, sex-dependent neurochemical consequences of predictable versus unpredictable shocks were studied in the frontal cortex and the medulla-pons area. Similar to Experiment 1, both brain parts showed large shock-induced increments in the activity of the catecholaminergic systems. Differential effects of predictable and unpredictable shock were not found (frontal cortex) or were rather small (medulla-pons) and appeared sex-dependent for serotonin in this area. The sex differences in neurochemical change found in the first experiment were largely replicated in the second experiment. The relevance of the observed sex differences in central neurotransmitter reactivity for sex differences in behavior is discussed.

Chronic cocaine administration alters corticotropin-releasing factor receptors in the rat brain

Two groups of 12 rats received daily injections of cocaine (20 mg/kg, i.p.) or saline for 15 days following bilateral infusions of 6-hydroxydopamine or vehicle into the lateral ventricles. Cocaine administration resulted in significant decreases in CRF receptor labeling primarily in brain areas associated with the mesolimbic/mesocortical dopaminergic system. All of the cocaine-induced changes in CRF binding were attenuated in the lesioned animals, suggesting that these effects may be mediated, in part, through the actions of the drug on dopaminergic neuronal activity. Dopamine may also be involved in the release of CRF in the rat brain since the purported loss of dopaminergic innervations resulted in increased CRF binding in the saline-treated animals.

Differential effects of forced locomotion, tail-pinch, immobilization, and methyl-beta-carboline carboxylate on extracellular 3,4-dihydroxyphenylacetic acid levels in the rat striatum, nucleus accumbens, and prefrontal cortex: an in vivo voltammetric study

In vivo voltammetry with carbon fiber electrodes was used to assess extracellular 3,4-dihydroxyphenylacetic acid (DOPAC) levels in striatum, nucleus accumbens, and anteromedial prefrontal cortex of freely moving rats subjected to altered motor activity or anxiogenic stimuli. Forced locomotion on a rotarod for 40 min caused an increase in extracellular DOPAC levels in the striatum and to a lesser extent in the nucleus accumbens but not in the prefrontal cortex. Subcutaneous injection of the anxiogenic agent methyl-beta-carboline carboxylate (10 mg/kg) increased extracellular DOPAC levels to a similar extent in prefrontal cortex and nucleus accumbens. Immobilization for 4 min augmented dopamine (DA) metabolism preferentially in the nucleus accumbens and to a lesser extent in the prefrontal cortex. Tail-pinch caused a selective activation of DA metabolism in the nucleus accumbens. None of these stimuli altered extracellular striatal DOPAC levels. These results confirm the involvement of dopaminergic systems projecting to the striatum and nucleus accumbens in motor function and suggest that mesolimbic and mesocortical dopaminergic systems can be specifically activated by certain kinds of anxiogenic stimuli; the relative activation of either of these latter systems could depend primarily on the nature (sensory modality, intensity) of the acute stressor.

Preexposure to foot-shock sensitizes the locomotor response to subsequent systemic morphine and intra-nucleus accumbens amphetamine

The effect of repeated exposure to foot-shock on locomotor activity was examined by testing rats in the shock boxes for one hour following shock exposure. Early in testing activity was elevated relative to the nonshocked control group, between 40-60 min following shock. Over days this period of elevated activity occurred sooner in time and lengthened in duration. When these animals were tested in the absence of shock, those preexposed to shock were more active following either saline or morphine (0.5 and 5.0 mg/kg IP) injections. In a second experiment, elevated spontaneous and morphine-induced activity was also found when rats had been preexposed to shock in boxes distinct from the activity test boxes. In a final experiment, animals preexposed to shock were tested after bilateral infusions of either amphetamine (5 and 10 micrograms/microliters/side) or morphine (5 micrograms/microliters/side) into the nucleus accumbens (NAS). On the amphetamine tests, previously shocked animals were significantly more active than control animals. In contrast, intra-NAS infusions of morphine failed to differentiate between the two groups. These results suggest that repeated mild foot-shock sensitizes the mesolimbic dopamine system by mechanisms similar to those mediating the sensitized behavioral and dopaminergic responses seen following repeated opioid or stimulant administration.

Mesocorticolimbic dopaminergic systems and emotional states

We have used the technique of in vivo voltammetry with carbon fibre electrodes to investigate further the involvement of ascending mesencephalic dopaminergic systems in emotional states in freely moving rats. In Sprague-Dawley rats, forced locomotion caused an increase in extracellular DOPAC levels in the striatum and nucleus accumbens but not in the prefrontal cortex. Immobilization (4 min) or systemic injection of the anxiogenic agent methyl-beta-carboline carboxylate enhanced extracellular DOPAC in both prefrontal cortex and nucleus accumbens but not in striatum whereas tail-pinch provoked a selective increase in this parameter in the nucleus accumbens. These data suggest that mesolimbic and mesocortical dopaminergic systems can be specifically activated by certain kinds of anxiogenic stimuli. To evaluate the relationship between emotional status and the response of mesocortical dopaminergic neurons to stress, we investigated the effects of stressful conditions on dopamine metabolism in the prefrontal cortex of 2 genetically selected lines of rats which differ drastically in their level of emotionality. Introduction of the animals into an unfamiliar environment, application of a high-intensity loud noise or immobilization were associated with an increase in extracellular cortical DOPAC levels in the hypoemotional (RHA) but not in the hyperemotional (RLA) line. These results suggest that the increase in cortical dopamine metabolism induced by stress is not connected to the emotional reaction caused by the aversive nature of the stressor but may reflect activation of cognitive processes in an attempt to cope with the stressor.

Preferential decrease in dopamine utilization in prefrontal cortex by zopiclone, diazepam and zolpidem in unstressed rats

This study has compared the effects of a cyclopyrrolone, zopiclone, a benzodiazepine, diazepam, and an imidazopyridine, zolpidem, on dopamine (DA) and DOPAC levels, and DA utilization (DOPAC/DA ratio) in rat striatum and prefrontal cortex. The endogenous levels of DA were significantly increased by both zopiclone (2.5, 10 and 40 mg kg-1 p.o.) and diazepam (10 and 40 mg kg-1 p.o.) in the prefrontal cortex, whereas striatal DA content was significantly increased only with the highest dose of diazepam (40 mg kg-1 p.o.). Diazepam (10 and 40 mg kg-1 p.o.) decreased cortical level of DOPAC more markedly than striatal levels, whereas zopiclone (40 mg kg-1 p.o.) only slightly decreased striatal DOPAC levels. Zopiclone and diazepam dose-dependently decreased DA utilization, an effect which was more marked in prefrontal cortex than in striatum. This result was confirmed with zolpidem, another benzodiazepine ligand. Zopiclone was most potent at decreasing DA utilization at the cortical level. The diazepam-induced decreases in DA metabolism and utilization were antagonized by Ro 15-1788, suggesting that the effects seen were mediated by specific benzodiazepine receptors. Thus, our results clearly show that ligands acting on the benzodiazepine receptor GABA receptor chloride ionophore complex can decrease the utilization of dopamine in unstressed rats. The preferential decrease in cortical DA utilization induced by benzodiazepine ligands may be compared to the well-known activation by stress of the mesocortical DAergic system.

Dopaminergic involvement in the cocaine-induced up-regulation of benzodiazepine receptors in the rat caudate nucleus

One group of 12 rats received discrete 6-hydroxydopamine (6-OHDA) injections into the caudate nucleus on one side of the brain and sham infusions on the other. Following chronic daily injections of cocaine (20 mg/kg, i.p.) or saline (1 ml/kg, i.p.) for 15 days, the caudate nuclei were separately dissected, and the number of benzodiazepine receptors labeled with [3H]Ro 15-1788 were assessed using individual homogenate receptor binding assays. A second group of 24 rats received bilateral infusions of 6-hydroxydopamine or sham infusions into the lateral ventricles followed by chronic cocaine or saline administration as described above. The animals were sacrificed by cardiac perfusion, and the brains were sectioned and prepared for light microscopic quantitative autoradiography. The extent of the lesion was assessed by measuring dopaminergic and noradrenergic uptake sites visualized with [3H]mazindol, while [3H]Ro 15-1788 was used to estimate the number of benzodiazepine receptors. Chronic cocaine administration resulted in significant increases in benzodiazepine receptors in the caudate nucleus, and these effects were attenuated following dopamine depletion. These data suggest that the effects of cocaine on benzodiazepine receptors may be mediated, in part, through the effects of the drug on dopaminergic neuronal activity.

Involvement of prefrontal dopamine neurones in behavioural blockade induced by controllable vs uncontrollable negative events in rats

The present study was undertaken to investigate the involvement of dopaminergic (DA) neurones afferent to the prefrontal cortex in stress-related behaviours induced by controllable vs uncontrollable negative events. Rats were either sham-operated or given a bilateral infusion of 6-hydroxydopamine (4 micrograms in 0.4 microliter) into the prefrontal cortex which resulted in a specific and almost complete (80%) reduction of local DA. Three weeks after surgery, sham and lesioned rats were subjected to one of the following experimental procedures involving (1) controllable or (2) uncontrollable events: (1) the punished drinking test and a FR1/FR7 schedule of food/shock presentation; (2) the forced swimming test and the learned helplessness paradigm. DA depletion in the prefrontal cortex resulted in an increase in punished responding in the drinking test and under the FR schedule; the anti-punishment effects of diazepam (2 mg/kg) were not modified. Lesions also induced a reduction in immobility duration in the forced swimming test but failed to affect the induction of escape deficits in rats trained for learned helplessness. In the latter two models, DA depletion in the prefrontal cortex did not modify the antidepressant effects of desipramine (32 mg/kg and 24 mg/kg/day, respectively). These results suggest that controllable and acute aversive situations may be modulated by DA neurones in the prefrontal cortex. DA neurones, however, may not be crucial in the modulation of delayed and uncontrollable stress-related behaviours. Taken together, the present findings suggest that an increased tendency to perseverate could be the main behavioural feature associated with DA lesion in the prefrontal cortex. Acute vs delayed consequences of negative events could be an additional relevant factor for the involvement of DA neurons in stress-related behaviours.

Local administration of flurazepam has different effects on dopamine release in striatum and nucleus accumbens: a microdialysis study

The action of local administration of flurazepam on extracellular levels of dopamine (DA) and its metabolites 3,4 dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA) in the anterior striatum and medial nucleus accumbens have been investigated using microdialysis. Flurazepam (10 microM), administered through the perfusion medium for 20 min, reduced levels of DA in dialysates from the nucleus accumbens by 60% while the same concentration of the drug had no effect on levels of DA in perfusates from the striatum. Pretreatment with the benzodiazepine antagonist Ro 15-1788 (flumazenil) or with picrotoxin, a drug which blocks the GABAA receptor-associated chloride channel, inhibited the effect of flurazepam on levels of DA in the nucleus accumbens, which suggests that the effect was mediated by the multimolecular GABAA/benzodiazepine receptor complex. Administration of flurazepam had little effect on the two metabolites of DA, DOPAC and HVA, in either the nucleus accumbens or striatum. The inverse partial benzodiazepine agonist, FG 7142, had no significant action on the release of DA in the nucleus accumbens. These results suggest that the dopaminergic projection to the nucleus accumbens is more sensitive to benzodiazepine-induced inhibition than the projection to the striatum.

Antidepressant-anxiolytic interactions: involvement of the benzodiazepine-GABA and serotonin systems

1. Recent studies have demonstrated that antidepressant drugs are actually more effective than BZ's in the treatment of anxiety states. The role of two major neurochemical substrates that may be implicated in the anxiolytic activity of antidepressants, the benzodiazepine (BZ)-GABA receptor chloride ionophore complex and central serotonergic pathways, are focused on in this review. 2. A wide range of antidepressants elicit a reduction in BZ receptors and display anxiolytic effects within a conflict paradigm. 3. The anxiolytic activity of antidepressants, however, does not appear to be mediated via the BZ receptor, but possibly via another component of the complex such as the chloride channel-associated with the GABAA receptor. 4. Additionally, as possible candidates for the mechanism of anxiolytic activity of these compounds, results of pharmacological, behavioral and clinical studies point to the importance of serotonin (5-HT)1A receptors and 5-HT transporter sites as targets for the action of antidepressants, triazolobenzodiazepines and anxioselective piperazine derivatives.

The anxiogenic beta-carboline FG-7142 increases in vivo and in vitro tyrosine hydroxylation in the prefrontal cortex

Systemic administration of the anxiogenic beta-carboline FG-7142, a benzodiazepine inverse agonist, results in a regionally selective increase in dopamine (DA) utilization in the anteromedial prefrontal cortex (PFC). We have examined both in vivo and in vitro tyrosine hydroxylation in the PFC and other mesotelencephalic DA system terminal fields in order to determine if FG-7142 effects changes in DA synthesis, and to determine if the beta-carboline biochemically activates certain DA neurons through an action occurring at the cell body level (impulse-dependent regulation) or at the terminal field level (presynaptic regulation). FG-7142 increased in vivo tyrosine hydroxylation in the PFC and in the ventral tegmental area, midbrain source of the DA innervation of the PFC; no changes were observed in mesolimbic or nigrostriatal regions. The beta-carboline also increased in vitro tyrosine hydroxylation in the PFC, but decreased tyrosine hydroxylation in striatal slices. The effects of FG-7142 were blocked by the benzodiazepine antagonist RO 15-1788. Another beta-carboline inverse agonist, methyl-beta-carboline-3-carboline-3-carboxylate, also increased in vitro tyrosine hydroxylation in the PFC. GABA exerted opposite effects to those of the beta-carbolines, decreasing in vitro tyrosine hydroxylation in the PFC and increasing DA synthesis in the CP. These data indicate that the benzodiazepine inverse agonists increase both in vivo and in vitro tyrosine hydroxylation in the PFC, and that the beta-carboline may act to increase DA synthesis at both the terminal field and the cell body level.

Restraint stress-induced changes in saccharin preference: the effect of antidepressive treatment and diazepam

The effect of antidepressive treatment and of diazepam on saccharin preference has been studied in a model of acute restraint stress-induced saccharin preference deficit. It has been shown that 1-hr stressor produces short-term, and significant decrease of saccharin preference in a two-bottle test, measured at 24-hr periods of time. Single doses of desipramine and citalopram (10 mg/kg, IP) given prior to stress session significantly attenuated the deficit in saccharin preference. Less strong, but similar effects appeared after postshock antidepressant administration. On the other hand, electroconvulsive shock treatment rather enhanced the depressive influence of the stressor, while diazepam (1 mg/kg, IP) antagonized the suppression of saccharin preference, especially when the drug was given immediately after restraint stress. It is concluded that the acute immobilization-induced decrease in saccharin preference most probably reflects changes in brain emotional processes. The role of disturbances in central motivational mechanisms and its contribution to the effects of antidepressive drugs remains to be established.

Blockade by diazepam of conditioned fear-induced activation of rat mesoprefrontal dopamine neurons

The effect of diazepam on activation of the mesoprefrontal dopamine (DA) system by an emotional stress model without direct physical stimuli was examined. Environmental stimuli previously paired with inescapable footshock (conditioned fear) elicited increases in levels of the DA metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), in the medial prefrontal cortex and of plasma corticosterone in rats. The increases in both levels were blocked by pretreatment with diazepam (5 mg/kg, IP); such blocking effects were reversed by Ro 15-1788 (15 mg/kg, IP), the benzodiazepine (BZD) receptor antagonist. These data suggest that diazepam can block activation of mesoprefrontal DA neurons as well as hypothalamo-pituitary-adrenocortical system elicited by the conditioned fear paradigm. This action appears to be a specific action of BZDs mediated through BZD receptors. We suggest that blocking effects of BZDs on the hyperactivity of the mesoprefrontal DA neurons may be one neural mechanism of their anxiolytic actions.

Effects of mild stress on adrenal and heart catecholamines in male and female rats

The present study was undertaken with the aim of evaluating the sensitivity and convenience of a stress model reflecting sympatho-adrenal activation. Rats of both sexes were subjected to mild stress, consisting of four body temperature recordings, and investigated with regard to adrenal and heart catecholamine levels. Adrenal dopamine (DA) levels were considered to reflect medullary synthesis activity and heart adrenaline (A) concentrations were presumed to reflect A released from the adrenals. Expressed in relation to heart weight, adrenal catecholamine levels were about 50% higher in female rats. Following stress, adrenal DA levels were enhanced in both male and female rats; the magnitude of the stress response appeared similar in the two sexes. Concentrations of A in the hearts of unstressed animals were about 85% higher in females than in males but rose to a similar extent in male and female rats following stress. On the other hand, the stress-induced alterations in heart DA and NA concentrations, reflecting sympathetic activity, were gender-dependent. The advantages of the present model in relation to other techniques for measuring sympatho-adrenal activation in response to mild stress are discussed.

NMDA antagonists block restraint-induced increase in extracellular DOPAC in rat nucleus accumbens

The effects of the N-methyl-D-aspartate (NMDA) receptor antagonists CPP, TCP, PK 26124 and ifenprodil, and of the minor tranquillizer diazepam on stress-induced changes of dopamine metabolism in the nucleus accumbens were investigated in the rat. Dopamine metabolism was assessed by measuring the extracellular levels of 3,4-dihydroxyphenylacetic acid (DOPAC) by means of in vivo differential pulse voltammetry with electrochemically pretreated carbon fiber electrodes. Physical immobilization of the rats for 4 min caused a marked and long-lasting increase in extracellular DOPAC levels in the nucleus accumbens. A similar, though shorter-lasting, augmentation of extracellular DOPAC was observed in the nucleus accumbens after systemic administration of the anxiogenic agent methyl-beta-carboline-3-carboxylate (beta-CCM) (10 mg/kg s.c.). Pretreatment with CPP (1 mg/kg i.p.), TCP (3 mg/kg i.p.), PK 26124 (3 mg/kg i.p.), ifenprodil (3 mg/kg i.p.) or diazepam (2 mg/kg i.p.) totally antagonized the immobilization-induced increase in extracellular DOPAC in the nucleus accumbens. Diazepam and the benzodiazepine (omega 1-2) receptor antagonist flumazenil (30 mg/kg i.p.), but not ifenprodil, also antagonized the beta-CCM-induced activation of dopamine metabolism in the nucleus accumbens. Finally, systemic administration of haloperidol (25 micrograms/kg i.p.) increased the extracellular concentrations of DOPAC in the nucleus accumbens, but pretreatment with ifenprodil (3 mg/kg i.p.) did not modify this response. These data indicate that NMDA receptor antagonists prevent the activation of dopamine metabolism in the nucleus accumbens caused by immobilization stress but not by beta-CCM-induced anxiogenic stimulation. These results suggest that NMDA receptor antagonists may possess an anxiolytic-like action in the rodent, which is exerted via neuroanatomical circuits distinct from those acted upon by diazepam.

Stress-related activation of cerebral dopaminergic systems

The changes in dopamine catabolites in various regions of mouse brain have been studied following a variety of behavioral treatments. In confirmation of the results of many others, we find that treatments such as footshock or restraint result in a pronounced activation of dopaminergic systems in the prefrontal cortex, as determined by increases in the content of DOPAC (3,4-dihydroxyphenylacetic acid). However, we also find small but statistically significant increases of DOPAC in the hypothalamus and brain stem even with mild treatments. With restraint and more intense footshock we observe increases of DOPAC in all regions studied, including nucleus accumbens, olfactory tubercle, amygdala, and the striatum. Thus in contrast to previous reports, we find that the DA response in stress is global like that of norepinephrine [as determined by increases of 3-methoxy,4-hydroxyphenylethyleneglycol, (MHPG)], and not specific to the prefrontal cortex. The activation of prefrontal cortex DA metabolism is associated with an activation of the synthetic enzyme tyrosine hydroxylase. The response pattern of catecholamine metabolites is similar following a variety of stressors, including conditioned footshock, training with one footshock in passive avoidance behavior, performance of passive avoidance behavior, and even following exposure to an apparatus in which mice have been shocked previously. Injection of mice with Newcastle disease virus increases plasma corticosterone, and DOPAC and MHPG in the hypothalamus and brain stem, but not the prefrontal cortex. Thus a virus infection can be considered a stressor. Furthermore, intracerebroventricular (ICV) injection of corticotropin-releasing factor (CRF) produces stresslike increases in DOPAC and MHPG concentrations, suggesting that the release of CRF in the brain during stress may mediate the changes in catecholamine metabolism.

Stressful environmental stimuli increase extracellular DOPAC levels in the prefrontal cortex of hypoemotional (Roman high-avoidance) but not hyperemotional (Roman low-avoidance) rats. An in vivo voltammetric study

The effects of a variety of stressful environmental situations on dopamine metabolism in the prefrontal cortex (as assessed by in vivo voltammetry with carbon fiber electrodes) have been compared in two genetically selected lines of rat (Roman high (RHA/Verh) and low (RLA/Verh) avoidance) which differ drastically in their level of emotionality. Heart rate was continuously monitored in these animals (via chronically implanted subcutaneous electrodes) so as to index the emotional reaction to the stressors. An electrochemical signal corresponding to the oxidation of dihydroxyphenylacetic acid (DOPAC) was recorded in the deeper laminae of the anteromedial prefrontal cortex in both lines of rats. Under normal conditions, this signal was stable for at least 4 h and its amplitude was similar in both lines. Introduction of the animals into an unfamiliar environment (30 min), application of a mild tail pinch (10 min) or of a high-intensity loud noise (30 min) or immobilization (20 min) were all associated with an increase in extracellular cortical DOPAC levels in the hypoemotional RHA/Verh line but not in the hyperemotional RLA/Verh line. Similarly, forced locomotion on a rotarod (40 min) provoked a dramatic increase in the amplitude of the cortical DOPAC oxidation peak in RHA/Verh rats and only a mild increase in this parameter in RLA/Verh rats. In RHA/Verh rats, tolerance to this increase was observed when animals were subjected to forced locomotion every day for 5 days. All of the stressful situations investigated provoked an immediate augmentation of heart rate which resumed gradually after cessation of the stressful stimulus; the magnitude and duration of this increase were much greater in RLA/Verh than in RHA/Verh rats. Moreover, in all stress situations, RLA/Verh but not RHA/Verh rats showed behavioral signs of emotional response e.g. defecation, freezing and self-grooming. It is concluded that the increase in cortical dopamine metabolism induced by stress is not connected to the emotional reaction caused by the aversive nature of the stressor but may rather reflect a heightened attention of the animal or activation of cognitive processes in an attempt to cope with the stressor.

Suppression of neuroleptic-induced persistent abnormal movements in Cebus apella monkeys by enantiomers of 3-PPP

Effects of the enantiomers of the dopamine (DA) autoreceptor agonist 3-PPP (0.5-8.0 mg/kg body weight, i.m.) were studied in three Cebus apella monkeys with persistent abnormal movements induced by prior long-term treatment with fluphenazine enanthate. In 2 of the animals, (-)-3-PPP abolished the abnormal movements while producing only negligible acute motor effects (trembling and stereotypy). (+)-3-PPP, administered to one of these monkeys, also produced a dose-dependent suppression of the persistent abnormal movements, along with the appearance of acute motor signs including tongue protrusions, hyperkinesia, and stereotypy; at the highest dose, there was a biphasic effect. In the first phase, there were pronounced acute motor signs but no persistent abnormal movements. In the second phase, there were neither acute nor persistent abnormal movements. One monkey was unaffected by (-)-3-PPP or low doses of (+)-3-PPP; a higher dose (4 mg/kg) produced hyperkinesia and increased persistent abnormal movements in one experimental setting. The suppression of neuroleptic-induced persistent abnormal movements by 3-PPP enantiomers may be related to their ability to act as autoreceptor agonists, while the acute motor signs produced by higher doses of (+)-3-PPP may be due to activation of postsynaptic DA receptors. The present findings suggest that (-)-3-PPP and drugs with a similar pharmacological profile might be effective as symptomatic treatments for tardive dyskinesia, with little chance of inducing acute extrapyramidal side-effects.

Stress-induced alterations in neurotensin, somatostatin and corticotropin-releasing factor in mesotelencephalic dopamine system regions

The effects of exposure to acute mild footshock stress on concentrations of neurotensin-, somatostatin-, and corticotropin-releasing factor-like immunoreactivity (li) in mesotelencephalic dopamine system regions of the rat were examined. Mild stress exposure resulted in a selective and regionally specific increase in neurotensin-li concentrations in the ventral tegmental area (VTA), source of the dopaminergic innervation of the mesocortical and mesolimbic dopaminergic terminal fields. Concentrations of somatostatin- or corticotropin-releasing factor-li were not changed in any area examined. Levels of the dopamine metabolite, 3,4-dihydroxyphenylacetic acid, were increased only in the VTA and medial prefrontal cortex. These data suggest that neurotensin in the VTA may be involved in environmentally elicited activation of certain mesotelencephalic dopamine neurons.

Dopamine neurons projecting to the medial prefrontal cortex possess release-modulating autoreceptors

The ability of dopamine (DA) agonists and antagonists to modulate the K+-evoked overflow of radioactivity from superfused slices of prefrontal cortex of the rat, preincubated with [3H]DA in the presence of 1 microM desipramine, was examined. Apomorphine and the putative autoreceptor-selective DA agonist EMD 23 448 inhibited the K+-evoked overflow of radioactivity, while the DA antagonist sulpiride enhanced the evoked overflow in a dose-dependent and stereoselective manner. The latter effect was partially reversed by EMD 23 448. More than 95% of the radioactivity retained by the slices chromatographed with DA, while deaminated metabolites represented the majority of both the basal efflux (84% metabolites, 4-5% DA) and evoked overflow (84% metabolites, 14% DA) of radioactivity. These findings indicate that mesoprefrontal DA neurons possess release-modulating nerve terminal autoreceptors. Previous studies have shown that these neurons lack synthesis-modulating autoreceptors. Thus, autoreceptors on prefrontal DA terminals appear to be coupled to regulation of the release but not the synthesis of DA.

The effects of footshock stress on regional brain dopamine metabolism and pituitary beta-endorphin release in rats previously sensitized to amphetamine

The repeated intermittent administration of amphetamine (AMP) produces an enduring enhancement in the response of dopamine (DA) systems in the brain to a subsequent "challenge" with amphetamine. However, former amphetamine addicts are not only hypersensitive to amphetamine, but also to "physical or psychological stress". This suggests that sensitization to amphetamine may change the response of DA neurons in brain to subsequent stress. To explore this idea, the effects of footshock stress on regional metabolism of DA in brain, and on the concentrations of plasma beta-endorphin and N-acetylated beta-endorphin, were studied in rats previously exposed to amphetamine or saline. It was found that: Prior treatment with amphetamine produced enduring (at least 7 days) changes in the dopaminergic response to footshock in the medial frontal cortex, hypothalamus, dorsolateral striatum and nucleus accumbens. Generally, rats pretreated with amphetamine showed a greater initial reduction in concentrations of DA in response to footshock, and a greater elevation in concentrations of metabolites of DA and/or metabolite/transmitter ratios, compared to nonhandled control rats. In some regions of the brain repeated injections of saline produced changes in the response to subsequent footshock that were comparable to those produced by amphetamine. Prior treatment with amphetamine enhanced the release of beta-endorphin and N-acetylated beta-endorphin from the pituitary elicited by footshock stress. It is concluded that repeated intermittent treatment with amphetamine or stress (injections of saline) produce enduring changes in the response of DA neurons and the pituitary to subsequent stress. These changes may be responsible for the hypersensitivity to stress reported in former amphetamine addicts, and in rats previously sensitized to amphetamine.

The activation of mesoprefrontal dopamine neurons by FG 7142 is absent in rats treated chronically with diazepam

Administration of methyl-beta-carboline-3-carboxamide (FG 7142, 15 mg/kg i.p.) to rats has previously been shown to cause a selective increase in the levels of 3,4-dihydroxy-phenylacetic acid (DOPAC) in the prefrontal cortex and ventral tegmental area (VTA) via an interaction with benzodiazepine receptors. On withdrawal 3 days following chronic treatment with diazepam for 21 days, FG 7142 no longer increased DOPAC levels in either the prefrontal cortex or the VTA. Chronic diazepam treatment alone was ineffective in altering dopamine metabolism in the eight brain regions examined. The present findings indicate that chronic diazepam treatment may cause changes at the level of GABA/benzodiazepine receptor macromolecular complex, which is normally functionally integrated with the mesoprefrontal dopaminergic neurons, so that FG 7142 can no longer exert its intrinsic actions.

Tail-pinch stress increases extracellular DOPAC levels (as measured by in vivo voltammetry) in the rat nucleus accumbens but not frontal cortex: antagonism by diazepam and zolpidem

The effect of a tail-pinch stress on dopamine metabolism in the nucleus accumbens and frontal cortex was investigated in the awake unrestrained rat by measuring extracellular 3,4-dihydroxyphenylacetic acid (DOPAC) levels through the use of in vivo differential pulse voltammetry. Mild tail pressure for 8 min caused a large (maximal effect + 70%) and sustained (more than 2 h) increase in the amplitude of the DOPAC oxidation peak in the nucleus accumbens but not in the prefrontal cortex. A similar increase in DOPAC levels was observed in the nucleus accumbens postmortem 1 h after tail-pinch stress. The tail-pinch induced increase in extracellular DOPAC levels in the nucleus accumbens was antagonized by pretreatment with diazepam (5 mg/kg i.p.) or zolpidem (5 mg/kg i.p.), a novel non-benzodiazepine hypnotic possessing anxiolytic properties. These results suggest that in contrast to other stressors, tail-pinch selectively activates dopaminergic systems projecting to the nucleus accumbens.

The anxiolytic beta-carboline ZK 93423 prevents the stress-induced increase in dopamine turnover in the prefrontal cortex

The effects of electric foot-shock on the activity of the mesocortical dopaminergic (DAergic) neurons were estimated by measuring the changes in dihydrophenylacetic acid (DOPAC) and DA content in the prefrontal cortex of the rat. A marked rise in DOPAC content (+80%) and a significant decrease in DA levels (-23%) were observed after a 20 min foot-shock session. These effects were completely prevented by pretreatment with diazepam (5 mg/kg i.p.). ZK 93423, a recently synthesized beta-carboline with benzodiazepine-like properties, prevented the decrease in DA content induced by foot-shock at the dose of 20 mg/kg. Moreover, the stress-induced increase in DOPAC levels was partly or completely blocked by pretreatment with 20 or 40 mg/kg of ZK 93423, respectively. These results provide further support for the view that the mesocortical DAergic system can be modulated by drugs that selectively interact with the benzodiazepine recognition site.

Environmentally-induced modification of the benzodiazepine/GABA receptor coupled chloride ionophore

The benzodiazepine/GABA receptor coupled chloride ionophore was examined in brain membranes of rats maintained in either a conventional animal facility or a "protected" (low-stress) environment. Following a 10 min ambient temperature swim, animals maintained in both environments had qualitatively similar increases in the number (Bmax) of [35S]t-butylbicyclophosphorothionate (TBPS) binding sites, the apparent affinity of this radioligand, and the efficacy and potency of Cl- to enhance [3H]flunitrazepam binding. Nonetheless, the Bmax of [35S]TBPS and efficacy of Cl- to enhance [3H]flunitrazepam binding were significantly lower in animals housed in the protected environment compared to those maintained in a conventional facility both before and after swim stress. Furthermore, in rats housed in a protected environment, sequential removal of animals from a common cage (cohort removal), produced a very rapid increase (less than or equal to 15 s) in Cl(-)-enhanced [3H]flunitrazepam binding in cortical and hippocampal but not cerebellar membranes. Cohort removal also produced a sequential increase in the number of [35S]TBPS binding sites and apparent affinity of this radioligand in cerebral cortical membranes. The effects of cohort removal were not observed in animals subjected to ambient temperature swim or if animals were removed from different cages. Changes in the benzodiazepine/GABA receptor coupled chloride ionophore produced by cohort removal from a common cage preceded any statistically significant changes in circulating levels of alpha-MSH, beta-endorphin, ACTH or corticosterone. These findings suggest that the benzodiazepine/GABA receptor chloride ionophore complex (supramolecular complex) is under both tonic and acute regulation by the environment, and may subserve a physiologically relevant function in the response to stressful or anxiety producing stimuli.

Anxiolytic-like action of the 3-PPP enantiomers in the Vogel conflict paradigm

The effect of the (+)- and (-)-enantiomers of 3-PPP [conventional and atypical dopamine (DA)-receptor active agent, respectively] were investigated in a commonly used animal model of anxiety: the Vogel licking-conflict test. Low doses (less than or equal to 0.5 mg/kg SC) of both 3-PPP enantiomers resulted in anti-conflict (= anxiolytic-like) actions in this test. (-)-3-PPP proved to be almost as potent as apomorphine in releasing the punished responding (minimum effective doses; (-)-3-PPP: 0.016, and apomorphine: 0.006 mg/kg SC), whereas (+)-3-PPP was about 10 times less effective than apomorphine. In the higher dose range (greater than or equal to 1.0 mg/kg), both 3-PPP enantiomers instead induced an apparent "pro"-conflict effect; i.e. decreased responding to a level significantly below baseline, thus resulting in a biphasic dose-response curve. Simple alterations in the animals' motivation to drink, in shock threshold or in motor capabilities did not seem to be major explanatory factors either for the anti- or for the "pro"-conflict effects. With regard to the latter, the possibility is discussed of an interaction between the experimental test situation and non conflict-related effects of the drugs, thus interfering with the punished drinking. The findings are interpreted within the concept that low doses of the 3-PPP enantiomers, in particular (-)-3-PPP, may attenuate anxiety-elicited increases in the neurotransmission in certain meso-cortical/limbic DA pathways, i.e. consistent with the previously shown preferentially "limbic" net antidopaminergic profile of action of (-)-3-PPP.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in plasma corticosterone and cerebral biogenic amines and their catabolites during training and testing of mice in passive avoidance behavior

Concentrations of cerebral biogenic amines and their catabolites, and of plasma corticosterone were determined 10 min after training and testing of passive avoidance behavior in mice. Training and testing of mice that had acquired the task well resulted in statistically significant increases of plasma corticosterone, of the DOPAC:DA ratio [an index of dopamine (DA) metabolism] in prefrontal cortex, and of MHPG:NE ratios [an index of norepinephrine (NE) metabolism] in hypothalamus and brain stem. There were also decreases of NE in hypothalamus and brain stem, and an increase of 5-HIAA:5-HT [an index of serotonin (5-HT) metabolism] and of tryptophan in brain stem. Some of these changes also occurred in mice merely exposed to the apparatus but not trained. Plasma corticosterone concentrations were significantly higher in mice that performed the task well compared to those that did not, and there were significant correlations between this measure and the avoidance performance. Although there was only one statistically significant correlation between a cerebral metabolite and the avoidance performance (a decrease in hypothalamic NE), there were indications of relationships between cerebral biogenic amine metabolism and the performance. The patterns of neurochemical and endocrine changes closely resemble those previously observed in response to various stressors. Thus, the changes could reflect stress responses, which may or may not be related directly to the performance of the avoidance task.

Tyrosine hydroxylase activation in mesocortical 3,4-dihydroxyphenylethylamine neurons following footshock

Mild electric footshock resulted in activation of tyrosine hydroxylase (TH) in prefrontal cortex of mice and rats. In mice, the activation was also observed following restraint. Shock-evoked activation of prefrontal cortex TH was characterized by a decrease of apparent Km for the pterin cofactor 6-methyl-5,6,7,8-tetrahydropterin and an increase of Vmax. Activation of prefrontal cortical TH was also demonstrated in vitro following preincubation under conditions that activate cyclic AMP-dependent protein kinase. Treatment of mice with the noradrenergic neurotoxin N-2-chloroethyl-N-ethyl-2-bromobenzylamine (DSP-4) caused a 70% decrease in prefrontal cortex norepinephrine levels but had no significant effect on the activity of TH in that brain region. Footshock resulted in the activation of prefrontal cortex TH of DSP-4-treated mice, suggesting that shock-evoked activation of the enzyme occurs in terminals of mesocortical 3,4-dihydroxyphenylethylamine neurons.

Altered neurobiological responses to acute immobilization in social-isolated mice

Social isolation results in dynamic changes of neurobiological functions. The altered internal state of the CNS is reflected in changes in spontaneous behavior, changed responses to transmission-related substances and changed responsiveness to an additional impairment of normal relations between the organism and its environment. We analysed the influence of an acute 2-hour immobilization on such isolation-dependent changes. Whereas the susceptibility to pentetrazole-induced seizures increased continuously with lengthening of isolation and was not affected by the additional impairment, the responsiveness to transmission-related substances changed dynamically depending upon isolation-induced alterations. An immobilization-induced increase in responsiveness to LSD and propranolol was demonstrable in grouped controls and after short-term isolation. The apomorphine stimulation during prolonged isolation experienced a down- and an upregulation which were repeated in a stronger manner by immobilization responses especially after long-term isolation. It is suggested that the dynamics of isolation-induced changes coincided with changed acute adaptive functions.

Anticonflict effects of low doses of the dopamine agonist apomorphine in the rat

The effects of low, "autoreceptor" doses (3.13-100 micrograms/kg, SC) of the dopamine (DA) agonist apomorphine were investigated in a modified Vogel's conflict paradigm. The compound was found to exert a marked, dose-dependent increase in the number of shocks taken in the conflict situation (maximum: approximately 230% of control responding, obtained at 12.5 micrograms/kg), thus indicating an anxiolytic action. However, the dose-response curve was biphasic, inversely U-shaped, with the highest dose tried actually suppressing the punished response rate to below control levels. Neither low- nor high-dose apomorphine modified the rats' drinking "motivation" (glucose intake after 48 hr of water deprivation). On the other hand, while unaltered by 12.5 micrograms/kg, the pain threshold tended to be lowered by 100 micrograms/kg. It is suggested that the anxiolytic-like action of apomorphine might be due to central DA autoreceptor stimulation, possibly in limbic/cortical forebrain regions. The conflict-promoting effect seen at 100 micrograms/kg is likely related to the concomitantly elicited hyperalgesia. The possibility of developing novel DA-modulating agents for the treatment of anxiety is raised.

Activation of specific central dopamine pathways: locomotion and footshock

The present study examined whether neostriatal monoamine biochemistry was activated in a bilaterally symmetrical fashion during a non-lateralized forward locomotor task, and whether specific midbrain dopamine (DA) neuronal systems were influenced selectively by specific behavioral tasks. Monoamine concentrations (DA, serotonin and their metabolites) were measured, using high pressure liquid chromatography, in the neostriatum, nucleus accumbens, and medial prefrontal cortex in rats that were either induced to walk forward in a motorized rotating wheel (two speeds) or were exposed to footshock stress (two shock intensities). Our results demonstrate that during locomotor behavior there is an increase in neostriatal DA metabolism, but not in serotonin metabolism. Furthermore, the increase in DA metabolism was found: (a) in both right and left neostriatal nuclei, but with significantly less asymmetry than occurred in non-locomoting control rats; and (b) within the neostriatum at both speeds and also in the nucleus accumbens at the higher speed. Locomotion had no effect on DA metabolism in the prefrontal cortex. With both shock intensities there was increased DA metabolism in the prefrontal cortex, whereas during the low shock intensity there was also an increased DA metabolism in the nucleus accumbens. At the high level of footshock, which evoked jumping and running escape behavior, there was also an increase in neostriatal DA metabolism. These data indicate that a non-lateralized forward locomotor task activates DA metabolism primarily in the less metabolically active hemisphere. Secondly, we found that specific subgroups of midbrain DA neurons can be selectively activated by specific behavioral tasks.

Self-biting with multiple finger amputations following spinal cord injury

We have observed mutilative self-biting leading to multiple finger amputations in two patients following C4 complete spinal cord injury (SCI). Both men were of normal intelligence without psychosis and each had a neurotic personality and history of fingernail biting. They related the self-biting to anxiety and depression. We believe these to be the first English language reports of multiple finger amputations due to self-biting following SCI.

Effect of short-term swimming stress and diazepam on 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) levels in the caudate nucleus: an in vivo voltammetric study

The effects of swimming stress on dopaminergic and serotonergic neurons were studied by an in vivo voltammetry technique. 3,4-Dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) levels in rat striatum were measured by differential pulse voltammetry with an electrochemically treated carbon fiber electrode. Exposure to swimming stress for 1 to 10 min to the animal increased the DOPAC and 5-HIAA peaks, which depended on the length of stress. Pretreatment of the rats with diazepam (10 mg/kg, i.p.) prevented completely the stress-induced increase in DOPAC levels but only partially reduced the increase in 5-HIAA levels.

Enduring enhancement in frontal cortex dopamine utilization in an animal model of amphetamine psychosis

It is reported that in rats the repeated intermittent administration of amphetamine produces a long-lasting enhancement in medial frontal cortex dopamine utilization. This change in mesocortical dopamine activity may be involved in the behavioral sensitization produced by psychomotor stimulant drugs, and some of the cognitive abnormalities (e.g. amphetamine psychosis) associated with stimulant drug abuse in humans.

Behaviorally equivalent stressors differentially modify the monoamine altering property of d-amphetamine

We previously demonstrated that behaviorally equivalent heat and cold stressors interacted with d-amphetamine (AMPH) treatment to produce different effects in rats responding for food on a fixed ratio 15 (FR15) schedule of reinforcement [25]. The present study was carried out to determine if these stressors differentially affect the disposition of AMPH to brain and/or if the stressors alone or in combination with AMPH affect CNS monoamines in a dissimilar manner. Exposure to either heat or cold stressor produced equivalent elevations of [3H]-AMPH in brain following 3 mg AMPH/kg but not 1 mg AMPH/kg. Neither stressor alone significantly altered any of the neurochemical parameters measured in any of the brain regions studied. In forebrain, heat and cold stressors interacted with AMPH treatment in different manners. Thus, although [3H]-AMPH was equally elevated in stressed groups following the high dose, cold-induced stress was not associated with an increase in dopamine (DA) levels, which was observed in Nonstressed and Heat-Stressed subjects. Although serotonin (5-HT) levels were not changed by any manipulation, 5-hydroxyindoleacetic acid (5-HIAA) levels were lowered in Nonstressed and Cold-Stressed subjects following both doses of AMPH. This effect was not associated with heat-induced stress. The apparent attenuation of AMPH behavioral toxicity observed in Cold-Stressed and/or exacerbation in Heat-Stressed rats observed in the earlier study may involve a pharmacodynamic interaction of AMPH and stress with transmitter substances, including DA and/or 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)