Chronic antidepressant administration fails to attenuate apomorphine-induced decreases in rat striatal dopamine metabolites

Antidepressant-induced Dopamine Receptor Dysregulation: A Valid Animal Model of Manic-Depressive Illness

Background: Mania seems to be associated with an increased dopamine (DA) transmission. Antidepressant treatments can induce mania in humans and potentiated DA transmission in animals, by sensitizing DA D2 receptors in the mesolimbic system. We have suggested that the sensitization of D2 receptors may be responsible of antidepressant-induced mania. This review aims to report the experimental evidence that led to the hypothesis that antidepressant-induced DA receptors dysregulation can be considered an animal model of bipolar disorder.

Methods: We reviewed papers reporting preclinical and clinical studies on the role of DA in the mechanism of action of antidepressant treatments and in the patho-physiology of mood disorders.

Results: A number of preclinical and clinical evidence suggests that mania could be associated with an increased DA activity, while a reduced function of this neurotransmission might underlie depression. Chronic treatment with imipramine induces a sensitization of DA D2 receptors in the mesolimbic system, followed, after drug discontinuation, by a reduced sensitivity associated with an increased immobility time in forced swimming test of depression (FST). Blockade of glutamate NMDA receptors by memantine administration prevents the imipramine effect on DA receptors sensitivity and on the FST.

Conclusion: We suggest that chronic treatment with antidepressants induces a behavioural syndrome that mimics mania (the sensitization of DA receptors), followed by depression (desensitization of DA receptors and increased immobility time in the FST), i.e. an animal model of bipolar disorder. Moreover the observation that memantine prevents the “bipolar-like” behavior, suggests that the drug may have an antimanic and mood stabilizing effect. Preliminary clinical observations support this hypothesis.

Long-term effects of an Apocynum venetum extract on brain monoamine levels and beta-AR density in rats

The present study was designed to get further insight into the mode of antidepressant action of an extract prepared of the leaves of Apocynum venetum L. (AV). To evaluate biochemical changes, we used a high-performance liquid chromatography system to examine the effects of short-term (2 weeks) and long-term (8 weeks) administration of imipramine (15 mg/kg po) and an AV-extract (15, 60 and 250 mg/kg) on regional levels of serotonin (5-HT), norepinephrine (NE), dopamine (DA) and their metabolites in the rat hypothalamus, striatum and hippocampus. Pronounced changes in 5-HT, NE and DA levels were detected mainly after 8 weeks of daily imipramine treatment. Similar to imipramine, AV-extract reduced NE and DA concentrations after 8 weeks, whereas it failed to affect 5-HT levels. We speculate that the decrease in NE levels after chronic AV treatment might be based partly on the subsensitivity of presynaptic alpha(2)-receptors. In addition to the determination of central monoamine concentrations, quantitative radioligand receptor-binding studies were used to examine the effects of long-term administration of imipramine and AV-extract on beta-adrenergic binding in rat frontal cortex. [125I]CYP binding to beta-adrenergic receptors was found to be decreased after 8 weeks treatment with imipramine, whereas AV-extract had no effect on beta-receptor binding.

Long-term effects of St. John's wort and hypericin on monoamine levels in rat hypothalamus and hippocampus

Hypericum perforatum L. (St. John's wort) is one of the leading psychotherapeutic phytomedicines and, because of this, great effort has been devoted to clarifying its mechanism of action. Chronic effects of St. John's wort and hypericin, one of its major active compounds, on regional brain amine metabolism have not been reported yet. We used a high-performance liquid chromatography system to examine the effects of short-term (2 weeks) and long-term (8 weeks) administration of imipramine, Hypericum extract or hypericin on regional levels of serotonin (5-HT), norepinephrine, dopamine and their metabolites in the rat brain. We focused our interest on the hypothalamus and hippocampus, as these brain regions are thought to be involved in antidepressant drug action. Imipramine (15 mg/kg, p.o.), Hypericum extract (500 mg/kg, p.o.), and hypericin (0.2 mg/kg, p.o.) given daily for 8 weeks significantly increased 5-HT levels in the hypothalamus (P<0.05). The 5-HT turnover was significantly lowered in both brain regions after 8 weeks of daily treatment with the Hypericum extract (both P<0.05). Consistent changes in catecholamine levels were only detected in hypothalamic tissues after long-term treatment. Comparable to imipramine, Hypericum extract as well as hypericin significantly decreased 3,4-dihydroxyphenylacetic acid and homovanillic acid levels in the hypothalamus (P<0.01). Our data clearly show that long-term, but not short-term administration of St. John's wort and its active constituent hypericin modify levels of neurotransmitters in brain regions involved in the pathophysiology of depression.

The role of dopamine in the mechanism of action of antidepressant drugs

The present paper reviews evidence on the effect of antidepressant treatments on dopamine transmission. Chronic treatment with antidepressant drugs potentiates the behavioural stimulant responses elicited by the stimulation of dopamine receptors, including reward-related behaviours. Moreover, antidepressants affect dopamine release in several brain areas. The reviewed literature is discussed in terms of the possible mechanisms underlying antidepressant-induced supersensitivity to dopamine-mediated behavioural responses, and of the possible implications for the therapeutic effect of these drugs. It is concluded that the potentiation of dopaminergic neurotransmission induced by chronic antidepressant treatments might contribute to their therapeutic effect.

The effect of prolonged treatment with imipramine on the biosynthesis and functional characteristics of D2 dopamine receptors in the rat caudate putamen

1. The present study shows the effects of imipramine in a single dose (10 mg kg(-1), p.o.) or following repeated (14 days, twice a day) treatment on the level of mRNA coding for D2 dopamine receptors in the rat caudate putamen (CP). Repeated administration of imipramine resulted in the increase of the level of mRNA coding for D2 dopamine receptors. 2. Radioligand binding studies with the D2 receptor agonist, [3H]-N-0437, indicated, that following imipramine administration, the affinity of the agonist for the D2 dopamine receptor significantly increased, though without any alterations in the Bmax. 3. Pharmacological manipulations (by use of forskolin, GppNHp and quinpirole) of the cyclic AMP generating system, ex vivo following administration of imipramine indicated that an up-regulation of factors inhibiting cyclic GMP formation takes place. 4. Most probably it is the D2 dopamine receptor which undergoes functional up-regulation, resulting from the enhancement of its biosynthesis.

Ascorbic acid and atypical antipsychotic drugs: modulation of amineptine-induced behavior in mice

To provide a detailed characterization of individual kinds of behavior produced by ascorbic acid in combination with typical (haloperidol) or atypical (clozapine, sulpiride and remoxipride) antipsychotic drugs, the 'open-field' test was selected. Amineptine, an indirect dopamine agonist, was used as an explicit model of dopaminergic activity. Results showed that amineptine (5-10-20 mg/kg i.p.), dose-dependently, increased ambulation and rearing. Ascorbic acid (62.5-125-250 mg/kg i.p.) markedly inhibited the behavior of mice as well as the amineptine-induced hyperactivity. A combination of each typical or atypical antipsychotic drug (except clozapine 2.5 mg/kg i.p.) with amineptine (20 mg/kg i.p.) induced a significant increase in ambulation and rearing over that seen with the antipsychotic drugs alone. The combination of antipsychotic drugs with ascorbic acid 250 mg/kg i.p. led to a decrease in open-field parameters when compared with controls. In conclusion, these data provide further in vivo support for the effect of ascorbic acid on dopaminergic system and demonstrate that the antidopaminergic effects of both typical and atypical antipsychotic drugs may be enhanced with concurrent administration of ascorbic acid.

Role of the dopaminergic system in depression

A hypothesis implicating dopamine in depression was proposed over 15 years ago (Randrup et al 1975). The identification of multiple new subtypes of dopamine receptors and evolving views regarding the function of the dopamine systems in the brain require a reexamination of this hypothesis. Results from studies in depression, Parkinson's disease, and animal models of depression suggest a deficiency of dopamine in depression. Dopamine precursors, dopamine agonists, and dopamine reuptake inhibitors show therapeutic efficacy in depression. Electroconvulsive therapy (ECT) and standard pharmacological antidepressants enhance dopamine function. Studies using receptor-specific drugs in clinical trials and neuroimaging studies are needed to further clarify the role of dopamine in depression.

Long-term effects of imipramine on striatal dopamine autoreceptor function: involvement of both noradrenergic and serotonergic systems

1. The effects of apomorphine (APO) administration on DA system activity were assessed by measuring dopamine metabolite levels (HVA) in several circumstances. 2. Pretreatment with IMI reduced the effect of APO on HVA levels. 3. Pretreatments with either IDE or DMI did not reduce the effect of APO on HVA levels. 4. Reductions of either NE and 5-HT levels after DSP4 and pCPA restored the effect of APO after IMI pretreatment.

Possible role of dopamine D1 receptor in the behavioural supersensitivity to dopamine agonists induced by chronic treatment with antidepressants

The effect of chronic treatment with antidepressants (ADs) on the behavioral responses to LY 171555, a selective D2 receptor agonist, SKF 38393, a selective D1 receptor agonist, and B-HT 920, a selective DA autoreceptor agonist, was studied in rats. In normal rats small, intermediate and high doses of LY 171555 produced hypomotility, hyperactivity and stereotypies, respectively. Chronic but not acute pretreatment with imipramine (IMI) greatly potentiated the motor stimulant effect of LY 171555, but failed to modify its stereotypic and sedative effect. The potentiation of the motor stimulant effect of LY 171555 was observed also after chronic, but not acute, treatment with desmethylimipramine (DMI), mianserin (MIA) or repeated electroconvulsive shock (ECS). Chronic treatment with IMI failed to modify the effect of SKF 38393 (motor stimulation, grooming and penile erection), but reversed the sedative effect of B-HT 920 into a motor stimulant response. The motor stimulant response to LY 171555 in IMI-pretreated animals was suppressed by L-sulpiride, a D2 antagonist, and by a combination of reserpine with alpha-methyltyrosine (alpha-MT), but it was only partially antagonized by high doses of SCH 23390, a selective D1 antagonist. The results indicate that chronic treatment with ADs potentiates the behavioural responses mediated by the stimulation of postsynaptic D2 receptors in the mesolimbic system and suggest that this behavioural supersensitivity is due to enhanced neurotransmission at the D1 receptor level.

Effects of chronic treatments with amineptine and desipramine on motor responses involving dopaminergic systems

The acute effects of increasing doses of the antidepressant drugs amineptine (5-40 mg/kg, IP) and desipramine (5-20 mg/kg IP) were studied in mice on three parameters of the activity (the horizontal activity, the vertical activity and the number of small movements without displacement) measured in a computerized Digiscan actimeter. The horizontal and vertical activities were dose dependently and similarly increased by acute amineptine, whereas the number of movements without displacement was increased up to 10 mg/kg with no further significant modification up to 40 mg/kg; in contrast, all three parameters were reduced in an identical manner by desipramine. The changes in the responses to the selective D-1 dopamine (DA) receptor agonist SK&F 38393 (1.87-30 mg/kg, SC), to the selective D-2 DA receptor agonist LY 171555 (0.1-1.6 mg/kg, SC) and to the selective DA uptake inhibitor GBR 12783 (1.25-20 mg/kg, IP) were measured on the three parameters of activity in mice chronically treated with amineptine (20 mg/kg, IP twice daily during 15 days) or by desipramine (10 mg/kg, IP, twice daily during 15 days). The chronic treatments with amineptine or desipramine did not modify the motor stimulant effects GBR 12783 and of SK&F 38393 on the three parameters (excepted for a slight modification of the horizontal activity for 7.5 mg/kg SK&F 38393 in mice chronically treated with amineptine). In contrast, the motor inhibitory effects of the lowest doses of LY 171555 (0.1-0.4 mg/kg) were strongly reduced in mice chronically treated with amineptine or desipramine but only on the horizontal activity with no change on the vertical activity and on the number of small movements without displacement.(ABSTRACT TRUNCATED AT 250 WORDS)

Different effects of short- and long-term treatment with imipramine on the apomorphine- and food-induced place preference conditioning in rats

The effect of imipramine (IMI) on the rewarding properties of pharmacological and natural reinforcers was studied with a place preference paradigm. The pairing of distinctive environmental stimuli with either injection of different doses of apomorphine (APO) or presentation of food to hungry rats resulted in a conditioned preference for those stimuli. The development of APO- and food-induced place preference was prevented by short-term administration of IMI. In contrast, long-term pretreatment with IMI significantly potentiated the APO- and food-induced conditioned effect. In separate experiments aversive properties of IMI by itself were also found, as the conditioned avoidance response to the environmental stimuli paired with administration of single doses of IMI was demonstrated. The results indicate an enhancing effect of the long-term IMI administration on the dopamine-mediated reward functions and the rewarding value of natural reinforcers.

Desipramine given repeatedly enhances behavioural effects of dopamine and d-amphetamine injected into the nucleus accumbens

The effect of desipramine (DMI) was studied after its repeated administration (10 mg/kg p.o., twice daily, 14 days) to rats, on the action of dopamine and d-amphetamine injected bilaterally into the nucleus accumbens. DMI, applied repeatedly but not acutely, prevented the sedative effect of dopamine and enhanced its stimulating action, as assessed by the open-field test. Repeated administration of DMI also enhanced d-amphetamine-induced locomotor hyperactivity. The number of [3H]SCH 23390 binding sites (D-1) in the limbic system decreased while the number of [3H] spiperone ones (D-2) remained unchanged. The results indicate that, like other antidepressant drugs studied earlier, DMI enhances neurotransmission in the dopamine mesolimbic system (nucleus accumbens) of the rat.

Chronic imipramine administration reduces apomorphine inhibitory effects

Changes in activity of dopaminergic and serotonergic systems were assessed after acute and chronic (14 days) imipramine (10 mg/kg) administration in mice. For this purpose, biochemical and behavioural tests were performed at different intervals of time after withdrawal of treatment. Brain levels of 5-hydroxytryptamine, 5-hydroxyindoleacetic acid, homovanillic acid and 3,4-dihydroxyphenylacetic acid were assayed by a fluorometric method. Locomotion and stationary behaviour were investigated in the open-field test. The results of the experiments suggest that chronic imipramine reduces the inhibitory effects of apomorphine upon the dopaminergic system.

Chronic treatment with iprindole reduces immobility of rats in the behavioural 'despair' test by activating dopaminergic mechanisms in the brain

Iprindole, 10 mg kg-1 i.p., once daily for 21 days, enhanced the metabolism of dopamine in the frontal cortex and striatum of rats with no effect in the nucleus accumbens 1 h after the last injection. Noradrenaline metabolism in the brainstem and telencephalon was also increased in these conditions. No effect on dopamine or noradrenaline metabolism was seen 24 h after the last injection. The same repeated treatment schedule with iprindole markedly reduced the immobility of rats in the behavioural 'despair' test 1 h after the last injection and the effect was prevented by 0.5 mg kg-1 i.p. haloperidol and 100 mg kg-1 i.p. sulpiride but not by 3 mg kg-1 s.c. prazosin or 5 mg kg-1 i.p. (+/-)-propranolol. The data show that enhanced metabolism of brain dopamine and noradrenaline is associated with the presence of iprindole during repeated treatment and the effect on dopamine mechanism is important in iprindole's ability to reduce rats' immobility in the behavioural 'despair' test.