Some behavioural effects of antidepressant drugs are time-dependent

Time-course of changes in key catecholaminergic receptors and trophic systems in rat brain after antidepressant administration

Several biochemical parameters within the brain are altered by antidepressants. However, it is still uncertain which parameters are important for the evaluation of the effectiveness of these drugs. What seems certain is that the response of the nervous system is dynamic. The dynamic nature of the nervous system is still poorly understood, although it has implications in clinical management. Criteria for evaluating treatment resistant depression are based on this temporal variability. The present study was designed to evaluate dynamic alterations in catecholaminergic receptors and calcyon (associated with monoaminergic theory of depression) in the rat brain as well as brain-derived neurotrophic factor (BDNF) and tyrosine kinase beta (TRKB; related to neurotrophin theory) induced by three antidepressant drugs (ADs) with various pharmacological profiles (imipramine, desipramine, and citalopram) administered for 21 days or acutely, followed by various drug-free periods. Receptor autoradiography and in situ hybridization studies allowed us to identify changes in various brain regions simultaneously in each rat. Repeated treatment with ADs induced biochemical alterations, which were in agreement with the results of previous studies. These alterations include the downregulation of β1, β2, and α1 adrenergic receptors, upregulation of α2-adrenergic receptors and dopamine D2 receptors, and increased expression of BDNF in the hippocampus. Additionally, we observed dynamic alterations in the measured parameters after acute drug administration, particularly at the level of dopamine receptors, which were extremely sensitive to a single dose of ADs followed by various drug-free periods. All three ADs induced the upregulation of dopamine D2 receptor mRNA levels in the nucleus accumbens. The same effect was induced by single doses of ADs followed by various drug-free periods. The obtained results indicate that alterations in the availability of neurotransmitters at synapses induced by ADs are strong enough to induce immediate and long-lasting adaptive changes in the neuronal network.

Analysis of region-specific changes in gene expression upon treatment with citalopram and desipramine reveals temporal dynamics in response to antidepressant drugs at the transcriptome level

RATIONALE

The notion that the onset of action of antidepressant drugs (ADs) takes weeks is widely accepted; however, the sequence of events necessary for therapeutic effects still remains obscure.

OBJECTIVE

We aimed to evaluate a time-course of ADs-induced alterations in the expression of 95 selected genes in 4 regions of the rat brain: the prefrontal and cingulate cortices, the dentate gyrus of the hippocampus, and the amygdala.

METHODS

We employed RT-PCR array to evaluate changes during a time-course (1, 3, 7, 14, and 21 days) of treatments with desipramine (DMI) and citalopram (CIT). In addition to repeated treatment, we also conducted acute treatment (a single dose of drug followed by the same time intervals as the repeated doses).

RESULTS

Time-dependent and structure-specific changes in gene expression patterns allowed us to identify spatiotemporal differences in the molecular action of two ADs. Singular value decomposition analysis revealed differences in the global gene expression profiles between treatment types. The numbers of characteristic modes were generally smaller after CIT treatment than after DMI treatment. Analysis of the dynamics of gene expression revealed that the most significant changes concerned immediate early genes, whose expression was also visualized by in situ hybridization. Transcription factor binding site analysis revealed an over-representation of serum response factor binding sites in the promoters of genes that changed upon treatment with both ADs.

CONCLUSIONS

The observed gene expression patterns were highly dynamic, with oscillations and peaks at various time points of treatment. Our study also revealed novel potential targets of antidepressant action, i.e., Dbp and Id1 genes.

The effect of psychotropic drugs on cytochrome P450 2D (CYP2D) in rat brain

The aim of the study was to investigate the influence of selected antidepressants and neuroleptics on the protein level and activity of cytochrome P450 2D (CYP2D) in rat brain. The obtained results showed that imipramine, fluoxetine, nefazodone, thioridazine and perazine, added to brain microsomes of control rats, inhibited CYP2D activity to a lower extent (K(i)=255-485μM) than when added to liver microsomes (K(i)=1-45μM), which may result from their stronger affinity for liver CYP2D2 (K(i)=2.7 and 1.25μM for imipramine and fluoxetine, respectively) than for brain CYP2D4 (K(i)=25 and 10μM for imipramine and fluoxetine, respectively), as well as from their high non-specific binding in brain microsomes. Two-week treatment with fluoxetine evoked decreases in the level and activity of CYP2D in the striatum and the nucleus accumbens. In contrast, fluoxetine increased CYP2D expression in the cerebellum, while nefazodone considerably enhanced the activity (but not the protein level) of CYP2D in the truncus cerebri. Imipramine and mirtazapine (active in the liver) did not affect brain CYP2D. Chronic thioridazine decreased CYP2D activity in the substantia nigra and nucleus accumbens, but significantly increased that activity in the striatum and cerebellum. Clozapine significantly enhanced CYP2D activity in the truncus cerebri. In conclusion, psychotropics influence CYP2D in the brain, but their effect is different than in the liver and depends on the cerebral structure. The observed psychotropics-brain CYP2D interactions may be important for the metabolism of neurosteroids and monoaminergic neurotransmitters, and for the local biotransformation of drugs.

Dopamine D3 receptor antisense oligodeoxynucleotide potentiates imipramine-induced dopaminergic behavioural supersensitivity

Chronic antidepressant treatments result in the potentiation of dopaminergic transmission in the mesolimbic dopamine system revealed as an increased motor response to dopamine D2-like agonists. On the basis of the involvement of this system in the control of motivation and reward-related behaviour, which are impaired in depression, it has been suggested that such supersensitivity might play an important role in the mechanism of action of these drugs. Several studies have provided evidence suggesting a role of dopamine D3 receptors in mediating antidepressant-induced increased motor response to dopamine agonists. To test this hypothesis, we studied the effect of the intracerebroventricular infusion of a dopamine D3 receptor antisense oligodeoxynucleotide (10 microg/3 microl, 2-3 daily injections) on the expression of imipramine-induced supersensitivity (20 mg/kg daily intraperitoneal injections for 21 days) to the motor effect of the dopamine D2-like receptor agonist quinpirole (a single 0.3 mg/kg subcutaneous injection 24-48 h after imipramine withdrawal). The results show that a treatment previously shown to reduce the synthesis of dopamine D3 receptors, rather than resulting in an inhibitory effect, potentiated the ability of imipramine to induce dopaminergic motor supersensitivity. The present results suggest that increased dopamine D3 receptor expression following antidepressant treatments is not involved in the mechanism of dopaminergic supersensitivity, and are consistent with evidence supporting an inhibitory role for dopamine D3 receptors in motor activity, both in normal and in sensitized subjects.

Delayed effects of antidepressant drugs in rats

The present study has addressed the question of what is more important for the occurrence of adaptive changes observed in the organism treated with antidepressant drugs: a daily dosing of the drug or the period of time necessary for the plastic events to develop. Here, we report on the effects of desipramine given to rats acutely (and tested following 2 drug-free weeks) as when the drug was administered repeatedly, on behavior in the forced swim test (i.e. significant shortening of immobility time by ca. 60%) and on the binding of [3H]CGP12177 to beta-adrenergic receptors in the rat brain cortex (significant decrease of the binding by ca. 15%). Additionally, using the procedure of the repeated forced swim test (six times over 21 days), we show that the shortening of immobility time induced by a single dose of imipramine persisted throughout the whole experimental period and was similar to that seen in a group of animals treated repeatedly with the drug. Also, the effects of citalopram on immobility and climbing were similar after acute treatment and delayed testing to those seen after repeated drug exposure. The results obtained in the present study may question some conclusions that are usually drawn from the behavioral and, especially, biochemical studies concerning the need for repeated treatment with antidepressant drugs to induce various adaptive changes in the brain, which are thought to be responsible for the therapeutic efficacy of these drugs.

Norepinephrine transporter knockout-induced up-regulation of brain alpha2A/C-adrenergic receptors

The norepinephrine transporter (NET) is responsible for the rapid removal of norepinephrine released from sympathetic neurons; this release is controlled by inhibitory alpha(2)-adrenergic receptors (alpha(2)ARs). Long-term inhibition of the NET by antidepressants has been reported to change the density and function of pre- and postsynaptic ARs, which may contribute to the antidepressant effects of NET inhibitors such as desipramine. NET-deficient (NET-KO) mice have been described to behave like antidepressant-treated mice. By means of quantitative real-time PCR we show that mRNAs encoding the alpha(2A)-adrenergic receptor (alpha(2A)AR) and the alpha(2C)-adrenergic receptor (alpha(2C)AR) are up-regulated in the brainstem, and that alpha(2C)AR mRNA is also elevated in the hippocampus and striatum of NET-KO mice. These results were confirmed at the protein level by quantitative autoradiography. The NET-KO mice showed enhanced binding of the selective alpha(2)AR antagonist [(3)H]RX821002 in several brain regions. Most robust increases (20-25%) in alpha(2)AR expression were observed in the hippocampus and in the striatum. Significant increases (16%) were also seen in the extended amygdala and thalamic structures. In an 'in vivo' test, the alpha(2)AR agonist clonidine (0.1 mg/kg) caused a significantly greater reduction of locomotor activity in NET-KO mice than in wild-type mice, showing the relevance of our findings at the functional level.