Chronic antidepressant drug treatment attenuates motor-suppressant effects of apomorphine without changing [3H]GBR 12935 binding

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.

Unchanged density of caudate nucleus dopamine uptake sites in depressed suicide victims

In depressive states, theories concerning serotonin and norepinephrine have been dominating, but there are several lines of evidence indicating the involvement of the dopamine system as well, especially in suicidal depression. In this post-mortem study, the binding of the ligand [3H]WIN 35,428 to dopamine uptake sites in the caudate nucleus was investigated in 13 depressed suicide victims and 19 controls. There were no differences in Bmax or Kd between the suicide group and controls. Subdividing the suicide group into subgroups regarding the presence of major depression, antidepressant medication and suicide method, respectively, did not yield any differences. Previous findings regarding reduced CSF HVA in suicidal depression and indications of striatal dopaminergic biochemical and receptor changes in depression seem, according to the present study, not to be reflected by alterations in density or affinity of dopamine uptake sites in depressed suicide victims.

Apomorphine-induced aggressiveness and [3H]citalopram binding after antidepressant treatment in rats

The effects of acute and repeated administration of antidepressive drugs on apomorphine-induced aggressive behavior and [3H]citalopram binding were studied. In acute behavioral experiments with apomorphine pretreated (1.0 mg/kg, once daily) animals, desipramine (10 mg/kg) and clomipramine (10 mg/kg) enhanced, buspirone (2.5 and 5.0 mg/kg) completely blocked, but fluoxetine, amitriptyline, imipramine (10 mg/kg), and citalopram (10 and 20 mg/kg) had no effect on the intensity of aggressive behavior. Repeated concomitant apomorphine (1.0 mg/kg) and citalopram (10 mg/kg) administration reduced the affinity (Kd) of the 5-HT transporter binding sites in three brain regions. This finding was confirmed by an additional experiment as the effect of citalopram treatment. Repeated apomorphine (1.0 mg/kg) or apomorphine (1.0 mg/kg) plus desipramine (10 mg/kg) treatment had no unidirectional effect on Kd, the maximal number of apparent binding sties (Bmax) was unchanged in all experiments. Our study indicates that the 5-HT reuptake blockade has no major influence on the apomorphine-induced aggressive behavior, but the 5-HT1A receptor subtype may be involved in the mediation of the aggressive behavior in this paradigm.

Dopamine uptake sites, labelled with [3H]GBR12935, in brain samples from depressed suicides and controls

We have quantitated dopamine uptake sites, labelled with [3H]GBR12935, in caudate, putamen and nucleus accumbens of suicides with a retrospective diagnosis of depression, and age and gender-matched controls. Suicides were subdivided into those who had been free of antidepressant drugs for at least three months, and those in whom prescription of antidepressant drugs was clearly documented. We found no significant differences between controls and suicides overall, or when the suicides were divided on the basis of antidepressant treatment or violence of death. A significant negative correlation between the number of dopamine uptake sites and age was found in each region studied. Our results suggest dopamine uptake sites are not critically involved in depression or antidepressant drug action.

Effect of antidepressants on striatal and accumbens extracellular dopamine levels

The effect of the selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor, fluoxetine (10 mg/kg s.c.), two tricyclic antidepressants, clomipramine (10 mg/kg s.c.) and imipramine (10 mg/kg s.c.), and vehicle on extracellular dopamine levels was studied in rat nucleus accumbens and striatum by in vivo microdialysis. Fluoxetine produced significant decreases in extracellular dopamine levels in both the nucleus accumbens and striatum (mean maximum percentage decrease: 58% and 57% of pre-drug baseline, respectively). In contrast, imipramine and clomipramine significantly increased extracellular dopamine in the striatum (148% and 150%, respectively) compared to the effect of vehicle alone (118%). These results suggest that the selective serotonin reuptake inhibitor, fluoxetine, and the tricyclic antidepressants, clomipramine and imipramine, affect dopaminergic activity in diverse ways and in a region-specific manner. Thus, the antidepressant effect of these drugs is unlikely to be related to their acute effects on dopaminergic neurotransmission. The differential effects of the selective serotonin reuptake inhibitor and tricyclic antidepressants on extracellular dopamine could account for other differences in their clinical and side effect profiles. Further studies of the chronic effects of the selective serotonin reuptake inhibitor and the tricyclic antidepressants on dopaminergic activity are required to elucidate the role of dopamine in the antidepressant effect.

Chronic administration of the antidepressants phenelzine, desipramine, clomipramine, or maprotiline decreases binding to 5-hydroxytryptamine2A receptors without affecting benzodiazepine binding sites in rat brain

1. The effects of chronic administration of five antidepressant drugs on the benzodiazepine and 5-HT2A binding sites in the same rat brain were assessed. 2. Clomipramine, desipramine, maprotiline, fluoxetine, and phenelzine (all 10 mg/kg/day) were administered s.c. for 21 days by Alzet osmotic minipumps. 3. Results showed that none of the drugs changed the density or affinity of benzodiazepine binding sites, yet at the same dose all the drugs with the exception of fluoxetine decreased binding to 5-HT2A receptors in the same animals.

Behavioural response to SKF 38393 and quinpirole following chronic antidepressant treatment

The effects of chronic administration of antidepressant drugs (21-22 days s.c. via osmotic mini-pumps) on the behavioural responses of male Sprague-Dawley rats to (-)-quinpirole hydrochloride (0.05 mg kg-1 s.c., 5 min) and (+/-)-SKF 38393 hydrochloride (10 mg kg-1 s.c., 5 min) were investigated. Desipramine hydrochloride (10 mg kg-1 per day), phenelzine sulphate (10 mg kg-1 per day) and clorgyline hydrochloride (1 mg kg-1 per day) attenuated the suppression of locomotor activity induced by quinpirole, a dopamine D2-like receptor agonist, while clomipramine hydrochloride (10 mg kg-1 per day) was without effect. Yawning elicited by quinpirole was absent in phenelzine- and clorgyline-treated rats, but unaffected in rats treated chronically with desipramine and clomipramine. SKF 38393, a dopamine D1-like receptor agonist, significantly increased locomotor activity and time spent grooming in control animals. There were no significant effects of antidepressants on the behavioural responses to SKF 38393.

Early postnatal antidepressant treatment and juvenile stereotyped behaviour in rats

The effect of antidepressants on stereotyped behaviour in rats during development was examined. Rats were injected s.c. once a day from the 6th to the 22th day after birth with 0.9% sodium chloride, with desipramine 5 mg/kg body weight, with nomifensine 10 mg/kg, or with zimelidine 25 mg/kg. Stereotyped behaviour was assessed when the rats were 1 month and 2 months of age. Desipramine intensified and prolonged apomorphine 0.5 mg/kg induced stereotyped behaviour at 1 month but not at 2 months of age. Nomifensine and zimelidine did not affect stereotyped behaviour at either 1 month or 2 months of age. Thus, 2-week treatment with desipramine during early development was shown to increase stereotyped behaviour at a juvenile age.