Neurochemical and behavioural profile of Lu 17-133, (±)-trans-4-[3-(3,4-dichlorophenyl)-indan-1-yl]-1-piperazineethanol, an inhibitor of the uptake of dopamine and noradrenaline

Conventional and new antidepressant drugs in the elderly

Depression in the elderly is nowadays a predominant health care problem, mainly due to the progressive aging of the population. It results from psychosocial stress, polypathology, as well as some biochemical changes which occur in the aged brain and can lead to cognitive impairments, increased symptoms from medical illness, higher utilization of health care services and increased rates of suicide and nonsuicide mortality. Therefore, it is very important to make an early diagnosis and a suitable pharmacological treatment, not only for resolving the acute episode, but also for preventing relapse and enhancing the quality of life. Age-related changes in pharmacokinetics and in pharmacodynamics have to be kept into account before prescribing an antidepressant therapy in an old patient. In this paper some of the most important and tolerated drugs in the elderly are reviewed. Tricyclic antidepressants have to be used carefully for their important side effects. Nortriptyline, amytriptiline, clomipramine and desipramine as well, seem to be the best tolerated tricyclics in old people. Second generation antidepressants are preferred for the elderly and those patients with heart disease as they have milder side effects and are less toxic in overdose and include the so called atypicals, such as selective serotonin reuptake inhibitors, serotonin noradrenalene reuptake inhibitors and noradrenaline reuptake inhibitors. Monoamine oxidase (MAO) inhibitors are useful drugs in resistant forms of depression in which the above mentioned drugs have no efficacy; the last generation drugs (reversible MAO inhibitors), such as meclobemide, seem to be very successful. Mood stabilizing drugs are widely used for preventing recurrences of depression and for preventing and treating bipolar illness. They include lithium, which is sometimes used especially to prevent recurrence of depression, even if its use is limited in old patients for its side effects, the anticonvulsants carbamazepine and valproic acid. Putative last generation mood stabilizing drugs include the dihydropyridine L-type calcium channel blockers and the anticonvulsants phenytoin, lamotrigine, gabapentin and topiramate, which have unique mechanisms of action and also merit further systematic study. Psychotherapy is often used as an adjunct to pharmacotherapy, while electroconvulsant therapy is used only in the elderly patients with severe depression, high risk of suicide or drug resistant forms.

Effects of diazepam, citalopram, methadone and naloxone on PCP-induced stereotyped behaviour and social isolation in the rat social interaction test

Phencyclidine (PCP) can induce a model psychosis in humans that mimics the positive and negative symptoms of schizophrenia. In the social interaction test PCP induces stereotyped behaviour and social isolation in rats, and these behaviours can be inhibited by antipsychotic drugs. In order to further evaluate the predictive validity of this model of schizophrenia the anxiolytic diazepam (0.02-17.5 micromol/kg; 0.005-5.0 mg/kg), the antidepressant citalopram (0.62-19.8 micromol/kg; 0.3-4.0 mg/kg), the opioid agonist methadone (0.36-5.8 micromol/kg; 0.13-2.0 mg/kg) and the opioid antagonist naloxone (0.34-22.0 micromol/kg; 0.13-8.0 mg/kg) were tested as examples of drugs without antipsychotic activity. The experiments demonstrated that these compounds did not specifically inhibit the behavioural effects of PCP. So far only antipsychotic drugs have been able to specifically inhibit the PCP-induced behaviours.

Partial and full dopamine D1 receptor agonists in mice and rats: relation between behavioural effects and stimulation of adenylate cyclase activity in vitro

The dopamine (DA) D1 agonists, SK&F 83959, SK&F 75670, SK&F 38993, SK&F 81297 and SK&F 80723, had variable abilities to stimulate adenylate cyclase activity in rat striatal homogenates. Their efficacies, in relation to the effect of 100 microM DA were 0, 33, 69, 68 and 81%, respectively. In rats, all compounds induced (1) contralateral circling behaviour after unilateral 6-hydroxy-DA lesions, (2) ipsilateral circling behaviour after midbrain hemitransection after cotreatment with the D2 agonist quinpirole and (3) oral stereotypies after their combination with quinpirole. Maximum effects and rank order of potencies were similar in the three test models. In mice SK&F 83959, SK&F 75670 and SK&F 38393 inhibited methylphenidate-induced gnawing behaviour and induced no or only weak hypermotility. SK&F 81297 induced marked hypermotility which was partially inhibited by SK&F 83959 and SK&F 75670 and was completely blocked by the D1 antagonist, SCH 23390. It is concluded that no relation could be demonstrated between the efficacy to stimulate adenylate cyclase and to induce circling behaviours and stereotypies in rats. In contrast, a relation between biochemical and behavioural efficacies was found in the mouse models. The results suggest that different subtypes of D1 receptors mediate the behavioural effects reported in this study.

Effect of imipramine in the "learned helplessness" model of depression in rats is not mimicked by combinations of specific reuptake inhibitors and scopolamine

Administration of imipramine, which blocks noradrenergic, serotonergic and cholinergic reuptake, to rats for 4 days counteracts the shuttlebox escape failures otherwise seen in rats which have been exposed to inescapable shock (the "learned helplessness" model of depression). The effects of the more selective reuptake inhibitors talsupram (noradrenergic), citalopram (serotonergic) and the anticholinergic compound scopolamine were assessed alone and in combination after acute or 4 days' administration on escape behavior. Their possible synergistic effects when combined with imipramine were also assessed. Talsupram and citalopram were ineffective, whereas scopolamine counteracted the escape failures. Combinations of talsupram, citalopram and a subeffective dose of scopolamine were ineffective. A synergistic effect was only seen when scopolamine was combined with a suboptimal dose of imipramine. Thus, the effect of imipramine on "learned helplessness" might rely partly on its anticholinergic component. However, as an acute high dose of imipramine (25 mg/kg) was ineffective [unlike the acute administration of scopolamine (0.12 mg/kg)], this drug retains a pharmacological effect which is not mimicked by scopolamine alone or by combining the specific reuptake inhibitors with scopolamine.

In vivo neurochemical profile of dopamine uptake inhibitors and releasers in rat caudate-putamen

The in vivo neurochemical profile of recently synthesized dopamine (DA) uptake inhibitors (Lu 19-005, Lu 17-133 and GBR 12.921) is described. The antidepressant, nomifensine, as well as another typical DA uptake inhibitor, methylphenidate, was also tested with the microdialysis technique. Most of the new DA uptake inhibitors induced a gradual dose- and time-dependent accumulation of extracellular DA with a weak influence on DA metabolites, similar to that of methylphenidate. Nomifensine, however, caused a DA overflow during the first hour after injection. This was distinguishable from the effect of other uptake inhibitors but comparable to amphetamine. The moderate increase of DOPAC induced by nomifensine compared to the marked decrease produced by amphetamine corroborates reports that the DA 'release' induced by these drugs is mediated by different mechanisms, originating from different intracellular storage pools of DA. The fact that nomifensine can be distinguished from other uptake inhibitors shows clearly that evaluation of dynamic changes in transmitter overflow provides information pertinent to the overall neurochemical characterization of a drug.