Chronic treatment with desipramine caused a sustained decrease of 3,4-dihydroxyphenylglycol-sulphate and total 3-methoxy-4-hydroxyphenylglycol in the rat brain

Cyclic AMP in the rat cerebral cortex after stimulation of the locus coeruleus: decrease by antidepressant drugs

The study concerned the effect of repeated treatment with antidepressant drugs on the elevation of cyclic AMP levels in the rat cerebral cortex following electrical stimulation of the locus coeruleus. Some of the tricyclic and tetracyclic antidepressant drugs inhibited the cyclic AMP response. Desmethylimipramine was the most potent (effective when given 5 mg/kg/day for 2 weeks). Imipramine and nomifensine (daily dose 10 mg/kg for 2 weeks) produced slight decreases, while iprindol and clomipramine were ineffective. After 6 weeks of treatment (daily 10 mg/kg) iprindol, clomipramine and mianserin were without effect. The cyclic AMP response was suppressed by higher doses of the latter two drugs (2 weeks, 20 mg/kg/day). These results indicate that tricyclic and tetracyclic antidepressant drugs are able to decrease cerebral noradrenergic neurotransmission of locus coeruleus neurons, as far as this is mediated by cyclic AMP. It is not clear, however, whether such modification is related to the therapeutic action of antidepressant drugs.

The effect of repeated administration of antidepressant drugs on the responsiveness of rats to catecholamine agonists

The antidepressant drugs, imipramine (10 mg/kg s.c.), amitriptyline (10 mg/kg s.c.), mianserin (2 mg/kg i.p.), danitracen (3 mg/kg i.p.) or the vehicle were administered to rats twice a day for 4 or 10 days. Clonidine (0.5 mg/kg s.c.) induced in rats chronically treated with the compounds studied an increase in locomotor activity but, at the same time, did not affect or decreased this activity in rats chronically treated with the vehicle or a single dose of an antidepressant. This refers, in particular, to imipramine, amitriptyline and danitracen which have a similar effect. This effect, an increase in motility, was most pronounced and common for all the three drugs (after a 4- and 10-day treatment) when clonidine was administered 72 hours after the last dose of an antidepressant. Only in a few cases the amphetamine-induced hypermotility was enhanced by a chronic administration of antidepressants (a 4-day amitriptyline treatment, 72 hours after the last injection; a 4-day mianserin or danitracen treatment, 48 hours after the last injection). The results obtained seem to suggest that a chronic administration of the antidepressant drugs may cause a change in the sensitivity of the central noradrenaline receptors.

Effect of acute and chronic treatment of tandamine, a new heterocyclic antidepressant, on biogenic amine metabolism and related activities

The effects of tandamine, a clinically effective heterocyclic antidepressant, administered either acutely (10 mg/kg i.p.) or chronically (10 mg/kg i.p. daily for 21 days) on biogenic amine uptake and metabolism in the rat were determined and a comparison with desipramine was made. Tandamine, similarly to desipramine, blocked norepinephrine (NE) uptake in rat brain and heart following both acute and chronic administration. No effect of tandamine on dopamine (DA) or serotonin (5-HT) uptake was observed. Both drugs lowered endogenous brain NE when given chronically but not acutely. In contrast, no such effect on brain DA and 5-HT or heart NE was observed. Tandamine, like desipramine, administered chronically prior to an intraventricular injection of 3H-NE, produced increases in the decline of 3H-NE as indicated by decreased 3H-NE with increased levels of 3H-normetanephrine in brain stem of rats, suggesting an increased turnover of NE. No such effect was observed following acute treatment. Both drugs increased the behavioural effects of L-Dopa following and acute oral administration, with tandamine appearing superior to desipramine at the lower dose examined (10 mg/kg). Tandamine was 57--833 times less effective in binding to rat brain muscarinic receptors than desipramine, imipramine, butriptyline and amitriptyline, respectively. Thus, tandamine affects biogenic amine mechanism following either acute or chronic administration in a fashion similar to desipramine, but unlike desipramine, it exhibits relatively little anticholinergic properties, a further indication of the potential use of tandamine in the treatment of human depression, particularly where an increase in drive is desired.

The effect of acute and chronic desipramine and amitriptyline treatment on rat brain total 3methoxy-4-hydroxyphenylglycol

The effect of acute (single dose), short-term (4 days), and chronic treatment (21 days) with two tricyclic antidepressants desipramine and amitriptyline on brain 3-methoxy-4-hydroxyphenylglycol (MHPG) was examined in the rat. Amitriptyline had no effect on brain total MHPG irrespective of the duration of the treatment and did not interfere with the lowering effect of clonidine on brain total MHPG. Acute and short-term desipramine treatment decreased brain total MHPG in rats, while chronic desipramine treatment increased it. The differential effect of acute and chronic treatment of desipramine on the brain total MHPG was further demonstrated by the lack of interference with the lowering effect of clonidine on brain total MHPG by one single dose of desipramine; partial interference after 4 days and complete interference after 21 days of desipramine treatment.

Effects of single and multiple doses of desipramine (DMI) on endogenous levels of 3-methoxy-4-hydroxyphenylglycol-sulfate (MOPEG-SO4) in rat brain

A single administration of desipramine (DMI) (10 mg/kg, i. p.) decreased brain levels and probenecid-induced accumulation rate of 3-methoxy-4-hydroxyphenylglycol-sulfate (MOPEG-SO4) in rats. To investigate the mechanism of this action, the interaction of DMI with NA receptor blockers and its effects on electrical stimulation were evaluated. It was found that phenoxybenzamine (20 mg/kg) or chlorpromazine (10 mg/kg) completely prevented the DMI-induced decrease in MOPEG-SO4 brain levels. On the other hand, DMI did not antagonize the increase in MOPEG-SO4 induced in the cortex-hippocampus by stimulation of the locus coeruleus. These observations indicate that the effect of DMI on MOPEG-SO4 is more likely to be due to a reduction of neuronal impulse flow mediated by a negative feed-back mechanism resulting from impairment of reuptake than to a direct effect on NA catabolism. In contrast to the effect of a single dose, the repeated administration of DMI (10 mg/kg, twice a day for 3 days) did not significantly reduce the rate of probenecid-induced accumulation of MOPEG-SO4. This development of tolerance to the metabolite-decreasing effects of DMI indicates that complex adaptive changes occur in the NA system upon repeated DMI administration.