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PubMed2002

Inhibition and possible induction of rat CYP2D after short- and long-term treatment with antidepressants.

The aim of this study was to investigate the influence of tricyclic antidepressants (imipramine, amitriptyline, clomipramine, desipramine), selective serotonin reuptake inhibitors (SSRIs: fluoxetine, sertraline) and novel antidepressant drugs (mirtazapine, nefazodone) on the activity of CYP2D, measured as a rate of ethylmorphine O-deethylation. The reaction was studied in control liver microsomes in the presence of the antidepressants, as well as in microsomes of rats treated intraperitoneally for one day or two weeks (twice a day) with pharmacological doses of the drugs (imipramine, amitriptyline, clomipramine, nefazodone 10 mg kg(-1) i.p.; desipramine, fluoxetine, sertraline 5 mg kg(-1) i.p.; mirtazapine 3 mg kg(-1) i.p.), in the absence of the antidepressants in-vitro. Antidepressants decreased the activity of the rat CYP2D by competitive inhibition of the enzyme, the potency of their inhibitory effect being as follows: clomipramine (K(i) = 14 microM) > sertraline approximate, equals fluoxetine (K(i) = 17 and 16 microM, respectively) > imipramine approximate, equals amitriptyline (K(i) = 26 and 25 microM, respectively) > desipramine (K(i) = 44 microM) > nefazodone (K(i) = 55 microM) > mirtazapine (K(i) = 107 microM). A one-day treatment with antidepressants caused a significant decrease in the CYP2D activity after imipramine, fluoxetine and sertraline. After prolonged administration of antidepressants, the decreased CYP2D activity produced by imipramine, fluoxetine and sertraline was still maintained. Moreover, amitriptyline and nefazodone significantly decreased, while mirtazapine increased the activity of the enzyme. Desipramine and clomipramine did not produce any effect when administered in-vivo. The obtained results indicate three different mechanisms of the antidepressants-CYP2D interaction: firstly, competitive inhibition of CYP2D shown in-vitro, the inhibitory effects of tricyclic antidepressants and SSRIs being stronger than those of novel drugs; secondly, in-vivo inhibition of CYP2D produced by both one-day and chronic treatment with tricyclic antidepressants (except for desipramine and clomipramine) and SSRIs, which suggests inactivation of the enzyme apoprotein by reactive metabolites; and thirdly, in-vivo inhibition by nefazodone and induction by mirtazapine of CYP2D produced only by chronic treatment with the drugs, which suggests their influence on the enzyme regulation.

Animals↗
PubMed2005

Effect of long-term administration of antidepressants on the lipid composition of brain plasma membranes.

The connection between changes in lipid pattern in brain plasma membranes and long-term administration of therapeutically effective doses of antidepressants has not been sufficiently demonstrated so far. Therefore, we analyzed effect of antidepressants that differ in pharmacological selectivity on membrane lipid composition in the rat brain tissue. Laboratory rats were given desipramine, maprotiline, citalopram, moclobemide or lithium for a 4-week period. We observed a significant decrease in phosphatidylethanolamine representation after administration of maprotiline, citalopram and moclobemide when compared with controls. Membrane cholesterol content was decreased after desipramine administration and increased after citalopram or lithium treatment. Electroneutral phospholipids were decreased after the administration of all tested antidepressants except for desipramine. Decrease in phosphatidylserine was found following long-term administration of maprotiline or desipramine; relative representation of phosphatidylinositol was reduced after lithium treatment. Statistically significant negative correlation between cholesterol and electroneutral phospholipids was discovered. Membrane microviscosity evaluated by fluorescence anisotropy of membrane probes was only slightly decreased after desipramine and increased after citalopram administration. Hypothesis was supported that changes in brain neurotransmission produced by antidepressants could be, at least partially, associated with adaptive changes in membrane cholesterol and phospholipids.

Adaptation, Physiological↗
PubMed1984

Imipramine-cimetidine interaction: impairment of clearance and enhanced absolute bioavailability.

Six healthy volunteers each received imipramine on four occasions in random sequence, i.v. (12.5 mg) and p.o. (50 mg) in a drug-free state and i.v. and p.o. while taking cimetidine 300 mg every 6 hr. After i.v. doses, elimination half-life of imipramine was increased during cimetidine treatment (22.1 vs. 15.5 hr, P less than .02) as a result of decreased total metabolic clearance (623 vs. 1048 ml/min, P less than .05) with no change in volume of distribution (17.2 vs. 19.8 liters/kg) or plasma protein binding (unbound percent, 17.7 vs. 16.5%). After single p.o. imipramine doses, peak imipramine blood levels achieved were greater during cimetidine therapy (34.4 vs. 19.3 ng/ml, P less than .05) and area under the time/concentration curve was greatly increased (569 vs. 306 ng/ml X hr, P less than .05). Desipramine, the biologically active metabolite of imipramine, was measurable only after p.o. doses. Desipramine area under the time/concentration curve was increased during cimetidine therapy after p.o. imipramine doses (274 vs. 152 ng/ml X hr, P less than .05), suggesting that desipramine clearance was inhibited as well. Comparison of i.v. and p.o. imipramine doses indicated absolute bioavailability was 40.2% in the control state and increased to 75.3% (P less than .05) during cimetidine treatment. Imipramine, with both impaired total metabolic clearance and enhanced bioavailability, in conjunction with increased accumulation of desipramine, would have marked increases in steady-state plasma concentration of both imipramine and desipramine with concurrent cimetidine therapy during chronic p.o. treatment.

Administration, Oral↗
PubMed1996

Functional classification of antidepressants based on antagonism of swim stress-induced fos-like immunoreactivity.

Autoradiographic analysis of 14C-2-deoxyglucose (2-DG) uptake and immunocytochemical assessment of Fos-like immunoreactivity (Fos-LI) were used to assess swim stress-induced changes in metabolic activity in brain and to define the effect of chronic treatment with antidepressants from different pharmacological classes. Saline-treated rats processed in the forced swim test exhibited marked increases in Fos-LI in limbic cortical regions, lateral septum, medial amygdala and paraventricular nucleus of the hypothalamus (PVN). Uptake of 2-DG was increased by swim stress in some of the same brain regions where Fos-LI was induced, with the notable exception of a lack of a change in the PVN. Rats received injections for 3 wk with imipramine, desipramine, fluoxetine, nisoxetine, tranylcypromine or mianserin before being processed in the forced swim test. Chronic treatment with imipramine and desipramine alone induced Fos-LI in the central nucleus of the amygdala and the dorsolateral bed nucleus of the stria terminalis. After tranylcypromine treatment, Fos-LI was induced in many brain regions including limbic cortex, amygdala and paraventricular nucleus of the hypothalamus. None of the other antidepressants induced Fos-LI in any brain region examined. Chronic administration of imipramine, desipramine and nisoxetine antagonized the swim induced expression of Fos-LI in the PVN and in limbic cortical regions, including the medial prefrontal ventrolateral orbital and cingulate cortices. Chronic treatment with fluoxetine, tranylcypromine and mianserin did not alter swim stress-induced Fos-LI in any brain region. Thus, only antidepressant drugs that affect norepinephrine uptake (i.e., imipramine, desipramine and nisoxetine) antagonized swim stress-induced Fos-LI. In contrast to the action of chronic imipramine on Fos-LI induced by swim, chronic administration of imipramine did not antagonize the stress-induced changes in 2-DG uptake in limbic cortical regions. Acute administration of propranolol, which blocks beta-adrenergic receptors, reduced the number of cells staining for Fos-LI in limbic cortical regions, resembling the effects produced by chronic imipramine, desipramine and nisoxetine. In the PVN, neither propranolol nor prazosin (an alpha 1 antagonist) blocked the swim-induced Fos-LI, suggesting that swim-induced Fos-LI in the PVN is not under control of beta- or alpha 1-adrenergic receptors. These latter results imply that adaptation of noradrenergic receptors by chronic imipramine may not be related to the antagonism of stress-induced Fos-LI. The clear functional differences of the various antidepressant agents on swim stress-induced Fos-LI after chronic administration provide a functional classification of antidepressant drug action not previously identified.

Animals↗
PubMed1994

Psychotherapy and pharmacotherapy for ambulatory cocaine abusers.

BACKGROUND: At present, there is no consensus regarding effective treatment for cocaine abuse or the most productive roles for the two major forms of treatment, pharmacotherapy and psychotherapy. We conducted the first randomized clinical trial evaluating psychotherapy and pharmacotherapy, alone and in combination, as treatment for ambulatory cocaine abusers. METHODS: One hundred thirty-nine subjects were assigned to one of four conditions offered over a 12-week abstinence initiation trial: relapse prevention plus desipramine hydrochloride, clinical management plus desipramine, relapse prevention plus placebo, and clinical management plus placebo. All treatments were manual-guided, delivered by experienced therapists, and monitored to promote the integrity of both forms of treatment. RESULTS: First, although all groups showed significant improvement, significant main effects for medication or psychotherapy, or their combination, were not found for treatment retention, reduction in cocaine use, or other outcomes at 12 weeks. Second, baseline severity of cocaine use interacted differently with psychotherapy and pharmacotherapy: higher-severity patients had significantly better outcome when treated with relapse prevention than with clinical management, while desipramine was associated with improved abstinence initiation among lower-severity subjects. Third, desipramine was significantly more effective than placebo in reducing cocaine use over 6, but not 12, weeks of treatment. Fourth, depressed subjects had greater reduction in cocaine use than nondepressed subjects and had better response to relapse prevention than to clinical management. CONCLUSION: These findings underscore the significance of heterogeneity among cocaine abusers and the need to develop specialized treatments for clinically distinct subgroups of cocaine abusers.

Adult↗
PubMedDate not supplied

Managing rapid metabolizers of antidepressants.

Depressed patients who rapidly metabolize antidepressants may be common, and may not respond to even high doses of antidepressants if subtherapeutic plasma levels are produced. Rapid metabolizers (RMs) are identifiable if patients are on tricyclic antidepressants (TCAs), and TCA plasma levels (commonly available) are monitored. Strategies to achieve therapeutic levels in RMs include: (1) megaprescribing, or (2) inhibiting the metabolism of the parent drug. Megaprescribing TCAs runs the risk of markedly elevating levels of potentially toxic hydroxy metabolites. In this study twelve depressed, non-responding RMs were identified while taking the TCA, desipramine. Fluoxetine or paroxetine, selective serotonin re-uptake inhibitors (SSRIs) known to potently inhibit cytochrome P450 2D6 (the isoenzyme responsible for desipramine metabolism), was then added to continuing desipramine. Therapeutic range desipramine levels were achieved in ten patients, and seven of the ten achieved excellent or good sustained responses. The combination SSRI and TCA therapy was well tolerated. Whether response primarily reflected the TCA at therapeutic range levels, or a synergistic serotonin-noradrenaline interaction between the respective antidepressants, requires further clarification. The results of this open study suggest the need for controlled trials of antidepressant metabolism inhibition in RMs.

Adult↗
PubMed1986

Inhibition of fast axonal transport in bullfrog nerves by dibenzazepine and dibenzocycloheptadiene calmodulin inhibitors.

The effects of the calmodulin inhibitors amitriptyline, desipramine, imipramine, and clomipramine on fast axonal transport, oxidative metabolism, and density of axonal microtubules were measured in bullfrog spinal nerves in vitro. The four drugs tested inhibited the fast orthograde transport of [3H]leucine-labelled proteins and the fast retrograde transport of acetylcholinesterase at a concentration of 0.2 mM. Amitriptyline, desipramine, and imipramine were equipotent inhibitors of transport, and clomipramine was a more potent inhibitor than imipramine. The adenosine triphosphate content of the nerves was reduced by at most 19% by the compounds under study; such a reduction cannot account for the inhibition of fast axonal transport. Desipramine and imipramine had no significant effect on the density of microtubules in unmyelinated axons, whereas amitriptyline only reduced it by 18%; the inhibition of axonal transport by these three drugs can therefore not be explained by microtubule disruption. Clomipramine reduced microtubular density by 40%, and this effect may have contributed to the inhibition of fast axonal transport. The inhibition of fast axonal transport by desipramine, imipramine, and amitriptyline may be related to the inhibition of calmodulin function by these drugs. The similar potency of these three drugs as inhibitors of fast axonal transport goes in parallel with their known similar potency as calmodulin antagonists.

Acetylcholinesterase↗
PubMed1992

Disposition of endogenous adrenaline compared to noradrenaline released by cardiac sympathetic nerves in the anaesthetized dog.

The fate of adrenaline released from cardiac sympathetic nerves was compared with that of noradrenaline before and during two periods of electrical stimulation of the left ansa subclavia in eight anaesthetized dogs. Cardiac spillovers and extractions of both catecholamines were estimated simultaneously using infusions of 3H-labelled adrenaline and noradrenaline. Animals were studied before and after neuronal uptake blockade with desipramine. Cardiac spillover of adrenaline, detectable at rest at 1.4 +/- 0.3 pmol/min, increased to 4.0 +/- 1.1 and 5.3 +/- 1.2 pmol/min during sympathetic stimulation. Cardiac noradrenaline spillover increased from 49 +/- 12 to 205 +/- 40 and 451 +/- 118 pmol/min. After desipramine, cardiac spillovers of adrenaline were decreased, whereas those of noradrenaline were increased so that the ratio of adrenaline to noradrenaline spillover, meaned before and during stimulation, decreased substantially from 1:42 to 1:166. The desipramine-induced decrease in cardiac extractions of 3H-labelled catecholamines indicated adrenaline was removed 60% less efficiently than noradrenaline by neuronal uptake, whereas the extractions remaining indicated adrenaline was removed 50% more efficiently by extraneuronal uptake. The differences in removal processes indicated that 35% of the adrenaline released by cardiac sympathetic nerves was recaptured compared to 88% for noradrenaline, leaving 53% to be removed extra-neuronally compared to 6.6% for noradrenaline, so that proportionally more released adrenaline than noradrenaline escaped to spillover into plasma (12% versus 5.4%). Since extra-neuronal uptake was more efficient for adrenaline than noradrenaline, proportionally less released adrenaline than noradrenaline escaped local removal to spillover into plasma when neuronal uptake was blocked (17% versus 45%). This reversed the situation before blockade so that desipramine substantially decreased the ratio of adrenaline to noradrenaline spillover. Thus, differences in the efficiencies of neuronal or extraneuronal uptake are important determinants of the amounts of locally released adrenaline and noradrenaline that escape removal processes to act at neuroeffector sites or spillover into plasma.

Animals↗
PubMed1989

Multiple effects of cocaine upon evoked secretion in bovine adrenal medullary chromaffin cells. Additional insight into the mechanism of action of cardiac glycosides.

Experiments to determine the effects of the catecholamine neuronal uptake blockers cocaine and desipramine, and of the cardiac glycoside, ouabain, upon 3H-(noradrenaline) efflux have been performed with bovine adrenal medullary chromaffin cells in tissue culture. Both cocaine and desipramine reduced 3H-noradrenaline uptake into chromaffin cells. Inhibitable uptake was 80% of total accumulation over 60 min; this degree of inhibition was produced by cocaine (30 mumol/l) or desipramine (1 mumol/l). Cocaine (30 mumol/l) had no effect upon spontaneous 3H-efflux measured over 60 min, but reduced that evoked over the same period by carbachol (EC50), veratridine (EC50) and by ouabain (100 mumol/l). Cocaine did not reduce that efflux evoked by raised levels of K+ (28 mmol/l; EC50). Desipramine (1 mumol/l), like cocaine, had no effect upon spontaneous efflux of 3H, but reduced that efflux evoked by carbachol, veratridine and ouabain. Tetrodotoxin (TTX) inhibited veratridine-evoked 3H efflux (IC50 0.2 mumol/l). The degree of inhibition caused by TTX (0.2 mumol/l) was not increased by cocaine (30 mumol/l). TTX also inhibited ouabain-evoked 3H efflux: this was reduced by 55% by a concentration of TTX (1 mumol/l) sufficient to virtually abolish veratridine-evoked efflux. Cocaine (30 mumol/l) in the presence of TTX (1 mumol/l) did not further inhibit ouabain-evoked efflux. Cocaine (30 mumol/l) did not alter 86Rb+ uptake into chromaffin cells, nor did it alter that inhibition of 86Rb+ uptake produced by ouabain (100 mumol/l) indicating that cocaine has no effect upon Na,K-ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Medulla↗
PubMed1976

Effect of veratridine on the fluxes of 3H-noradrenaline and 3h-bretylium in the rat vas deferens in vitro.

The effect of the depolarizing agent veratridine on the accumulation and release of of 3H-noradrenaline and 3H-bretylium in in the rat vas deferens in vitro was examined. Veratridine produced inhibition of the accumulation and induced marked release of the amines. In vas deferens from non-reserpinized rats the release of noradrenaline evoked by veratridine was partially antagonized by omission of Ca2+ in the incubation medium and partially inhibited by low concentrations of desipramine. In reserpinized vas deferens the release of noradrenaline like that of bretylium in normal vas was not affected by omission of Ca2+ but inhibited by low concentrations (3-5 X 10(-7) M) of desipramine. Tetrodotoxin and the local anesthetics millicaine and lidocaine antagonized the effect of veratridine on the accumulation and release of the amines, probably due to prevention of the depolarization. High concentration (3 X 10(-5) M) of desipramine had a similar effect on the release of noradrenaline in normal tissue in presence of external Ca2+. It is concluded that noradrenaline is released by veratridine from normal vas deferens by two mechanisms: 1) an exocytosis release, 2) a carrier mediated desipramine sensitive outward transport; In reserpinized tissue the second mechanism is solely responsible for the release of noradrenaline. Bretylium is only released by the second mechanism. It is suggested that the inhibiton of the amine accumulation by veratridine is due to an equilibrium of the influx at a low tissue to medium ratio.

Aminobenzoates↗
PubMed1984

The transport of (+)-amphetamine by the neuronal noradrenaline carrier.

PC-12 cells (a clonal line of rat phaeochromocytoma cells) take up noradrenaline by a transport system which is identical with the neuronal amine transport system ("uptake1"). The uptake of 3H-noradrenaline into reserpine-pretreated PC-12 cells (monoamine oxidase inhibited) was saturable (Km = 0.6 +/- 0.1 mumol/l), dependent on sodium and chloride, and competitively inhibited by (+)-amphetamine (Ki = 0.18 +/- 0.04 mumol/l), cocaine (Ki = 0.55 +/- 0.15 mumol/l) and desipramine (Ki = 4.3 +/- 0.6 nmol/l). The uptake and accumulation of 3H (+)-amphetamine showed characteristics comparable to those of 3H-noradrenaline, since the uptake of 3H (+)-amphetamine (0.1 mumol/l) was reduced by omission of sodium or chloride from the incubation medium. The sodium-sensitive component of uptake and accumulation of 3H (+)-amphetamine was fully inhibited by cocaine and desipramine. The IC50 of desipramine for inhibition of the sodium-sensitive component of the 1-min uptake of 3H (+)-amphetamine (20 nmol/l) was about 2 nmol/l, i.e., identical with the Ki for inhibition of uptake of 3H-noradrenaline. At concentrations above 1 mumol/l, desipramine additionally caused an inhibition of the sodium-independent permeation of 3H (+)-amphetamine into PC-12 cells. Hence, by using a homogeneous population of cells endowed with "uptake1", it is possible to demonstrate - besides a pronounced lipophilic entry - a carrier-mediated uptake of 3H (+)-amphetamine.

Adrenal Gland Neoplasms↗
PubMed1986

Sodium-dependence of the potency of inhibitors of the neuronal noradrenaline carrier in the rat vas deferens.

Vasa deferentia obtained from reserpine-pretreated rats were incubated (monoamine oxidase and catechol-O-methyltransferase inhibited) in media containing various concentrations of 3H-(-)noradrenaline and Na+ and initial rates of the neuronal uptake of 3H-noradrenaline measured both in the absence and presence of uptake inhibitors after 1 min of incubation. When rates of uptake were determined at various 3H-noradrenaline (1.0-12.2 mumol/l) and two fixed Na+ concentrations (25 and 140 mmol/l), the inhibition of uptake produced by (+)amphetamine, (-)metaraminol, desipramine, nomifensine and cocaine was competitive with respect to 3H-noradrenaline at both Na+ concentrations. While the Ki for (+)amphetamine, (-)metaraminol desipramine and nomifensine increased when the Na+ concentration was lowered, that for cocaine decreased. When the Na+ concentration was varied (10-140 mmol/l) and the 3H-noradrenaline concentration held constant (1.2 mumol/l), (+)amphetamine, (-)metaraminol, nomifensine and desipramine acted as mixed-type inhibitors with respect to Na+, and the inhibition of uptake produced by these drugs was the more pronounced, the higher the Na+ concentration. On the other hand, cocaine was competitive with Na+ and the inhibition produced by this drug was the more pronounced, the lower the Na+ concentration. It is concluded that the inhibitors of neuronal uptake tested here act in dependence on the external Na+ concentration. Desipramine and nomifensine resemble alternative amine substrates in being more potent at high than at low Na+ concentrations. On the other hand, cocaine is more potent at low than at high Na+ concentrations.

Animals↗
PubMed1989

Inhibition of noradrenaline release in the rat brain cortex via presynaptic H3 receptors.

The effects of histamine and related drugs on the evoked tritium overflow from superfused rat brain cortex slices preincubated with 3H-noradrenaline were determined. Tritium overflow was stimulated electrically (3 Hz; slices superfused with normal physiological salt solution) or by introduction of CaCl2 1.3 mmol/l (slices superfused with Ca2(+)-free medium containing K+ 20 mmol/l). Histamine slightly decreased the electrically evoked 3H overflow in slices superfused in the presence of desipramine. The degree of inhibition obtained with histamine was doubled when both desipramine and phentolamine were present in the superfusion medium (pIC15 6.46). Under the latter condition, the evoked overflow was inhibited by the H3 receptor agonist R-(-)-alpha-methylhistamine and its S-(+) enantiomer (pIC15 7.36 and 5.09, respectively), but was not affected by the H2 receptor agonist dimaprit and the H1 receptor agonist 2-thiazolylethylamine (both at up to 32 mumols/l). The concentration-response curve of histamine was shifted to the right by the H3 receptor antagonists thioperamide, impromidine and burimamide (apparent pA2 8.37, 6.86 and 7.05, respectively), by the H2 receptor antagonist ranitidine (apparent pA2 4.27) and was not affected by the H1 receptor antagonist dimetindene (32 mumols/l). The inhibitory effect of R-(-)-alpha-methylhistamine on the evoked overflow was also counteracted by thioperamide. Given alone, none of the five histamine receptor antagonists affected the evoked overflow. In the absence of desipramine plus phentolamine, impromidine and burimamide facilitated the electrically evoked 3H overflow whereas thioperamide had no effect. The facilitatory effects of impromidine and burimamide were abolished by phentolamine, but not affected by desipramine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Interaction between antidepressants and d-amphetamine on variable-interval performance.

Four experiments were carried out investigating the interactions between some antidepressant drugs (imipramine, desipramine, fluvoxamine, trazodone (4 and 8 mg/kg) and d-amphetamine (0.1-3.2 mg/kg) on operant behaviour maintained under a variable-interval 80-s schedule of sucrose reinforcement; each experiment employed 12 rats. d-Amphetamine exerted a dose-related suppressant effect on response rate. Imipramine and desipramine given alone had no effect on response rate, whereas fluvoxamine (both doses) and the higher dose of trazodone produced significant increases in response rate. Pretreatment with imipramine, desipiramine or fluvoxamine significantly potentiated the suppressant effect of d-amphetamine on responding; pretreatment with trazodone had no significant effect. The potentiating effect of imipramine and desipramine may be related to their well known uptake blocking actions. The fact that fluvoxamine, a selective inhibitor of 5-hydroxytryptamine (5HT) uptake, also potentiated the effect of d-amphetamine suggests that the suppressant effect of d-amphetamine on operant behaviour may involve 5HT as well as catecholamine release. The lack of effect of trazodone may reflect its failure to influence uptake mechanisms. On the basis of a formal model couched in terms of Herrnstein's (1970) equation, it is suggested that imipramine, desipramine and fluvoxamine may have enhanced d-amphetamine's ability to reduce response capacity; it is suggested that the data do not provide evidence for an interaction between the antidepressants and the putative "motivation-enhancing" effect of d-amphetamine.

Animals↗
PubMed1990

An investigation of the role of 5-hydroxytryptamine in the attenuation of presynaptic alpha 2-adrenoceptor-mediated responses by antidepressant treatments.

Changes in the function of presynaptic alpha 2-adrenoceptors in the brain were assessed by rating the hypoactivity (sedation) response of mice to clonidine (0.1 mg/kg). A single injection of 5,7-dihydroxytryptamine (5,7-DHT, 75 micrograms ICV) or administration of p-chlorophenylalanine (PCPA; 200 mg/kg) daily for 11-15 days produced 62-77% reductions in brain 5-HT concentrations and marked supersensitivity of 5-HT2 receptor function, as indicated by the enhancement of the head-twitch response to 5-methoxy-N,N-dimethyltryptamine (2 mg/kg). Clonidine-induced hypoactivity was moderately enhanced after 5,7-DHT lesioning, but not after repeated PCPA injection. In addition, 5,7-DHT lesioning prevented the adaptive attenuation of this alpha 2-adrenoceptor-mediated response produced by daily injection of desipramine (10 mg/kg) for 14 days, but had no effect on the reduction caused by five electroconvulsive shocks (ECS, 200 V, 2 s) spread over 10 days. In contrast, repeated PCPA treatment did not prevent the reduction of clonidine-induced hypoactivity produced by repeated desipramine or ECS administration. Together, these results indicate that 5-HT (or possibly a cotransmitter contained within 5-hydroxytryptamine neurones) influences presynaptic alpha 2-adrenoceptor function. Furthermore, an intact 5-HT neuronal input is a prerequisite for the attenuation of clonidine-induced hypoactivity by desipramine, but not ECS. The probable explanation for a contrasting requirement for a functional 5-HT input is that desipramine and ECS induce this common adaptive response by different pharmacological mechanisms.

5,7-Dihydroxytryptamine↗
PubMed1998

Effect of antidepressant drugs on dopamine D1 and D2 receptor expression and dopamine release in the nucleus accumbens of the rat.

This study examined the effect of repeated treatment with the antidepressant drugs, fluoxetine, desipramine and tranylcypromine, on dopamine receptor expression (mRNA and binding site density) in sub-regions of the nucleus accumbens and striatum of the rat. The effect of these treatments on extracellular levels of dopamine in the nucleus accumbens was also measured. Experiments using in situ hybridisation showed that the antidepressants caused a region-specific increase in D2 mRNA, this effect being most prominent in the nucleus accumbens shell. In contrast, none of the treatments increased D1 mRNA in any of the regions examined. Measurement of D2-like binding by receptor autoradiography, using the ligand [3H]YM-09151-2, revealed that both fluoxetine and desipramine increased D2-like binding in the nucleus accumbens shell; fluoxetine had a similar effect in the nucleus accumbens core. Tranylcypromine, however, had no effect on D2-like binding in the nucleus accumbens but decreased binding in the striatum. In micro-dialysis experiments, our data showed that levels of extracellular dopamine in the nucleus accumbens were not altered in rats treated with either fluoxetine or desipramine, but increased by tranylcypromine. From our findings, we propose that the antidepressant drugs tested enhance dopamine function in the nucleus accumbens through either increased expression of post-synaptic D2 receptors (fluoxetine and desipramine) or increased dopamine release (tranylcypromine).

Animals↗
PubMed1999

Metyrapone displays antidepressant-like properties in preclinical paradigms.

A possible involvement of glucocorticoids in the aetiology of depression is suggested by commonly reported hypothalamo-pituitary-adrenocortical (HPA) axis abnormalities in depressed patients, the modulation of the HPA axis by antidepressant drugs and clinical reports of antidepressant efficacy with antiglucocorticoid agents. The effects of treatment with metyrapone, a glucocorticoid synthesis inhibitor, and the tricyclic antidepressant, desipramine, in two rodent models of depression, namely the forced swim test and olfactory bulbectomized (OB) rat, were investigated. In addition, the effect of chronic metyrapone and desipramine treatments on the hypothermic response to a challenge with the 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) was assessed. There is experimental evidence to suggest that attenuation of the hypothermic response to this agonist occurs following chronic antidepressant treatment. In the forced swim test, metyrapone (50 mg/kg) and desipramine (10 mg/kg) significantly reduced the immobility time. In the olfactory bulbectomized rat model of depression, chronic administration (14 days) of metyrapone (50 mg/kg b.i.d.) and desipramine (5 mg/kg b.i.d.) attenuated the OB-related hyperactivity in a novel stressful environment. Chronic metyrapone treatment (50 mg/kg b.i.d.) attenuated the hypothermic response to an acute challenge with 8-OH-DPAT (0.05 mg/kg s.c.), indicating a change to the sensitivity of 5-HT1A receptors. These preclinical tests demonstrate an antidepressant-like profile for metyrapone. Further exploration of the therapeutic potential and possible mechanism of action of glucocorticoid antagonism in depression is warranted.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1994

Tumor necrosis factor-alpha: presynaptic sensitivity is modified after antidepressant drug administration.

Presynaptic adrenergic functioning was coupled to cytokine sensitivity in order to further establish the mechanism of action of a tricyclic antidepressant drug. Antidepressant administration of desipramine to rats twice-daily for 2 weeks increased hippocampal TNF levels and transformed the presynaptic TNF response. One day of desipramine administration resulted in increased locus coeruleus TNF mRNA accumulation and, simultaneously, hippocampal TNF levels escalated. The fractional release of [3H]norepinephrine during field stimulation of control hippocampal slices was decreased by the addition of TNF in a concentration-dependent manner, an effect which was potentiated by the alpha 2-adrenergic antagonist idazoxan. While no change in sensitivity to TNF was observed in the hippocampus after one day of desipramine administration, TNF enhanced, rather than inhibited [3H]norepinephrine release after 14 days. In addition, TNF potentiation of [3H]norepinephrine release after chronic desipramine administration was reversed in the presence of idazoxan to a greater inhibition than in control slices exposed to idazoxan. Therefore, TNF-induced regulation of [3H]norepinephrine release appears to be associated with an alteration of alpha 2-adrenergic receptor responsiveness. The reversal in presynaptic TNF responsiveness after 14 days of tricyclic antidepressant drug administration describes a mechanism of action for their delayed clinical effect.

Animals↗