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Examination of the relationship between the uptake system for 5-hydroxytryptamine and the high-affinity [3H]imipramine binding site--I. Inhibition by drugs.

The relationship between the binding site for imipramine and the uptake system for 5-hydroxytryptamine was examined. This was determined from the interaction between various drugs (including tricyclic antidepressants) and the high affinity accumulation of [3H]5-hydroxytryptamine in cortical synaptosomes from the rat, and with the high affinity binding of [3H]imipramine to cortical membranes of the rat. Imipramine and clomipramine, but not desipramine, were potent inhibitors of both binding of [3H]imipramine and the uptake of [3H]5-hydroxytryptamine. However, ouabain, panuramine and 5-hydroxytryptamine itself, all inhibited the binding of [3H]imipramine only at concentrations greater than those required to inhibit the uptake of [3H]5-hydroxytryptamine. Kinetic analysis revealed that inhibitors of the uptake system for 5-hydroxytryptamine produced inhibition by different mechanisms, but this did not account for their differential potency against uptake and binding. It is concluded that the binding site for [3H]imipramine and the uptake site for 5-HT are not directly linked and that drugs may inhibit the uptake of 5-HT at sites other than the binding site for [3H]imipramine.

Animals↗

Effects of treatment with a lithium-imipramine combination on components of adenylate cyclase in the cerebral cortex of the rat.

This study was aimed at investigating the effects of treatment with a lithium-imipramine combination on the activity of adenylate cyclase in membranes from the cerebral cortex of the rat. Treatment with (1) lithium for 2 weeks, yielding a level of lithium in serum of 0.54 +/- 0.12 mmol/l, (2) imipramine for 4 weeks (10 mg/kg i.p. twice per day) and (3) a combination of the two drugs reduced isoprenaline-induced stimulation of adenylate cyclase by GTP, with a greater decrement with the combined treatment. None of the treatments exerted any effect on the activity of the enzyme stimulated by GTP alone. Lithium ex vivo inhibited the calcium (Ca2+)- and Gpp(NH)p-stimulated activity of adenylate cyclase, but imipramine ex vivo did not affect the activity of adenylate cyclase, stimulated by these activators. The lithium-imipramine treatment reduced Ca2(+)- and Gpp(NH)p-stimulated activity of adenylate cyclase, but this was not different from that observed in the lithium-treated group. In conclusion, the beta-adrenoceptor-stimulated adenylate cyclase was affected markedly by administration of lithium and imipramine together. In contrast to lithium ex vivo, imipramine ex vivo did not impair the activity of either the guanine nucleotide regulatory protein or the catalytic subunit, since no change in activity was observed in the presence of beta,gamma-imidoguanosine-5' triphosphate (Gpp(NH)p) or Ca2+. Furthermore, lithium ex vivo exerted its post-receptor effects on the adenylate cyclase, independent of imipramine. The decrement in activity of beta-adrenergic adenylate cyclase, induced by administration of the two drugs together may partly be involved in the therapeutic action of the augmentation of antidepressants by lithium in refractory depression.

Adenylyl Cyclases↗

Imipramine-induced erection, masturbation, and ejaculation in male horses.

Imipramine hydrochloride was administered to five male horses (400-500 kg b.wt.): one experienced young stallion, two mature normal breeding stallions, one 5-year-old stallion with erection and ejaculatory dysfunction, and one long-term castrated male horse. Oral imipramine treatment (100 to 600 mg, twice daily) led to frequent erection and masturbation while at rest in the stall in a nonsexual context. Intravenous imipramine treatment over a range of doses (50 to 1000 mg) similarly induced erection and masturbation in all animals. Erection typically occurred within 10 minutes after injection, and the erection and masturbation continued intermittently for 1 to 2 hours. These erections proceeded as during sexual excitement to a normal firmness and eventual engorgement of the glans penis. Two stallions ejaculated while masturbating. Mild ataxia and drowsiness appeared at the higher doses, but the animals remained responsive to auditory, visual, and tactile stimuli. Erection and masturbation were often interrupted by activities about the barn or the approach of the handler, suggesting cortical inhibitory control of the erection. When tested in a sexual context immediately following IV treatment (500 mg), the two mature breeding stallions bred normally. The 5-year-old stallion, which had not ejaculated over several months of breeding attempts, spontaneously ejaculated following IV imipramine treatment. Subsequently, this stallion has ejaculated during copulation while on low dose oral (100 mg. twice daily) imipramine treatment. Plasma total androgens increased during treatment in these stallions. The long-term castrate showed erection and masturbation following IV imipramine treatment, suggesting that the effect of imipramine is not testosterone dependent.

Androgens↗

Dopamine D2 receptor blocking effect of imipramine in the rat hippocampus.

The effect of dopamine receptor agonists on the spontaneous bioelectrical activity of CA1 layer neurons in the hippocampal slice preparation from the rat brain was studied. Two groups of rats were used: control and imipramine-pretreated ones (twice a day, for two weeks, 10 mg/kg PO). Dopamine and the selective D2 receptor agonist quinpirole induced an excitatory reaction; a similar effect was evoked by amphetamine, an indirect dopamine agonist. The effects of the three compounds were diminished by sulpiride. Perfusion of control slices with imipramine decreased the excitatory effect of dopamine, amphetamine, and quinpirole. The effect of dopamine agonists was also inhibited 2 h after repeated pretreatment with imipramine. The excitatory effect of the dopamine agonist was enhanced 48 h after the last dose of imipramine, the latter effect was blocked by a 60-min perfusion of slices with imipramine or sulpiride in the experimental chamber. The obtained data show that acute imipramine induces blockade of dopamine D2 receptors in the hippocampus. This effect is probably responsible for development of supersensitivity of dopamine D2 mechanisms after prolonged treatment with imipramine in this brain region.

Amphetamine↗

Juvenile desipramine reduces adult sensitivity to imipramine in two behavioral tests.

The behavioral effects of adult imipramine administration were examined in female rats treated with desipramine as juveniles (JDES), treated with saline as juveniles (JSAL), and untreated as juveniles (JUNT). In the forced swimming test, the juvenile groups displayed similar behavioral effects of imipramine when administered short term following a pretest forced swimming exposure. Similar effects of imipramine were observed when administered long term prior to the only test exposure. When rats were not given a pretest forced swimming test exposure, short-term imipramine had no effect on JDES rats but did influence JSAL and JUNT rats. In the open-field test, short- and long-term imipramine treatment affected the behavior of JUNT and JSAL rats. Short-term imipramine treatment influenced open-field behavior of JDES animals, but long-term imipramine treatment had no effect. These results suggest that JDES treatment may permanently alter the neural mechanism underlying the behavioral effects of antidepressant treatment.

Animals↗

Imipramine effect on hypothalamic-pituitary-adrenal axis response to hypoglycemia.

Six control subjects underwent an insulin tolerance test before and after the administration of therapeutic doses of imipramine hydrochloride for 10 days to investigate effects of tricyclic antidepressants on hypothalamic-pituitary-adrenal axis response to hypoglycemia. The mean steady-state tricyclic blood level was 141 (SD = 66) ng/ml. Baseline levels of glucose, cortisol, and adrenocorticotropic hormone (ACTH) were not affected by the administration of imipramine. After administration of imipramine for 10 days, subjects uniformly had a significantly lower glucose nadir than before its administration (before imipramine: mean = 32 mg/dl; SD = 5; after imipramine: mean = 24 mg/dl; SD = 6). There was no difference in ACTH or cortisol response before and after the administration of imipramine. These findings suggest that imipramine hydrochloride increases sensitivity to the hypoglycemic effects of insulin, but does not alter the counterregulatory response of ACTH and cortisol.

Adrenocorticotropic Hormone↗

Imipramine stimulates phospholipase C activity in rat brain.

We previously demonstrated that antidepressant drugs (ADs) cause Ca2+ release from inositol 1,4,5-trisphosphate-sensitive Ca2+ stores in cultured neurons of rat frontal cortex. The present study examines the mechanism by which tricyclic ADs activate phospholipase C (PLC) in rat frontal cortex. Using an exogenous substrate to measure PLC activity, we demonstrated that a tricyclic AD, imipramine, stimulated PLC activity of the frontal cortex membrane in a concentration-dependent manner. Two tricyclic ADs, desipramine and amitriptyline, also stimulated PLC activity, while Li+ or pargyline had no effect on PLC activity. Although imipramine did not activate PLC in the membrane in the absence of Ca2+, imipramine synergistically activated PLC in the presence of Ca2+. This result indicates that the mechanism of PLC activation by imipramine is different from its activation by Ca2+. Imipramine stimulated PLC activity in the cytosol of rat frontal cortex as well as in the membrane. Preincubation of the cytosol with anti-PLC-beta 1 antibody prevented the imipramine-mediated activation of PLC. However, preincubation with anti-PLC-gamma 1 or anti-PLC-delta 1 did not prevent activation of PLC. These results suggest that imipramine activates PLC-beta 1 directly without receptor or guanine nucleotide binding protein mediation.

Animals↗

Repeated treatment with imipramine enhances the excitatory response of hippocampal neurons to dopamine.

The effect of imipramine on the responsiveness of CA1 pyramidal neurons to dopamine was studied in hippocampal slices, obtained from rats treated acutely or repeatedly with imipramine (10 mg/kg, 14 days, twice a day p.o.). In slices from non-treated rats the bath-applied dopamine evoked mainly potentiation, while SKF 38393 produced diminution of the firing rate of hippocampal CA1 neurons. Acute imipramine did not significantly affect the reactiveness of neurons to dopamine, whereas repeated imipramine administration increased both the strength and duration of the response to dopamine. In animals pretreated both acutely and repeatedly with imipramine, SKF 38393 induced the excitatory, and not the inhibitory response, the obtained effect being more potent after repeated administration of imipramine. Haloperidol antagonized the excitatory reaction to dopamine but not to SKF 38393. SCH 23390 did not affect the excitation evoked by dopamine and SKF 38393. It is concluded that repeated imipramine administration induces supersensitivity of hippocampal dopamine D2 receptors in the rat which--in the light of our earlier studies--are responsible for the dopamine-evoked excitatory effect in the rat hippocampal slices.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

Imipramine treatment of cocaine abuse: possible boundaries of efficacy.

A 12-week placebo-controlled, randomized clinical trial was undertaken to evaluate imipramine as a treatment for cocaine abuse, and to examine whether its effect may be limited to subgroups defined by route of use or by diagnosis of depression. One-hundred thirteen patients were randomized, stratified by route of use and depression. All patients received weekly individual counseling. Compared to placebo the imipramine group showed greater reductions in cocaine craving, cocaine euphoria, and depression, but the effect of imipramine on cocaine use was less clear. A favorable response, defined as at least 3 consecutive, urine-confirmed, cocaine-free weeks was achieved by 19% (11/59) of patients on imipramine compared to 7% (4/54) on placebo (P < 0.09). The imipramine effect was greater among nasal users--33% (9/27) response on imipramine vs. 5% (1/22) on placebo (P < 0.02). Response was also more frequent, but not significantly so, among depressed users on imipramine (26%, 10/38) than on placebo (13%, 4/31) (P < 0.19). Response rates were low in intravenous and freebase users and those without depression. Considered together with the literature on desipramine, these data suggest tricyclic antidepressants are not promising as a mainstay of treatment for unselected cocaine abusers. However, tricyclics may be useful for selected cocaine abusers with comorbid depression or intranasal use, or in conjunction with a more potent psychosocial intervention.

Adolescent↗

Chronic imipramine administration alters the activity and phosphorylation state of tyrosine hydroxylase in dopaminergic regions of rat brain.

In the present study the influence of imipramine, a tricyclic antidepressant, on the expression and function of tyrosine hydroxylase (TH) in dopaminergic rat brain regions was examined. Chronic administration of imipramine (18 days) decreased levels of TH enzyme activity in ventral tegmental area (VTA) and substantia nigra (SN), dopaminergic cell body regions, as well as in caudate-putamen (CP), nucleus accumbens (ACB), prefrontal cortex (PFC), and olfactory tubercle (OT), dopaminergic terminal fields. These effects were dependent on chronic drug treatment, as imipramine administration for 1 or 7 days did not significantly influence levels of TH activity in either SN or VTA. In contrast to drug regulation of enzyme activity, chronic imipramine treatment did not decrease levels of TH immunoreactivity in any of the dopaminergic cell body or terminal field regions studied, although levels of TH immunoreactivity were decreased in locus coeruleus (LC) as previously reported. However, imipramine treatment increased levels of TH back phosphorylation in VTA, suggesting that the antidepressant-induced decrease in levels of TH activity is a result of decreased phosphorylation of the enzyme. These results demonstrate that imipramine treatment regulates levels of TH enzyme activity in dopaminergic brain regions, and may account for some of the previously observed effects of these drugs on dopaminergic function. Finally, imipramine regulation of TH enzyme activity in VTA and immunoreactivity in LC was observed in Sprague Dawley, but not Wistar rats, demonstrating that different rat strains exhibit different biochemical responses to antidepressant treatment.

Animals↗

The effect of chronic treatment with imipramine on the responsiveness of hippocampal CA1 neurons to phenylephrine and serotonin in a chronic mild stress model of depression.

The effect of chronic mild stress (CMS) and chronic treatment with the tricyclic antidepressant drug imipramine (10 mg/kg/day for 5 weeks) on neuronal responsiveness to the alpha 1-noradrenergic agonist phenylephrine and serotonin (5-HT) was examined ex vivo, in the CA1 cell layer of the rat hippocampal slice preparation. We corroborated some previous findings that CMS, which had been used as an animal model of depression, decreased the consumption of a 1% sucrose solution and that that effect was reversed by chronic administration of imipramine. Imipramine did not change the sucrose consumption in control animals. In both control and stressed animals, phenylephrine (5 microM) and 5-HT (10 microM) attenuated the amplitude of the population spikes evoked in the CA1 pyramidal cell layer by stimulation of Schaffer collateral/commissural fibers. Those inhibitory effects of phenylephrine and 5-HT were significantly potentiated by chronic treatment with imipramine. The imipramine-induced potentiation was similar in slices from control and stressed animals. These results suggest that the imipramine-induced functional changes in alpha 1-noradrenergic and serotonergic receptors in the hippocampus are not involved in the anti-anhedonic effect of chronic imipramine administration in the CMS model of depression.

Animals↗

Blockade of calcium entry in smooth muscle cells by the antidepressant imipramine.

The present study was designed to evaluate the effects of antidepressants on smooth muscle contractile activity. In rat aortic rings, the antidepressants imipramine, mianserin and sertraline provoked concentration-dependent inhibitions of the mechanical responses evoked by K+ (30 mM) depolarization. These myorelaxant effects were not modified by the presence of glibenclamide or 80 mM K+ in the bathing medium. Moreover, the vasodilator properties of imipramine were not affected by atropine, phentolamine and pyrilamine. Radioisotopic experiments indicated that imipramine failed to enhance 86Rb outflow from prelabelled and perifused aortic rings whilst counteracting the increase in 45Ca outflow provoked by a rise in the extracellular K+ concentration. Simultaneous measurements of contractile activity and fura-2 fluorescence revealed that, in aortic rings, imipramine reduced the mechanical and fluorimetric response to K+ challenge. In A7r5 smooth muscle cells, whole cell recordings further demonstrated that imipramine inhibited the inward Ca2+ current. Under different experimental conditions, the ionic and relaxation responses to the antidepressants were reminiscent of those mediated by the Ca2+ entry blocker verapamil. Lastly, it should be pointed out that imipramine exhibited a myorelaxant effect of similar amplitude on rat aorta and on rat distal colon. All together, these findings suggest that the myorelaxant properties of imipramine, and probably also setraline and mianserin, could result from their capacity to inhibit the voltage-sensitive Ca2+ channels.

Animals↗

Effects of rolipram, a phosphodiesterase 4 inhibitor, in combination with imipramine on depressive behavior, CRE-binding activity and BDNF level in learned helplessness rats.

The brain cAMP regulating system and its downstream elements play a pivotal role in the therapeutic effects of antidepressants. We previously reported the increase in activities of phosphodiesterase 4, a major phosphodiesterase isozyme hydrolyzing cAMP, in the frontal cortex and hippocampus of learned helplessness rats, an animal model for depression. The present study was undertaken to examine the combination of effects of rolipram, a phosphodiesterase 4 inhibitor, with imipramine, a typical tricyclic antidepressant, on depressive behavior in learned helplessness rats. Concurrently, cAMP-response element (CRE)-binding activity and brain-derived neurotrophic factor (BDNF) levels related to the therapeutic effects of antidepressants were determined. Repeated administration of imipramine (1.25-10 mg/kg, i.p.) or rolipram (1.25 mg/kg, i.p.) reduced the number of escape failures in learned helplessness rats. Imipramine could not completely ameliorate the escape behavior to a level similar to that of non-stressed rats even at 10 mg/kg. However, repeated coadministration of rolipram with imipramine (1.25 and 2.5 mg/kg, respectively) almost completely eliminated the escape failures in learned helplessness rats. The reduction of CRE-binding activities and BDNF levels in the frontal cortex or hippocampus in learned helplessness rats were ameliorated by treatment with imipramine or rolipram alone. CRE-binding activities and/or BDNF levels of the frontal cortex and hippocampus were significantly increased by treatment with a combination of rolipram and imipramine compared to those in imipramine-treated rats. These results indicated that coadministration of phosphodiesterase type 4 inhibitors with antidepressants may be more effective for depression therapy and suggest that elevation of the cAMP signal transduction pathway is involved in the antidepressive effects.

3',5'-Cyclic-AMP Phosphodiesterases↗

Imipramine but not 5-HT(1A) receptor agonists or neuroleptics induces adaptive changes in hippocampal 5-HT(1A) and 5-HT(4) receptors.

It has been reported that the treatment with a tricyclic antidepressant imipramine induces an increase in the sensitivity of 5-HT(1A) receptors and a decrease in the sensitivity of 5-HT(4) receptors in the rat hippocampus. 5-HT(1A) receptor agonists and neuroleptics also affect 5-HT(1A) receptors in different brain areas; therefore, it was of interest to compare their effects on hippocampal 5-HT receptors with the influence of the well-established antidepressant imipramine. We studied the effects of repeated treatment with imipramine, the 5-HT(1A) receptor agonists 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT) and buspirone, and the neuroleptics haloperidol and clozapine on the sensitivity of rat hippocampal CA1 neurons to 5-HT(1A)- and 5-HT(4) receptor activation. Imipramine was administered for 21 days (10 mg/kg p.o., twice daily), 8-OH-DPAT for 7 days (1 mg/kg s.c., twice daily) and buspirone for 21 days (5 mg/kg s.c., twice daily). The rats received haloperidol (1 mg/kg) and clozapine (30 mg/kg) for 6 weeks in drinking water. Hippocampal slices were prepared 2 days after the last treatment with imipramine, 8-OH-DPAT or buspirone, and 5 days after the last treatment with the neuroleptics. Using an extracellular in vitro recording, we studied changes in the amplitude of stimulation-evoked population spikes, induced by 5-HT, 8-OH-DPAT and the 5-HT(4) receptor agonist zacopride. Activation of 5-HT(1A) receptors decreased, while activation of 5-HT(4) receptors increased the amplitude of population spikes. Imipramine significantly enhanced the inhibitory effects of 5-HT and 8-OH-DPAT, and attenuated the excitatory effect of zacopride. No other treatment used in the present study changed the sensitivity of hippocampal CA1 neurons to 5-HT(1A) and 5-HT(4) receptors activation. These findings indicate that adaptive changes in the sensitivity of hippocampal neurons to 5-HT(1A) and 5-HT(4) receptors agonists are specific to imipramine and may thus-at least partly-mediate its effects.

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

The effect of imipramine on the amount of mRNA coding for rat dopamine D2 autoreceptors.

Several reports have investigated the possibility that chronic antidepressant treatment alters dopamine autoreceptors. Since radioligand binding studies do not differentiate between presynaptic and postsynaptic dopamine D2 receptors in the rat forebrain, we used the in situ hybridization technique to measure the amount of mRNA coding for dopamine D2 autoreceptors in the dopaminergic cell bodies. The amount of mRNA coding for dopamine D2 autoreceptors in the rat mesencephalon was analyzed following acute and repeated treatment with imipramine, the most widely used antidepressant drug. No significant changes in the amount of mRNA were observed in the substantia nigra of the rat, after acute or repeated treatment with imipramine. In the ventral tegmental area repeated treatment with imipramine (14 days, twice a day) increased the amount of dopamine D2 autoreceptor mRNA in the lateral part of this brain region (containing nucleus paranigralis and n. parabrachialis pigmentosus), without there being any significant changes in the more medial part (n. interfascicularis and n. linearis). The increase in the amount of dopamine D2 autoreceptor mRNA in the ventral tegmental area started to be significant 72 h after acute imipramine. Moreover, this increase was also observed after 14 drug-free days following the acute administration of the drug. The results indicate the different sensitivity of neurons synthesizing dopamine autoreceptors for imipramine. Another interesting finding is the observation that acute treatment with imipramine seems to be sufficient to trigger changes as a function of time regardless of whether imipramine is again administered, providing a possible explanation for the delayed therapeutic effect of the drug.

Animals↗

Conservative treatment of female stress incontinence with imipramine.

The results of a clinical study of conservative treatment of women with stress incontinence are presented. A daily dose of 75 mg. imipramine hydrochloride was given for 4 weeks. Special attention was paid to the effects of imipramine on the functional urethral length and maximum urethral closure pressure. A total of 21 women (71 per cent) stated that they were continent after treatment with imipramine, while 9 (29 per cent) did not improve and treatment was stopped. According to our results, imipramine extended the functional urethral length and made it independent of stress factors in women who were continent after treatment with imipramine. In patients with persistent incontinence the functional urethral length was extended significantly but was shortened with stress despite imipramine therapy. We believe that imipramine could be an alternative treatment in selected cases with stress incontinence.

Adult↗

Alpha-1-acid glycoprotein in major depressive disorder. Relationships to severity, response to treatment and imipramine plasma levels.

BACKGROUND: Increased plasma levels of alpha-1-acid glycoprotein (AGP) were reported in major depressive disorder. However, the relationship between AGP levels, severity of depression, treatment response and antidepressant levels are still unclear. METHODS: Plasma AGP levels were measured in 36 subjects with major depressive disorder before and after a 6-week treatment with imipramine and in 30 controls. Free imipramine plasma levels of depressed patients were measured at 6 weeks. Comparative analysis between depressed patients and controls, between non-responders (N = 12) and responders (N = 24), and between severely depressed patients (N = 14) and moderately depressed patients (N = 22) were made. RESULTS: Depressed patients had significantly higher mean values of AGP than control subjects. Imipramine non-responders and specially severely depressed patients had significantly greater increases of AGP levels during treatment than other depressed subgroups. There was no correlation between baseline AGP levels and severity of depression or free imipramine levels. LIMITATIONS: The most significant limitations of this study are the small sample size and the fact that all the subjects were out-patients. Results should not be generalized to in-patient populations. CONCLUSIONS: Depressed patients showed high baseline concentrations of AGP. AGP levels did not predict either free imipramine plasma levels or differential response after 6 weeks of treatment with imipramine. A greater increase of AGP during treatment was associated with severity of depression and treatment non-response. CLINICAL IMPLICATIONS: The relationship between high plasma levels of AGP, severity of depression and lack of treatment response is clarified. The influence of imipramine levels is minimized.

Adolescent↗

Actions and interactions of ethanol and imipramine on the rat sinus node.

We studied the actions and interactions of ethanol and imipramine on the sinus node. Strips of the right rat atrium including the sinus node were superfused with Tyrode's solution at 37 degrees C while beating spontaneously. The preparations were exposed to imipramine or ethanol alone as well as to the two drugs in combination while recording membrane potentials with standard intracellular microelectrodes. The results obtained show that ethanol 0.8 and 2.4 g/l exerted a positive chronotropic action. On the other hand, imipramine 0.25 mg/l did not modify the sinus node rate. However, it reduced significantly the positive chronotropic action of ethanol. The sinus node rate decreased under the action of a higher concentration of imipramine (1 mg/l). When ethanol was tested in combination with this concentration of imipramine, the effect of the latter prevailed. In conclusion, a concentration of imipramine that did not affect the sinus node rate antagonized the positive chronotropic action of ethanol. In addition, the negative chronotropic action of a higher concentration of imipramine prevailed over the positive action of ethanol. The results obtained provide additional support to the notion that the use of ethanol and cardioactive drugs in combination may result in significant changes in the actions of either of the two, or both. This is of clinical relevance, since at least some of the individuals under treatment with cardioactive drugs will be alcoholics and/or social drinkers.

Analysis of Variance↗