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

Long-term effects of St. John's wort and hypericin on monoamine levels in rat hypothalamus and hippocampus

Hypericum perforatum L. (St. John's wort) is one of the leading psychotherapeutic phytomedicines and, because of this, great effort has been devoted to clarifying its mechanism of action. Chronic effects of St. John's wort and hypericin, one of its major active compounds, on regional brain amine metabolism have not been reported yet. We used a high-performance liquid chromatography system to examine the effects of short-term (2 weeks) and long-term (8 weeks) administration of imipramine, Hypericum extract or hypericin on regional levels of serotonin (5-HT), norepinephrine, dopamine and their metabolites in the rat brain. We focused our interest on the hypothalamus and hippocampus, as these brain regions are thought to be involved in antidepressant drug action. Imipramine (15 mg/kg, p.o.), Hypericum extract (500 mg/kg, p.o.), and hypericin (0.2 mg/kg, p.o.) given daily for 8 weeks significantly increased 5-HT levels in the hypothalamus (P<0.05). The 5-HT turnover was significantly lowered in both brain regions after 8 weeks of daily treatment with the Hypericum extract (both P<0.05). Consistent changes in catecholamine levels were only detected in hypothalamic tissues after long-term treatment. Comparable to imipramine, Hypericum extract as well as hypericin significantly decreased 3,4-dihydroxyphenylacetic acid and homovanillic acid levels in the hypothalamus (P<0.01). Our data clearly show that long-term, but not short-term administration of St. John's wort and its active constituent hypericin modify levels of neurotransmitters in brain regions involved in the pathophysiology of depression.

Stress versus depression

1. Exhaustive evidence is quoted showing that uncontrollable (uncoping) stress provoked in experimental mammals leads to depletion of central noradrenergic activity+ adrenomedullary-cortical gland hyperactivity. These physiological disorders cause the typical neuroendocrine peripheral profile: a) raised catecholamines (CA) in plasma [noradrenaline (NA)+adrenaline (Ad)+dopamine (DA), b) reduced NA/Ad ratio in plasma and c) raised plasma cortisol. 2. Exhaustive evidence is quoted which indicates that severely ill humans show peripheral neuroendocrine profile similar to that found in mammals submitted to uncontrollable stress situation. Further, the NA/Ad ratio does not increase but decreases during orthostasis and exercise stress challenges, as well as oral glucose stress (tolerance) test. 3. Exhaustive evidence is quoted which indicates that endogenous depressed subjects show a neuroendocrine profile opposite to that observed in stressed mammals and severely ill humans. This profile consists of central NA (neural sympathetic) hyperactivity+ adrenomedullary glands hyporresponsivity. These disorders are reflected in a three to ten fold increase of the NA/Ad ratio in plasma. 4. Exhaustive evidence is also quoted showing that dysthymic depressed patients show low plasma catecholamines+low NA/Ad plasma ratio (< 2) during supine-resting condition, it is normalized at orthostasis and exercise periods. 5. It is quoted evidence showing that whereas platelet serotonin is increased in dysthymics, the same is reduced in both endogenous depressed and stressed mammals as well as severely ill humans. 6. It is quoted evidence showing that free serotonin in plasma is greatly raised in uncoping stressed mammals and severely ill humans. The same parameter is normal or slightly increased in dysthymic and endogenous depressed humans. These findings are consistent with the increased platelet aggregability observed in "uncontrollable" stressed mammals and in severely ill, but not depressed patients. 7. It is also quoted evidence showing that whereas parasympathetic activity is absent in uncontrollable stressed mammals and severely ill humans, the same is increased in both types of depressed humans. 8. According to the above, the authors postulate the existence of 3 distinct central+ peripheral neuroendocrine profiles for endogenous depression, dysthymic depression and maladaptation to stress syndrome. These different profiles should lead researchers to attempt different therapeutical approach. 9. In view of the fact that the authors found much clinical overlap among the three syndromes (endogenous depression, dysthymic depression and severely ill patients), they believe that a differential diagnosis should be based on neurochemical, neuroendocrine, physiologic, metabolic and neuropharmacological grounds. 10. The experimentally induced uncontrollable stress (behavioral despair) syndrome in mammals should not be used as a valid model of human depressive syndrome.

Correlative changes of serotonin and catecholamines with pharmacokinetic alterations of imipramine in rat brain

Rats were given i.p. imipramine (20 mg/kg), acutely or chronically, and the levels of serotonin (5-HT), norepinephrine (NE), dopamine (DA) and their metabolites in the brain at different times were compared with the concentrations of imipramine and desipramine. The levels of 5-HT, DA, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the brain did not appear to be affected by quantitative alterations in the concentrations of imipramine and desipramine. The level of 5-hydroxyindole acetic acid (5-HIAA) was reduced and the level of 3-methoxy-4-hydroxyphenylglycol (MHPG) tended to decrease 3 h after imipramine administration in acutely treated rats. The reduced level of 5-HIAA was maintained during the chronic treatment with imipramine, whereas the MHPG level increased and the NE level decreased. The decrease in 5-HIAA depended on the concentration of imipramine in the brain, whereas the changes in the levels of NE and MHPG appeared to be caused by desipramine. The present studies show that pharmacokinetic variations of imipramine in the brain might correlate with the altered levels of 5-HIAA, NE and MHPG.

Effect of low alcohol dose on behavioral "despair" in rats neonatally treated with antidepressant drugs

Rat pups were treated with monoamine uptake inhibiting antidepressant drugs, desipramine, imipramine or nomifensine (5 mg/kg) during the second and third postnatal weeks, and their later behavioral "despair," measured by Porsolt's swim test, was examined. At the age of two months, the desipramine-treated rats showed lengthened immobility in the swim test, and thus probably increased behavioral "despair." They also responded to 1 g/kg alcohol by shortening the immobility to the level of control rats. Neonatal treatment with either imipramine or nomifensine did not affect the swim test behavior. The results suggest that a low, stimulatory dose of alcohol was able to reverse the lengthened immobility in the swim test of rats treated with desipramine during the early postnatal period.

Simultaneous determination of noradrenaline and 3-methoxy-4-hydroxyphenylglycol in plasma with high-performance liquid chromatography using electrochemical detection

We herein report the simultaneous determination of the levels of noradrenaline (NA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), a major metabolite of NA. The sample was subjected to a Sep Pak C18 cartridge prior to the NA and MHPG assay by high-performance liquid chromatography with an electrochemical detector. The results correlated well with the established methods. The average percentage of recovery was 91.2 and 98.7% for NA and MHPG, respectively. The intraassay coefficients of variation were 3.7 and 4.6% for NA and MHPG. The interassay coefficients of variation were 3.5 and 7.5% for NA and MHPG, respectively.

Norepinephrine and (Na+, K+)-ATPase: evidence for stabilization by lithium or imipramine

These experiments examined the effects of lithium and imipramine on the regulation by norepinephrine in vivo of (Na+, K+)-ATPase in brain and heart. The binding of ouabain and the activity of K+-phosphatase were used as indices of (Na+, K+)-ATPase. In the cerebral cortex, imipramine prevented, and lithium reduced, the increase in (Na+, K+)-ATPase associated with repeated injections of yohimbine. Imipramine and yohimbine had synergistic effects on the increased release of norepinephrine and on decreased binding to beta-receptors. Effects on the binding of beta-noradrenergic receptors suggested that imipramine partially reduced stimulation of ATPase by reducing the maximum effect of beta-receptors, while the effect of lithium may have involved a reduction in the exposure of receptors to norepinephrine. Imipramine also increased (Na+, K+)-ATPase in the cerebral cortex of reserpine-treated rats. These results suggest that lithium and imipramine, by different mechanisms, can stabilize fluctuations in the physiological consequences of binding to noradrenergic receptors.

Increased adult behavioral 'despair' in rats neonatally exposed to desipramine or zimeldine: an animal model of depression?

Occurrence of depressive behavior at mature age was studied in rats exposed neonatally to antidepressant drugs. Early antidepressant treatments have been shown to increase voluntary alcohol consumption and the percentage of rapid-eye-movement (REM) sleep relative to total sleep time in adult rats as well as to cause long-lasting reduction in the concentrations of monoamines in the forebrain. In the present study rats were daily given either 5 mg/kg desipramine or 25 mg/kg zimeldine from the 7th to the 18th postnatal days. When they were 2 months and 5 months of age behavioral 'despair' was studied by using a modified version of Porsolt's swim-test. At both ages the desipramine-treated and zimeldine-treated rats expressed lengthened immobility times in the water pail. The findings indicate that neonatal exposure of rats to desipramine or zimeldine induces behavioral 'despair' at mature age. Thus, early exposure of rats to antidepressants causes long-lasting behavioral disorders, and, moreover, may be used to devise an animal model of subsequent depression.

Neonatal desipramine or zimeldine treatment causes long-lasting changes in brain monoaminergic systems and alcohol related behavior in rats

To study the relationship between neonatal antidepressant administration, active (REM) sleep and adult alcohol-related behavior, rat pups were treated daily with 5 mg/kg desipramine (DMI) or 25 mg/kg zimeldine SC from the 6th to the 19th postnatal days. Movement sensitive mattress ("SCSB") measurements showed that zimeldine treatment suppressed active sleep throughout the whole treatment period, but DMI was more effective during the first 8 days than during the last treatment days. At the age of 70 days, the zimeldine-treated rats expressed a selective increase of some components of activity in the open field test, and the DMI rats had a higher defecation score compared to the controls. Furthermore, the zimeldine-rats responded with a decrease in ambulation in the open field to an alcohol dose which generally stimulates locomotion in rats. At the age of 3 months the DMI and zimeldine rats showed increased voluntary intake of 10% (v/v) alcohol. Measurement of brain monoamines revealed that the neonatal treatment with DMI or zimeldine interfered with the normal development and function of the monoamine neuronal systems: the concentrations of noradrenaline, dopamine and 5-hydroxytryptamine (5-HT), and their metabolites were altered in several brain regions. The results thus suggest that neonatal treatment with DMI or zimeldine suppresses active sleep and has an influence on later alcohol-related behavior, possibly due to a long-lasting defect in brain monoaminergic transmission.

Studies on rat brain catecholamine synthesis and beta-adrenoceptor number following administration of electroconvulsive shock, desipramine and clenbuterol

The effects of administration to rats of repeated electroconvulsive shock (ECS), clenbuterol and desipramine (DMI) on beta-adrenoceptor number in cortex, and noradrenaline (NA) and dopamine (DA) turnover in whole brain has been investigated by examining the rate of decline of NA concentration (kNA) following injection of alpha-methyl-p-tyrosine. A single injection of clenbuterol (5 mg/kg) raised brain NA content and decreased the rate constant (kNA), leaving the turnover rate unaltered. Acute DMI injection decreased kNA and turnover rate, while a single ECS did not change NA metabolic rate. Repeated treatment with either ECS (5 seizures over 10 days), clenbuterol (5 mg/kg for 14 days) or DMI (5 mg/kg twice daily for 14 days) decreased beta-adrenoceptor density in cortex. No change in NA content, rate constant or turnover rate was observed after repeated ECS or clenbuterol administration. Ninety min after the last dose of DMI brain NA content was significantly decreased but kNA was unchanged compared with control animals, possibly because of the presence of subsensitive presynaptic alpha 2-adrenoceptors. At 18 hours after the last dose brain NA content was still lower than control animals but kNA was enhanced. This presumably a "withdrawal" effect, the uptake inhibitory effect of the drug now being decreased. The treatments had little effect on DA turnover apart from DMI decreasing synthesis rate. Clearly there is no obvious relationship between the ability of antidepressant treatments to alter NA turnover and decrease beta-adrenoceptor number.

Characterization of serotonin receptors and lack of effect of antidepressant therapy on monoamine functions in various regions of the rabbit brain

The effects of single and long-term administration of the antidepressants imipramine, desimipramine, amitriptyline, zimelidine and maprotiline were studied in the rabbit brain. Special attention was given to the brain serotonin (5-HT) receptors. Our results show that in different areas of the rabbit brain, the binding sites for 5-HT display pharmacological characteristics very similar to those of the 5-HT1 and 5-HT2 receptors described for the rat brain. No significant correlation could be shown between the distribution of either of the receptors and the distribution of serotonergic nerve terminals (as measured by the 5-HT content and the [3H]5-HT accumulation). Addition of antidepressants to rabbit brain slices, in vitro, caused an inhibition of the [3H]5-HT accumulation. The compounds only weakly inhibited the binding of [3H]5-HT and [3H]ketanserin as compared to the inhibition caused by serotonergic agonists and antagonists. The [3H]5-HT accumulation in brain slices was markedly reduced 2 h after a single i.p. injection of imipramine. After a two-week administration of the antidepressants, the specific binding of neither [3H]5-HT nor [3H]ketanserin was significantly altered. The simultaneous determination of monoamine metabolites and of dopamine-beta-hydroxylase in the cerebrospinal fluid of these treated rabbits did not reveal any significant difference from the control animals.

Behavioral, biochemical, and blood pressure responses to alprazolam in healthy subjects: interactions with yohimbine

The effect of single doses of alprazolam (1.5 mg) and yohimbine (30 mg) and alprazolam and yohimbine given together on plasma free 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), cortisol, blood pressure, and subjective behavioral ratings was studied in eight healthy subjects. In comparison to placebo, alprazolam significantly reduced plasma MHPG and cortisol, systolic and diastolic blood pressure, and increased subjective ratings of drowsiness and mellow. Yohimbine and the alprazolam-yohimbine combination significantly increased plasma free MHPG. Concomitant yohimbine administration antagonized the effects of alprazolam on blood pressure and attenuated alprazolam-induced changes in cortisol and subjective ratings. The ability of alprazolam to decrease plasma MHPG and blood pressure contrasts with previously reported effects of diazepam. The implications of the findings of the present investigation to the postulated role of brain noradrenergic function in the etiology of panic anxiety and the therapeutic mechanism of action of antipanic treatment are discussed.

Opposite effects of chronic imipramine treatment on brain and urine MHPG levels in the rat

Acute imipramine (IMI; 20 mg/kg, ip) in rats decreased the brain concentration of 3-methoxy-4-hydroxyphenethylene glycol (MHPG), a metabolite of norepinephrine (NE), to 85% of control 24 hr after injection. In contrast, chronic IMI (20 mg/kg, ip, daily for 14 days) significantly raised brain MHPG levels to 123% of control, while reducing brain NE levels. Urinary MHPG levels were reduced by both acute and chronic IMI treatments, to 52% and 51%, respectively. These data suggest that the brain turnover of NE is reduced after acute IMI, but is elevated after chronic treatment. Although urinary levels of MHPG changed in parallel with brain levels following an acute administration of IMI, such was not the case after chronic administration. We conclude that caution must be used in extrapolating drug-induced changes in urinary metabolite levels to brain amine function.

Effect of chronic desipramine treatment on adrenoceptor modulation of [3H]dopamine release from rat nucleus accumbens slices

The effects of alpha 2- and beta-adrenoceptor agonists on the 25 mM K+-induced release of [3H]dopamine [( 3H]DA) from the nucleus accumbens slices of chronic desipramine (DMI)- and saline-treated rats were investigated using a superfusion technique. The K+-induced release of [3H]DA from nucleus accumbens slices was shown to be Ca2+ dependent and to be enhanced by ascorbic acid. In experiments with isoproterenol, ascorbic acid was added to the superfusion media in order to prevent the otherwise rapid oxidation of the drug. The K+-induced release of [3H]DA from nucleus accumbens slices of saline-treated rats was significantly decreased by the alpha 2-adrenoceptor agonist, clonidine (10 microM; 89 +/- 2.4% of control values; P less than 0.002), and significantly enhanced by the beta-adrenoceptor agonist, isoproterenol (1 and 10 microM; 122 +/- 4.3 and 171 +/- 2.9% of control values, P less than 0.002 and P less than 0.001, respectively). The basal release of [3H]DA was strongly enhanced by 10 microM but not 1 microM isoproterenol. Chronic DMI pretreatment (10 mg/kg i.p. for 28 days) did not significantly alter the K+-induced release of [3H]DA. Chronic DMI treatment attenuated the alpha 2-adrenoceptor-mediated inhibition of [3H]DA release, while the beta-adrenoceptor-mediated stimulation remained unchanged. The net effect of chronic DMI treatment therefore would appear to be a facilitation of dopaminergic neurotransmission in the mesolimbic system. This is consistent with behavioural evidence which suggests that the function of the mesolimbic dopaminergic reward system is facilitated by chronic treatment with antidepressant drugs.

Fear-enhanced acoustic startle is not attenuated by acute or chronic imipramine treatment in rats

The effect of acute or chronic administration of imipramine on fear-enhanced startle (potentiated startle) in rats was investigated. Thirty male albino rats were initially given preliminary startle testing, assigned to one of three matched groups, and trained for potentiated startle by presenting ten light-shock pairings on each of 2 days. Subsequent startle testing following a single injection of 0, 5 or 10 mg/kg imipramine revealed that the degree of startle potentiation (increased responding in the presence of the light previously paired with shock) was similar across treatment conditions. A significant and comparable potentiation of startle was observed in animals treated chronically with saline or imipramine (10 mg/kg/day) for 21 days between training and testing. Potentiated startle was also observed in these animals on the next (22 nd) day after injection of an additional dose of the drug (10 mg/kg) 5 min prior to testing. Plasma levels of imipramine and its metabolite, desipramine, were relatively high after each of these treatments. Since previous studies have shown that potentiated startle is decreased by diazepam, the present findings suggest that the potentiated startle paradigm is a valid model for studying simple fear or anxiety rather than panic disorder.

An automated method to measure monoamines and metabolites using elevated temperature reversed phase HPLC with electrochemical detection. Application to striatal dopamine and hippocampal serotonin turnover

High pressure liquid chromatography with electrochemical detection has been successfully used for the analysis of noradrenaline, dopamine(DA), serotonin(5-HT), and selected metabolites in brain. Automated sample injection allows up to 100 samples per day to be analyzed; precise thermostatic control of the chromatography at 45 degrees C increases both method reproducibility and separation efficiency while increasing column life. The method requires minimal sample pretreatment and is rapid and inexpensive. It has been applied to the analysis of rat and mouse whole brain and, in particular, to milligram samples of rat striatum and hippocampus, thus permitting the measurement of regional DA and 5-HT turnover. Effects of selected psychotropic drugs on these processes illustrate the value of the method to either DA or 5-HT turnover studies.

Reduced metabolism and turnover rates of rat brain dopamine, norepinephrine and serotonin by chronic desipramine and zimelidine treatments

As part of of an ongoing effort to compare changes in whole body turnover of catecholamines and serotonin in man with those induced by antidepressants in the rat brain, we have evaluated the chronic effects of desipramine (DMI) and zimelidine (ZMI) on brain catecholamines and serotonin in the rat. The amines and metabolites measured include norepinephrine (NE), dopamine (DA) and their metabolites, 3-methoxy-4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). Three brain areas were analysed; the hypothalamus, caudate nucleus and frontal cortex. Chronic DMI and ZMI reduced hypothalamic MHPG and caudate nucleus DA metabolites, in particular HVA. Both drugs reduced NE and DA turnover rates (estimated after alpha-methyl-p-tyrosine injection) and the rate of MHPG formation in the hypothalamus (estimated after pargyline treatment). They did not change NE turnover rate, but reduced DA turnover rate and rate of HVA formation in the caudate nucleus. Chronic DMI but not ZMI reduced DOPAC rate of formation in the caudate nucleus. Apparently changes in DA turnover and metabolism produced by these antidepressants are better related to changes in HVA than DOPAC concentrations. Similar to their influence on hypothalamic and caudate nucleus catecholamines, both chronic DMI and ZMI produced changes in serotonin concentration in the caudate nucleus and frontal cortex serotonin that suggest a reduction in its turnover rate and metabolism. The reduction in NE turnover in hypothalamus is consistent with the effects of chronic DMI and ZMI on whole body NE turnover observed in man.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic and acute administration of typical and atypical antidepressants on activity of brain noradrenaline systems in the rat thiopentone anaesthesia model

A behavioural model sensitive to manipulation of brain noradrenaline systems and with characteristics of beta-receptor mediation has been developed using the duration of thiopentone anaesthesia in the rat. Acute and chronic administration of various antidepressant agents was examined. In the acute phase, (30 min prior to thiopentone) the noradrenaline uptake-inhibiting tricyclic drugs and viloxazine increased anaesthesia duration in a dose-dependent fashion. The atypical antidepressants trazodone, iprindole, and mianserin did this only weakly, while the dopaminergic and serotonergic uptake-inhibiting antidepressants (respectively bupropion, nomifensine, and zimelidine, fluoxetine) markedly shortened anaesthesia duration. Chronic administration (for 15 days) prolonged anaesthesia duration measured 2 or 5 days after the last drug injection for all tricyclic agents, for the atypical antidepressants mianserin, iprindole, fluoxetine, and zimelidine, and for viloxazine.

Relative importance of 3-methoxy-4-hydroxyphenylglycol and 3,4-dihydroxyphenylglycol as norepinephrine metabolites in rat, monkey, and humans

A gas chromatographic-mass spectrometric assay, which allowed simultaneous measurement of 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG), was used to show that the concentration of MHPG in primate CNS far exceeded that of DHPG and that both metabolites were mainly in the unconjugated form. In rat brain, DHPG concentration was generally higher than that of MHPG, and both existed predominantly as conjugates. Rat and primate plasma contained more MHPG than DHPG. In plasma of primates but not of rats, higher proportions of the metabolites were conjugated, compared to those in brain. Significant correlations existed between MHPG and DHPG in rat brain, monkey brain, human plasma, and both monkey CSF and plasma. In monkeys, a significant CSF-plasma correlation was found for MHPG, but not for DHPG. Acute administration of piperoxane raised rat brain MHPG and DHPG concentration; desipramine prevented this rise in DHPG, but not in MHPG. Desipramine alone decreased DHPG, but not MHPG, concentration. Piperoxane increased monkey brain MHPG, but not DHPG, concentration. These data suggest that DHPG is a valuable metabolite to measure when assessing norepinephrine metabolism in the rat. Under certain conditions, measurement of rat brain MHPG and DHPG may provide information concerning the site of norepinephrine metabolism. However, in primates the importance of monitoring DHPG, in addition to MHPG, is uncertain.

Alpha-2 adrenergic receptor sensitivity and the mechanism of action of antidepressant therapy. The effect of long-term amitriptyline treatment

It has been hypothesized that the mechanism of action of antidepressant treatments is related to their ability to decrease the sensitivity of the alpha-2 adrenergic autoreceptor. In order to assess alpha-adrenergic autoreceptor sensitivity, the effects of clonidine, the alpha-2 adrenergic receptor agonist, on plasma levels of the norepinephrine metabolite 3-methoxy-4-hydroxyphenethyleneglycol (MHPG), blood pressure (BP) and patient-rated sedation were measured in nine depressed patients before and during amitripytline treatment. Postsynaptic alpha-2 adrenergic receptor sensitivity was assessed by determining the growth hormone (GH) response to clonidine before and during treatment. Amitriptyline significantly attenuated the effects of clonidine on plasma MHPG, standing systolic BP, and sedation, indicating that alpha-2 adrenergic autoreceptors had become subsensitive. In addition, baseline plasma MHPG levels were significantly reduced. Amitriptyline had no effect on the GH response to clonidine.

A calcium hypothesis of antidepressant action

The biogenic amine hypothesis of affective disorders has served as a valuable model for investigations concerning the mechanism of action of antidepressant drugs. Despite numerous publications on the subject, the manner in which tricyclic antidepressants elicit their therapeutic effect remains unknown. Recent findings which involve tricyclic antidepressant interactions with thyroid hormone, along with an appraisal of the older literature concerned with dyscalcemias and affective disorders, provides the basis for an hypothesis featuring a role for calcium in mediating antidepressant responses.

Behavioural evidence that chronic treatment with the antidepressant desipramine causes reduced functioning of brain noradrenaline systems

A behavioral system sensitive to the net functional activity of the locus coeruleus noradrenergic system, with characteristics of a beta-adrenoceptor mediated response, has been developed based on the duration of thiopentone anaesthesia in the rat. The effects of acute and chronic treatment with the tricyclic antidepressant desipramine (DMI) were determined. Acute DMI from 5 to 25 mg/kg increased thiopentone sleeping-time in a dose-dependent fashion. This was due to an action on noradrenergic systems, since it was mimicked by treatment with the selective neurotoxin 6-hydroxydopamine, which itself increased thiopentone sleeping-time and prevented any additional effect of DMI. Chronic treatment with DMI had no effect on thiopentone sleeping-time when carried out for 2 or 5 days but markedly prolonged it when carried out for 10 or 20 days, thus paralleling the time course of clinical action of the drug.

Chronic antidepressant therapy and associated changes in central monoaminergic receptor functioning

Acutely administered antidepressants possess a multiplicity of pharmacological actions. However, the fact that agents possessing similar pharmacological actions are devoid of antidepressant activity, together with the lack of correlation between doses required for acute pharmacological effects and clinical efficacy, suggest that the mechanism(s) of action of antidepressants cannot be directly attributed to the acute pharmacological properties of the drugs. The lag phase in onset of clinical effectiveness emphasizes the importance of adaptive changes following chronic antidepressant administration. A rapidly accelerating trend in attempting to delineate the precise molecular mechanisms of action of antidepressants is the shift in emphasis following chronic antidepressant therapies from alterations in uptake, storage, synthesis and release of neurotransmitters to adaptive changes in receptor functioning. These adaptations occur both pre- and postsynaptically. Examples of the former are alpha 2 and DA presynaptic receptors, both being down-regulated by certain forms of chronic antidepressant therapy. The fact that the NE-coupled adenylate cyclase system in rat brain slices is down-regulated by tricyclics, atypical antidepressants, MAO inhibitors and ECT emphasizes the importance of the system. Electrophysiological and behavioral studies point to the up-regulation of central alpha 1 and 5-HT receptor functioning following long-term antidepressant therapy. In contrast to the beta-adrenoceptor, these findings cannot be correlated with data from radioligand binding studies. In general central alpha 1-adrenoceptor binding remains unaltered. This is also true for 5-HT1 binding whereas cortical 5-HT2 binding is both increased and decreased depending on the type of antidepressant therapy being investigated. The relationship of these adaptive changes to the clinical efficacy of antidepressants in man is not clear since there is generally a lack of good models for studying human central receptor functioning. A review of current data from animal studies would tend to disfavour the view that all forms of antidepressant therapy possess a common mechanism of action. Perhaps multiple intervention sites exist. The introduction and evaluation of agents possessing a specificity of pharmacological action will undoubtedly aid psychotherapeutic research. The knowledge that peptides and 'classical' neurotransmitters can co-exist in the same neurone will undoubtedly generate studies of the significance and importance of the co-transmitter function of peptides in the mechanisms of action of antidepressant therapies.

Possible subsensitization of alpha 2-adrenergic receptors by chronic monoamine oxidase inhibitor treatment in psychiatric patients

Clonidine was administered to nine psychiatric patients before and after chronic treatment (3 to 4 weeks) with clorgyline, a selective monoamine oxidase type A inhibitor with antidepressant efficacy. The hypotensive response to clonidine, believed to be mediated by brain alpha 2-adrenergic receptors, was significantly attenuated by chronic but not acute (2 to 3 days) clorgyline treatment, with a time course similar to the onset of its clinical efficacy. This study supports the hypothesis that subsensitization of alpha 2-adrenergic receptors plays an important role in clorgyline's antidepressant effects and may constitute a key contribution to the mode of action of other antidepressant treatments as well.

Effect of acute and chronic treatment with tricyclic antidepressants on 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) contents in various regions of rat brain

1. Effects of acute and chronic treatment with desipramine (DMI) and amitriptyline (AMI) on 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) levels in eight brain regions were examined in rats. 2. A single injection of DMI decreased MHPG-SO4 levels in all brain regions except the midbrain, whereas the effect disappeared after the chronic treatment except in the septal area. MHPG-SO4 levels in the hippocampus and thalamus were increased after the chronic treatment with the drug. 3. A single and chronic administration of AMI decreased MHPG-SO4 levels in the thalamus and hippocampus, respectively. 4. These results indicate that the effects of acute and chronic treatment with the tricyclic antidepressants on the central noradrenergic systems differ in different regions of rat brain.

Plasma MHPG in depression: effects of acute and chronic desipramine treatment

The effects of acute and chronic desmethylimipramine (DMI) administration on 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) in plasma and urine were examined in eight depressed inpatients. DMI treatment induced an immediate and continuous highly significant reduction in plasma MHPG throughout the 30-day treatment period. This effect was not related to treatment response. In contrast to plasma MHPG, there was no uniform effect of DMI treatment on urinary MHPG. Chronic DMI treatment increased or did not change urinary MHPG in the three treatment responders and decreased urinary MHPG in five nonresponders. The correlation between plasma and urinary MHPG during the placebo period was not significant, and the effect of DMI treatment on the two measures differed markedly.

Chronic treatment with some atypical antidepressants increases the brain level of 3-methoxy-4-hydroxyphenylglycol (MHPG) in rats

We examined the effects of some atypical antidepressants with central antiserotonergic activity (mianserin, trazodone, danitracen, pizotifen), and 5-HT receptor blocking agents (cyproheptadine and metergoline), on whole rat brain levels of the main noradrenaline (NA) metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG). In acute experiments, when drugs were injected in a single dose 1, 2, 4, 24 or 48 h before decapitation, only mianserin elevated the MHPG level. In chronic experiments (drugs given b. i. d. for 3 weeks, the last dose being given 4 or 48 h before decapitation), all the drugs significantly increased the concentration of whole brain MHPG. The results indicate that chronic administration of atypical antidepressants leads to activation of the central NA system. It seems, with the exception of mianserin, that this is a secondary phenomenon, resulting from the antiserotonergic activity of the drugs. Our results further corroborate the existence of a serotonergic-noradrenergic interaction, consisting of an inhibitory influence of serotonin on the noradrenergic system.

Effects of chronic desipramine treatment on rat brain noradrenergic responses to alpha-adrenergic drugs

It has been previously reported that long-term tricyclic antidepressant treatment in the rat causes a subsensitivity of central beta-receptor-stimulated adenylate cyclase along with alterations of brain norepinephrine (NE) content and metabolism. We have confirmed earlier findings that after one week of desipramine treatment (5.0 mg/kg b.i.d.) brain NE levels decline while NE metabolism is similar to control animals, but is above control after 12 days of treatment. Single cell recordings from noradrenergic neurons of the locus coeruleus (LC) show that after one week of desipramine treatment, neuronal firing rate is lower than in control rats but greater than that seen in response to acutely administered drug. Furthermore, desipramine injection in a dose which profoundly altered LC impulse flow in control rats produced little or no effect on impulse flow in chronically treated rats. Of 25 or 250 microgram/kg doses of clonidine, which are equieffective for decreasing brain NE metabolism in control animals, only the larger dose decreased NE metabolism in 12 day desipramine-treated rats. The postsynaptic alpha-antagonist prazosin (5.0 mg/kg) increased NE metabolism in both groups. These results suggest that presynaptic (alpha 2) adrenoreceptors become subsensitive during long-term desipramine treatment, thus allowing recovery of noradrenergic impulse flow in the presence of NE uptake inhibition.