Desipramine and some other antidepressant drugs decrease the major norepinephrine metabolite 3,4-dihydroxyphenylglycol-sulphate in the rat brain

Summary The O-methylated and non-O-methylated end metabolites of norepinephrine (NE) in the rat brain were measured to investigate a presumed shift in metabolism of NE from intra- to extraneuronal metabolism by uptake inhibitory antidepressant drugs. Desipramine (DMI), protriptyline and maprotiline in doses from 2.5–20 mg/kg reduced the concentration of the major non-O-methylated NE metabolite 3,4-dihydroxyphenylglycolsulphate (DOPEG-SO₄) in the whole rat brain to about 60–70% of controls, while imipramine, amitriptyline, butriptyline and clorimipramine (20 mg/kg, 21/2 h) caused no significant decrease. The major O-methylated NE metabolite free plus conjugated 3-methoxy-4-hydroxyphenylglycol (total-MOPEG) was almost unaffected by all the drugs 21/2 h after administration. At longer time intervals, however, i.e. 5 h, a high dose of DMI (10 mg/kg, s.c.) decreased total-MOPEG to 75% of controls. DOPEG-SO₄ was decreased by DMI in all brain regions examined: cortex, hippocampus, cerebellum and brain rest. ³H-normetanephrine was increased 1/2h and 1 h after intraventricular injection of ³H-dopamine, and at the same time interval both total-³H-MOPEG and ³H-DOPEG-SO₄ were decreased. Amine storage in granules was not necessary for the action of DMI since DMI retained its metabolite-lowering effects in reserpinized rats. Inhibition of NE uptake in vivo did not induce the expected increase in the major extraneuronal NE metabolite MOPEG, but only the expected decreased in DOPEG-SO₄. The reduction of both the major NE metabolites by DMI suggests a decreased metabolism and turnover of NE.Abbreviations Used NE norepinephrine - DOPEG 3,4-dihydroxyphenylglycol - DOPEG-SO₄ DOPEG sulphate ester - MOPEG 3-methoxy-4-hydroxyphenylglycol - total-MOPEG free plus conjugated MOPEG - DOPAC 3,4-dihydroxyphenylacetic acid - HVA homovanillic acid - NM normetanephrine - DA dopamine - DMI desipramine - MAO monoamine oxidase     

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

Summary The effect of acute (single dose), short-term (4 days), and chronic treatment (21 days) with two tricyclic antidepressants desipramine and amitriptyline on brain 3-methoxy-4-hydroxyphenylglycol (MHPG) was examined in the rat. Amitriptyline had no effect on brain total MHPG irrespective of the duration of the treatment and did not interfere with the lowering effect of clonidine on brain total MHPG. Acute and shortterm desipramine treatment decreased brain total MHPG in rats, while chronic desipramine treatment increased it. The differential effect of acute and chronic treatment of desipramine on the brain total MHPG was further demonstrated by the lack of interference with the lowering effect of clonidine on brain total MHPG by one single dose of desipramine; partial interference after 4 days and complete interference after 21 days of desipramine treatment.A preliminary report of this work was presented at the Second World Congress of Biological Psychiatry, Barcelona September 1–6, 1978Ontario Mental Health Foundation Research Fellow 1977–1978     

Increase of 3-methoxy-4-hydroxyphenylethylene glycol in rat brain by neuroleptic drugs

The potency of various neuroleptic drugs in increasing the content of endogenous 3-methoxy-4-hydroxyphenyl-ethylene glycol (MOPEG) in rat brain decreased in the order methiothepin, haloperidol, clozapine, thioridazine, chlorpromazine, pimozide. The neuroleptics, except pimozide and chlorpromazine, also caused a slight to moderate diminution of the endogenous cerebral noradrenaline (NA).Based on these and earlier findings it is concluded that (a) changes in brain NA turnover induced by neuroleptics can be estimated, in a relatively simple way, by measuring cerebral MOPEG; (b) these drugs markedly differ in their ability to activate noradrenergic neurons; and (c) the activation of noradrenergic neurons by neuroleptics does not seem to parallel that of dopaminergic neurons.     

The effect of clonidine withdrawal on total 3-methoxy-4-hydroxyphenylglycol in the rat brain

The effect of clonidine withdrawal on the brain norepinephrine system was studied in the rat. Clonidine suppresses brain total 3-methoxy-4-hydroxyphenylglycol (MHPG) significantly and no tolerance to this effect was observed up to 21 days. Cessation of clonidine treatment resulted in an elevation in the level of brain total MHPG. The suitability of the clonidine withdrawal syndrome as a model of bipolar depression is discussed.Ontario Mental Health Foundation Research Fellow 1977–1978     

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.     

Chronic dietary treatment with antidepressants decrease brain Met-enkephalin-like immunoreactivity in the rat

This report describes the effect of chronic dietary treatment with antidepressants or antimanic drugs on brain Met-enkephalin-like immunoreactivity in the rat. The chronic treatment was administered through food containing 250–1000 mg desipramine, imipramine or clomipramine, 200–800 mg amoxapine or mianserin, 750–1500 mg lithium chloride, or 50 mg haloperidol per 1 kg food for 40 days. In the striatum, each antidepressant decreased the enkephalin content, while lithium or haloperidol, having an antimanic effect, increased the enkephalin content. Following the chronic administration of each antidepressant tested, the concentration of the peptide was reduced in the nucleus accumbens, hypothalamus and thalamus. We further examined the acute effect of the antidepressant (10 or 20 mg/kg) on the striatal enkephalin content at 60 min after a single intraperitoneal injection. The striatal content was decreased after the acute treatment with each antidepressant tested. These results indicate that the antidepressants had an effect on the neuronal activity of Met-enkephalin not only after chronic treatment, but also after acute treatment. The reduction in Met-enkephalin-like immunoreactivity after prolonged treatment with the antidepressant may possible contribute to the mechanism of antidepressive action. Offprint requests to: A. Kurumaji     

Stimulation and destruction of the locus coeruleus: opposite effects on 3-methoxy-4-hydroxyphenylglycol sulfate levels in the rat cerebral cortex

The effect of electrical stimulation or electrothermic destruction of the locus coeruleus on cortical (including hippocampus) levels of 3-methoxy-4-hydroxyphenylglycol sulfate (MHPG-sulfate) was studied in rats. The locus coeruleus, which consists of norepinephrine (NE-containing nerve cell bodies, projects to the cerebral cortex and the hippocampus. 10 days after unilateral destruction of the locus coeruleus NE was decreased 78% and MHPG-sulfate, a central NE metabolite, was lowered by 69% in these areas. No alterations in levels of norepinephrine or MHPG-sulfate were observed on the contralateral side.Stimulation of the locus coeruleus induced a frequency-dependent increase in MHPG-sulfate. The most effective frequency was 20 pulses per sec. After 15 min of stimulation the MHPG-sulfate had reached a new steady state level of about 80% over the contralateral side.These findings indicate that MHPG-sulfate levels are dependent upon the integrity of NE neurons and that the level of rate of formation of MHPG-sulfate in the brain can be a reflection of the physiological activity of these neurons.     

Chronic amphetamine treatment reduces NGF and BDNF in the rat brain

Amphetamines (methamphetamine and d-amphetamine) are dopaminergic and noradrenergic agonists and are highly addictive drugs with neurotoxic effect on the brain. In human subjects, it has also been observed that amphetamine causes psychosis resembling positive symptoms of schizophrenia. Neurotrophins are molecules involved in neuronal survival and plasticity and protect neurons against (BDNF) are the most abundant neurotrophins in the central nervous system (CNS) and are important survival factors for cholinergic and dopaminergic neurons. Interestingly, it has been proposed that deficits in the production or utilization of neurotrophins participate in the pathogenesis of schizophrenia. In this study in order to investigate the mechanism of amphetamine-induced neurotoxicity and further elucidate the role of neurotrophins in the pathogenesis of schizophrenia we administered intraperitoneally d-amphetamine for 8 days to rats and measured the levels of neurotrophins NGF and BDNF in selected brain regions by ELISA. Amphetamine reduced NGF levels in the hippocampus, occipital cortex and hypothalamus and of BDNF in the occipital cortex and hypothalamus. Thus the present data indicate that chronic amphetamine can reduce the levels of NGF and BDNF in selected brain regions. This reduction may account for some of the effects of amphetamine in the CNS neurons and provides evidences for the role of neurotrophins in schizophrenia.     

Reduction of 3,4-diaminopyridine-induced biogenic amine synthesis and release in rat brain by gabapentin

The anticonvulsant drug gabapentin has been shown recently to exhibit anxiolytic and analgesic actions in animals. Such actions have been postulated in part to reflect effects on biogenic amine neuronal activity. Therefore the effects of gabapentin on biogenic amine neuronal activity were assessed by measuring the synthesis of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in rat brain and on the release of [³H] NE from rat hippocampal slices both in the presence and absence of the depolarizing agent 3,4-diaminopyridine (DAP). Gabapentin (30 and 100 mg/kg, IP) did not alter the basal synthesis rates of NE and DA as assessed by the unchanged accumulation of L-dihydroxyphenylalanine (DOPA) in the NE-enriched hippocampus and cortex and in the DA-enriched striatum and mesolimbic areas. Gabapentin also did not alter 5-HT synthesis as determined by the unaltered accumulation of 5-hydroxytryptophan (5-HTP) in the same brain areas. DAP (2 mg/kg, IP) induced a modest but significant increase in DOPA accumulation in the hippocampal, mesolimbic and striatal regions. This DAP-induced increase in DOPA accumulation was antagonized significantly in the hippocampus and mesolimbic regions by gabapentin at 30 and 100 mg/kg and in striatum by 100 mg/kg; a 10 mg/kg dose was inactive. DAP increased selectively 5-HT synthesis in hippocampus and this effect was blocked by gabapentin. These findings indicate that the increased synthesis of biogenic amines induced by DAP is antagonized by gabapentin. In support of the in vivo studies, gabapentin was also shown to inhibit the DAP-evoked release of [³H]NE from hippocampal slices. Although the underlying mechanism for these effects is unclear, the present findings nevertheless demonstrate that gabapentin has inhibitory effects on stimulated NE, DA and 5-HT neurons that may be involved in explaining in part the CNS effects of this drug. Received: 6 August 1997/Final version: 12 November 1997     

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

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

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)     

Effect of a novel monamine oxidase-a inhibitor,bw 1370U87, on urinary 3-methoxy-4-hydroxyphenylglycol in normal volunteers

Urinary 3-methoxy-4-hydroxyphenlglycol (MHPG) levels were measured in 14 normal volunteers during a Phase I study of the novel, reversible monoamine oxidase-A (MAO-A) inhibitor BW 1370U87 targeted for the treatment of depression. baseline MHPG excretion (day 0) showed a significant diurnal increase (n = 14, P < 0.05) between 1200 and 2000 h. Oral administration of BW 1370U87 produced significant (35-45% maximal, P < 0.05) decreases from these basal levels during the same 1200-2000 h time interval Twenty-four hours after the dose (dose was given at 0800 h), urinary MHPG levels returned to baseline, consistent with a reversible mechanism of inhibition by BW 1370U87. Decreases in urinary MHPG did not appear to be dose-dependent between 200-800 mg BW 1370U87 per day, suggesting that maximal MAO-A inhibition was achieved at the 200 mg dose. These effects on MHPG excretion may be helpful in predicting the efficacy of BW 1371370U87 in the treatment of depression. © 1993 wiley-Liss, Inc.     

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 despramine (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.     

Determination of 3-methoxy-4-hydroxyphenylglycol conjugates in urine. Application to the study of central noradrenaline metabolism in unmedicated chronic schizophrenic patients

On the basis of post-mortem studies it has been proposed that the central deficit in schizophrenia may be in noradrenergic transmission. It has also been proposed that there is a substantial central contribution to the excretion of the noradrenaline metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) and more particularly of its sulphate conjugate in man. There is thought to be a lesser central contribution to the excretion of the other major noradrenaline metabolites, vanillylmandelic acid (VMA) and the glucuronide conjugate of MHPG.A strong negative correlation was found between severity of illness in a group of 18 unmedicated chronic schizophrenic patients and their 24-h excretion of MHPG-sulphate but not of MHPG-glucuronide or VMA. However there was no significant difference in the mean excretion of MHPG conjugates or of VMA between the schizophrenic group and an institutional control group.This supports the idea of a relation between MHPG-sulphate excretion and central noradrenergic activity, but suggests that reduced brain noradrenaline turnover is neither necessary nor sufficient for schizophrenia to occur. One possible explanation is that reduced turnover pre-disposes towards a more severe illness in schizophrenics.     

Effect of chronic clonidine treatment on the turnover of noradrenaline and dopamine in various regions of the rat brain

Summary The turnover of noradrenaline (NA) and dopamine (DA) was estimated in various rat brain regions by measuring the depletion of the amines after inhibition of their biosynthesis by -methyltyrosine. Acute treatment with clonidine (0.1 mg/kg) reduced NA turnover in the brain stem, hypothalamus and rest of the brain but had no effect on DA turnover in the corpus striatum and rest of the brain. After chronic clonidine treatment (0.1 mg/kg, twice daily for 15 days), NA turnover was not affected by an additional injection of clonidine in the brain stem or in the hypothalamus but was still markedly reduced in the rest of the brain. In addition, DA turnover was reduced in the corpus striatum and rest of the brain, an effect which was also observed after a single injection of a high dose of clonidine (1 mg/kg). These findings suggest that a chronic administration of clonidine may cause regionally differential changes in the sensitivity of central NA receptors.     

Effects of acute and chronic desipramine treatment on somatostatin receptors in brain

The effects of acute (5 mg/kg, IP twice daily for 2 days) and chronic (5 mg/kg IP twice daily for 21 days) administration of desipramine (DMI) on [¹²⁵I]-Tyr¹¹-somatostatin binding sites in brain were examined. There was no change in [¹²⁵I]Tyr¹¹-somatostatin binding in membranes prepared from the frontal cortex, striatum, and hippocampus of rats acutely or chronically treated with DMI as compared to non treated animals. [¹²⁵I]Tyr¹¹-Somatostatin binding was increased in membranes prepared from the rat nucleus accumbens only after chronic DMI administration. Scatchard analysis of the binding data from the nucleus accumbens showed that [¹²⁵I]Tyr¹¹-somatostatin labels a single population of somatostatin binding sites with an affinity constant, K_d, of 1.8±0.60 nM and a B_max of 330±90 fmol/mg protein. Chronic treatment with DMI increased the B_max (500±140 fmol/mg protein) but had no effect on the K_d. This finding shows a regional effect of DMI on [¹²⁵I]Tyr¹¹-somatostatin binding sites in rat brain and suggests that somatostatin may play a role in the pathophysiology of depression.     

Acute treatment with the cyclic antidepressant desipramine,but not fluoxetine,increases membrane-associated G protein-coupled receptor kinases 2/3 in rat brain

The homologous regulation of receptors is mediated by G protein-coupled receptor kinases (GRKs) which phosphorylate the agonist-activated receptor. This study was designed to assess the in vivo indirect activation of adrenoceptors or 5-HT receptors by the reuptake blocker desipramine or fluoxetine on the cellular distribution of GRK 2/3 in rat brain. Immunoblot analysis (frontal cortex) with a GRK 2 antibody revealed a unique 80 kDa protein (mixed GRK 2/3) in total homogenate (H) and in membrane (P2) and cytosolic (S2) fractions. The proportion of GRK 2/3 in each fraction, relative to that of H, was: P2/H=0.11 and S2/H=0.45. Acute desipramine (noradrenaline reuptake blocker) increased in a dose- (1-30 mg/kg, i.p.) and time- (1-6 h) dependent manner the content of GRK 2/3 in the membrane (P2/H ratios increased by 37-164%). This effect vanished with a prolonged desipramine (30 mg/kg) exposure (24 h). Desipramine did not alter the content of GRK 2/3 in the cytosol (S2/H ratios). Chronic desipramine (10 mg/kg every 24 h) for 14 days did not change significantly the immunodensity of GRK 2/3 in the membrane or the cytosol. The acute administration (2 h) of fluoxetine (5-HT reuptake blocker; 3-30 mg/kg) did not induce significant changes in the content of GRK 2/3 in the membrane (P2/H ratio) or cytosol (S2/H ratio). The results indicate that the in vivo activation of adrenoceptors by desipramine is associated with a time-dependent modulation of membrane-associated GRK 2/3 (i.e. an acute increase in the kinase content which is followed by a return to the basal expression upon repeated treatment). In contrast, the acute in vivo activation of 5-HT receptors induced by fluoxetine does not result in modulation of GRK 2/3.