Chronic effects of clomipramine and clorgyline on regional levels of brain amines and acid metabolites in rats

Antidepressant-like effect of flavonoids extracted from Apocynum venetum leaves on brain monoamine levels and dopaminergic system

ETHNOPHARMACOLOGICAL RELEVANCE

Apocynum venetum L. (Apocynaceae), a traditional medicinal plant, has been used for the improvement of emotions in Asian countries.

AIM OF THE STUDY

We explored the antidepressant-like effect and monoaminergic mechanism of a flavonoids extract from Apocynum venetum leaves (AV-extract).

MATERIALS AND METHODS

Effect of AV-extract (25, 50 and 100 mg/kg, i.g.) on mice's immobility time was assessed in forced swim test (FST) and tail suspension test (TST). The locomotor activity was evaluated in the open-field test (OFT). Additionally, the main monoamine neurotransmitters serotonin (5-HT), noradrenaline (NA) and dopamine (DA) and their metabolites 5-hydroxyindole-3-acetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the mouse hippocampus involved in the antidepressant-like effect of AV-extract was also determined by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS-MS).

RESULTS

AV-extract (50 and 100 mg/kg, i.g.) administration significantly reduced the immobility time in both the FST and TST without accompanying changes in locomotor activity in the OFT. It was also found that the AV-extract significantly increased the concentrations of the main neurotransmitters NE and DA along with their respective metabolites DOPAC, HVA in the hippocampus. The antidepressant-like effect of the AV-extract (50 mg/kg, i.g.) was prevented by the pretreatment of mice with SCH23390 (0.05 mg/kg, i.g., a dopamine D1 receptor antagonist) or sulpiride (50 mg/kg, i.g., a dopamine D2 receptor antagonist).

CONCLUSION

The AV-extract produced significant antidepressant-like effects, which likely attribute to increased NE and DA along with their respective metabolites DOPAC, HVA in the mouse hippocampus, and dependent on interaction with dopaminergic (D1 and D2 receptor) systems.

Effects of chronic antidepressant drug administration and electroconvulsive shock on activity of dopaminergic neurons in the ventral tegmentum

Increasing attention is now focused on reduced dopaminergic neurotransmission in the forebrain as participating in depression. The present paper assessed whether effective antidepressant (AD) treatments might counteract, or compensate for, such a change by altering the neuronal activity of dopaminergic neurons in the ventral tegmental area (VTA-DA neurons), the cell bodies of the mesocorticolimbic dopaminergic system. Eight AD drugs or vehicle were administered to rats for 14 d via subcutaneously implanted minipumps, at which time single-unit electrophysiological activity of VTA-DA neurons was recorded under anaesthesia. Further, animals received a series of five electroconvulsive shocks (ECS) or control procedures, after which VTA-DA activity was measured either 3 d or 5 d after the last ECS. Results showed that the chronic administration of all AD drugs tested except for the monoamine oxidase inhibitor increased the spontaneous firing rate of VTA-DA neurons, while effects on 'burst' firing activity were found to be considerably less notable or consistent. ECS increased both spontaneous firing rate and burst firing of VTA-DA neurons. It is suggested that the effects observed are consistent with reports of increased dopamine release in regions to which VTA neurons project after effective AD treatment. However, it is further suggested that changes in VTA-DA neuronal activity in response to AD treatment should be most appropriately assessed under conditions associated with depression, such as stressful conditions.

Long-term effects of an Apocynum venetum extract on brain monoamine levels and beta-AR density in rats

The present study was designed to get further insight into the mode of antidepressant action of an extract prepared of the leaves of Apocynum venetum L. (AV). To evaluate biochemical changes, 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 (15 mg/kg po) and an AV-extract (15, 60 and 250 mg/kg) on regional levels of serotonin (5-HT), norepinephrine (NE), dopamine (DA) and their metabolites in the rat hypothalamus, striatum and hippocampus. Pronounced changes in 5-HT, NE and DA levels were detected mainly after 8 weeks of daily imipramine treatment. Similar to imipramine, AV-extract reduced NE and DA concentrations after 8 weeks, whereas it failed to affect 5-HT levels. We speculate that the decrease in NE levels after chronic AV treatment might be based partly on the subsensitivity of presynaptic alpha(2)-receptors. In addition to the determination of central monoamine concentrations, quantitative radioligand receptor-binding studies were used to examine the effects of long-term administration of imipramine and AV-extract on beta-adrenergic binding in rat frontal cortex. [125I]CYP binding to beta-adrenergic receptors was found to be decreased after 8 weeks treatment with imipramine, whereas AV-extract had no effect on beta-receptor binding.

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.

Effects of chronic administration of sibutramine on body weight, food intake and motor activity in neonatally monosodium glutamate-treated obese female rats: relationship of antiobesity effect with monoamines

When the hypothalamic ventromedial nucleus and arcuate nucleus were destroyed in rats by treatment with monosodium glutamate in the neonatal stage, increase in the Lee index (body weight 1/3/body length) and in retroperitoneal fat as well as decreases in spontaneous motor activity, food consumption and growth hormone secretion function associated with hypothalamic low body length obesity (monosodium glutamate-treated obesity; MSG-OB) were observed as these rats grew. Treatment with sibutramine at 3 and 10 mg/kg p.o. once a day continuously for 14 days improved these parameters, and the degree of improvement was dose related. The plasma lipid values in MSG-OB rats, which were the same as those in normal rats, were decreased by consecutive administration of sibutramine. Levels of hypothalamic monoamines (MAs) such as norepinephrine, 5-HT (serotonin) and dopamine and their metabolites DOPAC, HVA and 5-HIAA were decreased in MSG-OB rats, and further decrease in them, though slight, was observed with consecutive daily administration of sibutramine, probably as a result of the feedback attributable to an increase in MA in synapses caused by inhibition of MA uptake by sibutramine. These results suggest that sibutramine can activate the MA nervous system by MA uptake inhibition in regions of the brain such as the lateral hypothalamic area and the paraventricular nucleus, which control food intake and sympathetic nerve activity, and the nigrostriatal area related to the extrapyramidal motor system, and thereby exhibit anti-obesity effects in the MSG-OB rat.

Alterations in responses to LSD in humans associated with chronic administration of tricyclic antidepressants, monoamine oxidase inhibitors or lithium

This study sought to investigate possible interactions between antidepressant agents and lysergic acid diethylamide (LSD) in humans through the use of retrospective questionnaires. Ten subjects were identified who used LSD during chronic (3 weeks or longer) periods of antidepressant administration. These subjects were asked to describe the phenomenological effects of self-administered hallucinogens prior to and during antidepressant treatment; a structured, standardized questionnaire was used to evaluate LSD experiences. Chronic tricyclic antidepressant administration was associated with subjective increases in physical, hallucinatory and psychological responses to LSD. Similarly, subjects receiving lithium chronically also reported increases in their responses to LSD. In contrast, subjects who had been chronically taking an monoamine oxidase (MAO) inhibitor reported subjective decreases in the effects of LSD. This is similar to a previous report by our group of a decreased response to LSD in individuals who were chronically taking serotonin-selective antidepressants. These altered responses to LSD most likely involve differential changes in central serotonin and dopamine receptor systems and are consistent with other recent data suggesting that the clinical efficacy of different classes of antidepressants may not necessarily rely on a common mechanism of action in the brain.

The interaction of thyroid state, MAOI drug treatment, and light on the level and circadian pattern of wheel-running in rats

In order to examine the relationship between thyroid status, the circadian system, and antidepressant drug response, the antidepressant drug clorgyline, a monoamine oxidase inhibitor (MAOI), was administered chronically to sham-operated or thyroparathyroidectomized rats. Wheel-running was monitored continuously in a light-dark (LD) cycle, and then in constant dim light. In LD, MAOI treatment increased levels of running. This effect was delayed in hypothyroid rats relative to euthyroid rats. In constant light, the MAOI-induced increase in running was diminished in euthyroid but not hypothyroid animals. Hypothyroid animals were less responsive to the change in lighting than were euthyroid animals, and this was more apparent in hypothyroid rats given MAOI. The daily pattern of running differed with lighting condition as well as with treatment group. MAOI-treatment of hypothyroid animals phase-advanced the pattern of wheel-running. MAOI-treatment of control animals increased the amplitude of wheel-running particularly in the LD cycle. These results indicate that thyroid status, lighting, and MAOI treatment interact to alter the behavioral response to chronic drug treatment.

Diurnal variations of serotonin and dopamine levels in discrete brain regions of Syrian hamsters and their modification by chronic clorgyline treatment

In Syrian hamsters, chronic administration of the type A monoamine oxidase inhibitor, clorgyline (CLG), alters the intrinsic period and daily pattern of the circadian rhythm of wheel running, and changes the intensity-response curve for phase-shifting of the rhythm by light pulses. Chronic treatment with CLG also decreases hypothalamic and peritoneal temperatures, particularly during the rest phase of the activity-rest cycle. To help identify monoamines that may mediate CLG's effects on circadian rhythms, we measured levels of dopamine (DA) and serotonin (5-HT) at nine time points over a 24-h period in micro-dissected brain regions in chronic CLG-treated or saline-treated hamsters. For 5-HT, a diurnal variation was detected in all regions in saline-treated animals; for DA, no diurnal variation was detected in any region. In all regions, 5-HT levels and, to a lesser extent, DA levels were higher after CLG treatment. The acrophase of the 5-HT rhythm in the suprachiasmatic nucleus (SCN) was delayed by CLG-treatment, while the acrophase in the dorsal raphe nucleus was unchanged. The diurnal variation of 5-HT in the paraventricular nucleus of the hypothalamus, medial preoptic area, and median raphe nuclei was no longer detectable after chronic CLG-treatment. The phase-delay induced by CLG treatment in the daily rhythm of serotonin levels in the SCN, which functions as a circadian pacemaker, may be an important mechanism underlying the drug's capacity to slow the intrinsic rhythm of the pacemaker and to phase-delay behavioral rhythms that are under its control.

Phenylalanine in the caudate nucleus of dopamine depleted rats

Dopamine depleting lesions of the substantia nigra result in a reduction of the striatal accumulation of 2-phenylethylamine following monoamine oxidase inhibition. It is established that this effect may not be due to a change in availability of aromatic L-amino acid decarboxylase in striatum. Nevertheless, the possibility remains that striatal concentrations of phenylalanine (the precursor of 2-phenylethylamine) may be altered by dopamine-depleting lesions. The present experiments assessed the effects of dopamine depletion induced by 6-OHDA (7 days following 8 micrograms/4 microliters unilateral substantia nigra injection) on striatal concentrations of phenylalanine, dopamine, 5-hydroxytryptamine and their metabolites. In addition, the effects of reserpine-induced (10 mg kg-1, 2h, sc) amine depletion on these striatal levels were also assessed. Under equivalent conditions reserpine is reported to increase striatal accumulation of 2-phenylethylamine. 6-OHDA induced a significant unilateral depletion of dopamine, DOPAC and HVA and increased 5-HIAA but had no significant effect on phenylalanine levels. Reserpine decreased dopamine and 5-hydroxytryptamine and increased DOPAC, HVA and 5-HIAA levels, no changes in phenylalanine were observed. This pattern of results was also observed when lesioned animals or reserpine-treated animals were pretreated with (-)-deprenyl (2 mg kg-1, 2 hr, sc), the treatment previously used to induce accumulation of 2-phenylethylamine. These data indicate that changes in 2-phenylethylamine previously observed under these conditions may not simply be secondary to a change in striatal phenylalanine concentrations.

Clomipramine increases firing rate in lateral septal neurons related with hippocampus

Long-term clomipramine administration (CMI: 2.5 mg/kg IP, 25 days) effects on 274 identified hippocampus-septal neurons was assessed in rats. Stimulation of CA 1/dentate areas produced a biphasic response in 61% of lateral septal neurons. A brief activation was followed by a period of suppression of firing. In CMI-treated rats, the neurons showing this biphasic response increased their firing rate about fourfold, while the suppression of firing shortened around threefold. Other septal neurons (36%), in which only the burst of activation appeared but not suppression of firing, did not change their firing rate even after long-term CMI. In conclusion, CMI produces an increase of firing rate in lateral septal neurons receiving inhibitory hippocampal influence which is likely to be mediated by a disinhibitory process.

The tricyclic antidepressant clomipramine dose-dependently reduces regional cerebral metabolic rates for glucose in awake rats

The time course and the relation to dose of regional cerebral metabolic rates for glucose (rCMRglc) were measured in awake male Fischer-344 rats after administration of clomipramine (CMI), a serotonin (5-HT) uptake inhibitor and clinical antidepressant. rCMRglc was determined, using the quantitative autoradiographic [14C]2-deoxyglucose technique, in 64 brain regions at 20, 40, 60, 120, and 180 min after administration of CMI 50 mg/kg IP and 120 min after CMI 2 and 10 mg/kg IP. The peak metabolic effect was observed at 120 min after CMI. At that time, CMI 2 and 10 mg/kg IP significantly reduced rCMRglc from control values in 12 (19%) and 14 (22%) brain regions, which correspond to areas with high densities of 5-HT reuptake sites (e.g. visual and limbic areas and raphe nuclei). CMI 50 mg/kg produced widespread rCMRglc reductions in 34 (53%) brain regions, including cortical, hippocampal, raphe and cerebellar areas. The topographic distribution and the relation to time and dose of CMI effects on rCMRglc are different from those of 5-HT1A [8-hydroxy-2(di-N-propylamino) tetralin], 5-HT1B-C (m-chlorophenylpiperazine) and 5-HT3 (quipazine) agonists and resemble those produced by 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), an agonist of 5-HT2 receptors, suggesting that CMI may prefentially stimulate this 5-HT receptor subtype.

Effect of chronic ritanserin or clorgyline on amine and metabolite levels in rat frontal cortex

As part of an investigation of ritanserin-induced receptor down-regulation, monoamine and metabolite levels in rat frontal cortex were measured following chronic ritanserin (2 mg/kg per day) or clorgyline (10 mg/kg per day) administration. Clorgyline increased 5-hydroxytryptamine (5-HT) by 83%, noradrenaline (NA) by 54%, and dopamine (DA) by 16% and decreased 5-hydroxyindoleacetic acid (5-HIAA) by 28%, homovanillic acid (HVA) by 57% and 3,4-dihydroxyphenylacetic acid (DOPAC) by 67%. All these changes were statistically significant (P less than 0.001) except for the increase in DA. Ritanserin increased 5-HT by 30%, NA by 33% and DA by 26% and decreased 5-HIAA by 22%, HVA by 23% and DOPAC by 40%; however, only the increases in 5-HT and NA reached statistical significance (P less than 0.05). Monoamine oxidase (MAO) activity in cortical homogenates was also measured following the chronic ritanserin and clorgyline regimens and also following ritanserin administration in vitro. Chronic clorgyline and ritanserin inhibited MAO activity by 60 and 39%, respectively. In vitro, ritanserin administration at concentrations of less than 10(-6) M had no effect on MAO activity but at doses higher than 10(-6) M, MAO activity was inhibited in a dose-dependent manner from 18 +/- 0.5% at 3 x 10(-6) M to 63 +/- 9% at 10(-4) M. Thus, ritanserin appears to act as an MAO inhibitor in addition to being a 5-HT2 antagonist and this may be related to its ability to induce 5-HT2 receptor down-regulation.

Chronic citalopram action and the maturing mouse brain's indoleamine levels

1. Mice of various ages between birth and adulthood were injected daily for 12 days with the serotonin specific uptake inhibitor citalopram (LU 10-171). 2. Two hours, 1 day and 3 days following the last injection animals were killed and their brains assayed for 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA). 3. Changes in levels of both metabolites varied by age of the animal, brain region and time after last injection. These patterns differed from previous studies of shorter duration citalopram exposure. 4. The data support the view that 5-HT and 5-HIAA levels are probably not dependently related in immature brain. Indeed 5-HIAA modulation in the immature seems to lack the firm control of the adult and can be modified for extended periods by citalopram action.