Antidepressant efficacy and cognitive effects of repetitive transcranial magnetic stimulation in vascular depression: an open trial.

BACKGROUND: Beneficial effects of repetitive transcranial magnetic stimulation (rTMS) were demonstrated by many controlled studies in major depression. Moreover, this promising and non invasive therapeutic tool seems to be better tolerated than electroconvulsive therapy.Vascular depression is a subtype of late-life depression, associated with cerebrovascular disease and means a poorer response to antidepressant treatment. We employed rTMS over the left prefrontal cortex in 11 patients with late-onset resistant vascular depression. The primary purpose of this two-week open study was to examine antidepressant efficacy of rTMS in vascular depression. The secondary aim was to evaluate cognitive effects of rTMS in our sample. METHODS: Clinical status, as measured with the Hamilton Depression Rating Scale (HDRS), and cognitive effects, as evaluated by neuropsychological tests, were assessed at baseline and after two weeks of rTMS. Brain measurements to obtain an index of prefrontal atrophy were performed at both the motor cortex and prefrontal cortex. RESULTS: Five out of 11 resistant patients with late-onset vascular depression were responders. They showed a clinically meaningful improvement in HDRS scores, with a decrease of 11, 4 points (p<0.01). Antidepressant response is correlated to the relative degree of prefrontal atrophy (p = 0.05). After two weeks, verbal fluency and visuospatial memory improved. No cognitive performance deteriorated except for verbal memory, as the delayed recall decreased significantly in the responders' group. CONCLUSIONS: Our preliminary observations prompt to perform a subsequent controlled study to examine if rTMS may constitute an alternative to electroconvulsive therapy.

Assessment of the serotonin and norepinephrine reuptake blocking properties of duloxetine in healthy subjects.

Duloxetine is a dual inhibitor of norepinephrine (NE) and serotonin (5-HT) uptake. Initial trials conducted in depressed patients using regimens of 20 mg/day or less did not convincingly demonstrate its efficacy as an antidepressant. The aim of this study was to assess the effects of duloxetine on the 5-HT and NE reuptake processes in healthy human volunteers. Twenty-seven healthy young males without a history of psychiatric disorder were randomly assigned to four groups, each group receiving one of the following daily drug regimens: placebo, clomipramine (a potent 5-HT/NE reuptake blocker) 100 mg/day, duloxetine 20 mg/day, or duloxetine 60 mg/day. In order to assess the NE reuptake process, the pressor response to intravenous tyramine (4 and 6 mg) was measured. Determination of the whole blood 5-HT content was used to evaluate the 5-HT reuptake blockade. These measurements were performed at baseline and repeated after 7 and 14 days of drug intake. Both duloxetine, at doses of 20 to 60 mg/day, and clomipramine significantly interfered with the 5-HT reuptake process, as demonstrated by marked decreases in blood 5-HT concentrations. However, the same doses of duloxetine, unlike clomipramine, failed to impede the usual increase in blood pressure that follows a tyramine intravenous infusion, indicating that clomipramine but not duloxetine blocked NE reuptake. At doses tested in a population of healthy volunteers, duloxetine acted as a selective 5-HT reuptake inhibitor, having no clear effect on the NE reuptake process. Nevertheless, given that the highest dose of duloxetine increased supine systolic blood pressure, it is possible that it represents the threshold regimen for NE reuptake inhibition.

Potentiation by (-)Pindolol of the activation of postsynaptic 5-HT(1A) receptors induced by venlafaxine.

The increase of extracellular 5-HT in brain terminal regions produced by the acute administration of 5-HT reuptake inhibitors (SSRI's) is hampered by the activation of somatodendritic 5-HT(1A) autoreceptors in the raphe nuclei. The present in vivo electrophysiological studies were undertaken, in the rat, to assess the effects of the coadministration of venlafaxine, a dual 5-HT/NE reuptake inhibitor, and (-)pindolol on pre- and postsynaptic 5-HT(1A) receptor function. The acute administration of venlafaxine and of the SSRI paroxetine (5 mg/kg, i.v.) induced a suppression of the firing activity of dorsal hippocampus CA(3) pyramidal neurons. This effect of venlafaxine was markedly potentiated by a pretreatment with (-)pindolol (15 mg/kg, i.p.) but not by the selective beta-adrenoceptor antagonist metoprolol (15 mg/kg, i.p.). That this effect of venlafaxine was mediated by an activation of postsynaptic 5-HT(1A) receptors was suggested by its complete reversal by the 5-HT(1A) antagonist WAY 100635 (100 microg/kg, i.v.). A short-term treatment with VLX (20 mg/kg/day x 2 days) resulted in a ca. 90% suppression of the firing activity of 5-HT neurons in the dorsal raphe nucleus. This was prevented by the coadministration of (-)pindolol (15 mg/kg/day x 2 days). Taken together, these results indicate that (-)pindolol potentiated the activation of postsynaptic 5-HT(1A) receptors resulting from 5-HT reuptake inhibition probably by blocking the somatodendritic 5-HT(1A) autoreceptor, but not its postsynaptic congener. These results support and extend previous findings providing a biological substratum for the efficacy of pindolol as an accelerating strategy in major depression.

Effects of sustained administration of the serotonin and norepinephrine reuptake inhibitor venlafaxine: I. in vivo electrophysiological studies in the rat.

The effect of a 21-day treatment with the dual 5-HT and NE reuptake blocker venlafaxine (delivered s.c. by osmotic minipumps) was assessed on the time required for a 50% recovery (RT(50)) of the firing activity of dorsal hippocampus CA(3) pyramidal neurons from the suppression induced by microiontophoretic applications of 5-HT and NE. The RT(50) values for 5-HT were increased by both 10 and 40 mg/kg/day regimens of venlafaxine, whereas those for NE were increased only by the 40 mg/kg/day regimen, indicative of a greater potency of venlafaxine in blocking 5-HT reuptake. The sensitivity of the postsynaptic 5-HT(1A) and alpha(2)-adrenergic receptors was altered by neither regimen of venlafaxine. Using a paradigm by which the 5-HT(1A) antagonist WAY 100635 can induce a disinhibition of firing activity of CA(3) pyramidal neurons, it was demonstrated that the high, but not the low, dose of venlafaxine led to an enhanced tonic activation of postsynaptic 5-HT(1A) receptors in the dorsal hippocampus. The duration of the suppressant effect of the firing activity of CA(3) hippocampus pyramidal neurons produced by the electrical stimulation of the ascending 5-HT pathway was significantly reduced when the frequency of the stimulation was enhanced from 1 Hz to 5 Hz in control rats and in rats treated with 10 mg/kg/day, but not with 40 mg/kg/day of venlafaxine. Hence, venlafaxine induced a desensitization of the terminal 5-HT(1B) autoreceptor only at the high dose. A 2-day treatment with 10 mg/kg/day of venlafaxine induced a suppression of the firing activity of 5-HT neurons of the dorsal raphe. The firing activity of these neurons was back to control level in rats that had been treated for 21 days with the same dose of venlafaxine. The suppressant effect of the i.v. administration of the 5-HT autoreceptor agonist LSD on the firing activity of dorsal raphe 5-HT neurons was reduced in rats that had been treated for 21 days with 10 mg/kg/day of venlafaxine. A 2-day treatment with 40 mg/kg/day of venlafaxine, unlike the 10 mg/kg/day regimen, induced a marked suppression of the firing activity of locus coeruleus NE neurons. However, in contrast to 5-HT neurons, NE neurons did not recover their firing activity after a 21-day treatment. Taken together, the results from this study indicate that the low dose of venlafaxine blocked selectively the reuptake of 5-HT, whereas the high dose blocked the reuptake of both 5-HT and NE. Moreover, an enhancement of serotonergic neurotransmission by venlafaxine was only achieved under conditions whereby the desensitization of the terminal 5-HT(1B) autoreceptor is appended to that of the somatodendritic 5-HT(1A) receptor.

Effects of sustained administration of the serotonin and norepinephrine reuptake inhibitor venlafaxine: II. In vitro studies in the rat.

The effects of long-term administrations of a low (10 mg/kg/day) and a high (40 mg/kg/day) dose of the dual 5-HT and NE reuptake inhibitor venlafaxine (delivered s.c. by osmotic minipumps for 21 days) were assessed on the electrically-evoked release of tritium from hippocampal slices preloaded with either [(3)H]5-HT or [(3)H]NE, 48 h after the removal of the minipump. The high, but not the low, dose regimen of venlafaxine enhanced the electrically-evoked release of [(3)H]5-HT while treatment with the high dose of venlafaxine failed to alter the electrically-evoked release of [(3)H]NE. The inhibitory effect of the 5-HT(1B) agonist CP 93,129 on the electrically evoked release of [(3)H]5-HT was unaltered by the low dose regimen of venlafaxine while it was attenuated in rats treated with the high dose of venlafaxine, indicative of a functional desensitization of the terminal 5-HT(1B) autoreceptor. Unexpectedly, neither regimen of venlafaxine altered the inhibitory effect of UK 14,304 on the electrically evoked release of both [(3)H]5-HT and [(3)H]NE, indicating that neither the alpha(2)-adrenergic auto- nor heteroreceptors were desensitized. Finally, the functions of the 5-HT and NE reuptake process were assessed. None of the treatment regimens altered the basal uptake of [(3)H]5-HT from hippocampal or mesencephalic slices nor that of [(3)H]NE from hippocampal slices. Finally, the enhancing effect of 1 microM of paroxetine in the perfusion medium on the electrical release of [(3)H]5-HT was unaltered in hippocampal slices prepared from rats that had been treated for 21 days with 40 mg/kg/day of venlafaxine. Taken together, these results indicate that, in terms of alteration of the sensitivity of the terminal 5-HT(1B) autoreceptor, alpha(2)-adrenergic auto-and heteroreceptors, the effects of long-term administration of venlafaxine are no different than those observed with classical SSRI's.

Effects of the co-administration of mirtazapine and paroxetine on serotonergic neurotransmission in the rat brain.

The alpha(2)-adrenoreceptor antagonist mirtazapine, which is also a 5-HT(2), 5-HT(3) and H(1) receptors antagonist and the selective serotonin (5-HT) reuptake inhibitor paroxetine are effective antidepressant drugs which enhance 5-HT neurotransmission via different mechanisms. The present studies were undertaken to determine whether the mirtazapine-paroxetine combination could induce an earlier and/or a greater effect on the 5-HT system than either drug alone. Using in vivo electrophysiological paradigms, the firing activity of dorsal raphe 5-HT neurons was decreased by 70% in rats treated with paroxetine (10 mg/kg/day, s.c.) for 2 days and was back to normal after 21 days. In contrast, a 2-day treatment with mirtazapine (5 mg/kg/day, s.c.) did not alter the firing of 5-HT neurons whereas it was increased by 60% after 21 days of treatment. A low dose of mirtazapine (5 mg/kg/day, s.c.x2 days) failed to offset the decremental effect of paroxetine on the 5-HT neuron firing activity, but a higher dose (10 mg/kg/day, s.c.x2 days) did attenuate the decremental effect of paroxetine. In the dorsal hippocampus, neither mirtazapine (5 mg/kg/day, s.c.) nor a paroxetine (10 mg/kg/day, s.c.) treatment altered the responsiveness of 5-HT(1A) receptors to microiontophoretically-applied 5-HT. Both in controls and in rats treated for 2 days with paroxetine alone, the administration of the 5-HT(1A) antagonist WAY 100635 (25-100 microg/kg, i.v.) did not change the firing activity of dorsal hippocampus CA(3) pyramidal neurons. However, WAY 100635 increased significantly the firing activity of these neurons in rats treated with mirtazapine alone but to a greater extent with both mirtazapine and paroxetine for 2 days. After 21 days of treatment, WAY 100635 increased to a greater degree the firing rate of CA(3) pyramidal neurons in rats which received the combination over rats given either drug alone. It is concluded that the mirtazapine-paroxetine combination shortened the delay in enhancing the tonic activation of postsynaptic 5-HT(1A) receptors and produced a greater activation of the postsynaptic 5-HT(1A) receptors than either drug given alone. The present results suggested that mirtazapine may have a faster onset of action than a SSRI, and that the co-administration of mirtazapine and paroxetine may accelerate the antidepressant response and as well as being more effective than either drug alone.

Increased tonic activation of rat forebrain 5-HT(1A) receptors by lithium addition to antidepressant treatments.

The present study was undertaken to determine whether lithium addition to long-term treatment with different classes of antidepressant drugs could induce a greater effect on the serotonin (5-HT) system than the drugs given alone. Because 5-HT(1A) receptor activation hyperpolarizes and inhibits the firing activity of CA(3) pyramidal neurons in the dorsal hippocampus, the degree of disinhibition produced by the selective 5-HT(1A) receptor antagonist WAY 100635 was determined using in vivo extracellular recordings. In controls, as well as in rats receiving a lithium diet for 3 days, the administration of WAY 100635 (25-100 microg/kg, IV) did not modify the firing activity of dorsal hippocampus CA(3) pyramidal neurons. When the tricyclic antidepressant imipramine (10 mg/kg/day, SC), the monoamine oxidase inhibitor tranylcypromine (2.5 mg/kg/day, SC) and the selective 5-HT reuptake inhibitor paroxetine (10 mg/kg/day, SC) were administered alone for 21 days, a dose of 50 microg/kg of WAY 100635 was needed to increase significantly the firing activity of these neurons. On the other hand, WAY 100635, at a dose of only 25 microg/kg, increased significantly the firing rate of CA(3) pyramidal neurons in rats receiving both a long-term antidepressant treatment and a short-term lithium diet. It is concluded that the addition of lithium to antidepressant treatments produced a greater disinhibition of dorsal hippocampus CA(3) pyramidal neurons than any treatments given alone. The present results support the notion that the addition of lithium to antidepressants may produce a therapeutic response in treatment-resistant depression by enhancing 5-HT neurotransmission.

Effect of sustained administration of the 5-HT1A receptor agonist flesinoxan on rat 5-HT neurotransmission.

A short-term treatment with flesinoxan (2.5 and 5 mg/kg/day x 2 days, s.c., delivered using osmotic minipumps) decreased significantly the spontaneous firing activity of dorsal raphe serotonin (5-HT) neurons of male Sprague-Dawley rats. This firing was still decreased following 1 week of treatment with flesinoxan (5 mg/kg/day) but was back to normal after a treatment of 2 weeks. This recovery of firing was associated with a 3-fold shift to the right of the dose-response curve of the effect of the 5-HT autoreceptor agonist lysergic acid diethylamide on the firing activity of 5-HT neurons, indicating a desensitization of somatodendritic 5-HT1A autoreceptors. At the postsynaptic level, long-term treatment with flesinoxan (5 mg/kg/day x 14 days) did not modify the responsiveness of dorsal hippocampus CA3 pyramidal neurons to microiontophoretic applications of 5-HT and flesinoxan nor to endogenous 5-HT released by the electrical stimulation of the ascending 5-HT pathway, indicating an unchanged sensitivity of postsynaptic 5-HT1A receptors. Finally, in rats treated with flesinoxan for 2 weeks, the administration of the selective 5-HT1A receptor antagonist (N-{2-[4(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridinyl)cyclohe xanecarboxamide trihydroxychloride (WAY 100635, 100 and 500 microg/kg, i.v.) did not increase the firing activity of dorsal hippocampus CA3 pyramidal neurons, thus failing to reveal an enhanced tonic activation of postsynaptic 5-HT1A receptors as for other antidepressant drugs, including the 5-HT1A receptor agonist gepirone. The marked potency and the long dissociation constant of flesinoxan for the 5-HT1A receptors may account for the latter discrepancy. In conclusion, as for selective 5-HT re-uptake inhibitors, monoamine oxidase inhibitors and 5-HT1A receptor agonists, flesinoxan produced most of the adaptive changes exerted by these antidepressant drugs on the 5-HT system.

Venlafaxine in treatment-resistant major depression: a Canadian multicenter, open-label trial.

This was an 8-week, multicenter, open-label study of the efficacy and tolerability of venlafaxine in patients with treatment-resistant depression conducted in Canada. Inpatients or outpatients aged 18 to 70 years with major depression were eligible if they had a 21-item Hamilton Rating Scale for Depression (HAM-D-21) score of 2 > or = 18 and a documented history of unsatisfactory improvement after a minimum of 8 weeks of treatment with an adequate dose of an antidepressant. Treatment with venlafaxine was started at 37.5 mg twice daily, and the dose could be titrated upward to a maximum of 375 mg/day during the first 4 weeks on the basis of the investigator's assessment of clinical response and tolerability. Of the 159 patients enrolled, 152 were evaluable for efficacy. The mean daily venlafaxine dose was 260 mg/day. The mean HAM-D-21 score decreased by 52%, and the mean Montgomery-Asberg Depression Rating Scale score decreased by 50% from baseline to day 56. A response (50% improvement from baseline) was achieved by 58% of patients on the HAM-D-21, and a remission (> or = 75% improvement in the HAM-D-21) was observed in 28% at day 56. By day 56, 88% of patients had improved from baseline on the Clinical Global Impression Improvement scale. Only 8% of the patients discontinued for adverse events. The most common adverse events were headache, insomnia, nausea, constipation, diaphoresis, and xerostomia. In conclusion, these results suggest that venlafaxine is effective and well tolerated for the management of patients with treatment-resistant major depression.

Assessment of the serotonin reuptake blocking property of YM992: electrophysiological studies in the rat hippocampus and dorsal raphe.

YM992 is a selective serotonin (5-HT) reuptake inhibitor and a 5-HT(2A) antagonist with potential antidepressant activity. As expected from a 5-HT reuptake inhibitor, which induces an accumulation of 5-HT in the dorsal raphe, YM992 inhibited the firing activity of these 5-HT neurons (ED50: 2.0+/-0.2 mg/kg, i.v.). This effect was reversed by the 5-HT(1A) antagonist WAY 100635. YM992 also dose-dependently prolonged the time for CA3 neurons to recover 50% of their firing rate following microiontophoretic applications of 5-HT, a reliable index of the function of the 5-HT reuptake carrier. In a second series of experiments, the adaptative properties of 5-HT neurons were examined during sustained administration of YM992 (20 mg/kg/day, s.c., delivered by osmotic minipumps) after 2 days of treatment. YM992 decreased by more than 60% the firing activity of the 5-HT neurons. There was a partial recovery of firing after 7 days and a complete one after 14 days of treatment in the presence of the minipump still delivering the drug. In a third series of experiments, the sensitivity of pre- and postsynaptic 5-HT(1A) receptors in the dorsal raphe and the dorsal hippocampus were assessed. The results showed that YM992 attenuated the inhibitory effect of intravenous administration of LSD and the 5-HT(1A) agonist 8-OH-DPAT on the firing activity of 5-HT neurons. As did the selective 5-HT reuptake inhibitor fluvoxamine, YM992 markedly increased the effectiveness of the electrical stimulation of ascending 5-HT fibres on firing activity of the postsynaptic hippocampus pyramidal neurons. This enhancement of 5-HT neurotransmission by YM992 was attributable to a desensitization of the terminal 5-HT(1B) autoreceptors since the postsynaptic 5-HT(1A) receptors in the hippocampus remained normosensitive.

Pregnancy reduces brain sigma receptor function.

1. Sigma (sigma) receptors have recently been cloned, though their endogenous ligand(s) remain unidentified. However, some neuroactive steroids, such as progesterone, have a high affinity for these receptors. Some sigma ligands, such as DTG, (+)-pentazocine and DHEA, act as sigma 'agonists' by potentiating the neuronal response to NMDA. Others, such as haloperidol, NE-100 and progesterone, act as sigma 'antagonists' by reversing the potentiations induced by sigma 'agonists'. 2. We compared the effects of sigma 'agonists' in four series of female rats: in controls, at day 18 of pregnancy, at day 5 post-partum, and in ovariectomized rats following a 3-week treatment with a high dose of progesterone. 3. In pregnant rats and following a 3-week treatment with progesterone, 10 fold higher doses of DTG, (+)-pentazocine and DHEA were required to elicit a selective potentiation of the NMDA response comparable to that obtained in control females. Conversely, at day 5 post-partum and following the 3-week treatment with a progesterone and after a 5-day washout, the potentiation of the NMDA response induced by the sigma 'agonist' DTG was greater than in control females. 4. The present data suggest that endogenous progesterone acts as an 'antagonist' at sigma receptors. The resulting changes in the function of sigma receptors during pregnancy and post-partum may be implicated in emotional phenomena occurring during these periods.

Serotonin and drug-induced therapeutic responses in major depression, obsessive-compulsive and panic disorders.

The therapeutic effectiveness of antidepressant drugs in major depression was discovered by pure serendipity. It took over 20 years before the neurobiological modifications that could mediate the antidepressive response were put into evidence. Indeed, whereas the immediate biochemical effects of these drugs had been well documented, their antidepressant action generally does not become apparent before 2 to 3 weeks of treatment. The different classes of antidepressant treatments were subsequently shown to enhance serotonin neurotransmission albeit via different pre- and postsynaptic mechanisms. Clinical trials based on this hypothesis led to the development of treatment strategies producing greater efficacy and more rapid onset of antidepressant action; that, is lithium addition and pindolol combination, respectively. It is expected that the better understanding recently obtained of the mechanism of action of certain antidepressant drugs in obsessive-compulsive and panic disorders will also lead to more effective treatment strategies for those disorders.

Modulation of the firing activity of rat serotonin and noradrenaline neurons by (+/-)pindolol.

BACKGROUND: (+/-)Pindolol is a beta-adrenergic/5-HT1A receptor antagonist used in combination with certain antidepressant drugs to accelerate the onset of the antidepressive response. METHODS: The aim of the present study was to assess, using an in vivo electrophysiologic paradigm, the effect of (+/-)pindolol on the spontaneous firing activity of rat dorsal raphe serotonin (5-HT) and locus coeruleus noradrenaline (NA) neurons. RESULTS: (+/-)Pindolol did not modify the firing activity of dorsal raphe 5-HT neurons at low doses (10 and 200 micrograms/kg, i.v.), but it prevented the suppressant effect of the 5-HT autoreceptor agonist lysergic acid diethylamide (LSD, 10 micrograms/kg, i.v.) but not that of the 5-HT1A receptor 8-hydroxy-N,N-dipropyl-aminotetralin (8-OHDPAT, 5 micrograms/kg, i.v.). At a higher dose (500 micrograms/kg, i.v.), (+/-)pindolol decreased 5-HT neuronal firing and this effect was reversed by the selective 5-HT1A receptor antagonist WAY 100635 (100 micrograms/kg, i.v.), suggesting that it could act as a partial 5-HT1A autoreceptor agonist. In the locus coeruleus, the high dose of (+/-)pindolol decreased the firing activity of NA neurons and this effect was reversed by the 5-HT2A receptor antagonist MDL 100907 (200 micrograms/kg, i.v.). Finally, both a lesion of NA neurons and the administration of MDL 100907 prevented the suppressant effect of (+/-)pindolol on the firing of 5-HT neurons. CONCLUSIONS: It is suggested that, at low doses, (+/-)pindolol acts as a somatodendritic 5-HT1A autoreceptor antagonist whereas at a higher dose, it decreases the tonic excitatory input from NA neurons to 5-HT neurons.

Venlafaxine: discrepancy between in vivo 5-HT and NE reuptake blockade and affinity for reuptake sites.

Using an in vivo electrophysiological paradigm, venlafaxine and paroxetine displayed similar potency for suppressing the firing activity of dorsal raphe 5-HT neurons (ED50: 233 and 211 microg/kg i.v., respectively), while venlafaxine was three times less potent than desipramine (ED50: 727 and 241 microg/kg i.v., respectively) to suppress the firing activity of locus coeruleus NE neurons. The selective 5-HT1A receptor antagonist WAY 100635 (100 microg/kg, i.v.) reversed the suppressant effect of venlafaxine and paroxetine on the firing activity of 5-HT neurons and the alpha2-adrenoceptor antagonist piperoxane (1 mg/kg, i.v.) reversed those of venlafaxine and desipramine on the firing activity of NE neurons. The ED50 of venlafaxine on the firing activity of 5-HT neurons was not altered (ED50: 264 microg/kg) in noradrenergic-lesioned rats, while the suppressant effect of venlafaxine on the firing activity of NE neurons was greater in serotonergic-lesioned rats (ED50: 285 microg/kg). Taken together, these results suggest that, in vivo, venlafaxine blocks both reuptake processes, its potency to block the 5-HT reuptake process being greater than that for NE. Since the affinities of venlafaxine for the 5-HT and NE reuptake carriers are not in keeping with its potencies for suppressing the firing activity of 5-HT and NE neurons, the suppressant effect of venlafaxine on the firing activity of 5-HT and NE neurons observed in vivo may not be mediated solely by its action on the [3H]cyanoimipramine and [3H]nisoxetine binding sites. In an attempt to unravel the mechanism responsible for this peculiarity, in vitro superfusion experiments were carried out in rat brain slices to assess a putative monoamine releasing property for venlafaxine. (+/-)Fenfluramine and tyramine substantially increased the spontaneous outflow of [3H]5-HT and [3H]NE, respectively, while venlafaxine was devoid of such releasing properties.

Modulation of noradrenergic neuronal firing by selective serotonin reuptake blockers.

Using in vivo extracellular unitary recording, the effect of short term (2-day) and long-term (21-day) administration of the selective 5-HT reuptake inhibitor (SSRI) paroxetine (10 mg kg(-1) day(-1), s.c. using osmotic minipumps) was examined on the spontaneous firing activity of locus coeruleus noradrenergic neurons. Long-term but not short-term treatment significantly decreased firing activity. Thus, it appears that enhancing 5-HT neurotransmission by sustained SSRI administration leads to a reduction of the firing rate of noradrenergic neurons. The SSRI paroxetine therefore alters the activity of noradrenergic neurons with a delay that is consistent with its therapeutic action in depression and panic disorder.

Treatment resistant depression: methodological overview and operational criteria.

A wide variety of definitions are used for Treatment Resistant Depression (TRD), considering various criteria and different concepts. Some of the key issues are: the diagnosis, the treatment adequacy in terms of dose and duration, the treatment response assessment and the number of failed therapeutic trials required. Systematic research has been characterizing the concept and criteria to define the different variables involved. Lack of consensus on these issues limits comparison across clinical trials and interpretation of treatment efficacy in the management of treatment resistant patients. Through reanalyzes of available data, we point out the limits of TRD definitions and propose conceptual and operational criteria for a collaborative research project on TRD. It appears that a number of variables commonly associated to treatment resistance are independent of patients characteristics and mainly refer to misdiagnosis and inadequate treatment. The proposed criteria are intended for therapeutic trials in TRD, combining the evaluation of treatment efficiency and the validation of the concept of TRD itself. Major depression with poor response to two adequate trials of different classes of antidepressants is proposed for an operational definition of TRD. Rationale for this definition is discussed in contrast to alternative definitions.

Long-term antidepressant treatments result in a tonic activation of forebrain 5-HT1A receptors.

We report here the first direct functional evidence of an increase in the tonic activation of postsynaptic 5-HT1A receptors by antidepressant treatments. Because 5-HT1A receptor activation hyperpolarizes and inhibits CA3 pyramidal neurons in the dorsal hippocampus, we determined, using in vivo extracellular recording, whether the selective 5-HT1A receptor antagonist WAY 100635 could disinhibit these neurons. Unexpectedly, no disinhibition could be detected in controls. However, after long-term treatment with the tricyclic antidepressant imipramine, the selective 5-HT reuptake inhibitor paroxetine, the reversible monoamine oxidase-A inhibitor befloxatone, the alpha2-adrenergic antagonist mirtazapine, or the 5-HT1A receptor agonist gepirone or multiple electroconvulsive shock (ECS) administration, WAY 100635 markedly increased (60-200%) the firing activity of CA3 pyramidal neurons. Such a disinhibition was absent in rats treated with the nonantidepressant drug chlorpromazine, in rats receiving only one ECS, or in rats receiving multiple ECSs in combination with an intrahippocampal pertussis toxin treatment to inactivate Gi/o-coupled 5-HT1A receptors. These data indicate that such antidepressant treatments, acting on entirely different primary targets, might alleviate depression by enhancing the tonic activation of forebrain postsynaptic 5-HT1A receptors.

Blockade of 5-hydroxytryptamine and noradrenaline uptake by venlafaxine: a comparative study with paroxetine and desipramine.

1. Venlafaxine is an antidepressant agent which blocks in vitro the reuptake of both 5-HT and NA. The present in vivo electrophysiological studies were undertaken, in the rat, to compare the effects of venlafaxine on 5-HT and NA reuptake to those of the selective 5-HT reuptake inhibitor paroxetine and the selective NA reuptake inhibitor desipramine. 2. Administered acutely, venlafaxine dose-dependently prolonged the time required for a 50% recovery (RT50) of the firing activity of dorsal hippocampus CA3 pyramidal neurons from the suppression induced by microiontophoretic applications of 5-HT and NA. Venlafaxine and paroxetine increased with a similar potency the RT50 values for 5-HT, while desipramine was more potent than venlafaxine at increasing the RT50 values for NA. Moreover, venlafaxine demonstrated a greater potency at increasing the RT50 values for 5-HT compared to that of NA. 3. A two-day treatment with venlafaxine (delivered s.c. by osmotic minipumps) increased the RT50 values for both 5-HT and NA applications. The RT50 values for 5-HT were significantly increased at a dose of 10 mg kg(-1) day(-1), whereas those for NA were increased at a dose of 20 mg kg(-1) day(-1), consistent with the data obtained following the acute administration of venlafaxine. 4. Taken together, these results indicate that, in vivo, venlafaxine blocks both reuptake processes, with a potency greater for the 5-HT than for the NA reuptake process. This dual action, combined with the differential potency of venlafaxine, might constitute the biological substratum responsible for its apparent unique clinical efficacy in major depression.

Effect of ergotamine on serotonin-mediated responses in the rodent and human brain.

In the rat dorsal hippocampus and dorsal raphe nucleus, the microiontophoretic application of ergotamine and 5-HT suppressed the firing activity of CA3 pyramidal neurons and 5-HT neurons, an effect antagonized by selective 5-HT1A receptor antagonists. Co-application of ergotamine prevented the inhibitory action of 5-HT on the firing activity of CA3 pyramidal neurons but not of 5-HT neurons, indicating that ergotamine acted as a partial 5-HT1A receptor agonist in the dorsal hippocampus and as a full agonist at 5-HT1A autoreceptors. Ergotamine decreased, in a concentration-dependent manner, the electrically evoked release of [3H]5-HT in preloaded rat and guinea pig hypothalamus slices; this effect was prevented by the nonselective 5-HT receptor antagonist methiothepin but not by the selective 5-HT1B/1D receptor antagonist GR 127935 or the alpha 2-adrenoceptor antagonist idazoxan. Although body temperature in humans remained unchanged following inhaled ergotamine, in the rat, subcutaneously injected ergotamine produced a hypothermia that was prevented by a pretreatment with the 5-HT1A/1B receptor/beta-adrenoceptor antagonist pindolol. Finally in humans, ergotamine did not alter prolactin or adrenocorticotropic hormone levels, but increased growth hormone level, which was prevented by pindolol. Cortisol level was increased in humans by ergotamine, but this enhancement was unaltered by pindolol. In conclusion, the present results suggest that ergotamine acted in the rat brain as a 5-HT1A receptor agonist and as an agonist of terminal 5-HT autoreceptor of a yet undefined subtype. In humans, ergotamine also displayed some 5-HT1A receptor activity but, probably because of lack of receptor selectivity, it did not present the same profile as other 5-HT1A receptor agonists.

Possible serotonergic mechanisms underlying the antidepressant and anti-obsessive-compulsive disorder responses.

Considerable evidence is now available to support the pivotal role of the serotonin (5-HT) system is exerting the antidepressant response in humans. Different type of antidepressant treatments enhance 5-HT neurotransmission via different pre- or postsynaptic mechanisms. The time course for the occurrence of these adaptive changes in the brain of laboratory animals is consistent with the delayed onset of the antidepressant response in humans. The drugs effective in obsessive-compulsive disorder (OCD) also enhance 5-HT neurotransmission in brain regions involved in mediating OCD symptoms but with a more prolonged delay, consistently with the larger time necessary to obtain therapeutic effect in OCD than in depression. The elucidation of these mechanisms of action lead to the development of new pharmacologic strategies to potentiate the therapeutic effect of the drugs currently available and the identification of novel targets to accelerate and further improve treatment response in depression and OCD.