The identification, assessment and management of difficult-to-treat depression: An international consensus statement

BACKGROUND

Many depressed patients are not able to achieve or sustain symptom remission despite serial treatment trials - often termed "treatment resistant depression". A broader, perhaps more empathic concept of "difficult-to-treat depression" (DTD) was considered.

METHODS

A consensus group discussed the definition, clinical recognition, assessment and management implications of the DTD heuristic.

RESULTS

The group proposed that DTD be defined as "depression that continues to cause significant burden despite usual treatment efforts". All depression management should include a thorough initial assessment. When DTD is recognized, a regular reassessment that employs a multi-dimensional framework to identify addressable barriers to successful treatment (including patient-, illness- and treatment-related factors) is advised, along with specific recommendations for addressing these factors. The emphasis of treatment, in the first instance, shifts from a goal of remission to optimal symptom control, daily psychosocial functional and quality of life, based on a patient-centred approach with shared decision-making to enhance the timely consideration of all treatment options (including pharmacotherapy, psychotherapy, neurostimulation, etc.) to optimize outcomes when sustained remission is elusive.

LIMITATIONS

The recommended definition and management of DTD is based largely on expert consensus. While DTD would seem to have clinical utility, its specificity and objectivity may be insufficient to define clinical populations for regulatory trial purposes, though DTD could define populations for service provision or phase 4 trials.

CONCLUSIONS

DTD provides a clinically useful conceptualization that implies a search for and remediation of specific patient-, illness- and treatment obstacles to optimizing outcomes of relevance to patients.

Astroglial Control of the Antidepressant-Like Effects of Prefrontal Cortex Deep Brain Stimulation

Although deep brain stimulation (DBS) shows promising efficacy as a therapy for intractable depression, the neurobiological bases underlying its therapeutic action remain largely unknown. The present study was aimed at characterizing the effects of infralimbic prefrontal cortex (IL-PFC) DBS on several pre-clinical markers of the antidepressant-like response and at investigating putative non-neuronal mechanism underlying DBS action. We found that DBS induced an antidepressant-like response that was prevented by IL-PFC neuronal lesion and by adenosine A₁ receptor antagonists including caffeine. Moreover, high frequency DBS induced a rapid increase of hippocampal mitosis and reversed the effects of stress on hippocampal synaptic metaplasticity. In addition, DBS increased spontaneous IL-PFC low-frequency oscillations and both raphe 5-HT firing activity and synaptogenesis. Unambiguously, a local glial lesion counteracted all these neurobiological effects of DBS. Further in vivo electrophysiological results revealed that this astrocytic modulation of DBS involved adenosine A₁ receptors and K⁺ buffering system. Finally, a glial lesion within the site of stimulation failed to counteract the beneficial effects of low frequency (30 Hz) DBS. It is proposed that an unaltered neuronal–glial system constitutes a major prerequisite to optimize antidepressant DBS efficacy. It is also suggested that decreasing frequency could heighten antidepressant response of partial responders.

•

The antidepressant effect of prefrontal cortex DBS was prevented by neuronal lesion and adenosine A₁ receptor antagonists.

•

DBS rapidly increased hippocampal mitosis, cortical oscillations, raphe 5-HT firing activity and synaptogenesis.

•

Local glial lesions prevented the neurobiological effects of DBS in a frequency-dependent manner.

•

Although deep brain stimulation (DBS) is a promising therapy for patients with treatment-resistant depression, the neurobiological bases underlying its therapeutic action remain largely unknown. Here, we demonstrated that DBS produced a robust antidepressant-like effect that was associated with a fast induction of markers of the antidepressant-like response. Unambiguously, the effects of high-frequency, but not low-frequency, DBS were counteracted by a glial lesion within the site of stimulation. Thus, it is proposed that an unaltered neuronal–glial system constitutes a major prerequisite to optimize antidepressant DBS efficacy. It is also suggested that decreasing frequency of DBS could heighten antidepressant response of partial responders.

The effects on children of depressed mothers' remission and relapse over 9 months

BACKGROUND

The high rate of depression among children of depressed mothers is well known. Suggestions that improvement in maternal acute depression has a positive effect on the child have emerged. However, data on the mechanisms of change have been sparse. The aim was to understand how remission and relapse in the mother might explain the changes in the child's outcome.

METHOD

Participants were 76 depressed mothers who entered into a medication clinical trial for depression and 135 of their eligible offspring ages 7-17 years. The mothers and children were assessed at baseline and periodically over 9 months by independent teams to understand the relationship between changes in children's symptoms and functioning and maternal remission or relapse. The main outcome measures were, for mothers, the Hamilton Depression Rating Scale (HAMD), the Social Adjustment Scale (SAS) and the Parental Bonding Instrument (PBI) and, for children, the Children's Depression Inventory (CDI), the Columbia Impairment Scale (CIS), the Multidimensional Anxiety Scale for Children (MASC) and the Children's Global Assessment Scale (CGAS).

RESULTS

Maternal remission was associated with a decrease in the child's depressive symptoms. The mother's subsequent relapse was associated with an increase in the child's symptoms over 9 months. The effect of maternal remission on the child's improvement was partially explained by an improvement in the mother's parenting, particularly the change in the mother's ability to listen and talk to her child, but also reflected in her improvement in parental bonding. These findings could not be explained by the child's treatment.

CONCLUSIONS

A depressed mother's remission is associated with her improvement in parenting and a decrease in her child's symptoms. Her relapse is associated with an increase in her child's symptoms.

Consensus treatment plans for induction therapy of newly diagnosed proliferative lupus nephritis in juvenile systemic lupus erythematosus

OBJECTIVE

To formulate consensus treatment plans (CTPs) for induction therapy of newly diagnosed proliferative lupus nephritis (LN) in juvenile systemic lupus erythematosus (SLE).

METHODS

A structured consensus formation process was employed by the members of the Childhood Arthritis and Rheumatology Research Alliance after considering the existing medical evidence and current treatment approaches.

RESULTS

After an initial Delphi survey (response rate = 70%), a 2-day consensus conference, and 2 followup Delphi surveys (response rates = 63-79%), consensus was achieved for a limited set of CTPs addressing the induction therapy of proliferative LN. These CTPs were developed for prototypical patients defined by eligibility characteristics, and included immunosuppressive therapy with either mycophenolic acid orally twice per day, or intravenous cyclophosphamide once per month at standardized dosages for 6 months. Additionally, the CTPs describe 3 options for standardized use of glucocorticoids, including a primarily oral, a mixed oral/intravenous, and a primarily intravenous regimen. There was consensus on measures of effectiveness and safety of the CTPs. The CTPs were well accepted by the pediatric rheumatology providers treating children with LN, and up to 300 children per year in North America are expected to be candidates for the treatment with the CTPs.

CONCLUSION

CTPs for induction therapy of proliferative LN in juvenile SLE based on the available scientific evidence and pediatric rheumatology group experience have been developed. Consistent use of the CTPs may improve the prognosis of proliferative LN, and support the conduct of comparative effectiveness studies aimed at optimizing therapeutic strategies for proliferative LN in juvenile SLE.

Consensus treatment plans for induction therapy of newly diagnosed proliferative lupus nephritis in juvenile systemic lupus erythematosus

OBJECTIVE

To formulate consensus treatment plans (CTPs) for induction therapy of newly diagnosed proliferative lupus nephritis (LN) in juvenile systemic lupus erythematosus (SLE).

METHODS

A structured consensus formation process was employed by the members of the Childhood Arthritis and Rheumatology Research Alliance after considering the existing medical evidence and current treatment approaches.

RESULTS

After an initial Delphi survey (response rate = 70%), a 2-day consensus conference, and 2 followup Delphi surveys (response rates = 63-79%), consensus was achieved for a limited set of CTPs addressing the induction therapy of proliferative LN. These CTPs were developed for prototypical patients defined by eligibility characteristics, and included immunosuppressive therapy with either mycophenolic acid orally twice per day, or intravenous cyclophosphamide once per month at standardized dosages for 6 months. Additionally, the CTPs describe 3 options for standardized use of glucocorticoids, including a primarily oral, a mixed oral/intravenous, and a primarily intravenous regimen. There was consensus on measures of effectiveness and safety of the CTPs. The CTPs were well accepted by the pediatric rheumatology providers treating children with LN, and up to 300 children per year in North America are expected to be candidates for the treatment with the CTPs.

CONCLUSION

CTPs for induction therapy of proliferative LN in juvenile SLE based on the available scientific evidence and pediatric rheumatology group experience have been developed. Consistent use of the CTPs may improve the prognosis of proliferative LN, and support the conduct of comparative effectiveness studies aimed at optimizing therapeutic strategies for proliferative LN in juvenile SLE.

Electrophysiological effects of the co-administration of escitalopram and bupropion on rat serotonin and norepinephrine neurons

Clinical studies indicate that addition of bupropion to selective serotonin (5-HT) reuptake inhibitors (SSRIs) provides incremental benefit over SSRI monotherapy in depression. This study was designed to investigate the effects of co-administration of bupropion with escitalopram on the firing rate of 5-HT and norepinephrine (NE) neurons in anesthetized rats. Escitalopram (10 mg/kg/day x 2 days), given via subcutaneously (s.c.) implanted minipumps, decreased the firing of 5-HT and NE neurons by 70% and 55%, respectively. The firing of 5-HT neurons, unlike that of NE neurons, recovered after the 14-day escitalopram regimen. Bupropion, injected once daily (30 mg/kg/day, s.c. x 2 days), did not increase 5-HT firing but decreased that of NE by 55%. After 14 days of repeated bupropion administration, 5-HT firing was increased by 50%, and NE firing was back to baseline. Co-administration of escitalopram and bupropion doubled 5-HT firing after 2 and 14 days, whereas NE neurons were inhibited by 60% after 2 days, but partially recovered after 14 days. The responsiveness of 5-HT(1A) autoreceptors was significantly attenuated in the combination-treated rats after 2 days, indicating an early desensitization. These results provide support for contributions from 5-HT and NE mechanisms for enhanced effectiveness of combination of SSRI and bupropion treatment.

Atomoxetine, but not paroxetine, blocks norepinephrine reuptake in depressed patientss

Purpose: Paroxetine is a potent serotonin (5-HT) reuptake inhibitor. However, a purported norepinephrine (NE) reuptake blockade action remains to be established. Atomoxetine is a potent NE reuptake inhibitor with the indication of attention deficit hyperactivity disorder (ADHD). The present study was aimed at confirming a NE reuptake inhibitory action with ascending doses of atomoxetine and possibly with paroxetine in depressed patients. Methods: Patients were randomized to escalating doses of either paroxetine (20 to 50 mg/day), or atomoxetine (25-80 mg/day) in a four to six week period. Inhibition of NE reuptake was assessed using the attenuation of systolic blood pressure (SBP) elevations produced by intravenous injections of tyramine. Tyramine penetrates into peripheral NE terminals via the NE reuptake transporter and releases NE. Then, NE acts on the vascular adrenoceptors, which causes an elevation of SBP. Drugs that block NE reuptake attenuate the pressor effects of tyramine. Two-way ANOVA for repeated measures for doses of tyramine and treatments were used to assess the effects of the different drug regimens on the pressor response to loads of 3–6 mg of tyramine. Sixteen patients with unipolar major depressive disorder were assessed weekly after increasing the dose of paroxetine (9 patients) and atomoxetine (7 patients). Results: Atomoxetine exerted a robust inhibition of the tyramine response, starting at the dose of 25mg/day in a dose-dependent pattern. Neither the low nor the high doses of paroxetine altered the tyramine pressor response. Conclusions: These results provide evidence that atomoxetine started significantly inhibiting NE reuptake at subtherapeutic dose for ADHD, whereas paroxetine leaves the activity of the NE transporter unaltered, even at the highest recommended dose for depression.

Serotonin (1A) receptor ligands act on norepinephrine neuron firing through excitatory amino acid and GABA(A) receptors: a microiontophoretic study in the rat locus coeruleus

It was previously shown that the excitatory effect of the 5-HT(1A) agonist 8-OH-DPAT on firing activity of locus coeruleus (LC) norepinephrine (NE) neurons and the inhibitory action of the 5-HT(1A) antagonist WAY 100,635 are dependent on the presence of 5-HT neurons, whereas the inhibitory action of the 5-HT(2) agonist DOI is not. Using in vivo extracellular unitary recordings performed in anesthetized rats, iontophoretic applications of the excitatory amino acid antagonist kynurenate attenuated the enhancement in firing produced by glutamate and kainate. In contrast, GABA applications decreased the firing activity of NE neurons which was attenuated by the enhancement produced by glutamate and kainate. In contrast, GABA applications decreased the firing activity of NE neurons which was attenuated by the GABA(A) receptor antagonist bicuculline. 8-OH-DPAT (10-60 microg kg(-1), i.v.) produced a dose-dependent enhancement in the firing activity of NE neurons that was abolished in the presence of kynurenate application. The selective 5-HT(1A) receptor antagonist WAY 100,635 (100 microg kg(-1), i.v.) suppressed NE firing which was reversed by the selective 5-HT(2A) antagonist MDL 100,907 (200 microg kg(-1), i.v.). In the presence of bicuculline, the inhibitory effect of WAY 100,635 was blunted. These results suggest that WAY 100,635 mainly attenuates NE neuron firing by blocking inhibitory 5-HT(1A) receptors on glutamatergic neurons, thereby enhancing glutamate release and activating excitatory amino acid receptors, possibly of the kainate subtype, on 5-HT terminals. The ensuing increased 5-HT release would then act on excitatory 5-HT(2A) receptors on GABA neurons that would ultimately mediate the inhibition of NE neurons. The prevention of the excitatory action of 8-OH-DPAT on NE neuron firing by kynurenate is also consistent with this neurocircuitry.

Functional and pharmacological characterization of the modulatory role of serotonin on the firing activity of locus coeruleus norepinephrine neurons

Previous studies, using in vivo extracellular unitary recordings in anaesthetized rats, have shown that the selective 5-HT(1A) receptor antagonist WAY 100,635 suppressed the firing rate of locus coeruleus (LC) norepinephrine (NE) neurons and that this effect was abolished by lesioning 5-HT neurons. In the present experiments, the selective 5-HT(2A) receptor antagonist MDL 100,907, while having no effect on the spontaneous firing activity of LC neurons in controls, was able to restore NE neuronal discharges following the injection of WAY 100,635. The 5-HT(1A) receptor agonist 8-OH-DPAT enhanced the firing activity of NE neurons and this action was entirely dependent on intact 5-HT neurons, unlike the inhibitory effect of the 5-HT(2) receptor agonist DOI. Taken together, these data indicate that 5-HT(2A) but not 5-HT(1A) receptors controlling LC firing activity are postsynaptic to 5-HT neurons. Prolonged, but not subacute, administration of selective 5-HT reuptake inhibitors (SSRIs) produces a decrease in the spontaneous firing activity of LC NE neurons. MDL 100,907 partially reversed this suppressed firing activity of LC neurons in paroxetine-treated rats. Although the alpha(2)-adrenoceptor antagonist idazoxan also enhanced the firing activity of NE neurons in paroxetine-treated rats, this increase was similar to that obtained in controls. In conclusion, prolonged SSRI treatment enhances a tonic inhibitory influence by 5-HT on LC neurons through postsynaptic 5-HT(2A) receptors that are not located on NE neurons. A speculative neuronal circuitry accounting for these phenomena on LC NE activity is proposed.

Effects of the selective norepinephrine reuptake inhibitor reboxetine on norepinephrine and serotonin transmission in the rat hippocampus

Given that norepinephrine (NE) and serotonin (5-HT) neurons are implicated in the mechanisms of action of antidepressant drugs and both project to the hippocampus, the impact of acute and long-term administration of the selective NE inhibitor reboxetine was assessed on CA(3) pyramidal neuron firing in this postsynaptic structure. Cumulative injections of reboxetine (1-4 mg/kg, i.v.) dose-dependently increased the recovery time of the firing of these neurons following iontophoretic applications of NE, but not 5-HT. In rats treated with reboxetine for 2.5 mg/kg/day for 21 days, a robust increase in the recovery time following NE applications was observed, and a small but significant prolongation occurred following 5-HT applications. In controls and reboxetine-treated rats, 1 and 5 Hz stimulations of the afferent 5-HT bundle to the hippocampus, which allows determination of terminal 5-HT(1B) autoreceptor sensitivity, produced similar frequency-dependent decreases in pyramidal neuron firing in both groups. However, after low and high doses of clonidine (10 and 400 microg/kg, i.v.), which assesses alpha(2)-adrenergic auto- and heteroreceptor sensitivity, respectively, only the effect of the high dose of clonidine was attenuated. Interestingly, administration of the selective 5-HT(1A) receptor antagonist WAY 100,635 induced a 140% increase in basal pyramidal neuron firing in reboxetine as compared to saline-treated rats. This increase in tonic activation of postsynaptic 5-HT(1A) receptors might be attributable in part to a desensitization of alpha(2)-adrenergic heteroreceptors, presumably resulting from sustained NE reuptake inhibition. These results indicate that even a selective NE reuptake inhibitor can modulate 5-HT transmission.

Reduction in serotonin synthesis following acute and chronic treatments with paroxetine, a selective serotonin reuptake inhibitor, in rat brain: an autoradiographic study with alpha-[14C]methyl-L-tryptophan(2)

Serotonin (5-HT) synthesis rates were calculated on the basis of the assumption that trapping of alpha-[14C]methyl-L-tryptophan (alpha-[14C]MTrp) is directly related to brain 5-HT synthesis. In the first series of experiments, an acute intraperitoneal injection of paroxetine (10 mg/kg) produced a significant reduction in 5-HT synthesis in brain structures containing serotonergic cell bodies (the dorsal, median, and pallidum raphe nuclei), as well as in most projection areas: the ventral tegmental area, median forebrain bundle, hippocampus CA3 region, and nigrostriatal structures (substantia nigra, lateral and medial caudate nuclei). The reductions in the projection areas were greater (between 25 and 53%) than in those areas containing serotonergic cell bodies (between 18 and 23%). In the cerebral cortex, 5-HT synthesis rates were not modified by acute paroxetine treatment. In a second series of experiments, rats were treated with paroxetine (10 mg/kg/day, s.c., delivered by osmotic minipumps) for 14 days. There was a marked decrease (39-69%) in 5-HT synthesis in every structure examined. In conclusion, the present data suggest that the effects of paroxetine on 5-HT synthesis in the cerebral cortex are different from its effects in the cell body area of the brainstem.

Sustained blockade of neurokinin-1 receptors enhances serotonin neurotransmission

BACKGROUND

Antagonists of neurokinin-1 (NK(1)) receptors, through which substance P acts, have been proposed to belong to a new class of antidepressants with a unique mode of action. It was postulated that they exert this putative therapeutic effect independently of the serotonin (5-HT) neurons.

METHODS

The aim of the present study was to assess, using in vivo electrophysiological paradigms, the effects of sustained administration of the nonpeptidic NK(1) antagonist CP-96,345 on the firing activity of rat dorsal raphe 5-HT neurons, the responsiveness of pre- and postsynaptic 5-HT(1A) receptors, and overall 5-HT neurotransmission in the hippocampus.

RESULTS

Both short- and long-term treatments with CP-96,345 significantly increased the spontaneous firing activity of dorsal raphe 5-HT neurons, and this increase was associated with an attenuation of somatodendritic 5-HT(1A) autoreceptor responsiveness. In contrast, the inactive enantiomer of CP-96,345 at NK(1) receptors, CP-96,344, did not alter these parameters after short-term administration. Because 5-HT(1A) receptor activation inhibits the firing activity of dorsal hippocampus CA(3) pyramidal neurons, the degree of disinhibition produced by the selective 5-HT(1A) receptor antagonist WAY 100635 was determined to assess the net change in 5-HT neurotransmission. Intravenous injection of WAY 100635 did not disinhibit CA(3) pyramidal neuron firing in rats given saline, CP-96,345 for 2 days, or CP-96,344 for 14 days, but produced a significant enhancement of firing in rats treated with CP-96,345 for 2 weeks. Therefore, only long-term treatment with CP-96,345 enhanced the tonic activation of postsynaptic 5-HT(1A) receptors.

CONCLUSIONS

Similar to all other major types of antidepressant treatments, these data indicate that substance P antagonists might alleviate anxiety and major depression, at least in part, by enhancing the degree of activation of some 5-HT receptors in the forebrain.

Response of the norepinephrine system to antidepressant drugs

Environmental stimuli and drugs affect the norepinephrine (NE) system and may be linked to the manifestation and treatment of anxiety and affective disorders. The activity of locus ceruleus NE neurons in the brainstem can alter the function of forebrain structures associated with several psychiatric disorders. In particular, NE neurons send and receive projections from sensory afferents, limbic areas, and cortical areas implicated in higher-order brain malfunctions and the symptomatology of anxiety and affective disorders. In turn, anxiolytic and antidepressant drugs are able to offset perturbations of NE activity and forebrain structures with a time course congruent with their therapeutic action. All antidepressants, even the agents selective for other biogenic amines or peptides, act on the NE system. In the present review, the effects of antidepressants on NE neurons are summarized and applied to the treatment of neuropsychiatric disorders, with emphasis placed on mechanisms of action.

Pharmacology of rapid-onset antidepressant treatment strategies

Although selective serotonin reuptake inhibitors (SSRIs) block serotonin (5-HT) reuptake rapidly, their therapeutic action is delayed. The increase in synaptic 5-HT activates feedback mechanisms mediated by 5-HT1A (cell body) and 5-HT1B (terminal) autoreceptors, which, respectively, reduce the firing in 5-HT neurons and decrease the amount of 5-HT released per action potential resulting in attenuated 5-HT neurotransmission. Long-term treatment desensitizes the inhibitory 5-HT1 autoreceptors, and 5-HT neurotransmission is enhanced. The time course of these events is similar to the delay of clinical action. The addition of pindolol, which blocks 5-HT1A receptors, to SSRI treatment decouples the feedback inhibition of 5-HT neuron firing and accelerates and enhances the antidepressant response. The neuronal circuitry of the 5-HT and norepinephrine (NE) systems and their connections to forebrain areas believed to be involved in depression has been dissected. The firing of 5-HT neurons in the raphe nuclei is driven, at least partly, by alpha1-adrenoceptor-mediated excitatory inputs from NE neurons. Inhibitory alpha2-adrenoceptors on the NE neuroterminals form part of a feedback control mechanism. Mirtazapine, an antagonist at alpha2-adrenoceptors, does not enhance 5-HT neurotransmission directly but disinhibits the NE activation of 5-HT neurons and thereby increases 5-HT neurotransmission by a mechanism that does not require a time-dependent desensitization of receptors. These neurobiological phenomena may underlie the apparently faster onset of action of mirtazapine compared with the SSRIs.

Effect of the selective noradrenergic reuptake inhibitor reboxetine on the firing activity of noradrenaline and serotonin neurons

Reboxetine is a non-tricyclic antidepressant with selective noradrenergic (NA) reuptake-blocking effects. The effects of acute and sustained administration of reboxetine, on the firing activity of locus coeruleus NA neurons and dorsal raphe 5-HT neurons, were assessed using in vivo extracellular unitary recording in rats anaesthetized with chloral hydrate. Reboxetine (0.1-1.25 mg/kg, i.v.) dose-dependently decreased the firing activity of NA neurons (ED50 = 480 +/- 14 microg/kg). A 2-day treatment with reboxetine at 1.25, 2.5, 5, or 10 mg/kg per day (using osmotic minipumps implanted subcutaneously) produced significant decreases of 52%, 68%, 81%, and 83%, respectively, of NA firing activity. When the reboxetine treatment (2.5 mg/kg per day) duration was prolonged to 7 days, a 66% decrease in NA firing activity was observed which further decreased to 80% after 21 days of treatment. In contrast, 5-HT neuron firing rate remained unaltered following short- and long-term reboxetine treatments. The suppressant effect of the alpha2-adrenoceptor agonist clonidine on the firing activity of NA neurons was unchanged in long-term reboxetine-treated rats, but its effect on the firing activity of 5-HT neurons was blunted. The enhancement of NA firing activity by the 5-HT1A agonist 8-OH-DPAT was abolished in long-term reboxetine-treated rats, whereas, the inhibitory effect of the 5-HT2 agonist DOI was attenuated by about three-fold. In conclusion, sustained NA reuptake blockade by reboxetine lead to profound alterations in the function of NA neurons and of 5-HT receptors modulating their firing activity.

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.

Brain Regional alpha-[11C]methyl-L-tryptophan trapping in impulsive subjects with borderline personality disorder

OBJECTIVE

Neurotransmission of serotonin (or 5-hydroxytryptamine [5-HT]) is thought to be disturbed in patients exhibiting impulsive behaviors. However, until recently it has not been possible to test this hypothesis in the brains of living humans.

METHOD

Unidirectional trapping of the 5-HT precursor analog alpha-[(11)C]methyl-L-tryptophan (alpha-[(11)C]MTrp) has been proposed as an index of 5-HT synthesis capacity. The authors measured brain regional alpha-[(11)C]MTrp trapping with positron emission tomography in medication-free subjects with borderline personality disorder (N=13) and a healthy comparison group (N=11). Impulsivity was assessed by using a laboratory measure of behavioral disinhibition, go/no-go commission errors.

RESULTS

Compared to healthy men, the men with borderline personality disorder had significantly lower alpha-[(11)C]MTrp trapping in corticostriatal sites, including the medial frontal gyrus, anterior cingulate gyrus, superior temporal gyrus, and corpus striatum. In the women with borderline personality disorder, significantly lower alpha-[(11)C]MTrp trapping was seen in fewer regions, but in both men and women, negative correlations with impulsivity scores were identified in the medial frontal gyrus, anterior cingulate gyrus, temporal gyrus, and striatum.

CONCLUSIONS

Low 5-HT synthesis capacity in corticostriatal pathways may contribute to the development of impulsive behaviors in persons with borderline personality disorder.

Depressive relapse following acute tryptophan depletion in patients with major depressive disorder

Acute tryptophan depletion (ATD) lowers serotonin synthesis and elicits depressive symptoms in some, though not all, remitted patients with major depressive disorder (MDD). In the present study, eight medication-free remitted patients with MDD, seasonal pattern, were tested twice, once following the ingestion of a tryptophan-containing mixture, once following ATD. ATD significantly increased Hamilton depression scores (p < 0.001). Four of the patients had a family history of psychiatric disorders: substance abuse (n = 4), mood disorders (n = 3) or Cluster B personality disorders (n = 3). The mood-lowering response to ATD was significantly greater in those patients with, than without, affected relatives (p < 0.001). These preliminary findings (1) support the hypothesis that depressed states are related to disturbed serotonin neurotransmission and (2) suggest that depressive symptoms following ATD might identify a subgroup of patients at high genetic risk for disorders associated with affective lability and dysregulated impulse-control, conditions thought to be related to low serotonin neurotransmission.

Modification of norepinephrine and serotonin, but not dopamine, neuron firing by sustained bupropion treatment

RATIONALE

Bupropion is widely used in the treatment of depression and as an anti-craving medication for the cessation of tobacco smoking. Because it is a very weak inhibitor of norepinephrine (NE) and dopamine (DA) reuptake, its mechanisms of action remain to be elucidated.

METHODS

Bupropion was administered subcutaneously via osmotic minipumps over 2 days to determine its effects on the spontaneous firing activity of NE, serotonin (5-HT), and DA neurons in the brain of anaesthetised male Sprague-Dawley rats. This treatment was used in order to obtain levels of the parent compound and its putatively active metabolites that would more adequately reflect the clinical condition than utilizing acute injections.

RESULTS

When given by minipump for 2 days, bupropion produced a dose-dependent attenuation of the mean spontaneous firing NE neurons (7.5 mg/kg per day: 15%; 15 mg/kg per day: 61%; 30 mg/kg per day: 80%) which was reversed by the alpha 2-adrenoceptor antagonist idazoxan. At the highest regimen, the mean firing rate of 5-HT neurons was 100% higher than in control rats, but unaffected in NE-lesioned rats. In contrast, DA neurons in the ventral tegmental area displayed a normal firing rate during the latter bupropion treatment.

CONCLUSIONS

Sustained bupropion administration decreased the firing rate of NE neurons due to an increased activation of their inhibitory somatodendritic alpha 2-adrenoceptors. This effect of the bupropion treatment would be attributable mainly to an enhancement of NE release and not to reuptake inhibition. This contention is based essentially on the observation that NE reuptake blockers leave unaltered the firing rate of 5-HT neurons, whereas bupropion enhanced it via a NE-dependent mechanism. The present study did not put into evidence any DA activity of bupropion at the level of the cell body of mesolimbic/cortical DA neurons at a regimen exerting profound alterations of the firing activity of NE and 5-HT neurons.

Possible neurobiological mechanisms underlying faster onset of antidepressant action

All antidepressant drugs have a delayed onset of action. There is, however, evidence that some agents may attenuate depressive symptoms more rapidly than others. The present review examines the mechanisms by which selective serotonin reuptake inhibitors, the dual 5-HT norepinephrine reuptake inhibitor venlafaxine, and the alpha2-adrenoceptor antagonist mirtazapine alter 5-HT and/or norepinephrine neurotransmission. Particular attention is given to the time course with which these effects manifest themselves in relation to the possibility that these 3 types of drugs may act more rapidly, or exert a greater antidepressant action, than other agents. Based on the effects of antidepressant drugs presently available, strategies to accelerate or augment the antidepressant response are described, some of which have already been examined in patients.

An ideal trial to test differential onset of antidepressant effect

Although various published clinical studies have suggested that some antidepressants may have a more rapid onset of therapeutic effect than others, none of these trials was adequately designed to measure differential time to onset of effect. Thus, existing data do not support claims that one drug reduces the symptoms of depression faster than another. In this article, we propose a study that would be ideal for measuring comparative onset of antidepressant effect. The key features of this ideal trial include (1) a prospective definition of early onset of action, (2) increased frequency of assessment, (3) a data-analytic approach capable of capturing the dynamic nature of symptomatic change, and (4) various strategies to minimize bias and heterogeneity of response.

Modifications of the serotonergic system in mice lacking serotonin transporters: an in vivo electrophysiological study

The serotonin transporter (5-HTT) plays a key role in the regulation of serotonin (5-hydroxytryptamine, 5-HT) transmission in the pathophysiology and therapeutics of several psychiatric disorders. The mean spontaneous firing rate of midbrain dorsal raphe 5-HT neurons was recorded in chloral hydrate-anesthetized mice. The serotonin transporter (5-HTT), which plays a key role in the regulation of serotonin was significantly decreased in homozygous mice lacking the 5-HT transporter (5-HTT -/-) by 66% and in heterozygous (5-HTT +/-) mice by 36% compared with their normal littermates (5-HTT +/+). Systemic injection of the selective 5-HT(1A) receptor antagonist WAY 100635 enhanced 5-HT neuronal firing by 127% in 5-HT -/- mice, thus indicating an enhanced synaptic availability of 5-HT at inhibitory 5-HT(1A) receptors. Nevertheless, the cell body 5-HT(1A) autoreceptors were desensitized in both 5-HTT -/- and 5-HTT +/- mice. At the postsynaptic level, the recovery time (RT(50)) of the firing rate of hippocampus CA(3) pyramidal neurons following iontophoretic applications of 5-HT was significantly prolonged only in 5-HTT -/- mice. The selective 5-HT reuptake inhibitor paroxetine significantly prolonged the RT(50) in 5-HTT +/+ and 5-HTT +/- mice, without altering the maximal inhibitory effect of 5-HT. These neurons in 5-HTT -/- mice showed an attenuated response to the 5-HT(1A) agonist 8-hydroxy-2-diproplyaminotetralin, but not to 5-HT itself. These results establish that the lack of 5-HTT causes a prolonged recovery of firing activity following 5-HT applications. The genetic deletion of the 5-HTT plays a key role on 5-HT(1A) receptor adaptation: a desensitization at pre- and postsynaptic levels in 5-HTT -/- mice, but to a different extent, and only at the presynaptic level in the 5-HTT +/- group.

Genetic and pharmacological disruption of neurokinin 1 receptor function decreases anxiety-related behaviors and increases serotonergic function

Alterations in serotonin (5-hydroxytriptamine, 5-HT), norepinephrine, and gamma-aminobutyric acid have been linked to the pathophysiology of anxiety and depression, and medications that modulate these neurotransmitters are widely used to treat mood disorders. Recently, the neuropeptide substance P (SP) and its receptor, the neurokinin 1 receptor (NK1R), have been proposed as possible targets for new antidepressant and anxiolytic therapies. However, animal and human studies have so far failed to provide a clear consensus on the role of SP in the modulation of emotional states. Here we show that both genetic disruption and acute pharmacological blockade of the NK1R in mice result in a marked reduction of anxiety and stress-related responses. These behavioral changes are paralleled by an increase in the firing rate of 5-HT neurons in the dorsal raphe nucleus, a major source of serotonergic input to the forebrain. NK1R disruption also results in a selective desensitization of 5-HT1A inhibitory autoreceptors, which resembles the effect of sustained antidepressant treatment. Together these results indicate that the SP system powerfully modulates anxiety and suggest that this effect is at least in part mediated by changes in the 5-HT system.

Putative mechanisms of action of antidepressant drugs in affective and anxiety disorders and pain

An enhancement of neurotransmission of serotonin (5-HT), noradrenaline, or both, underlies the antidepressant response associated with most agents presently available to treat major depression. With respect to the 5-HT system, antidepressant drugs exert immediate effects on some neuronal elements controlling overall transmission, but it is the gradual changes in neuronal responses to such treatments that are ultimately responsible for producing their therapeutic benefits. In major depression, an increase in 5-HT1A transmission is thought to be a crucial determinant of the antidepressant response, whereas an enhancement of 5-HT2 transmission in the orbitofrontal cortex may mediate the therapeutic effect of 5-HT reuptake inhibitors in obsessive-compulsive disorder (OCD). The doses of medication and the durations of treatment necessary to obtain these alterations in 5-HT transmission in various brain structures of laboratory animals are fully consistent with the conditions in the clinic necessary to attenuate symptoms in depression and OCD. It is also possible that the relief of chronic pain produced by some antidepressants may be mediated, in part, by the blockade of peripheral 5-HT2A receptors. These observations emphasize the notion that the 5-HT system is endowed with different adaptive properties in various parts of the body, which, in addition to the multiplicity of 5-HT receptors, makes this chemospecific network important in many disorders.

Crosstalk between the norepinephrine and serotonin systems and its role in the antidepressant response

Many behavioural overlaps exist in the effects of norepinephrine (NE), serotonin (5-HT) and dopamine, and it is now thought that complex behaviour patterns may reflect interactions among these neurotransmitters. There is a wide variety of evidence for the pivotal role of the NE system in the pathogenesis and treatment of major depression. This paper discusses the functioning of the NE system, specifically the regulation of neuronal firing and the postsynaptic responses to NE, which can be controlled by norepinephrine reuptake inhibitors and other drugs. In addition, interactions between NE neurons and 5-HT neurons have implications for the treatment of depression and anxiety disorders. Specifically, the projections of 5-HT neurons have an inhibitory effect on NE neurons, which means that selective serotonin reuptake inhibitors also affect the NE system. Further experiments and long-term studies will increase knowledge of the mechanisms of action of various psychopharmacologic agents and may eventually lead to better therapeutic choices.

Role of cholinergic and GABAergic systems in the feedback inhibition of dorsal raphe 5-HT neurons

Several observations indicate that 5-HT1A receptors found on a long neuronal feedback loop, originating from the medial prefrontal cortex, regulate 5-HT neuronal firing. In the present study, the muscarinic (M) receptor antagonists atropine and scopolamine as well as the M2 receptor antagonist AF-DX 116, but not the preferential M1 receptor antagonist pirenzepine, reduced the suppressant effect of the 5-HT1A receptor agonist 8-OH-DPAT on the spontaneous firing activity of rat dorsal raphe 5-HT neurons. Moreover, AF-64A-induced lesions of cholinergic neurons directly in the medial prefrontal cortex and after its i.c.v. injection attenuated the effect of 8-OH-DPAT. Finally, the NMDA receptor antagonist (+)MK-801 and the GABA(B) receptor antagonist SCH-50911, but not the GABA(A) receptor antagonist (-)bicuculline, dampened the latter response. The present study unveiled a key role for the cholinergic and GABAergic systems in the feedback inhibition of dorsal raphe 5-HT neurons.

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 (+/-)pindolol administration on serotonin neurotransmission in rats

OBJECTIVE

Given reports that (+/-)pindolol, a beta-adrenergic-5-HT1A/1B receptor antagonist, accelerates the onset of the therapeutic effect of certain antidepressant drugs in major depression, the aim of this study was to assess the effect of sustained (+/-)pindolol administration on the sensitivity of pre- and postsynaptic 5-HT1A receptors, terminal 5-HT1B autoreceptors and on overall 5-HT neurotransmission.

DESIGN

Prospective animal study.

ANIMALS

Sprague-Dawley rats.

OUTCOME MEASURES

Modifications of the sensitivity of somatodendritic and postsynaptic 5-HT1A receptors using in vivo electrophysiological paradigms in animals treated with vehicle or (+/-)pindolol (20 mg/kg/day, subcutaneously) through osmotic minipumps for 2 weeks.

RESULTS

(+/-)Pindolol attenuated the suppressant effect of the 5-HT autoreceptor agonist lysergic acid diethylamide (LSD) on the firing activity of 5-HT neurons, suggesting that (+/-)pindolol antagonized somatodendritic 5-HT1A autoreceptors in the dorsal raphe nucleus. However, following a 2-day washout period, the suppressant effect of LSD was still attenuated, indicating rather a desensitization of 5-HT1A autoreceptors had occurred. In the CA3 region of the dorsal hippocampus, (+/-)pindolol treatment did not modify the responsiveness of postsynaptic 5-HT1A receptors to microiontophoretic applications of 5-HT. Moreover, such a treatment modified neither the effectiveness of the electrical stimulation of 5-HT fibers nor the function of terminal 5-HT autoreceptors. Finally, the administration of the selective 5-HT1A receptor antagonist WAY 100635 (100 micrograms/kg, intravenously) did not increase the firing activity of dorsal hippocampus CA3 pyramidal neurons in rats treated with (+/-)pindolol, thus failing to reveal the enhanced tonic activation of postsynaptic 5-HT1A receptors associated with major classes of antidepressant treatments.

CONCLUSION

Prolonged administration of (+/-)pindolol by itself is not sufficient to enhance overall 5-HT neurotransmission; pindolol should therefore not be endowed with intrinsic antidepressant activity. Although pindolol is capable of antagonizing the 5-HT1A autoreceptor upon the initiation of a 5-HT reuptake-blocker treatment, it also induces a desensitization of this 5-HT1A autoreceptor, which could explain why patients do not relapse upon its discontinuation when they continue taking a 5-HT reuptake blocker.

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.

A comparison of the effects of acute tryptophan depletion and acute phenylalanine/tyrosine depletion in healthy women

Acute tryptophan depletion (ATD), which is thought to lower serotonin levels, can result in a lowering of mood. In the present study we compared the effect of ATD with acute phenylalanine/tyrosine depletion (APTD) in healthy women. Although considerable evidence relates catecholamines to the regulation of anxiety, there was no difference in anxiety responses in the ATD and APTD groups when the women underwent a mildly stressful psychological challenge. Both ATD and APTD caused a similar lowering of mood. Both depletions also increased heart rate. These results suggest that APTD is a useful method for studying the effect of low catecholamine levels in humans, and that catecholamines are involved in the regulation of mood.

In vivo electrophysiological examination of 5-HT2 responses in 5-HT2C receptor mutant mice

The present study used 5-HT2C receptor mutant mice and their wild-type littermates to characterize the 5-HT2 receptor using the 5-HT2 agonists (+/-)-2-dimethoxy-4-iodoamphetamine hydrochloride (DOI) and 1-(3-chlorophenyl)piperazine (mCPP) applied locally in the orbitofrontal cortex (OFC) and head of the caudate nucleus. Microiontophoretically-applied 5-HT, DOI and mCPP induced current-dependent inhibition of neuronal firing activity in both brain regions. There was no difference between 5-HT2C receptor mutants and wild-type mice in the ability of 5-HT or DOI to inhibit neuronal firing at any current used. In contrast, there was a reduced ability of mCPP to inhibit firing activity in the OFC when ejected at 10 nA. Unexpectedly, there was a small but significant increase in mCPP-induced inhibition in the caudate nucleus of mutant mice. In the OFC, the 5-HT2A antagonist MDL 100907 (2 mg/kg, i.p.) significantly antagonized the effect of both DOI and mCPP. In contrast, the non-selective 5-HT antagonist clozapine (10 mg/kg, i.p.) significantly antagonized only mCPP in the wild-type mice. However, neither MDL 100907 nor clozapine antagonized DOI or mCPP in the caudate nucleus. Finally, it required significantly less quisqualate to activate neurons in the 5-HT2C receptor mutants than in the wild-type mice, suggesting that 5-HT2C receptors serve a tonic inhibitory role in membrane excitability. The present results indicate that the inhibitory action of DOI is predominantly mediated by the 5-HT2A receptor in the OFC. mCPP, when applied locally, inhibits OFC firing activity by acting on both 5-HT2A and 5-HT2C receptors. However, DOI and mCPP might be acting in the caudate nucleus through an atypical 5-HT2 receptor yet to be characterized.

Branchial Na(+)K(+)ATPase activity in brook charr (Salvelinus fontinalis): effect of gonadal development in hypo- and hyperosmotic environments

Changes in gill Na(+)K(+)ATPase activity were examined following the transfer of brook charr (Salvelinus fontinalis) from fresh water (FW) to seawater (SW). Gonadal development was altered at the hatching stage using three doses of ionizing radiation (IR): 6.2, 7.8, and 11.4 Gray (Gy). A non-irradiated control group was also included in the experimental set-up. Following 15 and 19 months of growth in FW, assessment of gill activity in regard to gonadal status (sterile vs. mature) and level of IR exposure was realized by conducting two estuarine challenge tests. A first introduction was performed during June (period of highest osmoregulatory capacities for this species) (summer experiment). A second introduction was conducted during October (period of diminished osmoregulatory capacities) (fall experiment). Gill Na(+)K(+)ATPase activity and water content were measured at different times and two FW control samplings were added in October and January. In the summer experiment (June-December), normal gonadal development of female brook charr was related to reduced gill Na(+)K(+)ATPase activity during the spawning period as compared to sterile fish (4.0+/-1.5 and 7.2+/-1.9 micromole Pi. mg protein(-1). hr(-1)) (P<0.0002). Similar results were not observed in FW conditions, implying that a lack of gonadal growth does not initiate a significant advantage when the osmoregulatory system including the gills are not highly in demand, i.e. in a FW environment. Ionizing radiation exposure of < or =11.4 Gy at the hatching stage had no significant negative or positive effect on Na(+)K(+)ATPase activity either in FW or SW conditions.

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.

Effect of neurokinin-I receptor antagonists on the function of 5-HT and noradrenaline neurons

Substance P antagonists have been proposed to be a new class of antidepressants. The present study aimed to determine the effect of the selective non-peptide rat neurokinin-1 (NK1) receptor antagonists WIN 51,708 and CP-96,345 on the firing activity of rat dorsal raphe serotonin (5-HT) and locus coeruleus noradrenaline (NA) neurons. While WIN51,708 (2mg/kg, i.v.) and CP-96,345 (0.15 mg/kg, i.v.) did not modify the firing activity of 5-HT and NA neurons, both antagonists attenuated the suppressant effect of the alpha2-adrenoceptor agonist clonidine on the firing activity of both types of neurons. In contrast, the responsiveness of 5-HT neurons to the i.v. administration of the 5-HT autoreceptor agonist LSD and the 5-HT1A receptor agonist 8-OH-DPAT remained unchanged. These findings suggest that NK1 receptor antagonists affect markedly the NA system via an attenuation of the function of alpha2-adrenoceptors on the cell body of NA neurons and, consequently, may also modulate 5-HT neurotransmission.

Acute tyrosine depletion and alcohol ingestion in healthy women

BACKGROUND

Recently we reported that, in vervet monkeys, ingestion of an amino acid mixture deficient in the catecholamine precursors, phenylalanine and tyrosine, produced a decrease in alcohol self-administration. We now report the results of a similar study in humans.

METHODS

Three groups of healthy female social drinkers were administered a nutritionally balanced amino acid mixture (B, n = 13), a mixture deficient in the serotonin precursor, tryptophan (Trp-free, n = 14), or a phenylalanine/tyrosine deficient mixture (Phe/Tyr-free, n = 12). Six hours after administration of the amino acid mixture, alcohol ingestion was measured during a free-choice "Taste Test."

RESULTS

Compared to the B mixture, Phe/Tyr-free, but not Trp-free, significantly decreased the ingestion of alcohol [p < 0.02]. Neither Phe/Tyr-free nor Trp-free significantly decreased orange juice ingestion or the self-reported "Liking" of either substance. Some subjects experienced transient nausea and/or regurgitated the amino acid mixtures, but excluding these subjects did not change the results.

CONCLUSIONS

The results suggest that (a) Phe/Tyr-free may be a suitable method for investigating the role of catecholamines in the self-administration and subjective effects of alcohol, (b) acutely decreased catecholamine neurotransmission might disrupt mechanisms mediating alcohol self-administration, and (c) acutely decreased serotonin neurotransmission seems not to alter alcohol self-administration.

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 the beta-adrenoceptor agonist flerobuterol on serotonin synthesis in the rat brain

The influence of 2- and 14-day treatments with flerobuterol, a preferential beta(2)-adrenoceptor agonist, on regional serotonin (5-HT) synthesis in the rat brain was studied by autoradiography using alpha-[(14)C]methyl-L-tryptophan. Flerobuterol was delivered at a rate of 0.5 mg/kg/day using osmotic pumps implanted s.c. The 2-day flerobuterol treatment significantly increased plasma Trp, both free and total, and decreased plasma Leu and Ile. This resulted in a significant increase in the facilitated transport of Trp. There was a significant increase in the synthesis of 5-HT in the 2-day treatment group in the dorsal and median raphe as well as in all postsynaptic structures, with the exception of the hypothalamus. In contrast, after a 14-day treatment, the enhanced facilitated transport of Trp was no longer present, and the increase in the rate of 5-HT synthesis persisted only in the parietal and occipital cortex and the superior colliculus. These data suggest that flerobuterol, similar to other beta-adrenergic agonists, acutely increases 5-HT synthesis, in part, through an elevation of brain Trp availability.

Effects on mood of acute phenylalanine/tyrosine depletion in healthy women

Catecholamines have been implicated in the etiology and pathophysiology of mood and anxiety disorders. In the present study, we investigated the effects of experimentally reducing catecholamine neurotransmission by means of acute phenylalanine/tyrosine depletion (APTD). Healthy female volunteers ingested: (1) a nutritionally balanced amino acid (AA) mixture (n = 14); (2) a mixture deficient in the serotonin precursor, tryptophan (n = 15); or (3) one deficient in the catecholamine precursors, phenylalanine and tyrosine (n = 12). Mood was measured at three times: at baseline and both immediately before and after an aversive psychological challenge (public speaking and mental arithmetic) conducted 5 hours after AA mixture ingestion. Acute tryptophan depletion (ATD) lowered mood and energy and increased irritability scores. These effects were statistically significant only after the psychological challenge. The effect of APTD on mood was similar to that of ATD. APTD did not attenuate the anxiety caused by the psychological challenge. These findings suggest that, in healthy women, reduced serotonin and/or catecholamine neurotransmission increases vulnerability to lowered mood, especially following exposure to aversive psychological events.

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.

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.

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.

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.