Potent and long-lasting potentiation of two 5-hydroxytryptophan- induced effects in mice by three selective 5-ht uptake inhibitors

Neuronal atg1 Coordinates Autophagy Induction and Physiological Adaptations to Balance mTORC1 Signalling

The mTORC1 nutrient-sensing pathway integrates metabolic and endocrine signals into the brain to evoke physiological responses to food deprivation, such as autophagy. Nevertheless, the impact of neuronal mTORC1 activity on neuronal circuits and organismal metabolism remains obscure. Here, we show that mTORC1 inhibition acutely perturbs serotonergic neurotransmission via proteostatic alterations evoked by the autophagy inducer atg1. Neuronal ATG1 alters the intracellular localization of the serotonin transporter, which increases the extracellular serotonin and stimulates the 5HTR7 postsynaptic receptor. 5HTR7 enhances food-searching behaviour and ecdysone-induced catabolism in Drosophila. Along similar lines, the pharmacological inhibition of mTORC1 in zebrafish also stimulates food-searching behaviour via serotonergic activity. These effects occur in parallel with neuronal autophagy induction, irrespective of the autophagic activity and the protein synthesis reduction. In addition, ectopic neuronal atg1 expression enhances catabolism via insulin pathway downregulation, impedes peptidergic secretion, and activates non-cell autonomous cAMP/PKA. The above exert diverse systemic effects on organismal metabolism, development, melanisation, and longevity. We conclude that neuronal atg1 aligns neuronal autophagy induction with distinct physiological modulations, to orchestrate a coordinated physiological response against reduced mTORC1 activity.

The cellular and molecular basis of major depressive disorder: towards a unified model for understanding clinical depression

Major depressive disorder (MDD) is considered a serious public health issue that adversely impacts an individual's quality of life and contributes significantly to the global burden of disease. The clinical heterogeneity that exists among patients limits the ability of MDD to be accurately diagnosed and currently, a symptom-based approach is utilized in many cases. Due to the complex nature of this disorder, and lack of precise knowledge regarding the pathophysiology, effective management is challenging. The aetiology and pathophysiology of MDD remain largely unknown given the complex genetic and environmental interactions that are involved. Nonetheless, the aetiology and pathophysiology of MDD have been the subject of extensive research, and there is a vast body of literature that exists. Here we overview the key hypotheses that have been proposed for the neurobiology of MDD and highlight the need for a unified model, as many of these pathways are integrated. Key pathways discussed include neurotransmission, neuroinflammation, clock gene machinery pathways, oxidative stress, role of neurotrophins, stress response pathways, the endocannabinoid and endovanilloid systems, and the endogenous opioid system. We also describe the current management of MDD, and emerging novel therapies, with particular focus on patients with treatment-resistant depression (TRD).

Paroxetine hydrochloride: polymorphs and solvatomorphs

The polymorphic (crystal systems for which a substance can exist in structures defined by different unit cells, and where each of the forms has the same elemental composition) and solvatomorphic (systems where the crystal structures of the substance are defined by different unit cells, but where these unit cells differ in their elemental composition through the inclusion of one or molecules of solvent) landscape of paroxetine hydrochloride have been critically evaluated in order to learn how many authentic crystal forms have actually been discovered. After a survey of the patent and open literature, it was determined that paroxetine hydrochloride has been crystallized in four genuine nonsolvated polymorphic forms and in four fully characterized solvatomorphic forms.

Chronic citalopram administration causes a sustained suppression of serotonin synthesis in the mouse forebrain

BACKGROUND

Serotonin (5-HT) is a neurotransmitter with important roles in the regulation of neurobehavioral processes, particularly those regulating affect in humans. Drugs that potentiate serotonergic neurotransmission by selectively inhibiting the reuptake of serotonin (SSRIs) are widely used for the treatment of psychiatric disorders. Although the regulation of serotonin synthesis may be an factor in SSRI efficacy, the effect of chronic SSRI administration on 5-HT synthesis is not well understood. Here, we describe effects of chronic administration of the SSRI citalopram (CIT) on 5-HT synthesis and content in the mouse forebrain.

METHODOLOGY/PRINCIPAL FINDINGS

Citalopram was administered continuously to adult male C57BL/6J mice via osmotic minipump for 2 days, 14 days or 28 days. Plasma citalopram levels were found to be within the clinical range. 5-HT synthesis was assessed using the decarboxylase inhibition method. Citalopram administration caused a suppression of 5-HT synthesis at all time points. CIT treatment also caused a reduction in forebrain 5-HIAA content. Following chronic CIT treatment, forebrain 5-HT stores were more sensitive to the depleting effects of acute decarboxylase inhibition.

CONCLUSIONS/SIGNIFICANCE

Taken together, these results demonstrate that chronic citalopram administration causes a sustained suppression of serotonin synthesis in the mouse forebrain. Furthermore, our results indicate that chronic 5-HT reuptake inhibition renders 5-HT brain stores more sensitive to alterations in serotonin synthesis. These results suggest that the regulation of 5-HT synthesis warrants consideration in efforts to develop novel antidepressant strategies.

Localization of the serotonergic terminal fields modulating seizures in the genetically epilepsy-prone rat

Serotonin (5-HT) has been shown to exert antiepileptic effects in a variety of generalized convulsive seizure models, particularly the genetically epilepsy-prone rat (GEPR). The present study was designed to identify the region/site(s) where 5-HT exerts anticonvulsant effects in the GEPR-9, a model in which sound-evoked generalized tonic-clonic seizures (GTCS) are highly sensitive to manipulations in 5-HT concentration. Because the 5-HT reuptake inhibitor, fluoxetine, was known to exert anticonvulsant effects in GEPR-9s via a 5-HT-dependent mechanism, we utilized selective regional 5-HT depletion in combination with systemic fluoxetine administration to find the site where a 5-HT deficit would prevent the anticonvulsant action of fluoxetine. Widespread destruction of serotonergic terminal fields or regionally specific terminal field destruction was achieved using intracerebroventricular and more target specific infusions of 5,7-dihydroxytryptamine. The capacity of fluoxetine to suppress seizures in GEPR-9s following a loss of 5-HT was then examined. The present findings show the anticonvulsant action of fluoxetine is markedly attenuated following the loss of midbrain 5-HT, particularly in the region of the superior colliculus, while forebrain and spinal cord 5-HT do not appear to play a role in the action of fluoxetine. The importance of the deep layers of the SC was confirmed by demonstrating that direct microinfusion of fluoxetine into the SC can suppress seizures in rats pretreated with the 5-HT(1A) receptor antagonist pindolol.

Preclinical pharmacology of F-98214-TA, a novel potent serotonin and norepinephrine uptake inhibitor with antidepressant and anxiolytic properties

RATIONALE

Serotonin (5-HT) and norepinephrine (NE) re-uptake inhibitors (SNRIs) have been proposed to have a higher efficacy and/or faster onset of action than previously available antidepressants.

OBJECTIVES

We examined in biochemical, electrophysiological and behavioural assays the antidepressant properties of (S)-(-)-4-[(3-fluorophenoxy)-phenyl]methyl-piperidine (F-98214-TA), a compound that displays very high affinity for 5-HT and NE transporters.

RESULTS

F-98214-TA potently inhibited the uptake of both 5-HT and NE into rat brain synaptosomes (IC50 = 1.9 and 11.2 nM, respectively) and decreased the electrical activity of dorsal raphe serotonergic neurones (ED50 = 530.3 microg/kg i.v.), an effect completely abolished by the 5-HT(1A) antagonist WAY100,635. In acute behavioural assays in mice, the orally administered compound potentiated the 5-hydroxy-tryptophan (5-HTP)-induced syndrome [minimal effective dose (MED) = 10 mg/kg], antagonized the hypothermia induced by a high dose of apomorphine (ED50 = 2 mg/kg) and reduced the immobility in the tail suspension test (MED = 10 mg/kg). Moreover, it also decreased the immobility in the forced swimming test in mice and rats (30 mg/kg, p.o.). Chronic administration of F-98214-TA (14 days, 30 mg kg(-1) day(-1), p.o.) attenuated the hyperactivity induced by olfactory bulbectomy in rats, confirming its antidepressant-like properties. Interestingly, the same dosage regimen significantly increased the social interaction time in rats, suggesting an additional potential anxiolytic activity. In most assays the compound was more potent than fluoxetine, venlafaxine and desipramine.

CONCLUSIONS

F-98214-TA is a novel SNRI that displays greater potency than other reference antidepressants in animal models predictive of antidepressant and anxiolytic activities.

Paroxetine: a review of its pharmacology, pharmacokinetics and utility in the treatment of a variety of psychiatric disorders

Paroxetine is a selective serotonin re-uptake inhibitor (SSRI). In vitro studies show that it is able to produce a concentration-dependent competitive inhibition of serotonin uptake into brain synaptosomes. This effect can also be demonstrated following in vivo administration of the compound to animals. Paroxetine is almost completely absorbed following oral administration. However, the drug undergoes extensive first pass metabolism. As a result, less than 50% of a single dose of paroxetine reaches the general circulation. Paroxetine is primarily metabolised by the cytochrome P4502D6 isoenzyme. The compound has also been shown to inhibit the activity of this enzyme. As a result, plasma levels of compounds metabolised by the cytochrome P4502D6 isoenzyme can be increased in patients given paroxetine. Paroxetine has been extensively evaluated in clinical studies in depressed patients. The compound shows efficacy superior to placebo, and similar to that obtained with standard tricyclic or tetracyclic agents. Paroxetine also appears to be as efficacious as other SSRIs. The efficacy seen in short-term studies with paroxetine in the treatment of depression is maintained when the drug is given chronically. More recently, paroxetine has been shown to be efficacious in the treatment of panic disorder, obsessive-compulsive disorder, and social anxiety disorder. Nausea, headache and somnolence are the most common adverse events reported by patients given paroxetine. As with other selective serotonin re-uptake inhibitors, a significant percentage of men under therapy with paroxetine report abnormal ejaculation. Paroxetine is well-tolerated by elderly patients, and appears to be associated with few serious adverse events.

Comparison of the effects of antidepressants on norepinephrine and serotonin concentrations in the rat frontal cortex: an in-vivo microdialysis study

The present study employed in-vivo microdialysis techniques in the freely moving rat to systematically compare the neurochemical effects of various antidepressant agents on extracellular concentrations of norepinephrine (NE) and serotonin (5-HT) in the frontal cortex. We found that acute administration of the tricyclic antidepressant, desipramine (3-30 mg/kg, s.c.) and the dual serotonin/norepinephrine reuptake inhibitor, venlafaxine (3-30 mg/kg, s.c.), produced dose-dependent and robust increases in cortical NE concentrations (498% and 403%, respectively). Conversely, acute injection of the selective serotonin reuptake inhibitors, fluoxetine (30 mg/kg, s.c.) and paroxetine (1-10 mg/kg, s.c.), did not alter forebrain NE concentrations. However, paroxetine did produce a significant increase in cortical NE concentrations (164%) when administered at 30 mg/kg. These changes in NE were not paralleled by 5-HT, which showed no increase following administration of desipramine, venlafaxine, paroxetine or fluoxetine. Combination treatment with the 5-HT1A receptor antagonist, WAY-100635 (0.3 mg/kg, s.c.), significantly enhanced extracellular 5-HT concentrations following venlafaxine (10 and 30 mg/kg), fluoxetine (30 mg/kg) and paroxetine (3-30 mg/kg). Alternatively, WAY-100635 produced no augmentation of the antidepressant-induced changes in extracellular NE. Collectively, these studies show that paroxetine, at low to intermediate doses, and fluoxetine are selective for 5-HT versus NE systems, whereas venlafaxine produces similar effects on both 5-HT and NE levels at the effective doses tested.

Effect of a selective 5-hydroxytryptamine reuptake inhibitor on brain extracellular noradrenaline: microdialysis studies using paroxetine

The clinical efficacy of selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitors (SSRIs) is normally attributed to their ability to increase brain 5-HT function although recent preclinical findings indicate that their selectivity for 5-HT over noradrenaline may be less evident in vivo. The present study investigated the effects of the SSRI, paroxetine, on extracellular levels of noradrenaline. Microdialysis was carried out in the hippocampus of the awake rat. In rats treated twice daily for 14 days with paroxetine (5 mg/kg s.c.), dialysate levels of noradrenaline showed a maintained two-fold increase compared to saline-injected controls. Paroxetine (5 mg/kg s.c.) administered once daily for 14 days did not cause a sustained increase in noradrenaline but levels showed a moderate (+58%) increase in response to a paroxetine challenge. Acute injection of paroxetine (5 mg/kg s.c.) did not elevate noradrenaline levels. Paroxetine (5 mg/kg s.c.) elevated dialysate 5-HT after both acute and repeated (twice daily for 14 days) treatment. The paroxetine-induced increase in noradrenaline (and 5-HT) was positively correlated with plasma concentrations of the drug, which were around the therapeutic range. In comparison to paroxetine, desipramine (10 mg/kg s.c.) caused a four-fold increase in dialysate noradrenaline (but did not change 5-HT) following repeated (once daily for 14 days) treatment and a two-fold increase at for acute treatment. In summary, despite its selectivity as a 5-HT reuptake inhibitor, paroxetine increased extracellular levels of noradrenaline in rat hippocampus following repeated administration. We discuss the possibility that a facilitation of noradrenaline function might be involved in the antidepressant effect of paroxetine, and possibly other SSRIs.

Psychopharmacological profile of the selective serotonin reuptake inhibitor, paroxetine: implication of noradrenergic and serotonergic mechanisms

The present study was designed to evaluate the psychopharmacological profile of the selective serotonin reuptake inhibitor paroxetine, and thus assess potential noradrenergic and/or serotonergic activity. Paroxetine dose-dependently increased mobility time in the mouse forced swimming test (8, 16, 32 and 64 mg/kg, i.p.) and reduced spontaneous locomotor activity when administered at a high dose (64 mg/kg, i.p.). Prior administration of 8-hydroxy-2-(di-n-propylamino)tetralin (1 mg/kg, i.p.), (+/-) pindolol (32 mg/kg, i.p.) or 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridyl)-1H-indole (RU 24969) (1 mg/kg, i.p.) potentiated the antidepressant-like effects of subactive doses of paroxetine (1, 2 and 4 mg/kg, i.p.) in the mouse forced swimming test. These effects were antagonized by prior administration of 1-(2-methoxyphenyl)-4-[-(2-phthalimido)butyl]piperazine) (0.5 mg/kg, i.p.). Complementary studies suggested that RU24969-induced anti-immobility effects were a result of an increase in locomotor activity; other interactions were without increase/decrease in locomotor activity. Acute administration of paroxetine (8, 16, and 32 mg/kg, i.p.) antagonized the hypothermia induced by the D2/D1 receptor agonist, apomorphine (16 mg/kg, s.c.), while repeated treatment with paroxetine (32 mg/kg) attenuated clonidine-induced (0.5 mg/kg, i.p.) hypothermia. Pre-treatment with the serotonergic neurotoxin, para-chlorophenylalanine attenuated the anti-immobility effects of low doses of paroxetine (8 and 16 mg/kg, i.p.) in the forced swimming test, whereas a higher dose of paroxetine remained active (32 mg/kg, i.p.). The results of the present study indicated that paroxetine displayed both noradrenergic-like and serotonergic-like activity in the pre-clinical psychopharmacological tests employed.

Crucial role for 5-HT in cholera toxin but not Escherichia coli heat-labile enterotoxin-intestinal secretion in rats

BACKGROUND & AIMS

Many consider cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT) to be functionally identical. Both increase intracellular adenosine 3',5'-cyclic monophosphate concentration; however, differences between the two and the severity of the diseases they cause have been reported. The secretagogue 5-hydroxytryptamine (5-HT) is implicated in CT-induced secretion, but its role in LT-induced secretion is unclear. We tested the hypothesis that LT fails to recruit 5-HT in its secretory processes.

METHODS

In vivo small intestinal perfusions were undertaken in adult male Wistar rats after incubation with equipotent doses of CT or LT, or saline. Small intestinal 5-HT release and the effect on net small intestinal water and electrolyte transport of (1) pharmacological depletion of 5-HT; (2) blockade of 5-HT type 2, 3, and 4 receptors; and (3) pretreatment with lidocaine, hexamethonium, and atropine were determined.

RESULTS

CT- but not LT-induced secretion was accompanied by 5-HT release, reduced by 5-HT depletion, and inhibited by each 5-HT antagonist. By contrast, lidocaine and hexamethonium inhibited secretion induced by both toxins.

CONCLUSIONS

LT induces secretion without recruiting a 5-HT-dependent cascade. This may account for differences in clinical severity of the diseases CT and LT cause and has implications for the development of antisecretory therapies.

Effects of carbamazepine on hippocampal serotonergic system

To establish the mechanism of action of the antiepileptic and psychotropic effects of carbamazepine (CBZ), its effects on serotonin (5-HT) transmission, metabolism and re-uptake activity in the rat hippocampus were studied. After acute and chronic administrations of 25 mg/kg CBZ, the plasma concentration of CBZ was found to be within the therapeutic range, whereas both acute and chronic administrations of 50 and 100 mg/kg CBZ resulted in a supratherapeutic plasma concentration. Acute administration of the therapeutic dose of CBZ resulted in an increase in the hippocampal extracellular and total level of 5-HT, its metabolite, 5-hydroxydoleacetic acid (5-HIAA) and its precursor, 5-hydroxytryptophan (5-HTP). The acute administration of 50 mg/kg CBZ resulted in an increase in the hippocampal levels of extracellular 5-HT and 5-HIAA as well as in the total levels of 5-HTP, whereas hippocampal levels of extracellular 5-HTP, total 5-HT and 5-HIAA remained unaffected. CBZ at a dose of 100 mg/kg decreased the levels of all of these substances. After chronic administration, 25 mg/kg/day CBZ increased hippocampal total levels of 5-HT, 5-HTP and 5-HIAA, whereas 100 mg/kg/day CBZ decreased all of these total levels. CBZ at a dose of 50 mg/kg/day decreased total levels of 5-HT, however neither total levels of 5-HIAA nor 5-HTP were affected. Both therapeutic and supratherapeutic plasma concentrations of CBZ inhibited 5-HTP accumulation, and did not affect 5-HT re-uptake activity in vitro. These results suggest that a therapeutic concentration of CBZ enhances 5-HT turnover and transmission, whereas a supratherapeutic concentration of CBZ inhibits 5-HT turnover and transmission without affecting 5-HT re-uptake activity. These effects of CBZ on serotonergic systems may be, at least partially, involved in the mechanisms of action of CBZ.

Evaluation of the neuropharmacodynamics of paroxetine in vivo utilizing microdialysis

The effect of paroxetine, a selective serotonin reuptake inhibitor used in the treatment of depression, on extracellular serotonin levels was evaluated in freely moving conscious rats. Microdialysis, a powerful in vivo technique to monitor the extracellular levels of neurotransmitters, was used to monitor the baseline changes in the levels of serotonin in rat brain anterior lateral striatum post paroxetine administration, which is a measure of the neuropharmacodynamic effect of the drug. Microdialysis sampling was performed for 210 min prior to and for 240 min after intraperitoneal administration of paroxetine (10 mg/kg). Paroxetine caused a statistically significant increase in the extracellular levels of serotonin in the anterior lateral striatum sampled by microdialysis. The present study demonstrates the utility of microdialysis for studying the in vivo neuropharmacodynamics of paroxetine in conscious rats.

Simultaneous measurement of serotonin and paroxetine in rat brain microdialysate by a single-pump column-switching technique

Simultaneous quantitation of paroxetine and serotonin in rat brain microdialysate is presented as a means to study the neuropharmacokinetics and neuropharmacodynamics of paroxetine, a selective serotonin reuptake inhibitor. In order to achieve this objective, a single-pump column-switching technique was developed. Optimization of the mobile phase in terms of the concentration of ion-pairing agent, pH of mobile phase, temperature of the stationary phase and concentration of organic modifier was investigated and a single mobile phase was developed for both separations. The design was such that the switching valve employed column I (50 mm length) and column II (250 mm length) in series in position A. At 15.3 min, the valve was switched to position B, in which the flow of the mobile phase was directed only through the short column (column I). A flow gradient program was used to increase the flow-rate from 0.125 ml/min to 0.4 ml/min, which enabled a reduction in total analysis time to less than 20 min. The limits of detection for serotonin and paroxetine were 6 fmol and 300 fmol, respectively. The accuracy of the method demonstrated percent differences from spiked samples that were within 12.5% and the precision was found to be within 10% R.S.D.

An autoradiographic study of dextromethorphan high-affinity binding sites in rat brain: sodium-dependency and colocalization with paroxetine

1. The distribution and some pharmacological properties of centrally located dextromethorphan high-affinity binding sites were investigated by in vitro autoradiography. 2. Sodium chloride (50 mM) induced a 7 to 12 fold increase in dextromethorphan binding to rat brain in all areas tested. The effect of sodium was concentration-dependent with a higher dose (120 mM) exerting a smaller effect on binding. 3. [3H]-dextromethorphan binding in the presence of sodium was inhibited in the presence of the anticonvulsant phenytoin at a concentration of 100 microM, while the sigma ligand (+)-3-(-3-hydroxyphenyl)-N-(1-propyl)pipendine ((+)-PPP) had no effect on the binding, suggesting an interaction with the DM2 site. 4. The distribution of the sodium-dependent binding identified in this study correlated significantly with the distribution of the selective 5-HT uptake inhibitor [3H]-paroxetine, and paroxetine and dextromethorphan mutually displaced their binding at concentrations in the low nanomolar range. 5. These data show that dextromethorphan and paroxetine share a sodium-dependent high affinity binding site in rat brain, and suggest that dextromethorphan might interact, in the presence of sodium, with the 5-HT uptake mechanism in rat brain.

The anticonvulsant action of fluoxetine in substantia nigra is dependent upon endogenous serotonin

Fluoxetine, a serotonin (5-HT) reuptake inhibitor, has been documented to exert a protective action against convulsive seizures in animal models, when administered either systemically, or focally into substantia nigra. It is likely that the mechanism of anticonvulsant action of fluoxetine is due to an enhancement of endogenous 5-HT transmission. To evaluate this possibility in the context of the anticonvulsant action of intranigral fluoxetine, we examined the influence of 5-HT-mediated transmission in substantia nigra on seizure susceptibility in a rat model of focally evoked complex partial seizures. In addition to fluoxetine (3.5 nmol), we found that the directly acting 5-HT receptor agonists, 1-[3-(trifluoromethyl)phenyl]piperazine (TFMPP) (10 nmol), 1-(3-chlorophenyl)piperazine (m-CPP) (7.4 nmol), gepirone (70 nmol) and 2-dipropylamino-8-hydroxy-1,2,3,4-tetrahydronaphthalene hydrobromide (8-OH-DPAT) (10 nmol), when microinjected bilaterally into substantia nigra, protected rats from limbic motor seizures evoked focally from area tempestas, an epileptogenic site in the deep rostral piriform cortex. This indicates that multiple 5-HT receptor subtypes in substantia nigra may contribute to seizure regulation. Consistent with this, the 5-HT antagonist, metergoline, partially reversed the anticonvulsant action of intranigral fluoxetine. Depletion of endogenous 5-HT, by pretreatment with parachlorophenylalanine (PCPA), completely prevented the anticonvulsant action of intranigral fluoxetine, without modifying the anticonvulsant effect of intranigral TFMPP. These findings support the proposal that the anticonvulsant action of fluoxetine in substantia nigra is due to an enhancement of the synaptic action of endogenous 5-HT in substantia nigra which in turn is mediated via multiple 5-HT receptors. Endogenous 5-HT transmission in substantia nigra is therefore capable of limiting the development and propagation of seizure activity generated in limbic circuits.

Abnormalities in brain serotonin concentration, high-affinity uptake, and tryptophan hydroxylase activity in severe-seizure genetically epilepsy-prone rats

We characterized the nature of the deficit in brain serotonin (5-HT) exhibited by genetically epilepsy-prone rats (GEPR-9s) by regionally assessing three markers for 5-HT terminals/neurons (5-HT content, 5-HT uptake into the P2-synaptosomal fraction, and tryptophan hydroxylase activity) in GEPR-9s and nonepileptic control rats. As compared with controls, GEPR-9s had reduced brain 5-HT concentration, synaptosomal 5-HT uptake, and tryptophan hydroxylase activity (measured in vivo and in vitro) in most regions of the forebrain and in selected regions of brainstem. Analysis of kinetic constants for synaptosomal [(3)H]5-HT uptake and in vitro tryptophan hydroxylase activity showed that the decrements in these parameters exhibited by GEPR-9s resulted from reductions in V(max) rather than changes in K(m). In general, the reduction in each of the presynaptic markers for 5-HT terminals/neurons was similar in both magnitude and in their regional distribution in the GEPR-9 brain. An exception to this was noted in the midbrain tegmentum of GEPR-9s, which displayed a significant reduction in tryptophan hydroxylase activity without showing alterations in 5-HT concentration or in high-affinity 5-HT uptake. The present findings support the hypothesis that there is a widespread reduction in the number of serotonergic/neurons in GEPR-9 brain.

Multicenter double blind study of paroxetine and amitriptyline in elderly depressed inpatients

Paroxetine is a phenylpiperidine compound which is a selective serotonin reuptake inhibitor (SSRI). Ninety-one hospitalised patients with a major depression (DSM-III) aged 65 and over from six Austrian and one German center were entered into the study, which compared the efficacy and tolerability of paroxetine versus amitriptyline. After 6 weeks both groups showed similarly good therapeutic results. In the paroxetine group, 64.3% of the patients had a 50% or more reduction of the HAMD total score compared to 58.1% in the amitriptyline group. Side effects were distributed similarly in both groups. Patients in the paroxetine group showed a higher incidence of anxiety and agitation; anticholinergic side effects were registered more often in the amitriptyline group.

Synthesis of 4'-iodo-5-methoxy-valerophenone O-(2-aminoethyl)oxime as an agent for exploration of serotoninergic transporter

The serotonin reuptake process is observed in the central nervous system and in cells derived from the neural crest. It would therefore be of great interest to visualize this reuptake for brain exploration and to visualize the tumors derived from these cells (Apudome). Fluvoxamine has been described as a specific uptake inhibitor for serotonin uptake and we therefore supposed that an iodinated derivative of this compound would be a suitable tracer for this purpose. We had shown by computer-assisted investigation that the trifluoromethyl group of fluvoxamine can be replaced by iodine without changing the steric hindrance of the structure. We therefore expected that this result would allow the development of a new iodinated ligand for human exploration by SPECT which would inhibit for the serotoninergic transporter. This new ligand is 4'-iodo-5-methoxyvalerophenone O-(2-aminoethyl)oxime in its E configuration. In vitro binding studies demonstrated that this iodinated ligand has a weaker affinity for the serotonin uptake sites than fluvoxamine. Steric hindrance is not sufficient to predict affinity, other structural factors such as electronic density and dipole moment must be considered to explain the biological difference between fluvoxamine and its iodinated analog.

Serotonin uptake inhibitors: uses in clinical therapy and in laboratory research

Fluoxetine, zimelidine, sertraline, paroxetine, fluvoxamine, indalpine and citalopram are the selective inhibitors of serotonin uptake that have been most widely studied. Some of these compounds are or have been used clinically in the treatment of mental depression, obsessive-compulsive disorder and bulimia, and therapeutic benefit has been claimed in additional diseases as well. By blocking the membrane uptake carrier which transports serotonin from the extracellular space to inside the serotonin nerve terminals, these compounds increase extracellular concentrations of serotonin and amplify signals sent by serotonin neurons. Because serotonin neurons are widespread in the central nervous system, the functional consequences of blocking serotonin uptake are diverse, but are generally subtle. Animals treated with serotonin uptake inhibitors look normal in gross appearance, but effects such as reduced aggressive behavior, decreased food intake and altered food selection, analgesia, anticonvulsant activity, endocrine changes and neurochemical changes have been demonstrated and characterized. Serotonin uptake inhibitors have helped in revealing some dynamics of serotonin neurons; for example, when uptake is inhibited and extracellular serotonin concentration increases, presynaptic as well as postsynaptic receptors for serotonin are activated to a greater degree. A consequence of increased activation of autoreceptors on serotonin cell bodies and nerve terminals is a reduction in firing of serotonin neurons and a decrease in serotonin synthesis and release. The result is a limit on the degree to which extracellular serotonin and serotonergic neurotransmission are increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of potentiation of anticonvulsant effect by fluoxetine in drug-resistant epilepsy

To test the hypothesis that fluoxetine may be a useful adjunct to antiepileptic therapy, we treated with fluoxetine (20-40 mg/day) nine patients suffering from medically intractable epilepsy with daily seizures. Five patients remained unchanged and four worsened. Worsening was more evident at 40 mg/day. One patient improved when receiving the lower dose (20 mg/day) and worsened with the higher dose (40 mg/day). These data suggest: (1) that fluoxetine is not effective as add-on antiepileptic treatment; (2) that caution should be exerted when using fluoxetine as an antidepressive treatment in epileptic patients.

Occupancy of the serotonin transporter by fluoxetine, paroxetine, and sertraline: in vivo studies with [125I]RTI-55

[125I]RTI-55 was used tracer doses to label serotonin (5-HT) transporters in vivo in the mouse brain. Fluoxetine, paroxetine, and sertraline, potent antidepressants and selective inhibitors of serotonin transporter sites, were administered in various doses and at various times. The doses and times that result in significant binding of the drugs to transporters correspond to doses and times where they are reported to have physiological effects. Estimates of occupancy rate and duration of binding to serotonin transporters were made. The rate of occupancy of the 5-HT transporter site was fastest for sertraline, intermediate for paroxetine and slowest for fluoxetine. Similarly, the duration of occupancy was significantly shorter for sertraline and paroxetine (approximately 10 h) than for fluoxetine (approximately 50 h). The results indicate that in competition studies, [125I]RTI-55 can be used to identify doses of drugs that are physiologically effective, to determine their relative rate of occupancy, and most importantly, to measure the residency time on the central serotonin transporter in vivo.

Platelet 3H-paroxetine binding in control subjects and depressed patients: relationship to serotonin uptake and age

3H-paroxetine is regarded as a better ligand for the serotonin (5-hydroxytryptamine; 5-HT) uptake site than 3H-imipramine. In the present study, platelet 14C-5-HT uptake and 3H-paroxetine binding were simultaneously measured in 12 control subjects. There was a significant positive correlation between the individual Bmax value for 3H-paroxetine binding and the Vmax value for 14C-5-HT uptake. Platelet 3H-paroxetine binding was also determined in 21 drug-free patients who satisfied DSM-III-R criteria for major depression and 21 control subjects. A negative correlation was found between the Bmax values for 3H-paroxetine binding with age in control subjects. There was no change in 3H-paroxetine binding in depressed patients compared with control subjects. Our results indicated that 3H-paroxetine was a good ligand for evaluating 5-HT uptake sites, and the influence of age ought to be taken into consideration in the study of 3H-paroxetine binding. The present study indicated that there was no change in 5-HT uptake sites in platelets from depressed patients.

[3H]paroxetine and [3H]citalopram as markers of the human brain 5-HT uptake site: a comparison study

The binding of [3H]paroxetine and [3H]citalopram to the human brain serotonin (5-HT) uptake site has been characterized and compared. Our results reveal that the binding exclusively involved with the 5-HT uptake site is identical for both [3H]ligands. The selective 5-HT uptake inhibitor citalopram displays the highest affinity for this uptake site, as compared with the affinities obtained for desipramine and norzimeldine, which is in accordance with their respective blockage of 5-HT uptake. Similar Bmax values were obtained for both radioligands in the brain regions studied, indicating their binding to the same presynaptic membrane protein. Together these findings suggest that both [3H]paroxetine and [3H]citalopram are good markers of the 5-HT transporter as both bind selectively and with high affinity to the serotonin uptake sites. However, the higher affinity of [3H]paroxetine confirms that this compound is the best radioligand for the 5-HT uptake site available today.

Paroxetine: a selective serotonin reuptake inhibiting antidepressant

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical investigations, adverse effects, and dosing strategies of paroxetine as a treatment of major depression.

DATA SOURCES

Specific paroxetine information was selected from a MEDLINE search using paroxetine as the search term. Other sources included manual searches of pertinent journal article references, meeting abstracts, and the manufacturer.

STUDY SELECTION

Clinical investigations with a blind, controlled (placebo and/or active), randomized design were selected. With the exception of treatment-resistant depression, no short-term, open investigations were selected.

DATA EXTRACTION

Clinical investigations were evaluated for design, sample size, diagnosis, duration, definition of response, and outcome. Data from all investigations were selected by one author and reviewed by both authors.

DATA SYNTHESIS

Paroxetine is a selective serotonin reuptake inhibitor (SSRI) recently approved for the treatment of major depression. It is a potent and selective inhibitor of serotonin reuptake and has weak or no activity on the other monoamines; it is also weakly anticholinergic. Although pharmacokinetic parameters are variable, paroxetine is generally well absorbed, highly protein bound, hepatically cleared, and has no active metabolites. Clinical investigations support paroxetine's effectiveness as an antidepressant in an outpatient population with moderately severe depression. Its effectiveness is superior to that of placebo and is comparable to that of active controls. The majority of investigations have been six weeks in duration. Additional data are required to support paroxetine's promise for longer treatment periods (i.e., > or = 1 y), in the elderly, and for treatment-resistant depression. Adverse effects appear to be similar to those caused by the other SSRIs; some of the most common are nausea, diarrhea, insomnia, dry mouth, and nervousness. Significant drug interactions may occur with the monoamine oxidase inhibitors, phenobarbital, and phenytoin.

CONCLUSIONS

Paroxetine is safe and effective for treatment of outpatients with moderately severe depression. Further clinical data and experience are necessary to determine this agent's place in the long-term treatment of major depression.

Fluoxetine, a selective serotonin-uptake inhibitor, enhances the anticonvulsant effects of phenytoin, carbamazepine, and ameltolide (LY201116)

Dose-response curves for the prototypical anticonvulsants phenytoin (PHT) and carbamazepine (CBZ), and a novel anticonvulsant, ameltolide (LY201116), were determined with and without pretreatment with the selective serotonin-uptake inhibitor fluoxetine by maximal electroshock seizure (MES) test in mice. Fluoxetine (2.5, 5, and 10 mg/kg intraperitoneally, i.p.) produced a dose-related decrease in the ED50 values for the anticonvulsants (i.p. administration) to protect against MES-induced tonic-extensor seizures. Fluoxetine (10 mg/kg i.p.) also decreased the intravenous (i.v.) ED50 doses of the three anticonvulsants by a factor of approximately 2. These data suggest that fluoxetine, through its selective inhibition of serotonergic reuptake, may have beneficial advantages as compared with common antidepressant drugs in treatment of depressed patients with epilepsy and may also enhance the seizure control of prototypical anticonvulsants in treatment of epilepsy.

Cloning and expression of a functional serotonin transporter from rat brain

Selective antagonism of serotonin (5-hydroxytryptamine, 5HT) and noradrenaline transport by antidepressants is a key element in the 'amine' hypothesis of affective disorders. Uptake and/or transport sites of 5HT have been reported to be reduced in platelets of patients suffering from depression and in post-mortem brain samples of depressed patients and suicide victims. To date there has been little molecular information available on the structure and regulation of 5HT transporters. Using the polymerase chain reaction with degenerate oligonucleotides derived from two highly conserved regions of the transporters for noradrenaline and gamma-aminobutyric acid (GABA), we have identified a large family of related gene products expressed in rodent brain. One of these products hybridizes to a single 3.7-kilobase RNA restricted to rat midbrain and brainstem, where it is highly enriched within the serotonergic raphe complex. Transfection with a single 2.3-kilobase brainstem complementary DNA clone is sufficient to confer expression of a Na(+)-dependent 5HT transporter upon nonneural cells, with transport selectively and potently antagonized by 5HT uptake-specific antidepressants, including paroxetine, citalopram and fluoxetine.

3H-paroxetine binding in brains of alcoholics

High affinity 3H-paroxetine binding was studied in human frontal cortex and hippocampus obtained from normal controls and alcoholics. On the basis of Scatchard analyses, a significant decrease in the maximal number of binding sites (Bmax) was found in the hippocampus of alcoholics (n = 8) as compared with that of controls (n = 10) (mean +/- SD = 63 +/- 35 vs. 114 +/- 70 fmoles/mg protein). There was no significant difference in the dissociation constants (Kd) between the two groups. The presumed effect of chronic alcohol abuse on 3H-paroxetine binding may be region-specific since no significant difference in either Bmax or Kd for 3H-paroxetine binding was found in the frontal cortex between normal controls and alcoholics. No significant correlation of 3H-paroxetine binding with age or postmortem interval was observed. The decrease in 3H-paroxetine binding in the hippocampus of alcoholics is probably indicative of reduced density of serotonergic nerve terminals either as a preexisting condition or as a result of neuronal damage caused by ethanol or the sequelae of alcoholism, such as nutritional deficiencies.

Citalopram. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in depressive illness

Citalopram is an antidepressant belonging to a new class of drugs which enhance serotoninergic neurotransmission through potent and selective inhibition of serotonin reuptake. Preliminary trials suggest that its short term therapeutic efficacy is significantly greater than that of placebo and mianserin, and comparable to that of amitriptyline, maprotiline and imipramine. It appears to be a weaker antidepressant agent than clomipramine, but better tolerated. Its elimination half-life of 33 hours permits once daily oral administration. Symptomatic improvement obtained with short term treatment has been maintained when therapy has been extended for up to 1 year; in the few patients studied for this extended period, the relapse rate was lower than with fluvoxamine, fluoxetine or imipramine. Compared to standard antidepressant agents, citalopram is well tolerated. It does not appear to be cardiotoxic, has not been associated with seizures in humans, and is relatively nonsedating. Unlike the tricyclic antidepressants, citalopram has minimal anticholinergic effects. Mild and transient nausea, with or without vomiting, is the most frequent adverse effect--occurring in 20% of patients--and increased perspiration, headache, dry mouth, tremor and insomnia are experienced by 15 to 18% of patients. Citalopram thus offers similar therapeutic efficacy and a more favourable tolerability profile than the tricyclic antidepressants. Preliminary data suggest that it may be particularly useful in patients who cannot tolerate the anticholinergic or cardiovascular side effects of tricyclic antidepressants and in those for whom sedation is not indicated.

Paroxetine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in depressive illness

Paroxetine is a potent and selective inhibitor of the neuronal reuptake of serotonin, thereby facilitating serotoninergic transmission; this action appears to account for the antidepressant activity observed with this drug. A mean terminal elimination half-life of approximately 24 hours permits once daily administration. Results of short term clinical trials have shown paroxetine to be significantly superior to placebo, and comparable to amitriptyline, clomipramine, imipramine, dothiepin and mianserin in relieving symptoms associated with major depressive disorders. Paroxetine has shown some preliminary promise in the treatment of depressive illness resistant to tricyclic antidepressant therapy but further studies are required before any conclusions can be drawn. Paroxetine in therapeutic doses has been very well tolerated, and the favourable tolerability profile of this agent appears to be its primary advantage over traditional antidepressant agents. Paroxetine causes minimal anticholinergic-type adverse effects, and unlike tricyclic antidepressants, it does not precipitate cardiovascular effects or provoke cardiac conduction disturbances. Nausea has been the most frequently reported adverse event during short term use of paroxetine, but it is generally mild and transient and subsides with continued use. With longer term use headache, sweating and constipation were the most frequently reported side effects but the incidence rate was not significantly different from that noted for comparator antidepressants. Furthermore, the frequency of withdrawal due to adverse effects is less with paroxetine than with tricyclic antidepressant agents. Overall, available data appear to indicate that while the efficacy of paroxetine is similar to that of traditional antidepressant drugs, the newer agent possesses much improved tolerability. In addition, the wide therapeutic index of paroxetine may be beneficial when treating patients with an increased risk of suicide. Thus, paroxetine clearly looks to become a valuable addition to the range of drugs currently available to treat depressive illness. Future research may help to further define the relative place of this newer agent in antidepressant therapy and determine how its overall therapeutic efficacy compares with that of other related antidepressant agents such as fluoxetine.

Synthesis of a selective serotonin uptake inhibitor: [11C]citalopram

Citalopram, a selective serotonin uptake inhibitor, was labeled with 11C for non-invasive in vivo studies of serotonin uptake sites in the human brain using positron emission tomography. The synthesis was completed in approximately 17 min using [11C]methyl iodide as the precursor. The synthesis, purification, characterization, and determination of specific activity are described.

An overview of the animal pharmacology of paroxetine

Animal studies show that paroxetine is a potent and selective inhibitor of 5-hydroxytryptamine (5-HT) neuronal uptake. It shows excellent activity after oral administration, and pharmacological studies on its principal metabolites indicate that they are much less active than the parent compound. Paroxetine possesses no overt sedative or antihistaminergic properties and it does not potentiate the effects of alcohol. Weak activating properties are observed in EEG studies in animals at doses generally greater than those required to inhibit 5-HT uptake in the CNS, and the activated EEG in rats is associated with slight locomotor stimulation. However, specific studies indicate that this activation is not amphetamine-like. Paroxetine does not inhibit monoamine oxidase in vitro. Paroxetine is well tolerated by the cardiovascular system, being qualitatively and quantitatively less cardiotoxic than amitriptyline. The weak affinity of paroxetine for muscarinic cholinergic receptors in vitro is associated with mydriasis in vivo, but only at doses well in excess of those required to potentiate the effects of 5-HT in the CNS. It is therefore concluded that paroxetine should be an effective antidepressant with a reduced propensity to induce the adverse events that are characteristic of the tricyclic class of antidepressants.

In vivo labeling of serotonin uptake sites with [3H]paroxetine

Previous work has shown that [3H]paroxetine is a potent and selective in vitro label for serotonin uptake sites in the mammalian brain. In the present study, [3H]paroxetine was tested in mice as an in vivo label for serotonin uptake sites. Maximum tritium concentration in the whole brain (1.4% of the intravenous dose) was reached 1 h after injection into a tail vein. Distribution of the tracer at 3 h after injection followed the distribution of serotonin uptake sites known from previous in vitro binding studies (r = 0.85). The areas of highest [3H]paroxetine concentration, in decreasing order, were: hypothalamus greater than frontal cortex greater than olfactory tubercles greater than thalamus greater than upper colliculi greater than brainstem greater than hippocampus greater than striatum greater than cerebellum. Preinjection of carrier paroxetine (1 mg/kg) significantly decreased [3H]paroxetine concentration in all areas except in the cerebellum, which is known to contain a relatively low number of specific binding sites. Kinetic studies showed highest specific [3H]paroxetine binding (tissue minus cerebellum) at 2 h after injection and slow clearance of activity thereafter (half-time of dissociation from the hypothalamus, 215 min). The specificity of in vivo [3H]paroxetine binding was studied by preinjecting monoamine uptake blockers or receptor antagonists 5 min before administration of [3H]paroxetine. Serotonergic or muscarinic cholinergic receptor antagonists and dopamine or norepinephrine uptake blockers did not reduce the in vivo binding of [3H]paroxetine. In contrast, there was an excellent correlation (r = 0.99) between the in vivo inhibitory potencies of serotonin uptake blockers in this study and previously published in vitro data on inhibition of [3H] serotonin uptake in brain synaptosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of paroxetine on the electrocardiogram

The electrocardiographic effects of paroxetine have been studied. High speed electrocardiograms were recorded on 20 patients with major depression before and after 4 weeks' treatment with either paroxetine or placebo. No patient had a history or clinical evidence of cardiovascular disease. The ECG measurements were made blind to patient, treatment and treatment interval. No significant changes in heart rate, PR, and QTc intervals or in T-wave height were found after treatment with active drug or placebo but there was a small increase from 81 to 85 ms in the QRS width in the paroxetine group which was significantly different from the small decrease that occurred in the placebo group. No significant changes in blood pressure were noted. The findings show that paroxetine has no clinically relevant cardiac effects when given in therapeutic doses to relatively young healthy subjects.

Nialamide-induced hypermotility in mice treated with inhibitors of monoamine uptake, 5-HT antagonists and lithium

When administered orally to mice 1 h before nialamide 100 mg/kg SC two non-selective and nine selective 5-HT uptake inhibitors enhanced the hypermotility produced by nialamide, whereas two inhibitors of NA uptake showed no influence on the nialamide response. Paroxetine was the most potent nialamide potentiator; 100% increase in motility response was obtained at 0.012 mg/kg. Pretreatment with the 5-HT2 antagonist ritanserin 1 and 10 mg/kg SC reduced the hypermotility produced by nialamide 200 mg/kg SC, but the 5-HT1 antagonist L-propranolol 10 mg/kg administered similarly was found inactive. Nialamide 100 mg/kg was given SC to groups of mice being treated for 4 weeks with paroxetine and lithium given through the diet. At daily intakes of paroxetine and lithium resulting in therapeutic plasma or serum levels a distinctive nialamide potentiation was found.

Effects of paroxetine and maprotiline on mood, perceptual-motor skills and eye movements in healthy volunteers

Sixteen healthy young volunteers (seven females, nine males) received repeated doses of either 30 mg paroxetine, 100 mg maprotiline or placebo in a double-blind crossover study. Each of the three treatments lasted 1 week separated by 2 weeks of no treatment. Treatment order was counterbalanced. Subjects were tested before each treatment period, and after 1 and 7 days of treatment. Measurements were made of mood, perceptual-motor skills, and eye movements including pupil size when subjects were watching a traffic film.

Autoradiography of antidepressant binding sites in the human brain: localization using [3H]imipramine and [3H]paroxetine

[3H]Imipramine and [3H]paroxetine were used to label sites associated with serotonin uptake mechanisms in post-mortem brain tissue from control subjects. The anatomical localization of these sites was examined by autoradiography and densities measured by microdensitometry. We found [3H]imipramine binding to increase with age in the cortex and amygdala, but to be independent of gender and post-mortem delay. Preliminary results indicate that the binding of both [3H]imipramine and [3H]paroxetine is diminished in the brain of patients treated with imipramine. The distribution of [3H]imipramine and [3H]paroxetine high-affinity binding sites was very similar, and correlated well with the distribution of serotonergic presynaptic markers in the brain. The highest densities of binding sites were found in the raphé nuclei and the midline thalamic nuclei. Other structures presenting high levels of binding were the substantia nigra, nucleus interpeduncularis, locus coeruleus, nucleus nervi hypoglossi, nucleus nervi facialis, mammillary bodies and other parts of the hypothalamus. In contrast, regions such as the neocortex, hippocampus, amygdala and cerebellum showed low densities of [3H]imipramine and [3H]paroxetine binding sites. This distribution seems to indicate that the ascending serotonergic pathways are the main site of action of antidepressants.

Regional and subcellular localization in human brain of [3H]paroxetine binding, a marker of serotonin uptake sites

The characteristics of the binding of [3H]paroxetine, a selective serotonin (5-HT) uptake blocker, were investigated in human brain. The Kd value was 0.23 +/- 0.07 nM, and the Bmax value was 190 +/- 39 fmol/mg protein in the putamen. The capacity of various antidepressive drugs to inhibit [3H]paroxetine-specific binding in human brain was well correlated with their capacity to inhibit [3H]5-HT uptake in rat brain. The highest concentrations of [3H]paroxetine-specific binding sites were found in the substantia nigra, hypothalamus, and hippocampus. Lower values were obtained in the basal ganglia and the thalamus. The specific binding was very low in cerebral and cerebellar cortices. The regional distribution of [3H]paroxetine binding sites differs from that of [3H]ketanserin binding to S2 serotonin receptors. The subcellular distribution of the [3H]paroxetine-specific binding sites obtained by differential centrifugation revealed a synaptosomal enrichment in the frontal cortex and striatum, whereas an enrichment in the microsomal fraction was found in striatum. The results show that [3H]paroxetine is a ligand of choice to label the 5-HT uptake molecular complex in human brain.

Paroxetine, a selective 5-hydroxytryptamine uptake inhibitor with antidepressant properties, lacks amphetamine-like stimulus properties in an operant drug discrimination bioassay in rodents

To evaluate whether the novel antidepressant paroxetine has any possible amphetamine-like actions, rats were trained to discriminate (+)-amphetamine sulphate in a standard two lever operant drug discrimination (DD) procedure using a fixed ratio 10 schedule of food reinforcement with a quantal, lever selection, index of the amphetamine stimulus. The 'training' dose of amphetamine was 1 mg kg-1, i.p. Rats trained with this dose of amphetamine (n = 15) learned the drug discrimination rapidly over 30 training sessions and discriminative performance in these animals was subsequently maintained at a high level of accuracy (90% correct) over a prolonged time. In tests in these trained animals, amphetamine itself and the antidepressant agents nomifensine and tranylcypromine all produced clear, unequivocal dose-related generalization to amphetamine with ED50s of 0.2, 0.5 and 1.6 mg kg-1 respectively (as determined by probit analyses). In tests with paroxetine hydrochloride it was established that, over the dose range 0.3 to 10 mg kg-1, no evidence was seen of generalization to the amphetamine stimulus. These data confirm earlier studies which suggested that some antidepressants may possess abuse potential because of their ability to induce amphetamine-like internal states. In contrast, paroxetine is devoid of such properties.

Serotonin and noradrenaline concentrations and serotonin uptake in platelets from hyperphenylalaninaemic patients

In three untreated patients with phenylketonuria (PKU), three PKU and six hyperphenylalaninaemic (HPA) patients in good metabolic control, the kinetic constants of platelet in vitro uptake of [14C]serotonin (5HT) did not significantly differ from those in 12 control subjects matched for age. The platelet concentrations of endogenous 5HT and noradrenaline (NA), taken as long-term indices of the amount of these amines circulating in plasma, were lower than normal in PKU and HPA patients, whether or not they were kept on a diet. However, a reduction in plasma NA concentrations at the moment of blood collection was seen only in untreated PKU patients. These data indicate that there may be a chronic inhibition of 5HT and possibly of NA synthesis even in PKU or HPA subjects in good metabolic control, with normal psychomotor development and only slightly raised plasma phenylalanine levels.

Noradrenergic function and the dexamethasone suppression test in depression

We measured the plasma free 3-methoxy-4-hydroxyphenylglycol (MHPG) levels and the serum cortisol levels before and after the oral administration of dexamethasone. There was not a significant difference in the plasma free MHPG levels between the patients with major depression and normal subjects. There was a significant positive correlation between the plasma MHPG levels and postdexamethasone cortisol levels in patients with major depression. This indicates that there exists a certain relation between abnormalities of the central noradrenergic systems and hypothalamic-pituitary-adrenal axis in patients with major depression. The mean total scores of the Hamilton Rating Scale for Depression of the first (MHPG less than 5 ng/ml) and third (10 ng/ml less than or equal to MHPG) groups were significantly higher than those of the second (5 less than or equal to MHPG less than 10 ng/ml) group.

The activity of 25 paroxetine/femoxetine structure variants in various reactions, assumed to be important for the effect of antidepressants

Structure-activity relationships for 25 structural variants around the 5-hydroxytryptamine (5-HT) uptake inhibitors paroxetine and femoxetine have been investigated. Three parameters related to the 5-HT system were investigated: (i) The inhibition of [3H]5-HT uptake into rat brain synaptosomes, (ii) the inhibition of [3H]paroxetine binding to rat neuronal membranes and (iii) the effect of the compounds on the affinity of [3H]imipramine for the human platelet membrane binding site, measured as the dissociation rate of the [3H]imipramine human platelet membrane binding site complex. A highly significant correlation was found for 5-HT uptake inhibition and inhibition of [3H]paroxetine binding for the different substances, indicating that the two parameters are closely connected. However the slope of the regression line was only 0.6 and not 1.0; this may indicate that [3H]paroxetine binding is necessary, but not sufficient for 5-HT uptake inhibition. No correlation was found between the inhibition of [3H]paroxetine binding and the affinity of the compounds for the [3H]imipramine binding site complex. The two binding sites are therefore probably situated on different parts of the 5-HT transport system, the [3H]paroxetine binding site being part of the 5-HT transport mechanism whereas the [3H]imipramine binding site may represent a site modulating the activity of, and affinity for, 5-HT in the 5-HT transport mechanism. Structure-activity relationships among the substances showed that stereochemical changes from (-)- to (+)-trans changed the activity towards both 5-HT uptake inhibition and [3H]paroxetine displacement for most of the (-)-/(+)-pairs. The substitution of -H with -F or -CH3 also affected the activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical effects of the antidepressant paroxetine, a specific 5-hydroxytryptamine uptake inhibitor

Paroxetine was shown to be a potent (Ki = 1.1 nM) and specific inhibitor of [3H]-5-hydroxytryptamine (5-HT) uptake into rat cortical and hypothalamic synaptosomes in vitro. Lineweaver-Burk kinetic analysis determined that this inhibition was competitive in nature, implying a direct interaction with the 5-HT uptake transporter complex. Oral administration of paroxetine produced a dose-related inhibition of [3H]-5-HT uptake (ED50 = 1.9 mg/kg) into rat hypothalamic synaptosomes ex vivo with little effect on [3H]-l-noradrenaline (NA) uptake (ED50 greater than 30 mg/kg). This selectivity for 5-HT uptake was maintained after oral dosing for 14 days. Paroxetine (ED50 1-3 mg/kg PO) prevented the 5-HT depleting effect of p-chloroamphetamine (PCA) in rat brain, demonstrating 5-HT uptake blockade in vivo. Radioligand binding techniques in rat brain in vitro showed that paroxetine has little affinity for alpha 1, alpha 2 or beta adrenoceptors, dopamine (D2), 5-HT1, 5-HT2 or histamine (H1) receptors at concentrations below 1000 nM. Paroxetine demonstrated weak affinity for muscarinic receptors (Ki = 89 nM) but was at least 15 fold weaker than amitriptyline (Ki = 5.1 nM). Paroxetine, therefore, provides a useful pharmacological tool for investigating 5-HT systems and furthermore should be an antidepressant with reduced tricyclic-like side-effects.

Autoradiographic localization of 3H-paroxetine-labeled serotonin uptake sites in rat brain

Paroxetine is a potent and selective inhibitor of serotonin uptake into neurons. Serotonin uptake sites have been identified, localized, and quantified in rat brain by autoradiography with 3H-paroxetine; 3H-paroxetine binding in slide-mounted sections of rat forebrain was of high affinity (KD = 10 pM) and the inhibition affinity constant (Ki) values of various drugs in competing 3H-paroxetine binding significantly correlated with their reported potencies in inhibiting synaptosomal serotonin uptake. Serotonin uptake sites labeled by 3H-paroxetine were highly concentrated in the dorsal and median raphe nuclei, central gray, superficial layer of the superior colliculus, lateral septal nucleus, paraventricular nucleus of the thalamus, and the islands of Calleja. High concentrations of 3H-paroxetine binding sites were found in brainstem areas containing dopamine (substantia nigra and ventral tegmental area) and norepinephrine (locus coeruleus) cell bodies. Moderate concentrations of 3H-paroxetine binding sites were present in laminae I and IV of the frontal parietal cortex, primary olfactory cortex, olfactory tubercle, regions of the basal ganglia, septum, amygdala, thalamus, hypothalamus, hippocampus, and some brainstem areas including the interpeduncular, trigeminal, and parabrachial nuclei. Lower densities of 3H-paroxetine binding sites were found in other regions of the neocortex and very low to nonsignificant levels of binding were present in white matter tracts and in the cerebellum. Lesioning of serotonin neurons with 3,4-methylenedioxyamphetamine caused large decreases in 3H-paroxetine binding. The autoradiographic distribution of 3H-paroxetine binding sites in rat brain corresponds extremely well to the distribution of serotonin terminals and cell bodies as well as with the pharmacological sites of action of serotonin.