Oxaprotiline, a noradrenaline uptake inhibitor with an active and an inactive enantiomer

Meta-analysis of imipramine and moclobemide versus placebo

Meta-analysis of several double-blind, placebo-controlled studies, including 1277 patients, has been performed in order to compare the efficacy of moclobemide, a new reversible and selective MAO-A inhibitor (RIMA) and imipramine. The main interest of the analysis was to test the time course of improvement and the impact of the pre-defined outcome criteria (50% reduction of total HAMD score) on the response to treatment, if initial severity of depression and drop-outs due to inefficacy are taken into consideration. In order to analyze the interdependence of the severity of the disease and outcome, patient sample was subdivided into three HAMD (17 items) baseline score groups: low- (score ≤ 21), medium- (22-27) and high (≥ 28) scorers. We found that reliable assessment of the point in time at which a drug begins to show therapeutic effect in each individual is a critical factor in the determination of the time course of improvement. We defined therefore the onset of improvement as the time point of a significant decrease (20%) of HAMD baseline score without subsequent deterioration. The threshold for the distinction between a significant change and spontaneous fluctuations, or error variations due to instrument or observer, was the natural variability of the HAMD score during the first two observation days. The results of the analysis replicated our earlier findings and confirmed that in treatment responders the time course of improvement is identical under placebo and antidepressants. Neither the time-points of the onset of effect, nor the time-points at which a 50% decrease of HAMD was reached, differed between the groups. In particular, no treatment- Specific time lag showed up in the onset of action. The difference in efficacy between antidepressants and placebo was evident only in the total number of responders and non-responders. Moreover, onset of improvement within the first 10 days of treatment, which was observed in 40-50% of patients, was highly predictive of the final response to treatment. The rate of correctly predicted responders in our sample was 70% for all three treatment modalities. With respect to the severity of the disease, a slight shift towards earlier onset of improvement was found for more severe cases. This finding was true for placebo and drug responders hut there was no clear-cut other interdependence with the treatment outcome. Drop-out rales due to inefficacy were in this study similar under all treatments (20-24%) anil occurred mostly during the first two weeks of the trial (64-71%.).

Delayed onset of action of antidepressant drugs? Survey of recent results

The onset of action of antidepressant drugs was investigated on the basis of two independent multicenter, double-blind efficacy studies comparing amitriptyline (n = 120), oxaprotiline (n = 120), imipramine (n = 506) and moclobemide (n = 580) with placebo (n = 189 + 191). The samples consisted of in- and outpatients diagnosed, according to Diagnostic and Statistical Manual (DSM)-III criteria, as suffering from major depressive disorder. Measures of efficacy criteria were the Hamilton Rating Scale for Depression (HAM-D), the Hamilton Rating Scale for Anxiety (HAM-A) and the Zung Self-Rating Depression scale. By using the Sustained Relative Improvement (SRI) criterion, onset of action was determined in each individual patient as that time point in the 30 day observation period at which a 20% baseline score reduction was achieved without subsequent deterioration. Analogously, a response to treatment was defined as a 50% baseline score reduction. As expected, highly significant differences between active drugs and placebo were found with respect to the total number of improvers and responders. Significant differences between treatment modalities surfaced in the percentage rate as well as the time distribution of premature withdrawals. Yet, unexpectedly, among improvers, the time spans to onset of improvement were found to be independent of treatment modality as indicated by virtually identical cumulative percentages of improvers throughout the whole observation period. The picture was essentially the same for the HAM-A and Zung assessments, except for a significant time lag between observer- and self-ratings. In particular, our analyses revealed no evidence for a delayed onset of action under various antidepressants with large biochemical and pharmacological differences in comparison to placebo. Moreover, the early onset of improvement was highly predictive of later outcome: on average, 70% of the patients showing improvement within the first 14 days became responders. Applying survival-analytical methods, we found that differences between active treatments and placebo emerged within the first 5 days and reached a point of maximum distinction around day 14. After this time point, differences between treatment modalities remained constant until the end of the observation period. According to our data, 20–25% of the patients were, on average, ‘true’ drug responders, thus suggesting that the therapeutic qualities of antidepressants do not lie in the suppression of symptoms, but rather are related to their ability to elicit and maintain certain conditions which allow recovery in a subgroup of patients who would otherwise remain non-responders.

Synthesis of 11C-labelled (R)-OHDMI and CFMME and their evaluation as candidate radioligands for imaging central norepinephrine transporters with PET

(R)-1-(10,11-Dihydro-dibenzo[b,f]azepin-5-yl)-3-methylamino-propan-2-ol ((R)-OHDMI) and (S,S)-1-cyclopentyl-2-(5-fluoro-2-methoxy-phenyl)-1-morpholin-2-yl-ethanol (CFMME) were synthesized and found to be potent inhibitors of norepinephrine reuptake. Each was labelled efficiently in its methyl group with carbon-11 (t(1/2)=20.4 min) as a prospective radioligand for imaging brain norepinephrine transporters (NET) with positron emission tomography (PET). The uptake and distribution of radioactivity in brain following intravenous injection of each radioligand into cynomolgus monkey was examined in vivo with PET. After injection of (R)-[(11)C]OHDMI, the maximal whole brain uptake of radioactivity was very low (1.1% of injected dose; I.D.). For occipital cortex, thalamus, lower brainstem, mesencephalon and cerebellum, radioactivity ratios to striatum at 93 min after radioligand injection were 1.35, 1.35, 1.2, 1.2 and 1.0, respectively. After injection of [(11)C]CFMME, radioactivity readily entered brain (3.5% I.D.). Ratios of radioactivity to cerebellum at 93 min for thalamus, occipital cortex, region of locus coeruleus, mesencephalon and striatum were 1.35, 1.3, 1.3, 1.2 and 1.2, respectively. Radioactive metabolites in plasma were measured by radio-HPLC. (R)-[(11)C]OHDMI represented 75% of plasma radioactivity at 4 min after injection and 6% at 30 min. After injection of [(11)C]CFMME, 84% of the radioactivity in plasma represented parent at 4 min and 20% at 30 min. Since the two new hydroxylated radioligands provide only modest regional differentiation in brain uptake and form potentially troublesome lipophilic radioactive metabolites, they are concluded to be inferior to existing radioligands, such as (S,S)-[(11)C]MeNER, (S,S)-[(18)F]FMeNER-D(2) and (S,S)-[(18)F]FRB-D(4), for the study of brain NETs with PET in vivo.

Differential effects of K(ATP) channel blockers on [(3)H]-noradrenaline overflow after short- and long-term exposure to (+)-oxaprotiline or desipramine

To test whether prolonged uptake blockade can lead to changes in the function of ATP-dependent potassium (K(ATP)) channels we investigated in rat neocortex slices the effects of K(ATP) channel blockers on electrically evoked [(3)H]-noradrenaline ([(3)H]-NA) overflow after short- (45 min) and long-term (210 min) exposure to the NA uptake blockers (+)-oxaprotiline or desipramine (1 microM each). The K(ATP) channel blocker glibenclamide (1 micro M) increased the evoked [(3)H]-NA overflow by 42% after short-term uptake inhibition. This effect was confirmed by tolbutamide and glipizide, two other K(ATP) channel antagonists. The evoked [(3)H]-NA overflow was enhanced by 73% following short-term uptake blockade (15 min) and by 110% following long-term blockade (180 min). After long-term blockade (210 min), however, glibenclamide failed to further enhance the overflow of [(3)H]-NA. The alpha(2)-autoreceptor-mediated feedback control was not involved in the glibenclamide-induced increase in [(3)H]-NA overflow after short-term uptake blockade or in the increase in [(3)H]-NA overflow due to long-term uptake blockade per se. The Na(+)/K(+)-ATPase inhibitor ouabain diminished the glibenclamide-induced enhancement of [(3)H]-NA overflow after short-term uptake blockade, suggesting that an operative Na(+)/K(+)-ATPase is the prerequisite of activation of K(ATP) channels. These results suggest that short-term uptake blockade activates the Na(+)/K(+)-ATPase, thereby reducing intracellular ATP which allows transient opening of K(ATP) channels. Activation of the Na(+)/K(+)-ATPase may increase the Na(+) gradient, probably over the membrane of noradrenergic nerve terminals. The resulting hyperpolarisation leads to inhibition of the evoked overflow which can be reversed, i.e. enhanced, by K(ATP) channel blockers. In contrast, longer lasting uptake blockade seems to reduce the activity of the Na(+)/K(+)-ATPase and hence the consumption of ATP. As a consequence, reduced Na(+) and K(+) gradients may facilitate transmitter release. Closure of K(ATP) channels by accumulating ATP may further promote membrane depolarisation and transmitter release. The unexpected effect of longer exposure to uptake blockers could be somehow related to the clinical time latency of the antidepressant efficacy of monoamine uptake blockers.

Do alpha2-adrenoceptors play an integral role in the antinociceptive mechanism of action of antidepressant compounds?

Antidepressants are analgesic in the absence or presence of depression. The underlying mechanisms probably involve a complex interplay between several neurotransmitter systems and neuroreceptors. Alpha-adrenoceptors play an important role in pain processing and alpha2-adrenoceptor agonists have been used in clinical pain management so we have investigated whether alpha-adrenoceptor sub-types mediate the antinociceptive activity of antidepressants. Thus, the abdominal constriction assay in mice was used to examine the antinociceptive responses of a diverse range of antidepressants following alpha1- or alpha2-adrenoceptor antagonism. The antidepressants or monoamine reuptake inhibitors included the serotonin selective reuptake inhibitor paroxetine, the serotonin-noradrenaline reuptake inhibitor sibutramine, the resolved (+)- and (-)-enantiomers of the noradrenaline reuptake inhibitor oxaprotiline, plus the tricyclics amitriptyline and dothiepin. All these compounds have been previously shown to be antinociceptive in this paradigm. The respective alpha1- and alpha2-adrenoceptor antagonists prazosin and RX821002 ([2-(2-methoxy-1,-4-benzodioxan-2-yl)-2-imidazoline]) did not produce antinociception though at 1.0 mg kg(-1); s.c., RX821002 but not prazosin blocked clonidine antinociception. The antinociceptive activity produced by sub-maximal doses of amitriptyline, dothiepin, sibutramine, paroxetine, (+)- and (-)-oxaprotiline were all blocked by RX821002 but not by prazosin. Additionally, both morphine and aspirin antinociception was resistant to alpha1- and alpha2-adrenoceptor antagonism. Thus, alpha2- rather than alpha1-adrenoceptors may play an integral role in antidepressant antinociception irrespective of the propensity for inhibiting reuptake of not only noradrenaline but also serotonin. It is probable, however, that other differing pharmacological properties of some antidepressants, such as opioid-like activity, may complicate any empirical correlation between monoamine uptake and analgesia.

Increased synaptic availability of norepinephrine following desipramine is not essential for increases in GR mRNA. Short communication

Male Sprague-Dawley rats were treated for 7 days with the norepinephrine (NE) uptake inhibitors desipramine (DMI) or (+)-oxaprotiline or the inactive (-)-enantiomer of oxaprotiline. DMI, as previously reported, significantly increased hippocampal glucocorticoid receptor (GR) mRNA while the equipotent NE uptake inhibitor (+)-oxaprotiline like the inactive (-)-oxaprotiline did not alter hippocampal levels of GR mRNA. The results indicate that an increase in the synaptic availability of NE as a consequence of uptake inhibition is not responsible for the action of DMI on GR gene expression.

Expression of the extraneuronal monoamine transporter (uptake2) in human glioma cells

Tritiated methylphenylpyridinium ([3H]MPP+), a substrate of the neuronal and extraneuronal noradrenaline transporter (uptake1 and uptake2, respectively) and of the organic cation transporter (OCT1), was used to characterize the amine transport system of the established human glioma cell line SK-MG-1. Uptake of [3H]MPP+ (25 nM) into SK-MG-1 cells increased linearly with time for up to 15 min. Selective uptake1 inhibitors (e.g. (+)oxaprotiline) or omission of Na+ or Cl-ions did not affect [3H]MPP+ uptake, whereas uptake2 inhibitors such as O-methyl-isoprenaline (OMI) or corticosterone as well as depolarizing concentrations of K+ or Ba2+ strongly reduced [3H]MPP+ uptake. Initial rates of OMI(100 microM)-sensitive [3H]MPP+ uptake were saturable, with a K(m) of about 17 microM and a maximal rate of about 50 pmol/(min x mg protein). IC50 (or Ki) values for inhibition of [3H]MPP+ uptake by substrates and inhibitors of uptake2 or OCT1 were highly significantly correlated with published IC50 values for inhibition of uptake2 but not with corresponding values for inhibition of OCT1. The results presented here clearly demonstrate that human glioma cells express an uptake2 transporter. Thus, glial cells in the human central nervous system endowed with this transporter are likely to contribute to the inactivation of neuronally released noradrenaline.

Autoradiographic studies on the uptake of 3H-noradrenaline and 3H-serotonin by neurones and astrocytes in explant and primary cultures of rat CNS: effects of antidepressants

Autoradiographic studies were made on the uptake of 3H-noradrenaline and 3H-serotonin in explant cultures and primary astrocyte cultures from various regions of rat central nervous system (cortex, cerebellum, locus coeruleus, nucleus raphé, spinal cord). In explant cultures from locus coeruleus and nucleus raphé cell bodies and processes of many neurones revealed intense labelling by 3H-noradrenaline and 3H-serotonin, respectively. In cultures from cortex, cerebellum and spinal cord the cell bodies of neurones did not show labelling by the monoamines but many nerve fibres in the outgrowth zone had taken up 3H-noradrenaline and 3H-serotonin. Astrocytes in explant cultures did not take up 3H-noradrenaline and 3H-serotonin whereas astrocytes in primary cultures showed heavy uptake of both monoamines. In contrast, amino acid transmitters such as 3H-GABA and 3H-glutamate were accumulated by astrocytes in explant as well as in primary cultures. Uptake of both 3H-noradrenaline and 3H-serotonin by neurones and astrocytes was considerably reduced or inhibited in Na(+)-free incubation medium or at low temperature, suggesting an active uptake mechanism. Addition of the antidepressants maprotiline and (+)oxaprotiline inhibited the uptake of 3H-noradrenaline by neuronal cell bodies and fibres in explant cultures and by astrocytes in primary cultures. The uptake of 3H-serotonin by neurones and astrocytes was blocked by citalopram and paroxetine. Our studies demonstrate that astrocytes in primary cultures are able to actively take up 3H-noradrenaline and 3H-serotonin whereas there was no uptake of monoamines into astrocytes in explant cultures, suggesting that there is a difference between astrocytes in different culture systems (explant cultures vs primary cultures) with respect to the uptake of monoamine transmitters.

Cultured chick sympathetic neurons: prostanoid EP1 receptor-mediated facilitation of noradrenaline release

Prostanoid EP receptor-mediated modulation of noradrenaline release from cultured chick sympathetic neurons was investigated. Transmitter release from dissociated cell cultures of embryonic paravertebral ganglia, loaded with [3H]-noradrenaline, was elicited either by electrical field stimulation (36 pulses/3 Hz) or by elevating the extracellular concentration of K+ (to 30 mM; for 2 min). Prostaglandin E2 (PGE2; 0.01-3 microM) enhanced electrically evoked [3H]-noradrenaline release in a concentration-dependent manner with a maximal increase by about 50% at 1 microM. Also iloprost (0.1-3 microM) increased transmitter release concentration- dependently, whereas misoprostol (0.1-3 microM) had no effect. Indometacin (10 microM) influenced neither evoked release per se nor the enhancement caused by PGE2- AH6809 (3 microM), a selective EP1 receptor antagonist, blocked the enhancement caused by both PGE2 and iloprost K(+)-evoked noradrenaline release, which was virtually insensitive to tetrodotoxin (0.3 microM), was increased by PGE2 to an extent comparable to that observed after electrical stimulation. In summary, the present data indicate that PGE2 facilitates noradrenaline release from cultured chick sympathetic neurons by a receptor which shows the pharmacological profile of the EP1 subtype and is probably located at the processes of the neuron.

Effects of 5-HT receptor agonists on depolarization-induced [3H]-noradrenaline release in rabbit hippocampus and human neocortex

1. The present study attempted to determine whether noradrenaline (NA) release in rabbit hippocampus and human neocortex is modulated by presynaptic 5-hydroxytryptamine (5-HT) receptors. 2. Slices of rabbit hippocampus and human neocortex, loaded with [3H]-noradrenaline ([3H]-NA) were superfused and the effects of 5-hydroxytryptamine (5-HT) receptor ligands on electrically evoked [3H]-NA release were investigated. 3. In rabbit hippocampus, 5-HT, 5-carboxamidotryptamine (5-CT; 32 microM) and 2-CH3-5-HT (32 microM) increased [3H]-NA release elicited with 360 pulses/3 Hz. Facilitation of transmitter release was not influenced by the 5-HT3 receptor antagonist, tropisetron but was prevented by the alpha 2-adrenoceptor antagonist, rauwolscine. When autoinhibition was avoided by stimulating the tissue with 4 pulses/100 Hz (pseudo-one pulse-(POP) stimulation), 2-CH3-5-HT decreased evoked transmitter release, whereas 5-HT and 5-CT had no effect. Inhibition caused by 2-CH3-5-HT was not affected by tropisetron but counteracted by the alpha 2-adrenoceptor ligands, clonidine and rauwolscine. Inhibition caused by clonidine was diminished in the presence of 5-CT or 2-CH3-5-HT. 4. In human neocortex, [3H]-NA release elicited with 360 pulses/3 Hz was increased by 10 microM 5-HT and 32 microM 5-CT, whereas 2-CH3-5-HT was ineffective. [3H]-NA release evoked with a modified POP stimulation (2 bursts of 4 pulses/100 Hz, 3.5 min apart) was not affected by 2-CH3-5-HT or 5-CT. 5. The present results indicate that 5-HT, 2-CH3-5-HT and 5-CT can act on presynaptic alpha 2-autoreceptors as partial agonists (2-CH3-5-HT; in rabbit hippocampal tissue) or antagonists (5-HT and 5-CT; in tissue of rabbit hippocampus and human neocortex). Furthermore the existence of autoinhibition dictates whether these drugs cause facilitation of release, inhibition or have no effect.

Cultured chick sympathetic neurons: ATP-induced noradrenaline release and its blockade by nicotinic receptor antagonists

The ATP-induced increase in tritium outflow from cultured chick sympathetic neurons prelabelled with [3H]-noradrenaline was investigated. Seven days-old dissociated cell cultures of embryonic paravertebral ganglia, loaded with [3H]-noradrenaline (0.05 microM), were superfused in the presence of (+)-oxaprotiline and exposed to ATP, ATP-analogues, or 1,1-dimethyl-4-piperazinium (DMPP) for 2 min. ATP (3 microM-3 mM), 2-methylthio-ATP (3-100 microM), as well as DMPP (10 and 100 microM) induced a significant overflow of tritium. The EC50-value of ATP was 20 microM. Both the ATP-induced and the DMPP-induced tritium overflow was Ca(2+)-dependent and sensitive to tetrodotoxin (0.3 microM) and omega-conotoxin (0.1 microM); in addition, it was inhibited by the alpha 2-adrenoceptor agonist 5-bromo-6-(2-imidazoline-2-ylamino)-quinoxaline (UK-14,304; 1 microM). The effects of ATP and DMPP were not additive. The ATP-induced as well as the DMPP-induced overflow of tritium was diminished by the P2-purinoceptor antagonists suramin (300 microM) and reactive blue 2 (3 microM); in all 4 cases, the inhibition amouted to approximately 40%. The tritium overflow induced by ATP or DMPP was almost abolished by the nicotinic receptor antagonist mecamylamine (10 microM) and markedly inhibited by hexamethonium (100 microM). Neither ATP nor electrical stimulation caused an overflow of tritium from cultures loaded with [3H]-choline. The results suggest that ATP at mumolar concentrations induces noradrenaline release from cultured chick sympathetic neurons via an action on a subclass of the nicotinic cholinoceptor.

Inhibition of spinal noradrenaline uptake in rats by the centrally acting analgesic tramadol

Tramadol is a centrally acting analgesic with low affinity to opioid receptors. A further mode of action is inhibition of noradrenaline uptake as measured in standard assays. Since tramadol shows antinociception at the spinal site, it was to be tested whether uptake blockade could be verified in spinal tissue. Therefore, synaptosomes and slices had to be prepared from the dorsal half of the spinal cord and the uptake of [3H]noradrenaline into synaptosomes to be characterized. The uptake was linear for at least 3 min. The apparent Km was 0.16 microM and Vmax was 7.9 pmol/min/mg protein. Tramadol inhibited the uptake competitively as analysed with Dixon plots with a Ki of 0.6 microM. Uptake inhibition was effected in order of potency by (+)-oxaprotiline > nisoxetine > (-)-tramadol > (-)-oxaprotiline = tramadol > (+)-tramadol. Slices were preincubated with [3H]noradrenaline then superfused and stimulated electrically. Nisoxetine, tramadol and its (-)-enantiomer enhanced mainly the stimulation-evoked overflow indicating uptake inhibition without releasing effects. Experiments with inclusion of the noradrenaline uptake inhibitor desipramine provided evidence that tramadol interfered with the noradrenaline transporter. The results show that spinal synaptosomes and slices are valid preparations to study local noradrenaline uptake and release. Tramadol enhances extraneuronal noradrenaline levels in the spinal cord by competitive interference with the noradrenaline uptake mechanism.

Cloning and expression of the bovine sodium- and chloride-dependent noradrenaline transporter

A cDNA encoding a functional bovine, tricyclic antidepressant-sensitive noradrenaline transporter has been identified by screening a lambda gt11 cDNA library of the bovine adrenal medulla using the cDNA of the human noradrenaline transporter [1991, Nature 350, 350-354]. The sequence predicts a protein of 615 amino acids (M(r) 68,900). The bovine transporter shares 93% amino acid identity with the human sequence, but displays two more consensus sites for phosphorylation by protein kinase C. Transient expression of the transporter in COS-7 cells resulted in a sodium- and chloride-dependent uptake of noradrenaline with a pharmacology typical for a neuronal noradrenaline transporter.

Inhibition of uptake 1 by (+)-oxaprotiline reveals a differential central regulation of noradrenaline and adrenaline release

Inhibition of uptake 1 in the central nervous system leads to a decrease of sympathetic outflow to many tissues; central alpha 2-adrenoceptors are involved in this decrease. The aim of the present study was to compare the effects of the selective uptake 1 inhibitor (+)-oxaprotiline on the plasma kinetics of noradrenaline and adrenaline in anaesthetized and in conscious rabbits. [3H]Noradrenaline and [3H]adrenaline were infused i.v. The arterial plasma concentrations of endogenous and radiolabelled noradrenaline and adrenaline were measured, and the clearance from and spillover into the plasma of noradrenaline and adrenaline were calculated. Results obtained in conscious and anaesthetized rabbits were similar. (+)-Oxaprotiline 0.2, 0.6 and 1.8 mg kg-1 i.v. dose-dependently reduced the clearance of [3H]noradrenaline from the plasma. The clearance of [3H]adrenaline was reduced less. The spillover of endogenous noradrenaline was decreased by up to 35%. In contrast, the spillover of adrenaline tended to be enhanced. Prazosin 0.1 and 1 mg kg-1 was injected i.v. in a second part of each experiment. It lowered the blood pressure and caused a marked increase in noradrenaline spillover but no increase or even a decrease in adrenaline spillover. The results are compatible with the following hypothesis. The sympathetic outflow from the central nervous system is subject to a twofold alpha-adrenoceptor-mediated modulation: alpha 2-adrenoceptor-mediated inhibition and alpha 1-adrenoceptor-mediated excitation. In the control of the sympathetic outflow to many extra-adrenal tissues, the alpha 2-adrenergic inhibition prevails. Uptake 1 inhibitors depress sympathetic outflow to such tissues by enhancing the alpha 2-adrenergic inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral cortex injury: effect of blockers of re-uptake of catecholamines

In rats, surgical injury of the neocortex enhances the level of procholecystokinin-mRNA in the ipsilateral cortex. This increase in procholecystokinin gene expression was significantly reduced by the blockers of catecholamine re-uptake nomifensine (4 mg/kg), cocaine (5 mg/kg) and (+)-oxaprotiline (1.5 mg/kg) given i.m. 30 min before the injury. The ganglionic blocking agent hexamethonium (3 mg/kg) prevented this effect of (+)-oxaprotiline and nomifensine. Also the alpha 1-adrenoceptor antagonists corynanthine (2 mg/kg) and prazosin (2 mg/kg) blocked this effect of (+/-)-oxaprotiline (1.5 mg/kg). It is concluded that catecholamines acting on alpha 1-adrenoceptors can reduce the increase in procholecystokinin-mRNA caused by cortex injury. The catecholamines may be released from the sympathetic nervous system.

Endogenous noradrenaline activates alpha 2-adrenoceptors on serotonergic nerve endings in human and rat neocortex

Slices from human neocortex preincubated with [3H]serotonin ([3H]5-HT) were superfused and stimulated electrically to investigate whether the alpha 2-adrenoceptors on serotonergic terminals can be stimulated by endogenous noradrenaline (NA) released from neighboring noradrenergic fibers. The stimulation-evoked 3H overflow, representing action potential-induced, exocytotic release of 5-HT, was depressed by the NA uptake blocker (+)-oxaprotiline. Rauwolscine (a mixed alpha 2-adrenoceptor antagonist/5-HT autoreceptor agonist) or phentolamine [a combined alpha-adrenoceptor/5-HT autoreceptor antagonist; the latter drug in the presence of (+)-oxaprotiline] enhanced the release when the 5-HT autoreceptors had previously been blocked by metitepine. Under hypothermia the release of 5-HT was found to be decreased and that of NA to be increased; under these conditions idazoxan (an alpha 2-adrenoceptor antagonist) enhanced the release of 5-HT. In neocortex slices from rats (+)-oxaprotiline similarly depressed the release of 5-HT (measured with the same methods) as in human tissue. When rats were pretreated with 6-hydroxydopamine, the inhibitory effect of exogenous NA on 5-HT release was increased, and in slices from rats pretreated with desipramine, it was decreased. In conclusion, alpha 2-heteroreceptors can be activated by endogenous NA released from neighboring noradrenergic fibers. Because regulatory processes analogous to those in rats probably occur in humans as well, an up- or down-regulation of alpha 2-heteroreceptors in depressed patients with a (pathological) decrease or a (therapeutic) enhancement of the noradrenergic neurotransmission may also be assumed to occur.

Differential effects of the enantiomers R(-) and S(+) oxaprotiline on major endogenous depression, the sleep EEG and neuroendocrine secretion: studies on depressed patients and normal controls

The effects of the optically active enantiomers of oxaprotiline (OXP), R(-) OXP and S(+) OXP, on depressive symptomatology and the sleep EEG were investigated in two separate exploratory studies. In addition, the neuroendocrine profile of both compounds was characterized in normal controls. In the patients treated with a daily oral dose of 150 mg S(+) OXP we found a Hamilton depression score that decreased from 29.1 +/- 1.8 (SEM) on day 0 to 14.7 +/- 3.2 on day 28 (P < 0.01). Six patients were judged to be full responders (HAMD score 0-7 points), three were improved (HAMD score 8-15) and four were nonresponders (HAMD score > 16). The therapeutic effect achieved with 150 mg R(-) OXP daily was less pronounced: the HAMD score decreased from 27.8 +/- 2.5 on day 0 to 19.4 +/- 3.2 on day 28 (P < 0.05). There were two full responders, one improved patient and seven nonresponders. The sleep EEG scoring revealed a marked suppression of REM sleep among patients treated with S(+) OXP but not with R(-) OXP. In the normal controls, a single oral dose of 75 mg S(+) OXP prompted an increase in the secretion of cortisol and growth hormone, whereas 75 mg R(-) OXP did not. Neither enantiomer influenced the secretion of testosterone or prolactin.

Time course of improvement under antidepressant treatment: a survival-analytical approach

A meta-analysis of an earlier multicenter, double-blind efficacy study comparing placebo, oxaprotiline and amitriptyline was performed in order to test the survival-analytical approach in modelling the onset of improvement and response to treatment with antidepressants. The sample consisted of moderately depressed male (n = 154) and female (n = 275) patients (aged 17-73), diagnosed according to DSM-III criteria for major depression. Of these, 120 were treated with oxaprotiline, 120 with amitriptyline and 189 with placebo. Efficacy criteria were Hamilton Depression (HAMD) and Anxiety (HAMA) and Zung Self-Rating scales. Up to eight ratings over a period of 40 days were available for analysis. The results showed that the sensitivity in discriminating between groups was substantially enhanced through the inclusion of drop-outs and consideration of the effect of time to withdrawal from the study due to lack of improvement. Withdrawal from the trial due to inefficacy occurred earliest under placebo (50% within the first 8 days), whereas less than 40% dropped out within the first 12 days under active treatments. The most interesting and unexpected finding of the analysis was that the time course of improvement among responders was independent of the treatment modality, and thus identical in all three groups. Specifically, the efficacy of any of the given treatments was reflected only by the total number of responders or nonresponders. Once triggered, the time course of recovery from illness becomes identical to that of spontaneous remissions as observed, for example, under placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

A clinical test of noradrenergic involvement in the therapeutic mode of action of an experimental antidepressant

The noradrenaline (NA) hypothesis of depression is founded primarily on preclinical and clinically indirect evidence. In two three-compartment randomized parallel clinical trials conducted serially, we examined the significance of NA uptake for antidepressant activity. The racemic compound oxaprotiline (hydroxymaprotiline) is a highly specific inhibitor of NA uptake, whereas its R-(-) enantiomer levoprotiline is totally devoid of this property. Oxaprotiline significantly resembled amitriptyline in its antidepressant potential. Conversely, levoprotiline significantly resembled placebo in antidepressant potential. Therefore, NA uptake was necessary for the observed therapeutic effect of this experimental antidepressant.

Effect of some stereoisomeric tricyclic antidepressants on 45Ca uptake in synaptosomes from rat hippocampus

The present study has examined the inhibition of synaptosomal 45calcium uptake by trimipramine, oxaprotiline and doxepin, and their stereoisomers, in synaptosomes from the rat hippocampus. No significant difference in potency could be established for inhibition of net depolarization-induced 45calcium uptake for any pair of antipodes, and the IC50 values for calcium channel blockade were in the vicinity of 30 microM for this group of compounds. Trimipramine, doxepin and oxaprotiline also inhibited the 45calcium uptake mediated by Na(+)-Ca2+ exchange, with IC50 values of 71 microM, 110 microM, and 100 microM, respectively. The similar potency of doxepin isomers for inhibition of voltage-dependent calcium channels is in harmony with their reported similar potency in the clinic. A slight difference in potency is reported between the isomers of oxaprotiline in the behavioral despair test in rats, and the dextrorotatory isomer of trimipramine is reported to be a much more potent antidepressant than the levorotatory isomer: these order of potencies do not correspond perfectly with the similar potency of the antipodes against voltage-dependent calcium channels. The present study of stereoisomeric tricyclic antidepressants therefore fails to provide unequivocal support for the hypothesis that calcium channel blockade by tricyclic antidepressants is involved in their therapeutic effect.

Oxaprotiline: enantioselective noradrenaline uptake inhibition indicated by intravenous amine pressor tests but not alpha 2-adrenoceptor binding to intact platelets in man

The optically active isomers of the racemic tetracyclic antidepressant oxaprotiline, R (-) oxaprotiline CGP 12,103 A (levoprotiline) and the S (+) oxaprotiline CGP 12,104 A, have been used as tools for a methodological Phase I study. Only the S (+) enantiomer CGP 12,104 A inhibits noradrenaline uptake. Intravenous amine pressor tests and ex vivo measurement of alpha 2-adrenoceptor binding to intact human platelets were compared with respect to their reliability in indicating CGP 12,104 A-induced amine uptake inhibition and possibly associated alpha 2-receptor down-regulation in healthy subjects. alpha 2-Adrenoceptor binding on intact human platelets did not distinguish between CGP 12,104 and CGP 12,103 A. However, amine pressor tests reflected the amine uptake inhibiting effect of CGP 12,104 A as a 5-fold decrease in tyramine pressor sensitivity and a 5-fold increase in noradrenaline pressor sensitivity.

Actions of oxaprotiline in the rat hippocampal slice

1. Recordings were obtained from transverse slices of rat hippocampus, which were placed in a perfusion chamber and superfused with oxygenated artificial cerebrospinal fluid. 2. The effects of 10 microM (+)- or (-)-oxaprotiline applied by the bath were examined on the population spike, postsynaptic excitability in low Ca2+-high Mg2+ medium, the epileptiform discharge in Mg2+-free medium and long-term potentiation (LTP). Only the last paradigm (LTP) was significantly enhanced by (+)-oxaprotiline. 3. In rats chronically injected with (+)-oxaprotiline, neither LTP nor the actions of a variety of neurotransmitters in low Ca2+-high Mg2+ medium were significantly altered. 4. Intracellular recordings showed a small depolarization (3.5 +/- 1.6 mV) in response to 10 microM (+)- or (-)-oxaprotiline. Neither input resistance nor inward rectification, long-lasting afterhyperpolarization or accommodation were significantly altered. 5. Acute application, but not chronic treatment with (+)-oxaprotiline affects long-term potentiation in the hippocampal slice, presumably due to an effect on gabaergic inhibition.

The suppression of olfactory bulbectomy-induced muricide by antidepressants and antihistamines via histamine H1 receptor blocking

The effects of antidepressants [(+)-oxaprotiline, (-)-oxaprotiline, imipramine, maprotiline, and trazodone] and antihistamines (mepyramine, dimethindene, ketotifen, methapyrilene, and antazoline) on muricidal behaviour in olfactory bulbectomized rats were investigated. All drugs except for dimethindene, which only minimally passes across the blood-brain barrier, suppressed muricide. The drugs which have high affinity for histamine H1 receptor showed potent suppressive effect on muricide. It is suggested that the central histaminergic system is involved via H1 receptors in the expression of muricide in olfactory bulbectomized rats.

Repeated treatment with levoprotiline, a novel antidepressant, up-regulates histamine H1 receptors and phosphoinositide hydrolysis response in vivo

The effects of repeated administration of levoprotiline, a novel type of tetracyclic antidepressant on histamine H1, muscarinic acetylcholine and alpha 1-adrenergic receptors and the response of phosphoinositide hydrolysis (PI) stimulated by histamine in the cortex of the rat brain were investigated. Histamine H1 receptors were up-regulated to 120% and PI response stimulated by histamine was enhanced to 160%-200% after repeated treatment with levoprotiline (20 mg/kg, i.p., once a day for 28 days) when compared to that of the saline-treated group. No significant alterations of muscarinic acetylcholine and alpha 1-adrenergic receptors were observed. This demonstrates that the repeated treatment with levoprotiline has prominent action on the regulation of histamine H1 receptors and PI response coupling to histamine H1 receptors in vivo.

Pharmacokinetics of the antidepressant levoprotiline after intravenous and peroral administration in healthy volunteers

To investigate the pharmacokinetics and the disposition of levoprotiline after i.v. and p.o. administration and to assess the absolute bioavailability, 12 healthy volunteers (11 women, 1 man) were given a 10 min i.v. infusion of 15 mg and a p.o. dose of 75 mg in a two-way crossover study. Blood and urine samples were collected after each dose. Unchanged levoprotiline and the sum of unchanged and glucuronidated levoprotiline (= total levoprotiline) were determined by a specific gas chromatographic-mass spectro-metric method. Intravenous levoprotiline was rapidly and extensively distributed into extravascular sites of the body; the steady-state volume of distribution was 18.81 kg-1. The elimination of levoprotiline from blood was independent of the dosing route, the half-life being 18.8 h. Only 1.8 and 0.6 per cent of the i.v. and p.o. dose, respectively, were excreted unchanged in the urine, whereas 57 per cent of each dose were renally excreted as total levoprotiline. The absolute bioavailability of p.o. levoprotiline was 40 per cent. About 60 per cent of the dose was subject to a first-pass effect in the liver. The systemic blood clearance of levoprotiline, determined after i.v. dosing, was 885 ml min-1, the renal blood clearance after i.v. and p.o. dosing was only 16.0 and 14.2 ml min-1, respectively. Presystemic and systemic clearance of levoprotiline occurred predominantly by direct glucuronidation.

The acute and chronic effects of (+) and (-) oxaprotiline upon melatonin secretion in normal subjects

Ten healthy male subjects were treated for three weeks with (+)oxaprotiline, a selective inhibitor of noradrenaline (NA) uptake and with (-)oxaprotiline which does not inhibit NA uptake. Plasma melatonin concentrations were measured throughout the night at 0, 1, 7 and 21 days and were higher during treatment with (+)oxaprotiline than with (-)oxaprotiline for the entire three weeks of treatment. Since NA stimulates the production and secretion of melatonin, these results are consistent with a sustained increase in noradrenergic activity within the pineal, during 21 days of treatment with an effective NA uptake inhibitor.

Determination of the antidepressant levoprotiline and its N-desmethyl metabolite in biological fluids by gas chromatography/mass spectrometry

A specific and sensitive gas chromatographic/mass spectrometric method was developed and validated for the determination of the antidepressant levoprotiline in blood, plasma and urine and the simultaneous determination of levoprotiline and its desmethyl metabolite in urine. Deuterium-labelled analogues were used as internal standards. The compounds were isolated from the biological fluids by liquid-liquid extraction under basic conditions. Following derivatization with perfluoropropionic anhydride, the samples were analysed by capillary column gas chromatography/electron impact mass spectrometry with selected ion monitoring. The analysis of spiked samples demonstrated the high accuracy and precision of the method. Blood concentrations of levoprotiline down to 0.7 nmol l-1 (1 ml used for analysis) could be quantified with a coefficient of variation of 10% or less. The method is suitable for use in pharmacokinetic and bioavailability studies of levoprotiline in humans.

Oxaprotiline enantiomers stimulate ACTH and corticosterone secretion in the rat

The effect of oxaprotiline (OXA) enantiomers--of which (+)-OXA inhibits noradrenaline (NA) uptake, whereas (-)-OXA does not--on the secretion of adrenocorticotropin hormone (ACTH) and corticosterone was studied in rats. Both enantiomers dose-dependently and with a similar potency increased the plasma level of ACTH and corticosterone, the effect of (-)-OXA on corticosterone being of a longer duration. The stimulation of ACTH secretion and the inability of (+)- and (-)-OXA to increase the plasma corticosterone concentration in animals pretreated with dexamethasone indicate that secretion of the latter hormone results from the action of the enantiomers at a level superior to the adrenal cortex, i.e. the hypothalamus/pituitary. The corticosterone response to (+)- or (-)-OXA was not modified in rats with a selective lesion of NA nerve endings induced by the neurotoxin DSP-4, nor was it affected by the selective alpha 1-antagonist prazosin, the selective alpha 2-antagonist yohimbine, the mixed alpha 1/alpha 2-antagonist phentolamine, the selective dopamine (D2) receptor antagonist sulpiride and the non-selective 5-hydroxytryptamine (5-HT) receptor antagonist metergoline. These results indicate that neither the NA system nor D2 and 5-HT receptors are involved in the hormonal response to the OXA enantiomers. Although the (+)- and (-)-OXA-induced stimulation of corticosterone secretion was not antagonized by diazepam, ipsapirone, naloxone, or propranolol, it cannot be excluded that both these enantiomers act as non-specific stressors.

Studies on the interaction between presynaptic alpha 2-adrenoceptors and adenosine A1 receptors located on noradrenergic nerve terminals

The aim of the present study was to obtain a more detailed understanding of the interaction between presynaptic alpha 2-adrenoceptors and A1 adenosine receptors mediating inhibition of noradrenaline release in the central nervous system. Slices of rabbit hippocampus, prelabelled with [3H]noradrenaline, were superfused in the presence of the re-uptake inhibitor (+)-oxaprotiline and electrically stimulated during superfusion. During stimulation with 36 pulses at 3 Hz the alpha 2-adrenoceptor antagonist yohimbine induced a five-fold increase of noradrenaline release indicating a pronounced autoinhibition of approximately 80%. In these experiments the inhibition of release caused by R-PIA, a preferential A1 agonist, as well as its facilitation caused by DPCPX, a selective A1 antagonist, were smaller in comparison to the effects of these compounds on release virtually free of autoinhibition (i.e. by stimulating the tissue with 4 pulses at 100 Hz (POP-stimulation) or with 36 pulses at 3 Hz in presence of yohimbine). Clonidine, an alpha 2-adrenoceptor agonist, was used to impose a distinct alpha 2-adrenoceptor-mediated inhibition of release elicited by POP-stimulation. Only, however, in the presence of 30 nmol/l clonidine, causing maximum inhibition of approximately 80% of 3H-overflow, but not in the presence of 6 nmol/l clonidine, causing approximately 50% inhibition, a significant diminution of the inhibitory effect of R-PIA was seen. Similarly, the alpha 2-adrenoceptor mechanism was affected only by 10 mumols/l R-PIA causing maximum inhibition of approximately 80%, but remained unchanged in the presence of 30 nmol/l R-PIA diminishing release by 50%.(ABSTRACT TRUNCATED AT 250 WORDS)

The noradrenaline uptake inhibitor, (+)-oxaprotiline, but not the inactive enantiomer, (-)-oxaprotiline, inhibits sympathetic nerve activity in the rabbit: involvement of adrenoceptors

The effect of the enantiomers of oxaprotiline on the sympathetic nervous system was studied in anesthetized rabbits. (+)-Oxaprotile 0.2, 0.6 and 1.8 mg kg-1 dose dependently reduced prostganglionic renal sympathetic nerve activity and the clearance of [3H]noradrenaline from the plasma but increased the plasma noradrenaline concentration. The spillover of noradrenaline into the blood was not changed significantly, nor were blood pressure and heart rate, except transiently. The same doses of (-)-oxaprotiline had no effect on any of the parameters measured. (+)-Oxoprotiline also reduced lumbar preganglionic sympathetic nerve activity. The effect of (+)-oxaprotiline on renal sympathetic nerve activity was only minimally antagonized by yohimbine given alone. (+)-Oxaprotiline also inhibited renal sympathetic nerve activity after treatment with prazosin and propranolol. Subsequent administration of yohimbine restored sympathetic nerve activity to the value seen before the administration of (+)-oxaprotiline. The results show that inhibition of the re-uptake of released noradrenaline is the basis of the sympathoinhibition produced by (+)-oxaprotiline. Noradrenaline probably acts on alpha 2-adrenoceptors in the central nervous system to produce sympathoinhibition.

The effect of (+)- and (-)-oxaprotiline administered repeatedly on the dopamine system

The behavioural and biochemical effects of repeated (14 and 28 days) treatment with (+)-oxaprotiline (a noradrenaline uptake inhibitor) and (-)-oxaprotiline (levoprotiline, without influence on noradrenaline uptake; the clinically active antidepressant) were studied in rats. Both those enantiomers given repeatedly increased the locomotor and exploratory activity and reduced the immobility time in Porsolt's test. The D-amphetamine-induced locomotor hyperactivity, as well as the stereotypies induced by D-amphetamine and apomorphine, were increased by the oxaprotilines. Single-dose treatment with both the oxaprotilines was not effective in the tests mentioned above. Repeated (+)-oxaprotiline administration reduced the binding (Bmax but not KD) to dopamine D-1 receptors in the striatum and limbic system; levoprotiline was inactive. The binding to dopamine D-2 receptors was not changed by either drug. Both the enantiomers showed only low affinity for brain dopamine D-1 and D-2 receptors in vitro. The obtained results indicate that chronic treatment with (+)- and (-)-oxaprotiline increases behavioural responsiveness of the dopamine mesolimbic and striatal systems.

Supraspinal and spinal monoamine-modified function and the expression of opioid antinociception

Opioids are highly valuable clinical agents for the treatment of pain which are thought to act both at the spinal and supraspinal level. During the course of their actions, they have complex interactions with monoamine systems. These include 5-hydroxytryptamine (5-HT) and noradrenaline (NA), so this topic is discussed using these two transmitter systems, their locations and receptor sub-types, as prime candidates for modulating nociceptive and antinociceptive processes. Several classes of 5-HT receptors, as well as α(2)-adrenoceptors, appear to be clearly involved in antinociception and the functions of systems carrying these receptors may be modified using psychotropic agents. In particular, some antidepressants may acutely augment opioid antinociception and this property may be exploited to delay the onset of opioid tolerance in the sub-acute situation.

Oxaprotiline enantiomers given repeatedly and brain alpha-adrenoceptors

The influence of (+)- and (-)-oxaprotiline (OXA) given repeatedly on the behavioural effects mediated by alpha 1- and alpha 2-adrenoceptors as well as on the binding to brain alpha 1-adrenoceptors was studied. (+)-OXA given repeatedly for 14 days (but not 3 or 7 days) enhanced exploratory hyperactivity of rats induced by methoxamine injected intracerebroventricularly; (-)-OXA given for 3, but not 7 or 14 days, increased the methoxamine-induced exploration in rats. The locomotor hyperactivity induced in mice by d,1-threo-3,4-dihydroxyphenylserine was increased by repeated (14 days) (-)-OXA but not (+)-OXA. Neither OXA enantiomers given repeatedly modified the clonidine-induced locomotor hypoactivity in mice. Both enantiomers given repeatedly did not change the binding of [3H] prazosin to alpha 1-adrenoceptors (Bmax, KD) in the thalamus and hippocampus. Repeated (+)-OXA increased the affinity of alpha 1-adrenoceptors for phenylephrine in the cortex, thalamus and hippocampus. A similar effect of (-)-OXA was observed in the hippocampus only. The results indicate that both OXA enantiomers are able to enhance the responsiveness of brain alpha 1-adrenergic system, probably via the increase in the affinity of alpha 1-adrenoceptors for their agonists.

Some central pharmacological effects of (+)- and (-)-oxaprotiline

The central action of oxaprotiline (OXA) enantiomers, administered in a single dose, was studied in rats and mice. (+)-OXA and (-)-OXA attenuated reserpine- and apomorphine-induced hypothermia [(+)-OXA in a more potent manner] in mice and reduced the immobility time in the behavioural despair test in rats. Both OXA enantiomers inhibited locomotor activity in mice and rats, and enhanced and prolonged amphetamine- and apomorphine-induced stereotypy in rats. (-)-OXA potentiated the amphetamine hyperactivity in rats, but not in mice. Nomifensine hyperactivity in rats was unaffected by either enantiomer, and locomotor hypoactivity induced by low doses of apomorphine was also unchanged, as was L-DOPA-induced locomotor hyperactivity in mice. Apomorphine-induced climbing in mice was attenuated by (+)-OXA. Clonidine locomotor hypoactivity and hypothermia were unchanged, and clonidine-induced aggressiveness was attenuated by (+)-OXA. Neither OXA enantiomer affected the action of oxotremorine. In some tests the effect of OXA was stronger at 3 h than at 1 h after administration. The above results indicate that both OXA enantiomers--in particular (-)-OXA--increase some dopaminergic behavioural effects in rats.

Effects of single and repeated treatment with antidepressants on apomorphine-induced yawning in the rat: the implication of alpha-1 adrenergic mechanisms in the D-2 receptor function

Acute (10 or 20 mg/kg IP) and subchronic (2 x 5 or 10 mg/kg IP daily for 7 days) effects of desipramine, imipramine, maprotiline, (+)- and (-)-oxaprotiline enantiomers as well as selective 5-HT-uptake inhibitors citalopram and ifoxetine on yawning, induced by low doses of apomorphine, were investigated in the rat. In addition, the effects of alpha-1 receptor agonist adrafinil and antagonist prazosin were also tested. After acute treatment, desipramine, the stereoselective NA-uptake inhibiting (+)-enantiomer of oxaprotiline, and the alpha-1 agonist adrafinil, markedly and significantly suppressed yawning. Prazosin, in contrast, clearly potentiated it. This potentiating effect was abolished by the pretreatment with (+)-oxaprotiline and adrafinil. Other drugs were inactive. After subchronic administration, yawning was antagonized by NA-uptake-inhibiting antidepressants, including imipramine and maprotiline. By comparison to the acute treatment, the inhibitory effects of desipramine and (+)-oxaprotiline were considerably enhanced. Neither selective 5-HT-uptake inhibitors nor (-)-oxaprotiline (levoprotiline) were active. Antidepressants therefore modulate the functional activity of D-2 receptors, activated by low doses of apomorphine, predominantly by the virtue of their noradrenergic enhancing properties. This modulatory effect appears to be mediated by alpha-1 adrenergic receptors.

The mechanism of action of antidepressants revised

The discovery of the clinical efficacy of imipramine and of the MAO-inhibitor iproniazid intensively stimulated biochemical-pharmacological research on the mechanism of action of antidepressants. Due to these investigations, until recently an enhanced activity of the central noradrenergic and/or serotonergic transmitter system was considered essential for the clinical antidepressive action. Such enhancement could be achieved either presynaptically by blocking alpha 2-adrenergic receptors, or in the synaptic cleft by inhibiting the transmitter reuptake or the main metabolic enzyme, MAO. The common final result, especially of chronic treatment, was the down-regulation of postsynaptic beta-receptors, modulated by interaction with the serotonergic system, neuropeptides, and hormones. The delay of clinical response corresponded better with such receptor alterations. However, the introduction of new, more selective antidepressants led to new reflections upon the mechanism of action. On the level of transmitters, alpha 1-upregulation, increased activity of the dopaminergic system, an alteration in the balance between the different transmitter systems, are reported and seem to be important. Most promising are recent investigations of the second messenger systems, the adenylate cyclase system and the phosphatidylinositol system. Both systems are modulated by antidepressant drugs including lithium and carbamazepine. These second messengers, in turn, modulate the phosphorylation status of neuronal proteins via protein kinase, which may lead to elevations of the above mentioned receptors and again their transduction systems.

Antidepressant drugs potentiate the alpha 1-adrenoceptor effect in hippocampal slices

The effect of prolonged treatment with antidepressant drugs on the phenylephrine- and norepinephrine (NE)-evoked reaction in hippocampal slices was examined by extracellular recording of the spontaneous activity of CA1 layer neurons. The alpha 1-adrenoceptor agonists, phenylephrine and methoxamine, depressed the neuronal discharges of most of the units tested, while NE evoked both excitatory and inhibitory effects which were blocked by propranolol and phentolamine or prazosin, respectively. Imipramine, mianserin, (+)- and (-)-oxaprotiline administered subchronically (10 mg/kg p.o., twice daily for 14 days, withdrawal 48 h), potentiated the inhibitory reaction to phenylephrine. Mianserin was the only drug tested in the acute dose to effectively augment the reaction to alpha 1-adrenoceptor stimulation. Prolonged administration of mianserin and imipramine attenuated the excitatory effect to NE, which probably reflects beta-receptor down-regulation; however, only mianserin, but not imipramine, enhanced the NE-induced inhibition. The observed potentiation of the alpha 1-adrenoceptor-related inhibitory reaction to phenylephrine produced by antidepressant drugs may reflect the development of the alpha 1-adrenergic system supersensitivity in the hippocampus.

The influence of repeated treatment with imipramine, (+)- and (-)-oxaprotiline on behavioural effects of dopamine D-1 and D-2 agonists

The paper examined the action of imipramine, (+)- and (-)-oxaprotiline, administered repeatedly to rats, on the behavioural effects of the dopamine D-1 and D-2 agonists, SKF 38393 and quinpirole, respectively. The three antidepressants studied, given in the single dose or repeatedly, attenuate the enhanced grooming evoked by SKF 38393. The locomotor hyperactivity, evoked by quinpirole administered s.c., is increased by repeated but not single-dose treatment with imipramine and (+)-oxaprotiline [but not with (-)-oxaprotiline]. Quinpirole at a low dose produces the locomotor hypoactivity which is attenuated by repeated, but not single-dose, treatment with the anti-depressants studied here. Repeated imipramine and (+)-oxaprotiline [but not (-)-oxaprotiline] increase the locomotor activity effect of quinpirole injected into the nucleus accumbens. The results indicate that the enhanced responsiveness of the dopamine system, observed previously after repeated treatment with antidepressants, may be mediated by the dopamine D-2 receptors.

Implications of chirality and geometric isomerism in some psychoactive drugs and their metabolites

Many drugs contain a chiral centre, or such a centre is introduced during metabolism of the drug in man and in animals. If a single chiral centre is present, the drug will normally exist as a mixture of two enantiomers, of which one may have quite different pharmacologic and/or toxic effects than the other. Chiral drugs that are used in psychiatry, and some other pharmacologically related drugs are identified, and the implications of the presence of one or two chiral centres in these drugs are discussed. Differences in pharmacologic properties of drug and metabolite enantiomers are identified and discussed. Also reviewed are the properties of some drugs used in psychiatry that both are chiral and display geometric isomerism.