Effect of memantine combination therapy on symptoms in patients with moderate-to-severe depressive disorder: randomized, double-blind, placebo-controlled study.

WHAT IS KNOWN AND OBJECTIVE: Current treatments for depressive disorders are far from optimum. This study was planned to evaluate possible antidepressant effects and safety of memantine, a selective N-methyl-d-aspartate receptor antagonist, in humans. METHODS: Sixty-six outpatients with the diagnosis of moderate-to-severe major depressive disorder, based on DSM-V diagnostic criteria, were recruited to participate in a parallel, randomized, controlled trial. Sixty-two participants completed 6 weeks of treatment with either memantine (20 mg/day) plus sertraline (200 mg/day) or placebo plus sertraline (200 mg/day). Patients were evaluated using the Hamilton Depression Rating Scale (HDRS) at baseline and at weeks 2, 4 and 6. Comparison of treatment efficacy in improving depressive symptoms between the two groups was the principal outcome measure. RESULTS AND DISCUSSION: A repeated-measures analysis demonstrated significant time × treatment interaction on HDRS score [F (2·09, 125·67) = 5·09, P = 0·007]. Significantly greater improvement was seen at all three follow-up sessions as well as significantly greater response rates at weeks 4 and 6 (P = 0·018 and P < 0·001, respectively) in the memantine group. Significantly more early improvers and more rapid response to treatment were observed in the memantine group (P = 0·001 and P < 0·001, respectively). A significant reduction was observed in HDRS score from baseline to the study endpoint in both memantine (P < 0·001, Cohen's d = 12·71) and placebo groups (P < 0·001, Cohen's d = 5·13). No serious adverse event occurred. No significantly greater remission rate was seen in the adjunctive memantine therapy. WHAT IS NEW AND CONCLUSION: A 6-week course of treatment with memantine as adjunct to sertraline showed a favourable safety and efficacy profile in patients with major depressive disorder. Nonetheless, larger controlled studies of longer duration are necessary to assess long-term safety, efficacy and optimal dosing.

SKF 38393 and SCH 23390 inhibit reuptake of serotonin by rat hypothalamic synaptosomes.

BACKGROUND/AIMS: Both the dopamine receptor D(1) agonist SKF 38393 and the antagonist SCH 23390 are benzazepine derivatives that have been widely used as pharmacological tools and radioligands. Evidence suggests that behavioral effects of both compounds do not always correspond to their established receptor subtype selectivity. Here, we assessed the effects of SKF 38393 and SCH 23390 on the synaptosomal uptake of tritiated serotonin. METHODS: Uptake experiments were performed by using [(3)H]serotonin and synaptosomal fractions prepared from the hypothalamus of rat brain. RESULTS: Both SKF 38393 and SCH 23390 inhibited synaptosomal uptake of [(3)H]serotonin, with IC(50) values of 910 ± 60 nmol/l and 1,400 ± 80 nmol/l, respectively. Clomipramine, a known inhibitor of serotonin uptake, and (+)-amphetamine, a weak inhibitor, had IC(50) values of 14 ± 1 nmol/l and more than 10,000 nmol/l, respectively, under the same experimental conditions. The IC(50) values for SKF 38393 and SCH 23390 fall within the broad range of corresponding values for antidepressants that have been shown to inhibit the uptake of serotonin. This finding indicates that SKF 38393 and SCH 23390 can enhance the activity of the serotonergic system in the brain, a mechanism that may be responsible for some of the effects of these drugs. CONCLUSION: SKF 38393 and SCH 23390 are useful tools to differentiate D(1) from D(2) receptors, but their indirect effects on serotonergic mechanisms have to be considered.

Possible involvement of mu-opioid receptors in effect of lithium on inhibitory avoidance response in mice.

In the present study, effects of intracerebroventricular (i.c.v.) injections of mu-opioid receptor agonist and antagonist on lithium state-dependency were investigated. For memory assessment, a one-trial step-down inhibitory avoidance task was used in adult male NMRI mice. Intraperitoneal (i.p.) administration of lithium (10 mg/kg) after training impaired memory when retrieval was tested 24 h later. The memory impairment was reversed by pretest administration of the same dose of lithium, suggesting state-dependency induced by lithium. In addition, i.c.v. administration of both lithium (2 and 4 microg/mouse, i.c.v.) and morphine (3 and 6 microg/mouse, i.c.v.) before the test reversed memory impairment induced by post-training lithium (10 mg/kg, i.p.). On the other hand, pretest administration of naloxone (1 and 2 mg/kg) which had no effects alone on inhibitory avoidance response, prevented the improving effects of both morphine (3 microg/mouse, i.c.v.) and lithium (2 microg/mouse, i.c.v.) on memory retrieval. The results suggest that the mu-opioid receptors in the central nervous system may be involved in the retrieval of lithium state-dependent learning.

Harmaline-induced amnesia: Possible role of the amygdala dopaminergic system.

In this study, we examined the effect of bilateral intra-basolateral amygdala (intra-BLA) microinjections of dopamine receptor agents on amnesia induced by a ß-carboline alkaloid, harmaline in mice. We used a step-down method to assess memory and then, hole-board method to assess exploratory behaviors. The results showed that pre-training intra-BLA injections of dopamine D1 receptor antagonist and agonist (SCH23390 (0.5µg/mouse) and SKF38393 (0.5µg/mouse), respectively) impaired memory acquisition. In contrast, pre-training intra-BLA injections of dopamine D2 receptor antagonist and agonist (sulpiride and quinpirole, respectively) have no significant effect on memory acquisition. Pre-training intra-peritoneal (i.p.) injection of harmaline (1mg/kg) decreased memory acquisition. However, co-administration of SCH 23390 (0.01µg/mouse) with different doses of harmaline did not alter amnesia. Conversely, pre-training intra-BLA injection of SKF38393 (0.1µg/mouse), sulpiride (0.25µg/mouse) or quinpirole (0.1µg/mouse) reversed harmaline (1mg/kg, i.p.)-induced amnesia. Furthermore, all above doses of drugs had no effect on locomotor activity. In conclusion, the dopamine D1 and D2 receptors of the BLA may be involved in the impairment of memory acquisition induced by harmaline.

Role of dorsal hippocampal orexin-1 receptors in memory restoration induced by morphine sensitization phenomenon.

The present study was examined the blockade of CA1 orexin-1 receptors (OX1Rs) of the dorsal hippocampus in the induction or expression phase on morphine sensitization-induced memory restoration using the Morris water maze (MWM) apparatus. Results showed that pre-training administration of morphine (5mg/kg, s.c.) increases escape latency and traveled distance, while does not alter swimming speed. This supports the impairing effect of morphine on the spatial memory acquisition in male adult rats. Also, in the retrieval session (probe trial) this treatment decreased the time spent in the target quadrant. Moreover, morphine-induced sensitization (15 or 20mg/kg, s.c.; once daily for 3days and followed by 5days no drug treatment) restored the memory acquisition/retrieval deficit which had been induced by pre-training administration of morphine (5mg/kg, s.c.). Intra-CA1 microinjection of subthreshold doses of SB-334867 (OX1Rs antagonist; 10, 20 and 40nmol/rat), 5min before morphine (20mg/kg/day×3days, s.c.; induction phase for morphine sensitization) did not alter restoration of memory acquisition/retrieval produced by the morphine sensitization phenomenon. In contrast, microinjection of subthreshold doses of SB-334867 (10, 20 and 40nmol/rat) into the CA1 region in the training session, 5min prior to morphine (5mg/kg, s.c.; expression phase for morphine sensitization) blocked the spatial memory acquisition/retrieval in morphine-sensitized rats. In conclusion, these findings show that morphine sensitization reverses morphine-induced amnesia. Furthermore, the blockade of CA1 OX1Rs in the expression phase, but not in the induction phase, disrupts memory restoration induced by morphine sensitization.

CART peptide and opioid addiction: Expression changes in male rat brain.

Previous studies have shown the prominence of cocaine- and amphetamine-regulated transcript (CART) peptide in rewarding and reinforcing effects of drugs of abuse specially psychostimulants. The data regarding the effects of different stages of opioid addiction on CART expression and the interconnection between CART and opioids are not much available. Here we have studied the changes in the expression level of CART mRNA and protein in various parts of the brain reward pathway in different stages of opioid addiction. Groups of male rats received acute low-dose (10mg/kg), acute high-dose (80mg/kg) and chronic escalating doses of morphine. In addition, withdrawal and abstinence states were evaluated after injection of naloxone (1mg/kg) and long-term maintenance of addicted animals, respectively. Expression of CART mRNA in the brain was measured by real-time PCR method. Western blotting was used to quantify the protein level. CART mRNA and protein were both up-regulated in high-dose morphine-administered animals and also in the withdrawal group in the nucleus accumbens (NAc), striatum and prefrontal cortex (PFC). In the addicted group, CART mRNA and protein were both down-regulated in NAc and striatum. In the abstinent group, CART mRNA was down-regulated in NAc. In the hippocampus, the only observed change was the up-regulation of CART mRNA in the withdrawal group. We suggest that the modulatory role of CART peptide in rewarding and reinforcing effects of opioids weakens when opioids are used for a long time and is stimulated when acute stress such as naloxone-induced withdrawal syndrome or acute high-dose administration of morphine occurs to the animal.

Synergistic effect between prelimbic 5-HT3 and CB1 receptors on memory consolidation deficit in adult male Sprague-Dawley rats: An isobologram analysis.

The serotonergic system has often been defined as a neuromodulator system, and is specifically involved in learning and memory via its various receptors. Serotonin is involved in many of the same processes affected by cannabinoids. The present study investigated the influence of bilateral post-training intra-prelimbic (PL) administrations of serotonergic 5-hydroxytryptamine type-3 (5-HT3) receptor agents on arachidonylcyclopropylamide (ACPA) (cannabinoid CB1 receptor agonist)-induced amnesia, using the step-through inhibitory avoidance (IA) task to assess memory in adult male Sprague-Dawley rats. The results indicated that sole intra-PL microinjection of ACPA (0.1 and 0.5 µg/rat) and 5-HT3 serotonin receptor agonist (m-Chlorophenylbiguanide hydrochloride, m-CPBG; 0.001, 0.01 and 0.1 µg/rat) impaired, whereas Y-25130 (a selective 5-HT3 serotonin receptor antagonist; 0.001 and 0.01 and 0.1 µg/rat) did not alter IA memory consolidation, by itself. Moreover, intra-PL administration of subthreshold dose of m-CPBG (0.0005 µg/rat) potentiated, while Y-25130 (0. 1 µg/rat) restored ACPA-induced memory consolidation deficit. The isobologram analysis showed that there is a synergistic effect between ACPA and m-CPBG on memory consolidation deficit. These findings suggest that 5-HT3 receptor mechanism(s), at least partly, play(s) a role in modulating the effect of ACPA on memory consolidation in the PL area.

Effect of circadian rhythm disturbance on morphine preference and addiction in male rats: Involvement of period genes and dopamine D1 receptor.

It is claimed that a correlation exists between disturbance of circadian rhythms by factors such as alteration of normal light-dark cycle and the development of addiction. However, the exact mechanisms involved in this relationship are not much understood. Here we have studied the effect of constant light on morphine voluntary consumption and withdrawal symptoms and also investigated the involvement of Per1, Per2 and dopamine D1 receptor in these processes. Male wistar rats were kept under standard (LD) or constant light (LL) conditions for one month. The plasma concentration of melatonin was evaluated by enzyme-linked immunosorbent assay (ELISA). Real-time PCR was used to determine the mRNA expression of Per1, Per2 and dopamine D1 receptor in the striatum and prefrontal cortex. Morphine preference (50mg/L) was evaluated in a two-bottle-choice paradigm for 10 weeks and withdrawal symptoms were recorded after administration of naloxone (3mg/kg). One month exposure to constant light resulted in a significant decrease of melatonin concentration in the LL group. In addition, mRNA levels of Per2 and dopamine D1 receptor were up-regulated in both the striatum and prefrontal cortex of the LL group. However, expression of Per1 gene was only up-regulated in the striatum of LL rats in comparison to LD animals. Furthermore, after one month exposure to constant light, morphine consumption and preference ratio and also severity of naloxone-induced withdrawal syndrome were significantly greater in LL animals. It is concluded that exposure to constant light by up-regulation of Per2 and dopamine D1 receptor in the striatum and prefrontal cortex and up-regulation of Per1 in the striatum and the possible involvement of melatonin makes animals vulnerable to morphine preference and addiction.

Discrepancy between effects of milligram and nanogram doses of a COX-2 inhibitor (celecoxib) on morphine state-dependent memory of passive avoidance in mice.

This experiment examined and compared the effects of pre-test administration of a selective COX-2 inhibitor (celecoxib), at the doses in the range of mg/kg and ng/kg on morphine state-dependent learning in step-down passive avoidance task in mice. Pre-training administration of 5mg/kg of morphine-impaired memory retrieval tested 24h later, which was restored by pre-test administration of the same dose of the drug. Pre-test administration of celecoxib (12.5, 25 and 50mg/kg), alone or in combination with morphine (1mg/kg) prevents morphine-induced memory impairment. Ultra-low doses (ULDs) of celecoxib (2, 10 and 50 ng/kg) produced no change in morphine-induced memory impairment. However, co-administration of nanogram doses of celecoxib with 5mg/kg of morphine in the test day prevented morphine-induced memory improvement, an action different from mg/kg doses. These findings implicate the involvement of COX-2 in memory retrieval and demonstrate that the effect of celecoxib ULD is different from that of mg/kg doses.

The modulatory effect of CA1 GABAb receptors on ketamine-induced spatial and non-spatial novelty detection deficits with respect to Ca(2+).

Glutamate and γ-aminobutyric acid (GABA) are among the most abundant neurotransmitters in the central nervous system. Ketamine and other noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonists are known to induce deficits in learning and the performance of cognitive tasks. The present study was designed to assess the effects of dorsal hippocampal (CA1) GABAb receptors on ketamine-induced spatial and non-spatial memory deficits with regard to the role of Ca(2+) as a defining factor. Spatial and non-spatial novelty detection of male NMRI mice were investigated in a circular open-field apparatus. According to our results, the intraperitoneal injection of ketamine at its higher dose (0.1 mg/kg) impaired both spatial and non-spatial novelty detection. Moreover, the intra-CA1 injection of baclofen (a GABAb receptor agonist) at higher doses (0.02 and 0.2 µg/mouse) impaired the spatial but not non-spatial novelty detection. In addition, phaclofen (a GABAb receptor antagonist at 0.2 µg/mouse) impaired both spatial and non-spatial novelty detection. Baclofen restored and induced a modulatory effect on ketamine-induced responses in the spatial and non-spatial novelty detection task, respectively. On the contrary, phaclofen restored and induced a modulatory effect on ketamine-induced responses in the non-spatial and spatial novelty detection task, respectively. Finally, the subthreshold dose of SKF96365 (a Ca(2+) channel blocker) impaired only the spatial but not non-spatial restoration effects of baclofen or phaclofen following a higher dose of ketamine. Such findings suggest that the ketamine-induced impairment of memory consolidation may occur through GABAb receptors of the CA1 neurons. Moreover, baclofen and phaclofen were shown to possibly exert their effects on the ketamine-induced spatial novelty detection deficits through Ca(2+) channels.

5-HT1A receptor blockade targeting the basolateral amygdala improved stress-induced impairment of memory consolidation and retrieval in rats.

The aim of the present study was to investigate the possible role of basolateral amygdala (BLA) 5-HT1A receptors in memory formation under stress. We also examined whether the blockade of these receptors is involved in stress-induced state-dependent memory. Adult male Wistar rats received cannula implants that bilaterally targeted the BLA. Long-term memory was examined using the step-through type of passive avoidance task. Behavioral stress was evoked by exposure to an elevated platform (EP) for 10, 20 and 30min. Post-training exposure to acute stress (30min) impaired the memory consolidation. In addition, pre-test exposure to acute stress-(20 and 30min) induced the impairment of memory retrieval. Interestingly, the memory impairment induced by post-training exposure to stress was restored in the animals that received 20- or 30-min pre-test stress exposure, suggesting stress-induced state-dependent memory retrieval. Post-training BLA-targeted injection of a selective 5-HT1A receptor antagonist, (S)-WAY-100135 (2µg/rat), prevented the impairing effect of stress on memory consolidation. Pre-test injection of the same doses of (S)-WAY-100135 that was targeted to the BLA also reversed stress-induced memory retrieval impairment. It should be considered that post-training or pre-test BLA-targeted injection of (S)-WAY-100135 (0.5-2µg/rat) by itself had no effect on the memory formation. Moreover, pre-test injection of (S)-WAY-100135 (2µg/rat) that targeted the BLA inhibited the stress-induced state-dependent memory retrieval. Taken together, our findings suggest that post-training or pre-test exposure to acute stress induced the impairment of memory consolidation, retrieval and state-dependent learning. The BLA 5-HT1A receptors have a critical role in learning and memory under stress.

The effect of CA1 dopaminergic system in harmaline-induced amnesia.

In the present study, the effects of bilateral injections of dopaminergic drugs into the hippocampal CA1 regions (intra-CA1) on harmaline-induced amnesia were examined in male mice. A one-trial step-down passive avoidance task was used for the assessment of memory retention in adult male mice. Pre-training intra-peritoneal (i.p.) administration of harmaline (1 mg/kg) induced impairment of memory retention. Moreover, intra-CA1 administration of dopamine D1 receptor antagonist, SCH23390 (0.02 µg/mouse), dopamine D1 receptor agonist, SKF38393 (0.5 µg/mouse), dopamine D2 receptor antagonist, sulpiride (1 µg/mouse) and dopamine D2 receptor agonist, quinpirole (0.25 and 0.5 µg/mouse) suppressed the learning of a single-trial passive avoidance task. Also, pre-training intra-CA1 injection of subthreshold doses of SCH23390 (0.001 µg/mouse) or sulpiride (0.25 µg/mouse) with the administration of harmaline (1 mg/kg, i.p.) reversed impairment of memory formation. However, pre-training intra-CA1 injection of SKF38393 (0.1 µg/mouse) or quinpirole (0.1 µg/mouse) increased pre-training harmaline (0.25 and 0.5 mg/kg, i.p.)-induced retrieval impairment. Moreover, SKF Ca blocker (SKF) (0.01 µg/mouse) decrease the amnesia induced by harmaline (1 mg/kg), while co-administration of SKF (0.01 µg/mouse)/sulpiride (0.25 µg/mouse) or SCH23390 (0.001 µg/mouse)/sulpiride (0.25 µg/mouse) potentiate amnesia caused by harmaline. These findings implicate the involvement of CA1 dopaminergic mechanism in harmaline-induced impairment of memory acquisition.

Cognitive impairments and neuronal injury in different brain regions of a genetic rat model of absence epilepsy.

Growing numbers of evidence indicate that cognitive impairments are part of clinical profile of childhood absence epilepsy. Little is known on neuropathological changes accompanied by cognitive deficits in absence epilepsy. The aim of the present study was to investigate age-dependent neuropathological changes accompanied by learning and memory impairments in Wistar Albino Glaxo from Rijswijk (WAG/Rij) rat model of absence epilepsy. Experimental groups were divided into four groups of six rats of both WAG/Rij and Wistar strains with 2 and 6 months of age. The learning and memory performances were assessed using passive avoidance paradigm and neuropathological alterations were investigated by the evaluation of the number of dark neurons and apoptotic cells as well as the expression of caspase-3 in the neocortex, the hippocampus, and different regions of the thalamus. Results revealed a decline in learning and spatial memory of 6-month-old WAG/Rij rats compared to age-matched Wistar rats as well as 2-month-old WAG/Rij and Wistar rats. The mean number of dark neurons was significantly higher in the hippocampal CA1 and CA3 areas as well as in the laterodorsal, centromedial, and reticular thalamic nuclei and the somatosensory cortex of 6-month-old WAG/Rij rats. In addition, a higher number of apoptotic cells as well as a higher expression of caspase-3 was observed in the hippocampal CA1 and CA3 regions, the laterodorsal thalamic nucleus, and the somatosensory cortex of 6-month-old WAG/Rij rats compared to other animal groups. These results indicate significant enhancement of neuronal damage and cell death accompanied by memory deficits after seizure attacks in a rat model of absence epilepsy. Seizure-induced neuronal injury and death may underlie cognitive impairments in absence epilepsy.

Dopamine-like properties of ephedrine in rat brain.

1 Ephedrine (3.1-50 mg/kg) was given intraperitoneally to rats and was found to cause a marked increase in spontaneous locomotor activity. 2 In rats with a unilateral lesion in the substantia nigra made by stereotaxic injections of 6-hydroxydopamine, ephedrine (12.5-150 mg/kg i.p.) caused a dose-dependent turning towards the lesioned side. 3 Turning behaviour and increase in locomotion produced by ephedrine were antagonized by pretreatment of the animals with pimozide, amino-oxyacetic acid or reserpine plus alpha-methyl-p-tyrosine, but not by pretreatment with phenoxybenzamine, propranolol or methergoline. 4 In in vitro studies with synaptosomes prepared from rat brain, ephedrine blocked the uptake and caused the release of [3H]-dopamine. 5 Similar results with regard to locomotion and turning behaviour were obtained with (+)-amphetamine. 6 It is concluded that the increase in locomotion and turning behaviour produced by ephedrine is mediated through an indirect dopaminergic mechanism.

Methylxanthine-induced attenuation of pecking in chickens.

1. Apomorphine induced dose-dependent pecking in chickens. 2. The response was decreased by theophylline or caffeine in a dose-dependent manner. 3. Administration of theophylline or caffeine alone did not exert any effect on pecking behaviour. 4. Dipyridamole administration neither induced pecking nor altered the pecking induced by apomorphine. 5. Administration of 5-N-ethylcarboxamide-adenosine to animals caused variable effects on pecking induced by apomorphine. The drug did not induce pecking by itself. 6. It is concluded that the inhibitory response to methylxanthines may be mediated through blockade of adenosine receptors. However, to prove this, more experiments are needed.

Inhibitory effect of morphine on yawning induced by cholinoceptor and dopamine D2 receptor activation in rats.

1. Bromocriptine (2, 4 and 8 mg kg-1, i.p.), physostigmine (0.05, 0.1 and 0.2 mg kg-1, i.p.) and pilocarpine (1, 3 and 5 mg kg-1, i.p.) induced dose-dependent yawning in rats. 2. These responses were reduced in a dose-dependent manner by pretreatment with morphine. 3. The inhibitory effect of morphine was reversed by naloxone. 4. Naloxone alone induced slight but significant yawning. 5. The present results suggest that morphine inhibits yawning in rats at an opiate receptor downstream from the sites at which cholinoceptor and dopamine D2 activation induce yawning. The anatomical location of these sites remains to be established.

Interactions of drugs acting on central dopamine receptors and cholinoceptors on yawning responses in the rat induced by apomorphine, bromocriptine or physostigmine.

1. Yawning was induced by subcutaneous (s.c.) injection of low doses of apomorphine to rats. This effect decreased with increasing doses of the drug. 2. Intraperitoneal (i.p.) pretreatment of animals with sulpiride (D2-receptor blocker) reduced the frequency of the yawns induced by apomorphine, while SCH 23390 (D1-receptor blocker, s.c.) pretreatment increased the small number of yawns which was induced by higher doses of apomorphine. Administration of SCH 23390 alone to rats also produced a low degree of yawning. 3. Apomorphine-induced yawning was decreased in animals treated with SK&F 38393 (D1-agonist, i.p.), atropine (i.p.) or theophylline (i.p.). 4. Intraperitoneal injection of bromocriptine (D2-agonist) in rats also induced dose-dependent yawning. The effect was decreased in animals pretreated with sulpiride, while SCH 23390 pretreatment did not change bromocriptine-induced yawning significantly. Pretreatment of animals with SK&F 38393, atropine or theophylline reduced the number of yawns induced by bromocriptine. 5. Physostigmine (i.p.) but not neostigmine (i.p.) also induced yawning. The effect was antagonized by atropine or theophylline but not by sulpiride. Administration of SK&F 38393 decreased yawning induced by physostigmine. This inhibitory influence of SK&F 38393 was reduced by SCH 23390 in pretreated animals. Treatment of animals with SCH 23390 or bromocriptine increased the frequency of yawns induced by physostigmine. 6. It is concluded that D2-receptor activation elicits yawning through influence on cholinergic mechanisms, whereas D1-receptor stimulation decreases yawning behaviour by a negative influence on the cholinergic system.

Mazindol anorexia is mediated by activation of dopaminergic mechanisms.

1 Anorexia in rats following injections of mazindol (0.1-8 mg/kg i.p.) could be antagonized by pretreatment with a dopamine receptor blocker (primozide) but not by pretreatment with an alpha-adrenoceptor blocker (phenoxybenzamine), a beta-adrenoceptor blocker ((-)-propranolol), or a 5-hydroxytryptamine receptor blocker (methergoline). 2 In rats with a unilateral lesion in the substantia nigra made by stereotaxic injection of 6-hydroxydopamine, mazindol caused a dose-dependent turning towards the lesioned side, indicating an indirect mechanism of action. This effect could be antagonized by pretreatment with a dopamine receptor blocker. 3 In rats pretreated with reserpine and alpha-methyl-p-tyrosine, mazindol did not have any motor stimulant action. 4 In vitro studies with synaptosomes prepared from rat brain, indicated that mazindol blocks uptake and causes release of dopamine. 5 It is concluded that the anorectic action of mazindol is mediated by a dopaminergic mechanism.

The effect of ethacrynic acid on the guinea-pig and rat isolated vas deferens.

1 The effect of ethacrynic acid (EA) was studied on guinea-pig and rat vas deferens in vitro.2 EA contracted the guinea-pig but not the rat vas deferens in a dose-dependent manner (50-800 mug/ml). Tyramine caused contraction in 10 out of 18 guinea-pig vas deferens; EA caused contraction in 17 of the preparations which did not respond to tyramine. Repeated doses of EA produced tachyphylaxis, but there was no cross tachyphylaxis to tyramine.3 The contractions produced by EA were prevented by phentolamine or reserpine pretreatment and potentiated by cocaine. A low concentration of desipramine (3 ng/ml) potentiated and higher concentrations (0.6 and 3.0 mug/ml) inhibited the response of vas deferens to EA.4 Hexamethonium (100 mug/ml) or atropine (0.1 mug/ml) did not inhibit the effect of EA, excluding the nicotinic and muscarinic receptors as the sites of action.5 The effect of noradrenaline (NA) on the guinea-pig and rat vas deferens was enhanced by EA pretreatment, which may be due to inhibition of NA uptake.6 It is concluded that EA releases NA from guinea-pig vas deferens. The mechanism of release seems to be different from that of tyramine.

Tachyphylaxis to ethacrynic acid in the isolated atrium of guinea-pig and its relation to noradrenaline stores.

1 The isolated electrically-paced atrium of the guinea-pig developed a dose-dependent increase in the force of contraction in response to ethacrynic acid (12-100 microgram/ml) which was blocked by pretreatment of the animals with reserpine but was unaffected by desipramine or colchicine added to the bathing medium. 2 There was a rapidly developing tachyphylaxis to repeated doses of ethacrynic acid which was not reversed by rest or incubation of the tissue with noradrenaline. 3 There was no cross tachyphylaxis between ethacrynic acid and tyramine, amphetamine or nicotine. 4 Ethacrynic acid (200 microgram/ml) decreased the noradrenaline content of the atria by 32%. 5 It is concluded that ethacrynic acid exerts its effects indirectly through the release of endogenous noradrenaline and that the mechanism of release seems to be different from that of other known indirect sympathomimetic drugs.