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PubMed1993

The NMDA positive modulator D-cycloserine potentiates the neuroleptic activity of D1 and D2 dopamine receptor blockers in the rat.

According to the view that N-methyl-D-aspartate (NMDA) agonists could be seen as putative therapeutic agents in schizophrenia, the present study was aimed at investigating whether the NMDA positive modulator D-cycloserine (DCS) could show neuroleptic activity. When given alone, DCS (1.5, 3, 6, 12 mg/kg) failed to affect the stereotyped behavior induced by 0.5 mg/kg SC apomorphine, a test routinely used to detect neuroleptic activity. Nevertheless, the administration of different doses of DCS (1.5, 3, 6 mg/kg) in combination with the D1 dopamine receptor blocker SCH 23390 or the D2 antagonist YM 09151-2, both given in doses which by themselves were ineffective in blocking apomorphine elicited behavior, induced a dose- dependent neuroleptic effect. Furthermore the positive NMDA modulator allowed (-)-sulpiride, which given alone never antagonized the apomorphine-induced stereotypy, to exhibit a full neuroleptic activity. The lower dose of DCS effective in potentiating antipsychotic effect of dopaminergic blockers also counteracted the behavioral response (hypermotility) induced by the NMDA negative modulator MK-801 (0.25 mg/kg), thus indicating the specificity of DCS effect. The results strengthen the view that drugs which increase NMDA receptor function could be a useful supplement in the therapy of psychotic disorders.

Animals↗
PubMed2000

Anticonflict effect of the glycineB receptor partial agonist, D-cycloserine, in rats. Pharmacological analysis.

RATIONALE: Several studies have provided evidence that antagonists and partial agonists of glycine(B) receptors exhibit an anxiolytic-like activity in different animal models. OBJECTIVE: Using the conflict-drinking Vogel test in rats as a model, in the present study we examined the anxiolytic-like activity of D-cycloserine (DCS), a partial agonist of the glycine(B) site of the N-methyl-D-aspartate (NMDA) receptor complex. Diazepam was used as a reference drug. RESULTS: DCS (200 and 300 mg/kg) and diazepam (5 mg/kg) produced an anxiolytic-like effect in rats by increasing the number of shocks accepted. We also demonstrated that NMDA (15 mg/kg) reduced the anxiolytic-like activity of DCS (200 mg/kg), whereas glycine (800 mg/kg) and flumazenil (10 mg/kg) did not affect the anticonflict effect of DCS (200 mg/kg). The anticonflict effect of diazepam (5 mg/kg) was totally blocked by flumazenil (10 mg/kg). CONCLUSION: The obtained results have shown that DCS exhibits an anxiolytic-like activity which depends on NMDA receptors rather than on glycine(B) or benzodiazepine sites.

Animals↗
PubMed1990

D-cycloserine acts as a partial agonist at the glycine modulatory site of the NMDA receptor expressed in Xenopus oocytes.

In the Xenopus oocyte preparation, D-cycloserine (DCS) had the profile of a partial agonist at the glycine modulatory site of the NMDA receptor. Maximal NMDA responses in the presence of DCS were only 40-50% of those in the presence of glycine. Glycine and D-serine were agonists at this site. The actions of DCS were competitively antagonized by HA-966, a known glycine antagonist.

Animals↗
PubMed1991

D-cycloserine, a putative cognitive enhancer, facilitates activation of the N-methyl-D-aspartate receptor-ionophore complex in Alzheimer brain.

The action of D-Cycloserine (DCS) at the strychnine-insensitive glycine recognition site of the NMDA receptor-ionophore complex has been studied with membranes from inferior parietal cortex of patients with Alzheimer's disease. The maximal response of the site, measured using [3H]MK-801 binding, was 64% of that observed with glycine. Stimulation of binding induced by DCS in the presence of fixed concentrations of glycine resulted in a family of dose-response curves, consistent with the antibiotic having the property of a partial agonist at this glycine site. It is proposed that because of circumscribed glutamatergic pyramidal cell pathology DCS will have benefit for Alzheimer's patients over and above all other types of cognitive impairment.

Aged↗
PubMed1992

Effect on memory processing by D-cycloserine, an agonist of the NMDA/glycine receptor.

Glycine has been shown to modulate N-methyl-D-aspartate (NMDA) subclass of acidic amino acid receptors which have been implicated in learning and memory. We report that d-cycloserine (DCS) which has a high affinity for the glycine modulatory site in the NMDA receptor complex modulated memory processing in a dose-dependent manner. Mice were trained on a footshock avoidance task. Immediately after training DCS was administered (2.5 to 50 mg/kg s.c.). When retention was tested a week later, 20 mg/kg facilitated retention the best with lower and higher doses be less effective in weakly trained young mice. DCS also facilitated retention in 'senescence-accelerated mice' in which impairment of learning and memory increases with age. DCS had to be administered at higher doses to improve retention as impairment of learning and memory increased.

Age Factors↗
PubMed1993

Age-related decrease of the NMDA receptor-mediated noradrenaline release in rat hippocampus and partial restoration by D-cycloserine.

The release of [3H]noradrenaline ([3H]NA) evoked by N-methyl-D-aspartate (NMDA) from superfused rat hippocampus synaptosomes was monitored during aging. The maximal effects of NMDA decreased with age from 50% (1.5 months) to 10% enhancement (24 months). Quisqualic acid (100 microM) also enhanced [3H]NA release. Its effect decreased with age with a pattern partly different from that of NMDA. Glycine (1 microM) potentiated the [3H]NA releasing effect of 100 microM NMDA. Unexpectedly, the potentiation which amounted to 50% at 1.5 months, reached almost 200% and 300% in the 18- and 24-month-old rats, respectively, thus compensating in part for the age-related loss of the NMDA-induced effect. Concentration-response relationships for glycine at 3 vs. 24 months suggest that the glycine receptor is superresponsive in the aged brain. This may be due to more efficient glycine removal or/and to impaired release since uptake of the amino acid was increased by 350% in 24- vs. 3-month-old rats, while the K(+)-evoked tritium release from synaptosomes prelabeled with [3H]glycine was decreased. D-Cycloserine, although about 10 times less potent than glycine, strongly enhanced the NMDA-evoked [3H]NA release and may prove useful in cognitive deficits associated with aging and dementia.

Aging↗
PubMed1994

The NMDA positive modulator D-cycloserine inhibits dopamine-mediated behaviors in the rat.

The NMDA positive modulator D-cycloserine (DCS), which failed to modify rat spontaneous behavior, inhibited the hypermotility induced by the dopamine releaser methamphetamine as well as the behavioral responses to the selective stimulation of D1 or D2 dopamine receptors (SKF 38393 induced grooming and LY 171555 elicited hyperactivity, respectively). In contrast, behavioral responses to different doses of apomorphine (hypermotility and stereotypies) were not modified by the administration of DCS. No change in apomorphine-induced stereotyped behavior was observed during DCS repeated treatment (21 days), but an antagonism of dopaminergic stimulation occurred when DCS was repeatedly administered together with low doses of D1 and D2 dopamine receptor blockers [SCH 23390 and (-)-sulpiride]. Five days following the combined repeated treatment, behavioral dopaminergic supersensitivity was observed. The results are consistent with the view that an increase in glutamatergic function could decrease the response to dopaminergic stimulation.

Animals↗
PubMed1989

D-cycloserine, a positive modulator of the N-methyl-D-aspartate receptor, enhances performance of learning tasks in rats.

Glycine has recently been shown to positively modulate the N-methyl-D-aspartate (NMDA) subclass of acidic amino acid receptors which are important in neural pathways involved in learning and memory. We report that d-cycloserine (DCS), an antimycobacterial agent known to cross the blood-brain barrier, binds with high affinity to this glycine modulatory site, functions as a positive modulator, and facilitates performance of learning tasks in rats. In addition, DCS appears to be a potent cognitive enhancer at doses lower than those required for antibacterial activity. Based on these data, we propose that modulation of NMDA receptors via glycinergic mechanisms may be a means of influencing cognitive processes.

Animals↗
PubMed1990

Effects of D-cycloserine and cycloleucine, ligands for the NMDA-associated strychnine-insensitive glycine site, on brain-stimulation reward and spontaneous locomotion.

D-Cycloserine (DCS) binds with high affinity to the glycine site associated with the NMDA receptor in rat brain. Systemic injections of DCS have been reported to facilitate performance on learning tasks, possibly by promoting long-term changes at the NMDA receptor complex. In the present study, DCS failed to affect spontaneous locomotor activity or variable-interval self-stimulation response rate. Cycloleucine, a competitive antagonist of glycine at the glycine site, produced a brief depression of self-stimulation, but only after relatively large doses which were not antagonised by injection of DCS in the dose reported to be optimal for the facilitation of learning. Improvements in learning and retention reported after administration of DCS are therefore unlikely to be accounted for by nonassociative motivational, or performance, factors.

Animals↗
PubMed1993

Effect of D-cycloserine on rapid tolerance to ethanol.

We recently reported that the noncompetitive NMDA antagonists, (+)MK-801 and ketamine, block the development of rapid tolerance to ethanol. In the present article, we show that D-cycloserine (CS), an agonist at the glycine site of the NMDA receptor that enhances learning and memory, also enhances the development of rapid tolerance to ethanol. Rats were pretreated on day 1 with saline or CS, followed 30 min later by ethanol (2.3 g/kg, IP) or saline. At the end of motor impairment testing on the tilt-plane apparatus, a second injection of CS (3 mg/kg, IP, each time) or saline was given, followed 30 min later by ethanol or saline. Ethanol pretreatment alone (at this dose) did not result in rapid tolerance to ethanol on day 2. However, the group pretreated with CS and ethanol on day 1 showed significant tolerance on day 2 compared to other groups. Pretreatment with CS on day 1 did not affect the motor impairment response to the first exposure to ethanol whether this was on day 1 or day 2. In another experiment, administration of (+)MK-801 (0.25 mg/kg, IP) prior to CS abolished the rapid tolerance enhancement by CS. These findings are further evidence that the NMDA system, which requires activation by the glycine receptor, plays a major role in the development of at least some forms of ethanol tolerance.

Animals↗
PubMed2003

Cycloserine and threo-dihydrosphingosine inhibit TNF-alpha-induced cytotoxicity: evidence for the importance of de novo ceramide synthesis in TNF-alpha signaling.

Measuring the cell death induced by tumor necrosis factor (TNF-alpha) in L929 cells, we discovered for the first time that L-cycloserine, an established inhibitor of serine palmitoyltransferase, as well as DL-threo-dihydrosphingosine (threo-DHS, threo-sphinganine) significantly protected against TNF-alpha-induced cytotoxicity. Under the same conditions sphingosine and DL-erythro-dihydrosphingosine (erythro-DHS) did not change TNF-alpha-induced cytotoxicity, thus underlining the specificity of threo-DHS. In serine-labeled cells, newly (de novo) synthetized labeled ceramide was significantly diminished by threo-DHS alone or together with TNF-alpha, which makes the (dihydro) ceramide synthase the likely target of threo-DHS. These results suggest the decisive role of ceramide de novo synthesis in TNF signaling.

Animals↗
PubMed2004

Responsiveness to brightness change in male and female rats following treatment with the partial agonist of the N-methyl-D-aspartate receptor, D-cycloserine.

Male and female hooded rats were intraperitoneally injected with 0 (vehicle only), 5 or 10 mg/kg D-cycloserine (DCS) and then individually allowed free access to the arms of a Y maze (acquisition trial), one of which was black and the other white. Their ability to later recognize the arm that had changed from white to black was assessed from the first arm entered, and the number of times the novel changed arm was repeatedly entered as well as the total time they spent in this arm. DCS increased the number of times the novel arm was entered first and, at the higher dose, repeated entries of and time spent in this arm by female rats. Males showed increases after the lower but not higher dose. In a second experiment, DCS was administered after rather than before the acquisition trial. With the exception of the first arm entered for males only, DCS did not significantly affect choices of the novel arm. However, contrary to treatment with vehicle, such choices were significantly higher than chance expectancies after 5 mg/kg DCS, thereby indicating that the treated rats were able to recognize the novel arm. It was concluded that, in the first experiment, DCS had mainly improved attention and/or encoding, and had slightly enhanced memory in the second. Any effects on memory were most likely due to prevention of forgetting. There was also evidence of anxiolytic effects of DCS that may have facilitated responses to both arms without affecting specific choices of the novel alternative.

Analysis of Variance↗
PubMed2005

D-cycloserine facilitates extinction of learned fear: effects on reacquisition and generalized extinction.

BACKGROUND: d-cycloserine (DCS) facilitates extinction of learned fear. The aim of this study was to examine whether DCS 1) affects reacquisition of fear (Experiment 1) and 2) produces generalized extinction of fear (Experiment 2). METHODS: Following fear conditioning, where a light or a tone conditioned stimulus (CS) was paired with a white-noise burst unconditioned stimulus (US), rats received nonreinforced exposure to one CS (i.e., extinction training). Fear was assessed by measuring CS-elicited freezing, a species-specific defense response. RESULTS: Rats given DCS exhibited facilitated extinction of fear but were able to reacquire fear of that CS in a similar manner as saline-treated control animals (Experiment 1). Furthermore, DCS-treated rats exhibited generalized extinction (i.e., they were less fearful of a non-extinguished CS) in comparison to controls (Experiment 2). CONCLUSIONS: DCS facilitates extinction of learned fear to the extinguished CS, but also appears to reduce fear of a nonextinguished CS. These findings suggest that this drug may have substantial clinical value in the treatment of anxiety disorders.

Animals↗
PubMed2006

Effects of D-cycloserine on extinction: translation from preclinical to clinical work.

Administration of benzodiazepines or serotonin reuptake inhibitors in combination with behavior therapy for the treatment of many anxiety disorders has generally lead to only modest gains. In this article we suggest that pharmacotherapy aimed not at treating the symptoms of anxiety but instead aimed at improving the learning that takes place in exposure therapy might actually improve the effectiveness of exposure therapy. This idea was based on animal work showing that the partial N-methyl-D-aspartate (NMDA) agonist D-cycloserine (DCS) facilitated extinction of fear when given either before or shortly after exposure to fearful cues, reduced return of fear that is normally seen when extinction training is followed by stress, and led to generalized extinction, where DCS given in combination with exposure to one fearful cue led to extinction to another cue previously paired with the same aversive event. These finding suggested that DCS might facilitate exposure-based psychotherapy, which was verified in a small clinical study showing that DCS facilitated exposure therapy for fear of heights in a well-controlled virtual reality environment.

Animals↗
PubMed2004

Glycine and D-cycloserine attenuate vacuous chewing movements in a rat model of tardive dyskinesia.

Presently there is no established treatment for antipsychotic drugs-induced tardive dyskinesia (TD), which remains a major clinical issue in psychiatry. Based on the principles of the glutamatergic hypothesis of schizophrenia, the amino acid glycine (GLY) and the antituberculosis drug D-cycloserine (DCS) have been assessed, during the last decade, as adjuvants to antipsychotic drugs. Observations stemming from these studies suggest that, in addition to improving schizophrenia symptoms, these compounds may also be beneficial against drug-induced dyskinesias. In order to investigate this hypothesis, GLY and DCS effects were studied using the putative TD analogue vacuous chewing movements (VCM) rat model. Following 24 weeks of treatment with haloperidol decanoate (0.38 mg/kg/4 weeks) rats (N=40) were randomized to receive one intraperitoneal injection with 1.6 g/kg GLY, 10 mg/kg ("low dose") DCS; 100 mg/kg ("high dose") DCS or saline ("placebo"), respectively. Behavior was videotaped at intervals during the experiment and all VCM, rearing, grooming and immobility episodes were analyzed and scored. A control group (N=9) received saline for 24 weeks. Haloperidol administration decreased motor activity and significantly induced VCM. High dose DCS significantly reduced VCM without affecting other motor parameters. GLY treatment resulted in significantly less VCM but also reduced rearing, grooming and mobility. In contrast, low dose DCS and placebo did not significantly affect any of these parameters. These findings indicate that the use of GLY and DCS results in attenuation of VCM in rats and may have an effect on TD in humans. Clinical trials with this type of compounds for patients suffering from TD are warranted.

Animals↗
PubMed2005

Behavioral effects of d-cycloserine in rats: the role of anxiety level.

It has been reported that the glutamatergic N-methyl-D-aspartate (NMDA) receptor is involved in stress responses and that anxiety is the primary response to stress. Although individual differences in anxiety levels of rats have been demonstrated by using the elevated plus-maze (PM) test, the role of NMDA receptor activity in such individuality of anxiety is not clear. Here, we examined whether low (LA) and high (HA) anxiety rats might respond differently to treatment with d-cycloserine (DCS), a partial agonist of the glycine binding site located on NMDA receptors. Male Wistar rats were screened by using the PM and divided into LA and HA subgroups. On the next day, these rats were again tested in the PM, 30 min after the treatment with DCS (5, 10, or 30 mg/kg ip). Five days later, the rats were subjected to a 2-day forced swim (FS) test, receiving the DCS treatment again 30 min before the second day session. The PM data showed that DCS had anxiogenic effects in LA but not HA rats. The immobility of LA or HA rats in the FS test was not affected by DCS. The results indicate that the behavioral effects of DCS depend on the anxiety level of rats and have task-dependent behavioral consequences, suggesting that glycine binding sites on NMDA receptors are involved in individual differences of anxiety level.

Animals↗
PubMed2006

A randomized controlled trial of the effect of D-cycloserine on extinction and fear conditioning in humans.

Previous research has shown that D-cycloserine (DCS) facilitates extinction of Pavlovian fear conditioning in rats and enhances exposure therapy in humans. The aim of this study was to test the effect of DCS on extinction of fear conditioning in humans. In three experiments, 238 participants were given either DCS (50 or 500 mg) or placebo 2-3 h before extinction training following a differential shock conditioning paradigm. Clear extinction and recovery (return of fear) effects were observed on both skin conductance and self-reported shock expectancy measures in three studies. DCS had no influence on these effects. The same pattern was observed when the analysis was restricted to aware participants or to good conditioners, when fear-relevant cues (pictures of snakes) were used as the conditioned stimuli, or when analysis was restricted to heightened snake-fearful participants. These results suggest that DCS may not enhance the extinction, or prevent the recovery, of learned fear in a differential Pavlovian conditioning paradigm in humans. Further experimental research is needed to better understand the mechanisms underlying the therapeutic effects of DCS.

Adult↗
PubMed2006

Controlled trial of D-cycloserine adjuvant therapy for treatment-resistant major depressive disorder.

BACKGROUND: Compounds that reduce N-methyl-d-aspartate receptor (NMDAR) function, including NMDAR antagonists and partial agonists at the NMDAR-associated glycine (GLY) site, may act as antidepressants. The antibiotic drug d-cycloserine (DCS) acts as a partial agonist at the NMDAR-GLY site. Preclinical and clinical data suggest that at dosages >or=100 mg/day DCS acts as a functional NMDAR antagonist and may have antidepressant effects. METHODS: Twenty-two treatment resistant major depression patients participated in a double-blind, placebo-controlled 6-week crossover trial with 250 mg/day DCS added to their ongoing antidepressant medications. RESULTS: DCS treatment was well tolerated and resulted in symptom reductions. However, biweekly-performed clinical assessments, including the Hamilton Depression Rating Scale, Hamilton Rating Scale for Anxiety and Zung Self-Rating Depression Scale did not reveal statistically significant therapeutic advantages of DCS vs. placebo adjuvant treatment. LIMITATIONS: Small sample, uneven treatment resistance criteria across subjects. The exposure to DCS (dose/length of treatment) may not have been sufficient. CONCLUSIONS: This exploratory study represents the first attempt to assess the effects of a NMDAR-GLY site partial agonist in depression treatment. The findings and limitations of this study should be taken into account in the planning of future clinical trials with NMDAR modulators in depression.

Adult↗