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Biomedical subjects

P L Wood

Publications and source records attributed to P L Wood.

At least 19 recordsLinked to original sources
PubMed2000

Characterization of the anxiolytic properties of a novel neuroactive steroid, Co 2-6749 (GMA-839; WAY-141839; 3alpha, 21-dihydroxy-3beta-trifluoromethyl-19-nor-5beta-pregnan-20-one), a selective modulator of gamma-aminobutyric acid(A) receptors.

The purpose of this study was to evaluate the effects of a novel neuroactive steroid, Co 2-6749 (GMA-839; WAY-141839; 3alpha, 21-dihydroxy-3beta-trifluoromethyl-19-nor-5beta-pregnan-20-one), on gamma-aminobutyric acid(A) receptors in vitro and to define its anxiolytic-like effects and side effect profile in vivo. Co 2-6749 fully inhibited [(35)S]t-butylbicyclophosphorothionate binding in rat brain cortical membranes with an IC(50) value of 230 nM and in human gamma-aminobutyric acid(A) receptor subunit combinations of alpha1beta2gamma2L, alpha2beta2gamma2L, alpha3beta2gamma2L, alpha4beta3gamma2L, alpha5beta2gamma2L, and alpha6beta3gamma2L receptors (IC(50) values of 200, 200, 96, 2300, 210, and 2000 nM). Rats were trained in a Geller-Seifter operant conflict paradigm. Co 2-6749 caused a dose-related increase in punished responding with a minimum effective dose of 1.6 mg/kg, p.o., a wide therapeutic index relative to a decrease in unpunished responding and relative to ataxia, and no tolerance. Additionally, ethanol caused less than a 2-fold shift to the left in the dose-response function of Co 2-6749 in the rotorod procedure in rats. In a pigeon conflict paradigm, punished responding was maximally increased to 784% of vehicle control by 30 mg/kg, p.o., with a 2-h duration and no effect on unpunished responding at this dose. Similarly, punished responding in squirrel monkeys was maximally increased to 1774% of control by 10 mg/kg, p.o., with no effect on unpunished responding at this dose. With robust anxiolytic-like activity across species, a large separation between anxiolytic-like effects and sedation/ataxia, a minimal interaction with ethanol, a lack of tolerance, and apparent oral bioavailability, Co 2-6749 makes an ideal candidate for development as a novel anxiolytic drug.

Alprazolam↗
PubMed1999

Positive allosteric modulators of the GABA(A) receptor: differential interaction of benzodiazepines and neuroactive steroids with ethanol.

Endogenous pregnane steroids, such as allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one; 3alpha, 5alpha-P) and pregnanolone (3alpha-hydroxy-5beta-pregnan-20-one; 3alpha,5beta-P), allosterically modulate GABA(A) receptor function and exhibit behavioral effects similar to benzodiazepines, though acting at a distinct recognition site. Inasmuch as some positive allosteric modulators of GABA(A) receptor function exhibit profound interactions with ethanol, the effects of 3alpha,5alpha-P and 3alpha,5beta-P were compared to those of two benzodiazepines, triazolam and diazepam, on the motor function of mice and rats when administered either alone or in combination with ethanol. All four test compounds exhibited dose-related impairment of motor function in the horizontal wire task in mice and the rotorod task in rats. Ethanol caused a marked enhancement of triazolamand diazepam-induced motor impairment. In contrast, ethanol enhanced to a lesser extent the motor impairment induced by both neurosteroids in mice and not at all in rats. All four compounds increased ethanol-induced behavioral sleep time in mice, although the benzodiazepines did so at a much smaller fraction of their ataxic doses as compared to the neurosteroids. As one of the undesired side-effects of therapeutic use of benzodiazepines is their interaction with ethanol, development of neuroactive steroids as drugs may offer therapeutic advantages.

Allosteric Regulation↗
PubMed1999

Reinforcing and discriminative stimulus effects of the neuroactive steroids pregnanolone and Co 8-7071 in rhesus monkeys.

RATIONALE AND OBJECTIVES: The present study was designed to assess possible abuse-related effects of the endogenous neuroactive steroid pregnanolone (3alpha-hydroxy-5beta-pregnan-20-one) and the orally bioavailable, water-soluble neuroactive steroid pro-drug Co 8-7071 (3alpha,21-dihydroxy-3beta-trifluoromethyl-5beta-pregnan-20- one, 21-hemisuccinate). METHODS: Four rhesus monkeys were prepared with chronic intravenous (i.v.) catheters and trained to press a lever under a ten-response fixed-ratio (FR) schedule of methohexital injection (0.1 mg/kg per injection). Three rhesus monkeys were trained to discriminate intragastric infusions of pentobarbital (10 mg/kg) from saline infusions under a FR5 schedule of stimulus-shock termination. RESULTS: At least two doses of pregnanolone (0.003-0.1 mg/kg per injection) maintained injections per session above saline levels in the four monkeys tested, whereas Co 8-7071 (0.01-1.0 mg/kg per injection) maintained injections per session above saline levels in two of four monkeys at relatively low levels of injections per session. In rhesus monkeys trained to discriminate pentobarbital, i.v. pregnanolone injections (0.1-1.7 mg/kg, 5-min presession) dose-dependently reproduced the discriminative stimulus effects of pentobarbital in all monkeys tested. Intravenous administration of Co 8-7071 (1-10 mg/kg, 5-min presession) resulted in a dose-dependent increase to >80% pentobarbital-appropriate responding in two of three monkeys tested. Following intragastric infusions of Co 8-7071 (1.0-30 mg/kg), > or =80% pentobarbital-appropriate responding occurred in one out of three monkeys at 10 mg/kg when administered 60 min before the session. When administered 120 min before the session, however, 10-30 mg/kg Co 8-7071 reproduced the discriminative stimulus effects of pentobarbital in each of the three monkeys tested. CONCLUSIONS: These data demonstrate barbiturate-like abuse-related effects that differed between two pregnane steroids. Whereas pregnanolone functioned as a reinforcer, suggesting that this compound has abuse potential, Co 8-7071 did not, despite having pentobarbital-like discriminative effects.

Animals↗
PubMed1999

Maternal serum screening for Down syndrome in women aged 40 years and over.

Two hundred and thirty-nine women aged 40 years were booked for delivery at Kettering General Hospital from 1992 to 1997. Six women were not eligible for the triple test (TT) as they booked too late. Eighty-eight women declined TT. The reasons were; fear and anxiety about the risk of miscarriage associated with amniocentesis if the test result were a high risk (70.5%), worries about the false negative result associated with the TT (20.5%) and reluctance to terminate the pregnancies if the fetus were abnormal (9%). One hundred and forty-five women (62.2%) elected for TT of whom 91 (62.8%) had received a high risk results. Of the women who received a high-risk result 61/91 (67%) had an amniocentesis. The study provides an accurate probability of receiving a high risk TT screening in women aged 40 years and highlights the need for a more sensitive screening test or a less invasive diagnostic test for the detection of Down syndrome.

Journal Article↗
PubMed1999

The outcome of five years' implementation of maternal serum screening for Down's syndrome comparing actual age risks and mode of delivery.

In this paper 13 613 triple test results from the period 1992- 1997 were analysed. The probability of receiving a high risk result for Down's syndrome from a serum screen, related to the patient's age, was calculated. The modes of delivery of the patients receiving a high risk result were also compared with the rest of the population. The probability of receiving a high risk result increased from 1.2% at 25 years of age to 43.9% at 40 years of age. There was a decrease in the likelihood of having operative intervention at delivery amongst the high risk group but this did not reach statistical significance. This highlights the need for accurate information in risk and probability when counselling a patient undergoing serum screening. Patient's anxiety relating to mode of delivery may also be alleviated by knowing they have no greater risk of operative delivery.

Journal Article↗
PubMed1997

Novel phosphoserine phosphatase inhibitors.

Phosphoserine phosphatase (EC 3.1.1.3) catalyzes the final step in the major pathway of L-serine biosynthesis in brain. This enzyme may also regulate the levels of glycine and D-serine, the known and putative co-agonists for the glycine site of the N-methyl-D-aspartate receptor in caudal and rostral brain regions, respectively. Using L-phosphoserine as substrate, the rank order potency for inhibition of phosphoserine phosphatase was p-chloromercuriphenylsulfonic acid (CMPSA) > glycerophosphorylcholine >> hexadecylphosphocholine > or = phosphorylcholine > N-ethylmaleimide > or = L-serine > fluoride > D-2-amino-3-phosphonopropionic acid (D-AP3). Glycerylphosphorylcholine (IC50 18 microM) was found to be an uncompetitive inhibitor of phosphoserine phosphatase. Glycerylphosphorylcholine probably binds a novel site on the enzyme since the known allosteric inhibitor L-serine is highly selective for its feedback regulatory site, indicated by the inactivity of 25 L-serine analogs. Fluoride ion (IC50 770 microM) may bind the active site as has been shown for other Mg2+-dependent enzymes. The sulfhydryl reagent CMPSA is a potent, noncompetitive inhibitor of the enzyme using L-phosphoserine as substrate (IC50 9 microM) but is > 300-fold less potent using D-phosphoserine as substrate. Substrate-dependent differences are also observed with the sulfhydryl alkylator N-ethylmaleimide, which inhibits L-phosphoserine, but stimulates D-phosphoserine hydrolysis. These sulfhydryl reagents may dissociate multimeric forms of the enzyme to form monomers; the multimeric forms and monomers may preferentially cleave L- and D-phosphoserine, respectively. Phosphorylcholine esters and sulfhydryl reagents may prove useful in determining the contribution of phosphoserine phosphatase to the biosynthesis of glycine and D-serine in neuronal tissue in vitro.

Animals↗
PubMed1997

Anxiolytic and anticonvulsant activity of a synthetic neuroactive steroid Co 3-0593.

Endogeneously occurring neuroactive steroids, metabolites of progesterone and deoxycorticosterone, have been shown previously to interact with the GABAA receptor with great specificity in vitro and to have anticonvulsant, anxiolytic and sedative activity in vivo. However, these endogenously occurring steroids are not useful as therapeutic agents due to their potential metabolism to hormonally active steroids and their poor oral bioavailability. In an attempt to develop therapeutic agents which would maintain the pharmacological profiles of endogeneous neuroactive steroids but with increased oral bioavailability and reduced metabolic liability, we explored simple substitutions at the 3 beta-position of the endogenous neuroactive steroid, 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha, 5 alpha-P). This report describes part of the in vitro and in vivo pharmacological profile of a 3 beta-substituted analog, 3 beta-ethenyl-3 alpha-hydroxy-5 alpha-pregnan-20-one (Co 3-0593). The compound exhibited anticonvulsant activity against pentylenetrazol-induced seizures in mice and rats (ED50 = 5.6 and 11.5 mg/kg, i.p., respectively). Co 3-0593 showed robust anxiolytic effects, comparable to benzodiazepines in the Geller-Seifter test after both SC and oral administration. Furthermore, the anxiolytic activity was maintained after chronic administration suggesting an absence of tolerance. The compound did not affect the acquisition of a learned response at both anticonvulsant and anxiolytic doses. However, at higher doses the compound showed rotorod deficit which was further enhanced by ethanol. In summary, 3 beta-ethenyl-substituted 3 alpha, 5 alpha-P appeared to maintain the pharmacological activities of the endogenous neuroactive steroid with apparent oral activity.

Animals↗
PubMed1997

N-methyl-D-aspartate antagonists for stroke and head trauma.

The N-methyl-D-aspartate (NMDA) receptor is a ligand-gated ion channel which is widely distributed in the central nervous system (CNS), and which mediates most of the fast excitatory neuronal transmission in the CNS. As with other ligand-gated ion channels, the NMDA receptor is a macromolecular complex which possesses a number of intricate regulatory sites within and around a central ion channel. The key regulatory components for which prototypic antagonists have been developed are the competitive NMDA antagonist binding site, the non-competitive NMDA antagonist binding site within the ion channel, and the NMDA receptor-associated glycine antagonist site. The binding domains for each of these binding sites possess discrete and non-overlapping SAR with regard to the chemical series developed to date. The potential utility of NMDA antagonists in the treatment of stroke and traumatic brain injury was investigated soon after the synthesis of the first bioavailable NMDA antagonists. Efficacy in preclinical models was demonstrated with both competitive and non-competitive NMDA antagonists. However, preclinical testing also revealed potentially clinically-limiting side-effects which included phencyclidine (PCP)-like actions indicative of possible psychotomimetic activity, cerebral vacuolisation of limbic cortical neurones, low therapeutic indices relative to incapacitating motor side-effects and, in the case of non-competitive antagonists, hypertension. These limitations have led to the design of clinical trials that should define the therapeutic index for this type of compound in humans. Currently, the first competitive antagonist to enter clinical trials, selfotel, is on hold, while D-CPPene is still in development. The non-competitive antagonist, aptiganel, is currently in Phase III clinical trials and its therapeutic efficacy and index should be defined in 1997 and 1998. The well-defined limitations of competitive and non-competitive NMDA antagonists have been a key impetus in the investigation of alternative approaches to modulating the NMDA receptor complex. In the case of glycine site antagonists, these compounds have been shown in preclinical studies to be devoid of PCP-like actions and the neuronal vacuolisation associated with the competitive and non-competitive NMDA antagonists. This has induced the development of a number of chemical series with at least three compounds currently in Phase I and II clinical trials. These include ACEA 1021, GV150526A and ZD9379. Clinical efficacies and therapeutic indices of these compounds should be defined in 1998 and 1999. An alternative approach using a partial agonist of the glycine site (1-aminocyclopropane-carboxylic acid, ACPC) has been halted in Phase I. Another approach which has led to the development of NMDA receptor antagonists, selective for the NMDA receptor subunits 1A/2B (NR1A/2B subtype), was the discovery in early studies of the neuroprotective actions of ifenprodil. Structural analogues include eliprodil, CP-101,606 and lubeluzole. In the cases of eliprodil and lubeluzole, these compounds have demonstrated neuroprotection in preclinical models, but they possess the extremely dangerous side-effect of increasing cardiac repolarisation time (i.e., increased QTc interval). The therapeutic index for these compounds is low. This has led to the termination of eliprodil's development and has limited the current dosing strategy with lubeluzole. It has not been disclosed if CP-101,606 possesses this dose-limiting side-effect. In summary, strategies for drug design and development based on our knowledge of the NMDA receptor complex have led to the development of a new generation of compounds for the treatment of stroke and traumatic brain injury, which remain to be evaluated in the clinic. The success of this approach will be defined in the next two to three years.

Journal Article↗
PubMed1997

Characterization of the anticonvulsant properties of ganaxolone (CCD 1042; 3alpha-hydroxy-3beta-methyl-5alpha-pregnan-20-one), a selective, high-affinity, steroid modulator of the gamma-aminobutyric acid(A) receptor.

Ganaxolone (CCD 1042) is a 3beta-methyl-substituted analog of the endogenous neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one. Ganaxolone inhibited binding of the gamma-aminobutyric acid (GABA)A receptor-chloride channel ligand t-[35S]butylbicyclophosphorothionate (IC50 of 80 nM) and enhanced binding of the benzodiazepine site ligand [3H]flunitrazepam (EC50 of 125 nM) and the GABA site ligand [3H]muscimol (EC50 of 86 nM), consistent with activity as a positive allosteric modulator of the GABA(A) receptor. Electrophysiological recordings showed that, whereas nanomolar concentrations of ganaxolone potentiated GABA-evoked chloride currents in Xenopus oocytes expressing the human GABA(A) receptor subunits alpha1beta1gamma2L, alpha2beta1gamma2L or alpha3beta1gamma2L, direct activation of chloride flux occurred to a limited extent only at micromolar concentrations. Ganaxolone was effective in nontoxic doses against clonic convulsions induced by s.c. pentylenetetrazol administration in mice and rats (ED50 values of 4.3 and 7.8 mg/kg i.p., respectively). Ganaxolone also exhibited potent anticonvulsant activity against seizures induced by s.c. bicuculline (ED50 of 4.6 mg/kg i.p.), i.p. TBPS (ED50 of 11.7 mg/kg i.p.) and i.p. aminophylline (ED50 of 11.5 mg/kg i.p.) in mice. Although ganaxolone effectively blocked tonic seizures induced by maximal electroshock in mice (ED50 of 29.7 mg/kg i.p.), it did so only at doses that produced ataxia on the Rotorod (TD50 of 33.4 mg/kg i.p.). Conversely, ganaxolone was a potent anticonvulsant against fully kindled stage 5 seizures induced by corneal kindling in rats (ED50 of 4.5 mg/kg i.p.), producing these effects at doses well below those that resulted in ataxia (TD50 of 14.2 mg/kg i.p.). The seizure threshold, as determined by an increase in the dose of i.v. infused pentylenetetrazol required to induce clonus, was also significantly elevated by nontoxic doses of ganaxolone in mice. In summary, these data indicate that ganaxolone is a high-affinity, stereoselective, positive allosteric modulator of the GABA(A) receptor complex that exhibits potent anticonvulsant activity across a range of animal procedures. The profile of anticonvulsant activity obtained for ganaxolone supports clinical evaluation of this drug as an antiepileptic therapy with potential utility in the treatment of generalized absence seizures as well as simple and complex partial seizures.

Animals↗
PubMed1997

CCD-3693: an orally bioavailable analog of the endogenous neuroactive steroid, pregnanolone, demonstrates potent sedative hypnotic actions in the rat.

An endogenous neuroactive steroid, pregnanolone, and an orally available synthetic analog, CCD-3693, were administered to rats at the middle of their circadian activity phase (6 hr after lights off). Electroencephalogram-defined sleep-wake states, locomotor activity and body temperature were concurrently measured 30 hr before and after treatment. Identical procedures were used to test triazolam and zolpidem. Triazolam (0.1-1.6 mg/kg), zolpidem (2.5-10 mg/kg) and the neuroactive steroids (10-30 mg/kg) produced dose-dependent increases in non-rapid eye movement (NREM) sleep. At this dose and time of day (in which the rats were predominantly awake during the 6 hr before treatment) the neuroactive steroids appeared more intrinsically efficacious in promoting NREM sleep than the benzodiazepine ligands. The neurosteroids did not, however, significantly interfere with rapid eye movement sleep and were more selective in reducing (EEG) wakefulness, with relatively less locomotor activity impairment during waking than triazolam and zolpidem. In addition, the benzodiazepine receptor ligands showed distinct "rebound" wakefulness after the NREM sleep-promoting effect subsided, although the neuroactive steroids did not. In addition, in vitro binding studies and in vivo pharmacological data confirmed that CCD-3693 was orally active in standard tests of anxiety, anticonvulsant, loss-of-righting and passive avoidance.

Administration, Oral↗
PubMed1996

The metabotropic glutamate receptor antagonist L-2-amino-3-phosphonopropionic acid inhibits phosphoserine phosphatase.

Phosphoserine phosphatase catalyzes the final step in the major pathway of L-serine biosynthesis in brain. Using D-phosphoserine as substrate, the metabotropic glutamate receptor antagonist L-2-amino-3-phosphonopropionic acid (L-AP3) inhibits phosphoserine phosphatase partially purified from rat brain with a Ki of 151 microM. In contrast to AP3 enantioselectivity at metabotropic receptors, D-AP3 (Ki 48 microM) is more potent as an inhibitor of phosphoserine phosphatase than L-AP3, whereas DL-AP3 has intermediate potency. D-, L-, and DL-AP3 are 6- to 8-fold more potent inhibitors using D-phosphoserine rather than L-phosphoserine as substrate, suggesting that AP3 may have selectivity for isoforms of phosphoserine phosphatase which preferentially cleave D-phosphoserine. D-AP3 decreases the apparent affinity of D- and L-phosphoserine with little or no change in maximal velocity indicating that it is a competitive inhibitor of the enzyme. Whereas L-AP3 has similar potency at metabotropic glutamate receptors and phosphoserine phosphatase, D-AP3 is selective for phosphoserine phosphatase and is the most potent and only known competitive inhibitor of this enzyme.

Alanine↗
PubMed1996

Steroid inhibition of [3H]SR 95531 binding to the GABAA recognition site.

The interaction of three types of steroids with the GABAA recognition site labeled by the antagonist ligand [3H]SR 95531 was evaluated in rat brain cortical membranes. The first type is the GABA site antagonist RU 5135, which potently (IC50 7 nM) but also incompletely (Imax 82%) displaced [3H]SR 95531. RU 5135 probably binds only to high affinity [3H]SR 9553] sites recognized by GABA and unlabelled SR 95531. The second type are the neuroactive steroids which act as positive allosteric modulators, including 3 alpha-hydroxy-5 beta-pregnan-20-one (3 alpha, 5 beta-P) and 5 beta-tetrahydrodeoxycorticosterone (5 beta-THDOC), which inhibited [3H]SR 95531 binding with limited efficacy (IC50 460 nM and 1.4 microM, Imax 41 and 31%, respectively). In contrast, 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha, 5 alpha-P) was inactive. The third type are the neurosteroids acting as negative allosteric modulators, such as pregnenolone sulfate, which inhibited [3H]SR 95531 binding with limited efficacy (IC50 10 microM, Imax 23%). In the presence of a saturating concentration of pregnenolone sulfate, 3 alpha, 5 beta-P further inhibited [3H]SR 95531 binding suggesting that these two steroids act through different sites or, possibly, at different populations of GABAA receptors. The allosteric modulation was selective for steroids since benzodiazepines and barbiturates were inactive up to 100 microM. Taken together, these data suggest that 3 alpha, 5 beta-P and 5 beta-THDOC modulate [3H]SR 95531 binding by interacting with a unique site on the GABAA receptor complex distinct from the sites for 3 alpha, 5 alpha-P, pregnenolone sulfate, GABA, benzodiazepines, and barbiturates.

Allosteric Regulation↗
PubMed1996

Characterization of peripheral benzodiazepine type sites in a cultured murine BV-2 microglial cell line.

It is known that the density of peripheral benzodiazepine receptors (PBR) increases after brain damage. Astrocytes are among the cell types where PBR ligand binding has been detected and may be involved in the response to neuronal injury and regeneration. Consistent with the hypothesis, the apparent density of PBR sites in astrocytes is increased by both cytokines and neurotoxins. However, microglia, the resident macrophages which represent 5-15% of glial cell populations have not been evaluated for the presence of the PBR. In the present study, we report the presence of [3H]Ro5-4864 binding in microglial cells. In particular, we used BV-2 cells, an immortalized cell line of murine microglial cells. High affinity binding of [3H]Ro5-4864 to a single site was detected in membranes prepared from BV-2 cells (KD = 4.4 nM, Bmax = 3,800 fmoles/mg protein). Various ligands for the PBR displaced [3H]Ro5-4864 binding with the following rank order of potencies: PK11195 = Ro5-4864 > FGIN-1-27 > triazolam = diazepam > beta-pro-pyl-beta-carboline-3-carboxylate = clonazepam > lorazepam = flurazepam >> chlordiazepoxide = clorazepate. Subcellular fractionationstudies indicate that the majority of the Ro5-4864 binding sites is in the mitochondrial fraction. The remainder is found in nonmitochondrial cell fractions. The [3H]Ro5-4864 binding observed on intact cells had characteristics similar to those found on membranes. The presence of a high density of PBRs in these cells establish the basis for additional investigations into their possible functional role, if any, in the microglial response to neuronal injury.

Animals↗
PubMed1996

A metabotropic glutamate receptor agonist regulates neurotrophin messenger RNA in rat forebrain.

We have examined the role of metabotropic glutamate receptor activation in regulating neurotrophin messenger RNA levels in the brain with the use of the selective agonist (1S,3R)-1-aminocy-clopentane-1,3-dicarboxylic acid. Intracerebroventricular injection of (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid into adult adult rats resulted in increased expression of nerve growth factor and brain-derived neurotrophic factor messenger RNA in the hippocampal and pyriform cortex and decreased levels of neurotrophin-3 messenger RNA in the hippocampal dentate gyrus granule cell layer. C-fos messenger RNA levels were also increased throughout hippocampal and cortical subfields following (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid administration. (1S,3R)-1-Aminocyclopentane-1,3-dicarboxylic acid-induced changes in messenger RNA levels occurred without behavioral seizures, yet these changes were similar in magnitude and time course to early changes in neurotrophin and c-fos messenger RNA levels observed following recurrent limbic seizures. In contrast quisqualate, a potent agonist of metabotropic as well as ionotropic kainate/alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors, was only capable of inducing increased expression of brain-derived neurotrophic factor messenger RNA at doses which produced recurrent motor seizures, and both effects were completely inhibited by the non-N-methyl-D-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. Neurotrophin messenger RNA changes induced by (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid were also partially susceptible to 6-cyano-7-nitroquinoxaline-2,3-dione antagonism, as well as the specific N-methyl-D-aspartate receptor antagonist (+)-5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)-cyclohepten-5,10- iminedizoleipine. These results suggest that (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid-sensitive metabotropic glutamate receptors can dramatically increase the expression of neurotrophin and c-fos messenger RNAs in rat forebrain without producing significant behavioral trauma and that these influences may involve ionotropic glutamate receptors in certain brain regions.

Animals↗
PubMed1996

Formation of D-serine from L-phosphoserine in brain synaptosomes.

Although glycine has been assumed to be the sole endogenous coagonist at NMDA-associated glycine receptors, recent descriptions of endogenous D-serine in the brain indicate that this assumption is probably not valid. D-Serine is a stereospecific agonist of the NMDA-associated glycine receptor, with an affinity equal to or greater than that of glycine but with no affinity for the strychnine-sensitive glycine receptor. In the current studies, we assessed the levels and metabolic sources of D-serine in rat neocortical synaptosomal preparations. Previous studies have demonstrated that CNS serine and glycine are synthesized de novo primarily via a phosphorylated pathway, originating with the glycolytic intermediate phosphoglycerate. The rate-limiting step in the synthesis of serine is the hydrolysis of phosphoserine by phosphoserine phosphatase (EC 3.1.3.3). In synaptosomal preparations we have demonstrated high endogenous levels of D-serine and the uptake of L-phosphoserine along with its hydrolysis to both L-serine and D-serine, which are preferentially released into the medium. Experiments with both intact and lysed synaptosomal preparations demonstrated hydrolysis of D-phosphoserine to only D-serine and inhibition of hydrolysis by the phosphoserine phosphatase inhibitor 2-amino-3-phosphonopropionic acid (AP3). The lack of stereospecificity for synaptosomal hydrolysis of phosphoserine and the inhibitory actions of AP3 are consistent with the presence of phosphoserine phosphatase in synaptosomes and further indicate that epimerization of serine can occur during or subsequent to the hydrolysis of L-phosphoserine but not D-phosphoserine. In conclusion, these studies demonstrate that phosphoserine phosphatase may be an important enzyme in regulating the steady-state levels of D-serine in neocortical synaptosomes.

Alanine↗