Male-male aggression is unlikely to stabilize a poison frog polymorphism.

Phenotypic polymorphism is common in animals, and the maintenance of multiple phenotypes in a population requires forces that act against homogenizing drift and selection. Male-male competition can contribute to the stability of a polymorphism when males compete primarily with males of the same phenotype. In and around a contact zone between red and blue lineages of the poison frog Oophaga pumilio, we used simulated territorial intrusions to test the nonexclusive predictions that males would direct more aggression towards males of (i) their own phenotype and/or (ii) the phenotype that is most common in their population. Males in the monomorphic red and blue populations that flank the contact zone were more aggressive towards simulated intruders that matched the local coloration. However, males in the two polymorphic populations biased aggression towards neither their own colour nor the colour most common in their population. In sympatry, the rarer colour morph gains no advantage via reduced male-male aggression from territorial males in these O. pumilio populations, and so male aggression seems unlikely to stabilize colour polymorphism on its own. More broadly, these results suggest that the potential for divergent male aggression biases to maintain phenotypic diversity depends on the mechanism(s) that generate the biases and the degree to which these mechanisms persist in sympatry.

Diabetes and the risk of infections with immunomodulator therapy in inflammatory bowel diseases.

BACKGROUND: Infections are an important concern in patients using immunosuppressive therapy for their inflammatory bowel disease (IBD). Diabetes affects nearly 10% of Americans. Whether it confers an additional risk with immunosuppression in IBD has not been examined previously. AIM: To examine the association between diabetes and infections with immunomodulator use in IBD METHODS: Using a validated, multi-institutional IBD cohort, we identified all patients who received at least one prescription for immunomodulators (thiopurines, methotrexate). Our primary outcome was infection within 1 year of the prescription of the immunomodulator. Multivariable logistic regression adjusting for relevant confounders was used to estimate the independent association with diabetes. RESULTS: Our study included 2766 patients receiving at least one prescription for immunomodulators among whom 210 (8%) developed an infection within 1 year. Patients who developed an infection were likely to be older, have more comorbidities, more likely to have received a prescription for steroids but similar in initiation of anti-TNF therapy within that year. Only 8% of those without an infection had diabetes compared to 19% of those who developed an infection within 1 year [odds ratio (OR) 2.74, 95% confidence interval (CI) 1.88-3.98, P < 0.001]. On multivariate analysis, diabetes was independently associated with a nearly two-fold increase in risk of infections (OR: 1.80, 95% CI: 1.20-2.68). There was no increase in risk of infections with addition of anti-TNF therapy (OR: 1.14, 95% CI: 0.80-1.63). CONCLUSION: Diabetes is an independent risk factor for infection in IBD patients using immunomodulator therapy.

Prenatal antidepressant exposure is associated with risk for attention-deficit hyperactivity disorder but not autism spectrum disorder in a large health system.

Previous studies suggested that risk for Autism Spectrum Disorder (ASD) may be increased in children exposed to antidepressants during the prenatal period. The disease specificity of this risk has not been addressed and the possibility of confounding has not been excluded. Children with ASD or attention-deficit hyperactivity disorder (ADHD) delivered in a large New England health-care system were identified from electronic health records (EHR), and each diagnostic group was matched 1:3 with children without ASD or ADHD. All children were linked with maternal health data using birth certificates and EHRs to determine prenatal medication exposures. Multiple logistic regression was used to examine association between prenatal antidepressant exposures and ASD or ADHD risk. A total of 1377 children diagnosed with ASD and 2243 with ADHD were matched with healthy controls. In models adjusted for sociodemographic features, antidepressant exposure prior to and during pregnancy was associated with ASD risk, but risk associated with exposure during pregnancy was no longer significant after controlling for maternal major depression (odds ratio (OR) 1.10 (0.70-1.70)). Conversely, antidepressant exposure during but not prior to pregnancy was associated with ADHD risk, even after adjustment for maternal depression (OR 1.81 (1.22-2.70)). These results suggest that the risk of autism observed with prenatal antidepressant exposure is likely confounded by severity of maternal illness, but further indicate that such exposure may still be associated with ADHD risk. This risk, modest in absolute terms, may still be a result of residual confounding and must be balanced against the substantial consequences of untreated maternal depression.

Higher plasma vitamin D is associated with reduced risk of Clostridium difficile infection in patients with inflammatory bowel diseases.

BACKGROUND: Patients with inflammatory bowel diseases (IBD) have an increased risk of clostridium difficile infection (CDI). Cathelicidins are anti-microbial peptides that attenuate colitis and inhibit the effect of clostridial toxins. Plasma calcifediol [25(OH)D] stimulates production of cathelicidins. AIM: To examine the association between plasma 25(OH)D and CDI in patients with IBD. METHODS: From a multi-institutional IBD cohort, we identified patients with at least one measured plasma 25(OH)D. Our primary outcome was development of CDI. Multivariate logistic regression models adjusting for potential confounders were used to identify independent effect of plasma 25(OH)D on risk of CDI. RESULTS: We studied 3188 IBD patients of whom 35 patients developed CDI. Patients with CDI-IBD were older and had greater co-morbidity. The mean plasma 25(OH)D level was significantly lower in patients who developed CDI (20.4 ng/mL) compared to non-CDI-IBD patients (27.1 ng/mL) (P = 0.002). On multivariate analysis, each 1 ng/mL increase in plasma 25(OH)D was associated with a 4% reduction in risk of CDI (OR 0.96, 95% CI 0.93-0.99, P = 0.046). Compared to individuals with vitamin D >20 ng/mL, patients with levels <20 ng/mL were more likely to develop CDI (OR 2.27, 95% CI 1.16-4.44). The mean plasma 25(OH)D in patients with CDI who subsequently died was significantly lower (12.8 ± 8.1 ng/mL) compared to those who were alive at the end of follow-up (24.3 ± 13.2 ng/mL) (P = 0.01). CONCLUSIONS: Higher plasma calcifediol [25(OH)D] is associated with reduced risk of C. difficile infection in patients with IBD. Further studies of therapeutic supplementation of vitamin D in patients with inflammatory bowel disease and C. difficile infection may be warranted.

Psychiatric co-morbidity is associated with increased risk of surgery in Crohn's disease.

BACKGROUND: Psychiatric co-morbidity, in particular major depression and anxiety, is common in patients with Crohn's disease (CD) and ulcerative colitis (UC). Prior studies examining this may be confounded by the co-existence of functional bowel symptoms. Limited data exist examining an association between depression or anxiety and disease-specific endpoints such as bowel surgery. AIMS: To examine the frequency of depression and anxiety (prior to surgery or hospitalisation) in a large multi-institution electronic medical record (EMR)-based cohort of CD and UC patients; to define the independent effect of psychiatric co-morbidity on risk of subsequent surgery or hospitalisation in CD and UC, and to identify the effects of depression and anxiety on healthcare utilisation in our cohort. METHODS: Using a multi-institution cohort of patients with CD and UC, we identified those who also had co-existing psychiatric co-morbidity (major depressive disorder or generalised anxiety). After excluding those diagnosed with such co-morbidity for the first time following surgery, we used multivariate logistic regression to examine the independent effect of psychiatric co-morbidity on IBD-related surgery and hospitalisation. To account for confounding by disease severity, we adjusted for a propensity score estimating likelihood of psychiatric co-morbidity influenced by severity of disease in our models. RESULTS: A total of 5405 CD and 5429 UC patients were included in this study; one-fifth had either major depressive disorder or generalised anxiety. In multivariate analysis, adjusting for potential confounders and the propensity score, presence of mood or anxiety co-morbidity was associated with a 28% increase in risk of surgery in CD (OR: 1.28, 95% CI: 1.03-1.57), but not UC (OR: 1.01, 95% CI: 0.80-1.28). Psychiatric co-morbidity was associated with increased healthcare utilisation. CONCLUSIONS: Depressive disorder or generalised anxiety is associated with a modestly increased risk of surgery in patients with Crohn's disease. Interventions addressing this may improve patient outcomes.

Using electronic medical records to enable large-scale studies in psychiatry: treatment resistant depression as a model.

BACKGROUND: Electronic medical records (EMR) provide a unique opportunity for efficient, large-scale clinical investigation in psychiatry. However, such studies will require development of tools to define treatment outcome. METHOD: Natural language processing (NLP) was applied to classify notes from 127 504 patients with a billing diagnosis of major depressive disorder, drawn from out-patient psychiatry practices affiliated with multiple, large New England hospitals. Classifications were compared with results using billing data (ICD-9 codes) alone and to a clinical gold standard based on chart review by a panel of senior clinicians. These cross-sectional classifications were then used to define longitudinal treatment outcomes, which were compared with a clinician-rated gold standard. RESULTS: Models incorporating NLP were superior to those relying on billing data alone for classifying current mood state (area under receiver operating characteristic curve of 0.85-0.88 v. 0.54-0.55). When these cross-sectional visits were integrated to define longitudinal outcomes and incorporate treatment data, 15% of the cohort remitted with a single antidepressant treatment, while 13% were identified as failing to remit despite at least two antidepressant trials. Non-remitting patients were more likely to be non-Caucasian (p<0.001). CONCLUSIONS: The application of bioinformatics tools such as NLP should enable accurate and efficient determination of longitudinal outcomes, enabling existing EMR data to be applied to clinical research, including biomarker investigations. Continued development will be required to better address moderators of outcome such as adherence and co-morbidity.

Detecting drug interactions from adverse-event reports: interaction between paroxetine and pravastatin increases blood glucose levels.

The lipid-lowering agent pravastatin and the antidepressant paroxetine are among the most widely prescribed drugs in the world. Unexpected interactions between them could have important public health implications. We mined the US Food and Drug Administration's (FDA's) Adverse Event Reporting System (AERS) for side-effect profiles involving glucose homeostasis and found a surprisingly strong signal for comedication with pravastatin and paroxetine. We retrospectively evaluated changes in blood glucose in 104 patients with diabetes and 135 without diabetes who had received comedication with these two drugs, using data in electronic medical record (EMR) systems of three geographically distinct sites. We assessed the mean random blood glucose levels before and after treatment with the drugs. We found that pravastatin and paroxetine, when administered together, had a synergistic effect on blood glucose. The average increase was 19 mg/dl (1.0 mmol/l) overall, and in those with diabetes it was 48 mg/dl (2.7 mmol/l). In contrast, neither drug administered singly was associated with such changes in glucose levels. An increase in glucose levels is not a general effect of combined therapy with selective serotonin reuptake inhibitors (SSRIs) and statins.

Optimizing healthcare research data warehouse design through past COSTAR query analysis.

Over the past two years we have reviewed and implemented the specifications for a large relational database (a data warehouse) to find research cohorts from data similar to that contained within the clinical COSTAR database at the Massachusetts General Hospital. A review of 16 years of COSTAR research queries was conducted to determine the most common search strategies. These search strategies are relevant to the general research community, because they use the Medical Query Language (MQL) developed for the COSTAR M database which is extremely flexible (much more so than SQL) and allows searches by coded fields, text reports, and laboratory values in a completely ad hoc fashion. By reviewing these search strategies, we were able to obtain user specifications for a research oriented healthcare data warehouse that could support 90% of the queries. The data warehouse was implemented in a relational database using the star schema, allowing for highly optimized analytical processing. This allowed queries that performed slowly in the M database to be performed very rapidly in the relational database. It also allowed the data warehouse to scale effectively.

The guideline interchange format: a model for representing guidelines.

OBJECTIVE: To allow exchange of clinical practice guidelines among institutions and computer-based applications. DESIGN: The GuideLine Interchange Format (GLIF) specification consists of GLIF model and the GLIF syntax. The GLIF model is an object-oriented representation that consists of a set of classes for guideline entities, attributes for those classes, and data types for the attribute values. The GLIF syntax specifies the format of the test file that contains the encoding. METHODS: Researchers from the InterMed Collaboratory at Columbia University, Harvard University (Brigham and Women's Hospital and Massachusetts General Hospital), and Stanford University analyzed four existing guideline systems to derive a set of requirements for guideline representation. The GLIF specification is a consensus representation developed through a brainstorming process. Four clinical guidelines were encoded in GLIF to assess its expressivity and to study the variability that occurs when two people from different sites encode the same guideline. RESULTS: The encoders reported that GLIF was adequately expressive. A comparison of the encodings revealed substantial variability. CONCLUSION: GLIF was sufficient to model the guidelines for the four conditions that were examined. GLIF needs improvement in standard representation of medical concepts, criterion logic, temporal information, and uncertainty.

Using web technology and Java mobile software agents to manage outside referrals.

A prototype, web-based referral application was created with the objective of providing outside primary care providers (PCP's) the means to refer patients to the Massachusetts General Hospital and the Brigham and Women's Hospital. The application was designed to achieve the two primary objectives of providing the consultant with enough data to make decisions even at the initial visit, and providing the PCP with a prompt response from the consultant. The system uses a web browser/server to initiate the referral and Java mobile software agents to support the workflow of the referral. This combination provides a light client implementation that can run on a wide variety of hardware and software platforms found in the office of the PCP. The implementation can guarantee a high degree of security for the computer of the PCP. Agents can be adapted to support the wide variety of data types that may be used in referral transactions, including reports with complex presentation needs and scanned (faxed) images Agents can be delivered to the PCP as running applications that can perform ongoing queries and alerts at the office of the PCP. Finally, the agent architecture is designed to scale in a natural and seamless manner for unforeseen future needs.

Using software agents to maintain autonomous patient registries for clinical research.

A software agent is an application that can function in an autonomous and intelligent fashion. We have used mobile software agents to maintain clinicians' patient research databases (patient registries). Agents were used to acquire data from the clinician and place it into the registries, copy data from hospital databases into the registries, and report data from the registries. The agents were programmed with the intelligence to navigate through complex network security, interact with legacy systems, and protect themselves from various forms of failure at multiple levels. To maximize the separation between our system and the hospital information infrastructure we often used Java, a platform-independent language, to program and distribute our software agents. By using mobile agents, we were able to distribute the computing time required by these applications to underutilized host machines upon which the registries could be maintained.

Achieving automated narrative text interpretation using phrases in the electronic medical record.

Stereotypic phrases are used by clinicians throughout the medical record, as seen in an analysis of our COSTAR medical record database. These phrases are often associated with an underling semantic concept; for example the phrase CLEAR LUNGS may be linked with the concept "normal lung exam" for a particular physician. Formalizing these associations with concepts from the UMLS using the MEDPhrase application allowed us to automate interpretation of narrative text within our electronic medical record.

Nitrendipine and omega-conotoxin modulate gonadotropin release and gonadotrope [Ca2+]i.

We have examined the pharmacology of the voltage-sensitive Ca2+ channels (VSCCs) that mediate gonadotropin secretion from primary cultures of rat pituitary cells, stimulated by either cell depolarization or by binding of gonadotropin-releasing hormone (GnRH). We also measured single-cell [Ca2+]i transients using fura-2 in gonadotropes identified by a reverse hemolytic plaque assay employing an antiserum to luteinizing hormone (LH). Cell depolarization evoked by either 50 mM K+ or 30 microM veratridine induced 2- to 6-fold increases in gonadotropin secretion over basal levels. GnRH caused 6- to 20-fold increases in follicle-stimulating hormone (FSH) and LH secretion, respectively, with maximal stimulation at 100 nM GnRH. K(+)- or GnRH-induced FSH release was largely prevented by co-incubation with 1 mM CdCl. Tetrodotoxin (TTX, 5 microM) prevented the veratridine-, but not the K(+)- or GnRH-induced, stimulation of FSH secretion. Nitrendipine (Ntd, 1 microM) produced 35-50% inhibition (NS) of both FSH and LH release stimulated by either 50 mM K+ or 100 nM GnRH. Ntd also inhibited the K(+)-induced [Ca2+]i rise (greater than 90%), as well as the secondary, plateau phase of the GnRH-induced elevation of [Ca2+]i (100% inhibition). Omega-conotoxin (omega-CgTx, 100 nM) partially suppressed FSH and LH release (NS) due to both K+ (33% each) and GnRH (44% and 18%, respectively). omega-CgTx showed variable effects on [Ca2+]i transients evoked by K+ or GnRH ranging from clear inhibition to no effect. We conclude that influx of extracellular Ca2+ is one of several fundamental events underlying the depolarization- or receptor-activated release of LH and FSH, and that this influx can be inhibited by dihydropyridine-sensitive ('L') Ca2+ channels. Two classes of L-channels may exist in gonadotropes, that differ in their sensitivity to omega-CgTx.

Two distinct quisqualate receptors regulate Ca2+ homeostasis in hippocampal neurons in vitro.

Addition of quisqualate to mouse hippocampal neurons in vitro elicited two types of changes in [Ca2+]i as assessed by fura-2-based microfluorimetry. The first was a transient spike or group of oscillations and the second was a long lasting "plateau" response. The long-lasting response was abolished on removal of either Ca2+ or Na+ from the external medium or by blocking voltage-sensitive Ca2+ channels. Furthermore, the novel glutamate antagonist 6-nitro-7-cyano-quinoxaline-2,3-dione was a competitive inhibitor of this response. In contrast, none of these manipulations abolished the transient [Ca2+]i spike. Transient [Ca2+]i spikes or oscillations could also be produced by the alpha 1-adrenergic agonist phenylephrine. Production of such an alpha 1-response reduced the size of a subsequently elicited quisqualate response. However production of transient [Ca2+]i spikes with caffeine did not alter the size of the quisqualate-induced spike. We conclude that hippocampal neurons possess two different types of quisqualate receptors. The first mediates quisqualate-induced depolarization and the second mediates Ca2+ mobilization from intracellular stores.

Regulation of Ca++ influx into striatal neurons by kainic acid.

We investigated the mechanisms by which kainic acid (KA) produces increases in [Ca++]i in single striatal neurons in vitro using fura-2-based microfluorimetry. When neurons were depolarized by perfusion with high K+ or veratridine containing solutions, [Ca++]i rose rapidly to a peak and then declined to a lower sustained plateau that persisted as long as the depolarizing stimulus. The peak high K+-induced rise in [Ca++]i occurred at [K+]o greater than 50 mM and the plateau was largest at 30 mM K+. [K+]o that was greater than 70 mM caused the magnitude of the plateau to decrease. Responses to high K+ stimulation were completely dependent on [Ca++]o and presumably represented Ca++ influx. Nitrendipine partially blocked the peak of the high K+-induced response and completely blocked the sustained plateau Ca++ influx. The nitrendipine-resistant portion of the high K+ response could be completely blocked by predepolarization of the cell in Ca++-free solution. KA also produced large increases in [Ca++]i that were abolished on removal of external Ca++. Predepolarization/nitrendipine greatly reduced the effect of lower [KA] (100 microM). However, KA-induced increases in [Ca++]i became increasingly resistant to block of voltage-sensitive Ca++ channels as [KA] rose above 100 microM, indicating a second route of Ca++ entry that may be the KA receptor-gated ionophore. About one-half the responses to KA (100 microM) also displayed a large oscillation. [Ca++]i rose to a peak, fell and then rose again before finally declining to a plateau level. This oscillation was abolished when all external Na+ was replaced by Li+ and may result from alterations in the buffering of [Ca++]i as a result of KA-induced Na+ influx.

A glutamate receptor regulates Ca2+ mobilization in hippocampal neurons.

We investigated the effect of various excitatory amino acids on intracellular free Ca2+ concentration ( [Ca2+]i) in single mouse hippocampal neurons in vitro by using the Ca2+-sensitive dye fura-2. In normal physiological solution, glutamate, kainate, N-methyl-D-aspartate, and quisqualate all produced increases in [Ca2+]i. When all extracellular Ca2+ was removed, kainate and N-methyl-D-aspartate were completely ineffective, but quisqualate and glutamate were able to produce a spike-like Ca2+ transient, presumably reflecting the release of Ca2+ from intracellular stores. Ca2+ transients of similar shape could also be produced by the alpha 1-adrenergic agonist phenylephrine. After the production of a Ca2+ transient a second addition of quisqualate was ineffective unless intracellular stores were refilled by loading the cell with Ca2+ following depolarization in Ca2+-containing medium. None of the conventional excitatory amino acid receptor antagonists inhibited the Ca2+-mobilizing effects of quisqualate. Furthermore alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) was unable to produce Ca2+ mobilization in Ca2+-free medium, although it could produce Ca2+ influx in Ca2+-containing medium. Thus, glutamate can produce mobilization of Ca2+ from intracellular stores in hippocampal neurons by acting on a quisqualate-sensitive but AMPA-insensitive receptor. This receptor is therefore distinct from the quisqualate receptor that produces cell depolarization. The possibility that this Ca2+-mobilizing effect is mediated by inositol triphosphate production is discussed.

Gonadotropin-releasing hormone-induced Ca2+ transients in single identified gonadotropes require both intracellular Ca2+ mobilization and Ca2+ influx.

We examined the effects of gonadotropin-releasing hormone (GnRH) on the intracellular free Ca2+ concentration ([Ca2+]i) in single rat anterior pituitary gonadotropes identified by a reverse hemolytic plaque assay. Concentrations of GnRH greater than 10 pM elicited increases in [Ca2+]i in identified cells but not in others. In contrast, depolarization induced by 50 mM K+ increased [Ca2+]i in all cells. Ca2+ transients induced by GnRH exhibited a complex time course. After an initial rapid rise, the [Ca2+]i fell to near basal levels only to be followed by a secondary extended rise and fall. Analysis of the Ca2+ transients on a rapid time base revealed that responses frequently consisted of several rapid oscillations in [Ca2+]i. Removal of extracellular Ca2+ or addition of the dihydropyridine Ca2+-channel blocker nitrendipine completely blocked the secondary rise in [Ca2+]i but had no effect whatsoever on the initial spike. Nitrendipine also blocked 50 mM K+-induced increases in [Ca2+]i in identified gonadotropes. The secondary rise induced by GnRH could be enhanced by a phorbol ester in a nitrendipine-sensitive fashion. Multiple spike responses to GnRH stimulation of the same cell could only be obtained if subsequent Ca2+ influx was permitted either by allowing a secondary rise to occur or by producing a Ca2+ transient by depolarizing the cells with 50 mM K+. It therefore appears that the response to GnRH consists of an initial phase of Ca2+ mobilization, probably mediated by inositol trisphosphate, and a subsequent phase of Ca2+ influx through nitrendipine-sensitive Ca2+ channels that may be activated by protein kinase C. The relative roles of these phases in the control of gonadotropin secretion are discussed.

The effects of excitatory amino acids on intracellular calcium in single mouse striatal neurons in vitro.

Using microspectrofluorimetry and the calcium-sensitive dye fura-2, we examined the effect of excitatory amino acids on [Ca2+]i in single striatal neurons in vitro. N-methyl-D-aspartic acid (NMDA) produced rapid increases in [Ca2+]i. These were blocked by DL-2-amino-5-phosphonovaleric acid (AP5), by Mg2+, by phencyclidine, and by MK801. The block produced by Mg2+ and MK801 could be relieved by depolarizing cells with veratridine. When external Ca2+ was removed, NMDA no longer increased [Ca2+]i. Furthermore, the effects of NMDA were not blocked by concentrations of La3+ that blocked depolarization induced rises in [Ca2+]i. Substitution of Na+o by Li+ did not block the effects of NMDA. Concentrations of L-glutamate greater than or equal to 10(-6) M also increased [Ca2+]i. The effects of moderate concentrations of glutamate were blocked by AP5 but not by La3+ or by substitution of Na+ by Li+. The effects of glutamate were blocked by removal of external Ca2+ but were not blocked by concentrations of Mg2+ or MK801 that completely blocked the effects of NMDA. The glutamate analogs kainic acid (KA) and quisqualic acid also increased [Ca2+]i. The effects of KA were blocked by removal of external Ca2+ but not by La3+, Mg2+, MK801, or replacement of Na+ by Li+. Although AP5 was able to block the effects of KA partially, very high concentrations were required. These results may be explained by considering the properties of glutamate-receptor-linked ionophores. Excitatory amino acid induced increases in [Ca2+]i are consistent with the possibility that Ca2+ mediates excitatory amino acid induced neuronal degeneration.

3H-labeled MK-801 binding to the excitatory amino acid receptor complex from rat brain is enhanced by glycine.

We have studied the binding of the excitatory amino acid antagonist 3H-labeled MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohept-5,10-imine maleate] to extensively washed rat brain membranes. Binding of 3H-labeled MK-801 was inhibited by phencyclidine, Mg2+, and 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid in a manner dependent on the presence of L-glutamate or N-methyl-D-aspartate, suggesting that it labeled a site linked to the N-methyl-D-aspartate subtype of the glutamate receptor. Glycine also regulated 3H-labeled MK-801 binding, enhancing it in the concentration range of 0.01-10 microM. The actions of glutamate and glycine involved increases in binding affinity, without altering the number of 3H-labeled MK-801 binding sites. The effects of glycine in this system were mimicked by L- and D-alanine and L- and D-serine. However, beta-alanine and taurine were much less effective, and strychnine did not block the actions of glycine indicating that they were not mediated by the classical glycine receptors. Glycine also enhanced the ability of N-methyl-D-aspartate to increase Ca2+ influx into primary cultures of mouse striatal neurons measured using the Ca2+-sensitive fluorescent dye fura-2. These results support the suggestion that glycine may be an important regulator of the physiological actions of glutamate in vivo.