[Translated article] The effect of showing preoperative photographs on patient satisfaction following forefoot surgery.

BACKGROUND: Postoperative outcome measurement typically relies on postoperative radiological results and clinical-functional scales; however, there is a growing interest in considering patient satisfaction (including subjective aspects) as part of the success of forefoot surgery. OBJECTIVE: To determine whether showing a preoperative photograph improves satisfaction in postoperative forefoot surgery patients. MATERIAL AND METHODS: An observational, cross-sectional, analytical study was conducted in the foot and ankle unit of our centre. We included 120 participants between 18 and 90 years old who underwent forefoot surgery. The degree of satisfaction was compared using the PSQ-10 questionnaire between a group of patients who received a preoperative foot appearance image at their 3-month postoperative follow-up and those who did not receive it. RESULTS: The overall satisfaction rate was 78.33% at 3 months after the intervention. The 93.6% of patients who received the photograph were satisfied at the postoperative follow-up, while in the control group, it was 86.2% with a p value of 0.218. CONCLUSION: The degree of satisfaction in patients undergoing forefoot surgery is not associated with the presentation of preoperative photographs.

The effect of showing preoperative photographs on patient satisfaction following forefoot surgery. / Influencia de la fotografía preoperatoria en el grado de satisfacción en pacientes postoperados de cirugía de antepié.

BACKGROUND: Postoperative outcome measurement typically relies on postoperative radiological results and clinical-functional scales; however, there is a growing interest in considering patient satisfaction (including subjective aspects) as part of the success of forefoot surgery. OBJECTIVE: To determine whether showing a preoperative photograph improves satisfaction in postoperative forefoot surgery patients. MATERIAL AND METHODS: An observational, cross-sectional, analytical study was conducted in the foot and ankle unit of our center. We included 120 participants between 18 and 90 years old who underwent forefoot surgery. The degree of satisfaction was compared using the PSQ-10 questionnaire between a group of patients who received a preoperative foot appearance image at their 3-month postoperative follow-up and those who did not receive it. RESULTS: The overall satisfaction rate was 78.33% at 3 months after the intervention. The 93.6% of patients who received the photograph were satisfied at the postoperative follow-up, while in the control group, it was 86.2% with a p-value of 0.218. CONCLUSION: The degree of satisfaction in patients undergoing forefoot surgery is not associated with the presentation of preoperative photographs.

Low frequency of cytomegalovirus (CMV) disease despite high prevalence of CMV viraemia in patients with advanced HIV infection: a clinical and immunological 48-week follow-up study.

OBJECTIVES: The aim of the study was to investigate the dynamics of cytomegalovirus (CMV) replication and CMV-specific immune response recovery after antiretroviral treatment (ART) initiation in patients with advanced HIV infection. METHODS: A prospective observational study of patients with HIV infection and CD4 counts of < 100 cells/µL was carried out (September 2015 to July 2018). HIV viral load (VL), CD4 count and CMV VL were determined by quantitative polymerase chain reaction (PCR) at baseline and at 4, 12, 24 and 48 weeks, and CMV-specific immune response was determined by QuantiFERON-CMV assay at baseline and 48 weeks. All patients were started on ART but only those with CMV end-organ disease (EOD) received anti-CMV treatment. RESULTS: Fifty-three patients with a median age of 43.6 [interquartile range (IQR) 36.7-52.4] years were included in the study. At baseline, the median CD4 count was 30 cells/µL (IQR 20-60 cells/µL) and the median HIV VL was 462 000 HIV-1 RNA copies/mL (IQR 186 000-1 300 000 copies/mL). At baseline, 32% patients had detectable CMV viraemia but none had detectable CMV viraemia at 48 weeks. Only one of 53 (1.9%) patients developed EOD during follow-up. Seven (13.2%) patients were lost to follow-up and six (11.3%) died; none of the deaths was related to CMV. Similar percentages of patients had a CMV-specific immune response at baseline (71.7%) and at 48 weeks (70.0%). The magnitude of this response tended to increase over time [median 1.63 (IQR 0.15-5.77) IU/mL at baseline vs. median 2.5 (IQR 0.1-8.325) IU/mL at 48 weeks; P = 0.11]. We did not find any risk factors associated with 48-week mortality. CONCLUSIONS: Although the prevalence of CMV viraemia in patients with advanced HIV infection remains high, achieving a good immunological recovery through ART is enough to suppress CMV viraemia, without an increased risk of CMV EOD. The prevalence of a CMV-specific immune response was high and endured over time.

Safety and Efficacy of Prolonged Use of Dalbavancin in Bone and Joint Infections.

Dalbavancin is a lipoglycopeptide with potent activity against Gram-positive microorganisms, a long half-life, a favorable safety profile, and a high concentration in bone, which makes it an interesting alternative for treatment of osteoarticular infections. We performed a multicentric retrospective study of all patients with an osteoarticular infection (septic arthritis, spondylodiscitis, osteomyelitis, or orthopedic implant-related infection) treated with at least one dose of dalbavancin between 2016 and 2017 in 30 institutions in Spain. In order to evaluate the response, patients with or without an orthopedic implant were separated. A total of 64 patients were included. Staphylococcus epidermidis and Staphylococcus aureus were the most frequent microorganisms. The reasons for switching to dalbavancin were simplification (53.1%), adverse events (25%), or failure (21.9%). There were 7 adverse events, and no patient had to discontinue dalbavancin. In 45 cases, infection was related to an orthopedic implant. The implant material was retained in 23 cases, including that in 15 (65.2%) patients that were classified as cured and 8 (34.8%) that presented improvement. In 21 cases, the implants were removed, including those in 16 (76.2%) cases that were considered successes, 4 (19%) cases were considered improved, and 1 (4.8%) case that was considered a failure. Among the 19 cases without implants, 14 (73.7%) were considered cured, 3 (15.8%) were considered improved, and 2 (10.5%) were considered failures. The results show that dalbavancin is a well-tolerated antibiotic, even when >2 doses are administered, and is associated with a high cure rate. These are preliminary data with a short follow-up; therefore, it is necessary to gain more experience and, in the future, to establish the most appropriate dose and frequency.

[Somatization symptoms. An emerging pediatric entity]. / Trastornos somatomorfos: una entidad emergente en pediatría.

BACKGROUND: Somatization symptoms are a clinical reality in our environment. However, many pediatricians have little information about this condition or experience of its management. OBJECTIVE: To determine the clinical and differential characteristics of these patients. The early identification of these patients and initiation of therapy in the initial stages of the process would improve prognosis. MATERIAL AND METHOD: A retrospective review was performed of the children admitted to the short-stay unit of a tertiary hospital because of somatic complaints and whose final diagnosis was that of a somatization disorder. RESULTS: Sixty medical records were analyzed, of which 38 (63 %) corresponded to girls, with a mean age of 11 years at presentation. The most frequent reasons for consultation were related to the digestive and neurological systems. Thirty-four patients (57 %) had previously consulted for the same reason. In the sample analyzed, the most frequent personality trait was anxiety. The main triggers were familial and school factors. The most frequent diagnosis was pain disorder in 42 children (70 %). All patients received psychotherapy and 39 received complementary pharmacological treatment. CONCLUSIONS: The data analyzed in this study indicate that somatization symptoms most frequently occur in anxious, prepubescent girls, with migraine or non-specific abdominal pain of approximately one month's duration. Patients have usually made several previous visits and no organic causes are discovered on physical examination.

Trastornos somatomorfos: una entidad emergente en pediatría / Somatization symptoms. An emerging pediatric entity

Antecedentes: Los trastornos somatomorfos son una realidad clínica en nuestro medio; sin embargo, es una entidad de la que muchos pediatras tienen poca información y escasa experiencia en su manejo. Objetivo Determinar los rasgos característicos y diferenciales de este tipo de pacientes, con el fin de poderlos identificar precozmente, y garantizar que el abordaje terapéutico se haga en las fases iniciales del proceso, condicionando un mejor pronóstico. Material y método Se ha realizado una revisión retrospectiva de los niños ingresados por una molestia somática, en la unidad de estancia corta (UEC) de un hospital pediátrico de tercer nivel, y cuyo diagnóstico final es el de un trastorno somatomorfo. Resultados Se analizaron 60 historias clínicas, de las que 38 (63 per cent) correspondían a niñas, con una edad media de presentación del trastorno de 11 años. Los motivos de consulta más frecuentes fueron los referidos al aparato digestivo y al sistema neurológico. En 34 casos (57 per cent) ya habían consultado previamente por la misma sintomatología, sin llegarse al diagnóstico en ese momento. La personalidad de base ansiosa es la más frecuente en la muestra evaluada. Se ha observado que los factores familiares y los escolares son los principales desencadenantes. El trastorno por dolor es el diagnóstico mayoritario, en 42 de los niños (70 per cent).Respecto al abordaje terapéutico, se realizó psicoterapia de base en todos los pacientes, y tratamiento farmacológico complementario, en 39 de ellos (65 per cent).Conclusiones A partir de los datos analizados en esta revisión, se encontró que el paciente tipo que padece un trastorno somatomorfo suele ser una chica preadolescente, ansiosa, con cefalea y/o dolor abdominal inespecífico, de un mes de evolución aproximadamente, por el que ya ha consultado previamente en varias ocasiones, sin hallazgos orgánicos que lo justifiquen (AU)

Superimposition-based protocol as a tool for determining bioactive conformations. I. Application to ligands of the glycinergic receptor (GlyR).

The natural templates (NT) approach, which is a superimposition-based protocol that has been successfully employed in several studies, is here applied to ligands of the glycine ligand-gated ion channel receptor. Bioactive conformations for glycine and its analogs were obtained using strychnine (a natural and specific competitive antagonist) as template. Experimental evidence was used to guide the superimposition protocol. Three essential regions have been defined in strychnine's structure that serve as a pharmacophore for agonist and antagonist activities. Reasonable alignments of known ligands were found in the majority of the cases. Molecular mechanics (i.e., conformational searches for the relatively flexible ligands) and molecular dynamics (for relatively rigid ligands such as strychnine and 5,6,7,8-tetrahydro-4H-isoxazolo[3,4-d]azepin-3-ol) were used to assess the energetic accessibility of the proposed bioactive conformations.

Superimposition-based protocol as a tool for determining bioactive conformations. II. Application to the GABA(A) receptor.

The natural templates (NT) superimposition method is used to determine the pharmacophoric requirements of the A subtype of the gamma-aminobutyric acid (GABA) receptor. Bioactive conformations for antagonists and agonists are found by superimposing them on a relatively rigid alkaloid bicuculline, which itself is a competitive antagonist at this ligand-gated ion channel receptor. As has been usual in the application of this modeling method, consideration of available experimental data is the cornerstone for obtaining realistic models. The identification of two substructural fragments of bicuculline permitted classification of the ligands. Analysis of the antagonists and agonists with respect to the two substructural fragments revealed two bioactive conformations of the highly flexible GABA molecule, one of which is extended with the nonhydrogenic atoms roughly coplanar torsional angles of -37 and -179 degrees at N-C-C-C and C-C-C-C (carboxyl), respectively. The second bioactive compound is clearly non planar (torsional angles of -81 and -109 degrees at N-C-C-C and C-C-C-C (carboxyl), respectively).

Prostaciclina nebulizada como tratamiento de la hipertensión pulmonar primaria en una niña de 2 años / Nebulized prostacyclin treatment for pulmonary hypertension in a 2-year-old girl

INTRODUCCIÓN: La hipertensión pulmonar primaria es una entidad de origen desconocido e infrecuente en la edad pediátrica. Se define como un aumento de la presión media de la arteria pulmonar superior a 25 mmHg en reposo con presión de enclavamiento normal y ausencia de causas secundarias. En el tratamiento se usan los diuréticos, bloqueadores del canal del calcio y, en los pacientes que no responden, prostaciclina endovenosa continua. Presentamos una paciente tratada con prostaciclina nebulizada objetivándose una mejoría clínica durante 4 meses. CASO CLÍNICO: Niña de 2 años de edad ingresada por presentar fallo cardíaco derecho que se estabiliza con oxigenoterapia, restricción de líquidos y diuréticos. La paciente es diagnosticada de hipertensión pulmonar primaria tras excluirse las etiologías secundarias. Se realiza cateterismo cardíaco confirmatorio del diagnóstico, sin respuesta positiva al test de vasodilatación. Dado el deterioro clínico se inicia tratamiento con prostaciclina nebulizada. Se observa una mejoría clínica y una disminución de las necesidades de oxígeno y diuréticos durante 4 meses. Tras este período presenta un empeoramiento clínico, por lo que se decide instaurar tratamiento con PGI2 endovenosa continua. La paciente fallece a los 6 meses del diagnóstico por fallo cardíaco. DISCUSIÓN: El uso de prostaciclina en el manejo de la hipertensión pulmonar primaria es una alternativa aceptada en aquellos pacientes que no responden al tratamiento habitual. La mejoría transitoria en la calidad de vida y las necesidades de oxígeno en nuestra paciente apoya el uso de prostaciclina nebulizada como opción útil en pacientes pediátricos (AU)

Intoxicaciones voluntarias como intento de suicidio / Voluntary intoxication as a form of attempted suicide

ANTECEDENTES: La intoxicación voluntaria como intento de suicidio es actualmente un problema importante entre la población adolescente. La tentativa de suicidio es la urgencia psiquiátrica más frecuente en la adolescencia. Presentamos nuestra experiencia sobre intoxicaciones voluntarias durante un período de 2 años. MATERIAL Y MÉTODOS: Estudio retrospectivo y descriptivo de los pacientes ingresados por intoxicaciones voluntarias desde enero de 1996 hasta diciembre de 1997. Se analizan: sexo, edad y hora de la intoxicación, antecedentes de hábitos tóxicos, controles psiquiátricos o intoxicaciones previas, tipo y obtención del tóxico utilizado, sintomatología presentada en el momento de acudir a urgencias, actitud terapéutica y exploraciones complementarias más utilizadas, y días de estancia hospitalaria. RESULTADOS: Durante el período de estudio ingresaron 46 pacientes. La edad mediana fue de 15,6 años, siendo más frecuente en el sexo femenino (40 casos) (87 por ciento). Un 60,9 por ciento (28 casos) había sido controlado previamente en algún servicio de psiquiatría. El tóxico utilizado fue de naturaleza farmacológica, y es obtenido en 38 pacientes (82,6 por ciento) del botiquín del hogar. En 22 casos (47,8 por ciento) se trata de intoxicación múltiple. El 13 por ciento (6 pacientes) requirió hospitalización en cuidados intensivos. La duración media de la estancia hospitalaria fue de 3 días. COMENTARIOS: Las intoxicaciones voluntarias como intento de suicidio representan un problema importante entre la población adolescente, y sobre todo entre las adolescentes de sexo femenino. La identificación de la población de riesgo sería la mejor medida preventiva, constituida por adolescentes, de sexo femenino en su mayoría, con depresión, trastornos de la conducta alimentaria o tentativas de suicidio anteriores (AU)

Prevalence of germline mutations of hMLH1, hMSH2, hPMS1, hPMS2, and hMSH6 genes in 75 French kindreds with nonpolyposis colorectal cancer.

Hereditary nonpolyposis colorectal cancer (HNPCC) is a syndrome characterized by familial predisposition to colorectal carcinoma and extracolonic cancers of the gastrointestinal, urological, and female reproductive tracts. This dominant disorder is caused by germline defects in one of at least five DNA mismatch repair (MMR) genes: hMLH1, hMSH2, hPMS1, hPMS2, and hMSH6 (GTBP). Germline mutations of hMSH2 and hMLH1 are also frequently identified in families not fulfilling all the Amsterdam criteria, thereby demonstrating that the involvement of these genes is not confined to typical HNPCC. To evaluate the respective involvement of the various MMR genes in typical and incomplete HNPCC syndromes, we have performed an analysis of the hMLH1, hMSH2, hPMS1, hPMS2, and hMSH6 genes in a large series of French kindreds (n=75) with colorectal tumors and/or aggregation of extracolonic cancers belonging to the HNPCC spectrum. Mutational analysis has been performed in all families, without preselection for the tumor phenotype. We have detected 26 pathogenic germline mutations of the hMLH1 and hMSH2 genes and several novel variants of the hPMS1, hPMS2, and hMSH6 genes. Our data confirm that, regardless of the type of families and the tumor phenotype, hPMS1, hPMS2, and hMSH6 germline mutations are rare in familial aggregation of colorectal cancers. Furthermore, they suggest that the presence of multiple primary malignancies in a single individual and the observation of extracolonic tumors in relatives of a colorectal cancer patient should be included among the guidelines for referring patients for genetic testing.

A computational model of the nicotinic acetylcholine binding site.

We have derived a model of the nicotinic acetylcholine binding site. This was accomplished by using three known agonists (acetylcholine, nicotine and epibatidine) as templates around which polypeptide side chains, found to be part of the receptor cavity from published molecular biology studies, are allowed to flow freely in molecular dynamics simulations and mold themselves around these templates. The resulting supramolecular complex should thus be a complement, both in terms of steric effects as well as electronic effects, to the agonists and it should be a good estimation of the true receptor cavity structure. The shapes of those minireceptor cavities equilibrated rapidly on the simulation time scale and their structural congruence is very high, implying that a satisfactory model of the nicotinic acetylcholine binding site has been achieved. The computational methodology was internally tested against two rigid and specific antagonists (dihydro-beta-erytroidine and erysoidine), that are expected to give rise to a somewhat differently shaped binding site compared to that derived from the agonists. Using these antagonists as templates there were structural reorganizations of the initial receptor cavities leading to distinctly different cavities compared to agonists. This indicates that adequate times and temperatures were used in our computational protocols to achieve equilibrium structures for the agonists. Overall, both minireceptor geometries for agonists and antagonists are similar with the exception of one amino acid (ARG209).

Neurofibromatosis and early onset of cancers in hMLH1-deficient children.

Hereditary nonpolyposis colon cancer is a common hereditary disorder caused by the germ-line mutations of DNA mismatch repair (MMR) genes, especially hMLH1 and hMSH2. We report here the first identification of human compounds with a homozygous inactivation of a MMR gene. In a typical hereditary nonpolyposis colon cancer family, MMR-deficient children conceived from matings between heterozygotes for a hMLH1 deleterious mutation exhibited clinical features of de novo neurofibromatosis type I and early onset of extracolonic cancers. This observation demonstrates that MMR deficiency is compatible with human development but may lead to mutations during embryogenesis. On the basis of clinical symptoms observed in MMR-deficient children, we speculate that the neurofibromatosis type 1 gene is a preferential target for such alterations.

Arylpiperazines with serotonin-3 antagonist activity: a comparative molecular field analysis.

Comparative molecular field analysis (CoMFA) is applied to antagonists of the 5-HT3 receptor. Analysis is done separately on three published sets of arylpiperazines and on a combination of the three sets. d-Tubocurarine, a conformationally restricted 5-HT3 ligand, is used as a template to assist in selecting the conformation of the antagonists for CoMFA alignment. Two forms of the arylpiperazines (neutral and protonated) and three different kinds of calculated charges (Gasteiger-Hückel, AM1, and AM1 with solvation effect included) are compared. Protonated structures give better statistical results than the neutral species. The way in which charges are calculated does not greatly affect the results. In terms of molecular fields, the behavior in each separate set of compounds cannot be extrapolated to the combined set of 47 compounds. The average value of r2cv from PLS cross-validation on the combined set is 0.70 and varies between 0.56 and 0.80 depending on the orientation of the molecules in the coordinate system. The CoMFA model is tested on four compounds not in the training set: quipazine, N-methylquipazine, 4-phenyl-N-methylquipazine, and KB-6933. Mean agreement of experimental and predicted pKi values of the antagonists is 0.7 log unit. Novel structural modifications are interpreted by the CoMFA model.

The nicotinic cholinergic receptor: a theoretical model.

Based on published affinity-labeling and mutagenesis experiments describing the effect of changes in specific amino acids in molecular biological studies on the nicotinic acetylcholinergic receptor (nAChR), we have identified 12 amino acids which are important in functioning at the nicotinic cholinergic receptor. The work presented here provides an atomistic model of this important receptor based on our molecular modeling studies. We found five of these amino acids (TRP86, ASP89, TYR93, ASP138, and THR191) to be associated with the cationic end of acetylcholine (ACh), which is electron-deficient. Three other amino acids (ARG209, TYR190, and TYR198) are associated with the ester end, where an enhanced electron density is present. After hydrogen bonding between the two oxygen atoms at the ester end, and two of the guanidinium hydrogen atoms in ARG209. ASP200 hydrogen bonds to the other two hydrogen atoms of the guanidinium group, thus forming a pseudo-ring. Two aromatic amino acids (TRP149 and TYR151) then enhance the binding at the pseudo-ring through additional hydrogen bonding and charge-transfer complexation, with THR150 functioning to further stabilize this evolving charge-transfer complex. We postulate that this latter process allows the ion channel to twist, thus opening it. From the published amino acid sequence in the polypeptides at the 5HT-3, GABA, and glycine receptors (Maricq et al.: Science 254:432-437, 1991), we also speculate on which amino acids are involved in these three receptors.

Glycine and GABA receptors: molecular mechanisms controlling chloride ion flux.

We have been able to show that the three clearly identified atoms common to the inhibitory neurotransmitters glycine and GABA, that we previously hypothesized to serve as attachment points at the glycinergic and gabanergic receptor, can indeed interact through both electrostatic and hydrogen bonding to several amino acids, which have been identified in molecular biological investigations as both present and critical in the physiological functioning of key polypeptides common to these inhibitory receptors. In addition, amino acids also involved in stabilizing the interaction between the antagonists strychnine and R5135 at the glycinergic and gabanergic receptors, respectively, have been shown to fit our complex model. We identify in detail molecular mechanisms to explain how glycine and GABA initiate chloride ion movement from extraneuronal fluid in the synaptic cleft to intraneuronal volume. In addition, we also identify the molecular mechanisms involved in the blocking of chloride ion movement by strychnine at the glycinergic receptor and by R5135 at the gabanergic receptor. We also present two computer-generated color prints, one for the glycine receptor and one for the GABA receptor, which show the quantum mechanically geometry optimized complex formed between receptor side chains, i.e., the part of the amino acids in the polypeptide that interacts with the zwitterionic inhibitory neurotransmitters. These computer-generated color figures also show a) the important electrostatic and hydrogen bonding in these interactions, b) a van der Waals model of this complex to illustrate that no steric repulsions exist, and c) the molecular electrostatic potential energy map showing the electrostatic potentials of neurotransmitter bound to the receptor model. Finally, we show with computer calculations that the pseudo-rings, formed between the positive quanidinium group in arginine and one of the oxygen atoms in the carboxyl group in both glycine or GABA, result in a positive planar region which appears to be involved in a charge-transfer complex with aromatic benzene groups in amino acids such as phenylalanine and tryosine.

Comparison of binding mechanisms at cholinergic, serotonergic, glycinergic and GABAergic receptors.

Employing computational methods and published data from molecular biological studies involving amino acid sequences in the polypeptide receptors, the authors studied and compared how two excitatory neurotransmitters, ACh and 5-HT, and two inhibitory neurotransmitters, glycine and GABA, can bind to their respective recognition sites at CNS receptors. Models for each neurotransmitter interaction with specific amino acids are described and identified. Molecular mechanisms are identified that can explain how the binding process initiates ion flow through channels located within the postsynaptic membrane such that if the neurotransmitter is inhibitory, hyperpolarization occurs, and if excitatory, depolarization occurs. Although the theoretical work described indicates that there is a difference in molecular mechanisms operative at the anionic and cationic channels, and provides an explanation why the former is more specific, the molecular modeling data and the similarities of specific amino acids in the sequence in all four receptor polypeptides used to construct the four models support ACh, 5-HT, glycine and GABA as being members of the same ligand-gated ion channel superfamily.

Identifying agonistic and antagonistic mechanisms operative at the GABA receptor.

Based on our molecular modeling investigations of the glycinergic receptor, we expanded our studies to similarly investigate the GABAergic receptor. New data suggest there may exist a slightly different agonistic mechanism for the molecules described herein as compared to glycine. The origin of this is undoubtedly the fact that, while glycine has a positive and two negative binding sites, it is significantly shorter than GABA and the other GABA agonists. Clearly, discovery of more glycine agonists is needed to further clarify this point. Moreover, we find a remarkedly different antagonistic mechanism exists for this phylogenetically newer inhibitory system in the central nervous system (CNS) than recently reported for strychnine and eight weaker glycine antagonists. We used GABA and six agonists (muscimol, dihydromuscimol, THIP, isoguvacine, trans-3-aminocyclopentane-1-carboxylic acid, piperidine-4-sulfonic acid) and five antagonists (bicuculline-N15-methobromide, R5135, pitrazepin, iso-THAZ and securinine) to derive our conclusions. We found that each of the agonists have three clearly defined atoms that can serve as attachment points at the GABAA receptor site. One of the three attachment atoms includes a carbonyl or carboxylate oxygen. The role of the carbonyl or carboxylate atom is very important. First, we theorize that a rapid two-point attachment occurs (one from the positive end and one from one of the other two negative atoms on the ligand) at the recognition site in the receptor where GABA or a GABAergic agonist binds. The positive end of the agonist perhaps associates through hydrogen bonding to a beta-carboxyl group in one of the aspartate molecules in the polypeptide. The negative attachment points perhaps bind through hydrogen bonding to arginine molecules in this polypeptide. The second negative site in the agonist immediately triggers a conformational change by pulling together the aforementioned groups by electrostatic attraction, and hence opening the chloride channel. We propose the carbonyl oxygen is partly responsible for triggering the opening by formation of a double hydrogen bond to arginine. We postulate that this attraction is the first step inducing the conformational change. In the case of the GABA antagonists investigated, a fourth attachment site was not found. In fact only two sites have been identified similar to the group II glycine antagonists. Our data support a hypothesis for GABAergic antagonist activity which suggests that the antagonist simply binds to the recognition site and blocks the neurotransmitter, GABA, from entering this site thereby preventing the opening of the chloride channel; it just stays closed. This mechanism is different from the mechanism proposed for the large number of Group I glycine antagonists (Aprison et al.: J Neurosci Res 41: 259-269, 1995).

On identifying a second molecular antagonistic mechanism operative at the glycine receptor.

We used molecular modeling techniques to examine six reported antagonists of glycine with varying Ki values against strychnine. We found the data suggest two groups operating with different mechanisms. In group 1 (strychnine, brucine, Pitrazepin, and bicuculline methobromide) the antagonist contains two or three sites that can electrostatically bind to the three comparable groups of opposite charge in the recognition site where the natural neurotransmitter binds, thus opening the chloride channel. In addition, when in this position, the antagonist is able to also block the now opened chloride channel with a different portion of its structure. In many cases, this involves an interaction between a carbonyl group on the antagonist and the guanidinium group of arginine which is part of the polypeptide segment of the outer mouth of the chloride channel (Grenningloh et al., Nature 330:25-26, 1987). In group 2 (R5135 and 1,5-diphenyl-3,7-diazaadamantan-9-ol) the antagonist contains charged sites but when one of these molecules attaches to the recognition site, the chloride channel is not opened. In addition, R5135 contains a carbonyl group which attaches to arginine as pointed out in the text, whereas 1,5-diphenyl-3,7-diazaadamantan-9-ol contains a phenyl group that can block the channel.