Lack of mGluR6‐related cascade elements leads to retrograde trans‐synaptic effects on rod photoreceptor synapses via matrix‐associated proteins

Heterotrimeric G‐proteins couple metabotropic receptors to downstream effectors. In retinal ON bipolar cells, G_o couples the metabotropic receptor mGluR6 to the TRPM1 channel and closes it in the dark, thus hyperpolarizing the cell. Light, via GTPase‐activating proteins, deactivates G_o, opens TRPM1 and depolarizes the cell. G_o comprises Gα_o1, Gβ3 and Gγ13; all are necessary for efficient coupling. In addition, Gβ3 contributes to trafficking of certain cascade proteins and to maintaining the synaptic structure. The goal of this study was to determine the role of Gα_o1 in maintaining the cascade and synaptic integrity. Using mice lacking Gα_o1, we quantified the immunostaining of certain mGluR6‐related components. Deleting Gα_o1 greatly reduced staining for Gβ3, Gγ13, Gβ5, RGS11, RGS7 and R9AP. Deletion of Gα_o1 did not affect mGluR6, TRPM1 or PCP2. In addition, deleting Gα_o1 reduced the number of rod bipolar dendrites that invaginate the rod terminal, similar to the effect seen in the absence of mGluR6, Gβ3 or the matrix‐associated proteins, pikachurin, dystroglycan and dystrophin, which are localized presynaptically to the rod bipolar cell. We therefore tested mice lacking mGluR6, Gα_o1 and Gβ3 for expression of these matrix‐associated proteins. In all three genotypes, staining intensity for these proteins was lower than in wild type, suggesting a retrograde trans‐synaptic effect. We propose that the mGluR6 macromolecular complex is connected to the presynaptic rod terminal via a protein chain that includes the matrix‐associated proteins. When a component of the macromolecular chain is missing, the chain may fall apart and loosen the dendritic tip adherence within the invagination.     

The effect of prestorage irradiation on posttransfusion red cell survival

Transfusion-associated graft-versus-host disease (TA-GVHD) may occur whenever immunologically competent allogeneic lymphocytes are transfused to an immunocompromised recipient. Irradiation of blood components eliminates the risk of TA-GVHD but may damage the cellular elements in the transfused component, particularly if the cells are stored for prolonged periods in the irradiated state. To study the effect of irradiation on long-term storage of red cells, AS-1 red cells from eight normal subjects were prepared on two occasions. On one occasion, the units were stored as standard AS-1 red cells for 42 days at 4 degrees C; on the other, they were exposed to 3000 cGy radiation within 4 hours of collection and then were stored as AS-1 red cells for 42 days at 4 degrees C. The donations were at least 12 weeks apart. Irradiated units demonstrated significant elevations in poststorage plasma hemoglobin (Hb) (623 +/- 206 vs. 429 +/- 194 g/dL [6230 +/- 2060 vs. 4290 +/- 1940 g/L], p less than 0.02) and plasma potassium (78 +/- 4 vs. 43 +/- 9 mEq/L [78 +/- 4 vs. 43 +/- 9 mmol/L], p less than 0.01) and significant decreases in red cell ATP (1.9 +/- 0.2 vs. 2.1 +/- 0.3 microM/g Hb, p less than 0.04) and 24-hour posttransfusion red cell recovery (68.5 vs. 78.4%, p less than 0.02), as compared to nonirradiated units. It can be concluded that irradiation with 3000 cGy damages red cells and that long-term storage in the irradiated state may enhance this damage. Red cells should not be stored for 42 days after irradiation with 3000 cGy.     

Fractionation of Spatial Memory in GRM2/3 (mGlu2/mGlu3) Double Knockout Mice Reveals a Role for Group II Metabotropic Glutamate Receptors at the Interface Between Arousal and Cognition

Group II metabotropic glutamate receptors (mGluR2 and mGluR3, encoded by GRM2 and GRM3) are implicated in hippocampal function and cognition, and in the pathophysiology and treatment of schizophrenia and other psychiatric disorders. However, pharmacological and behavioral studies with group II mGluR agonists and antagonists have produced complex results. Here, we studied hippocampus-dependent memory in GRM2/3 double knockout (GRM2/3^−/−) mice in an iterative sequence of experiments. We found that they were impaired on appetitively motivated spatial reference and working memory tasks, and on a spatial novelty preference task that relies on animals'' exploratory drive, but were unimpaired on aversively motivated spatial memory paradigms. GRM2/3^−/− mice also performed normally on an appetitively motivated, non-spatial, visual discrimination task. These results likely reflect an interaction between GRM2/3 genotype and the arousal-inducing properties of the experimental paradigm. The deficit seen on appetitive and exploratory spatial memory tasks may be absent in aversive tasks because the latter induce higher levels of arousal, which rescue spatial learning. Consistent with an altered arousal–cognition relationship in GRM2/3^−/− mice, injection stress worsened appetitively motivated, spatial working memory in wild-types, but enhanced performance in GRM2/3^−/− mice. GRM2/3^−/− mice were also hypoactive in response to amphetamine. This fractionation of hippocampus-dependent memory depending on the appetitive-aversive context is to our knowledge unique, and suggests a role for group II mGluRs at the interface of arousal and cognition. These arousal-dependent effects may explain apparently conflicting data from previous studies, and have translational relevance for the involvement of these receptors in schizophrenia and other disorders.     

Allosteric modulators of NR2B-containing NMDA receptors: molecular mechanisms and therapeutic potential

N-methyl-D-aspartate receptors (NMDARs) are ion channels gated by glutamate, the major excitatory neurotransmitter in the mammalian central nervous system (CNS). They are widespread in the CNS and are involved in numerous physiological and pathological processes including synaptic plasticity, chronic pain and psychosis. Aberrant NMDAR activity also plays an important role in the neuronal loss associated with ischaemic insults and major degenerative disorders including Parkinson''s and Alzheimer''s disease. Agents that target and alter NMDAR function may, thus, have therapeutic benefit. Interestingly, NMDARs are endowed with multiple extracellular regulatory sites that recognize ions or small molecule ligands, some of which are likely to regulate receptor function in vivo. These allosteric sites, which differ from agonist-binding and channel-permeation sites, provide means to modulate, either positively or negatively, NMDAR activity. The present review focuses on allosteric modulation of NMDARs containing the NR2B subunit. Indeed, the NR2B subunit confers a particularly rich pharmacology with distinct recognition sites for exogenous and endogenous allosteric ligands. Moreover, NR2B-containing receptors, compared with other NMDAR subtypes, appear to contribute preferentially to pathological processes linked to overexcitation of glutamatergic pathways. The actions of extracellular H⁺, Mg²⁺, Zn²⁺, of polyamines and neurosteroids, and of the synthetic compounds ifenprodil and derivatives (‘prodils’) are presented. Particular emphasis is put upon the structural determinants and molecular mechanisms that underlie the effects exerted by these agents. A better understanding of how NR2B-containing NMDARs (and NMDARs in general) operate and how they can be modulated should help define new strategies to counteract the deleterious effects of dysregulated NMDAR activity.     

Ponseti technique of correcting idiopathic clubfoot deformity

The efficacy of the Ponseti method of clubfoot treatment at Queen Elizabeth Central Hospital (QECH) was analysed from December 2000 to December 2001. Ninety one patients, 60 boys and 31 girls were prospectively and consecutively enrolled. 31 patients had a unilateral clubfoot and 60 had bilateral clubfeet. 77 patients had primary idiopathic clubfoot and 14 patients had clubfeet associated with other congenital anomalies such as arthrogryposis. 32 patients (35%) were lost to follow up; records were inadequate for 6 patients leaving 54 patients (59%) available for analysis. Three main groups were assessed. Group 1 (24 patients): virgin previously untreated primary idiopathic clubfeet: Ponseti method used from outset. Group 2 (19 patients): complex, primary idiopathic clubfeet: Ponseti method introduced after other manipulation techniques. Group 3 (11 patients): clubfeet associated with other congenital anomalies. In group 1, the mean age at start of treatment was 9.7 weeks and the mean time to correction of deformity was 7.4 weeks. 20 out of 24 patients (84%) had correction of deformity and remained corrected. 4 patients had recurrence of deformity mainly due to non compliance with treatment and correction was achieved once treatment restarted. In group 2, 19 patients had been on treatment for a mean period of 32 weeks prior to commencement of Ponseti treatment. In 17 of these patients the deformity was still uncorrected. Ponseti treatment was commenced at a mean age of 36 weeks and correction was achieved in all 17 patients after a mean treatment duration of 7.1 weeks. In group 3, correction of deformity was initially achieved in only 60%. The period to achieve correction was long and incidence of recurrence of deformity was high.The success of conservative treatment of clubfeet using the Ponseti method has resulted in large decrease in the number of surgical procedures performed under general anaesthaesia such as posteromedial releases in the treatment of clubfeet at QECH. This method has now been adopted as the Standard treatment of clubfoot and is being advocated nationwide.     

Gene Probe Analysis in an Informative Family with Multiple Endocrine Neoplasia Syndrome Type 2A (MEN 2A). Improvement in Carrier Risk Estimation

Gene probe analysis of the MEN 2A locus on chromosome 10 hasbeen undertaken using the markers TB10.163, RBP 3 and TB14.34in a large kindred with familial medullary thyroid carcinomas,with or without phaeochromocytomas or primary hyperparathyroidism.A maximum LOD score of 2.97 gave strong evidence of close linkagewith zero recombination. For 12 members of the family so far not known to be affectedby any form of the disease the estimated risk of carrying thegene has been considerably decreased in all but one, whose riskhas been greatly increased.