No abstract

Ionotropic glutamate receptors of the kainate and AMPA subtypes share a number of structural features, both topographical and in terms of stoichiometry. In addition, AMPA and kainate receptors share similar pharmacological and biophysical properties in that they are activated by common agonists and display rapid activation and desensitization characteristics. However, we show here that in contrast to AMPA receptor-mediated responses (native or recombinant GluR3 receptor), the response of native and recombinant (GluR6) kainate receptors to glutamate was drastically reduced in the absence of extracellular Na+ (i.e., when replaced by Cs+). Removal of Na+ increases the rate of desensitization, indicating that external Na+ modulates channel gating. Whereas the size of the substituting cation is important in mimicking the action of Na+ (Li+>K+>Cs+), modulation was voltage independent. These results indicate the existence of different gating mechanisms for AMPA and kainate receptors. By using chimeric AMPA-kainate receptors derived from GluR3 and GluR6, we have identified a key residue in the S2 segment of GluR6 (M770) that is largely responsible for the sensitivity of the receptor to external Na+. Thus, these results show the existence of a specific kainate receptor gating mechanism that requires external Na+ to be operative.

SUMMARY The association of joint hypermobility and motor development was sequentially investigated in 715 infants from the ages of 8 to 14 months. Seven joints were evaluated for mobility, and each infant underwent a physical and neurological examination. Parents were given a Denver Developmental Parents' Questionnaire. All subjects with a general developmental delay, systemic illness or syndrome were excluded. The infants were classified as having normal or delayed motor development with normal or delayed joint mobility. They were re-examined six months later. Multivariate statistical techniques was used for categorical analysis, and three joints were found to be significantly associated with motor delay at the first examination-hip abduction, elbow hyperextension, and foot dorsiflexion. Of the 715 infants, 126 had joint hypermobility and of these 38 (30-2%) had motor delay. Sixty four of 589 (10.9%) with normal joints had delayed motor development. Six months later 23 out of 35 of the group with joint hypermobility and 42 out of 53 of the group with normal joints had normal motor function.Joint hypermobility is associated with an increased incidence of motor delay in infancy. Over the ensuing six months most of the subjects will catch up. These findings, indicating a favourable prognosis, have implications regarding clinical assessment and parental counselling.Paediatricians frequently encounter infants presenting with delayed gross motor development. The evaluation of such cases entails comprehensive paediatric and neurodevelopmental examination, and when cerebral palsy, mental retardation, and other neuromuscular aetiologies have been excluded, a group of slow motor developers of unknown aetiology and prognosis remains. The rather dramatic presentation of an infant who does not attain sitting, crawling, or walking at the same time as his peers often engenders anxiety in the parents. It has been our experience that a number of these infants have hypermobile joints and that they ultimately seem to catch up in motor development.Previous reports suggest that hypermobile joints can be the result of either increased laxity of the ligaments and joint capsule' or muscle hypotonia.2

The single tooth implant is a treatment option for the replacement of missing single teeth and in many cases is the treatment of choice. It is, however, an expensive treatment requiring a co-ordinated approach to the surgical and restorative aspects of treatment. In this study, a group of dentists in general and restorative dental practice and with no previous experience in implant surgery underwent an intensive training course in all aspects of implant treatment for single teeth. Using a system of simplified instrumentation with a strict adherence to protocol, the group installed and restored single tooth implants ad modum Brånemark in a wide range of clinical situations. At the one year follow-up period following crown insertion, the success rate of treatment compared favourably with results reported from centres using the specialist team approach to treatment. The results of this study indicate that further consideration should be given to the training of general dentists so that improved delivery of dental health care can be provided at a more economic level.