This paper discusses the application of a reagentless, selective microbiosensor as a useful alternative tool for monitoring D-serine in neural samples. The main components of the 125-μm-diameter disk biosensor were D-amino acid oxidase for D-serine sensitivity (linear region slope, 61 ± 7 μA cm(-2) mM(-1); limit of detection, 20 nM), and poly-phenylenediamine for rejection of electroactive interference. The response time of the biosensor was of the order of 1 s, ideal for 'real-time' monitoring, and detection of systemically administered D-serine in brain extracellular fluid is demonstrated. Exploitation of this probe might resolve queries involving regulation of D-serine in excitotoxicity, and modulation of N-methyl-D-aspartate receptor function by D-serine and glycine in the central nervous system.
Schizophrenia is a complex biological disorder with multifactorial mode of transmission where non-genetic determinants are also play important role. It is now clear that it involves combined effect of many genes, each conferring a small increase in liability to the illness. Thus no causal disease genes or single gene of major effects, only susceptible genes are operating. Given this complexity, it comes as no surprise of the difficulty to find susceptible genes. However, schizophrenia genes have been found at last. Recent studies on molecular genetics of schizophrenia which focused on positional and functional candidate genes postulated to be associated with schizophrenia are beginning to produce findings of great interest. These include neuregulin (NRG-1, 8p12-21), dysbindin, (DTNBP1,6p22.3), G72 (13q34) / D-amino acid oxidase (DAAO,12q24), proline dehydrogenase (PRODH-2, 22q11.21), catechol-O-methyltransferase (COMT, 22q11.21), regulator of G protein signaling (RGS-4), 5HT2A and dopamine D3 receptor (DRD3). Applications of microarrays methods were able to locate positional candidate genes related to dopaminergic, serotonergic and glutamatergic neurotransmission. New genome scan project, seen in the light of previous scans, provide support for schizophrenia candidate region on chromosome 1q, 2q, 5q, 6p, 8p, 10p, 13q,15q and 22q. Other reports described including the application of LD mapping and positional cloning technique, microarray technology and efforts to develop quantitative phenotype. More exciting finding is expected in near future with the completion of Hap Map project.
D-serine has been implicated as a brain messenger, promoting not only neuronal signalling but also synaptic plasticity. Thus, a sensitive tool for D-serine monitoring in brain is required to understand the mechanisms of D-serine release from glia cells. A biosensor for direct fixed potential amperometric monitoring of D-serine incorporating mammalian D-amino acid oxidase (DAAO) immobilized on a Nafion coated poly-ortho-phenylenediamine (PPD) modified Pt-Ir disk electrode was therefore developed. The combined layers of PPD and Nafion enhanced the enzyme activity and biosensor efficiency by approximately 2-fold compared with each individual layer. A steady state response time (t(90%)) of 0.7+/-0.1s (n=8) and limit of detection 20+/-1 nM (n=8) were obtained. Cylindrical geometry showed lower sensitivity compared to disk geometry (61+/-7 microA cm(-2) mM(-1), (n=4), R(2)=0.999). Interference by ascorbic acid (AA), the main interference species in the central nervous system and other neurochemical electroactive molecules was negligible. Implantation of the electrode and microinjection of D-serine into rat brain striatal extracellular fluid demonstrated that the electrode was capable of detecting D-serine in brain tissue in vivo.