NMDA receptors are preeminent neurotransmitter-gated channels in the central nervous system, which respond to glutamate in a manner that integrates multiple external and internal cues. They belong to the ionotropic glutamate receptor family and fulfill unique and critical roles in neuronal development and function. These roles depend on characteristic response kinetics, which reflect the receptor’s operation. Here, we review biologically salient features of the NMDA receptor signal and their mechanistic origins. Knowledge of distinctive NMDA receptor biophysical properties, their structural determinants, and physiological roles is necessary to understand the physiologic and neurotoxic actions of glutamate, and to design effective therapeutics.

Recent analyses in flies, mice, zebrafish, and humans showed that mutations in prickle orthologs result in epileptic phenotypes, although the mechanism responsible for generating the seizures was unknown. Here, we show that Prickle organizes microtubule polarity and affects their growth dynamics in axons of Drosophila neurons, which in turn influences both anterograde and retrograde vesicle transport. We also show that enhancement of the anterograde transport mechanism is the cause of the seizure phenotype in flies, which can be suppressed by reducing the level of either of two Kinesin motor proteins responsible for anterograde vesicle transport. Additionally, we show that seizure-prone prickle mutant flies have electrophysiological defects similar to other fly mutants used to study seizures, and that merely altering the balance of the two adult prickle isoforms in neurons can predispose flies to seizures. These data reveal a previously unidentified pathway in the pathophysiology of seizure disorders and provide evidence for a more generalized cellular mechanism whereby Prickle mediates polarity by influencing microtubule-mediated transport.epilepsy | planar cell polarity | spiny-legs | EB1-GFP | neurodegeneration E pilepsy, which affects ∼1% of the population, is a disabling and debilitating disease characterized by recurrent seizures. Coupling genetic analysis of human epilepsy cases with functional validation in animal models, we previously showed that mutations in human PRICKLE1 and PRICKLE2, as well as mutations in mouse, zebrafish and fly prickle (pk) orthologs, increase susceptibility to seizures (1-3). We recently showed that both mouse and fly Prickle can associate with Synapsin (4). However, little is known regarding what cellular process connects Prickle with epilepsy. Products of the prickle gene work in concert with a group of cytoplasmic and membrane-associated proteins including Frizzled (Fz) and Dishevelled (Dsh) to establish polarity of structures such as hairs and bristles in the fly epidermis (5-8). The fly pk locus expresses three alternately spliced isoforms, two of which, pk sple (prickle-spiny-legs) and pk pk (prickle-prickle), are expressed in postembryonic animals (5, 7). Homozygous pk pk and pk sple fly mutants show strong planar cell polarity (PCP) phenotypes in the wing and in the legs, respectively, in addition to other regions of the adult body (6, 7). Prickle (Pk) protein isoforms are localized to the proximal end of fly wing cells, whereas Fz and Dsh are localized distally (8).Here, we show that vesicle transport dynamics are altered in neurons of Drosophila mutant for either adult isoform of prickle. Seizure-prone pk sple heterozygotes show enhanced vesicle transport (along with electrophysiological defects similar to other seizure-prone mutant flies), and the seizure phenotypes can be rescued by lowering the dose of vesicle transport motor proteins. However, pk pk heterozygotes show severely reduced vesicle transport, with loss of both copies of pk pk showing a marked decrease i...

The application of nanotechnology in biological research is beginning to have a major impact leading to the development of new types of tools for human health. One focus of nanobiotechnology is the development of nanoparticle-based formulations for use in drug or gene delivery systems. However most of the nano probes currently in use have varying levels of toxicity in cells or whole organisms and therefore are not suitable for in vivo application or long-term use. Here we test the potential of a novel silica based nanoparticle (organically modified silica, ORMOSIL) in living neurons within a whole organism. We show that feeding ORMOSIL nanoparticles to Drosophila has no effect on viability. ORMOSIL nanoparticles penetrate into living brains, neuronal cell bodies and axonal projections. In the neuronal cell body, nanoparticles are present in the cytoplasm, but not in the nucleus. Strikingly, incorporation of ORMOSIL nanoparticles into the brain did not induce aberrant neuronal death or interfered with normal neuronal processes. Our results in Drosophila indicate that these novel silica based nanoparticles are biocompatible and not toxic to whole organisms, and has potential for the development of long-term applications.

N-methyl-d-aspartate (NMDA) receptors are glutamate- and glycine-gated channels that flux Na and Ca into postsynaptic neurons during synaptic transmission. The resulting intracellular Ca transient is essential to physiological and pathological processes related to synaptic development, plasticity, and apoptosis. It also engages calmodulin (CaM) to reduce subsequent NMDA receptor activity in a process known as Ca-dependent inactivation (CDI). Here, we used whole-cell electrophysiology to measure CDI and computational modeling to dissect the sequence of events that underlies it. With these approaches, we estimate that CaM senses NMDA receptor Ca influx at ∼9 nm from the channel pore. Further, when we controlled the frequency of Ca influx through individual channels, we found that a kinetic model where apoCaM associates with channels before their activation best predicts the measured CDI. These results provide, to our knowledge, novel functional evidence for CaM preassociation to NMDA receptors in living cells. This particular mechanism for autoinhibitory feedback reveals strategies and challenges for Ca regulation in neurons during physiological synaptic activity and disease.