ACTIVATION of the N-methyl-d-aspartate (NMDA) receptor is important for certain forms of activity-dependent synaptic plasticity, such as long-term potentiation (reviewed in ref. 1), and the patterning of connections during development of the visual system (reviewed in refs 2, 3). Several subunits of the NMDA receptor have been cloned: these are NMDAR1 (NR1), and NMDAR2A, 2B, 2C and 2D (NR2A-D)4–8. Based on heterologous co-expression studies, it is inferred that NR1 encodes an essential subunit of NMDA receptors and that functional diversity of NMDA receptors in vivo is effected by differential incorporation of subunits NR2A–NR2D5–8. Little is known, however, about the actual subunit composition or heterogeneity of NMDA receptors in the brain. By co-immunoprecipitation with subunit-specific antibodies, we present here direct evidence that NMDA receptors exist in rat neocortex as heteromeric complexes of considerable heterogeneity, some containing both NR2A and NR2B subunits. A progressive alteration in subunit composition seen postnatally could contribute to NMDA-receptor variation and changing synaptic plasticity during cortical development.

Changing subunit composition of heteromeric NMDA receptors during development of rat cortex

Biologically active compounds which are light-responsive offer experimental possibilities which are otherwise very difficult to achieve. Since light can be manipulated very precisely, for example, with lasers and microscopes rapid jumps in concentration of the active form of molecules are possible with exact control of the area, time, and dosage. The development of such strategies started in the 1970s. This review summarizes new developments of the last five years and deals with "small molecules", proteins, and nucleic acids which can either be irreversibly activated with light (these compounds are referred to as "caged compounds") or reversibly switched between an active and an inactive state.

Biologically active molecules with a "light switch".

The endoplasmic reticulum (ER) is the largest single intracellular organelle, which is present in all types of nerve cells. The ER is an interconnected, internally continuous system of tubules and cisterns, which extends from the nuclear envelope to axons and presynaptic terminals, as well as to dendrites and dendritic spines. Ca2+ release channels and Ca2+ pumps residing in the ER membrane provide for its excitability. Regulated ER Ca2+ release controls many neuronal functions, from plasmalemmal excitability to synaptic plasticity. Enzymatic cascades dependent on the Ca2+ concentration in the ER lumen integrate rapid Ca2+ signaling with long-lasting adaptive responses through modifications in protein synthesis and processing. Disruptions of ER Ca2+ homeostasis are critically involved in various forms of neuropathology.

https://www.physiology.org/doi/pdf/10.1152/physrev.00004.2004

Physiology and Pathophysiology of the Calcium Store in the Endoplasmic Reticulum of Neurons

Representations of Odor in the Piriform Cortex

It is widely assumed that long-term changes in synaptic strength underlie information storage in the brain and, ultimately, behavioral memory. Recent years have seen a major effort to identify and analyze electrophysiological model systems in which particular patterns of neural activity give rise to such enduring changes. Most of this attention has been focused upon hippocampal long-term synaptic potentiation (LTP), in which brief activation of a set of afferents gives rise to a persistent increase in synaptic strength of the activated synapses. LTP is a broad term. It has come to mean any persistent increase in synaptic strength induced by a variety of mechanisms in a large number of locations in the nervous system. The purpose of the present review is to examine the opposite phenomenon, use-dependent long-lasting decreases in synaptic strength, which have been collectively termed long-term synaptic depression (LTD). Also a blanket term, LTD denotes depression induced according to a variety of synaptic modification rules, mediated by various electrophysiological and biochemical events, and occurring extensively in the nervous system.

Long-term synaptic depression

The ideal lavage volume for removing bradykinin, interleukin-6, and protein from the temporomandibular joint by arthrocentesis ☆

Magnetic and Mossbauer effect measurements on the nitrides with hcp metal lattice of V, Cr, Mn and Fe are carried out as a function of composition. Hexagonal VN x and hexagonal CrM x are Pauli paramagnetic. Hexagonal MnN x shows antiferromagnetism, while both hexagonal and orthorhombic FeN x show ferromagnetism at low temperatures. In these Phases, nitrogen atoms suppress magnetic ordering in consequence of the reduction of magnetic moments. As a whole, the observed types of magnetism of hexagonal nitrides resemble those of their metals in spite of the difference in crystal structures. Type II superconductivity is found in hexagonal VN x although it is not yet conclusive.

MAGNETIC STUDY ON HEXAGONAL NITRIDES OF 3d TRANSITION METALS.

Molecular cloning has demonstrated a diversity of artificially expressed N-methyl-D-aspartate (NMDA) receptors, implying a similar diversity of naturally occurring NMDA receptors in situ. Particularly significant was the success in expression of NMDA receptor classes exhibiting various sensitivities to Mg2+ block, a voltage-dependent channel blockade by Mg2+ that is essential to NMDA receptor functioning. Release from Mg2+ block often allows or facilitates the occurrence of long-term potentiation, a form of synaptic plasticity. Here we show that in the immature visual cortex, which is more susceptible to long-term potentiation than adult visual cortex, synaptically activated NMDA receptors, unlike those in the adult, have varying but clearly reduced sensitivities to Mg2+ block. We propose that the initially expressed, later-eliminated NMDA receptors exhibiting a reduced Mg2+ block may underlie the greater susceptibility to plasticity in the immature neocortex.

Reduced Mg2+ block of N-methyl-D-aspartate receptor-mediated synaptic potentials in developing visual cortex

Structure and function of the brain are use-dependent variables based on "synapse plasticity". Since synapses are driven by chemical transmitters, synaptic functions are liable to be modified by extrinsic chemicals displaying affinities for synaptic receptors or modulators. Caffeine is a widely used chemical substance that can invade synapses, and has several biochemical and metabolic actions on synaptic activities. This review focuses on the actions of caffeine on changes in structure and function in the region of the hippocampal formation and neocortex, which exhibit high synapse plasticity. At the synapse level, various synaptic receptors and channel activities are modulated by caffeine via mobilization of intracellular calcium, inhibition of phosphodiesterase, antagonism of adenosine receptors and GABA receptors. These actions of caffeine enable neurons to induce plastic changes in the properties of synaptic activities, such as synaptic transmission efficiency and morphology. At the network level, caffeine has the ability to activate cortical neural oscillators that deliver repetitive N-methyl-D-aspartate receptor-dependent signals to surrounding areas, causing strengthening of long-range inter-cortical communications. Caffeine might thus allow reorganization of cortical network functions via synaptic mobilizations.

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The potential of caffeine for functional modification from cortical synapses to neuron networks in the brain.

Objectives. To evaluate the relationship between the volume of joint effusion (JE), determined by T2-weighted magnetic resonance imaging (MRI), and microscopic findings of synovial inflammation in internal derangement of the temporomandibular joint (TMJ). Study design. Magnetic resonance images of 53 symptomatic TMJs (53 patients) associated with painful hypomobility were taken to evaluate the degree of JE on a scale of 0 to 3. Within 2 months after MRI, biopsy specimens obtained by arthroscopy were quantitatively assessed, on the basis of Gynther's grading system, for severity of hyperplasia of synovial lining cell layers, vascularity, and the presence of inflammatory cells. Each synovitis score was compared among the 4 JE grades, as well as between 2 groups—effusion present (grades 2 and 3) and effusion absent (grades 0 and 1)—by using the Spearman correlation coefficiency and the Mann-Whitney U test. Results. The distribution of JE was as follows: 14 joints had grade 0, 9 joints had grade 1, 19 joints had grade 2, and 11 joints had grade 3. Significant relationships were found between the grades of JE and scores of synovial lining cell layers (P =.0012) as well as between the grades of JE and scores of presence of inflammatory cells (P =.0064). The joints with effusion had significantly higher scores for synovial lining cell layers (2.0 ± 0.2) than the joints without effusion (1.3 ± 0.2) (P =.029). There was no statistically significant correlation between the scores of vascularity and JE (P =.394). Conclusions. The evidence of JE on MRI might correlate with synovial inflammatory activity. It confirms the common consensus that JE probably reflects synovitis, especially when synovial hyperplasia has a key role in the pathogenesis of JE. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003;95:761-6)

Does joint effusion on T2 magnetic resonance images reflect synovitis? Part 3. Comparison of histologic findings of arthroscopically obtained synovium in internal derangements of the temporomandibular joint.

Hiroshi Yoshimura

Papers

The ideal lavage volume for removing bradykinin, interleukin-6, and protein from the temporomandibular joint by arthrocentesis ☆

MAGNETIC STUDY ON HEXAGONAL NITRIDES OF 3d TRANSITION METALS.

Reduced Mg2+ block of N-methyl-D-aspartate receptor-mediated synaptic potentials in developing visual cortex

The potential of caffeine for functional modification from cortical synapses to neuron networks in the brain.

Does joint effusion on T2 magnetic resonance images reflect synovitis? Part 3. Comparison of histologic findings of arthroscopically obtained synovium in internal derangements of the temporomandibular joint.