Coupled heterocellular arrays in the brain.

Gap junctions are transcellular pathways that enable a dynamic metabolic coupling and a selective exchange of biological signaling mediators. Throughout the course of the brain development these intercellular channels are assembled into regionally and temporally defined patterns. The present review summarizes the possibilities of heterocellular gap junctional pairing in the brain parenchyma, involving glial cells, neurons and neural precursors as well as it highlights on the meaningfulness of these coupled arrays to the concept of brain functional compartments.

Differences in the isodesmin pattern between the electric organs of Electrophorus electricus L.

Desmin, the intermediate filament protein of muscle, is present in the electric organs of Electrophorus electricus L. as five isovariants, instead of the one to two isovariants found in muscle. We analyzed the isodesmin pattern in the three different electric organs using densitometry of Coomassie blue-stained bands in electrofocusing polyacrylamide gel electrophoresis. We were able to compare the relative amount of each of the five desmin isovariants in an isodesmin pattern characteristic of each electric organ. These patterns proved to be, in some cases, statistically different. Desmin in each electric organ could have slightly different functions in order to correlate with the organ-specific isovariant patterns.

Cell migration in the postnatal subventricular zone.

New neurons are constantly added to the olfactory bulb of rodents from birth to adulthood. This accretion is not only dependent on sustained neurogenesis, but also on the migration of neuroblasts and immature neurons from the cortical and striatal subventricular zone (SVZ) to the olfactory bulb. Migration along this long tangential pathway, known as the rostral migratory stream (RMS), is in many ways opposite to the classical radial migration of immature neurons: it is faster, spans a longer distance, does not require radial glial guidance, and is not limited to postmitotic neurons. In recent years many molecules have been found to be expressed specifically in this pathway and to directly affect this migration. Soluble factors with inhibitory, attractive and inductive roles in migration have been described, as well as molecules mediating cell-to-cell and cell-substrate interactions. However, it is still unclear how the various molecules and cells interact to account for the special migratory behavior in the RMS. Here we will propose some candidate mechanisms for roles in initiating and stopping SVZ/RMS migration.

Is pannexin the pore associated with the P2X7 receptor?

The P2X7 receptor (P2X7R), an ATP-gated cation channel, is expressed predominantly in leukocytes. Activation of P2X7R has been implicated in the formation of a cytolytic pore (i.e., a large conductance channel) that allows the passage of molecules up to 900 Da in macrophages. At least two hypotheses have been presented to explain the conversion of a nonselective cation channel to a cytolytic pore. One hypothesis suggests that the pore is a separate molecular structure activated by P2X7R, and the second asserts that this is an intrinsic property of P2X7R (pore dilation). Based on connexin knockout and hemichannel antagonist studies, some groups have concluded that connexins and pannexins, the hemichannel-forming proteins in vertebrates, are fundamental components of the large conductance channel associated with P2X7R. Dye uptake and electrophysiology experiments were used to evaluate the efficacy and specificity of some hemichannel antagonists under conditions known to open the large conductance channel associated with P2X7R. Hemichannel antagonists and interference RNA (RNAi) targeting pannexin-1 did not affect P2X7R macroscopic currents [ATP, 1,570±189 pA; ATP+100 µM carbenoxolone (CBX), 1,498±100 pA; ATP+1 mM probenecid (Prob), 1,522±9 pA] or dye uptake in a FACS assay (ATP, 63±5%; ATP+100 µM CBX, 51.51±8.4%; ATP+1 mM Prob, 57.7±4.3%) in mouse macrophages. These findings strongly suggest that the high-permeability pore evident after prolonged P2X7R activation does not occur through connexin or pannexin hemichannels in murine macrophages. Another membrane protein may be involved in P2X7R pore formation.

Gap junction-mediated coupling in the postnatal anterior subventricular zone.

We have studied gap junctional communication in the anterior subventricular zone (SVZa) of postnatal rodents, revealed by intercellular diffusion of dyes in brain slices. Extensive intercellular dye spread was evident in the SVZa. Coupling was not uniform, being characteristically larger in the outer borders of this layer, overlapping the previously described peripheral zone of concentration of S-phase cells. Intercellular spread of the dye was unaffected by acidification, but totally blocked by high Ca(2+) concentrations. In addition, application of some known uncoupling agents as carbenoxolone and halothane led to a marked reduction of dye spread in the SVZa. Our results demonstrate the presence of dye coupling mediated by gap junctions in the SVZa. Furthermore, the spatial organization of dye coupling in these slices strongly suggests the existence of cell compartments in the postnatal SVZa.

Histomorphometric and histopathological study of the human cricopharyngeus muscle: in health and in motor neuron disease.

Abnormalities in muscle histology have been reported frequently for the cricopharyngeus muscle of patients with oculopharyngeal muscular dystrophy, motor neuron disease and other neurological disorders in which dysphagia is a common clinical sign. However, there are few detailed reports of the normal structure of this muscle nor quantitative baseline data with which to compare the diseased state. In this study, cricopharyngeus muscles from 21 healthy individuals and four patients with motor neuron disease underwent quantitative histological and histochemical examination. In addition to the extensive connective tissue content (40%), comprising abundant elastic fibres, cricopharyngeus muscles from normal individuals possessed small calibre striated muscle fibres (mean narrow diameter 30 microns) of widely varying size (coefficient of variation 41%). The majority of fibres were histochemically type I (82%) and highly oxidative. All muscles comprised numerous muscle fibres with aberrant histological and histochemical features (internalized nuclei, 'ragged red' crescents, splits, degenerating fibres, 'moth-eaten' fibres, or nemaline rods.) The histomorphometric and histopathological features were similar in males and females and some showed a correlation with age. There were increases in fibre size and roundedness and decreases in the numerical density and percentage of type I and split fibres in the specimens from older individuals. Cricopharyngeus muscles from patients with motor neuron disease were not significantly different from the controls for most parameters. It is therefore suggested that previous descriptions of specific cricopharyngeal pathology accompanying neuromuscular disease or dysphagia be interpreted with caution. The importance of obtaining normal structural, morphometric and histopathological data from muscles other than the usually biopsied limb muscles, is emphasized.

Muscle morphometry in motor neuron disease.

It has previously been suggested that the pathological abnormalities seen in muscle biopsies from patients with motor neuron disease (MND) are of predictive value in relation to the rate of progression of the disease. In this study, quadriceps muscle biopsies from 19 patients with MND and 20 age matched controls were prepared for histochemistry and analysed morphometrically. Pathological features of denervation and reinnervation were observed in all MND patients although considerable variation between patients was noted. Motor neuron disease biopsies also showed increased connective tissue, an increased variation in fibre size, and a random fibre type distribution. Several of these abnormalities were more severe in female patients. Many of these 'abnormalities' were also frequent, albeit to a milder degree, in control biopsies and emphasize the need for age matched controls. The morphometric data was not related to the age of the patient, disease duration, type of MND or muscle strength, thus suggesting that the progression and severity of MND and its prognosis cannot be judged on the basis of quadriceps muscle pathology alone.

Gap-junctional coupling between neurons and astrocytes in primary central nervous system cultures.

Gap-junctional communication between neurons and astrocytes dissociated from rat brain was identified in culture by using dye-transfer assays and electrophysiological measurements. Cell types were identified by using antibodies against beta-tubulin III, glial fibrillary acidic protein, and 2',3'-cyclic-nucleotide phosphohydrolase, which are antigenic determinants of neurons, astroglia, and oligodendrocytes, respectively. Dye coupling was examined as a function of time after dissociated embryonic brain cells were plated onto confluent monolayers of postnatal astrocytes by intracellularly injecting the fluorochrome Lucifer yellow. Coupling of neurons to the astrocytic monolayer was most frequent between 48 h and 72 h in culture and declined over the next 4 days. This gradual uncoupling was accompanied by progressive neuronal maturation, as indicated by morphological measurements in camera lucida drawings. Dye spread was abolished reversibly by octanol, an agent that blocks gap junction channels in other systems. Double whole-cell voltage-clamp measurements confirmed the presence of heterocellular electrical coupling in these cocultures. Coupling was also seen between neurons and astrocytes in cocultures of cells dissociated from embryonic cerebral hemispheres but was rarely detectable in cocultures of postnatal brain cells. These data strongly suggest that junctional communication may provide metabolic and electrotonic interconnections between neuronal and astrocytic networks at early stages of neural development and that such interactions are weakened as differentiation progresses.

Cell migration in the postnatal subventricular zone

New neurons are constantly added to the olfactory bulb of rodents from birth to adulthood. This accretion is not only dependent on sustained neurogenesis, but also on the migration of neuroblasts and immature neurons from the cortical and striatal subventricular zone (SVZ) to the olfactory bulb. Migration along this long tangential pathway, known as the rostral migratory stream (RMS), is in many ways opposite to the classical radial migration of immature neurons: it is faster, spans a longer distance, does not require radial glial guidance, and is not limited to postmitotic neurons. In recent years many molecules have been found to be expressed specifically in this pathway and to directly affect this migration. Soluble factors with inhibitory, attractive and inductive roles in migration have been described, as well as molecules mediating cell-to-cell and cell-substrate interactions. However, it is still unclear how the various molecules and cells interact to account for the special migratory behavior in the RMS. Here we will propose some candidate mechanisms for roles in initiating and stopping SVZ/RMS migration