Cortical Band Research Articles

New possible roles for aquaporin‐4 in astrocytes: cell cytoskeleton and functional relationship with connexin43

Aquaporin-4 (AQP4), the main water channel in the brain, is expressed in the perivascular membranes of mouse, rat, and human astrocytes. In a previous study, we used small interfering RNA (siRNA) to specifically knock down AQP4 in rat astrocyte primary cultures and found that together with reduced osmotic permeability, AQP4 knockdown (KD) led to altered cell morphology. However, a recent report on primary cultured astrocytes from AQP4 null mice (KO) showed no morphological differences compared with wild types. In this study, we compared the effect of AQP4 KD in mouse, rat, and human astrocyte primary cultures and found that AQP4 KD in human astrocytes resulted in a morphological phenotype similar to that found in rat. In contrast, AQP4 KD in mouse astrocytes caused only very mild morphological changes. The actin cytoskeleton of untreated astrocytes exhibited strong species-specific differences, with F-actin being organized in cortical bands in mouse and in stress fibers in rat and human astrocytes. Surprisingly, as a consequence of AQP4 KD, F-actin cytoskeleton was depolymerized in rat and human whereas it was completely rearranged in mouse astrocytes. Although AQP4 KD induced alterations of the cell cytoskeleton, we found that the expression of dystrophin (DP71), beta-dystroglycan, and alpha-syntrophin was not altered. AQP4 KD in cultured mouse astrocytes produced strong down-regulation of connexin43 (Cx43) with a concomitant reduction in cell coupling while no major alterations in Cx43 expression were found in rat and human cells. Taken together, these results demonstrate that with regard to these properties, human astrocytes in culture are more similar to rat than to mouse astrocytes. Moreover, even though AQP4 KD in mouse astrocytes did not result in a dramatic morphological phenotype, it induced a remarkable rearrangement of F-actin, not related to disruption of the dystrophin complex, indicating a primary role of this water channel in the cytoskeleton changes observed. Finally, the strong down-regulation of Cx43 and cell coupling in AQP4 KD mouse astrocytes indicate that a functional relationship likely exists between water channels and gap junctions in brain astrocytes.

Cerebral cortical laminar necrosis on diffusion‐weighted MRI in hypoglycaemic encephalopathy

Laminar necrosis of the cerebral cortex characterized neuropathologically by delayed selective neuronal necrosis occurs in hypoglycaemic encephalopathy and other brain diseases. A 37-year-old male with insulin-treated Type 1 diabetes mellitus developed hypoglycaemic encephalopathy associated with respiratory failure. Brain diffusion-weighted MRI during the subacute period demonstrated high signals along the cerebral cortex. Brain single-photon emission computed tomography showed diffuse, severe cerebral hypoperfusion. The patient remained comatose and died 1 month later. High signals along the cortical bands on diffusion-weighted MRI suggest cortical laminar necrosis, although a postmortem examination was unavailable. Sustained hypoglycaemic brain injury, possibly associated with respiratory hypoxia, may be the underlying mechanism.

C-Terminal Anchoring of mid1p to Membranes Stabilizes Cytokinetic Ring Position in Early Mitosis in Fission Yeast

mid1p is a key factor for the central positioning of the cytokinetic ring in Schizosaccharomyces pombe. In interphase and early mitosis, mid1p forms a medial cortical band overlying the nucleus, which may represent a landmark for cytokinetic ring assembly. It compacts before anaphase into a tight ring with other cytokinetic ring components. We show here that mid1p binds to the medial cortex by at least two independent means. First, mid1p C-terminus association with the cortex requires a putative amphipathic helix adjacent to mid1p nuclear localization sequence (NLS), which is predicted to insert directly into the lipid bilayer. This association is stabilized by the polybasic NLS. mid1p mutated within the helix and the NLS forms abnormal filaments in early mitosis that are not properly anchored to the medial cortex. Misplaced rings assemble in late mitosis, indicating that mid1p C-terminus binding to membranes stabilizes cytokinetic ring position. Second, the N terminus of mid1p has the ability to associate faintly with the medial cortex and is sufficient to form tight rings. In addition, we show that mid1p oligomerizes. We propose that membrane-bound oligomers of mid1p assemble recruitment "platforms" for cytokinetic ring components at the medial cortex and stabilize the ring position during its compaction.

The GIN4 family kinase, Cdr2p, acts independently of septins in fission yeast.

Two relatives of the GIN4 protein kinase family, Cdr1p and Cdr2p, exist in the yeast Schizosaccharomyces pombe. Although in Saccharomyces cerevisiae GIN4-related kinases influence septin ring organization and septin rings influence the localization and function of GIN4-related protein kinases, it is unknown whether this relationship is conserved in S. pombe. Here, we have probed the relationship between Cdr2p activity and septins and find that Cdr2p and septins are functionally independent. Cdr2p localizes in a cortical band overlying the nucleus during interphase, whose dimension is proportional to cell length, and to a medial ring structure in late mitosis. Both localizations are septin-independent and disrupted by treatment with filipin. Structure/function analysis indicates that the intracellular targeting domain of Cdr2p is largely contained within its non-catalytic C-terminus. Cdr2 protein kinase activity, while unimportant for its localization, is critical for its cell cycle function. Our data indicate that Cdr2p functions at two positions within the cell at discrete cell cycle stages to influence the timing of mitotic entry and cytokinesis, respectively.

Efecto de la infección por el virus de la rabia sobre la expresión de parvoalbúmina, calbindina y calretinina en la corteza cerebral de ratones.

Some clinical features of rabies and experimental evidence from cell culture and laboratory animals suggest impairment of gabaergic neurotransmission. Several types of gabaergic neurons occur in the cerebral cortex. They can be identified by three neuronal markers: the calcium binding proteins (CaBPs) parvalbumin (PV), calbindin (CB) and calretinin (CR). Rabies virus spreads throughout the cerebral cortex; however, rabies cytopathic effects on gabaergic neurons are unknown. The expression of calcium-binding proteins (CaBPs) parvalbumin (PV), calbindin (CB) and calretinin (CR) was studied in the frontal cortex of mice. The effect of gabaergic neurons was evaluated immunohistochemically. The distribution patterns of CaBPs in normal mice and in mice infected with 'fixed' or 'street' rabies virus were compared. PV was found in multipolar neurons located in all cortical layers except layer I, and in pericellular clusters of terminal knobs surrounding the soma of pyramidal neurons. CB-immunoreactivity was distributed in two cortical bands. One was composed of round neurons enclosed by a heavily labeled neuropil; this band corresponds to supragranular layers II and III. The other was a weakly stained band of neuropil which contained scattered multipolar CB-ir neurons; this corresponds to infragranular layers V and VI. The CR-ir neurons were bipolar fusiform cells located in all layers of cortex, but concentrated in layers II and III. A feature common to samples infected with both types of viruses was a more intense immunoreactivity to PV in contrast to normal samples. The infection with 'street' virus did not cause additional changes in the expression of CaBPs. However, the infection with 'fixed' virus produced a remarkable reduction of CB-immunoreactivity demonstrated by the loss of CB-ir neurons and low neuropil stain in the frontal cortex. In addition, the size of CR-ir neurons in the cingulate cortex was decreased.

Electroencephalographic Correlates of Mental Performance of Emotional Autobiographic and Scenic Situations: II. Characteristics of Spatial Synchronization

The EEG spatial synchronization in the frequency bands Δ, θ, α1, α2, β1, and β2 was studied on the basis of estimations of corresponding mean values of the coherence function in two groups of subjects (students actors and nonactors) during internal induction of emotional states by means of recall of autobiographic experience and mental performance of given scenic situations as a known character. Emotion-induced changes in the state of the cortex were reflected in statistically significant heterogeneous changes in the EEG spatial synchronization in many cortical areas and different frequency bands. The results obtained are discussed in combination with data presented earlier on changes in EEG local synchronization obtained in the course of the same experiments. The EEG β bands stand out against the background of extensive changes in the local and spatial EEG synchronization: the EEG changes in these bands are most prominent. Also, the changes in the prefrontal and temporal cortical areas, most involved in actualization of emotional states, are noteworthy. Some of the findings can be interpreted as confirming the hypothesis about neurophysiological mechanisms of brain defense from functionally excessive emotions.

Epidermal growth factor induces an increase in cell adhesion and an arrangement of actin skeleton in stress fibres in pituitary cultured cells from infantile rats but not adult rats.

The rat anterior pituitary gland undergoes changes in its cyto-architecture during the second and third weeks of postnatal life. However, little is known about the factors that regulate these tissue conformational changes. The epidermal growth factor (EGF) is one of the growth factors that are synthesized by the pituitary gland, and almost all of the pituitary cells have EGF receptors (EGFR). In addition to the effects of the EGF on mitosis and differentiation, this growth factor can modulate cell adhesion, cell migration, and cytoskeletal organization. In this study we focussed our attention in examining the effects of EGF on the adhesion of cells to the extracellular matrix and on the actin cytoskeletal arrangement of pituitary cells from infantile and adult rats. Our results show that in infantile cells the EGF induces cell adhesion with increase in cell surface area. The arrangement of actin-F in infantile EGF-treated cells was in stress fibers and vinculin acquired a striped shape at the membrane border, suggesting the assembly of focal adhesion contacts. In contrast, in adult pituitary cells EGF does not induce any change in cell adhesion, and the cells maintain a rounded shape with an arrangement of actin-F in thin cortical bands even though, immuno-localization of the EGFR was observed in adult cells cultured in defined medium. We also looked for the EGFR in membrane preparations from infantile and adult pituitaries, and a marked difference in membrane EGFR was observed between them, the infantile pituitaries showing a significantly higher amount. Our results suggest that in infantile cells EGF induces the assembly of focal adhesion contacts, and that in adult cells the receptor of this growth factor is uncoupled of the signaling pathway by which a rearrangement of actin cytoskeleton occurs.

Associative interactions within the superficial layers of the entorhinal cortex of the guinea pig.

Associative fiber systems in the entorhinal cortex (EC) have been extensively studied in different mammals with tracing techniques. The largest contingent of intra-EC cortico-cortical fibers runs in the superficial layers and is distributed predominantly within longitudinal cortical bands. We studied the patterns of intrinsic EC connectivity in the in vitro isolated guinea pig brain preparation by performing current-source density analysis of field potential laminar profiles recorded with multi-channel silicon probes. The response pattern evoked by stimulation of the lateral olfactory tract was utilized to identify the lateral (l-EC) and medial (m-EC) entorhinal cortex. Stimulation of the deep layers did not evoke consistent responses. Local stimulation of the superficial layers in different portions of the EC induced an early, possibly direct response restricted to layer II-III in the close proximity to the stimulating electrode, followed by a late potential in the superficial layer I, that propagated at distance with a progressively increasing latency. The monosynaptic nature of the delayed response was verified by applying a pairing test. The results demonstrated that stimulation in the rostral-medial part of the EC generated activity restricted to the rostral pole of the l-EC, stimulation of the m-EC induced an associative activation that propagated rostrocaudally within the m-EC, stimulation of the caudal pole of the m-EC induced an additional response directed laterally, and stimulation of the lateral band of the EC determined a prominent longitudinal propagation of neuronal activity, but also induced associative potentials that propagated medially. The results are in partial agreement with the general picture derived from the anatomical studies performed in different species. Even though the largest associative interactions between superficial layers are restricted within either the m-EC or the l-EC, both rostral and caudal stimuli in the EC region close to the rhinal sulcus induced activity that propagated across the border between l- and m-EC.

Structural and functional relationships between Ca2+ puffs and mitochondria in Xenopus oocytes.

Ca2+ uptake and release from endoplasmic reticulum (ER) and mitochondrial Ca2+ stores play important physiological and pathological roles, and these processes are shaped by interactions that depend on the structural intimacy between these organelles. Here we investigate the morphological and functional relationships between mitochondria, ER, and the sites of intracellular Ca2+ release in Xenopus laevis oocytes by combining confocal imaging of local Ca2+ release events ("Ca2+ puffs") with mitochondrial localization visualized using vital dyes and subcellularly targeted fluorescent proteins. Mitochondria and ER are localized in cortical bands approximately 6-8 microm wide, with the mitochondria arranged as densely packed "islands" interconnected by discrete strands. The ER is concentrated more superficially than mitochondria, and the mean separation between Ca2+ puff sites and mitochondria is approximately 2.3 microm. However, a subpopulation of Ca2+ puff sites is intimately associated with mitochondria (approximately 28% within <600 nm), a greater number than expected if Ca2+ puff sites were randomly distributed. Ca2+ release sites close to mitochondria exhibit lower Ca2+ puff activity than Ca2+ puff sites in regions with lower mitochondrial density. Furthermore, Ca2+ puff sites in close association with mitochondria rarely serve as the sites for Ca2+ wave initiation. We conclude that mitochondria play important roles in regulating local ER excitability, Ca2+ wave initiation, and, thereby, spatial patterning of global Ca2+ signals.

Corticonuclear projections of the cerebellum preserve both anteroposterior and mediolateral pairing patterns.

The aim of the present study was to establish whether a diverging arrangement of the corticonuclear cerebellar projections exists and, if so, what relation it has with the inferior olivary complex. Iontophoretic injections of a 1 : 1 mixture of tetramethylrhodamine dextran amine and biotinylated dextran amine into the cerebellar cortex orthogradely labelled fibre terminals in the cerebellar nuclei and retrogradely labelled cell bodies in the inferior olivary complex. The injections were into A, B, C2, C3, D1 and D2 bands. These injections showed diverging projections to the cerebellar nuclei, with 'primary projections' directed to the nuclear region previously reported to be specifically connected with the injected band and 'secondary projections' directed to other nuclear regions. Secondary projections from the A, C2 and C3 bands diverged to nuclear regions primarily controlled by cortical bands lateral to those injected. Secondary projections from the D1, and D2 bands diverged to nuclear regions primarily controlled by cortical bands medial to those injected. Moreover, injections distributed along the D1 and D2 bands showed similar sets of nuclear targets, while those distributed along the A, C2 and C3 bands showed two sets of nuclear targets in relation to the anteroposterior location of the injected area within these bands. The cortical areas that projected to the same set of nuclear targets were innervated from single olivary regions, while those that projected to different sets of nuclear targets were innervated from different subsets of single regions of the inferior olive. The results suggest that the olivary bands of the cerebellar cortex project to the cerebellar nuclei with a diverging pattern that is organized in both the mediolateral and the anteroposterior axes.

Preserving Plasticity: New Directions in Research for the Developing Brain

After completing this article, readers should be able to: 1. Characterize the process of corticogenesis. 2. Describe findings of magnetic resonance imaging of the developing brain. Cerebral development of the fetus is under genetic control, and during the third trimester of gestation, synapse development, dendritic spine elaboration, and cortical-cortical connections proceed as the period of developmental plasticity begins. In contrast to infants born at term, those who are born preterm can suffer significant developmental disability; many reports have shown that the neurodevelopmental outcome of very low-birthweight preterm infants is related directly to gestational age at birth. Infants weighing less than 1,000 g at birth now represent almost 1% of all live births in the United States, and the survival rate for this population approaches 85%. In stark contrast to the improved survival, however, are the emerging reports of neurodevelopmental disability in these very tiny and frequently critically ill infants. The incidence of cerebral palsy is increasing as the survival rate increases, and the incidence of cognitive deficits in this population has not changed during the past decade. The incidence of major neurodevelopmental handicaps in very preterm infants ranges from 12% to 32%, and even “healthy” preterm infants experience a high degree of educational difficulties. When we examined 200 very low-birthweight survivors of the Randomized Indomethacin Intraventricular Hemorrhage Prevention Trial who had reached 8 years of age, more than 50% required special assistance in school or were educated in full-time special education classrooms, and 25% already had repeated at least one grade in school. These data are consistent with those of other observers and indicate that preterm birth disrupts the normal genetically programmed series of events regulating corticogenesis in the developing brain. Intracranial hemorrhage (ICH), or hemorrhage into the germinal matrix tissues of the developing brain, is a major cause of neurodevelopmental handicap …

Local cutaneous water barrier in cold- and heat-acclimated pigeons (Columba livia) in relation to cutaneous water evaporation.

The thermoregulatory function of the skin differs in adult cold-acclimated and heat-acclimated rock pigeons (Columba livia). In general, the cutaneous evaporative cooling mechanism is not activated by appropriate stimuli in cold-acclimated pigeons in contrast to heat-acclimated pigeons. We studied with electron microscopy whether the differences in the function of the skin are reflected in the structure of the epidermal water barrier of these two extreme acclimation states. The epidermis of cold-acclimated pigeons is attenuated, and the underlying dermis lacks any intimate vascularization. Both the extracellular and the intracellular domains in the stratum corneum contain organized lamellar lipids. At the stratum transitivum-stratum corneum interface, multigranular body secretion is indicated by the highly convoluted cell membranes and membraneous sacculae enclosing the multigranular bodies. Alternatively, multigranular bodies retain in the corneocytes, and the lipoid material originated from them is reprocessed to broad lamellae. The keratohyalin (KH) granules are spotlike and oriented as cortical bands beneath the plasma membrane. In heat-acclimated pigeons, the epidermis displays modified patches side by side with basic structural type of epidermis. The modified areas are characterized by hypertrophy and abundance of dermal capillaries adjacent to the hypertrophied patch. No lamellar lipids are discerned in the dilated extracellular space. The structure of multigranular bodies is abnormal, and the numbers of lipid droplets in the outer viable epidermis and stratum corneum are decreased. The transitional cells contain stellate KH granules, which form a network throughout the cell. It is concluded that cold-acclimated pigeons have a lamellar, extracellular water barrier, the cutaneous water evaporation is minimized, and heat is stored in the body core. Acclimation to heat leads to formation of structurally heterogeneous skin. The structurally modified skin patches show disruption of the barrier-forming machinery in the multigranular bodies and marked reorganization of fibrillar proteins and electron-dense KH masses in the transitional layer. Thus water barrier adjustments in cold- and heat-acclimated pigeons manifest the dynamic function of avian skin as a thermoregulatory organ.

The role of anillin in meiotic cytokinesis of Drosophila males.

Anillin is a 190 kDa actin-binding protein that concentrates in the leading edges of furrow canals during Drosophila cellularization and in the cleavage furrow of both somatic and meiotic cells. We analyzed anillin behavior during D. melanogaster spermatogenesis, and focused on the relationships between this protein and the F-actin enriched structures. In meiotic anaphases anillin concentrates in a narrow band around the cell equator. Cytological analysis of wild-type meiosis and examination of mutants defective in contractile ring assembly (chickadee and KLP3A), revealed that the formation of the anillin cortical band occurs before, and does not require the assembly of the F-actin based contractile ring. However, once the acto-myosin ring is assembled, the anillin band precisely colocalizes with this cytokinetic structure, accompanying its contraction throughout anaphase and telophase. In chickadee and KLP3A mutant ana-telophases the cortical anillin band fails to constrict, indicating that its contraction is normally driven by the cytokinetic ring. These findings, coupled with the analysis of anillin behavior in twinstar mutants, suggested a model on the role of anillin during cytokinesis. During anaphase anillin would concentrate in the cleavage furrow before the assembly of the contractile ring, binding the equatorial cortex, perhaps through its carboxy-terminal pleckstrin homology (PH) domain. Anillin would then interact with the actin filaments of the acto-myosin ring through its actin-binding domain, anchoring the contractile ring to the plasma membrane throughout cytokinesis.

Role of polo kinase and Mid1p in determining the site of cell division in fission yeast.

The fission yeast Schizosaccharomyces pombe divides symmetrically using a medial F-actin- based contractile ring to produce equal-sized daughter cells. Mutants defective in two previously described genes, mid1 and pom1, frequently divide asymmetrically. Here we present the identification of three new temperature-sensitive mutants defective in localization of the division plane. All three mutants have mutations in the polo kinase gene, plo1, and show defects very similar to those of mid1 mutants in both the placement and organization of the medial ring. In both cases, ring formation is frequently initiated near the cell poles, indicating that Mid1p and Plo1p function in recruiting medial ring components to the cell center. It has been reported previously that during mitosis Mid1p becomes hyperphosphorylated and relocates from the nucleus to a medial ring. Here we show that Mid1p first forms a diffuse cortical band during spindle formation and then coalesces into a ring before anaphase. Plo1p is required for Mid1p to exit the nucleus and form a ring, and Pom1p is required for proper placement of the Mid1p ring. Upon overexpression of Plo1p, Mid1p exits the nucleus prematurely and displays a reduced mobility on gels similar to that of the hyperphosphorylated form observed previously in mitotic cells. Genetic and two-hybrid analyses suggest that Plo1p and Mid1p act in a common pathway distinct from that involving Pom1p. Plo1p localizes to the spindle pole bodies and spindles of mitotic cells and also to the medial ring at the time of its formation. Taken together, the data indicate that Plo1p plays a role in the positioning of division sites by regulating Mid1p. Given its previously known functions in mitosis and the timing of cytokinesis, Plo1p is thus implicated as a key molecule in the spatial and temporal coordination of cytokinesis with mitosis.

MR Features of Lissencephaly with Clinical Correlations

We aimed to demonstrate the MRI features of lissencephaly and to correlate these features with associated anomalies and clinical features in an attempt to classify them. This study included eight infants with lissencephaly. They presented with seizures, hypotonia, microcephaly, large head or failure to thrive. They were examined using a 1.5 Tesla scanner. Both T1 and T2 weighted scan were done. Our patients showed a smooth surface of both cerebral hemispheres with complete loss of gyri and sulci (agyria) (n=5) or agyria with areas of pachygyria (n=3). The cortex was thickened with thinning of the underlying white matter and loss of normal grey-white matter interdigitations (n=8). A shallow Sylvian fissure with hourglass or oval configuration of the brain was also noted (n=8). A linear cortical band of low SI on T1 WI and high SI on T2WI was noted in five cases. Other associated findings included: Dandy-Walker malformations (n=5), hydrocephalus (n=4), microcephaly (n=2), callosal agenesis (n=2), occipital encephalocele (n=1), microphalamia with retinal dysplasia (n=1), absent septum pellucidum (n?1) and colpocephaly (n=1). MR imaging is the imaging modality of choice for the demonstration of the pathognomonic features of lissencephaly. It helps the classification of lissencephaly into different types according to their MR appearance, associated anomalies and clinical features.

Sulfur Mustard Induces Apoptosis and Necrosis in Endothelial Cells

Sulfur Mustard (SM) is a vesicant or blistering chemical warfare agent, for which there still is no effective therapy. Endothelial cells are one of the major cellular targets for SM. The mechanism of endothelial cell death during SM injury is poorly understood. We studied the effect of exposure of endothelial cells to 0–1000 μMSM over the time course of 2–24 hr to determine the role of apoptotic and necrotic patterns of cell death in endothelial injury induced by SM. SM concentrations ≤250 μMinduced exclusively apoptosis which was observed after 5 hr in 30% of endothelial cells. Exposure to SM concentrations ≥500 μMcaused apoptosis and necrosis to the same extent in 60–85% of all cells after 5 to 6 hr. Necrosis was accompanied by a significant (∼50%) depletion of intracellular ATP, while in apoptotic cells ATP remained at the level similar to healthy cells. Interestingly, disruption of the long actin filament stress fibers and rounding of cells preceded other features of apoptosis—DNA fragmentation, membrane budding, and apoptotic body formation. In apoptotic cells, microfilaments formed constricted perinuclear bands, which were not observed in necrotic cells. Pretreatment with 50 mMN-acetyl-L-cysteine (NAC), a sulfhydryl donor and antioxidant, nearly eliminated the apoptotic features of cell death but did not prevent necrosis in response to SM. NAC pretreatment alone induced reorganization of actin filaments into an enhanced network of long stress fibers instead of a dominant cortical band of actin. NAC pretreatment prevented loss of cell adherence and cell rounding following exposure to 250 μMSM. The effect of NAC on cytoskeletal organization and its ability to eliminate SM-induced apoptosis suggests that actin filament organization may be an important element in cellular susceptibility to apoptotic stimuli.

Development and Liberation of Cauline Gemmae in the Moss Aulacomnium androgynum(Hedw.) Schwaegr. (Bryales): An Ultrastructural Study

The leafy shoots of the moss Aulacomnium androgynumform clusters of gemmae borne terminally on long pseudopodial axes. The gemmae arise from single initial cells produced by the activity of a superficial meristem. Mature gemmae comprise an apical and a basal cell with four to seven cells forming two, sometimes three, tiers in between. The basal cell is connected to the tip of the pseudopodium by a uniseriate filament consisting of an abscission (tmema) cell and a stalk cell. The first division of the initial cell produces a proximal cell and a distal cell. The proximal cell elongates without further division forming the stalk of the gemma; the distal cell gives rise to a lower and an upper cell by transverse division. The upper cell divides repeatedly by oblique septa forming the apical and middle cells of the gemma; the basal cell and tmema cell arise from a transverse division of the lower cell. The first two divisions in gemma development are highly asymmetrical and exogenous, i.e. preceeded by cell expansion. A broad interphase cortical band of microtubules is associated with intercalary cellular growth during this stage. Subsequent gemma development follows an endogenous pattern with cellular expansion following the completion of proliferative divisions and involving a conventional system of cortical microtubules. While elongating to about four times its original length without deposition of a distinct new wall the tmema cell undergoes cytoplasmic degeneration and eventually breaks, causing gemma liberation. The stalk cell elongates about eight-fold and its contents also degenerate after gemma liberation. Plasmodesmata in the basal and stalk cells are obliterated by the deposition of additional wall materials. The highly electron-opaque outer walls of the mature gemmae and tips of the stalk cells are water-repellant. The gemmae are dispersed either in water films or by air currents.

Entry of Foreign Bacteria and of its Own Epibionts (Epixenosomes) into an Hypotrichous Ciliate, Euplotidium itoi, by Cortical Invaginations

Summary A characteristic feature of Euplotidium itoi is the cortical band which containsepixenosomes. In some specimens the formation of deep cortical invaginations has been observed in the cortical band. These invaginations contain foreign bacteria and a few epixenosomes. Successively, intracellular vacuoles are formed, delimited by the whole cortex with the plasmamembrane inward and the alveolar system toward the ciliate cytoplasm. No signs of digestion could be observed within these vacuoles. The alveolar system is gradually dissolved in small regions. Very likely, bacteria and epixenosomes escape from the vacuole at these sites which are delimited by a single unit membrane only. Once in the Euplotidium cytoplasm bacteria are surrounded by rough endoplasmic reticulum membranes. The significance of this process, quite unusual in ciliates, is far from being understood; it is not even clear whether epixenosomes have a role in it and why it takes place only at the level of the epixenosomal band. Moreover is not known what happens to the episymbionts once introduced inside the host cell. As far as bacteria are concerned, the constant alterations of mitochondrial features found in specimens with cortical vacuoles, suggest an infectious nature.

The consistency, extent, and locations of early-onset changes in cortical nerve dominance aggregates following injury of nerves to primate hands

The somatosensory cortex of primates contains patch- and bandlike aggregates of neurons that are dominantly activated by cutaneous inputs from the radial, median, and ulnar nerves to the hand. In the present study, the area 3b hand cortex of adult monkeys was mapped immediately before and after combined median and ulnar nerve transection to evaluate the consistency, extent, and location of early post-injury alterations in the deprived median and ulnar nerve cortical bands. Several alterations were observed acutely after injury. (1) The patchlike cortical aggregates of intact radial nerve inputs from the hand underwent a two- to three-fold expansion. This expansion was not related to peripheral changes in the radial nerve skin territory, but was due to rapid central decompression of radial nerve dominance patches. (2) The largest changes involved patches in lateral to central locations of the hand map. (3) The expanded patches occupied cortical zones that were activated by inputs from the digits, palm, and posterior hand prior to injury. These receptive field shifts were initiated within minutes after injury. (4) Receptive fields of neurons within expanded radial nerve patches were normal in size. (5) Besides changes involving radial nerve inputs from the hand, there was a small expansion of forelimb inputs into the preinjury hand cortex; however, the representation of face inputs did not expand into this cortex. (6) Finally, neurons across 50-69% of the hand cortex were unresponsive to tactile stimuli acutely after this injury. These findings indicate that the distribution patterns of nerve dominance aggregates in adult primates begin changing within minutes after nerve injury. Cortical changes involving specific inputs occupy similar extents and locations of cortex, and are arranged in highly consistent patterns, in different individuals. It is suggested that this consistency reflects specific patterns of central sensitization or disinhibition that are triggered by the injury.

Ceramium cimbrium (Rhodophyceae, Ceramiales) from Scandinavia; structure, reproduction and systematics

Ceramium cimbricum, originally described from Limfjorden, Denmark was isolated into unialgal culture form several localities in southern Norway. The distinguishing features include straight, often unequal apices, 4–5 periaxial cells and narrow cortical bands. Reproductive structures are described for the first time in European material and a Polysiphonia‐type of life history was demonstrated, though irregularities were also seen. Culture observations of phenotypic variability and examination of type material suggest that C. cimbricum and the widely recorded C. fastigiatum may be conspecific. However, the latter binomial is illegitimate.