Antisera to basal lamina and glial endfeet disturb the normal extension of axons on retina and pigment epithelium basal laminae

In order to determine the role of the extracellular matrix in regulating the directed growth of embryonic neurites, antisera to retina (a-RBL I and II), to pigment epithelium (a-PBL) and to glomerular (a-GBL) basal lamina were probed for an effect on the ordered extension of neurites. In the assays, retina explants from chick and quail were cultured on basal lamina from embryonic chick retina and pigment epithelium either in the presence of anti-basal lamina antisera or in the presence of the corresponding preimmune sera. In the presence of all anti-basal lamina antisera, normal extension of axons was greatly inhibited both on retina and on pigment epithelium basal lamina. The antisera affected the growth pattern and the morphology of the individual axons in two ways: in the presence of a-RBL I the short axons were less directed, developed more and longer side branches, and the lamellipodia of the growth cones were reduced in size compared to axons from control cultures. In the presence of a-RBL II and a-GBL, axons grew slowly out from the explants as very thick bundles, strikingly different from axons in control cultures. The antiserum to pigment epithelium basal lamina induced both strong fasciculation and disorganization of the linear fiber extension, being intermediate between the two types of effects observed after antiserum addition. The results suggest that adhesive matrix molecules in basal laminae have important functions in elongation, fasciculation and in the morphology of growing axons.     

Diencephalic neuronal populations projecting axons into the basal plate in a lizard (Gallotia galloti).

Lizard diencephalic populations sending axons into the basal plate were studied by the in vitro HRP technique in the lizard Gallotia. Retrograde labeled cells were concentrated in distinct neuronal groups within alar plates of prosomeres p1 and p3, whereas the alar plate of p2 was poorly labeled. Efferent fibers from alar p1 and p3 populations entered the basal plate of the diencephalon along topologically dorsoventral courses, bifurcating thereafter into longitudinal ascending (rostral) and descending (caudal) trajectories. Thus, diencephalic segments p1 and p3 have alar cell populations contributing to the longitudinal premotor connectivity of the neural axis , whereas the alar p2 segment projects via the fasciculus retroflexus, the efferent tract of the epithalamus. However, the axons from the habenular complex bifurcate within or adjacent to the floor plate and not within the basal plate.     

Ion transport across the frog olfactory mucosa: the basal and odorant-stimulated states

The Ussing method was adapted to study the basal electrolyte transfer as well as the events that occur upon odorant stimulation in frog olfactory mucosa. The unstimulated short-circuit current was due mainly to a furosemide-sensitive ion transport system on the apical side of the olfactory mucosa. This current was not amiloride sensitive. The current-voltage relationship of the unstimulated state was linear. That of the odorant-evoked current was non-linear and amiloride-sensitive. Ouabain caused collapse of both the unstimulated and odorant-stimulated short-circuit current. In this case, voltage-clamping the tissue to non-zero values restored the odorant-evoked current with polarity depending on that of the clamping voltage. This suggested that the direction of the current is determined by that of the sodium electrochemical potential difference. Our results indicate that the unstimulated short-circuit current occurs through an apical sodium cotransport system, while the odorant-evoked current is due to odorant-activated, passive sodium channels that are amiloride sensitive.     

DCC plays a role in navigation of forebrain axons across the ventral midbrain commissure in embryonic xenopus

In the developing vertebrate brain, growing axons establish a scaffold of axon tracts connected across the midline via commissures. We have previously identified a population of telencephalic neurons that express NOC-2, a novel glycoform of the neural cell adhesion molecule N-CAM that is involved in axon guidance in the forebrain. These axons arise from the presumptive telencephalic nucleus, course caudally along the principal longitudinal tract of the forebrain, cross the ventral midline in the midbrain, and then project to the contralateral side of the brain. In the present study we have investigated mechanisms controlling the growth of these axons across the ventral midline of the midbrain. The axon guidance receptor DCC is expressed by the NOC-2 population of axons both within the longitudinal tract and within the ventral midbrain commissure. Disruption of DCC-dependent interactions, both in vitro and in vivo, inhibited the NOC-2 axons from crossing the ventral midbrain. Instead, these axons grew along aberrant trajectories away from the midline, suggesting that DCC-dependent interactions are important for overcoming inhibitory mechanisms within the midbrain of the embryonic vertebrate brain. Thus, coordinated responsiveness of forebrain axons to both chemostimulatory and chemorepulsive cues appears to determine whether they cross the ventral midline in the midbrain.     

Ion transport across the frog olfactory mucosa: the action of cyclic nucleotides on the basal and odorant-stimulated states

The action of cyclic nucleotides on the short-circuit current across the isolated bullfrog olfactory mucosa was studied both in the absence and presence of odorants. 8-Bromo-cAMP applied to the ciliated side of the mucosa caused a concentration-dependent, reversible increase in the basal short-circuit current, but not when it was applied to the submucosal side. The current had a sigmoidal concentration dependence described by the Hill equation. The magnitude of the odorant-evoked current was enhanced after bathing the ciliated side with cAMP analogs or modulators of intracellular cAMP. GTP gamma S added to the ciliated side increased the odorant-evoked current, while GDP beta S caused a decrease. Current transients induced by stimulating the ciliated side with either pulses of odorant or 8-bromo-cAMP were partially suppressed by amiloride, but only when amiloride and stimulant were presented simultaneously. Pulses of 8-bromo-cAMP and odorant presented simultaneously resulted in currents that added nonlinearly. In the absence of odorant, 8-bromo-cGMP caused a concentration-dependent decrease in net inward current that was reversed by 8-bromo-cAMP. Odorant-evoked currents were also reduced by 8-bromo-cGMP, and these could not be reversed by 8-bromo-cAMP. The results indicate that one type of olfactory transduction process involves the activation by cAMP of an inward current through an amiloride-sensitive apical ion channel and that this mechanism is mediated by a stimulatory G-protein.     

Loss of Nkx2.1 homeobox gene function results in a ventral to dorsal molecular respecification within the basal telencephalon: evidence for a transformation of the pallidum into the striatum.

The telencephalon is organized into distinct longitudinal domains: the cerebral cortex and the basal ganglia. The basal ganglia primarily consists of a dorsal region (striatum) and a ventral region (pallidum). Within the telencephalon, the anlage of the pallidum expresses the Nkx2.1 homeobox gene. A mouse deficient in Nkx2.1 function does not form pallidal structures, lacks basal forebrain TrkA-positive neurons (probable cholinergic neurons) and has reduced numbers of cortical cells expressing GABA, DLX2 and calbindin that migrate from the pallidum through the striatum and into the cortex. We present evidence that these phenotypes result from a ventral-to-dorsal transformation of the pallidal primordium into a striatal-like anlage.     

Inhibitory effect of sodium ursodeoxycholate on basal and stimulated short-circuit current across the isolated toad skin

The effect of sodium ursodeoxycholate (U) on short-circuit current (SCC), an index of basal and stimulated net ion transport across isolated skins of Bufo arenarum toads, was tested. U inhibited basal SCC when added to the epidermal side of the skins. The inhibitory effect was reversible after rinsing the preparation during 60 min. U also inhibited the natriferic response to oxytocin, db-cAMP and theophylline by 82%, 49% and 47%, respectively. Inhibition of SCC by exposure to U was reversed by the polyene antibiotic nystatin. In turn, SCC induced by nystatin in the amiloride-treated skin was insensitive to U and blocked by ouabain, a Na⁺, K⁺-ATPase inhibitor. These results strongly suggest that the effect of U is exerted at the apical membrane of sodium transporting cells, and rule out the existence of an additional site of inhibitory action of U.     

Mathematical analysis of cancer chemotherapy: The effects of chemotherapeutic agents on the cell cycle traverse

For the tumor model of Skipper and Zubrod, which has been analyzed previously for the theoretical FLM function and the effect of chemotherapy against tumors of known or assumed kinetic characteristics, the theoretical continuous labeling (CL) function is derived by considering an equivalent tumor (in terms of unlabeled cell populations) in which the density function of phase duration of cells inS-phasef ₂(a ₂)=δ(a ₂−∞) and the loss functionL ₂(t)=0. This mathematical concept of blocking is applied to the analysis of synchronization in tumor growth and blocking effects in cancer chemotherapy. These effects of chemical agents on the cell cycle progression are being incorporated into a previously written computer simulation program for cancer chemotherapy. Whereas, a program is written and used to simulate the CL functions for L1210 leukemia, and primary and metastatic Lewis lung carcinoma.     

Characterization of the integrin alpha 8 subunit: a new integrin beta 1-associated subunit, which is prominently expressed on axons and on cells in contact with basal laminae in chick embryos.

In this article, we describe the primary structure, the biochemical characterization and the tissue distribution of a novel integrin alpha subunit, named alpha 8. This subunit associates with the integrin beta 1 subunit to form alpha 8 beta 1 heterodimers. By sequence analysis, alpha 8 is more closely related to the alpha 5 and alpha v subunits than to other characterized integrin alpha subunits, but is clearly distinct from each of these. The alpha 8 subunit is expressed at moderate levels in several epithelial cells where its localization adjacent to basal laminae suggests that alpha 8-containing heterodimers interact with at least one extracellular matrix constituent. In embryos, the highest levels of alpha 8 protein expression are seen in the nervous system where alpha 8 is strongly expressed by several classes of projection neurons. The alpha 8 subunit is concentrated in axon tracts, including major projections in the spinal cord, optic system and auditory system. This tissue specific expression and cellular localization suggest that alpha 8-containing integrin receptors might promote axon outgrowth in the embryonic nervous system.     

Effect of phosphatidylserine on the basal and GABA-activated Cl− permeation across single nerve membranes from rabbit Deiters' neurons

The permeation of labeled Cl^– ions across single plasma membranes from Deiter's neurons has been studied in the presence of various concentrations of phosphatidylserine (PS) on their extracellular side. PS reduces significantly basal Cl^– permeation only at 10^–5 M on the membrane exterior. No effect was found at other concentrations. GABA activable³⁶Cl^– permeation is heavily reduced and almost abolished at 10^–11–10^–5 M phosphatidylserine. This exogenous phosphatidylserine effect is difficult to interpret in relation to the function of the endogenous phospholipid. However, it may be involved in the epileptogenic effect in vivo of exogenous phosphatidylserine administration to rats.     

基于NDVI绿洲-荒漠过渡带宽度识别——以河西走廊中部荒漠绿洲为例

绿洲-荒漠过渡带是荒漠与绿洲之间的生态缓冲区,在维持绿洲能量流动、物质循环和景观稳定方面具有重要作用。过渡带宽度和属性直接影响到了其在整个绿洲系统中的功能发挥。以河西走廊中部张掖绿洲的Landsat(OLI)NDVI(归一化植被指数,Normalized Difference Vegetation Index)数据为基础,结合野外调查将过渡带类型划分为绿洲与石质裸山、砾质荒漠、沙质荒漠和人工固沙区4类。采用缓冲分析、分段线性趋势分析和尺度分别为30 m、90 m、210 m、330 m焦点分析等方法研究了不同类型过渡带宽度和尺度依赖特征。结果表明,在不同尺度上绿洲外缘NDVI变化存在二种线性回归趋势,趋势线交点至绿洲边界距离可确定为过渡带宽度。不同尺度分析表明,绿洲-石质裸山过渡带宽度为165—220 m,在其内NDVI线性变化趋势显著(P<0.05)。绿洲-砾质荒漠过渡带宽度保持在330 m,在其内NDVI变化趋势极显著(P<0.001)。绿洲-沙质荒漠过渡带宽度变化在230—290 m,NDVI变化趋势也为极显著(P<0.001)。绿洲-人工固沙区过渡带宽度变化在...     

Histone acetylation: a switch between repressive and permissive chromatin. Second in review series on chromatin dynamics

The organization of eukaryotic chromatin has a major impact on all nuclear processes involving DNA substrates. Gene expression is affected by the positioning of individual nucleosomes relative to regulatory sequence elements, by the folding of the nucleosomal fiber into higher-order structures and by the compartmentalization of functional domains within the nucleus. Because site-specific acetylation of nucleosomal histones influences all three aspects of chromatin organization, it is central to the switch between permissive and repressive chromatin structure. The targeting of enzymes that modulate the histone acetylation status of chromatin, in synergy with the effects mediated by other chromatin remodeling factors, is central to gene regulation.     

Giant basal cell carcinoma of the forehead: a case report

Giant basal cell carcinoma (GBCC) is defined as a tumor 5cm or greater in diameter. They present less than 1% of all basal cell carcinomas. We present a case of an 85-year-old male patient with a giant ulcerating tumor of the left forehead (measuring 7x6 cm). Under local anesthesia tumor was surgically excised. No involvement of the underlying periostal or bone structure was noted. Pathohystological exam revealed the giant basal cell carcinoma, with free surgical margins. Giant basal cell carcinomas are rare tumors and are usually result of a long duration and patient neglect. In comparison to the ordinary basal cell carcinoma these tumors have a higher metastatic potential. Surgical resection with negative surgical margin is the best possible treatment option.