摘要:

AbstractDegenerate primers from conserved regions in nerve growth factor, brain‐derived neurotrophic factor (BDNF) and neurotrophin‐3 (NT‐3) were used in the polymerase chain reaction to isolate DNA fragments from the chicken BDNF and NT‐3 genes. A genomic clone coding for chicken NT‐3 was isolated and the structure of the chicken NT‐3 mature protein was subsequently deduced from nucleotide sequence analysis of the isolated chicken NT‐3 gene. Comparison of the chicken BDNF and NT‐3 with the corresponding rat molecules showed that the avian molecules are very similar to their mammalian homologues. Northern blot analyses of messenger RNA (mRNA) from chicken embryos from embryonic day 3.5 (E3.5), E4.5, E8, E12 and E18 showed that expression of both BDNF and NT‐3 mRNA peaked at E4.5 and decreased at later stages of development. Both probes revealed two transcripts; larger mRNAs of 4.5 kilobases (kb) for BDNF and 4.0 kb for NT‐3 predominated over the smaller transcripts of 1.4 and 1.3 kb, respectively. The cellular localization of BDNF and NT‐3 mRNA in the E4 and E6 embryos was studied byin situhybridization. In the E4 embryo, labelling for BDNF was seen over cells in restricted parts of the epithelium of the otic vesicle. Analysis of adjacent sections for the low‐affinity nerve growth factor receptor mRNA showed that regions in the otic vesicle epithelium which labelled for BDNF mRNA also labelled for low‐affinity nerve growth factor receptor mRNA. No labelling for NT‐3 was detected in the otic vesicle. Labelling for BDNF mRNA was also found over mesenchyme dorsal to the wing bud, in the wing bud and in the splanchnopleural lining of the stomach. Labelling for NT‐3 mRNA was found at E4 over the epidermis on the ventral side in the region of the branchial arches. The labelling extended up the maxillary processes to Rathke's pouch. The closely located infundibulum was weakly labelled for NT‐3 mRNA. NT‐3 mRNA was also detected in the mesenchyme surrounding the oesophagus and lung buds. The regional expression pattern is in agreement with the established role for BDNF and NT‐3 as target‐derived neurotrophic factors, but the results also suggest that BDNF may be an intrinsic factor important for the development of the inner ear. The results support the emerging view that neurotrophic factors can play a role in early differentiation of b

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00199.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractCells in the cerebral cortex project to many distant regions in the brain. Each cortical target receives input from a specific population of cells which have a characteristic morphology and which are located in a distinct cortical layer. In an attempt to learn about the mechanisms by which this stereotypic output pattern is generated during development, we have studied the formation of cortical projections in anin vitrosystem. Slices from developing rat visual cortex were cocultured with slices from the superior colliculus, the major target of cells in layer 5, and the lateral geniculate nucleus, the major target of cells in layer 6. Cortical neurons which established connections with tectal and thalamic explants were retrogradely labelled with fluorescent dyes. It was found that,in vitro, different populations of neurons project to these two targets, and that the laminar position and cellular morphology of the projecting cells were similar to theirin vivocounterparts. These specific connections were established when the target explants were placed either next to the white matter or next to the pial side of cortical slice cultures. The axons of cells projecting to ectopic positioned explants reoriented their trajectories and grew through the cortical grey matter directly towards their targets. Thus subcortical targets exert an orienting effect specifically on their innervating cells and attract growing axons of the appropriate cells at a distance. These results suggest that different targets release different molecules that act selectively on specific populations of neurons. Therefore, chemotropic guidance is likely to play a significant role in the development of specific connections between cortical neurons and their target areas.

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00200.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractCiliary neurotrophic factor (CNTF) is a pleiotropic molecule that acts as a neurotrophic factor for a wide range of embryonic neurons as well as a differentiation factor for sympathetic neuroblasts and O2A progenitor cells in culture. CNTF messenger RNA (mRNA) is present at very low levels in the normal adult rat central nervous system (CNS), but is dramatically up‐regulated after an aspiration lesion of dorsal hippocampus and overlying cortex, in the area coincident with glial scar. The increased level of CNTF mRNA in lesioned hippocampus is maximal by 3 days and is sustained for up to 20 days, the longest time point examined. In contrast, mRNA levels for brain‐derived neurotrophic factor (BDNF) and neurotrophin‐3 (NT‐3) were slightly decreased during the same period.In situhybridization experiments revealed that cells expressing CNTF mRNA were concentrated at the margin of the wound, and also present within the gelfoam which filled the lesion cavity. This distribution of CNTF‐expressing cells corresponded very closely to that of cells expressing high levels of glial fibrillary acidic protein mRNA at the wound site. Paralleling the observed increase in CNTF mRNA, increased levels of CNTF‐like neurotrophic activity were apparent in soluble extracts of the lesioned tissues. This neurotrophic activity for ciliary ganglion neurons was completely blocked by the addition of neutralizing antiserum against CNTF. Basic fibroblast growth factor, which has been shown by others to increase after a similar lesion paradigm (Frautschyet al., Brain Res.,553, 291–299, 1991), does not contribute appreciably to this trophic activity. We conclude that CNTF is markedly increased as a function of injury to the CNS and that its expression is most likely restricted to reactive astrocytes in t

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00201.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe L2/HNK‐1 carbohydrate epitope shared by several neural adhesion molecules has been implicated in cell‐to‐cell and cell‐to‐laminin adhesion (Keilhaueret al., Nature,316, 728–730, 1985; Künemundet al., J. Cell Biol.,106, 213–223, 1988). As demonstrated previously for chicken retinal ganglion cells (Coleet al., Neurosci. Lett.,93, 170–175, 1988), cerebral cortex astrocytes or cerebellar neurons could not be shown to adhere to the substrate‐bound L2/HNK‐1 carbohydrate. The cell‐bound L2/HNK‐1 carbohydrate, however, was a potent mediator of astrocytic and neuronal cell adhesion to laminin, which was strongly reduced in the presence of the L2/HNK‐1 carbohydrate‐carrying glycolipids or Fab fragments of a monoclonal antibody against it. Inhibition of adhesion could not be observed in the presence of the negatively charged gangliosides or sulphatide, but in the presence of heparin. To investigate whether the L2/HNK‐1 carbohydrate and heparin use the same or different binding sites on laminin, adhesion of cells to laminin was determined in the presence of heparin and Fab fragments of a monoclonal L2 antibody, which gave an additive value of inhibition as compared to the inhibition caused by the single compounds. This result, as well as studies of the binding of the L2/HNK‐1 glycolipids to laminin in the presence of heparin, indicates that the L2/HNK‐1 carbohydrate and heparin are implicated in different aspects

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00202.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effects of glutamate,N‐methyl‐d‐aspartate (NMDA), (+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo‐(a,d)‐cyclohepten 5,10‐imine maleate (MK801), α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionate (AMPA) and quisqualate on the accumulation of inositol phosphates (IP) from the breakdown of phosphoinositidesin vitrohave been studied in tissue prisms derived from a region of the chick forebrain, the intermediate medial hyperstriatum ventrale (IMHV). In prisms from the left IMHV, glutamate stimulated IP accumulation by 10–20%, AMPA by 55% and quisqualate by 650%. These effects were more marked in the right IMHV, where AMPA stimulated IP accumulation by 157% and quisqualate by 920%. MK801 and NMDA had no significant effect on IP accumulation in either hemisphere. The left IMHV is known to be the site of a biochemical cascade resulting in synaptic remodelling following training day‐old chicks on a one‐trial passive avoidance task. The effect of such training was to reduce glutamate‐stimulated accumulation of IP by 27% (P<0.05) in prisms taken 30 min after training. There was no effect on prisms taken at 5 or 180 min after training, and no effect at any time in the right IMHV. MK801, injected intraperitoneally before training at a concentration known to produce amnesia for the passive avoidance task, abolished the training‐induced decrease without itself affecting IP accumulation. Taken in conjunction with pharmacological and autoradiographic evidence, these results indicate that memory formation for the passive avoidance task involves the activation of NMDA receptor channels, but not quisqualate or AMPA receptors, in

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00203.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractVoltage‐sensitive dyes and activity‐dependent intrinsic optical signals were used to study the spatio‐temporal activity in the antennal lobes of honeybees. The intrinsic signals are somewhat slower than the dye signals but show a 10‐fold larger intensity change. These intrinsic signals consist of at least two components—one is wavelength‐independent and the other strongly wavelength‐dependent, with a maximum at ∼500 nm. Local inhibitory connections within the antennal lobes were examined by recording the activity elicited by an electrical stimulus to the antennal nerve of a slice preparation before and after applying picrotoxin to manipulate GABAergic inhibitory synapses. The inhibition starts with a delay of ∼10 ms after onset of the response and has at least two components. The spatial distribution of the inhibition is extremely inhomogeneous, with areas of small inhibition adjacent to areas of large inhibition. Thus inhibitory interactions in the antennal lobes are not evenly distributed among the glomerular organization. Stimulation of anin vivopreparation with an odour yields a spatially restricted activity. However, the spatial map appears highly dynamic in time because the size of the activated area is a function of the time during and a

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00204.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTxIA and TxIB, peptides with 27‐amino acid residues recently isolated from the molluscivorous marine snailConus textile neovicarius, exhibit strong paralytic activity in molluscs, with no paralytic effects on arthropods and vertebrates. At concentrations of 0.25 – 0.5 μM the toxins cause spontaneous repetitive firing and dramatic broadening of the action potential of culturedAplysianeurons. The action potential duration partially recovers within 30 min in the presence of the toxins. Under these conditions a second toxin application does not change the spike duration. TxI‐induced spike broadening occurs when potassium and calcium conductances are blocked. Voltage‐clamp experiments revealed that the toxins alter the kinetics of the sodium current either by slowing down the rate of sodium current inactivation or by recruiting silent sodium channels with slower activation and inactivation kinetics. The toxins shift the voltage‐dependent steady‐state Na+current inactivation curve to more positive values by 6 mV. These changes are not associated with alteration in the rate of sodium current activation, in the peak sodium current, or the sodium current reversal potential. TxI apparently represents a new class of conotoxins with an unusual phylogenic specificity and may therefore be useful as a probe for the study of molluscan neuronal sod

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00205.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractWhole‐cell and single‐channel currents evoked by γ‐aminobutyric acid (GABA) were recorded from rat cerebellar granule cells in culture. The electro‐physiological properties of these currents were studied in control condition and in the presence of external Zn2+(10 – 30μM). GABA (10 μM) induced bicuculline‐sensitive whole‐cell currents which desensitized. The desensitization was more rapid for higher concentrations of GABA (30 – 300 μM). The current – voltage relation of GABA currents was linear from – 70 to +50 mV. Two different types of cells were found with respect to the stoichiometry for agonist binding, one with Hill coefficient 1.5 and another one with coefficient 1. The half‐maximum concentration displayed more variability, with values varying from 10 to 50 μM. The time constant of recovery from desensitization (Tr) was estimated to be 36 s. Zn2+(30 μM) blocked GABA‐activated whole‐cell currents in a non‐competitive and voltage‐independent way without a significant change in the current kinetics. In excised outside‐out patches, GABA (0.5 μM) activated single‐channel events of 19 and 31 pS. Kinetic analysis yielded two mean shut times (Tc1= 2.70 ms, Tc2= 205 ms) and one mean open time (To= 3.64 ms). Zn2+(10 μM) did not affect single‐channel conductances and mean open and shut times, but significantly reduced the probability of opening from 0.17 to 0.06. It is probable that Zn2+binds to a site located on the extracellula

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00206.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractWe are interested in the mechanisms that generate the mature cerebral cortex. We used bromodeoxyuridine (BrdU) to label cortical cells as they were being born. We followed the fates of specific sets of cortical precursors in normal mice and in mice in which other groups of cortical progenitors had been destroyed with the antimitotic agent methylazoxymethanol acetate (MAM Ac). In normal mice, most cells destined for the cerebral cortex were produced from embryonic day 12 (E12) to E16 in the expected inside‐to‐outside sequence (deep layers first, superficial layers last). Injection of MAM Ac at E13 killed cells that would normally have contributed to the deep cortical layers. As a consequence, the cortex was thinned by ∼25% at postnatal day 21 (P21). However, all laminae were present and had normal connections with subcortical structures, although all were proportionately thinner. BrdU injected on E16 labelled a normally sized complement of cells that spanned a larger proportion of the depth of the thinned cortex. Thus, the deep cortical layers comprised many cells that were born several days later than normal. At embryonic ages prior to E12, a transient set of cells is produced in the early telencephalon. After injection with MAM Ac at E10, the cortex appeared histologically and histochemically normal at P21. However, many cells that would normally have contributed to superficial cortex (born on E15) were significantly deeper than normal. These results suggest that, during the early stages of cortical development, the nervous system is sufficiently plastic to compensate to some extent for the destruction of specific precursor cells by altering the fates of neurons born later. They indicate that the embryonic date on which a cortical cell is born does not necessarily determine its eventual phen

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00207.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe aim of the present study was to examine whether inhibition of the microglial cell reaction around axotomized motoneurons affects the subsequent regeneration process of the injured axons. The microglial cell reaction in the hypoglossal nucleus of the rat was blocked by infusion of cytosine‐arabinoside (ARA‐C) into the ventricular system. Axon regeneration was evaluated by determining the number and size distribution of myelinated axons at a defined level distal to the crush site, the number of neurons which could be retrogradely labelled from the distal stump as well as the number of motor endplates in the tongue at various times following injury. No significant difference was observed for any of these parameters between ARA‐C‐treated and untreated animals. Therefore, it is concluded that the microglial cell reaction is not necessary for peripheral nerves to regenerate and restore target contact at a normal rate and to a normal

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1993.tb00208.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY