摘要:

AbstractNeuroepithelial cells appear as a homogeneous population of cells in the cell cycle that seem to behave as pluripotent neural precursors. The study of the intrinsic heterogeneity and subtle developmental changes among neuroepithelial cells has been hindered by the lack of specific markers. To address that study, a panel of monoclonal antibodies was produced against early developing chick retina. The monoclonal antibody precursor marker 1 (PM1) labels most, if not all, of the early neuroepithelial cells in embryonic day 4 retinal sections. This pattern is transient since the labelling becomes restricted to the peripheral retina as development proceeds and eventually disappears from the neuroepithelial cells. However, apparently in parallel, the differentiating retinal ganglion cells become PM1‐positive. The expression of the PM1 antigen, a 73 × 103Mrprotein, as shown by western blotting, also decreases with development. In addition, a chick retina dissociated‐cell culture system, where retinal neuroepithelial cells actively proliferate and undergo differentiation under defined conditions, in combination with monoclonal antibody PM1, allowed us to characterize and quantify the proliferating and differentiating neuroepithelial cells. Interestingly, the fraction of total neuroepithelial cells that are stained with PM1 sharply decreases as retinal development proceeds, in correlation with the staining pattern in sections from matched stages. These data thus reveal that the pluripotent neural precursors in the chick retina already represent an intrinsically heterogeneous population, and that this population changes with develop

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00252.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe metabotropic autoreceptor of glutamatergic nerve terminals from the cerebral cortex of adult rats has been characterized. Receptor activation involves a rapid and transient increase in diacylglycerol, which is sensitive to l‐2‐amino‐3‐phosphonopropionate (l‐AP3) and l‐2‐amino‐4‐phosphonobutanoic acid (l‐AP4) and is partially blocked by pertussis toxin. Protein kinase C (PKC) has a negative feedback control in this transduction pathway because the activation of the kinase, either by phorbol esters or by the endogenous diacylglycerol produced by the receptor, results in a reversible receptor desensitization, with loss of the ability to further facilitate glutamate release. It is concluded that the facilitatory metabotropic receptor located at the glutamatergic nerve endings belongs to the subclass coupled to phosphoinositide hydrolysis and that the rapid and use‐dependent desensitization of the facilitatory pathway may underlie a mechanism to prevent its permanent activation and thereby t

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00253.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractBy grafting solid pieces of cerebellar anlage onto the surface of the adult rat cerebellum, we have investigated the problem of the interactions between embryonic and adult neurons in an intact brain. A few days after grafting, embryonic astrocytic processes crossed the graft‐host interface and radiated into the recipient molecular layer. Several grafted Purkinje cells also migrated into the host brain along such processes as well as adult Bergmann glia. Adult climbing fibres, labelled by means ofPhaseolus vulgarisleucoagglutinin (PHA‐L), sprouted new collateral branches which terminated on embryonic Purkinje cells at both extra‐ and intraparenchymal levels. No sign of activation of host astroglia or microglia was evident in the host cerebellum in relation to these processes. Embryonic Purkinje cells which migrated into the host cerebellum developed an adult‐like morphology. Intraparenchymal grafts of neocortical embryonic tissue induced conspicuous growth of host olivary axons, characterized by a pattern which was different from that observed following cerebellar grafts. By contrast, when neocortical tissue was placed onto the surface of the recipient cerebellum, graft‐host interactions were limited and climbing fibre sprouting was rarely seen. These results show that (i) supernumerary Purkinje cells can penetrate and settle in the adult intact cerebellar cortex, (ii) adult climbing fibres are able to innervate these new targets in the absence of any injury or activation of non‐neuronal cells of the adult brain, and (iii) in the absence of damage to the adult brain, the plasticity of adult olivary axons is specifically elicited and controlled by embryonic Pur

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00254.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe regional cerebral blood flow (rCBF) was measured with15O‐butanol and positron emission tomography (PET) in 10 healthy subjects in order to compare cerebral activation involved in the somatosensory discrimination of microgeometric features with cerebral activation associated with the discrimination of macrogeometric features. Subjects performed two‐alternative forced choice (2‐AFC) discriminations of pairs of stimuli from a series of quantified standardized stimuli that differed in roughness (microgeometry), and a separate 2‐AFC task of smooth tactile stimuli that differed in length (macrogeometry). Results are presented from three conditions: (1) a roughness discrimination task; (2) a length discrimination task; and (3) a control trial in which subjects were required to reproduce similar exploratory finger movements only, but without a specific stimulus to feel. Mean subtraction images were computed using the computerized adjustable brain atlas of Greitzet al.(1991,J. Comput. Assisted Tomogr., 15, 26–38) and areas of significant blood flow change were identified. Both the roughness and the length discrimination tasks activated overlapping cortical fields contralaterally in the anterior and posterior lip of the postcentral sulcus. However, in the length discrimination, activation of the posterior lip of the postcentral sulcus extended deeper into the sulcus and there was also a separate additional area of activation in the anterior part of the precentral gyrus. Furthermore, the length discrimination task activated fields in the overt part of the supramarginal gyrus bilaterally as well as fields in the angular gyrus bilaterally. Thus roughness discrimination uses only a subset of the cortical regions that are needed for the recovery of length information, which requires more extensive somatosensory processing. This finding may be partly explained in that length perception needs both edge detection of the stimuli used, as well as integrated information of surface length and velocity, which is not necessary for roughness perception. Specific differences in the acquisition of necessary tactile information between the two discrimination tasks was reflected in different sampling s

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00255.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe ability to localize sounds in azimuth was tested in five cats that had been binocularly deprived of vision from birth for several months and in three normal age‐matched controls. Brief tone bursts were presented in an eight‐choice apparatus along 360°of the azimuthal plane at constant elevation. Using positive reinforcement techniques, the cats were trained to walk from the centre of the 3 m diameter circular enclosure to the hidden loudspeakers. The distribution of sound localization error from 55 trials per cat at each speaker position was measured, and its standard deviation was used to assess the precision of sound localization. All cats localized tones straight ahead of them most precisely; performance at lateral and rear positions was gradually less precise. When the sound localization ability of normal and binocularly deprived cats was compared across speakers, a significantly enhanced precision was found for binocularly deprived cats overall (P<0.002; two‐way analysis of variance). An improvement was found at each individual speaker position, but it was greatest at lateral and rear positions. In two sets of control experiments normal cats were retested (i) in the dark with the aid of an infrared camera and (ii) after 3 months of binocular lid suture. Normal cats in the dark did not show any differences in their sound localization behaviour. Late‐deprived cats showed a tendency for better performance, which fell short of statistical significance. Our results in visually deprived cats agree well with some reports on the sound localization ability of blind humans, but disagree with others. Our data provide support for a hypothesis of compensatory plasticity, in which sensory functions get sharpened with the loss of another modality. They seem to rule out the necessity for vision to play a role in the postnatal calibration of audito

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00256.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe contribution of NMDA and non‐NMDA receptors to visual synaptic transmission in the superficial layers of the superior colliculus of the cat has been studied using extracellular recording and iontophoretic techniques. Neuronal responses to natural visual stimulation and the ejection of NMDA and AMPA were observed in the absence and presence of the antagonists CNQX, CPP and AP5. CNQX routinely reduced the responses to visual stimulation at ejection currents which selectively blocked the responses to AMPA but not those to NMDA. Agonist selective ejection currents of CPP and AP5 also reduced visual responses of most SC neurons, but there was a substantial majority whose visual responses were resistant to these antagonists. Neurons with CPP/AP5 resistant visual responses were more commonly found 750–1000 μm from the dorsal surface of the SC. The data indicate that, while non‐NMDA receptors are heavily involved in visual synaptic transmission in the superficial SC, the involvement of NMDA receptors varies with recording

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00257.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00258.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY