摘要:

AbstractThe interactions between dying neurons and phagocytotic cells within the developing and injured retina remain controversial. The present work explored the role of microglia and investigated whether so‐called resident microglial cells are permanently responsible for removing cell debris whenever it is produced. As a first goal, I characterized some quantitative and morphometric features of the small ipsilateral retinocollicular projections and analysed the permanent function of phagocytosing microglia with these projections as a paradigm. To achieve this, I combined the fluorescent dyes Dil and 4Di–10ASP, both of which persist in the labelled ganglion cells after injection into the superior colliculus (SC), and retrograde labelling. After neuronal degradation, the dyes accompany the degradation products, become interiorized and then persist within the phagocytosing microglia. Consequently, early labelling of microglial cells can be assessed by injecting one dye into the SC during the first postnatal day of life, that is, prior to advanced natural neuronal cell death. Labelling of the remaining ipsilaterally projecting neurons with the second dye following intraorbital axotomy in adulthood and during subsequent neuronal death would therefore result in double labelling of some microglial cells, if these were involved in phagocytosis during both the natural and the induced phases of neuronal degradation. The ganglion cells which survived natural neuronal cell death remained fluorescent for 3 months after labelling with either dye on the day of the animal's birth, indicating that both fluorescent probes persisted within neurons. Quantitatively, 1770±220 ganglion cells/mm2were labelled within the contralateral retina and a total population of 1442±120 cells/retina were observed within the periphery of the inferior/temporal quadrant of the ipsilateral retina. A smaller, ipsilateral projection of 150±24 cells/retina was uniformly scattered throughout the rest of the retinal surface. Transient projections of ganglion cells to either the contralateral or the ipsilateral colliculi and death of labelled ganglion cells during the first postnatal days resulted in labelling of 210 ±36 microglial cells/mm2within the contralateral retina and a total number of 800 ±120 cells/retina within the inferior/temporal and 200 ±22 cells/retina within the rest of the retina. These labelled microglial cells were observed in adulthood and indicated that after taking away the neuronal cell debris they persisted within the retinal tissue. The small number of prelabelled ganglion cells which formed persistent ipsilateral projections until adulthood were axotomized by transecting the optic nerve, and resulted in additional labelling of microglial cells with the second fluorescent dye as well. Double‐labelled microglia were observed within the inferior/temporal quadrant (3500 ±240 cells/retina) and to a lesser extent (340 ±40 cells/retina) scattered over the entire retinal surface. The chronotopological sequence of microglial labelling paralleled that of ganglion cell degeneration. Injection of protease inhibitors into the vitreous body during optic nerve transection retarded retrograde glial cell degeneration, probably by blocking microglial proteases. The results directly proved that the same microglial cells which remove neuronal cell debris in the postnatal retina were reactivated later in life to proteolytically degrade and then phagocytose neurons which had altered because o

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00054.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractGABAergic presynaptic inhibition has been investigated in primary afferents using anin vitropreparation of the crayfish,Procambarus clarkii.Presynaptic terminals of a leg proprioceptor, the coxo‐basal (CB) chordotonal organ, were impaled in the neuorpil of the 5th thoracic ganglion. Pressure ejection of small volumes of the GABAAor GABABreceptor agonists, muscimol and 3‐aminopropylphosphinic acid (3‐APA), both induce depolarizing responses in the impaled CB sensory terminal. These depolarizations are not blocked by the specific GABAAand GABABreceptor antagonists, SR‐95531 and phaclofen, but they are abolished by picrotoxin. Both muscimol‐ and 3‐APA‐induced depolarizations are carried by an increase in conductance to Cl‐. The presynaptic increase in conductance to C1‐by GABA receptor activation leads to a depression of sensory synaptic transmission through a shunting of the incoming spikes. Monosynaptic EPSPs elicited in motor neurons by CB sensory nerve stimulation are depressed by muscimol and 3‐APA. GABA‐mediated presynaptic modulation occurs in crayfish primary afferents which can adjust the gain of reflexes. These results show that GABA‐activated Cl‐channels can induce a modulation of synaptic transmission, but also that the distinction between GABAAand GABABreceptors, as in vertebrates, is not applicable to the cru

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00055.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractAnin vitropreparation of the crayfish nervous system has been utilized to study an interjoint reflex pathway and its variability during rhythmic locomotor activity. The coxo‐basal chordotonal organ (CBCO) is a joint stretch receptor spanning the second joint of walking legs in crayfish, where it encodes joint movements and position. Mechanical stimulation (stretch and release) of the CBCO and electrical stimulation of the CBCO nerve elicits reflex responses in promotor and remotor motor neurons innervating muscles moving the basal thoraco‐coxal (TC) leg joint. Promotor and remotor motor neurons receive monosynaptic excitatory inputs from at least four CBCO afferents, including both stretch‐ and release‐sensitive CBCO afferents. In a tonic preparation, in which there is no tendency to produce alternating bursts of activity in antagonistic motor neurons, the reflex responses were evoked during each cycle of imposed movement. However, when the preparation became rhythmic and produced bouts of fictive locomotion, the reflex responses were unstable and their gain was phasically modulated. Paired recordings indicate that such a modulation of the monosynaptic interjoint reflex could be due to both a phasic change in the excitability of the motor neurons and presynaptic inhibition that reduces the excitatory input from CBCO primary af

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00056.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIntracortical mechanisms contributing to orientation and direction specificity were investigated with a method of local cortical inactivation. Single‐unit activity was recorded in area 17 of the anaesthetized cat while a small volume of cortical tissue 400–2900 μm lateral to the recorded cell was inactivated by γ‐aminobutyric acid (GABA) microiontophoresis. Cells were stimulated with moving bars of variable orientation and changes of the response were monitored. Recording and inactivation sites were histologically verified. Statistically significant changes in orientation tuning during GABA‐induced remote inactivation were observed in 80 of 145 cells (55%), and consisted in a reduced orientation specificity due to either increased (36%) or decreased (19%) responses. Increases of responses were more pronounced for the non‐optimal orientations. This effect mainly occurred with GABA application at distances around 500 μm and is interpreted as loss of inhibition. Reduced orientation specificity as a result of decreasing response mainly to the optimal orientation was interpreted as loss of excitation. This effect most frequently occurred with inactivation at distances around 1000 μm. Loss of inhibition was also elicited from a distance of 1000μm; such inhibition, however, affected only directionality, without inducing changes in orientation tuning. For several cells at distances<1000 μm from the inactivation site a temporal sequence consisting of a change in direction specificity followed by a reduction of orientation specificity, and finally by direct GABAergic inhibition of the cell under study, could be induced with gradually increasing ejecting currents. The results indicate that excitation and inhibition originating from populations of neurons at different horizontal distances differentially contribute to direction and orientation specificity of a given visua

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00057.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIn each of four cats gentle pressure was applied to one optic nerve by means of an inflatable cuff in order to disrupt the largest axons (Y fibres) and so produce a conduction block in them. It has previously been shown that this technique, as used by us, causes Wallerian degeneration in the fibres posterior to the site of application of the pressure (the crush site). The optic nerves and retinas in these cats were examined 2–2.8 years later. The optic nerves were prepared for electron microscopy and the retinas were flat‐mounted. Here we report an average 90% loss of large axons (>5 μm diameter) in the nerve posterior to the crush site. However, in the part of the nerve anterior to the crush site there was only a 33% loss and in the retina only a 57.5% reduction in the number of neurons of soma diameter>25 μm (i.e. alpha cells, the cell bodies of the Y neurons). These last two sets of values were significantly different, suggesting that the retinal ganglion cells had shrunk relatively more than the axons. Thus, the crushing technique has effectively axotomized almost all the Y fibres but, in spite of this, about half of the alpha retinal ganglion cells have survived this particular form of axotomy, with their axons intact at least for some distance into the optic nerve. This long survival raises the possibility that these neurons may have regenerated axons which have found targets and thus ensured their sur

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00058.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe distribution of callosal axons interconnecting lateral area 17 and medial area 18 of the rodent's occipital cortex is dramatically altered by neonatal enucleation, but it is not known how this manipulation affects the morphology of individual callosal axons or whether the enucleation‐induced changes in this pathway reflect maintenance of a transient developmental state by these fibres. In the present study, these questions were addressed by tracing the individual callosal axons in normal adult and neonatally enucleated adult hamsters withPhaseolus vulgarisleucoagglutinin (PHAL) and by anterograde labelling of developing callosal axons with the carbocyanine dye, Di‐l. In normal adults, injections of PHAL into the region of the 17–18a border produced dense labelling in all layers in the region of the contralateral 17–18a border. Larger injections resulted in callosal labelling that extended across the lateral one‐half of area 17, primarily in layers l and V. Thirty‐four callosal axons from normal adult hamsters were reconstructed through all the cortical laminae. Most of these had very simple terminal arbors. They gave off short collaterals in the infragranular layers and branched more extensively in the uppermost part of layer II‐III and in lamina l. Small injections of PHAL into the occipital cortex of neonatally enucleated adult hamsters resulted in labelled axons throughout most of areas 17 and 18a in the contralateral hemisphere. The terminal arbors of most individual callosal axons in eyeless hamsters were not appreciably different from those in sighted animals. However, 26.8% of 28 fibres reconstructed through all cortical laminae in the neonatally enucleated hamsters had much more widespread branches than any of the axons recovered from normal hamsters. As a result, the average total length of the callosal axons from the blinded hamsters was significantly greater than that for such fibres from the sighted animals. Anterograde labelling with Di‐l demonstrated axons in the anterior commissure and anterior part of the corpus callosum on P‐O. Labelled fibres extended into the white matter underlying the occipital cortex on P‐1 and entered the cortical plate on P‐2. Some of these axons reached into the marginal layer. Many developing callosal axons had short branches in the white matter, but generally extended only a single collateral into the cortical grey matter. Callosal axons in perinatal animals branched very little within the cortex and, in this respect, resembled fibres labelled with PHAL in adult hamsters. These results support the conclusion that the expanded tangential distribution of the occipital callosal projection in neonatally enucleated adult hamsters results, at least in part, from individual axons with abnormally widespread terminal arbors which are not present in large numbers at any time duri

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00059.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have studied outward currents of neurons acutely isolated from superficial layers of the entorhinal cortex with whole‐cell patch‐clamp recordings. If cells were held more negative than ‐50 mV, depolarizing voltage commands activated a transient A‐type current together with a sustained outward current. Both currents were sensitive to 4‐aminopyridine, while only the sustained current was blocked by tetraethylammonium. The sustained outward current showed a considerable rundown in amplitude over prolonged recording periods. At the same time its half‐maximal inactivation shifted from ‐74 to ‐ 114 mV. Nystatin perforated patch recordings were used to minimize these perfusion effects. Under such conditions the amplitude and the steady‐state inactivation properties of the sustained outward current remained stable for more than 1 h. Pharmacological investigations revealed that only a small part of the sustained outward current could be attributed to a calcium‐activated potassium current. Therefore most of the rundown has to be due to changes in the delayed rectifier outward current. These results may suggest that the delayed rectifier current is under considerabl

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00060.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe light microscopic localization of aspartate‐like immunoreactivity (Asp‐LI) was compared to that of glutamate‐like immunoreactivity (Glu‐LI) in hippocampal slices by means of specific polyclonal antibodies recognizing the amino acids fixed by glutaraldehyde. After incubation in Krebs' solution with normal (5 mM) or depolarizing concentrations of K+, and various additives, the slices were fixed with glutaraldehyde, resectioned and processed according to the peroxidase ‐ antiperoxidase procedure. At 5 mM K+, Glu‐LI was localized in nerve‐terminal like dots with a conspicuous laminar distribution, the highest Glu‐LI concentrations coinciding with the terminal fields of major excitatory pathways thought to use glutamate or aspartate as transmitters. The localization of Asp‐LI showed some similarity to that of Glu‐LI, but the laminar distribution was less differentiated and the immunoreactivity was much weaker. At 40 and 55 mM K+the nerve terminal localizations of Glu‐LI and Asp‐LI were strongly reduced. Concomitantly, both immunoreactivities appeared in astroglial cells. These changes were Ca2+‐dependent. The nerve ending staining patterns of Asp‐LI and Glu‐LI could be sustained during depolarization if the medium was supplemented with glutamine (0.5 mM). Under these conditions Asp‐LI became more intense and its distribution approached that of Glu‐LI. This suggests that, when stimulated, some nerve endings can increase their reservoir of releasable aspartate. The presence of glutamine during depolarization strongly reduced glial Asp‐LI and Glu‐LI, possibly due to its providing nitrogen for conversion of glutamate to glutamine. α‐Ketoglutarate, another glia‐derived precursor of neuronal glutamate, was virtually ineffective in supporting Glu‐LI and Asp‐LI in nerve endings, and did not suppress Glu‐LI or Asp‐LI in glia. Our findings provide morphological support for the view that excitatory nerve endings under certain conditions can contain high levels of both aspartate and glutamate (possibly in the same terminals), and that aspartate as well as glutamate can be released synaptically. Further, they underline the importance of the glial supply of the nerve endings with precursor glutamine, which allows them to build up and sustain high concen

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00061.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe role of theN‐methyl‐D‐aspartate (NMDA) type of glutamate receptor in long‐term potentiation (LTP) of the medial (MPP) and lateral (LPP) divisions of the perforant path‐granule cell system was investigated in urethane‐anaesthetized rats. A stimulating electrode was positioned in the dorsomedial or ventrolateral aspect of the angular bundle for selective activation of either the MPP or LPP, respectively. A push‐pull cannula served to focally perfuse artificial cerebrospinal fluid (ACSF) across the perforant path synaptic zone, while evoked potentials were monitored in the dentate hilus. Identification of LPP and MPP responses was based on (1) differences in population excitatory postsynaptic potential (EPSP) waveform obtained during stimulus depth profiles, and (2) differential sensitivity of evoked EPSPs to the glutamate receptor agonist L‐aminophosphonobutyrate (AP4), and the antagonist γ‐D‐glutamylglycine (DGG). High‐frequency stimulation (400 Hz, 8 bursts of 8 pulses) applied to the lateral and medial perforant path elicited LTP of the EPSP and population spike in rats perfused with standard medium. In the MPP, LTP was almost completely blocked when D‐aminophosphonopentanoate (AP5; 100 μM), a selective NMDA receptor antagonist, was perfused during the tetanus. Surprisingly, in the LPP experiments, AP5 did not impair induction of the ‘synaptic’ EPSP component of LTP. This occurred despite the ability of AP5 to block LTP of the LPP evoked population spike. The results suggest the existence of a novel, NMDA receptor‐independent form of synaptic LT

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00062.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA genomic clone containing 7 kb of 5’flanking sequences from the rat choline acetyltransferase (ChAT) gene was isolated and shown to contain a TATA box‐like sequence and several consensus binding sites for the transcription factor AP1. Two constructs containing 450 and 1450 base pairs (bp), respectively, of 5’flanking sequences promoted expression of a fused chloramphenicol acetyltransfersase (CAT) gene when transfected into fibroblast FR3T3, Sertoli TM4, phaeochromocytoma PC12 and cholinergic neuronal SN6 cell lines. In contrast, a longer construct containing 3850 bp of 5’flanking sequence allowed CAT activity only in the cholinergic cell line SN6. CAT activity with this construct was suppressed in the three other cell lines, indicating that the distal region of the ChAT promoter contains a cell type‐specific silencer‐like element that restricts ChAT gene expression to cholinergic cells. Treatment of PC12 cells with nerve growth factor (NGF) increased the promoter activity of the ‐450 and ‐1450 constructs approximately four‐fold and allowed promoter activity from the ‐3850 construct, indicating that elements involved in NGF responsiveness of the ChAT promoter are contained in the first 450 bp of upstream sequence. These results support a model in which gene transcription controlled by cell‐type specific regulatory elements contribute to the establishment, maintenance and plasticity of the cholinergic transmitter phenotype

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00063.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY