共查询到20条相似文献,搜索用时 15 毫秒
1.
Gene V. Wallenstein 《Biological cybernetics》1994,71(3):271-280
Until recently, the presence of γ-aminobutyric acid (GABA) in the thalamus has usually been associated with the "classical" GABA
A
Cl−-dependent receptor. However, the discovery of a slower, long-lasting, K+-dependent inhibitory postsynaptic potential (IPSP) mediated by GABA
B
receptors in projection cells of the dorsal lateral geniculate nucleus has led researchers to reconsider its role in modulating
the behavior of these cell groups (Crunelli et al. 1988; Crunelli and Leresche 1991). Of particular interest is the role of
this K+ current in the activation of the low-threshold Ca2+ current, I
T
, of thalamocortical relay (TCR) neurons responsible for bursting activity (Jahnsen and Llinás 1984 a, b). Considering the
time scale on which the GABA
B
-receptor-activated K+ current operates, it is ideally suited to foster sustained rhythmicity in TCR cells reciprocally connected to neurons of
the nucleus reticularis thalami (NRT) as well as interneurons at frequencies observed in vivo (Steriade and Llinás 1988). In this study we show that small changes in the duration and amplitude of the K+-dependent IPSPs can have marked effects on TCR cell groups including a shift from single-spike firing (tonic) to bursting
behavior. We further show that a single GABA
B
-mediated IPSP is sufficient to activate the low-threshold Ca2+ response and that sustained oscillations are possible given the presence of excitatory TCR connections to GABAergic NRT cells
or interneurons of the dorsal lateral thalamus. These combined effects are examined with regard to their role in generating
the well known 7 – 14 Hz spindle rhythm as well as slower 6 – 8 Hz oscillations observed in TCR cells in vivo (Steriade and Llinás 1988).
Received: 13 October 1993 / Accepted in revised form: 24 February 1994 相似文献
2.
An intracellular recording made from the retinal luminosity horizontal cell (LHC) demonstrated that repetitive red flashes
enhanced the cell's responsiveness to red stimulus and depressed its responsiveness to green stimulus and that repetitive
green flashes suppressed the cell's red response but produced little change in its green response. Based on the idea that
the spectral plasticity of LHCs may reflect some synaptic efficacy changes between the LHC and various cones, a self-organizing
system is proposed to investigate the possible manner of information processing and storage within the synapses. The results
of model analysis suggest that the stimulus-pattern-related spectral plasticity is attributable to the excitatory interaction
within the same kinds of synapses and the inhibitory interaction between different kinds of synapses. This system is able
to encode and store the history of signal transmission in a graded and cumulative fashion.
Received: 7 December 2001 / Accepted: 26 November 2002 /
Published online: 28 March 2003
Correspondence to: Pei-Ji Liang (email: pjliang@sjtu.edu.cn, Tel./Fax: (86) 2164070495)
Acknowledgements. This research was supported by the National Basic Research Program (G1999054000) of China and the National Foundation of
Natural Science of China (No. 30170263). 相似文献
3.
A theory of hippocampal memory based on theta phase precession 总被引:10,自引:0,他引:10
Yamaguchi Y 《Biological cybernetics》2003,89(1):1-9
The neural dynamics of the hippocampal network for memory encoding of novel temporal sequences is proposed based on the theta
rhythm modulated firing of place cells called theta phase precession. It is hypothesized that theta phase precession is generated
at the entorhinal cortex by phase locking between local field theta oscillation and neural oscillators and that the hippocampal
closed network with feedforward and backward projections employ theta phase precession to create selectivity in the associative
connections needed for temporal sequence storage. Our analyses and computer experiments reveal that the phase precession generated
by phase locking instantaneously endows stable phase relations among neural activities in the successively changing neural
population. It is concluded that theta phase precession provides biologically plausible dynamics for the memory encoding of
novel temporal sequences as episodic events.
Received: 18 December 2002 / Accepted: 18 March 2003 /
Published online: 20 May 2003
Correspondence to: Y. Yamaguchi (e-mail: yokoy@brain.riken.go.jp, Fax: +81-48-4676938)
Acknowledgements. The author would like to express acknowledgement to Drs. McNaughton and Skaggs for their discussion and comment and to Dr.
Amari for his continuous encouragement. Further thanks are given to Mr. Haga and Dr. Wu for their discussion and cooperation. 相似文献
4.
A model is presented that allows prediction of the probability for the formation of appositions between the axons and dendrites
of any two neurons based only on their morphological statistics and relative separation. Statistics of axonal and dendritic
morphologies of single neurons are obtained from 3D reconstructions of biocytin-filled cells, and a statistical representation
of the same cell type is obtained by averaging across neurons according to the model. A simple mathematical formulation is
applied to the axonal and dendritic statistical representations to yield the probability for close appositions. The model
is validated by a mathematical proof and by comparison of predicted appositions made by layer 5 pyramidal neurons in the rat
somatosensory cortex with real anatomical data. The model could be useful for studying microcircuit connectivity and for designing
artificial neural networks.
Received: 11 February 2002 / Accepted: 5 November 2002 / Published online: 20 February 2003
Correspondence to: H. Markram (e-mail: Henry.Markram@epfl.ch Tel.: +41-21-6939537, Fax: +41-21-6935350)
Acknowledgements. This study was supported by the National Alliance for Autism Research, the Minerva Foundation, the US Navy, the Ebner Center
for Biomedical Research, and the Edith Blum Foundation. 相似文献
5.
The properties of calcium channels were studied at the period of neurogenesis in the early embryonic chick retina. The whole neural retina was isolated from embryonic day 3 (E3) chick and loaded with a Ca2+-sensitive fluorescent dye (Fura-2). The retinal cells were depolarized by puff application of high-K+ solutions. Increases in intracellular Ca2+ concentrations were evoked by the depolarization through calcium channels. The type of calcium channel was identified as l-type by the sensitivity to dihydropyridines. The Ca2+ response was completely blocked by 10 μM nifedipine, whereas it was remarkably enhanced by 5 μM Bay K 8644. Then we sought a factor to activate the calcium channel and found that GABA could activate it by membrane depolarization at the E3 chick retina. Puff application of 100 μM GABA raised intracellular Ca2+ concentrations, and this Ca2+ response to GABA was also sensitive to the two dihydropyridines. Intracellular potential recordings verified clear depolarization by bath-applied 100 μM GABA. The Ca2+ response to GABA was mediated by GABAA receptors, since the GABA response was blocked by 10 μgM bicuculline or 50 μM picrotoxin, and mimicked by muscimol but not by baclofen. Neither glutamate, kainate, nor glycine evoked any Ca2+ response. We conclude that l-type calcium channels and GABAA receptors are already are already expressed before differentiation of retinal cells and synapse formation in the chick retina. A possibility is proposed that GABA might act as a trophic factor by activating l-type calcium channels via GABAA receptors during the early period of retinal neurogenesis. © 1993 John Wiley & Sons, Inc. 相似文献
6.
A model of the CA3 region of the hippocampus was used to simulate the P50 auditory-evoked potential response to repeated
stimuli in order to study the neuronal circuits involved in a sensory-processing deficit associated with schizophrenia. Normal
subjects have a reduced P50 auditory-evoked potential amplitude in response to the second of two paired auditory click stimuli
spaced 0.5 s apart. However, schizophrenic patients do not gate or reduce their response to the second click. They have equal
auditory-evoked response amplitudes to both clicks. When schizophrenic patients were medicated with traditional neuroleptics,
the evoked potential amplitude to both clicks increased, but gating of the second response was not restored or improved. Animal
studies suggest a role for septohippocampal cholinergic activity in sensory gating. We used a computational model of this
system in order to study the relative contributions of local processing and afferent activity in sensory gating. We first
compared the effect of information representation as average firing rate to information representation as cell assemblies
in order to evaluate the best method to represent the response of hippocampal neurons to the auditory click. We then studied
the effects of nicotinic cholinergic input on the response of the network and the effect of GABAB receptor activation on the ability of the local network to suppress the test response. The results of our model showed that
nicotinic cholinergic input from the septum to the hippocampus can control the flow of sensory information from the cortex
into the hippocampus. In addition, postsynaptic GABAB receptor activation was not sufficient to suppress the test response when the interstimulus interval was 500 ms. However,
presynaptic GABAB receptor activity may be responsible for the suppression of the test response at this interstimulus interval.
Received: 3 December 2001 / Accepted: 23 October 2002 / Published online: 28 February 2003
Correspondence to: K. A. Moxon (e-mail: karen.moxon@drexel.edu, Tel.:+1-215-8951959, Fax: +1-215-8954983)
Supported by USPHS, MH01245, MH58414, MH-50787, MH-01121, and research grants from the Department of Veterans Affairs and
the National Alliance for Research on Schizophrenia and Depression. 相似文献
7.
Summary It is known that estrogen can protect neurons from excitotoxicity. Since isoflavones possess estrogen-like activity, it is
of interest to determine whether isoflavones can also protect neurons from glutamate-induced neuronal injury. Morphological
observation and lactate dehydrogenase (LDH) release assay were used to estimate the cellular damage. It is surprising that,
contrary to estrogen, isoflavones, specifically genistein and daidzein, are toxic to primary neuronal culture at high concentration.
Treatment of neurons with 50 μM genistein and daidzein for 24 h increased LDH release by 90% and 67%, respectively, indicating a significant cellular damage.
Under the same conditions, estrogen such as 17β-estradiol did not show any effect on primary culture of brain cells. At 100 μM, both genistein and daidzein increased LDH release by 2.6- and 3-fold, respectively with a 30-min incubation. Furthermore,
both genistein and daidzein at 50 μM increased the intracellular calcium level, [Ca2+]i, significantly. To determine their mode of action, genistein and daidzein were tested on glutamate and GABAA receptor binding. Both genistein and daidzein were found to have little effect on glutamate receptor binding, while the binding
of [3H]muscimol to GABAA receptors was markedly inhibited. However, 17β-estradiol did not affect GABAA receptor binding suggesting that the toxic effect of genistein and daidzein could be due to their inhibition of the GABAA receptor resulting in further enhancement of excitation by glutamate and leading to cellular damage.
Ying Jin, Heng Wu contributed equally to this article. 相似文献
8.
Cupello A 《Amino acids》2003,24(4):335-346
Summary. It has long been accepted that GABA is the main inhibitory neurotransmitter in the mammalian brain, acting via GABAA or GABAB receptors. However, new evidences have shown that it may work as an excitatory transmitter, especially in the brain of newly-born
animals and acting via GABAA receptors. The difference in the end results of GABAA receptors activation in the two cases is not due to the receptor associated channels, which in both cases are chloride channels.
The different physiological effect in the two cases is due to different electrochemical gradients for chloride. When GABA
acting via GABAA receptors is inhibitory, either there is no transmembrane electrochemical gradient for chloride or there is one forcing such
negative ions into the nerve cell, once chloride channels are open. Viceversa, GABA is excitatory when the electrochemical
gradient is such to make chloride ions flow outside the cell, upon opening of the GABA activated chloride channels.
In this review this concept is discussed in details and evidence in the scientific literature for the existence of different
types of chloride pumps (either internalizing or extruding chloride) is compiled.
Received August 5, 2002 Accepted October 30, 2002 Published online March 17, 2003
Acknowledgement The author thanks Dr. Simona Scarrone, Genova, for helping him with the schemes in Fig. 1.
Author's address: Dr. Aroldo Cupello, Istituto di Bioimmagini e Fisiologia Molecolare, Via De Toni 5, I-16132 Genova, Italy, Fax: 39-010354180,
E-mail: dcupel@neurologia.unige.it 相似文献
9.
10.
Neural oscillation is one of the most extensively investigated topics of artificial neural networks. Scientific approaches
to the functionalities of both natural and artificial intelligences are strongly related to mechanisms underlying oscillatory
activities. This paper concerns itself with the assumption of the existence of central pattern generators (CPGs), which are the plausible neural architectures with oscillatory capabilities, and presents a discrete and generalized
approach to the functionality of locomotor CPGs of legged animals. Based on scheduling by multiple edge reversal (SMER), a primitive and deterministic distributed algorithm, it is shown how oscillatory building block (OBB) modules can be created and, hence, how OBB-based networks can be formulated as asymmetric Hopfield-like neural networks
for the generation of complex coordinated rhythmic patterns observed among pairs of biological motor neurons working during
different gait patterns. It is also shown that the resulting Hopfield-like network possesses the property of reproducing the
whole spectrum of different gaits intrinsic to the target locomotor CPGs. Although the new approach is not restricted to the
understanding of the neurolocomotor system of any particular animal, hexapodal and quadrupedal gait patterns are chosen as
illustrations given the wide interest expressed by the ongoing research in the area.
Received: 14 June 2002 / Accepted: 18 February 2003 /
Published online: 20 May 2003
Correspondence to: Z. Yang (e-mail: zhijun.yang@ed.ac.uk)
Acknowledgements. This work was partially supported by CNPq, the Brazilian Research Agency, under support number 143032/96-8. We are grateful
for the helpful discussions with Prof. V.C. Barbosa, Dr. A.E. Xavier, Dr. M.S. Dutra, and Dr. A.F.R. Araújo. The donations
of FPGA hardware and software from XILINX Incorporation under the order No. XUP2930 and XUP3576 are also highly appreciated. 相似文献
11.
Stereopsis is the ability to perceive three-dimensional structure from disparities between the two-dimensional retinal images.
Although disparity-sensitive neurons have been proposed as a neural representation of this ability many years ago, it is still
difficult to link all qualities of stereopsis to properties of the neural correlate of binocular disparities. The present
study wants to support efforts directed at closing the gap between electrophysiology and psychophysics. Populations of disparity-sensitive
neurons in V1 were simulated using the energy-neuron model. Responses to different types of stimuli were evaluated with an
efficient statistical estimator and related to psychophysical findings. The representation of disparity in simulated population
responses appeared to be very robust. Small populations allowed good depth discrimination. Two types of energy neurons (phase-
and position-type models) that are discussed as possible neural implementations of disparity-selectivity could be compared
to each other. Phase-type coding was more robust and could explain a tendency towards zero disparity in degenerated stimuli
and, for high-pass stimuli, exhibited the breakdown of disparity discrimination at a maximum disparity value. Contrast-inverted
stereograms led to high variances in disparity representation, which is a possible explanation of the absence of depth percepts
in large contrast-inverted stimuli. Our study suggests that nonlocal interactions destroy depth percepts in large contrast-inverted
stereograms, although these percepts occur for smaller stimuli of the same class.
Received: 21 December 2001 / Accepted: 29 April 2002
RID="*"
ID="*" Present address: Bayer AG BTS-PT-MVT-MKM, Geb. K9, 51368 Leverkusen, Germany
Acknowledgement. This work was supported by a scholarship from the Studienstiftung des deutschen Volkes to J.L.
Correspondence to: J. Lippert (e-mail: joerg.lippert.jl@bayer-ag.de) 相似文献
12.
We extend the analysis of simple, energy-conserving models for the dynamics of insect locomotion in the horizontal plane
developed in Schmitt and Holmes (2000a,b, 2001), where gaits characteristic of steady cockroach running and turning were evoked.
In this paper, we include dissipation and energy inputs via active “muscles” in three forms: via prescribed torques at the
“hip” pivot, via an active spring element of variable length, and via a pair of Hill-type muscle models representing an extensor/flexor
system. Due to mechanical feedback of passive elastic forces, the stable gaits of the conservative models are preserved, and
now energy input and absorption balances to additionally stabilize a preferred speed, with only modest neural sensing and
feedback being required. However, these bipedal models still cannot simultaneously match observed moment-yaw magnitudes and
fore-aft dynamics.
Received: 17 September 2001 / Accepted: 20 February 2003 /
Published online: 20 May 2003
Correspondence to: P. Holmes (e-mail: pholmes@math.Princeton.EDU)
Acknowledgements. This work was supported by DARPA/ONR: N00014-98-1-0747 and DoE: DE-FG02-95ER25238. John Schmitt was partially supported by
a DoD Graduate Fellowship, a Wu Fellowship of the School of Engineering and Applied Science, and a George Van Ness Lothrop
Honorific Fellowship of the Graduate School at Princeton University. We thank Kenneth Meijer for allowing us to use his muscle
model in Sect. 4 and Bob Full and Dan Koditschek for numerous helpful suggestions. 相似文献
13.
Timing information in the range of seconds is significantly correlated with our behavior. There is growing interest in the
cognitive behaviors that rely on perception, comparison, or generation of timing. However, little is known about the neural
mechanisms underlying such behaviors. Here we model two different neural mechanisms to represent timing information in the
range of seconds. In one model, a recurrent network of bistable spiking neurons shows a quasistable state that is initiated
by a brief input and typically lasts for a few to several seconds. The duration of this quasistable activity may be regarded
as the neural representation of internal time obeying a psychophysical law of time recognition. Another model uses synfire
chains to provide the timing information necessary for predicting the times of anticipated events. In this model, the neurons
projected to by multiple synfire chains are conditioned to fire synchronously at the times when an external event (GO signal)
is expected. The conditioning is accomplished by spike-timing-dependent plasticity. The two models are inspired by the prefrontal
activities of the monkeys engaging in different timing-information-related tasks. Thus, this cortical region may provide the
timing information required for organizing various behaviors.
Received: 12 March 2002 / Accepted in revised form: 26 November 2002 /
Published online: 28 March 2003
Correspondence to: T. Fukai (e-mail: tfukai@eng.tamagawa.ac.jp, Tel.: +81-42-7398434, Fax: +81-42-7397135)
Acknowledgements. K. Kitano was supported by Japan Society for the Promotion of Science. 相似文献
14.
V. I. Khorevin 《Neurophysiology》2007,39(4-5):337-338
The participation of intrinsic inhibitory networks in providing the velocity selectivity of neurons of the superior colliculus (SC) of the Syrian hamster was tested using iontophoretic application of bicuculline methiodide, a GABAA receptor competitive antagonist. The impulse activity of 22 low pass-tuned (LP) cells was recorded extracellularly. Following
application of bicuculline, 10 cells exhibited an increase in the velocity selectivity, while the other 12 units showed decreases
in their tuning. We assume that SC intrinsic inhibitory networks contributing to the velocity tuning of neurons of this structure are driven in a dissimilar
way by afferent volleys arriving from the retina through “fast” Y and “slow” W channels.
Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 385–387, July–October, 2007. 相似文献
15.
Inhibitory control of neural differentiation in mammalian cells 总被引:2,自引:0,他引:2
In Xenopus embryos, a truncated type II activin receptor (Δ1XAR1), capable of blocking signals by several transforming growth factor
(TGF)-β family members, can induce neural tissue suggesting neural fate is under inhibitory control. Activin and bone morphogenetic
protein 4 (BMP4) can act as neural inhibitors but only BMP4 can induce epidermis in Xenopus ectodermal cells. We have used the pluripotent mouse embryonal carcinoma cell line P19 to examine whether the mechanisms of
ectodermal cell fate decisions are conserved among vertebrates. We show that a P19 cell line expressing Δ1XAR1 will differentiate
into neurons. In addition, BMP4 inhibits retinoic acid (RA)-induced neural differentiation of P19 cells and induces keratin
expression. These results suggest that in mammals as in amphibians neural fate is under inhibitory control and BMP4 can alter
ectodermal differentiation.
Received: 23 September 1996 / Accepted: 8 January 1997 相似文献
16.
Möhler H 《Cell and tissue research》2006,326(2):505-516
Because of its control of spike-timing and oscillatory network activity, γ-aminobutyric acid (GABA)-ergic inhibition is a key element in the central regulation of somatic and mental functions. The recognition of GABAA receptor diversity has provided molecular tags for the analysis of distinct neuronal networks in the control of specific pharmacological and physiological brain functions. Neurons expressing α1GABAA receptors have been found to mediate sedation, whereas those expressing α2GABAA receptors mediate anxiolysis. Furthermore, associative temporal and spatial memory can be regulated by modulating the activity of hippocampal pyramidal cells via extrasynaptic α5GABAA receptors. In addition, neurons expressing α3GABAA receptors are instrumental in the processing of sensory motor information related to a schizophrenia endophenotype. Finally, during the postnatal development of the brain, the maturation of GABAergic interneurons seems to provide the trigger for the experience-dependent plasticity of neurons in the visual cortex, with α1GABAA receptors setting the time of onset of a critical period of plasticity. Thus, particular neuronal networks defined by respective GABAA receptor subtypes can now be linked to the regulation of various clearly defined behavioural patterns. These achievements are of obvious relevance for the pharmacotherapy of certain brain disorders, in particular sleep dysfunctions, anxiety disorders, schizophrenia and diseases associated with memory deficits. 相似文献
17.
M.L. Tierney B. Birnir N.P. Pillai J.D. Clements S. M. Howitt G. B. Cox P.W. Gage 《The Journal of membrane biology》1996,154(1):11-21
The conserved leucine residues at the 9′ positions in the M2 segments of α1 (L264) and β1 (L259) subunits of the human GABAA receptor were replaced with threonine. Normal or mutant α1 subunits were co-expressed with normal or mutant β1 subunits in Sf9 cells using the baculovirus/Sf9 expression system. Cells in which one or both subunits were mutated had a
higher ``resting' chloride conductance than cells expressing wild-type α1β1 receptors. This chloride conductance was blocked by 10 mm penicillin, a recognized blocker of GABAA channels, but not by bicuculline (100 μm) or picrotoxin (100 μm) which normally inhibit the chloride current activated by GABA: nor was it potentiated by pentobarbitone (100 μm). In cells expressing wild-type β1 with mutated α1 subunits, an additional chloride current could be elicited by GABA but the rise time and decay were slower than for wild-type
α1β1 receptors. In cells expressing mutated β1 subunits with wild-type or mutated α1 subunits (αβ(L9′T) and α(L9′T)β(L9′T)), no response to GABA could be elicited: this was not due to an absence of GABAA receptors in the plasmalemma because the cells bound [3H]-muscimol. It was concluded that in GABAA channels containing the L9′T mutation in the β1 subunit, GABA-binding does not cause opening of channels, and that the L9′T mutation in either or both subunits gives an
open-channel state of the GABAA receptor in the absence of ligand.
Received: 17 April 1996/Revised: 5 July 1996 相似文献
18.
This article presents a space-variant version of a standard spatial filter model of texture segregation of the “back-pocket”
type (i.e., two filter layers with an intermediate pointwise nonlinearity). The model was tested with psychophysical data
from experiments with line textures in which target lines differed in orientation from background lines. The textures were
presented briefly and then masked. Segregation performance was evaluated along the horizontal meridian up to retinal eccentricities
of about 10 deg. Data are reported from two experiments with different line densities (Kehrer 1989) and two experiments with
different orientation contrasts between target lines and background lines (Kehrer 1990). Segregation performance proved to
depend strongly on these texture variations, and it peaked several degrees from fixation in all cases. The filter model provided
satisfactory predictions of experimental data when model parameters were adjusted appropriately. It is concluded (1) that
filter models defined in strictly spatial terms (i.e., without temporal properties) offer a sufficient framework to account
for the psychophysical data and (2) that the particular course of the performance curve (i.e., the performance peak outside
the central region) must be attributed to the characteristics of second-layer filters.
Received: 28 June 2001 / Accepted in revised form: 10 October 2002 / Published online: 13 February 2003
Correspondence to: L. Kehrer (e-mail: lothar.kehrer@uni-bielefeld.de)
Acknowledgements. This work was supported by Grant Ke 388/3-2 from the Deutsche Forschungsgemeinschaft (DFG). We wish to thank Jonathan Harrow
for improving the English text and an anonymous reviewer for many constructive comments. 相似文献
19.
A common theme of diverse neural systems is that circuits that are important for initial acquisition of learning do not necessarily serve as a substrate for the long-term storage of that memory. The neural basis of vocal learning in songbirds provides an example of this phenomenon, since a circuit that is necessary for vocal production during initial stages of vocal development apparently plays no subsequent role in controlling learned vocalizations. This striking functional change suggests the possibility of marked physiological changes in synaptic transmission within this circuit. We therefore examined intrinsic and synaptic properties of neurons in the cortical nucleus lMAN (lateral magnocellular nucleus of the anterior neostriatum), which forms part of this developmentally regulated circuit, in an in vitro preparation of the zebra finch forebrain. Although both functional and morphological characteristics of these neurons change substantially during vocal development, we did not observe widespread, substantive changes in the electrophysiological characteristics of juvenile versus adult lMAN neurons examined in vitro. Overall, both the intrinsic properties and synaptic responses of lMAN neurons were similar in slices from juvenile birds (at ages when lesions of lMAN disrupt vocal production) and in slices from adult birds (when lMAN lesions have no effect on song production). However, one intrinsic property that did vary between juvenile and adult cells was spike duration, which was longer in juvenile cells, suggesting the potential for activation of second-messenger cascades and/or enhanced synaptic transmission onto target cells of lMAN neurons. The pattern of synaptic response observed in both juvenile and adult cells suggests that lMAN projection neurons receive direct excitatory afferent inputs, as well as disynaptic inhibitory inputs from interneurons within lMAN. Activation of inhibitory interneurons rapidly curtails the excitatory response seen in projection neurons. This inhibition was abolished by bicuculline, indicating that the inhibitory interneurons normally exert their postsynaptic response via GABAA receptors on projection neurons. The inhibitory response could also be blocked by CNQX (6-cyano-7-nitroquinoxaline-2,3-dione), suggesting that the activation of inhibitory interneurons within lMAN may be governed primarily by AMPA receptors. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 642–658, 1998 相似文献
20.
Summary Glycine is one of the essential neurotransmitters modulating visual signals in retina. Glycine activates Cl- permeable receptors that conduct either inhibitory or excitatory actions, depending on the Cl− electrical–chemical gradient (E
Cl) positive or negative to the resting potential in the cells. Interestingly, both glycine-induced inhibitory and excitatory
responses are present in adult retinas, and the effects are confined in the inner and outer retinal neurons. Glycine inhibits
glutamate synapses in the inner plexiform layer (IPL), resulting in shaping light responses in ganglion cells. In contrast,
glycine excites horizontal cells and On-bipolar dendrites in the outer plexiform layer (OPL). The function of glycinergic
synapse in the outer retina represents the effect of network feedback from a group of centrifugal neurons, glycinergic interplexiform
cells. Moreover, immunocytochemical studies identify glycine receptor subunits (α1, α2, α3 and β) in retinas, forming picrotoxin-sensitive α-homomeric and picrotoxin-insensitive α/β-heteromeric receptors. Glycine receptors are modulated by intracellular Ca2+ and protein kinas C and A pathways. Extracellular Zn2+ regulates glycine receptors in a concentration-dependent manner, nanomolar Zn2+ enhancing glycine responses, and micromolar Zn2+ suppressing glycine responses in retinal neurons. These studies describe the function and mechanism of glycinergic synapses
in retinas. 相似文献