共查询到20条相似文献,搜索用时 15 毫秒
1.
Sound localization relies on minute differences in the timing and intensity of sound arriving at both ears. Neurons of the lateral superior olive (LSO) in the brainstem process these interaural disparities by precisely detecting excitatory and inhibitory synaptic inputs. Aging generally induces selective loss of inhibitory synaptic transmission along the entire auditory pathways, including the reduction of inhibitory afferents to LSO. Electrophysiological recordings in animals, however, reported only minor functional changes in aged LSO. The perplexing discrepancy between anatomical and physiological observations suggests a role for activity-dependent plasticity that would help neurons retain their binaural tuning function despite loss of inhibitory inputs. To explore this hypothesis, we use a computational model of LSO to investigate mechanisms underlying the observed functional robustness against age-related loss of inhibitory inputs. The LSO model is an integrate-and-fire type enhanced with a small amount of low-voltage activated potassium conductance and driven with (in)homogeneous Poissonian inputs. Without synaptic input loss, model spike rates varied smoothly with interaural time and level differences, replicating empirical tuning properties of LSO. By reducing the number of inhibitory afferents to mimic age-related loss of inhibition, overall spike rates increased, which negatively impacted binaural tuning performance, measured as modulation depth and neuronal discriminability. To simulate a recovery process compensating for the loss of inhibitory fibers, the strength of remaining inhibitory inputs was increased. By this modification, effects of inhibition loss on binaural tuning were considerably weakened, leading to an improvement of functional performance. These neuron-level observations were further confirmed by population modeling, in which binaural tuning properties of multiple LSO neurons were varied according to empirical measurements. These results demonstrate the plausibility that homeostatic plasticity could effectively counteract known age-dependent loss of inhibitory fibers in LSO and suggest that behavioral degradation of sound localization might originate from changes occurring more centrally. 相似文献
2.
Heidi K. Grnlien Arne M. Lvlie Olav Sand 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2001,130(4)
The ciliate Tetrahymena vorax is normally insensitive to light. However, after uptake of acridine orange, blue light evokes instant backward swimming. The dye accumulates mainly in posterior vacuoles, with half-maximal uptake after 1 min. Illumination for 10 s induced a depolarisation of approximately 15 mV lasting less than 2 s, followed by a sustained hyperpolarisation of approximately 20 mV. Deciliated cells displayed a similar response. The hyperpolarisation was linked to reduced membrane resistance, showed a reversal potential of approximately −55 mV and was blocked by 1 mmol l−1 TEA. The rate of rise of electrically evoked Ca2+-spikes was reduced during the hyperpolarisation, which is compatible with elevated cytosolic Ca2+ concentration. This suggests that the hyperpolarisation may be caused by activation of Ca2+-sensitive K+ channels. The depolarisation was abolished in Ca2+-free medium, whereas the hyperpolarisation was unaffected. Illumination for 2 s, or prolonged stimulation restricted to the anterior part of the cell, induced depolarisation only. Illumination of the posterior part caused delayed hyperpolarisation with no preceding depolarisation. We conclude that the induced backward swimming is associated with Ca2+ influx through anterior channels, while Ca2+ released from intracellular stores activates K+ channels responsible for the delayed hyperpolarisation. 相似文献
3.
Mathematical or computational models of activity–dependent neural competition typically impose competition in anatomically
fixed networks by the use of synaptic normalisation, for which there is very little experimental support. Recent experimental
evidence, however, strongly implicates neurotrophic factors in neural plasticity and competition, in addition to their well–known
potent effects on neurite outgrowth and synaptogenesis. We therefore present a simple, mathematical model of anatomical segregation
induced by activity–dependent competition for a limited supply of a neurotrophic factor provided by target cells to afferents.
We extract the behaviour of the model in various regimes, in which the neurotrophic factor is either in critical supply or
in abundant supply, by a combination of analytical and numerical methods, and study the effects of correlations in afferent
inputs on competition. We apply the model to three different systems: ocular dominance column formation; elimination of polyneuronal
innervation at the vertebrate neuromuscular junction; trigeminal brain stem whisker–related structure formation. Several classes
of related predictions emerge, including the prediction that kittens reared with strabismus should require a higher concentration
of neurotrophic factor infusion into their primary visual cortex than normally reared cats in order to induce the anatomical
desegregation of ocular dominance columns. We also speculate on the mechanisms of support of inhibitory rather than excitatory
neurons, and suggest the existence of a separate, Cl–mediated activity–dependent pathway for their neurotrophic support.
Received: 17 May 1996 / Accepted in revised form: 27 July 1996 相似文献
4.
Recent experimental data indicate that both neurotrophic factors (NTFs) and intracortical inhibitory circuitry are implicated
in the development and plasticity of ocular dominance columns. We extend a neurotrophic model of developmental synaptic plasticity,
which previously failed to account correctly for the differences between monocular deprivation and binocular deprivation,
and show that the inclusion of lateral cortical inhibition is indeed necessary in understanding the effects of visual deprivation
in the model. In particular, we argue that monocular deprivation causes a differential shift in the balance between inhibition
and excitation in cortical columns, down-regulating NTFs in deprived-eye columns and up-regulating NTFs in undeprived-eye
columns; during binocular deprivation, however, no such shift occurs. We thus postulate that the response to visual deprivation
is at the level of the cortical circuit, while the mechanisms of afferent segregation are at the molecular or cellular level.
Such a dissociation is supported by recent experimental work challenging the assumption that columnar organisation develops
in an activity-dependent, competitive fashion. Our extended model also questions recent attempts to distinguish between heterosynaptic
and homosynaptic models of synaptic plasticity.
Received: 17 April 2001 / Accepted in revised form: 7 November 2001 相似文献
5.
Y. Hosokawa J. Horikawa M. Nasu I. Taniguchi 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,181(6):607-614
Spatio-temporal patterns of binaural interaction in the guinea pig auditory cortex (AC) were observed using optical recording
with a 12 × 12 photodiode array and a voltage-sensitive dye. The amplitudes of the sound-induced light signals from the cortex
were transformed into sequential two-dimensional images every 0.58 ms. Binaural sound stimuli evoked an excitatory response
followed by a strong inhibition, and contralateral stimuli evoked a strong excitatory response followed by a weak inhibition.
Ipsilateral sound stimuli evoked a weak response. Binaural stimulation induced two types of ipsilateral inhibition: a fast
binaural inhibition which was detected only after the contralateral and ipsilateral responses were subtracted from the binaural
responses, and which appeared 12–25 ms after the onset of stimulation, and a slow binaural inhibitory effect which was clearly
observed in the binaural responses themselves, appearing 70–95 ms after the onset of stimulation. The fast binaural inhibition
was observed in the same area as the contralateral excitatory response. The inhibited area became stronger and more widespread
with increasing intensity of ipsilateral stimulation. We did not observe the specialized organization of binaural neurons
as electrophysiologically found in the cat AC, in which binaural neurons of the same binaural response type are clustered
together and alternate with clusters of other response types.
Accepted: 14 August 1997 相似文献
6.
Kandler K 《Current opinion in neurobiology》2004,14(1):96-104
In contrast to our detailed knowledge about the development and plasticity of excitatory neuronal circuits, little is known about the development of inhibitory circuits. Recent studies from the developing mammalian auditory system have revealed the presence of substantial activity-dependent synaptic reorganization in several inhibitory pathways. These studies importantly shed some new light on the general rules and cellular mechanisms that manage the organization of precise inhibitory circuits in the developing brain. 相似文献
7.
H K Gr?nlien A M L?vlie O Sand 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2001,130(4):633-641
The ciliate Tetrahymena vorax is normally insensitive to light. However, after uptake of acridine orange, blue light evokes instant backward swimming. The dye accumulates mainly in posterior vacuoles, with half-maximal uptake after 1 min. Illumination for 10 s induced a depolarisation of approximately 15 mV lasting less than 2 s, followed by a sustained hyperpolarisation of approximately 20 mV. Deciliated cells displayed a similar response. The hyperpolarisation was linked to reduced membrane resistance, showed a reversal potential of approximately -55 mV and was blocked by 1 mmol l(-1) TEA. The rate of rise of electrically evoked Ca(2+)-spikes was reduced during the hyperpolarisation, which is compatible with elevated cytosolic Ca(2+) concentration. This suggests that the hyperpolarisation may be caused by activation of Ca(2+)-sensitive K(+) channels. The depolarisation was abolished in Ca(2+)-free medium, whereas the hyperpolarisation was unaffected. Illumination for 2 s, or prolonged stimulation restricted to the anterior part of the cell, induced depolarisation only. Illumination of the posterior part caused delayed hyperpolarisation with no preceding depolarisation. We conclude that the induced backward swimming is associated with Ca(2+) influx through anterior channels, while Ca(2+) released from intracellular stores activates K(+) channels responsible for the delayed hyperpolarisation. 相似文献
8.
Speech and birdsong require auditory feedback for their development and maintenance, necessitating precise auditory encoding of vocal sounds. In songbirds, the telencephalic song premotor nucleus HVC contains neurons that respond highly selectively to the bird's own song (BOS), a property distinguishing HVC from its auditory afferents. We examined the contribution of inhibitory and excitatory synaptic inputs to BOS-evoked firing in those HVC neurons innervating a pathway essential for audition-dependent vocal plasticity. Using in vivo intracellular techniques, we found that G protein-coupled, potassium-mediated inhibition, tuned to the BOS, interacts with BOS-tuned excitation through several mechanisms to shape neuronal firing patterns. Furthermore, in the absence of this inhibition, the response bias to the BOS increases, reminiscent of cancellation mechanisms in other sensorimotor systems. 相似文献
9.
10.
Gaïarsa JL 《Journal of cellular and molecular medicine》2004,8(1):31-37
While the development and plasticity of excitatory synaptic connections have been studied into detail, little is known about the development of inhibitory synapses. As proposed for excitatory synapses, recent studies have indicated that activity-dependent forms of synaptic plasticity, such as long-term potentiation and long-term depression, may play a role in the establishment of functional inhibitory synaptic connections. Here, I review these different forms of plasticity and focus on their possible role in the developing neuronal network. 相似文献
11.
Nikodemus Gessele Elisabet Garcia-Pino Damir Omerba?i? Thomas J. Park Ursula Koch 《PloS one》2016,11(1)
Naked mole-rats (Heterocephalus glaber) live in large eu-social, underground colonies in narrow burrows and are exposed to a large repertoire of communication signals but negligible binaural sound localization cues, such as interaural time and intensity differences. We therefore asked whether monaural and binaural auditory brainstem nuclei in the naked mole-rat are differentially adjusted to this acoustic environment. Using antibody stainings against excitatory and inhibitory presynaptic structures, namely the vesicular glutamate transporter VGluT1 and the glycine transporter GlyT2 we identified all major auditory brainstem nuclei except the superior paraolivary nucleus in these animals. Naked mole-rats possess a well structured medial superior olive, with a similar synaptic arrangement to interaural-time-difference encoding animals. The neighboring lateral superior olive, which analyzes interaural intensity differences, is large and elongated, whereas the medial nucleus of the trapezoid body, which provides the contralateral inhibitory input to these binaural nuclei, is reduced in size. In contrast, the cochlear nucleus, the nuclei of the lateral lemniscus and the inferior colliculus are not considerably different when compared to other rodent species. Most interestingly, binaural auditory brainstem nuclei lack the membrane-bound hyperpolarization-activated channel HCN1, a voltage-gated ion channel that greatly contributes to the fast integration times in binaural nuclei of the superior olivary complex in other species. This suggests substantially lengthened membrane time constants and thus prolonged temporal integration of inputs in binaural auditory brainstem neurons and might be linked to the severely degenerated sound localization abilities in these animals. 相似文献
12.
Homeostatic synaptic plasticity, or synaptic scaling, is a mechanism that tunes neuronal transmission to compensate for prolonged, excessive changes in neuronal activity. Both excitatory and inhibitory neurons undergo homeostatic changes based on synaptic transmission strength, which could effectively contribute to a fine-tuning of circuit activity. However, gene regulation that underlies homeostatic synaptic plasticity in GABAergic (GABA, gamma aminobutyric) neurons is still poorly understood. The present study demonstrated activity-dependent dynamic scaling in which NMDA-R (N-methyl-D-aspartic acid receptor) activity regulated the expression of GABA synthetic enzymes: glutamic acid decarboxylase 65 and 67 (GAD65 and GAD67). Results revealed that activity-regulated BDNF (brain-derived neurotrophic factor) release is necessary, but not sufficient, for activity-dependent up-scaling of these GAD isoforms. Bidirectional forms of activity-dependent GAD expression require both BDNF-dependent and BDNF-independent pathways, both triggered by NMDA-R activity. Additional results indicated that these two GAD genes differ in their responsiveness to chronic changes in neuronal activity, which could be partially caused by differential dependence on BDNF. In parallel to activity-dependent bidirectional scaling in GAD expression, the present study further observed that a chronic change in neuronal activity leads to an alteration in neurotransmitter release from GABAergic neurons in a homeostatic, bidirectional fashion. Therefore, the differential expression of GAD65 and 67 during prolonged changes in neuronal activity may be implicated in some aspects of bidirectional homeostatic plasticity within mature GABAergic presynapses. 相似文献
13.
14.
Central processing of acoustic cues is critically dependent on the balance between excitation and inhibition. This balance is particularly important for auditory neurons in the lateral superior olive, because these compare excitatory inputs from one ear and inhibitory inputs from the other ear to compute sound source location. By applying GABA(B) receptor antagonists during sound stimulation in vivo, it was revealed that these neurons adjust their binaural sensitivity through GABA(B) receptors. Using an in vitro approach, we then demonstrate that these neurons release GABA during spiking activity. Consequently, GABA differentially regulates transmitter release from the excitatory and inhibitory terminals via feedback to presynaptic GABA(B) receptors. Modulation of the synaptic input strength, by putative retrograde release of neurotransmitter, may enable these auditory neurons to rapidly adjust the balance between excitation and inhibition, and thus their binaural sensitivity, which could play an important role as an adaptation to various listening situations. 相似文献
15.
16.
Synaptic secretion of BDNF after high-frequency stimulation of glutamatergic synapses. 总被引:10,自引:0,他引:10
The protein brain-derived neurotrophic factor (BDNF) has been postulated to be a retrograde or paracrine synaptic messenger in long-term potentiation and other forms of activity-dependent synaptic plasticity. Although crucial for this concept, direct evidence for the activity-dependent synaptic release of BDNF is lacking. Here we investigate secretion of BDNF labelled with green fluorescent protein (BDNF-GFP) by monitoring the changes in fluorescence intensity of dendritic BDNF-GFP vesicles at glutamatergic synaptic junctions of living hippocampal neurons. We show that high-frequency activation of glutamatergic synapses triggers the release of BDNF-GFP from synaptically localized secretory granules. This release depends on activation of postsynaptic ionotropic glutamate receptors and on postsynaptic Ca(2+) influx. Release of BDNF-GFP is also observed from extrasynaptic dendritic vesicle clusters, suggesting that a possible spatial restriction of BDNF release to specific synaptic sites can only occur if the postsynaptic depolarization remains local. These results support the concept of BDNF being a synaptic messenger of activity-dependent synaptic plasticity, which is released from postsynaptic neurons. 相似文献
17.
Nicholas Fisher Sachin S. Talathi Paul R. Carney William L. Ditto 《Biological cybernetics》2010,102(5):427-440
Recent experimental results by Talathi et al. (Neurosci Lett 455:145–149, 2009) showed a divergence in the spike rates of
two types of population spike events, representing the putative activity of the excitatory and inhibitory neurons in the CA1
area of an animal model for temporal lobe epilepsy. The divergence in the spike rate was accompanied by a shift in the phase
of oscillations between these spike rates leading to a spontaneous epileptic seizure. In this study, we propose a model of
homeostatic synaptic plasticity which assumes that the target spike rate of populations of excitatory and inhibitory neurons in the brain is a function of the phase difference between the excitatory
and inhibitory spike rates. With this model of homeostatic synaptic plasticity, we are able to simulate the spike rate dynamics
seen experimentally by Talathi et al. in a large network of interacting excitatory and inhibitory neurons using two different
spiking neuron models. A drift analysis of the spike rates resulting from the homeostatic synaptic plasticity update rule
allowed us to determine the type of synapse that may be primarily involved in the spike rate imbalance in the experimental
observation by Talathi et al. We find excitatory neurons, particularly those in which the excitatory neuron is presynaptic,
have the most influence in producing the diverging spike rates and causing the spike rates to be anti-phase. Our analysis
suggests that the excitatory neuronal population, more specifically the excitatory to excitatory synaptic connections, could
be implicated in a methodology designed to control epileptic seizures. 相似文献
18.
Background
Vestibulo-ocular reflex (VOR) gain adaptation, a longstanding experimental model of cerebellar learning, utilizes sites of plasticity in both cerebellar cortex and brainstem. However, the mechanisms by which the activity of cortical Purkinje cells may guide synaptic plasticity in brainstem vestibular neurons are unclear. Theoretical analyses indicate that vestibular plasticity should depend upon the correlation between Purkinje cell and vestibular afferent inputs, so that, in gain-down learning for example, increased cortical activity should induce long-term depression (LTD) at vestibular synapses.Methodology/Principal Findings
Here we expressed this correlational learning rule in its simplest form, as an anti-Hebbian, heterosynaptic spike-timing dependent plasticity interaction between excitatory (vestibular) and inhibitory (floccular) inputs converging on medial vestibular nucleus (MVN) neurons (input-spike-timing dependent plasticity, iSTDP). To test this rule, we stimulated vestibular afferents to evoke EPSCs in rat MVN neurons in vitro. Control EPSC recordings were followed by an induction protocol where membrane hyperpolarizing pulses, mimicking IPSPs evoked by flocculus inputs, were paired with single vestibular nerve stimuli. A robust LTD developed at vestibular synapses when the afferent EPSPs coincided with membrane hyperpolarisation, while EPSPs occurring before or after the simulated IPSPs induced no lasting change. Furthermore, the iSTDP rule also successfully predicted the effects of a complex protocol using EPSP trains designed to mimic classical conditioning.Conclusions
These results, in strong support of theoretical predictions, suggest that the cerebellum alters the strength of vestibular synapses on MVN neurons through hetero-synaptic, anti-Hebbian iSTDP. Since the iSTDP rule does not depend on post-synaptic firing, it suggests a possible mechanism for VOR adaptation without compromising gaze-holding and VOR performance in vivo. 相似文献19.
Cynthia F. Barber Ramon A. Jorquera Jan E. Melom J. Troy Littleton 《The Journal of cell biology》2009,187(2):295-310
Ca2+ influx into synaptic compartments during activity is a key mediator of neuronal plasticity. Although the role of presynaptic Ca2+ in triggering vesicle fusion though the Ca2+ sensor synaptotagmin 1 (Syt 1) is established, molecular mechanisms that underlie responses to postsynaptic Ca2+ influx remain unclear. In this study, we demonstrate that fusion-competent Syt 4 vesicles localize postsynaptically at both neuromuscular junctions (NMJs) and central nervous system synapses in Drosophila melanogaster. Syt 4 messenger RNA and protein expression are strongly regulated by neuronal activity, whereas altered levels of postsynaptic Syt 4 modify synaptic growth and presynaptic release properties. Syt 4 is required for known forms of activity-dependent structural plasticity at NMJs. Synaptic proliferation and retrograde signaling mediated by Syt 4 requires functional C2A and C2B Ca2+–binding sites, as well as serine 284, an evolutionarily conserved substitution for a key Ca2+-binding aspartic acid found in other synaptotagmins. These data suggest that Syt 4 regulates activity-dependent release of postsynaptic retrograde signals that promote synaptic plasticity, similar to the role of Syt 1 as a Ca2+ sensor for presynaptic vesicle fusion. 相似文献
20.
The activity-dependent modulation of GABA-A receptor (GABA(A)R) clustering at synapses controls inhibitory synaptic transmission. Several lines of evidence suggest that gephyrin, an inhibitory synaptic scaffold protein, is a critical factor in the regulation of GABA(A)R clustering during inhibitory synaptic plasticity induced by neuronal excitation. In this study, we tested this hypothesis by studying relative gephyrin dynamics and GABA(A)R declustering during excitatory activity. Surprisingly, we found that gephyrin dispersal is not essential for GABA(A)R declustering during excitatory activity. In cultured hippocampal neurons, quantitative immunocytochemistry showed that the dispersal of synaptic GABA(A)Rs accompanied with neuronal excitation evoked by 4-aminopyridine (4AP) or N-methyl-D-aspartic acid (NMDA) precedes that of gephyrin. Single-particle tracking of quantum dot labeled-GABA(A)Rs revealed that excitation-induced enhancement of GABA(A)R lateral mobility also occurred before the shrinkage of gephyrin clusters. Physical inhibition of GABA(A)R lateral diffusion on the cell surface and inhibition of a Ca(2+) dependent phosphatase, calcineurin, completely eliminated the 4AP-induced decrease in gephyrin cluster size, but not the NMDA-induced decrease in cluster size, suggesting the existence of two different mechanisms of gephyrin declustering during activity-dependent plasticity, a GABA(A)R-dependent regulatory mechanism and a GABA(A)R-independent one. Our results also indicate that GABA(A)R mobility and clustering after sustained excitatory activity is independent of gephyrin. 相似文献