1
|
Manis PB, Kasten MR, Xie R. Classification of neurons in the adult mouse cochlear nucleus: Linear discriminant analysis. PLoS One 2019; 14:e0223137. [PMID: 31581200 PMCID: PMC6776397 DOI: 10.1371/journal.pone.0223137] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Accepted: 09/13/2019] [Indexed: 12/23/2022] Open
Abstract
The cochlear nucleus (CN) transforms the spike trains of spiral ganglion cells into a set of sensory representations that are essential for auditory discriminations and perception. These transformations require the coordinated activity of different classes of neurons that are embryologically derived from distinct sets of precursors. Decades of investigation have shown that the neurons of the CN are differentiated by their morphology, neurotransmitter receptors, ion channel expression and intrinsic excitability. In the present study we have used linear discriminant analysis (LDA) to perform an unbiased analysis of measures of the responses of CN neurons to current injections to objectively categorize cells on the basis of both morphology and physiology. Recordings were made from cells in brain slices from CBA/CaJ mice and a transgenic mouse line, NF107, crossed against the Ai32 line. For each cell, responses to current injections were analyzed for spike rate, spike shape, input resistance, resting membrane potential, membrane time constant, hyperpolarization-activated sag and time constant. Cells were filled with dye for morphological classification, and visually classified according to published accounts. The different morphological classes of cells were separated with the LDA. Ventral cochlear nucleus (VCN) bushy cells, planar multipolar (T-stellate) cells, and radiate multipolar (D-stellate) cells were in separate clusters and separate from all of the neurons from the dorsal cochlear nucleus (DCN). Within the DCN, the pyramidal cells and tuberculoventral cells were largely separated from a distinct cluster of cartwheel cells. principal axes, whereas VCN cells were in 3 clouds approximately orthogonal to this plane. VCN neurons from the two mouse strains overlapped but were slightly separated, indicating either a strain dependence or differences in slice preparation methods. We conclude that cochlear nucleus neurons can be objectively distinguished based on their intrinsic electrical properties, but such distinctions are still best aided by morphological identification.
Collapse
Affiliation(s)
- Paul B. Manis
- Department of Otolaryngology/Head and Neck Surgery, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- * E-mail:
| | - Michael R. Kasten
- Department of Otolaryngology/Head and Neck Surgery, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Ruili Xie
- Department of Otolaryngology, The Ohio State University, Columbus, Ohio, United States of America
| |
Collapse
|
2
|
Yang S, Ben-Shalom R, Ahn M, Liptak AT, van Rijn RM, Whistler JL, Bender KJ. β-Arrestin-Dependent Dopaminergic Regulation of Calcium Channel Activity in the Axon Initial Segment. Cell Rep 2016; 16:1518-1526. [PMID: 27452469 DOI: 10.1016/j.celrep.2016.06.098] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2016] [Revised: 05/27/2016] [Accepted: 06/29/2016] [Indexed: 11/26/2022] Open
Abstract
G-protein-coupled receptors (GPCRs) initiate a variety of signaling cascades, depending on effector coupling. β-arrestins, which were initially characterized by their ability to "arrest" GPCR signaling by uncoupling receptor and G protein, have recently emerged as important signaling effectors for GPCRs. β-arrestins engage signaling pathways that are distinct from those mediated by G protein. As such, arrestin-dependent signaling can play a unique role in regulating cell function, but whether neuromodulatory GPCRs utilize β-arrestin-dependent signaling to regulate neuronal excitability remains unclear. Here, we find that D3 dopamine receptors (D3R) regulate axon initial segment (AIS) excitability through β-arrestin-dependent signaling, modifying CaV3 voltage dependence to suppress high-frequency action potential generation. This non-canonical D3R signaling thereby gates AIS excitability via pathways distinct from classical GPCR signaling pathways.
Collapse
Affiliation(s)
- Sungchil Yang
- Center for Integrative Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA; Alcohol and Addiction Research Group, Department of Neurology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Roy Ben-Shalom
- Center for Integrative Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA; Alcohol and Addiction Research Group, Department of Neurology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Misol Ahn
- Department of Pathology and Institute for Neurodegenerative Diseases, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Alayna T Liptak
- Center for Integrative Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA; Alcohol and Addiction Research Group, Department of Neurology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Richard M van Rijn
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, IN 47907, USA
| | - Jennifer L Whistler
- Alcohol and Addiction Research Group, Department of Neurology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Kevin J Bender
- Center for Integrative Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA; Alcohol and Addiction Research Group, Department of Neurology, University of California, San Francisco, San Francisco, CA 94158, USA.
| |
Collapse
|
3
|
Abstract
The dorsal cochlear nucleus (DCN) is one of the first stations within the central auditory pathway where the basic computations underlying sound localization are initiated and heightened activity in the DCN may underlie central tinnitus. The neurotransmitter serotonin (5-hydroxytryptamine; 5-HT), is associated with many distinct behavioral or cognitive states, and serotonergic fibers are concentrated in the DCN. However, it remains unclear what is the function of this dense input. Using a combination of in vitro electrophysiology and optogenetics in mouse brain slices, we found that 5-HT directly enhances the excitability of fusiform principal cells via activation of two distinct 5-HT receptor subfamilies, 5-HT2A/2CR (5-HT2A/2C receptor) and 5-HT7R (5-HT7 receptor). This excitatory effect results from an augmentation of hyperpolarization-activated cyclic nucleotide-gated channels (Ih or HCN channels). The serotonergic regulation of excitability is G-protein-dependent and involves cAMP and Src kinase signaling pathways. Moreover, optogenetic activation of serotonergic axon terminals increased excitability of fusiform cells. Our findings reveal that 5-HT exerts a potent influence on fusiform cells by altering their intrinsic properties, which may enhance the sensitivity of the DCN to sensory input.
Collapse
|
4
|
Apostolides PF, Trussell LO. Regulation of interneuron excitability by gap junction coupling with principal cells. Nat Neurosci 2013; 16:1764-72. [PMID: 24185427 PMCID: PMC3963432 DOI: 10.1038/nn.3569] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Accepted: 09/30/2013] [Indexed: 12/14/2022]
Abstract
Electrical coupling of inhibitory interneurons can synchronize activity across multiple neurons, thereby enhancing the reliability of inhibition onto principal cell targets. It is unclear whether downstream activity in principal cells controls the excitability of such inhibitory networks. Using paired patch-clamp recordings, we show that excitatory projection neurons (fusiform cells) and inhibitory stellate interneurons of the dorsal cochlear nucleus form an electrically coupled network through gap junctions containing connexin36 (Cxc36, also called Gjd2). Remarkably, stellate cells were more strongly coupled to fusiform cells than to other stellate cells. This heterologous coupling was functionally asymmetric, biasing electrical transmission from the principal cell to the interneuron. Optogenetically activated populations of fusiform cells reliably enhanced interneuron excitability and generated GABAergic inhibition onto the postsynaptic targets of stellate cells, whereas deep afterhyperpolarizations following fusiform cell spike trains potently inhibited stellate cells over several hundred milliseconds. Thus, the excitability of an interneuron network is bidirectionally controlled by distinct epochs of activity in principal cells.
Collapse
Affiliation(s)
- Pierre F Apostolides
- 1] Neuroscience Graduate Program, Oregon Health and Science University, Portland, Oregon, USA. [2] Vollum Institute and Oregon Hearing Research Center, Oregon Health and Science University, Portland, Oregon, USA
| | | |
Collapse
|
5
|
Golding NL. Neuronal Response Properties and Voltage-Gated Ion Channels in the Auditory System. SYNAPTIC MECHANISMS IN THE AUDITORY SYSTEM 2012. [DOI: 10.1007/978-1-4419-9517-9_2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
|
6
|
Sustained firing of cartwheel cells in the dorsal cochlear nucleus evokes endocannabinoid release and retrograde suppression of parallel fiber synapses. J Neurosci 2011; 31:15807-17. [PMID: 22049424 DOI: 10.1523/jneurosci.4088-11.2011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Neurons in many brain regions release endocannabinoids from their dendrites that act as retrograde signals to transiently suppress neurotransmitter release from presynaptic terminals. Little is known, however, about the physiological mechanisms of short-term endocannabinoid-mediated plasticity under physiological conditions. Here we investigate calcium-dependent endocannabinoid release from cartwheel cells (CWCs) of the mouse dorsal cochlear nucleus (DCN) in the auditory brainstem that provide feedforward inhibition onto DCN principal neurons. We report that sustained action potential firing by CWCs evokes endocannabinoid release in response to submicromolar elevation of dendritic calcium that transiently suppresses their parallel fiber (PF) inputs by >70%. Basal spontaneous CWC firing rates are insufficient to evoke tonic suppression of PF synapses. However, elevating CWC firing rates by stimulating PFs triggers the release of endocannabinoids and heterosynaptic suppression of PF inputs. Spike-evoked suppression by endocannabinoids selectively suppresses excitatory synapses, but glycinergic/GABAergic inputs onto CWCs are not affected. Our findings demonstrate a mechanism of transient plasticity mediated by endocannabinoids that heterosynaptically suppresses subsets of excitatory presynaptic inputs to CWCs that regulates feedforward inhibition of DCN principal neurons and may influence the output of the DCN.
Collapse
|
7
|
Bender KJ, Ford CP, Trussell LO. Dopaminergic modulation of axon initial segment calcium channels regulates action potential initiation. Neuron 2010; 68:500-11. [PMID: 21040850 DOI: 10.1016/j.neuron.2010.09.026] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/08/2010] [Indexed: 11/18/2022]
Abstract
Action potentials initiate in the axon initial segment (AIS), a specialized compartment enriched with Na(+) and K(+) channels. Recently, we found that T- and R-type Ca(2+) channels are concentrated in the AIS, where they contribute to local subthreshold membrane depolarization and thereby influence action potential initiation. While periods of high-frequency activity can alter availability of AIS voltage-gated channels, mechanisms for long-term modulation of AIS channel function remain unknown. Here, we examined the regulatory pathways that control AIS Ca(2+) channel activity in brainstem interneurons. T-type Ca(2+) channels were downregulated by dopamine receptor activation acting via protein kinase C, which in turn reduced neuronal output. These effects occurred without altering AIS Na(+) or somatodendritic T-type channel activity and could be mediated by endogenous dopamine sources present in the auditory brainstem. This pathway represents a new mechanism to inhibit neurons by specifically regulating Ca(2+) channels directly involved in action potential initiation.
Collapse
Affiliation(s)
- Kevin J Bender
- Oregon Hearing Research Center, Oregon Health and Science University, Portland, OR 97239, USA.
| | | | | |
Collapse
|
8
|
Negative shift in the glycine reversal potential mediated by a Ca2+- and pH-dependent mechanism in interneurons. J Neurosci 2009; 29:11495-510. [PMID: 19759298 DOI: 10.1523/jneurosci.1086-09.2009] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Cartwheel cells are glycinergic auditory interneurons which fire Na(+)- and Ca(2+)-dependent spike bursts, termed complex spikes, and which synapse on both principal cells and one another. The reversal potential for glycine (E(gly)) can be hyperpolarizing or depolarizing in cartwheel cells, and many cells are even excited by glycine. We explored the role of spike activity in determining E(gly) in mouse cartwheel cells using gramicidin perforated-patch recording. E(gly) was found to shift toward more negative potentials after a period of complex spiking or Ca(2+) spiking induced by depolarization, thus enhancing glycine's inhibitory effect for approximately 30 s following cessation of spiking. Combined perforated patch electrophysiology and imaging studies showed that the negative E(gly) shift was triggered by a Ca(2+)-dependent intracellular acidification. The effect on E(gly) was likely caused by bicarbonate-Cl(-) exchanger-mediated reduction in intracellular Cl(-), as H(2)DIDS and removal of HCO(3)(-)/CO(2) inhibited the negative E(gly) shift. The outward Cl(-) flux underlying the negative shift in E(gly) opposed a positive shift triggered by passive Cl(-) redistribution during the depolarization. Thus, a Ca(2+)-dependent mechanism serves to maintain or enhance the strength of inhibition in the face of increased excitatory activity.
Collapse
|
9
|
Finlayson PG, Kaltenbach JA. Alterations in the spontaneous discharge patterns of single units in the dorsal cochlear nucleus following intense sound exposure. Hear Res 2009; 256:104-17. [PMID: 19622390 DOI: 10.1016/j.heares.2009.07.006] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2009] [Revised: 07/14/2009] [Accepted: 07/15/2009] [Indexed: 10/20/2022]
Abstract
Electrophysiological recordings in the dorsal cochlear nucleus (DCN) were conducted to determine the nature of changes in single unit activity following intense sound exposure and how they relate to changes in multiunit activity. Single and multiunit spontaneous discharge rates and auditory response properties were recorded from the left DCN of tone exposed and control hamsters. The exposure condition consisted of a 10 kHz tone presented in the free-field at a level of 115 dB for 4h. Recordings conducted at 5-6 days post-exposure revealed several important changes. Increases in multiunit spontaneous neural activity were observed at surface and subsurface levels of the DCN of exposed animals, reaching a peak at intermediate depths corresponding to the fusiform cell layer and upper level of the deep layer. Extracellular spikes from single units in the DCN of both control and exposed animals characteristically displayed either M- or W-shaped waveforms, although the proportion of units with M-shaped spikes was higher in exposed animals than in controls. W-shaped spikes showed significant increases in the duration of their major peaks after exposure, suggestive of changes in the intrinsic membrane properties of neurons. Spike amplitudes were not found to be significantly increased in exposed animals. Spontaneous discharge rates of single units increased significantly from 8.7 spikes/s in controls to 15.9 spikes/s after exposure. Units with the highest activity in exposed animals displayed type III electrophysiological responses patterns, properties usually attributed to fusiform cells. Increases in spontaneous discharge rate were significantly larger when the comparison was limited to a subset of units having type III frequency response patterns. There was an increase in the incidence of simple spiking activity as well as in the incidence of spontaneous bursting activity, although the incidence of spikes occurring in bursts was low in both animal groups (i.e., <30%). Despite this low incidence, approximately half of the increase in spontaneous activity in exposed animals was accounted for by an increase in bursting activity. Finally, we found no evidence of an increase in the mean number of spontaneously active units in electrode penetrations of exposed animals compared to those in controls. Overall our results indicate that the increase in multiunit activity observed at the DCN surface reflects primarily an increase in the spontaneous discharge rates of single units below the DCN surface, of which approximately half was contributed by spikes in bursts. The highest level of hyperactivity was observed among units having the response properties most commonly attributed to fusiform cells.
Collapse
Affiliation(s)
- Paul G Finlayson
- Department of Otolaryngology, Wayne State University School of Medicine, 5E-UHC, Detroit, MI 48201, USA.
| | | |
Collapse
|
10
|
Blackmer T, Kuo SP, Bender KJ, Apostolides PF, Trussell LO. Dendritic calcium channels and their activation by synaptic signals in auditory coincidence detector neurons. J Neurophysiol 2009; 102:1218-26. [PMID: 19553482 DOI: 10.1152/jn.90513.2008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The avian nucleus laminaris (NL) encodes the azimuthal location of low-frequency sound sources by detecting the coincidence of binaural signals. Accurate coincidence detection requires precise developmental regulation of the lengths of the fine, bitufted dendrites that characterize neurons in NL. Such regulation has been suggested to be driven by local, synaptically mediated, dendritic signals such as Ca(2+). We examined Ca(2+) signaling through patch clamp and ion imaging experiments in slices containing nucleus laminaris from embryonic chicks. Voltage-clamp recordings of neurons located in the NL showed the presence of large Ca(2+) currents of two types, a low voltage-activated, fast inactivating Ni(2+) sensitive channel resembling mammalian T-type channels, and a high voltage-activated, slowly inactivating Cd(2+) sensitive channel. Two-photon Ca(2+) imaging showed that both channel types were concentrated on dendrites, even at their distal tips. Single action potentials triggered synaptically or by somatic current injection immediately elevated Ca(2+) throughout the entire cell. Ca(2+) signals triggered by subthreshold synaptic activity were highly localized. Thus when electrical activity is suprathreshold, Ca(2+) channels ensure that Ca(2+) rises in all dendrites, even those that are synaptically inactive.
Collapse
Affiliation(s)
- Trillium Blackmer
- Vollum Institute and Oregon Hearing Research Center, Oregon Health and Science University, Portland, Oregon 97239, USA
| | | | | | | | | |
Collapse
|
11
|
Mancilla JG, Manis PB. Two distinct types of inhibition mediated by cartwheel cells in the dorsal cochlear nucleus. J Neurophysiol 2009; 102:1287-95. [PMID: 19474167 DOI: 10.1152/jn.91272.2008] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Individual neurons have been shown to exhibit target cell-specific synaptic function in several brain areas. The time course of the postsynaptic conductances (PSCs) strongly influences the dynamics of local neural networks. Cartwheel cells (CWCs) are the most numerous inhibitory interneurons in the dorsal cochlear nucleus (DCN). They are excited by parallel fiber synapses, which carry polysensory information, and in turn inhibit other CWCs and the main projection neurons of the DCN, pyramidal cells (PCs). CWCs have been implicated in "context-dependent" inhibition, producing either depolarizing (other CWCs) or hyperpolarizing (PCs) post synaptic potentials. In the present study, we used paired whole cell recordings to examine target-dependent inhibition from CWCs in neonatal rat DCN slices. We found that CWC inhibitory postsynaptic potentials (IPSPs) onto PCs are large (1.3 mV) and brief (half-width = 11.8 ms), whereas CWC IPSPs onto other CWCs are small (0.2 mV) and slow (half-width = 36.8 ms). Evoked IPSPs between CWCs exhibit paired-pulse facilitation, while CWC IPSPs onto PCs exhibit paired-pulse depression. Perforated-patch recordings showed that spontaneous IPSPs in CWCs are hyperpolarizing at rest with a mean estimated reversal potential of -67 mV. Spontaneous IPSCs were smaller and lasted longer in CWCs than in PCs, suggesting that the kinetics of the receptors are different in the two cell types. These results reveal that CWCs play a dual role in the DCN. The CWC-CWC network interactions are slow and sensitive to the average rate of CWC firing, whereas the CWC-PC network is fast and sensitive to transient changes in CWC firing.
Collapse
Affiliation(s)
- Jaime G Mancilla
- Department of Otolaryngology/Head and Neck Surgery, University of North Carolina, Chapel Hill, North Carolina 27599-7070, USA
| | | |
Collapse
|
12
|
Bender KJ, Trussell LO. Axon initial segment Ca2+ channels influence action potential generation and timing. Neuron 2009; 61:259-71. [PMID: 19186168 DOI: 10.1016/j.neuron.2008.12.004] [Citation(s) in RCA: 120] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Revised: 10/30/2008] [Accepted: 12/01/2008] [Indexed: 12/31/2022]
Abstract
Although action potentials are typically generated in the axon initial segment (AIS), the timing and pattern of action potentials are thought to depend on inward current originating in somatodendritic compartments. Using two-photon imaging, we show that T- and R-type voltage-gated Ca(2+) channels are colocalized with Na(+) channels in the AIS of dorsal cochlear nucleus interneurons and that activation of these Ca(2+) channels is essential to the generation and timing of action potential bursts known as complex spikes. During complex spikes, where Na(+)-mediated spikelets fire atop slower depolarizing conductances, selective block of AIS Ca(2+) channels delays spike timing and raises spike threshold. Furthermore, AIS Ca(2+) channel block can decrease the number of spikelets within a complex spike and can even block single, simple spikes. Similar results were found in cortex and cerebellum. Thus, voltage-gated Ca(2+) channels at the site of spike initiation play a key role in generating and shaping spike bursts.
Collapse
Affiliation(s)
- Kevin J Bender
- Vollum Institute and Oregon Hearing Research Center, Oregon Health and Science University, Portland, OR 97239, USA.
| | | |
Collapse
|
13
|
Fidelity of complex spike-mediated synaptic transmission between inhibitory interneurons. J Neurosci 2008; 28:9440-50. [PMID: 18799676 DOI: 10.1523/jneurosci.2226-08.2008] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Complex spikes are high-frequency bursts of Na+ spikes, often riding on a slower Ca2+-dependent waveform. Although complex spikes may propagate into axons, given their unusual shape it is not clear how reliably these bursts reach nerve terminals, whether their spikes are efficiently transmitted as a cluster of postsynaptic responses, or what function is served by such a concentrated postsynaptic signal. We examined these questions by recording from synaptically coupled pairs of cartwheel cells, neurons which fire complex spikes and form an inhibitory network in the dorsal cochlear nucleus. Complex spikes in the presynaptic soma were reliably propagated to nerve terminals and elicited powerful, temporally precise postsynaptic responses. Single presynaptic neurons could prevent their postsynaptic partner from firing complex but not simple spikes, dramatically reducing dendritic Ca2+ signals in the postsynaptic neuron. We suggest that rapid transmission of complex spikes may control the susceptibility of neighboring neurons to Ca2+-dependent plasticity.
Collapse
|
14
|
Gradwohl G, Grossman Y. Analysis of the Interaction Between the Dendritic Conductance Density and Activated Area in Modulating α-Motoneuron EPSP: Statistical Computer Model. Neural Comput 2008; 20:1385-410. [DOI: 10.1162/neco.2008.03-07-490] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Five reconstructed α-motoneurons (MNs) are simulated under physiological and morphological realistic parameters. We compare the resulting excitatory postsynaptic potential (EPSP) of models, containing voltage-dependent channels on the dendrites, with the EPSP of a passive MN and an active soma and axon model. In our simulations, we apply three different distribution functions of the voltage-dependent channels on the dendrites: a step function (ST) with uniform spatial dispersion; an exponential decay (ED) function, with proximal to the soma high-density location; and an exponential rise (ER) with distally located conductance density. In all cases, the synaptic inputs are located as a gaussian function on the dendrites. Our simulations lead to eight key observations. (1) The presence of the voltage-dependent channels conductance (gActive) in the dendrites is vital for obtaining EPSP peak boosting. (2) The mean EPSP peaks of the ST, ER, and ED distributions are similar when the ranges of G (total conductance) are equal. (3) EPSP peak increases monotonically when the magnitude of gNa_step (maximal gNa at a particular run) is increased. (4) EPSP kinetics parameters were differentially affected; time integral was decreased monotonically with increased gNa_step, but the rate of rise (the decay time was not analyzed) does not show clear relations. (5) The total G can be elevated by increasing the number of active dendrites; however, only a small active area of the dendritic tree is sufficient to get the maximal boosting. (6) The sometimes large variations in the parameters values for identical G depend on the gNa_step and active dendritic area. (7) High gNa_step in a few dendrites is more efficient in amplifying the EPSP peak than low gNa_step in many dendrites. (8) The EPSP peak is approximately linear with respect to the MNs' RN (input resistance).
Collapse
Affiliation(s)
- Gideon Gradwohl
- Department of Physiology, Faculty of Health Sciences, and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel, and Department of Software Engineering, Sami Shamoon College of Engineering, Beer-Sheva 84100, Israel,
| | - Yoram Grossman
- Department of Physiology, Faculty of Health Sciences, and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
| |
Collapse
|
15
|
Kullmann PHM, Kandler K. Dendritic Ca2+ responses in neonatal lateral superior olive neurons elicited by glycinergic/GABAergic synapses and action potentials. Neuroscience 2008; 154:338-45. [PMID: 18400406 DOI: 10.1016/j.neuroscience.2008.02.026] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2007] [Revised: 02/14/2008] [Accepted: 02/15/2008] [Indexed: 10/22/2022]
Abstract
During development, GABA/glycinergic connections from the medial nucleus of the trapezoid body (MNTB) to the lateral superior olive (LSO) gradually change from being depolarizing to being hyperpolarizing. Previous studies have shown that depolarizing MNTB-LSO synapses can trigger action potentials and increase the concentration of intracellular calcium. In the present study we used confocal calcium imaging combined with whole-cell patch clamp recordings to investigate how depolarizing MNTB inputs in neonatal rats and mice increase the calcium concentration in the dendrites of LSO neurons. Our results show that subthreshold synaptic responses can elicit local dendritic calcium responses while suprathreshold responses reliably generate global calcium responses that are observed in all dendritic processes. The amplitude of global dendritic calcium responses increased with distance from the soma. Global calcium responses were blocked by tetrodotoxin and could not be recovered by somatic injection of action potential waveforms indicating that global calcium responses are generated by back-propagating sodium action potentials.
Collapse
Affiliation(s)
- P H M Kullmann
- Department of Neurobiology and Center for the Neural Basis of Cognition, University of Pittsburgh School of Medicine, 3500 Terrace Street, Pittsburgh, PA 15208, USA
| | | |
Collapse
|
16
|
Caspary DM, Hughes LF, Schatteman TA, Turner JG. Age-related changes in the response properties of cartwheel cells in rat dorsal cochlear nucleus. Hear Res 2006; 216-217:207-15. [PMID: 16644158 DOI: 10.1016/j.heares.2006.03.005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Revised: 03/01/2006] [Accepted: 03/03/2006] [Indexed: 11/26/2022]
Abstract
The fusiform cell and deep layers of the dorsal cochlear nucleus (DCN) show neurotransmitter and functional age-related changes suggestive of a downregulation of inhibitory efficacy onto DCN output neurons. Inhibitory circuits implicated in these changes include vertical and D-multipolar cells. Cartwheel cells comprise a large additional population of DCN inhibitory neurons. Cartwheel cells receive excitatory inputs from granule cell parallel fibers and provide a source of glycinergic inhibitory input onto apical dendrites of DCN fusiform cells. The present study compared the response properties from young and aged units meeting cartwheel-cell criteria in anesthetized rats. Single unit recordings from aged cartwheel cells revealed significantly higher thresholds, increased spontaneous activity and significantly altered rate-level functions characterized by hyperexcitability at higher intensities. Aged cartwheel cells showed a significant reduction in off-set suppression. Collectively, these findings suggest a loss of tonic and perhaps response inhibition onto aged DCN cartwheel neurons. These changes likely reflect a compensatory downregulation of synaptic inhibition in response to a loss of excitatory drive from auditory and non-auditory excitatory inputs via granule cells. The impact of increased excitability of cartwheel cells on DCN output neurons is likely to be complex, influenced by loss of glycinergic release and/or subunit receptor changes which would only partially off-set age-related loss of inhibition onto the somata and basal dendrites of fusiform cells.
Collapse
Affiliation(s)
- Donald M Caspary
- Department of Pharmacology, Southern Illinois University School of Medicine, P.O. Box 19629, Springfield, IL 62794-9629, USA.
| | | | | | | |
Collapse
|
17
|
Abstract
Characterizing the functional phenotypes of neurons is essential for understanding how genotypes can be related to the neural basis of behaviour. Traditional classifications of neurons by single features (such as morphology or firing behaviour) are increasingly inadequate for reflecting functional phenotypes, as they do not integrate functions across different neuronal types. Here, we describe a set of rules for identifying and predicting functional phenotypes that combine morphology, intrinsic ion channel species and their distributions in dendrites, and functional properties. This more comprehensive neuronal classification should be an improvement on traditional classifications for relating genotype to functional phenotype.
Collapse
Affiliation(s)
- Michele Migliore
- Yale University School of Medicine, Department of Neurobiology, P.O. BOX 208001, New Haven, Connecticut 06520-8001, USA
| | | |
Collapse
|
18
|
Tzounopoulos T, Kim Y, Oertel D, Trussell LO. Cell-specific, spike timing–dependent plasticities in the dorsal cochlear nucleus. Nat Neurosci 2004; 7:719-25. [PMID: 15208632 DOI: 10.1038/nn1272] [Citation(s) in RCA: 237] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2003] [Accepted: 05/11/2004] [Indexed: 11/08/2022]
Abstract
In the dorsal cochlear nucleus, long-term synaptic plasticity can be induced at the parallel fiber inputs that synapse onto both fusiform principal neurons and cartwheel feedforward inhibitory interneurons. Here we report that in mouse fusiform cells, spikes evoked 5 ms after parallel-fiber excitatory postsynaptic potentials (EPSPs) led to long-term potentiation (LTP), whereas spikes evoked 5 ms before EPSPs led to long-term depression (LTD) of the synapse. The EPSP-spike protocol led to LTD in cartwheel cells, but no synaptic changes resulted from the reverse sequence (spike-EPSP). Plasticity in fusiform and cartwheel cells therefore followed Hebbian and anti-Hebbian learning rules, respectively. Similarly, spikes generated by summing EPSPs from different groups of parallel fibers produced LTP in fusiform cells, and LTD in cartwheel cells. LTD could also be induced in glutamatergic inputs of cartwheel cells by pairing parallel-fiber EPSPs with depolarizing glycinergic PSPs from neighboring cartwheel cells. Thus, synaptic learning rules vary with the postsynaptic cell, and may require the interaction of different transmitter systems.
Collapse
Affiliation(s)
- Thanos Tzounopoulos
- Oregon Hearing Research Center and Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA.
| | | | | | | |
Collapse
|
19
|
Abstract
The shapes of the head and ears of mammals are asymmetrical top-to-bottom and front-to-back. Reflections of sounds from these structures differ with the angle of incidence, producing cues for monaural sound localization in the spectra of the stimuli at the eardrum. Neurons in the dorsal cochlear nucleus (DCN) respond specifically to spectral cues and integrate them with somatosensory, vestibular and higher-level auditory information through parallel fiber inputs in a cerebellum-like circuit. Synapses between parallel fibers and their targets show long-term potentiation (LTP) and long-term depression (LTD), whereas those between auditory nerve fibers and their targets do not. This paper discusses the integration of acoustic and the proprioceptive information in terms of possible computational roles for the DCN.
Collapse
Affiliation(s)
- Donata Oertel
- Department of Physiology, University of Wisconsin, 1300 University Avenue, Madison, WI 53706, USA.
| | | |
Collapse
|