1
|
Gillet C, Kurth S, Kuenzel T. Muscarinic modulation of M and h currents in gerbil spherical bushy cells. PLoS One 2020; 15:e0226954. [PMID: 31940388 PMCID: PMC6961914 DOI: 10.1371/journal.pone.0226954] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Accepted: 12/10/2019] [Indexed: 11/18/2022] Open
Abstract
Descending cholinergic fibers innervate the cochlear nucleus. Spherical bushy cells, principal neurons of the anterior part of the ventral cochlear nucleus, are depolarized by cholinergic agonists on two different time scales. A fast and transient response is mediated by alpha-7 homomeric nicotinic receptors while a slow and long-lasting response is mediated by muscarinic receptors. Spherical bushy cells were shown to express M3 receptors, but the receptor subtypes involved in the slow muscarinic response were not physiologically identified yet. Whole-cell patch clamp recordings combined with pharmacology and immunohistochemistry were performed to identify the muscarinic receptor subtypes and the effector currents involved. Spherical bushy cells also expressed both M1 and M2 receptors. The M1 signal was stronger and mainly somatic while the M2 signal was localized in the neuropil and on the soma of bushy cells. Physiologically, the M-current was observed for the gerbil spherical bushy cells and was inhibited by oxotremorine-M application. Surprisingly, long application of carbachol showed only a transient depolarization. Even though no muscarinic depolarization could be detected, the input resistance increased suggesting a decrease in the cell conductance that matched with the closure of M-channels. The hyperpolarization-activated currents were also affected by muscarinic activation and counteracted the effect of the inactivation of M-current on the membrane potential. We hypothesize that this double muscarinic action might allow adaptation of effects during long durations of cholinergic activation.
Collapse
Affiliation(s)
- Charlène Gillet
- Auditory Neurophysiology Group, Department of Chemosensation, RWTH Aachen University, Worringerweg, Aachen, Germany
| | - Stefanie Kurth
- Department of Chemosensation, RWTH Aachen University, Worringerweg, Aachen, Germany
| | - Thomas Kuenzel
- Auditory Neurophysiology Group, Department of Chemosensation, RWTH Aachen University, Worringerweg, Aachen, Germany
- Department of Chemosensation, RWTH Aachen University, Worringerweg, Aachen, Germany
- * E-mail:
| |
Collapse
|
2
|
Dos Santos E Alhadas É, Correa AMB, Naves LA, Kushmerick C. Mechanisms and functional impact of Group I metabotropic glutamate receptor modulation of excitability in mouse MNTB neurons. Synapse 2019; 74:e22137. [PMID: 31584700 DOI: 10.1002/syn.22137] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 09/27/2019] [Accepted: 09/30/2019] [Indexed: 12/20/2022]
Abstract
We examined effects of Group I metabotropic glutamate receptors on the excitability of mouse medial nucleus of the trapezoid body (MNTB) neurons. The selective agonist, S-3,5-dihydroxyphenylglycine (DHPG), evoked a dose-dependent depolarization of the resting potential, increased membrane resistance, increased sag depolarization, and promoted rebound action potential firing. Under voltage-clamp, DHPG evoked an inward current, referred to as IDHPG , which was developmentally stable through postnatal day P56. IDHPG had low temperature dependence in the range 25-34°C, consistent with a channel mechanism. However, the I-V relationship took the form of an inverted U that did not reverse at the calculated Nernst potential for K+ or Cl- . Thus, it is likely that more than one ion type contributes to IDHPG and the mix may be voltage dependent. IDHPG was resistant to the Na+ channel blockers tetrodotoxin and amiloride, and to inhibitors of iGluR (CNQX and MK801). IDHPG was inhibited 21% by Ba2+ (500 μM), 60% by ZD7288 (100 μM) and 73% when the two antagonists were applied together, suggesting that KIR channels and HCN channels contribute to the current. Voltage clamp measurements of IH indicated a small (6%) increase in Gmax by DHPG with no change in the voltage dependence. DHPG reduced action potential rheobase and reduced the number of post-synaptic AP failures during high frequency stimulation of the calyx of Held. Thus, activation of post-synaptic Group I mGlu receptors modifies the excitability of MNTB neurons and contributes to the reliability of high frequency firing in this auditory relay nucleus.
Collapse
Affiliation(s)
- Éverton Dos Santos E Alhadas
- Graduate Program in Physiology and Pharmacology, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Ana Maria Bernal Correa
- Graduate Program in Physiology and Pharmacology, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Ligia Araújo Naves
- Department of Physiology and Biophysics, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Christopher Kushmerick
- Department of Physiology and Biophysics, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| |
Collapse
|
3
|
Felix RA, Elde CJ, Nevue AA, Portfors CV. Serotonin modulates response properties of neurons in the dorsal cochlear nucleus of the mouse. Hear Res 2016; 344:13-23. [PMID: 27838373 DOI: 10.1016/j.heares.2016.10.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Revised: 10/10/2016] [Accepted: 10/26/2016] [Indexed: 01/15/2023]
Abstract
The neurochemical serotonin (5-hydroxytryptamine, 5-HT) is involved in a variety of behavioral functions including arousal, reward, and attention, and has a role in several complex disorders of the brain. In the auditory system, 5-HT fibers innervate a number of subcortical nuclei, yet the modulatory role of 5-HT in nearly all of these areas remains poorly understood. In this study, we examined spiking activity of neurons in the dorsal cochlear nucleus (DCN) following iontophoretic application of 5-HT. The DCN is an early site in the auditory pathway that receives dense 5-HT fiber input from the raphe nuclei and has been implicated in the generation of auditory disorders marked by neuronal hyperexcitability. Recordings from the DCN in awake mice demonstrated that iontophoretic application of 5-HT had heterogeneous effects on spiking rate, spike timing, and evoked spiking threshold. We found that 56% of neurons exhibited increases in spiking rate during 5-HT delivery, while 22% had decreases in rate and the remaining neurons had no change. These changes were similar for spontaneous and evoked spiking and were typically accompanied by changes in spike timing. Spiking increases were associated with lower first spike latencies and jitter, while decreases in spiking generally had opposing effects on spike timing. Cases in which 5-HT application resulted in increased spiking also exhibited lower thresholds compared to the control condition, while cases of decreased spiking had no threshold change. We also found that the 5-HT2 receptor subtype likely has a role in mediating increased excitability. Our results demonstrate that 5-HT can modulate activity in the DCN of awake animals and that it primarily acts to increase neuronal excitability, in contrast to other auditory regions where it largely has a suppressive role. Modulation of DCN function by 5-HT has implications for auditory processing in both normal hearing and disordered states.
Collapse
Affiliation(s)
- Richard A Felix
- School of Biological Sciences and Integrative Physiology and Neuroscience, Washington State University, Vancouver, WA, USA.
| | - Cameron J Elde
- School of Biological Sciences and Integrative Physiology and Neuroscience, Washington State University, Vancouver, WA, USA
| | - Alexander A Nevue
- School of Biological Sciences and Integrative Physiology and Neuroscience, Washington State University, Vancouver, WA, USA
| | - Christine V Portfors
- School of Biological Sciences and Integrative Physiology and Neuroscience, Washington State University, Vancouver, WA, USA
| |
Collapse
|
4
|
Kopp-Scheinpflug C, Pigott BM, Forsythe ID. Nitric oxide selectively suppresses IH currents mediated by HCN1-containing channels. J Physiol 2015; 593:1685-700. [PMID: 25605440 PMCID: PMC4386966 DOI: 10.1113/jphysiol.2014.282194] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Accepted: 01/16/2015] [Indexed: 12/12/2022] Open
Abstract
Hyperpolarization-activated non-specific cation-permeable channels (HCN) mediate I(H) currents, which are modulated by cGMP and cAMP and by nitric oxide (NO) signalling. Channel properties depend upon subunit composition (HCN1-4 and accessory subunits) as demonstrated in expression systems, but physiological relevance requires investigation in native neurons with intact intracellular signalling. Here we use the superior olivary complex (SOC), which exhibits a distinctive pattern of HCN1 and HCN2 expression, to investigate NO modulation of the respective I(H) currents, and compare properties in wild-type and HCN1 knockout mice. The medial nucleus of the trapezoid body (MNTB) expresses HCN2 subunits exclusively, and sends inhibitory projections to the medial and lateral superior olives (MSO, LSO) and the superior paraolivary nucleus (SPN). In contrast to the MNTB, these target nuclei possess an I(H) with fast kinetics, and they express HCN1 subunits. NO is generated in the SOC following synaptic activity and here we show that NO selectively suppresses HCN1, while enhancing IH mediated by HCN2 subunits. NO hyperpolarizes the half-activation of HCN1-mediated currents and slows the kinetics of native IH currents in the MSO, LSO and SPN. This modulation was independent of cGMP and absent in transgenic mice lacking HCN1. Independently, NO signalling depolarizes the half-activation of HCN2-mediated I(H) currents in a cGMP-dependent manner. Thus, NO selectively suppresses fast HCN1-mediated I(H) and facilitates a slow HCN2-mediated I(H) , so generating a spectrum of modulation, dependent on the local expression of HCN1 and/or HCN2.
Collapse
Affiliation(s)
- Cornelia Kopp-Scheinpflug
- Division of Neurobiology, Department Biology II, Ludwig-Maximilians-University Munich, Großhadernerstr. 282152, Planegg-Martinsried, Germany
| | - Beatrice M Pigott
- Department of Cell Physiology and Pharmacology, University of LeicesterLeicester, LE1 9HN, UK
| | - Ian D Forsythe
- Department of Cell Physiology and Pharmacology, University of LeicesterLeicester, LE1 9HN, UK
| |
Collapse
|
5
|
Abstract
Saccadic oscillations are continuous back-to-back saccades that cause excessive image motion across fovea and threaten clear vision. Acquired processes, related to immune or metabolic mechanisms, are common culprits. Saccadic oscillations are also seen in degenerative cerebellar disease or as a part of a familial syndrome of saccadic oscillations and limb tremor. Some normal individuals have innate ability to voluntarily trigger saccadic oscillations (i.e. voluntary nystagmus). Contemporary theory for the pathogenesis for saccadic oscillations has emphasized hyperexcitable or disinhibited state of the brainstem saccadic burst neuron membrane. This review discusses etiologies and treatment of saccadic oscillations in light of novel cell membrane based theory.
Collapse
Affiliation(s)
- Aasef G Shaikh
- Department of Neurology, University Hospitals Case Medical Center, Case Western Reserve University, Cleveland, OH
| |
Collapse
|
6
|
Shaikh AG, Finlayson PG. Forskolin induced increase in spontaneous activity of auditory brainstem neurons is comparable to acoustic stimulus evoked responses. Neurosci Lett 2012; 531:69-73. [PMID: 23127850 DOI: 10.1016/j.neulet.2012.10.053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2012] [Revised: 10/05/2012] [Accepted: 10/26/2012] [Indexed: 10/27/2022]
Abstract
Contemporary proposals for the pathophysiology of tinnitus due to cochlear damage underscore increased spontaneous activity of auditory brainstem neurons. One of the several consequences of the cochlear injury is the activation of the ERK pathway, suppression of phosphodiestase E activity, and putatively setting a long-term increase in intracellular levels of cyclic AMP at central auditory neurons. Local application of forskolin also increases intracellular cyclic AMP and spontaneous neural activity. We measured the effects of locally applied forskolin on spontaneous firing rate of isolated neurons in the peri-olivary region of the superior olive complex in anesthetized adult Long Evan rats. Forskolin induced increase in spontaneous neural activity was comparable to supra-threshold tone evoke neural responses. These results are viewed in context of hyperexcitability as a correlate of tinnitus.
Collapse
Affiliation(s)
- Aasef G Shaikh
- Department of Neurology, Case Western Reserve University, Cleveland, OH, United States.
| | | |
Collapse
|
7
|
Shaikh AG, Zee DS, Optican LM, Miura K, Ramat S, Leigh RJ. The effects of ion channel blockers validate the conductance-based model of saccadic oscillations. Ann N Y Acad Sci 2011; 1233:58-63. [PMID: 21950976 DOI: 10.1111/j.1749-6632.2011.06130.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Conductance-based models of reciprocally inhibiting burst neurons suggest that intrinsic membrane properties and postinhibitory rebound (PIR) determine the amplitude and frequency of saccadic oscillations. Reduction of the low-threshold calcium currents (I(T)) in the model decreased the amplitude but increased the frequency of the simulated oscillations. Combined reduction of hyperpolarization-activated cation current (I(h)) and I(T) in the model abolished the simulated oscillations. We measured the effects of a selective blocker of I(T) (ethosuximide) in healthy subjects on the amplitude and frequency of saccadic oscillations evoked by eye closure and of a nonselective blocker of I(h) and I(T) (propronolol) in a patient with microsaccadic oscillation and limb tremor syndrome (mSOLT). Ethosuximide significantly reduced the amplitude but increased the frequency of the saccadic oscillations during eye closure in healthy subjects. Propranolol abolished saccadic oscillations in the mSOLT patient. These results support the hypothetical role of postinhibitory rebound, I(h), and I(T) , in generation of saccadic oscillations and determining their kinematic properties.
Collapse
Affiliation(s)
- Aasef G Shaikh
- Department of Neurology, Case Western Reserve University, Cleveland, Ohio 44106-5040,
| | | | | | | | | | | |
Collapse
|
8
|
Nagtegaal AP, Borst J. In Vivo Dynamic Clamp Study of Ih in the Mouse Inferior Colliculus. J Neurophysiol 2010; 104:940-8. [DOI: 10.1152/jn.00264.2010] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Approximately half of the cells in the mouse inferior colliculus have the hyperpolarization-activated mixed cation current Ih, yet little is known about its functional relevance in vivo. We therefore studied its contribution to the processing of sound information in single cells by making in vivo whole cell recordings from the inferior colliculus (IC) of young-adult anesthetized C57Bl/6 mice. Following pharmacological block of the endogenous channels, a dynamic clamp approach allowed us to study the responses to current injections or auditory stimuli in the presence and absence of Ih within the same neuron, thus avoiding network or developmental effects. The presence of Ih changed basic cellular properties, including depolarizing the resting membrane potential and decreasing resting membrane resistance. Sound-evoked excitatory postsynaptic potentials were smaller but at the same time reached a more positive membrane potential when Ih was present. With Ih, a subset of cells showed rebound spiking following hyperpolarizing current injection. Its presence also changed more complex cellular properties. It decreased temporal summation in response to both hyperpolarizing and depolarizing repetitive current stimuli, and resulted in small changes in the cycle-averaged membrane potential during sinusoidal amplitude modulated (SAM) tones. Furthermore, Ih minimally decreased the response to a tone following a depolarization, an effect that may make a small contribution to forward masking. Our results thus suggest that previously observed differences in IC cells are a mixture of direct effects of Ih and indirect effects due to the change in membrane potential or effects due to the co-expression with other channels.
Collapse
Affiliation(s)
- A. P. Nagtegaal
- Departments of Neuroscience and
- Otorhinolaryngology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands
| | | |
Collapse
|
9
|
Yang RH, Wang WT, Hou XH, Hu SJ, Chen JY. Ionic mechanisms of the effects of sleep deprivation on excitability in hippocampal pyramidal neurons. Brain Res 2010; 1343:135-42. [DOI: 10.1016/j.brainres.2010.05.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Revised: 02/25/2010] [Accepted: 05/05/2010] [Indexed: 11/24/2022]
|
10
|
Hassfurth B, Magnusson AK, Grothe B, Koch U. Sensory deprivation regulates the development of the hyperpolarization-activated current in auditory brainstem neurons. Eur J Neurosci 2009; 30:1227-38. [PMID: 19788576 DOI: 10.1111/j.1460-9568.2009.06925.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels are highly expressed in the superior olivary complex, the primary locus for binaural information processing. This hyperpolarization-activated current (I(h)) regulates the excitability of neurons and enhances the temporally precise analysis of the binaural acoustic cues. By using the whole-cell patch-clamp technique, we examined the properties of I(h) current in neurons of the lateral superior olive (LSO) and the medial nucleus of the trapezoid body (MNTB) before and after hearing onset. Moreover, we tested the hypothesis that I(h) currents are actively regulated by sensory input activity by performing bilateral and unilateral cochlear ablations before hearing onset, resulting in a chronic auditory deprivation. The results show that after hearing onset, I(h) currents are rapidly upregulated in LSO neurons, but change only marginally in neurons of the MNTB. We also found a striking difference in maximal current density, voltage dependence and activation time constant between the LSO and the MNTB in mature-like animals. Following bilateral cochlear ablations before hearing onset, the I(h) currents were scaled up in the LSO and scaled down in the MNTB. Consequently, in the LSO this resulted in a depolarized resting membrane potential and a lower input resistance of these neurons. This type of activity-dependent homeostatic change could thus result in an augmented response to the remaining inputs.
Collapse
Affiliation(s)
- Benjamin Hassfurth
- Department Biologie II, Division of Neurobiology, Ludwig-Maximilans University München, 82152 Martinsried, Germany
| | | | | | | |
Collapse
|
11
|
Abstract
Saccadic oscillations threaten clear vision by causing image motion on the retina. They are either purely horizontal (ocular flutter) or multidimensional (opsoclonus). We propose that ion channel dysfunction in the burst cell membrane is the underlying abnormality. We have tested this hypothesis by simulating a neuromimetic computational model of the burst neurons. This biologically realistic model mimics the physiologic properties and anatomic connections in the brainstem saccade generator. A rebound firing after sustained inhibition, called post-inhibitory rebound (PIR), and reciprocal inhibition between premotor saccadic burst neurons are the key features of this conceptual scheme. PIR and reciprocal inhibition make the circuits that generate the saccadic burst inherently unstable and can lead to oscillations unless stabilized by external inhibition. Our simulations suggest that alterations in membrane properties that lead to an increase in PIR, a reduction in external glycinergic inhibition, or both can cause saccadic oscillations.
Collapse
|
12
|
Liu Q, Davis RL. Regional Specification of Threshold Sensitivity and Response Time in CBA/CaJ Mouse Spiral Ganglion Neurons. J Neurophysiol 2007; 98:2215-22. [PMID: 17715200 DOI: 10.1152/jn.00284.2007] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previous studies of spiral ganglion neuron electrophysiology have shown that specific parameters differ according to cochlear location, with apical neurons being distinctly different from basal neurons. To align these features more precisely along the tonotopic axis of the cochlea, we developed a novel spiral ganglion culture system in which positional information is retained. Patch-clamp recordings made from neurons of known gangliotopic location revealed two basic firing pattern distributions. Membrane characteristics related to spike timing, such as accommodation, latency and onset tau, were distinctly heterogeneous, yet when averaged, they were distributed in a graded manner along the length of the cochlea. Action potential threshold levels also displayed a wide range, the averages of which were distributed nonmonotonically such that neurons with the greatest sensitivity were localized to the mid-regions of the ganglion. These studies shed new light on the complexity and sophistication of the intrinsic firing features of spiral ganglion neurons. Because timing-related elements are organized in an overall tonotopic manner, it is hypothesized that they contribute to aspects of frequency-dependent acoustic processing. On the other hand, the different distribution of threshold levels, with the greatest sensitivity in the middle region of the tonotopic map, suggests that this neuronal parameter is regulated differently and thus may contribute a distinct realm of auditory sensory processing.
Collapse
Affiliation(s)
- Qing Liu
- Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ 08854, USA
| | | |
Collapse
|
13
|
Tan ML, Borst JGG. Comparison of responses of neurons in the mouse inferior colliculus to current injections, tones of different durations, and sinusoidal amplitude-modulated tones. J Neurophysiol 2007; 98:454-66. [PMID: 17507505 DOI: 10.1152/jn.00174.2007] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We made in vivo whole cell patch-clamp recordings from the inferior colliculus of young-adult, anesthetized C57/Bl6 mice to compare the responses to constant-current injections with the responses to tones of different duration or to sinusoidal amplitude-modulated (SAM) tones. We observed that voltage-dependent ion channels contributed in several ways to the response to tones. A sustained response to long tones was observed only in cells showing little accommodation during current injection. Cells showing burst-onset firing during current injection showed a small response to SAM tones, whereas burst-sustained cells showed a good response to SAM tones. The hyperpolarization-activated nonselective cation channel I(h) had a special role in shaping the responses: I(h) was associated with an increased excitability, with chopper and pauser responses, and with an afterhyperpolarization following tones. Synaptic properties were more important in determining the responses to tones of different durations. A short-latency inhibitory response appeared to contribute to the long-pass response in some cells and short-pass and band-pass neurons were characterized by their slow recovery from synaptic adaptation. Cells that recovered slowly from synaptic adaptation showed a relatively small response to SAM tones. Our results show an important role for both intrinsic membrane properties -- most notably the presence of I(h) and the extent of accommodation -- and synaptic adaptation in shaping the response to tones in the inferior colliculus.
Collapse
Affiliation(s)
- M L Tan
- Department of Neuroscience, Erasmus MC, Rotterdam, The Netherlands
| | | |
Collapse
|
14
|
Leao KE, Leao RN, Sun H, Fyffe REW, Walmsley B. Hyperpolarization-activated currents are differentially expressed in mice brainstem auditory nuclei. J Physiol 2006; 576:849-64. [PMID: 16916913 PMCID: PMC1890420 DOI: 10.1113/jphysiol.2006.114702] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The hyperpolarization-activated cation current (I(h)) may influence precise auditory processing by modulating resting membrane potential and cell excitability. We used electrophysiology and immunohistochemistry to investigate the properties of I(h) in three auditory brainstem nuclei in mice: the anteroventral cochlear nucleus (AVCN), the medial nucleus of the trapezoid body (MNTB) and the lateral superior olive (LSO). I(h) amplitude varied considerably between these cell types, with the order of magnitude LSO > AVCN > MNTB. Kinetically, I(h) is faster in LSO neurons, and more active at rest, compared with AVCN and MNTB cells. The half-activation voltage is -10 mV more hyperpolarized for AVCN and MNTB cells compared with LSO neurons. HCN1 immunoreactivity strongly labelled AVCN and LSO neurons, while HCN2 staining was more diffuse in all nuclei. The HCN4 subunit displayed robust membrane staining in AVCN and MNTB cells but weak labelling of the LSO. We used a dynamic clamp, after blocking I(h), to reinsert I(h) to the different cell types. Our results indicate that the native I(h) for each cell type influences the resting membrane potential and can delay the generation of action potentials in response to injected current. Native I(h) increases rebound depolarizations following hyperpolarizations in all cell types, and increases the likelihood of rebound action potentials (particularly in multiple-firing LSO neurons). This systematic comparison shows that I(h) characteristics vary considerably between different brainstem nuclei, and that these differences significantly affect the response properties of cells within these nuclei.
Collapse
Affiliation(s)
- Katarina E Leao
- Synapse and Hearing Laboratory, Division of Neuroscience, John Curtin School of Medical Research, Australian National University, PO Box 334, Canberra, ACT, Australia.
| | | | | | | | | |
Collapse
|
15
|
Shaikh AG, Finlayson PG. Excitability of auditory brainstem neurons, in vivo, is increased by cyclic-AMP. Hear Res 2005; 201:70-80. [PMID: 15721562 DOI: 10.1016/j.heares.2004.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/25/2004] [Accepted: 10/08/2004] [Indexed: 11/17/2022]
Abstract
Physiological control of auditory neural responses is critical for accurate representation of acoustic information, such as sound source localization and speech perception. Central auditory neural responses are almost certainly regulated by a range of mechanisms, including second messenger systems, such as the cAMP pathway. An increase in spontaneous neural discharge is known to accompany cochlear insults. Here we report that an increase in spontaneous as well as tone-evoked discharge can also be induced by pressure application of forskolin, a pharmacological agent that elevates intracellular cAMP level by activating adenyl cyclase. The forskolin induced increase in superior olivary complex (SOC) brainstem neurons is specific, dose-dependent, and reversible, whereas application of artificial cerebrospinal fluid (aCSF, the vehicle) does not alter activity. Forskolin-application also has a relatively greater effect on spontaneous activity compared to tone evoked responses. Blockade of the hyperpolarization-activated current, Ih, by ZD7288, consistently reversed the effects of forskolin. Based on these findings, we propose that the second messenger, cAMP, can significantly modulate neural excitability and spontaneous discharge in SOC neurons, principally by shifting the activation of Ih channels.
Collapse
Affiliation(s)
- Aasef G Shaikh
- Department of Otolaryngology, School of Medicine, Wayne State University, Detroit, MI 48201, USA.
| | | |
Collapse
|
16
|
Leao RN, Svahn K, Berntson A, Walmsley B. Hyperpolarization-activated (I) currents in auditory brainstem neurons of normal and congenitally deaf mice. Eur J Neurosci 2005; 22:147-57. [PMID: 16029204 DOI: 10.1111/j.1460-9568.2005.04185.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have investigated the membrane properties of brainstem auditory neurons in a mouse model of congenital deafness (dn/dn). Whole-cell recordings were made from visualized neurons in slices of the medial nucleus of the trapezoid body (MNTB) and anteroventral cochlear nucleus (AVCN). We have recently demonstrated that MNTB neurons in deaf mice are more excitable than in normal mice, due in part to a reduced expression of low-threshold potassium currents. In this study, we have examined the contribution of hyperpolarization-activated (Ih) channels to the membrane properties of MNTB and AVCN neurons. Our results show that Ih is larger in MNTB neurons from deaf mice than in normal mice. In contrast, no significant differences were found in Ih or excitability between AVCN bushy cells from dn/dn and normal mice. Experimental evidence and neuronal modelling suggests that, in the MNTB of normal mice, a small contribution of Ih helps to reduce temporal summation of synaptic potentials. A larger Ih in neurons from deaf mice has a much greater effect in reducing temporal summation of synaptic potentials, counteracting to some extent the greater excitability of these cells. Our results provide further insight into the role of activity during development in regulating the membrane and firing properties of central neurons.
Collapse
Affiliation(s)
- Richardson N Leao
- Synapse and Hearing Laboratory, The John Curtin School of Medical Research, The Australian National University, PO Box 334, Canberra, ACT 0200, Australia
| | | | | | | |
Collapse
|