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Efferent Vestibular Neurons Show Homogenous Discharge Output But Heterogeneous Synaptic Input Profile In Vitro.

Mathews MA, Murray A, Wijesinghe R, Cullen K, Tung VW, Camp AJ - PLoS ONE (2015)

Bottom Line: While previous work has shown that activation of the efferent vestibular system results in modulation of afferent vestibular neuron discharge, the intrinsic and synaptic properties of efferent neurons themselves are largely unknown.Despite this heterogeneous mixture of inputs, we show that synaptic inputs onto EVN neurons are predominantly excitatory.Together these findings suggest that the inputs onto EVN neurons, and more specifically the origin of these inputs may underlie EVN neuron function.

View Article: PubMed Central - PubMed

Affiliation: Discipline of Biomedical Science, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia.

ABSTRACT
Despite the importance of our sense of balance we still know remarkably little about the central control of the peripheral balance system. While previous work has shown that activation of the efferent vestibular system results in modulation of afferent vestibular neuron discharge, the intrinsic and synaptic properties of efferent neurons themselves are largely unknown. Here we substantiate the location of the efferent vestibular nucleus (EVN) in the mouse, before characterizing the input and output properties of EVN neurons in vitro. We made transverse serial sections through the brainstem of 4-week-old mice, and performed immunohistochemistry for calcitonin gene-related peptide (CGRP) and choline acetyltransferase (ChAT), both expressed in the EVN of other species. We also injected fluorogold into the posterior canal and retrogradely labelled neurons in the EVN of ChAT:: tdTomato mice expressing tdTomato in all cholinergic neurons. As expected the EVN lies dorsolateral to the genu of the facial nerve (CNVII). We then made whole-cell current-, and voltage-clamp recordings from visually identified EVN neurons. In current-clamp, EVN neurons display a homogeneous discharge pattern. This is characterized by a high frequency burst of action potentials at the onset of a depolarizing stimulus and the offset of a hyperpolarizing stimulus that is mediated by T-type calcium channels. In voltage-clamp, EVN neurons receive either exclusively excitatory or inhibitory inputs, or a combination of both. Despite this heterogeneous mixture of inputs, we show that synaptic inputs onto EVN neurons are predominantly excitatory. Together these findings suggest that the inputs onto EVN neurons, and more specifically the origin of these inputs may underlie EVN neuron function.

No MeSH data available.


Related in: MedlinePlus

Identification and classification of excitatory and inhibitory profiles in EVN neurons.(A) Schematic view of transversely sectioned mouse brainstem. Inset shows map of recording sites (22/23 recorded neurons). VN: vestibular nucleus; G7n: genu of seventh cranial nerve (facial nerve); 6n: sixth cranial nerve nucleus (abducens nucleus); 4V: fourth ventricle; EVN: efferent vestibular nucleus. (B)Top trace: EPSCs recorded under normal conditions before the addition of drugs. Second trace: addition of CNQX (10 μM) and TTX (1 μM). Third trace: mIPSCs recorded under normal conditions before the addition of drugs. Bottom trace: addition of strychnine (1 μM) and bicuculline (10 μM) abolished all synaptic activity. Some neurons received excitatory inputs in conjunction with: GABAAR-mediated events (C)Bottom trace: addition of bicuculline to the bath abolished activity remaining after the addition of TTX and CNQX (second trace); GlyR-mediated events (D)Bottom trace: addition of strychnine abolished remaining activity following the addition of TTX and CNQX (second trace). (E) Other neurons received a combination of mIPSCs in addition to EPSCs. In these neurons, the addition of bicuculline reduced the frequency of synaptic activity (third trace) that was abolished by addition of strychnine (bottom trace). Scale bar in (B) is the same for all traces. (F) Frequencies of EPSCs and mIPSCs per cell calculated over a period of 30 seconds under the influence of excitatory and inhibitory synaptic activity blockers.
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pone.0139548.g003: Identification and classification of excitatory and inhibitory profiles in EVN neurons.(A) Schematic view of transversely sectioned mouse brainstem. Inset shows map of recording sites (22/23 recorded neurons). VN: vestibular nucleus; G7n: genu of seventh cranial nerve (facial nerve); 6n: sixth cranial nerve nucleus (abducens nucleus); 4V: fourth ventricle; EVN: efferent vestibular nucleus. (B)Top trace: EPSCs recorded under normal conditions before the addition of drugs. Second trace: addition of CNQX (10 μM) and TTX (1 μM). Third trace: mIPSCs recorded under normal conditions before the addition of drugs. Bottom trace: addition of strychnine (1 μM) and bicuculline (10 μM) abolished all synaptic activity. Some neurons received excitatory inputs in conjunction with: GABAAR-mediated events (C)Bottom trace: addition of bicuculline to the bath abolished activity remaining after the addition of TTX and CNQX (second trace); GlyR-mediated events (D)Bottom trace: addition of strychnine abolished remaining activity following the addition of TTX and CNQX (second trace). (E) Other neurons received a combination of mIPSCs in addition to EPSCs. In these neurons, the addition of bicuculline reduced the frequency of synaptic activity (third trace) that was abolished by addition of strychnine (bottom trace). Scale bar in (B) is the same for all traces. (F) Frequencies of EPSCs and mIPSCs per cell calculated over a period of 30 seconds under the influence of excitatory and inhibitory synaptic activity blockers.

Mentions: To investigate the contribution of glutamate-, GABAA-, and glycine-receptor mediated EPSCs and mIPSCs to the overall synaptic input profile of EVN neurons, whole-cell patch-clamp recordings were made in voltage-clamp configuration. As described above for action potential and discharge properties, each neuron (except one where mapping was unavailable), was mapped onto a standard schematic from the mouse brain atlas (Fig 3A). Recordings were made from 23 EVN neurons across the dorsoventral extent of the EVN in the presence of TTX (1 μM) and CNQX (10 μM) or bicuculline (10 μM) and strychnine (1 μM), to isolate inhibitory and excitatory synaptic activity respectively. Fig 3B shows that in a subset of neurons, addition of TTX and CNQX abolished all activity (top two traces). Conversely, in some neurons addition of bicuculline and strychnine abolished all activity (bottom two traces). These subsets were classified as exclusively excitatory or exclusively inhibitory expressing neurons respectively (Fig 3B).


Efferent Vestibular Neurons Show Homogenous Discharge Output But Heterogeneous Synaptic Input Profile In Vitro.

Mathews MA, Murray A, Wijesinghe R, Cullen K, Tung VW, Camp AJ - PLoS ONE (2015)

Identification and classification of excitatory and inhibitory profiles in EVN neurons.(A) Schematic view of transversely sectioned mouse brainstem. Inset shows map of recording sites (22/23 recorded neurons). VN: vestibular nucleus; G7n: genu of seventh cranial nerve (facial nerve); 6n: sixth cranial nerve nucleus (abducens nucleus); 4V: fourth ventricle; EVN: efferent vestibular nucleus. (B)Top trace: EPSCs recorded under normal conditions before the addition of drugs. Second trace: addition of CNQX (10 μM) and TTX (1 μM). Third trace: mIPSCs recorded under normal conditions before the addition of drugs. Bottom trace: addition of strychnine (1 μM) and bicuculline (10 μM) abolished all synaptic activity. Some neurons received excitatory inputs in conjunction with: GABAAR-mediated events (C)Bottom trace: addition of bicuculline to the bath abolished activity remaining after the addition of TTX and CNQX (second trace); GlyR-mediated events (D)Bottom trace: addition of strychnine abolished remaining activity following the addition of TTX and CNQX (second trace). (E) Other neurons received a combination of mIPSCs in addition to EPSCs. In these neurons, the addition of bicuculline reduced the frequency of synaptic activity (third trace) that was abolished by addition of strychnine (bottom trace). Scale bar in (B) is the same for all traces. (F) Frequencies of EPSCs and mIPSCs per cell calculated over a period of 30 seconds under the influence of excitatory and inhibitory synaptic activity blockers.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4589407&req=5

pone.0139548.g003: Identification and classification of excitatory and inhibitory profiles in EVN neurons.(A) Schematic view of transversely sectioned mouse brainstem. Inset shows map of recording sites (22/23 recorded neurons). VN: vestibular nucleus; G7n: genu of seventh cranial nerve (facial nerve); 6n: sixth cranial nerve nucleus (abducens nucleus); 4V: fourth ventricle; EVN: efferent vestibular nucleus. (B)Top trace: EPSCs recorded under normal conditions before the addition of drugs. Second trace: addition of CNQX (10 μM) and TTX (1 μM). Third trace: mIPSCs recorded under normal conditions before the addition of drugs. Bottom trace: addition of strychnine (1 μM) and bicuculline (10 μM) abolished all synaptic activity. Some neurons received excitatory inputs in conjunction with: GABAAR-mediated events (C)Bottom trace: addition of bicuculline to the bath abolished activity remaining after the addition of TTX and CNQX (second trace); GlyR-mediated events (D)Bottom trace: addition of strychnine abolished remaining activity following the addition of TTX and CNQX (second trace). (E) Other neurons received a combination of mIPSCs in addition to EPSCs. In these neurons, the addition of bicuculline reduced the frequency of synaptic activity (third trace) that was abolished by addition of strychnine (bottom trace). Scale bar in (B) is the same for all traces. (F) Frequencies of EPSCs and mIPSCs per cell calculated over a period of 30 seconds under the influence of excitatory and inhibitory synaptic activity blockers.
Mentions: To investigate the contribution of glutamate-, GABAA-, and glycine-receptor mediated EPSCs and mIPSCs to the overall synaptic input profile of EVN neurons, whole-cell patch-clamp recordings were made in voltage-clamp configuration. As described above for action potential and discharge properties, each neuron (except one where mapping was unavailable), was mapped onto a standard schematic from the mouse brain atlas (Fig 3A). Recordings were made from 23 EVN neurons across the dorsoventral extent of the EVN in the presence of TTX (1 μM) and CNQX (10 μM) or bicuculline (10 μM) and strychnine (1 μM), to isolate inhibitory and excitatory synaptic activity respectively. Fig 3B shows that in a subset of neurons, addition of TTX and CNQX abolished all activity (top two traces). Conversely, in some neurons addition of bicuculline and strychnine abolished all activity (bottom two traces). These subsets were classified as exclusively excitatory or exclusively inhibitory expressing neurons respectively (Fig 3B).

Bottom Line: While previous work has shown that activation of the efferent vestibular system results in modulation of afferent vestibular neuron discharge, the intrinsic and synaptic properties of efferent neurons themselves are largely unknown.Despite this heterogeneous mixture of inputs, we show that synaptic inputs onto EVN neurons are predominantly excitatory.Together these findings suggest that the inputs onto EVN neurons, and more specifically the origin of these inputs may underlie EVN neuron function.

View Article: PubMed Central - PubMed

Affiliation: Discipline of Biomedical Science, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia.

ABSTRACT
Despite the importance of our sense of balance we still know remarkably little about the central control of the peripheral balance system. While previous work has shown that activation of the efferent vestibular system results in modulation of afferent vestibular neuron discharge, the intrinsic and synaptic properties of efferent neurons themselves are largely unknown. Here we substantiate the location of the efferent vestibular nucleus (EVN) in the mouse, before characterizing the input and output properties of EVN neurons in vitro. We made transverse serial sections through the brainstem of 4-week-old mice, and performed immunohistochemistry for calcitonin gene-related peptide (CGRP) and choline acetyltransferase (ChAT), both expressed in the EVN of other species. We also injected fluorogold into the posterior canal and retrogradely labelled neurons in the EVN of ChAT:: tdTomato mice expressing tdTomato in all cholinergic neurons. As expected the EVN lies dorsolateral to the genu of the facial nerve (CNVII). We then made whole-cell current-, and voltage-clamp recordings from visually identified EVN neurons. In current-clamp, EVN neurons display a homogeneous discharge pattern. This is characterized by a high frequency burst of action potentials at the onset of a depolarizing stimulus and the offset of a hyperpolarizing stimulus that is mediated by T-type calcium channels. In voltage-clamp, EVN neurons receive either exclusively excitatory or inhibitory inputs, or a combination of both. Despite this heterogeneous mixture of inputs, we show that synaptic inputs onto EVN neurons are predominantly excitatory. Together these findings suggest that the inputs onto EVN neurons, and more specifically the origin of these inputs may underlie EVN neuron function.

No MeSH data available.


Related in: MedlinePlus