Mixed excitatory and inhibitory GABA‐mediated transmission in chick cochlear nucleus

Lu, Tao; Trussell, Laurence O.

doi:10.1111/j.1469-7793.2001.t01-1-00125.x

Cited by 81 publications

(104 citation statements)

References 31 publications

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“…Bidirectional effects have also been observed by Lu and Trussell [25]. Our first studies simply recorded evoked activity in NM using field potential recordings.…”

Section: Neurotransmitter Systemsmentioning

confidence: 97%

“…Activation of GABA A receptors on both NM and NL neurons produces a depolarization [24,25]. This depolarization, however, is inhibitory in that it blocks action potentials evoked by stimulating the afferent axons and action potentials generated by injection of depolarizing current into the cell.…”

Section: Neurotransmitter Systemsmentioning

confidence: 99%

“…It appears that both NM and NL neurons have a high internal Cl − concentration resulting in a chloride equilibrium potential that is depolarized from resting potential. Evidence that the native Cl − equilibrium potential is depolarized from rest comes from recordings using sharp electrodes filled with potassium acetate, that would not be expected to dramatically affect internal Cl − concentrations [9] and from perforated patch clamp recordings [25]. The inhibition of action potentials most likely occurs because of the shunting of current produced opening the Cl − channels and additional shunting owing to the opening of the low threshold K + channels discussed above.…”

Section: Neurotransmitter Systemsmentioning

confidence: 99%

“…The main source of the GABAergic input appears to be from fibers descending from the ipsilateral superior olive (SO) [22], but there is also a small population of GABAergic cells located between NM and NL that send processes into both nuclei [23]. The large GABAergic input to these areas begs questions about the possible role of this inhibitory input in temporal processing.Activation of GABA A receptors on both NM and NL neurons produces a depolarization [24,25]. This depolarization, however, is inhibitory in that it blocks action potentials evoked by stimulating the afferent axons and action potentials generated by injection of depolarizing current into the cell.…”

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The analysis of interaural time differences in the chick brain stem

Hyson

2005

Physiology & Behavior

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The brain stem auditory system of the chick has proven to be a useful model system for analyzing how the brain encodes temporal information. This paper reviews some of the work on a circuit in the brain stem that compares the timing of information coming from the two ears to determine the location of a sound source. The contralateral projection from the cochlear nucleus, nucleus magnocellularis (NM), to nucleus laminaris (NL) forms a delay line as it proceeds from medial to lateral across NL. NL neurons function like coincidence detectors in that they respond maximally when input from the two ears arrive simultaneously. This arrangement may allow NL to code sound space by the relative level of activity across the nucleus. The head anatomy of the chick allows for enhancement of the functional interaural time differences. Comparing the functional interaural time differences to the length of the neural delay line suggests that each NL can encode approximately one hemifield of sound space. Finally it is suggested that inhibitory input into the NM-NL circuit may provide a means to dynamically adjust the gain of the circuit to allow accurate coding of sound location despite changes in overall sound intensity. KeywordsAuditory system; Sound localization; Nucleus magnocellularis; Nucleus laminaris; Coincidence detection; Interaural canal; GABA Temporal information is important in the auditory system both for identification of different sources of sound and for determining the location of sounds. Identification of different sound sources can be accomplished, to a large extent, using monaural cues. While localization of a sound source can also be accomplished, to some extent, with only one ear, significant localization cues are contained in the comparison of binaural information. Sounds located to one side will arrive at the near ear slightly before they arrive at the distant ear and, in general, these offset sounds will be slightly louder in the near ear than in the distant ear. By analyzing differences in the timing and intensity of information at the two ears, the brain can compute the location of a sound source.The circuitry for computing the location of a sound source begins in the brain stem. This report will review some of our work over the past several years on the circuit that begins the neural analysis of interaural time differences in the chick. Emphasis will be given to the anatomical, physiological and neurochemical adaptations in this model system to accomplish binaural sound localization. This manuscript is not meant to be an exhaustive review of the literature in the field, but rather, a story that exemplifies how adaptations at different levels of a system each contribute to enhancing the precision of an important task. Fig. 1A, provides a circuit for transforming time differences at the two ears into a place of maximal activation along an array of neurons. There are two main features of this model: 1) delay lines to an array of neurons and 2) neurons that function as coincidence detectors. As wi...

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“…Bidirectional effects have also been observed by Lu and Trussell [25]. Our first studies simply recorded evoked activity in NM using field potential recordings.…”

Section: Neurotransmitter Systemsmentioning

confidence: 97%

Section: Neurotransmitter Systemsmentioning

confidence: 99%

Section: Neurotransmitter Systemsmentioning

confidence: 99%

mentioning

confidence: 99%

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The analysis of interaural time differences in the chick brain stem

Hyson

2005

Physiology & Behavior

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“…We call this parameter V CA because it applies to cell-attached recordings. We initially used the method of K ϩ channel reversal to measure V CA (Zhang and Jackson, 1993;Verheugen et al, 1999;Lu and Trussell, 2001). In this method, the pipette is filled with a K ϩ -rich solution (composition as above) so that the reversal potential of K ϩ -sensitive channels is very close to 0 mV.…”

Section: Estimate Of the Bias In The Measure Of The Mean Resting Potementioning

confidence: 99%

Coexistence of Excitatory and Inhibitory GABA Synapses in the Cerebellar Interneuron Network

Chavas¹,

Marty²

2003

J. Neurosci.

170

164

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Functional GABA synapses are usually assumed to be inhibitory. However, we show here that inhibitory and excitatory GABA connections coexist in the cerebellar interneuron network. The reversal potential of GABAergic currents (E GABA ) measured in interneurons is relatively depolarized and contrasts with the hyperpolarized value found in Purkinje cells (Ϫ58 and Ϫ85 mV respectively). This finding is not correlated to a specific developmental stage and is maintained in the adult animal. E GABA in interneurons is close to the mean membrane potential (Ϫ56.5 mV, as measured with a novel "equal firing potential" method), and both parameters vary enough among cells so that the driving force for GABA currents can be either inward or outward. Indeed, using noninvasive cell-attached recordings, we demonstrate inhibitory, excitatory, and sequential inhibitory and excitatory responses to interneuron stimulation [results obtained both in juvenile (postnatal days 12-14) and subadult (postnatal days 20 -25) animals]. In hyperpolarized cells, single synaptic GABA currents can trigger spikes or trains of spikes, and subthreshold stimulations enhance the responsiveness to subsequent excitatory stimulation over at least 30 msec. We suggest that the coexistence of excitatory and inhibitory GABA synapses could either buffer the mean firing rate of the interneuron network or introduce different types of correlation between neighboring interneurons, or both.

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Avian superior olivary nucleus provides divergent inhibitory input to parallel auditory pathways

et al. 2004

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The avian auditory brainstem displays parallel processing, a fundamental feature of vertebrate sensory systems. Nuclei specialized for temporal processing are largely separate from those processing other aspects of sound. One possible exception to this parallel organization is the inhibitory input provided by the superior olivary nucleus (SON) to nucleus angularis (NA), nucleus magnocellularis (NM), and nucleus laminaris (NL) and contralateral SON (SONc). We sought to determine whether single SON neurons project to multiple targets or separate neuronal populations project independently to individual target nuclei. We introduced two different fluorescent tracer molecules into pairs of target nuclei and quantified the extent to which retrogradely labeled SON neurons were double labeled. A large proportion of double-labeled SON somata were observed in all cases in which injections were made into any pair of ipsilateral targets (NA and NM, NA and NL, or NM and NL), suggesting that many individual SON neurons project to multiple targets. In contrast, when injections involved the SONc and any or all of the ipsilateral targets, double labeling was rare, suggesting that contralateral and ipsilateral targets are innervated by distinct populations of SON neurons arising largely from regionally segregated areas of SON. Therefore, at the earliest stages of auditory processing, there is interaction between pathways specialized to process temporal cues and those that process other acoustic features. We present a conceptual model that incorporates these results and suggest that SON circuitry, in part, functions to offset interaural intensity differences in interaural time difference processing.

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Mixed excitatory and inhibitory GABA‐mediated transmission in chick cochlear nucleus

Cited by 81 publications

References 31 publications

The analysis of interaural time differences in the chick brain stem

The analysis of interaural time differences in the chick brain stem

Coexistence of Excitatory and Inhibitory GABA Synapses in the Cerebellar Interneuron Network

Avian superior olivary nucleus provides divergent inhibitory input to parallel auditory pathways

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