MinireviewPhysiology, pharmacology and plasticity at the inner hair cell synaptic complex
Section snippets
AMPA-preferring receptors mediate fast synaptic neurotransmission
Analysis of ionotropic glutamate (Glu) receptors with gene expression, immunocytochemistry and in situ hybridization indicates that spiral ganglion neurons expressed NMDA (NR1 and NR2A-D), AMPA (GluR2-4, see Fig. 1B), kainate (GluR5-7) receptor sub-units, as well as the high affinity kainate binding proteins (KA1 and KA2) (Pujol et al., 1985, Pujol et al., 1993, Gil-Loyzaga and Pujol, 1990, Puel, 1995). This suggests that NMDA, AMPA and kainate receptors might co-exist in ganglion neurons.
The Glu transporter Glast regulates fast synaptic transmission
Glutamate transporters form a powerful uptake system that rapidly eliminates glutamate from the extracellular spaces (Seal and Amara, 1999, Sims and Robinson, 1999, Tanaka, 2000, Danbolt, 2001). Five subtypes of Na+-dependent glutamate transporters have been cloned and identified to date, in various species, including humans: GLAST (excitatory amino acid transporter, EAAT1, glutamate aspartate transporter; Storck et al., 1992, Tanaka, 1993); GLT-1 (EAAT2, glutamate transporter; Pines et al.,
Modulation of the Glu synapse by the lateral olivocochlear efferents
Most of the data for lateral olivocochlear (LOC) efferents are based on lesioning studies of the entire olivocochlear bundle, including both LOC and MOC (medial olivo-cochlear) efferents. Only two studies have reported changes in auditory nerve response following complete cochlear de-efferentation in adult animals (Liberman, 1990, Zheng et al., 1999). The de-efferented ears showed very little change in threshold levels, but a very large decrease in the spontaneous discharge rate. Selective
Glutamate excitotoxicity and regeneration
To date, kainate, AMPA and glutamate have been reported to be neurotoxic in the cochlea in vivo. An acute exposure to these agonists results in a dose dependent swelling of radial dendrites (Pujol et al., 1985, Gil-Loyzaga and Pujol, 1990, Puel et al., 1991, Puel et al., 1994). Kainate, after a week survival time, also causes a loss of spiral ganglion neurons (Juiz et al., 1989, Janssen et al., 1991). There is a striking similarity of damage at the level of radial dendrites between acute
Conclusions
As already pointed out in describing electron microscopic findings, the mechanism of regeneration of auditory dendrites and neo-synaptogenesis after an excitotoxic injury seems to mimic normal development. Thus it would be important to investigate also for an involvement of neurotrophic factors and other molecules which are known to play a role in the growth and guidance of neurites. Another type of molecule could also play a more specific role: the lateral efferent neurotransmitters (see Fig. 1
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2023, Hearing ResearchDiverse identities and sites of action of cochlear neurotransmitters
2022, Hearing ResearchExcitotoxic damage to auditory nerve afferents and spiral ganglion neurons is correlated with developmental upregulation of AMPA and KA receptors
2021, Hearing ResearchCitation Excerpt :Glutamate is recognized at the neurotransmitter released by IHCs on to the peripheral type I afferent terminals of SGNs. AMPA, kainate and NMDA receptors are expressed on type I auditory nerve fibers and SGNs (Puel, 1995; Ruel et al., 2007). The release and reuptake of glutamate from IHCs and the number of GluRs expressed on the afferent nerve terminal is tightly regulated to optimize fast synaptic transmission and maintain homeostatic conditions (Chen et al., 2009; Furness and Lehre, 1997; Peppi et al., 2012; Puel et al., 2002b).