However, binaural acoustic stimulation and/or the addition of noise to the opposite ear can increase MOC discharge rate still further (up to 140 Hz) (Liberman, 1988)

However, binaural acoustic stimulation and/or the addition of noise to the opposite ear can increase MOC discharge rate still further (up to 140 Hz) (Liberman, 1988). studies on cellular and molecular mechanisms of cholinergic inhibition and the regulation of those molecular components, in particular the involvement of intracellular calcium. Facilitation at the efferent synapse is compared in a variety of animals, as well as other possible mechanisms of modulation of ACh release. Rabbit polyclonal to PITPNM3 These results suggest that short-term plasticity contributes to effective cholinergic inhibition of hair cells. == 1. Introduction == Mechanosensory hair cells in the organ of Corti send acoustic information to the brain through synapses with peripheral afferent neurons. In return, feedback provided by efferent neurons located in the brainstem and projecting to the cochlea modulates that afferent activity. Efferent inhibition of the auditory end-organs was first shown byGalambos (1956). Electrical stimulation of the olivocochlear axons reduced the amplitude of the compound action potential (CAP) recorded extracellularly from the VIIIth nerve in response to an acoustic click or brief tone burst. It is now widely accepted that this CAP reduction resulted from medial olivocochlear (MOC) efferent inhibition of the active electromotile response of OHCs that amplifies basilar membrane motion to increase acoustic sensitivity (Brownell et al., 1985;Ashmore, 1987) for review see (Guinan and Stankovic, 1996;Cooper and Guinan, 2006;Ashmore, 2008). In mammals, the efferent neurons can be classified into two anatomically and functionally distinct groups named according to their origin in the lateral or medial region of the superior olivary complex (Warr and Guinan, 1979): lateral olivocochlear (LOC) efferents project to the region near the inner hair cells (IHCs) and terminate on the dendrites of type I auditory afferents postsynaptic to the IHCs. Medial olivocochlear Cimetidine (MOC) efferents originate in the medial and rostral region of the superior olivary complex and send thicker myelinated axons to innervate predominantly outer hair cells (OHCs) in the mature cochlea as well the IHCs of pre-hearing animals (see for review (Simmons, 2002;Bruce et al., 2000). This review will summarize physiological studies of efferent inhibition in hair cells of vertebrates ranging from fish to mammals. Studies in the mammalian cochlea focused initially on the transient MOC synapses on immature inner hair cells (IHCs), but improving methodologies have increased attention to older OHCs. However, postsynaptic recordings of LOC effects in type I afferents are only beginning, and so are not available for this review. The interested Reader is referred to previous studies of LOC function (Ruel et al., 2007). The mechanism of cholinergic inhibition is well-conserved among vertebrate hair cells, mediated by an unusual ionotropic ACh receptor and associated calcium-activated potassium channels. In addition, efferent terminals may contain other neurotransmitters, receptors and channels that could modulate synaptic strength. These candidate signaling molecules will be summarized first. Secondly, we will discuss emerging knowledge on the mechanics of synaptic transmission and its modulation by neurotransmitters or small proteins. Short-term facilitation of inhibition has been observed in several species, and may be a fundamental property of efferent feedback. Finally, we reviewin vivoolivocochlear physiology, in particular those studies providing information on the discharge rate of MOC neurons to assess further the role of activity-dependent plasticity in olivocochlear function. == 2. Cellular mechanism of MOC efferent inhibition == Although recent studies have concentrated on efferent inhibition of mammalian cochlear hair cells, the initial descriptions of cellular mechanisms came from studies in non-mammalian vertebrates. In the lateral line organ of fish (the burbot) electrical stimulation of efferent fibers evoked Cimetidine inhibitory post-synaptic potentials (IPSPs) that hyperpolarized the hair cells and reduced the amplitude of spontaneous or evoked EPSPs recorded from afferent nerve terminals (Flock and Russell, 1976). Similar results Cimetidine were observed in frog saccular hair cells (Ashmore and Russell, 1983) as well as in the turtle Cimetidine basilar papilla where hair cell hyperpolarization and afferent inhibition were strengthened by higher frequency efferent stimulation (Art et al., 1984). Furthermore, efferent inhibition decreased the receptor potential specifically at the characteristic frequency, effectively detuning the hair cell. Although this effect is related to the electrical tuning mechanism in turtle hair cells (Art et al., 1985), efferent inhibition in.