Abstract
Cholinergic brainstem neurones make inhibitory synapses on outer hair cells (OHCs) in the mature mammalian cochlea and on inner hair cells (IHCs) prior to the onset of hearing. We used electrical stimulation in an excised organ of Corti preparation to examine evoked release of acetylcholine (ACh) onto neonatal IHCs from these efferent fibres. Whole-cell voltage-clamp recording revealed that low frequency (0.25-1 Hz) electrical stimulation produced evoked inhibitory postsynaptic currents (IPSCs) at a relatively high fraction of failures (65%) and with mean amplitudes of about -20 pA at -90 mV, corresponding to a quantum content of approximately 1. Evoked IPSCs had biphasic waveforms at -60 mV, were blocked reversibly by alpha-bungarotoxin and strychnine and are most likely mediated by the alpha9/alpha10 acetylcholine receptor, with subsequent activation of calcium-dependent potassium (SK2) channels. Paired pulse stimulation with intervals of 10-100 ms caused facilitation of 200-300% in the mean IPSC amplitude. A train of 10 pulses with an interpulse interval of 25 ms produced increasingly larger IPSCs with maximum amplitudes greater than -100 pA due to facilitation and summation throughout the train. Repetitive efferent stimulation at 5 Hz or higher hyperpolarized IHCs by 5-10 mV and could completely prevent the generation of calcium action potentials normally evoked by depolarizing current injection.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.