Short term plasticity (STP) changes during development of the medial olivocochlear-inner hair cell synapse in the mouse cochlea

ZORRILA DE SAN MARTIN J; BALLESTERO J; FUCHS P; ELGOYHEN AB; KATZ E

Huerta Grande, Córdoba, Argentina

Congreso; II Reunión Conjunta de la SAN y TAN, IIRCN; 2010

In the organ of Corti, the sensory cells of the mammalian auditory system, inner hair cells (IHCs) transduce sound stimuli into electrical signals that are conveyed to the central nervous system. Before the onset of hearing, IHCs are transiently innervated by cholinergic medial olivo-cochlear (MOC) fibers. Synaptic activity was recorded in voltage-clamped IHCs from excised apical turns of the mouse cochlea at two developmental stages (postnatal days (P) 5-7 and 9-11), during electrical stimulation of the MOC fibers. Ten-pulse trains at 10, 20, 40 and 100 Hz applied to P5-7 MOC-IHC synapses led to 2.9±0.7; 2.1±0.4; 2.4±0.5 and 2.0±0.4 fold increase in synaptic efficacy, respectively, estimated as the ratio between the amplitude of the fifth and the first evoked synaptic current (S5/S1); n=7-8. Facilitation induced by the 40 and 100 Hz trains was followed by a slight depression. The same protocols applied to P9-11 synapses led to a progressive decrease of the S5/S1 value (0.9±0.1; 0.8±0.1; 0.8±0.1; 0.5±0.1 for the 10, 20, 40 and 100 Hz trains, respectively; n=12-19). Depression upon high frequency stimulation at P9-11 was reversed to facilitation when reducing [Ca2+]o. Our results suggest differences in the coupling between Ca2+ influx and transmitter release at the two stages. Synaptic activity was recorded in voltage-clamped IHCs from excised apical turns of the mouse cochlea at two developmental stages (postnatal days (P) 5-7 and 9-11), during electrical stimulation of the MOC fibers. Ten-pulse trains at 10, 20, 40 and 100 Hz applied to P5-7 MOC-IHC synapses led to 2.9±0.7; 2.1±0.4; 2.4±0.5 and 2.0±0.4 fold increase in synaptic efficacy, respectively, estimated as the ratio between the amplitude of the fifth and the first evoked synaptic current (S5/S1); n=7-8. Facilitation induced by the 40 and 100 Hz trains was followed by a slight depression. The same protocols applied to P9-11 synapses led to a progressive decrease of the S5/S1 value (0.9±0.1; 0.8±0.1; 0.8±0.1; 0.5±0.1 for the 10, 20, 40 and 100 Hz trains, respectively; n=12-19). Depression upon high frequency stimulation at P9-11 was reversed to facilitation when reducing [Ca2+]o. Our results suggest differences in the coupling between Ca2+ influx and transmitter release at the two stages.