Neural excitability, synaptic transmission and neuron-glia interactions
Author: Camila Catalano Di Meo | email: ccatalano98@gmail.com
Camila Catalano Di Meo 1°, Regis Nouvian 2°, Juan Goutman 1°
1° INGEBI (CONICET)
2° The Institute for Neuroscience of Montpellier
During the development of the auditory system, sensory independent activity drives neurons to spike in a coordinated manner that is important for shaping brain connections. This activity originates in the cochlea where inner hair cells (IHCs) fire action potentials eliciting the release of tens of glutamate-filled vesicles onto auditory nerve neurons. Due to the mechanism for concentrating glutamate into the vesicular lumen, a very low pH is also found in this organelle. Protons are co-released with neurotransmitter into the synaptic cleft producing a transient reduction of the extracellular pH. Here, we investigated the effect of protons on the spiking activity of the developing IHCs. Recording these cells, we found that the perfusion of an extracellular solution with low pH (6.8) produced a reduction of the firing rate, whereas the opposite occurred in pH 8.2. Seeking for the mechanisms of this modulation, IHCs conductances were measured at these two pH values. Ca2+ and K+ channels (L-type and inward rectifier, respectively) showed a modest change that could not account for the effect observed on the spiking rate. Efferent cholinergic fibers originating in the brainstem contact IHCs and produce synaptic inhibition which is key for regulating its spiking rate. The effect of pH on this synapse is also insufficient to explain the global action on IHCs excitability and therefore, other conductances should also be evaluated to understand IHCs activity during development.