Neural excitability, synaptic transmission and neuron-glia interactions
Author: Walen Leonardo Gribaudo | Email: walen.gribaudo@gmail.com
Walen L. Gribaudo1°, Juan D. Goutman1°
1° Laboratorio de Transmision Sinaptica del Sistema Auditivo (INGEBI-CONICET)
AMPA receptors in the mammalian brain mediate fast neurotransmission and are typically found in the postsynaptic densities (PSDs). Across synapses a great variability of PSDs sizes and number of AMPA receptors has been described . In the mammalian inner ear, glutamatergic synapses are formed between inner hair cells (IHCs) and spiral ganglion neurons (SGNs). All aspects of sound information are encoded and transmitted to the brain through this synapse. A key aspect of the presynapse (IHCs) is the presence of a ‘synaptic body’ or ‘ribbon’ that concentrates large amounts of synaptic vesicles, ensuring high rates of exocytotic events. Postsynaptic terminals of SGNs are characterized by large PSDs, 5 to 10 times bigger than those found in the brain. The role that these large PSDs play in synaptic function is unknown. We speculate that normal neurotransmission activates only a portion of the PSDs area, resulting in non-saturation of the AMPA receptors. To investigate this, we implemented a glutamate photolysis method by which a laser pulse is flashed upon the entire postsynapse, previously bathed with a caged-glutamate compound, producing fast transients in glutamate concentration. Responses to glutamate uncaging were recorded by patch-clamp directly on SGNs terminals. Both the intensity and the duration of laser pulses could be modulated to generate transients of different sizes