Unravelling the molecular components of the cholinergic efferent system in zebrafish lateral line

AGUSTIN CARPANETO FREIXAS; MARCELO MOGLIE; PAOLA V. PLAZAS; ANA BELEN ELGOYHEN.

Congreso; XXXIV Reunión Anual. de la. Sociedad Argentina de Investigación en Neurociencias; 2019

Zebrafish (z) lateral line (LL) is a mechanosensory system that consists of hair cells (HC) innervated by afferent neurons that transmit information to the CNS and by efferent neurons that make direct contact with hair cells. LL HC share many characteristics with those in vertebrate inner ear, namely efferent stimulation to these systems leads to similar effects, suggesting the existence of similar synaptic mechanisms. It is known that the alpha9 alpha10 (α9α10) nicotinic receptor (nAChR) mediates efferent transmission in the cochlea, however this information is lacking for zLL. RNAseq studies have recently shown that α9 is differentially expressed both in LL and inner-ear HCs. We have cloned zα9, expressed it in X. laevis oocytes and performed two-electrode voltage-clamp recordings. α9 homomeric nAChR are activated by Ach, and reversibly blocked by α-Bungarotoxin (α-Btx). α9 nAChRs exhibit high calcium (Ca2+) permeability and large desensitization rates. To study the properties of the native zLL nAChR, we performed in vivo Ca2+ imaging in transgenic zebrafish larvae that express a genetically encoded Ca2+ sensor specifically in HC. We measured Ca2+ entering HC through Cav1.3a channels during mechanical stimulation as a proxy of its electrical state. ACh reduces evoked Ca+2 influx and this effect is blocked by α-Btx. These results support the idea that a nAChR composed of the α9 subunit could be mediating transmission at the efferent synapse of zLL.