In vivo and in vitro biophysical properties of hair cells from the lateral line and inner ear of developing and adult zebrafish

Abstract

Hair cells detect and process sound and movement information, and transmit this with remarkable precision and efficiency to afferent neurons via specialized ribbon synapses. The zebrafish is emerging as a powerful model for genetic analysis of hair cell development and function both in vitro and in vivo. However, the full exploitation of the zebrafish is currently limited by the difficulty in obtaining systematic electrophysiological recordings from hair cells under physiological recording conditions. Thus, the biophysical properties of developing and adult zebrafish hair cells are largely unknown. We investigated potassium and calcium currents, voltage responses and synaptic activity in hair cells from the lateral line and inner ear in vivo and using near-physiological in vitro recordings. We found that the basolateral current profile of hair cells from the lateral line becomes more segregated with age, and that cells positioned in the centre of the neuromast show more mature characteristics and those towards the edge retain a more immature phenotype. The proportion of mature-like hair cells within a given neuromast increased with zebrafish development. Hair cells from the inner ear showed a developmental change in current profile between the juvenile and adult stages. In lateral line hair cells from juvenile zebrafish, exocytosis also became more efficient and required less calcium for vesicle fusion. In hair cells from mature zebrafish, the biophysical characteristics of ion channels and exocytosis resembled those of hair cells from other lower vertebrates and, to some extent, those in the immature mammalian vestibular and auditory systems. We show that although the zebrafish provides a suitable animal model for studies on hair cell physiology, it is advisable to consider that the age at which the majority of hair cells acquire a mature-type configuration is reached only in the juvenile lateral line and in the inner ear from >2 months after hatching.

Hearing sensitivity differs between zebrafish lines used in auditory research

“…Adult zebrafish are used in a variety of auditory studies, including research on hair cell death and putative mechanisms of regeneration (Bang et al, 2002; Schuck et al, 2011; Liang et al, 2012, Burns et al, 2013; Uribe et al, 2013a). In particular, a recent study demonstrated that biophysical hair cell properties are mature in zebrafish over two months old, suggesting that adult animals are preferable for some auditory physiology experiments (Olt et al, 2014). Our data show that care is needed in selecting a fish line for auditory studies and in comparing results between fish lines, particularly for research using adult animals.…”

Ribbon synapses in zebrafish hair cells

“…In particular, the development of a loose patch method of recording spiking activity in afferent neurons of the lateral line organ has been instrumental in describing defects in various mutants (Trapani and Nicolson, 2010). Moreover, new methods for quantifying calcium transients in zebrafish hair cells (Kindt et al, 2012) have made valuable contributions to understanding mutant phenotypes, and finally, the ability to directly measure hair-cell currents and capacitance using patch clamp recordings in larvae (Olt et al, 2014; Ricci et al, 2013) opens the door to more detailed analysis in future studies.…”

The genetics of hair-cell function in zebrafish

“…Thus, another type of recording was recently established in zebrafish larvae: whole-cell recordings of lateral-line hair cells (Olt et al, 2014, 2016a, 2016b; Ricci et al, 2013). The technique is challenging and to date, direct measurements of mechanotransduction currents are sparse, but further use and development of this method will be critical for characterizing different types of currents in various mutants.…”