Calcium‐binding protein immunoreactivity characterizes the auditory system of Gekko gecko

Abstract

Geckos use vocalizations for intraspecific communication, but little is known about the organization of their central auditory system. We therefore used antibodies against the calciumbinding proteins calretinin (CR), parvalbumin (PV), and calbindin-D28k (CB) to characterize the gecko auditory system. We also examined expression of both glutamic acid decarboxlase (GAD) and synaptic vesicle protein (SV2). Western blots showed that these antibodies are specific to gecko brain. All three calcium-binding proteins were expressed in the auditory nerve, and CR immunoreactivity labeled the first-order nuclei and delineated the terminal fields associated with the ascending projections from the first-order auditory nuclei. PV expression characterized the superior olivary nuclei, whereas GAD immunoreactivity characterized many neurons in the nucleus of the lateral lemniscus and some neurons in the torus semicircularis. In the auditory midbrain, the distribution of CR, PV, and CB characterized divisions within the central nucleus of the torus semicircularis. All three calcium-binding proteins were expressed in nucleus medialis of the thalamus. These expression patterns are similar to those described for other vertebrates.Keywords cochlear nucleus; magnocellularis; laminaris; angularis; torus Over 30 years have passed since Foster and Hall (1978) reported that the ascending auditory pathways of the iguana resemble both the mammalian and the avian auditory pathways, from the level of the first-order neurons in the VIIIth nerve to the telencephalon. They recognized a basic plan for the organization of the auditory system in terrestrial vertebrates but also pointed out that the auditory capacities of the lizards were largely unknown. We now know more about the peripheral (Manley, 1990;Wever, 1978) and central (for reviews see Carr, 1992;Grothe et al., 2005;ten Donkelaar et al., 1987) auditory systems of lizards, but still know little about central auditory processing. We have therefore used Gekko gecko for further analysis of the lizard central auditory system.Geckos are auditory specialists that use vocalizations for intraspecific communication (Marcellini, 1977;Tang et al., 2001). Their ears differ from those of other reptiles such as archosaurs and turtles. Lepidosaur ears are highly directional, with middle ears connected through the mouth cavity (Christensen-Dalsgaard and Manley, 2008). This patent connection enhances the directionality of the ear by allowing sound access to both sides of NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript each tympanic membrane. The acoustically coupled ear creates directional responses from the tympanum Manley, 2005, 2008). Additionally, lizards have independently evolved micromechanical hair cell tuning, permitting emergence of sensitive high-frequency hearing in a specialized region of the papilla (Manley, 2002). Thus lizard auditory systems might reveal specializations for hearing high frequencies and sound localization.We have begun our analysis of liza...

Binaural processing by the gecko auditory periphery

“…Lizards have two types of auditory nerve fibers, which differ both in peripheral features Mulroy and Oblak 1985;Mulroy 1986) and electrophysiology Weiss et al 1976). The auditory nerve fibers also have separate projection patterns into the brain (Barbas-Henry and Lohman 1988; Szpir et al 1990;Yan et al 2010). Tectorial fibers, which appear to correspond to mammalian type I fibers and avian cochlear nerve fibers, respond to lower best frequencies and project to both first order nuclei, an arrangement thought to have been present from the stem reptiles (Baird 1974;Miller 1980;Manley 1981;Carr and Code 2000).…”

“…Gecko phase locking is acute Ͻ500 Hz (Fig. 4) and they have a discernable nucleus laminaris (Yan et al 2010). Above ϳ1 kHz, phase locking is degraded (Fig.…”