The Efferent Auditory System in Doppler-Shift Compensating Bats

Abstract

Studies on the innervation of outer hair cells (OHCs) of common laboratory animals have repeatedly demonstrated a general pattern of efferent terminals throughout the cochlea (Smith and Sjostrand, 1961; Iurato et al., 1978; Spoendlin, 1979). Many efferent endings typically contact each OHC in the basal turn of the cochlea and the number decreases in more apical regions, particularly on the outermost rows. The present study on the efferent innervation of outer hair cells in different species of Doppler-shift compensating bats has revealed marked interspecies differences as well as striking departures from the basic plan known to occur in common laboratory animals. Studies were carried out on the cochlea of the neotropical mormoopid, Pteronotus p. parnellii and on the Old World rhinolophids, Rhinolophus rouxi and Hipposideros lankadiva. The rhinolophids and P. parnellii have independently evolved sophisticated biosonar systems; although the frequency resolving properties of their ears are similar, marked structural and physiological differences exist (Bruns, 1980; Kossl and Vater, 1985; Henson et al., 1985).