Use of the pinna reflex as a test of hearing in mutant mice

Although it is a gross measure, the pinna reflex test is easily administere d and is, therefore, incorporated as a general screening tool in mutagenesi s programs. Our recent application of this approach indicated that mutant m ice lacking one of the small Maf proteins, in this case MafG, failed to exh ibit a pinna reflex. In contrast, littermate controls, with the same mixed 129/CD1 background, and including both wild type and heterozygous mutant an imals, passed the test. Because previous studies indicate that mafG is expr essed in both cochlear and vestibular parts of the mouse inner ear, the sou rce of this 'presumed deafness' was further assessed by making round window recordings to determine compound action potential thresholds. Auditory bra instem responses were also acquired to assess function along portions of th e central auditory pathway. In all cases, responses in homozygous mutants ( -/-) were comparable to those obtained from littermate controls, either wil d type (+/+) or heterozygous mutants (+/-). Gross anatomy of the organ of C orti was also found to be similar in all three groups of mice. Hence, the l ack of a pinna reflex must relate to nonauditory causes. Copyright (C) 2001 S. Karger AG, Basel.