The measurement of function in the intact organ of Corti has up to now
been achieved by three methods: electrophysiology, mechanical measure
ment and biochemical analysis. The two former methods have supplied in
formation at the level of single identified cells. We have used a four
th method, optical fluorimetry, to measure hair cell function at the c
ellular level in the intact organ of Corti. Here we describe the metho
ds involved in fluorescence labelling and video-enhanced microscopy in
combination with electrophysiological recording of cochlear microphon
ic (CM) and summating potentials (SP). The guinea pig temporal bone co
ntaining an intact ear drum, ossicular chain and cochlea can be mainta
ined in the isolated state by perfusion of the scala tympani with oxyg
enated tissue culture medium. Substances added to the perfusate readil
y diffuse through the basilar membrane into the organ of Corti. In thi
s way cells in the organ can be stained by a number of fluorescent pro
bes which label different structures and functions. Here we have used
two dyes which label mitochondria and fluoresce with an intensity prop
ortional to metabolic activity. By simultaneous measurement of CM and
SP the functional state of the organ can be monitored.