Abstract
Endocochlear potential (EP) and cochlear microphonics (CM) were recorded in guinea pig litters at some stages before and after birth. Endolymph and scala tympani perilymph samples were collected for ions quantification and the cochlei were processed for surface analysis by scanning electron microscopy.
While CM was recorded as early as on the 55th gestation day, EP did not show positive values before the 62nd day. At this stage, the labyrinthine fluids have already acquired their specific ionic composition, although the potassium level in the perilymph was still higher than in adults. The negative potential prevailed for at least 10 days, until the EP altered to positive.
Gradual disappearance of the microvilli and kinocilium was the last change to occur before the sensory epithelium reached a mature shape on the 62nd gestation day (5 days before birth). At the same time, the tectorial membrane appeared to lose its firm attachment to the organ of Corti.
