FINE-STRUCTURE AND LECTIN HISTOCHEMISTRY OF THE APICAL SURFACE OF THEFREE NEUROMAST OF LAMPETRA-JAPONICA

The surface coat, ciliary process, and microvilli of the lamprey neuro mast were examined with electron microscopy after tannic acid prefixat ion and lectin histochemistry. The neuromast was found to exist in the form of a dermal mound with a furrow in the middle. On the bottom of the furrow, the hair cell was characterized by a kinocilium and 15-20 stereocilia, arranged along the longitudinal axis of the furrow. Spann ing structures were demonstrated between the kinocilium and stereocili a as well as between stereocilia. The surface coat, enhanced by tannic acid prefixation, was particularly rich over the surface of the suppo rting cell; by contrast, it was thin over the hair cell. Some lectins (PNA, GS-I, SBA, WGA) showed affinity to the surface coat of tile supp orting cell as well as the hair cell, and the others (RCA-I, MPA, ConA ) showed affinity only to the supporting cell. These differences in th e structure and affinities of the surface coat suggest an extracellula r milieu highly specialized for the hair cell in this particular form of the mechanoreceptor.