The extracellular matrix of rat Pacinian corpuscles: an analysis of its fine structure

The Pacinian corpuscle consists of a sensory axon terminal that is envelope d by two different structures, the inner core and the capsule. Since proteo glycans are extremely water soluble and are extracted by conventional metho ds for electron microscopy, the current picture of the structural compositi on of the extracellular matrix in the inner core and the capsule of the Pac inian corpuscle is incomplete. To study the structural composition of the e xtracellular matrix of the Pacinian corpuscles, cationic dyes (ruthenium re d, alcian blue, acridine orange) and tannic acid were applied simultaneousl y with the aldehyde fixation. The interosseal Pacinian corpuscles of the ra t were fixed either in 2% formaldehyde and 1.5% glutaraldehyde, with the ad dition of one of these cationic dyes or, in Zamboni's fixative, with tannic acid added. The cationic dyes and tannic acid revealed a different structu ral pattern of proteoglycans in the extracellular matrix in the inner core and in the capsule of the rat Pacinian corpuscles. The inner core surroundi ng the sensory axon terminal is a compartment containing proteoglycans that were distributed not only in the extracellular matrix but also in the cyto plasm of the lamellae. In addition, this excitable domain was separated fro m the capsular fluid by a thick layer of proteoglycans on its surface. An e nlarged interlamellar space of the capsule contained large amounts of prote oglycans that were removed by digestion with chondroitinase-ABC. Ruthenium red and alcian blue provided only electron dense granules, probably corresp onding to collapsed monomeric proteoglycan molecules. Acridine orange and t annic acid preserved proteoglycans very well and made it possible to visual ize them as "bottlebrush'' structures in the electron microscope. These res ults show that the inner core and the capsule of rat Pacinian corpuscles ha ve different structural patterns of proteoglycans, which are probably invol ved in different functions.