We examined cells from the nucleus pulposus and annulus
fibrosus of adult bovine intervertebral discs, using
confocal laser scanning microscopy on living unfixed tissue. These
cells were visualised using chloromethyl
fluorescein diacetate, a membrane-impermeant fluorescent dye. The
organisation of cells from the outer
annulus was also determined using confocal microscopy after fixation
and staining the actin-filaments with
FITC-phalloidin. We found that cellular processes were a dominant
feature of cells from all regions of the
disc including the cells of the nucleus pulposus and inner annulus.
These processes were also visible in
histological sections of disc examined both at the light and electron
microscope level, even though cells from
the nucleus and inner annulus appeared chondrocyte-like, being rounded
and enclosed in a capsule. The
function of these processes is at present unknown. We suggest that they
may serve to sense mechanical strain.