Relatively little is known about the effects of
melatonin on the aging of the pineal, the organ which is
the main place for synthesis of this hormone. Using
simple morphometric methods, some parameters of the
pineal gland, such as total volume, number of
pinealocytes and pinealocyte volume were estimated in
two mice strains: normal CBA and melatonin-deficient
C57BLl6J. Two age groups, 6 weeks and 10 months,
were studied in order to evaluate possible differential
age-related changes between both strains. Pineals of both
strains have similar morphometric and morphological
features at 6 weeks of age. This suggests that pineal
development, which has already concluded at 6 weeks of
age, is not affected by the absence of melatonin
synthesis in the pinealocytes. Later on, CBA pineal
showed an increase in size caused by cellular
hypertrophy. In contrast, the C57BLl6J pineal volume
decreased by loss of pinealocytes in the same period of
time. Semithin sections analysed by light microscopy did
not show that this cell death was evident in the
C57BL16J strain at any of the ages studied. Thus, a
gradual loss of pinealocytes could be hypothesised in
these pineals. These results suggest that pineal melatonin
could have a role in the maintenance of pinealocyte
viability and the increase of pineal size which takes
place after development. The abnormal pattern observed
in the C57BL16J pineal should be taken into account in
future studies on this gland