Department of Ophthalmology, Dunedin Hospital, New Zealand.
AIM: To examine the histology of the tuatara pineal complex and to compare
findings with those of Dendy. Some reptiles have an anatomically
sophisticated pineal complex with a median pineal eye, a paraphysis and a
pineal sac. In comparison, the human pineal gland is simple and homogenous
and thought to be a phylogenetic relic. It is now considered a
neuroendocrine gland the function of which is still not fully understood.
Its simple anatomical structure is in contrast to its biochemical
complexity; its secretions (the most studied being melatonin) modifying
the function of the adeno- and neurohypophysis, thyroid and parathyroids,
adrenal cortex and medulla, endocrine pancreas and the gonads.
METHODS: Histological sections of the brain of a neonatal tuatara were
studied by light microscopy.
RESULTS: The histological findings of the pineal eye demonstrated a
cornea-like structure, rudimentary lens and simple retina. The adjacent
paraphysis was a large, multisaccular organ and the pineal sac a very
large saccular organ with a poorly differentiated retina.
CONCLUSION: The pineal eye of the tuatara has a remarkably eye-like
structure with photoreceptors that in other reptiles have been shown to
exhibit photoreceptive capabilities. The paraphysis appeared to have a
secretory function that is as yet undetermined, while the pineal sac had
the appearance of a poorly differentiated retina. Thus it appears that the
complex biochemistry of the human pineal gland is reflected in the complex
anatomical structure of this primitive reptile.
