An enigmatic eye: the histology of the tuatara pineal complex.
OBJECTIVE
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.


CONCLUSIONS
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.
Ung
Casey Y-J
CY
Department of Ophthalmology, Dunedin Hospital, New Zealand.
Molteno
Anthony C B
AC
D000818:Animals; D000831:Animals, Newborn; D005075:Biological Evolution; D009799:Ocular Physiological Phenomena; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology / Q000502:physiology; D010802:Phylogeny; D010870:Pineal Gland / Q000033:anatomy & histology* / Q000502:physiology; D012104:Reptiles / Q000033:anatomy & histology* / Q000502:physiology