Ultrastructural peculiarities of the supraoptic nucleus of Mauremys caspica (turtle): its evolutionary interest in reptiles.

The hypothalamic Supraoptic Nucleus (SON) supposes an evolutionary achievement in the reptiles, zoological group in which this nucleus is first differentiated. Its scarce development in the chelonian, subject of the present study, is related to their primitive brain pattern. The peculiar location and the topographical configuration of the SON in the hypothalamus of the turtle Mauremys caspica allows to evidence morphologically the successive steps in the evolutionary process from lower to higher vertebrates. The marked neurosecretory character of the chelonian SON is the unequivocal proof of its philogenetic origin derived from the magnocellular preoptic nucleus of lower vertebrates.

Similarity between cytoplasmic inclusions in the paraventricular hypothalamic nucleus neurons of the turtle Mauremys caspica and the cytoplasmic structures as reaction to viral infections (hepatitis) and SIDA ultrastructural tracers.

Two types of "inclusions" observed in the neurons of the hypothalamic paraventricular nucleus of the turtle Mauremys caspica, "tubular systems" and "fingerprint-like" structures, may be added to the inventory of those described in apparently normal neurons. Despite their enigmatic significance, we are inclined to think that they could be a morphological expression of viral diseases in the neuron cytoplasm. These structures have a striking similarity with those observed on pathological cells (hepatitis and SIDA).