Structural changes of the periosteocytic area in Vipera aspis (L.) (Ophidia, Viperidae) bone tissue in various physiological conditions

Microradiographs of ribs and vertebrae of the snake Vipera aspis, over an annual cycle, show a significant enlargement of the osteocytic lacunae in the winter months and, for the breeding females, during the period of embryo development. This enlargement is due to resorption of bone substance (periosteocytic osteolysis). The objection that such morphological findings could as well be explained by the formation of new, larger osteocytes derived from recent osteoblasts does not apply to the present animal model. No internal bone remodelling occurs during the annual seasonal cycle and therefore no new osteoblasts would have differentiated to osteocytes in the interior of the bone. In the vertebrae, an additional process is indicated as an area of decreased mineral density, termed demineralization halo, around the periosteocytic lacunae. An electron microscopy study suggests that this process of demineralization is not the first stage of periosteocytic resorption, but an additional process of demineralization. Thus, both osteolysis and demineralization halos in the perilacunar osteocytic region of the bone tissue represent reversible biological processes mediated by the osteocytes.