Distinct differences in partial oxygen pressure at micrometer ranges in the rat hippocampal region.

ABSTRACT

A mapping at micrometer ranges of the partial oxygen pressure in the rat hippocampus was performed. The oxygen tension in the rat hippocampal region was measured using a glass oxygen microsensor in 30-microm steps along straight lines at a set of stereotactic coordinates. In the hippocampus the pattern of the oxygen tensions reflected the autometallographic zinc sulphide (AMG(ZnS)) pattern, i.e. the pattern of zinc enriched (ZEN) terminals. The highest levels of oxygen tension were recorded in the areas that are most heavily stained with the autometallographic zinc sulphide (AMG(ZnS)) method, like hilus fasciae dentatae. The zinc ions located in synaptic vesicles of the ZEN terminals can also be demonstrated by AMG silver amplification in brains from animals in vivo treated with sodium selenite. This method depends on the presence of a substantial reduction capacity of the tissues as selenite ions (SeO(2)(3)-) must to be reduced to selenide ions (Se2-) before the catalytic zinc selenide crystals can be formed. At some point, either during the transport from the infusion site to the actual target tissue or in the target tissue itself, selenium is reduced from Se(+ IV) to Se(- II). The importance of the reduction capacity of the target tissue in this process is demonstrated by the fact that areas found to have the highest concentration of zinc ions, e.g. hilus fasciae dentatae and the mossy fibres of CA3, are almost unstained after 1 h of i.p. Na2SeO3 exposure. An explanation of this phenomenon could be that the reduction process Se(+ IV) <==> Se(- II) leading to the formation of Se2- is moved to the left by the presence of oxygen, thus inhibiting the precipitation of ZnSe crystals. It is suggested that the subtle oxygen pressure pattern found in the rat hippocampus might also reflect essential biological zinc-related mechanisms vital to brain function.