Abstract: Purpose: Moderate normobaric hypoxia causes long-lasting protection
against damage induced by a second ischemic or traumatic insult. The changes
induced by such conditioning hypoxia are not yet fully understood. The
protective effect has been described in various publications but other effects
seem possible. Methods: In order to search for effects of conditioning
normobaric hypoxia yet unknown, we measured O-Mg++ potentiation and classical
long-term potentiation (LTP) in the CA, region of hippocampal slices seven days
after the conditioning procedure. Furthermore, tests were also carried out in
chronically implanted rats as to whether LTP was changed in the dentate gyrus
after conditioning hypoxia. Results: In slices taken from animals which
received conditioning hypoxia, O-Mg++ potentiation and classical LTP of the
population spike were significantly enhanced, when compared to population in
two control groups. Anoxic LTP, i.e. increase in the population spike of the
field potential in the dentate gyrus immediately after finishing the procedure,
and a tendency to elevation of LTP seven days after conditioning were also
found in chronically implanted animals which were subjected to conditioning
hypoxia. Conclusions: lt. may be hypothesized that elevated Ca++ transport in
the neurons during conditioning hypoxia is responsible for both long- lasting
increases in plastic reactions and the protective effect.
Keywords: Hypoxia, Preconditioning, Hippocampal slices, Long-term potentiation, O-Mg2+, CA l, Dentate gyrus, Perforant pat, Rats
