Purine concentrations in the cerebrospinal fluid of unanesthetized rats during and after hypoxia

A new technique for achieving repeated sampling of fourth ventricular cerebrospinal fluid (CSF) from the cisterna magna of unanesthetized rats is described. The sampling cannula is positioned extracranially, in contrast to previously published techniques which require insertion through the skull. CSF samples, withdrawn from unanesthetized rats before, during and after a 25 min period of inhalation of 5% oxygen in nitrogen, were analyzed for their adenosine and inosine contents by high pressure liquid chromatography. Adenosine and inosine levels increased during the hypoxic episode and were even higher 1 h later. They had declined, but were still above basal levels, 2-3 h after the hypoxic episode. Elevated CSF adenosine concentrations may be responsible for the generation of such persistent effects of hypoxia as post-hypoxic respiratory depression.