OBJECTIVETo study the protective effects of multiple course hyperbaric oxygen (HBO) treatment against hypoxic-ischemic brain damage (HIBD) in neonatal rats when HBO treatment is delayed (96 hrs after the HIBD event).

METHODSEighty-eight 7-day-old Sprague-Dawley rat pups were randomly assigned to control, HIBD and HBO groups. The HBO group was subdivided into cohorts receiving treatment 2 h, 48 h and 96 h, respectively, after HIBD was induced. The three subgroups comprising different therapeutic windows were further randomly assigned to receive 1, 2 or 3 courses of HBO treatment ("HBO-1, -2 and -3 sub-groups"). HBO was administered once daily (2 ATA), a course lasting for seven days. There was an interval of three days between the courses. All pups were sacrificed at the end of HBO treatment (31 days after HIBD). TUNEL staining was used for testing neuronal apoptosis in the cortex and the CA1 of the hippocampus, and NSE staining was used to ascertain cortical neuronal population.

RESULTS1.There were significantly more TUNEL positive cells in the HIBD group than in the control group; NSE positive cells were significantly lower than in controls (P<0.01). 2. With the more delayed therapeutic window, the effects of apoptosis inhibition and neuronal protection of a single course of HBO were gradually reduced. 3. With increasing courses of HBO treatment, the effects of apoptosis inhibition and neuronal protection of HBO increased gradually in rats receiving treatment 48 and 96 hrs after HIBD. In the HBO group receiving treatment 2 hrs after HIBD, the number of apoptotic cells and NSE positive cells were close to that of the control group after one course of HBO treatment.

CONCLUSIONSOne course of HBO administered within 2 hrs after HIBD can effectively inhibit neuron apoptosis and protect neurons. The effects of apoptosis inhibition and neuron protection of HBO can be increased through increasing the number of HBO treatment courses in neonatal rats with HIBD even if initiation of treatment is delayed after HIBD.