[Role of minocycline in an immature rat model of hypoxic-ischemic brain damage].

Objective: To establish a model of immature rat hypoxic-ischemic brain damage (HIBD) which was expected to be similar to periventricular leukomalacia in human preterm infants pathologically and neuroethologically, and to investigate the role of minocycline (MN) in this model.

Method: Totally 192 Sprague-Dawley rats (postnatal day 2, P(2)), of either sex, were randomly divided into 4 groups: normal-group, sham operation group, HIBD-group, HIBD + MN group, each group had 48 rats. HIBD group and HIBD + MN group survived the left common carotid artery (CCA) ligation followed by 4h exposure to 8% O(2). Rats in sham operation group only survived the left CCA isolation. Rats in normal group were not treated with anything. In HIBD + MN group, the rats were treated with intraperitoneal injection of minocycline 45 mg/kg, immediately after HI and every 24 h for 2 days. Brain tissues were collected on day 3, 1 week, 2 weeks, 4 weeks after HI, for hematoxylin-eosin staining and histological scoring. Frozen sections of the brains were stained with anti-O4, anti-O1 immunohistochemistry on day 3 after HI, and MBP immunohistochemistry 2 weeks after HI. Rats in the four groups underwent neuroethologic examination 4 weeks after HI.

Result: In the HIBD group, there were pathological changes in the periventricular white matter. The pathological changes were milder in HIBD + MN group; There was no statistically significant difference between the normal group and HIBD + MN group in the number of positively stained O4 cell (P > 0.05). The number of positively stained O4 cell in the HIBD group was significantly reduced, compared with that of normal group, sham operation group, and HIBD + MN group (23.67 ± 12.00 vs. 52.89 ± 10.68, 39.28 ± 11.78, 41.63 ± 8.41, P < 0.05). The differences in the number of positively stained O1 cell among the normal group, sham operation group, HIBD group and HIBD + MN group had no statistical significance (P = 0.093). The numbers of myelin basic protein (MBP) positively immunostained fiber bundles in the HIBD + MN group were significantly less than that of the normal group and sham operation group (P < 0.05). The numbers of MBP positively immunostained fiber bundles in the HIBD group were significantly less than that of the normal group, sham operation group, and HIBD + MN group (14.71 ± 7.42 vs. 36.67 ± 6.50, 35.50 ± 3.24, 26.33 ± 5.92, P < 0.05). The HIBD group had long-term neuroethologic abnormality. There was no statistically significant difference in the inclined plane test, hanging test and cylinder test among the HIBD + MN group, normal group, and sham operation group (P > 0.05). The scores of the HIBD group had statistical significantly among the normal group, sham operation group and HIBD + MN group (P < 0.05). In the open field test, there was no statistically significant difference between the HIBD group and HIBD + MN group (P = 0.772), but there was significant difference between these two groups and the normal group, sham operation group (P < 0.05).

Conclusion: Minocycline protects the pre-oligodendrocyte and has protective effects in terms of long-term neuroethology.