Purpose: To explore the effect of Tetramethylpyrazine(TMP) on retinal neuronal apoptosis and its morphological changes in oxygen induced retinopathy(OIR) mice.
Methods: Forty-eight Neonatal C57BL/6 mice were randomly divided into 3 groups. Eighteen mice were raised in room air as normoxia control (Group 1).Thirty postnatal day 7 (P7) mice were exposed to 75±3% oxygen for 5 days and returned to room air to establish OIR model, including eighteen OIR control mice (Group 2) and twelve TMP treated group mice (Group 3). TMP (intraperitoneal injection, 200mg/Kg) was administered once a day from P12 to P16 and six mice were sacrificed respectively at P14 or P17. Normoxia control (Group 1) and OIR control (Group 2) were injected with Normal Saline (NS) from P12 to P16 and six mice were sacrificed respectively at P12, P14 and P17. Paraffin embedded mouse right eyes were cut per 3μm serially and sagittally. To observe retinal apoptosis, HE staining and TUNEL assay were used to measure on 6 sections per eye crossing the optic nerve. The interval between each section was 15μm.
Results: The structure of retina in Group 1 was clear. At P12, there were a few of chromatin condensation and pycnic nuclei in the central INL in Group 2. At P14, abundant of chromatin condensation and pycnic nuclei in the central INL were seen in Group 2, while there were fewer of chromatin condensation and pycnic nuclei in the central INL in Group 3 than Group 2. At P17, The centle INL, IPL and OPL of mouse eyes at P17 in Group 2 were found to be severely reduced in thickness, compared with Group 1. Changes in the INL, IPL and OPL of mouse eyes at P17 in Group 3, although thinner compared with Group 1, were much less pronounced compared with Group 2. Group 1 didn’t show obvious TUNEL-positive cells. TUNEL-positive cells in Group 2 at P12 and P14 were (6.39±1.29), (30.04±6.39) per picture respectively, mostly at P14 and mainly in the central inner nuclear layer, nearly 6 folds (P<0.001) at P12 and 28 folds (P<0.001) at P14, compared with Group 1. TMP decreased the apoptotic cells by 82.3% (P<0.001) at P14 (5.33±2.04) in Group 3, compared with Group 2. There were no significant differences in retinal apoptotic cells among Group 1, 2 and 3 at P17.    Conclusions: TMP inhibits retinal neuronal apoptosis in OIR mice and may have clinical utility to protect the hypoxic retina from degeneration, confirming that it may have potential value for the treatment of ischemic retinopathy.