Neurons in the hippocampal CA1 region, but not the dentate gyrus, are susceptible to oxidative stress in rats with streptozotocin-induced type 1 diabetes

Abstract

In this study, we investigated the effects of streptozotocin-induced type 1 diabetes on antioxidant-like protein-1 immunoreactivity, protein carbonyl levels, and malondialdehyde formation, a marker for lipid peroxidation, in the hippocampus. For this study, streptozotocin (75 mg/kg) was intraperitoneally injected into adult rats to induce type 1 diabetes. The three experimental parameters were determined at 2, 3, 4 weeks after streptozotocin treatment. Fasting blood glucose levels significantly increased by 20.7-21.9 mM after streptozotocin treatment. The number of antioxidant-like protein-1 immunoreactive neurons significantly decreased in the hippocampal CA1 region, but not the dentate gyrus, 3 weeks after streptozotocin treatment compared to the control group. Malondialdehyde and protein carbonyl levels, which are modified by oxidative stress, significantly increased with a peak at 3 weeks after malondialdehyde treatment, and then decreased 4 weeks after malondialdehyde treatment. These results suggest that neurons in the hippocampal CA1 region, but not the dentate gyrus, are susceptible to oxidative stress 3 weeks after malondialdehyde treatment.

Keywords: dentate gyrus; hippocampus; lipid peroxidation; malondialdehyde; nerve regeneration; neural regeneration; neurons; type 1 diabetes.

Figure 1

Fasting blood glucose levels in control and streptozotocin (STZ)-treated rats. Fasting blood glucose level was increased in rats after STZ treatment. Differences among the means were analyzed statistically by one-way analysis of variance followed by Bonferroni's post-hoc analysis (n = 15 per group; *P < 0.05, vs. control group). The bars indicate the standard error of the mean (SEM). STZ-2W, STZ-3W and STZ-4W mean 2, 3, and 4 weeks after STZ treatment, respectively.

Figure 2

Antioxidant-like protein-1 (AOP-1) immunoreactivity in the hippocampal CA1 region of control and streptozotocin (STZ)-treated rats. AOP-1 immunoreactivity was decreased in rats after STZ treatment. (A–D) Photomicrographs of immunohistochemistry for AOP-1 immunoreactivity in the hippocampal CA1 region of controls (A) and rats treated with STZ for 2 (B), 3 (C) and 4 weeks (D). AOP-1 immunoreactivity is found in non-pyramidal cells of the CA1 region. SO: Stratum oriens; SP: stratum pyramidale; SR: stratum radiatum. Scale bar: 100 μm. (E) Number of AOP-1-immunoreactive cells per section from each group. Differences between groups were analyzed statistically by oneway analysis of variance followed by Bonferroni's post-hoc analysis (n = 5 per group; *P < 0.05, vs. control group). The bars indicate the standard error of the mean (SEM). STZ-2W, STZ-3W, and STZ-4W mean treatment with STZ for 2, 3 and 4 weeks, respectively.

Figure 3

Antioxidant-like protein-1 (AOP-1) immunoreactivity in the hippocampal CA3 region of control and streptozotocin (STZ)-treated rats. AOP-1 immunoreactivity was decreased in rats after STZ treatment. (A–D) Photomicrographs of immunohistochemistry for AOP-1 immunoreactivity in the hippocampal CA1 region of controls (A) and rats treated with STZ for 2 (B), 3 (C) and 4 weeks (D). AOP-1 immunoreactivity is found in non-pyramidal cells of the CA3 region. SO: Stratum oriens; SP: stratum pyramidale; SR: stratum radiatum. Scale bar: 100 μm. (E) Number of AOP-1-immunoreactive cells per section from each group. Differences between groups were analyzed statistically by one-way analysis of variance followed by Bonferroni's post-hoc analysis (n = 5 per group; *P < 0.05, vs. control group; #P < 0.05, vs. STZ-2W group). The bars indicate the standard error of the mean (SEM). STZ-2W, STZ-3W, and STZ-4W mean treatment with STZ for 2, 3 and 4 weeks, respectively.

Figure 4

Changes in antioxidant-like protein-1 (AOP-1) immunoreactivity in the hippocampal dentate gyrus of rats after strep tozotocin (STZ) treatment. No obvious change in AOP-1 immunoreactivity was observed in rats after STZ treatment. (A–D) Photomicrographs of immunohistochemistry for AOP- 1 immunoreactivity in the hippocampal dentate gyrus in controls (A) and rats treated with STZ for 2 (B), 3 (C) and 4 weeks (D). AOP-1 immunoreactivity is found in interneurons in the polymorphic layer (PoL) of the dentate gyrus. ML: Molecular layer; GCL: granule cell layer. Scale bar: 100 μm. (E) Number of AOP-1-immunoreactive cells per section of each group. Differences between groups were analyzed statistically by one-way analysis of variance followed by Bonferroni's post-hoc analysis (n = 5 per group). There are no significant differences in the number of AOP-1 immunoreactive cells between groups. The bars indicate the standard error of the mean (SEM). STZ-2W, STZ-3W, STZ- 4W mean treatment with STZ for 2, 3 and 4 weeks, respectively.

Figure 5

Malondialdehyde (MDA) level (A) and protein carbonyl level modified by oxidative stress (B) in the hippocampi of control rats and rats that received streptozotocin (STZ) treatment for 2, 3 and 4 weeks (STZ-2W, STZ-3W, STZ-4W, respectively). Both of these two indices were increased in rats after STZ treatment. Differences between groups were analyzed statistically by one-way analysis of variance followed by Bonferroni's post-hoc analysis (n = 5 per group; *P < 0.05, vs. control group; #P < 0.05, vs. STZ-2W group; †P < 0.05, vs. STZ- 3W group). The bars indicate the standard error of the mean (SEM).