Acrylamide neurotoxicity on the cerebrum of weaning rats

Abstract

The mechanism underlying acrylamide-induced neurotoxicity remains controversial. Previous studies have focused on acrylamide-induced toxicity in adult rodents, but neurotoxicity in weaning rats has not been investigated. To explore the neurotoxic effect of acrylamide on the developing brain, weaning rats were gavaged with 0, 5, 15, and 30 mg/kg acrylamide for 4 consecutive weeks. No obvious neurotoxicity was observed in weaning rats in the low-dose acrylamide group (5 mg/kg). However, rats from the moderate- and high-dose acrylamide groups (15 and 30 mg/kg) had an abnormal gait. Furthermore, biochemical tests in these rats demonstrated that glutamate concentration was significantly reduced, and γ-aminobutyric acid content was significantly increased and was dependent on acrylamide dose. Immunohistochemical staining showed that in the cerebral cortex, γ-aminobutyric acid, glutamic acid decarboxylase and glial fibrillary acidic protein expression increased remarkably in the moderate- and high-dose acrylamide groups. These results indicate that in weaning rats, acrylamide is positively associated with neurotoxicity in a dose-dependent manner, which may correlate with upregulation of γ-aminobutyric acid and subsequent neuronal degeneration after the initial acrylamide exposure.

Keywords: cerebrum; cortex; glial fibrillary acidic protein; glutamate; glutamic acid decarboxylase; nerve regeneration; neural regeneration; neurotoxicity; organ index; weaning; γ-aminobutyric acid.

Figure 1

Effect of acrylamide on glutamate (A) and GABA (B) concentrations in the cerebral cortex at 4 weeks. Data are expressed as the mean ± SD (n = 6). The differences between groups were compared with one-way analysis of variance, followed by Dunnett's post hoc test. *P < 0.05, vs. I (0 mg/kg); #P < 0.05, vs. II (5 mg/kg); &P < 0.05, vs. III (15 mg/kg). GABA: Gamma aminobutyric acid; I: control group; II: low-dose acrylamide group (5 mg/kg); III: moderate-dose acrylamide group (15 mg/kg); IV: high-dose acrylamide group (30 mg/kg).

Figure 2

Neuronal morphology in the cerebral cortex of weaning rats at 4 weeks after acrylamide treatment (hematoxylin-eosin staining). The images show the changes of neurons in the cerebral cortex in the control group (A), low- (B), moderate- (C) and high-dose acrylamide groups (D). Arrows represent abnormal neurons. Scale bar: 25 μm.

Figure 3

GFAP-immunoreactive cells in cerebral cortex at 4 weeks after acrylamide treatment. The images show the expression of GFAP in the cerebral cortex in the control (A), low- (B), moderate- (C), and high-dose acrylamide groups (D). Scale bar: 25 μm. (E) Number of GFAP-immunoreactive cells. (F) Densitometry of GFAP immunoreactivity. Data are expressed as the mean ± SD (n = 6). The differences between groups were compared with one-way analysis of variance, followed by Dunnett's post hoc test. *P < 0.05, vs. I (0 mg/kg); #P < 0.05, vs. II (5 mg/kg); &P < 0.05, vs. III (15 mg/kg). GFAP: Glial fibrillary acidic protein; I: control group; II: low-dose acrylamide group (5 mg/kg); III: moderate-dose acrylamide group (15 mg/kg); IV: high-dose acrylamide group (30 mg/kg).

Figure 4

GABA-immunoreactive neurons in cerebral cortex at 4 weeks after acrylamide treatment. The images show the immunoreactivity of GABA in the cerebral cortex in the control (A), low- (B), moderate- (C), and high-dose acrylamide groups (D). Scale bar: 25 μm. (E) Densitometry of GABA immunoreactivity. Data are expressed as the mean ± SD (n = 6). The differences between groups were compared with one-way analysis of variance, followed by Dunnett's post hoc test. *P < 0.05, vs. I (0 mg/kg); #P < 0.05, vs. II (5 mg/kg); &P < 0.05, vs. III (15 mg/kg). GABA: Gamma aminobutyric acid; I: control group; II: low-dose acrylamide group (5 mg/kg); III: moderate-dose acrylamide group (15 mg/kg); IV: high-dose acrylamide group (30 mg/kg).

Figure 5

GAD65-immunoreactive neurons in cerebral cortex at 4 weeks after acrylamide treatment. The images show the immunoreactivity of GAD65 in the cerebral cortex in the control (A), low- (B), moderate- (C), and high-dose acrylamide groups (D). (E) Densitometry of GAD65 immunoreactivity. Data are expressed as the mean ± SD (n = 6). The differences between groups were compared with one-way analysis of variance, followed by Dunnett's post hoc test. *P < 0.05, vs. I (0 mg/kg), #P < 0.05, vs. II (5 mg/kg); &P < 0.05, vs. III (15 mg/kg). GAD65: Glutamic acid decarboxylase 65; I: control group; II: low-dose acrylamide group (5 mg/kg); III: moderate-dose acrylamide group (15 mg/kg); IV: high-dose acrylamide group (30 mg/kg).