Study Of The Effects Of Fumonisin B₁ On Circumventricular Organs In BALB/c Mice

Objective: There has been growing concern about the role of the damage effects of mycotoxin on brain. However, there has no study on Circumventricular organs (CVOs) injuried by FB₁ in domestic and overseas literatures. CVOs are some miniorgans around cerebral ventricles that include subfornical organ (SFO), median eminence, organum vasculosum of lamina terminalis, choroid plexus, subcommissural organ, pineal body and area postrema etc. SFO is more sensitive to stimulus than other encephalic regions because of the absentment of blood-brain barrier (BBB). Choroid plexus (CP) lie in vevtriculus lateralis and vevtriculus quartus mainly, it can prevent some water-solubilitied molecules into the cerebrospinal fluid (CSF). So the CVOs are the better sites to study the effect of FB₁ on brain injuries.To demonstrate the effects of FB₁ on CVOs (SFO and CP), the animal model was constructed in approach of administration of FB₁ by peritoneal injection in this study. Then the ultrastructural changes in intercolumnar tubercle and choroid plexus were observed by scanning electron microscope (SEM). Furthermore,the expression of COX-2 and HSP70 at protein level in SFO and CP were detected by immunohistochemistrial staining.Methods: 1 Eighty male BALB/c mice, weighed 18²0g, were randomly and equally divided into 4 groups. The diluted FB₁ by normal saline were injected into abdominal cavity with 2500μg/kg. Both treatment groups were given FB₁ 1 time or 5 times. Meanwhile, the control groups were given commensurate normal saline. In each group, 5 mice were taken randomly to prepare specimens for SEM, and the remanents for immunohistochemistrial staining to detect the expression of COX-2 and HSP70 in SFO and CP.2 Statistical analyses: Analysis of data was done with SPSS13.0 statistical analysis software. Results were analyzed as ANOVA.Results:1 The effects of FB₁ on SFO1.1 The results of SEM1.1.1 The ultrastructural morphology of SFO in control group:The SFO in the rostrocaudal direction is a elliptic site in low power without cilium for 400μm in anteroposterior diameter and 300μm in transverse diameter with surrounding of few cilium field transitionally. In high power, the pebble-like ependymal cells in central region intrude into brain ventricle with the form of spherical, hexagon and pentagon. And the demarcation was observed clearly for different size of ependymal cells with 3¹0μm in diameter. In surrounding region, microvillus appear on the surface of the flat and smooth ependymocyte.1.1.2 The ultrastructural morphology of SFO in FB₁ treated group:Contrusting to the control group, there was no obvious changes for SFO in one day treatment group by SEM in low power. And in high power, the morphology of ependymal cells was as the same as the control group forementionedly. But in five-day treatment group, the cell boundary and the junction was obscure. The crater-like surface of cells was covered with adhesive lodging microvilli and silty materials.1.2 The expression of COX-2 in SFO ependymal cells:The expression ratio of COX-2 in SFO ependymal cells was 1.15±0.25%,2.32±0.31%and 5.48±0.76% in one-day control group, five-day control group and one-day treatment group respectively. Few cells appeared as positive expression with Buffy particles. There was no significant difference between both groups in these three groups(p>0.05).The expression ratio of COX-2 in five-day treatment group was 52.59±9.08%, which was significantly increased compared with one-day treatment group and five-day control group(p<0.05).1.3 The expression of HSP70 in SFO ependymal cells:The positive cells could be observed in cytoplasm and membrane with Buffy particles. The ratio of positive cells in one-day control group, five-day control group and one-day treatment group was 13.05±5.35%,12.63±6.18%å’Œ11.17±4.63% respectively. No significant difference was statisticed out between both groups in these three groups(p>0.05). However, the expression of HSP70 in five-day treatment group(64.40±9.70%)was significant higher than that in one-day treatment group and in five-day control group(p<0.05).2 The effects of FB₁ on Choroid plexus (CP)2.1 The results of SEM2.1.1 The ultrastructural morphology of CP in control group:The normal cordal CP was circuitous and tortuous in low power in one-day and five-day control group. In high power, the CP cells with clear boundary were covered with microvilli on smooth surface. The intumescent extremity of microvilli was drumstick. Many satiated particles with 1²Î¼m in diameter distributed diffusedly. The fenestrated membrane was observed on some CP cells.2.1.2 The ultrastructural morphology of CP in FB₁ treated group:In one-day treatment group, no significant difference could be observed. However, in five-day treatment group the surface of cordal CP cells showed a small quantity of secretory granule, adhesive villus and poriform damage with irregular perimeter. The cell boundary was obscure, crude and swollen.2.2 The expression of COX-2 in CP cells:The expression ratio of COX-2 in CP cells was 5.18± 0.46%,6.71±0.88% and 11.03±3.26% in one-day control group, five-day control group and one-day treatment group respectively. There was no significant difference between both groups in these three groups(p>0.05).while the expression ratio of COX-2 in five-day treatment group(54.56±9.87%) was significantly increased comparing with one-day treatment group and five-day control group(p<0.05).2.3 The expression of HSP70 in CP cells:The positive cells could be observed in cytoplasm and membrane with Buffy particles. The ratio of positive cells in one-day control group, five-day control group and one-day treatment group was 9.78±3.14%,11.49±3.65% and 15.08±5.66% respectively. No significant difference was found between both groups in these three groups(p>0.05). However, the expression of HSP70 in five-day treatment group, whose the expression ratio was 61.39±10.98%, was significant comparing with one-day treatment group and five-day control group (p<0.05).Conclusions:1. There was no significant injury in the cells of SFO and CP in mice by one-day FB₁ intraperitoneal injection.2. After treated FB₁( 2500μg/kg)for five days, there were some changes in the cells of SFO. The cell boundary and the junction became obscure, the crater-like surface of cells was covered with adhesive lodging microvilli and silty materials.3. In five-day treatment group, the surface of cordal CP cells showed a small quantity of secretory granule, adhesive villus and poriform damage with irregular perimeter. The cell boundary was obscure, crude and swollen.4. The positive proteins, including of HSP70 and COX-2, were increased in five-day treatment group. Associating morphology changes in SEM, it suggested that HSP70 and COX-2 played some roles in the injuries of circumventricular organs by FB₁ treatment.