Inibição do receptor de glutamato do tipo NMDA em um modelo de hipóxia-isquemia prenatal: avaliação morfofuncional do cerebelo

Abstract

Peri and prenatal systemic lesions alter CNS development leading to motor and cognitive problems in children that might persist throughout life. A particular kind of injury, the hypoxic ischemic (HI), is characterized by a permanent or temporary blockage of blood flow. One of the proposed mechanisms downstream from a HI event is called glutamatergic excitotoxicity. The administration of glutamate inhibitors has been studied in HI models for several years. In this work, we evaluated the effects of administration of a non-competitive antagonist of glutamate receptor, NMDA, on cerebellar development and behavioral tests of HI animals. Pregnant rats in the 18th gestational day were anesthetized, the uterine horns were exposed and the four uterine arteries were clamped for 45 minutes (group H). Sham controls had the uterine horns exposed, but no arteries were clamped (group S). Gestation proceeded after surgery. Only full term animals were used. One day after birth half the animals was assigned to receive either SALINE (groups SS and HS) or MK801 (groups SM and HM). Animals were anesthetized and perfused with 4% paraformaldehyde at 9, 23, 30 and 60 days of age. Parasagittal cerebellar sections were submitted to Calbindin, GFAP, GLAST, PDGFRα and MBP immunohistochemistry. Beginning at P45 animals were subjected to a battery of behavioral tests: elevated plus maze (EPM), hole board (HB), ROTAROD, ladder test and stride length. At P9 the dendritic tree of Purkinje cells were thinner in SM, HS/HM animals, indicating that both HI and MK801 are deleterious regarding this Purkinje cell differentiation. A lower number of PDGFRα+ cells was observed in HS/HM animals, with no effects of MK801 administration. At P23 a greater number of PDGFRα+ cells was found in HM animals when compared to the other 3 groups, demonstrating a neuroprotector effect of MK801. A lower number of myelinated fibers (MBP+) was observed in HS animals at P9, and MK801 administration reverse this effect. At P9, GLAST distribution was altered in HS animals, and MK801 partially reverse this altered distribution. No effects of HI and MK801 were observed in the EPM and ROTAROD tests. HI decreased motor performance of hind limbs in the ladder test, though no effect of MK801 was noted. In the HB test, we do not observe HI effects regarding the novelty seeking behavior and locomotor activity, otherwise the administration of MK801 decreased the number of grooming and locomotor activity. In the stride length test, we do not observed effects of HI although MK801 augmented the length variation of the fore limbs. Our results show that inhibition of NMDA receptors exerts a neuroprotector effect on oligodendrocyte progenitor cells and myelination, probably by temporarily inhibiting differentiation of those, providing more time to proliferate. NMDA activity exerts a crucial role in Purkinje cell differentiation as well as in GLAST distribution. Taken together our results lead us to conclude that NMDA receptor activity has an important role in the genesis of lesions caused by HI events.