Efeitos da hipóxia-isquemia perinatal sobre o comportamento motor, distribuição da Tirosina Hidroxilase na substância negra e da NADPH diaforase no hipocampo durante o desenvolvimento em ratos

Abstract

Perinatal hypoxia-ischemia (HI) is one of the major causes of mortality and chronic neurological diseases in newborns that can show permanent effects such as mental retardation, cerebral palsy, learning difficulty and epilepsy. It is probable that these impairs may be related to a delay in the neural development, astrogliosis and to the death of neurons and oligodendrocytes. Cognitive and functional deficits are related to degeneration of dopaminergic pathways and hippocampus. The enzyme tyrosine hydroxylase (TH) is a limiting step in the dopamine synthesis and its levels are impaired in HI insults. Nitric oxide (NO) is a diffusible gas that acts by modulating different systems and participates in several phenomena such as synaptic plasticity and neuromodulation in the central nervous system and is produced in higher levels in events of injury and inflamation as in the case of HI. This study aimed to evaluate the effects of HI on the motor behavior and to evaluate the development of brain structures related to this behavior as the substantia nigra (SN) and the hippocampal complex, using the model developed by Robinson and colleagues in 2005. HI was induced by clamping the uterine arteries of pregnant rats, for 45 minutes, on the eighteenth day of gestation (group HI). In a group of females, the surgery was performed, but no clamping of the arteries (group SHAM) was made. Assessment of motor behavior was performed with the ROTAROD test and open field test in animals of 45 days (P45) of age. The brains were processed histologically at ages P9, P16, P23 and P90, and then submitted to immunohistochemistry for TH and NADPH diaphorase (NADPH-d) histochemistry for evaluation of NOS. Our results demonstrated an apparent decrease in TH immunoreactivity in cell bodies in the SN at P16 in the HI group and an increase in immunoreactivity of the fibers in the SN pars reticulata at P23 with the presence of TH immunoreactive cell bodies at this same region in the HI group. We also showed an increase in the number of NADPH-d stained cells in the dentate gyrus in the HI group, at all ages, as also an increase in the intensity of staining in the Ammon s horn (CA1 and CA3) at P9 in the HI group and, after that, a decrease in this staining at P23 and P90 in this same group. In the behavioral tests we observed a decrease in the motor activity in the HI group with a partial recovery all over the several sessions in the ROTAROD test, however this group did not reach the same performance as the SHAM group. HI animals did not show a higher level of anxiety when compared to SHAM animals, ruling out the hypothesis that anxiogenic factors may be impairing the results in the motor behavior tests. Our results showed that the model of uterine arteries clamping could be an important tool in the study of the effects of perinatal HI, by producing several consequences that are very similar to the effects observed in newborn children who suffered an HI event.