RESUMO
This study was designed for the identification of possible and distinct abilities for behavioral recovery after prenatal cerebral damage. We adopted an interesting tool for promotion of cell's death. Due to the fact that neuroblastic cells and early postmitotic neurons on the beginning of differentiation are particularly sensible for the promotion of apoptosis, we used a low whole-body dose of X radiation on pregnant female mice on E16 (sixteenth gestational day) to promote damage on specific cerebral areas of the progeny, given that the pattern of cerebral neurogenesis is not homogeneous. The morphological results were previously described by our team. Here we noticed that the recovery of behavioral functions after prenatal damage seems to be related to specific factors of local cortical circuitry organization. The deficits found on visual navigation and working memory contrast with the recovery of primary visual functions and also with reference memory, where the mice have a delay on acquisition of learning but get it. As a conclusion we reasoning that changes on laminar organization on frontal cortex as well as the inter hemispheric cortical integration through the corpus callosum could promote relatively fixed cognitive dysfunctions, as those observed on performances that require strategies for navigation (decision making) and working memory, with consequences also observed on the subsequent learning.
Assuntos
Agenesia do Corpo Caloso , Aprendizagem em Labirinto/fisiologia , Memória de Curto Prazo/fisiologia , Memória/fisiologia , Lesões Experimentais por Radiação/psicologia , Córtex Visual/anormalidades , Animais , Apoptose/fisiologia , Aprendizagem por Discriminação/fisiologia , Reação de Fuga/fisiologia , Feminino , Hipocampo/patologia , Camundongos , Rede Nervosa/anormalidades , Rede Nervosa/fisiologia , Gravidez , Efeitos Tardios da Exposição Pré-Natal , Lesões Experimentais por Radiação/patologia , Percepção Espacial/fisiologiaRESUMO
A previous study reported that adult mice irradiated at the 16th embryonic day present a severe neuronal number reduction in the dorsal lateral geniculate thalamic nucleus. In the present study, we investigated the time course of the effects of prenatal irradiation on this thalamic nucleus. One day after irradiation, a great number of pyknotic figures were seen mainly in the cerebral proliferative zones. In the geniculate nucleus, only scattered pyknotic figures were identified. On the first week after birth, the geniculate nucleus presented frequent pyknotic figures. From five days after birth onwards, a severe shrinkage of the occipital cortex and a great reduction in the geniculate nucleus neuronal number were found. On the second week after birth this neuronal number reduction reached as high as 75%. At each postnatal analyzed age, severe volumetric geniculate nucleus shrinkage was combined to non-significant neuronal density variations. The presence of few pyknotic figures in the geniculate nucleus one day after irradiation and its delayed neuronal loss indicate an indirect effect of irradiation. We suggest that the effect upon the geniculate nucleus is secondary to the damage of the occipital cortex. A possible interpretation for thalamic neuronal loss is that geniculate neurons fail to establish cortical arbors after major target loss. In this case, the loss of trophic support should also be considered.
Assuntos
Diferenciação Celular/fisiologia , Raios gama , Corpos Geniculados/anormalidades , Neurônios/metabolismo , Degeneração Retrógrada/fisiopatologia , Córtex Visual/anormalidades , Vias Visuais/anormalidades , Envelhecimento/fisiologia , Envelhecimento/efeitos da radiação , Animais , Apoptose/fisiologia , Apoptose/efeitos da radiação , Contagem de Células , Diferenciação Celular/efeitos da radiação , Divisão Celular/fisiologia , Divisão Celular/efeitos da radiação , Núcleo Celular/metabolismo , Núcleo Celular/patologia , Núcleo Celular/efeitos da radiação , Tamanho Celular/fisiologia , Tamanho Celular/efeitos da radiação , Feminino , Corpos Geniculados/patologia , Corpos Geniculados/efeitos da radiação , Masculino , Camundongos , Neocórtex/anormalidades , Neocórtex/patologia , Neocórtex/efeitos da radiação , Neurônios/patologia , Neurônios/efeitos da radiação , Degeneração Retrógrada/etiologia , Degeneração Retrógrada/patologia , Tálamo/anormalidades , Tálamo/patologia , Tálamo/efeitos da radiação , Córtex Visual/patologia , Córtex Visual/efeitos da radiação , Vias Visuais/patologia , Vias Visuais/efeitos da radiaçãoRESUMO
We investigated the histochemical positivity to NADPH-diaphorase, which reveals nitric oxide synthase activity, in area 17 of rats malnourished early in life, both in the post-weaning period (group M1), and in adulthood after nutritional recovering (group M2). Control pups (C1 and C2 groups) received ad libitum after weaning the same diets as their mothers. Rats of group M2 were nutritionally recovered by receiving the control diet from post-natal day 42 until adulthood. Aldehyde-fixed sections (200-microm thick) through area 17 were processed for NADPH-diaphorase histochemistry following the malic enzyme indirect method. The features of NADPH-diaphorase-containing neurons of area 17 of malnourished young (M1) and adult (M2) rats were analyzed quantitatively in comparison to the matched groups C1 and C2. Permanent changes, represented by increase in the density and dendritic field areas of NADPH-diaphorase-positive cells, and transitory ones, represented by decreased values of soma areas, were observed in area 17 of the M1 and M2 cases. However, some other features, such as dendritic branch angle and number of dendrites per cell in the gray matter, remained unchanged after malnutrition. Thus, the findings indicate a possible relationship between early malnutrition and alterations in nitric oxide synthase-containing cells in the visual cortex. Physiological implications of these data may be related to synaptic plasticity and refinement of developmental brain circuits.