Cerebellar parameters in developing 15 day old rat pups treated with propylthiouracil in comparison with 5 and 24 day old

Abstract

To investigate and quantify structural parameters in the developing cerebellum during hypothyroidism in pre and postnatal stages in 15 day old rat pups in comparison with 5 and 24 day old. Propylthiouracil (PTU) was fed to rat dams during mating, pregnancy and nursing and their pups in drinking water. Consequently hypothy roxinemia was induced in the dams and the developing foeti during prenatal period and maintained in the dams and pups. The number of treated and control dams was five in each group. The treated and control pups were eight and eleven respectively. The whole cerebellum was dissected out and routinely processed for histological and morphometric analysis. Structural changes in cerebellum were estimated using "design based" stereological methods. The total volume of cerebellum, intracerebellar nuclei and cerebellar compartments were estimated using Cavalieri Principle. Numerical density of cells was estimated using the disector method and the total cell number was then calculated. In the 15 day pups there was significant reduction (P<0.05) in the mean volumes of cerebellum, internal granular layer, molecular layer, cerebellar cortex, mean ratio of the total volume of intracerebellar nuclei to the cerebellar volume and increased mean volume of external granular layer in treated pup group compared with control. The mean volumes of intracerebellar nuclei and white matter and the mean numerical densities and total numbers of neurons and Purkinje cells in intracerebellar nuclei and cerebellum respectively were nearly equal in control and treated groups. Significant increase (P<0.05) in the mean numerical density and total number of glial cells in treated pups compared with control was observed. There was significant decrease (P<0.05) in the mean neuron/neuroglia ratio in the intracerebellar nuclei, mean numerical density and mean total number of granule cells and reduction in the mean ratio of total number of granule/Purkinje cells in the treated group compared with control. The linear regression comparison for the total volume of the intracerebellar nuclei to total volume of the cerebellum in 5, 15 and 24 day control and treated pups and for the total number of glial cells on the total volume of intracerebellar nuclei in the same were significantly different (P<0.05). Total numbers of neurons and glial cells in the intracerebellar nuclei showed peak values in 15 day pups. Thus PTU-induced hypothyroidism causes variation in quantitative structural parameters in developing cerebellum and disrupts progressive cellular developmental processes. Maintenance of normal T4 and T3 levels during growth and maturation of cerebellum is absolutely essential.