[Abstract Title]. - Society for Neuroscience

numbers of neuronal and non-neuronal cells, we estimated the cellular composition of the brain
in animals with congenital hypothyroidism.
Sixty Wistar rats (29 controls and 31 hypothyroid animals) of 1, 2, 3, 4 and 5 months of age were
euthanized and perfused with 4% paraformaldehyde. Their brains were dissected into five
regions of interest (cerebral cortex, hippocampus, cerebellum, olfactory bulb and remaining
areas) which were weighted and analyzed separately with the Isotropic Fractionator.
Hypothyroidism was induced by ingestion of metimazole 0,002% from the 12th day of gestation
until the experimental age.
We find no significant differences in body mass, brain mass, and numbers of cells between
controls and hypothyroid animals of one month of age. Beginning at 2 months, brain and body
mass increase more slowly in hypothyroid animals compared to controls, such that, at 5 months,
body mass is 47% smaller and brain mass 7% smaller in hypothyroids than in controls. In
contrast to the slight reduction in brain mass, at 5 months we find in all brain structures a striking
decrease in numbers of neurons compared to controls (cerebral cortex, -58%; hippocampus, -
67%; cerebellum, 61%; olfactory bulb, -50%; remaining areas, -70%). This reduction is
progressive and starts at 2 months in the olfactory bulb, at 3 months in the cerebral cortex,
cerebellum and remaining areas, and at 4 months in the hippocampus.
Our data indicate that the reduced brain size in hypothyroidism is not due to delayed
development or generation of abnormal numbers of neurons in the brain, since cellular
composition is normal at 1 month, but rather to a pronounced loss of neurons that begins at the
age of 2-3 months. This striking loss of neurons cannot be predicted from the mild tissue loss,
and suggests that a compensatory increase in neuronal cell size takes place in hypothyroidism.
Disclosures: P.M. Rodrigues , None; A. Kinupe, None; A. Vargas, None; S. Herculano-
Houzel, None.
Poster
232. Developmental Cell Death: Biological Effects
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 232.6/B46
Topic: A.06.a. Developmental cell death: Biological effects
Support: NH&MRC
Title: Effect of betemethasone treatment on apoptotic cell death and neurosteriodogenic
pathways in a guinea pig model of growth restriction
Authors: *R. K. SULLIVAN 1,2 , H. K. PALLISER 1,2 , A. A. MCKENDRY 1,2 , D. M. YATES 1,2 ,
D. W. WALKER 3 , J. J. HIRST 1,2 ;