The effect of experimentally induced hypothyroidism on neural plasticity and memory at first, second and third trimester of pregnancy

Thyroid hormone (TH) is very important for central nervous system development. TH deficiency in critical periods of central nervous system development causes delay of maturation of glial cells and neurons.Many studies pointed out that cell adhesion molecules (NCAM) have very important roles on development of brain and synaptic plasticity. It is known that deficiencies of TH causes the abnormalities at synthesis and release of adhesion molecules. It was reported that Glial Fibrillar Acidic Protein (GFAP) was a good marker showing astrocyte maturation. It was reported that GFAP levels were decreased in astrocyte maturation defects.We aimed to investigate the effects of experimentally induced maternal hypothyroidism on GFAP and NCAM expression in offsprings hypocampus at first, second and third trimester of pregnancy so that maturation of astrocytes, consolidation of learning and memory functions at their adult periods.At the experimental practising; for each group 15 new born rats from the mothers experimentally induced hypothyroidism at the first, second, third trimester of pregnancy and 15 rats for the control group were used. Thus four groups were formed. Rats were fed for 2.5 months after the birth. For learning test a widely used , the Morris Water Maze test was used. The levels of NCAM and GFAP were studied by the Western Blot method.It was seen that learning ability for each groups was increased day by day from the first day to fifth day. But increasing of learning capacity in control and 1th trimester hypothyroidism induced group was higher than the 2nd and 3th trimester hypothyroidism groups.We determined decrease in GFAP levels of offspring hypocampus when they become adult in 2nd and 3th trimester hypothyroidism groups when compared with the control and 1th trimester hypothyroidism groups. Similarly all of NCAM isoforms were statistically lower in 2nd and 3th trimester hypothryoidism groups than the control and 1th trimester hypothyroidism group.Results of our study show that the insufficiency of maternal thyroid hormone prevents the maturation of central neural system and causes the incapacities of learning and memory. It was seen that levels of NCAM and GFAP in hypocampus statistically decrease in 2nd and 3th trimester hypothyroidism groups than the control and 1th trimester hypothyroidism groups. Finally, it is obvious that maternal thyroid hormone deficiency effects unfavourably the young animals? psychomotor developments.