Developmental Iodine Deficiency and Hypothyroidism Impair Spatial Memory in Adolescent Rat Hippocampus: Involvement of CaMKII, Calmodulin and Calcineurin

Abstract

Developmental iodine deficiency (ID) leads to inadequate thyroid hormone that impairs learning and memory with an unclear mechanism. Here, we show that hippocampal calcium/calmodulin-dependent protein kinase II (CaMKII), calmodulin and calcineurin are implicated in the impaired spatial memory in adolescent rats following developmental ID and hypothyroidism. Three developmental rat models were created by administrating dam rats with either iodine-deficient diet or propylthiouracil (PTU, 5 or 15ppm)-added drinking water from gestational day (GD) 6 till postnatal day (PN) 28. Then, the spatial memory to a water maze test was studied in pups before PN42. After testing periods, the latency to platform and the number of error in iodine-deficient and 15ppm PTU-treatment groups were significantly higher than those in the controls (P<0.05). Total and phosphorylated CaMKII, calmodulin, and calcineurin in the hippocampus were detected with both the immunohistochemistry and western blotting. Without going through water maze test, iodine-deficient and 15ppm PTU-treatment groups showed significantly lower CaMKII and calmodulin and significantly higher calcineurin than the controls in hippocampal CA1 and CA3 regions (P<0.05). After trials of water maze task, however, CaMKII and calmodulin were up-regulated and calcineurin was down-regulated in control group (P<0.05), but not in iodine-deficient and 15ppm PTU-treatment groups. Data indicate that hippocampal CaMKII, calmodulin, and calcineurin are involved in the impaired spatial memory induced by developmental ID and hypothyroidism.