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DEVELOPMENTAL HYPOTHYROIDISM ALTERS SYNAPTIC TRANSMISSION IN DENTATE GYRUS AND AREA CA1 OF HIPPOCAMPUS.
Citation:
Gilbert, M. E. DEVELOPMENTAL HYPOTHYROIDISM ALTERS SYNAPTIC TRANSMISSION IN DENTATE GYRUS AND AREA CA1 OF HIPPOCAMPUS. Presented at Neurobehavioral Teratology Society, Montreal, Canada, 6/24-27/2001.
Description:
Hypothyroidism during critical periods of brain developmental leads to learning deficits and alterations in hippocampal structure. Neurophysiological properties of the hippocampus, however, have not been well characterized. The present study examined field potentials evoked in the dentate gyrus in vivo and in area CA1 of hippocampal slices following propylthiouracil (PTU)-induced hypothyroidism. Pregnant rats were administered 0 or 15 ppm PTU in the drinking water from GD18 until PND 21. As adults, male offspring (PND60-160) were anesthetized with urethane and electrodes placed in the perforant path and dentate gyrus. Hippocampal slices were derived from littermates between PND200-340. Stimulating electrodes were placed in stratum radiatum and evoked field potentials were recorded from the CA1 pyramidal cell layer and the stratum radiatum. Input/output (I/O) functions revealed reductions in baseline synaptic transmission in dentate gyrus in vivo, but not area CA1in the ex vivo preparation. Short-term plasticity was disrupted in area CA1, and LTP was altered in both regions. PS LTP was augmented in both hippocampal subfields, while EPSP slope LTP was impaired only in the dentate gyrus. This pattern of augmented potentiation of somatic responses reflected in PS amplitude following LTP in both hippocampal subregions may represent a physiological compensation for developmental alterations in cell number or dendritic structure associated with severe developmental hypothyroidism. (This work was supported by US EPA but does not reflect EPA policy)