Triiodothyronine effects on RNA polymerase activities in isolated neuronal and glial nuclei of the mature rat brain cortex.
Our previous study demonstrated that a high level of nuclear triiodothyronine receptors (NT3R), which are identical to the hepatic NT3R, exists in neuronal nuclei of the cerebral cortex from an adult rat brain. To investigate whether thyroid hormone acts through binding to nuclear receptors, we measured RNA polymerase activities in isolated neuronal and glial nuclei of cerebral cortices prepared from three groups of rats with different T3 levels: T3 (20 micrograms/100 g BW/d, for three days)-injected hyperthyroid rats, control normal rats, and thyroidectomized rats. The enzyme activities in both nuclear fractions were assayed under the condition of dose-response linearity. When RNA polymerase I activity in neuronal nuclei from control rats was expressed as 100%, the activities from T3-injected and hypothyroid rats were 112.3 +/- 3.4% (n = 5, P less than .05) and 86.9 +/- 3.5% (n = 5, P less than .05), respectively. The increase in the enzyme activities were parallel to the increase in T3 content in neuronal nuclei among the groups. Glial nuclear RNA polymerase I showed the same tendency in response to T3, although the enzyme activity was smaller than from neuronal nuclei. RNA polymerase II, however, showed no significant change in response to altered T3 levels. The existence of numerous receptors and an induction of increased RNA polymerase I activity by T3 in neuronal nuclei raise the possibility that thyroid hormone through a NT3R pathway in the cerebral cortex of even the mature rat brain.
Nakamura
H
H
Department of Internal Medicine, Kyoto University School of Medicine, Japan.
Yokota
T
T
Akamizu
T
T
Mori
T
T
Imura
H
H
D000818:Animals; D001921:Brain / Q000201:enzymology*; D002467:Cell Nucleus / Q000201:enzymology*; D002540:Cerebral Cortex / Q000201:enzymology; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D006980:Hyperthyroidism / Q000201:enzymology; D007037:Hypothyroidism / Q000201:enzymology; D008297:Male; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009457:Neuroglia / Q000201:enzymology; D009474:Neurons / Q000201:enzymology*; D012318:RNA Polymerase I / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014284:Triiodothyronine / Q000097:blood / Q000502:physiology*
D009419:Nerve Tissue Proteins; D014284:Triiodothyronine; D012321:DNA-Directed RNA Polymerases; D012318:RNA Polymerase I