The Effects of Acute and Chronic Treatment with Triiodothyronine and Thyroxine on the Hypothalamic and Telencephalic Catecholamine Nerve Terminal Systems of the Hypophysectomized Male Rat

Abstract

Using catecholamine (CA) fluorescence histochemistry in combination with quantitative microfluorimetry, it has been shown that chronic treatment with triiodothyronine (T3) and thyroxine (T4; 2 X 10 and 2 X 36 micrograms/kg i.p., respectively, twice daily for 10 days), but not acute treatment (1 and 3.6 mg/kg i.p., respectively, 2 h before killing), increases CA utilization in the medial and lateral palisade zones of the median eminence and reduces noradrenaline (NA) utilization in the parvocellular part and magnocellular part of the paraventricular hypothalamic nucleus of the hypophysectomized male rat. Following chronic T4 treatment it could also be shown that the CA levels in the medial and lateral palisade zones of the median eminence were increased, while the NA levels were reduced in the parvocellular part of the paraventricular hypothalamic nucleus. Chronic T3 treatment induced similar changes - increased CA levels in the medial palisade zone and reduced NA levels in the magnocellular part of the paraventricular hypothalamic nucleus. Within the telencephalon, chronic but not acute treatment with T3 or T4 selectively increased dopamine (DA) utilization within the diffuse type of DA nerve terminal systems of the nucleus accumbens. This action of chronic treatment of T3 or T4 was highly selective and no changes in DA levels could be demonstrated in any DA nerve terminals analyzed in the nucleus caudatus putamen; nucleus accumbens and tuberculum olfactorium. In all the expe…