Intraocular Development and Adrenergic Innervation of Cortical and Subcortical Brain Areas: Influence of Thyroid Hormone Deficiency

Abstract

Various immature brain regions have been isolated by grafting to the anterior chamber of the eye of adult recipients. The role of thyroid hormones for the growth of these isolated brain areas as well as their morphological maturation and adrenergic innervation in the eye have been investigated by surgical thyroidectomy of adult recipients prior to the intraocular brain grafting. Cortex cerebri showed a donor stage correlated thyroid hormone dependency so that 18-day donor fetuses gave rise to larger cortex grafts, whereas full-term donor fetuses resulted in smaller cortex grafts in thyroidectomized hosts. Brain stem showed an overall enhanced intraocular growth in thyroidectomized recipients, whereas both cerebellum and hippocampus did not seem to be influenced in oculo by a thyroid hormone deficiency. The morphological maturation of cortex cerebri grafts showed no alterations in thyroidectomized hosts as judged from light microscopy and cresyl violet staining. The density of sympathetic adrenergic nerves innervating the cortex cerebri grafts from the host iris was reduced by 50% in thyroidectomized hosts. This was paralleled by a reduction in noradrenaline concentration in cortex cerebri grafts in the experimental groups. Thus, the reduced number of nerves visible with Falck-Hillarp histochemistry in cortex cerebri grafts during thyroid hormone deficiency probably corresponds to a true reduction in adrenergic innervation. The present report points to a number of regionally as well as temporally selective effects on brain maturation and neuronal interaction of severe thyroid hormone deficiency.