Regulation of VIP mRNA expression by thyroid hormone in different brain areas of adult rat.

A role of thyroid hormone in the regulation of neuropeptide synthesis has been demonstrated in different tissues. In this paper we investigated the vasoactive intestinal peptide (VIP) mRNA expression by means of in situ hybridization in several brain areas of hypo- and hyperthyroid adult rats. Neither hypo- nor hyperthyroidism modified the VIP mRNA levels in the thalamus and in the hypothalamic suprachiasmatic nucleus. In contrast, in the anterior cingulate and frontoparietal motor cortex of hypothyroid rats there was a marked increase in the signal for VIP mRNA per cell, but the number of VIP expressing neurons did not change. These data indicate that also central VIP synthesis can be influenced by the levels of circulating thyroid hormone, but that this effect is confined to specific areas and cell populations of the brain.