NEUROTROPHINS AND THEIR RECEPTORS IN THE RAT PITUITARY-GLAND - REGULATION OF BDNF AND TRKB MESSENGER-RNA LEVELS BY ADRENAL HORMONES

We studied the expression of messenger ribonucleic acids'(mRNAs) for n eurotrophins and neurotrophin receptors in the rat pituitary gland and examined the influence of adrenal hormones on their mRNA levels, usin g in situ hybridization and Northern blot analysis. The only neurotrop hin present at detectable levels in the pituitary was brain-derived ne urotrophic factor (BDNF), which was observed in the anterior and inter mediate lobes. Several transcripts of the putative receptor for BDNF, trkB, were present in the anterior and posterior lobes of the pituitar y. A low amount of trkC mRNA was found in both the anterior and the in termediate lobe. Dexamethasone treatment decreased both BDNF and trkB mRNA levels in the anterior lobe of the pituitary. Adrenalectomy had n o effect on trkB expression, but it decreased BDNF mRNA levels in comp arison to the control animals. This effect could not be reversed by de xamethasone substitution, suggesting that BDNF mRNA levels may be regu lated not only by glucocorticoids but also by other adrenal hormones. These results demonstrate that BDNF, trkB and trkC are expressed in th e pituitary gland and that glucocorticoids and possibly other adrenal hormones may modulate pituitary functions by regulating the expression of neurotrophic factors and their receptors. Whether BDNF acts as a s ecreted hormone, a trophic factor, or has autocrine/paracrine function s within the pituitary through its receptor, trkB, remains to be studi ed,