ONTOGENY OF GLUCOCORTICOID AND D2 RECEPTORS IN THE RAT PITUITARY - ANIN-SITU HYBRIDIZATION STUDY

The expression of glucocorticoid and D2 dopamine receptors (GR and D2R ) during rat pituitary ontogenesis was studied by in situ hybridizatio n (ISH). On early stages, E13-E14, a weak specific signal for GR mRNA was obvious in the whole Rathke's pouch (RP) whereas subsequently, fro m E17-E18, strong labelling was restricted to the anterior lobe (AL) a nd the neural lobe (NL). At the same time, D2R mRNAs appeared in the i ntermediate lobe (IL) and the long isoform of the D2R (D2R 444) was de tectable with specific probes. On the postnatal stages, until adult, G R mRNA, if present, was always undetectable in the IL using the conven tional ISH technique. These data indicate a possible early regulation of POMC gene expression by glucocorticoid in corticotrophic cells of t he AL and by dopamine in the melanotrophic cells of the IL. The possib ility of a negative regulation of GR mRNA by dopamine (DA) in the IL a s soon as E17 is discussed.