A ROLE FOR BURSA FABRICII AND BURSIN IN THE ONTOGENY OF THE PINEAL BIOSYNTHETIC ACTIVITY IN THE CHICKEN

The tripeptide bursin (Lys-His-Gly-NH2) is a B cell differentiation ho rmone derived from the bursa fabricii. The latter is a cloacal diverti culum and the site of B lymphocyte differentiation and selection in av es; also the bursa fabricii is involved in endocrine functions. Herein we demonstrate that in the chicken, the bursa fabricii and bursin are crucial to the ontogeny of both the pineal response to antigenic chal lenge and pineal circadian synthetic activity. In early embryonically bursectomized chickens, the plasma melatonin response to immunization by porcine thyroglobulin (Tg) was abolished. Also, the amplitudes of b oth plasma melatonin and pineal N-acetyltransferase (NAT) circadian rh ythms were reduced by 50%, whereas the activity of hydroxyindole-O-met hyltransferase (HIOMT) remained unchanged. Conversely, administration of either minute amounts (100 pg, 100 fg) or highly dilute (5 x 10(-27 ) g) bursin, with the exception of a highest dose (100 mu g), to bursa less embryos induced recovery of normal antigen-induced melatonin resp onse and normal amplitudes of melatonin and NAT rhythms. These finding s establish that early in embryonic life, the bursa fabricii and its d erived signal (bursin) are essential for normal development of pineal synthetic activity and underline the efficacy of very dilute bursin as an informative signal.