Presence of prolactin mRNA in extra-pituitary brain areas in the domestic turkey

It is well known that prolactin plays diverse roles in vertebrate reproduction. Besides expression in the pituitary, prolactin is also found in extra-pituitary tissues. In the present study, prolactin mRNA expression was studied utilizing in situ hybridization histochemistry. Prolactin mRNA, while found throughout the turkey brain, was predominantly localized within the pituitary, confirming a pivotal role of prolactin in turkey reproduction. The expression of prolactin mRNA was also observed within extra-pituitary brain areas including the cerebellum, nucleus accumbens, lateral septum, anterior hypothalamic nucleus, lateral hypothalamus, paraventricular nucleus, ventromedial nucleus, and infundibular nuclear complex. In the hypothalamus, an abundance of prolactin mRNA-expressing cells was observed in the anterior hypothalamic nucleus, lateral hypothalamus, and ventromedial nucleus. Cells expressing the least prolactin mRNA were found in the lateral septum, paraventricular nucleus, and the infundibular nuclear complex. This study reveals, for the first time, that prolactin mRNA was expressed in extra-pituitary brain areas in birds. In addition, the diverse expression of prolactin mRNA in the brain areas suggests that prolactin plays various physiological roles in birds.