PROLIFERATION OF CROP-SAC EPITHELIUM IN INCUBATING AND IN PROLACTIN-INJECTED PIGEONS STUDIED WITH THE COLCHICINE METHOD

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Abstract
Apparently all mitoses in the crop-sac epithelium of adult pigeons weighing 450 gms. are arrested in metaphase from the 6th to the 16th hr. after intramusc. inj. of 0.6 mgms. of colchicine. With the aid of colchicine treatment an increased proliferation of the crop-sac is observed to follow promptly the intramusc. inj. of 60 units of prolactin. This increased proliferation attains its maximum after 2 hrs., and is no longer observable after 10-12 hrs. A 2d inj. of prolactin made 8 hrs. after an initial inj. produced, at 2 and 4 hrs. later a much higher mitotic rate than that which followed the 1st inj. The employment of this same colchicine technique in pigeons immediately preceding and following the initiation of broody behavior indicates a close coincidence of increased release of prolactin from the bird''s own pituitary and the time of onset of this incubation (broody) behavior. At one day after the beginning of broodiness the preceding normal or repair rate of mitosis in the crop-sac has already increased by approximately 600%. This new rate is fully maintained during the 1st half of the incubation period, and is known to be still further increased during the last half of incubation. These results give further support to the conclusion earlier stated by Riddle, Bates and Lahr concerning a significant role of prolactin in the cyclic development of broody and maternal behavior in higher animals.