Development of hydroxytryptophan decarboxylase activity in the pineal gland, cerebral hemispheres, and cerebellum of the chick embryo and young chick.

The courses of increase in 5-hydroxytryptophan decarboxylase activity in the chick pineal gland, cerebral hemispheres, and cerebellum have been followed from the 10-day embryo to 2-weeks post-hatch. Activity was first detected in the pineal gland and cerebral hemispheres of 12-day embryos, and in the cerebellum of 18-day embryos. In each tissue, there was a rapid initial rise in activity to about the stage of hatching, followed by a further less rapid rise to levels of 50–100% of those found for adult birds.