Diffusion between the neurohypophysis and the adenohypophysis of lampreys, Petromyzon marinus.

Horseradish peroxidase (HRP), a protein that can be visualized by appropriate histochemical procedures, was injected into the third ventricle of the brain of adult lampreys, Petromyzon marinus. Within 5 to 15 min HRP had passed through the neurohypophysis, which forms the floor of the third ventricle. It appeared at this time to have diffused throughout the connective tissue separating the adenohypophysial follicles from the neurohypophysis and from each other. This observation would indicate that it is possible for neurosecretory peptides like gonadotropin-releasing hormone to diffuse from the brain (neurohypophysis) to the adenohypophysis and thus regulate its secretory activity in lampreys.