Penile polsters: functional structures or atherosclerotic changes?

The distribution of blood flow within the penis during erection and detumescence is thought to be controlled by polsters, columns of smooth muscle cells within the intima of penile arteries and veins. We have examined penile tissue from 4 men and 2 children, and have been unable to find incontrovertible evidence of polsters as classically described. Occasional structures superficially resembling polsters were encountered not only in penile tissue but also in vessels in the spermatic cord in patients undergoing vasectomy. In each instance these structures were recognizable as either branching points of vessels, intimal smooth muscle cell cushions or atherosclerotic lesions at various stages of development. Our findings strongly refute the hypothesis that polsters contribute to the normal physiology of erection.

Identification of early neurons in the brainstem and spinal cord: I. An autoradiographic study in the chick.

Early stages in chick neurogenesis were investigated with tritiated thymidine (3H-Tdr) autoradioraphy to determine the location and identity of the first neurons produced for the central nervous system. These cells have been shown to arise prior to neural tube closure (Sechrist, '75). Chicks were treated at selected intervals between 20 and 72 hours of incubation with 3H-Tdr in a modified pulse-labeling technique, and terminated on the 18th day of embryonic development (E18), when neuronal types could be determined. Some of the earliest neurons start their final DNA synthesis before 20 hours of incubation (head process, Hamburger-Hamilton stage 5). These are primarily medium-sized cells of the reticular formation in the medulla and at the diencephalic-mesencephalic junction, but also in the intermediate zone of the spinal cord. Motor neurons of the brainstem and spinal cord begin to appear next, after 26-28 hours incubation; the first sensory neurons arise after 32 hours. Other workers (Ramon y Cajal, '60; Tello, '23; Windle and Austin, '36) found that neurons of the reticular formation were the first to differentiate neurofibrils, during the latter part of E2, indicating that fibrillogenesis in these cells begin about 24 hours after the initial cessation of DNA replication.