Oxytocin Influences Male Sexual Activity via Non-synaptic Axonal Release in the Spinal Cord.

Oxytocinergic neurons in the paraventricular nucleus of the hypothalamus that project to extrahypothalamic brain areas and the lumbar spinal cord play an important role in the control of erectile function and male sexual behavior in mammals. The gastrin-releasing peptide (GRP) system in the lumbosacral spinal cord is an important component of the neural circuits that control penile reflexes in rats, circuits that are commonly referred to as the "spinal ejaculation generator (SEG)." We have examined the functional interaction between the SEG neurons and the hypothalamo-spinal oxytocin system in rats. Here, we show that SEG/GRP neurons express oxytocin receptors and are activated by oxytocin during male sexual behavior. Intrathecal injection of oxytocin receptor antagonist not only attenuates ejaculation but also affects pre-ejaculatory behavior during normal sexual activity. Electron microscopy of potassium-stimulated acute slices of the lumbar cord showed that oxytocin-neurophysin-immunoreactivity was detected in large numbers of neurosecretory dense-cored vesicles, many of which are located close to the plasmalemma of axonal varicosities in which no electron-lucent microvesicles or synaptic membrane thickenings were visible. These results suggested that, in rats, release of oxytocin in the lumbar spinal cord is not limited to conventional synapses but occurs by exocytosis of the dense-cored vesicles from axonal varicosities and acts by diffusion-a localized volume transmission-to reach oxytocin receptors on GRP neurons and facilitate male sexual function.

A study of fundamental courses in the great cardiac vein.

We studied an extremely rare great cardiac vein anomaly in a 65-year-old woman during dissection practice at the Akita University School of Medicine (2013). The great cardiac vein has two main roots, one accompanied by a left marginal vein that pours into the coronary sinus, and the other ascending along the anterior interventricular sulcus from the apex, and running over the circumflex branch of the left coronary artery. It then runs along the atrial side of the transverse sinus of the pericardium, and drains directly into the superior vena cava. No anastomosis between these veins was evident. The great cardiac vein might originate from two venous systems, one in the posterior wall of the left ventricle, and the other running along the anterior interventricular sulcus. These venous systems flow in the venous network of the left edge of the coronary sulcus. The former venous system always selected the course, which went to the coronary sinus in the venous network. The latter system may drain into one of the following four courses: the first one contacts the former course; the second passes to the transverse sinus of the pericardium and flows to the (right) superior vena cava; the third passes between a pulmonary trunk and ascending aorta from the dorsum of the pulmonary trunk, turns around in a ventral aspect, and then flows into the left superior vena cava; and the fourth flows to the anterior cardiac vein. The first of these belongs to the normal great cardiac vein, but the others are anomalous.