The hypothalamic neurosecretory systems of the Japanese quail as revealed by retrograde transport of horseradish peroxidase.

Within 24-48 h after injection of horseradish peroxidase (HRP) into the neural lobe or into the median eminence of adult Japanese quail dense accumulations of its reaction product (HRP-RP) can be demonstrated in axons of the hypothalamo-hypophysial tract and in the magnocellular neurosecretory perikarya of the supraoptic and paraventricular nuclei as well as in scattered neurons of the accessory hypothalamic neurosecretory nuclei. The HRP-RP-containing nerve fibers, which are beaded in appearance, occur prominently in the internal zone of the median eminence. They turn dorsally at its anterior border to become widely distributed in the retrochiasmatic region and extended to the paraventricular, supraoptic areas. These observations confirm more directly conclusions drawn earlier from Gomori-type preparations and from immunologic demonstration of arginine vasotocin, mesotocin and neurophysin. HRP-RP was also found in perikarya of parvocellular secretory neurons in the infundibular nucleus 48 h after injection of HRP into the median eminence but not after injection into the pars nervosa. This provides direct evidence that a conspicuous component of the tubero-infundibular tract is formed by axons of tuberal neurons that originate from the infundibular nucleus and pass directly into the median eminence.