Radioautographic studies on the neurohypophysial projections of the supraoptic and paraventricular nuclei in the rat.
The distribution of labelled axonal pathways was studied after unilateral stereotaxic injection of 3H-leucine into either supraoptic (SON) or paraventricular nuclei (PVN). In addition to extrahypothalamic projections of both nuclei, the main efferents appeared to run towards the neurohypophysis, yet with a strikingly different pattern. At the neurohypophysial levels, the SO-neurohypophysial tract crossed the inner layers of the median eminence (ME) before scattering in the neural lobe. The PV-neurohypophysial pathway, by contrast, provided an exclusive innervation to the external layer of the whole neurohypophysial organ, including the median eminence, infundibular stalk and neural lobe. The functional correlates of the clear-cut anatomical distinctness between the two magnocellular neurosecretory systems are discussed.
D000818:Animals; D001345:Autoradiography; D001369:Axons / Q000648:ultrastructure*; D004525:Efferent Pathways; D007031:Hypothalamus / Q000648:ultrastructure*; D008297:Male; D008473:Median Eminence / Q000648:ultrastructure; D010286:Paraventricular Hypothalamic Nucleus / Q000648:ultrastructure; D010904:Pituitary Gland, Posterior / Q000294:innervation*; D051381:Rats; D011919:Rats, Inbred Strains; D013495:Supraoptic Nucleus / Q000648:ultrastructure*