Adrenergic synaptic vesicles in the anterior hypothalamus of the rat

Abstract After formaldehyde perfusion a small area of the anterior hypothalamus was extirpated, identified neuroanatomically and studied under the electron microscope. The preparative technique consisted in refixation of the piece in 1% osmium tetroxide for two hours, immersion in 2% uranyl acetate and embedding in Epon 812. Sections were stained with lead acetate. The main areas comprised in the tissue were the nucleus hypothalamicus anterior, nucleus periventricularis inferior and anterior hypothalami area. In the neuropiles of these regions varicose axons containing neurotubules and granular vesicles are observed. There are also numerous nerve endings containing typical synaptic vesicles in addition to some having a dense granule of reduced osmium. Measurements demonstrate that there are two different populations of vesicles with means of 510 Å and 1,300 Å respectively. The possible significance of the granular vesicles is discussed and related to the high content of catecholamines in this region of the CNS. The possibility that these nerve endings may synthesize and store more than one transmitter substance is also discussed. The wide variety of vesicles found in axons and synaptic endings of the anterior hypothalamus is also considered as supporting a unified theory of neurosecretion postulated by one of the authors.