Plasticity of Neurohypophysial Terminals with Increased Hormonal Release During Dehydration: Ultrastructural and Biochemical Analyses SEIJI MIYATA, 1 * HIROYUKI TAKAMATSU, 1 SHOHEI MAEKAWA, 2 NAOKO MATSUMOTO, 1 KAZUTADA WATANABE, 3 TOSHIKAZU KIYOHARA, 1 AND GLENN I. HATTON 4 1 Department of Applied Biology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan 2 Division of Bioscience, Graduate School of Science and Technology, Kobe University, Nada-ku, Kobe 657-8501, Japan 3 Department of Cell Recognition, Tokyo Metropolitan Institute of Gerontology, Sakaecho, Itabashi-ku, Tokyo 173-0015, Japan 4 Department of Cell Biology & Neuroscience, University of California, Riverside, California 92521 ABSTRACT Arginine vasopressin- (AVP) and oxytocin- (OXT) secreting magnocellular neurons undergo gross structural changes with chronic physiological stimulation. Here, we investigated subcellu- lar aspects of plasticity in rat neurohypophysial terminals during dehydration. Ultrastructural analyses demonstrated that chronic dehydration by 2% NaCl drinking for 7 days significantly decreased the numbers of neurosecretory granules and microvesicles but not the numbers of mitochondria. Moreover, in dehydrated rats, terminals making neurovascular contacts enlarged, whereas terminals in apposition to astrocytes, i.e., neuroglial contacts, became smaller. Western blot analyses demonstrated significant decreases in the levels of F3 and Thy-1 together with those of AVP- and OXT-neurophysin, but the levels of synaptophysin, SNAP-25, and GAP-43 were unchanged. Both F3 and Thy-1 were recovered in the buffer-insoluble pellet, and phos- phatidyl inositol-specific phospholipase C treatment released both molecules from the crude membrane fraction, indicating that they are attached to terminal membranes by glycosylphos- phatidyl inositol anchors. Confocal microscopic observations demonstrated that F3 colocalized with Thy-1 in the same terminals of magnocellular neurons. In contrast, the level of calretinin, a Ca 2+ binding protein was significantly increased with chronic dehydration. Thus, the present results suggest that enhancement of neurovascular contacts results from rearrangement of terminal-astrocyte and terminal-vessel contacts rather than enlargement or sprouting of mag- nocellular terminals themselves. The down-regulation of F3 and Thy-1 may contribute to en- hancement of neurovascular contacts that accompany increased peptide release during dehydra- tion. J. Comp. Neurol. 434:413– 427, 2001. © 2001 Wiley-Liss, Inc. Indexing terms: F-3; Thy-1; calretinin; CAMs; oxytocin; vasopressin The neurohypophysial hormones arginine-vasopressin (AVP) and oxytocin (OXT) are synthesized mainly in the magnocellular neurons of the supraoptic (SON) and para- ventricular nucleus (PVN) in the hypothalamus (Sawchenko and Swanson, 1982). In the hypothalamo-neurohypophysial system (HNS), structural plasticity is observed under chronic physiological stimulation such as lactation and dehydration (for reviews, see Hatton, 1990, 1997, 1999). In the hypothalamic nuclei, the structural reorganization is caused by retraction of glial cells from their usual posi- tions between adjacent cell bodies and/or neighboring den- drites, which results in soma-somatic, soma-dendritic, and dendro-dendritic membrane appositions, and multiple Grant sponsor: Japan Society for the Promotion of Science; Grant num- ber: 11640663; Grant sponsor: NIH; Grant number: NS 09140. *Correspondence to: Dr. Seiji Miyata, Department of Applied Biology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585 Japan. E-mail: smiyata@ipc.kit.ac.ip Received 31 October 2000; Revised 18 January 2001; Accepted 26 Feb- ruary 2001 THE JOURNAL OF COMPARATIVE NEUROLOGY 434:413– 427 (2001) © 2001 WILEY-LISS, INC.