HYPERTONICITY INCREASES NO PRODUCTION TO MODULATE THE FIRING RATE OF MAGNOCELLULAR NEURONS OF THE SUPRAOPTIC NUCLEUS OF RATS

Author(s)

Da Silva, M. P. ^[1] ; Ventura, R. R. ^[2] ; Varanda, W. A. ^[1]

Affiliation

^[1] Univ Sao Paulo, Sch Med Ribeirao Preto, Dept Physiol, BR-14049900 Ribeirao Preto, SP - Brazil

^[2] Univ Fed Alfenas, Inst Biomed Sci, Dept Physiol Sci, BR-37130000 Alfenas, MG - Brazil

• Document type: Journal article
• Source: Neuroscience; v. 250, p. 70-79, OCT 10 2013.
• Web of Science Citations: 8

Abstract

Increases in plasma osmolality enhance nitric oxide (NO) levels in magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus (SON) and modulate the secretion of both vasopressin (VP) and oxytocin (OT). In this paper, we describe the effects of hypertonicity on the electrical properties of MNCs by focusing on the nitrergic modulation of their activity in this condition. Membrane potentials were measured using the patch clamp technique, in the presence of both glutamatergic and GABAergic neurotrans-mission blockers, in coronal brain slices of male Wistar rats. The recordings were first made under a control condition (295 mosm/kg H2O), then in the presence of a hypertonic stimulus (330 mosm/kg H2O) and, finally, with a hypertonic stimulus plus 500 mu M L-Arginine or 100 mu M N-nitro-L-Arginine methyl ester hydrochloride (L-NAME). Hypertonicity per se increased the firing frequency of the neurons. L-Arginine prevented the increase in fire frequency induced by hypertonic stimulus, and L-NAME (inhibitor of nitric oxide synthase) induced an additional increase in frequency when applied together with the hypertonic solution. Moreover, L-Arginine hyperpolarizes the resting potential and decreases the peak value of the after-hyperpolarization; both effects were blocked by L-NAME and hypertonicity and/or L-NAME reduced the time constant of the rising phase of the after-depolarization. These results demonstrate that an intrinsic nitrergic system is part of the mechanisms controlling the excitability of MNCs of the SON when the internal fluid homeostasis is disturbed. (c) 2013 IBRO. Published by Elsevier Ltd. All rights reserved. (AU)

• FAPESP's process: 10/16600-9 - Calcium handling and secretion in Leydig cells
• Grantee: Wamberto Antonio Varanda
• Support Opportunities: Regular Research Grants
• FAPESP's process: 06/50954-7 - Ionic currents and receptors in the physiology of excitable and non-excitable cells
• Grantee: Wamberto Antonio Varanda
• Support Opportunities: Research Projects - Thematic Grants