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Dehydration switches emphasis from hypothalamus to medulla oblongata for maintenance of sympathetic nerve activity (SNA)
Author(s) -
Colombari Debora Simoes Almeida,
Colombari Eduardo,
Murphy David,
Paton Julian F. R.
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.959.7
Subject(s) - medulla oblongata , hypothalamus , losartan , medicine , endocrinology , spinal cord , medulla , chemistry , agonist , receptor , angiotensin ii , central nervous system , psychiatry
The mechanisms underlying the increase in SNA after dehydration are not fully established. In the present study, we investigated the sequential effects of systemic administration of Losartan (20 μM, AT 1 receptor antagonist), brain transections and inhibition of commissural nucleus tractus solitarii (cNTS) on ongoing thoracic SNA after water deprivation for 3 days. Male Wistar rats (65‐85 g) were decorticated to make insentient and perfused intra‐arterially. In euhydrated (EH) rats (290 mOsmol perfusate, n=5), systemic application of Losartan and subsequent pre‐collicular transection (to remove the hypothalamus) reduced SNA by ‐20 ± 3% and ‐44 ± 2% relative to baseline respectively. In contrast, in 3 day dehydrated (DH) rats (340 mOsmol perfusate, n=6) Losartan, subsequent pre‐collicular and pontine transections failed to reduce SNA (‐1 ± 4%, ‐3 ± 8% and ‐12 ± 4% respectively). However, transection at the medulla‐spinal cord junction reduced SNA by ‐70±8%. In intact DH, but not EH rats, reversible inactivation of cNTS using isoguvacine, (a GABA A receptor agonist; 100 mM, 100 nl), reduced significantly baseline SNA (‐33 ± 7% vs 3 ± 8% in EH). These data indicate that in the EH rat baseline SNA is dependent on both the hypothalamus and AT 1 receptors. Following chronic dehydration, the regulation of SNA transfers to the medulla oblongata, particularly cNTS. Funded by CNPq and CAPES (Brazil), The Royal Society.