Altered Temporal Profile of Heat Shock Factor 1 Phosphorylation and Heat Shock Protein 70 Expression Induced by Heat Shock in Nucleus Tractus Solitarii of Spontaneously Hypertensive Rats

Abstract

Background-We demonstrated recently that heat shock (HS)-induced heat shock protein 70 (HSP70) expression in bilateral nucleus tractus solitarii (NTS), the terminal site in the brain stem for primary baroreceptor afferents, confers cardiovascular protection against heatstroke by potentiating baroreceptor reflex (BRR) response. This study evaluated the hypothesis that altered regulation of HSP70 expression may be associated with the heightened susceptibility to heatstroke during hypertension. Methods and Results-Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats anesthetized with propofol were used. Compared with WKY rats, significant induction in HSP70 or phosphorylation of heat shock factor 1 (HSF1), but not HSF2, in the NTS and potentiation of BRR response in SHR occurred earlier (4 versus 8 hours), reaching peak magnitude sooner (16 versus 24 hours), and declined more rapidly after a brief hyperthermic HS (42Ϯ0.5°C for 15 minutes). The protection conferred by HS against hypotension and bradycardia during the onset of heatstroke (45°C for 60 minutes), although effective, was less effective in SHR. Microinjection bilaterally into the NTS of the selective protein kinase A (PKA) inhibitor H-89 (100 pmol) or the selective PKC inhibitor calphostin C (100 pmol) significantly attenuated all of the above events induced in SHR by HS. However, only H-89 was effective in WKY rats. Conclusions-An

Nitric Oxide Regulates c-fosExpression in Nucleus Tractus Solitarii Induced by Baroreceptor Activation via cGMP-Dependent Protein Kinase and cAMP Response Element-Binding Protein Phosphorylation

“…Bilateral and sequential microinjection of test agents into the NTS was performed according to procedures reported in our recent studies (Chan et al, 1998b(Chan et al, , 1999(Chan et al, , 2000(Chan et al, , 2003. The stereotaxic coordinates used were 0.5 to 0.9 mm below the surface of the fourth ventricle, 0 to Ϫ0.5 mm caudal from and 0.3 to 0.6 mm lateral to the obex.…”

Receptor-Independent Activation of GABAergic Neurotransmission and Receptor-Dependent Nontranscriptional Activation of Phosphatidylinositol 3-kinase/Protein Kinase Akt Pathway in Short-Term Cardiovascular Actions of Dexamethasone at the Nucleus Tractus Solitarii of the Rat

“…Rats were anesthetized initially with pentobarbital sodium (50 mg/kg i.p.) to perform preparatory surgery (Li et al, 2001;Chan et al, 2003Chan et al, , 2004. This routinely included intubation of the trachea to facilitate ventilation and cannulation of the femoral artery and vein to measure systemic arterial pressure or administer test chemicals.…”

“…Test agents were microinjected bilaterally and sequentially, at a volume of 50 nl, into the NTS (Li et al, 2001;Chan et al, 2003Chan et al, , 2004. The coordinates for the NTS were Ϫ0.5 to ϩ0.5 mm from the obex, 0.3 to 0.8 mm lateral to the midline, and 0.5 to 1.0 mm below the dorsal surface of the medulla oblongata.…”

“…Test agents used included a synthetic glucocorticoid, Dex (Sigma-Aldrich, St. Louis, MO); a selective glucocorticoid type II receptor antagonist (Clapham and Turner, 1997;Limbourg et al, 2002), mifepristone (RU486; SigmaAldrich), that does not bind to the type I mineralocorticoid receptor or to aldosterone receptors (Brogden et al, 1993); a selective GABA A receptor antagonist (Galvez-Ruano et al, 1995), bicuculline methiodine (Sigma-Aldrich); a GABA B receptor antagonist (Al-Dahan et al, 1990), 2-hydroxy saclofen (2-OH saclofen; Sigma-Aldrich); a nonselective nitric-oxide synthase (NOS) inhibitor (Reif and McCreedy, 1995), N G -monomethyl-L-arginine acetate (L-NMMA; SigmaAldrich); a PI3K inhibitor (Vlahos et al, 1994), LY294002 (Calbiochem, San Diego, CA); and an RNA synthesis inhibitor , actinomycin D (AMD; Calbiochem). The dose and treatment scheme were adopted from previous reports (Clapham and Turner, 1997;Ouyang and Wang, 2000;Hafezi-Moghadam et al, 2002;Limbourg et al, 2002;Moreno et al, 2002;Chan et al, 2003), which used the same test agents for the same purpose as in this study. With the exception of mifepristone, LY294002, and AMD, which used, respectively, 1 or 0.2% DMSO or 3% methanol as the solvent, all test agents were prepared with aCSF.…”

“…To extract protein, tissues on both sides of the dorsomedial part of the medulla oblongata, at the level of caudal NTS (1 mm rostral to 1 mm caudal from the obex) were collected by micropunches made with a stainless steel bore (1-mm i.d.) and were frozen immediately in liquid nitrogen (Li et al, 2001;Chan et al, 2002Chan et al, , 2003Chan et al, , 2004. Medullary tissues thus obtained from five to six rats that received the same treatment were homogenized, centrifuged, and the cytosolic fraction was saved in liquid nitrogen until use.…”