Myocardial infarction sensitizes medial prefrontal cortex to inhibitory effect of locus coeruleus stimulation in rats.

RATIONALE: Anxiety is a common comorbidity that develops after myocardial infarction and is now an established independent risk factor for cardiovascular mortality. OBJECTIVE: Here, we assessed anxiety and mapped neural activity of forebrain regions that regulate anxiety in a rat model of myocardial infarction in order to identify sites of dysregulation. METHODS: Anxiety responses to novel (open field) or aversive stimuli (discriminative auditory fear conditioning) were assessed in rats subjected to coronary artery ligation (CAL) or sham ligation. Forebrain metabolic activity was measured by cytochrome oxidase (CO) histochemistry. Changes in CO activity and the incidence of ventricular arrhythmias were also assessed during modulation of fear circuitry induced by electrical stimulation of the locus coeruleus. RESULTS: Coronary artery ligation had negligible effects on open-field behavior, but increased expression of learned fear and impaired fear cue discrimination. Cytochrome oxidase activity was increased in the medial prefrontal cortex and in the lateral amygdala after CAL. Locus coeruleus stimulation reduced CO activity in the infralimbic medial prefrontal cortex only in rats subjected to CAL. Stimulation of the LC also elicited new ventricular arrhythmias in rats subjected to CAL. CONCLUSION: Coronary artery ligation sensitizes the infralimbic medial prefrontal cortex to the inhibitory effects of locus coeruleus stimulation. Suppression of infralimbic medial prefrontal cortical activity may impair the ability of rats subjected to CAL to discriminate between cues that signal aversive and neutral events which, in turn, may promote excessive sympathetic activation of the cardiovascular system in response to innocuous stimuli.

Complex reinnervation pattern after unilateral renal denervation in rats.

Renal denervation (DNX) is a treatment for resistant arterial hypertension. Efferent sympathetic nerves regrow, but reinnervation by renal afferent nerves has only recently been shown in the renal pelvis of rats after unilateral DNX. We examined intrarenal perivascular afferent and sympathetic efferent nerves after unilateral surgical DNX. Tyrosine hydroxylase (TH), CGRP, and smooth muscle actin were identified in kidney sections from 12 Sprague-Dawley rats, to distinguish afferents, efferents, and vasculature. DNX kidneys and nondenervated kidneys were examined 1, 4, and 12 wk after DNX. Tissue levels of CGRP and norepinephrine (NE) were measured with ELISA and mass spectrometry, respectively. DNX decreased TH and CGRP labeling by 90% and 95%, respectively (P < 0.05) within 1 wk. After 12 wk TH and CGRP labeling returned to baseline with a shift toward afferent innervation (P < 0.05). Nondenervated kidneys showed a doubling of both labels within 12 wk (P < 0.05). CGRP content decreased by 72% [3.2 ± 0.3 vs. 0.9 ± 0.2 ng/gkidney; P < 0.05] and NA by 78% [1.1 ± 0.1 vs. 0.2 ± 0.1 pmol/mgkidney; P < 0.05] 1 wk after DNX. After 12 wk, CGRP, but not NE, content in DNX kidneys was fully recovered, with no changes in the nondenervated kidneys. The use of phenol in the DNX procedure did not influence this result. We found morphological reinnervation and transmitter recovery of afferents within 12 wk after DNX. Despite morphological evidence of sympathetic regrowth, NE content did not fully recover. These results suggest a long-term net surplus of afferent influence on the DNX kidney may be contributing to the blood pressure lowering effect of DNX.

Impaired excitability of renal afferent innervation after exposure to the inflammatory chemokine CXCL1.

Recently, we showed that renal afferent neurons exhibit a unique firing pattern, i.e., predominantly sustained firing, upon stimulation. Pathological conditions such as renal inflammation likely alter excitability of renal afferent neurons. Here, we tested whether the proinflammatory chemokine CXCL1 alters the firing pattern of renal afferent neurons. Rat dorsal root ganglion neurons (Th11-L2), retrogradely labeled with dicarbocyanine dye, were incubated with CXCL1 (20 h) or vehicle before patch-clamp recording. The firing pattern of neurons was characterized as tonic, i.e., sustained action potential (AP) firing, or phasic, i.e., <5 APs following current injection. Of the labeled renal afferents treated with vehicle, 58.9% exhibited a tonic firing pattern vs. 7.8%, in unlabeled, nonrenal neurons (P < 0.05). However, after exposure to CXCL1, significantly more phasic neurons were found among labeled renal neurons; hence the occurrence of tonic neurons with sustained firing upon electrical stimulation decreased (35.6 vs. 58.9%, P < 0.05). The firing frequency among tonic neurons was not statistically different between control and CXCL1-treated neurons. However, the lower firing frequency of phasic neurons was even further decreased with CXCL1 exposure [control: 1 AP/600 ms (1-2) vs. CXCL1: 1 AP/600 ms (1-1); P < 0.05; median (25th-75th percentile)]. Hence, CXCL1 shifted the firing pattern of renal afferents from a predominantly tonic to a more phasic firing pattern, suggesting that CXCL1 reduced the sensitivity of renal afferent units upon stimulation.

5-HT1A receptors of the nucleus tractus solitarii facilitate sympathetic recovery following hypotensive hemorrhage in rats.

The role of serotonin in the hemodynamic response to blood loss remains controversial. Caudal raphe serotonin neurons are activated during hypotensive hemorrhage, and their destruction attenuates sympathetic increases following blood loss in unanesthetized rats. Caudal raphe neurons provide serotonin-positive projections to the nucleus tractus solitarii (NTS), and disruption of serotonin-positive nerve terminals in the NTS attenuates sympathetic recovery following hemorrhage. Administration of 5-HT1A-receptor agonists following hemorrhage augments sympathetic-mediated increases in venous tone and tissue hypoxia. These findings led us to hypothesize that severe blood loss promotes activation of 5-HT1A receptors in the NTS, which facilitates sympathetic recovery and peripheral tissue perfusion. Here, we developed an adeno-associated viral vector encoding an efficacious small hairpin RNA sequence targeting the rat 5-HT1A receptor. Unanesthetized rats subjected to NTS injection of the anti-rat 5-HT1A small hairpin RNA-encoding vector 4 wk prior showed normal blood pressure recovery, but an attenuated recovery of renal sympathetic nerve activity (-6.4 ± 12.9 vs. 42.6 ± 15.6% baseline, P < 0.05) 50 min after 21% estimated blood volume withdrawal. The same rats developed increased tissue hypoxia after hemorrhage, as indicated by prolonged elevations in lactate (2.77 ± 0.5 vs. 1.34 ± 0.2 mmol/l, 60 min after start of hemorrhage, P < 0.05). 5-HT1A mRNA levels in the commissural NTS were directly correlated with renal sympathetic nerve activity (P < 0.01) and inversely correlated with lactate (P < 0.05) 60 min after start of hemorrhage. The data suggest that 5-HT1A receptors in the commissural NTS facilitate tissue perfusion after blood loss likely by increasing sympathetic-mediated venous return.

Chronic fluoxetine reduces autonomic control of cardiac rhythms in rats with congestive heart failure.

Up to 40% of patients with heart failure develop depression, and depression is an independent risk factor for cardiovascular mortality in this patient population. Consequently, increasing numbers of patients with heart failure are treated with antidepressants. Selective serotonin reuptake inhibitors are typically the antidepressant of choice since this drug class has limited cardiovascular toxicity. However, little is known about the effects of selective serotonin reuptake inhibitors on autonomic cardiac regulation in congestive heart failure (CHF). Here, indexes of cardiac autonomic control were evaluated before and during chronic fluoxetine (FLX) treatment (20 mg·kg(-1)·day(-1), 5 wk) in rats that developed CHF after coronary artery ligation. FLX reduced the low-frequency (LF) component of heart rate variability (HRV; P < 0.01) as well as the sympathetic contribution to LF HRV (P < 0.01) in both CHF and sham-operated rats. Both FLX and CHF reduced high-frequency HRV (P < 0.01). Spontaneous baroreflex gain was decreased in CHF rats 8 wk after ligation (P < 0.01). Cross-spectral coherence between the interbeat interval and mean arterial pressure was reduced in the LF domain 3 wk after ligation in CHF rats (P < 0.01) and was further reduced after chronic FLX treatment (P < 0.01). Plasma catecholamines and LF blood pressure variability were not affected by FLX. Chronotropic responses to both efferent vagal nerve stimulation and isoproterenol administration were reduced in CHF rats and by FLX (P < 0.01), whereas inotropic responses to isoproterenol were reduced only in CHF rats (P < 0.01). These data indicate that chronic FLX reduces the responsiveness to autonomic output controlling cardiac rhythm and may further compromise autonomic regulation of cardiac function in CHF.

Sympathetic innervation of the splanchnic region mediates the beneficial hemodynamic effects of 8-OH-DPAT in hemorrhagic shock.

Administration of the 5-HT(1A) receptor agonist, 8-OH-DPAT, improves cardiovascular hemodynamics and tissue oxygenation in conscious rats subjected to hypovolemic shock. This effect is mediated by sympathetic-dependent increases in venous tone. To determine the role of splanchnic nerves in this response, effects of 8-OH-DPAT (30 nmol/kg iv) were measured following fixed-arterial blood pressure hemorrhagic shock (i.e., maintenance of 50 mmHg arterial pressure for 25 min) in rats subjected to bilateral splanchnic nerve denervation (SD). Splanchnic denervation decreased baseline venous tone as measured by mean circulatory filling pressure (MCFP) and accelerated the onset of hypotension during blood loss. Splanchnic denervation did not affect the immediate pressor effect of 8-OH-DPAT but did reverse the drug's lasting pressor effect, as well as its ability to increase MCFP and improve metabolic acidosis. Like SD, adrenal demedullation (ADMX) lowered baseline MCFP and accelerated the hypotensive response to blood withdrawal but also reduced the volume of blood withdrawal required to maintain arterial blood pressure at 50 mmHg. 8-OH-DPAT raised MCFP early after administration in ADMX rats, but the response did not persist throughout the posthemorrhage period. In a fixed-volume hemorrhage model, 8-OH-DPAT continued to raise blood pressure in ADMX rats. However, it produced only a transient and variable rise in MCFP compared with sham-operated animals. The data indicate that 8-OH-DPAT increases venoconstriction and improves acid-base balance in hypovolemic rats through activation of splanchnic nerves. This effect is due, in part, to activation of the adrenal medulla.

5-hydroxytryptamine (5-HT) reduces total peripheral resistance during chronic infusion: direct arterial mesenteric relaxation is not involved.

Serotonin (5-hydroxytryptamine; 5-HT) delivered over 1 week results in a sustained fall in blood pressure in the sham and deoxycorticosterone acetate (DOCA)-salt rat. We hypothesized 5-HT lowers blood pressure through direct receptor-mediated vascular relaxation. In vivo, 5-HT reduced mean arterial pressure (MAP), increased heart rate, stroke volume, cardiac index, and reduced total peripheral resistance during a 1 week infusion of 5-HT (25 µg/kg/min) in the normotensive Sprague Dawley rat. The mesenteric vasculature was chosen as an ideal candidate for the site of 5-HT receptor mediated vascular relaxation given the high percentage of cardiac output the site receives. Real-time RT-PCR demonstrated that mRNA transcripts for the 5-HT2B, 5-HT1B, and 5-HT7 receptors are present in sham and DOCA-salt superior mesenteric arteries. Immunohistochemistry and Western blot validated the presence of the 5-HT2B, 5- HT1B and 5-HT7 receptor protein in sham and DOCA-salt superior mesenteric artery. Isometric contractile force was measured in endothelium-intact superior mesenteric artery and mesenteric resistance arteries in which the contractile 5- HT2A receptor was antagonized. Maximum concentrations of BW-723C86 (5- HT2B agonist), CP 93129 (5-HT1B agonist) or LP-44 (5-HT7 agonist) did not relax the superior mesenteric artery from DOCA-salt rats vs. vehicle. Additionally, 5-HT (10-9 M to 10-5 M) did not cause relaxation in either contracted mesenteric resistance arteries or superior mesenteric arteries from normotensive Sprague- Dawley rats. Thus, although 5-HT receptors known to mediate vascular relaxation are present in the superior mesenteric artery, they are not functional, and are therefore not likely involved in a 5-HT-induced fall in total peripheral resistance and MAP.

Norepinephrine reduces ω-conotoxin-sensitive Ca2+ currents in renal afferent neurons in rats.

Sympathetic efferent and peptidergic afferent renal nerves likely influence hypertensive and inflammatory kidney disease. Our recent investigation with confocal microscopy revealed that in the kidney sympathetic nerve endings are colocalized with afferent nerve fibers (Ditting T, Tiegs G, Rodionova K, Reeh PW, Neuhuber W, Freisinger W, Veelken R. Am J Physiol Renal Physiol 297: F1427-F1434, 2009; Veelken R, Vogel EM, Hilgers K, Amman K, Hartner A, Sass G, Neuhuber W, Tiegs G. J Am Soc Nephrol 19: 1371-1378, 2008). However, it is not known whether renal afferent nerves are influenced by sympathetic nerve activity. We tested the hypothesis that norepinephrine (NE) influences voltage-gated Ca(2+) channel currents in cultured renal dorsal root ganglion (DRG) neurons, i.e., the first-order neuron of the renal afferent pathway. DRG neurons (T11-L2) retrogradely labeled from the kidney and subsequently cultured, were investigated by whole-cell patch clamp. Voltage-gated calcium channels (VGCC) were investigated by voltage ramps (-100 to +80 mV, 300 ms, every 20 s). NE and appropriate adrenergic receptor antagonists were administered by microperfusion. NE (20 µM) reduced VGCC-mediated currents by 10.4 ± 3.0% (P < 0.01). This reduction was abolished by the α-adrenoreceptor inhibitor phentolamine and the α(2)-adrenoceptor antagonist yohimbine. The ß-adrenoreceptor antagonist propranolol and the α(1)-adrenoceptor antagonist prazosin had no effect. The inhibitory effect of NE was abolished when N-type currents were blocked by ω-conotoxin GVIA, but was unaffected by other specific Ca(2+) channel inhibitors (ω-agatoxin IVA; nimodipine). Confocal microscopy revealed sympathetic innervation of DRGs and confirmed colocalization of afferent and efferent fibers within in the kidney. Hence NE released from intrarenal sympathetic nerve endings, or sympathetic fibers within the DRGs, or even circulating catecholamines, may influence the activity of peptidergic afferent nerve fibers through N-type Ca(2+) channels via an α(2)-adrenoceptor-dependent mechanism. However, the exact site and the functional role of this interaction remains to be elucidated.

Serotonin nerve terminals in the dorsomedial medulla facilitate sympathetic and ventilatory responses to hemorrhage and peripheral chemoreflex activation.

Serotonin neurons of the caudal raphe facilitate ventilatory and sympathetic responses that develop following blood loss in conscious rats. Here, we tested whether serotonin projections to the caudal portion of the dorsomedial brain stem (including regions of the nucleus tractus solitarius that receive cardiovascular and chemosensory afferents) contribute to cardiorespiratory compensation following hemorrhage. Injections of the serotonin neurotoxin 5,7-dihydroxytryptamine produced >90% depletion of serotonin nerve terminals in the region of injection. Withdrawal of ∼21% of blood volume over 10 min produced a characteristic three-phase response that included 1) a normotensive compensatory phase, 2) rapid sympathetic withdrawal and hypotension, and 3) rapid blood pressure recovery accompanied by slower recovery of heart rate and sympathetic activity. A gradual tachypnea developed throughout hemorrhage, which quickly reversed with the advent of sympathetic withdrawal. Subsequently, breathing frequency and neural minute volume (determined by diaphragmatic electromyography) declined below baseline following termination of hemorrhage but gradually recovered over time. Lesioned rats showed attenuated sympathetic and ventilatory responses during early compensation and later recovery from hemorrhage. Both ventilatory and sympathetic responses to chemoreceptor activation with potassium cyanide injection were attenuated by the lesion. In contrast, the gain of sympathetic and heart rate baroreflex responses was greater, and low-frequency oscillations in blood pressure were reduced after lesion. Together, the data are consistent with the view that serotonin innervation of the caudal dorsomedial brain stem contributes to sympathetic compensation during hypovolemia, possibly through facilitation of peripheral chemoreflex responses.

Serotonin neurons of the caudal raphe nuclei contribute to sympathetic recovery following hypotensive hemorrhage.

Serotonin is thought to contribute to the syncopal-like response that develops during severe blood loss by inhibiting presympathetic neurons of the rostroventrolateral medulla (RVLM). Here, we tested whether serotonin cells activated during hypotensive hemorrhage, i.e., express the protein product of the immediate early gene c-Fos, are critical for the normal sympathetic response to blood loss in unanesthetized rats. Serotonin-immunoreactive cells of the raphe obscurus and raphe magnus, parapyramidal cells of the B3 region, subependymal cells of the ventral parapyramidal region, and cells of the ventrolateral periaqueductal gray region were activated by hypotensive hemorrhage, but not by hypotension alone. In contrast to findings in anesthetized animals, lesion of hindbrain serotonergic cells sufficient to produce >80% loss of serotonin nerve terminal immunoreactivity in the RVLM accelerated the sympatholytic response to blood loss, attenuated recovery of sympathetic activity after termination of hemorrhage, and exaggerated metabolic acidosis. Hindbrain serotonin lesion also attenuated ventilatory and sympathetic responses to stimulation of central chemoreceptors but increased spontaneous arterial baroreflex sensitivity and decreased blood pressure variability. A more global neurotoxic lesion that also eliminated tryptophan hydroxylase-immunoreactive cells of the ventrolateral periaqueductal gray region had no further effect on the sympatholytic response to blood loss. Together, the data indicate that serotonin cells of the caudal hindbrain contribute to compensatory responses following blood loss that help maintain oxygenation of peripheral tissue in the unanesthetized rat. This effect may be related to facilitation of chemoreflex responses to acidosis.

Morphology and distribution of neurons expressing serotonin 5-HT1A receptors in the rat hypothalamus and the surrounding diencephalic and telencephalic areas.

Disorders of serotonergic neurotransmission are involved in disturbances of numerous hypothalamic functions including circadian rhythm, mood, neuroendocrine functions, sleep and feeding. Among the serotonin receptors currently recognized, 5-HT(1A) receptors have received considerable attention due to their importance in the etiology of mood disorders. While previous studies have shown the presence of 5-HT(1A) receptors in several regions of the rat brain, there is no detailed map of the cellular distribution of 5-HT(1A) receptors in the rat diencephalon. In order to characterize the distribution and morphology of the neurons containing 5-HT(1A) receptors in the diencephalon and the adjacent telencephalic areas, single label immunohistochemistry was utilized. Large, multipolar, 5-HT(1A)-immunoreactive (IR) neurons were mainly detected in the magnocellular preoptic nucleus and in the nucleus of diagonal band of Broca, while the supraoptic nucleus contained mainly fusiform neurons. Medium-sized 5-HT(1A)-IR neurons with triangular or round-shaped somata were widely distributed in the diencephalon, populating the zona incerta, lateral hypothalamic area, anterior hypothalamic nucleus, substantia innominata, dorsomedial and premamillary nuclei, paraventricular nucleus and bed nucleus of stria terminalis. The present study provides schematic mapping of 5-HT(1A)-IR neurons in the rat diencephalon. In addition, the morphology of the detected 5-HT(1A)-IR neural elements is also described. Since rat is a widely used laboratory animal in pharmacological models of altered serotoninergic neurotransmission, detailed mapping of 5-HT(1A)-IR structures is pivotal for the neurochemical characterization of the neurons containing 5-HT(1A) receptors.

The spleen is required for 5-HT1A receptor agonist-mediated increases in mean circulatory filling pressure during hemorrhagic shock in the rat.

The 5-HT(1A) receptor agonist, 8- OH-DPAT, increases whole body venous tone (mean circulatory filling pressure; MCFP), and attenuates metabolic acidosis in a rat model of unresuscitated hemorrhagic shock. To determine whether improved acid-base balance was associated with sympathetic activation and venous constriction, MCFP, sympathetic activity (SA), and blood gases were compared in hemorrhaged rats following administration of 5-HT(1A) receptor agonist 8-OH-DPAT, the arterial vasoconstrictor arginine vasopressin (AVP), or saline. To further determine whether protection of acid-base balance was dependent on splenic contraction and blood mobilization, central venous pressure (CVP), MCFP, and blood gases were determined during hemorrhage and subsequent 8-OH-DPAT-administration in rats subjected to real or sham splenectomy. Subjects were hemorrhaged to an arterial pressure of 50 mmHg for 25 min and subsequently were treated with 8-OH-DPAT (30 nmol/kg iv), AVP titrated to match the pressor effect of 8-OH-DPAT (approximately 2 ng/min iv), or infusion of normal saline. 8-OH-DPAT increased MAP, CVP, MCFP, and SA, and decreased lactate accumulation. AVP did not affect CVP or SA, but raised MCFP slightly to a level intermediate between 8-OH-DPAT- and saline-treated rats. Infusion of AVP also produced a modest protection against metabolic acidosis. Splenectomy prevented the rise in CVP, MCFP, and protection against metabolic acidosis produced by 8-OH-DPAT but had no effect on the immediate pressor response to the drug. Together, the data indicate that 8-OH-DPAT produces a pattern of cardiovascular responses consistent with a sympathetic-mediated venoconstriction that is, in part, responsible for the drug's beneficial effect on acid-base balance. Moreover, blood mobilization stimulated by the spleen is required for the beneficial effects of 8-OH-DPAT.

CRNK gene transfer improves function and reverses the myosin heavy chain isoenzyme switch during post-myocardial infarction left ventricular remodeling.

PYK2 is a Ca(2+)-dependent, nonreceptor protein tyrosine kinase that is involved in the induction of left ventricular hypertrophy (LVH) and its transition to heart failure. We and others have previously investigated PYK2's function in vitro using cultured neonatal and adult rat ventricular myocytes as model systems. However, the function of PYK2 in the in vivo adult heart remains unclear. Here we evaluate the effect of PYK2 inhibition following myocardial infarction (MI) using adenoviral (Adv) overexpression of the C-terminal domain of PYK2, known as CRNK. First we demonstrate that CRNK functions as a dominant-negative inhibitor of PYK2-dependent signaling, presumably by displacing PYK2 from focal adhesions and costameres. Then, male Sprague-Dawley rats (~300 g) underwent permanent left anterior descending coronary artery ligation. One wk post-MI, either Adv-GFP (n=34) or Adv-CRNK (n=28) was administered (10(10) pfu, 0.1 ml) via catheter-based, Optison-mediated gene transfer. LV structure and function were evaluated by echocardiography 1 and 3 wk after gene transfer, and LV tissue was analyzed by real-time RT-PCR and Western blotting. CRNK overexpression was readily detected by Western blotting 1 wk following gene transfer. Adv-CRNK improved overall survival (P=0.03; Logrank Test) and LV fractional shortening (23+/-2% vs. 31+/-2% for Adv-GFP vs. Adv-CRNK infected animals, respectively; P<0.05). Whereas MI hearts exhibited increased beta-, and decreased alpha-myosin heavy chain (MHC) mRNA expression characteristic of LVH, Adv-CRNK reversed the MHC isoenzyme switch (3.3+/-1.4 fold increase in alpha MHC; 0.4+/-0.1 fold decrease in beta MHC; P<0.05 for both). In summary, CRNK gene transfer improves survival, increases LV function, and alters MHC gene expression suggesting an attenuation of LV remodeling post-MI.

Persistent alterations in heart rate variability, baroreflex sensitivity, and anxiety-like behaviors during development of heart failure in the rat.

Depressed heart rate variability and mood are associated with increased mortality in patients with congestive heart failure (CHF). Here autonomic indexes were assessed 3 and 7 wk after left coronary artery ligation in telemetered rats, after which anxiety-like behaviors were assessed in an elevated plus maze. Low frequency (LF) and high frequency (HF) heart rate variability were reduced in CHF rats 3 wk after infarction (LF, 1.60 +/- 0.52 vs. 6.97 +/- 0.79 ms(2); and HF, 1.53 +/- 0.39 vs. 6.20 +/- 1.01 ms(2); P < 0.01). The number of sequences of interbeat intervals that correlated with arterial pressure was decreased in CHF rats at 3 and 7 wk (week 3, 26.60 +/- 10.85 vs. 59.75 +/- 11.4 sequences, P < 0.05; and week 7, 20.80 +/- 8.97 vs. 65.38 +/- 5.89 sequences, P < 0.01). Sequence gain was attenuated in CHF rats by 7 wk (1.34 +/- 0.06 vs. 2.70 +/- 0.29 ms/mmHg, P < 0.01). Coherence between interbeat interval and mean arterial blood pressure variability in the LF domain was reduced in CHF rats at 3 (0.12 +/- 0.03 vs. 0.26 +/- 0.05 k(2), P < 0.05) and 7 (0.16 +/- 0.02 vs. 0.31 +/- 0.05 k(2), P < 0.05) wk. CHF rats invariably entered the open arm of the elevated plus maze first and spent more time in the open arms (36.0 +/- 15% vs. 4.6 +/- 1.9%, P < 0.05). CHF rats also showed a tendency to jump head first off the apparatus, whereas controls did not. Together the data indicate that severe autonomic dysfunction is accompanied by escape-seeking behaviors in rats with verified CHF.

Vascular KCNQ potassium channels as novel targets for the control of mesenteric artery constriction by vasopressin, based on studies in single cells, pressurized arteries, and in vivo measurements of mesenteric vascular resistance.

Pressor effects of the vasoconstrictor hormone arginine vasopressin (AVP), observed when systemic AVP concentrations are less than 100 pM, are important for the physiological maintenance of blood pressure, and they are also the basis for therapeutic use of vasopressin to restore blood pressure in hypotensive patients. However, the mechanisms by which circulating AVP induces arterial constriction are unclear. We examined the novel hypothesis that KCNQ potassium channels mediate the physiological vasoconstrictor actions of AVP. Reverse transcriptase polymerase chain reaction revealed expression of KCNQ1, KCNQ4, and KCNQ5 in rat mesenteric artery smooth muscle cells (MASMCs). Whole-cell perforated patch recordings of voltage-sensitive K+ (Kv) currents in freshly isolated MASMCs revealed 1,3-dihydro-1-phenyl-3,3-bis(4-pyridinylmethyl)-2H-indol-2-one (linopirdine)- and 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone (XE-991)-sensitive KCNQ currents that were electrophysiologically and pharmacologically distinct from other Kv currents. Suppression of KCNQ currents by AVP (100 pM) was associated with significant membrane depolarization, and it was abolished by the protein kinase C (PKC) inhibitor calphostin C (250 nM). The KCNQ channel blocker linopirdine (10 microM) inhibited KCNQ currents in MASMCs, and it induced constriction of isolated rat mesenteric arteries. The vasoconstrictor responses were not additive when combined with 30 pM AVP, and they were prevented by the L-type Ca2+ channel blocker verapamil. Ethyl-N-[2-amino-6-(4-fluorophenylmethylamino)pyridin-3-yl] carbamic acid (flupirtine) significantly enhanced KCNQ currents, and it reversed constrictor responses to 30 pM AVP. In vivo, i.v. administration of linopirdine induced a dose-dependent increase in mesenteric artery resistance and blood pressure, whereas flupirtine had the opposite effects. We conclude that physiological concentrations of AVP induce mesenteric artery constriction via PKC-dependent suppression of KCNQ currents and L-type Ca2+ channel activation in MASMCs.

Hypertensive crisis, catecholamine cardiomyopathy, and death associated with pseudoephedrine use in a patient with pheochromocytoma.

OBJECTIVE: To describe a woman with a previously unrecognized pheochromocytoma who died after ingesting over-the-counter pseudoephedrine-containing medications. METHODS: We present a case report including laboratory, radiographic, and pathologic findings in a patient with a previously unrecognized pheochromocytoma. RESULTS: A 31-year-old woman had symptoms consistent with intermittent, excessive release of catecholamines since childhood. She developed an upper-respiratory infection and used over-the-counter medications containing pseudoephedrine. Subsequently, she developed a hypertensive crisis with congestive heart failure and died of a cardiac arrhythmia and shock. Findings from postmortem examination included a right adrenal pheochromocytoma, congestive heart failure, and catecholamine cardiomyopathy. CONCLUSION: This patient death may be linked to the use of pseudoephedrine hydrochloride. Physicians and pharmacists should warn patients with known pheochromocytoma or those at risk for having pheochromocytoma on the basis of family history or genetic testing that pseudoephedrine use may be harmful. Over-the-counter packaging should include such warning.

Selective impairment of central mediation of baroreflex in anesthetized young adult Fischer 344 rats after chronic intermittent hypoxia.

Baroreflex control of heart rate (HR) is impaired after chronic intermittent hypoxia (CIH). However, the location and nature of this response remain unclear. We examined baroreceptor afferent, vagal efferent, and central components of the baroreflex circuitry. Fischer 344 (F344) rats were exposed to room air (RA) or CIH for 35-50 days and were then anesthetized with isoflurane, ventilated, and catheterized for measurement of mean arterial blood pressure (MAP) and HR. Baroreceptor function was characterized by measuring percent changes of integrated aortic depressor nerve (ADN) activity (Int ADNA) relative to the baseline value in response to sodium nitroprusside- and phenylephrine-induced changes in MAP. Data were fitted to a sigmoid logistic function curve. HR responses to electrical stimulation of the left ADN and the right vagus nerve were assessed under ketamine-acepromazine anesthesia. Compared with RA controls, CIH significantly increased maximum baroreceptor gain or maximum slope, maximum Int ADNA, and Int ADNA range (maximum - minimum Int ADNA), whereas other parameters of the logistic function were unchanged. In addition, CIH increased the maximum amplitude of bradycardic response to vagal efferent stimulation and decreased the time from stimulus onset to peak response. In contrast, CIH significantly reduced the maximum amplitude of bradycardic response to left ADN stimulation and increased the time from stimulus onset to peak response. Therefore, CIH decreased central mediation of the baroreflex but augmented baroreceptor afferent function and vagal efferent control of HR.

The 5-hydroxytryptamine1A receptor agonist, (+)-8-hydroxy-2-(di-n-propylamino)-tetralin, increases cardiac output and renal perfusion in rats subjected to hypovolemic shock.

The 5-hydroxytryptamine(1A) receptor agonist, (+)-8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), raises blood pressure (BP) and venous tone in rats subjected to hemorrhagic shock. Here, BP, ascending aortic blood flow [i.e., estimate of cardiac output (CO)] and venous blood gases were measured to determine the hemodynamic effects of 8-OH-DPAT (30 nmol/kg i.v., n = 10), saline (n = 10), or an equipressor infusion of epinephrine (n = 10) in unanesthetized rats subjected to hemorrhagic shock (25 min of hypotensive hemorrhage, approximately 50 mm Hg). Renal and iliac blood flow were measured in separate groups of similarly hemorrhaged rats given the same dose of 8-OH-DPAT (n = 7) or saline (n = 6). Compared with saline treatment, 8-OH-DPAT produced a sustained rise in BP (+32 +/- 4 versus +9 +/- 2 mm Hg, 15 min after injection, P < 0.01) and CO (+27 +/- 5 versus +4 +/- 6 ml/min/kg, P < 0.01) but did not affect total peripheral resistance (TPR). Infusion of epinephrine reduced CO (-12 +/- 6 ml/min/kg, P < 0.01) and dramatically increased TPR [+0.37 +/- 0.11 versus +0.05 +/- 0.05 log (mm Hg/ml/min/kg), P < 0.01]. 8-OH-DPAT increased renal conductance (+7 +/- 1 versus +4 +/- 1 microl/min/mm Hg, P < 0.01) but did not significantly affect iliac conductance. 8-OH-DPAT attenuated further development of acidosis compared with either saline or epinephrine (-5.6 +/- 1.6 versus -13.0 +/- 2.0 versus -11.3 +/- 2.6 mmol/liter base excess 45 min after start of hemorrhage, both P < 0.01 versus 8-OH-DPAT). These data demonstrate that 8-OH-DPAT improves hemodynamics during circulatory shock, in part, through renal vasodilation and mobilizing of blood stores.

The serotonin 5-Hydroxytryptaphan1A receptor agonist, (+)8-hydroxy-2-(di-n-propylamino)-tetralin, stimulates sympathetic-dependent increases in venous tone during hypovolemic shock.

Adjuvant treatment of hypovolemic shock with vasoconstrictors is controversial due to their propensity to raise arterial resistance and exacerbate ischemia. A more advantageous therapeutic approach would use agents that also promote venoconstriction to augment perfusion pressure through increased venous return. Recent studies indicate that 5-hydroxytryptophan (5-HT)(1A) receptor agonists increase blood pressure by stimulating sympathetic drive when administered after acute hypotensive hemorrhage. Given that venous tone is highly dependent upon sympathetic activation of alpha(2)-adrenergic receptors, we hypothesized that the 5-HT(1A) receptor agonist, (+)8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), would increase venous tone in rats subject to hypovolemic shock through sympathetic activation of alpha(2)-adrenergic receptors. Systemic administration of 8-OH-DPAT produced a sustained rise in blood pressure (+44 +/- 3 mm Hg 35 min after injection, P < 0.01 versus saline) and mean circulatory filling pressure (+4.2 +/- 0.7 mm Hg, P < 0.01 versus saline) in conscious rats subjected to hypovolemic shock. An equipressor infusion of epinephrine failed to influence mean circulatory filling pressure (MCFP). Ganglionic blockade, alpha(1)-, or peripheral alpha(2)-adrenergic receptor blockade prevented the rise in MCFP observed with 8-OH-DPAT, but only alpha(1)-adrenergic receptor blockade diminished the pressor effect of the drug (P < 0.01). 8-OH-DPAT raises blood pressure in rats in hypovolemic shock through both direct vascular activation and sympathetic activation of alpha(1)-adrenergic receptors. The sympathoexcitatory effect of 8-OH-DPAT contributes to elevated venous tone through concurrent activation of both alpha(1)- and alpha(2)-adrenergic receptors. The data suggest that 5-HT(1A) receptor agonists may provide an advantageous alternative to currently therapeutic interventions used to raise perfusion pressure in hypovolemic shock.

Role of the arterial baroreflex in 5-HT1A receptor agonist-mediated sympathoexcitation following hypotensive hemorrhage.

5-HT1A-receptor agonists rapidly restore blood pressure and sympathetic activity in conscious rats subjected to hypotensive hemorrhage. 5-HT1A-receptor activation has also been shown to produce a robust increase in baroreceptor-dependent, pulse-synchronous firing of cardiac sympathetic nerves in anesthetized cats. To determine whether 5-HT1A-receptor agonists reverse hemorrhage-induced suppression of sympathetic activity through facilitation of the arterial baroreflex, the effects of the 5-HT1A-receptor agonist, 8-OH-DPAT, were assessed in male Sprague-Dawley rats subjected to sinoaortic baroreceptor denervation and subsequent hypotensive hemorrhage. 8-OH-DPAT produced rapid pressor and sympathoexcitatory responses in hemorrhaged animals that were attenuated, but not blocked, by sinoaortic denervation (SAD) (+49 +/- 4 vs. +37 +/- 4 mmHg; +165 +/- 30 vs. +92 +/- 24% baseline, P < 0.01). Spectral analysis of sympathetic activity showed that SAD abolished the 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT)-mediated increases in pulse-synchronous (13 +/- 1 vs. 5 +/- 1% total power for intact vs. SAD rats, P < 0.01) and Mayer wave-related bursting (18 +/- 3 vs. 8 +/- 1% total power, P < 0.05). However, 8-OH-DPAT continued to increase total power (+72 +/- 22 vs. -63 +/- 7% prehemorrhage total power, P < 0.05) and power at the respiratory frequency (35 +/- 2 vs. 25 +/- 4% total power) in SAD animals. These data indicate that full expression of the sympathoexcitatory effect of 8-OH-DPAT requires a functional arterial baroreflex. However, a portion of the effect is due to activation of arterial baroreflex-independent sympathetic pathways.