Fawn-hooded Hypertensive Research Articles

Abstract 3142: Exaggerated K Ca Channel Current Activity Accounts for Reduced Myogenic Constriction in the Cerebral Vasculature of the Fawn Hooded Hypertensive (FHH) rats

The ionic mechanism by which pressure induces myogenic arterial constriction is not completely understood. In the present study we compared the Fawn Hooded Hypertensive (FHH) rat strain bred that does not autoregulate CBF and the FHH.1 BN rat strain created by transfer of a 2.6 Mb region of a Brown Norway (BN) rat chromosome 1 and introgressed into the FHH genetic background and recovered the myogenic phenotype, with respect to K Ca channel activity and pressure-induced myogenic constriction. We investigated the functional role of Ca 2+- activated K + channel in the impaired pressure-induced myogenic response in cannulated and pressurized middle cerebral arterial segments of FHH and compared with that of the FHH.1 BN rat strain. The cannulated arterial segments of FHH rat strain elicited significantly reduced pressure-induced myogenic constriction, whereas those of the FHH.1 BN exhibited more than 40-50 % constriction or reduction in diameter during step increases in intravascular pressure from 40 to 140 mmHg. Pretreatment of the he FHH rat cerebral arterial segments with the K Ca channel inhibitor iberiotoxin (100 nM) rendered the FHH rat cannulated arterial segments elicit near equal level of myogenic constriction as that of the FHH.1 BN . The magnitude and density (pA/pF) of a macroscopic whole-cell K Ca channel current recorded from FHH and FHH.1 BN rat cerebral arterial muscle cells during a 10 mV step depolarization from -70 mV to +80 mV was 2- to 3-fold greater in the FHH than that in the FHH.1 BN rat cerebral arterial muscle cells. Similarly, the NPo of the K Ca single-channel currents recorded at +40 mV using symmetrical KCl solution was significantly higher in the FHH (0.0035 ± 0.0002) than in the FHH.1BN (0.0013 ± 0.0003, n =5), albeit the unitary conductances were not different. These findings indicate that exaggerated K Ca channel current activity in the FHH rat cerebral arterial muscle cell membrane could account for the impaired pressure-induced myogenic constriction in the FHH rat strain and may have implications for stroke susceptibility in the FHH rat model.

Genetic influences on survival time after severe hemorrhage in inbred rat strains

To find a genetic basis for differential ability to survive severe hemorrhage, we previously showed eightfold differences in survival times among inbred rat strains. We assumed that rat strains had similar normalized blood volumes (NBV; ml/100 g body wt). As NBV might vary among strains and constitute one genetic variable affecting survival time to hemorrhage, in experiment 1 of the current studies we first measured total blood volumes and calculated NBV in specific inbred rat strains (Brown Norway/Medical College of Wisconsin, BN; Dark Agouti, DA; Fawn Hooded Hypertensive, FHH; Lewis, LEW; and Dahl Salt-Sensitive, SS) previously found to be divergent in survival time. NBV differed by 20% (P < 0.01; BN > SS > FHH = LEW = DA) and had a heritability (h(2)) of 0.56. Hence, differential survival times in our previously published study might reflect strain-dependent differences in NBV. Then studies were conducted wherein rats were catheterized and, ∼24 h later, 47% of their blood volume was removed; these rats were observed for a maximum of 4 h. In experiment 2, blood volumes were measured the day prior to hemorrhage. Percent survival and survival time did not differ among strains. To obviate possible confounding effects of blood volume determination, in experiment 3 the average NBV for each strain was used to determine hemorrhage volumes. Percent survival (P < 0.01) and survival times (P < 0.001) were different with DA demonstrating the best (62.5%, 190 ± 29 min) and BN the worst (0%, 52 ± 5 min) survival responses. These data indicate that both blood volume and survival time after hemorrhage in rats are heritable quantitative traits, and continue to suggest that genetic assessment of these phenotypes might lead to novel therapeutics to improve survival to hemorrhage.

Genetic basis of altered myogenic response and renal injury in FHH rats

This study examined the effect of substitution of a 2.6Mb segment from Brown Norway (BN) rat Chr 1 into the Fawn Hooded Hypertensive (FHH) rat genetic background on autoregulation of renal blood flow (RBF) and development of renal injury. FHH rats exhibited poor autoregulation of RBF and GFR rose by 60% when renal perfusion pressure (RPP) was increased from 100 to 150 mmHg while the FHH.1BN congenic strain exhibited perfect autoregulation of RBF. Protein excretion rose from 51±5 to 259±41 mg/day in 9 to 21 week FHH rats but only increased to 147±24 mg/day in the FHH.1BN congenic strain. Diameter of isolated perfused afferent arterioles from FHH rats did not change significantly when transmural pressure was increased from 60 to 140 mmHg. In contrast, diameter of the congenic decreased 19.4% with the same pressure increase. Patch clamping experiments indicate that large conductance Calcium activated K+ channel (BK) current was 5 fold greater in vascular smooth muscle (VSM) cells isolated from renal vessels of FHH rats than the congenic strain. This data indicates that the gene responsible for restoring autoregulation of RBF lies within this 2.6 Mb region containing 11 genes and transfer of this region restores the myogenic response and slows the progression of renal disease. The impaired myogenic response is likely due to hyperpolarization of VSM cells due to increased BK channel activity. NIH HL36279, DK079306 and HL69321.

Genetic basis of impaired myogenic response and cerebral blood flow autoregulation FHH rats

This study examined the effect of transfer of a small region from chromosome 1 (Chr 1) of the Brown Norway (BN) rat (FHH.1BN AR+ strain) into the Fawn Hooded Hypertensive (FHH) rat genetic background on autoregulation of cerebral blood flow (CBF) and the myogenic response of isolated perfused middle cerebral arteries (MCA). FHH rats exhibited poor autoregulation measured by laser Doppler flowmetry and CBF rose by 50% when perfusion pressure was increased from 100 to 150 mmHg. Autoregulation of CBF was completely restored in the AR+ strain. The diameter of isolated middle cerebral artery (MCA) of FHH rats increased by 10% when transmural pressure was increased from 40 to 140 mmHg. In contrast, the diameter of the MCA fell from 127±16 to 65±14 μm in the AR+ strain when pressure was increased over this range. FHH rats exhibited a much more prolonged hyperemia and larger infarct than that seen in the AR+ strain following ischemia/reperfusion. These results indicate that a gene that plays a critical role in the myogenic response of cerebral arteries lies within this critical 2.6 Mb region containing just 11 genes and that transfer of this region restores autoregulation of CBF and reduces infarct size following ischemia/reperfusion injury. The impaired myogenic response is likely due to hyperpolarization of VSM cells due to increased BK channel activity. NIH HL36279, DK79306, HL59996.

Enhanced BK (IK(ca)) channel activity contributes to lack of myogenic response in the cerebral circulation of Fawn Hooded Hypertensive (FHH) Rats

The present study examined the role of alterations in Iberiotoxin (IBTX) sensitive IK(ca) channel activity in impaired myogenic response in the cerebral circulation of Fawn Hooded Hypertensive (FHH) rats. Isolated perfused middle cerebral arterioles from FHH rats exhibited no myogenic response when pressure was increased from 40 to 140 mmHg. In contrast, vascular diameter decreased by about 50% in an FHH.1BN AR+ congenic strain in which a 2.6 Mb region of BN chromosome 1 was introgressed into the FHH genetic background. Whole‐cell patch‐clamp (1μM free calcium; +40mV) of cerebral vascular smooth muscle cells revealed amplified IK(ca) current densities (pA/pF) in FHH rats compared to AR+ and SD rats (23.2±6;6.9±1.9 and 7.1±1.3 respectively). Additionally, in inside‐out patch clamping, IK(ca) exhibited similar unitary conductance (235 and 245 pS) in both strains. However, open probability of IK(ca) were significantly higher in FHH rats compared to AR+ rats (0.82±0.04 and 0.3±0.09 respectively). These results suggest that enhanced activity of the IK(ca) channel contributes to loss of myogenic response in the cerebral circulation of FHH rats. NIH HL36279, HL59996, DK79306. Roman.

Diabetic rats are unable to elicit cardioprotection by isoflurane: role of mitochondrial dysfunction

We investigated whether differences in mitochondrial genome play a role in anesthetic-induced preconditioning (APC) in the diabetic heart model with “swapped” mitochondria. These rats have identical nuclear genome, but some bear Wistar (T2DNmtWistar) while others bear Fawn Hooded Hypertensive (T2DNmtFHH) mitochondrial genome. The production of reactive oxygen species (ROS) and changes in flavoproteins (FPs) fluorescence were monitored from ventricular myocytes in the presence of 1 MAC isoflurane by laser scanning confocal microscopy. Opening of mitochondrial permeability transition pore (mPTP) was detected by tetramethylrhodamine dye. During isoflurane, ROS were increased by 165% and 107% in T2DNmtFHH and T2DNmtWistar cardiomyocytes, respectively. In addition, isoflurane induced oxidation of mitochondrial FPs in T2DNmtFHH by 94% and by 35% in T2DNmtWistar myocytes. Compared to respective controls, APC increased the mPTP opening time in T2DNmtWistar but not in T2DNmtFHH myocytes. Our findings suggest that mitochondrial genome-related differences in the function of respiratory chain complexes have an impact on anesthetic sensitivity of the mitochondria. This in part could explain that APC protection against mPTP opening is compromised in T2DNmtFHH but not in T2DNmtWistar cardiomyocytes. Supported by P01GM066730 (ZJB) from the NIH, Bethesda, MD.

Food intake and interdigestive gastrointestinal motility in ghrelin receptor mutant rats

Ghrelin is the endogenous ligand for the growth hormone secretagogue receptor (GHSR). Ghrelin regulates feeding activity and interdigestive contractions of the stomach in rodents. To investigate the role of endogenous ghrelin in the digestive system, we have developed GHSR-mutant rats, named FHH-Ghsr(m1Mcwi), using the Fawn-Hooded Hypertensive (FHH) parental strain. N-ethyl-N-nitrosourea (ENU) was used as a mutagen. Genomic DNA prepared from a tail clip was analyzed using the targeting induced local lesions in genomes (TILLING) approach. The non-synonymous mutation in position 343 (NM_032075) led to the generation of a premature stop codon, causing deletion of the last 22 amino acids at the C-terminal of ghrelin receptor protein. Spontaneous and ghrelin-stimulated food intake was measured in wild-type (WT) FHH and FHH-Ghsr(m1Mcwi) rats. For interdigestive motility recording, two strain gauge transducers were sutured on the antrum and duodenum. Spontaneous gastroduodenal contractions were recorded in freely moving conscious rats. Ghrelin (40 μg/kg) failed to stimulate food intake in the mutant rats, while spontaneous food intake was not significantly different between the WT rats and FHH-Ghsr(m1Mcwi) rats. Phase III-like contractions were observed in stomach and duodenum both in the WT and FHH-Ghsr(m1Mcwi) rats. In the WT rats, ghrelin (12 μg/kg) administration enhanced spontaneous phase III-like contractions, and a GHSR antagonist, (D-lys3)GHRP-6 (0.28 mg/kg), abolished the spontaneous phase III-like contractions. In FHH-Ghsr(m1Mcwi) rats, ghrelin and (D-lys3)GHRP-6 did not affect phase III-like contractions. It is suggested that the intact GHSR structure is essential for the ghrelin-dependent regulation of interdigestive motility and feeding behavior. Even in FHH-Ghsr(m1Mcwi) rats, spontaneous gastric phase III-like contractions were still observed, suggesting the development of a compensatory mechanism to maintain these contractions.

Aggregatibacter actinomycetemcomitans–Induced Bone Loss and Antibody Response in Three Rat Strains

The aim of this study is to compare the colonization, immunoglobulin (Ig) G response, and alveolar bone loss in Aggregatibacter actinomycetemcomitans (Aa)-inoculated Fawn Hooded Hypertensive (FHH), Dahl Salt-Sensitive (DSS), and Brown Norway (BN) rats. Each rat strain was divided into wild-type Aa-inoculated and non-inoculated control groups. Blood taken at 12 weeks after inoculation was assessed for Aa-specific IgG antibodies by an enzyme-linked immunosorbent assay. Colonization was assessed 12 weeks postinoculation. Bone loss was estimated by measuring the distance from the cemento-enamel junction (CEJ) to the alveolar bone crest (ABC) at 20 molar sites. Colonization and antibody levels were compared by using the Student t test. Diseased rats were defined as having two sites per quadrant with CEJ-ABC distances that were significantly greater than the control CEJ-ABC distances. The Aa colonization of FHH rats was significantly higher than in other strains (P <0.05). The Aa-specific IgG levels in the DSS Aa-inoculated group were significantly higher than in its control group (P <0.05). Only FHH rats showed Aa disease-associated bone loss (P = 0.0021). Aa colonized and caused more disease in FHH rats than in the other rat strains. The rat strains each responded differently to the same Aa strain.

Refined Mapping of the Renal Failure Rf-3 Quantitative Trait Locus

Rf-3, a quantitative trait locus (QTL) on rat chromosome 3, affects the development of CKD in Fawn-Hooded Hypertensive (FHH) rats. This QTL spans 110 Mb and approximately 1400 genes; therefore, narrowing the position of this locus is necessary to elucidate potential candidate genes. Here, we used congenic models and comparative genomics to refine the Rf-3 candidate region. We generated congenic lines carrying smaller intervals (subcongenics) of the Rf-3 region and used these lines to reduce the Rf-3 candidate region by 94% (to 7.1 Mb). We used comparative genomics to identify QTL for both nephropathy and albuminuria in the syntenic region of this interval for both human and mouse. We also used the overlapping homologous regions to reduce the number of likely positional candidate genes to 13 known or predicted genes. By combining congenic models and cross-species studies, we narrowed the list of candidate genes to a level that we could sequence the whole interval to further identify the causative gene in future studies.

Temporal characterization of the development of renal injury in FHH rats and FHH.1BNcongenic strains

The present study examined the effect of transfer of portions of chromosome 1 that includes (FHH.1(BN) AR(+) strain) or excludes (control FHH.1(BN) AR(-) strain) a 4.3-Mb region from the Brown Norway (BN) rat that restores the autoregulation (AR) of renal blood flow (RBF) on the development of hypertension and renal injury in congenic strains of Fawn Hooded Hypertensive (FHH) rats. FHH and control AR(-) rats exhibited poor autoregulation of RBF, and glomerular capillary pressure (Pgc) rose by 19 ± 2 mmHg in FHH rats when renal perfusion pressure (RPP) was increased from 100 to 150 mmHg. In contrast, RBF was well autoregulated in the AR(+) strain, and Pgc only increased by 3 ± 1 mmHg when RPP was increased over this range. Baseline mean arterial pressure (MAP) at 12 wk of age was similar in all strains and averaged 122 mmHg. MAP increased significantly in FHH rats and was significantly higher by 12 mmHg in 21-wk-old FHH rats than in the FHH.1(BN) congenic strains. Protein excretion rose from 5 ± 1 to 397 ± 29 mg/day in 6- vs. 21-wk-old FHH rats. In contrast, protein excretion only increased to 139 ± 21 mg/day in the control AR(-) strain, and it did not increase significantly in the AR(+) strain. Glomerular permeability to albumin was similar in all strains at 6 wk of age. It increased significantly in 9-wk-old FHH and control AR(-) rats, but not in the AR(+) strain. The levels of matrix metalloproteinase (MMP)-2 and transforming growth factor (TGF)-β2 protein were significantly higher in the renal cortex of 9-wk-old FHH rats compared with the levels seen in the AR(+) strain. These data indicate that transfer of a 4.3-Mb region of BN chromosome 1 into the FHH genetic background improves autoregulation of RBF, normalizes Pgc, and slows the progression of renal disease.

Vascular responses in aortic rings of a consomic rat panel derived from the Fawn Hooded Hypertensive strain

The present experiments, utilizing the high-throughput vascular protocol of PhysGen (Program for Genomic Applications) characterized the responses of aortic rings to vasoconstrictor (phenylephrine) and vasodilator (acetylcholine, sodium nitroprusside, and reduced tissue bath Po(2)) stimuli in consomic rat strains derived from a cross between the Fawn Hooded Hypertensive rat (FHH/EurMcwi) and the Brown Norway normotensive (BN/NHsdMcwi) rat. The effects of substituting individual BN chromosomes into the FHH genetic background were determined in animals that were maintained on a low-salt (0.4% NaCl) diet or switched to a high-salt (4% NaCl) diet for 3 wk. Sex-specific differences were evaluated in male and female consomic rats on similar dietary salt intake. Multiple chromosomes affected various vascular reactivity phenotypes in the FHH × BN consomic panel, and substantial salt-dependent changes in vascular reactivity and sex-specific differences in aortic reactivity were observed in individual consomic strains. However, compared with earlier studies of consomic rats derived from a cross between the BN rat and the Dahl salt-sensitive (SS) rat, only 3-7% of the vascular phenotypes were affected in a similar manner by substituting specific BN chromosomeschromosomes into the FHH genetic background versus the SS genetic background. The findings of the present study stress the potential value of consomic rat panels in gaining insight into genetic factors influencing vascular reactivity and suggest that the chromosomes that appear to be involved in the determination of aortic ring reactivity in different rodent models of hypertension are highly strain- and sex specific.

Effects of angiotensin type 1 receptor blockade on arginine and ADMA synthesis and metabolic pathways in fawn-hooded hypertensive rats

The fawn-hooded hypertensive (FHH) rat develops spontaneous glomerulosclerosis that is ameliorated by inhibition of the angiotensin II type 1 receptor (AT-1). Since kidney damage is associated with nitric oxide (NO) deficiency, we investigated how AT-1 antagonism influenced nitric oxide synthase (NOS), as well as NOS substrate [L-arginine (L-Arg)] and inhibitor [asymmetric dimethylarginine (ADMA)]. L-Arg is synthesized by renal argininosuccinate synthase/argininosuccinate lyase (ASS/ASL) and then either consumed within the kidney by arginase II or NOS or released into the circulation. L-Arg is then taken up from plasma into cells where it can be utilized by NOS and other pathways. The competitive inhibitor of NOS, ADMA, is degraded by dimethylarginine dimethylaminohydrolase (DDAH). Male FHH rats were put on a 40% casein diet for 13 weeks, and some received AT-1 antagonist which reduced blood pressure and kidney weight and prevented glomerulosclerosis and hyperfiltration. The AT-1 antagonist reduced the expression of DDAH2, increased DDAH1 and increased total DDAH activity in the kidney cortex, although there was no change in plasma or kidney cortex ADMA levels. The AT-1 antagonist caused no change in the expression of renal ASS/ASL, but reduced renal and aortic arginase expression and renal arginase activity, which could explain the increased plasma L-Arg. In separate studies, 1 week of AT-1 blockade in young FHH rats had no effect on any of these parameters. Thus, the net result of AT-1 antagonist was an improved L-Arg to ADMA ratio due to the prevention of renal and vascular arginase activation which favours increased NO production. Since 1 week of AT-1 blockade in the absence of kidney damage was without effect on arginases, this suggests that the reduction in arginase activity is secondary to the prevention of structural damage rather than a direct immediate effect of AT-1 antagonism.

Taste Solution Consumption by FHH-Chr nBN Consomic Rats

There has been extensive work to elucidate the behavioral and physiological mechanisms responsible for taste preferences of the rat but little attempt to delineate the underlying genetic architecture. Here, we exploit the FHH-Chr n(BN)/Mcwi consomic rat strain set to identify chromosomes carrying genes responsible for taste preferences. We screened the parental Fawn Hooded Hypertensive (FHH) and Brown Norway (BN) strains and 22 FHH-Chr n(BN) consomic strains, with 96-h 2-bottle tests, involving a choice between water and each of the following 16 solutions: 10 mM NaCl, 237 mM NaCl, 32 mM CaCl(2), 1 mM saccharin, 100 mM NH(4)Cl, 32 mM sucrose, 100 mM KCl, 4% ethanol, 1 mM HCl, 10 mM monosodium glutamate, 1 mM citric acid, 32 microM quinine hydrochloride, 1% corn oil, 32 microM denatonium, 1% Polycose, and 1 microM capsaicin. Depending on the taste solution involved, between 1 and 16 chromosomes were implicated in the response. Few of these chromosomes carried genes believed to mediate taste transduction in the mouse, and many chromosomes with no candidate taste genes were revealed. The genetic architecture of taste preferences is considerably more complex than has heretofore been acknowledged.

M1725 Food Intake and Interdigestive Gastrointestinal Motility in Ghrelin Receptor Mutant Rats

Background Ghrelin is the endogenous ligand for the growth hormone secretagogue receptor (GHSR). Ghrelin regulates feeding activity and interdigestive contractions of the stomach in rodents. To investigate the role of endogenous ghrelin in the digestive system, we have developed GHSR-mutant rats, named FHH-Ghsrm1Mcwi, using the Fawn-Hooded Hypertensive (FHH) parental strain.

Perinatal Micronutrient Supplements Ameliorate Hypertension and Proteinuria in Adult Fawn-Hooded Hypertensive Rats

In fawn-hooded hypertensive (FHH) rats, a model of hypertension, impaired preglomerular resistance, hyperfiltration, and progressive renal injury, we recently observed that supporting perinatal nitric oxide (NO) availability with the NO donor molsidomine persistently reduced blood pressure (BP) and ameliorated renal injury in male and female offspring. However, beneficial effects of perinatal molsidomine treatment were more pronounced in female than in male FHH rats. To evaluate whether such protective effects could also be achieved with micronutrients, and whether the gender-dependent differences could be confirmed, we tested perinatal exposure to the micronutrients L-arginine, taurine, vitamin C, and vitamin E (ATCE) in FHH rats. Perinatal micronutrients increased urinary NO metabolite, sodium and potassium excretion only at 4 weeks of age, i.e., at the end of treatment. From 12 weeks onwards, control males had a significantly higher systolic BP (SBP) than females (P < 0.01); however after perinatal micronutrients, this difference was no longer present, indicating a pronounced antihypertensive effect of perinatal micronutrients in males (interaction P < 0.001). Development of proteinuria was attenuated by perinatal micronutrients in males and females. However, only females showed reduced glomerular filtration rate, filtration fraction, and glomerulosclerosis (GS) after perinatal micronutrients. In sum, perinatal micronutrients that enhance NO availability ameliorated development of hypertension and proteinuria in FHH rats. Antihypertensive effects were more pronounced in male FHH offspring, whereas renal protective effects were more pronounced in female FHH offspring. Mechanisms underlying gender-specific consequences of perinatal micronutrients require further study.

Brain stem heme oxygenase 1 (HO‐1) mRNA expression in inbred rat strains after severe hemorrhage

Previously Klemcke et al. showed 8‐fold difference in survival time among inbred rat strains after severe hemorrhage (Shock 29:748, 2008). For Brown Norway (BN/Mcwi) rats we also found a 2.7‐fold increase in cardiac HO‐1 mRNA expression in catheterized plus hemorrhaged rats (Bled) compared to unmanipulated controls (CN; FASEB J. 23:801.2, 2009). To further examine HO‐1 as a possible intermediary of cellular responses to hemorrhage, in the same study we measured HO‐1 mRNA expression in brain stem of DA, Fawn Hooded Hypertensive (FHH), and BN/Mcwi strains. Using real time PCR, the relative quantity (RQ) of HO‐1 mRNA was measured with multiple housekeeping genes (Genome Biology 8:R19, 2007). Across all treatments (CN, catheterized only, and Bled) RQs were greater (P&lt;0.05) in BN/Mcwi (0.47 ± 0.02; mean ± SEM) and FHH (0.48 ± 0.02) than in DA rats (0.41 ± 0.02). When considering all strains, HO‐1 mRNA RQ increased 12% (P&lt;.05) in Bled rats compared with CN. Within strains and treatments, BN/Mcwi CN rats had greater (P&lt;.05) RQs (0.46 ± 0.01) than did DA control rats (0.38 ± 0.03). The data imply that rat brain stem has minor strain‐dependent differences in HO‐1 mRNA expression, and that basal expression is modestly increased after the combined stressors of catheterization and hemorrhage.

Survival time after hemorrhage (STaH) in inbred rats with known blood volumes

Eight‐fold differences in STaH were detected among 15 inbred rat strains (Klemcke et al., Shock 29:748, 2008) suggesting genetic effects on STaH. In that study, blood volumes (BV) for all strains were assumed to be 5.83 % of body weight and 55% of that BV was removed. We also showed that differences in STaH might reflect strain‐dependent differences in BV (Klemcke et al., FASEB J 23: 801.1, 2009). To address this hypothesis, each rat of 5 inbred rat strains was hemorrhaged based on its own BV measured using Evans Blue dye 24 hr prior to hemorrhage and its STaH determination. BV varied (P &lt;0.01) among Brown Norway (BN/Mcwi; n = 14; 7.43 ± .10 ml/100 g body weight, mean ± SEM), Salt Sensitive (S; n = 10; 7.08 ± .15), Fawn Hooded Hypertensive (FHH; n=10; 6.74 ± .08), Lewis (LEW; n=10; 6.74 ± .08), and DA (n=10; 6.74 ± .08) rat strains. With equal hemorrhages (47.1 ± .05 % of measured BV), STaH did not differ among rat strains (155 ± 12 min; P = 0.95). When considering both studies it is apparent that: 1) Strain‐related differences in BV contributed to differences in STaH in our 1st study; 2) In FHH rats 1.3% more of total BV was removed in the current study, yet they survived 1.5 hr longer; and 3) In LEW rats identical BV were removed in both studies, yet currently LEW rats survived 1 hr longer. Such observations suggest that Evans Blue dye and/or blood sampling for BV determinations might be preconditioning stimuli that improve STaH in some rat strains.

Inter‐ and intra‐strain variability for survival time after hemorrhage in inbred rats

In an effort to identify genes influencing survival time after hemorrhage (STaH) we earlier reported 8‐fold differences in STaH among 15 inbred rat strains, indicating a genetic basis for STaH (Klemcke et al., Shock 29:748, 2008). Subsequently, we identified that the inbred rat strains differed in blood volume (BV) which could account for differences in STaH. Thus, to re‐address the question of genetic influences on STaH, 5 inbred rat strains [Brown Norway (BN/Mcwi, n=9), Dark Agouti (DA, n=8), Fawn Hooded Hypertensive (FHH, n=10), Lewis (Lew, n=9) and Salt Sensitive (SS, n=9)] were bled using strain specific BVs. For each rat, 47% of its BV was removed and STaH was measured. Threefold differences for STaH among the strains (p&lt;0.0001) were observed (Table). Rats of an inbred strain are genetically very similar with a small degree of genetic variability. Thus, it was of interest to observe considerable intra‐strain variation for STaH (Table). Strain Mean STaH ± SEM (min) Range (min) Coefficient of Variation (%) BN/Mcwi 52 ± 5 35 – 79 28 DA 190 ± 29 42 – 240 43 FHH 113 ± 24 31 – 240 66 LEW 95 ± 19 62 – 240 60 SS 114 ± 17 70 – 235 44 Environmental conditions were highly controlled in this study, thus: 1) observed inter‐strain variability confirms the presence of a genetic component to STaH; and 2) intra‐strain variability may be explained by alternatives such as epigenetic mechanisms. (Funding provided by USAMRMC).

Differences between three inbred rat strains in number of K+ channel-immunoreactive neurons in the medullary raphé nucleus

Ventilatory sensitivity to hypercapnia is greater in Dahl salt-sensitive (SS) rats than in Fawn Hooded hypertensive (FHH) and Brown Norway (BN) inbred rats. Since pH-sensitive potassium ion (K(+)) channels are postulated to contribute to the sensing and signaling of changes in CO(2)-H(+) in chemosensitive neurons, we tested the hypothesis that there are more pH-sensitive K(+) channel-immunoreactive (ir) neurons within the medullary raphé nuclei of the highly chemosensitive SS rats than in the other two strains. Medullary tissues from male and female BN, FHH, and SS rats were stained with cresyl violet or with antibodies targeting TASK-1, K(v)1.4, and Kir2.3 channels. K(+) channel-ir neurons were quantified and compared with the total neurons in the region. The total number of neurons in the medullary raphé 1) was greater in male FHH than the other male rats, 2) did not differ among the female rats, and 3) did not differ between sexes. The average number of K(+) channel-ir neurons per section was 30-60 neurons higher in the male SS than in the other rat strains. In contrast, for the females, the number of K(+) channel-ir neurons was greatest in the BN. We also found significant differences in the number of K(+) channel-ir neurons between sexes in SS (males > females) and BN (females > males) rats, but not the FHH strain. Our findings support the hypothesis for males but not for females, suggesting that both genetic background and sex are determinants of K(+) channel immunoreactivity of medullary raphé neurons, and that the expression of pH-sensitive K(+) channels in the medullary raphé does not correlate with the ventilatory sensitivity to hypercapnia.

Introgression of Brown Norway Chromosome 1 onto the Fawn Hooded Hypertensive Background Rescues Long-Term Fear Memory Deficits

The isolation of genes influencing long-term memory is critical for an understanding of learning at the molecular level. Recently, chromosomal substitution rat strains, known as consomics, have been developed. Here we report the results of the first study on aversive learning and memory with these consomic rats. We compared the Fawn Hooded Hypertensive (FHH) and Brown Norway (BN) parent strains with a Brown Norway chromosome 1 substitution on the FHH background (FHH-1(BN)). Results indicated that while all strains had normal short-term memory, the FHH animals were impaired relative to BN in tests of long-term memory for a discrete auditory cue. This deficit was rescued by the introgression of the BN1 chromosome onto the FHH background. Furthermore, the FHH-1(BN) consomic showed an enhancement in long-term contextual fear memory relative to the FHH strain. These changes were not due to differences in pain sensitivity as both strains performed equally on two different pain tests. These results provide preliminary support that consomic rat strains can be a useful tool in identifying genes related to long-term fear memory formation.