Tissue Catecholamine Levels Research Articles

240-LB: Unrestrained Sympathetic Signaling Is a Key Driver of Obesity-Induced Insulin Resistance

Obesity is the major driver of type 2 diabetes. The mechanisms that account for overnutrition induced insulin resistance are yet to be delineated as impaired cellular insulin signaling may or may not account for the impaired insulin action. We find that overnutrition rapidly impairs insulin action and increase plasma norepinephrine, suggesting heightened activation of the sympathetic nervous system (SNS), possibly due to brain insulin resistance as earlier studies from our group suggested. Here, we hypothesize that unrestrained SNS activity (SNA) is a key driver of obesity induced insulin resistance. To test this hypothesis, we examined a mouse model of inducible and peripherally restricted tyrosine hydroxylase (th) gene deletion (THΔper) that have profoundly lower catecholamine levels in peripheral tissues is protected from high fat diet (HFD) induced insulin resistance. Despite similar food intake, obesity and cellular insulin signaling in liver and adipose tissue, THΔper mice were protected from both short-term and long-term HFD feeding-induced glucose intolerance, increases in plasma catecholamines and hyperglucagonemia. Hyperinsulinemic euglycemic clamp studies revealed that overnutrition induced hepatic insulin resistance was markedly ameliorated in the THΔper mice, even though cellular insulin signaling in liver and adipose tissue was comparable. Moreover, THΔper mice were protected from HFD-induced adipose tissue dysfunction characterized by reduced lipogenic capacity, unrestrained lipolysis and increased low-grade inflammation as well as hepatic steatosis, possibly due to decreased lipolytic flux and hepatic de novo lipogenesis. In addition, fibrosis genes were markedly reduced in the liver of the THΔper mice, suggesting that reducing SNA can prevent metabolic dysfunction-associated fatty liver disease. These results demonstrate that unrestrained SNA is a pivotal driver of insulin resistance, hyperglucagonemia and metabolic dysfunction in obesity. Disclosure K. Sakamoto: None. G. Maurizi: None. B. Chen: None. A. Shawkat: None. L. Patlolla: None. A. Tahiri: None. A. Butera: None. C. Buettner: None.

HIV-1 Viral Protein R Couples Metabolic Inflexibility With White Adipose Tissue Thermogenesis.

Persons living with HIV (PLWH) manifest chronic disorders of brown and white adipose tissues that lead to diabetes and metabolic syndrome. The mechanisms that link viral factors to defective adipose tissue function and abnormal energy balance in PLWH remain incompletely understood. Here, we explored how the HIV accessory protein viral protein R (Vpr) contributes to adaptive thermogenesis in two mouse models and human adipose tissues. Uncoupling protein 1 (UCP1) gene expression was strongly increased in subcutaneous white adipose tissue (WAT) biopsy specimens from PLWH and in subcutaneous WAT of the Vpr mice, with nearly equivalent mRNA copy number. Histology and functional studies confirmed beige transformation in subcutaneous but not visceral WAT in the Vpr mice. Measurements of energy balance indicated Vpr mice displayed metabolic inflexibility and could not shift efficiently from carbohydrate to fat metabolism during day-night cycles. Furthermore, Vpr mice showed a marked inability to defend body temperature when exposed to 4°C. Importantly, Vpr couples higher tissue catecholamine levels with UCP1 expression independent of β-adrenergic receptors. Our data reveal surprising deficits of adaptive thermogenesis that drive metabolic inefficiency in HIV-1 Vpr mouse models, providing an expanded role for viral factors in the pathogenesis of metabolic disorders in PLWH.

Adrenergic Signaling in Circadian Control of Immunity.

Circadian rhythms govern a multitude of physiologic processes, both on a cell-intrinsic level and systemically, through the coordinated function of multi-organ biosystems. One such system—the adrenergic system—relies on the catecholamine neurotransmitters, adrenaline and noradrenaline, to carry out a range of biological functions. Production of these catecholamines is under dual regulation by both neural components of the sympathetic nervous system and hormonal mechanisms involving the hypothalamus-pituitary-adrenal axis. Importantly, both neural and hormonal arms receive input from the body's central clock, giving rise to the observed rhythmic variations in catecholamine levels in blood and peripheral tissues. Oscillations in catecholamine signals have the potential to influence various cellular targets expressing adrenergic receptors, including cells of the immune system. This review will focus on ways in which the body's central master clock regulates the adrenergic system to generate circadian rhythms in adrenaline and noradrenaline, and will summarize the existing literature linking circadian control of the adrenergic system to immunologic outcomes. A better understanding of the complex, multi-system pathways involved in the control of adrenergic signals may provide immunologists with new insight into mechanisms of immune regulation and precipitate the discovery of new therapeutics.

Intravascular imaging, histopathological analysis, and catecholamine quantification following catheter-based renal denervation in a swine model: the impact of prebifurcation energy delivery.

The purpose of this study was to evaluate the impact of prebifurcation renal denervation in a swine model and assess its safety through optical coherence tomography (OCT). Prebifurcation renal denervation with a multi-electrode catheter was performed in one renal artery of 12 healthy pigs, with the contralateral artery and kidney being used as controls. Angiograms and OCT pullbacks were obtained peri-procedurally and 1 month post procedure. Renal tissue catecholamines were quantified, and the arterial wall and peri-adventitial tissue were analyzed histologically. Intraluminal changes (endothelial swelling, spasm, and thrombus formation) were observed acutely by OCT in most of the treated arteries and were no longer visible at follow-up. Histology revealed a statistically significant accumulation of collagen (fibrosis) and a near absence of tyrosine hydroxylase labeling in the denervated artery, suggesting a clear reduction in nervous terminals. Renal tissue catecholamine levels were similar between both sides, probably due to the low number of ablation points and the renorenal reflex. The present study demonstrates that renal denervation is associated with acute intimal disruptions, areas of fibrosis, and a reduction in nervous terminals. The lack of difference in renal tissue catecholamine levels is indicative of the need to perform the highest and safest number of ablation points in both renal arteries. These findings are important because they demonstrate the histological consequences of radiofrequency energy application and its medium-term safety.

Abstract 201: Beta-Adrenergic Stimulation Promotes Early Electrical Failure During Simulated VF-Induced Cardiac Arrest And Delays Electrical Recovery Upon Reperfusion

During cardiac arrest adrenergic stimulation is enhanced due to both endogenous increase in myocardial tissue catecholamine levels and exogenous epinephrine administration during resuscitation. Whereas alpha-adrenergic stimulation may be beneficial for hemodynamic recovery, there is growing evidence that beta-adrenergic stimulation is detrimental. Clinically, there is controversy as to whether epinephrine administration improves overall survival in cardiac arrest. Here we investigated the effects of beta-adrenergic stimulation on electrical activity during simulated ventricular fibrillation (VF) [[Unable to Display Character: –]] induced cardiac arrest and subsequent reperfusion. We performed optical mapping of the voltage-sensitive dye RH237 in the anterior right and left ventricles (RV and LV) of Langendorff-perfused rabbit hearts subjected to normothermic global no-flow ischemia and rapid pacing (cycle length 200 ms) in the presence or in the absence of isoproterenol (ISO, 30 nM). 2,3-butanedione monoxime (20 mM) was used to reduce motion artifact. Excitable area was measured in optical maps based on the criterion of the minimum time-derivative of the upstroke of the optical action potential. ISO markedly accelerated electrical depression in both LV and RV (more in LV) compared to control hearts (see Figure, * indicate comparisons with significant difference between groups at p<0.05). In addition, ISO delayed recovery of electrical activity upon reperfusion (62±14% recovery in ISO vs.98±2% recovery in control at 5 min of reperfusion, p<0.01). Furthermore, ISO tended to increase the incidence of post-reperfusion arrhythmias compared to control (83% vs. 25%, respectively; p=NS). We conclude that beta-adrenergic stimulation aggravates electrical dysfunction under conditions typically present during cardiac arrest/resuscitation, which might contribute to the overall detrimental outcomes of natural or induced catecholamine increase in this setting.

Influence of selected anti-inflammatory drugs on catecholamine levels in serum and tissues of rats with cecal ligation and puncture-induced sepsis

Influence of selected anti-inflammatory drugs on catecholamine levels in serum and tissues of rats with cecal ligation and puncture-induced sepsis

Indirect Evaluation of Microbial Spoiling Activity in Grape Marcs by Near-Infrared Spectroscopy

Norepinephrine, a natural transmitter, is stored in vesicles of sympathetic nerve endings. Small amounts of this amine are released continuously into the circulation to maintain tonic activity; increasing amounts are released in response to sympathetic nerve stimulation. Cardiac catecholamine concentrations remained unaltered even in the face of vigorous sympathetic activity produced by 1) prolonged sympathetic nerve stimulation, 2) exposure to cold for 6 hr and 3) administration of histamine or β-tetrahydronaphthylamine. Such maintenance of endogenous amine levels was not possible when synthesis of norepinephrine was inhibited by the tyrosine hydroxylase inhibitor, α-methyltyrosine. In this case tissue catecholamine levels were reduced. This reduction, however, was antagonized by pretreatment of animals with ganglionic blocking agents, adrenergic neuron blocking agents or monoamine oxidase inhibitors or by destruction of the brain and spinal cord. The usual elevation in catecholamine levels after inhibition of monoamine oxidase or ganglionic blockade was not observed when synthesis was inhibited by α-methyltyrosine. The common factor in all these experiments is the inhibition of spontaneous release due to tonic impulses in sympathetic nerve fibers. This suggests that once synthesis is inhibited, tonic release of catecholamine is sufficient to cause a gradual depletion of the amine. This depletion after α-methyltyrosine was increased when sympathetic nerve activity was increased by various procedures. Since α-methyltyrosine did not affect the accumulation of H³-norepinephrine in the rat heart, these findings suggest that catecholamine synthesis is indeed increased in response to increased sympathetic nerve activity which helps to maintain normal levels of tissue catscholamine. Thus the present study shows that maintenance of endogenous amine levels is based largely on adjustment of local norepinephrine synthesis which is presumably regulated by activity in the sympathetic nerves.

Neuroendocrine and metabolic responses of Pacific whiteleg shrimp Litopenaeus vannamei exposed to acute handling stress

The neuroendocrine mechanisms mediating stress in crustaceans are different and less understood than those of vertebrates, although indirect evidence suggests the participation of catecholamines (CA). However, few studies have analyzed their levels during stress response of crustaceans. We examined hemolymph and tissue levels of catecholamines and other biochemical indicators, in response to handling stress in whiteleg shrimp Litopenaeus vannamei. Shrimp were stressed by transfer, chasing, and confinement and the responses were analyzed at several intervals (10–240 min). Lactate levels in hemolymph increased from 10 to 30 min, glucose increased at 60 min, and both returned to baseline levels by 240 min. An increase in lactate levels before hyperglycemia suggests a possible activation of gluconeogenesis as a main clearance pathway for lactate. Epinephrine increased in hepatopancreas from 10 to 20 min, which indicates it could mediate lactate uptake, glucogenogenesis, and lipid catabolism in this organ. Norepinephrine levels in the eyestalk decreased by 92% between 20 and 30 min and a concomitant 10-fold increase in levels of dopamine was observed. This response suggested that the putative norepinephrine release in the X-organ sinus gland complex could mediate lactate effects in this organ (e.g. lactate positive feedback of crustacean hyperglycemic hormone release).

Male Sexual Behavior and Brain Catecholamine Levels in Middle-Aged Rats

During aging, increased qualitative variations in copulatory behavior are observed in male rats. At the age of 18-19 months, only a small proportion of male rats (16%) still display the complete mating behavior, including mounts, intromissions, and ejaculations, but the rest of these middle-aged animals (84%) fail to exhibit one, two or all of the three behavioral components. With distinct behavioral phenotypes, the middle-aged male rats provide us a useful animal model to investigate the neuroendocrine mechanisms responsible for the age-related reduction in sexual behavior. We have previously elucidated the correlation between the loss of specific copulatory behavioral components and tissue levels of catecholamines in the medial preoptic area (MPOA), nucleus accumbens (NAc) and the bed nucleus of stria terminalis (BNST) of middle-aged male rats. Thus, our findings not only demonstrate that levels of dopamine and norepinephrine in the MPOA, NAc and BNST are critical for eliciting copulatory behavior, but also suggest that these two neurotransmitters play distinct roles in different brain regions to control specific behavioral components in male rats.

Cardiac Norepinephrine Contents are Influenced by Natriuretic Peptide Receptors

The purpose of the present study was to define the effect of natriuretic peptide receptor (NPR) alterations on tissue catecholamine levels. Transgenic mice lacking functional natriuretic peptide A receptors (NPR-A) were obtained from Dr. D. Garbers (UT Southwestern) and NPR-C deficient mice were purchased from Jackson Research Laboratories. Mice were anesthetized with pentobarbital sodium at 25 to 35 days of age and tissues were removed. Catecholamines were extracted and analyzed by high performance liquid chromatography with electrochemical detection. Cardiac norepinephrine contents were suppressed with decreasing functional NPR-A levels (1.65 ± 0.24 ng/mg in homozygotes and 2.81 ± 0.63 ng/mg in wild type) although these differences did not reach statistical significance (p = 0.15). The hearts from homozygote mice were hypertrophied at this age (8.0 ± 0.4 mg/g vs 6.5 ± 0.2 mg/g in homozygote vs wild-type hearts) and this difference was significant (p = 0.003). Alterations in NPR-C levels produced the opposite effect on cardiac catecholamine concentrations. Ablation of functional NPR-C produced elevated cardiac catecholamine concentrations (6.1 ± 1.5 ng/mg) compared to wild-type mice (2.97 ± 0.4 ng/mg) and these differences were statistically significant (p = 0.03). There was no influence of NPR-C alterations on cardiac size. These data indicate that sympathetic innervation is influenced by the natriuretic peptide system with the presence of NPR-A being associated with greater cardiac catecholamine content and the presence of NPR-C tending to suppress cardiac catecholamine content. (Study supported by a grant-in-aid from the Minnesota Medical Foundation).

Vitamin C Is an Important Cofactor for Both Adrenal Cortex and Adrenal Medulla

The adrenal gland is among the organs with the highest concentration of vitamin C in the body. Interestingly, both the adrenal cortex and the medulla accumulate such high levels of ascorbate. Ascorbic acid is a cofactor required both in catecholamine biosynthesis and in adrenal steroidogenesis. Here we provide an overview on the role of vitamin C in the adrenal cortex and medulla derived from in vitro and in vivo studies. In addition, recent insights gained from an animal model with a deletion in the gene for the ascorbic acid transporter will be summarized. Mutant mice lacking the plasma membrane ascorbic acid transporter (SVCT2) have severely reduced tissue levels of ascorbic acid and die soon after birth. There is a significant decrease of tissue catecholamine levels in the adrenals. On the ultrastructural level, adrenal chromaffin cells in SVCT2 null mice show depletion of catecholamine storage vesicles, signs of apoptosis, and increased glycogen storage. Decreased plasma levels of corticosterone and altered morphology of mitochondrial membranes indicate additional effects of the deficiency on adrenal cortical function. The data derived from these animal models and various cell culture studies confirm a crucial role for vitamin C for both the adrenal cortex as well as the adrenal medulla further underlining the interdependence of the two endocrine systems united in one gland.

Catecholamine levels in rat adrenals increase post-mortem

Catecholamine (CA) levels in rat adrenals increase significantly over the first day post-mortem, but then decrease. This suggests that adrenal CA synthesis is active after death and stress the possibility that tissue levels of CAs may increase post-mortem. This has to be considered when evaluating post-mortem tissue CA levels.

Diabetes-induced biochemical changes in central and peripheral catecholaminergic systems.

A great variety of alterations have been described in the nervous system of diabetic animals. They are named as diabetic neuropathy and affect the brain, spinal cord and peripheral nerves. In diabetic animals, plasma and tissue catecholamine levels have been reported to be increased, decreased or unchanged, and these disparities have been explained by differences in the tissues selected, severity or duration of diabetes. Dopamine, norepinephrine and epinephrine from different tissues were extracted by absorption onto alumina, and measured by high performance liquid chromatography with electrochemical detection. We found that diabetes alters catecholaminergic systems in a highly specific manner. The dopamine content is reduced in the dopaminergic nigrostriatal system only. Norepinephrine is differently altered in several areas of the sympathetic nervous system. It is increased in cardiac ventricles, and decreased in stellate ganglia and the blood serum. However, it is not altered in the central nervous system. Finally, epinephrine is only altered in the adrenal gland where it is increased, and in the serum where it is reduced. Our results suggest that diabetes reduces the activity of the nigrostriatal dopaminergic system. Changes found at the sympathoadrenal level could be explained by reduced norepinephrine and epinephrine synthesis, with increased storage due to a reduced release from synaptic vesicles.

Chemoreceptor activity is normal in mice lacking the NK1 receptor.

Substance P has been proposed to be an important neurotransmitter in the carotid body with the neurokinin 1 (NK1) receptor, mediating excitation between the glomus cells and afferent nerve endings. In order to better understand the role of substance P, this study examined chemoreceptor afferent activity, in vitro, and tissue catecholamine levels and release in adult, wild-type mice and mice lacking the gene for the NK1 receptor (NK1-KO). Groups did not differ significantly in body weight, carotid body dopamine content or carotid body norepinephrine content. In wild-type mice, single unit activity increased from 0.59 +/- 0.14 Hz to 19.78 +/- 2.27 Hz during superfusion with strong hypoxia (PO2 approximately 25 Torr). Chemoreceptor activity in NK1-KO mice, increased from 0.71 +/- 0.23 to 21.50 +/- 3.62 Hz, and neither baseline or peak frequencies were significantly different from the wild-type group. Less severe hypoxia (PO2 approximately 45 torr), evoked peak activities of 12.50 +/- 1.88 and 10.64 +/- 3.72 Hz in wild-type and NK1-KO mice, which were also not significantly different. In response to severe hypoxia, free-tissue catecholamine increased to 4.92 +/- 0.85 microm in wild-type mice and 4.26 +/- 0.63 microm in NK1-KO mice, which were also not significantly different. It may therefore be concluded that loss of NK1 receptors has little effect on chemoreceptor function in the mouse, and thus they play, at best, a minor role in the hypoxic chemoreception process.

Cardiovascular effects of nepicastat (RS-25560-197), a novel dopamine beta-hydroxylase inhibitor.

Nepicastat (RS-25560-197) is a novel, selective, and potent inhibitor of dopamine beta-hydroxylase, which modulates catecholamine levels (reduces norepinephrine and elevates dopamine) in cardiovascular tissues. This study was designed to evaluate the cardiovascular effects of nepicastat. Acute oral administration of nepicastat (0.3, 1, 3, 10, and 30 mg/kg) produced attenuation of the pressor and positive chronotropic responses to preganglionic sympathetic nerve stimulation (about twofold to sixfold shift in the frequency-response curve) in pithed spontaneously hypertensive rats (SHRs). In inactin-anesthetized SHRs, the antihypertensive effects of nepicastat (3 mg/kg, i.v.) were accompanied by a significant decrease in renal vascular resistance (38%), a tendency toward an increase in renal blood flow (22%), and no adverse effects on urine output and Na/K excretion. In conscious, unrestrained, telemetry-implanted SHRs, nepicastat (30 and 100 mg/kg/day for 30 days) produced dose-dependent decreases in mean arterial blood pressure (peak decrease of 20 and 42 mm Hg, respectively) without evoking reflex tachycardia. Long-term, concurrent administration of nepicastat (30 mg/kg/day, p.o.) and a subthreshold dose of enalapril (1 mg/kg/day, p.o.) produced greater antihypertensive effects than those produced by nepicastat alone. In normal dogs, nepicastat (5.0 mg/kg, p.o., b.i.d., for 4.5 days) blunted the positive chronotropic and pressor response to tyramine. These findings suggest that nepicastat functionally modulates sympathetic drive to cardiovascular tissues and may be of value in the treatment of cardiovascular disorders associated with overactivation of the sympathetic nervous system such as hypertension and congestive heart failure.

Extrinsic intestinal reinnervation after canine small bowel autotransplantation

Background: The process of extrinsic reinnervation after small bowel transplantation is poorly understood. Methods: Jejunal and ileal specimens, obtained from the dogs that underwent intestinal autotransplantation by an end-to-end (E-E) or end-to-side arterial reconstruction, were analyzed at 1 (n = 7), 3 (n = 6), 6 (n = 6), 12 (n = 6), or 24 (n = 2) months and compared with control specimens (n = 7). Tissue catecholamine levels and indirect immunohistochemistry results for extrinsic neuropeptides, calcitonin gene–related peptide, neuropeptide Y, substance P, and tyrosine hydroxylase (TH) were examined. Results: Catecholamine levels in the grafts were undetectable until 6 months but increased significantly after 12 months, particularly in the E-E group. Immunohistochemistry results showed no significant indication of extrinsic reinnervation until 12 months, when TH fibers were observed in five of six dogs. The E-E group revealed some TH fibers extending across the arterial anastomosis toward the graft mesentery. Examination of the intestinal anastomosis at 12 months showed abundant peptidergic and TH extrinsic fibers in the host side, whereas there were few or none on the graft side. Conclusions: These results suggest that extrinsic reinnervation of the graft intestinal wall does occur but requires a prolonged period, and the major route of extrinsic reinnervation is along the arterial axis of the intestinal graft, not beyond the enteric anastomosis. (Surgery 1998;123:25-35.)

Membrane phosphorylation protects the cardiac sarcoplasmic reticulum Ca(2+)-ATPase against chlorinated oxidants in vitro.

The calcium (Ca) pump of cardiac sarcoplasmic reticulum (SR) membranes is vulnerable to oxidation and hence likely to be damaged by chlorinated compounds, specifically hypochlorite (NaOCl) and monochloramine (NH2Cl), the most potent oxidants produced upon neutrophil activation. This could occur during prolonged ischemia or myocardial infarction when tissue levels of catecholamines are high. Phospholamban (PLN), the phosphorylatable regulator of the Ca pump, plays a central role in the effects of beta-adrenergic agonists on the heart. The purpose of this study was to investigate a possible role of PLN in determining the pump's sensitivity to NaOCl and NH2Cl. Ca-uptake and Ca(2+)-ATPase activities in purified phosphorylated and control canine cardiac microsomes, incubated at increasing concentrations of NaOCl or NH2Cl, were related to the extent of PLN phosphorylation by protein kinase A, which was quantitated by PhosphorImager analysis. Our data indicate that microsomal phosphorylation protects the Ca pump fully against 10 microM NaOCl or NH2Cl, which inhibit Ca-uptake by 21-41% when assayed at 25 or 37 degrees C and saturating Ca2+ in unphosphorylated microsomes, and protects partially at higher oxidant concentrations. The protective effect of protein kinase A on Ca-uptake is proportional to the amount of phosphorylated PLN. No comparable protection against similar oxidative damage of the Ca pump is observed when light fast skeletal muscle microsomes, which lack PLN, are incubated under conditions favorable for phosphorylation nor when PLN's inhibition of the cardiac Ca pump is relieved by proteolytic cleavage of its cytoplasmic domain. Our findings contribute toward an understanding of possible endogenous protective mechanisms that may promote calcium homeostasis in myocardial cells in inflammatory states associated with neutrophil activation and may suggest an approach toward development of protective strategies against oxidative damage in the heart.

Blood pressure response to chronic episodic hypoxia: role of the sympathetic nervous system.

Previous studies in several strains of rats have demonstrated that 35 consecutive days of recurrent episodic hypoxia (7 h/day) cause an 8- to 13-mmHg persistent increase in diurnal systemic blood pressure (BP). Carotid chemoreceptors and the sympathetic nervous system have been shown to be necessary for development of this BP increase. The present study was undertaken to further define the role of renal artery sympathetic nerves and the adrenal medulla in this BP increase. Male Sprague-Dawley rats had either adrenal medullectomy, bilateral renal artery denervation, or sham surgery. Rats from each of these groups were subjected to episodic hypoxia for 35 days. Control groups received either compressed air or were left unhandled. Adrenal demedullation or renal artery denervation eliminated the chronic diurnal mean BP response (measured intra-arterially) to episodic hypoxia, whereas sham-operated controls continued to showed persistent elevation of systemic BP. Plasma and renal tissue catecholamine levels at the end of the experiment confirmed successful adrenal demedullation or renal denervation in the respective animals. The chronic episodic hypoxia-mediated increase in diurnal BP requires both intact renal artery nerves as well as an intact adrenal medulla.

Monoamines in the dorsomedial hypothalamus of rats following exposure to different tests of “anxiety”

1. 1. Adult male Sprague-Dawley rats were subjected to the fear-potentiated startle, elevated plus-maze and social interaction tests and the levels of norepinephrine, dopamine and serotonin in the dorsomedial hypothalamus were determined by high-performance liquid chromatography. 2. 2. Only rats subjected to the full fear potentiated startle test and not the other tests of anxiety or components (foot shocks or acoustic startle) of fear-potentiated startle showed significant increases in norepinephrine and dopamine levels after 24 hours. 3. 3. A time course experiment specific for the norepinephrine changes in the dorsomedial hypothalamus of fear-potentiated startle rats revealed a significant increase in tissue content as compared to controls at both the 12 and 24 hour post-test time points. 4. 4. Tyrosine hydroxylase activity in the dorsomedial hypothalamus of the fear-potentiated startle rats did not show a significant change from controls. 5. 5. An in vitro release study found a significant decrease in potassium-stimulated release of norepinephrine in the dorsomedial hypothalamus as compared to controls at 24 hours posttest. 6. 6. These results suggest that animals exposed to fear-potentiated startle and not other tests of “anxiety” have a change in tissue catecholamine levels and that the norepinephrine change may be the result of a decrease in release and not an increase in synthesis.

Overexpression of NGF within the Heart of Transgenic Mice Causes Hyperinnervation, Cardiac Enlargement, and Hyperplasia of Ectopic Cells

Nerve growth factor (NGF) supports the survival of developing sympathetic and a subpopulation of sensory neurons. In the adult it participates in maintenance of the neurotransmitter phenotype of responsive neurons. The amount of NGF synthesized by a given target tissue determines its final innervation density; those developing neurons that fail to receive sufficient NGF undergo apoptosis. In order to examine the ramifications of this principle in the context of a specific target organ, a transgenic mouse model was developed in which NGF expression was increased in developing and adult cardiac tissue by placing a NGF mini-gene under the transcriptional control of the cardiac-specific α-myosin heavy chain promoter. Transgenic mice developed cardiac enlargement secondary to both an increase in myocardial mass and the presence of an abundant ectopic cell population. Immunohistochemical analyses with the neural marker S-100 revealed staining of a subpopulation of ectopic cells, suggesting their derivation from the neural crest. Whereas immunostaining for the neuronal-specific protein neuron-specific enolase demonstrated labeling of another subpopulation of ectopic cells within the heart. Measurements of cardiac tissue catecholamine levels revealed a marked elevation in transgenic mice, consistent with sympathetic hyperinnervation. Analysis of mediastinal sympathetic ganglia revealed increases in both the size and the number of neurons. In this model, increased expression of NGF produced hyperinnervation of the heart, pathological cardiac growth, and the recruitment and/or expansion of an ectopic, neural crest-derived cell type.