New Aspects for the Treatment of Cardiac Diseases Based on the Diversity of Functional Controls on Cardiac Muscles: The Regulatory Mechanisms of Cardiac Innervation and Their Critical Roles in Cardiac Performance

Heterogeneous cardiac sympathetic innervation gradients promote arrhythmogenesis in murine dilated cardiomyopathy

Ventricular arrhythmias (VAs) in heart failure are enhanced by sympathoexcitation. However, radiotracer studies of catecholamine uptake in failing human hearts demonstrate a proclivity for VAs in patients with reduced cardiac sympathetic innervation. We hypothesized that this counterintuitive finding is explained by heterogeneous loss of sympathetic nerves in the failing heart. In a murine model of dilated cardiomyopathy (DCM), delayed PET imaging of sympathetic nerve density using the catecholamine analog [11C]meta-Hydroxyephedrine demonstrated global hypoinnervation in ventricular myocardium. Although reduced, sympathetic innervation in 2 distinct DCM models invariably exhibited transmural (epicardial to endocardial) gradients, with the endocardium being devoid of sympathetic nerve fibers versus controls. Further, the severity of transmural innervation gradients was correlated with VAs. Transmural innervation gradients were also identified in human left ventricular free wall samples from DCM versus controls. We investigated mechanisms underlying this relationship by in silico studies in 1D, 2D, and 3D models of failing and normal human hearts, finding that arrhythmogenesis increased as heterogeneity in sympathetic innervation worsened. Specifically, both DCM-induced myocyte electrical remodeling and spatially inhomogeneous innervation gradients synergistically worsened arrhythmogenesis. Thus, heterogeneous innervation gradients in DCM promoted arrhythmogenesis. Restoration of homogeneous sympathetic innervation in the failing heart may reduce VAs.

Efficacy of an Anti-Semaphorin 3A Neutralizing Antibody in a Male Experimental Retinal Vein Occlusion Mouse Model

Purpose

Semaphorin 3A (Sema3A) is a promising therapeutic target for macular edema in age-related macular degeneration, diabetic retinopathy, and retinal vein occlusion (RVO). Anti-vascular endothelial growth factors (anti-VEGFs) are the current standard of care for many retinal diseases. This study investigated the Sema3A neutralizing antibody BI-X and/or anti-VEGF therapy (aflibercept) in an RVO mouse model. Treatment efficacy was examined and grouped by timing subsequent to the RVO mouse model induction: efficacy against the onset of intraretinal edema 1 day postinduction and protective effects at 7 days postinduction.

Methods

We examined the changes in expression of Sema3A in the retina of an RVO mouse model. In addition, changes in expression of tumor necrosis factor (TNF)-α and semaphorin-related proteins (neuropilin-1 and plexin A1) in the retina upon treatment were analyzed by Western blotting. The effects of BI-X and/or aflibercept were evaluated using measures of retinal edema, blood flow, and thinning of the inner nuclear layer.

Results

Induction of vein occlusion in the RVO mouse model significantly increased Sema3A expression in the retina, particularly in the inner nuclear layer. BI-X was effective as a monotherapy and in combination with anti-VEGF therapy, demonstrating a beneficial effect on intraretinal edema and retinal blood flow. Moreover, in the RVO mouse model, BI-X monotherapy normalized the changes in expression of TNF-α and semaphorin-related proteins.

Conclusions

These findings support targeting Sema3A to treat intraretinal edema and retinal ischemia.

Activation of Neural Modeling-Related Genes in the Heart of Mice after Gamma Irradiation

OBJECTIVE

Radiation-induced heart disease (RIHD) is a common sequela of thoracic irradiation. At the same time, nerve remodeling is involved in the progression of heart disease. However, the activation of the nerve remodeling related genes in radiation-induced heart disease is still lacking.

METHODS

In this study, C57BL/J mice was anesthetized by intraperitoneal injection with pentobarbital sodium (2%, 40 mg/kg), and radiation was delivered using a cobalt-60 (60Co) teletherapy unit (Cirus). When the mice were anesthetized, none of them showed the signs of peritonitis, pain, or discomfort. The mice hearts were exposed to a γ-radiation field of 5 mm × 5 mm. The total dose of γ-radiation was 3 Gy/day for each animal for 5 consecutive days. The mice were executed by severed neck, and its limbs were weak. Quantitative Polymerase Chain Reaction (qPCR) and immunohistochemistry were used to explore the possible mechanism of arrhythmia in patients with RIHD.

RESULTS

Our results demonstrated that Growth-Associated Protein 43 (GAP43) was increased significantly after radioactive heart injury compared with the control group. Moreover, the protein expression of Tyrosine hydroxylase (TH) and Choline acetyl-transferase (CHAT) was significantly decreased compared with the control group and gradually increased with time rend. The nerve growth factor (NGF) was remarkably increased after radiation-induced heart injury compared with the control group. Immunohistochemistry results indicated that the nerve growth factors GAP43 and NGF were significantly increased after radiation-induced heart injury.

CONCLUSIONS

Chest radiotherapy could activate the neural modeling related genes in RIHD. This may provide a new treatment plan for the future treatment of heart problems caused by chest radiotherapy.

Pleiotropic activity of nerve growth factor in regulating cardiac functions and counteracting pathogenesis

Cardiac innervation density generally reflects the levels of nerve growth factor (NGF) produced by the heart—changes in NGF expression within the heart and vasculature contribute to neuronal remodelling (e.g. sympathetic hyperinnervation or denervation). Its synthesis and release are altered under different pathological conditions. Although NGF is well known for its survival effects on neurons, it is clear that these effects are more wide ranging. Recent studies reported both in vitro and in vivo evidence for beneficial actions of NGF on cardiomyocytes in normal and pathological hearts, including prosurvival and antiapoptotic effects. NGF also plays an important role in the crosstalk between the nervous and cardiovascular systems. It was the first neurotrophin to be implicated in postnatal angiogenesis and vasculogenesis by autocrine and paracrine mechanisms. In connection with these unique cardiovascular properties of NGF, we have provided comprehensive insight into its function and potential effect of NGF underlying heart sustainable/failure conditions. This review aims to summarize the recent data on the effects of NGF on various cardiovascular neuronal and non‐neuronal functions. Understanding these mechanisms with respect to the diversity of NGF functions may be crucial for developing novel therapeutic strategies, including NGF action mechanism‐guided therapies.

Mechanisms underlying the cardio-protection of total ginsenosides against myocardial ischemia in rats in vivo and in vitro: Possible involvement of L-type Ca2+ channels, contractility and Ca2+ homeostasis

Here we aimed to observe the effects of total ginsenosides (TG) against isoproterenol (ISO) induced myocardial ischemia (MI) and to explore its underlying mechanisms based on L-type Ca²⁺ current (I_Ca-L), intracellular Ca²⁺ ([Ca²⁺]_i) and contraction in isolated rat myocytes. Rat model of MI was induced by subcutaneously injection of ISO (85 mg/kg) for 2 consecutive days. J-point elevation, heart rate, serum levels of creatine kinase (CK) and lactated dehydrogenase (LDH), and heart morphology changes were observed. Influences of TG on I_Ca-L, [Ca²⁺]_i and contraction in isolated rat myocytes were observed by the patch-clamp technique and IonOptix detection system. TG significantly reduced J-point elevation, heart rate, serum levels of CK and LDH, and improved heart pathologic morphology. TG decreased I_Ca-L in concentration-dependent manner with a half-maximal inhibitory concentration (IC₅₀) of 31.65 μg/mL. TG (300 μg/mL) decreased I_Ca-L of normal and ischemic ventricular myocytes by 64.33 ± 1.28% and 61.29 ± 1.38% respectively. At 30 μg/mL, TG reduced Ca²⁺ transient by 21.67 ± 0.94% and cell shortening by 38.43 ± 6.49%. This study showed that TG displayed cardioprotective effects on ISO-induced MI rats and the underlying mechanisms may be related to inhibition of I_Ca-L, damping of [Ca²⁺]_i and decrease of contractility.

Semaphorins and their Signaling Mechanisms

Semaphorins are extracellular signaling proteins that are essential for the development and maintenance of many organs and tissues. The more than 20-member semaphorin protein family includes secreted, transmembrane and cell surface-attached proteins with diverse structures, each characterized by a single cysteine-rich extracellular sema domain, the defining feature of the family. Early studies revealed that semaphorins function as axon guidance molecules, but it is now understood that semaphorins are key regulators of morphology and motility in many different cell types including those that make up the nervous, cardiovascular, immune, endocrine, hepatic, renal, reproductive, respiratory and musculoskeletal systems, as well as in cancer cells. Semaphorin signaling occurs predominantly through Plexin receptors and results in changes to the cytoskeletal and adhesive machinery that regulate cellular morphology. While much remains to be learned about the mechanisms underlying the effects of semaphorins, exciting work has begun to reveal how semaphorin signaling is fine-tuned through different receptor complexes and other mechanisms to achieve specific outcomes in various cellular contexts and physiological systems. These and future studies will lead to a more complete understanding of semaphorin-mediated development and to a greater understanding of how these proteins function in human disease.

BDNF - A key player in cardiovascular system

Neurotrophins (NTs) were first identified as target-derived survival factors for neurons of the central and peripheral nervous system (PNS). They are known to control neural cell fate, development and function. Independently of their neuronal properties, NTs exert unique cardiovascular activity. The heart is innervated by sensory, sympathetic and parasympathetic neurons, which require NTs during early development and in the establishment of mature properties, contributing to the maintenance of cardiovascular homeostasis. The identification of molecular mechanisms regulated by NTs and involved in the crosstalk between cardiac sympathetic nerves, cardiomyocytes, cardiac fibroblasts, and vascular cells, has a fundamental importance in both normal heart function and disease. The article aims to review the recent data on the effects of Brain-Derived Neurotrophic Factor (BDNF) on various cardiovascular neuronal and non-neuronal functions such as the modulation of synaptic properties of autonomic neurons, axonal outgrowth and sprouting, formation of the vascular and neural networks, smooth muscle migration, and control of endothelial cell survival and cardiomyocytes. Understanding these mechanisms may be crucial for developing novel therapeutic strategies, including stem cell-based therapies.

Neprilysin inhibition in heart failure: mechanisms and substrates beyond modulating natriuretic peptides

The autonomic nervous system, the renin-angiotensin-aldosterone system, and the natriuretic peptide system represent critical regulatory pathways in heart failure and as such have been the major targets of pharmacological development. The introduction and approval of angiotensin receptor neprilysin inhibitors (ARNi) have broadened the available drug treatments of patients with chronic heart failure with reduced ejection fraction. Neprilysin catalyses the degradation of a number of vasodilator peptides, including the natriuretic peptides, bradykinin, substance P, and adrenomedullin, as well as vasoconstrictor peptides, including endothelin-1 and angiotensin I and II. We review the multiple, potentially competing, substrates for neprilysin inhibition, and the resultant composite clinical effects of ARNi therapy. A mechanistic understanding of this novel therapeutic class may provide important insights into the expected on-target and off-target effects when this agent is more widely prescribed.

Functional Diversity of Neurotrophin Actions on the Oculomotor System

Neurotrophins play a principal role in neuronal survival and differentiation during development, but also in the maintenance of appropriate adult neuronal circuits and phenotypes. In the oculomotor system, we have demonstrated that neurotrophins are key regulators of developing and adult neuronal properties, but with peculiarities depending on each neurotrophin. For instance, the administration of NGF (nerve growth factor), BDNF (brain-derived neurotrophic factor) or NT-3 (neurotrophin-3) protects neonatal extraocular motoneurons from cell death after axotomy, but only NGF and BDNF prevent the downregulation in ChAT (choline acetyltransferase). In the adult, in vivo recordings of axotomized extraocular motoneurons have demonstrated that the delivery of NGF, BDNF or NT-3 recovers different components of the firing discharge activity of these cells, with some particularities in the case of NGF. All neurotrophins have also synaptotrophic activity, although to different degrees. Accordingly, neurotrophins can restore the axotomy-induced alterations acting selectively on different properties of the motoneuron. In this review, we summarize these evidences and discuss them in the context of other motor systems.

Estrogen and female reproductive tract innervation: cellular and molecular mechanisms of autonomic neuroplasticity

The female reproductive tract undergoes remarkable functional and structural changes associated with cycling, conception and pregnancy, and it is likely advantageous to both individual and species to alter relationships between reproductive tissues and innervation. For several decades, it has been appreciated that the mammalian uterus undergoes massive sympathetic axon depletion in late pregnancy, possibly representing an adaptation to promote smooth muscle quiescence and sustained blood flow. Innervation to other structures such as cervix and vagina also undergo pregnancy-related changes in innervation that may facilitate parturition. These tissues provide highly tractable models for examining cellular and molecular mechanisms underlying peripheral nervous system plasticity. Studies show that estrogen elicits rapid degeneration of sympathetic terminal axons in myometrium, which regenerate under low-estrogen conditions. Degeneration is mediated by the target tissue: under estrogen's influence, the myometrium produces proteins repulsive to sympathetic axons including BDNF, neurotrimin, semaphorins, and pro-NGF, and extracellular matrix components are remodeled. Interestingly, nerve depletion does not involve diminished levels of classical sympathetic neurotrophins that promote axon growth. Estrogen also affects sympathetic neuron neurotrophin receptor expression in ways that appear to favor pro-degenerative effects of the target tissue. In contrast to the uterus, estrogen depletes vaginal autonomic and nociceptive axons, with the latter driven in part by estrogen-induced suppression of BMP4 synthesis. These findings illustrate that hormonally mediated physiological plasticity is a highly complex phenomenon involving multiple, predominantly repulsive target-derived factors acting in concert to achieve rapid and selective reductions in innervation.

Exogenous nerve growth factor promotes the repair of cardiac sympathetic heterogeneity and electrophysiological instability in diabetic rats

OBJECTIVES

Diabetic cardiac autonomic neuropathy can lead to an increased incidence of ventricular arrhythmias (VAs). However, few data are available regarding the pathogenesis and therapy of the VAs accompanying diabetic cardiac autonomic neuropathy. We aimed to explore whether or not exogenous nerve growth factor (NGF) can reduce the sympathetic heterogeneity and the incidence of VAs in diabetes mellitus (DM).

METHODS

Male Wistar rats were randomly divided into 3 groups: controls, rats with DM with saline infused into the left stellate ganglion (LSG), i.e. the DS group and rats with DM with NGF infused into the LSG, i.e. the DN group. After 28 weeks, all rats were subjected to electrophysiological experiments. Sympathetic innervations and NGF were studied by immunostaining, RT-PCR or Western blot analysis.

RESULTS

The incidence of inducible VAs was significantly higher in the DS group than in the control group, but was markedly decreased in the DN group. In the DS group, the tyrosine hydroxylase (TH) and NGF expression were significantly lower than in the other groups, and significant proximal-distal heterogeneities existed regarding the TH and NGF expression in the left ventricle, but were markedly repaired in the DN group.

CONCLUSIONS

NGF intervention in the LSG can reduce the heterogeneity of cardiac sympathetic innervations and the incidence of VAs in diabetic rats.

Pharmacological evidence that dopamine inhibits the cardioaccelerator sympathetic outflow via D2-like receptors in pithed rats

It has been suggested that N,N-di-n-propyl-dopamine (dopamine analogue) decreased heart rate in rats through stimulation of dopamine receptors. Nevertheless, the role of prejunctional dopamine D1/2-like receptors or even α2-adrenoceptors to mediate cardiac sympatho-inhibition induced by dopamine remains unclear. Hence, this study identified the pharmacological profile of the cardiac sympatho-inhibition to dopamine in pithed rats. Male Wistar rats were pithed and prepared to stimulate the cardiac sympathetic outflow or to receive i.v. bolus of exogenous noradrenaline. I.v. continuous infusions of dopamine (endogenous ligand) or quinpirole (D2-like agonist) dose-dependently inhibited the tachycardic responses to sympathetic stimulation, but not those to exogenous noradrenaline. In contrast, SKF-38393 (100 μg/kg∙min, D1-like agonist) failed to modify both of these responses. The sympatho-inhibition to dopamine (1.8 μg/kg∙min) or quinpirole (100 μg/kg∙min): i) remained unaltered after saline or the antagonists SCH-23390 (D1-like, 300 μg/kg) and rauwolscine (α2-adrenoceptors, 300 μg/kg); and ii) was significantly antagonized by raclopride (D2-like, 300 μg/kg). These antagonists, at the above doses, failed to modify the sympathetically-induced tachycardic responses. The above results suggest that the inhibition of the cardiac sympathetic outflow to dopamine and quinpirole is primarily mediated by prejunctional D2-like receptors but not D1-like receptors or α2-adrenoceptors.

Painless myocardial ischemia is associated with mortality in patients with chronic kidney disease

BACKGROUND

Painless myocardial ischemia (PMI) is associated with poor outcomes in the general population. We hypothesized that the presence of PMI is inversely related to the level of kidney function and is associated with impaired survival in chronic kidney disease (CKD).

METHODS

A total of 356 patients who underwent percutaneous coronary intervention were assessed for PMI, which was defined as the absence of chest pain in response to balloon dilation of the affected vessel. Cox proportional hazards analysis was used to calculate 10-year all-cause mortality.

RESULTS

There was an increase in PMI occurrence by strata of estimated glomerular filtration rate (eGFR), whereby PMI was present in only 20.6% of individuals with eGFR ≥ 90 ml/min/1.73 m(2), but was found in 50.0% of individuals with eGFR <30 ml/min/1.73 m(2) (p = 0.004 for trend). Classification of individuals as having either CKD or PMI showed significant differences in adjusted mortality between groups (p < 0.001 for trend), with individuals having both CKD and PMI demonstrating the highest 10-year mortality. Compared to individuals with neither CKD nor PMI, individuals with CKD and no PMI had a hazard ratio (HR) for mortality of 1.64 (95% CI: 1.03-2.63, p = 0.038), while individuals with both PMI and CKD had an HR of 2.08 (1.30-3.33, p = 0.002).

CONCLUSION

PMI is common in the CKD population, is inversely related to the level of eGFR, and confers a substantially increased risk in CKD. These findings may partially explain the high mortality traditionally attributed to cardiovascular disease in CKD patients.

Exogenous nerve growth factor supplementation elevates myocardial immunoreactivity and attenuates cardiac remodeling in pressure-overload rats

It is postulated that supplementation of exogenous nerve growth factor (NGF) might mediate improvement of the cardiac sympathetic nerve function in heart failure (HF). Local intramuscular injection of NGF near the cardiac sympathetic ganglia could influence the innervation pattern, norepinephrine transporter (NET) gene expression, and improve the cardiac remodeling in experimental HF animals. In this study, we injected NGF into the scalenus medius muscles of Sprague-Dawley rats with abdominal aortic constriction (AC). The nerve innervated pattern, left ventricular morphology, and function following injection in rats with AC were investigated respectively by immunohistochemistry and echocardiography. Levels of mRNA expression of NET, growth associated protein 43 (GAP 43), NGF and its receptors TrkA and p75(NTR), and brain natriuretic peptide (BNP) were measured by real-time polymerase chain reaction. The results showed that myocardial NGF mRNA levels were comparable in rats with AC. Short-term supplementation of exogenous NGF raised the myocardial NGF immunoreactivity, but did not cause hyperinnervation and NET mRNA upregulation in the AC rats. Furthermore, myocardial TrkA mRNA was found to be remarkably decreased and p75(NTR) mRNA was increased. Myocardial TrkA downregulation may play a beneficial effect for avoiding the hyperinnervation, and it is reasonable to postulate that p75(NTR) can function as an NGF receptor in the absence of TrkA. Interestingly, local NGF administration into the neck muscles near the ganglia could attenuate cardiac remodeling and downregulate BNP mRNA. These results suggest that exogenous NGF can reach the target tissue along the axons anterogradely, and improve the cardiac remodeling.

Nerve growth factor and inducible nitric oxide synthase expression in the mesencephalon and diencephalon, as well as visual- and auditory-related nervous tissues, in a macaque model of type 2 diabetes

The present study detected distribution and expression of nerve growth factor and inducible nitric oxide synthase in the mesencephalon and diencephalon, as well as visual- and auditory-related nervous tissues, in a macaque model of type 2 diabetes using immunohistochemistry. Results showed that nerve growth factor expression decreased, but inducible nitric oxide synthase expression increased, in the mesencephalon and diencephalon, as well as visual- and auditory- related nervous tissues. These results suggested that nerve growth factor and inducible nitric oxide synthase play an important role in regulating the development of diabetic visual- and auditory-related diseases.

Estrogen up-regulation of semaphorin 3F correlates with sympathetic denervation of the rat uterus

Current evidence indicates that rises in systemic levels of estrogen create in the uterus an inhibitory environment for sympathetic nerves. However, molecular insights of these changes are far from complete. We evaluated if semaphorin 3F mRNA, a sympathetic nerve repellent, was produced by the rat uterus and if its expression was modulated by estrogen. We also analyzed whether uterine nerves express the semaphorin 3F binding receptor, neuropilin-2. Uterine levels of semaphorin 3F mRNA were measured using real time reverse transcriptase-polymerase chain reaction in prepubertal rat controls and following chronic estrogen treatment. Localization of semaphorin 3F transcripts was determined by in situ hybridization and the expression of neuropilin-2 was assessed by immunohistochemistry. These studies showed that: (1) chronic estrogen treatment led to a 5-fold induction of semaphorin 3F mRNA in the immature uterus; (2) estrogen provoked a tissue-specific induction of semaphorin 3F which was particularly localized in the connective tissue that borders muscle bundles and surrounds intrauterine blood vessels; (3) two major cell-types were recognized in the areas where transcripts were concentrated, fibroblast-like cells and infiltrating eosinophil leukocytes; and (4) some delicate nerve terminal profiles present in the estrogenized uterus were immunoreactive for neuropilin-2. Temporal and spatial expression patterns of semaphorin 3F/neuropilin-2 are consistent with a possible role of this guidance cue in the remodeling of uterine sympathetic innervation by estrogen. Though correlative in its nature, these data support a model whereby semaphorin 3F, in combination with other inhibitory molecules, converts the estrogenized myometrium to an inhospitable environment for sympathetic nerves.

Cardiovascular risk evaluation and prevalence of silent myocardial ischemia in subjects with asymptomatic carotid artery disease

Introduction:

Silent ischemia is an asymptomatic form of myocardial ischemia, not associated with angina or anginal equivalent symptoms, which can be demonstrated by changes in ECG, left ventricular function, myocardial perfusion, and metabolism. The aim of this study was to evaluate the prevalence of silent myocardial ischemia in a group of patients with asymptomatic carotid stenosis.

Methods:

A total of 37 patients with asymptomatic carotid plaques, without chest pain or dyspnea, was investigated. These patients were studied for age, sex, hypertension, diabetes, dyslipidemia, smoking, and family history of cardiac disease, and underwent technetium-99 m sestamibi myocardial stress-rest scintigraphy and echo-color Doppler examination of carotid arteries.

Results:

A statistically significant relationship (P = 0.023) was shown between positive responders and negative responders to scintigraphy test when both were tested for degree of stenosis. This relationship is surprising in view of the small number of patients in our sample. Individuals who had a positive scintigraphy test had a mean stenosis degree of 35% ± 7% compared with a mean of 44% ± 13% for those with a negative test. Specificity of our detection was 81%, with positive and negative predictive values of 60% and 63%, respectively.

Conclusion:

The present study confirms that carotid atherosclerosis is associated with coronary atherosclerosis and highlights the importance of screening for ischemic heart disease in patients with asymptomatic carotid plaques, considering eventually plaque morphology (symmetry, composition, eccentricity or concentricity of the plaque, etc) for patient stratification.

Nerve growth factor regulates the firing patterns and synaptic composition of motoneurons

Target-derived neurotrophins exert powerful synaptotrophic actions in the adult brain and are involved in the regulation of different forms of synaptic plasticity. Target disconnection produces a profound synaptic stripping due to the lack of trophic support. Consequently, target reinnervation leads to synaptic remodeling and restoration of cellular functions. Extraocular motoneurons are unique in that they normally express the TrkA neurotrophin receptor in the adult, a feature not seen in other cranial or spinal motoneurons, except after lesions such as axotomy or in neurodegenerative diseases like amyotrophic lateral sclerosis. We investigated the effects of nerve growth factor (NGF) by retrogradely delivering this neurotrophin to abducens motoneurons of adult cats. Axotomy reduced the density of somatic boutons and the overall tonic and phasic firing modulation. Treatment with NGF restored synaptic inputs and firing modulation in axotomized motoneurons. When K252a, a selective inhibitor of tyrosine kinase activity, was applied to specifically test TrkA effects, the NGF-mediated restoration of synapses and firing-related parameters was abolished. Discharge variability and recruitment threshold were, however, increased by NGF compared with control or axotomized motoneurons. Interestingly, these parameters returned to normal following application of REX, an antibody raised against neurotrophin receptor p75 (p75(NTR)). In conclusion, NGF, acting retrogradely through TrkA receptors, supports afferent boutons and regulates the burst and tonic signals correlated with eye movements. On the other hand, p75(NTR) activation regulates recruitment threshold, which impacts on firing regularity. To our knowledge, this is the first report showing powerful synaptotrophic effects of NGF on motoneurons in vivo.

An unbiased stereological method for efficiently quantifying the innervation of the heart and other organs based on total length estimations

Quantitative information about the innervation is essential to analyze the structure-function relationships of organs. So far, there has been no unbiased stereological tool for this purpose. This study presents a new unbiased and efficient method to quantify the total length of axons in a given reference volume, illustrated on the left ventricle of the mouse heart. The method is based on the following steps: 1) estimation of the reference volume; 2) randomization of location and orientation using appropriate sampling techniques; 3) counting of nerve fiber profiles hit by a defined test area within an unbiased counting frame on paraffin sections stained immunohistochemically for protein gene product 9.5; 4) electron microscopic estimation of the mean number of axon profiles contained in one nerve fiber profile; 5) estimation of the degree of tissue shrinkage of specimens in paraffin; and 6) calculation of the total axon length within the reference volume, taking tissue shrinkage into account. In a set of five mouse hearts, the total length of axons ramifying between cardiomyocytes ranged between ∼50 and 100 m, with a mean of 75.98 m (SD 23.73). The time required for the microscopical analysis was ∼8 h/animal for an experienced observer. Using antibodies specific for different neuron subtypes and immunoelectron microscopy, this method is also suited to estimate the total axon length of neurons expressing different transmitters. This new and efficient method is particularly useful when structural remodeling takes place and is suspected to involve gain or loss of axons.