Nerve growth factor synthesis in vascular smooth muscle

Nonwoven spidroin materials as scaffolds for ex vivo cultivation of aortic fragments and dorsal root ganglia

Recombinant spidroins (RS; the analogues of silk proteins of spider's web) have multiple properties beneficial for bioengineering, including their suitability for electrospinning and thus, for production of materials with oriented fibers. This makes RS-based matrices potentially effective in stimulating regeneration of peripheral nerves. The restoration of injured nerves also depends on prompt regrowth of blood vessels. Therefore, prospective scaffold materials for neuro-regenerative therapy should positively affect both the nerves and the blood vessels. Currently, the experimental models suitable for culturing and quantitative assessment of the vascular and neuronal cells on the same material are lacking. Here, we assessed the suitability of electrospun RS-based matrices for cultivation of the mouse aorta and dorsal root ganglia (DRG) explants. We also quantified the effects of matrix topography upon both types of tissues. The RS-based materials have effectively supported aortic explants survival and sprouting. The cumulative length of endothelial sprouts on rS1/9-coated inserts was significantly higher as compared to type I collagen coatings, suggesting stimulatory effects on angiogenesis in vitro. In contrast to matrices with random fibers, on matrices with parallel fibers the migration of both smooth muscle and endothelial cells was highly oriented. Furthermore, alignment of RS fibers effectively directs the growth of axons and the migration of Schwann cells from DRGs. Thus, the electrospun RS matrices are highly suitable to culture both, the DRGs and aortic explants and to study the effects of matrix topography on cell migration. This model has a high potential for further endeavor into interactions of nerve and vascular cells and tissues.

Plasma and Urinary Levels of Nerve Growth Factor Are Elevated in Primary Hypertension

Nerve growth factor (NGF) is the main neurotrophic factor that can control sympathetic nerve innervation and sympathetic neural activity in cardiovascular organs. Although NGF overproduction and its influences on the sympathetic nervous system have been shown in hypertensive animals, NGF status and its association with sympathetic nerve activity have not yet been explored in human hypertension. In the present study, therefore, plasma and urinary levels of NGF and those of catecholamines (i.e., indices for NGF status and sympathoadrenal activity, respectively) were compared between 83 untreated primary hypertensives without apparent cardiovascular damages and 81 healthy normotensive subjects. Plasma and urinary levels of NGF were significantly greater in the hypertensive group (311 ± 158 pg/mL and 72.7 ± 54.0 ng/g of Cr) than in the normotensive group (168 ± 188 pg/mL and 54.5 ± 38.8 ng/g of Cr) (p < 0.05 for each measurement), even if the baseline differences of age and gender between the groups were adjusted. Similarly, plasma and urinary levels of catecholamines were significantly higher in the hypertensive group than in the normotensive group except for plasma noradrenaline. In addition, despite no significant correlations between plasma levels of NGF and catecholamines in both groups, urinary NGF significantly correlated positively with both urinary noradrenaline and urinary adrenaline in the hypertensive group (r = 0.259, p=0.018 and r = 0.232, p=0.035), but not in the normotensive group (r = 0.115, p=0.307 and r = −0.018, p=0.871). On the contrary, plasma and urinary levels of NGF as well as those of catecholamines did not associate with any systemic hemodynamic indices such as blood pressure and pulse rate in either group. Thus, primary hypertension was characterized by the enhancements of both NGF status and sympathoadrenal activity and the positive relationship between them. Our data indicate that enhanced NGF status and subsequent NGF-induced sympathoadrenal overactivity could occur in primary hypertension.

Simulated Microgravity Induces Regionally Distinct Neurovascular and Structural Remodeling of Skeletal Muscle and Cutaneous Arteries in the Rat

Introduction: Mechanical forces and sympathetic influences are key determinants of vascular structure and function. This study tested the hypothesis that hindlimb unloading (HU) exerts diverse effects on forelimb and hindlimb small arteries of rats in functionally different regions of the skeletal muscle and skin. Methods: Male Wistar rats were subjected to HU for 2 weeks, then skeletal muscle arteries (deep brachial and sural) and skin arteries (median and saphenous) were examined in vitro using wire myography or isobaric perfusion and glyoxylic acid staining. Results: HU increased lumen diameter of both forelimb arteries but decreased diameter of the sural artery; the saphenous artery diameter was not affected. Following HU, maximal contractile responses to noradrenaline and serotonin increased in the forelimb but decreased in the hindlimb skeletal muscle feed arteries with no change in skin arteries; all region-specific alterations persisted after endothelium removal. HU increased the sensitivity to vasoconstrictors in the saphenous artery but not in the sural artery. In the saphenous artery, initially high sympathetic innervation density was reduced by HU, sparse innervation in the sural artery was not affected. Electrical stimulation of periarterial sympathetic nerves in isobarically perfused segments of the saphenous artery demonstrated a two-fold decrease of the contractile responses in HU rats compared to that of controls. Conclusion: HU induces contrasting structural and functional adaptations in forelimb and hindlimb skeletal muscle arteries. Additionally, HU had diverse effects in two hindlimb vascular regions. Hyper-sensitivity of the saphenous artery to vasoconstrictors appears to result from the shortage of trophic sympathetic influence. Importantly, HU impaired sympathetically induced arterial vasoconstriction, consistent with the decreased sympathetic constrictor response in humans following space flight.

Putting together the clues of the everlasting neuro-cardiac liaison

Starting from the late embryonic development, the sympathetic nervous system extensively innervates the heart and modulates its activity during the entire lifespan. The distribution of myocardial sympathetic processes is finely regulated by the secretion of limiting amounts of pro-survival neurotrophic factors by cardiac cells. Norepinephrine release by the neurons rapidly modulates myocardial electrophysiology, and increases the rate and force of cardiomyocyte contractions. Sympathetic processes establish direct interaction with cardiomyocytes, characterized by the presence of neurotransmitter vesicles and reduced cell-cell distance. Whether such contacts have a functional role in both neurotrophin- and catecholamine-dependent communication between the two cell types, is poorly understood. In this review we will address the effects of the sympathetic neuron activity on the myocardium and the hypothesis that the direct neuro-cardiac contact might have a key role both in norepinephrine and neurotrophin mediated signaling. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

Bladder outlet obstruction causes up-regulation of nicotinic acetylcholine receptors in bladder-projecting pelvic ganglion neurons

Pelvic ganglion (PG) neurons relay sympathetic and parasympathetic signals to the lower urinary tract, comprising the urinary bladder and bladder outlet, and are thus essential for both storage and voiding reflexes. Autonomic transmission is mediated by activation of the nicotinic acetylcholine receptor (nAChR) in PG neurons. Previously, bladder outlet obstruction (BOO), secondary to benign prostatic hyperplasia, was found to increase soma sizes of bladder-projecting PG neurons. To date, however, it remains unknown whether these morphological changes are accompanied by functional plasticity in PG neurons. In the present study, we investigated whether BOO alters acetylcholine receptor (nAChR) transcript expression and current density in bladder PG neurons. Partial ligation of the rat urethra for six weeks induced detrusor overactivity (DO), as observed during cystometrical measurement. In rats exhibiting DO, membrane capacitance of parasympathetic bladder PG neurons was selectively increased. Real-time PCR analysis revealed that BOO enhanced the expression of the transcripts encoding the nAChR α3 and β4 subunits in PG neurons. Notably, BOO significantly increased ACh-evoked current density in parasympathetic bladder PG neurons, whereas no changes were observed in sympathetic bladder and parasympathetic penile PG neurons. In addition, other ligand-gated ionic currents were immune to BOO in bladder PG neurons. Taken together, these data suggest that BOO causes upregulation of nAChR in parasympathetic bladder PG neurons, which in turn may potentiate ganglionic transmission and contribute to the development of DO.

Spatiotemporal distribution of neurovascular alignment in remodeling adult rat mesentery microvascular networks

An emerging area of microvascular research focuses on the links between neural and vascular patterning. However, the functional dependence between vascular and neural growth in adult tissues remains underinvestigated. The objective of this study was to determine the spatial and temporal coordination between vascular and neural networks over a time course of adult microvascular growth. Mesentery tissues from adult male Wistar rats were harvested prior to stimulation, and 2, 10 and 30 days after angiogenesis stimulated by mast cell degranulation. Tissues were immunolabeled for PECAM (endothelial cell marker) and class III β-tubulin (peripheral nerve marker). Neurovascular alignment was quantified per vessel category: arterioles (>20 µm), pre-capillary arterioles (10-20 µm), post-capillary venules (10-20 µm), venules (>20 µm), capillaries (<10 µm) and capillary sprouts. Neurovascular alignment along pre-capillary arterioles, capillaries, post-capillary venules and venules was decreased compared to unstimulated levels on days 2 and 10. These decreases inversely correlated with increases in vessel density per vessel category. By day 30, alignment either returned to unstimulated levels or was increased compared to day 10. These results suggest that neurovascular alignment arises after microvascular network growth and is present along arterioles, venules and even capillaries.

Type-1 angiotensin receptors are expressed and transported in motor and sensory axons of rat sciatic nerves

Angiotensin II (Ang II) and its type-1 receptor (AT(1)) occur in neurons at multiple locations within the organism, but the basic biology of the receptor in the nervous system remains incompletely understood. We previously observed abundant AT(1)-like binding sites and intense expression of AT(1) immunoreactivity in perikarya of the dorsal root ganglion and ventral horn of the rat spinal cord. We have now examined the receptor in rat sciatic nerve, including the dynamics of its axonal transport. Ligand-binding autoradiography of resting nerve showed "hot spots" of (125)I-Ang II binding that could be specifically blocked by the AT(1) antagonist, losartan. Immunohistochemistry with an AT(1)-antibody validated by Western blots also showed patches of AT(1)-reactivity in nerve. These patches were localized around large myelinated axons with faint immunoreactivity in their lumens. Sixteen hours after nerve ligation there was no change in the patches or hot spots, but luminal AT(1)-reactivity increased dramatically in a narrow zone immediately above the ligature. With double ligation there was a pronounced accumulation of AT(1) immunoreactivity proximal to the upstream ligature and a very slight accumulation distal to the second ligature. This asymmetric pattern of accumulation, confirmed by quantitative receptor binding autoradiography, probably reflected axonal transport rather than local production of receptor. Retrograde tracing and stereological analysis to determine the source of transported AT(1) indicated that many AT(1)-positive fibers arise in the ventral horn, and a larger number arise in dorsal root ganglia. A corresponding result was obtained with double-label immunohistochemistry of ligated nerve, which showed AT(1) accumulations in both motor and sensory fibers. We conclude that somatic sensory and motor neurons of the rat export substantial quantities of AT(1) into axons, which transport them to the periphery. The physiologic implications of this finding require further investigation.

Aging reduces hypoxia-induced microvascular growth in the rodent hippocampus

The effect of aging on microvascular density and plasticity in the rodent hippocampus, a brain region critically important for learning and memory, was investigated in F344xBN rats. Capillary density and angiogenesis were measured in three regions of the hippocampus in young and old rats and in old rats administered growth hormone, a treatment that improves cognitive function in older animals. Animals were housed under control conditions or in hypoxic conditions (11% ambient oxygen levels) to stimulate vascular growth. Our results indicate that aging is not associated with a reduction in hippocampal capillary density. However, aged animals demonstrate a significant impairment in hypoxia-induced capillary angiogenesis compared to young animals. Growth hormone treatment to aged animals for 6 weeks did not alter hippocampal capillary density and did not ameliorate the age-related deficit in angiogenesis. We conclude that aging significantly reduces hippocampal microvascular plasticity, which is not improved with growth hormone therapy.

Amadori-glycated albumin-induced vascular smooth muscle cell proliferation and expression of inhibitor of apoptosis protein-1 and nerve growth factor-gamma

We investigated the effects of Amadori-glycated serum albumin (GSA) on cell proliferation as well as expressions of antioxidant enzyme genes and marker genes associated with signal transduction pathways in rat aortic vascular smooth muscle cells (VSMCs). Quiescent VSMCs treated with GSA (0-500 microg/mL, 48 h) exhibited a dose-dependent increase in proliferation that was prevented by PD98059 (25 microM), suggesting a MAPK-dependent signaling pathway. Compared with bovine serum albumin (BSA)-treated cells, the GSA (500 microg/mL, 24~h)-treated VSMCs showed a higher superoxide dismutase 2 gene expression in quantitative RT-PCR, suggesting the involvement of oxidative stress. In a focused oligonucleotide array containing 96 signal transduction-related genes, expression of inhibitor of apoptosis protein-1 (IAP-1), nerve growth factor-gamma (NGF-gamma), and c-jun genes was significantly higher in the GSA-treated VSMCs. These results suggest that induction of antiapoptotic proteins like IAP-1 and strong mitogens like NGF-gamma by GSA might further contribute to the VSMC proliferation and accelerated vascular remodeling in diabetes.

Estrogen increases sensory nociceptor neuritogenesis in vitro by a direct, nerve growth factor-independent mechanism

Estrogen affects many aspects of the nervous system, including pain sensitivity and neural regulation of vascular function. We have shown that estrogen elevation increases sensory nociceptor innervation of arterioles in Sprague-Dawley rat mammary gland, external ear and mesentery, suggesting widespread effects on sensory vasodilatory innervation. However, it is unclear whether estrogen elicits nociceptor hyperinnervation by promoting target release of neurotrophic factors, or by direct effects on sensory neurons. To determine if estrogen may promote axon sprouting by increasing release of target-derived diffusible factors, dorsal root ganglia explants were co-cultured with mesenteric arterioles for 36 h in the absence or presence of 17beta-estradiol (E2). Mesenteric arteriolar target substantially increased neurite outgrowth from explanted ganglia, but estrogen had no effect on outgrowth, suggesting that estrogen does not increase the availability of trophic proteins responsible for target-induced neurite outgrowth. To assess the direct effects of estrogen, dissociated neonatal dorsal root ganglion neurons were cultured for 3 days in the absence or presence of E2 and nerve growth factor (NGF; 1-10 ng/mL), and immunostained for the nociceptor markers peripherin or calcitonin gene-related peptide. NGF increased neuron size, survival and numbers of neurons with neurites, but did not affect neurite area per neuron. Estrogen did not affect neuron survival, size or numbers of neurons with neurites, but did increase neurite area per neuron. The effects of these agents were not synergistic. We conclude that estrogen exerts direct effects on nociceptor neurons to promote axon outgrowth, and this occurs through an NGF-independent mechanism.

Rescue of NGF-deficient mice I: transgenic expression of NGF in skin rescues mice lacking endogenous NGF

Mice lacking a functional NGF gene (ngf-/- mice) have less than one third of the normal complement of sensory neurons, few sympathetic postganglionic neurons and die shortly after birth. We report here that transgenic expression of NGF under control of the K14 keratin promoter can rescue some elements of the peripheral nervous system and restore normal growth and viability to ngf-/- mice. While hybrid transgenic-ngf-/- mice (ngfTKOs) displayed marginal rescue of trigeminal ganglion neurons, the percentage of CGRP-positive neurons was restored to normal. Restoration of CGRP-positive terminals in skin and spinal cord was also found and accompanied by recovery of behavioral responses to noxious stimuli. ngfTKO mice displayed a normal number of superior cervical ganglion neurons and recovery of sympathetic innervation of skin. These results demonstrate that substitution of a functional NGF locus by a transgene directing expression largely to skin can result in normal growth and viability. Thus, the most vital functions of NGF are not dependent on faithful recapitulation of the normal spatiotemporal pattern of gene expression.

Effects of eosinophils on mast cells: a new pathway for the perpetuation of allergic inflammation

Mast cells have a clear-cut pathologic role in allergy, participating in a number of chronic inflammatory conditions, in helmintic parasitosis, and in some solid tumor reactions, but also in physiological situations, such as wound healing and innate immunity. Mast cells release a large number of proinflammatory, immunoregulatory, and tissue regulatory mediators after activation induced by either IgE-dependent or IgE-independent mechanisms. While much information has been gathered on the immunological mast cell activation both in rodent and human systems, only minimal knowledge exists on the non-immunological activation especially in human mast cells. Mast cell IgE-independent activation occurs through G(i3alpha) which has been identified as the pertussis toxin (Ptx)-sensitive heterotrimeric G protein that interacts with cationic secretagogues inducing PLC-independent mast cell exocytosis. Mast cell IgE-independent activation in allergy probably occurs when mast cells encounter eosinophils, the main inflammatory cells of the allergic reactions that persist throughout the late phase and when the inflammatory condition becomes chronic. This review summarizes regarding the influence of eosinophils on mast cell activation, thus demonstrating that IgE-independent activation has a relevant role in pathophysiological processes as well as in mast cell IgE-dependent activation.

Loss of cardiac sympathetic neurotransmitters in heart failure and NE infusion is associated with reduced NGF

Sympathetic neurotransmitters are diminished in cardiac efferent nerve endings in congestive heart failure (CHF). Similar changes occur after exogenous norepinephrine (NE) infusion. Since NE reduces nerve growth factor (NGF) in cultured cardiomyocytes, we proposed to determine whether the loss of noradrenergic transmitters in the failing heart is caused by the NE-mediated reduction of NGF or its neurotrophic receptor tyrosine kinase A (TrKA). Dogs were assigned to receive either rapid ventricular pacing (225 beats/min) or NE infusion (0.5 microg/kg/min) for 8 wk. Control animals received either cardiac pacing of 100 beats/min or saline infusion. We measured NGF and TrKA proteins by Western blot and immunocytochemistry and measured NGF and TrKA mRNAs by reverse transcription polymerase chain reaction, neuronal catecholaminergic histofluorescence, tyrosine hydroxylase-immunostained profiles, and plasma NE. Rapid ventricular pacing produced CHF with increased plasma NE, decreased myocardial NGF protein (0.61 +/- 0.07 vs. 1.04 +/- 0.04, P < 0.05), TrKA protein (0.75 +/- 0.08 vs. 0.98 +/- 0.06, P < 0.05), NGF and TrKA mRNAs and reduced catecholaminergic histofluorescence (197 +/- 23 vs. 485 +/- 43, P < 0.05), and tyrosine hydroxylase profiles (360 +/- 51 vs. 773 +/- 36, P < 0.05). Decreases in tissue NGF and TrKA protein were also noted by immunocytochemistry. Similar changes occurred in NE-treated animals. Tissue NGF and TrKA levels correlated closely with the noradrenergic transmitter profiles. We conclude that cardiac NGF and TrKA are reduced by rapid ventricular pacing and NE infusion, and that these changes correlate with decreases of cardiac catecholaminergic and tyrosine hydroxylase profiles. Findings indicate that decrease of cardiac sympathetic transmitters in heart failure is associated with NE-mediated reduction of NGF and TrKA.

Selective expression of the proprotein convertases furin, pc5, and pc7 in proliferating vascular smooth muscle cells of the rat aorta in vitro

The aim of this study was to investigate whether transformation of quiescent vascular smooth muscle cells (VSMCs) into proliferating secretory cells is accompanied by an expression of processing enzymes that activate de novo-synthesized growth factors. Three enzymes belonging to the family of the kexin/subtilisin-like mammalian proprotein convertases (PCs), furin, PC5, and PC7, were found to be upregulated after balloon denudation in vivo. To determine their importance in these cell processes, we investigated their gene regulation using a short-term organ culture system. After incubation of rat aorta for 4 and 24 hr in serum-free medium, we demonstrated a significant induction of VSMC proliferation. The affected subset of VSMCs, positive for alpha-smooth muscle actin, also expressed proliferating cell nuclear antigen (PCNA). Our results revealed a parallel upregulation of furin, PC5, and PC7 in PCNA-immunolabeled cells. As a substrate model for comparison with PCs we used nerve growth factor (NGF). NGF is known to be activated by PCs. As shown by Northern blotting analysis, NGF mRNA concentration was significantly increased in cultured explants. NGF was released into the culture medium. In conclusion, both PCs and NGF are coordinately modulated on induction of VSMC proliferation.

Nerve growth factor (NGF) and NGF mRNA change in rat uterus during pregnancy

During pregnancy, the uterus undergoes a profound sympathetic denervation. To explore whether this is associated with changes in neurotrophic factors, we assayed nerve growth factor (NGF) and NGF mRNA in the uterus of non-pregnant and pregnant rats. In the uterine horn, the concentration of NGF and its mRNA decreased during middle and late pregnancy. However, when values were corrected for the increase of uterine weight and total RNA yield during pregnancy, NGF content and mRNA per horn increased during middle and late pregnancy. Similar, but less pronounced, changes were observed in the cervix. By seven days postpartum, both parameters returned to near normal.

Stretch-activated signaling of nerve growth factor secretion in bladder and vascular smooth muscle cells from hypertensive and hyperactive rats

Elevated vascular (VSMC) and bladder smooth muscle (BSMC) NGF are associated with altered visceral innervation in the spontaneously hypertensive rat (SHR: hypertensive, behaviorally hyperactive) compared with control Wistar-Kyotos (WKYs). Stretch stimulates increased NGF production in BSMCs. To elucidate whether stretch induces NGF synthesis in VSMCs, and to determine if disturbances in stretch-mediated NGF production contribute to the elevated tissue levels of NGF in SHRs, we subjected VSMCs and BSMCs cultured from four established inbred rat strains (WKY, WKHA: hyperactive; SHR and WKHT: hypertensive) to several stretch paradigms. For VSMCs, acute and cyclic stretch affected cells derived from hypertensive rats (80-100% increase over control) but not from normotensive strains. For BSMCs, cyclic and static stretch increased NGF secretion in all four strains, but had a two- to threefold greater effect in cells from SHRs and WKHTs (increase up to 600%) at early time points. At later time points of a 24-h experimental period, stretch increased NGF output up to 400% in SHR and WKHA cultures. Thus, defects that influence early induction of stretch-mediated SHR NGF secretion cosegregate with the hypertensive phenotype. Stretch-gated ion channel inhibitors, voltage-gated ion channel inhibitors, and protease inhibitors failed to affect stretch-induced BSMC NGF secretion. In contrast, gene transcription, intracellular calcium, protein kinase C (PKC), and autocrine release of an unknown factor may play a role in the elevated NGF secretion observed in smooth muscle from hypertensive animals. Altered stretch-induced smooth muscle NGF secretion may contribute to the augmented vascular and bladder NGF content associated with high blood pressure and hyperactive voiding in SHRs.

Reduced myocardial nerve growth factor expression in human and experimental heart failure

Maintenance of cardiac performance is tightly controlled by the autonomic nervous system. In congestive heart failure (CHF), although the adverse pathophysiological effects of cardiac sympathetic overactivity are increasingly recognized, the paradoxical finding of reduced sympathetic innervation density in the failing heart remains unexplained. Given these observations, we tested the hypothesis that a reduction in the myocardial production of nerve growth factor (NGF), which is important for the maintenance of sympathetic neuronal survival, could explain the conflicting neurochemical and neuroanatomical profile of CHF. In healthy humans (n=11), there was a significantly greater transcardiac venoarterial plasma NGF gradient than in CHF patients (n=11, P<0.05). In a rat model of CHF, a 40% reduction (P<0.05) NGF mRNA expression was apparent in association with a 24% reduction in tissue NGF content (P<0.05). In conjunction, evidence of reduced sympathetic innervation in the failing heart was apparent, as measured histologically by catecholamine fluorescence and by expression of the neuronal NGF receptor trkA. Norepinephrine (10 micromol/L) exposure reduced both NGF mRNA and protein expression in isolated cardiomyocytes, suggesting that myocardial NGF downregulation may represent an adaptive response to sympathetic overactivity. These data indicate that NGF expression in the heart is dynamic and may be altered in cardiovascular disease states. In CHF, reduced NGF expression may account for alterations in sympathetic neuronal function and neuroanatomy. The full text of this article is available at http://www.circresaha.org.

Mitochondrial impact on nerve growth factor production in vascular smooth muscle-derived cells

Ht30</=Ht10>/=Ht5). Cells with reduced mitochondrial activity also showed abnormal responses to the stimulation of NGF output. Thrombin and phorbol ester elevated NGF production from Ht100, Ht30 and Ht10 cells, but not from Ht5 cells. Ht30 cells, despite secreting less NGF basally than Ht100 cells, reached a similar or greater NGF output upon stimulation. Mitogens increased NGF output and NGF mRNA levels with the largest effect on NGF protein in Ht30 cells. Free radical production and the ability of cells to respond to NGF-inducing agents were related. These data suggest that chronic impairment of mitochondrial function associates with disturbances in cellular production of a signaling protein.

Increased nerve growth factor mRNA stability may underlie elevated nerve growth factor secretion from hypertensive vascular smooth muscle cells

Altered nerve growth factor (NGF) regulation has been linked to the pathophysiology of hypertension. Vascular smooth muscle cells from an inbred hypertensive, but normoactive rat strain (WKHT) secreted NGF at a greater rate than from a hyperactive, normotensive strain (WKHA). Exposure to phorbol ester increased NGF secretion rates from WKHT by 400-800% but not from WKHA vascular muscle. NGF secretion rates from both WKHT and WKHA vascular cells were elevated by co-application of platelet-derived growth factor (PDGF) and transforming growth factor-beta1 (TGF-beta1) by 300-1000%. This response was partially attenuated by actinomycin D, an inhibitor of RNA transcription. These results suggest that regulation of NGF production does not occur solely at the level of transcription and post-transcriptional mechanisms operate. Analysis of NGF mRNA stability in the two strains following PDGF and TGF-beta1 treatment showed that NGF mRNA in WKHT had a half-life of 126.2+/-11.68 min while in WKHA vascular smooth muscle cells, the half-life was 47. 33+/-11.98 min. In addition to increased NGF mRNA stability in WKHT vascular muscle, these cells have an increased translational efficiency of NGF protein; elevated synthesis of NGF protein per unit NGF mRNA. Differences in signaling pathways may result in increased NGF mRNA stability and translational efficiency that may account for the elevated NGF protein in WKHT vascular smooth muscle cells.

Arterial nerve growth factor (NGF) mRNA, protein, and vascular smooth muscle cell NGF secretion in hypertensive and hyperactive rats

Elevated levels of nerve growth factor (NGF) protein and NGF mRNA have been reported in the vessels of spontaneously hypertensive rats (SHR: hypertensive, hyperactive) compared to Wistar-Kyoto (WKY) rats. Elevated NGF may be involved in the development of hypertension in SHRs. We examined vascular NGF mRNA and protein content and the regulation of NGF secretion by vascular smooth muscle cells (VSMCs) from two inbred strains (WKHT: hypertensive; WKHA: hyperactive) derived from SHRs and WKYs. Our goal was to determine if receptor-mediated defects in NGF regulation play a role in increased secretion of VSMC NGF from hypertensive animals. Tissue NGF mRNA content was determined by competitive, quantitative RT-PCR. Tissue NGF and NGF content in cultured VSMC-conditioned medium was quantified using a two-site ELISA. Tail artery NGF mRNA was elevated in WKHTs compared to WKHAs. Tissue NGF protein was elevated in WKHT aorta, mesenteric, and tail artery compared to WKHAs. Pharmacologically induced increases in NGF output were blocked with inhibition of transcription or protein synthesis. Basal NGF secretion by WKHT VSMCs was significantly higher than WKHAs. The observed increases in VSMC NGF output in SHRs over WKYs in response to beta-adrenergic agents are not preserved in the WKHT:WKHA comparison. Protein kinase C-dependent increases in SHR VSMC NGF appear in both WKHTs and WKHAs. In contrast, elevated NGF levels due to disturbances in alpha-adrenergic, peptidergic, and purinergic control of NGF output are features common to both genetic models of hypertension (SHR and WKHT). These results suggest that the defect in smooth muscle NGF metabolism observed in SHRs cosegregates with a hypertensive rather than a hyperactive phenotype. Moreover, altered receptor-mediated regulation (alpha-adrenergic, peptidergic, and purinergic) of VSMC NGF production may contribute to elevated vascular tissue NGF, suggesting a mechanism leading to the high levels of NGF associated with hypertension in SHRs and WKHTs.

Altered regulation of bladder nerve growth factor and neurally mediated hyperactive voiding

Elevated bladder smooth muscle cell (BSMC) nerve growth factor (NGF) secretion and related neuroplasticity are associated with hyperactive voiding in spontaneously hypertensive rats (SHRs: hypertensive, behaviorally hyperactive), compared with control Wistar-Kyotos (WKYs). We used two inbred strains (WKHT: hypertensive; WKHA: hyperactive) to further investigate this phenomenon. WKHA BSMCs secreted higher basal levels of NGF than WKHT BSMCs. Antagonists did inhibit NGF output in WKHA but not WKHT cultures. Thus augmented basal secretion of NGF cosegregates with a hyperactive phenotype, whereas a lack of regulatory inhibition of NGF output cosegregates with a hypertensive phenotype. Bladder norepinephrine content paralleled NGF content, with WKHTs > SHRs > WKHAs > WKYs, providing evidence that a lack of inhibition is the greatest contributor to elevated bladder NGF and noradrenergic innervation. Protein kinase C (PKC) agonists affected NGF production differentially depending on strain, suggesting that altered PKC signaling may contribute to strain differences in NGF secretion. Finally, 6-h voiding frequency differed between the strains, with SHRs > WKHTs = WKHAs > WKYs. Thus aspects of both the hypertensive and hyperactive phenotypes may be associated with elevated SHR bladder NGF and hyperactive voiding.

Mechanisms of increased NGF production in vascular smooth muscle of the spontaneously hypertensive rat

The spontaneously hypertensive rat (SHR) was developed as a genetic model of essential hypertension. In vivo and in vitro evidence demonstrates that vascular smooth muscle cells (VSMCs) from the SHR produce more nerve growth factor (NGF) than the normotensive Wistar-Kyoto (WKY) control strain. This increased NGF production is accompanied by excessive innervation of target tissues in the SHR. In the present study, a sensitive, competitive, quantitative, reverse-transcriptase polymerase chain reaction (C Q RT-PCR) assay is characterized and used to analyze levels of NGF mRNA in cultured VSMCs derived from the SHR and WKY strains as well as bladder tissue. Differences in NGF secretion rates between SHR and WKY VSMCs were partially due to an increased stability of NGF mRNA in SHR VSMCs. Following treatment with platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta 1) to elevate NGF production, the half-life of the NGF mRNA was 104.5 +/- 18.0 min in SHR VSMCs, compared to only 36.5 +/- 11.6 min in WKY VSMCs. Sequence analysis of the 3' untranslated region (UTR) revealed no strain differences in cis-acting sequences potentially involved in determining mRNA stability. Thus, it seems unlikely to be a 3'UTR mutation that prolongs mRNA lifetime. Rather, differential regulation of an RNA-binding protein may play a role in the abnormal NGF mRNA stability in SHR VSMCs. SHR VSMCs also demonstrate an increased translational efficiency of NGF protein; more NGF protein is synthesized per unit of NGF mRNA. The use of a C Q RT-PCR assay has allowed the determination that abnormal NGF mRNA stabilization as well as altered translational efficiency may contribute to excess NGF synthesis and progressive hypertension in the SHR.

Neurally mediated hyperactive voiding in spontaneously hypertensive rats

The development of hypertension in spontaneously hypertensive rats (SHR) and hyperactive voiding in rats with urethral obstruction are characterized by abnormal smooth muscle growth, increased tissue levels of nerve growth factor (NGF) and altered patterns of innervation. The present study was undertaken to determine if bladder smooth muscle from SHRs contains and secretes elevated levels of NGF, and if so, whether the augmented NGF contributes to changes in bladder innervation and function without tissue hypertrophy. Voiding behavior was monitored using specially designed metabolic cages. NGF levels in tissue homogenates and conditioned cell culture media were measured by ELISA. NGF mRNA in cultured bladder smooth muscle cells (BSMCs) was quantified using reverse transcriptase PCR. Noradrenergic innervation was assessed by staining with glyoxylic acid and assaying norepinephrine (NE) content in bladders with high performance liquid chromatography. SHRs voided more frequently than WKY rats. NGF content was higher in bladders from adult SHRs when compared to Wistar-Kyoto normotensive rats (WKYs). No significant difference in NGF mRNA content was observed between SHR and WKY BSMCs. However, SHR BSMCs secreted NGF at a higher rate and amount per unit mRNA than did WKY BSMCs. SHR bladders contained more NE and were more densely stained for catecholaminergic fibers than bladders from WKY rats. The results support the hypothesis that elevated NGF secretion by bladder smooth muscle is associated with hyperinnervation of bladder and hyperactive voiding in SHRs. Thus, the SHR strain may represent a genetic model to study changes in bladder function resulting from altered patterns of innervation.

Gene expression of neurotrophins and their receptors in cultured rat vascular smooth muscle cells

Most previous researches on neurotrophins including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) have focused on the nervous system, because their receptors are widely distributed in neuronal tissues. Recently, however, the participation of neurotrophins in inflammation and atherosclerosis has been proposed. Therefore, the gene expression of neurotrophins is now an urgent issue is to be investigated in nonneuronal tissues. Here, we evaluated the gene expression of neurotrophins and their receptors in rat cultured vascular smooth muscle cells (VSMCs) by the reverse transcriptase-polymerase chain reaction method. The transcripts of NGF, NT-3, and TrkC (high-affinity receptor for NT-3), and two BDNF alternative spliced transcript variants with exons 3 and 4 were clearly detected in VSMCs cultured under conventional culture conditions. The upregulation of mRNA levels for NGF, two BDNF variants with exons 1 and 2, low-affinity neurotrophin receptor, and high-affinity receptors, TrkA (for NGF) and TrkB (for BDNF), was observed in response to the treatment with serum and phorbol-ester following the serum-starvation. In contrast, the expression of NT-3 and TrkC genes was downregulated under these conditions. Co-expression of these factors and their receptors and the characteristic regulation of their gene transcriptions suggest that these factors play crucial roles in the function of VSMCs through an autocrine mechanism.

Persistent reduction in renal nerve growth factor mRNA after perindopril treatment of young spontaneously hypertensive rats

Nerve growth factor (NGF) determines sympathetic innervation of target tissues, and NGF levels are increased in young spontaneously hypertensive rats (SHR). Angiotensin can affect NGF levels, and the persistent reduction in blood pressure after brief angiotensin-converting enzyme inhibition in young SHR may involve long-term changes in NGF and sympathetic innervation. We measured the relative abundance of renal NGF mRNA by reverse transcription-polymerase chain reaction in SHR during and after treatment from 6 to 10 weeks of age with vehicle, perindopril (3 mg/kg per day), the bradykinin B2 antagonist Hoe 140 (0.5 mg/kg per day), both perindopril and Hoe 140, or angiotensin II (Ang II; 200 ng/kg per minute). Glomerular filtration rates were estimated at 10 and 20 weeks of age. At 10 weeks of age, Ang II caused a significant (P<.01) increase and perindopril caused a significant (P<.01) decrease in renal NGF mRNA levels. Blockade of the bradykinin B2 receptor during perindopril treatment attenuated (P<.05) the reduction in NGF mRNA levels. Renal NGF mRNA (P=.005) and blood pressure (P<.001) remained significantly lower than control 10 weeks after perindopril treatment was stopped. The partial reduction in blood pressure at 20 weeks of age in rats that had received perindopril and Hoe 140 was not associated with any difference in renal NGF mRNA. Perindopril-induced long-term reduction in renal NGF mRNA levels may decrease sympathetic innervation and thereby contribute to the long-term posttreatment blood pressure reduction.

Plasticity in adult and ageing sympathetic neurons

The nature of neural plasticity and the factors that influence it vary throughout life. Adult neurons undergo extensive and continual adaptation in response to demands that are quite different from those of early development. We review the main influences on the survival, growth and neurotransmitter expression in adult and ageing sympathetic neurons, comparing these influences to those at work in early development. This "developmental" approach is proposed because, despite the contrasting needs of different phases of development, each phase has a profound influence on the mechanisms of plasticity available to its successors. Interactions between neurons and their targets, whether effector cells or other neurons, are vital to all of these aspects of neural plasticity. Sympathetic neurons require access to target-derived diffusible neurotrophic factors such as NGF, NT3 and GDNF, as well as to bound elements of the extracellular matrix such as laminin. These factors probably influence plasticity throughout life. In adult life, and even in old age, sympathetic neurons are relatively resistant to cell death. However, they continue to require target-derived diffusible and bound factors for their maintenance, growth and neurotransmitter expression. Failure to maintain appropriate neuronal function in old age, for example in the breakdown of homeostasis, may result partly from a disturbance of the dynamic, trophic relationship between neurons and their targets. However, there is no clear evidence that this is due to a failure of targets to synthesize neurotrophic factors. On the neural side of the equation, altered responsiveness of sympathetic neurons to neurotrophic factors suggests that expression of the trk and p75 neurotrophin receptors contributes to neuronal survival, maintenance and growth in adulthood and old age. Altered receptor expression may therefore underlie the selective vulnerability of some sympathetic neurons in old age. The role of neural connectivity and activity in the regulation of synthesis of target-derived factors, as well as in neurotransmitter dynamics, is reviewed.

Nerve growth factor induces the expression of certain cytokine genes and bcl-2 in mast cells. Potential role in survival promotion

Nerve growth factor (NGF) promotes mast cell survival in vitro (Horigome, K., Bullock, E. D., and Johnson, E. M., Jr. (1994) J. Biol. Chem. 269, 2695-2702). NGF survival promotion is cell density-dependent, and conditioned medium experiments have shown that NGF increases the production of an autocrine mast cell survival activity. Cytokines are potential candidates for autocrine survival factors. In rat peritoneal mast cells (RPMC), NGF caused an increase in the messenger RNAs for interleukin (IL)-3, IL-4, IL-10, tumor necrosis factor-alpha, and granulocyte-macrophage colony-stimulating factor. This induction was NGF dose-dependent, was blocked by NGF-neutralizing antibodies, and was not observed in the non-mast peritoneal cell population. The immunosuppressive agent, cyclosporin A, blocked both cytokine induction and NGF-activated survival promotion but not survival promotion activated by IL-3 or stem cell factor, suggesting that NGF enhanced RPMC survival by increasing cytokine production. We also examine the effects of NGF on the expression levels of some members of the bcl-2 family and the interleukin-1beta-converting enzyme-like cysteine protease families. NGF markedly increased bcl-2 expression but had little or no effect on the other genes studied. The induction of bcl-2 mRNA by NGF was not blocked by cyclosporin A. These data suggest that induced cytokine gene expression but not increased expression of bcl-2 mediates NGF-survival promotion in RPMC.

Catecholamines, stress, and disease: a psychobiological perspective

OBJECTIVE

Research on the relationship between physiological responses to stressful stimulation and the onset of psychosomatic illnesses has been an area of intense interest for many years. Studies using animal models have contributed significantly to this field of inquiry by taking several complementary approaches.

METHOD

Three specific research strategies taken in our laboratory will be highlighted here. Each involves studies in conscious, freely behaving animals.

RESULTS

Genetically selected animals have been exposed to acute stressors to unmask neuroendocrine and autonomic abnormalities related to disease susceptibility. In addition, studies of aged animals suggest that exaggerated physiological responses to acute stress may underlie some age-related pathologies. Finally, a series of studies has revealed that exposure of laboratory animals to stressful stimulation may exert long-lasting influences on the ways in which these subjects respond in the future to the same or novel stressors.

CONCLUSIONS

These findings illustrate how studies with laboratory animals have the potential for refining the questions that are posed in research with clinical populations and for providing insight into the underlying physiological mechanisms of individual variability in disease susceptibility and the development of appropriate therapeutic interventions.

Preweanling administration of terazosin decreases blood pressure of hypertensive rats in adulthood

To examine the contribution of the sympathetic nervous system to the development of hypertension, we injected spontaneously hypertensive rat (SHR) pups and normotensive Wistar-Kyoto rat (WKY) pups twice daily with saline (1.0 mL/kg SC) or terazosin (0.5 mg/kg SC), an alpha 1-adrenoceptor antagonist, from postnatal day 1 through 21. We determined the effectiveness and duration of action of this terazosin dose in pilot studies with adult SHR and WKY. Body weights of WKY pups were greater than body weights of SHR pups from postnatal day 1 through 21. In addition, body weights of terazosin-treated pups of both strains were comparable to body weights of saline-injected littermate controls. Indirectly measured systolic pressures of terazosin-treated SHR were reduced significantly at 60 and 90 days of age but not at 30 days of age compared with saline-injected littermate controls. Terazosin did not affect systolic pressures of WKY, measured at 30, 60, and 90 days of age. At 100 days of age, in chronically catheterized rats, mean arterial pressures of terazosin-treated SHR were reduced significantly compared with those of saline-injected littermate controls. In contrast, terazosin did not affect mean arterial pressures of WKY at 100 days of age. Finally, preweanling treatment with terazosin did not alter patterns of open field behavior of adult SHR or WKY. SHR were significantly more active and reared more frequently compared with WKY. These findings indicate that the time between birth and weaning at 21 days of age is critical for the full expression of the hypertensive phenotype in SHR. Chronic blockage of alpha 1-adrenoceptors during the preweanling period in SHR may reduce vascular hypertrophy, leading to long-term reductions in arterial pressure.

Can the neurotrophic hypothesis explain degeneration and loss of plasticity in mature and ageing autonomic nerves?

The causes of age-related degeneration in the peripheral nervous system remain unclear. The search for clues has focused on developmental mechanisms and particularly on the neurotrophic hypothesis and its principal player, nerve growth factor, reduced levels of which are thought to cause degeneration of some autonomic and central neurons in old age. Nerve growth factor may well be important in the mature and ageing nervous system, but recent experiments on sympathetic nerves in ageing rats suggest that lack of NGF is not the only limiting factor in neuronal growth and survival. Other candidates include laminin, which is bound in the extracellular matrix and may act in synergy with NGF to regulate neuronal maintenance and growth in maturity. Reduced, region-specific patterns of availability of one or both of these substances may underlie age-related degeneration in autonomic nerves. Different combinations of these factors may influence particular aspects of neuronal plasticity, such as collateral sprouting and regeneration. In addition to extrinsic factors, it appears increasingly likely that altered neuronal responsiveness to neurotrophic factors in old age contributes to structural and functional deficits in autonomic nerves.

CGRP innervation and receptors during aging of male and female hepatic rat portal veins

Calcitonin gene-related peptide (CGRP) innervation and binding sites were studied on hepatic portal veins of male and female rats from 19 days to 22 months of age. CGRP containing nerve fibers were present both in adventitial and medial nerve plexuses, closely apposing to or penetrating into the muscular layers. The density of CGRP innervation was estimated on whole mount preparations and compared during aging. In females, aging did not affect the number of fibers per unit length, although the vessel circumference decreased after 6 months of age. In males, the vessel circumference remained constant during aging, while the density of innervation significantly decreased. Whatever the age or sex of the animals was, no CGRP binding sites were found on portal veins sections by autoradiography. CGRP had no effect on spontaneous contractions of perfused portal veins. The difference observed in the evolution of CGRP innervation density between males and females suggests that CGRP innervation in the rat portal vein may be influenced by gonadal steroids during aging.

Altered signalling in vascular smooth muscle from spontaneously hypertensive rats may link medial hypertrophy, vessel hyperinnervation and elevated nerve growth factor

1. Secretion of nerve growth factor (NGF) by cultured vascular smooth muscle cells (VSMC) derived from spontaneously hypertensive rats (SHR) and the normotensive Wistar-Kyoto (WKY) strain was measured via two site immunoassay (ELISA). 2. Basal NGF secretion rates of quiescent SHR VSMC in serum-free culture medium were elevated compared to similar WKY VSMC. 3. SHR VSMC displayed increased NGF secretion in response to activation of sympathetic neurotransmitter receptors while VSMC of WKY were largely unresponsive to the agents (phenylephrine, isoproterenol, alpha-beta-methyl ATP, neuropeptide Y). 4. Mitogenic stimulation with platelet-derived growth factor (PDGF) raised SHR NGF secretion rates almost three times more than PDGF increased WKY secretion. 5. SHR VSMC also failed to demonstrate normal inhibitory control over NGF secretion seen in WKY and previously in Sprague-Dawley and Wistar strain VSMC with adenylate cyclase activation and down-regulation of protein kinase C. High concentrations of forskolin stimulated, instead of inhibiting, secretion in SHR. Stimulation was also seen after pretreatment with phorbol ester for 24 h while this inhibited secretion in the WKY. 6. These results confirm that the SHR VSMC are hyperresponsive to growth stimuli such as contractile agonists and mitogens. This hyperresponsiveness includes an abnormal control over NGF secretion such that normally inhibitory treatments stimulate NGF output in the SHR. 7. Because the SHR demonstrates important defects in the major intracellular growth-signalling systems that also regulate NGF output and vessel innervation, the predicted result of the defects is a destructive feed-forward cycle of growth and innervation. This is the SHR phenotype in vivo.

Nerve growth factor, vessel innervation and hypertensive progression in the inbred Dahl SS/Jr and SR/Jr rats

1. To test whether the inbred Dahl salt-sensitive hypertensive rat strain shares disturbed vessel innervation with the spontaneously hypertensive rat (SHR) model, highly innervated and sparsely innervated tissues from the SR/Jr and SS/Jr strains at several ages were assayed for tissue norepinephrine (NE) content and nerve growth factor (NGF). 2. Only two significant differences were found: (i) 1 week old SS/Jr rat kidneys had more NGF than SR/Jr kidneys; and (ii) six week old mesenteric arteries from SS/Jr contained significantly more NE than those in the SR/Jr animals. 3. The differences are in the expected direction for vessel hyperinnervation as a consequence of high vessel NGF, but the data do not support the hypothesis of a central role for vessel NGF and innervation in the hypertensive progression of the Dahl strain. The vessels of young Dahl inbred rat strains do not display the same degree of vessel hyperinnervation associated with hypertension as found in the young SHR compared to WKY strains. 4. The Dahl strain may lack the disturbed NGF metabolism of the SHR. This might suggest that the Dahl inbred strains and the SHR represent two distinct genetic mechanisms that predispose to hypertension via essentially independent processes and that all forms will evidence at least mildly altered vessel innervation.

Protein kinase C in cyclic stretch-induced nerve growth factor production by urinary tract smooth muscle cells

Cyclic stretch of cultured urinary tract smooth muscle cells has been used to mimic some of the events that occur with bladder obstruction. The stretch stimulus induces production of nerve growth factor (NGF), which has been implicated in changes in bladder innervation. Stretch-induced NGF production was blocked by actinomycin. Involvement of protein kinase C (PKC) in the stretch-induced NGF production is strongly suggested by the following observations. Phorbol ester activators of PKC mimicked the stretch response as did platelet-derived growth factor (PDGF), which acts, in part, through generation of endogenous diacylglycerols. Both stretch- and PDGF-induced NGF production were blocked by prolonged incubation with phorbol ester to downregulate PKC. Western blot analysis confirmed partial downregulation of the Ca(2+)-dependent PKC-alpha and PKC-beta 1 and near complete downregulation of the Ca(2+)-independent PKC isozymes delta, epsilon, and zeta. The involvement of PKC in transducing a physical stimulus (stretch) into a biochemical response (NGF production) has implications for novel types of therapeutic intervention in ailments such as bladder obstruction.

The influence of the renin angiotensin system on abnormal expression of nerve growth factor in the spontaneously hypertensive rat

1. The levels of the neurotrophic factor, nerve growth factor (NGF) in the mesenteric vascular bed of the spontaneously hypertensive rat (SHR) were greater than those in the corresponding vascular bed of normotensive Wistar-Kyoto rats (WKY). 2. Administration of angiotensin II (200 ng/kg per min, by minipump) for 2 weeks to juvenile WKY rats increased the levels of NGF in the mesenteric vasculature to those seen in untreated SHR. 3. Administration of the angiotensin II receptor antagonists losartan (30 mg/kg per day, p.o.) or PD144277 (10 mg/kg per day, p.o.) to juvenile SHR for 4 weeks reduced the levels of NGF such that they were indistinguishable from the values obtained for normotensive WKY rats. 4. The results confirm the elevated level of NGF in the mesenteric vasculature of the SHR and suggest that angiotensin II may play a role in regulating the abnormal concentrations of the protein in this tissue.

Regulation of rat sympathetic nerve density by target tissues and NGF in maturity and old age

Previous studies in our laboratory using a transplantation model have shown that target tissues of some autonomic neurons, including cerebral blood vessels, exert a controlling influence on nerve fibre loss in old age. The present study was undertaken in order to discover whether the influence of targets extends to controlling age changes in specific populations of nerves. In old rats, we have demonstrated a significant decrease of approximately 50% in the sympathetic innervation of middle cerebral arteries, using tyrosine hydroxylase-like immunoreactivity. Following transplantation, tyrosine hydroxylase-like immunoreactive nerve density on both young and old implanted middle cerebral arteries mirrored the nerve densities seen in normal, non-transplanted vessels. Furthermore, implanted tissue from old donors became reinnervated with a nerve density approximately 50% less than that of young implanted vessels. Treatment of transplants with nerve growth factor, however, was able to reverse these age changes and restore the sympathetic innervation of aged middle cerebral arteries to levels above those seen in young middle cerebral arteries. These results suggest that the pattern and density of sympathetic innervation that the middle cerebral artery receives is determined by the target rather than by the neurons supplying the tissue. The ability of nerve growth factor to induce regrowth in sympathetic neurons innervating ageing target tissues implies that age-related neuronal atrophy may be due to reduced synthesis or availability of target-derived neurotrophic factors.

On the plasticity of the cerebellar renin-angiotensin system: localization of components and effects of mechanical perturbation

This study focuses on the renin-angiotensin system (RAS) in the cerebellar cortex and changes within this system after mechanically induced cerebellar injury. Using radioactive and non-radioactive in situ hybridization and immunocytochemistry angiotensinogen mRNA, angiotensinogen, angiotensin II and, for the first time, N-terminal angiotensin fragment (1-7) immunoreactivities, respectively, were demonstrated in the rat cerebellum. Angiotensinogen mRNA and angiotensinogen immunoreactivity (IR) were both present in glial cell populations of all layers, especially in the Purkinje and granular cell layers and within the cerebellar nuclei. Angiotensin II IR was demonstrated in glial cell populations in all layers using a monoclonal angiotensin II antibody, while with a polyclonal angiotensin II antiserum (Denise) some Purkinje cell bodies were labelled. After lesioning the cerebellar cortex mechanically by an injection cannula a strong increase in angiotensinogen gene expression as well as in angiotensin II and angiotensin (1-7) immunoreactivities were observed in the glial cell populations. Furthermore, putative Bergmann glial processes, as indicated from the morphological appearance became strongly angiotensin II and angiotensinogen immunoreactive in the region close to the mechanically induced lesion. It could inter alia be demonstrated for the first time using confocal laser microscopy of ANG II IR and GFAP IR that ANG II in vivo in the intact cerebellar cortex is present in astroglial processes in the molecular layer and presumably secreted into the extracellular space in form of small spheric bodies and/or taken up by other cell types. In contrast, the N-terminal fragment angiotensin (1-7) IR was restricted to the glial cell populations and appeared only after the lesion event. Thus, it is suggested that the cerebellar RAS shows marked changes in response to mechanically induced lesions. The expression of angiotensinogen as well as the production of angiotensinogen IR and angiotensin II like IR is even after mechanical lesion restricted to astrocytes, i.e., cerebellar astrocytes and putative Bergmann glial cells, and in case of immunoreactivities it spreads to the radially oriented Bergmann glial processes in the molecular layer.

Immunohistochemical localization of the high-affinity NGF receptor (gp140-trkA) in the adult human dorsal root and sympathetic ganglia and in the nerves and sensory corpuscles supplying digital skin

BACKGROUND

Nerve growth factor (NGF) is produced in target tissues of sympathetic and neural-crest derived sensory neurons, including skin, to provide them trophic support. The biological effects of NGF on responsive cells are mediated by specific high-affinity receptors. Recently, a protein tyrosine kinase of congruent to 140 kDa molecular weight, encoded by the proto-oncogene trkA, has been identified as the high-affinity NGF receptor (gp140-trkA). The present work was undertaken to study the localization of gp140-trkA-like immunoreactivity (IR) in human peripheral ganglia (sympathetic and dorsal root ganglia), and in glabrous skin.

METHODS

Lumbar dorsal root ganglia, para- and prevertebral sympathetic ganglia, and digital glabrous skin were studied immunohistochemically using a rabbit anti-gp140-trkA polyclonal antibody. In order to accurately establish the localization of gp140-trkA IR, the neurofilament proteins and S-100 protein were studied in parallel in: (1) sensory and sympathetic ganglia, to label neuron cell bodies and satellite or supporting cells, respectively; (2) human skin, to label axons, Schwann and related cells within nerves and sensory corpuscles. Moreover, a quantitative study (neuron size, intensity of immunostaining) was carried out on sympathetic and dorsal root ganglia neuron cell bodies.

RESULTS

A specific gp140-trkA-like IR was found in: (1) a subpopulation (65%) of primary sensory neuron cell bodies, including most of the large-sized ones but also small- and intermediate-sized ones; (2) most of sympathetic neuron cell bodies (82%); (3) the perineurial cell, Schwann cells, and large axons of the nerve trunks supplying digital skin; (4) the lamellar cells of Meissner corpuscles; (5) the central axon, inner-core, outer-core, and capsule of Pacinian corpuscles. In addition, the occurrence of gp140-trkA-like IR was observed in some non-nervous tissues of the skin, including epidermis (mainly in the basal layer), sweat glands, and arterial blood vessels.

CONCLUSIONS

Present results provide evidence for the localization of gp140-trkA-like IR in: (1) nerve cells which are known to be NGF-responsive, and (2) non-nervous cutaneous tissues which are innervated by NGF-dependent peripheral neurons. These findings suggest that, in addition to the well-established role of NGF on sensory and sympathetic neurons, this neurotrophin may be able to regulate some other functions on non-nervous cells which are targets for NGF-dependent peripheral neurons.

Neural input regulates tissue NGF and growth of the adult rat urinary bladder

To gain insight into the effect of innervation on neurotrophin production, NGF levels in the urinary bladder were measured following unilateral ganglionectomy (bladder denervation) or separation of the post-ganglionic bladder neurons from the central nervous system of the adult rat (bladder and ganglion decentralization). These interruptions of the neural input to half of the bladder caused histological evidence of smooth muscle growth, increased bladder weight (denervation-3 weeks: 98.6 +/- 6 mg; decentralization-3 weeks: 94.0 +/- 7 mg vs. control: 79.6 +/- 4 mg, P < 0.05), transient increases in tissue NGF up to 10-fold (1.99 +/- 0.65 pg NGF/bladder control vs. 20.24 +/- 0.53 (P < 0.05) denervated, ipsilateral, 1 week) and hypertrophy of the neurons in the pelvic ganglia supplying the bladder (control: 340 +/- 4.4 microns2; denervated-3 weeks: 530 +/- 6.8 microns2, P < 0.05; decentralized-3 weeks: 463 +/- 6.8 microns2, P < 0.05). These data suggest that neural input has a significant role in regulating growth of the bladder. Furthermore, the findings show that innervation influences tissue levels of NGF in the bladder.

NGF, bFGF and CNTF increase survival of major pelvic ganglion neurons cultured from the adult rat

The responsiveness of cultured major pelvic ganglion (MPG) neurons, isolated from adult rats, to nerve growth factor (NGF), basic fibroblastic growth factor (bFGF) and ciliary neuronotrophic factor (CNTF) was tested using in vitro survival assay. MPG neurons respond to NGF with increased survival (+35 +/- 13.3%, mean +/- S.E.), a response completely blocked by antibodies specific to NGF. bFGF (+85 +/- 9.6%) and CNTF (+10.5 +/- 0.5%) also augment survival of MPG neurons in vitro. The effect of bFGF was partially blocked by bFGF antibody. Anti-NGF antibody reduced neuronal survival by 25 +/- 4.1% in conditioned medium from cultures of bladder smooth muscle, suggesting bladder produces NGF. Combining antibodies against NGF and bFGF reduced survival by 19 +/- 0.5% in medium supplemented with bladder extracts, suggesting the extracts contain neurotrophic activity in addition to NGF. These results support the hypothesis that neurons regulating bladder function respond to NGF and other growth factors. Therefore, previously documented changes in bladder neurotrophic factors following hypertrophy, inflammation and injury may elicit growth or change in the autonomic nervous system.