Nerve growth factor mRNA content parallels altered sympathetic innervation in the spontaneously hypertensive rat

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.

Nerve Growth Factor: Early Studies and Recent Clinical Trials

Since its discovery, nerve growth factor (NGF) has long occupied a critical role in developmental and adult neurobiology for its many important regulatory functions on the survival, growth and differentiation of nerve cells in the peripheral and central nervous system. NGF is the first discovered member of a family of neurotrophic factors, collectively indicated as neurotrophins, (which include brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin 4/5). NGF was discovered for its action on the survival and differentiation of selected populations of peripheral neurons. Since then, an enormous number of basic and human studies were undertaken to explore the role of purified NGF to prevent the death of NGF-receptive cells. These studies revealed that NGF possesses important therapeutic properties, after topical administration, on human cutaneous pressure ulcer, corneal ulcers, glaucoma, retinal maculopathy, Retinitis Pigmentosa and in pediatric optic gliomas and brain traumas. The aim of this review is to present our previous, recent and ongoing clinical studies on the therapeutic properties of NGF.

Kidney Cografts Enhance Fiber Outgrowth from Ventral Mesencephalic Grafts to the 6-Ohda–Lesioned Striatum, and Improve Behavioral Recovery

Recent studies have demonstrated the presence of many different neurotrophic factors in the developing and adult kidney. Due to its production of this mixture of neurotrophic factors, we wanted to investigate whether fetal kidney tissue could be beneficial for neuritic fiber growth and/or cell survival in intracranial transplants of fetal ventral mesencephalic tissue (VM). A retrograde lesion of nigral dopaminergic neurons was performed in adult Fischer 344 male rats by injecting 6-hydroxydopamine into the medial forebain. The animals were monitored for spontaneous locomotor activity in addition to apomorphine-induced rotations once a week. Four weeks following the lesion, animals were anesthetized and embryonic day 14 VM tissue from rat fetuses was implanted stereotaxically into the dorsal striatum. One group of animals received a cograft of kidney tissue from the same embryos in the same needle track. The animals were then monitored behaviorally for an additional 4 months. There was a significant improvement in both spontaneous locomotor activity (distance traveled) and apomorphine-induced rotations with both single VM grafts and VM–kidney cografts, with the VM–kidney double grafts enhancing the motor behaviors to a significantly greater degree. Tyrosine hydroxylase (TH) immunohistochemistry and image analysis revealed a significantly denser innervation of the host striatum from the VM–kidney cografts than from the single VM grafts. TH-positive neurons were also significantly larger in the cografts compared to the single VM grafts. In addition to the dense TH-immunoreactive innervation, the kidney portion of cografts contained a rich cholinergic innervation, as evidenced from antibodies against choline acetyltransferase (ChAT). The striatal cholinergic cell bodies surrounding the VM–kidney cografts were enlarged and had a slightly higher staining density for ChAT. Taken together, these data support the hypothesis that neurotrophic factors secreted from fetal kidney grafts stimulated both TH-positive neurons in the VM cografts and cholinergic neurons in the host striatum. Thus, these factors may be combined for treatment of degenerative diseases involving both dopaminergic and cholinergic neurons.

Pubertal administration of antiserum against nerve growth factor regresses renal vascular remodeling in spontaneously hypertensive rats

To investigate the role of nerve growth factor (NGF) in the development of hypertensive renal vascular remodeling, antiserum against NGF (anti-NGF) or vehicle was injected at 3 weeks of age in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats (n = 9 for each treatment in each strain). Flow-pressure (F-P) and pressure-glomerular filtration rate (P-GFR) relationships at vasodilated perfused kidneys were determined at 10 weeks of age. In the vehicle rats, blood pressure, renal noradrenaline content, the gradient of F-P (minimal vascular resistance at pre- and post-glomerular vasculature) and the X-intercept of P-GFR (preglomerular : postglomerular vascular resistance ratio) were greater in SHR than in WKY rats, although the gradient of P-GFR (glomerular filtration capacity) did not differ significantly between the strains. Blood pressure and renal noradrenaline content were lower in SHR receiving anti-NGF than in SHR receiving vehicle, although such difference was not observed in WKY rats. The gradient of F-P was less but the gradient of P-GFR was greater in SHR receiving anti-NGF compared with SHR receiving vehicle, although the similar differences did not occur in WKY rats. Blood pressure and renal noradrenaline content remained greater in SHR treated with anti-NGF compared with WKY rats treated with vehicle; however, the gradient of F-P did not differ significantly between them. Contrary, anti-NGF did not affect the X-intercept of P-GFR in either strain. In conclusion, NGF could contribute to the genesis of renal vascular remodeling, at least in part, through modification of renal sympathetic activity and blood pressure in SHR.

The biology of neurotrophins: cardiovascular function

This chapter addresses the role of neurotrophins in the development of the heart, blood vessels, and neural circuits that control cardiovascular function, as well as the role of neurotrophins in the mature cardiovascular system. The cardiovascular system includes the heart and vasculature whose functions are tightly controlled by the nervous system. Neurons, cardiomyocytes, endothelial cells, vascular smooth muscle cells, and pericytes are all targets for neurotrophin action during development. Neurotrophin expression continues throughout life, and several common pathologies that impact cardiovascular function involve changes in the expression or activity of neurotrophins. These include atherosclerosis, hypertension, diabetes, acute myocardial infarction, and heart failure. In many of these conditions, altered expression of neurotrophins and/or neurotrophin receptors has direct effects on vascular endothelial and smooth muscle cells in addition to effects on nerves that modulate vascular resistance and cardiac function. This chapter summarizes the effects of neurotrophins in cardiovascular physiology and pathophysiology.

Cardiac sympathetic hyperinnervation in deoxycorticosterone acetate-salt hypertensive rats

Sympathetic activities are elevated in the central SNSs (sympathetic nervous systems) of hypertensive animals, but it is not known whether sympathetic innervation is also elevated in the heart. Sympathetic hyper-responsiveness in hypertension may result from oxidative stress. The aim of the present study was to investigate sympathetic hyperinnervation in DOCA (deoxycorticosterone acetate)-salt hypertensive rats with established hypertension. At 4 weeks after the start of DOCA-salt treatment and uninephrectomization, male Wistar rats were randomized into three groups for 8 weeks: vehicle, NAC (N-acetylcysteine) and triple therapy (hydralazine, hydrochlorothiazide and reserpine). DOCA-salt was associated with increased oxidant release. DOCA-salt produced concentric left ventricular hypertrophy and cardiomyocyte hypertrophy. Sympathetic hyperinnervation was observed in DOCA-salt rats, as assessed by myocardial noradrenaline levels, immunofluorescent analysis of tyrosine hydroxylase, growth-associated factor 43 and neurofilament and Western blotting and real-time quantitative RT-PCR (reverse transcription-PCR) of NGF (nerve growth factor). Arrhythmic scores during programmed stimulation in DOCA-salt rats were significantly higher than those in the control rats. Triple therapy, despite being effective on BP (blood pressure), offered neither attenuated cardiomyocyte hypertrophy nor anti-arrhythmia. The effects of DOCA-salt treatment on NGF expression, sympathetic hyperinnervation and arrhythmias were attenuated by NAC. Furthermore, the effects of NAC on NGF were abolished by administering BSO (L-buthionine sulfoximine), an inhibitor of glutamate-cysteine ligase. In conclusion, DOCA-salt treatment contributes to up-regulation of NGF proteins probably through a free radical-dependent pathway in a BP-independent manner. DOCA-salt rats treated with NAC attenuate sympathetic hyperinnervation and thus show a beneficial effect on arrhythmogenic response to programmed electrical stimulation.

Hyperinnervation of mesenteric arteries in spontaneously hypertensive rats by sympathetic but not primary afferent axons

Hypertrophy of the perivascular plexus is thought to play a role in the development of hypertension in spontaneously hypertensive rats (SHR). However, it is not known whether the sympathetic varicosities are more numerous or larger, or form more neurovascular junctions. Further, a parallel hypertrophy of primary afferent terminals around the vessels might modulate any effects of hypertrophied sympathetic terminals. We have investigated the perivascular plexus around second-order mesenteric arteries of SHR and Wistar-Kyoto (WKY) rats by electron microscopy. Noradrenergic terminals were identified by the presence of small granular vesicles after chromaffin fixation, and substance P (SP+) afferent axons were identified by immunohistochemistry. The numbers of noradrenergic axon and varicosity profiles were higher (48 and 25%, respectively) in SHR than in WKY rats, and the majority lay closer to the medio-adventitial border. In contrast, there was no difference in the numbers of SP+ axons. Sympathetic and SP+ varicosities were indistinguishable in size, shape, vesicle content and mitochondrion content between each other and between the strains. However, both the number of neuromuscular junctions and the proportion of varicosities that formed them in SHR arteries were more than double those in WKY vessels. The data clearly show that hyperinnervation in SHR is specific for noradrenergic axons.

Structural and neurochemical features of postganglionic sympathetic neurons in the superior mesenteric ganglion of spontaneously hypertensive rats

Postganglionic sympathetic neurons, which are exquisitely sensitive to small changes in levels of target-derived nerve growth factor (NGF), express two transmembrane receptors: 1) the trkA receptor mediates neuron survival and neurite outgrowth; and 2) the p75 neurotrophin receptor (p75NTR) enhances neuronal responsiveness of trkA to NGF. Elevating levels of NGF induces several morphological and neurochemical alterations in sympathetic neurons, including axonal sprouting, increased levels of p75NTR mRNA relative to trkA mRNA, and increased accumulations of NGF in hypertrophied somata. Spontaneously hypertensive rats (SHR) display both elevated NGF levels and increased sympathetic axonal innervation of the mesenteric vasculature. In this investigation we assessed whether sympathetic neurons innervating the mesenteric vasculature of SHR display other features indicative of increased levels of target-derived NGF. In 5-week-old SHR, levels of both p75NTR and trkA mRNA in mesenteric sympathetic neurons were significantly elevated compared to levels in age-matched control rats. By 15 and 30 weeks of age, levels of p75NTR mRNA expression in mesenteric sympathetic neurons were similar between SHR and control rats. Accumulations of NGF were depleted in the sympathetic somata of 15- and 30-week-old SHR compared to age-matched control rats. Moreover, sympathetic neurons in SHR were not hypertrophied, as the sizes of somata were comparable between SHR and control rats. Our data illustrate that despite having augmented levels of NGF in the mesenteric vasculature, SHR do not display many of the morphological and neurochemical features that are associated with an enhanced responsiveness by sympathetic neurons to elevated levels of target-derived NGF.

Neurotrophin 3 is increased in the spontaneously hypertensive rat

OBJECTIVE

To determine whether the noradrenergic sympathetic hyperinnervation in the spontaneously hypertensive rat (SHR), a genetic model of essential hypertension, is associated with changes in neurotrophin 3 (NT3) concentrations.

METHODS

NT3 levels were measured using a sensitive enzyme-linked immunosorbent assay (ELISA) in the superior cervical ganglia (SCG), heart, mesenteric artery (MA) and blood of postnatal and mature SHR and normotensive Wistar-Kyoto (WKY) rats.

RESULTS AND CONCLUSIONS

NT3 levels in SHR are significantly higher in the SCG during the first 4 postnatal weeks, and in the heart and MA from 2 to 10 weeks of age, compared with levels in WKY rats. The elevated NT3 found in the sympathetic ganglia and hyperinnervated organs of SHR indicates that NT3 may play an important role in the development of hyperinnervation, possibly by enhancing the survival and/or nerve sprouting of sympathetic neurons.

Absence of the p75 neurotrophin receptor alters the pattern of sympathosensory sprouting in the trigeminal ganglia of mice overexpressing nerve growth factor

Sympathetic axons invade the trigeminal ganglia of mice overexpressing nerve growth factor (NGF) (NGF/p75(+/+) mice) and surround sensory neurons having intense NGF immunolabeling; the growth of these axons appears to be directional and specific (). In this investigation, we provide new insight into the neurochemical features and receptor requirements of this sympathosensory sprouting. Using double-antigen immunohistochemistry, we demonstrate that virtually all (98%) trigeminal neurons that exhibit a sympathetic plexus are trk tyrosine kinase receptor (trkA)-positive. In addition, the majority (86%) of those neurons enveloped by sympathetic fibers is also calcitonin gene-related peptide (CGRP)-positive; a smaller number of plexuses (14%) surrounded other somata lacking this neuropeptide. Our results show that sympathosensory interactions form primarily between noradrenergic sympathetic efferents and the trkA/CGRP-expressing sensory somata. To assess the contribution of the p75 neurotrophin receptor (p75(NTR)) in sympathosensory sprouting, a hybrid strain of mice was used that overexpresses NGF but lacks p75(NTR) expression (NGF/p75(-/-) mice). The trigeminal ganglia of NGF/p75(-/-) mice, like those of NGF/p75(+/+) mice, have increased levels of NGF protein and display a concomitant ingrowth of sympathetic axons. In contrast to the precise pattern of sprouting seen in the ganglia of NGF/p75(+/+) mice, sympathetic axons course randomly throughout the ganglionic neuropil of NGF/p75(-/-) mice, forming few perineuronal plexuses. Our results indicate that p75(NTR) is not required to initiate or sustain the growth of sympathetic axons into the NGF-rich trigeminal ganglia but rather plays a role in regulating the directional patterns of axon growth.

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.

Nerve growth factor gene locus explains elevated renal nerve growth factor mRNA in young spontaneously hypertensive rats

Nerve growth factor (NGF) controls the growth of sympathetic nerves and is increased in young spontaneously hypertensive rats (SHR). The NGF gene has been linked genetically with hypertension in the SHR strain and may explain high NGF mRNA levels. To test for genetic linkage between the NGF gene and its expression in vivo, we examined renal NGF mRNA levels in male SHR, control Donryu rats (DRY), and F2 rats derived from SHR and DRY at ages 2, 4, 10, and 20 weeks. Tail-cuff blood pressure was measured at 4, 10, and 20 weeks of age. NGF mRNA levels in SHR (NGF genotype: SS) were higher than those in DRY (NGF genotype: DD) at 2, 4, and 10 weeks of age (P<0.0001) but the same at 20 weeks of age. In the F2 generation, the S allele was associated with significantly (P=0.01) higher renal NGF mRNA levels at 2 weeks of age. Mean NGF mRNA levels fell (P=0.01) with age in F2 rats, and the difference between SS and DD genotype F2 rats diminished at older ages and was not significant. In F2 rats there was a positive correlation between the number of NGF S alleles inherited and tail-cuff pressure (P<0.007). Our findings indicate that the NGF locus is an important regulator of NGF mRNA levels. It is likely that mutations in or near the NGF gene explain in part high early NGF gene expression in SHR.

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.

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.

Pharmacology of neurotrophic factors

The field of neurotrophic factor pharmacology emerged during the past decade with the discovery that these proteins can counteract neuronal atrophy and death in the adult nervous system. These concepts are being tested in clinical trials. Therapeutic use of neurotrophic proteins seems practical for diseases of the peripheral nervous system (PNS), where they can be given by systemic administration. For diseases of the CNS, special administration strategies will have to be developed to deliver the neurotrophic factors into the brain. The development of small molecule mimetics represents an alternative approach that is actively pursued to provide brain-penetrant neurotrophics.

Mutation of low affinity nerve growth factor receptor gene is associated with the hypertensive phenotype in spontaneously hypertensive inbred rat strains

We previously reported a missense mutation in the low affinity nerve growth factor receptor (LNGFR) gene of spontaneously hypertensive rats (SHR), proposing this gene as a promising candidate in genetic hypertension. In this study we provide further support for implicating this gene in genetic hypertension using two new inbred strains, WKHT and WKHA rats. These strains originated from crossbreeding SHR rats with normotensive Wistar-Kyoto rats (WKY): WKHT rats are hypertensive but not hyperactive, and WKHA rats are hyperactive but not hypertensive. Nucleotide sequence analysis of the LNGFR gene revealed that WKHT has the same mutation as SHR, whereas WKHA has the normal sequence, as seen in WKY. These results support our original hypothesis that the mutated LNGFR gene is linked to hypertension, since the mutation had co-segregated with the hypertensive trait, and not hyperactivity trait of SHR.

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.

Enhanced vascular neuropeptide Y-immunoreactive innervation in two hypertensive rat strains

Considerable evidence indicates an enhanced sympathetic innervation of resistance arterial smooth muscle in the spontaneously hypertensive rat (SHR) compared with its normotensive Wistar-Kyoto (WKY) control. In addition to sympathetic hyperinnervation, an increased vascular innervation by neuropeptide Y-containing fibers, which are known to exert a vasoconstrictive and trophic action in vascular smooth muscle, has also been described. In addition to genetic hypertension, the SHR expresses hyperactive behavior and hyperreactivity to stress. To determine whether the enhanced neuropeptide Y-immunoreactive vascular innervation is specifically associated with hypertension and/or these behavioral abnormalities, four genetically related, inbred rat strains were used: SHR, which are hypertensive and hyperactive; WKY rats, which are neither hypertensive nor hyperactive; WKHA, which are hyperactive but normotensive; and WKHT, which are hypertensive but not hyperactive. The present study demonstrated that whereas the hypertensive strains (SHR and WKHT) exhibited smooth muscle hypertrophy in both superior mesenteric and caudal arteries in adulthood (10 months) but not at a prehypertensive age (1 month), both arteries exhibited significantly increased neuropeptide Y-immunoreactive innervation at both ages. It was further observed that the mesenteric artery in WKHA, a normotensive strain, had significant smooth muscle hypertrophy at 10 months; however, neuropeptide Y innervation in this artery was no different from that of WKY controls. The findings indicate that there is a cosegregation of neuropeptide Y hyperinnervation of the vasculature with the hypertensive phenotype, evident as early as 1 month of life in the hypertensive strains, and this should be considered further as a contributory factor in genetic hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Neurotrophic factor therapy for nervous system degenerative diseases

The ability of neurotrophic factors to regulate developmental neuronal survival and adult nervous system plasticity suggests the use of these molecules to treat neurodegeneration associated with human diseases. Solid rationales exist for the use of NGF and neurotrophin-3 in the treatment of neuropathies of the peripheral sensory system, insulin-like growth factor and ciliary neurotrophic factor in motor neuron atrophy, and NGF in Alzheimer's disease. Growth factors have been identified for neurons affected in Parkinson's disease, Huntington's disease, and acute brain and spinal cord injury. Various strategies are actively pursued to deliver neurotrophic factors to the brain, and develop therapeutically useful molecules that mimic neurotrophic factor actions or stimulate their production or receptor mechanisms.