Thrombin regulates nerve growth factor secretion from vascular, but not bladder smooth muscle cells

The production of nerve growth factor (NGF) in peripheral organs may play a role in the pathophysiology of hypertension and in obstructive disorders of the bladder outlet. We have been examining the cellular processes of NGF delivery and secretion in smooth muscle. NGF secretion from vascular smooth muscle cells (VSMCs) cultured from genetically hypertensive (WKHT), hyperactive (WKHA), and a control Wistar rat strain were assayed using a two-site ELISA of the culture media. Bladder smooth muscle cells (BSMCs) from the Wistar strain were also studied. The serine protease, thrombin, increased NGF secretion from all types of VSMCs but had no effect on Wistar BSMCs. The thrombin-mediated increase in NGF secretion was prevented by actinomycin D and cycloheximide, suggesting that RNA transcription and protein synthesis are required. The effect of thrombin was additive with a phorbol ester-induced elevation in NGF secretion rates from 4 to 6 h and was attenuated by a 24-h downregulation of protein kinase C. These results suggest that extracellular protease activity may regulate NGF secretion in smooth muscle. Thrombin may act in response to vascular injury, increasing NGF secretion from VSMCs, initiating VSMC migration, and preparing the VSMCs for reinnervation following an insult.

Calcium homeostasis and reactive oxygen species production in cells transformed by mitochondria from individuals with sporadic Alzheimer's disease

Alzheimer's disease (AD) is associated with defects in mitochondrial function. Mitochondrial-based disturbances in calcium homeostasis, reactive oxygen species (ROS) generation, and amyloid metabolism have been implicated in the pathophysiology of sporadic AD. The cellular consequences of mitochondrial dysfunction, however, are not known. To examine these consequences, mitochondrially transformed cells (cybrids) were created from AD patients or disease-free controls. Mitochondria from platelets were fused to rho0 cells created by depleting the human neuroblastoma line SH-SY5Y of its mitochondrial DNA (mtDNA). AD cybrids demonstrated a 52% decrease in electron transport chain (ETC) complex IV activity but no difference in complex I activity compared with control cybrids or SH-SY5Y cells. This mitochondrial dysfunction suggests a transferable mtDNA defect associated with AD. ROS generation was elevated in the AD cybrids. AD cybrids also displayed an increased basal cytosolic calcium concentration and enhanced sensitivity to inositol-1,4, 5-triphosphate (InsP3)-mediated release. Furthermore, they recovered more slowly from an elevation in cytosolic calcium induced by the InsP3 agonist carbachol. Mitochondrial calcium buffering plays a major role after this type of perturbation. beta-amyloid (25-35) peptide delayed the initiation of calcium recovery to a carbachol challenge and slowed the recovery rate. Nerve growth factor reduced the carbachol-induced maximum and moderated the recovery kinetics. Succinate increased ETC activity and partially restored the AD cybrid recovery rate. These subtle alterations in calcium homeostasis and ROS generation might lead to increased susceptibility to cell death under circumstances not ordinarily toxic.

Regulation of nerve growth factor secretion in smooth muscle cells cultured from rat bladder body, base and urethra

PURPOSE

Interest in the regulation of nerve growth factor (NGF) production in the urinary tract derives from its probable involvement in obstructive, inflammatory and developmental disorders. This study examines receptor-mediated stimuli that alter NGF production in cells of the lower urinary tract.

MATERIALS AND METHODS

Cells were isolated and cultured from the bladder body, base and urethra, confirmed as smooth muscle type by alpha-actin expression, and examined for growth rate and NGF secretion in response to autonomic agonists, cytokines, neuropeptides and growth factors. NGF secreted into the culture medium was quantitated via 2-site enzyme-linked immunoassay. Regional tissue contents of NGF and norepinephrine (NE) were also measured. Only statistically significant differences (Student's t test, p <0.05) are reported.

RESULTS

Cultured urinary tract cells derived from different regions varied in growth rate and NGF secretory activity. Bladder body secreted less NGF than base, and base less than urethra. A similar gradient in growth rate occurred in vitro, with urethral cells most active. However, no regional differences were found in bladder tissue NGF content despite significant variations in NE levels. Platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) were among the most potent stimuli to NGF production by cultured cells while cAMP linked receptors and eicosinoids inhibited NGF output.

CONCLUSIONS

A complex system of regionally specific and stimulus-specific control regulates the production of NGF by urinary tract cells. While tissue levels of NGF do not correlate with the density of noradrenergic innervation, bladder innervation is sufficiently dynamic to respond to changes in NGF production and to participate in pathophysiology.

MPP+ induced apoptotic cell death in SH-SY5Y neuroblastoma cells: an electron microscope study

PD is a common, late-onset neurodegenerative disorder that results in part from the gradual loss of dopaminergic neurons in the substantia nigra pars compacta. The neurotoxin MPTP can induce PD-like clinical symptomatology and neuropathological destruction and, thus, has been used as a PD model. The human neuroblastoma cell line SH-SY5Y possesses many of the qualities of human neurons and, as such, has served as a model for them. Apoptosis is the mode of cell death induced in SH-SY5Y cells by MPTP, and this was confirmed with nick end labeling and bisbenzimide staining. Transmission electron microscopic analysis of the ultrastructural changes occurring in neurotoxin exposed SH-SY5Ys revealed many morphological characteristics consistent with apoptosis. These changes included plasmalemmal blebbing, altered cytosolic density, nuclear condensation and fragmentation, pronounced vacuole formation, ribosomal dispersion, and the disappearance of the golgi complex, microtubules, and smooth endoplasmic reticulum. Limited amounts of rough endoplasmic reticulum and mitochondria exhibited normal morphology throughout the apoptotic changes but then were disrupted during secondary necrotic changes. The in vitro induction of apoptosis by a parkinsonism neurotoxin might be reflective of the mechanisms of in vivo nigral degeneration occurring during PD.

Altered calcium homeostasis in cells transformed by mitochondria from individuals with Parkinson's disease

Parkinson's disease may be linked to defects in mitochondrial function. Mitochondrially transformed cells (cybrids) were created from Parkinson's disease patients or disease-free controls. Parkinson's disease cybrids had 26% less complex I activity, but maintained comparable basal calcium and energy levels. Parkinson's disease cybrids recovered from a carbachol-induced increase in cytosolic calcium 53% more slowly than controls even with lanthanum and thapsigargin blockade. Inhibition of complex I with the Parkinson's disease-inducing metabolite 1-methyl-4-phenylpyridinium (MPP+) similarly reduced the rate of recovery after carbachol. This MPP(+)-induced reduction in recovery rates was much more pronounced in control cybrids than in Parkinson's disease cybrids. Parkinson's disease cybrids had less carbonyl cyanide m-chlorophenylhydrazone-releasable calcium. Bypassing complex I with succinate partially restored Parkinson's disease cybrid, and MPP+ suppressed control cybrid recovery rates. The subtle alteration in calcium homeostasis of Parkinson's disease cybrids may reflect an increased susceptibility to cell death under circumstances not ordinarily toxic.

Synergistic increase in nerve growth factor secretion by cultured vascular smooth muscle cells treated with injury-related growth factors

Vascular smooth muscle (VSM) cells comprise one of the primary targets of the sympathetic nervous system and have been shown to secrete nerve growth factor (NGF). There is increasing evidence that changes in the levels of NGF in the adult may underlie certain pathological conditions. To investigate the potential role of altered NGF production in vascular disease, VSM cell cultures were treated with injury-related growth factors and the culture medium was assayed for NGF using a two-site enzyme-linked immunosorbent assay (ELISA). Platelet-derived growth factor (PDGF), a potent VSM mitogen, caused a dose-dependent increase in NGF secretion. After 4 hr, PDGF-treated cultures contained 10 times more NGF than control cultures. NGF release remained elevated for 48 hr, but the peak secretion occurred in the first 12 hr after treatment. Transforming growth factor beta (TGF-beta) caused a fivefold increase in NGF at 4 hr when added alone, but synergized with PDGF yielding approximately 50 times more NGF than control cultures. TGF-beta and epidermal growth factor (EGF) also displayed synergism. In contrast, basic fibroblast growth factor (bFGF), which had a modest effect alone, appeared to be additive with TGF-beta. Similarly, interleukin 1-beta (IL-1 beta), which mediates increased NGF synthesis in sciatic nerve lesions (Lindholm et al.: Nature 330:658-659, 1987), showed no synergism with TGF-beta.

Origin and functional consequences of the complex I defect in Parkinson's disease

The mitochondrial electron transport enzyme NADH:ubiquinone oxidoreductase (complex I), which is encoded by both mitochondrial DNA and nuclear DNA, is defective in multiple tissues in persons with Parkinson's disease (PD). The origin of this lesion and its role in the neurodegeneration of PD are unknown. To address these questions, we created an in vitro system in which the potential contributions of environmental toxins, complex I nuclear DNA mutations, and mitochondrial DNA mutations could be systematically analyzed. A clonal line of human neuroblastoma cells containing no mitochondrial DNA was repopulated with mitochondria derived from the platelets of PD or control subjects. After 5 to 6 weeks in culture, these cytoplasmic hybrid (cybrid) cell lines were assayed for electron transport chain activities, production of reactive oxygen species, and sensitivity to induction of apoptotic cell death by 1-methyl-4-phenyl pyridinium (MPP+). In PD cybrids we found a stable 20% decrement in complex I activity, increased oxygen radical production, and increased susceptibility to 1-methyl-4-phenyl pyridinium-induced programmed cell death. The complex I defect in PD appears to be genetic, arising from mitochondrial DNA, and may play an important role in the neurodegeneration of PD by fostering reactive oxygen species production and conferring increased neuronal susceptibility to mitochondrial toxins.

Immunity to nerve growth factor prevents afferent plasticity following urinary bladder hypertrophy

PURPOSE

The goal of this investigation was to examine the effect of immunity to nerve growth factor (NGF) on alterations in sensory nerves from the urinary bladder in the dorsal root ganglia (DRG) and their projections to the L6/S1 spinal cord following urethral obstruction in the rat.

MATERIALS AND METHODS

Female Wistar rats were immunized to murine 2.5S NGF, then obstructed by partial urethral ligation for 6 weeks. Retrograde axonal tracing with FluoroGold and WGA-HRP was used to measure areas of bladder DRG cells and afferent projections in the sacral spinal cord. Multiunit activity on bladder nerves allowed recording of micturition reflexes. Immunohistochemical staining for growth associated protein (GAP)-43 in the sacral parasympathetic nucleus (SPN) was used to assess potential growth or activity of axons in the spinal cord. Voiding frequencies were then measured in awake obstructed and NGF immune-obstructed rats.

RESULTS

Immunity to NGF prevented obstruction-induced hypertrophy of DRG neurons, reduced retrograde axonal labeling of sacral afferent projections, eliminated enhancement of a spinal micturition reflex and abolished the increased GAP-43 expression in the SPN. Immunity to NGF prevented the urinary frequency that accompanies obstruction.

CONCLUSIONS

Our results demonstrate that obstruction of the bladder elicits structural and functional plasticity in afferents as a result of ongoing neurotrophic interactions. Neurotrophic interactions offer a potential mechanism whereby symptoms and bladder hyperactivity develop with obstruction associated with benign prostatic hyperplasia.

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.

Altered regulation of nerve growth factor secretion by cultured VSMCs from hypertensive rats

Vascular tissues from spontaneously hypertensive rats (SHR) exhibit increased nerve growth factor (NGF) levels and increased density of sympathetic innervation compared with those from normotensive Wistar-Kyoto (WKY) rats. The present study asked whether basal NGF secretion or secretion elicited by agents analogous to sympathetic neurotransmitters differ in cultured vascular smooth muscle cells (VSMCs) from SHR and WKY rats. VSMCs were maintained in serum-free medium (SFM) for 72 h and then treated and sampled at 4, 6, 8, and 24 h. Conditioned medium was assayed for NGF using a two-site enzyme-linked immunoassay. NGF secretion by SHR (19.2 +/- 4.6 pg.well-1.48 h-1) and WKY VSMCs (16.7 +/- 5.4 pg.we..-1.48 h-1) was similar in cultures grown in serum-containing medium, whereas SHR VSMCs maintained in SFM secrete more NGF than WKY VSMCs (9.1 +/- 1.9 vs. 2.9 +/- 0.4 pg.well-1.24 h-1, respectively). Treatment of cultures with phenylephrine (0.1-10 microM), neuropeptide Y (1-1,000 nM), or alpha beta-methyleneadenosine 5'-triphosphate (10 and 100 microM) had no effect on NGF secretion by WKY VSMCs, while increasing NGF secretion by SHR VSMCs. Treatment with isoproterenol (0.1-10 microM) decreased NGF secretion by WKY VSMCs but not SHR VSMCs. These data indicate that the regulation of NGF secretion by sympathetic neurotransmitter receptors is different for cultured VSMCs from SHR and WKY rats. If similar differences exist in vivo, they could account for the alterations in NGF levels and sympathetic innervation that are observed.

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.

Differential distribution of purine metabolizing enzymes between glia and neurons

Previous studies showed that in cultured chick ciliary ganglion neurons and CNS glia, adenosine can be synthesized by hydrolysis of 5'-AMP and that the accumulation of the adenosine degradative products inosine and hypoxanthine was significantly greater in glial than in neuronal cultures. Furthermore, previous immunochemical and histochemical studies in brain showed that adenosine deaminase and nucleoside phosphorylase are localized in endothelial and glial cells but are absent in neurons; however, adenosine deaminase may be found in a few neurons in discrete brain regions. These results suggested that adenosine degradative pathways may be more active in glia. Thus, we have determined if there is a differential distribution of adenosine deaminase, nucleoside phosphorylase, and xanthine oxidase enzyme fluxes in glia, comparing primary cultures of central and ciliary ganglion neurons and glial cells from chick embryos. Hypoxanthine-guanine phosphoribosyltransferase and production of adenosine by S-adenosylhomocysteine hydrolase activity were also examined. Our results show that there is a distinct profile of purine metabolizing enzymes for glia and neurons in culture. Both cell types have an S-adenosylhomocysteine hydrolase, but it was more active in neurons than in glia. In contrast, in glia the enzymatic activities of xanthine oxidase (443 +/- 61 pmol/min/10(7) cells), nucleoside phosphorylase (187 +/- 8 pmol/min/10(7) cells), and adenosine deaminase (233 +/- 32 pmol/min/10(7) cells) were more active at least 100, 20, and five times, respectively, than in ciliary ganglion neurons and 100, 100, and nine times, respectively, than in central neurons.

Calcium channel antagonists prevent urinary bladder growth and neuroplasticity following mechanical stress

Cytosolic Ca2+ has been postulated to regulate smooth muscle hypertrophy and growth factor production. Consistent with this hypothesis we report that the Ca2+ channel antagonists verapamil and diltiazem prevent bladder and neuronal growth in rats in response to 3 wk of urethral obstruction. Ca2+ channel blockers prevented 30-45% of the increase in bladder weight, protein, and DNA content found in obstructed animals. Similarly, these drugs produced a 15-27% reduction in area profiles for retrogradely labeled (Fluoro-Gold) motoneurons in the major pelvic ganglia and afferents in the L6-S1 dorsal root ganglia after obstruction. The reduced growth in neuronal areas was attributed, in part, to less nerve growth factor (NGF) in bladders of obstructed rats receiving verapamil (8.5 pg/bladder) or diltiazem (14.5 pg/bladder) compared with obstructed animals not given these drugs (58.2 pg/bladder). The alpha 1-adrenergic antagonist, prazosin, while decreasing voiding frequency in obstructed rats, had no significant impact on bladder weight or neuronal size. These reductions in the increase in bladder hypertrophy and NGF content may be due to altered handling of Ca2+.

Receptor-mediated stimulation and inhibition of nerve growth factor secretion by vascular smooth muscle

Nerve growth factor (NGF) is a potent neurotrophin signaling protein, the best-known member of a family of similar neurotrophins. Specific neuronal populations depend upon the neurotrophins for normal function and disturbances in NGF and neurotrophin supply have been implicated in neurodegenerative disease, diabetes, and hypertension. This report details experiments in which the hourly pattern of NGF secretion by cultured vascular smooth muscle cells is examined. Vascular smooth muscle cells are major innervation targets of the neuronal population first discovered to be NGF-dependent: the sympathetic principal neurons. The results show that arginine vasopressin (AVP), angiotensin II (AngII), and alpha-adrenergic receptor activation, all contractile stimuli, elevate NGF secretion. However, AVP dependably does so alone while AngII requires coactivation of adenosine receptors. Adenosine alone inhibits secretion and the alpha-adrenergic increase in NGF output can be antagonized by activation of beta-adrenergic receptors. A change to fresh culture medium is also a potent stimulus to increased NGF output.

Muscle membrane preparation restores sensitivity to acetylcholine in cultured chick ciliary ganglion neurons

Ciliary ganglion (CG) neurons grown in culture in the absence of muscle cells rapidly lose sensitivity to acetylcholine (ACh), while neurons grown in the presence of muscle or muscle cell membranes maintain sensitivity to ACh for extended periods of time. The present study examined whether exposure to muscle membrane preparation or stimulation of cAMP-dependent processes could restore sensitivity to ACh in cultured neurons which had lost responsiveness to ACh. CG neurons from 11- to 14-day-old chick embryos were grown on collagen substrate in the absence of muscle cells. Sensitivity to ACh was assessed by measuring peak current responses following application of ACh (IACh) to neurons under whole-cell voltage clamp. In control cultures IACh decreased from an average of 837 pA the day of plating to 145 pA following 4 days in culture. Stimulation of cAMP-dependent processes with forskolin and 3-isobutyl-1-methylxanthine (IBMX) or 8'Br-cAMP and IBMX had variable effects on IACh. These treatments increased peak IACh in some neurons maintained in culture for less than 48 h. Treatment with these agents decreased peak IACh in cultures which were more than 48 h old. Exposure of neurons, which had lost sensitivity to ACh in culture, to muscle membranes increased IACh 2- to 3-fold over 24 to 48 h. This membrane-induced restoration of sensitivity to ACh was blocked by exposure to the protein synthesis inhibitor cycloheximide. Stimulation of cAMP-dependent processes in neurons exposed to muscle membrane decreased IACh. In conclusion, these results indicate that some element associated with the membranes of muscle cells has the ability to restore ACh responsiveness to CG neurons which have become insensitive to ACh in culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Ca(2+)-independent and Ca(2+)-dependent stimulation of quantal neurosecretion in avian ciliary ganglion neurons

1. Although it is generally agreed that Ca2+ couples depolarization to the release of neurotransmitters, hypertonic saline and ethanol (ETOH) evoke neurosecretion independent of extracellular Ca2+. One possible explanation is that these agents release Ca2+ from an intracellular store that then stimulates Ca(2+)-dependent neurosecretion. An alternative explanation is that these agents act independently of Ca2+. 2. This work extends previous observations on the action of ETOH and hypertonic solutions (HOSM) on neurons to include effects on [Ca2+]i. We have looked for Ca(2+)-independent or -dependent neurosecretion evoked by these agents in parasympathetic postganglionic neurons dissociated from chick ciliary ganglia and maintained in tissue culture. The change in concentration of free Ca2+ in the micromolar range inside neurons ([Ca2+]i) was measured with indo-1 with the use of a Meridian ACAS 470 laser scanning microspectrophotometer. 3. Elevated concentration of extracellular KCl increased [Ca2+]i and the frequency of quantal events. Also, a twofold increase in osmotic pressure (HOSM) produced a similar increase in quantal release and a significant rise in [Ca2+]i; however, the Ca2+ appeared to come from intracellular stores. 4. In contrast, ETOH stimulated quantal neurosecretion without a measurable change in [Ca2+]i. It appears the alcohol exerts its influence on some stage in the process of exocytosis that is distal to or independent of the site of Ca2+ action. 5. The effects of high [KCl]o and osmotic pressure were occlusive. This is explained in part by the observation that hypertonicity reduced Ca2+ current, but an action on Ca2+ stores is also likely.(ABSTRACT TRUNCATED AT 250 WORDS)

Nerve growth factor responsiveness of cultured major pelvic ganglion neurons from the adult rat

The bladder and other pelvic viscera are innervated in the rat by the major pelvic ganglion (MPG), a mixed sympathetic/parasympathetic population of neurons that participates in lower urinary pathophysiology. Neurons from the MPG of adult females were removed, dissociated and cultured in order to test retention of the neuronal phenotype and whether they responded to Nerve Growth Factor (NGF). The bladder-specific subset of MPG neurons were distinguished by retrograde labeling prior to culture. The adult ganglionic neurons adapted to culture with greater than 80% survival in the best cases. The cultured neurons retained excitability, as determined by measuring voltage-activated ionic currents. They were positive for neuron-specific beta-tubulin and many retained immunoreactivity for characteristic peptides and transmitter synthetic enzyme. The proportion of neurons in the different categories tested varied somewhat from that in vivo, but there was no evidence of selective death of a particular population. The cultured MPG neurons were responsive to NGF and anti-NGF antibody. NGF supported neuronal survival and expression of tyrosine hydroxylase. Added NGF also affected the expression of neuropeptide Y. Hypertrophied neurons from animals with experimental bladder outlet obstruction demonstrated increased responsiveness to NGF. The data suggest that NGF participates in adult neural plasticity due to continued responsiveness to the factor. Furthermore, questions concerning regulation of MPG neurons may be addressed in vitro.

Nerve growth factor synthesis in vascular smooth muscle

Details of the interdependent, trophic relation between smooth muscle and its neural innervation are not well known despite suggestions that neural influences may contribute significantly to hypertensive and other cardiovascular disease. Vascular smooth muscle is a major target of innervation by neurons of the sympathetic nervous system. Sympathetic neurons depend on a constant supply of the potent neurotrophic peptide nerve growth factor. Nerve growth factor regulates an impressive list of neuronal and perhaps muscle properties, yet its source in vessels and the determinants of its synthesis are not known. We have taken advantage of the cytoarchitecture of the aorta to demonstrate that vascular smooth muscle cells synthesize nerve growth factor. The survival of cultured sympathetic neurons is supported in a nerve growth factor-dependent manner by co-culture with pure rat aortic vascular smooth muscle cells. Furthermore, pure smooth muscle cell cultures contain nerve growth factor-specific messenger RNA. Levels of messenger nucleic acid coding for nerve growth factor in smooth muscle are regulated by contractile agonists (angiotensin II, arginine vasopressin) and the adrenergic agonist phenylephrine. This suggests a link between muscle activity and growth factor production. Secretion of nerve growth factor protein by vascular smooth muscle was measured using a sensitive two-site immunoassay. Secretion is highest during muscle growth. Secretion is elevated by angiotensin II and arginine vasopressin but slightly inhibited by phenylephrine. These results suggest that cultured vascular smooth muscle can serve as a useful model in which to study the cellular regulation of trophic factor synthesis in health and disease.

Nerve growth factor in the urinary bladder of the adult regulates neuronal form and function

Urethral obstruction produces increased voiding frequency (0.7 +/- 0.06 to 1.1 +/- 0.08 h-1) and hypertrophy of the urinary bladder (89 +/- 1.7 to 708 +/- 40 mg) with profound increments in the dimensions of afferent (4, 6) and efferent neurons (299 +/- 4.7 to 573 +/- 8.6 microns2) supplying this organ in the rat. We discovered that hypertrophied bladders of rat and human contain significantly more nerve growth factor (NGF) per milligram wet weight, protein, and DNA than normal bladders. The temporal correlation between NGF content, neuronal hypertrophy, and bladder weight was consistent with a role for this growth factor in the neurotrophic effects associated with obstruction. Autoimmunity to NGF abolished the hypertrophy of NGF-sensitive bladder neurons in the pelvic ganglion after obstruction. Relief of urethral obstruction reduced bladder size (349 +/- 78 mg), but neuronal hypertrophy (460.2 +/- 10.2 microns2) and elevated NGF levels were only partially reversed. Bladder hypertrophy (133 +/- 4.3 mg) induced by osmotic diuresis slightly increased ganglion cell area (365.2 +/- 6.1 microns2) and only doubled NGF content of the bladder. These findings provide important new evidence that parenchymal cells in the hypertrophied bladder can synthesize NGF and possibly other molecular messengers that act to alter the size and function of neurons in adult animals and man.

Spatial association of renin-containing cells and nerve fibers in developing rat kidney

The development of renin-containing cells and nerve fibers was studied in Sprague-Dawley rat kidneys during the last third of gestation and the first 15 days of postnatal life. Kidney tissue sections were stained for nerve fibers or double stained employing an anti-rat renin polyclonal antibody and a monoclonal antibody (TUJ1) directed against a neuron-specific class III beta-tubulin isotype. Renin-containing cells and nerve fibers were detected at 17 days of gestation, in close spatial relationship along the main branches of the renal artery. During fetal life, renin-containing cells and nerve fibers were spatially associated along arcuate and interlobular arteries, renin-containing cells being also present throughout the entire length of afferent arterioles supplying juxtamedullary glomeruli. During postnatal life the distribution of renin-containing cells progressively shifted to a restricted juxtaglomerular position in afferent arterioles. Simultaneously, density and organization of nerve fibers increased with age along the arterial vascular tree. Our results suggest that innervation of renin-containing cells is present in fetal life and follows the centrifugal pattern of renin distribution and nephrovascular development.