Nerve growth factor depletion by autoimmunization produces thermal hypoalgesia in adult rats

Nerve growth factor (NGF) plays a role in mechanisms of inflammation and hyperalgesia in adult animals. We sought to determine if NGF depletion produced by autoimmunization of adult rats altered their thermal sensitivity to an acute noxious thermal stimulus. Anti-NGF IgG was not detected in the cerebrospinal fluid of any tested samples. Only those rats with the highest anti-NGF serum titers showed significant (P<0.05) thermal hypoalgesia measured using the hot plate test (52°C): the mean (±S.D.) hind paw lick latency of rats in the high anti-NGF titer group was 18.0±4.6 s compared to means of 10.8±4.3 s, 9.2±2.6 s and 10.1±3.0 s in the medium, low and control groups, respectively. Thus, NGF depletion by autoimmunization is a useful model for investigating the role of NGF in behavioral responses of adult rats to noxious stimuli, providing high titers of antibody are present.     

神经生长因子对创伤性脊髓损伤大鼠膀胱功能和轴突损伤修复的作用研究

目的 探讨神经生长因子(Nerve growth factor, NGF)对创伤性脊髓损伤(Traumatic spinal cord injury, t-SCI)大鼠膀胱功能和脊髓神经轴突损伤修复的影响及其分子机制。方法 取30只雄性Sprague-Dawley(SD)大鼠,通过改良Allen’s击打法构建创伤性脊髓损伤模型,随机分为假手术组、损伤组和NGF组,每组各10只;采用血脑屏障(Blood-brain barrier, BBB)评分观察术前、术后大鼠的后肢运动功能;BL-420生物仪实验系统检测尿动力学;甲苯胺蓝染色吻合口远端截取的左侧腰6前根,计算有髓轴突数量;采用苏木精-伊红(Hematoxylin eosin, HE)染色大鼠膀胱组织;原位末端标记法(TdT-mediated dUTP nick and labeling, TUNEL)染色大鼠损伤严重的脊髓,观察脊髓神经细胞的凋亡率;蛋白免疫印迹法(Western blot)检测脊髓组织中原癌基因丝氨酸/苏氨酸蛋白激酶(proto-oncogene serine/threonine-protein kinase, R...     

Effects of gonadal steroids on nerve growth factor receptors in sympathetic and sensory ganglia of neonatal rats

The numbers of neurons in the rat superior cervical sympathetic ganglion (SCG) differ in males and females, with the males having 30% more SCG neurons than females at 60 days of age. This sex difference arises during the early postnatal period, when testosterone administration increases the numbers of neurons and alters the nerve growth factor (NGF) content of the rat SCG. In contrast, there is no gender difference in number of neurons in the L1 dorsal root ganglion. In both males and females, the amount of NGF bound per ganglion increased between postnatal days 5 and 15 (P5 and P15) in both dorsal root ganglia (DRGs) and the SCG. There is also a gender difference in NGF binding: SCGs and DRGs of female rats at both P5 and P15 bind more NGF per ganglion than do those of males. This effect was more marked in DRGs than in the SCG. Treatment of neonatal females with testosterone reduced NGF binding in both SCGs and DRGs to levels comparable to males at P5, and in DRGs at P15. In contrast, treatment of males with testosterone from birth resulted in a 2-3 fold increase of NGF binding in both SCGs and DRGs as compared to controls at P15. At P15, testosterone treatment of females increased NGF binding in the SCG. Males and females had opposing responses to neonatal exposure to estradiol. Treatment with estradiol from birth increased NGF binding in SCGs and DRGs of females, but had no effect on NGF binding of SCGs, and reduced NGF binding in DRGs of males.(ABSTRACT TRUNCATED AT 250 WORDS)     

Complete recovery by nerve growth factor of neuropeptide content and function in capsaicin-impaired sensory neurons

In the present study the ability of nerve growth factor (NGF) to facilitate the recovery of peptidergic primary sensory C-fibers after an acute capsaicin treatment (50 mg/kg s.c.) was investigated in adult rats. NGF (4 μg 1 /day for 3 days) was injected into the plantar of one hind paw starting 24 h after the capsaicin treatment. Without NGF, there was a significant reduction of calcitonin gene-related peptide (CGRP) and substance P content of the paw skin and the sciatic nerve. CGRP and substance P levels were completely replenished in the NGF-treated paw skin and in the innervating sciatic nerve they even increased over control levels as determined 40 h after the last injection of NGF. CGRP levels also recovered in the contralateral paw and sciatic nerve, but no recovery was observed in other tissues such as the front paw, the auricle, or the urinary bladder. Mustard oil-induced neurogenic plasma extravasation, taken as a functional parameter for peptidergic primary sensory C-fibers, was significantly decreased after the capsaicin treatment and showed a complete recovery by NGF in the injected paw as well as in the contralateral paw skin. These results show that NGF not only was able to reverse the decrease of transmitter content caused by capsaicin but also restored the peripheral function of primary afferent neurons.     

A possible role for nerve growth factor in the augmentation of sodium channels in models of chronic pain

Inflammation induces an upregulation of sodium channels in sensory neurons. This most likely occurs as a result of the retrograde transport of cytochemical mediators released during the inflammatory response. The purpose of this study was to determine the effect of the subcutaneous administration of one such mediator, nerve growth factor (NGF), on the production of sodium channels in neurons of the rat dorsal root ganglion. For this, hindpaw withdrawal from either a thermal or mechanical stimulus was measured in rats at selected intervals for up to 2 weeks following injections of NGF. Sodium channel augmentation was then examined in dorsal root ganglia using site-specific, anti-sodium channel antibodies. Both thermal and mechanical allodynia was observed between 3 and 12 h post-injection. The hyperalgesic response returned to baseline by approximately 24 h post-injection. Sodium channel labeling was found to increase dramatically in the small neurons of the associated dorsal root ganglia beginning at 23 h, reached maximum intensity by 1 week, and persisted for up to 3 months post-injection. Pre-blocking NGF with anti-NGF prevented the NGF-induced decrease in paw withdrawal latencies and significantly reduced the intensity of sodium channel labeling. The results indicate that NGF is an important mediator both in the development of acute hyperalgesia and in the stimulation of sodium channel production in dorsal root ganglia during inflammation.     

慢性癫痫大鼠脑组织神经生长因子阳性神经元的变化

应用免疫组织化学的方法观察了戊四氮诱导的慢性癫痫大鼠脑组织神经生长因子(NGF)阳性神经元的变化。结果发现慢性癫痫大鼠海马回、齿状回NGF阳性神经元数目明显增多。在所选取的时间点,即末次抽搐发作后24h、72h、7d均较对照组明显升高。结果提示:NGF参与了癫痫的发病过程,可能通过介导突触的重建面具有促痫作用。也可能作为一种保护因子而防止癫痫后脑损害。     

Time and dose dependencies of effects of nerve growth factor on sympathetic and sensory neurons in neonatal rats

Nerve growth factor (NGF) plays a role in the development of several components of the sympathetic and sensory nervous systems. The objectives of this study were to examine the time and dose dependencies of some of the well known effects of NGF on sympathetic ganglia and to examine qualitatively and quantitatively the recently described effects on sensory ganglia of neonatal rats. Single doses of NGF as low as 0.1 mg/kg produce increases in tyrosine hydroxylase (TOH) activity in superior cervical ganglia (SCG), and doses of 3 mg/kg produce maximal effects. Larger doses and longer treatments are required to see increases in protein content of the SCG. Larger doses are also required to affect TOH activity in the adrenal gland. Increases in TOH activity in SCG can be observed within 18 h of injection. Chronic NGF treatment for three weeks produces no change in blood pressure or heart rate in neonatal rats. Chronic administration of NGF (1 or 3 mg/kg/day) results in dose-related increases in the protein content of dorsal root ganglia (DRG). The increase in protein content of the DRG was associated with an increase in the diameter of smaller neurons (those<30 μm in diameter), but NGF caused no change in the number of neurons.     

No nerve growth factor response to treatment with memantine in adult rats

Summary. Nerve growth factor (NGF) is the most widely examined neurotrophin in the experimental models of Alzheimers disease (AD) and has been shown to prevent the retrograde degeneration of cholinergic neurons. In this study we examined NGF and cholineacetyltransferase (ChAT) changes in several rat brain regions after excitotoxic lesion of the entorhinal cortex with quinolinic acid and tested the effect of memantine on spatial learning in the radial maze after lesion. We observed a significant increase (+26%, p=0.02) of NGF concentrations in the hippocampus of the lesioned rats when compared to sham-lesioned rats. Chronic treatment with memantine showed no significant effect on the NGF increase in the hippocampus (p=0.72). The ChAT activity was significantly increased in the lesioned rats when compared to controls (+16%, p<0.05) and did not depend on treatment with memantine. In spite of this, memantine improved performance of the radial maze. This indicates that memory improving effects of memantine observed in experimental animals and in clinical studies are probably not related to changes in brain NGF content, whereas the observed NGF increase in the denervated hippocampus is probably trauma-related reflecting impaired retrograde transport of hippocampal NGF.Present address: Solvay Pharmaceuticals BV, Weesp, NiederlandePresent address: Institute of Pharmacology PAN, Cracow, Poland     

Vascular endothelial growth factor stimulates Schwann cell invasion and neovascularization of acellular nerve grafts

The aim of this study was to investigate the effects of vascular endothelial growth factor (VEGF) on regeneration of the rat sciatic nerve in vivo. To that end we used 10-mm long cell-free nerve grafts to bridge a gap in the sciatic nerve. The grafts were pretreated with either VEGF (50, 100 or 250 ng/ml), nerve growth factor (NGF, 100 ng/ml) or laminin (100 ng/ml) before implantation. Outgrowth of axons, Schwann cells, blood vessels and macrophages were studied 10 days post-implantation by the use of immunocytochemistry and histochemistry. Grafts pretreated with VEGF stimulated the outgrowth of Schwann cells and blood vessels but not axons. In such grafts, the Schwann cells also exhibited a dramatic change in morphology and became filled with large lipid-containing vacuoles. These cells also showed an intense immunoreactivity for the VEGF receptor flk-1. Neither pretreatment with laminin nor NGF affected the outgrowth of Schwann cells. However, NGF treatment increased the number of axons in the graft but was not able to counteract injury-induced downregulation of substance P in the dorsal root ganglia. The results show that local application of VEGF promotes at least two events, invasion of Schwann cells and neovascularization, which are important during nerve regeneration. The findings suggest that the effects of the pretreatment by the growth factors is local and limited to the graft, whereas central events like neuropeptide synthesis is not affected.     

神经生长因子对糖尿病神经病变大鼠神经肽和神经传导速度的影响

目的 探讨神经生长因子对糖尿病周围神经病变大鼠神经肽和神经传导速度的影响. 方法 雄性Wistar大鼠35只按随机数字表法分为健康对照组(n=10)、糖尿病模型组(n=13)和神经生长因子治疗组(n=12),后两组用链脲佐菌素制成糖尿病周围神经病变大鼠模型,并给予神经生长因子治疗组神经生长因子治疗(40μg/kg).显微镜下观察并计算背根神经节中P物质、降钙素基因相关肽(CGRP)免疫阳性细胞率,检测运动神经传导速度(MNCV)和感觉神经传导速度(SNCV). 结果 糖尿病模型组大鼠背根神经节中P物质、CGRP免疫阳性细胞率(27.710％±3.471％；36.360％±12.027％)以及神经生长因子治疗组治疗前MNCV [(35.80±6.19) m/s]、SNCV[(39.62±6.69) m/s]与健康对照组[P物质:44.225％±8.213％；CGRP:47.400％±13.723％；MNCV:(55.83±10.30) m/s; SNCV:(47.02±7.52) m/s]相比显著下降,差异有统计学意义(P＜0.05).经神经生长因子治疗后,P物质、CGRP免疫阳性细胞率(49.417％±6.753％;53.811％±7.125％)较糖尿病模型组显著增高,MNCV[(41.80±3.45) m/s]、SNCV[(42.92±6.69) m/s]均治疗前显著增高,差异有统计学意义(P＜0.05). 结论 糖尿病周围神经病变大鼠可出现神经传导速度下降和神经生长因子相关神经肽P物质、CGRP缺乏,而神经生长因子可促进神经肽的表达并提高神经传导速度.     

Expression and regulation of tyrosine hydroxylase in adult sensory neurons in culture: Effects of elevated potassium and nerve growth factor

To determine whether similar molecular mechanisms regulate the same proteins in diverse neuronal populations, the present study compared regulation of tyrosine hydroxylase (TOH) in placodal sensory and neural crest-derived sympathetic neurons in tissue culture. Long-term explant cultures of adult nodose and petrosal sensory ganglia (NPG) contained abundant TOH-immunoreactive neurons and exhibited TOH catalytic activity, as in vivo. After an initial decline during the first week of culture, enzyme activity was maintained at a stable plateau of 60% of zero time values for at least 3 weeks. However, exposure of 2-week-old cultures to depolarizing concentrations of potassium (K+; 40 mM) increased TOH activity approximately two-fold; total protein was unchanged, suggesting that the rise was due to increased TOH specific activity. Therefore, membrane depolarization in vitro appears to regulate this specific catecholaminergic (CA) trait in sensory, as in sympathetic CA cells. In sympathetic neurons, NGF regulates TOH activity throughout life. In marked contrast, TOH activity in adult NPG cultures was unchanged in the presence of 0, 10 or 100 units NGF/ml or in the presence of high concentrations of antiserum against the beta-subunit of NGF. Adult sympathetic neurons, however, grown under identical conditions, exhibited a 5- to 10-fold rise in TOH activity in the presence of NGF. Thus, unlike sympathetics, CA metabolism in adult NPG neurons is not regulated by NGF in vitro; NGF is therefore unlikely to mediate target effects on CA metabolism in placodal sensory neurons in vivo. Our findings indicate that certain mechanisms of CA regulation are shared by placodal sensory and neural crest-derived sympathetic neurons, whereas others are not.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neuronatin mRNA in PC12 cells: downregulation by nerve growth factor

Neuronatin was recently cloned from neonatal rat brain (Biochem. Biophys. Res. Commun., 201 (1994) 1227–1234). In subsequent studies, we noted that neuronatin mRNA was brain-specific and that there were two alternatively spliced forms, α and β (Brain Res., 690 (1995) 92–98). Furthermore, on sequencing the human neuronatin gene, it was determined that the α-form was encoded by three exons, and the β-form was encoded by the first and third exons only (Genomics, 33 (1996) 292–297). The middle exon was spliced out in the β-form. The human neuronatin gene is located in single copy on chromosome 20q11.2-12 (Brain Res., 723 (1996) 8–22). These studies called for an understanding of the function of this gene. Therefore, we studied the expression of neuronatin in PC12 cells, an established model of neuronal growth and differentiation. Neuronatin mRNA expression was found to be abundant in undifferentiated PC12 cells. Treatment with nerve growth factor (NGF), resulting in neuronal differentiation, was associated with a downregulation of neuronatin mRNA expression. Removal of NGF was associated with a return of neuronatin mRNA levels towards baseline. These effects appear to be specific for NGF as they were not seen with transforming growth factor, epidermal growth factor, 12-O-tetradecanoylphorbol-13-acetate or dexamethasone. Although, basic fibroblast growth factor also reduced neuronatin mRNA levels, the effect was less pronounced than with NGF. The NGF-induced decrease in neuronatin mRNA occurred even in the presence of protein and RNA syntheses inhibitors. Of the two spliced forms, only the α-form was expressed in PC12 cells. In conclusion, we report the presence of neuronatin mRNA in PC12 cells, and that NGF downregulates its expression. These findings provide a basis for investigating the role of neuronatin in neuronal growth and differentiation.     

神经再生素和神经生长液联合应用对成年兔视神经挫伤后修复的影响

目的研究中药神经再生素（NRF）和神经生长液对成年兔视神经挫伤后修复的影响。方法16只成年兔随机分成实验组和对照组．每组8只。建立兔右眼视神经挫伤模型后．分别将载有0．06mL NRF（浓度为2g／L，实验组）或等量磷酸盐缓冲液（PBS）（对照组）的组织工程化神经移植于视神经损伤处；并向右眼玻璃体腔内注入0．02mL NRF（浓度为2g／L，实验组）或等量PBS（对照组）。实验组兔术后每日喂服神经生长液（5mL／kg），共6周。伤后1d、2周、8周进行闪光视觉诱发电位（FVEP）检查。挫伤后8周时作光镜和电镜检查观察视网膜神经节细胞（RGC）、视网膜神经纤维层和视神经的改变，同时用计算机图像处理系统作视神经纤维计数。结果术后8周时实验组致伤眼与未致伤眼FVEP幅值比为0．774±0．184，对照组为0．409±0．119，差异有显著性（P〈0．01）。术后8周时的光镜和电镜检查示：实验组RGC、视神经纤维的退变较对照组轻。两组视神经纤维计数分别为（15045±716．2）根／mm^2（实验组）和（7898±608．8）根／mm^2（对照组），差异有显著性（P〈0．01）。结论NRF和神经生长液联合应用能够增加RGC的存活，促进轴突的再生，因而对视神经挫伤后的修复、视功能的恢复具有一定的促进作用。     

Substrate-bound nerve growth factor promotes neurite growth in peripheral nerve

Nerve growth factor (NGF), in addition to its well-known effects as a soluble neurite growth-promoting factor, also appears to promote the elongation of neurites when it is adsorbed to tissue culture substrates. Peripheral nerve Schwann cells appear to possess a receptor for NGF on their surfaces which is induced substantially after axotomy. We have found that the adsorption of NGF onto cryostat sections of the distal stump of previously severed sciatic nerve enhances neurite growth over this tissue. This finding, coupled with the two previous observations, suggests that Schwann cell surface NGF receptors serve to bind to NGF-like growth factors so as to provide favorable surfaces for regenerating peripheral nerve axons.     

Regulation of afferent connectivity in the adult spinal cord by nerve growth factor

During development, nerve growth factor (NGF) regulates the density and character of peripheral target innervation (Barde, Neuron , 2 , 1525–1534, 1989; Ritter et al., Soc. Neurosci. Abstr. , 17 , 546.2, 1991); its role in adult animals is less well defined. Here we have asked if the availability of growth factors such as NGF in peripheral tissues can influence the pattern of primary afferent connections in the CNS. Using osmotic minipumps, we raised the levels of NGF in rat skeletal muscle in vivo , a tissue where the levels of this factor are normally very low (Korsching and Thoenen, Proc. Natl. Acad. Sci. USA , 80 , 3513–3516, 1983; Shelton and Reichardt, Proc. Natl. Acad. Sci. USA , 81 , 7951–7955, 1984; Goedert et al., Mol. Brain Res. , 1 , 85–92, 1986). After 2 weeks of treatment we asked if the sensory neurons innervating this tissue showed an altered strength and distribution of connections with dorsal horn neurons. The contralateral (vehicle-treated) muscle, and totally untreated animals, served as controls. In normal and vehicle-treated animals, electrical stimulation of muscle afferents excited relatively few neurons in the dorsal horn, and these generally showed only weak responses. In contrast, on the NGF-treated side many more dorsal horn neurons in the lumbar enlargement of the spinal cord were excited by muscle afferents. The increased responsiveness could not be explained by a generalized increase in dorsal horn excitability, since spontaneous activity was not enhanced, nor by a change in A-fibre-mediated inhibitions from the treated afferents. Thus, these afferents appeared to establish new synaptic connections or strengthened previously weak ones as a result of increased neurotrophic factor availability. The data suggest that, in the adult rat, the levels of growth factors in peripheral targets may be used to regulate an appropriate degree of afferent connectivity within the central nervous system.     

Effects of nerve growth factor (NGF), fluoxetine, and amitriptyline on gene expression profiles in rat brain

Evidence suggests that nerve growth factor (NGF) may have antidepressant properties but the pharmacological mechanisms remain unknown. Previously, we found that NGF improved performance in the forced swim test in Flinders Sensitive Line rats, but did not appear to have similar biochemical actions with the antidepressant fluoxetine. Gene expression profiles for neurotransmitter receptors and regulator-related genes in the amygdala/hippocampus were determined in rats treated for 14 days with NGF, fluoxetine, amitriptyline, or saline. Gene expression was measured using an RT² profiler PCR Array System to determine the basis for this effect. Compared with saline, there were numerous genes with significantly altered mRNA levels in the amygdala/hippocampal region. Overlap was found between the mRNA levels of genes altered by NGF and the two antidepressant medications including genes related to the cholinergic and dopaminergic systems. However, decreased mRNA levels of Drd5, Sstr3, Htr3a, and Cckar genes in the amygdala/hippocampus were uniquely regulated by NGF. The results of this study are consistent with a previous conclusion that the antidepressant effects of NGF are mediated through non-traditional receptors for traditionally considered neurotransmitters and may suggest a particular utility of NGF in treating comorbid depression and addiction.     

Destruction of sympathetic and sensory neurons in the developing rat by a monoclonal antibody against the nerve growth factor (NGF) receptor

The ability of the monoclonal antibody, 192-IgG, directed against the rat nerve growth factor (NGF) receptor to mimic or inhibit the actions of NGF was examined in vitro and in vivo. 192-IgG had no effect on morphology, survival, or protein synthesis rates of sympathetic neuronal cultures. When injected into newborn rats, destruction of sympathetic, but not sensory, neurons was produced. Injection prenatally produced more dramatic destruction of sympathetic neurons and, in addition, destruction of neural crest-derived sensory neurons. Therefore, although 192-IgG had no discernible effects in vitro, it produced a pattern of neuronal destruction in vivo qualitatively similar to that produced by antibodies to NGF itself.     

Chronic parasite infection in mice induces brain granulomas and differentially alters brain nerve growth factor levels and thermal responses in paws

Schistosoma mansoni infection, both in humans and in animal models, is known to induce granulomas in the liver and intestine. It has also been reported that in humans the eggs of this parasite can reach the brain, causing psychiatric and neuropathological disorders. Whether this also occurs in rodents is unknown. To answer this question, mice were infected with this parasite and the central nervous system (CNS) examined at various time intervals. The results show that schistosomiasis induced granulomas in several regions of the CNS and increased nerve growth factor (NGF) levels in the cortex, hypothalamus and brain stem, but not in the hippocampus. The infection also caused paw hyperalgesia, as determined by the hot-plate test, and a local increase in NGF, but not in substance P. These findings indicate that the murine model of infection can be used for studying mechanisms leading to human neuroschistosomiasis and suggest that the neuropathological disorders and the sensory deficits observed in human schistosomiasis are associated with impaired levels of NGF in the peripheral and central nervous system. Received: 18 January 1996 / Revised, accepted: 16 April 1996     

碱性成纤维生长因子和神经生长因子联合应用培养成年大鼠海马神经干细胞向神经元样细胞的分化

背景：影响神经干细胞向神经元分化的因素很多,各种营养因子可以不同程度地刺激神经干细胞向神经元分化,如何使神经干细胞大量分化为神经元是研究的热点问题。 目的：观察联合应用碱性成纤维生长因子和神经生长因子对成年大鼠海马神经干细胞为神经元的影响。 方法：无菌条件下分离大鼠脑海马组织,传至第4代克隆球直径约为200 μm时,滴加DMEM/F12+2% B27+20 μg/L表皮生长因子+20 μg/L碱性成纤维细胞生长因子,进行单细胞克隆培养,传代的神经干细胞分成空白对照组、碱性成纤维细胞生长因子组、神经生长因子组、碱性成纤维细胞生长因子+神经生长因子组。观察传代后的克隆球进行神经干细胞免疫细胞化学染色鉴定,计数神经元特异性烯醇化酶阳性细胞率,检测神经干细胞向神经元的分化情况。 结果与结论：①单细胞克隆培养后,克隆球细胞表达巢蛋白,诱导分化后神经元特异性烯醇化酶、胶质纤维酸性蛋白均呈阳性表达。②与空白对照组神经干细胞分化为神经元的比例比较,碱性成纤维细胞生长因子组、神经生长因子组、碱性成纤维细胞生长因子组+神经生长因子组均明显提高(P < 0.05),且碱性成纤维细胞生长因子组+神经生长因子组神经元的比例最高(P < 0.05)。提示,碱性成纤维细胞生长因子可以提高神经生长因子诱和神经生长因子均可促进神经干细胞向神经元分化,且二者联合应用效果更佳。     

Effects of nerve growth factor on behavioral recovery following caudate nucleus lesions in rats

Rats with bilateral lesions of the caudate nucleus received intracaudate injections of either nerve growth factor protein (NGF) or inert buffer immediately following surgery. NGF-treated animals demonstrated a faster recovery of normal appetitive behavior and perseverated less than their buffer-treated counterparts on a spatial reversal task, but both groups were impaired relative to sham controls on acquisition of an active avoidance response. Glia to neuron ratios were significantly increased in both lesion groups when compared with sham controls. However, this increase was less in the NGF-treated animals than in the buffer-treated animals. NGF treatment had no effect on steady-state caudate dopamine levels, measured six months after surgery.