Neurotrophic factors: repair and regeneration in the central nervous system

Neurotrophic factors promote maintenance, repair and regeneration of selected neurons in vitro and in vivo. They include nerve growth factor (NGF) and other neurotrophins, ciliary neurotrophic factor (CNTF) and other cytokines, and a number of growth factors. Molecular properties of the trophic proteins and their transducing receptors are increasingly well characterized. Interest in the neurotrophic factors has greatly accelerated over the past decade with accumulating evidence that they play important roles in the adult mammalian CNS as well as in its development. Adult in vivo models for degenerative CNS conditions have demonstrated the ability of exogenous neurotrophic factors (NTFs) to protect against neuronal damage induced by traumatic or chemical experimental lesions, particularly with regard to easily identifiable neurons such as cholinergic and dopaminergic ones. Other models have shown beneficial effects of NTF administration with regard to axonal regeneration inside CNS tissue.

Unique contributions of distinct cholinergic projections to motor cortical plasticity and learning

The cholinergic basal forebrain projects throughout the neocortex, exerting a critical role in modulating plasticity associated with normal learning. Cholinergic modulation of cortical plasticity could arise from 3 distinct mechanisms by 1) "direct" modulation via cholinergic inputs to regions undergoing plasticity, 2) "indirect" modulation via cholinergic projections to anterior, prefrontal attentional systems, or 3) modulating more global aspects of processing via distributed inputs throughout the cortex. To segregate these potential mechanisms, we investigated cholinergic-dependent reorganization of cortical motor representations in rats undergoing skilled motor learning. Behavioral and electrophysiological consequences of depleting cholinergic inputs to either motor cortex, prefrontal cortex, or globally, were compared. We find that local depletion of cholinergic afferents to motor cortex significantly disrupts map plasticity and skilled motor behavior, whereas prefrontal cholinergic depletion has no effect on these measures. Global cholinergic depletion perturbs map plasticity comparable with motor cortex depletions but results in significantly greater impairments in skilled motor acquisition. These findings indicate that local cholinergic activation within motor cortex, as opposed to indirect regulation of prefrontal systems, modulate cortical map plasticity and motor learning. More globally acting cholinergic mechanisms provide additional support for the acquisition of skilled motor behaviors, beyond those associated with cortical map reorganization.

Topical ointment for preventing infection in preterm infants

BACKGROUND

Nosocomial sepsis is a frequent and serious complication of premature infants. The increased susceptibility of ELBW infants to infection has been attributed to less effective immune function compared to mature newborns and the invasive nature of necessary supportive care. Breakdown of the barrier function of the skin may be an additional risk factor for nosocomial sepsis.

OBJECTIVES

To assess the effect of prophylactic application of topical ointment on nosocomial sepsis rates and other complications of prematurity in preterm infants.

SEARCH STRATEGY

Searches were made of the Cochrane Central Registry of Controlled Trials (CENTRAL, The Cochrane Library, Issue 2, 2003), Ovid DC MEDLINE through June 2003, previous reviews including cross references, abstracts, conference and symposia proceedings, expert informants, and journal hand searching in the English language.

SELECTION CRITERIA

Randomized controlled trials which compared the effect of prophylactic application of topical ointment to routine (standard) skin care or as needed topical therapy in preterm infants are included in this review.

DATA COLLECTION AND ANALYSIS

Data regarding clinical outcomes including infection [including any bacterial infection, bacterial infection with a known pathogen, coagulase negative staphylococcal infection, fungal infection, and any nosocomial infection (bacterial or fungal)], patent ductus arteriosus, oxygen requirement at 28 days, chronic lung disease and mortality were excerpted from the reports of the clinical trials by the reviewers. Data analysis was done in accordance with the standards of the Cochrane Neonatal Review Group.

MAIN RESULTS

Four randomized controlled trials were identified. All four studies reported improved skin condition in infants treated with prophylactic topical ointment (results not reported here). All four studies reported on the incidence of any nosocomial infection, fungal infection and coagulase negative staphylococcal infection. Infants treated with prophylactic topical ointment are at increased risk of coagulase negative staphylococcal infection (typical relative risk 1.31, 95% CI 1.02, 1.70; typical risk difference 0.04, 95% CI 0.00, 0.08); and any nosocomial infection (typical relative risk 1.20, 95% CI 1.00, 1.43; typical risk difference 0.05, 95% CI 0.00, 0.09). A trend toward increased risk of any bacterial infection was found in infants treated with prophylactic topical ointment (typical relative risk 1.19, 95% CI 0.97, 1.46; typical risk difference 0.04, 95% CI -0.01, 0.08). There was no significant difference found in the risk of bacterial infection with a known pathogen, fungal infection, or other complications related to prematurity.

REVIEWER'S CONCLUSIONS

Prophylactic application of topical ointment increases the risk of coagulase negative staphylococcal infection and any nosocomial infection. A trend toward increased risk of any bacterial infection was noted in infants prophylactically treated. Topical ointment should not be used routinely in preterm infants.

Modulation of neuronal survival and axonal growth in vivo by tetracycline-regulated neurotrophin expression

Vector systems for the regulated and reversible expression of therapeutic genes are likely to improve the safety and efficacy of gene therapy for medical disease. In the present study, we investigated whether the expression of genes transferred into the central nervous system by ex vivo gene therapy can be regulated in vivo leading to controlled neuronal survival and axonal growth. Primary rat fibroblasts were transfected with a retrovirus containing a tetracycline responsive promoter for the expression of the neurotrophin nerve growth factor (NGF) or green fluorescent protein as a control (GFP). After lesions of basal forebrain cholinergic neurons, NGF-mediated neuronal rescue and axonal growth could be completely controlled over a 2-week period by the addition or removal of the tetracycline modulator doxycycline in the animals' drinking water. Further, continued expression of the reporter gene GFP could be reliably and repeatedly turned on and off in the injured CNS for at least 3 months post-grafting, the longest time point investigated. These data constitute the first report of regulated neuronal rescue and axonal growth by controlled neurotrophin gene delivery and long-term, regulated expression using ex vivo CNS gene therapy.

Nontropic actions of neurotrophins: subcortical nerve growth factor gene delivery reverses age-related degeneration of primate cortical cholinergic innervation

Normal aging is associated with a significant reduction in cognitive function across primate species. However, the structural and molecular basis for this age-related decline in neural function has yet to be defined clearly. Extensive cell loss does not occur as a consequence of normal aging in human and nonhuman primate species. More recent studies have demonstrated significant reductions in functional neuronal markers in subcortical brain regions in primates as a consequence of aging, including dopaminergic and cholinergic systems, although corresponding losses in cortical innervation from these neurons have not been investigated. In the present study, we report that aging is associated with a significant 25% reduction in cortical innervation by cholinergic systems in rhesus monkeys (P < 0.001). Further, these age-related reductions are ameliorated by cellular delivery of human nerve growth factor to cholinergic somata in the basal forebrain, restoring levels of cholinergic innervation in the cortex to those of young monkeys (P = 0.89). Thus, (i) aging is associated with a significant reduction in cortical cholinergic innervation; (ii) this reduction is reversible by growth-factor delivery; and (iii) growth factors can remodel axonal terminal fields at a distance, representing a nontropic action of growth factors in modulating adult neuronal structure and function (i.e., administration of growth factors to cholinergic somata significantly increases axon density in terminal fields). These findings are relevant to potential clinical uses of growth factors to treat neurological disorders.

Neonatal intensive care: satisfaction measured from a parent's perspective

Health care systems today are complex, technically proficient, competitive, and market-driven. One outcome of this environment is the recent phenomenon in the health care field of "consumerism." Strong emphasis is placed on customer service, with organized efforts to understand, measure, and meet the needs of customers served. The purpose of this article is to describe the current understanding and measurement of parent needs and expectations with neonatal intensive care services from the time the expectant parents enter the health care system for the birth through the discharge process and follow-up care. Through literature review, 11 dimensions of care were identified as important to parents whose infants received neonatal intensive care: assurance, caring, communication, consistent information, education, environment, follow-up care, pain management, participation, proximity, and support. Five parent satisfaction questionnaires-the Parent Feedback Questionnaire, Neonatal Index of Parent Satisfaction, Inpatient Parent Satisfaction-Children's Hospital Minneapolis, Picker Institute-Inpatient Neonatal Intensive Care Unit Survey, and the Neonatal Intensive Care Unit-Parent Satisfaction Form-are critically reviewed for their ability to measure parent satisfaction within the framework of the neonatal care delivery process. An immense gap was found in our understanding about what matters most and when to parents going through the neonatal intensive care experience. Additional research is required to develop comprehensive parent satisfaction surveys that measure parent perceptions of neonatal care within the framework of the care delivery process.

Anterograde transport of neurotrophin proteins in the CNS--a reassessment of the neurotrophic hypothesis

The basic tenets of the neurotrophic hypothesis are that i) limiting quantities of a given factor are produced in specific target tissues; ii) responsive neurons projecting to these targets compete for the limiting amounts of the factor; iii) the factor is bound within the target by selective receptors on afferent terminals, internalized, and retrogradely transported to the neuronal cell body where it provides signals affecting neuronal survival and differentiation. Although originally formulated on the basis of evidence for NGF's actions on peripheral sensory and sympathetic neurons, the neurotrophic hypothesis appeared to be upheld for CNS neuronal systems as well, where NGF was found to function primarily as a target-derived trophic factor for basal forebrain cholinergic neurons. With the discovery of additional neurotrophins sharing considerable structural homology with NGF, the question arose of whether the neurotrophic hypothesis held true for all members of this protein family. Recent investigations into the localization and function of neurotrophins other than NGF, particularly BDNF and NT-3, have provided evidence indicating that these molecules may not act in a manner consistent with the neurotrophic hypothesis, as originally postulated. Numerous studies in the peripheral and central nervous systems have now demonstrated that BDNF (and NT-3) may be preferentially trafficked anterogradely along axonal processes and stored within pre-synaptic terminals. Other studies have suggested that these factors may be released in an activity-dependent, rather than constitutive, manner and can act in autocrine or paracrine fashions to subserve an assortment of biological functions including anterograde effects on cell survival and differentiation, as well as more novel roles in synaptic transmission. These recent findings strongly suggest that, while the various neurotrophin proteins may be grouped into a single family based upon their structural homology, they should be considered as a heterogeneous group of trophic factors based upon function and mode of action.

Development and characterization of monoclonal antibodies specific to the serotonin 5-HT2A receptor

Serotonin (5-hydroxytryptamine, 5-HT) mediates many functions of the central and peripheral nervous systems by its interaction with specific neuronal and glial receptors. Fourteen serotonin receptors belonging to seven families have been identified through physiological, pharmacological, and molecular cloning studies. Monoclonal antibodies (MAbs) specific for each of these receptor subtypes are needed to characterize their expression, distribution, and function in embryonic, adult, and pathological tissues. In this article we report the development and characterization of MAbs specific to the serotonin 5-HT2A receptor. To generate MAbs against 5-HT2AR, mice were immunized with the N-terminal domain of the receptor. The antigens were produced as glutathionine S-transferase (GST) fusion proteins in insect cells using a Baculovirus expression system. The hybridomas were initially screened by ELISA against the GST-5-HT2AR recombinant proteins and subsequently against GST control proteins to eliminate clones with unwanted reactivity. They were further tested by Western blotting against recombinant GST-5-HT2AR, rat and human brain lysate, and lysate from cell lines transfected with 5-HT2AR cDNA. One of the MAbs G186-1117, which recognizes a portion of the 5-HT2AR N-terminus, was selected for further characterization. G186-1117 reacted with a band of molecular size 55 kD corresponding to the predicted size of 5-HT2AR in lysates from rat brain and a 5-HT2AR-transfected cell line. Its specificity was further confirmed by adsorption of immunoreactivity with recombinant 5-HT2AR but not with recombinant 5-HT2BR and 5-HT2CR. Rat brain sections and Schwann cell cultures were immunohistochemically labeled with this MAb. G186-1117 showed differential staining in various regions of the rat brain, varying from regions with no staining to regions of intense reactivity. In particular, staining of cell bodies and dendrites of the pyramidal neurons in the cortex was observed, which is in agreement with observations of electrophysiological studies.

Partial cortical devascularization results in elevations of cortical nerve growth factor and increases nerve growth factor protein within basal forebrain cholinergic neurons

Previous studies have demonstrated that partial cortical devascularization results in increased levels of nerve growth factor protein within the tissue immediately surrounding the infarcted region. In the present study, we have used this lesion model to further characterize the nerve growth factor increase by investigating: (i) the time course for this phenomenon; (ii) the impact of the devascularizing lesion on cortical regions not directly impinged upon by the lesion; and (iii) the response of nerve growth factor-sensitive nucleus basalis neurons providing afferent cortical innervation to the increased availability of nerve growth factor within their target territory. Our results indicate that, within the infarcted cortex, nerve growth factor levels increase rapidly following the lesion (up 51% by one day post lesion), reach a maximum of 136% above controls by three days and undergo a slow decline back to baseline levels by 23 days. Within the frontal and cingulate cortices, which are not devascularized by the lesion and show no signs of pathological damage, nerve growth factor levels increase over a similar time course, and with a similar magnitude, to those in the lesioned cortex. Nerve growth factor-sensitive nucleus basalis neurons on the side ipsilateral to the lesion respond to increased cortical nerve growth factor levels with an increased accumulation of nerve growth factor within their cell bodies (revealed by nerve growth factor immunohistochemistry and quantitative enzyme-linked immunosorbent assay) which was apparent at three days following the lesion, but no longer discernible at seven or 14 days or later. The present study investigated a model of cortical devascularization for its ability to alter nerve growth factor levels within the cortex. Nerve growth factor levels were rapidly increased within the infarcted cortical tissue beneath the lesion but were also elevated to a similar extent, and with a similar time course, in cortical regions not directly impinged upon by the lesion. The retrograde impact of elevated cortical nerve growth factor levels was demonstrated by an increased accumulation of nerve growth factor within the cell bodies of nucleus basalis neurons providing innervation to the cortex. This lesion model should provide a potential avenue for investigating the functional role(s) of nerve growth factor in the intact and lesioned adult central nervous system, as well as the internal mechanisms for regulating its synthesis, release, uptake, and degradation.

Impact of Insecticides Alone and in Rotation on Tomato Pinworm, Leafminer and Beneficial Arthro-Pods on Staked Tomato, 1997

Greenhouse-raised tomato seedings were planted 18 inches apart on 4 sets of 3 subirrigated beds, 32 inches wide and 240 ft long, on 12 Mar. Beds were fumigated with a 67/33% mixture of methyl bromide and chloropicrin at a rate of 220 lb acre, fertilized, and covered with black polyethylene film mulch. The middle ‘inoculum’ row of each 3-bed set was left untreated. The remaining 2 beds in each set were divided into 8 plots about 30 ft long to accommodate 14 treatments and untreated check in a RCB design replicated 4 times. Plants were sprayed weekly with a combination of Maneb 80 WP at 1 lb/acre plus Kocide 101 at 3 lb/acre for disease control. Two wing-type sticky traps, baited with TPW pheromone (Scentry) lures placed in the field to monitor the pinworm population, showed peaks on four dates 3,4, 25 Apr and 2 May when the daily trap catch was 21, 26, 30, and 32, respectively. All other dates had a daily trap average of less than 10. Pre-treatment means of 20.5 LM and 3.4 PW mines/plant were recorded on 11 Apr. Seven weekly treatments were applied from 14 Apr through 30 May using a high-clearance sprayer with 2 booms fitted with “yellow” Albuz® hollow-cone nozzles operating at a pressure of 200 psi. The first 2 applications used 4 nozzles, 2 per boom, to deliver 42 gpa and the last five used 6 nozzles for 65 gpa. Three treatments con-sisted of SpinTor applied for 2 weeks followed by an application of Trigard, Agri-Mek, or Mattch. RH-2485 and Confirm were tank mixed with the adjuvant Latron CS-7 (0.12% v/v). Five weekly counts were made of dead/empty mines and live larvae of the LM and PW from one side of two plants, 4 samples per plot. Weekly vacuum samples of 4 sees from one side of 6 plants were taken beginning 17 Apr using a modified leaf blower. Catch was identified as beneficial (primarily spiders, hymenoptera exclusive of ants and predaceous hemiptera), pests and incidental (mostly flies). Fruit was harvested 3 Jun from 6 plants per plot and the marketable fruit graded on a commercial table with weights and numbers recorded. Unmarketable fruit was separated into categories of infestation with TPW, other insects and disease. Crop value was estimated based on $5,6,7,9 market per box of small, medium, large, and extra large fruit, respectively.

Anterograde transport of brain-derived neurotrophic factor and its role in the brain

The role of neurotrophins as target-derived proteins that promote neuron survival following their retrograde transport from the terminals to the cell bodies of neurons has been firmly established in the developing peripheral nervous system. However, neurotrophins appear to have more diverse functions, particularly in the adult central nervous system. Brain-derived neurotrophic factor (BDNF), for example, produces a variety of neuromodulatory effects in the brain that are more consistent with local actions than with long-distance retrograde signalling. Here we show that BDNF is widely distributed in nerve terminals, even in brain areas such as the striatum that lack BDNF messenger RNA, and that inhibition of axonal transport or deafferentation depletes BDNF. The number of striatal neurons that contain the calcium-binding protein parvalbumin was decreased in BDNF+/- and BDNF-/- mice in direct proportion to the loss of BDNF protein, which is consistent with anterogradely supplied BDNF having a functional role in development or maintenance. Thus the anterograde transport of BDNF from neuron cell bodies to their terminals may be important for the trafficking of BDNF in the brain.

Developmental profile of NGF immunoreactivity in the rat brain: a possible role of NGF in the establishment of cholinergic terminal fields in the hippocampus and cortex

In the current investigation, we have examined the developmental profile of nerve growth factor immunoreactivity (NGF-ir) in the postnatal rat. During the first 3 weeks after birth, NGF-ir was observed within the hippocampal mossy fiber region, where it persists throughout adulthood and appeared transiently within three additional zones-the dentate gyrus supragranular zone, the tenia tecta/intermediate lateral septum, and the cingulate/retrosplenial cortex. In all cases, the appearance of NGF-ir progressed in a rostrocaudal pattern over time. A strong correlation was seen between the pattern of NGF-ir and cholinergic innervation in the dentate gyrus supragranular zone, both spatially and temporally, suggesting that NGF may direct the innervation of cholinergic afferents to this region. A spatial correlation was also observed between NGF-ir and cholinergic innervation within the retrosplenial cortex and tenia tecta. With our current techniques, however, we were unable to determine at what point during development the adult-like pattern of cholinergic terminal innervation in these regions occurred and, thus, were not able establish a temporal correlation in these regions. Within the cingulate cortex, there was no evidence suggesting that the developmental appearance of NGF-ir in this region was associated with a specific enhancement of cholinergic innervation. Thus, the results of the current investigation clearly identify the presence of transiently occurring zones of NGF-ir during postnatal CNS development, although defining their exact functional role will require additional investigation.

Distribution of brain-derived neurotrophic factor (BDNF) protein and mRNA in the normal adult rat CNS: evidence for anterograde axonal transport

A sensitive immunohistochemical technique was used, along with highly specific affinity-purified antibodies to brain-derived neurotrophic factor (BDNF), to generate a detailed mapping of BDNF immunoreactivity (BDNF-ir) throughout the adult rat CNS. A parallel analysis of sites of BDNF synthesis was performed with in situ hybridization techniques using a cRNA probe to the exon encoding mature rat BDNF protein. These combined data revealed (1) groups of cell bodies containing diffuse BDNF-ir throughout the CNS that were strongly correlated with fields of cells containing BDNF mRNA; (2) varying degrees of BDNF-ir outside of cell bodies, in what appeared to be fibers and/or terminals; and (3) many regions containing extremely heavy BDNF-immunoreactive fiber/terminal labeling that lacked BDNF mRNA (e.g., medial habenula, central nucleus of the amygdala, bed nucleus of stria terminalis, lateral septum, and spinal cord). The latter observation suggested that in these regions BDNF was derived from anterograde axonal transport by afferent systems. In the two cases in which this hypothesis was tested by the elimination of select afferents, BDNF immunostaining was completely eliminated. These data, along with the observation that BDNF-ir was rarely found within dendrites or fibers en passage, suggest that BDNF protein produced in adult CNS neurons is polarized primarily along axonal processes and is preferentially stored in terminals within the innervation target.

The role of NGF and afferent denervation in the process of sympathetic fiber ingrowth into the hippocampal formation

Nerve growth factor (NGF) has been postulated to play an important role in the process of sympathetic sprouting into the septally deafferented hippocampal formation. In the current investigation we have used transplants of NGF-dependent neonatal superior cervical ganglion (SCG) neurons to investigate the influence of NGF and septal denervation (either alone or in combination with one another) upon neuronal survival and intrahippocampal sprouting. In the current model, SCG transplants were placed onto the dorsal surface of the CA1 hippocampal subfield and a continuous infusion device was used to deliver either NGF or vehicle into the hippocampal parenchyma. Following 15 days of vehicle infusion, little or no sympathetic neuronal survival was observed and no hippocampal fiber outgrowth was detected. NGF infusions, however, promoted both neuronal survival and intrahippocampal fiber outgrowth directed mainly toward the location of the infusion cannula. Septal denervation, achieved by either a septal ablation or fimbria-fornix transection, had no discernible impact upon SCG neuronal survival or fiber outgrowth, with or without NGF infusions. Similar results were also obtained when SCG were transplanted directly within the cortex, with or without an intracortical infusion. It appears, therefore, that NGF may be a sufficient, as well as necessary, component for eliciting and guiding the invasion of a tissue by NGF-sensitive fibers.

Distribution of brain-derived neurotrophic factor in the rat pituitary gland

Immunohistochemical techniques were used to determine the distribution of brain-derived neurotrophic factor (BDNF) in the adult rat pituitary gland. In the posterior lobe, BDNF staining was found only within fibers. Within the intermediate lobe, nearly all cells were labeled intensely for BDNF. In the anterior lobe, varying degrees of BDNF immunoreactivity were observed exclusively in cells shown by double-labeling techniques to contain thyroid stimulating hormone (TSH), although not all TSH-positive cells contained detectable BDNF labeling. These results are consistent with and extend information from previous studies demonstrating BDNF expression in the pituitary gland and further support the idea that this neurotrophin plays a role in endocrine function.

Nerve growth factor (NGF) content in adult rat brain tissues is several-fold higher than generally reported and is largely associated with sedimentable fractions

Initial studies had revealed that the bioactivity of nerve growth factor (NGF) in sonicates of adult rat hippocampal formation (HF) is several-fold greater in their pellet than their supernatant fractions. Such observations have prompted an analysis of NGF antigen (NGF-Ag) contents in pellets and supernatants from a variety of adult rat CNS tissues, both in the absence and the presence of exogenous beta-NGF. With HF tissues, NGF-Ag in the supernatants was comparable to most literature values, but pellet NGF-Ag was 3 to 5 times that amount. All other CNS tissue sonicates also revealed 3-6 fold higher NGF-Ag in their pellets than their supernatants, hence overall NGF-Ag contents were greatly in excess of reported ones. Presentation of mouse beta-NGF to a tissue, its sonicate, or its standard pellet resulted in a transfer to the final pellet of 30-50% of the added soluble NGF-Ag (and 30% of the added bioactivity). This percentage is much lower than that present in native pellets (80%), suggesting that the association of endogenous NGF with particulate matter may involve at least two compartments. Treatments of pellets with salt, alkaline pH, and/or the detergent Triton X-100 have revealed a third subset, namely additional pellet NGF-Ag that was not initially recognized by the antibody in our ELISA assay. The treatments also caused substantial release of NGF from pellet to supernatant. Further studies should clarify the nature of the association between NGF and the three subsets of pellet NGF and allow the investigation of the pellet molecules responsible for it.

Maintenance of sympathetic innervation into the hippocampal formation requires a continuous local availability of nerve growth factor

The sprouting of peripheral sympathetic fibers into the septally denervated hippocampal formation is a well-characterized model of lesion-induced plasticity. While various studies have demonstrated the importance of nerve growth factor for evoking sympathetic sprouting, little is known concerning whether nerve growth factor continues to be required for maintaining innervation once it has occurred. In the present study we have addressed this point by (i) investigating the consequences of withdrawing exogenous nerve growth factor support from rats in which sympathetic innervation was enhanced by a nerve growth factor infusion and (ii) using blocking antibodies to interfere with the actions of endogenous nerve growth factor. The results of this investigation clearly indicate that a continuous supply of nerve growth factor (either exogenous or endogenous) is required to maintain sympathetic innervation within the hippocampal formation. Evidence is also provided demonstrating that the nerve growth factor must be made available locally within a given region to evoke and maintain the sympathetic innervation within this location. Axonal rearrangement within the developing and adult brain is believed to be an important mechanism underlying learning and memory is crucial for lesion-related plasticity. In various experimental paradigms, nerve growth factor has been shown to be an important cue for initiating axonal remodeling. In the current study, we have demonstrated that once such rearrangements have taken place, nerve growth factor may also be required to maintain them.

Characterization of antibodies to nerve growth factor: assay-dependent variability in the cross-reactivity with other neurotrophins

The neurotrophin family of growth factors consists of proteins sharing a sizable degree of amino acid sequence and structural homology. These similarities greatly increase the probability that antibodies directed against any single neurotrophin may cross-react with other family-members. Various investigators have documented such cross-reactivity can occur under experimental conditions, although the extent of cross-reactivity reported in different studies has varied greatly. Although the use of different antibody preparations may have contributed to the differing degrees of cross-reactivity observed, it is important to note that different assay conditions were also used to evaluate cross-reactivity in the various studies. Little information is currently known about how antibody-antigen interactions vary as a function of the assay conditions used for the evaluation. The present study addressed this question by evaluating the cross-reactivity occurring between various neurotrophins and a single preparation of antibodies directed against purified mouse nerve growth factor-beta (beta-NGF) in a wide variety of immunological assay systems. Our results indicate that cross-reactivity between NGF antibodies and related neurotrophins can vary greatly depending upon the assay system chosen for the evaluation. These data strongly argue against transferring cross-reactivity data across various assay systems.

Effects of exogenous nerve growth factor upon sympathetic sprouting into the hippocampal formation

Following septal denervation of the hippocampal formation, sympathetic fibers from a transplanted superior cervical ganglion will innervate hippocampal tissue in a topographically restricted manner. Previously, we have shown a strong correlation between the regions innervated by the sprouting sympathetic axons and the distribution of NGF immunoreactivity in the hippocampal formation, suggesting that a restricted availability of NGF trophic support may regulate the topography of innervation by the NGF-sensitive sympathetic fibers. It was possible, however, that other molecular cues were responsible for restricting neurite outgrowth to selected hippocampal regions. In the current investigation, this idea was explored by experimentally altering the distribution of hippocampal NGF using a continuous intraparenchymal infusion device. Our results indicate that some hippocampal regions, not innervated by sympathetic fibers in control animals, do become occupied when the necessary trophic factor is provided, suggesting that these regions already contained an appropriate substratum for sympathetic neurite outgrowth but lacked the necessary trophic stimulus. Other regions, however, did not become innervated even though infused NGF was verifiably present in them. Together, these findings propose that a spatial restriction of NGF may be a crucial molecular mechanism for controlling the distribution of sprouting NGF-sensitive sympathetic fibers but that other endogenous signals may regulate NGF's ability to stimulate local terminal sprouting. The data are also consistent with the idea that a limited availability of endogenous NGF is regulating both the density of sympathetic innervation into the hippocampal formation and the extent of neuronal survival within the transplanted ganglion.

NGF modulates sympathetic innervation of lymphoid tissues

Immune tissues are known to be innervated by the sympathetic nervous system, but little is known of what directs the innervation to specific tissue compartments. This report examines the sympathetic innervation of immune tissues in transgenic mice that overexpress nerve growth factor (NGF) in skin and other epithelial structures. NGF transgenic mice exhibited dramatic hyperinnervation in the splenic marginal zone, and the medulla and capsule of peripheral lymph nodes. In contrast, the transgenic mesenteric lymph nodes showed no hyperinnervation. This difference correlated with the location of these nodes; peripheral lymph nodes drain skin where the transgene was expressed while mesenteric lymph nodes drain non-transgene-expressing structures. In addition, the level of innervation correlated with the level of NGF peptide content as assayed by ELISA (3- and 13-fold increase in transgenic spleen and axillary lymph nodes, respectively; no increase in mesenteric nodes) and immunocytochemistry. RT-PCR showed that the NGF transgene was not being expressed in the immune tissues, suggesting that immune tissues can concentrate transgene-produced NGF. It was also demonstrated that the change in innervation had functional consequences. The mitogen response to concanavalin A (ConA) by spleen cells was decreased in the transgenics suggesting that elevated catecholamines or NGF can modulate the proliferative response of these cells. These mice demonstrate that NGF can modulate the sympathetic innervation and function of the immune system.

Nerve growth factor in Alzheimer's disease: defective retrograde transport to nucleus basalis

NGF immunohistochemistry was combined with quantitative optical densitometry to evaluate whether retrogradely transported NGF is altered within cholinergic basal forebrain (CBF) neurons in Alzheimer's disease (AD). In normal aged humans, almost all CBF neurons stained for NGF. Although fewer in total number, remaining CBF perikarya in AD displayed diminished (32%) or undetectable NGF immunoreactivity. Based upon these data we hypothesize that there is a defect in retrograde transport of NGF in AD which may be due to a abnormal production and/or utilization of the trk receptor. This defect may be a primary event mediating the degeneration of CBF neurons in AD.

Colocalization of NGF and TSH-like immunoreactivity in cultures of adult rat anterior pituitary cells

Nerve growth factor (NGF) has been well-characterized with respect to its role as a trophic agent for various peripheral nervous system (PNS) and central nervous system (CNS) neuronal populations. Recent evidence indicates that NGF may also play a functional role in endocrine systems, although investigations in this field are only beginning to define sites of action and molecular mechanisms involved in NGF-endocrine interactions. A potential site for such an interaction to occur is within the pituitary. Previous investigations have demonstrated the presence of NGF and NGF receptors in the pituitary and our group has recently reported the presence of NGF-like immunoreactivity exclusively within the thyrotrophic cells of the anterior pituitary of the adult rat. Since many questions regarding how NGF interacts in the anterior pituitary will be more efficiently addressed using an in vitro system, it was necessary to first determine if cultured adult anterior pituitary cells retain the NGF-like staining and unique association of NGF with thyroid-stimulating hormone-producing cells seen in vivo. Results of the present investigation confirm that cultured anterior pituitary cells retain the characteristics previously observed in vivo and further demonstrate the stability of these cells and their specific NGF and pituitary hormone contents in culture for as long as 6 days.

Nerve growth factor influences the distribution of sympathetic sprouting into the hippocampal formation by implanted superior cervical ganglia

Following cholinergic denervation of the hippocampal formation, peripheral sympathetic fibers from the superior cervical ganglion (SCG) sprout into hippocampal tissue. The molecular mechanism controlling this process is unknown, although a role by trophic factors seems likely. In the present study, neonatal SCG were used as biological probes to investigate the association between NGF-immunoreactive regions in the hippocampal formation and areas innervated by regrowing sympathetic fibers. Cholinergic deafferentation of the hippocampal formation was achieved by a fimbria-fornix transection and neonatal SCG were placed into the lesion cavity, abutting the rostral pole of the hippocampus. At 16 days following ganglia transplantation, NGF immunoreactivity within the hippocampal formation appeared indistinguishable from unlesioned controls and was localized within the mossy fiber region of the dentate gyrus and CA3 and CA2 hippocampal subfields. Sympathetic innervation, revealed in adjacent sections by dopamine beta-hydroxylase or p75LNGFR immunoreactivity, was also restricted primarily to the mossy fiber region. Ablation of the entorhinal cortex at the time of transplantation resulted in the appearance of an additional discrete band of NGF immunoreactivity within the outer molecular layer of the dentate gyrus. In animals receiving an entorhinal lesion concurrent with the SCG transplant, sympathetic fibers were observed not only within the mossy fiber region but also within the outer molecular layer of the dentate gyrus where the lesion-induced NGF immunoreactivity appeared. These results support the hypothesis that topographic distributions of NGF may be used in the hippocampal formation to define terminal fields for sprouting NGF-sensitive neuronal populations.

Nerve growth factor in CNS repair

The hypothesis that neurotrophic factors play important roles in the adult central nervous system (CNS) has been successfully investigated in the past decade with regard to experimental and pathologic situations. Trophic roles in adult CNS axonal regeneration, on the other hand, have received much less attention. We review three groups of recent studies that demonstrate the relevance of nerve growth factor (NGF) for the regeneration of selected axons into adult central nervous tissue. The first group concerns a septohippocampal model where transected septal cholinergic axons are allowed to regrow into the hippocampal formation through a peripheral nerve bridge implanted into the transection lesion gap. NGF is required in the bridge, enhances penetration of the hippocampal tissue when infused there, and both attracts and promotes sprouting within the septum when infused in the lateral ventricle or the septal tissue itself. The second group of studies concerns the development of a spinal cord sensory regeneration model, where dorsal root ganglionic axons regrow into a nerve bridge placed within the dorsal spinal cord. Preliminary data indicate that NGF infusion rostral to the bridge once again promotes substantial penetration of the adult cord tissue by the regenerating NGF-sensitive fibers. In the third group of studies, attention has been shifted to the location of endogenous NGF in the adult rat hippocampal formation and the normal or lesion-induced occurrence of extrasomal NGF immunoreactivity. These regions of anchored NGF have the ability to attract NGF-sensitive growing axons and may provide opportunities to investigate local cues for final definition of terminal fields.

Changes in nerve growth factor immunoreactivity following entorhinal cortex lesions: possible molecular mechanism regulating cholinergic sprouting

To assess the possible role of trophic factors in lesion-induced plasticity, we have used a sensitive immunohistochemical technique to evaluate changes in nerve growth factor (NGF) staining in the hippocampal formation 3, 8, 16, and 30 days following entorhinal cortex lesions. Our results indicate that a band of NGF immunoreactivity appears in the outer molecular layer of the ipsilateral dentate gyrus following entorhinal ablation. The distribution of the NGF-immunoreactive band exactly coincides with the distribution of sprouting cholinergic terminals revealed by acetylcholinesterase histochemistry or NGF-receptor immunostaining. Increased NGF-immunoreactivity is detectable at 3 days postlesion, is most intense at 8 days, and decreases to near control levels by 30 days. Lesion-induced increases in NGF immunostaining also occur in animals in which septohippocampal fibers had been removed by prior destruction of the fimbria-fornix. Increases in NGF-immunoreactivity, however, are substantially reduced in animals receiving intraventricular injections of colchicine, which presumably blocks NGF release. These results indicate that 1) increases in NGF immunostaining, which occur following entorhinal lesions, precede any changes in cholinergic sprouting parameters and are greatest during the period of maximal cholinergic sprouting; 2) increased NGF-immunoreactivity is not due to NGF binding by septohippocampal fibers; and 3) increased NGF-immunoreactivity appears to depend on the release of NGF by neurons that produce it. We hypothesize that, following entorhinal lesions, NGF immunostaining within the hippocampal formation may represent NGF "anchored" within the tissue and that NGF accumulation by such a mechanism may direct the sprouting response of NGF-sensitive cholinergic neurons.

Nerve growth factor-like immunoreactive profiles in the primate basal forebrain and hippocampal formation

The distribution of nerve growth factor (NGF), the prototypic neurotropin, within the basal forebrain and hippocampal formation of young adult monkeys and aged humans was characterized with an affinity purified polyclonal beta-NGF antibody raised against mouse beta-NGF. In the basal forebrain of both primates, a granular NGF-like immunoreactive (ir) reaction product was observed within neurons of the medial septum, nucleus of the diagonal band, and nucleus basalis of Meynert. NGF-like immunoreactivity exclusively colocalized within p75 NGF receptor (NGFR) containing basal forebrain neurons. The intensity of NGF immunolabeling varied between cell bodies. Many NGF-ir perikarya were highly immunoreactive. In other basal forebrain neurons, NGF-like immunoreactivity was either undetectable or minimally expressed. In the hippocampus of both species, NGF-like immunoreactivity was mainly localized within the hilus of the dentate gyrus and within CA3 and CA2 hippocampal subfields. A marked diminution in NGF-like staining was seen in CA1. Within the hippocampal formation, NGF-like immunoreactivity was heaviest within the neuropil of stratum radiatum, intermediate in stratum oriens, and lightest in stratum pyramidal. NGF-like immunoreactivity was not found within the granule or pyramidal cells of the dentate gyrus and hippocampal formation, respectively. These findings demonstrate the presence of an NGF-like antigen in association with monkey and human magnocellular basal forebrain neurons and within their hippocampal target sites. This lends support to the hypothesis that NGF is internalized from sources located within target regions of the primate cholinergic basal forebrain neurons and is retrogradely transported to these cell bodies where the NGF trophic effect likely occurs.

Nerve growth factor immunoreactivity in the anterior pituitary of the rat

Nerve growth factor (NGF) has long been recognized for its neurotrophic actions upon sensory and sympathetic neurons of the PNS and upon cholinergic neurons of the CNS basal forebrain. Much evidence, however, suggests that potential reciprocal interactions between NGF and various endocrine systems may also occur. In the present investigation we used immunohistochemical techniques to investigate whether NGF is found within the adult rat pituitary, thereby suggesting a possible interaction within this critical neuroendocrine gland. Our results indicate that NGF immunoreactivity is present only within the anterior lobe of the male and female rat pituitary and is exclusively localized within cells immunoreactive for thyroid stimulating hormone (TSH).

Distribution of nerve growth factor-like immunoreactive neurons in the adult rat brain following colchicine treatment

Using immunohistochemical techniques, we have previously localized nerve growth factor (NGF)-like immunoreactivity in the normal adult rat central nervous system (CNS) exclusively in the hippocampal mossy fiber region and within basal forebrain cholinergic neurons--a cell population believed to be primary NGF consumers within the CNS. In the present investigation, we have attempted to identify potential producers of NGF by pretreating animals with colchicine. Such a treatment would be expected to block microtubule-assisted neuritic transport mechanisms, thus preventing the accumulation of antigens normally obtained by retrograde transport and forcing the accumulation of cell products normally exported anterogradely. Forty-eight hours after colchicine administration within their innervation territories, basal forebrain cholinergic neurons showed a marked loss of NGF-like immunoreactivity. Conversely, following colchicine treatment, many new populations of NGF-like immunoreactive cells were detected, several of which have been previously observed with in situ hybridization techniques for NGF mRNA. Many NGF-like immunoreactive populations, however, were not previously recognized by in situ hybridization methods, including cells of the striatum, reticular thalamic nucleus, paraventricular hypothalamic nucleus, supraoptic nucleus, lateral and medial septum, substantia innominata, and nucleus basalis. Furthermore, evidence is provided that colchicine-blocked, NGF-like immunoreactive neurons within the basal forebrain are not cholinergic, thus reinforcing the hypothesis that trophic support for these NGF-dependent neurons may be derived from distant and local sources. The distinctive distribution of NGF-like immunoreactive cells observed in this study strongly correlates with the reported distribution of NGF mRNA in CNS neurons, thus suggesting that our antibodies are uniquely recognizing NGF and not other related neurotrophins.

The localization of nerve growth factor-like immunoreactivity in the adult rat basal forebrain and hippocampal formation

The role of nerve growth factor (NGF) as a target derived neurotrophic agent for specific cell populations in the peripheral nervous system has been well documented and much evidence suggests that NGF may serve a similar neurotrophic role in the CNS supporting the cholinergic neurons of the basal forebrain. Previous attempts to localize NGF by immunocytochemical methods, however, have not yielded evidence confirming the regional distribution expected based upon reported levels of extractable NGF. In the present study, affinity purified polyclonal antibodies to beta-NGF and a modified immunohistochemical protocol were used to demonstrate specific NGF-like immunoreactivity in the adult rat hippocampal formation and basal forebrain. In the hippocampal formation, NGF-like immunoreactivity was localized primarily within the hilus of the dentate gyrus and within stratum lucidum of the CA3 and CA2 hippocampal subfields. Staining appeared to be associated with cell processes and was similar to the reported distribution of mossy fibers suggesting that granule cells may either serve as a primary source of hippocampal NGF or that mossy fibers selectively accumulate NGF produced by other cell populations. In the basal forebrain, NGF-like immunoreactivity was localized within neuronal cell bodies of the medial septum, diagonal band, and nucleus basalis of Meynert and was further demonstrated to colocalize exclusively with LNGF-R positive neurons. These findings demonstrate the presence of an NGF-like antigen in association with cholinergic neurons of the basal forebrain and strongly support the hypothesis that NGF may serve as an endogenous trophic factor for this adult neuronal population.

Dose-dependent responses to nerve growth factor by adult rat cholinergic medial septum and neostriatum neurons

This study describes the relationship between the concentration of intraventricularly infused nerve growth factor (NGF) and several responses by axotomized cholinergic medial septum neurons and normal cholinergic neostriatal neurons of the adult rat. NGF infused for 14 days starting either immediately after a unilateral fimbria-fornix transection or after a 2-week delay period elicited similar dose-response relationships for the maintenance or restoration of ChAT and NGF receptor positivity and cell body size and for intraseptal 'sprouting' of the axotomized medial septum neurons. Thus, in the medial septum it appears that the expression of 'marker' molecules, cell body size and the induction of 'sprouting' are regulated by virtually the same concentrations of NGF in the two treatment strategies. This suggests that NGF has a general regulatory role and injured but untreated neurons remain fully susceptible to NGF at least up to 2 weeks after the lesion. A 14-day infusion with NGF also induced an above-normal cell body size (hypertrophy) both in axotomized medial septum and in intact striatal cholinergic neurons. The hypertrophic response of normal striatal neurons required less NGF than did that of medial septum neurons. Since the striatal response began to be detectable at a similar concentration as that required for the full maintenance or restoration of ChAT and NGF receptor positivity it could be seen as an unwanted side-effect. The definition of a sub-optimal dose with which a significant, but not maximal response can be elicited will allow future evaluations of potentially additive or synergistic actions by other agents.

Artifact formation during smoke trapping: an improved method for determination of N-nitrosamines in cigarette smoke

Studies in our laboratory revealed artifactual formation of N-nitrosamines during trapping of mainstream and sidestream tobacco smoke by the method of Hoffmann and coworkers (2, 4). Both volatile and tobacco-specific N-nitrosamines were produced. This artifact formation took place on the Cambridge filter, which is part of the collection train used in the previously published procedure. When the filter was treated with ascorbic acid before smoke collection, artifact formation was inhibited. The improved method resulting from these studies was applied to a comparative analysis of N-nitrosamines in smoke from cigarettes that heat, but do not burn, tobacco (the test cigarette) and several reference cigarettes. Concentrations of volatile and tobacco-specific N-nitrosamines in both mainstream and sidestream smoke from the test cigarette were substantially lower than in the reference cigarettes.

Nerve growth factor (NGF) reverses axotomy-induced decreases in choline acetyltransferase, NGF receptor and size of medial septum cholinergic neurons

Intraventricular nerve growth factor (NGF) infusion in the adult rat can prevent and also, if delayed, reverse the disappearance of most of the axotomized medial septum cholinergic neurons immunostained for choline acetyltransferase (ChAT). We have utilized the delayed NGF treatment protocol to (i) extend to 3 months the delay time between axotomy and NGF treatment, (ii) define the time course of their recovery, (iii) determine that immunostaining for the (lower affinity) NGF receptor (NGFR) parallels loss and reversal of the ChAT marker, and (iv) evaluate changes in cholinergic somal size following axotomy and subsequent NGF treatment. While NGF treatments starting only 7 days after the fimbria-fornix transection (axotomy) almost entirely restored the number of both ChAT- and NGFR-positive medial septum neurons, longer delayed (2-3 weeks) treatment brought about recovery from the baseline of 20-25% to only about 70% of the control numbers. This limited recoverability, however, persisted even after a 95 day delay period. In all cases examined maximal recoveries were achieved within 3-7 days of NGF treatment. Neuronal size analyses provided evidence for an axotomy-induced atrophy. NGF treatments, started with 1 or 2 week delays, not only reversed fully the average somal size loss but also induced an actual hypertrophy of several of those neurons. These results provide additional evidence that at least half of the apparent loss of cholinergic medial septum neurons upon axotomy is due to a loss of markers such as the transmitter-related enzyme ChAT and NGFR rather than to actual neuronal cell death. These results also show that NGF exerts a genuine trophic influence by regulating the size of its target neurons as well as their content of several proteins.