Protective effect of NGF atelocollagen mini-pellet on the hippocampal delayed neuronal death in gerbils

Aripiprazole combined with nerve growth factor improves cognitive function in mice with schizophrenia model

The pathogenesis and treatment of cognitive dysfunction in patients with schizophrenia (SCZ) remains a challenge. Exploring new effective treatment strategies is relevant for the improvement of cognitive function. Aripiprazole (ARI) is an atypical antipsychotic that improves some cognitive functions. Nerve growth factor (NGF) has been shown to improve cognitive function in certain neurological impairments and partial neurological deficits, but its mechanism of action in cognitive dysfunction in SCZ is unclear. In this study, we established schizophrenia mouse model with dizocilpine (MK-801); treated mice with ARI alone or in combination with NGF; assessed spontaneous activity and cognitive function using open field test and Morris water maze test; and measured brain-derived neurotrophic factor (BDNF) protein and mRNA expression levels using immunohistochemistry and molecular biology assays. The results showed that ARI alone or in combination with NGF can improve increased spontaneous activity and spatial learning memory deficits in model mice by elevating BDNF expression levels in prefrontal cortex (PFC) and hippocampus (HIP). The results suggest that ARI combined with NGF can improve cognitive function in SCZ, which provides new ideas and directions for the clinical treatment of cognitive dysfunction in SCZ.

Functional Characterization of Ngf-Secreting Cell Grafts to the Acutely Injured Spinal Cord

Previously we reported that grafts of cells genetically modified to produce human nerve growth factor (hNGF) promoted specific and robust sprouting of spinal sensory, motor, and noradrenergic axons. In the present study we extend these investigations to assess NGF effects on corticospinal motor axons and on functional outcomes after spinal cord injury. Fibroblasts from adult rats were transduced to express human NGF; control cells were not genetically modified. Fibroblasts were then grafted to sites of midthoracic spinal cord dorsal hemisection lesions. Three months later, recipients of NGF-secreting grafts showed deficits on conditioned locomotion over a wire mesh that did not differ in extent from control-lesioned animals. On histological examination, NGF-secreting grafts elicited specific sprouting from spinal primary sensory afferent axons, local motor axons, and putative cerulospinal axons as previously reported, but no specific responses from corticospinal axons. Axons responding to NGF robustly penetrated the grafts but did not exit the grafts to extend to normal innervation territories distal to grafts. Grafted cells continued to express NGF protein through the experimental period of the study. These findings indicate that 1) spinal cord axons show directionally sensitive growth responses to neurotrophic factors, 2) growth of axons responding to a neurotrophic factor beyond an injury site and back to their natural target regions will likely require delivery of concentration gradients of neurotrophic factors toward the target, 3) corticospinal axons do not grow toward a cellular source of NGF, and 4) functional impairments are not improved by strictly local sprouting response of nonmotor systems.

Treatment of focal cerebral ischemia with liposomal nerve growth factor

Liposomal nerve growth factor (NGF) was used for the treatment of focal cerebral ischemia in a rat model. Positive charge inducing agents of sphingosine (SP) and stearylamine (S) were formulated in the liposomal NGF. Dose-response of intraventricular injection of liposomal NGF showed significant reduction in infarct volume at the dose of 5 and 10 microg/rat of NGF. The liposomal NGF formulated with SP or S demonstrated similar results in the reduction of total infarct volume in rats. When we increased the molar ratio of SP and S from 0.15 to 0.3, the infarct volume from rats showed a similar value as that of the control treated with NGF solution. Liposomal NGF was given prior to the development of ischemia. We found that NGF was effective in prevention of neuronal death. The NGF concentrations in brain for liposomal NGF were maintained in a level significantly higher than those for NGF solution. This was attributed to the positively charged liposomal NGF bound effectively in brain ventricle and caused longer retention time than free NGF for localization in brain. Therefore, the effect of liposomal NGF on reduction of infarct volume was significant. We assumed that the transportation of NGF might go through the cerebrospinal fluid pathway throughout the ventricular system and subarachnoid system to cerebral cortex to produce a therapeutic effect on ischemia.

Transient ischemia-induced expression and changes of tyrosine kinase A in the hippocampal dentate gyrus of the gerbil

The present study examined ischemia-related changes in tyrosine kinase A (trkA) immunoreactivity and its protein content in the dentate gyrus after 5 min of transient forebrain ischemia in gerbils. One day after ischemic insult, cresyl violet-positive polymorphic cells showed ischemic degeneration. The ischemia-induced changes in trkA immunoreactivity were found in the polymorphic layer (PL) and granule cell layer (GCL) of the dentate gyrus. In the sham-operated group, trkA immunoreactivity in the dentate gyrus was very weak. From 30 min after ischemia, trkA immunoreactivity was increased in the dentate gyrus and peaked in the dentate gyrus at 12 h after ischemia-reperfusion. Thereafter, trkA immunoreactivity was decreased time-dependently after ischemia-reperfusion. Four days after ischemic insult, trkA immunoreactivity was similar to that of the sham-operated group. In addition, it was found that ischemia-related changes in trkA protein content were similar to the immunohistochemical changes. These results suggest that the chronological changes of trkA in the dentate gyrus after transient forebrain ischemia may be associated with ischemic damage in polymorphic cells of the dentate gyrus.

Neuroprotective role of neurotrophins: Relationship between nerve growth factor and apoptotic cell survival pathway after cerebral ischemia

Neurotrophins provide a neuroprotective effect in a variety of brain diseases. Recent reports demonstrate that neurotrophins play an important role in the regulation of apoptotic neuronal cell death and in the relationship between this machinery and activation of cell survival pathways. The cascade reactions of the two major cell survival pathways, mitogen-activated protein kinase and phosphatidylinositol 3-kinase, are known to play a critical role in the regulation of apoptotic neuronal cell survival pathways. Neurotrophins such as nerve growth factor regulate these two cell survival pathways in in vitro studies. However, the role of neurotrophins in cell survival remains unclear in in vivo apoptotic neuronal cell death. We discuss the mechanism of neuroprotection by neurotrophins and also discuss cell survival effect of nerve growth factor on apoptotic neuronal cell death after in vivo cerebral ischemia.

Antigenicity and immunogenicity of collagen

Pertinent issues of collagen antigenicity and immunogenicity are concisely reviewed as they relate to the design and application of biomedical devices. A brief discussion of the fundamental concepts of collagen immunochemistry is presented, with a subsequent review of documented clinical responses to devices containing reconstituted soluble or solubilized collagen. The significance of atelocollagen, concerns regarding collagen-induced autoimmunity, and other relevant topics are also addressed in the context of current understanding of the human immune response to collagen.

Tyrosine kinase A but not phosphacan/protein tyrosine phosphatase-ζ/β immunoreactivity and protein level changes in neurons and astrocytes in the gerbil hippocampus proper after transient forebrain ischemia

In the present study, ischemia-related changes in tyrosine kinase A (trkA) and phosphacan/protein tyrosine phosphatase-zeta/beta (PTP-zeta/beta) immunoreactivities and protein contents were examined in the hippocampus proper after transient forebrain ischemia for 5 min in a gerbil model. Our investigations showed that ischemia-induced changes occurred in trkA immunoreactivity in the hippocampal CA1 region, but not in the CA2/3 region of the hippocampus proper. In the sham-operated group, trkA immunoreactivity was barely detectable. trkA immunoreactivity increased from 30 min after ischemia and peaked at 12 h. Four days after ischemic insult, trkA immunoreactivity was observed in GFAP-immunoreactive astrocytes in the strata oriens and radiatum. In addition, we found that ischemia-related changes in trkA protein content were similar to immunohistochemical changes. On the other hand, PTP-zeta/beta immunoreactivities in the hippocampus proper were unaltered by forebrain ischemia. These results suggest that chronological changes of trkA after transient forebrain ischemia may be associated with an ischemic damage compensatory mechanism in CA1 pyramidal cells.

Enhanced Expression of Tyrosine Kinase Receptor A in Germ Cells of Rat Testis with Acute Experimental Testicular Torsion

OBJECTIVE AND METHODS

To examine the involvement of neurotrophic factor receptors in the testis with acute experimental testicular torsion, the expression of tyrosine kinase receptors (trk) A and B, and p75 nerve growth factor receptor (NGFR) were studied in the rat testis with ischemia/reperfusion (I/R) injury, using Western blotting and immunohistochemistry. Apoptosis was detected using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method.

RESULTS

There was a significant increase in TUNEL-positive reaction in spermatogonia in the seminiferous tubules in rat testes after testicular torsion. Western blot analysis showed that trk A expression reached a significant peak at 12 h after reperfusion (p < 0.01), as compared to sham-operated controls, whereas trk B was not increased in the testis after I/R. Constitutive expression of p75 NGFR was at or below the level detectable by Western blot analysis, and it remained unchanged in the testis after I/R. Immunohistochemistry demonstrated that after I/R trk A expression was increased in spermatocytes and spermatids in the seminiferous tubules, in contrast to the basal location of the TUNEL-positive reaction. Immunoreactivity of trk B was seen mainly in the interstitial cells in the sham-operated testis, and its localization was not changed after I/R.

CONCLUSION

It is postulated that trk A and B, but not p75 NGFR, are involved differently in the survival of testicular cells during acute experimental testicular torsion. In particular, increased trk A seems to be related to germ cell survival following I/R.

Postischemic administration of Sendai virus vector carrying neurotrophic factor genes prevents delayed neuronal death in gerbils

Sendai virus (SeV) vector-mediated gene delivery of glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF) prevented the delayed neuronal death induced by transient global ischemia in gerbils, even when the vector was administered several hours after ischemia. Intraventricular administration of SeV vector directed high-level expression of the vector-encoded neurotrophic factor genes, which are potent candidates for the treatment of neurodegenerative diseases. After occlusion of the bilateral carotid arteries of gerbils, SeV vector carrying GDNF (SeV/GDNF), NGF (SeV/NGF), brain-derived neurotrophic factor (SeV/BDNF), insulin-like growth factor-1 (SeV/IGF-1) or vascular endothelial growth factor (SeV/VEGF) was injected into the lateral ventricle. Administration of SeV/GDNF, SeV/NGF or SeV/BDNF 30 min after the ischemic insult effectively prevented the delayed neuronal death of the hippocampal CA1 pyramidal neurons. Furthermore, the administration of SeV/GDNF or SeV/NGF as late as 4 or 6 h after the ischemic insult also prevented the death of these neurons. These results indicate that SeV vector-mediated gene transfer of neurotrophic factors has high therapeutic potency for preventing the delayed neuronal death induced by transient global ischemia, and provides an approach for gene therapy of stroke.

Neuroprotective role of a proline-rich Akt substrate in apoptotic neuronal cell death after stroke: relationships with nerve growth factor

The Akt signaling pathway contributes to regulation of apoptosis after a variety of cell death stimuli. A novel proline-rich Akt substrate (PRAS) was recently detected and found to be involved in apoptosis. In our study, Akt activation was modulated by growth factors, and treatment with nerve growth factor (NGF) reduced apoptotic cell death after ischemic injury. However, the role of the PRAS pathway in apoptotic neuronal cell death after ischemia remains unknown. Phosphorylated PRAS (pPRAS) and the binding of pPRAS/phosphorylated Akt (pPRAS/pAkt) to 14-3-3 (pPRAS/14-3-3) were detected, and their expression transiently decreased in mouse brains after transient focal cerebral ischemia (tFCI). Liposome-mediated pPRAS cDNA transfection induced overexpression of pPRAS, promoted pPRAS/14-3-3, and inhibited apoptotic neuronal cell death after tFCI. The expression of pPRAS, pPRAS/pAkt, and pPRAS/14-3-3 increased in NGF-treated mice but decreased with inhibition of phosphatidylinositol-3 kinase and the NGF receptor after tFCI. These results suggest that PRAS phosphorylation and its interaction with pAkt and 14-3-3 might play an important role in neuroprotection mediated by NGF in apoptotic neuronal cell death after tFCI.

Concomitant up-regulation of astroglial high and low affinity nerve growth factor receptors in the CA1 hippocampal area following global transient cerebral ischemia in rat

We have examined the effect of global transient cerebral ischemia, evoked in rat by 10 min of cardiac arrest, upon the changes in the cellular expression of two nerve growth factor (NGF) receptors (TrkA and p75) in the hippocampus. We have used immunocytochemical procedures, including a quantitative analysis of staining, along with some quantitative morphological analyses. We have found, under ischemic conditions, a decrease of TrkA immunoreactivity in degenerating CA1 pyramidal neurons and in neuropil. On the other hand, a strong, ischemia-induced up-regulation of TrkA and p75 immunoreactivity was observed in the majority of reactive astroglia population in the adjacent CA1 hippocampal region. The colocalization of the two receptors in the same reactive astroglial cells was evidenced by double immunostaining and further supported by quantitative morphological analysis of TrkA and p75 immunoreactive glial cells. Our data implicate the involvement of NGF receptors in the postischemic regulation of astrocytic function; however, the lack of NGF receptor expression on some astrocytes suggests heterogeneity of astroglia population. Our results also indicate that the lack of neuroprotective action of astroglial NGF induced in the ischemic hippocampus [J Neurosci Res 41 (1995) 684; Acta Neurobiol Exp 57 (1997) 31; Neuroscience 91 (1999) 1027] is not caused by a paucity of NGF receptors but may rather be due to the counteraction of some proinflammatory substances, released simultaneously by glia cells. On the other hand, the up-regulated astroglial TrkA receptor may be an important target for exogenous NGF, which, as previously described [J Neurosci 11 (1991) 2914; Neurosci Lett 141 (1992) 161], exerts a neuroprotective effect in ischemia.

Continuous intrathecal fluid infusions elevate nerve growth factor levels and prevent functional deficits after spinal cord ischemia

Continuous intracerebroventricular or intrathecal infusions of neurotrophic factors have been reported to prevent neuronal degeneration, stimulate axonal sprouting and ameliorate behavioral deficits in various models of CNS injury and aging. In the present study, the ability of intrathecal infusions of recombinant human nerve growth factor (NGF) to reduce functional deficits following spinal cord ischemia was investigated. Adult rabbits underwent intrathecal cannulation and continuous infusions of either 300 microg/ml recombinant human NGF or artificial CSF (vehicle) at a rate of 143 microl/day for 7 days prior to induction of spinal cord ischemia. Continuous infusions were maintained after induction of ischemia. Four days later, both NGF-treated and vehicle-infused subjects showed a significant amelioration of functional motor deficits compared to lesioned, non-infused subjects (P<0.05). The average duration of tolerated ischemia increased from 23.4+/-1.8 min in lesioned, non-infused subjects to 35.5+/-3.1 min in lesioned, artificial CSF-infused subjects and 35.6+/-4.7 min in NGF-infused subjects (mean+/-S.E.M.). Significantly elevated NGF protein levels were attained within the spinal cords of both NGF-treated subjects and artificial CSF-infused subjects, although levels were substantially higher in NGF-treated subjects (9.8+/-3.8 ng/g in NGF-infused vs. 2.0+/-0.4 ng/g in vehicle-infused and only 0.4+/-0.2 ng/g in lesioned, non-infused animals). These findings indicate that the process of intrathecal cannulation and fluid infusion elicits alterations in the spinal cord environment that are neuroprotective, including spontaneous elevations in NGF levels.

A review of therapeutic potentials in ischemic stroke

Stroke is one of the leading causes of death in the world. There are as yet no effective treatments for the ischemic cerebral lesion itself. Nevertheless, five potential therapeutic objectives can be identified. For cerebral infarction, the best treatment is prevention, including targeted preventive treatments for specific subsets of patients or individuals with different risk factors. Incidence rates and mortality rates of stroke have been successfully reduced in certain developed countries by adoption of a public health approach to the prevention and control of risk factors. To rescue the still viable but injured nerve cells, within the ischemic penumbra, effective therapy should be begun at the earliest possible time. Measures to halt or reverse programmed cell death, to enhance the intrinsic autoprotective and repair mechanisms, are under active study. The existence of down-regulated brain regions, where normal nerve cells have far less activities to perform due to interruption of information exchange with the infarct area, and the possibility to reactivate them are worthy of attention.

Development of microspheres for neurological disorders: from basics to clinical applications

Drug delivery to the central nervous system remains a challenging area of investigation for both basic and clinical neuroscientists. Numerous drugs are generally excluded from blood to brain transfer due to the negligible permeability of the brain capillary endothelial wall, which makes up the blood brain barrier in vivo. For several years, we have explored the potential applications of the microencapsulation of therapeutic agents to provide local controlled drug release in the central nervous system. Due to their size, these microparticles can be easily implanted by stereotaxy in discreet, precise and functional areas of the brain without damaging the surrounding tissue. This type of implantation avoids the inconvenient insertion of large implants by open surgery and can be repeated if necessary. We have established the compatibility of poly(lactide-co-glycolide) microspheres with brain tissues. Presently, the most developed applications concern Neurology and Neuro-oncology, with local delivery of neurotrophic factors and antimitotic drugs into neurodegenerative lesions and brain tumours, respectively. The drugs that had been encapsulated by our group included nerve growth factor (NGF), 5-fluorouracil (5-FU), idoxuridine and BCNU. Preclinical studies have been performed with each drug. Studies with NGF are reported as an example. A phase I/II clinical trial has been carried out in patients with newly diagnosed glioblastomas to assess the potentialities of 5-FU-loaded microspheres when intracranially implanted.

Intracerebral implantation of NGF-releasing biodegradable microspheres protects striatum against excitotoxic damage

Intrastriatal implantation of genetically modified cells synthesizing nerve growth factor (NGF) constitutes one way to obtain a long-term supply of this neurotrophic factor and a neuronal protection against an excitotoxic lesion. We have investigated if NGF-loaded poly(d,l-lactide-co-glycolide) microspheres could represent an alternative to cell transplantations. These microspheres can be implanted stereotaxically and locally release the protein in a controlled and sustained way. In order to test this paradigm, the NGF release kinetics were characterized in vitro using radiolabeled NGF, immunoenzymatic assay, and PC-12 cells bioassay and then in vivo after implantation in the intact rat striatum. These microspheres were thus implanted into the rat striatum 7 days prior to infusing quinolinic acid. Control animals were either not treated or implanted with blank microspheres. The extent of the lesion and the survival of ChAT-, NADPH-d-, and DARPP-32-containing neurons were analyzed. In vitro studies showed that microspheres allowed a sustained release of bioactive NGF for at least 1 month. Microspheres implanted in the intact striatum still contained NGF after 2.5 months and they were totally degraded after 3 months. After quinolinic acid infusion, the lesion size in the group treated with NGF-releasing microspheres was reduced by 40% when compared with the control groups. A marked neuronal sparing was noted, principally concerning the cholinergic interneurons, but also neuropeptide Y/somatostatin interneurons and GABAergic striatofuge neurons. These results indicate that implantation of biodegradable NGF-releasing microspheres can be used to protect neurons from a local excitotoxic lesion and that this strategy may ultimately prove to be relevant for the treatment of various neurological diseases.

BDNF atelocollagen mini-pellet accelerates facial nerve regeneration

We investigated the effect of BDNF mini-pellet on the GAP-43 mRNA expression and functional status of facial nerve in a rat model of facial nerve transection and immediate repair. The facial function started to recover at 17 days in the placebo group and 14 days in the BDNF group. BDNF group had shorter period of increased GAP-43 mRNA expression than the placebo group. Topically applied BDNF may accelerate the facial nerve regeneration.

Intracranial delivery of recombinant nerve growth factor: release kinetics and protein distribution for three delivery systems

PURPOSE

Three different polymeric delivery systems, composed of either poly(ethylene-co-vinyl acetate) (EVAc) or poly(lactide-co-glycolide) (PLGA), were used to administer recombinant human nerve growth factor (rhNGF) intracranially in rats.

METHODS

The delivery systems were characterized with respect to release kinetics, both in the brain and in well-stirred buffer solutions.

RESULTS

During incubation in buffered saline, the delivery systems released rhNGF in distinct patterns: sustained (EVAc), immediate (PLGA1) and delayed (PLGA2). One 10-mg delivery system was implanted in each rat and an ELISA technique was used to determine the amount of rhNGF in 1-mm coronal brain slices produced immediately after removal of the delivery system. High levels of rhNGF (as high as 60,000 ng in a brain slice of approximately 50 microliters) were recovered from the brain tissue at 1, 2, and 4 weeks after implantation. With all three delivery systems, the amount of rhNGF in each brain slice decreased exponentially with distance from the implant site: the distance over which concentration decreased by 10-fold was 2-3 mm for all delivery systems. When rhNGF release was moderate (10 to 200 ng rhNGF/day), the total amount of rhNGF in the brain increased linearly with release rate, suggesting an overall rate of rhNGF elimination of 0.4 hr-1 or a half-life of 1.7 hr. With higher release rates (500 to 50,000 ng rhNGF/day), total amounts of rhNGF in the brain were considerably higher than anticipated based on this rate of elimination.

CONCLUSIONS

Polymeric controlled release can provide high, localized doses of rhNGF in the brain. All of the experimental data were consistent with penetration of rhNGF through the brain tissue with a diffusion coefficient approximately 8 x 10(-7) cm2/s, which is approximately 50% of the diffusion coefficient in water.

Expression of nerve growth factor and trkA after transient focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

In vitro studies have shown that nerve growth factor (NGF) is protective to cortical neurons against various insults. However, the role of NGF in relation to its high-affinity trkA receptor in the cortical neurons has not been well discussed. In this experiment, we studied the possible involvement of the NGF/receptor system in the ischemic injury of cortical neurons after focal cerebral ischemia in rats.

METHODS

Male Wistar rats received right middle cerebral artery occlusion of 90 minutes' duration. The rats were decapitated at different reperfusion time points: hour 4 and days 1, 3, 7, and 14 of recirculation. Brain sections at the level of striatum were immunostained against NGF, trkA, glial fibrillary acidic protein (GFAP), and stress protein HSP70. Double immunostaining against NGF and GFAP was also performed. Optical density of NGF immunoreactivity in the ischemic and nonischemic cortexes was compared between sham-control and ischemic animals.

RESULTS

In the sham-control rats, NGF immunoreactivity was present in the cortical and striatal neurons. However, beginning at hour 4 after recirculation, there was a significant decrease of NGF in the ischemic cortex and striatum. Beginning at day 1, NGF was absent completely in the infarcted striatum and cortex. However, in the peri-infarct penumbra area, despite a decrease in NGF at hour 4 and day 1, NGF recovered beginning at day 3 and returned almost to the sham-control level at day 14. In the nonischemic cortex, NGF increased beginning at hour 4, peaked at day 7, and returned almost to the sham-control level at day 14. The trkA and HSP70 immunoreactivities were not present in the sham-control cortex. However, trkA was induced at hour 4 in the ischemic cortex and at days 1 and 3 in the peri-infarct penumbra cortex. The HSP70 was induced at days 1 and 3 in the peri-infarct penumbra area. Double immunostaining showed that the number of GFAP-positive cells increased gradually, and NGF immunoreactivity in the GFAP-positive cells became gradually intense after ischemia.

CONCLUSIONS

Our study demonstrated a temporal profile of NGF and trkA in the ischemic cortex and NGF expression by reactive astrocytes. Our data suggest that the NGF/receptor system may play a role in the astrocyte/neuron interaction under certain pathological conditions, such as focal cerebral ischemia.

TGF-beta in the central nervous system: potential roles in ischemic injury and neurodegenerative diseases

The Transforming Growth Factor-betas (TGF-beta) are a group of multifunctional proteins whose cellular sites of production and action are widely distributed throughout the body, including the central nervous system (CNS). Within the CNS, various isoforms of TGF-beta are produced by both glial and neural cells. When evaluated in either cell culture or in vivo models, the various isoforms of TGF-beta have been shown to have potent effects on the proliferation, function, or survival of both neurons and all three glial cell types, astrocytes, microglia and oligodendrocytes. TGF-beta has also been shown to play a role in several forms of acute CNS pathology including ischemia, excitotoxicity and several forms of neurodegenerative diseases including multiple sclerosis, Parkinson's disease, AIDS dementia and Alzheimer's disease.

Platelet-derived growth factor-BB, but not -AA, prevents delayed neuronal death after forebrain ischemia in rats

Our previous studies demonstrated coordinate expression of platelet-derived growth factor (PDGF) -B chain and beta-receptor in neurons at risk in the rat brain with focal ischemia. To clarify a role of the -B chain in the brain further, we examined whether PDGF-A or -B chain protects CA1 pyramidal neurons from delayed neuronal death after forebrain ischemia in rats. Pretreatment with PDGF-BB, but not -AA, at 120 ng/d for 2 days until forebrain ischemia was performed markedly ameliorated delayed neuronal death in CA1 pyramidal neurons on day 7 after ischemia. This neuroprotective effect of PDGF-BB was dose-dependent, and pretreatment with PDGF-BB at 240 ng/d showed almost complete inhibition of delayed neuronal death. In contrast, posttreatment with PDGF-BB at 120 ng/d starting 20 minutes after ischemia demonstrated no significant neuroprotective effect. The current study established marked neuroprotective actions of PDGF-BB in ischemic neuronal damage.

Aging in the hippocampus: interrelated actions of neurotrophins and glucocorticoids

Over the past two decades, evidence has been accumulating that diffusible molecules, such as growth factors and steroids hormones, play an important part in neural senescence, particularly in the hippocampus. There is also evidence that these molecules do not act as independent signals, but show interrelated regulation and cooperative control over the aging process. Here, we review some of the changes that occur in the hippocampus with age, and the influence of two classes of signaling substances: glucocorticoids and neurotrophins. We also examine the interactions between these substances and how this could influence the aging process.

Marked age-dependent neuroprotection by brain-derived neurotrophic factor against neonatal hypoxic-ischemic brain injury

Hypoxic-ischemic brain injury in survivors of perinatal asphyxia is a frequently encountered clinical problem for which there is currently no effective therapy. Neurotrophins, such as brain-derived neurotrophic factor (BDNF), can protect responsive neurons against cell death in some injury paradigms. While the role of BDNF in hypoxic-ischemic brain injury is not clear, evidence suggests that BDNF may have different effects in the developing, as opposed to the adult, brain. We found that a single intracerebroventricular (ICV) injection of BDNF resulted in rapid and robust phosphorylation of trk receptors in multiple brain regions in the postnatal day (PD) 7 rat brain. BDNF also markedly protected against hypoxic-ischemic brain injury at PD7. It protected against 90% of tissue loss due to hypoxic-ischemia when given just prior to the insult and against 50% of tissue loss when give after the insult. In contrast, ICV injection of BDNF in PD21 and adult rats resulted in little trk phosphorylation and less dramatic protection against unilateral hypoxic-ischemic injury at PD21. Because of its potent neuroprotective actions in the developing brain, BDNF may be a potential treatment for asphyxia and other forms of acute injury in the perinatal period.

Selegiline enhances NGF synthesis and protects central nervous system neurons from excitotoxic and ischemic damage

It has been previously demonstrated that selegiline, an irreversible monoamine oxidase B (MAO-B) inhibitor, potentiates glial reaction to injury and possesses some 'trophic-like' activities which do not depend on the inhibition of MAO-B and which are probably associated with the induction of astrocyte-derived neurotrophic substances. Based on these findings, we tried to find out whether selegiline is able to modify the expression of nerve growth factor (NGF) and to protect central nervous system (CNS) neurons from excitotoxic and ischemic damage. Selegiline (10 pM-1 nM) induced NGF messenger RNA (mRNA) expression in cultured rat cortical astrocytes as determined by reverse transcription-polymerase chain reaction (RT-PCR) followed by a corresponding increase in NGF protein content measured by two-site NGF-enzyme-linked immunosorbent assay (ELISA) in astrocyte-conditioned medium. Additionally, exposure of hippocampal cultures containing neuronal and glial cells to this drug at the same concentrations enhanced significantly the content of NGF measured in the culture medium after 6 h of incubation. We hypothesize that selegiline could rescue hippocampal neurons from injury by induction of astrocyte-derived NGF in this cell culture system. To test this hypothesis, an excitotoxic damage was induced in the same type of cells by exposure to 0.5 mM L-glutamate for 1 h. Selegiline (10 pM-1 nM) present in the growth medium 6 h before until 18 h after induction of injury (the point of glutamate-toxicity measurement) protected hippocampal neurons from excitotoxic death. Furthermore, administered intraperitoneally (i.p.) (8 x 15 mg/kg per day) this drug enhanced the expression of NGF message in intact rat cerebral cortex and protected rat cortical tissue from ischemic insult due to permanent occlusion of the middle cerebral artery (MCA). The neuroprotective activity of selegiline (5 x 10 mg/kg per day i.p.) was also demonstrated in a mouse model of focal cerebral ischemia. The present data show that selegiline induced NGF expression in cultured rat cortical astrocytes. In mixed primary cultures of hippocampal neuronal and glial cells, selegiline increased NGF protein content and protected hippocampal neurons from excitotoxic degeneration. In vivo, this drug induced NGF gene expression in cerebral cortex from intact rats and protected rat and mouse cortical tissue from ischemic insult after occlusion of the MCA. Our results indicate that the induction of astrocyte-derived NGF could contribute to the neuroprotective activity of selegiline demonstrated both in vivo and in vitro and can explain, in part, the 'trophic-like' properties of this compound which has been observed by others.

Neuroprotective effect of 4'-(4-methylphenyl)-2,2':6',2-terpyridine trihydrochloride, a novel inducer of nerve growth factor

We have identified 4'-(4-methylphenyl)-2,2':6',2-terpyridine: trihydrochloride (SS701), which belongs to a family of a small unique neuroprotective agents. SS701 accelerated the production of nerve growth factor (NGF) in cultured astroglial cells, dose- and time-dependently. In in vivo studies, SS701, when administered 30 min after induced cerebral ischemia, neuroprotective effects on delayed neuronal death in Mongolian gerbils were evident. The neuroprotective effects of SS701 against ischemia-induced delayed neuronal death are attributed to stimulation of the production of NGF.

Temporal profile of nerve growth factor-like immunoreactivity after transient focal cerebral ischemia in rats

We studied the temporal profile of nerve growth factor-like immunoreactivity (NGF-LI) in the rat brains following 30 min of middle cerebral artery occlusion. The rats were decapitated at 4 h, 1, 3, 7, and 14 days of recirculation. Brain sections at the level of striatum were immunostained against NGF as well as a stress protein, HSP70. Also, double immunostaining of NGF and glial fibrillary acidic protein was performed. In the sham-control rats, NGF-LI was normally present in the cortical and striatal neurons. However, at 4 h of recirculation, there was a significant decrease of NGF-LI in the ischemic cortex and striatum. From 1 day, NGF-LI was absent completely in the ischemic striatum. However, in the ischemic cortex, NGF-LI decreased to the lowest level at 1 day, but it recovered gradually from 3 days and increased significantly to above sham-control level at 7 days. At 14 days of recirculation, NGF-LI returned to a near sham-control level. In the non-ischemic cortex, NGF-LI increased gradually from 4 h with a peak at 7 days, and returned to the sham-control level at 14 days of recirculation. A HSP70 was induced in the ischemic cortex at 1 and 3 days, when there was a significant reduction of NGF-LI. The number of reactive astrocytes increased gradually and NGF-LI in the reactive astrocytes became gradually intense after ischemia. The present finding showing that NGF-LI can be recovered in the stressed cortical neurons suggests a possible involvement of NGF in the process of neuronal survival after focal cerebral ischemia. The expression of NGF in reactive astrocytes indicates that astrocyte may also play a role in supporting neuronal survival after ischemia.

Expression of messenger RNA coding for the nerve growth factor receptor trkA in the hippocampus of the adult rat

Nerve growth factor is a member of the neurotrophin gene family and acts as a neurotrophic factor on a variety of neuronal populations. Nerve growth factor biological action is mediated by binding to the transmembrane tyrosine kinase trkA, although the low affinity neurotrophin receptor p75 may also play a role. TrkA messenger RNA in the central nervous system is localized within a small number of specific neuronal populations, as opposed to the widespread expression of the other members of the trk family, trkB and trkC. In particular, cholinergic neurons of the basal forebrain, the prototype of nerve growth factor-sensitive neurons in the brain express trkA. Several lines of evidence indicate that other populations of central neurons, in particular hippocampal neurons, may be responsive to nerve growth factor as well. In fact, nerve growth factor rescues hippocampal neurons from ischemic cell death in vivo and increases neurotransmitter release from hippocampal neurons in culture. Moreover, nerve growth factor has been implicated in spatial learning, a process known to be dependent on the hippocampal formation. The following paper reports expression of trkA messenger RNA in the rat hippocampus by in situ hybridization and reverse transcription-polymerase chain reaction. This finding supports the notion of hippocampal neurons as an nerve growth factor-sensitive population.

Nerve growth factor protects the neonatal brain against hypoxic-ischemic injury

Nerve growth factor (NGF) has been shown to protect specific neurons that express its signaling receptor, trkA, from a variety of insults. There are some data, in particular in the developing brain, indicating that NGF has neuroprotective actions that extend beyond cells expressing trkA. In this study, we asked whether NGF would protect against brain injury in a neonatal model of hypoxia-ischemia. Postnatal day (PD) 7 rat pups received a right carotid ligation and were then exposed to hypoxic conditions. Prior to carotid ligation and 48 hours later, pups received an intracerebroventricular injection of NGF or denatured NGF dissolved in vehicle or vehicle alone. Brains were then assessed at PD21. In vehicle- and denatured NGF-treated animals, there was significant damage (30-40% volume loss) to both the striatum and cortex ipsilateral to the carotid ligation. In contrast, little damage (10% volume loss) was observed in most NGF-treated animals. NGF injection studies revealed that NGF stimulated tyrosine phosphorylation of trkA in multiple brain regions. These results show that NGF appears globally neuroprotective to the developing brain in a neonatal model of hypoxia-ischemia and that there may be novel mechanisms in vivo through which NGF exerts its protective actions.

Cellular hybridization for BDNF, trkB, and NGF mRNAs and BDNF-immunoreactivity in rat forebrain after pilocarpine-induced status epilepticus

The messenger RNAs (mRNAs) for the neurotrophins, brain-derived neurotrophic factor (BDNF), and nerve growth factor (NGF), are upregulated during epileptic seizure activity, as visualized by in situ hybridization techniques. Neurotrophins might be protective against excitotoxic cell stress, and the upregulation during seizures might provide such cell protection. In this study, a high dose of pilocarpine (300 mg/kg) was used to induce long-lasting, limbic motor status epilepticus and a selective pattern of brain damage. The regulation of BDNF, trkB, and NGF mRNA was studied by in situ hybridization at 1, 3, 6, and 24 h after induction of limbic motor status epilepticus. BDNF immunoreactivity was examined with an anti-peptide antibody and the neuropathological process studied in parallel. BDNF mRNA increased in hippocampus, neocortex, piriform cortex, striatum, and thalamus with a maximum at 3-6 h. Hybridization levels increased earlier in the resistant granule and CA1 cells as compared to the vulnerable CA3 neurons. BDNF immunoreactivity was elevated in dentate gyrus at 3-6 h. trkB mRNA increased in the entire hippocampus. NGF mRNA in hippocampus appeared in dentate gyrus at 3-6 h and declined in hilar neurons at 6-24 h. Cell damage was found in the CA3 area, entire basal cortex, and layers II/III of neocortex. Endogenous neurotrophins are upregulated during status epilepticus caused by pilocarpine, which is related to the coupling between neuronal excitation and trophic factor expression. This upregulation of neurotrophic factors may serve endogenous protective effects; however, the excessive levels of neuronal hyperexcitation resulting from pilocarpine seizures lead to cell damage which cannot be prevented by endogenous neurotrophins.

Transient cerebral ischemia decreases calcium/calmodulin-dependent protein kinase II immunoreactivity, but not mRNA levels in the gerbil hippocampus

During transient cerebral ischemia, intracellular calcium increases initiating a cascade of events which leads to the delayed death of neurons located in the hippocampus. Coupled to this calcium disturbance is the rapid decrease of calcium/calmodulin kinase II (CaM kinase) activity, a protein kinase critical to neuronal functioning. The present study correlated the increased locomotor activity following ischemic insult with alterations in CaM kinase mRNA levels and immunocytochemical labeling of alpha and beta CaM kinase subunits in the hippocampus. The protective effect of hypothermia was also compared with CaM kinase mRNA levels and immunoreactivity. Levels of CaM kinase message for either alpha or beta subunits was not altered in ischemic gerbils compared to sham or hypothermic ischemic conditions. Immunoreactivity for both the alpha and beta subunits was markedly reduced in the vulnerable CA1 region of ischemic animals compared to sham controls. Gerbils that underwent the ischemic insult while hypothermic showed no decrement in staining. CaM kinase-like immunoreactivity in the ischemia-resistant CA3 sector was not altered following ischemia. These data suggest that the loss of hippocampal CaM kinase immunoreactivity observed at 24 h following ischemia is not associated with a reduction in CaM kinase mRNA levels and support the notion that the rapid decline in CaM kinase activity following ischemic insult is a result of a posttranslational modification and/or translocation of the enzyme.

Selective acid vulnerability of dopaminergic neurons and its recovery by brain-derived neurotrophic factor

Among the pathogenetic phenomena of Parkinson's disease, the character of the selective degeneration of nigrostriatal system with severe gliosis is not fully understood. Here, we have shown that dopaminergic neurons may be exclusively sensitive to elevated acidity elicited after the addition of glial mitogenic factors such as epidermal growth factor and basic fibroblast growth factor or after the direct treatment with hydrochloric acid. The acid sensitivity was specific to dopaminergic neurons. The neurons other than dopaminergic neurons in culture from the ventral mesencephalon were not sensitive to acidity and the neurons from several brain areas were the same as above, except for the hippocampal neurons which had slight acid vulnerability. Choline acetyltransferase assay studies demonstrated that the cholinergic neuronal population in the septum and corpus striatum had no acid sensitivity. The vulnerability of dopaminergic neurons either elicited by glial mitogenic factor or derived from the direct acid exposure was inhibited by the addition of brain-derived neurotrophic factor (BDNF), but not by neurotrophin-3 or nerve growth factor. These findings suggest that dopaminergic neurons have selective acid vulnerability on which BDNF has a pronounced protective effect.

Distribution of drugs following controlled delivery to the brain interstitium

Intracranial controlled release polymers have been used for drug delivery to the brain, bypassing the blood brain barrier (BBB). By understanding the rates and patterns of transport in the local tissues, it is possible to design delivery systems that provide the optimal spatial and temporal pattern of chemotherapy within the intracranial space. This paper reviews the kinetics of drug release from polymeric controlled release implants, and describes the fate of drug molecules following release into the brain interstitium. Potential improvements in drug delivery based on the understanding of the mechanisms of drug release, transport and elimination are discussed.

Expressions of nerve growth factor and p75 low affinity receptor after transient forebrain ischemia in gerbil hippocampal CA1 neurons

Expressions of nerve growth factor (NGF) and low affinity p75 NGF receptor (p75 NGFR) in gerbil hippocampal neurons after 3.5-min transient forebrain ischemia were studied. Most hippocampal CA1 neurons were lost (neuronal density = 44 +/- 12/mm) at 7 days after recirculation, while no cell death was found in the sham-control neurons (220 +/- 27/mm). NGF immunoreactivity was normally present in the sham-control hippocampal neurons. However, it decreased in hippocampal CA1 neurons, and slightly decreased in the neurons of CA3 and dentate gyrus areas from 3 hr after recirculation. By 7 days, NGF immunoreactivity returned almost completely to the sham-control level in the CA3 and dentate gyrus neurons but decreased markedly in the CA1 neurons. In contrast, p75 NGFR immunoreactivity was scarcely present in the sham-control hippocampal neurons but was induced from 1 hr after recirculation in the CA1 and CA3 neurons and from 3 hr in the dentate gyrus. At 7 days, p75 NGFR immunoreactivity was expressed greatly in the surviving CA1 neurons and the reactive astrocytes but was not seen in the other hippocampal neurons. The markedly decreased NGF and greatly induced p75 NGFR immunoreactivity found in the CA1 neurons after transient forebrain ischemia suggests that NGF and p75 NGFR may be involved in the mechanism of delayed neuronal death.

Prior mechanical injury inhibits rise in intracellular Ca2+ concentration by oxygen-glucose deprivation in mouse hippocampal slices

Prior mechanical brain microinjury has been found to have a preventive effect on brain ischemia. To investigate the mechanism responsible for this, the effect of mechanical brain injury on changes in intracellular free Ca2+ concentration ([Ca2+]i) in response to ischemic insult was studied in mouse hippocampal slices. The mechanical injury was made by inserting a 25G hypodermic needle into the CA1 region of the hippocampus in mice anesthetized with pentobarbital. Sagittal slices of the hippocampus were prepared two hours, and 1, 3, 7, and 14 days after the brain injury. Changes in [Ca2+]i in the slices by oxygen-glucose deprivation were analyzed from fluorescence images, using fura-2. Increases in [Ca2+]i induced by oxygen-glucose deprivation were inhibited in the vicinity of the injury 1 and 3 days after injury. [Ca2+]i levels were lower in the posterior side from the injury than in the anterior side 1 and 3 days after injury. No significant regional differences in [Ca2+]i responses were found 2 h or 7 and 14 days after the injury. Membrane potential and membrane resistance of CA1 neurons in the vicinity of the injury measured 1 day after the injury were not significantly altered in comparison with non-injured slices. These results indicate that mechanical brain injury inhibits ischemic [Ca2+]i increase. This inhibition may be induced not only by damage of the presynaptic fibers projecting to the CA1 neurons but also by the other certain factor(s) that prevent [Ca2+]i increase, and it appears to be related to the protective effect of prior mechanical injury against ischemic neuronal damage.

Neurotrophins and ciliary neurotrophic factor: their biology and pathology

Neurotrophins (NTFs) and ciliary neurotrophic factor (CNTF) induce the differentiation of neuronal cells, rescue them from naturally occurring death, and trigger neuronal regeneration. The NTFs bind to two classes of cell surface receptors, whereas CNTF receptor is composed of three subunits. The functions of these polypeptide survival factors with trophic action on nerve cells have recently been approached by the targeted disruption of the CNTF, NTF and their receptor genes by the homologous recombination technique. The embryonic growth and morphogenesis of these gene 'knock-out' mice is normal, but they develop with defects in various subsets of the peripheral nervous system, and the homozygous mutant mice often die during the early postnatal period. Disturbances in the biology of NTFs and CNTF have recently been implicated in the pathogenesis of certain common neurodegenerative disorders, such as Parkinson's disease, motor neurone diseases, and Alzheimer's disease. Intensive research on their pharmaceutical perspective has, therefore, been provoked. All neurotrophins and CNTF can now be synthesized on a large scale as biologically active recombinant proteins, and several alternatives for their local applications to the target tissue have been presented. Their therapeutic potential is discussed.

Brain-derived neurotrophic factor protects against ischemic cell damage in rat hippocampus

The neuroprotective action of brain-derived neurotrophic factor (BDNF) was evaluated in a rat model of transient forebrain ischemia. A continuous intraventricular infusion of BDNF for 7 days starting immediately before the onset of ischemia significantly increased the number of pyramidal cells in the vulnerable CA1 sector of the hippocampus. In situ hybridization experiments suggest the neuroprotection to be mediated via trkB-receptors in the hippocampus. The data indicate a therapeutic potential for the treatment of cerebral ischemia.

Drug targeting into the central nervous system by stereotactic implantation of biodegradable microspheres

Controlled drug release in the central nervous system through an implantable polymeric vector has been developed in recent years. For this purpose, different polymeric devices composed primarily of synthetic biocompatible and biodegradable polymers have been investigated. The first polymeric devices developed were macroscopic implants (monolithic devices), which required open surgery for implantation. Microencapsulation methods, however, allow the production of microparticles or nanoparticles loaded with neuroactive drugs. Because of their size, these micro- or nanoparticles may be easily implanted by stereotaxy in discrete, precise, and functional areas of the brain without causing damage to the surrounding tissue. Presently, this method is most frequently applied in the fields of neuro-oncology and neurodegenerative diseases, but neurologically, the potential applications of drug targeting by stereotactic implantation of drug-loaded particles are legion.

The immortalized astroglial cell line RC7 is a new model system for the study of nerve growth factor (NGF) regulation: stimulation by interleukin-1 beta and transforming growth factor-beta 1 is additive and affected differently by dibutyryl cyclic AMP

Nerve growth factor (NGF) synthesis was studied with an astroglial cell line derived from rat cerebellar astrocytes by transfection with a simian virus 40 T containing retroviral vector. As in primary astrocytes, NGF synthesis/secretion could be stimulated dose-dependently with interleukin-1 beta (IL-1 beta) and transforming growth factor-beta 1 (TGF-beta 1). We therefore have used this cell line as a model system to analyze putative intracellular signalling pathways underlying the effects of these factors. Protein kinase C inhibitors (calphostin and Ro 31-8830) as well as a lipoxygenase inhibitor (nordihydroguaiaretic acid) did not affect stimulation of NGF synthesis/secretion by IL-1 beta or TGF-beta 1. However, dibutyryl cyclic AMP partly inhibited the stimulation by TGF-beta 1 but did not affect that evoked by IL-1 beta. This finding, together with the fact that IL-1 beta and TGF-beta 1 stimulate NGF production/secretion in an additive manner, indicates that different intracellular signalling pathways are involved in the mediation of IL-1 beta and TGF-beta 1 induced NGF production/secretion.