Expression of the beta-nerve growth factor gene in hippocampal neurons

Cellular localization of nerve growth factor-like immunoreactivity in adult rat brain: quantitative and immunohistochemical study

To elucidate the role and the mechanism of action of nerve growth factor in the adult central nervous system, we investigated the localization of nerve growth factor-like immunoreactivity in adult rat brain, both quantitatively and immunohistochemically, using polyclonal anti-nerve growth factor immunoglobulin G. We raised rabbit polyclonal anti-mouse nerve growth factor antibody with an extremely high titer as 10(-9) determined by an enzyme immunoassay. The affinity-purified anti-nerve growth factor immunoglobulin G specifically recognized nerve growth factor with no cross-reaction to recombinant brain-derived neurotrophic factor and neurotrophin-3 evaluated by an enzyme immunoassay. We quantified nerve growth factor content in each layer of the adult rat cerebral cortex and in each small piece (0.225 mg wet weight tissue) of the diencephalon, brainstem and cerebellum with a highly sensitive two-site enzyme immunoassay. Nerve growth factor content was unevenly distributed in the cerebral cortex (dense in layers II/III and V/VI and sparse in layers I and IV). Moderate to high levels of nerve growth factor were registered in the habenular nuclei, zona incerta, ventral tegmental area, substantia nigra, locus coeruleus, ventral cochlear nucleus, trapezoid body, lateral vestibular nucleus, cerebellar nuclei and paraflocculus. Immunohistochemically, the nerve growth factor-like immunoreactivity was found in the cell bodies, dendrites and axons of adult rat central neurons, not only in the cerebral cortex, hippocampus and basal forebrain, but also in the diencephalon, brainstem and cerebellum. The population of neurons with nerve growth factor-like immunoreactivity was limited, but unexpectedly widespread, and the density of these cells correlated well with the content determined by an enzyme immunoassay in the present and a previous study [Nishio T. et al. (1992) Expl Neurol. 116, 76-84]. The monoamine neurons, including dopaminergic, noradrenergic and serotonergic neurons, showed intense nerve growth factor-like immunoreactivity, indicating that the central monoaminergic neuronal system may also be involved in the nerve growth factor trophic system. To visualize nerve growth factor transported in the axons and to enhance the immunostaining in the nerve growth factor-producing cells, we injected colchicine, a potent inhibitor of microtubule polymerization and a blocker of axoplasmic transport, into the lateral ventricle of adult Wistar rat brain. Colchicine treatment enhanced the intensities of nerve growth factor-like immunoreactivity in the axons and cell bodies, especially in the axon hillocks and the proximal axons of the nerve growth factor-producing neurons. This observation may suggest the existence of an orthograde axonal transport system for nerve growth factor in the central neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Interleukin-6 protects cultured rat hippocampal neurons against glutamate-induced cell death

We examined the effect of interleukin-6 (human recombinant) on glutamate-induced neuronal death of cultured 20-day fetal rat hippocampal neurons. After 7 days in culture, the hippocampal neurons were markedly degenerated by the addition of L-glutamate and also N-methyl-D-aspartate. The neuronal death was prevented by the addition of MK801, a potent N-methyl-D-aspartate antagonist. Interleukin-6 at the concentration of 50 ng/ml has a significant preventive effect on the glutamate-induced neuronal death. Basic fibroblast growth factor at the concentration of 100 ng/ml gave also significant protective effect on hippocampal neurons, but nerve growth factor was ineffective in preventing the toxicity. It has been postulated that glutamate plays an important role in the pathogenesis of neuronal death such as ischemia and the various neurological diseases. Interleukin-6 might have somewhat physiological or pathological role in these events.

Neurotrophic factor mRNA expression in dentate gyrus is increased following in vivo stimulation of the angular bundle

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are two structurally-related neurotrophins synthesized in dentate gyrus granule cells and pyramidal neurons of the hippocampal formation. These neurons receive excitatory glutamatergic afferents from the entorhinal cortex via the angular bundle/perforant path. In the present study, we tested whether electrophysiological stimulation of this glutamatergic pathway modifies NGF or BDNF messenger RNA (mRNA) expression in vivo. Within hours following brief trains of high frequency angular bundle stimulation, the levels of mRNA encoding both neurotrophins were increased exclusively in granule cells of the ipsilateral dentate gyrus. The increase in neurotrophic factor mRNA expression was found to be mediated through the N-methyl-D-aspartate (NMDA) glutamate receptor subtype, and occurred in the absence of seizure. These findings provide evidence that neurotrophic factor mRNA levels in the hippocampal formation are increased by direct activation of excitatory afferents originating in the entorhinal cortex. We suggest that the function of some neurotrophin-responsive neuronal populations may depend upon the integrity and activity of neurons in the entorhinal cortex, a population of neurons reported to be compromised in patients with Alzheimer's disease.

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.

Polymer-encapsulated cells genetically modified to secrete human nerve growth factor promote the survival of axotomized septal cholinergic neurons

Effective treatments for neurodegenerative disorders are limited by our inability to alter the progression of the diseases. A number of proteins have specific neuroprotective activities in vitro; however, the delivery of these factors into the central nervous system over the long term at therapeutic levels has been difficult to achieve. BHK cells engineered to express and release human nerve growth factor were encapsulated in an immunoisolation polymeric device and transplanted into both fimbria-fornix-lesioned rat brains and naive controls. In the lesioned rat brain, chronic delivery of human nerve growth factor by the encapsulated BHK cells provided nearly complete protection of axotomized medial septal cholinergic neurons. Human nerve growth factor continued to be released by encapsulated cells upon removal from the aspirative site after 3 weeks or from normal rat striatum after 3 and 6 months in vivo. Long-term encapsulated cell survival was confirmed by histologic analysis. This encapsulated xenogeneic system may provide therapeutically effective amounts of a number of neurotrophic factors, alone or in combination, to virtually any site within the body.

The neurotrophins and their receptors: structure, function, and neuropathology

The neurotrophins are a family of polypeptides that promote differentiation and survival of select peripheral and central neurons. Nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-4, and neurotrophin-5 are included in this group. In recent years, tremendous advances have been made in the study of these factors. This has stimulated our review of the field, characterizing the neurotrophins from initial isolation to molecular analysis. The review also discusses their synthesis, localization, and responsive tissues, in both the periphery and CNS. The complex receptor interactions of the neurotrophins are also analyzed, as are putative signal transduction mechanisms. Discussion of the observed and postulated involvement in neuropathological disorders leads to the conclusion that the neurotrophins are involved in the function and dysfunction of the nervous system.

Transient global ischemia induces dynamic changes in the expression of bFGF and the FGF receptor

To study the roles of bFGF and its receptor in the process of neuronal cell death and the wound repair response, we induced 10 min of transient global cerebral ischemia in rats and measured changes in expression of both bFGF and the FGF receptor, flg. CA1 pyramidal cells are selectively vulnerable to ischemia and die one to 3 days after 10 min of ischemia. In these cells, bFGF mRNA was induced by 6 hours, reached a maximal level by 24 h after ischemia, and subsequently decreased. Message for the FGF receptor, flg, was present in the pyramidal cells layer, and vanished almost completely in parallel with neuronal death. In the granule cell layer of dentate gyrus, the expression of bFGF mRNA increased more rapidly. It was maximal by 6 h and returned to the basal level by 3 days. In the hilus of the dentate gyrus, bFGF expression was maximal at 24 h and returned to control levels by 3 days. Despite the rapid changes in expression of bFGF mRNA, there was no significant change of bFGF immunoreactivity in either the CA1 pyramidal cell layer or in the granule cell layer of dentate gyrus within 3 days after ischemia. The apparent failure of the message to be efficiently translated supports the idea that translation is impaired under conditions where ischemia leads to delayed neuronal cell death. Expression of bFGF mRNA, FGFR mRNA and bFGF immunoreactivity increased dramatically in a broad area of CA1 subfield from 7 days until 30 days after ischemia because of increased expression by reactive glial cells. We suggest that these rapid and complex changes in the expression of bFGF mRNA and bFGF protein may be part of a coordinated response to ischemic injury that is designed to minimize the severity of neuron death.

Cell-type-specific expression and regulation of a c-fos-NGF fusion gene in neurons and astrocytes of transgenic mice

A mouse line transgenic for nerve growth factor (NGF) was developed using the mouse prepro-NGF cDNA inserted within a plasmid containing the proximal region (-10 to -550 bp) of the c-fos promoter and the transcription termination and polyadenylation signals of the rabbit beta-globin gene. No significant modification of gross behavior or central nervous system anatomy was detected in adult animals as assessed by immunohistochemistry and in situ hybridization for NGF and choline acetyltransferase. The expression of the transgene and the possible regulation of its expression by agents acting on the promoter were investigated in vitro. Despite the presence of an additional pool of NGF mRNA specific to the transgene, basal levels of NGF in the supernatant of transgenic astrocytes were similar to normal ones. On the other hand, transgenic neurons spontaneously synthesized and released levels of NGF two to three times higher than normal neurons, while mRNA levels were barely detectable by conventional Northern blotting. The tissue-specificity of NGF expression was respected, with higher levels in hippocampal than neocortical neurons. Increases of NGF mRNA by agents acting on the promoter could be observed in normal and transgenic astrocytes only after inhibition of the protein synthesis by cycloheximide, suggesting a similar rapid turnover of normal and transgenic transcripts. Cyclic AMP agonists specifically increased the secretion of NGF protein by transgenic astrocytes and neurons, while activators of the protein kinase C had a similar effect on transgenic and normal cells. Differences between amounts of NGF secreted by neurons and astrocytes with regards to their respective content in mRNA suggest that transgenic transcripts are subject to normal cell- and tissue-specific post-transcriptional regulations. Agents acting on the c-fos promoter through the protein kinase C or cyclic AMP routes differentially increased the secretion of NGF by transgenic astrocytes or neurons, supporting this hypothesis.

Chronic 1,25-dihydroxyvitamin D3-mediated induction of nerve growth factor mRNA and protein in L929 fibroblasts and in adult rat brain

We have proposed that elevating levels of nerve growth factor (NGF) in the CNS is a rational strategy for treating certain neurodegenerative disorders. The present studies were conducted to determine: (1) if pharmacologically induced levels of NGF could be sustained for an extended time, and (2) if correlations exist between increases in NGF mRNA and NGF protein in L929 cells and in vivo. Short-term treatment of L929 cells with 1,25-dihydroxyvitamin D3 resulted in a two-fold increase in both NGF mRNA and NGF protein. These increases were sustained for up to 48 h with continuous exposure to 1,25-dihydroxyvitamin D3. In rats, 1,25-dihydroxyvitamin D3 (2.5 nmol; i.c.v.) induced NGF mRNA transiently, with peak two-fold increases observed 4 h post-injection. In contrast to L929 cells, 1,25-dihydroxyvitamin D3 did not elicit an increase in NGF protein after a single administration in vivo. However, consistent with long-term exposure in L929 cells, chronic 6 day infusion of 1,25-dihydroxyvitamin D3 resulted in induction of both NGF mRNA and NGF protein in the brain. These results indicate that 1,25-dihydroxyvitamin D3-mediated NGF induction in cultured L929 cells may predict of NGF induction in vivo, suggesting that L929 cells may have utility in studying underlying mechanisms of NGF induction by 1,25-dihydroxyvitamin D3. On the basis of NGF's ability to increase cholinergic function in animal models of cholinergic degeneration, these results are supportive of a role for NGF inducers as potential drugs for neurodegenerative disorders.

Neurotrophic factor gene expression in astrocytes during development and following injury

Astrocyte cultures were utilized to examine regulation of the expression of several trophic factor genes. Regulation by the beta-adrenergic receptor was demonstrated by exposure of striatal and cortical astrocytes to isoproterenol, which resulted in increased content of mRNAs for nerve growth factor (NGF), brain-derived neurotrophic factor, and proenkephalin (PE), as well as NGF and Met-enkephalin. Developmental regulation was analyzed by preparing cortical astrocytes from animals of four different ages--embryonic day 20, postnatal days 3 and 8, and adult. Because both the PE and NGF genes showed developmental downregulation, we asked whether we could prepare reactive astrocytes from lesioned adult brain and see expression turned back on. Astrocytes prepared from 6-hydroxydopamine-lesioned rat striatum or MPTP-lesioned mouse striatum contained increased GFAP and NGF mRNA. Comparable changes in GFAP and NGF could be achieved by treatment of control cultures with interferon-gamma or interleukin-1 beta. These results suggest that locus coeruleus neurons could control astrocyte synthesis of neurotrophic factors through release of of norepinephrine, but that in injured brain other factors, such as cytokines, may become equally important.

Fos induction by nerve growth factor in the adult rat brain

The distribution of Fos, the protein product of the immediate early gene c-fos, was studied with immunocytochemistry in the adult male rat brain after nerve growth factor (NGF) administration. NGF was injected in the lateral cerebral ventricle through a previously implanted cannula. The total number of Fos-immunoreactive (ir) neurons in the brain was 2-3 times higher after NGF administration than in control animals (untreated or injected with cytochrome c). With respect to control rats, in the NGF-treated cases Fos-ir cells were more numerous in the anterior olfactory nucleus, in the medial prefrontal and anterior cingulate cortices, in the basal forebrain, in the preoptic and ventromedial nuclei of the hypothalamus, as well as anterior hypothalamic area, in the thalamic midline nuclei, and in some brainstem structures, such as the parabrachial nucleus. The relative quantitative increase of Fos-ir neurons varied in the different structures. In addition, Fos-ir neurons were evident after NGF administration in areas devoid of immunopositive cells in control animals. These included: frontoparietal and occipital cortical fields, the hypothalamic arcuate nucleus, and many brainstem structures, such as the dorsal nucleus of the lateral lemniscus, posterodorsal tegmental, medial and lateral vestibular, ventral cochlear, and prepositus hypoglossal nuclei. These findings demonstrate that the intracerebroventricular administration of NGF can induce c-fos expression in neurons in vivo. The distribution of Fos-ir neurons indicates that NGF can induce activation of functionally and chemically heterogeneous neuronal subsets in the brain.

Altered gene expression in cerebral ischemia

BACKGROUND

Using the techniques of molecular biology, recent experimental studies have shown that cerebral ischemia induces a variety of changes in gene expression in the brain.

SUMMARY OF REVIEW

During the early postischemic stages, protein synthesis in the brain is generally suppressed, but specific genes are expressed and their corresponding proteins may be synthesized, such as immediate-early gene products (c-fos, c-jun, and zinc finger gene), heat-shock proteins, and amyloid precursor protein. The ability of neurons to induce such stress responses, which depends on both the severity of ischemia and the intrinsic nature of the neuronal populations, may be directly associated with neuronal death and survival after ischemia. Nerve growth factor and fibroblast growth factor are also induced after ischemia and may be related to repair processes, in which a role of glial cells is suggested. Postischemic events that may be associated with the altered gene expression include (1) induction of tolerance to ischemia after pretreatment with sublethal ischemia, (2) slow, progressive neuronal changes and the development of neuronal plasticity after ischemia, and (3) delayed neuronal changes in remote areas outside the cerebral ischemic focus.

CONCLUSIONS

Because a variety of harmful stresses, including ischemia, elicit the same stress response and because this response is induced when total protein synthesis in the brain is nearly completely suppressed, this response may be vital to cell survival and repair. A successful induction of this response may induce resistance and survival of neurons after ischemia. However, failure or abortion of the response and persistent stresses may lead to neuronal death and possibly long-term changes and degeneration.

Increased expression of trkB and trkC messenger RNAs in the rat forebrain after focal mechanical injury

Tyrosine protein kinases trkA, trkB and trkC are signal transduction receptors for a family of neurotrophic factors known as the neurotrophins. Here we report on changes in the expression of messenger RNAs for trkA, trkB and trkC in the brain following an injury caused by insertion of a 30-gauge needle into adult rat hippocampus or neocortex. Quantitative in situ hybridization revealed no change in the level of trkA messenger RNAs in any brain region following this insult. In contrast, increased levels of trkB messenger RNA compared to untreated animals were seen in the granule cell layer of the dentate gyrus ipsilateral to the injury already 30 min after the injury. The increase reached maximal levels (four-fold) between 2 and 4 h, but returned to control levels 8 h after the injury. No change was seen in the contralateral dentate gyrus. The levels of trkC messenger RNA increased in the same brain regions as trkB messenger RNA, though with a delayed response, reaching a maximal increase of 3.3-fold 4 h after the injury. As for trkB messenger RNA, the level of trkC messenger RNA then tapered off and reached control levels 8 h after the injury. However, 4 h after the injury, a 1.7-fold increase of trkB and trkC messenger RNAs were seen in the ipsilateral piriform cortex. The increases of trkB and trkC messenger RNAs were confirmed using a nuclease protection assay. Increases of both trkB and trkC messenger RNAs were also seen in the piriform cortex, but not in the hippocampus, following needle insertion into the neocortex. Pretreatment of the animals with the non-competitive N-methyl-D-aspartate antagonist ketamine completely prevented the increases of trkB and trkC messenger RNAs, suggesting that the brain injury caused a release of glutamate with subsequent activation of N-methyl-D-aspartate receptors. In contrast, the anticonvulsive drug diazepam, the muscarinic antagonist atropine and the calcium-channel antagonist nimodipine had no effect on the increases of trkB and trkC messenger RNAs. Combined with previous data on the expression of neurotrophin messenger RNAs following similar injuries, our results support the hypothesis that increased levels of neurotrophins and their receptors could protect against neuronal damage following a brain insult.

Coexpression of neurotrophins and their receptors in neurons of the central nervous system

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are neuronal survival molecules which utilize the Trk family of tyrosine kinase receptors. Using double-label in situ hybridization, we demonstrate that mRNAs for BDNF and its high-affinity receptor TrkB are coexpressed in hippocampal and cortical neurons. Also, a large number of neurons in these areas coexpress NGF and BDNF mRNAs. Epileptic seizures lead to increased levels of both BDNF/TrkB and NGF/BDNF mRNAs in double-labeled cells. Our results show that individual neurons of the central nervous system can coexpress neurotrophins and their receptors and produce two neurotrophic factors. These factors could support neuronal survival after brain insults, not only via retrograde transport but also through autocrine mechanisms.

Widespread and developmentally regulated expression of neurotrophin-4 mRNA in rat brain and peripheral tissues

The neurotrophin gene family includes four structurally related proteins with neurotrophic activities. Two of them, nerve growth factor and brain-derived neurotrophic factor (BDNF), have been studied in detail and information has recently emerged on the expression and function of the third member, neurotrophin-3. In contrast, little information is available on neurotrophin-4 (NT-4), the most recently isolated member of this family. In this report we have used a sensitive RNAase protection assay to analyse the developmental expression of NT-4 mRNA in the rat brain and in 12 different rat peripheral organs. In heart, liver and muscle plus skin NT-4 mRNA levels were maximal at embryonic day (E) E13 (the earliest time point tested), with reduced levels at later times of development. In lung, kidney and thymus similar levels were seen from E13 to postnatal day (P) 1, with reduced levels in the adult. In testis, ovary and salivary gland NT-4 mRNA was detected at E16 with a peak shortly after birth. During brain development, NT-4 mRNA was maximal at E13 followed by a decrease around birth, after which the level increased. The postnatal increase of NT-4 mRNA was also seen in cerebral cortex and brain stem analysed separately, while in the hippocampus similar levels were found from P1 to adulthood. NT-4 mRNA was detected in all ten adult rat brain regions analysed with only small regional variations, being highest in pons-medulla, hypothalamus, thalamus and cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenalectomy attenuates kainic acid-elicited increases of messenger RNAs for neurotrophins and their receptors in the rat brain

Treatment with excitotoxin kainic acid is known to increase the level of messenger RNAs for nerve growth factor and brain-derived neurotrophic factor in the brain. In this study we have used quantitative in situ hybridization to analyse the effect of glucocorticoids on kainic acid-induced increase of nerve growth factor and brain-derived neurotrophic factor messenger RNA in the rat brain. In adrenalectomized animals, the kainic acid-mediated increase of brain-derived neurotrophic factor messenger RNA in the hippocampus and the cerebral cortex was reduced by 50% compared to sham-operated animals. The increase of nerve growth factor messenger RNA elicited by kainic acid in the dentate gyrus was almost completely abolished in adrenalectomized animals. No significant change was seen in c-fos messenger RNA in the hippocampus of adrenalectomized rat after kainic acid injection compared to sham-operated kainic acid-treated rats, while a three-fold reduction was seen in the cerebral cortex. Dexamethasone injection prior to kainic acid administration potentiated the kainic acid-induced increase of nerve growth factor messenger RNA in the dentate gyrus and the piriform cortex. In contrast, dexamethasone pretreatment did not potentiate the kainic acid-mediated increase of brain-derived neurotrophic factor messenger RNA. We also examined the effect of adrenalectomy and kainic acid injection on tropomyosin receptor kinase B and C messenger RNA, encoding essential components of high-affinity receptor for brain-derived neurotrophic factor/neurotrophin-4 and neurotrophin-3, respectively. Following adrenalectomy no change of tropomyosin receptor kinase B or C messenger RNA was detected in any of the brain regions studied compared to sham-operated animals. The injection of kainic acid caused four-fold and two-fold increases of tropomyosin receptor kinase B messenger RNA in the dentate gyrus and cerebral cortex, respectively, but no change in tropomyosin receptor kinase C messenger RNA in any of these regions. In adrenalectomized animals receiving kainic acid, the level of tropomyosin receptor kinase B messenger RNA was decreased both in the dentate gyrus and cerebral cortex as compared to sham animals treated with kainic acid. Taken together, the data suggest that excitotoxins and glucocorticoids both influence expression of brain-derived neurotrophic factor and nerve growth factor messenger RNA in the brain, but by two different mechanisms, where the effect of excitotoxin-evoked seizures is modulated by glucocorticoids.

Low-affinity p75 nerve growth factor receptor expression in the embryonic monkey telencephalon: timing and localization in diverse cellular elements

Monoclonal antibodies against the low-affinity (p75) subunit of the human nerve growth factor receptor have been used to determine the temporal appearance of this receptor and to identify the associated cellular elements in the developing occipital cortex of rhesus monkeys. Adult and fetal brains from embryos at embryonic days 45-121 were used. This embryonic time span includes periods of active neurogenesis, cell migration and initial formation of axonal connections in the cerebral cortex. The first immunolabeling in the developing cerebral wall was seen between embryonic days 56 and 64. The labeling was present in the transient subplate neurons, a small number of axonal processes and pericytes associated with blood vessels. By birth, labeled neurons of the subplate zone disappeared, but immunolabeled axonal processes could now be seen in large numbers in the cortex. These findings are consistent with the role of nerve growth factor in the coordination of cortical differentiation, but not with the initiation of neuronal proliferation, since the emergence of nerve growth factor receptor-labeled elements in the cortex occurs two to three weeks after the onset of neurogenesis in this species. Further, the diverse cellular elements labeled in the fetal cerebrum with the antibodies to the low-affinity nerve growth factor receptor suggests that a receptor or receptors associated with growth factor signaling for more than one growth factor family are recognized by these antibodies. Differential timing in the expression of families of growth factor receptors may be one mechanism by which developing neurons in the cerebral cortex could respond to the different signals which guide such processes as synaptogenesis and morphogenesis.

Distribution of [125I]nerve growth factor in the rat brain following a single intraventricular injection: correlation with the topographical distribution of trkA messenger RNA-expressing cells

The present study determined the topographical distribution of [125I] nerve growth factor in rat brain at various time points following an intraventricular injection. In addition, we quantified the tissue content of nerve growth factor in various brain tissues following the injection. Autoradiographic analysis of the distribution of [125] nerve growth factor indicated that the neurotrophin is rapidly distributed within the entire ventricular system. However, penetration of nerve growth factor into the brain parenchyma was very limited. At early time points following an injection of nerve growth factor, there was an accumulation of label in the immediate vicinity of the lateral ventricle and third ventricle with predominant labeling around the septum, hypothalamus and cerebellum. By 24 h following nerve growth factor administration, there was discreet labeling of the lateral septum, medial septum, diagonal band, hypothalamus, olfactory tubercle and nucleus of the olfactory tract, and some label was present in the hippocampus and subiculum. Quantitative ELISA of nerve growth factor in brain tissues 1 h following the injection indicated a 446% and 133% increase over basal levels of nerve growth factor in the basal forebrain and hippocampus, respectively. At 24 h nerve growth factor levels measured in brain were not significantly different from endogenous basal levels as determined by ELISA, whereas there were high quantities of 125I present in the thyroid gland, suggesting that the administered [125I] nerve growth factor was rapidly degraded following the intraventricular injection. We observed a similar labeling pattern of the medial septum/diagonal band cholinergic cell body group 24 h following either an intraventricular or intrahippocampal injection of [125I] nerve growth factor. There was a good correlation between the [125I] nerve growth factor labeling pattern and the presence of trkA messenger RNA. This suggested that, at least in the septohippocampal pathway, nerve growth factor accumulated in a region which contained trkA nerve growth factor receptors. Thus, this study shows that after a single unilateral intraventricular injection of nerve growth factor into rat brain there is effective uptake by diagonal band/septal cells on both sides of the brain, and by cells whose positions correlate with the locations of cholinergic and trk A messenger RNA-expressing cells. Significant uptake was also observed in the hypothalamus and cerebellum. The very limited penetration and rapid degradation of intraventricularly administered nerve growth factor suggests that tissue penetration may be a limiting factor when attempting to influence brain neurons by exogenous neurotropic factors.

Expression of members of the trk family in the developing postnatal rat brain

Tyrosine protein kinases trk, trkB and trkC are essential components of the high affinity receptors necessary to mediate biological effects of the neurotrophins NGF, BDNF, NT-3 and NT-4. Here we report on the expression of these receptors during postnatal development in the rat brain. Cells expressing mRNAs encoding different members of the trk family were identified by in situ hybridization using oligonucleotides complementary to their respective mRNA. In septum, striatum and brainstem, higher levels of trk mRNA were detected at 2 and 4 weeks than at 1 weeks of age. In thalamic nuclei associated with the limbic system, trkB and trkC mRNA were highly expressed at P1 to P7, but the expression declined gradually in 2 and 4 week old animals. Other structures where a developmentally regulated expression was seen included the tenia tecta and piriform cortex where trkB mRNA was not detected until 2 weeks of age. A high labeling was found for trkC mRNA in the deeper parts of neocortex in P1 and P4 animals, while in 2 and 4 weeks old animals the highest labeling was seen over the outer neocortical layers. Several brainstem nuclei showed a higher labeling for trkC mRNA at P1 to P7 than in animals of older age. These data show that expression of members of the trk family is developmentally regulated during postnatal brain development and suggest that high affinity neurotrophin receptors mediate a transient response to neurotrophins in many regions during brain ontogeny.

Nerve growth factor and a fibroblast growth factor-like neurotrophic activity in cerebrospinal fluid of brain injured human patients

We report here the presence of nerve growth factor (NGF) in the cerebrospinal fluid (CSF) of some brain-injured human patients soon after injury. The NGF was quantified against a recombinant human NGF standard in a two-site enzyme-linked immunoabsorbent assay using antibodies against murine B NGF. None of the samples collected more than 2 days after injury contained detectable levels of NGF. When the CSF was assayed for the ability to promote neurite outgrowth from PC12 cells, neurite outgrowth was reduced, but not completely blocked, by antibodies to B NGF, suggesting that there were other biologically active factors present. Fibroblast growth factor (FGF) also promotes neurite outgrowth in PC12 cells. In an initial screening for the presence of FGF, we employed PC12 cells and NR119 cells, PC12 variants in which recombinant human B NGF, but not recombinant human basic FGF, promotes neurite outgrowth. CSF from brain injury patients promoted greater neurite outgrowth from PC12 cells than from NR119 cells, suggesting that some of the biological activity associated with the injury CSF may be due a FGF. This possibility is further supported by the observation that the biological activity of the injury CSF significantly reduced by batch absorption with heparin Sepharose, suggesting the presence of a heparin binding neurotrophic factor. Neurotrophic factors appear in CSF as a consequence of diverse types of brain injury, including head trauma, intracerebral hemorrhage and subarachnoid hemorrhage. The appearance of these factors may reflect important common elements in the complex series of cellular changes occurring in response to acute brain injury.

Multiple promoters direct tissue-specific expression of the rat BDNF gene

Brain-derived neurotrophic factor (BDNF) supports the survival of a specific set of neurons in the vertebrate nervous system. Here we show that the rat BDNF gene consists of four short 5' exons and one 3' exon encoding the mature BDNF protein. Eight different BDNF mRNAs with four different 5' ends and two alternative polyadenylation sites are transcribed from this gene. BDNF mRNAs containing exons I, II, and III are expressed predominantly in the brain, whereas exon IV transcripts predominate in the lung and heart. mRNAs containing exons I, II, and III increase markedly in the brain after kainic acid-induced seizures, whereas exon IV mRNA increases only slightly. Several transcription initiation sites were mapped upstream of the four 5' exons, and transfection of promoter-reporter gene constructs confirmed that these sequences act as promoters. Combined, the data demonstrate that alternative usage of four promoters within the BDNF gene and differential splicing control tissue-specific and seizure-induced expression of BDNF mRNA.

Increased production of the TrkB protein tyrosine kinase receptor after brain insults

The protein-tyrosine kinases Trk, TrkB, and TrkC are signal-transducing receptors for a family of neurotrophic factors known as the neurotrophins. Here we show that seizures induced by hippocampal kindling lead to a rapid, transient increase of trkB mRNA and protein in the hippocampus. TrkB is a component of a high affinity receptor for brain-derived neurotrophic factor (BDNF). No change was detected in mRNAs for Trk or TrkC, components of the high affinity nerve growth factor or neurotrophin-3 receptors, respectively. trkB mRNA was also transiently increased in the dentate gyrus following cerebral ischemia and hypoglycemic coma; these treatments had no effect on trk and trkC mRNAs. The increase in trkB mRNA and protein showed the same time course and distribution as the increase in BDNF mRNA. These data suggest that BDNF and its receptor may play a local role within the hippocampus in kindling-associated neural plasticity and in neuronal protection following epileptic, ischemic, and hypoglycemic insults.

Effect of chronic ethanol on the septohippocampal system: a role for neurotrophic factors?

The mechanisms by which chronic ethanol exposure produces neuronal damage have not been established. Potentially ethanol may reduce normal neurotrophic influences necessary for neuronal survival, growth, and function. We hypothesized that chronic ethanol exposure might produce a decrease in the synthesis, availability, upregulation, delivery, and/or the biological activity of normally occurring neurotrophic factors, or may alter the capacity of target neurons to respond to these factors. The available evidence leading to this hypothesis and supporting data from our laboratory are discussed.

Arachidonic acid lipoxygenation may mediate interleukin-1 stimulation of nerve growth factor secretion in astroglial cultures

Interleukin-1 beta (IL-1) stimulates by about fivefold NGF secretion from rat neonatal cortical astrocytes in primary culture. We investigated the possible intracellular second messenger mechanisms involved in the IL-1 induced NGF secretion. Basal NGF secretion did not require extracellular Ca2+, whereas Ca2+ was necessary for the maximal NGF secretion stimulated by IL-1 (10 units/ml). The protein kinase C activator TPA stimulated by sixfold NGF secretion, but in this case, TPA acted synergistically with IL-1 to increase NGF secretion. Treatment of cells with the phospholipase A2 inhibitor mepacrine (30 microM) inhibited basal (by 50%) and IL-1 stimulated (by 80%) NGF secretion. Indomethacin, a cyclooxygenase inhibitor, produced a slight increase in basal NGF secretion at low concentrations, while PGE2 (10 microM) inhibited basal and IL-1 stimulated NGF secretion. In contrast, treatment of cells with nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, blocked in a concentration-dependent manner (IC50 = 10 microM) IL-1 stimulation of NGF secretion. The leukotriene LTB4 increased basal NGF secretion and this effect was not additive with IL-1 when both agents were added at saturating concentrations, indicating a common mechanism of action for these two agents. Thus, one possible mechanism by which IL-1 stimulates NGF secretion from astrocytes is by activation of the phospholipase A2-lipoxygenase pathway.

Cellular localization of brain-derived neurotrophic factor and neurotrophin-3 mRNA expression in the early chicken embryo

Degenerate primers from conserved regions in nerve growth factor, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) were used in the polymerase chain reaction to isolate DNA fragments from the chicken BDNF and NT-3 genes. A genomic clone coding for chicken NT-3 was isolated and the structure of the chicken NT-3 mature protein was subsequently deduced from nucleotide sequence analysis of the isolated chicken NT-3 gene. Comparison of the chicken BDNF and NT-3 with the corresponding rat molecules showed that the avian molecules are very similar to their mammalian homologues. Northern blot analyses of messenger RNA (mRNA) from chicken embryos from embryonic day 3.5 (E3.5), E4.5, E8, E12 and E18 showed that expression of both BDNF and NT-3 mRNA peaked at E4.5 and decreased at later stages of development. Both probes revealed two transcripts; larger mRNAs of 4.5 kilobases (kb) for BDNF and 4.0 kb for NT-3 predominated over the smaller transcripts of 1.4 and 1.3 kb, respectively. The cellular localization of BDNF and NT-3 mRNA in the E4 and E6 embryos was studied by in situ hybridization. In the E4 embryo, labelling for BDNF was seen over cells in restricted parts of the epithelium of the otic vesicle. Analysis of adjacent sections for the low-affinity nerve growth factor receptor mRNA showed that regions in the otic vesicle epithelium which labelled for BDNF mRNA also labelled for low-affinity nerve growth factor receptor mRNA. No labelling for NT-3 was detected in the otic vesicle. Labelling for BDNF mRNA was also found over mesenchyme dorsal to the wing bud, in the wing bud and in the splanchnopleural lining of the stomach. Labelling for NT-3 mRNA was found at E4 over the epidermis on the ventral side in the region of the branchial arches. The labelling extended up the maxillary processes to Rathke's pouch. The closely located infundibulum was weakly labelled for NT-3 mRNA. NT-3 mRNA was also detected in the mesenchyme surrounding the oesophagus and lung buds. The regional expression pattern is in agreement with the established role for BDNF and NT-3 as target-derived neurotrophic factors, but the results also suggest that BDNF may be an intrinsic factor important for the development of the inner ear. The results support the emerging view that neurotrophic factors can play a role in early differentiation of both neuronal and non-neuronal tissues.

Basic fibroblast growth factor rescues CNS neurons from cell death caused by high oxygen atmosphere in culture

In the present study, we cultured rat CNS neurons and tested the neurotrophic support provided by basic fibroblast growth factor (bFGF) to prevent the oxygen-induced neuronal cell death. When rat basal forebrain (septum and vertical limb of diagonal band of Broca) cells of embryonic day 20 were cultured in a serum-free medium containing 5 microM cytosine arabinoside in a 50% oxygen atmosphere, the neuronal cells, which were immunostained by an anti-microtubule-associated protein 2 (MAP2) antibody, gradually died after 1 day in culture. After 3.5 days in culture, only 2-5% of neuronal cells survived. This oxygen-induced cell death of cultured basal forebrain neurons was reversed by the addition of bFGF at a concentration of 100 ng/ml. This cell-saving effect was dose-dependent, and the ED50 value was 12 ng/ml. Nerve growth factor (NGF) and insulin-like growth factor II could not prevent cell death. The activity of choline acetyltransferase was also maintained when bFGF was present in the basal forebrain culture. Viable astroglial cells, which were immunostained by an anti-glial fibrillary acidic protein, accounted for a few percent of the total number of cells after 3 days in culture both with and without 100 ng/ml of bFGF. The survival-enhancing effect of bFGF was observed not only in basal forebrain neurons but also in neocortical and hippocampal neurons. However, the sensitivity to oxygen toxicity of cultured neurons from the 3 CNS regions varied greatly. The neocortical neurons were the most sensitive to oxidative stress, while the hippocampal neurons were the most resistant. These results suggest that bFGF plays an important role in saving neuronal cells from oxidative stress during their long life without division.

Effects of nerve growth factor and basic fibroblast growth factor on survival of cultured septal cholinergic neurons from adult rats

We have established a primary culture technique for neuronal cells from rat basal forebrain from postnatal day 58 (P58) to study the effects of neurotrophic factors on the neurons. The survival of acetylcholinesterase (AChE)-positive neurons of 2-week-old rat septum has already been reported to be strongly supported by nerve growth factor (NGF) in culture. In this culture study of neurons from adult rat brains, the survival of AChE-positive neurons from P58 rat septum was slightly improved by NGF, although low affinity NGF receptor expression was also observed on cultured P58 rat septum neurons as well as on those from 2-week-old rats. The addition of basic fibroblast growth factor (bFGF) improved the survival of AChE-positive neurons cultured from P58 rat septum, but did not promote the survival of neurons from P12 rat septum. These results suggest that NGF changes to a maintenance factor in adult rat brain from a survival factor in postnatal 2-week-old rats. The survival of cholinergic neurons in culture of adult rat septum might be supported by factor(s) other than NGF, such as bFGF.

K-252 compounds: modulators of neurotrophin signal transduction

K-252 compounds, which share a common polyaromatic aglycon structure, are rather general and potent inhibitors of various protein kinases, including protein kinase C and tyrosine-specific protein kinases, and possibly act by interfering at or near the ATP binding site. However, chemical modifications in their sugar moiety can result in high specificity of the inhibitory action and, furthermore, can induce other stimulatory and inhibitory effects on nerve cells. These compounds are of particular interest because, in intact cells, they inhibit the actions of NGF and other neurotrophins without diminishing comparable actions of other growth factors. This effect seems to reflect a direct inhibitory action on trk neurotrophin receptor proteins. At concentrations lower than those necessary to inhibit neurotrophin actions, K-252a and K-252b have been shown to potentiate the stimulatory effects of NT-3 on different neurons in culture and on PC12 cells. The structural requirements for this effect seem to be different from those for the inhibition of neurotrophin actions. These findings raise the possibility of development of compounds of high selectivity, able to inhibit or potentiate the transduction mechanisms of individual neurotrophins, and identify K-252a and K-252b as lead compounds for the development of such selective molecules. Specific inhibitors and stimulators of neurotrophins would be valuable tools to investigate biological functions of the neurotrophins in vitro and in vivo. Furthermore, it is possible that, in the future, highly selective drugs with agonistic or antagonistic actions on neurotrophin mechanisms could become therapeutically useful in the treatment of neurological disease and injury.

Neurotrophin expression in rat hippocampal slices: a stimulus paradigm inducing LTP in CA1 evokes increases in BDNF and NT-3 mRNAs

We report that stimulation inducing long-term potentiation (LTP) in the CA1 pyramidal cell layer of the hippocampus evokes significant increases in both BDNF and NT-3 mRNAs in CA1 neurons. No changes in BDNF or NT-3 mRNA levels were seen in the nonstimulated regions of the pyramidal cell layer or the dentate. No change was seen in the levels of NGF mRNA at the time point examined. These results suggest that relatively normal levels of activity may regulate region-specific neurotrophin levels in the hippocampus. Given that known effects of NGF (and presumably of BDNF and NT-3) include elevation of neurotransmitter levels, elevation of sodium channels, and promotion of axonal terminal sprouting, activity-associated changes in neurotrophin levels may play a role in regulating neural connections in the adult as well as the developing nervous system.

Chronic ethanol consumption reduces the neurotrophic activity in rat hippocampus

The effect of chronic ethanol treatment (CET) for 21-26 weeks on the neurotrophic activity contained in the rat hippocampus (HPC) was determined with a bioassay in cultures of dissociated dorsal root ganglion cells (DRG) obtained from E7-8 chick embryos. Extracts of the HPC from CET or pair-fed control rats were used as experimental media, and neuronal survival and neurite-outgrowth of DRG cultures were determined. Both neuronal survival (-25%) and neurite-outgrowth (-50%) were reduced in the presence of HPC extracts from CET rats relative to controls. These data suggest that CET reduces the neurotrophic content of the HPC which may result in damage to septohippocampal neurons.

Plasticity in the rat hippocampal formation following ibotenic acid lesion of the septal region: a quantitative [14C]deoxyglucose and acetylcholinesterase study

The local cerebral glucose utilization was measured in the hippocampal formation 3, 21, and 90 days after bilateral lesions of the medial septal nucleus and the nucleus of the diagonal band of Broca by multiple ibotenic acid injections. The CMRglc was determined in hippocampal areas and layers and various limbic and visual regions by quantitative [14C]2-deoxyglucose autoradiography using a computerized image-processing system. Three days after lesion, CMRglc was significantly decreased in 26 of the 38 structures examined. The most pronounced reductions were found in CA2 and CA3, the subiculum, and the parasubiculum. The CMRglc values of the 21- and 90-day postlesion groups did not differ significantly from control data when univariate statistics were used. However, by means of a factor analysis and subsequently a discriminant analysis as a multivariate test for group differences, significant lesion-induced CMRglc changes could be detected between the control group, the 3-day group, and the 90-day group. The 21-day group did not differ significantly from the controls. The data indicate that 90 days after lesion of the medial septum/diagonal band complex (MSDB), a considerable recovery of the mean CMRglc was found in the hippocampal region, although a normal level was not reached. In a parallel series, processing of sections for acetylcholinesterase (AChE) histochemistry revealed a severe destruction of AChE-positive fibers in the hippocampus at 3 days after lesion and a conspicuous recovery in the amount of stainable fibers and their staining intensity at 21 days postlesion. In the 90-day group, the AChE fibers recovered even further but did not reach the values of unlesioned sham-operated controls. The present study indicates that sprouting of surviving cholinergic afferents might be an important morphological substrate for CMRglc recovery in the hippocampus after MSDB lesion.

Light regulates expression of brain-derived neurotrophic factor mRNA in rat visual cortex

Specific sensory input has profound transient and long-lasting effects on the function of corresponding sensory cortical areas both during development and in adulthood. To study whether neurotrophic factors might play a role in such processes, we investigated the effects of light on the nerve growth factor and brain-derived neurotrophic factor (BDNF) mRNA levels in rat visual cortex. Keeping adult rats in the dark or preventing normal activity of retinal ganglion cells by intraocular injection of tetrodotoxin significantly decreased the levels of BDNF mRNA in the visual cortex but not in other cortical areas. Exposure to light after a period in darkness rapidly restored the mRNA to control levels. These alterations in visual input had no effect on nerve growth factor mRNA. The mRNA of trkB, the putative signal-transducing receptor unit for BDNF, was also decreased in darkness, although less than BDNF mRNA. BDNF mRNA levels increased in the visual cortex of newborn rats after eye-opening. This increase is retarded, although not completely abolished, by rearing the pups in darkness. Thus, the levels of BDNF mRNA are rapidly regulated by sensory input during development and in adulthood. BDNF may therefore play an important role in formation and in activity-dependent modulation of specific connections in the visual cortex.

Cellular targets and trophic functions of neurotrophin-3 in the developing rat hippocampus

The expression of the neurotrophins and trk receptors in the hippocampus has directed attention toward their roles in the development and maintenance of this region. We have examined the effects of the neurotrophins NT-3, BDNF, and NGF in cultures of developing rat hippocampal cells by two criteria: rapid induction of c-fos and neurotrophic responses. The selective induction of c-fos mRNA suggests the presence of functional receptors for NT-3 and BDNF, but not NGF, in embryonic hippocampal cultures. The NT-3-responsive cells were localized in pyramidal neurons of areas CA1 through CA3 and dentate granular and hilar cells of postnatal organotypic slices, as detected by c-Fos immunocytochemistry. In addition to immediate early responses, NT-3 caused a 10-fold increase in the number of cells expressing the neuronal antigen calbindin-D28k. This increase was dose dependent, with maximal stimulation at 10 ng/ml. In contrast, BDNF elicited small but significant calbindin responses. These results indicate biological responses to NT-3 in the CNS and suggest roles for for this neurotrophin during hippocampal neurogenesis.

In vivo activated brain astrocytes may produce and secrete nerve growth factor-like molecules

The cellular localization of the nerve growth factor-like immunoreactivity (NGF-LIR) has been studied in the septum and hippocampus of the rat brain 7 days following partial electrolytic lesion (2 mA, 30 s) of the septohippocampal pathways or after single intraventricular administration of 15 U of interleukin-1 beta (IL-1 beta). A double immunostaining technique which allowed a simultaneous localization of NGF-LIR and that of astroglia marker glial fibrillary acidic protein was used. Our data show that after both treatments, apart from neuronal localization of NGF-LIR typical for normal brain, many astrocytes both in the septum and hippocampus became NGF-like immunoreactive. Besides, NGF-LIR often formed a "halo" reaction around astrocytes. These results support the notion that activated in vivo brain astrocytes may, just as astrocytes growing in vitro, synthesize and secrete NGF-like molecules. Our findings may be of importance in considerations concerning trophic support to the cholinergic neurons of the basal forebrain nuclei whose impaired function is essentially responsible for some cognitive deficits in neurodegenerative diseases such as Alzheimer disease.

Cells Expressing mRNA for Neurotrophins and their Receptors During Embryonic Rat Development

In situ hybridization analysis of cells expressing messenger RNAs (mRNAs) for the neurotrophins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) and their high-affinity receptors (trk, trkB and trkC) in the rat embryo revealed a complex but specific expression pattern for each of these mRNAs. For all mRNAs a developmentally regulated expression was seen in many different tissues. BDNF and NT-3 mRNAs were expressed in the sensory epithelia of the cochlea and vestibule macula of the sacculus and utricle, and both trkB and trkC mRNA were expressed in the spiral and vestibule ganglia innervating these sensory structures. NGF and NT-3 mRNA were found in the iris, innervated by the sympathetic neurons of the superior cervical ganglion and sensory neurons from the trigeminal ganglion, which expressed both trk and trkC mRNAs. Both NGF and NT-3 mRNAs were also expressed in other target fields of the trigeminal ganglion, the epithelium of the whisker follicles (NT-3 mRNA) and in the epithelium of the nose, tongue and jaw. NT-3 mRNA was found in the cerebellar external granule layer and trkC mRNA in the Purkinje layer of the cerebellar primordia. These sites of synthesis are consistent with a target-derived neurotrophic interaction for NGF, BDNF and NT-3. However, in some cases mRNAs for both the neurotrophins and their high-affinity receptors were detected in the same tissue, including the dorsal root, geniculate, superior, jugular, petrose and nodose ganglia, as well as in the hippocampus, frontal cortical plate and pineal recess, implying a local mode of action. Combined, these data suggest a broad function for the neurotrophins and their receptors in supporting neural innervation during embryonic development. The results also identify several novel neuronal systems that are likely to depend on the neurotrophins in vivo.

Cortical neurons inhibit basal and interleukin-1-stimulated astroglial cell secretion of nerve growth factor

Primary cultures of neonatal rat cortical neurons and astrocytes synthesize and secrete nerve growth factor (NGF). Co-culturing neurons with astrocytes decreased NGF secretion in the co-cultures. The inhibition of co-culture NGF secretion was partially reversible upon selectively decreasing the number of neurons by glutamate treatment. Interleukin-1 beta (IL-1) stimulated NGF secretion from astrocytes, and the magnitude of this secretion was decreased in the co-cultures. Thus, co-culture with neurons decreases astroglial cell secretion of NGF and down-regulates astroglial responsiveness to IL-1.

Cytokine regulation of nerve growth factor-mediated cholinergic neurotrophic activity synthesized by astrocytes and fibroblasts

The neurotrophic activity of astrocytes and fibroblasts and its regulation by various cytokines were investigated. Astrocyte conditioned medium (ACM) enhanced the survival of neurons and the proliferation of astrocytes in embryonic cortical cultures grown in serum-free defined medium. However, these results were not affected by acidic fibroblast growth factor, interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF alpha), and transforming growth factor-beta 1. In contrast, ACM induced choline acetyltransferase expression in septal cholinergic neurons via nerve growth factor (NGF)-dependent and -independent mechanisms. However, neither acidic nor basic fibroblast growth factor is involved in this biological activity in ACM. The cytokines listed above mainly stimulate NGF-mediated cholinergic neurotrophic activity in ACM. A combination of IL-1 beta and TNF alpha significantly enhanced choline acetyltransferase activity in septal neurons co-cultured with astrocytes, and this effect was found to be mediated by NGF produced by activated astrocytes. Effects of astrocytes on GABAergic neurons were also examined. ACM was found to increase glutamate decarboxylase activity in neuronal cultures from septum in the presence of Ara-C. However, the cytokines did not enhance this activity in ACM. Moreover, a combination of IL-1 beta and TNF alpha had no effect on glutamate decarboxylase activity in septal neurons co-cultured with astrocytes. In a final set of experiments, cholinergic neurotrophic activity in skin-derived fibroblast conditioned medium (FCM) was examined. FCM was found to possess biological activity similar to that of ACM on septal neurons grown in serum-free defined medium with Ara-C. The cytokines also enhanced NGF-mediated cholinergic neurotrophic activity in FCM. Astrocytes and fibroblasts were found to possess NGF-type and non-NGF-type cholinergic neurotrophic activity, and various cytokines were found to regulate the NGF-type cholinergic neurotrophic activity in both types of cells. NGF produced by astrocytes and fibroblasts that are activated by cytokines is likely to be important for development and regeneration of NGF-sensitive neurons in the central and peripheral nervous systems.

In situ hybridization: a valuable tool in diagnostic pathology

In situ hybridization or hybridohistochemistry has evolved in recent years in a new histologic modality. In situ hybridization (ISH) can be used for the detection of DNA (DISH) or RNA (RISH). The potential diagnostic value within a pathologic setting are well recognized. In this review paper, we summarize the use of DISH in a pathologic setting for the detection of chromosomal aberrations and localization of DNA-viruses like cytomegalovirus and Epstein Barr virus. RISH which is still in a more experimental stage can be applied for the localization of RNA-virus, like human immunodeficiency virus. However, the most important application of RISH will be the detection of gene-expression at the level of mRNA. Potentially this has many applications especially in early diagnostics of neoplastic tissues. Finally, we have summarized some pitfalls which may hamper the introduction of in situ hybridization for diagnostic purposes and some future developments in ISH.

Temporal profiles of nerve growth factor beta-subunit level in rat brain regions after transient ischemia

To determine the role of nerve growth factor (NGF) in ischemic brain damage, we measured the temporal and regional changes in the level of NGF in the hippocampal subfields, the cerebral cortex, the striatum, and the septum at 1, 2, 7, and 30 days after transient forebrain ischemia using a highly sensitive sandwich-type enzyme immunoassay system for the beta-subunit of mouse 7S NGF (beta-NGF). We also analyzed glial fibrillary acidic protein immunoreactivity in the hippocampus to ascertain the contribution of reactive astrocytes to NGF production after an ischemic insult. In the CA1 subfield of the hippocampus, the level of beta-NGF decreased slightly 2 days after ischemia (not significant), at which time CA1 pyramidal cell loss began to occur, and increased by 40% 30 days after ischemia (p less than 0.05). A marked increase in glial fibrillary acidic protein-positive astrocytes in the CA1 subfield 2-30 days after ischemia suggests that the reactive astrocytes participated in a gradual increase in the level of beta-NGF after recirculation. The level of beta-NGF in the dentate gyrus decreased transiently 2 days (p less than 0.05) and 7 days (p less than 0.01) after ischemia, followed by recovery to the level of control animals 30 days after ischemia. The level of beta-NGF in the septum gradually decreased 7 days (-27%, p less than 0.05) and 30 days (-43%, p less than 0.01) after ischemia. The levels of beta-NGF in the cerebral cortex and striatum remained unaltered throughout the observation period.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of NGF protein level in rat dorsal hippocampus following administration of kainic acid

Intraperitoneal administration of kainic acid (KA) into adult rats caused a profound increase in nerve growth factor (NGF) mRNA and a significant reduction of NGF protein level in the hippocampus. Diazepam pretreatment suppressed both. The reduction of NGF level was apparent in the dorsal hippocampus at 2 h after KA administration, but a marked elevation of NGF protein was observed in the ventral hippocampus at 4 h. These results suggest that non-N-methyl-D-aspartate (NMDA) receptor agonists negatively influence NGF synthesis or stimulate NGF protein degradation in the dorsal hippocampus involving the CA1 sector.

Nerve growth factor precursors in the rat thyroid and hippocampus

A nerve growth factor (NGF) precursor form of about 24 kDa was identified in homogenates of rat thyroid and hippocampus by immunoprecipitation using three sera raised against a synthetic peptide that reproduces the sequence -71 to -46 of the proNGF molecule. Besides this species, a 31 kDa protein, as well as a cleavage product of 12 kDa were also immunoprecipitated in both tissues by one of these sera.

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.

Significance of nerve growth factor content levels after transient forebrain ischemia in gerbils

Involvement of nerve growth factor (NGF) in the pathogenesis of delayed neuronal death (DND) of CA1 neurons in the hippocampus has been suggested. We measured regional changes in the content of tissue NGF of the hippocampus in the Mongolian gerbil after 5 min forebrain ischemia. The NGF content was found to decrease significantly in the CA3 and dentate regions by 32% two days after ischemia. By contrast in the CA1 region, the level of NGF became significantly elevated by 50% two weeks after ischemia or later. The early reduction of NGF content in the afferent area projecting to the CA1 sector might be primarily linked to the pathogenesis of DND, whereas the delayed increase within the CA1 sector might be a secondary local response mainly of reactive astroglia.