Interleukin-1 regulates synthesis of nerve growth factor in non-neuronal cells of rat sciatic nerve

The Schwann cells and fibroblast-like cells of the intact sciatic nerve of adult rats synthesize very little nerve growth factor (NGF). After lesion, however, there is a dramatic increase in the amounts of both NGF-mRNA and NGF protein synthesized by the sciatic non-neuronal cells. This local increase in NGF synthesis partially replaces the interrupted NGF supply from the periphery to the NGF-responsive sensory and sympathetic neurons, whose axons run within the sciatic nerve. Macrophages, known to invade the site of nerve lesion during wallerian degeneration, are important in the regulation of NGF synthesis. Here we demonstrate that the effect of macrophages on NGF-mRNA levels in cultured explants of sciatic nerve can be mimicked by conditioned media of activated macrophages, and that interleukin-1 is the responsible agent.

ER stress and neurodegenerative diseases

Endoplasmic reticulum (ER) stress is caused by disturbances in the structure and function of the ER with the accumulation of misfolded proteins and alterations in the calcium homeostasis. The ER response is characterized by changes in specific proteins, causing translational attenuation, induction of ER chaperones and degradation of misfolded proteins. In case of prolonged or aggravated ER stress, cellular signals leading to cell death are activated. ER stress has been suggested to be involved in some human neuronal diseases, such as Parkinson's disease, Alzheimer's and prion disease, as well as other disorders. The exact contributions to and casual effects of ER stress in the various disease processes, however, are not known. Here we will discuss the possible role of ER stress in neurodegenerative diseases, and highlight current knowledge in this field that may reveal novel insight into disease mechanisms and help to design better therapies for these disorders.

Activity dependent regulation of BDNF and NGF mRNAs in the rat hippocampus is mediated by non-NMDA glutamate receptors

The mRNAs of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) exhibit a similar, though not identical, regional and cellular distribution in the rodent brain. In situ hybridization experiments have shown that BDNF, like NGF, is predominantly expressed by neurons. The neuronal localization of the mRNAs of these two neurotrophic molecules raised the question as to whether neuronal activity might be involved in the regulation of their synthesis. After we had demonstrated that depolarization with high potassium (50 mM) resulted in an increase in the levels of both BDNF and NGF mRNAs in cultures of hippocampal neurons, we investigated the effect of a large number of transmitter substances. Kainic acid, a glutamate receptor agonist, was by far the most effective in increasing BDNF and NGF mRNA levels in the neurons, but neither N-methyl-D-aspartic acid (NMDA) nor inhibitors of the NMDA glutamate receptors had any effect. However, the kainic acid mediated increase was blocked by antagonists of non-NMDA receptors. Kainic acid also elevated levels of BDNF and NGF mRNAs in rat hippocampus and cortex in vivo. These results suggest that the synthesis of these two neurotrophic factors in the brain is regulated by neuronal activity via non-NMDA glutamate receptors.

Molecular cloning, expression and regional distribution of rat ciliary neurotrophic factor

Ciliary neurotrophic factor (CNTF) was originally characterized as a survival factor for chick ciliary neurons in vitro. More recently, it was shown to promote the survival of a variety of other neuronal cell types and to affect the differentiation of E7 chick sympathetic neurons by inhibiting their proliferation and by inducing the expression of vasoactive intestinal peptide immunoreactivity (VIP-IR). In cultures of dissociated sympathetic neurons from newborn rats, CNTF induces cholinergic differentiation as shown by increased levels of choline acetyltransferase (ChAT). This increase is paralleled by a reduction of tyrosine hydroxylase (TH) activity. Moreover, CNTF promotes the differentiation of bipotential 02A progenitor cells to type-2-astrocytes in vitro. To help establish which, if any, of these functions CNTF exerts in vivo, it is necessary to determine its primary structure, cellular expression, developmental regulation and localization. The complementary DNA-deduced amino-acid sequence and subsequent expression of cDNA clones covering the entire coding region in HeLa-cells indicate that CNTF is a cytosolic protein. This, together with its regional distribution and its developmental expression, show that CNTF is not a target-derived neurotrophic factor. CNTF thus seems to exhibit neurotrophic and differentiation properties only after becoming available either by cellular lesion or by an unknown release mechanism.

Differential regulation of mRNA encoding nerve growth factor and its receptor in rat sciatic nerve during development, degeneration, and regeneration: role of macrophages

In newborn rats the levels of nerve growth factor (NGF) mRNA (mRNANGF) and NGF receptor mRNA (mRNA(rec)) in the sciatic nerve were 10 and 120 times higher, respectively, than in adult animals. mRNA(rec) levels decreased steadily from birth, approaching adult levels by the third postnatal week, whereas mRNANGF levels decreased only after the first postnatal week, although also reaching adult levels by the third week. Transection of the adult sciatic nerve resulted in a marked biphasic increase in mRNANGF with time. On the proximal side of the cut, this increase was confined to the area immediately adjacent to the cut; peripherally, a similar biphasic increase was present in all segments. mRNA(rec) levels were also markedly elevated distal to the transection site, in agreement with previous results obtained by immunological methods [Taniuchi, M., Clark, H. B. & Johnson, E. M., Jr. (1986) Proc. Natl. Acad. Sci. USA 83, 4094-4098]. Following a crush lesion (allowing regeneration), the mRNA(rec) levels were rapidly down-regulated as the regenerating nerve fibers passed through the distal segments. Down-regulation of mRNANGF also occurred during regeneration but was slower and not as extensive as that of mRNA(rec) over the time period studied. Changes in mRNANGF and mRNA(rec) occurring in vivo after transection were compared with those observed in pieces of sciatic nerve kept in culture. No difference was found for mRNA(rec). Only the initial rapid increase in mRNANGF occurred in culture, but the in vivo situation could be mimicked by the addition of activated macrophages. This reflects the situation in vivo where, after nerve lesion, macrophages infiltrate the area of the Wallerian degeneration. These results suggest that mRNANGF synthesis in sciatic non-neuronal cells is regulated by macrophages, whereas mRNA(rec) synthesis is determined by axonal contact.

Interplay between glutamate and gamma-aminobutyric acid transmitter systems in the physiological regulation of brain-derived neurotrophic factor and nerve growth factor synthesis in hippocampal neurons

In the central nervous system brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) are predominantly located in neurons. Here we demonstrate that the balance between the activity of the glutamatergic and gamma-aminobutyric acid (GABA)ergic systems controls the physiological levels of BDNF and NGF mRNAs in hippocampal neurons in vitro and in vivo. The blockade of the glutamate receptors and/or stimulation of the GABAergic system reduces BDNF and NGF mRNAs in hippocampus and NGF protein in hippocampus and septum. The reduction of NGF in the septum reflects the diminished availability of NGF in the projection field of NGF-dependent septal cholinergic neurons. These neurons do not synthesize NGF themselves but accumulate it by retrograde axonal transport. The refined and rapid regulation of BDNF and NGF synthesis by the glutamate and GABA transmitter systems suggests that BDNF and NGF might be involved in activity-dependent synaptic plasticity.

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.

Transforming growth factor-beta 1 in the rat brain: increase after injury and inhibition of astrocyte proliferation

Transforming growth factor-beta 1 (TGF-beta 1) has been shown to up-regulate the synthesis of nerve growth factor (NGF) in cultured rat astrocytes and in neonatal brain in vivo (Lindholm, D., B. Hengerer, F. Zafra, and H. Thoenen. 1990. NeuroReport. 1:9-12). Here we show that mRNA encoding TGF-beta 1 increased in rat cerebral cortex after a penetrating brain injury. The level of NGF mRNA is also transiently increased after the brain trauma, whereas that of brain-derived neurotrophic factor remained unchanged. In situ hybridization experiments showed a strong expression of TGF-beta 1 4 d after the lesion in cells within and in the vicinity of the wound. Staining of adjacent sections with OX-42 antibodies, specific for macrophages and microglia/brain macrophages, revealed a similar pattern of positive cells, suggesting that invading macrophages, and perhaps reactive microglia, are the source of TGF-beta 1 in injured brain. Both astrocytes and microglia express TGF-beta 1 in culture, and TGF-beta 1 mRNA levels in astrocytes are increased by various growth factors, including FGF, EGF, and TGF-beta itself. TGF-beta 1 is a strong inhibitor of astrocyte proliferation and suppresses the mitotic effects of FGF and EGF on astrocytes. The present results indicate that TGF-beta 1 expressed in the lesioned brain plays a role in nerve regeneration by stimulating NGF production and by controlling the extent of astrocyte proliferation and scar formation.

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.

The induction of LTP increases BDNF and NGF mRNA but decreases NT-3 mRNA in the dentate gyrus

We have investigated the expression of the mRNAs for brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) in the hippocampus before and after induction of long term potentiation (LTP) of synaptic transmission in the dentate gyrus through stimulation of the perforant path (PP). A unilateral PP stimulation produced a bilateral increase in the mRNA for both BDNF and NGF in granular neurones of the dentate gyrus but not in other neurones in the hippocampus. The mRNA for neurotrophin-3 (NT-3) was bilaterally decreased by LTP but that of NT-4 remained at the basal level. These results suggest that individual neurotrophic factors may play different roles in neuronal plasticity.

Positive feedback between acetylcholine and the neurotrophins nerve growth factor and brain-derived neurotrophic factor in the rat hippocampus

In the rat hippocampus, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are synthesized by neurons in an activity-dependent manner. Glutamate receptor activation increases whereas GABAergic stimulation decreases NGF and BDNF mRNA levels. Here we demonstrate that NGF and BDNF mRNA and NGF protein are up-regulated in the rat hippocampus by the activation of muscarinic receptors. Conversely, NGF and BDNF enhance the release of acetylcholine (ACh) from rat hippocampal synaptosomes containing the nerve endings of the septal cholinergic neurons. NGF also rapidly increases the high-affinity choline transport into synaptosomes. The reciprocal regulation of ACh, NGF and BDNF in the hippocampus suggests a novel molecular framework by which the neurotrophins might influence synaptic plasticity.

Brain-derived neurotrophic factor is a survival factor for cultured rat cerebellar granule neurons and protects them against glutamate-induced neurotoxicity

We have studied the effects of different neurotrophins on the survival and proliferation of rat cerebellar granule cells in culture. These neurons express trkB and trkC, the putative neuronal receptors for brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) respectively. Binding studies using iodinated BDNF and NT-3 demonstrated that both BDNF and NT-3 bind to the cerebellar granule neurons with a similar affinity of approximately 2 x 10(-9) M. The number of receptors per granule cell was surprisingly high, approximately 30 x 10(-4) and 2 x 10(5) for BDNF and NT-3, respectively. Both NT-3 and BDNF elevated c-fos mRNA in the granule neurons, but only BDNF up-regulated the mRNA encoding the low-affinity neurotrophin receptor (p75). In contrast to NT-3, BDNF acted as a survival factor for the granule neurons. BDNF also induced sprouting of the granule neurons and significantly protected them against neurotoxicity induced by high (1 mM) glutamate concentrations. Cultured granule neurons also expressed low levels of BDNF mRNA which were increased by kainic acid, a glutamate receptor agonist. Thus, BDNF, but not NT-3, is a survival factor for cultured cerebellar granule neurons and activation of glutamate receptor(s) up-regulates BDNF expression in these cells.

Activity-dependent and hormonal regulation of neurotrophin mRNA levels in the brain--implications for neuronal plasticity

The neurotrophins exhibit neurotrophic effects on specific, partially overlapping populations of neurons both in the peripheral and the central nervous system (CNS). In the periphery, they are synthesized by a variety of nonneuronal cells, and their synthesis seems to be independent of the neuronal input. In contrast, in the CNS all neurotrophins are expressed under physiological conditions primarily by neurons. The production of NGF and BDNF is controlled by neuronal activity: up-regulation by glutamate and acetylcholine, down-regulation by gamma-aminobutyric acid. In contrast, NT-3 regulation is independent of neuronal activity, but it is up-regulated by thyroid hormones and BDNF. The latter observation suggests that NT-3 might be controlled indirectly by neuronal activity via BDNF. In peripheral nonneuronal tissues, glucocorticoid hormones down-regulate NGF mRNA levels both in vitro and in vivo. In contrast, in the CNS, neuronal production of NGF is enhanced by glucocorticoids. The rapid regulation of NGF and BDNF by subtle physiological stimuli together with the recent demonstration that the neurotrophins release neurotransmitters such as acetylcholine opens up interesting perspectives for the function of neurotrophins as mediators of neuronal plasticity.

Lesion-induced increase in nerve growth factor mRNA is mediated by c-fos

Lesion of the sciatic nerve caused a rapid increase in c-fos and c-jun mRNA that was followed about 2 hr later by an increase in nerve growth factor (NGF) mRNA. To evaluate whether the initial increase in c-fos mRNA is causally related to the subsequent increase in NGF mRNA, we performed experiments with fibroblasts of transgenic mice carrying an exogenous c-fos gene under the control of a metallothionein promoter. In primary cultures of these fibroblasts, CdCl2 evoked a rapid increase in exogenous c-fos mRNA, followed immediately by an increase in endogenous c-jun mRNA and with a slight delay by an increase in NGF mRNA. In fibroblasts of C3H control mice, CdCl2 had no effect on the mRNA levels of the protooncogenes c-fos and c-jun or of NGF. Additional evidence for a causal relationship between c-fos induction and the subsequent increase in NGF mRNA was obtained in cotransfection experiments. Fibroblasts of C3H control mice were cotransfected with a metallothionein-promoter-driven c-fos expression vector and a NGF promoter-chloramphenicol acetyltransferase reporter gene construct. Induction of the exogenous c-fos by CdCl2 resulted in increased activity of the NGF promoter. DNase I footprint experiments demonstrated that a binding site for transcription factor AP-1 (Fos/Jun heterodimer) in the first intron of the NGF gene was protected following c-fos induction. That this protected AP-1 site indeed was functional in the regulation of NGF expression was verified by deletion experiments and by a point mutation in the corresponding AP-1 binding region in the NGF promoter-chloramphenicol acetyltransferase reporter construct.

Characterization of glial trkB receptors: differential response to injury in the central and peripheral nervous systems

In situ hybridization on sections from the adult rat peripheral and central nervous systems demonstrated that trkB mRNA was expressed not only by neurons but also by cells in central nervous system white matter as well as by Schwann cells in the sciatic nerve. In situ hybridization with an oligonucleotide complementary to the trkB tyrosine kinase domain could only demonstrate mRNA in neurons, indicating expression of truncated trkB receptors lacking the tyrosine kinase domain by glial cells. RNA blot analysis was performed on separately cultured central nervous system glial cells to study which cell types express trkB mRNA. Several transcripts encoding truncated trkB receptors were expressed at high levels in O-2A progenitors, astrocytes, and oligodendrocytes, but not trkB mRNA could be detected in microglia. The expression of trkB mRNA by glial cells in vivo was also investigated after injury; strongly elevated levels of mRNA encoding truncated receptors were detected in the glial scar formed after an incision in the spinal cord dorsal funiculus. In contrast, in the cut sciatic nerve, trkB mRNA decreased distal to the transection, and by 3 weeks only very low levels of mRNA could be detected. Immunoelectron microscopy located trkB-like immunoreactivity to axons and Schwann cells in the sciatic nerve. The expression of truncated trkB receptors by astrocytes, oligodendrocytes, and Schwann cells and the altered levels in response to injury indicate that glial trkB receptors may serve an important function in the intact and injured nervous system.

Regional and cellular codistribution of interleukin 1 beta and nerve growth factor mRNA in the adult rat brain: possible relationship to the regulation of nerve growth factor synthesis

We have found a regional distribution of IL 1 beta mRNA and IL 1 activity in the normal adult rat brain, which reveals at least partially a colocalization with nerve growth factor (NGF). The predominantly neuronal signal patterns were found over the granule cells of the dentate gyrus, the pyramidal cells of the hippocampus, the granule cells of the cerebellum, the granule and periglomerular cells of the olfactory bulb, and over dispersed cells of the ventromedial hypothalamus and of the frontal cortex. In these areas also the highest levels of IL 1 activity were observed. In the striatum and septum much lower levels of IL 1 beta mRNA and IL 1 activity (shown for the striatum), most likely synthesized by glial cells, could be determined. IL 1 beta-expressing cells were mainly found in brain regions that also synthesize NGF mRNA as shown by in situ hybridization. NGF mRNA could be demonstrated over pyramidal cells of the hippocampus, granule cells of the dentate gyrus, periglomerular cells of the olfactory bulb and over prefrontal cortex neurons. These data indicate that IL 1 beta, among other factors, might also play a regulatory role in the synthesis of NGF in the CNS, as has been demonstrated in the peripheral nervous system (Lindholm, D., R. Heumann, M. Meyer, and H. Thoenen. 1987. Nature (Lond.). 330:658-659).

BDNF and NT-3 induce intracellular Ca2+ elevation in hippocampal neurones

The effects of neurotrophins on intracellular Ca2+ levels in rat hippocampal neurones were studied in vitro using fura-2 fluorescence microscopy. BDNF and NT-3, but not NGF, rapidly increased cytoplasmic Ca2+ concentrations in these neurones ten-fold to reach 1 microM. Moreover in some of the neurones both BDNF and NT-3 elicited Ca2+ responses, indicative of the presence of functional receptors for these neurotrophins in the same cell. In these cultures approximately 80% of the hippocampal neurones were stained with antibodies against full-length TrkB. The expression of functional TrkB was also confirmed by RNA analysis. These results demonstrate the presence of functional receptors for BDNF and NT-3 in hippocampal neurones.

Interleukin-6 and transforming growth factor-beta 1 mRNAs are induced in rat facial nucleus following motoneuron axotomy

Transection of the rat facial nerve leads to a rapid activation of both astrocytes and microglia around axotomized motoneurons. The factors involved in glial activation in vivo are poorly defined but cytokines have been implicated as major regulators of glial activity in vitro. In the present study we have investigated the expression of cytokine mRNAs in the axotomized facial nucleus that might be involved in glial activation. Eight hours after axotomy unilateral transection of the facial nerve had already induced a rapid accumulation of interleukin (IL)-6-mRNA, with a peak at 24 hours. No IL-6 mRNA was detected on the unoperated control side. Transforming growth factor (TGF)-beta 1 mRNA was detected at low levels in the normal facial nucleus, increasing to three times the normal level 2 days after axotomy. After day 7 TGF-beta 1 mRNA levels gradually declined, with a second minor peak 21 days after axotomy. In situ hybridization experiments, 4 and 21 days after axotomy, localized TGF-beta 1 mRNA to activated microglial cells around regenerating motoneurons, as well as probably some astrocytes. Motoneurons did not express TGF-beta 1 mRNA. TGF-beta 3 was found to be normally expressed in the facial nucleus but was not regulated by axotomy. No mRNA for IL-1, tumour necrosis factor-alpha or interferon-gamma was found in the regenerating facial nucleus at any point in time.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and functional interaction of hepatocyte growth factor-scatter factor and its receptor c-met in mammalian brain

Hepatocyte growth factor-scatter factor (HGF-SF) is a pleiotropic cytokine with mito-, morpho-, and motogenic effects on a variety of epithelial and endothelial cells. HGF-SF activity is mediated by the c-met protooncogene, a membrane-bound tyrosine kinase. Here, we demonstrate that both genes are expressed in developing and adult mammalian brains. HGF-SF mRNA is localized in neurons, primarily in the hippocampus, the cortex, and the granule cell layer of the cerebellum, and it is also present at high levels in ependymal cells, the chorioid plexus, and the pineal body. c-met is expressed in neurons, preferentially in the CA-1 area of the hippocampus, the cortex, and the septum, as well as in the pons. In the embryonic mouse, brain HGF-SF and c-met are expressed as early as days 12 and 13, respectively. Neuronal expression of HGF-SF is evolutionary highly conserved and detectable beyond the mammalian class. Incubation of septal neurons in culture with HGF-SF leads to a rapid increase of c-fos mRNA levels. The results demonstrate the presence of a novel growth factor-tyrosine kinase signaling system in the brain, and they suggest that HGF-SF induces a functional response in a neuronal subpopulation of developing and adult CNS.

Neurotrophin-3 induced by tri-iodothyronine in cerebellar granule cells promotes Purkinje cell differentiation

Thyroid hormones play an important role in brain development, but the mechanism(s) by which triiodothyronine (T3) mediates neuronal differentiation is poorly understood. Here we demonstrate that T3 regulates the neurotrophic factor, neurotrophin-3 (NT-3), in developing rat cerebellar granule cells both in cell culture and in vivo. In situ hybridization experiments showed that developing Purkinje cells do not express NT-3 mRNA but do express trkC, the putative neuronal receptor for NT-3. Addition of recombinant NT-3 to cerebellar cultures from embryonic rat brain induces hypertrophy and neurite sprouting of Purkinje cells, and upregulates the mRNA encoding the calcium-binding protein, calbindin-28 kD. The present study demonstrates a novel interaction between cerebellar granule neurons and developing Purkinje cells in which NT-3 induced by T3 in the granule cells promotes Purkinje cell differentiation.

GABAergic stimulation switches from enhancing to repressing BDNF expression in rat hippocampal neurons during maturation in vitro

gamma-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the adult mammalian central nervous system. However, GABA depolarizes immature rat hippocampal neurons and increases intracellular Ca2+ ([Ca2+]i). Here we show, that GABA and the GABAA receptor agonist muscimol induce c-Fos immunoreactivity and increase BDNF mRNA expression in embryonic hippocampal neurons cultured for 5 days. In contrast, after 3 weeks in culture, GABA and muscimol failed to induce c-fos and BDNF expression. Fura-2 fluorescence microscopy revealed that muscimol produces a dihydropyridine-sensitive transient increase in [Ca2+]i, comparable to the effect of the non-NMDA receptor agonist kainic acid in neurons cultured for 5 days, but not in 3-week-old cultures. The increase in c-Fos immunoreactivity and BDNF mRNA levels by GABA were dependent upon the activation of voltage-gated Ca2+ channels, as shown using the L-type specific Ca2+ channel blocker nifedipine. The differential regulation of c-fos and BDNF expression by GABA and muscimol in developing and mature hippocampal neurons is due to a switch in the ability of GABAA receptors to activate voltage-gated Ca2+ channels. These observations support the hypothesis that GABA might have neurotrophic effects on embryonic or perinatal hippocampal neurons, which are mediated by BDNF.

Autocrine-paracrine regulation of hippocampal neuron survival by IGF-1 and the neurotrophins BDNF, NT-3 and NT-4

In contrast to sympathetic and sensory neurons in the peripheral nervous system, the neurotrophic requirements for neurons in the central nervous system (CNS) have not been clearly identified. The inactivation of specific neurotrophic factors and their receptors by gene targeting has shown that there are no major changes in neuron numbers in the CNS. This suggests an overlap between the action of different neurotrophic factors in the brain during development. Here we have studied the survival of hippocampal neurons prepared from embryonic rats using different culture conditions. Whereas the hippocampal neurons survive well in culture when plated at high density, they die at lower cell densities in the absence of appropriate neurotrophic factors. Under the latter conditions, both insulin-like growth factor-1 (IGF-1) and neurotrophins - brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) - rescued a large proportion of cultured neurons. In addition, hippocampal neurons from BDNF knockout mice exhibited enhanced cell death compared with cells from wild-type animals. BDNF and IGF-1 both increased the survival of the hippocampal neurons lacking BDNF, showing complementary action for these factors in supporting survival. Blocking antibodies against NT-3 and IGF-1 decreased hippocampal neuron survival at low cell densities, showing autocrine or paracrine action of the factors. At higher cell densities, however, the antibodies had no effect, demonstrating that there is a sufficient amount of endogenous factors in supporting survival. Blocking antibodies against NT-3 and IGF-1 decreased hippocampal neurons depend for survival on local neurotrophic factors such as IGF-1, BDNF and NT-3, which act in an autocrine/paracrine manner. The multifactorial support of hippocampal neurons ensures a maximal degree of neuron survival even in the absence of an individual factor

Brain-derived neurotrophic factor messenger RNA is expressed in the septum, hypothalamus and in adrenergic brain stem nuclei of adult rat brain and is increased by osmotic stimulation in the paraventricular nucleus

We have detected scattered brain-derived neurotrophic factor mRNA-producing neurons in the medial septal nucleus, which contains cholinergic neurons that are responsive to brain-derived neurotrophic factor and nerve growth factor. In the brainstem, many adrenergic neurons showed a positive signal for brain-derived neurotrophic factor messenger RNA. Several hypothalamic nuclei contain brain-derived neurotrophic factor messenger RNA-positive neurons, among them paraventricular, median preoptic, vetromedial and dorsomedial nuclei. Osmotic stimulus, which activates vasopressin-producing neurons increased brain-derived neurotrophic factor messenger RNA levels in the paraventricular nucleus demonstrating that this factor is regulated by neuronal activity not only in the hippocampus and cortex but also in the hypothalamus.

Interleukin-6 and interleukin-1 receptor antagonist in cerebrospinal fluid from patients with recent tonic-clonic seizures

We have previously reported increased concentrations of interleukin (1L)-6 in CSF from patients with tonic-clonic seizures, where increased cytokine production most likely is a consequence of neuronal epileptic activity associated with seizures. The biological effects of IL-6 are mediated by other cytokines, which are studied here in addition to IL-6. The purpose of this study was to analyze levels of soluble cytokines from plasma and CSF from patients with newly developed tonic-clonic seizures. The concentrations of IL-6, IL-1 receptor antagonist (IL-1RA), IL-1beta, tumor necrosis factor (TNFalpha) and nerve growth factor (NGF) were measured from plasma and CSF from 22 patients with newly developed tonic-clonic seizures within 24 h from the seizure and 18 controls. The mean concentrations of IL-6 were significantly increased in CSF (P<0.001) and plasma (P<0.01) after tonic-clonic seizures, there was some indication of increased concentrations of IL-1RA and no significant change in NGF, IL-1beta or TNFalpha. Our study shows that cytokine network is activated in patients after recent tonic-clonic seizures. We provide evidence of intrathecal production of IL-6 associated with electrical seizure activity.