PDIA3 inhibits mitochondrial respiratory function in brain endothelial cells and C. elegans through STAT3 signaling and decreases survival after OGD

Background

Protein disulfide isomerase A3 (PDIA3, also named GRP58, ER-60, ERp57) is conserved across species and mediates protein folding in the endoplasmic reticulum. PDIA3 is, reportedly, a chaperone for STAT3. However, the role of PDIA3 in regulating mitochondrial bioenergetics and STAT3 phosphorylation at serine 727 (S727) has not been described.

Methods

Mitochondrial respiration was compared in immortalized human cerebral microvascular cells (CMEC) wild type or null for PDIA3 and in whole organism C. Elegans WT or null for pdi-3 (worm homologue). Mitochondrial morphology and cell signaling pathways in PDIA3-/- and WT cells were assessed. PDIA3-/- cells were subjected to oxygen–glucose deprivation (OGD) to determine the effects of PDIA3 on cell survival after injury.

Results

We show that PDIA3 gene deletion using CRISPR-Cas9 in cultured CMECs leads to an increase in mitochondrial bioenergetic function. In C. elegans, gene deletion or RNAi knockdown of pdi-3 also increased respiratory rates, confirming a conserved role for this gene in regulating mitochondrial bioenergetics. The PDIA3-/- bioenergetic phenotype was reversed by overexpression of WT PDIA3 in cultured PDIA3-/- CMECs. PDIA3-/- and siRNA knockdown caused an increase in phosphorylation of the S727 residue of STAT3, which is known to promote mitochondrial bioenergetic function. Increased respiration in PDIA3-/- CMECs was reversed by a STAT3 inhibitor. In PDIA3-/- CMECs, mitochondrial membrane potential and reactive oxygen species production, but not mitochondrial mass, was increased, suggesting an increased mitochondrial bioenergetic capacity. Finally, PDIA3-/- CMECs were more resistant to oxygen–glucose deprivation, while STAT3 inhibition reduced the protective effect.

Conclusions

We have discovered a novel role for PDIA3 in suppressing mitochondrial bioenergetic function by inhibiting STAT3 S727 phosphorylation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12964-021-00794-z.

Vitamin-D receptor agonist calcitriol reduces calcification in vitro through selective upregulation of SLC20A2 but not SLC20A1 or XPR1

Vitamin D deficiency (hypovitaminosis D) causes osteomalacia and poor long bone mineralization. In apparent contrast, hypovitaminosis D has been reported in patients with primary brain calcifications (“Fahr’s disease”). We evaluated the expression of two phosphate transporters which we have found to be associated with primary brain calcification (SLC20A2, whose promoter has a predicted vitamin D receptor binding site, and XPR1), and one unassociated (SLC20A1), in an in vitro model of calcification. Expression of all three genes was significantly decreased in calcifying human bone osteosarcoma (SaOs-2) cells. Further, we confirmed that vitamin D (calcitriol) reduced calcification as measured by Alizarin Red staining. Cells incubated with calcitriol under calcifying conditions specifically maintained expression of the phosphate transporter SLC20A2 at higher levels relative to controls, by RT-qPCR. Neither SLC20A1 nor XPR1 were affected by calcitriol treatment and remained suppressed. Critically, knockdown of SLC20A2 gene and protein with CRISPR technology in SaOs2 cells significantly ablated vitamin D mediated inhibition of calcification. This study elucidates the mechanistic importance of SLC20A2 in suppressing the calcification process. It also suggests that vitamin D might be used to regulate SLC20A2 gene expression, as well as reduce brain calcification which occurs in Fahr’s disease and normal aging.

Prolonged local neurotrophin-3 infusion reduces ipsilateral collateral sprouting of spared corticospinal axons in adult rats

The corticospinal tract is widely used to study regeneration and is essential for voluntary movements in humans. In young rats, corticospinal axons on the uninjured side sprout and grow into the denervated side. Neurotrophin-3 (NT-3) induces such crossed collateral sprouting in adults. We investigated whether local intraspinal NT-3 infusions would promote collateral sprouting of spared corticospinal terminals from within a partially denervated side, as this would be more appropriate for enhancing function of unilateral and specific movements. Adult rats received a partial bilateral transection of the pyramids, leaving approximately 40% of each tract intact. Vehicle or vehicle plus NT-3 (3 or 10 microg/day) was infused for 14 days into the left side of the cervical (C5/6) or lumbar (L2) cord. The corticospinal processes on the left side were anterogradely traced with cholera toxin B (CTB; which labeled gray matter processes more robustly than biotinylated dextran amine) injected into the front or hind limb area of the right sensorimotor cortex, respectively, 3 days before analysis. Unexpectedly, approximately 40% fewer CTB-labeled corticospinal processes were detectable in the cervical or lumbar gray matter of NT-3-treated rats than in vehicle-infused ones. Vehicle-infused injured rats had more corticospinal processes in the center of the cord than normal rats, evidence for lesion-induced collateral sprouting. NT-3 caused sprouting of local calcitonin gene-related peptide-positive fibers. These results suggest that NT-3 reduces collateral sprouting of spared corticospinal axons from within the denervated regions, possibly because of the injury environment or by increasing sprouting of local afferents. They identify an unexpected context-dependent outgrowth inhibitory effect of NT-3.

Endogenous and exogenous ciliary neurotrophic factor enhances forebrain neurogenesis in adult mice

Neurogenesis in the adult mammalian CNS occurs in the subventricular zone (SVZ) and dentate gyrus. The receptor for ciliary neurotrophic factor (CNTF), CNTFRalpha, is expressed in the adult subventricular zone. Because the in vitro effects of CNTF on neural precursors have been varied, including proliferation and differentiation into neurons or glia, we investigated its role in vivo. Injection of CNTF in the adult C57BL/6 mice forebrain increased the number of cells labeled with ip BrdU in both neurogenic regions. In the dentate gyrus, CNTF also appeared to enhance differentiation of precursors into neurons, i.e., increased the proportion of NeuN+/BrdU+ cells from approximately 14 to approximately 29%, but did not affect differentiation into astrocytes (GFAP+) or oligodendrocytes (CNPase+). In the SVZ, CNTF increased the proportion of GFAP+/BrdU+ cells from approximately 1 to approximately 2%. CNTF enhanced the distance of migration of new neurons into the granule cell layer. Intraventricular injection of neutralizing anti-CNTF antibodies reduced the number of BrdU-labeled cells in the SVZ. These results suggest that endogenous CNTF regulates adult neurogenesis by increasing proliferation of neural stem cells and/or precursors. Alternatively, CNTF could maintain cells longer in the S-phase, resulting in increased BrdU labeling. In the neurogenic region of the SVZ, CNTFRalpha was exclusively present in GFAP-positive process-bearing cells, suggesting that CNTF affects neurogenesis indirectly via neighboring astroglia. Alternatively, these cells may be part of the neural precursor lineage. The restricted expression of CNTF within the nervous system makes it a potential selective drug target for cell replacement strategies.

α6β1 integrin directs migration of neuronal precursors in adult mouse forebrain

New neuroblasts are constantly generated in the adult mammalian subventricular zone (SVZ) and migrate via the very-restricted rostral migratory stream (RMS) to the olfactory bulb, where they differentiate into functional neurons. Several facilitating and repulsive molecules for this migration have been identified, but little is known about chemoattractive molecules involved in the directed nature of this migration in vivo. Here, we investigated the role of the alpha6beta1 integrin, and its ligand, laminin, in controlling guidance of the migrating neuroblasts in adult mice. Immunostaining for the alpha6beta1 integrin was present in neuroblasts and their processes in the anterior/rostral SVZ and the RMS. Inhibition of the endogenous alpha6 or beta1 subunit with locally injected antibodies disrupted the cohesive nature of the RMS, but did not kill the neuroblasts. Infusion of a 15 a.a. peptide, representing the E8 domain of the laminin alpha chains that bind alpha6beta1 integrin, into the neostriatum redirected the neuroblasts away from the RMS towards the site of infusion. Injection of a narrow tract of intact laminin also drew the neuroblasts away from the RMS, but in a more restricted localization. These results suggest a critical role for integrins and laminins in adult SVZ-derived neuroblast migration. They also suggest that integrin-based strategies could be used to direct or restrict neuroblasts to CNS regions where they are needed for cell replacement therapies in the nervous system.

Marked differences in olfactory sensitivity and apparent speed of forebrain neuroblast migration in three inbred strains of mice

In the adult forebrain, new neuroblasts constantly migrate from the subventricular zone along the rostral migratory stream to the olfactory bulb, where many become neurons. It is unclear whether this process is different in commonly used mouse strains and whether it is related to olfactory function. Adult male BALB/c, C57BL/6, and 129/S1 (formerly 129SV) mice were tested for olfactory sensitivity plus discrimination, using male mouse urine from the two other strains. BALB/c mice had the greatest olfactory sensitivity, followed by 129/S1, and C57BL/6 mice, by an order of magnitude each. Newly formed cells were pulse-labeled for 3 h with i.p. 5-bromo-2'-deoxyuridine (BrdU) injections and the animals analyzed 24 h later. In 129/S1 mice, a greater proportion of neuroblasts were present closer to the olfactory bulb than in BALB/c mice, followed by C57BL/6 mice. The total number of BrdU-labeled cells did not differ, suggesting differences in migration and not proliferation. The impaired olfactory function in C57BL/6 mice might be caused by the reduced number of neuroblasts that reach the olfactory bulbs. However, olfactory function in BALB/c and 129/S1 mice did not correlate with their putative migration speed, suggesting a more complex nature of cellular processes that contribute to olfactory function. These results caution against comparing studies of olfactory function or neural precursors that use different strains of mice, and question the use of C57BL/6 mice as a "normal" strain or as transgenic background. Perhaps more importantly, the results point to an opportunity to identify genes that regulate olfactory function and neuroblast behavior.

Tyrosine phosphatase inhibition enhances neurotrophin potency and rescues nigrostriatal neurons in adult rats

Neurotrophic factors regulate a variety of cellular processes, including neuronal survival during development and after injury. For instance, brain-derived neurotrophic factor (BDNF) can prevent the death of dopaminergic substantia nigra neurons in rats. Most neurotrophic factor receptors, such as TrkB for BDNF, are tyrosine kinases whose signaling is terminated by protein tyrosine phosphatases (PTPs). We tested the idea that inhibition of PTPs, and thus potentially enhancement of the efficiency of endogenous trophic factors and their receptors, would lead to increased neuronal survival. After a 2-week infusion of the small PTP inhibitor molecule peroxovanadium (pVa, pervanadate) close to the substantia nigra of adult rats, up to 66% of axotomized substantia nigra neurons had survived, compared to only 33% in control rats infused with PBS. PVa most likely affected TrkB and/or downstream signaling molecules, as ineffective doses of BDNF and pVa had a synergistic effect when given simultaneously, rescuing 82% of the neurons. PVa stimulated tyrosine hydroxylase (TH) expression in the noninjured substantia nigra but did not prevent axotomy-induced loss of TH. These results raise the possibility that PTP inhibition can prevent neuronal death by enhancing neurotrophic factor signaling pathways in the adult mammalian nervous system, identifies an important role for PTPs in neuronal functioning, and points to a novel small molecule treatment approach for neurologic disorders

Delayed NGF infusion fails to reverse axotomy-induced degeneration of basal forebrain cholinergic neurons in adult p75(LNTR)-deficient mice

The p75 low-affinity neurotrophin receptor (p75(LNTR)) appears to have various functions that include enhancing nerve growth factor (NGF)-mediated survival by increasing TrkA (high-affinity NGF receptor) efficiency, and mediating apoptosis by acting as a ligand-regulated pro-apoptotic receptor. Here, we investigated the role of p75(LNTR) for adult cholinergic basal forebrain neurons by comparing neuronal responses to injury in control and p75(LNTR)-deficient mice. In both types of mice, approximately 70% of the cholinergic neurons in the ipsilateral medial septum had lost their markers choline acetyltransferase and tyrosine kinase A by 28 days following unilateral transection of the dorsal septohippocampal pathway (fimbria fornix). A 7-day delayed infusion of NGF that started 28 days after the injury resulted in reversal of choline acetyltransferase expression and cell atrophy in control, but not in p75(LNTR)-deficient, mice. This lack of response to delayed NGF treatment in p75(LNTR)-deficient mice was most likely not due to cell death, as all of the septohippocampal neurons, labeled with Fluorogold before the lesion, were present at 28 days post-lesion, similar to control mice. p75(LNTR)-deficient cholinergic neurons can respond to NGF as they were protected by NGF infusions that started immediately after the injury. These observations, the fact that lesioned p75(LNTR)-deficient neurons atrophy faster, and that non-lesioned neurons hypertrophy in response to NGF in control but not in p75(LNTR)-deficient mice, suggest that p75(LNTR) is needed for tyrosine kinase A and NGF signaling efficiency.In conclusion, during adulthood p75(LNTR) appears to play a beneficial role in the response of cholinergic neurons to injury, consistent with the proposed role of p75(LNTR) in the enhancement of TrkA signaling and the transport of neurotrophins by these neurons.

Retrograde tracing techniques influence reported death rates of adult rat nigrostriatal neurons

Injury often causes loss of neuronal markers and prior retrograde labeling can circumvent this problem of identification. We have previously used a time-consuming protocol for labeling all dopaminergic substantia nigra pars compacta neurons in adult rats by injecting the fluorescent tracer DiI into six sites throughout each neostriatum. Here, 2 weeks after injection of DiI into two central locations, only half of these nigrostriatal neurons were labeled. With six sites, more medial and lateral neurons were labeled, and also more in the midportion along the medial-lateral extent of the pars compacta. Less than 0.5% of the contralateral neurons were labeled. Two injections of Fluorogold also labeled fewer neurons, but their morphology was clearer. Two to 4 weeks after injection of the neurotoxin 6-OHDA into the two neostriatal sites, the total number of surviving neurons appeared greater with six sites of DiI than with two. However, within the middle region of the nigra, survival was lower with the six sites. This suggests that neurons that project outside the two central striatal tracer and 6-OHDA injection regions may be spared initially, but that those in the midportion that project to the central region are more vulnerable with the six-site protocol. Some reports suggest that Fluorogold prelabeling increases neuronal death. Here, survival after 6-OHDA or axotomy was similar with DiI or Fluorogold. These results suggest that because of a complex projection pattern of the nigrostriatal neurons, detailed quantification of neuronal survival should rely on extensive labeling. However, for drug screening purposes, faster labeling with Fluorogold using two sites is more suitable and should provide reliable data.

Neutralizing antibodies against neurite growth inhibitor NI-35/250 do not promote regeneration of sensory axons in the adult rat spinal cord

Neutralization of the myelin-associated neurite growth inhibitors NI-35 and NI-250 by IN-1 antibodies can promote axonal regeneration of several types of central nervous neurons. Here, we investigated in adult rats whether IN-1 can promote regeneration of ascending sensory axons across a peripheral nerve bridge back into the spinal cord. IN-1 was administered by hybridoma cells injected in the cerebral cortex or thoracic cord, its presence confirmed in tissue sections and cerebrospinal fluid, and its effectiveness demonstrated in co-cultures of oligodendrocytes and sensory neurons. With a two week infusion of control vehicle into the dorsal spinal cord 3 mm rostral to the nerve graft, only 3+/-2% of the anterogradely labeled sensory fibers present at the rostral end of the nerve graft had grown up to 0.5 mm, but not farther into the spinal cord. A similar limited extent of regeneration was seen with IN-1 or with infusion of Dantrolene, an inhibitor of NI-35/250 activity in vitro. With infusion of nerve growth factor rostral to the nerve graft, 40% of the fibers at the rostral end of the graft were found at 0.5 mm, 34% at 1 mm, 24% at 2 mm and 14% at 3 mm (the infusion site) into the spinal cord. Treatment with IN-l antibodies did not enhance the growth-promoting effects of nerve growth factor. We suggest that the neurite growth inhibitors NI-35 or NI-250 do not play a major inhibitory role in the regeneration of the ascending sensory fibers across a nerve bridge and back into the spinal cord of the adult rat.

Naloxone prevents microglia-induced degeneration of dopaminergic substantia nigra neurons in adult rats

Resident microglia are involved in immune responses of the central nervous system and may contribute to neuronal degeneration and death. Here, we tested in adult rats whether injection of bacterial lipopolysaccharide (which causes inflammation and microglial activation) just above the substantia nigra, results in the death of dopaminergic substantia nigra pars compacta neurons. Two weeks after lipopolysaccharide injection, microglial activation was evident throughout the nigra and the number of retrogradely-labeled substantia nigra neurons was reduced to 66% of normal. This suggests that inflammation and/or microglial activation can lead to neuronal cell death in a well-defined adult animal model. The opioid receptor antagonist naloxone reportedly reduces release of cytotoxic substances from microglia and protects cortical neurons in vitro. Here, a continuous two-week infusion of naloxone at a micromolar concentration close to the substantia nigra, prevented most of the neuronal death caused by lipopolysaccharide, i.e. 85% of the neurons survived. In addition, with systemic (subcutaneous) infusion of 0. 1mg/d naloxone, 94% of the neurons survived. Naloxone infusions did not obviously affect the morphological signs of microglial activation, suggesting that naloxone reduces the release of microglial-derived cytotoxic substances. Alternatively, microglia might not cause the neuronal loss, or naloxone might act by blocking opioid receptors on (dopaminergic or GABAergic) neurons.Thus, local inflammation induces and the opioid antagonist naloxone prevents the death of dopaminergic substantia nigra neurons in adult rats. This may be relevant to the understanding of the pathology and treatment of Parkinson's disease, where these neurons degenerate.

SEK1/MKK4, c-Jun and NFKappaB are differentially activated in forebrain neurons during postnatal development and injury in both control and p75NGFR-deficient mice

The common neurotrophin receptor (p75NGFR) can signal in vitro through activation of the c-Jun N-terminal kinase (JNK) pathway and nuclear translocation of NFKappaB. Activation of JNK and its substrate c-Jun can lead to apoptosis. We investigated these activities in vivo by comparing immunoreactivity for phosphorylated(p) SEK-1 (or MKK4, which activates JNK), c-Jun (ser63, ser73) and nuclear translocation of NFKappaB-p50 in tissue sections through the forebrain of control and p75NGFR-deficient mice. During postnatal development, SEK1p-immunoreactivity was detectable in p75NGFR-positive cholinergic neurons and p75NGFR-negative neurons throughout the forebrain in control mice. During development, few cells contained c-Junp, although many neurons contained c-Jun. No obvious c-Jun immunostaining was present in the adult forebrain. At any age, NFKappaB-p50 immunoreactivity was seen in nuclei of most cells throughout the forebrain. Following fimbria fornix transection in adult mice, few basal forebrain neurons contained SEK1p while many axotomized choline acetyltransferase (ChAT)-positive neurons contained c-Junp and nuclear NFKappaB-p50. The immunostaining patterns of SEK1p, c-Junp and NFKB during development and following injury were largely similar in p75NGFR-deficient mice. During development, cells throughout the forebrain had TdT-mediated dUTP-biotin nick end labelling (TUNEL)-labelling (a potential marker for apoptosis), however, their presence was not predicted by number of neurons stained for SEK1p or c-Junp. These results suggest that the expected activation of the JNK pathway by p75NGFR, as well as the expected relationship between SEK1 and downstream activation of c-Jun do not occur in the mammalian forebrain. Also, these results suggest that this activation does not necessarily lead to cell death.

BDNF is needed for postnatal maturation of basal forebrain and neostriatum cholinergic neurons in vivo

Neurotrophins regulate survival, neurite outgrowth, and phenotypic maturation of developing neurons. Brain-derived neurotrophic factor (BDNF) can promote the survival of developing cholinergic forebrain neurons in vitro and reduce their degeneration following injury in adult rats. We investigated the role of endogenous BDNF during postnatal development of these cholinergic neurons by analyzing homozygous BDNF-deficient (-/-) mice and their littermates (+/+, +/-). At P6, the number of choline acetyltransferase- (ChAT) positive neurons in the medial septum was approximately 23% lower in BDNF-/- mice, although their brain and body weight was normal. At P15, control (+/+) littermates had approximately 45% more and approximately 45% larger ChAT-positive neurons and a much denser cholinergic hippocampal innervation than at P6, indicative of maturation of the septohippocampal system. In BDNF-/- mice, the number, size, and ChAT-immunostaining intensity of the cholinergic neurons remained the same between P6 and P15 (few mice survive longer). BDNF-/- mice had about three times more TUNEL-labeled (a marker of apoptosis) cells in the medial septum at P6, consistent with (but not proof of) the possibility that the cholinergic neurons were dying. The cholinergic hippocampal innervation in BDNF-/- mice expanded to a lesser extent than in controls and had reduced levels of acetylcholinesterase staining at P15. The developmental deficits were largely similar in the neostriatum of BDNF-/- mice. These findings suggest that BDNF is critical for postnatal development and maturation of cholinergic forebrain neurons.

P75 nerve growth factor receptor is important for retrograde transport of neurotrophins in adult cholinergic basal forebrain neurons

The role of the p75 nerve growth factor receptor in the retrograde transport of neurotrophins in the adult CNS was investigated by comparing the transport of 125I-labeled neurotrophins by normal and p75 nerve growth factor receptor-deficient cholinergic septohippocampal neurons. In control mice, nerve growth factor was selectively transported from the hippocampal formation to the cholinergic neurons in the septum. Nerve growth factor labeling was found in three to four times as many septal cholinergic neuronal cell bodies than labeling for neurotrophin-3 or neurotrophin-4/5, and transported brain-derived neurotrophic factor was barely detectable. Cells were considered as labeled when the number of grains per cell exceeded five times background. In p75 nerve growth factor receptor-deficient mice, the number of cholinergic neurons labeled with each of the neurotrophins was reduced by 85-95%. Retrograde labeling of septohippocampal neurons with Fluorogold was not obviously reduced in p75 nerve growth factor receptor-deficient mice, suggesting that general transport mechanisms were not impaired. Despite the reduced neurotrophin transport, cholinergic neurons of p75 nerve growth factor receptor-deficient mice were larger than controls and had an apparently normal density of immunostaining for choline acetyltransferase. Since nerve growth factor is reportedly involved in size regulation and choline acetyltransferase expression, this raises the possibility that the retrograde transport itself is not essential for these events. Thus, p75 nerve growth factor receptor plays an important, although not exclusive, role in the transport of neurotrophins by cholinergic basal forebrain neurons, and retrograde transport of nerve growth factor may not be needed for regulating certain cellular processes.

Cholinergic medial septum neurons do not degenerate in aged 129/Sv control or p75(NGFR)-/-mice

Cholinergic medial septum neurons express TrkA and p75 nerve growth factor receptor (p75(NGFR)) and interactions between TrkA and p75(NGFR) are necessary for high-affinity binding and signaling of nerve growth factor (NGF) through TrkA. In adult p75(NGFR)-deficient (-/-) mice, retrograde transport of NGF and other neurotrophins by these neurons is greatly reduced, however, these neurons maintain their cholinergic phenotype and size. Reduced transport of NGF has been proposed to play a role in Alzheimer's disease. Here, we investigated whether chronic and long-term absence of p75(NGFR) (and possibly reduced NGF transport and TrkA binding) would affect the cholinergic septohippocampal system during aging in mice. In young (6-8 months), middle aged (12-18 months), and aged (19-23 months) 129/Sv control mice the total number of choline acetyltransferase-positive medial septum neurons and the mean diameter and cross sectional area of the cholinergic cell bodies were similar. The cholinergic hippocampal innervation, as measured by the density of acetylcholinesterase-positive fibers in the outer molecular layer of the dentate gyrus was also similar across all ages. These parameters also did not change during aging in p75(NGFR) -/- mice and the number and size of the choline acetyltransferase-positive neurons and the cholinergic innervation density were largely similar as in control mice at all ages. These results suggest that p75(NGFR) does not play a major role in the maintenance of the number or morphology of the cholinergic basal forebrain neurons during aging of these mice. Alternatively, p75(NGFR) -/- mice may have developed compensatory mechanisms in response to the absence of p75(NGFR).

p75(NGFR) and cholinergic neurons in the developing forebrain: a re-examination

The low-affinity nerve growth factor receptor (p75(NGFR)) apparently can mediate apoptosis in a variety of cells in vitro and in vivo. Previously, our laboratory suggested that p75(NGFR) induced apoptosis in a subpopulation of cholinergic forebrain neurons during postnatal development, i.e., the number of choline acetyltransferase (ChAT)-positive neurons in a control strain of mice decreased whereas it remained higher in p75(NGFR)-deficient (-/-) mice. Discrepancies with subsequent data sets in our laboratory caused us to thoroughly re-analyze the fate of these cholinergic medial septum and neostriatal neurons in new sets of p75(NGFR) -/- and two DNA control strains of mice during development. Between postnatal day (P)6 and P15 the number of ChAT-positive neurons detected in the medial septum of 129/Sv mice and Balb/c mice increased by approximately 64% and approximately 62%, respectively. This increase is contrary to previous reports from our laboratory and indicative of normal postnatal development (including an increase in ChAT-enzyme) of the cholinergic forebrain neurons. In p75(NGFR) -/- mice the number of ChAT-positive neurons in the medial septum remained constant between P6 and P15 and was approximately 31% and approximately 56% higher at P6 than 129/Sv and Balb/c mice, respectively. At P15 and adulthood, p75(NGFR) -/- mice had similar numbers of cholinergic neurons as control mice. In the developing neostriatum, the number of ChAT-positive neurons increased by approximately 56% between P6 and P15 and did not differ between p75(NGFR) -/- and control mice at any time. Analyses for apoptotic DNA fragmentation (TUNEL labeling) at P8 revealed no differences between p75(NGFR) -/- and control mice in 12 forebrain regions, including the septum and neostriatum. At all times, all mice had similar levels of acetylcholinesterase-positive cholinergic innervation of the molecular layer in the dorsal dentate gyrus. These findings suggest that the p75(NGFR) does not necessarily mediate apoptosis in medial septum or neostriatal cholinergic neurons during the postnatal time period. The discrepant results of the previous study are most likely due to a less rigorous application of criteria for data acquisition, including anatomical boundaries that define the nucleus.

Neurotrophins promote regeneration of sensory axons in the adult rat spinal cord

We have investigated the effects of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) on the intraspinal regeneration of anterogradely labeled axotomized ascending primary sensory fibers in the adult rat. These fibers were allowed to grow across a predegenerated peripheral nerve graft and back into the thoracic spinal cord. In control animals that had been infused with vehicle for two weeks into the dorsal column, 3 mm rostral to the nerve graft, essentially no fibers had extended from the nerve graft back into the spinal cord. The number of sensory fibers in the rostral end of the nerve graft was not significantly different between control and neurotrophin-infused animals. With infusion of NGF, 37+/-2% of the fibers at the rostral end of the graft had grown up to 0.5 mm into the dorsal column white matter, 30+/-2% up to 1 mm, 19+/-3% up to 2 mm and 8+/-2% up to 3 mm, i.e., the infusion site. With infusion of NT-3, sensory fiber outgrowth was similar to that seen with NGF, but with BDNF fewer fibers reached farther distances into the cord. Infusion of a mixture of all three neurotrophins did not increase the number of regenerating sensory fibers above that seen after infusion of the individual neurotrophins. These findings suggest that injured ascending sensory axons are responsive to all three neurotrophins and confirm our previous findings that neurotrophic factors can promote regeneration in the adult central nervous system.

p75NGFR mediates death of cholinergic neurons during postnatal development of the neostriatum in mice

We have previously shown that p75 nerve growth factor receptor (p75NGFR) mediates apoptosis of approximately 25% of the cholinergic basal forebrain neurons in normal control mice between postnatal day 6 and 15, but only of cholinergic neurons that lacked the nerve growth factor receptor TrkA. Here, we investigated whether and when the cholinergic neurons of the neostriatum, which express TrkA and p75NGFR during early postnatal times, undergo p75NGFR-mediated death. The cholinergic neurons in the lateral neostriatal regions expressed choline acetyltransferase (ChAT) earlier (postnatal day 3-6) than those of the medial regions and TrkA appeared before ChAT in all regions. Between postnatal day 6 and 10, approximately 40% of the ChAT-positive neurons in the most lateral regions disappeared in control mice but not in p75NGFR-deficient mice. During this time, the neostriatum of control, but not p75NGFR-deficient, mice contained many apoptotic cells. This suggests that, similar to the cholinergic neurons of the basal forebrain, the neostriatal cholinergic neurons of control mice die and that this process is mediated by p75NGFR. However, the roles of p75NGFR and TrkA appear to be more complicated in the neostriatum where relatively few neurons express p75NGFR during the death phase (and predominantly in the lateral neostriatum where the neuronal loss is greatest), and TrkA-positive as well as TrkA-negative neurons may be lost.

Neurotrophins prevent death and differentially affect tyrosine hydroxylase of adult rat nigrostriatal neurons in vivo

Brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4) promote survival of mesencephalic dopaminergic neurons in vitro and affect normal and damaged ones in vivo. Here, these neurotrophins had markedly different potencies to prevent the death of axotomized nigrostriatal dopaminergic neurons when infused close to the rostral end of the nigral nucleus of adult rats (NT-4 > BDNF > NT-3; nerve growth factor or NGF without effect). With a high dose of BDNF (30 micrograms/day) complete protection was achieved in the rostral but not caudal nigral regions, consistent with its poor diffusion characteristics in brain tissue. Measurements of tyrosine hydroxylase immunoreactivity suggest that BDNF and NT-4 (presumably through their TrkB receptor) reduce the synthesis of this rate-limiting enzyme for dopamine synthesis in rescued as well as in normal neurons. In sharp contrast, survival-promoting doses of NT-3 (presumably through its TrkC receptor) maintained normal levels of tyrosine hydroxylase immunoreactivity in the rescued nigrostriatal neurons. These results suggest that for these adult central nervous system neurons, some neurotrophic factors are predominantly involved in facilitating cell survival, whereas others are more involved in regulating neurotransmitter function.

Glial cell line-derived neurotrophic factor prevents death, but not reductions in tyrosine hydroxylase, of injured nigrostriatal neurons in adult rats

Glial cell line-derived neurotrophic factor (GDNF) promotes survival of mesencephalic dopaminergic neurons in vitro and when injected locally into the brains of lesioned adult animals. Here, we show that GDNF (3 micrograms per day and higher) can promote the survival of all (retrogradely labeled) axotomized nigrostriatal dopaminergic neurons of adult rats when continuously infused for 2 weeks close to the substantia nigra, compared to only approximately 30% survival with control infusions. Based on our previous observations, GDNF was as potent as ciliary neurotrophic factor and neurotrophin-4 and approximately five to ten times more potent than brain-derived neurotrophic factor and was most effective in promoting survival. GDNF prevented neuronal death induced by 6-hydroxydopamine to a lesser extent than after axotomy. GDNF treatments begun 1 week after axotomy could maintain those neurons that had not yet died. When a 2 week GDNF treatment was interrupted, most of the GDNF-rescued neurons died over the following 2 weeks. This suggests that longer trophic factor treatments or nigrostriatal connections are needed to achieve permanent survival. Measurements of tyrosine hydroxylase (TH) immunoreactivity of the rescued neuronal cell bodies suggest that GDNF cannot prevent the lesion-induced loss of this rate-limiting enzyme for dopamine synthesis. In fact, GDNF induced a decrease in TH in normal animals, suggesting an active down-regulation of TH synthesis. Levels of TH immunoreactivity were recovered between 7 and 14 days after withdrawal of a 2 week GDNF infusion, in the neurons that survived axotomy. These results may have implications for developing new treatment strategies for Parkinson's disease.

Laminins of the adult mammalian CNS; laminin-alpha2 (merosin M-) chain immunoreactivity is associated with neuronal processes

Laminins are glycoproteins with three subunits, i.e. a longer alpha chain, a shorter beta chain and a shorter gamma chain. Well-characterized laminins are laminin-1 (EHS laminin; alpha1-beta1-gamma1), laminin-2 (merosin; alpha2-beta1-gamma1), laminin-3 (alpha1-beta2-gamma1) and laminin-4 (alpha2-beta2-gamma1). The present study shows that in the adult mammalian CNS (rat, rabbit, pig and monkey) alpha2 chain immunoreactivity is associated most evidently with neuronal fibers and punctate, potentially synaptic, structures of limbic brain regions. Third ventricle tanycytes and ensheathing cells of the olfactory nerve also express intense alpha2 chain immunoreactivity. Immunostaining for gamma1 chain is present throughout the central nervous system (CNS) in essentially all neuronal cell bodies and their most proximal processes. Immunoreactivity for all chains investigated (alpha1, alpha2, beta1, beta2 and gamma1) were present around blood vessels, especially evident in lightly fixed tissues. The finding that, other than blood vessels, neurons and other structures exhibited immunoreactivity for only one or two (and not three) chains, suggests that variant forms of laminin with yet undiscovered chains or other configurations than the heterotrimeric form are present in the CNS. The association of alpha2-like immunoreactivity with neuronal fibers and synaptic structures is of great interest in light of the known neurite-promoting and cell attachment activities of laminin-2.

Laminin-alpha2 chain-like antigens in CNS dendritic spines

The laminin-alpha2 chain is a component of brain capillary basement membranes and appears also to be present in neurons of rat, rabbit, pig and non-human primate brain as evidenced by immunohistochemistry. In the present study, we have further characterized this very distinct neuronal laminin-alpha2 chain-like immunoreactivity in the hippocampus of various species. Immunoelectron microscopy with poly- and monoclonal antibodies to the laminin-alpha2 chain G-domain localized laminin-alpha2 chain immunoreactivity in adult rat and rabbit hippocampus to dendritic processes, primarily to dendritic spines. In the developing rat hippocampus, spine-associated laminin-alpha2 chain-like immunoreactivity first appeared at a time corresponding to that of active synaptogenesis. After an entorhinal cortex lesion in adult rats, the time course of denervation-induced loss and reactive reappearance of spines in the molecular layer of the dentate gyrus was correlated closely to the loss and reappearance of laminin-alpha2 chain immunoreactivity. Immunoblot analysis of normal adult rat, rabbit and pig brain revealed a protein similar in size to the reported 80-kDa laminin-alpha2 chain fragment of human placenta as well as 140/160-kDa proteins. These results suggest the presence of proteins with antigenic homology to the laminin-alpha2 chain and/or laminin-alpha2 isoforms in dendrites and dendritic spines in selected areas of the brain, predominately in the hippocampus and other limbic structures. Given the adhesion and neurite promoting functions of laminins, it is possible that neuronal laminin-alpha2 chain-like proteins play a role in synaptic function and plasticity in the CNS.

Survival of cholinergic forebrain neurons in developing p75NGFR-deficient mice

The functions of the low-affinity p75 nerve growth factor receptor (p75(NGFR)) in the central nervous system were explored in vivo. In normal mice, approximately 25 percent of the cholinergic basal forebrain neurons did not express TrkA and died between postnatal day 6 and 15. This loss did not occur in p75(NGFR)-deficient mice or in normal mice systemically injected with a p75(NGFR)-inhibiting peptide. Control, but not p75(NGFR)-deficient, mice also had fewer cholinergic striatal interneurons. Apparently, p75(NGFR) mediates apoptosis of these developing neurons in the absence of TrkA, and modulation of p75(NGFR) can promote neuronal survival. Cholinergic basal forebrain neurons are involved in learning and memory.

Nerve growth factor promotes regeneration of sensory axons into adult rat spinal cord

Injured adult mammalian axons are unable to regenerate spontaneously in the central nervous tissue. This study investigated in two adult rat models the effects of nerve growth factor (NGF) on the capacity of central primary sensory axons to regenerate back into the spinal cord. Sensory fibers were conditioned by transection of the peripheral nerve 1 week prior to the experiment and identified by anterograde tracing with cholera toxin B subunit injected in the sciatic nerve. In the first model, a predegenerated autologous peripheral nerve graft was implanted as a bridge for the transected sensory fibers into a resection gap in the dorsal columns at the tenth thoracic (T10) spinal cord segment. Vehicle or vehicle with purified mouse or recombinant human NGF was continuously infused for 2 weeks directly into the dorsal column at T9, 3 mm from the rostral border of the nerve graft. With vehicle infusion many ascending sensory axons had grown across the nerve bridge, but essentially none had grown back into the rostral cord. In sharp contrast, NGF promoted the reentry into the denervated dorsal columns of 51% of the sensory axons that had reached the rostral level of the nerve graft. Twenty-six percent had grown 2 mm into the spinal tissue and 10% had reached the NGF-infusion site at 3 mm from the nerve graft. A few fibers were found circling around, but not beyond, the infusion site, perhaps due to the chemoattractant action of NGF. In a second model, the fourth lumbar (L4) dorsal root was crushed 2 mm from its insertion point into the spinal cord and the dorsal roots L2, L3, L5, and L6 were transected. Vehicle or vehicle with purified mouse NGF was infused for 2 weeks directly into the lumbar spinal cord, 2.5 mm rostral to the transition zone of the crushed L4 root. With vehicle, only 6% of the regenerating fibers at the transition zone had crossed the root-spinal cord barrier, but not farther than 0.5 mm into the spinal tissue. With NGF, 18% of the fibers at the transition zone were found at 0.5 mm, 9% at 1.5 mm, and 5% at 2.5 mm (the infusion site) from the transition zone. The present results demonstrate that NGF can promote the regeneration of adult sensory fibers into the otherwise nonpermissive spinal cord white matter.

Regeneration of adult rat sensory axons into intraspinal nerve grafts: promoting effects of conditioning lesion and graft predegeneration

The effect of intraspinally implanted predegenerated peripheral nerve grafts and/or conditioning lesions on the regenerative capacity of central ascending sensory axons was investigated in the adult rat. Regenerating sensory fibers were analyzed after their transganglionic labeling with cholera toxin B subunit, usually 1 month after implantation. A conditioning lesion (transection of the tibial and peroneal nerve) caused a fivefold increase in the number of sensory fibers within the fresh graft when applied on the day of grafting and a sevenfold increase when applied 1 week before. In the latter case, a small portion of the fibers (10%) had reached the rostral end of the nerve graft. In the absence of a conditioning lesion, the number of fibers regenerating into a predegenerated nerve graft (collected from the distal part of the peroneal nerve that had been axotomized 1 week earlier) was similar to that found in a fresh graft. However, predegenerated grafts received three and five times more fibers than a fresh graft when conditioning lesions were applied on or 1 week before the day of grafting. With the combination of a predegenerated graft and a 1-week conditioning, most (> 90%) of the regenerating fibers had reached the rostral graft-host border. In animals with a fresh graft, a portion of the axotomized fibers formed terminal club-like structures. Much fewer fibers displayed such clubs in animals with a predegenerated graft or a conditioning lesion, suggesting a preventive action of either treatment. A time-course study with the combined treatments showed that regenerating sensory fibers had already entered the graft after 3 days. Between 1 and 2 weeks, a maximum number of fibers had reached the rostral end of the nerve graft. However, after 2 months, the number of fibers was decreased, i.e., the initial advantage of predegeneration had diminished. The current results demonstrate the necessity of a conditioning lesion for successful regeneration of central sensory fibers, possibly resulting from an earlier induction of the neuronal growth response which allows the axon to enter the graft before the formation of a graft-host barrier. The predegeneration of the nerve graft augments the growth response of the axotomized central sensory fibers, probably by providing a more supportive terrain and/or enhancement of the neuronal response. The presence of a large number of fibers at the rostral graft-host border now provides the opportunity to investigate the effects of neurotrophic factors on the regenerative capacity of the ascending rat sensory fibers into the denervated spinal cord in vivo.

Distribution of corticospinal motor neurons in the postnatal rat: quantitative evidence for massive collateral elimination and modest cell death

The postnatal development of rat corticospinal motor neurons (CSMN) was studied by retrograde tracing with cholera toxin B subunit (CTB) injected into the upper cervical dorsal spinal cord on the first postnatal day (P0), P3, P10, P20, and at adulthood. CTB-labeled neurons were visualized by immunocytochemistry and extensively quantified throughout the cortex. At P0, CSMN were found to an extent similar to that reported in P3 animals with other neuronal tracers, now permitting in vitro studies of neonatal CSMN. Between P0 and P3, the number of labeled neurons increased by 30% to a total maximum of approximately 185,000 in both cortices. The increase occurred throughout the cortex. At P10, the number of labeled CSMN had decreased to 60% of the number at P3. Fewer CSMN were evident particularly in the perirhinal cortex. Between P10 and P20, the number of CSMN decreased further to 52% of the maximal number at P3. This decrease occurred predominantly in the cingulate and parietal cortex. The number of labeled CSMN in rats injected at P0 and analyzed at P20 was 10% lower than the number in P0-injected littermates that were analyzed at P3, which suggests that only a small portion of the "disappearing" CSMN undergoes developmental neuronal death. Thus, the spinal projection of the remaining 38% is apparently eliminated between P3 and P20. Detailed quantitative analysis of the CSMN distribution demonstrated that neuronal death occurs predominantly in the perirhinal cortex. In contrast, axonal elimination of corticospinal projections occurred throughout the CSMN field, i.e., primarily in the frontal, occipital, and perirhinal cortex between P3-P10 and in the cingulate and parietal cortex between P10-P20.

Ciliary neurotrophic factor (CNTF) promotes low-affinity nerve growth factor receptor and CD4 expression by rat CNS microglia

Ramified parenchymal microglia may provide immune surveillance in the nervous system and become activated in response to injury, showing increases in antigens found on macrophages, e.g. CD4 and MHCs. We investigated in adult rats the effects of a 2-week intraventricular infusion with ciliary neurotrophic factor (CNTF), a nervous system-associated cytokine, on microglia of the normal and injured corpus callosum. CNTF caused morphological changes, induced the expression of low-affinity nerve growth factor receptor and CD4 and increased the expression of complement receptor 3. Such changes were also observed after treatment of pure cultures of neonatal rat microglial cells with highly purified CNTF, suggesting a direct responsiveness to CNTF. Thus, endogenous astroglial and Schwann cell-derived CNTF may be an important component of the immune responses of the nervous system.

Ciliary neurotrophic factor prevents degeneration of adult rat substantia nigra dopaminergic neurons in vivo

We have investigated the neuroprotective effects of recombinant human ciliary neurotrophic factor (CNTF) for injured dopaminergic neurons of the adult rat substantia nigra compacta. Fourteen days after a unilateral transection of the nigrostriatal pathway two-thirds of the neurons (identified by retrograde labeling) had degenerated. In sharp contrast, 73% (a few cases, > 90%) of this cell loss was prevented by continuous infusion of CNTF close to the injured neurons. However, CNTF did not prevent the disappearance of the transmitter-synthesizing enzyme tyrosine hydroxylase. Thus, CNTF has potent neurotrophic effects for injured adult rat dopaminergic substantia nigra neurons, whose degeneration plays a major causative role in Parkinson disease.

Potential regulation by trophic factors of low-affinity NGF receptors in spinal motor neurons

Developing spinal motor neurons (SMN) express low-affinity nerve growth factor receptors (LNGFR) but not high-affinity transducing NGF receptors. Moreover, SMN are not supported by NGF in vitro. In the normal adult rat most SMN are not LNGFR immunoreactive (LNGFR-IR), but they transiently reexpress LNGFR (though not the high-affinity receptor) after peripheral nerve injury. With a cut lesion of the sciatic nerve (when only a neuroma forms), the number of LNGFR-IR SMN at L4-L6 rapidly increases to a maximum between day 1 and 7 and returns to baseline levels by day 30. After a crush lesion (accompanied by regeneration to the muscle), LNGFR-IR SMN appear in about the same numbers, but they start to disappear 1 week later. We speculate that the similar appearance and differential decline of LNGFR-IR seen after the two types of lesions are regulated by the availability of a common signal such as ciliary neurotrophic factor. The adult SMN model provides a good opportunity to investigate the reexpression of LNGFR after peripheral nerve injury, and more generally, the unknown role and regulation of LNGFR.

Neurotropism of nerve growth factor for adult rat septal cholinergic axons in vivo

Nerve growth factor (NGF) can induce sprouting of axotomized adult rat medial septum cholinergic neurons and promote their regeneration into septohippocampal nerve grafts and hippocampal formation. This study investigated the potential neurotropic (chemotactic/attracting) action of NGF in the adult rat cholinergic septohippocampal regeneration model. (i) Some animals received sciatic nerve grafts between the disconnected septum and hippocampal formations on each side. A 4-week infusion with NGF into the rostral portion of the lateral ventricle induced sprouting of cholinergic fibers in the dorsolateral septum with a gradient toward the lateral ventricle. However, the number of cholinergic axons entering the nerve bridge was only one-third that observed in vehicle-infused animals, suggesting that NGF had diverted many of the regrowing axons away from the nerve toward the ventricle. (ii) In animals implanted with nerves for 2 weeks and concurrently infused with NGF into the fornix, proximal to the lesion and grafts, cholinergic sprouting occurred in the mediodorsal septum, i.e., was oriented toward the infused fornix. Essentially no fibers had entered the nerve bridge, suggesting that all regrowing fibers had remained near the NGF source. (iii) When animals with a unilateral fimbria-fornix transection (but no nerve graft) were infused with NGF into the lateral ventricle on the opposite side, cholinergic sprouting was oriented toward the midline of the septum. (iv) Infusion of low doses of NGF directly into the (lesioned) septum induced a sprouting response localized around the infusion site. (v) No sprouting occurred when intraventricular NGF infusion was applied to normal (nonlesioned) animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Laminin immunohistochemistry in brain is dependent on method of tissue fixation

Normal adult and lesioned rat and mouse brains were fixed by formaldehyde perfusion by two methods that differ primarily in the length of the post-fixation period. Sections were subsequently immunostained using monoclonal and polyclonal antibodies to laminin. With relatively short post-fixation periods (up to 4 h), vascular basement membrane (BM)-laminin was immunostained, but intraneuronal laminin-like immunoreactivity was faint. With longer post-fixation periods (18-24 h), intraneuronal laminin-like immunoreactivity was distinct, while vascular BM-laminin immunoreactivity was reduced drastically. These findings are particularly relevant to studies examining laminin immunoreactive blood vessels in response to lesions, especially ischemic stroke. In fact, the present results suggest that the apparent neovascularization or up-regulation of vascular BM-laminin following CNS injury likely relates to differences in regional tissue fixation.

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.

Nerve growth factor receptor immunoreactivity in neurons of the normal adult rat spinal cord and its modulation after peripheral nerve lesions

Motoneurons of the rat spinal cord express low-affinity nerve growth factor receptor (LNGFR) and corresponding mRNA during development, and re-express it after their axotomy by peripheral nerve injury. The present study establishes the anatomical and quantitative baseline of LNGFR immunoreactive (LNGFR-IR) neurons of the entire normal adult female rat and then investigates the temporal course for the re-expression of LNGFR-IR in lumbar motoneurons after either a crush lesion (which is followed by regeneration and reconnection to the muscle) or a cut lesion with removal of the distal stump (where a neuroma but no reconnection is formed). In the normal adult spinal cord, two types of LNGFR-IR neurons were recognized: (1) small populations of large motoneurons located in the ventral horn mainly in correspondence to the regions of the phrenic, cremasteric and dorsolateral nuclei, and (2) a more numerous and more dorsally located population of small neurons. With a sciatic cut lesion, the number of LNGFR-IR motoneurons at spinal levels L4-L6 rapidly and dramatically increased to a maximum between post-lesion days 1 and 7, apparently involving most axotomized motoneurons of the region, and returned to the baseline level by day 30. With a crush lesion, similar numbers and virtually the same time-course of LNGFR-IR appearance were seen, but the onset of progressive disappearance of LNGFR-IR neurons was delayed by one week, so that at 30 days, the most caudal motoneurons (which are last to reach their target) were still LNGFR-IR. Comparison of these two time courses gives clues to the kind of signals that may be involved in initiating and/or maintaining the LNGFR response.

Immunolocalization of ciliary neuronotrophic factor in adult rat sciatic nerve

Two rabbit polyclonal antibodies were raised against synthetic peptides corresponding to residue numbers 45-59 and 181-200 of rat ciliary neuronotrophic factor (CNTF). The resulting antibodies were purified by affinity chromatography and both purified antibodies reacted by enzyme-linked immunoassay (ELISA) and immunoblotting with rat sciatic nerve CNTF. The anti-CNTF peptide antibodies were used to immunostain sections of adult rat sciatic nerve, previously known as the richest tissue source of CNTF. By light microscopy both antibodies appeared to stain exclusively Schwann cells and axons and both did so with the same pattern of specific staining. Immunostaining was eliminated by absorption of the anti-peptide antibodies with either their corresponding peptide or with purified rat nerve CNTF or by using purified nonspecific IgG. Schwann cells were stained and in semi-thin sections this staining appeared to be in the Schwann cell cytoplasm. Axons could be stained in addition to Schwann cells providing higher concentrations of antibodies were used. Epineurial, endoneurial and endothelial cells appeared unstained. Since all Schwann cells and axons appear to contain CNTF and since CNTF is known to act in vitro to support sensory and sympathetic ganglionic and motor neurons, we suggest that Schwann cells may normally provide CNTF to those neurons contributing axons to the peripheral nerve.

Ciliary neurotrophic factor prevents neuronal degeneration and promotes low affinity NGF receptor expression in the adult rat CNS

Recombinant human ciliary neurotrophic factor (CNTF) was infused for 2 weeks into the lateral ventricle of fimbria-fornix transected adult rats, and its effects were compared with those of purified mouse nerve growth factor (NGF). We provide evidence that CNTF can prevent degeneration and atrophy of almost all injured medial septum neurons (whereas NGF protects only the cholinergic ones). CNTF is also involved in up-regulation of immunostainable low affinity NGF receptor (LNGFR) in cholinergic medial septum and neostriatal neurons and in a population of lateral septum neurons. In contrast to NGF, CNTF did not stimulate choline acetyltransferase in the lesioned septum and normal neostriatum (pointing to different mechanisms for the regulation of choline acetyltransferase and LNGFR), cause hypertrophy of septal or neostriatal cholinergic neurons, or cause sprouting of LNGFR-positive (cholinergic) septal fibers.

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

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

Nerve growth factor promotes CNS cholinergic axonal regeneration into acellular peripheral nerve grafts

Peripheral nerve grafts promote vigorous regeneration of adult mammalian CNS axons. Elimination of nerve-associated cells by freeze-thawing abolishes this promoting quality, possibly by creating inhibitory cellular debris and/or destroying the production of stimulatory factors by living Schwann or other cells. Here, debris-free acellular peripheral nerve segments placed between the disconnected septum and the hippocampal formation acquired almost no cholinergic axons after 1 month. However, such acellular nerve grafts treated before implantation with purified beta-nerve growth factor (NGF) contained nearly as many longitudinally oriented cholinergic axons as did fresh cellular nerve grafts. These results suggest that (i) NGF is required for the regeneration of adult CNS cholinergic axons into nerve grafts and (ii) an important function of living cells within peripheral nerve may be the production of neuronotrophic factors such as NGF.

Nerve growth factor infusion into the denervated adult rat hippocampal formation promotes its cholinergic reinnervation

The well-documented but little-understood failure of lengthy axonal regeneration after injury of the adult mammalian CNS may be caused by an insufficient availability of local growth-promoting factors. If so, identifying and supplying the missing factors may result in better central axonal regeneration. This hypothesis was tested in an adult rat CNS model in which peripheral nerve grafts were placed into a lesion cavity between the septum and hippocampal formation. Continuous infusion of nerve growth factor (NGF) into the dorsal hippocampal tissue dramatically enhanced and accelerated the regrowth and penetration of cholinergic axons into the hippocampal formation. Thus, NGF can overcome the apparent resistance of the hippocampal CNS tissue to cholinergic reinnervation.

Septohippocampal cholinergic axonal regeneration through peripheral nerve bridges: quantification and temporal development

Axons of the adult mammalian CNS have been shown to regrow vigorously into peripheral nerve grafts. Using a cholinergic septohippocampal model for adult CNS regeneration, involving complete denervation of the hippocampal formation from its basal forebrain cholinergic afferents, this study has established quantitative parameters and a temporal baseline of cholinergic fiber regeneration into the dorsal hippocampal tissue through a peripheral sciatic nerve graft. In nerve-implanted animals (i) the nerve grafts are maximally invaded by AChE-positive fibers between 2 weeks and 1 month postlesion, (ii) the fibers entering the hippocampal formation from the graft show a peak numerical increase and rate of elongation around the first month and/or in the proximal hippocampal region, (iii) an apparently normal innervation pattern and fiber density in the most rostral 1.5 mm of the dorsal hippocampal formation is reached by 6 months postlesion. The present study provides a basis for future quantitative comparisons of manipulations of different components of the system, e.g., the contributing neurons, the bridging material, and the receiving central nervous tissue. The temporal/spatial pattern of fiber regeneration suggests that the hippocampal CNS tissue can be a good axonal growth-promoting environment, albeit with temporal and/or spatial limitations, and is therefore not an immutably restrictive environment for axonal regeneration.

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

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

Laminin-like antigen in rat CNS neurons: distribution and changes upon brain injury and nerve growth factor treatment

Using several antibodies against rat or human laminin and an avidin-biotin immunocytochemical protocol, laminin-like immunoreactivity was detectable in the rat nervous system in expected locations, i.e., associated with blood vessels and reactive astrocytes. However, laminin staining was also abundantly present within neuronal cell bodies in most parts of the developing and adult rat CNS. Medial septum neuronal immunoreactivity was lost after septo-hippocampal disconnection, but could be preserved or even restored by intraventricular administration of nerve growth factor. Thus, at least for medial septum neurons, this laminin-like molecule can be accumulated or produced independent of direct hippocampal (target) contact. It remains to be determined whether CNS neuronal "laminin" processes activities similar to those found for laminin in vitro.

Neuronotrophic factors in cellular functional and cognitive repair of adult brain

Neuronotrophic factors (NTFs) are special proteins that control survival, growth and functional competence of selected neuronal populations during their development. A recently articulated CNS neuronotrophic hypothesis proposes that adult central neurons continue to be dependent on endogenous supplies of their NTFs for maintenance, function and repair capabilities. The hypothesis has important implications in two major neurologic areas:i) involutive and degenerative processes and ii) CNS regeneration. Strong evidence favoring this general hypothesis has come from the recently observed effects of Nerve Growth Factor (NGF) on the forebrain cholinergic neurons in adult rats. Medial septum cholinergic (MSC) neuros project to the hippocampal formation largely via the fimbria-fornix tract. Transection of the fimbria-fornix interrupts the retrograde delivery of hippocampal NGF to the MSC neuronal somata, leading to reduction in their cholinergic enzyme and, possibly, progressive cellular atrophy. Intraventricular administration of exogenous NGF compensates for the loss of endogenous NGF supply and can reverse as well as protect against the neuronal damage. In a second model, intraventricular NGF infusions were applied to 2-year old (aged) rats displaying a deficient cognitive behavior. Four-weeks administration resulted in i) a correction of the cognitive deficit and ii) a increased body size of basal forebrain cholinergic neurons Cholinergic deficits are known to accompany cognitive deficits both in the brain aging process and Alzheimer's disease. The NGF effects on aged rats, therefore, strongly encourage the possibility of future clinical application in both such cases of brain dysfunction.

An improved device for continuous intraventricular infusions prevents the introduction of pump-derived toxins and increases the effectiveness of NGF treatments

The recent demonstrations of the ability of nerve growth factor (NGF) to protect and promote the welfare of certain cholinergic neurons in the adult CNS have increased the need for safe, accurate, and reliable procedures for intracerebral administration of protein and other experimental agents. Osmotic minipumps have been used to infuse NGF into the lateral ventricle of adult rats, but a sustained and harmless performance of such infusions has not been fully evaluated. The study reported here has led to (i) the recognition that cytotoxic substances, released from some minipumps into the infusion fluid, may be responsible for various degrees of periventricular tissue damage, and (ii) the redesigning of an infusion device which, among other modifications, uses the osmotic pump to propel infusion fluid into the ventricle but prevents pump-derived materials from entering the infusate itself. Besides several other advantages, the modified infusion device has permitted the demonstration that NGF can fully protect experimentally axotomized medial septum cholinergic neurons and can do so with less variability than previously observed and without creating tissue damage.

Nerve growth factor effects on cholinergic neurons of neostriatum and nucleus accumbens in the adult rat

Following intraventricular nerve growth factor infusion in adult rats, the choline acetyltransferase immunostaining of the neuropil and neuronal cell bodies of the neostriatum (caudate-putamen) and nucleus accumbens was more intense on the side of the infusion. Furthermore, the average cross-sectional size (micron2) of the cholinergic somata was increased by about 40 and 20% in the striatum and accumbens, respectively. This unilateral response could be elicited in intact rats as well as in rats receiving a prior aspirative transection of the fimbria-fornix. The reported lack of (low-affinity) nerve growth factor receptor immunostaining in these neurons suggests that the nerve growth factor effects are most likely transduced by high-affinity receptors. The ability of these apparently undamaged cholinergic interneurons to respond to exogenous nerve growth factor with an increase in choline acetyltransferase content and cell body size suggests that they are benefiting from a less-than-maximal support by endogenous nerve growth factor in the normal young adult rat.

Delayed treatment with nerve growth factor reverses the apparent loss of cholinergic neurons after acute brain damage

Previous studies have shown that the loss after brain injury of adult rat septal cholinergic neurons whose axons are transected can be prevented by immediate intraventricular nerve growth factor (NGF) administration. This loss of axotomized neurons may be due to a reduction in detectability of neurotransmitter-related enzyme rather than to neuronal death. Here we report that NGF treatment, started after most of the neurons were no longer detectable (i.e., 1, 2, and 3 weeks), induced a dramatic reappearance of the apparently lost cholinergic neurons. These results may have important implications for potential trophic factor treatments of CNS trauma and neurodegenerative diseases, such as Alzheimer's dementia, which are characterized by chronic and progressive losses in the function of specific sets of neurons.