Brain-derived neurotrophic factor and neurotrophin-4 increase neurotrophin-3 expression in the rat hippocampus

Hippocampal levels of mRNA encoding nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are rapidly induced by enhanced neuronal activity following seizures and glutamate or muscarinic receptor activation. However, the levels of neurotrophin-3 (NT-3) mRNA acutely decrease after limbic seizures suggesting that a different mode of regulation may exist for these neurotrophins. Here we show that BDNF and neurotrophin-4 (NT-4), but not NT-3 itself, up-regulate NT-3 mRNA in cultured hippocampal neurons. In the rat hippocampus, the muscarinic receptor agonist, pilocarpine increased BDNF mRNA levels rapidly and those of NT-3 with a delay of several hours. Injection of BDNF into neonatal rats elevated NT-3 mRNA in the hippocampus which demonstrates that BDNF is able to enhance NT-3 expression in vivo. The regulation of NT-3 by BDNF and NT-4 enlargens the neurotrophic spectrum of these neurotrophins to include neuron populations responsive primarily to NT-3.     

Serum levels of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) in depressed patients with schizophrenia

Aim: Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) are neurotrophins—proteins that induce the survival, development, and function of neurons. Their role in the development of schizophrenia and mood disorders is widely studied. This study was aimed to determine whether depression affects levels of BDNF and NT-3 in patients with schizophrenia. Methods: Data for 53 Caucasian adult hospitalized patients with chronic paranoid schizophrenia was compared with 27 healthy subjects. Clinical symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS) and positive, negative and general sub-scores, the Calgary Depression Scale for Schizophrenia (CDSS), the Hamilton Depression Rating Scale (HDRS), and the Clinical Global Impressions scale (CGI). Patients were defined as depressed (SHZ-DEP) with scores CDSS?>?6 and HDRS?>?7, otherwise they were included into the non-depressed group (SHZ-nonDEP). Results: In total, 17 patients (32.1%) with schizophrenia met criteria for depression. SHZ-DEP patients had higher scores in HDRS, CDSS, PANSS total, PANSS negative, PANSS general and CGI (p?p?=?0.045. NT-3 levels were higher in SHZ-DEP compared to SHZ-nonDEP: 133.31?±?222.19 versus 56.04?±?201.28 pg/mL, p?=?0.033. Conclusion: There were no differences in neurotrophin levels between patients with schizophrenia and controls. We found lower BDNF and higher NT-3 serum levels in depressed patients with schizophrenia.     

Determinants of nerve conduction recovery after nerve injuries: Compression duration and nerve fiber types

Introduction: The aims of this study were to determine the influences of: (1) timing of nerve decompression; and (2) nerve fiber types on the patterns of nerve conduction studies (NCS) after nerve injury. Methods: Nerve conduction studies (NCS) were performed on 3 models of nerve injury: (1) crush injury due to transient nerve compression (crush group); (2) chronic constriction injury (CCI), or permanent compression (CCI group); and (3) CCI with removal of ligatures, or delayed nerve decompression (De‐CCI group). Results: There were distinct patterns of NCS recovery. The crush and De‐CCI groups achieved similar motor nerve recovery, better than that of the CCI group. In contrast, recovery of sensory nerves was limited in the CCI and De‐CCI groups and was lower than in the crush group. Conclusions: Immediate relief of compression resulted in the best recovery of motor and sensory nerve conduction. In contrast, delayed decompression restored only motor nerve conduction. Muscle Nerve 52 : 107–112, 2015     

BDNF and NT-3 increase excitatory input connectivity in rat hippocampal cultures

The neurotrophic factors brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) have been shown to promote excitatory and inhibitory synapse development. However, a quantitative analysis of their influence on connectivity has proven in general difficult to achieve. In this work we use a novel experimental approach based on percolation concepts that provides a quantification of the average number of connections per neuron. In combination with electrophysiological measurements, we characterize the changes in network connectivity induced by BDNF and NT-3 in rat hippocampal cultures. We show that, on the one hand, BDNF and NT-3 accelerate the maturation of connectivity in the network by about 17 h. On the other hand, BDNF and NT-3 increase the number of excitatory input connections by a factor of about two, but without modifying the number of inhibitory input connections. This scenario of a dominant effect on the excitation is supported by the analysis of spontaneous population bursts in cultures treated with either BDNF or NT-3, which show burst amplitudes that are insensitive to the blockade of inhibition. A leaky integrate-and-fire model reproduces the experimental results well.     

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 the 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 supporting survival under these conditions. The present results show that 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.     

Follow-up evaluation with ultrasonography of peripheral nerve injuries after an earthquake

Published data on earthquake-associated peripheral nerve injury is very limited. Ultrasonography has been proven to be efficient in the clinic to diagnose peripheral nerve injury. The aim of this study was to assess the role of ultrasound in the evaluation of persistent peripheral nerve injuries 1 year after the Wenchuan earthquake. Thirty-four patients with persistent clinical symptoms and neurologic signs of impaired nerve function were evaluated with sonography prior to surgi- cal repair. Among 34 patients, ultrasonography showed that 48 peripheral nerves were entrapped, and 11 peripheral nerves were disrupted. There was one case of misdiagnosis on ultrasonogra- phy. The concordance rate of ultrasonographic findings with those of surgical findings was 98%. A total of 48 involved nerves underwent neurolysis and the symptoms resolved. Only five nerves had scar tissue entrapment. Preoperative and postoperative clinical and ultrasonographic results were concordant, which verified that ultrasonography is useful for preoperative diagnosis and postoperative evaluation of injured peripheral nerves.     

Expression of neurotrophins BDNF and NT-3, and their receptors in rat brain after administration of antipsychotic and psychotrophic agents

We have investigated the potential role of neurotrophic factors in antipsychotic drug action by examining the effects of antipsychotic and psychotropic treatments on the mRNA expression of brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and their receptors, trkB and trkC, respectively, in rat brain. Neither acute nor chronic clozapine treatment significantly affected the expression of these mRNAs in any brain area investigated, except for a decrease in trkB expression in the granule cells of the olfactory bulb. We then examined the effects of the psychotropic agent MK-801. MK-801 (5 mg/kg; 4h) significantly increased BDNF mRNA in the entorhinal cortex, but did not influence NT-3, trkB, or trkC expression in any brain area except for the olfactory bulb. The induction of BDNF mRNA by MK-801 was attenuated by pre-treatment (1 h prior to MK-801 administration) with the antipsychotics, clozapine (25 mg/kg) and haloperidol (2 mg/kg), but not with the antidepressant desipramine (15 mg/kg). Finally, we confirmed that the effects of MK-801 on BDNF mRNA were reflected in the respective changes in BDNF protein levels: MK-801 significantly increased anti-BDNF reactivity in the entorhinal cortex (126 ± 7% of control) while concomitantly decreasing in the hippocampus (71 ± 2% of control). These data do not support the hypothesis that neurotrophins play an important role in antipsychotic drug action, but rather suggest that induction of BDNF in the entorhinal cortex may play a significant role in the psychotropic action of MK-801.     

Regeneration and functional recovery in the upper extremity of rats after various types of nerve injuries

The aim was to establish an accurate, reproducible, and simple method to evaluate functional recovery after different types of nerve injuries to the brachial plexus of rats. To that end, pawprints, measured as distance between the first and fourth and second and third digits, were used for evaluation of injuries including crush injury, transection/repair, or graft repair of the median, ulnar, and radial nerves. Immunocytochemistry of the C-terminal flanking peptide of neuropeptide Y (CPON) and neurofilaments was used to investigate the cell body response and axonal outgrowth, respectively. Functional recovery was dependent on the severity as well as on the level of the lesion. Neither a single injury to the median nerve nor an injury to the ulnar nerve affected the pawprint, while an injury to both these nerves or a single injury to the radial nerve caused impairment of pawprints. There was a rapid recovery after crush injury to these nerves compared to previous reports of a similar injury to the sciatic nerve. The pattern of axonal outgrowth was related to the severity of the lesion. A conditioning lesion, i.e., an initial lesion of the same nerve preceding a test injury by a few days, of both motor/sensory fibers led to a quicker functional recovery. Surprisingly, conditioning of only sensory fibers had nearly the same effect. The cell body response was dependent on the level of the nerve lesion. The upper extremity of rats might be useful to evaluate the effects of new repair methods after nerve injuries using functional evaluation with pawprints as a simple and accurate method.     

Experimental strategies to promote functional recovery after peripheral nerve injuries

The capacity of Schwann cells (SCs) in the peripheral nervous system to support axonal regeneration, in contrast to the oligodendrocytes in the central nervous system, has led to the misconception that peripheral nerve regeneration always restores function. Here, we consider how prolonged periods of time that injured neurons remain without targets during axonal regeneration (chronic axotomy) and that SCs in the distal nerve stumps remain chronically denervated (chronic denervation) progressively reduce the number of motoneurons that regenerate their axons. We demonstrate the effectiveness of low-dose, brain-derived neurotrophic and glial-derived neurotrophic factors to counteract the effects of chronic axotomy in promoting axonal regeneration. High-dose brain-derived neurotrophic factor (BDNF) on the other hand, acting through the p75 receptor, inhibits axonal regeneration and may be a factor in stopping regenerating axons from forming neuromuscular connections in skeletal muscle. The immunophilin, FK506, is also effective in promoting axonal regeneration after chronic axotomy. Chronic denervation of SCs (>1 month) severely deters axonal regeneration, although the few motor axons that do regenerate to reinnervate muscles become myelinated and form enlarged motor units in the reinnervated muscles. We found that in vitro incubation of chronically denervated SCs with transforming growth factor-beta re-established their growth-supportive phenotype in vivo, consistent with the idea that the interaction between invading macrophages and denervated SCs during Wallerian degeneration is essential to sustain axonal regeneration by promoting the growth-supportive SC phenotype. Finally, we consider the effectiveness of a brief period of 20 Hz electrical stimulation in promoting the regeneration of axons across the surgical gap after nerve repair.     

Expression changes of nerve cell adhesion molecules L1 and semaphorin 3A after peripheral nerve injury

The expression of nerve cell adhesion molecule L1 in the neuronal growth cone of the central nervous system is strongly associated with the direction of growth of the axon, but its role in the regeneration of the peripheral nerve is still unknown. This study explored the problem in a femoral nerve section model in rats. L1 and semaphorin 3A m RNA and protein expressions were measured over the 4-week recovery period. Quantitative polymerase chain reaction showed that nerve cell adhesion molecule L1 expression was higher in the sensory nerves than in motor nerves at 2 weeks after injury, but vice versa for the expression of semaphorin 3A. Western blot assay results demonstrated that nerve cell adhesion molecule L1 expression was higher in motor nerves than in the sensory nerves at the proximal end after injury, but its expression was greater in the sensory nerves at 2 weeks. Semaphorin 3A expression was higher in the motor nerves than in the sensory nerves at 3 days and 1 week after injury. Nerve cell adhesion molecule L1 and semaphorin 3A expressions at the distal end were higher in the motor nerves than in the sensory nerves at 3 days, 1 and 2 weeks. Immunohistochemical staining results showed that nerve cell adhesion molecule L1 expression at the proximal end was greater in the sensory nerves than in the motor nerves; semaphorin 3A expression was higher in the motor nerves than in the sensory nerves at 2 weeks after injury. Taken together, these results indicated that nerve cell adhesion molecules L1 and semaphorin 3A exhibited different expression patterns at the proximal and distal ends of sensory and motor nerves, and play a coordinating role in neural chemotaxis regeneration.     

Electrophysiologic findings and grip strength after nerve injuries in the rat forelimb

We developed electrophysiologic methods for testing the three major forelimb nerves as a tool to evaluate motor and sensory recovery in rats. Median, ulnar, or radial nerves were transected and repaired in Sprague-Dawley rats. Compound muscle action potentials (CMAPs) and somatosensory evoked potentials (SSEPs) were recorded preoperatively and at various postoperative intervals. Correlation between grip strength and CMAPs was investigated. Reliable CMAPs were recorded for all three nerves. Median- or ulnar-nerve-derived SSEPs were reliably recorded; radial SSEPs could not be recorded. CMAPs followed typical regeneration patterns after nerve repair. SSEPs showed a consistent peak latency but fluctuating amplitude. Grip strength and median CMAP amplitude correlated positively. We conclude that it is possible to conduct minimally invasive electrophysiologic testing in rat forelimbs. The CMAP is a valid parameter that shows the typical time course of nerve regeneration and reinnervation.     

Chronic peripheral nerve injuries alter the somatotopic organization of the cuneate nucleus in kittens

The effect of chronic peripheral nerve injuries on the somatotopic organization of the cuneate nucleus was examined in kittens, using electrophysiological techniques. In normal kittens, most cells in the dorsal part of the nucleus possessed small receptive fields on the ipsilateral front paw. Several weeks after paw denervation in young kittens, however, many cells in the corresponding dorsal part of the nucleus responded to tactile stimulation of the wrist, forearm, or trunk. Consistent with this change in receptive fields, the neurons in the dorsal part of the nucleus were more responsive to electrical stimulation of the medial cutaneous nerve, which innervates part of the forearm, in kittens after paw denervation than in control kittens. These somatotopic changes were not an artifact of severe atrophy of the dorsal part of the nucleus. This experiment confirms that after chronic peripheral nerve injuries, central somatosensory neurons can begin to respond to ascending afferent volleys originating from other undamaged peripheral axons, which were previously incapable of exciting the cells. Moreover, this change in functional connectivity is evident at the first synapse central to the injury site.     

Factors predicting sensory and motor recovery after the repair of upper limb peripheral nerve injuries

OBJECTIVE： To investigate the factors associated with sensory and motor recovery after the repair of upper limb peripheral nerve injuries. DATA SOURCES： The online PubMed database was searched for English articles describing outcomes after the repair of median, ulnar, radial, and digital nerve injuries in humans with a publication date between 1 January 1990 and 16 February 2011. STUDY SELECTION： The following types of article were selected： （1） clinical trials describ- ing the repair of median, ulnar, radial, and digital nerve injuries published in English; and （2） studies that reported sufficient patient information, including age, mechanism of injury, nerve injured, injury location, defect length, repair time, repair method, and repair materials. SPSS 13.0 software was used to perform univariate and multivariate logistic regression analyses and to in- vestigate the patient and intervention factors associated with outcomes. MAIN OUTCOME MEASURES： Sensory function was assessed using the Mackinnon-Dellon scale and motor function was assessed using the manual muscle test. Satisfactory motor recovery was defined as grade M4 or M5, and satisfactory sensory recovery was defined as grade S3＋ or S4. RESULTS： Seventy-one articles were included in this study. Univariate and multivariate logistic regression analyses showed that repair time, repair materials, and nerve injured were inde- pendent predictors of outcome after the repair of nerve injuries （P 〈 0.05）, and that the nerve injured was the main factor affecting the rate of good to excellent recovery. CONCLUSION： Predictors of outcome after the repair of peripheral nerve injuries include age, gender, repair time, repair materials, nerve injured, defect length, and duration of follow-up.     

Low grade malignant peripheral nerve sheath tumor with smooth muscle differentiation

Malignant peripheral nerve sheath tumors are usually Schwann cell derived. Differentiation along mesenchymal lines is uncommon. Herein we present an example with smooth muscle differentiation occurring in the left distal forearm of a 62-year-old male with neurofibromatosis type I. Incisional biopsy of the slowly growing mass demonstrated a low-grade malignant peripheral nerve sheath tumor with strong S-100 protein immunoexpression as well as focal smooth muscle actin staining in atypical neoplastic cells. Immunostains for epithelial membrane antigen, neurofilament protein, glial fibrillary acidic protein, CD57, desmin, and myogenin were negative. The MIB-1 labeling index was 5.4%. Electron microscopy revealed arrays of microfilaments (actin myofilaments) variably associated with fusiform dense bodies, plasmalemmal micropinocytotic vesicles, and foci of external lamina (basement membrane) consistent with smooth muscle differentiation. Smooth muscle should be added to the spectrum of differentiation exhibited by malignant peripheral nerve sheath tumors. Its recognition requires exclusion of the alternative diagnosis of leiomyosarcoma.     

Effect of NT-4 and BDNF delivery to damaged sciatic nerves on phenotypic recovery of fast and slow muscles fibres

We investigated whether neurotrophin-4 (NT-4) and brain-derived neurotrophic factor (BDNF) affected the reinnervation of slow and fast motor units. Neurotrophin-impregnated or plain fibronectin (FN) conduits were inserted into a sciatic nerve gap. Fast extensor digitorum longus (EDL) and slow soleus muscles were collected 4 months postsurgery. Muscles were weighed and fibre type proportion and mean fibre diameters were derived from muscle cross-sections. All fibre types in muscles from FN animals were severely atrophied and this correlated well with type 1 fibre loss and atrophy in soleus and type 2b loss and atrophy in EDL. Treatment with NT-4 reversed soleus but not EDL mass loss above the FN group by significantly restoring type 1 muscle fibre proportion and diameters towards those of normal unoperated animals. BDNF did not increase muscle mass but did have minor effects on fibre type and diameter. Thus, NT-4 significantly improved slow motor unit recovery, and provides a basis for therapies intended to aid the functional recovery of muscles after denervating injury.     

Sensory reinnervation of muscle spindles after repair of tibial nerve defects using autogenous vein gratis

Motor reinnervation after repair of tibial nerve defects using autologous vein grafts in rats has previously been reported, but sensory reinnervation after the same repair has not been fully investigated. In this study, partial sensory reinnervation of muscle spindles was observed after repair of lO-mm left tibial nerve defects using autologous vein grafts with end-to-end anasto- mosis in rats, and functional recovery was confirmed by electrophysiological studies. There were no significant differences in the number, size, or electrophysiological function of reinnervated muscle spindles between the two experimental groups. These findings suggest that repair of short nerve defects with autologous vein grafts provides comparable results to immediate end-to-end anastomosis in terms of sensory reinnervation of muscle spindles.     

In Situ Hybridization of trkB and trkC Receptor mRNA in Rat Forebrain and Association with High-affinity Binding of [125I]BDNF, [125I]NT-4/5 and [125I]NT-3

The TrkB and TrkC receptor tyrosine kinases have been identified as high-affinity receptors for the neurotrophic factors brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5) and NT-3 respectively. These receptor classes were identified and mapped by the in situ hybridization of antisense riboprobes complementary to portions of the intracellular (tyrosine kinase) or extracellular (ligand-binding) domains of trkB and trkC mRNA, and by the distribution of high-affinity [¹²⁵I]BDNF, [¹²⁵I]NT-4/5 and [¹²⁵I]NT-3 binding sites in adjacent rat brain sections. Both methods showed that TrkB and TrkC receptors are abundant and widely expressed throughout the brain. Kinase or extracellular domain trkC probes labelled neuronal somata in a qualitatively similar manner in virtually every major area of the forebrain. Neither trkC probe labelled non-neuronal cells except for elements within cerebral arteries and arterioles. The kinase domain trkB probe hybridized exclusively to neurons. Neurons expressing trkB were even more widely distributed than those expressing trkC. The extracellular domain trkB probe labelled neurons with the same relative distribution as the trkB kinase domain probe, but also hybridized extensively with non-neural cells, particularly astrocytes, ependyma and choroid epithelium cells. The distribution of [¹²⁵I]NT-3 binding sites generally resembled that of trkC hybridization, particularly in the neocortex, striatum and thalamus. [¹²⁵I]BDNF and [¹²⁵I]NT-4/5 binding sites were more widely distributed and denser than those for [¹²⁵I]NT-3, and resembled the trkB hybridization pattern. These patterns are consistent with the preferential binding in the brain of TrkC receptors by [¹²⁵I]NT-3 and of TrkB receptors by [¹²⁵I]BDNF and [¹²⁵I]NT-4/5. That the predominantly neuronal patterns of hybridization obtained with kinase and extracellular domain probes for trkC are qualitatively indistinguishable suggests that truncated and full-length forms of TrkC are expressed within extensively overlapping populations of neurons. In marked contrast to TrkC, expression of the full-length and truncated forms of TrkB appears to be largely segregated, being expressed principally on neurons and non-neuronal cells respectively. The abundant and widespread neuronal distribution of full-length, signal-transducing forms of TrkB and TrkC predict that their cognate ligands, BDNF, NT-4/5 and NT-3, may exert direct effects on a large proportion of neurons within the mature brain.