Exercise-induced motor improvement after complete spinal cord transection and its relation to expression of brain-derived neurotrophic factor and presynaptic markers

<p>Abstract</p> <p>Background</p> <p>It has been postulated that exercise-induced activation of brain-derived neurotrophic factor (BDNF) may account for improvement of stepping ability in animals after complete spinal cord transection. As we have shown previously, treadmill locomotor exercise leads to up-regulation of BDNF protein and mRNA in the entire neuronal network of intact spinal cord. The questions arise: (i) how the treadmill locomotor training, supplemented with tail stimulation, affects the expression of molecular correlates of synaptic plasticity in spinal rats, and (ii) if a response is related to BDNF protein level and distribution.</p> <p>We investigated the effect of training in rats spinalized at low thoracic segments on the level and distribution of BDNF immunoreactivity (IR) in ventral quadrants of the lumbar segments, in conjunction with markers of presynaptic terminals, synaptophysin and synaptic zinc.</p> <p>Results</p> <p>Training improved hindlimb stepping in spinal animals evaluated with modified Basso-Beattie-Bresnahan scale. Grades of spinal trained animals ranged between 5 and 11, whereas those of spinal were between 2 and 4. Functional improvement was associated with changes in presynaptic markers and BDNF distribution. Six weeks after transection, synaptophysin IR was reduced by 18% around the large neurons of lamina IX and training elevated its expression by over 30%. The level of synaptic zinc staining in the ventral horn was unaltered, whereas in ventral funiculi it was decreased by 26% postlesion and tended to normalize after the training. Overall BDNF IR levels in the ventral horn, which were higher by 22% postlesion, were unchanged after the training. However, training modified distribution of BDNF in the processes with its predominance in the longer and thicker ones. It also caused selective up-regulation of BDNF in two classes of cells (soma ranging between 100-400 μm²and over 1000 μm²) of the ventrolateral and laterodorsal motor nuclei.</p> <p>Conclusion</p> <p>Our results show that it is not BDNF deficit that determines lack of functional improvement in spinal animals. They indicate selectivity of up-regulation of BDNF in distinct subpopulations of cells in the motor nuclei which leads to changes of innervation targeting motoneurons, tuned up by locomotor activity as indicated by a region-specific increase of presynaptic markers.</p

The large area detector onboard the eXTP mission

The Large Area Detector (LAD) is the high-throughput, spectral-timing instrument onboard the eXTP mission, a flagship mission of the Chinese Academy of Sciences and the China National Space Administration, with a large European participation coordinated by Italy and Spain. The eXTP mission is currently performing its phase B study, with a target launch at the end-2027. The eXTP scientific payload includes four instruments (SFA, PFA, LAD and WFM) offering unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. The LAD instrument is based on the design originally proposed for the LOFT mission. It envisages a deployed 3.2 m2 effective area in the 2-30 keV energy range, achieved through the technology of the large-area Silicon Drift Detectors - offering a spectral resolution of up to 200 eV FWHM at 6 keV - and of capillary plate collimators - limiting the field of view to about 1 degree. In this paper we will provide an overview of the LAD instrument design, its current status of development and anticipated performance

Local protein synthesis in neuronal dendrites: function in synaptic plasticity?

The article summarizes the most meaningful studies which have provided evidence that protein synthesis in the neuron can occur not only in cell perikarya but also locally in dendrites. Dendrites contain the complete machinery required to synthesize proteins. Until now 12 different mRNAs coding the proteins involved in neurotransmission and modulation of synaptic activity have been identified in dendrites. Among these molecules is a BDNF neurotrophic factor which is a strong regulator of neuronal activity. It is postulated that the phenomenon of local synthesis provides the mechanism of fast changes in the strength of neuronal connections and is the molecular background of synaptic plasticity. Local protein synthesis points to some autonomy of dendrites which makes them 'the brains of the neurons' (Jim Eberwine)

Tamed viruses serve science and medicine

Wirusy są, w powszechnym rozumieniu, chorobotwórczymi czynnikami, zbliżonymi do bakterii. W różnym stopniu szkodliwe dla zdrowia człowieka, zarażają go, aby - nie mając zdolności do samodzielnego rozmnażania się - wykorzystać komórki gospodarza do rozplemu. Traktują więc obcy organizm jak swoistą wylęgarnię. Mali i groźni najeźdźcy. Ale dla naukowców, którzy poszukują skutecznych metod terapeutycznych, wirusy to znakomite nośniki i dostarczyciele genów, które w toku ewolucji nabyły zdolność wydajnego przenoszenia własnego materiału genetycznego do obcych komórek. By móc je wykorzystywać bez ryzyka, trzeba je obłaskawić. W laboratoriach pozbawia się je zdolności do namnażania się lub modyfikuje tak, by zachowały zdolność atakowania i niszczenia komórek nowotworowych, nie uszkadzając komórek zdrowych. Tak zmienione cząstki wirusów, przenoszące pożądane geny, nazwano wektorami wirusowymi. Użytecznymi wektorami mogą być tylko te wirusy, które tolerują w swoim materiale genetycznym wprowadzone, obce geny, i które cechuje duża wydajność infekcji. Tylko niektóre typy wirusów spełniają te warunki. Są między nimi retrowirusy, adenowirusy i parwowirusy "stowarzyszone" z adenowirusami; tzw. dependowirusy (ang. adeno-associated virus, AAV). Te ostatnie zasługują na szczególną uwagę, gdyż bez wsparcia towarzyszącego im adenowirusa nie potrafią się namnażać i są nieszkodliwe dla człowieka. To właśnie ich obłaskawione formy okazały się obiecującym narzędziem w próbach leczenia chorób zwyrodnieniowych układu nerwowego. To narzędzie próbuje się wykorzystywać również do ochrony komórek nerwowych i poprawy ich funkcji po uszkodzeniach. Artykuł wprowadza czytelnika w świat wektorów wirusowych, opisuje sposoby ich konstruowania i użycia w doświadczalnych terapiach zaburzeń, wywołanych uszkodzeniami mózgu i rdzenia kręgowego. Przytoczono najnowsze dane na temat skuteczności i perspektyw prób klinicznych terapii genowych oraz użycia tych nośników w optogenetyce.Viruses may be used in science and medicine as efficient carriers and gene suppliers to various organs and tissues. They developed the ability to invade alien cells for self propagation with the use of the genome of the host. To use them with no risk, the scientists have to tame them. That is achieved by removal of the majority of their genes, including the genes responsible for replication. The modified viral particles are subjected to genetic modification of the viral capsid aimed to increase its infectivity and to target a virus to the specific cell. After introduction of the therapy-targeted genes they become viral vectors. Not all viruses can be used as vectors; among those which are safe for humans and cause a long-term transduction are adeno-associated viruses AAV, promising for human somatic gene therapy. Till now, experimental therapies carried out with AAV-based vectors have shown improvement of function following brain and spinal cord injuries in rats. Such vectors are currently used in clinical trials of Parkinson and Alzheimer diseases. In basic science, AAV vectors have been recently used to transduce neurons with opsins, receptor channel proteins sensitive to light and able to convert a photon light into an electrochemical signal. They become a promising tool in optogenetics, an emerging field in neuroscience which allows to investigate changes in function of neuronal circuits after light-induced or inhibited activity of a single cell

BDNF Spinal Overexpression after Spinal Cord Injury Partially Protects Soleus Neuromuscular Junction from Disintegration, Increasing VAChT and AChE Transcripts in Soleus but Not Tibialis Anterior Motoneurons

After spinal cord transection (SCT) the interaction between motoneurons (MNs) and muscle is impaired, due to reorganization of the spinal network after a loss of supraspinal inputs. Rats subjected to SCT, treated with intraspinal injection of a AAV-BDNF (brain-derived neurotrophic factor) construct, partially regained the ability to walk. The central effects of this treatment have been identified, but its impact at the neuromuscular junction (NMJ) has not been characterized. Here, we compared the ability of NMJ pre- and postsynaptic machinery in the ankle extensor (Sol) and flexor (TA) muscles to respond to intraspinal AAV-BDNF after SCT. The gene expression of cholinergic molecules (VAChT, ChAT, AChE, nAChR, mAChR) was investigated in tracer-identified, microdissected MN perikarya, and in muscle fibers with the use of qPCR. In the NMJs, a distribution of VAChT, nAChR and Schwann cells was studied by immunofluorescence, and of synaptic vesicles and membrane active zones by electron microscopy. We showed partial protection of the Sol NMJs from disintegration, and upregulation of the VAChT and AChE transcripts in the Sol, but not the TA MNs after spinal enrichment with BDNF. We propose that the observed discrepancy in response to BDNF treatment is an effect of difference in the TrkB expression setting BDNF responsiveness, and of BDNF demands in Sol and TA muscles

Early pre- and postsynaptic decrease in glutamatergic and cholinergic signaling after spinalization is not modified when stimulating proprioceptive input to the ankle extensor α-motoneurons: Anatomical and neurochemical study.

Alpha-motoneurons (MNs) innervating ankle extensor muscles show reduced peripheral inputs from Ia proprioceptive afferents and cholinergic afferents after chronic spinalization (SCT). That phenomenon is not observed on ankle flexor MNs, indicating a smaller vulnerability of the latter MNs circuit to SCT. Locomotor training of spinal rats which partially restored those inputs to extensor MNs tended to hyper innervate flexor MNs, disclosing a need for selective approaches. In rats with intact spinal cord 7-days of low-threshold proprioceptive stimulation of the tibial nerve enriched glutamatergic Ia and cholinergic innervation of lateral gastrocnemius (LG) MNs, suggesting usefulness of selective stimulation for restoration of inputs to extensor MNs after SCT. Accordingly, to examine its effectiveness after SCT, tibial nerves and soleus muscles were implanted bilaterally, and for MN identification fluorescence tracers to LG and tibialis anterior (TA) muscles were injected two weeks prior to spinalization. Stimulation of tibial nerve, controlled by H-reflex recorded in the soleus muscle, started on the third post-SCT day and continued for 7 days. Nine days post-SCT the number and volume of glutamatergic Ia and of cholinergic C-boutons on LG MNs was decreased, but stimulation affected neither of them. Postsynaptically, a threefold decrease of NMDAR NR1 subunit and thirtyfold decrease of M2 muscarinic receptor transcripts caused by SCT were not counteracted by stimulation, whereas a threefold decrease of AMPAR GluR2 subunit tended to deepen after stimulation. We conclude that LG MNs, supported with proprioceptive stimuli after SCT, do not transcribe the perceived cues into compensatory response at the transcriptional level in the early post-SCT period

Electrical Stimulation of Low-Threshold Proprioceptive Fibers in the Adult Rat Increases Density of Glutamatergic and Cholinergic Terminals on Ankle Extensor α-Motoneurons - Fig 4

<p><b>Changes in the number (A) and in the aggregate volume (B) of VGLUT1 IF synaptic terminals contacting LG α-MNs after seven days of stimulation of Ia fibers in the tibial nerve.</b> Data are reported as mean +/- SEM. Both the number and aggregate volume of VGLUT1 terminals were increased on the stimulated comparing to sham-stimulated side (*p = 0.03 and *p< 0.05, respectively, <i>Wilcoxon</i> test).</p

Overexpression of BDNF increases excitability of the lumbar spinal network and leads to robust early locomotor recovery in completely spinalized rats.

Strategies to induce recovery from lesions of the spinal cord have not fully resulted in clinical applications. This is a consequence of a number of impediments that axons encounter when trying to regrow beyond the lesion site, and that intraspinal rearrangements are subjected to. In the present study we evaluated (1) the possibility to improve locomotor recovery after complete transection of the spinal cord by means of an adeno-associated (AAV) viral vector expressing the neurotrophin brain-derived neurotrophic factor (BDNF) in lumbar spinal neurons caudal to the lesion site and (2) how the spinal cord transection and BDNF treatment affected neurotransmission in the segments caudal to the lesion site. BDNF overexpression resulted in clear increases in expression levels of molecules involved in glutamatergic (VGluT2) and GABAergic (GABA, GAD65, GAD67) neurotransmission in parallel with a reduction of the potassium-chloride co-transporter (KCC2) which contributes to an inhibitory neurotransmission. BDNF treated animals showed significant improvements in assisted locomotor performance, and performed locomotor movements with body weight support and plantar foot placement on a moving treadmill. These positive effects of BDNF local overexpression were detectable as early as two weeks after spinal cord transection and viral vector application and lasted for at least 7 weeks. Gradually increasing frequencies of clonic movements at the end of the experiment attenuated the quality of treadmill walking. These data indicate that BDNF has the potential to enhance the functionality of isolated lumbar circuits, but also that BDNF levels have to be tightly controlled to prevent hyperexcitability