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

Abstract

BackgroundIt 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.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.ResultsTraining 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 μm2 and over 1000 μm2) of the ventrolateral and laterodorsal motor nuclei.ConclusionOur 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.

A Single Bolus of Docosahexaenoic Acid Promotes Neuroplastic Changes in the Innervation of Spinal Cord Interneurons and Motor Neurons and Improves Functional Recovery after Spinal Cord Injury

“…Our study was not designed to identify whether sprouting or spared axons show increased synaptic transmission, but we did examine changes in synaptophysin, a synaptic vesicle protein that is present in presynaptic axons. Previous studies demonstrated that synaptophysin immunoreactivity is reduced in the spinal cord caudal to the lesion site after spinal cord hemisection or transection (Nacimiento et al, 1995;Macias et al, 2009;Ló pez-Dolado et al, 2013), which is similar to our data. The decreased global synaptophysin expression caudal to the lesion site in our vehicle-treated group was not present in DHA-treated animals.…”

Differential Effects of Low versus High Amounts of Weight Supported Treadmill Training in Spinally Transected Rats

“…Synaptophysin labeling was found primarily on the perimeter of motor neurons. Simple PCI 6 software (Compix, Inc. PA) was used to analyze synaptophysin labeling based on a technique developed by Macias and associates for analyzing synaptophysin around motor neurons (Macias et al, 2009). Using the elliptical object drawing tool, an outline was generated that extended just beyond the perimeter of HSP27-labeled motor neurons.…”

“…Moreover, biochemical and anatomical changes in the spinal cord were not examined in our previous study; therefore, the extent to which the different amounts of WSTT impacted the spinal cord circuitry was not known. A recent study has shown that the amount of synaptic inputs to motor neurons was greater in spinally transected (ST) rats that received daily treadmill training for 4 weeks (16-24 min/training session) relative to untrained ST rats (Macias et al, 2009). In addition, the ratio of excitatory to inhibitory synapses was increased in trained relative to untrained ST rats (Ichiyama et al, 2011).…”

“…To study plasticity, we examined the expression of the presynaptic marker, synaptophysin, the neurotrophin, brain-derived neurotrophic factor (BDNF), and its receptor, TrkB. WSTT has been shown to increase the expression of the presynaptic marker, synaptophysin, around large ventral horn motor neurons of ST rats and this was associated with improved stepping function (Macias et al, 2009). Hindlimb exercise also increased the expression of BDNF and TrkB, within the lumbar spinal cord after injury (Beaumont et al, 2008;Hutchinson et al, 2004;Ying et al, 2005).…”

The effect of timing electrical stimulation to robotic-assisted stepping on neuromuscular activity and associated kinematics

“…Recent studies have reported that synaptic inputs onto motor neurons found in the locomotor-generating region of the spinal cord were increased by treadmill training in spinally transected rats [64][65]. There is also evidence that treadmill training restored a normal balance of excitatory to inhibitory synapses, thereby improving motor neuron activity [45].…”