Behavioral recovery after a spinal deafferentation injury in monkeys does not correlate with extent of corticospinal sprouting

A long held view in the spinal cord injury field is that corticospinal terminal sprouting is needed for new connections to form, that then mediate behavioral recovery. This makes sense, but tells us little about the relationship between corticospinal sprouting extent and recovery potential. The inference has been that more extensive axonal sprouting predicts greater recovery, though there is little evidence to support this. Here we addressed this by comparing behavioral data from monkeys that had received one of two established deafferentation spinal injury models in monkeys (Darian-Smith et al., 2014, Fisher et al., 2019, 2020). Both injuries cut similar afferent pools supplying the thumb, index and middle fingers of one hand but each resulted in a very different corticospinal tract (CST) sprouting response. Following a cervical dorsal root lesion, the somatosensory CST retracted significantly, while the motor CST stayed largely intact. In contrast, when a dorsal column lesion was combined with the DRL, somatosensory and motor CSTs sprouted dramatically within the cervical cord. How these two responses relate to the behavioral outcome was not clear. Here we analyzed the behavioral outcome for the two lesions, and provide a clear example that sprouting extent does not track with behavioral recovery.

Intracerebral Transplantation of BDNF-overexpressing Human Neural Stem Cells (HB1.F3.BDNF) Promotes Migration, Differentiation and Functional Recovery in a Rodent Model of Huntington's Disease

Huntington's disease (HD) is a dominantly inherited neurodegenerative disorder caused by abnormally expanded CAG repeats in the huntingtin gene. The huntingtin gene mutation leads to the progressive degeneration of striatal GABAergic medium spiny neurons (MSN) and reduces the level of brain-derived neurotrophic factor (BDNF) in HD patient's brain. BDNF is an essential neurotrophic factor for the cortico-striatal synaptic activity and the survival of GABAergic neurons. In this study, we transplanted BDNF-overexpressing human neural stem cells (HB1.F3.BDNF) into the contra-lateral side of unilateral quinolinic acid (QA)-lesioned striatum of HD rat model. The results of in vivo transplantation were monitored using various behavioral tests, 4.7 T animal magnetic resonance imaging (MRI) and immunohistochemical staining. We observed that the QA-lesioned rats receiving HB1.F3.BDNF cells exhibited significant behavioral improvements in the stepping, rotarod and apomorphine-induced rotation tests. Interestingly, contralaterally transplanted cells were migrated to the QA-lesioned striatum and the size of lateral ventricle was reduced. Histological analyses further revealed that the transplanted cells, which had migrated to the QA lesion site, were differentiated into the cells of GABAergic, MSN-type neurons expressing DARPP-32, and neural networks were established between the transplanted cells and the host brain, as revealed by retrograde tracing. Finally, there was a significant reduction of inflammatory response in HB1.F3.BDNF-transplanted HD animal model, compared with vehicle-transplanted group. Taken together, these results suggest that HB1.F3.BDNF can be an effective therapeutic strategy to treat HD patients in the future.

Subarachnoid Space Transplantation of Schwann and/or Olfactory Ensheathing Cells Following Severe Spinal Cord Injury Fails to Improve Locomotor Recovery in Rats

Treatment of spinal cord injury by exogenous cells has brought both successful and unsuccessful results. Olfactory ensheathing cells and Schwann cells have been widely used for transplantation purposes. In this study, we investigated the effects of these cells on contused spinal cord by introducing cells into subarachnoid space. Fifty thousand Schwann cells or olfactory ensheathing cells or a mixture of both cell types were transplanted one week after a 3-second clip compression injury at T-9 spinal cord level in rats. Starting from the day one of spinal cord injury, animals were assessed for six months by BBB test and then were sacrificed for immunohistochemistry labeling of the spinal cord injury site. There was no locomotor recovery in any of the treatment groups including controls. Immunohistochemistry assessment indicated positive labeling of P75 and S100 markers in the cell-transplanted groups compared with control. Our data suggest that transplantation of Schwann cells and/or olfactory ensheathing cells into the subarachnoid space does not improve motor recovery in severely injured spinal cord, at least with the number of cells transplanted here. This, however, should not be regarded as an essentially negative outcome, and further studies which consider higher densities of cells are required.

Chloride Co-transporter NKCC1 Inhibitor Bumetanide Enhances Neurogenesis and Behavioral Recovery in Rats After Experimental Stroke

Bumetanide, a selective Na⁺-K⁺-Cl^--co-transporter inhibitor, is widely used in clinical practice as a loop diuretic. In addition, bumetanide has been reported to attenuate ischemia-induced cerebral edema and reduce neuronal injury. This study examined whether bumetanide could influence neurogenesis and behavioral recovery in rats after experimentally induced stroke. Adult male Wistar rats were randomly assigned to four groups: sham, sham treated with bumetanide, ischemia, and ischemia treated with bumetanide. Focal cerebral ischemia was induced by injection of endothelin-1. Bumetanide (0.2 mg/kg/day) was infused into the lateral ventricle with drug administration being initiated 1 week after ischemia and continued for 3 weeks. Behavioral impairment and recovery were evaluated by tapered/ledged beam-walking test on post-stroke days 28. Then, the rats were perfused for BrdU/DCX (neuroblast marker), BrdU/NeuN (neuronal marker), BrdU/GFAP (astrocyte marker), and BrdU/Iba-1 (microglia marker) immunohistochemistry. The numbers of neuroblasts in the subventricular zone (SVZ) were significantly increased after the experimentally induced stroke. Bumetanide treatment increased migration of neuroblasts in the SVZ towards the infarct area, enhanced long-term survival of newborn neurons, and improved sensorimotor recovery, but it did not exert any effects on inflammation. In conclusion, our results demonstrated that chronic bumetanide treatment enhances neurogenesis and behavioral recovery after experimentally induced stroke in rats.

Brain-Derived Neurotrophic Factor Knockdown Blocks the Angiogenic and Protective Effects of Angiotensin Modulation After Experimental Stroke

Angiotensin type 1 receptor blockers (ARBs) have been shown to be neuroprotective and neurorestorative in experimental stroke. The mechanisms proposed include anti-inflammatory, antiapoptotic effects, as well as stimulation of endogenous trophic factors leading to angiogenesis and neuroplasticity. We aimed to investigate the involvement of the neurotrophin, brain-derived neurotrophic factor (BDNF), in ARB-mediated functional recovery after stroke. To achieve this aim, Wistar rats received bilateral intracerebroventricular (ICV) injections of short hairpin RNA (shRNA) lentiviral particles or nontargeting control (NTC) vector, to knock down BDNF in both hemispheres. After 14 days, rats were subjected to 90-min middle cerebral artery occlusion (MCAO) and received the ARB, candesartan, 1 mg/kg, or saline IV at reperfusion (one dose), then followed for another 14 days using a battery of behavioral tests. BDNF protein expression was successfully reduced by about 70 % in both hemispheres at 14 days after bilateral shRNA lentiviral particle injection. The NTC group that received candesartan showed better functional outcome as well as increased vascular density and synaptogenesis as compared to saline treatment. BDNF knockdown abrogated the beneficial effects of candesartan on neurobehavioral outcome, vascular density, and synaptogenesis. In conclusion, BDNF is directly involved in candesartan-mediated functional recovery, angiogenesis, and synaptogenesis.

Plant-Derived Natural Products for Parkinson's Disease Therapy

Plant-derived natural products have made their own niche in the treatment of neurological diseases since time immemorial. Parkinson's disease (PD), the second most prevalent neurodegenerative disorder, has no cure and the treatment available currently is symptomatic. This chapter thoughtfully and objectively assesses the scientific basis that supports the increasing use of these plant-derived natural products for the treatment of this chronic and progressive disorder. Proper considerations are made on the chemical nature, sources, preclinical tests and their validity, and mechanisms of behavioural or biochemical recovery observed following treatment with various plants derived natural products relevant to PD therapy. The scientific basis underlying the neuroprotective effect of 6 Ayurvedic herbs/formulations, 12 Chinese medicinal herbs/formulations, 33 other plants, and 5 plant-derived molecules have been judiciously examined emphasizing behavioral, cellular, or biochemical aspects of neuroprotection observed in the cellular or animal models of the disease. The molecular mechanisms triggered by these natural products to promote cell survivability and to reduce the risk of cellular degeneration have also been brought to light in this study. The study helped to reveal certain limitations in the scenario: lack of preclinical studies in all cases barring two; heavy dependence on in vitro test systems; singular animal or cellular model to establish any therapeutic potential of drugs. This strongly warrants further studies so as to reproduce and confirm these reported effects. However, the current literature offers scientific credence to traditionally used plant-derived natural products for the treatment of PD.

Comparative analysis of pharmacological treatments with N-acetyl-DL-leucine (Tanganil) and its two isomers (N-acetyl-L-leucine and N-acetyl-D-leucine) on vestibular compensation: Behavioral investigation in the cat

Head roll tilt, postural imbalance and spontaneous nystagmus are the main static vestibular deficits observed after an acute unilateral vestibular loss (UVL). In the UVL cat model, these deficits are fully compensated over 6 weeks as the result of central vestibular compensation. N-Acetyl-dl-leucine is a drug prescribed in clinical practice for the symptomatic treatment of acute UVL patients. The present study investigated the effects of N-acetyl-dl-leucine on the behavioral recovery after unilateral vestibular neurectomy (UVN) in the cat, and compared the effects of each of its two isomers N-acetyl-L-leucine and N-acetyl-D-leucine. Efficacy of these three drug treatments has been evaluated with respect to a placebo group (UVN+saline water) on the global sensorimotor activity (observation grids), the posture control (support surface measurement), the locomotor balance (maximum performance at the rotating beam test), and the spontaneous vestibular nystagmus (recorded in the light). Whatever the parameters tested, the behavioral recovery was strongly and significantly accelerated under pharmacological treatments with N-acetyl-dl-leucine and N-acetyl-L-leucine. In contrast, the N-acetyl-D-leucine isomer had no effect at all on the behavioral recovery, and animals of this group showed the same recovery profile as those receiving a placebo. It is concluded that the N-acetyl-L-leucine isomer is the active part of the racemate component since it induces a significant acceleration of the vestibular compensation process similar (and even better) to that observed under treatment with the racemate component only.

Fluoxetine Enhances Neurogenesis in Aged Rats with Cortical Infarcts, but This is not Reflected in a Behavioral Recovery

Age is associated with poor outcome and impaired functional recovery after stroke. Fluoxetine, which is widely used in clinical practice, can regulate hippocampal neurogenesis in young rodents. As the rate of neurogenesis is dramatically reduced during aging, we studied the effect of post-stroke fluoxetine treatment on neurogenesis in the subventricular zone (SVZ) and subgranular zone (SGZ) of dentate gyrus (DG) and whether this would be associated with any behavioral recovery after the cortical infarct in aged rats. Aged rats were randomly assigned to four groups: sham-operated rats, sham-operated rats treated with fluoxetine, rats subjected to cerebral ischemia, and rats with ischemia treated with fluoxetine. Focal cortical ischemia was induced by intracranial injection of vasoconstrictive peptide, endothelin-1 (ET-1). Fluoxetine was administered in the drinking water for 3 weeks starting 1 week after ischemia at a dose of 18 mg/kg/day. Behavioral recovery was evaluated on post-stroke days 29 to 31 after which the survival rate and fate of proliferating cells in the SVZ and DG were assessed by immunohistochemistry. Apoptosis was measured with the TUNEL assay. The results indicated that chronic fluoxetine treatment after stroke enhanced the proliferation of newborn neurons in the SVZ, but not in SGZ, and it suppressed perilesional apoptosis. Fluoxetine treatment did not affect the survival or differentiation of newly generated cells in the SVZ i.e., the enhanced neurogenesis was not translated into a behavioral outcome.

Human bone marrow mesenchymal stem/stromal cells produce efficient localization in the brain and enhanced angiogenesis after intra-arterial delivery in rats with cerebral ischemia, but this is not translated to behavioral recovery

Intravascular cell therapy is a promising approach for the treatment of stroke. However, high accumulation of cells to lungs and other filtering organs is a major concern after intravenous (i.v.) cell transplantation. This can be circumvented by intra-arterial (i.a.) cell infusion, which improves homing of cells to the injured brain. We studied the effect of i.a. delivery of human bone marrow-derived mesenchymal cells (BMMSCs) on behavioral and histological outcome in rats after middle cerebral artery occlusion (MCAO). Sixty male Wistar rats were subjected to transient MCAO (60 min) or sham-operation. BMMSCs (1×10(6)) were infused into the external carotid artery on postoperative day 2 or 7. Histology performed after a 42-day follow-up did not detect any human cells (MAB1281) in the ischemic brain. Endothelial cell staining with RECA-1 revealed a significant increase in the number of blood vessels in the perilesional cortex in MCAO rats treated with cells on postoperative day 7. Behavioral recovery as assessed in three tests, sticky label, cylinder and Montoya's staircase, was not improved by human BMMSCs during the follow-up. In conclusion, human BMMSCs did not improve functional recovery in MCAO rats despite effective initial homing to the ischemic hemisphere and enhanced angiogenesis, when strict behavioral tests not affected by repeated testing and compensation were utilized.