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Abstract: Somatosensory evoked potentials (SSEPs) are a sensitive quantitative measure of conduction in somatosensory pathways of the central nervous system and are increasingly used in both clinical trials and animal experiments. SSEPs can be recorded in non-sedated rodents by magnetic stimulation (MS) of peripheral nerves. To overcome some disadvantages caused by using anesthesia and implanted recording electrodes, we used subdermal needle electrodes located on the midline of the skull to successfully record SSEPs in non-sedated rats, elicited by stimulating the tibial nerve with a magnetic stimulator. The wave form contains a typical P1 peak and N1 peak. Although there is a variation of P1 latency, N1 latency, and P1–N1 amplitude between right side and left side, it was not statistically significant. In addition, there is a significantly positive relationship between P1–N1 amplitude and MS strength, suggesting that the increase in magnetic stimulating strength resulted in the increase in P1–N1 amplitude. Results in the present study demonstrate that our modified method is a reliable and feasible paradigm for recording SSEPs in non-sedated rats. [Copyright &y& Elsevier]

Abstract: Intrathecal infusion has been widely used to directly deliver drugs or neurotrophins to a lesion site following spinal cord injury. Evidence shows that intrathecal infusion is efficient for 7 days but is markedly reduced after 14 days, due to time dependent occlusion. In addition, extensive fibrotic scarring is commonly observed with intrathecal infusion. These anomalies need to be clearly elucidated in histology. In the present study, all adult Long-Evans rats received a 25mm contusion injury on spinal cord T10 produced using the NYU impactor device. Immediately after injury, catheter tubing with an outer diameter of 0.38mm was inserted through a small dural opening at L3 into the subdural space with the tubing tip positioned near the injury site. The tubing was connected to an Alzet mini pump, which was filled with saline solution and was placed subcutaneously. Injured rats without tubing served as control. Rats were behaviorally tested for 6 weeks using the BBB locomotor rating scale and histologically assessed for tissue scarring. Six weeks later, we found that the intrathecal tubing caused extensive scarring and inflammation, related to neutrophils, macrophages and plasma cells. The tubing''s tip was occluded by scar tissue and inflammatory cells. The scar tissue surrounding the tubing consists of 20–70 layers of fibroblasts and densely compacted collagen fibers, seriously compressing and damaging the cord tissue. BBB scores of rats with intrathecal tubing were significantly lower than control rats (p <0.01) from 2 weeks after injury, implying serious impairment of functional recovery caused by the scarring. [Copyright &y& Elsevier]

Abstract: Walking or stepping has been considered the result from the activation of the central pattern generator (CPG). In most patients with spinal cord injury (SCI) the CPG is undamaged. To date, there are no noninvasive approaches for activating the CPG. Recently we developed a noninvasive technique, tail nerve electrical stimulation (TANES), which can induce positive hind limb movement of SCI rats. The purpose of this study is to introduce the novel technique and examine the effect of TANES on CPG activation. A 25mm contusion injury was produced at spinal cord T10 of female, adult Long-Evans rats by using the NYU impactor device. Rats received TANES (∼40mA at 4kHz) 7 weeks after injury. During TANES all injured rats demonstrated active body weight-supported stepping of hind limbs with left–right alternation and occasional front–hind coordination, resulting in significant, temporary increase in BBB scores (p <0.01). However, there is no response to TANES from rats with L2 transection, consistent with other reports that the CPG may be located at L1–2. S1 transection negatively implies the key role of TANES in CPG activation. The TANES not only renders paralyzed rats with a technique-induced ability to walk via activating CPG, but also is likely to be used for locomotor training. It has more beneficial effects for physical training over other training paradigms including treadmill training and invasive functional electrical stimulation. Therefore the TANES may have considerable potential for achieving improvement of functional recovery in animal models and a similar method may be suggested for human study. [Copyright &y& Elsevier]

Abstract: Extensive dendritic beading of MAP2 (microtubule-associated protein 2) immunoreactivity has previously been observed in the contused rat spinal cord. However, we have also observed dendritic beading in occasional uninjured animals. The purpose of this study was to examine the possibility that perfusion conditions contributed to the dendritic beading. Under deep anesthesia, uninjured rats (adult female Long-Evans, 200–225g) were transcardially perfused with 0.9% saline solution followed by 4% paraformaldehyde at cold (4°C) or warm (20°C) temperature, and at a low (20ml/min) or high (50ml/min) flow rate. Dendrites were visualized by MAP2 immunoreactivity. The results demonstrate that perfusion with cold solutions at a high flow rate induces pronounced dendritic beading, and when perfused at a low flow rate, results in moderate dendritic beading. Warm perfusates did not induce dendritic beading when administered at a low flow rate, but occasional beading was observed with a high flow rate. Western blots revealed spectrin breakdown, but not MAP2 loss, in rats perfused with cold saline solution at a high flow rate, conditions that also resulted in dendritic beading. These findings demonstrate that dendritic morphology is sensitive to both temperature and flow rate of the perfusate. Warm fixative and a low perfusion flow rate minimized the perfusion-induced dendritic beading. [Copyright &y& Elsevier]