Changes in the excitability of anterior horn cells in a mental rotation task of body parts.

INTRODUCTION/AIMS: Mental rotation (MR), a tool of implicit motor imagery, is the ability to rotate mental representations of two- or three-dimensional objects. Although many reports have described changes in brain activity during MR tasks, it is not clear whether the excitability of anterior horn cells in the spinal cord can be changed. In this study, we examined whether MR tasks of hand images affect the excitability of anterior horn cells using F-wave analysis. METHODS: Right-handed, healthy participants were recruited for this study. F-waves of the right abductor pollicis brevis were recorded after stimulation of the right median nerve at rest, during a non-MR task, and during an MR task. The F-wave persistence and the F/M amplitude ratio were calculated and analyzed. RESULTS: Twenty participants (11 men and 9 women; mean age, 29.2 ± 4.4 years) were initially recruited, and data from the 18 that met the inclusion criteria were analyzed. The F-wave persistence was significantly higher in the MR task than in the resting condition (p = .001) or the non-MR task (p = .012). The F/M amplitude ratio was significantly higher in the MR task than in the resting condition (p = .019). DISCUSSION: The MR task increases the excitability of anterior horn cells corresponding to the same body part. MR tasks may have the potential for improving motor function in patients with reduced excitability of the anterior horn cells, although this methodology must be further verified in a clinical setting.

Blocking CTGF/CCN2 reverses neural fibrosis and sensorimotor declines in a rat model of overuse-induced median mononeuropathy.

Encapsulation of median nerves is a hallmark of overuse-induced median mononeuropathy and contributes to functional declines. We tested if an antibody against CTGF/CCN2 (termed FG-3019 or Pamrevlumab) reduces established neural fibrosis and sensorimotor declines in a clinically relevant rodent model of overuse in which median mononeuropathy develops. Young adult female rats performed a high repetition high force (HRHF) lever-pulling task for 18 weeks. Rats were then euthanised at 18 weeks (HRHF untreated), or rested and systemically treated for 6 weeks with either an anti-CCN2 monoclonal antibody (HRHF-Rest/FG-3019) or IgG (HRHF-Rest/IgG), with results compared with nontask control rats. Neuropathology was evident in HRHF-untreated and HRHF-Rest/IgG rats as increased perineural collagen deposition and degraded myelin basic protein (dMBP) in median nerves, and increased substance P in lower cervical dorsal root ganglia (DRG), compared with controls. Both groups showed functional declines, specifically, decreased sensory conduction velocity in median nerves, noxious cold temperature hypersensitivity, and grip strength declines, compared with controls. There were also increases of ATF3-immunopositive nuclei in ventral horn neurons in HRHF-untreated rats, compared with controls (which showed none). FG-3019-treated rats showed no increase above control levels of perineural collagen or dMBP in median nerves, Substance P in lower cervical DRGs, or ATF3-immunopositive nuclei in ventral horns, and similar median nerve conduction velocities and thermal sensitivity, compared with controls. We hypothesize that neural fibrotic processes underpin the sensorimotor declines by compressing or impeding median nerves during movement, and that inhibiting fibrosis using an anti-CCN2 treatment reverses these effects.

[Electroacupuncture Improves Limb Locomotor Function Possibly by Suppressing Rho-ROCK â ¡ Pathway Related Factors in Anterior Horns of Spinal Cord in Rats with Acute Spinal Cord Injury].

OBJECTIVE: To observe the effect of electroacupuncture (EA) of "Jiaji" (EX-B 2) on limb locomotor function and expression of Ras homolog gene family member A (RhoA), Rho-associated kinase Ⅱ (ROCK Ⅱ) and myosin light chain (MLC) proteins in the anterior horn of spinal cord in acute spinal cord injury (ASCI) rats, so as to explore its mechanisms under-lying improvement of SCI-induced limb locomotor dysfunction. METHODS: Forty-eight female Wistar rats were randomly divided into sham operation (sham), ASCI model (model), EA EX-B 2 (EA) and ROCK inhibitor (Fasudil) groups which were further divided into 14 d and 28 d subgroups (n=6 in each). The ASCI model was made by using weight drop striking method. Three hours after modeling, EA (100 Hz, 0.4, 0.6 mA) was applied to EX-B 2 (T 9, T 11) for 30 min, once daily for 14 d and 28 d, respectively. The ROCK inhibitor (hydrochloride Fasudil, 10 mg/kg) was administrated by intraperitoneal injection immediately after modeling, once a day, continuously for 14 d or 28 d. The expression of RhoA, ROCK Ⅱ and MLC proteins in the spinal cord anterior horn tissue (T 10) was detected by immunohistochemistry. The rats' hindlimb locomotor function was assessed according to Basso, Beattie and Bresnahan (BBB) locomotor rating scale (21-points). RESULTS: After ASCI, the BBB scores were significantly lower in the model group than in the sham group on day 14 and 28 (P<0.05), and obviously higher in the EA and inhibitor groups than in the model group (P<0.05), suggesting an improvement of the hindlimb locomotor function after EA intervention or suppression of ROCK. Immunohistochemical results indicated that the numbers of RhoA, ROCK Ⅱ and MLC immune-reaction positive cells in the anterior horn of spinal cord were significantly more in the model group than in the sham group (P<0.05), and remarkably decreased in both EA and inhibitor groups on day 14 and 28 relevant to the model group (P<0.05). The therapeutic effects of EA were markedly weaker than those of inhibitor Fasudil in up-regulating BBB score and down-regulating the number of RhoA, ROCK Ⅱ and MLC positive cells (P<0.05). CONCLUSION: EA of EX-B 2 can improve the hindlimb locomotor function in ASCI rats, which may be associated with its effect in down-regulating the expression of RhoA, ROCK Ⅱ and MLC proteins (i.e., inhibiting the RhoA/ROCK signaling pathway) in the anterior horn of spinal cord.

Triggering of Autophagy by Baicalein in Response to Apoptosis after Spinal Cord Injury: Possible Involvement of the PI3K Activation.

High level apoptosis induced by spinal cord injury (SCI) evokes serious damage because of the loss and dysfunction of motor neurons. Our previous studies showed that inhibition of autophagy evokes the activation of apoptosis. Interestingly, Baicalein, a medicine with anti-apoptosis activity that is derived from the roots of herb Scutellaria baicalensis, largely induces autophagy by activating phosphatidylinositol 3-kinase (PI3K). In this study, we investigated the effects of intraperitoneal injection of Baicalein on autophagy and apoptosis in SCI mice and evaluated the relationship between autophagy and apoptosis. We demonstrated that Baicalein promoted the functional recovery of motor neurons at 7 d after SCI. In addition, Baicalein enhanced neuronal autophagy and the autophagy-related factor PI3K, while inhibiting the p62 protein. Baicalein treatment decreased neuronal apoptosis at 7 d after SCI. Moreover, when inhibiting autophagy, apoptosis was upgraded by Baicalein treatment after injury. Thus, Baicalein attenuated SCI by inducing autophagy to reduce apoptosis in neurons potentially via activating PI3K.

Tail Nerve Electrical Stimulation and Electro-Acupuncture Can Protect Spinal Motor Neurons and Alleviate Muscle Atrophy after Spinal Cord Transection in Rats.

Spinal cord injury (SCI) often results in death of spinal neurons and atrophy of muscles which they govern. Thus, following SCI, reorganizing the lumbar spinal sensorimotor pathways is crucial to alleviate muscle atrophy. Tail nerve electrical stimulation (TANES) has been shown to activate the central pattern generator (CPG) and improve the locomotion recovery of spinal contused rats. Electroacupuncture (EA) is a traditional Chinese medical practice which has been proven to have a neural protective effect. Here, we examined the effects of TANES and EA on lumbar motor neurons and hindlimb muscle in spinal transected rats, respectively. From the third day postsurgery, rats in the TANES group were treated 5 times a week and those in the EA group were treated once every other day. Four weeks later, both TANES and EA showed a significant impact in promoting survival of lumbar motor neurons and expression of choline acetyltransferase (ChAT) and ameliorating atrophy of hindlimb muscle after SCI. Meanwhile, the expression of neurotrophin-3 (NT-3) in the same spinal cord segment was significantly increased. These findings suggest that TANES and EA can augment the expression of NT-3 in the lumbar spinal cord that appears to protect the motor neurons as well as alleviate muscle atrophy.

Prolonged Motor Weakness With Syringomyelia in Japanese Encephalitis: A Case Study

Japanese encephalitis (JE) shows characteristic brain lesions, including bilateral thalamus, midbrain, internal capsule, basal ganglia, and occasionally involves an anterior horn cell. We encountered a case of a 44-year-old man who initially presented with encephalitis, which was finally diagnosed as Japanese encephalomyelitis with syringomyelia. The patient showed severe motor weakness followed by delayed recovery of functional motor activities. Cervical magnetic resonance imaging showed syrinx formation at the C5 level suggesting myelitis, and abnormal electromyographic findings were noted. Clinicians should consider the possibility that the spinal cord may be involved; an example would be syringomyelia due to myelitis in a case of JE presenting with severe and prolonged motor weakness.

The effect of combined hyperbaric oxygen and iloprost treatment on the prevention of spinal cord ischaemia-reperfusion injury: an experimental study.

OBJECTIVES: Hyperbaric oxygen (HBO) has been shown to be effective in preventing neurological injuries in animal models of ischaemia, whereas iloprost (IL) prevents ischaemia-related mitochondrial dysfunction and reduces infarction size after focal cerebral ischaemia in animal models. The aim of the present study was to investigate the effect of combined HBO and IL treatment on spinal cord ischaemia-reperfusion (IR) injury by neurological, histopathological and biochemical methods in an experimental study. METHODS: Eighty New Zealand white male rabbits were randomly allocated into one of five study groups. The HBO group received a single session of HBO treatment and the IL group received an infusion of 25 ng/kg/min IL; the HBO + IL group received both HBO and IL and the control group received only 0.9% saline; the fifth group was the sham group. Levels of S100ß protein, neuron-specific enolase (NSE) and nitric oxide (NO) were measured at onset, at the end of ischaemia period and at the 24th and 48th hour of reperfusion. Physical activity was assessed using Tarlov criteria 24, and the spinal cords of the sacrificed rabbits were evaluated histopathologically. Additionally, tissue malondialdehyde (MDA) and antioxidant enzyme activities [total superoxide dismutase (SOD); catalase (CAT) and glutathione peroxidase (GSH-Px) were assessed. RESULTS: Neurological scores in the HBO, IL and HBO + IL groups were statistically significantly better compared with the control group at the 24th (P = 0.001 for all) and 48th hour (P = 0.001 for all). Histopathological scores in the HBO, IL and HBO + IL groups were also significantly better compared with the control group (P = 0.003, 0.001 and 0.001, respectively). Whereas MDA, NSE, S100ß protein and NO concentrations were significantly lower, CAT and GSH-PX levels were significantly higher in either sham or treatment groups compared with the control group. CONCLUSIONS: Since we demonstrated beneficial effects on spinal cord IR injury, we think that both HBO and IL, either alone or in combination, may be reasonable in the treatment of IR injury. Furthermore, there did not appear to be synergistic effects with combined treatment. More research is needed for practical application in humans, following thoracoabdominal aortic surgery.

Cortical electrical stimulation promotes neuronal plasticity in the peri-ischemic cortex and contralesional anterior horn of cervical spinal cord in a rat model of focal cerebral ischemia.

PURPOSE: This study evaluated the effect of cortical electrical stimulation (CES) on function recovery, dendritic plasticity, astrogliosis, and neuron recruitment in the peri-ischemic cortex (PIC) and contralesional anterior horn of cervical spinal cord (CSC) in a rat model of focal cerebral ischemia. MATERIALS AND METHODS: Rats were pre-trained on single pellet retrieval task, then received focal ischemic lesions and electrodes implantation. Seven days after surgery, rats received CES (CES group) or no stimulation (NS group) during 18 days of training. Behavior data on stimulation days 2, 4, 6, 8, 10, 12, 14, 16 and 18 were pooled for use. Immunohistochemical investigations for microtubule-associated protein 2 (MAP-2), glial fibrillary acidic protein (GFAP) and neuronal nuclei antigen (NeuN) were performed. RESULTS: Rats in CES group showed greater functional recovery of the impaired forelimb compared to the NS group. Moreover, the functional improvement coincided with a significant increase in MAP-2-immunoreactive dendritic surface density in PIC and CSC (P=0.011; P=0.005, respectively). CES group had a significant decrease in GFAP-immunoreactive astrocytic surface density in PIC and CSC (P=0.039; P=0.013, respectively). In the immunoassaying of NeuN, there was no significant difference between the two groups in PIC and CSC (P=0.834, P=0.782, respectively). CONCLUSION: CES can promote dendritic plasticity and reduce astrogliosis in the PIC and CSC in a rat model of focal cerebral ischemia. CES is still an appealing method for post-stroke rehabilitation provided that viability of pathways is evaluated presurgically.

Transcranial magnetic stimulation and amyotrophic lateral sclerosis: pathophysiological insights.

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder of the motor neurons in the motor cortex, brainstem and spinal cord. A combination of upper and lower motor neuron dysfunction comprises the clinical ALS phenotype. Although the ALS phenotype was first observed by Charcot over 100 years ago, the site of ALS onset and the pathophysiological mechanisms underlying the development of motor neuron degeneration remain to be elucidated. Transcranial magnetic stimulation (TMS) enables non-invasive assessment of the functional integrity of the motor cortex and its corticomotoneuronal projections. To date, TMS studies have established motor cortical and corticospinal dysfunction in ALS, with cortical hyperexcitability being an early feature in sporadic forms of ALS and preceding the clinical onset of familial ALS. Taken together, a central origin of ALS is supported by TMS studies, with an anterograde transsynaptic mechanism implicated in ALS pathogenesis. Of further relevance, TMS techniques reliably distinguish ALS from mimic disorders, despite a compatible peripheral disease burden, thereby suggesting a potential diagnostic utility of TMS in ALS. This review will focus on the mechanisms underlying the generation of TMS measures used in assessment of cortical excitability, the contribution of TMS in enhancing the understanding of ALS pathophysiology and the potential diagnostic utility of TMS techniques in ALS.

The effect of safflower yellow on spinal cord ischemia reperfusion injury in rabbits.

Safflower yellow (SY) is the safflower extract and is the one of traditional Chinese medicine. The aim of the present work was to investigate the effect of SY on spinal cord ischemia reperfusion injury (SCIRI) in rabbits. The models of spinal cord ischemia reperfusion (SI/R) were constructed, and the degree of the post-ischemic injury was assessed by means of the neurological deficit scores and plasma levels of lipid peroxidation reactioin and neuronal morphologic changes. SCIRI remarkably affected the functional activities of the hind limbs and activated lipid peroxidation reaction. SY could attenuate apoptosis and SCIRI by enhancing Bcl-2 expression and inhibiting Bax and caspase-3 activation.

Effect of volitional relaxation and motor imagery on F wave and MEP: do these tasks affect excitability of the spinal or cortical motor neurons?

OBJECTIVE: To test if simple motor imagery, like thumb abduction, preferentially influences the excitability of the spinal or cortical motoneurons. METHODS: Ten healthy subjects underwent two separate experiments, each consisting of recording F waves and MEPs from abductor pollicis brevis (APB) in three consecutive sessions: (1) baseline, (2) after immobilizing APB for 3 h, and (3) after brief muscle exercise. During the immobilization, the subjects were instructed to volitionally relax APB in experiment 1 (relaxation task), and mentally simulate thumb abduction without actual movement in experiment 2 (imagery task). RESULTS: Relaxation task suppressed both MEPs and F waves. Motor imagery reduced this suppression, restoring F waves nearly completely (94%) and MEPs only partially (77%). Hence, the rest-induced decline of MEPs in part results from cortical modulation. In contrast, statistical analysis revealed no differences in imagery-induced recovery of motoneuron excitabilities whether assessed by F wave or MEP. Thus, increased excitability of spinal motoneurons responsible for F-wave changes also accounts for recovery of MEPs. CONCLUSIONS: Volitional relaxation depresses the spinal and cortical motoneurons, whereas mental simulation counters rest-induced suppression primarily by restoring spinal excitability. SIGNIFICANCE: The present findings help elucidate physiologic mechanisms underlying motor imagery.

Postnatal development of a segmental switch enables corticospinal tract transmission to spinal forelimb motor circuits.

Development of skilled movements and the corticospinal tract (CST) begin prenatally and continue postnatally. Because the CST is required for skilled movements in maturity, it is accepted that motor skills cannot occur until the CST develops a mature organization. We recently showed that the CST plays an essential role in postnatal development of interneurons comprising the spinal circuits it engages. We proposed that CST signals are more effectively transmitted to ventral motor circuits after interneuron maturation, thereby enabling expression of CST motor functions, suggesting development of a segmental switch promoting transmission. We tested this by recording CST-evoked focal synaptic potentials, extracellularly, in the cervical enlargement of cats before and after interneuron maturation [postnatal week 5 (PW5) to PW7]. We compared monosynaptic CST amplitude input to segmental circuits with oligosynaptic ventral horn responses, as a measure of CST-evoked segmental response transmission from input to output. The M1 primary motor cortex was unilaterally inactivated between PW5 and PW7 to determine activity dependence. CST interneuron contacts were identified using confocal microscopy. CST terminals contact diverse interneuron classes. CST stimulation strongly activated ventral motor circuits at the ages when both interneurons and CST spinal terminations have developed a mature phenotype, supporting development of segmental transmission of CST signals. CST activity blockade impeded development of effective segmental transmission by the inactivated CST and created a novel path for transmission from the ipsilateral, unaffected, CST. Our findings show that development of segmental CST signal transmission regulates nascent CST motor control functions and provide insight into systems-level mechanisms for protracted motor skill development.

Light-induced rescue of breathing after spinal cord injury.

Paralysis is a major consequence of spinal cord injury (SCI). After cervical SCI, respiratory deficits can result through interruption of descending presynaptic inputs to respiratory motor neurons in the spinal cord. Expression of channelrhodopsin-2 (ChR2) and photostimulation in neurons affects neuronal excitability and produces action potentials without any kind of presynaptic inputs. We hypothesized that after transducing spinal neurons in and around the phrenic motor pool to express ChR2, photostimulation would restore respiratory motor function in cervical SCI adult animals. Here we show that light activation of ChR2-expressing animals was sufficient to bring about recovery of respiratory diaphragmatic motor activity. Furthermore, robust rhythmic activity persisted long after photostimulation had ceased. This recovery was accomplished through a form of respiratory plasticity and spinal adaptation which is NMDA receptor dependent. These data suggest a novel, minimally invasive therapeutic avenue to exercise denervated circuitry and/or restore motor function after SCI.

Effect of motion imagery to counter rest-induced suppression of F-wave as a measure of anterior horn cell excitability.

OBJECTIVE: To test if motor imagery prevents the rest-induced suppression of anterior horn cell excitability. METHODS: Ten healthy subjects underwent two separate experiments, each consisting of stimulating the median nerve 100 times and recording F-waves from abductor pollicis brevis (APB) in three consecutive sessions: (1) after muscle exercise to standardize the baseline, (2) after immobilization of APB for 3h and (3) after muscle exercise to check recovery. We instructed the subject to volitionally relax APB in experiment 1 (relaxation task), and to periodically simulate thumb abduction without actual movement in experiment 2 (imagery task). RESULTS: F-wave persistence and amplitude declined after relaxation task and recovered quickly after exercise, but changed little with imagery task. F-wave latencies showed no change when analyzed individually. The frequency distribution of collective F-waves recorded from all subjects remained the same after relaxation task, but showed a shift toward longer latencies after imagery task. CONCLUSIONS: Mental imagery without overt motor output suffices to counter the effect of sustained volitional muscle relaxation, which would, otherwise, cause a reversible reduction in anterior horn cell excitability. SIGNIFICANCE: This finding documents the importance of central drive for spinal excitability, which affects F-wave studies of a paretic muscle.

[Spinal cord protection and opioids].

Opioids, when administered in large doses, were reported to produce brain damage primarily in limbic system and association areas in animals. We recently found the result that intrathecal (IT) morphine after a short interval of aortic occlusion in the rodent model induced transient spastic paraparesis via opioid receptor-coupled effects in the spinal cord. Histopathological analysis revealed the possibility that IT morphine could induce degeneration of spinal ventral neurons even after a short lasting of spinal cord ischaemia in rats, and this degeneration was associated with the activation of spinal N-methyl-D-aspartate receptors by elevation of glutamate release in cerebrospinal fluid after IT morphine. Therefore, we would like to emphasize that all anesthesiologists should be aware of the possibility of morphine-induced paraplegia after thoracic aortic surgery and that we should carefully select appropriate analgesic agents from the several available opioids for these patients.

Immunohistochemical and hodological characterization of calbindin-D28k-containing neurons in the spinal cord of the turtle, Pseudemys scripta elegans.

Neurons and fibers containing the calcium-binding protein calbindin-D28k (CB) were studied by immunohistochemical techniques in the spinal cord of adult and juvenile turtles, Pseudemys scripta elegans. Abundant cell bodies and fibers immunoreactive for CB were widely and distinctly distributed throughout the spinal cord. Most neurons and fibers were labeled in the superficial dorsal horn, but numerous cells were also located in the intermediate gray and ventral horn. In the dorsal horn, most CB-containing cells were located in close relation to the synaptic fields formed by primary afferents, which were not labeled for CB. Double immunohistofluorescence demonstrated distinct cell populations in the dorsal horn labeled only for CB or nitric oxide synthase, whereas in the dorsal part of the ventral horn colocalization of nitric oxide synthase was found in about 6% of the CB-immunoreactive cells in this region. Choline acetyltransferase immunohistochemistry revealed that only about 2% of the neurons in the dorsal part of the ventral horn colocalized CB, whereas motoneurons were not CB-immunoreactive. The involvement of CB-containing neurons in ascending spinal projections to the thalamus, tegmentum, and reticular formation was demonstrated combining the retrograde transport of dextran amines and immunohistochemistry. Similar experiments demonstrated supraspinal projections from CB-containing cells mainly located in the reticular formation but also in the thalamus and the vestibular nucleus. The revealed organization of the neurons and fibers containing CB in the spinal cord of the turtle shares distribution and developmental features, colocalization with other neuronal markers, and connectivity with other tetrapods and, in particular with mammals.

SMN, the product of the spinal muscular atrophy-determining gene, is expressed widely but selectively in the developing human forebrain.

The expression pattern of the survival motor neuron (SMN) protein has been investigated immunohistochemically in the human fetal forebrain from 14 to 38 weeks of gestation. Mutations in the SMN gene cause spinal muscular atrophy (SMA), an autosomal recessive disease characterized by degeneration of lower motor neurons in the spinal cord leading to progressive muscle wasting. SMN is a multifunctional protein and has been implicated in diverse cytoplasmic and nuclear processes. The monoclonal murine SMN antibody used in this study recognized a major band at approximately 34 kDa. In spinal cord anterior horn motor neurons at 13 weeks of gestation, the soma, proximal neurites, and nucleus were immunostained. In the nucleus, SMN immunolabeling was observed at the nuclear membrane, at the nucleolus, and at dot-like structures in the nucleoplasm likely to be coiled bodies and gems. In the fetal forebrain, SMN was immunodetected as early as 14 weeks of gestation. From 14 to 24 weeks of gestation, intense immunostaining was observed in the basal nucleus of Meynert, a major source of cholinergic afferents to the cortex. Less intensely labeled cells at lower packing density were also observed in the thalamus, reticular and perireticular nucleus, globus pallidus, hippocampus, amygdala, and enthorinal cortex. Immunolabeled cells were still detectable at 38 gestational weeks, the latest time point investigated. These findings provide an anatomical basis for future investigations of SMN functions during brain development and for the neuropathological characterization of severe SMA cases.

Molecular mapping of developing dorsal horn-enriched genes by microarray and dorsal/ventral subtractive screening.

The dorsal horn of the spinal cord consists of distinct laminae that serve as a pivotal region for relaying a variety of somatosensory signals such as temperature, pain, and touch. The molecular mechanisms underlying the development of the dorsal horn are poorly understood. To define a molecular map of the dorsal horn circuit, we have profiled dorsal horn-enriched (DHE) gene expression in dorsal spinal cords on embryonic day 15.5 (E15.5) by genome-wide microarray and smart subtractive screening based on polymerase chain reaction (PCR). High-throughput in situ hybridization (ISH) was carried out to validate the expression of 379 genes in the developing dorsal spinal cord. A total of 113 DHE genes were identified, of which 59% show lamina-specific expression patterns. Most lamina-specific genes were expressed across at least two laminae, however. About 32% of all DHE genes are transcription factors, which represent the largest percentage of the group of all DHE functional classifications. Importantly, several individual lamina-specific transcription factors such c-Maf, Rora, and Satb1 are identified for the first time. Epistasis studies revealed several putative effectors of known DHE transcription factors such as Drg11, Tlx3(Rnx), and Lmx1b. These effector genes, including Grp, Trpc3, Pcp4, and Enc1, have been implicated in synaptic transmission, calcium homeostasis, and structural function and thus may have similar roles in the dorsal horn. The identification of a large number of DHE genes, especially those that are lamina specific, lays a foundation for future studies on the molecular machinery that controls the development of the dorsal horn and on functional differences of these distinct laminae in the dorsal spinal cord.

Intraspinal microstimulation using cylindrical multielectrodes.

A cylindrical multielectrode system specifically designed for intraspinal microstimulation was mechanically and electrically evaluated in the ventral horn of the feline lumbo-sacral spinal cord. Electrode insertions proved to be straight as evaluated from radiographs. Impedances were measured in situ and force recruitment curves from quadriceps muscles were collected over a wide range of stimulus parameters. For a given charge, higher current amplitudes produced greater forces than proportionally longer pulse durations, indicating that charge is not the sole indicator of evoked force in applications utilizing electrical stimulation. Overlap measurements for calculating current-distance constants were collected at a variety of current amplitudes, electrode pair separations, and pair orientations in the spinal grey matter. Forces obtained in the majority of these trials demonstrated an order effect, presumably due to asymmetric neuronal connectivity within the spinal cord. In the cases showing no order effect, the dorso-ventral electrode pair orientation yielded a higher average current-distance constant (278 microA/mm2) than either the medio-lateral or rostro-caudal electrode pair orientations (197 microA/mm2). Specifications of an array of cylindrical multielectrodes for use in future intraspinal microstimulation prostheses were updated.

C1-C3 spinal cord projections to periaqueductal gray and thalamus: a quantitative retrograde tracing study in cat.

By far, the strongest spinal cord projections to periaqueductal gray (PAG) and thalamus originate from the upper three cervical segments, but their precise organization and function are not known. In the present study in cat, tracer injections in PAG or in thalamus resulted in more than 2400 labeled cells, mainly contralaterally, in the first three cervical segments (C1-C3), in a 1:4 series of sections, excluding cells in the dorsal column and lateral cervical nuclei. These cells represent about 30% of all neurons in the entire spinal cord projecting to PAG and about 45% of all spinothalamic neurons. About half of the C1-C3 PAG and C1-C3 thalamic neurons were clustered laterally in the ventral horn (C(1-3vl)), bilaterally, with a slight ipsilateral preponderance. The highest numbers of C(1-3vl)-PAG and C(1-3vl)-thalamic cells were found in C1, with the greatest density rostrocaudally in the middle part of C1. A concept is put forward that C(1-3vl) cells relay information from all levels of the cord to PAG and/or thalamus, although the processing of specific information from upper neck muscles and tendons or facet joints might also play a role.