Stereological estimate of the total number of neurons in spinal segment D9 of the red-eared turtle.

The red-eared turtle is an important animal model for investigating the neural activity in the spinal circuit that generates motor behavior. However, basic anatomical features, including the number of neurons in the spinal segments involved, are unknown. In the present study, we estimate the total number of neurons in segment D9 of the spinal cord in the red-eared turtle (Trachemys scripta elegans) using stereological cell counting methods. In transverse spinal cord sections stained with modified Giemsa, motoneurons (MNs), interneurons (INs), and non-neuronal cells were distinguished according to location and morphology. Each cell type was then counted separately using an optical disector with the cell nucleus as counting item. The number of cells in segment D9 was as follows (mean ± SE): MNs, 2049 ± 74; INs, 16,135 ± 316; non-neuronal cells, 47,504 ± 478 (n = 6). These results provide the first estimate of the total number of neurons in a spinal segment in a terrestrial vertebrate based on unbiased stereological methods and an upper bound on the number of neurons involved in segmental sensorimotor activity. These findings also form a crucial quantitative foundation for integrating electrophysiological data into mathematical circuit models.

Regulation of EphA 4 kinase activity is required for a subset of axon guidance decisions suggesting a key role for receptor clustering in Eph function.

Signaling by receptor tyrosine kinases (RTKs) is mediated by their intrinsic kinase activity. Typically, kinase-activating mutations result in ligand-independent signaling and gain-of-function phenotypes. Like other RTKs, Ephs require kinase activity to signal, but signaling by Ephs in vitro also requires clustering by their membrane bound ephrin ligands. The relative importance of Eph kinase activity and clustering for in vivo functions is unknown. We find that knockin mice expressing a mutant form of EphA4 (EphA4(EE)), whose kinase is constitutively activated in the absence of ephrinB ligands, are deficient in the development of thalamocortical projections and some aspects of central pattern generator rhythmicity. Surprisingly, other functions of EphA4 were regulated normally by EphA4(EE), including midline axon guidance, hindlimb locomotion, in vitro growth cone collapse, and phosphorylation of ephexin1. These results suggest that signaling of Eph RTKs follows a multistep process of induced kinase activity and higher-order clustering different from RTKs responding to soluble ligands.

Organization of projection-specific interneurons in the spinal cord of the red-eared turtle.

Using differential retrograde axonal tracing, we identified motoneurons (MNs) and projection-specific interneuron (IN) classes in lumbar segment D9 of the adult red-eared turtle spinal cord. We characterized the distribution of these neurons in the transverse plane, and estimated their numbers and proportions. Different labeling paradigms allowed us to distinguish ipsilateral INs (IINs) from commissural INs (CINs), and to identify IINs and CINs with either ascending (a) axons, descending (d) axons, or axons that bifurcate to both ascend and descend (ad). Local interneurons with axons shorter than 1 segment in length were not studied. We show that most retrogradely labeled INs are located dorsal to the MNs, in the ventral horn, the intermediate zone and the dorsal horn. IINs predominate in the dorsal horn. CINs are located on average more medially than the IINs in the ventral horn and intermediate zone. Within the IIN and CIN populations, aINs and dINs overlap extensively. The adIINs and adCINs make up only a small fraction of the total number of INs and are scattered throughout much of the respective IIN and CIN domains. The proportions of IINs and CINs are about equal, as are the proportions of aIINs versus dIINs, of aCINs versus dCINs, and of adIINs versus adCINs. The findings are compared to the organization of lumbar spinal INs in other vertebrate species.

Exoskeleton gait training after spinal cord injury: An exploratory study on secondary health conditions.

OBJECTIVE: To explore changes in pain, spasticity, range of motion, activities of daily living, bowel and lower urinary tract function and quality of life of individuals with spinal cord injury following robotic exoskeleton gait training. DESIGN: Prospective, observational, open-label multicentre study. METHODS: Three training sessions per week for 8 weeks using an Ekso™ GT robotic exoskeleton (EKSO Bionics). Included were individuals with recent (<1 year) or chronic (>1 year) injury, paraplegia and tetraplegia, complete and incomplete injury, men and women. RESULTS: Fifty-two participants completed the training protocol. Pain was reported by 52% of participants during the week prior to training and 17% during training, but no change occurred longitudinally. Spasticity decreased after a training session compared with before the training session (p <0.001), but not longitudinally. Chronically injured participants increased Spinal Cord Independence Measure (SCIM III) from 73 to 74 (p = 0.008) and improved life satisfaction (p = 0.036) over 8 weeks of training. Recently injured participants increased SCIM III from 62 to 70 (p < 0.001), but no significant change occurred in life satisfaction. Range of motion, bowel and lower urinary function did not change over time. CONCLUSION: Training seemed not to provoke new pain. Spasticity decreased after a single training session. SCIM III and quality of life increased longitudinally for subsets of participants.

Development of projection-specific interneurons and projection neurons in the embryonic mouse and rat spinal cord.

Interneurons and projection neurons in the lumbar spinal cord of mouse and rat embryos were labeled retrogradely with fluorescent dextran amines from a distance of one segment from the segment of origin [lumbar segment (L) 2]. Six classes with specific axonal projections (ipsilateral ascending, descending, and bifurcating, and commissural ascending, descending, and bifurcating) were identified by differential labeling in both species and followed from embryonic day (E)12 to birth in the mouse. Neurons with shorter projections (intrasegmental interneurons) were not studied. We show that the four nonbifurcating neuron classes occupy characteristic, partially overlapping domains in the transverse plane, indicating a systematic pattern of migration and settlement related to axon trajectories. The number of neurons in each of the nonbifurcating classes increased steadily during development. Bifurcating neurons represented a minor fraction of the total throughout development and had relatively scattered positions within the ipsilateral and commissural neuron domains. Combination of retrograde tracing and immunohistochemistry for the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) showed that none of the spinal neurons in the six projection-specific classes was GABA positive, suggesting that all GABA-positive spinal neurons, including previously described GABA-positive commissural neurons, are unlikely to have projections exceeding one or two segments in either direction.

Satisfaction with upper extremity surgery in individuals with tetraplegia.

OBJECTIVE: To supplement the scant information available regarding the satisfaction of patients with tetraplegia following upper extremity reconstructive surgery for such individuals with spinal cord injury (SCI). STUDY DESIGN: Retrospective study with questionnaire follow-up. SETTING: The Danish Spinal Cord Injury Centers. MATERIAL AND METHODS: In the initial review period, 119 upper extremity surgeries were performed on patients with tetraplegia (n = 49). Seven died and the remaining 42 were invited to complete a follow-up questionnaire with a five-level scale ranging from strongly agree to strongly disagree regarding satisfaction. Forty patients completed the questionnaire. RESULTS: Median time from first surgery was 13 years (2-36). Sixty-five percent of the sample had a C5-C6 SCI, with 64% experiencing complete injury. Initially, 76% of the sample expressed general satisfaction with life, but only 28% of the sample reported that hand appearance improved after surgery. Interestingly, those having surgery from 1991 to 2008 reported significantly greater satisfaction (P < 0.001) and were significantly more satisfied with activities of daily living (ADL) (P < 0.001) than those having surgery between the years 1973 and 1990. In particular, gain of independence was obtained with pinch/specific hand surgery compared to triceps activation. Accordingly, the pinch/specific hand surgery group was significantly more satisfied than the triceps group on the ADL (P = 0.027), and the independence questions (P < 0.001). CONCLUSION: Overall satisfaction with upper extremity surgery is high. It can have a positive impact on life in general, ability to perform ADL, as well as supplying an increased level of independence.

Projection patterns of commissural interneurons in the lumbar spinal cord of the neonatal rat.

We have studied the axonal projection patterns of commissural interneurons (CINs) in the neonatal rat spinal cord. Some CINs are integral components of the neuronal networks in the vertebrate spinal cord that generate locomotor activity. By using differential retrograde labeling protocols with fluorescent dextran amines, we show that CINs with ascending axons (ascending CINs, or aCINs) and CINs with descending axons (descending CINs, or dCINs) constitute largely different populations. We show that aCINs and dCINs occupy partially overlapping domains in the transverse plane. The aCINs are located at the dorsal margin, within the dorsal horn, centrally within the intermediate zone, and in the medial region of the ventral horn, whereas the dCINs are located predominantly among the ventral and central aCINs and in smaller numbers within the dorsal horn. The labeled aCINs and dCINs project for at least one and a half segment rostrally or caudally and are present in roughly equal numbers. We also demonstrate the presence of a third, smaller population of CINs whose axons bifurcate to project for at least one and a half segment both rostrally and caudally (adCINs). The adCINs are located predominantly among the central and ventral groups of aCINs and dCINs. Finally, we demonstrate the presence of CINs with axons projecting for fewer than one and a half segment in either direction. These "short-range CINs" are intermingled with the aCINs, dCINs, and adCINs. Our results provide an anatomical framework for further electrophysiological studies aimed at identifying the CINs that participate in the mammalian locomotor central pattern generator.