Spinal Cord Afferents Research Articles

Movement Stabilizing Using Afferent Control of Spinal Locomotor CPG Using Chaotic Takagi-Sugeno Fuzzy Logic Systems: A Simulation Study

Background: External control of the function of the central pattern generators (CPGs), exist in the spinal cord, is possible by electrical or chemical stimulation of some of the spinal Afferents. After restarting the activity of spinal cord CPG, the dynamics of movements such as gait can be changed through the time by controlling the rhythm of the CPG. Methods: The purpose of this study was provision of closed loop control algorithm based on the Takagi-Sugeno fuzzy controller in order to adjust the weight of the spinal cord afferents in a neuro-mechanical model with the aim of controlling the rhythm of the CPGs. Rhythm control of CPGs has been done with the aim of implementing the process of resetting the phase during gait in order to stabilize the movement against external disturbances. In this paper, the efficiency of a continuous Takagi-Sugeno fuzzy controller with the efficiency of 2 fuzzy Takagi-Sugeno chaotic controllers has been compared. Results: It was shown by the results obtained from the simulation that the process of resetting the motion phase of the skeletal angle in face of applying disturbance in method of chaotic Takagi-Sugeno fuzzy controller is done with good features in the presence of delayed feedback in decreasing overshoot and undershoot to the amount of 1.982 and 0.17 radians, respectively so that the best amount of afferent to reset the phase and return to the desired angle is provided at the shortest possible time. Conclusion: In this paper, the efficiency of a continuous Takagi-Sugeno fuzzy controller with the efficiency of 2 fuzzy Takagi-Sugeno chaotic controllers has been compared for movement stabilization using spinal cord afferent control. According to the results, the best performance was observed when the chaotic fuzzy Takagi-Sugenocontroller in the presence of delayed feedback was used.

Spinal Cord Injury Disrupts Resting-State Networks in the Human Brain.

Despite 253,000 spinal cord injury (SCI) patients in the United States, little is known about how SCI affects brain networks. Spinal MRI provides only structural information with no insight into functional connectivity. Resting-state functional MRI (RS-fMRI) quantifies network connectivity through the identification of resting-state networks (RSNs) and allows detection of functionally relevant changes during disease. Given the robust network of spinal cord afferents to the brain, we hypothesized that SCI produces meaningful changes in brain RSNs. RS-fMRIs and functional assessments were performed on 10 SCI subjects. Blood oxygen-dependent RS-fMRI sequences were acquired. Seed-based correlation mapping was performed using five RSNs: default-mode (DMN), dorsal-attention (DAN), salience (SAL), control (CON), and somatomotor (SMN). RSNs were compared with normal control subjects using false-discovery rate-corrected two way t tests. SCI reduced brain network connectivity within the SAL, SMN, and DMN and disrupted anti-correlated connectivity between CON and SMN. When divided into separate cohorts, complete but not incomplete SCI disrupted connectivity within SAL, DAN, SMN and DMN and between CON and SMN. Finally, connectivity changed over time after SCI: the primary motor cortex decreased connectivity with the primary somatosensory cortex, the visual cortex decreased connectivity with the primary motor cortex, and the visual cortex decreased connectivity with the sensory parietal cortex. These unique findings demonstrate the functional network plasticity that occurs in the brain as a result of injury to the spinal cord. Connectivity changes after SCI may serve as biomarkers to predict functional recovery following an SCI and guide future therapy.

Reticular Formation and Pain: The Past and the Future.

The involvement of the reticular formation (RF) in the transmission and modulation of nociceptive information has been extensively studied. The brainstem RF contains several areas which are targeted by spinal cord afferents conveying nociceptive input. The arrival of nociceptive input to the RF may trigger alert reactions which generate a protective/defense reaction to pain. RF neurons located at the medulla oblongata and targeted by ascending nociceptive information are also involved in the control of vital functions that can be affected by pain, namely cardiovascular control. The RF contains centers that belong to the pain modulatory system, namely areas involved in bidirectional balance (decrease or enhancement) of pain responses. It is currently accepted that the imbalance of pain modulation towards pain facilitation accounts for chronic pain. The medullary RF has the peculiarity of harboring areas involved in bidirectional pain control namely by the existence of specific neuronal populations involved in antinociceptive or pronociceptive behavioral responses, namely at the rostroventromedial medulla (RVM) and the caudal ventrolateral medulla (VLM). Furthermore the dorsal reticular nucleus (also known as subnucleus reticularis dorsalis; DRt) may enhance nociceptive responses, through a reverberative circuit established with spinal lamina I neurons and inhibit wide-dynamic range (WDR) neurons of the deep dorsal horn. The components of the triad RVM-VLM-DRt are reciprocally connected and represent a key gateway for top-down pain modulation. The RVM-VLM-DRt triad also represents the neurobiological substrate for the emotional and cognitive modulation of pain, through pathways that involve the periaqueductal gray (PAG)-RVM connection. Collectively, we propose that the RVM-VLM-DRt triad represents a key component of the “dynamic pain connectome” with special features to provide integrated and rapid responses in situations which are life-threatening and involve pain. The new available techniques in neurobiological studies both in animal and human studies are producing new and fascinating data which allow to understand the complex role of the RF in pain modulation and its integration with several body functions and also how the RF accounts for chronic pain.

Effects of methylmercury on spinal cord afferents and efferents—A review

Methylmercury (MeHg) is an environmental neurotoxicant of public health concern. It readily accumulates in exposed humans, primarily in neuronal tissue. Exposure to MeHg, either acutely or chronically, causes severe neuronal dysfunction in the central nervous system and spinal neurons; dysfunction of susceptible neuronal populations results in neurodegeneration, at least in part through Ca2+-mediated pathways. Biochemical and morphologic changes in peripheral neurons precede those in central brain regions, despite the fact that MeHg readily crosses the blood-brain barrier. Consequently, it is suggested that unique characteristics of spinal cord afferents and efferents could heighten their susceptibility to MeHg toxicity. Transient receptor potential (TRP) ion channels are a class of Ca2+-permeable cation channels that are highly expressed in spinal afferents, among other sensory and visceral organs. These channels can be activated in numerous ways, including directly via chemical irritants or indirectly via Ca2+ release from intracellular storage organelles. Early studies demonstrated that MeHg interacts with heterologous TRP channels, though definitive mechanisms of MeHg toxicity on sensory neurons may involve more complex interaction with, and among, differentially-expressed TRP populations. In spinal efferents, glutamate receptors of the N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and possibly kainic acid (KA) classes are thought to play a major role in MeHg-induced neurotoxicity. Specifically, the Ca2+-permeable AMPA receptors, which are abundant in motor neurons, have been identified as being involved in MeHg-induced neurotoxicity. In this review, we will describe the mechanisms that could contribute to MeHg-induced spinal cord afferent and efferent neuronal degeneration, including the possible mediators, such as uniquely expressed Ca2+-permeable ion channels.

Chondroitinase ABC Digestion of the Perineuronal Net Promotes Functional Collateral Sprouting in the Cuneate Nucleus after Cervical Spinal Cord Injury

Upregulation of extracellular chondroitin sulfate proteoglycans (CSPGs) after CNS injuries contributes to the impediment of functional recovery by restricting both axonal regeneration and synaptic plasticity. In the present study, the effect of degrading CSPGs with the application of the bacterial enzyme chondroitinase ABC (chABC) into the cuneate nucleus of rats partially denervated of forepaw dorsal column axons was examined. A dorsal column transection between the C6-C7 dorsal root entry zones was followed immediately by an ipsilateral brainstem injection of either chABC or a bacterial-derived control enzyme [penicillinase (P-ase)] and then subsequently (1 week later) followed with a second brainstem enzyme injection and cholera toxin B subunit (CTB) tracer injection into the ipsilateral forepaw digits and pads. After 1 additional week, the rats underwent electrophysiological receptive field mapping of the cuneate nucleus and/or anatomical evaluation. Examination of the brainstems of rats from each group revealed that CSPGs had been reduced after chABC treatment. Importantly, in the chABC-treated rats (but not in the P-ase controls), a significantly greater area of the cuneate nucleus was occupied by physiologically active CTB traced forepaw afferents that had been spared by the initial cord lesion. These results demonstrate, for the first time, a functional change directly linked to anatomical evidence of sprouting by spinal cord afferents after chABC treatment.

The study of the role of the GABA A and GABA B receptors in presynaptic inhibition of primary afferents of spinal cord of the frog Rana ridibunda

The role of GABAA- and GABAB-receptors in presynaptic inhibition of primary afferent fibers was studied on an isolated preparation of the spinal cord of the frog Rana ridibunda. It is shown that the inhibitory effect of GABA on synaptic transmission from afferent fiber to motoneuron is caused by activation of both GABAA- and GABAB-receptors. A temporal correlation (± 5 min) was shown between the blocking action of bicuculline (a specific antagonist of GABAA-receptors) on primary afferent fiber depolarization (PAD) and its potentiating effect on the excitatory postsynaptic potential (EPSP) at parallel intracellular recording of EPSP in motoneuron and PAD in axons of the dorsal root. As a basis of this correlation, the single GABAA-receptor mechanism is discussed, which mediates the effect of bicuculline on PAD and EPSP. When a specific agonist of GABAB-receptor, baclofen, and an antagonist of GABAB-receptor, 2(OH)-saclofen, were applied, the obtained data indicated an involvement of GABAB-receptors in inhibition of synaptic transmission from afferent fibers to the motoneuron. Analysis of parameters of the unitary synaptic responses recorded in the control experiments and of their changes under the effect of (− )-baclofen indicates that the inhibitory action caused by activation of GABAB-receptors develops at the presynaptic level.

Respiratory load compensation. III. Role of spinal cord afferents

In a previous study, we reported that inspiratory tracheal occlusion (TO) significantly inhibited the motor drive to the diaphragm in a decerebellated bilaterally vagotomized preparation (J. Appl. Physiol. 75:675-681, 1993). The hypothesis to be tested in the present study was that respiratory muscle afferents activated by inspiratory TO provided the inputs responsible for the observed inhibition. Adult cats were anesthetized, tracheotomized, and instrumented with diaphragm electromyographic (EMGdi) recording electrodes. The cerebellum, vagi, and dorsal spinal cord (C2-T2) were surgically exposed. Inspiratory TO was applied before and after cold blockade of the dorsal cord (C6) or dorsal root (C3-6) transection in the intact and decerebellated vagotomized cat. Respiratory timing (inspiratory and expiratory duration) was determined from the EMGdi record, and the peak integrated EMGdi (integral of EMGdi) response was used as an index of respiratory motor drive. Our results showed that 1) cold blockade at the dorsal C6 level in an intact preparation significantly increased the peak of the integral of EMGdi response to TO and was reversible upon rewarming; 2) as previously reported, decerebellation coupled with bilateral vagotomy significantly decreased the peak integral of EMGdi response to TO with no effect on timing; 3) cold blockade (-1 degree C) of the dorsal cord at C6 significantly attenuated this inhibition, and subsequent dorsal rhizotomy at C3-6 completely abolished this inhibition; and 4) decerebellation, cold blockade of the dorsal cord (C6), and dorsal rhizotomy (C3-6) did not significantly affect baseline values in bilaterally vagotomized cats.(ABSTRACT TRUNCATED AT 250 WORDS)

Segmental inhibitory response in the frog spinal cord during orthodromic motoneuron activation

Different types of reflex discharges were produced in various preparations by stimulating the dorsal root of isolated frog spinal cord. These ranged from multiphasic low-amplitude waves to distinctly synchronized monosynaptic response. The discharges were followed by facilitation in the former and deep, protracted inhibition of response to test dorsal root stimulation in the latter. When interstimulus intervals measured 40–50 msec, inhibitory action was less pronounced than at shorter (15–30 msec) or longer (60–100 msec) intervals, thus indicating that at least two types of inhibition were at work, one at an earlier and the other at a later stage. Strychnine at a concentration of 10−5 M effectively reinforced the former and blocked the latter, while 10−4 M d-tubocurarine attenuated both types of inhibition substantially. It is concluded that inhibition of response occurs mainly as a result of recurrent activation of inhibitory systems via recurrent motoneuron axon collaterals when frog spinal cord afferents are excited. Intensity of the later (presynaptic) and earlier (postsynaptic) inhibition of reflex transmission is determined by the degree of synchrony in motoneuronal discharge in response to orthodromic stimulation.

Afferent connections of cat facial nucleus; a study using retrograde axonal transport of horseradish peroxidase

Neuronal populations in the brainstem and spinal cord — the sources of fiber pathways to the facial nucleus — were investigated in adult cats by microiontophoretically injecting horseradish peroxidase into restricted areas of the facial nucleus. Projections were identified from thenucleus nervi hypoglossi, nucleus praepositus hypoglossi, nucleus raphe pallidus, nucleus intercalatus, medial nucleus of the solitary tract, dorsal motor nucleus of the vagus, neurons of genu of the facial nerve, ipsilateral red nucleus, and reticular formation of the midbrain to the facial nucleus. Projections from a number of other brain structures to the facial nucleus also received confirmation. A topographic map was drawn up, showing how brainstem and spinal cord afferents are distributed in the facial nucleus.

Somatotopic maps are disorganized in adult rodents treated neonatally with capsaicin.

The somatosensory system is characterized at each stage of the projection pathways by the presence of maps formed by an orderly arrangement of cells and of the incoming fibres. Each cell responds to a definite area of skin, its receptive field (RF). If cell locations and their RFs are plotted side by side, they make up a continuous map of the body surface. Given the stability and repeatability of these maps, it was of interest to find that lesions which destroyed the input to one part of the map of the spinal cord in adults were followed by a readjustment of the RFs of cells which had lost their normal input1. It was more surprising to discover in adult cats and rats that peripheral nerve lesions which do not produce an anatomical destruction of spinal cord afferents were followed by the appearance of novel RFs in cells deprived of their normal physiological input2,3. Capsaicin given to neonatal mice or rats destroys unmyelinated afferents. We report here that this is followed by an expansion of the normal receptive fields supplied by myelinated afferents2,3. Our results suggest that unmyelinated fibres may be involved in controlling the connectivity of myelinated afferents with first central cells.

Inhibitory action of vagal nerve and spinal cord afferents on discharge pattern of bulbar respiratory modulated neurons.

Single vagal nerve stimuli delivered during burst discharge of respiratory modulated neurons entailed lengthening of an interspike interval in 37% of all units tested. Occasionally stimuli delivered to the spinal cord caused lengthening of interspike intervals in respiratory modulated neurons and in other bulbar units the discharge of which was not modulated with respiration. Vagal stimuli often entailed lengthening of the following interspike interval, while the interval during which stimuli were applied remained unaltered; latencies suggested that inhibitory pathways were polysynaptic. In expiratory-inspiratory (EI) and inspiratory (I) neurons, lengthenings of intervals roughly doubled those noted in inspiratory-expiratory (IE) and expiratory (E) units. Lengthening of intervals depended on stimulus incidence within the intervals and was greatest when stimuli were delivered during the late part of the intervals. In EI and I units, lengthening of intervals occurred mainly during the middle part of burst discharge, in IE and E neurons, however, towards the end of the burst. Conditioning of discharge of respiratory modulated neurons could be demonstrated.

Ventrolateral spinal cord afferents to the brain stem in the domestic pig.

AbstractThe distribution and termination within the brain stem of nerve fiber systems which comprise the ventrolateral funiculus of the spinal cord were studied in the domestic pig. Guillery et al. ('61) modification of the Nauta‐Gygax technique for silver impregnation of degenerating nerve fibers was utilized in this study. It is concluded that a spinothalamic tract does exist in the domestic pig, but that it is secondary in prominence to a large spinoreticular fiber system. The distribution and terminations of fibers within the brain stem of the pig resemble the pattern described by Anderson and Berry ('59) for the cat.

The cytoarchitecture of the brain stem of the domestic pig

AbstractThe cytoarchitecture and topography of some brain stem nuclei of the pig have been studied intransversely and sagitally cut, Nissl and Weigert stained, semiserial section. The cytology of those brain stem nuclei which receive an afferent supply from the ventrolateral funculus of the spinal cord is described. This study was found to be a necessary prologue to the study of distribution and terminations of spinal cord afferents to the brain stem in this species.The recognition of a nuclear pattern within the brain stem of the pig which is quite similar to that described in other species is noted.