Intersegmental Reflexes Research Articles

Differential cardiovascular responses to cutaneous afferent subtypes in a nociceptive intersegmental spinal reflex

Electrical stimulation to segmental dorsal cutaneous nerves (DCNs) activates a nociceptive sensorimotor reflex and the same afferent stimulation also evokes blood pressure (BP) and heart rate (HR) responses in rats. To investigate the relationship between those cardiovascular responses and the activation of nociceptive afferents, we analyzed BP and HR responses to electrical stimulations at each DCN from T6 to L1 at 0.5 mA to activate A-fiber alone or 5 mA to activate both A- and C-fibers at different frequencies. Evoked cardiovascular responses showed a decrease and then an increase in BP and an increase and then a plateau in HR. Segmentally, both cardiovascular responses tended to be larger when evoked from the more rostral DCNs. Stimulation frequency had a larger effect on cardiovascular responses than the rostrocaudal level of the DCN input. Stimulation strength showed a large effect on BP changes dependent on C-fibers whereas HR changes were dependent on A-fibers. Additional A-fiber activation by stimulating up to 4 adjacent DCNs concurrently, but only at 0.5 mA, affected HR but not BP. These data support that cutaneous nociceptive afferent subtypes preferentially contribute to different cardiovascular responses, A-fibers to HR and C-fibers to BP, with temporal (stimulation frequency) and spatial (rostrocaudal level) dynamics.

Temporal and spatial dynamics of spinal sensorimotor processing in an intersegmental cutaneous nociceptive reflex.

The cutaneus trunci muscle (CTM) reflex produces a skin "shrug" in response to pinch on a rat's back through a three-part neural circuit: 1) A-fiber and C-fiber afferents in segmental dorsal cutaneous nerves (DCNs) from lumbar to cervical levels, 2) ascending propriospinal interneurons, and 3) the CTM motoneuron pool located at the cervicothoracic junction. We recorded neurograms from a CTM nerve branch in response to electrical stimulation. The pulse trains were delivered at multiple DCNs (T6-L1), on both sides of the midline, at two stimulus strengths (0.5 or 5 mA, to activate Aδ fibers or Aδ and C fibers, respectively) and four stimulation frequencies (1, 2, 5, or 10 Hz) for 20 s. We quantified both the temporal dynamics (i.e., latency, sensitization, habituation, and frequency dependence) and the spatial dynamics (spinal level) of the reflex. The evoked responses were time-windowed into Early, Mid, Late, and Ongoing phases, of which the Mid phase, between the Early (Aδ fiber mediated) and Late (C fiber mediated) phases, has not been previously identified. All phases of the response varied with stimulus strength, frequency, history, and DCN level/side stimulated. In addition, we observed nociceptive characteristics like C fiber-mediated sensitization (wind-up) and habituation. Finally, the range of latencies in the ipsilateral responses were not very large rostrocaudally, suggesting a myelinated neural path within the ipsilateral spinal cord for at least the A fiber-mediated Early-phase response. Overall, these results demonstrate that the CTM reflex shares the temporal dynamics in other nociceptive reflexes and exhibits spatial (segmental and lateral) dynamics not seen in those reflexes.NEW & NOTEWORTHY We have physiologically studied an intersegmental reflex exploring detailed temporal, stimulus strength-based, stimulation history-dependent, lateral and segmental quantification of the reflex responses to cutaneous nociceptive stimulations. We found several physiological features in this reflex pathway, e.g., wind-up, latency changes, and somatotopic differences. These physiological observations allow us to understand how the anatomy of this reflex may be organized. We have also identified a new phase of this reflex, termed the "mid" response.

Predictive control of intersegmental tarsal movements in an insect.

In many animals intersegmental reflexes are important for postural and movement control but are still poorly undesrtood. Mathematical methods can be used to model the responses to stimulation, and thus go beyond a simple description of responses to specific inputs. Here we analyse an intersegmental reflex of the foot (tarsus) of the locust hind leg, which raises the tarsus when the tibia is flexed and depresses it when the tibia is extended. A novel method is described to measure and quantify the intersegmental responses of the tarsus to a stimulus to the femoro-tibial chordotonal organ. An Artificial Neural Network, the Time Delay Neural Network, was applied to understand the properties and dynamics of the reflex responses. The aim of this study was twofold: first to develop an accurate method to record and analyse the movement of an appendage and second, to apply methods to model the responses using Artificial Neural Networks. The results show that Artificial Neural Networks provide accurate predictions of tarsal movement when trained with an average reflex response to Gaussian White Noise stimulation compared to linear models. Furthermore, the Artificial Neural Network model can predict the individual responses of each animal and responses to others inputs such as a sinusoid. A detailed understanding of such a reflex response could be included in the design of orthoses or functional electrical stimulation treatments to improve walking in patients with neurological disorders as well as the bio/inspired design of robots.

Human intersegmental reflexes from intercostal afferents to scalene muscles.

What is the central question of this study? The aim was to determine whether specific reflex connections operate between intercostal afferents and the scalene muscles in humans, and whether these connections operate after a clinically complete cervical spinal cord injury. What is the main finding and its importance? This is the first description of a short-latency inhibitory reflex connection between intercostal afferents from intercostal spaces to the scalene muscles in able-bodied participants. We suggest that this reflex is mediated by large-diameter afferents. This intercostal-to-scalene inhibitory reflex is absent after cervical spinal cord injury and may provide a way to monitor the progress of the injury. Short-latency intersegmental reflexes have been described for various respiratory muscles in animals. In humans, however, only short-latency reflex responses to phrenic nerve stimulation have been described. Here, we examined the reflex connections between intercostal afferents and scalene muscles in humans. Surface EMG recordings were made from scalene muscles bilaterally, in seven able-bodied participants and seven participants with motor- and sensory-complete cervical spinal cord injury (median 32years postinjury, range 5months to 44years). We recorded the reflex responses produced by stimulation of the eighth or tenth left intercostal nerve. A short-latency (∼38ms) inhibitory reflex was evident in able-bodied participants, in ipsilateral and contralateral scalene muscles. This bilateral intersegmental inhibitory reflex occurred in 46% of recordings at low stimulus intensities (at threetimes motor threshold). It was more frequent (in 75-85% of recordings) at higher stimulus intensities (six and nine times motor threshold), but onset latency (38±9ms, mean±SD) and the size of inhibition (23±10%) did not change with stimulus intensity. The reflex was absent in all participants with spinal cord injury. As the intercostal-to-scalene reflex did not increase with larger stimulus intensities, it is likely to be mediated by large-diameter intercostal muscle afferents. This is the first demonstration of an intercostal-to-scalene reflex. As the reflex requires intact spinal connections, it may be a useful marker for recovery of thoracic or cervical spinal injury.

Human Muscle Spindles Act as Forward Sensory Models

Modern theories of motor control incorporate forward models that combine sensory information and motor commands to predict future sensory states. Such models circumvent unavoidable neural delays associated with on-line feedback control. Here we show that signals in human muscle spindle afferents during unconstrained wrist and finger movements predict future kinematic states of their parent muscle. Specifically, we show that the discharges of type Ia afferents are best correlated with the velocity of length changes in their parent muscles approximately 100-160 ms in the future and that their discharges vary depending on motor sequences in a way that cannot be explained by the state of their parent muscle alone. We therefore conclude that muscle spindles can act as "forward sensory models": they are affected both by the current state of their parent muscle and by efferent (fusimotor) control, and their discharges represent future kinematic states. If this conjecture is correct, then sensorimotor learning implies learning how to control not only the skeletal muscles but also the fusimotor system.

Sacrolumbar intersegmental reflex circuit in men and its relation to the ejaculatory process

Objective We aimed to investigate electrophysiologically the intersegmental reflex circuit from sacral to lumbar cord segments in normopotent adult men, in patients with spinal cord injury and in patients with premature ejaculation. Methods Reflex EMG activity of the cremasteric (CM) and bulbocavernosus (BC) muscles was recorded simultaneously by needle electrodes during electrical stimulation of the upper lumbar and sacral dermatomes, respectively. Thirty-three healthy male volunteers, 16 patients with spinal cord injury (SCI) at the thoracic or cervical levels, and 26 men with premature ejaculation (PME) were included in the study. Results In controls, upper lumbar dermatomal stimulation (ULS) at the inner side of thigh only elicited a reflex response from the CM muscle and did not produce a regular response from the lower sacral myotomes such as in the BC muscle. However lower sacral dermatomal stimulation (LSS) at the dorsal nerve of penis consistently evoked reflex responses from both CM and BC muscles. These basic electrophysiological features were not different in patients with SCI. LSS did not elicit a reflex response from the CM muscle in about 39% of patients with PME, while the BC reflex was obtained from all patients with PME. Conclusions The neurophysiological pattern in BC and CM muscles during sacral or lumbar dermatomal stimulation reflects the sacrolumbar intersegmental reflex linkage that may be related to the ejaculatory process in men. The intersegmental sacrolumbar reflex circuit may be functionally disturbed in some patients with PME. Significance Interaction between the reflex activity of sacral to lumbar dermatomes could prove useful in defining electrophysiological mechanisms related to ejaculation in men.

Electrophysiologic evidence for an intersegmental reflex pathway between lumbar paraspinal tissues.

Electrophysiologic recordings were obtained from a lumbar paraspinal nerve or muscle in the anesthetized cat while electrically stimulating a paraspinal nerve or facet capsule in an adjacent lumbar segment. A variety of approaches were used to demonstrate the reflex nature of both the nerve and the muscle response. The primary purpose of this study was to seek electrophysiologic evidence for the presence of intersegmental reflexes between adjacent lumbar vertebral segments. A second purpose of this study was to confirm a previous procedure used to evoke paraspinal reflexes. This previous work had shown that electrical stimulation of the L1-L2 facet joint capsule elicits electromyographic activity from multifidus muscle one to two vertebral segments caudal to the stimulated facet in a porcine preparation. Biomechanical approaches have stressed the need for spinal stability to avoid conditions that could give rise to low back dysfunction. It seems reasonable to believe that reflex interactions between vertebral segments contribute to the sensorimotor integration of lumbar paraspinal tissues. It also seems reasonable to believe that alterations or abnormal elicitation of these reflexes could contribute to biomechanical changes associated with low back pain and paraspinal muscle spasm. Experiments were performed on 23 alpha-chloralose anesthetized adult cats. In eight cats the L3, L4, and L5 medial branch from each dorsal ramus was exposed and placed on a bipolar hook electrode. In six cats the L4 medial branch was stimulated and a compound action potential was recorded from the L3 medial branch. In three of the six cats the L5 medial branch was stimulated and a compound action potential was recorded from the L3 medial branch. In one cat the L4 medial branch was stimulated and a compound action potential was recorded from the L5 medial branch. In one cat the L3 medial branch was stimulated and a compound action potential was recorded from the L5 medial branch. At the end of each protocol the medial branch was cut just proximal to the stimulating electrode to confirm that the compound action potential was reflexive in nature and not initiated by volume conduction. In 15 cats three approaches were used to confirm that multifidus electromyographic activity evoked by electrical stimulation of a lumbar facet capsule was reflexive in nature: 1) by anesthetizing the site of the sensory endings, i.e., the facet capsule, 2) by injecting lidocaine intrathecally to block neural conduction centrally, i.e., within the spinal canal, or 3) by cutting the afferent pathway, i.e., the medial branch of the dorsal ramus. Electrical stimulation of the medial branch of the dorsal ramus innervating the medial-most lumbar paraspinal tissues evoked a compound action potential in the medial branch innervating the medial-most paraspinal tissues one and two segments away. Stimulating voltages between 2 and 70 V were necessary to evoke the compound action potential. Each compound action potential was reflexive in nature because cutting the lumbar medial branch proximal to its contact with the stimulating electrode abolished each compound action potential. The conduction velocity of the reflex ranged from 3.5 to 6.1 m/sec. Electrical stimulation of a lumbar facet capsule evoked lumbar multifidus muscle electromyographic activity. However, injecting lidocaine intrathecally or transecting the medial branch of the dorsal ramus had no effect on electromyographic activity. Injecting lidocaine into the facet or into the multifidus muscle around the facet joint (near the stimulating electrode) significantly decreased the magnitude of the multifidus electromyography. These results indicate that afferent impulses conveyed by the medial branch of the dorsal ramus reflexly altered efferent activity to an adjacent lumbar segment. This intersegmental paraspinal reflex may span at least one or two vertebral segments. The data suggest that electrical stimulation of the facet joint capsule may not have reflexly elicited multifidus activity because neither chemical interruption (intrathecal lidocaine) nor physical interruption (nerve transection) of the presumed reflex pathway diminished or abolished the electromyographic response. Volume conduction of the stimulating currents likely elicited multifidus activity during electrical stimulation of the facet capsule. When using electrical stimulation of neural paraspinal tissues to evoke reflex muscle activity, appropriate control experiments must be performed to clearly demonstrate the reflexive nature of the response.

Manipulation by the crab claw is dependent upon chordotonal organ afference

In crabs, the propus-dactylus (PD) chordotonal organ consists of about 80 bipolar sensory neurons whose dendrites are inserted into an elastic strand that spans the distalmost joint of chelae (claws) and walking legs. Movement of the dactyl to a closed position elongates the strand, while opening the dactyl shortens the strand. In response, the sensory neurons signal movements and positions. Is the crab dependent upon afference from the PD organ for voluntary control of the dactylus of the chelae? We quantified the manipulations of a standard food item by Dungeness crabs Cancer magister with intact chelipeds. Next, crabs were fed after the distal end of the elastic strand of the PD organ was detached (dPD) from the dactylus of both chelae or following a sham operation. All crabs fed avidly, but, in contrast to preoperative and sham crabs, statistical analysis revealed that dactyl-dependent manipulation (gripping, scraping, grasping, pull- ing, carrying, and cutting) by dPD crabs significantly decreased; crabs rarely used the dactyl fol- lowing detachment of the elastic strand. Manipulations not dactyl-dependent that involved the chelipeds and walking legs to aid feeding (cradling, stabilizing, and guiding) significantly increased. Physiological recordings indicate that the position-sensitive neurons of the PD organ fire tonically following detachment, but the firing rate is greater than that characteristic for the dactyl open position. Results support the hypothesis that feedback from the PD organ is required for the initiation and execution of precise contractions of the opener and closer muscles during directed movements of the dactyl. J. Exp. Zool. 279:579n586, 1997. © 1997 Wiley-Liss, Inc. Chordotonal organs (CO) are proprioceptors that provide feedback regarding joint movement and position in arthropod limbs. Those of Decapoda Crustacea have been subjects of considerable ana- tomical and electrophysiological study. Each or- gan consists of either an elastic strand or sheet in which are imbedded sensory neuron endings (Whitear, '62). The organs have been named with the initials of the joint they monitor. For instance, the organ spanning the propus-dactylus joint is referred to as the PD organ (Burke, '53). The elec- trophysiological responses of CO neurons fall into two general categories: large units that fire phasically during movements and small units that fire tonically to maintained positions of joints (Wiersma and Boettiger, '59; Wiersma, '59). Out- put by CO has been shown to mediate resistance (Bush, '62, '65; Evoy and Cohen, '69; Spirito et al., '72), assistance (Vedel, '80, '82; DiCaprio and Clarac, '81), and intersegmental reflexes (Vedel et al., '75; Bush et al., '78; Clarac et al., '78).

The possible role of C5 segment inspiratory interneurons investigated by cross-correlation with phrenic motoneurons in decerebrate cats.

We tested the role of C5 segment inspiratory interneurons in transcribing central respiratory drive to phrenic motoneurons and mediating intersegmental reflexes by cross-correlating the spontaneous activity of 26 interneurons with that of the ipsi -and contralateral C5 phrenic nerves in decerebrate cats. There were 10 interneurons that discharged only during inspiration (phrenic burst) and 16 that discharged tonically with increased firing during inspiration. Of the cross-correlograms for 26 of the interneurons with the ipsilateral phrenic, 20 were flat and 2 had peaks centred about time zero, interpreted as a common activation of the interneurons and motoneurons. The cross-correlograms for 4 other interneurons had troughs centred about time zero, interpreted as a synchronous excitation of the interneurons and inhibition of the motoneurons. Of the cross-correlograms for 23 interneurons with the contralateral phrenic, 22 were flat and 1 had a peak centred about time zero, interpreted as a common activation of the interneuron and motoneurons. Nine of ten cross-correlograms between pairs of interneurons were flat; one had a peak centred about time zero. We conclude that, despite their inspiratory modulated discharge patterns, there is no evidence from this study that the C5 segment inspiratory interneurons convey central respiratory drive to C5 phrenic motoneurons.

Identified nonspiking interneurons in leg reflexes and during walking in the stick insect

In the stick insect Carausius morosus identified nonspiking interneurons (type E4) were investigated in the mesothoracic ganglion during intraand intersegmental reflexes and during searching and walking.

The fate of specific motoneurons and sensory neurons of the pregenital abdominal segments inTenebrio molitor (Insecta : Coleoptera) during metamorphosis.

The anatomy and innervation of the lateral external muscle and sensory cells located in the ventral region of pregenital abdominal segments were examined at the larval and adult stages ofTenebrio molitor (Coleoptera). All seven muscles located in this region degenerate during the pupal stage, whilst only the lateral external median (lem) appears in the adult. Backfillings of the motor nerve innervating this muscle reveal that, at both larval and adult stages, it is innervated by ten neurons. Intracellular records from the muscle fibres show that two neurons are inhibitory, and at least five are excitatory. There are also two unpaired neurons. A variety of sensory organs are located in the ventral region of the larvae, whilst only campaniform sensilla are found in the adult. At both stages, the innervation pattern of the sensory nerve branches is very similar. Also, the central projections of the sensory cells occupy similar neuropilar areas. Finally, prolonged intracellular records from the lem muscle revealed that, at the larval stage, it participates only in segmental or intersegmental reflexes, whilst in the adult it has a primary expiratory role in ventilation. The results show that extensive changes occur in the number of muscles located in the ventral region of the pregenital abdominal segments, as well as in the arrangement and number of sensory neurons, in the structure of the exoskeleton, and even in the central nervous system. In contrast, only minor changes are observed in the sensory and motor nerve branches, in the sensory projections, and in the number and the location of the motoneurons innervating the lateral external median muscle.

An improved system for single unit isolation from multiunit nerve recordings by velocity analysis

A system for recording and decomposition of complex extracellular spike trains by analog computing is presented. Unlike other systems, it is not necessary to establish templates for the analysis. Rather by adjustments of a single knob, the velocity band can be adjusted. The velocity measurement can be made to a precision of better than 1%, where the velocity jitter in individual spikes of a unit becomes apparent. Spike trains on the connective of a stick insect are analyzed which occur during an intersegmental reflex, the CLP reflex.

Processing of mechanosensory signals in local reflex pathways of the locust.

The processing of mechanosensory signals responsible for the reflex adjustment of the posture or movement of the legs of the locust is described in terms of the actions and connections of identified neurones. Signals can be followed from the major classes of exteroceptors of a leg, through their various integrative stages in the central nervous system to their emergence as specific patterns in known motor neurones. Particular emphasis is placed on the integrative roles of two classes of local interneurones. The spiking local interneurones map the leg as a series of overlapping receptive fields and reverse the sign of the afferent input. The nonspiking local interneurones control the output of the motor neurones by the graded release of chemical transmitter and can adjust the gain of a local reflex depending on the position and movements of the joints of that leg. The reflex movements of one leg must not impair the stability of the animal and must therefore be influenced by events at the other legs. Populations of intersegmental interneurones convey sensory information from one segment to another to ensure such coordination. These interneurones do not produce stereotyped intersegmental reflexes but, instead, alter the performance of a local reflex in a distant leg by making synaptic connections with nonspiking local interneurones. These connections change the effectiveness of the outputs to the motor neurones and consequently the local reflex. The local interneurones therefore play a crucial role both in the production of local reflexes and in the integration of these actions with the movements of the other legs.

Behavioral recovery induced by applied electric fields after spinal cord hemisection in guinea pig.

Applied electric fields were used to promote axonal regeneration in spinal cords of adult guinea pigs. A propriospinal intersegmental reflex (the cutaneous trunci muscle reflex) was used to test lateral tract function after hemisection of the thoracic spinal cord. An electrical field (200 microvolts per millimeter, cathode rostral) applied across the lesion led to functional recovery of the cutaneous trunci muscle reflex in 25 percent of experimental animals, whereas the functional deficit remained in control animals, which were implanted with inactive stimulators.

Intersegmental Coordination of Central Neural Oscillators for Rhythmic Movements of the Walking Legs in Crayfish, Pacifastacus Leniusculus

ABSTRACT The neuronal circuits underlying rhythmical movements of the walking legs in crayfish Pacifastacus leniusculus are organized into central oscillators within each thoracic hemiganglion. These segmental networks are coupled in different modes of coordination during activities such as walking and limb waving. This paper examines the nature of the coupling between hemisegmental oscillators in the absence of sensory feedback, and the effect of phasic input from a major limb proprioceptor. In isolated preparations of the thoracic nerve cord, adjacent ipsilateral hemiganglia can generate a rhythmic motor output pattern in which homologous motor roots discharge approximately synchronously (the ‘in-phase’ rhythm). In contrast, contralateral hemiganglia show no evidence of any such phase-locking in their activity. A single proprioceptor at the base of each limb, the thoracic-coxal muscle receptor organ (TCMRO), can influence the timing and intensity of the rhythmic output of two or more ipsilateral thoracic ganglia. Rhythmical stretch-release of the TCMRO of the fourth ganglion on one side can entrain the motor rhythms of both the third and fourth ipsilateral hemiganglia, in the in-phase pattern of coordination. The TCMRO also elicits intra- and intersegmental reflexes during expression of the in-phase motor rhythm. These reflexes are centrally modulated in a phasedependent manner. Thus mechanical stimulation of the TCMRO co-activates homologous sets of motoneurones in adjacent ipsilateral hemiganglia only during their active (spiking) phase in the motor rhythm. We discuss the implications of these results for the generation and coordination of walking and other rhythmic behaviour of the thoracic limbs in decapod Crustacea. Our data shed further light on the properties of the motor rhythm generator for walking in crayfish, and suggest that the concept of a central pattern generator cannot be rigorously applied in this system.

Force-sensitive mechanoreceptors of the dactyl of the crab: single-unit responses during walking and evaluation of function.

The activities of individual force-sensitive mechanoreceptors of the dactyl (terminal leg segment) of the crab, Carcinus maenas, have been recorded during free walking. These receptors have also been mechanically and electrically stimulated in freely moving animals to directly evaluate their function in locomotion. All force-sensitive mechanoreceptors fired during the stance phase of walking and were silent during swing. Receptor discharges showed regular phase relationships to bursts in motor neurons of leg muscles. Crabs walk laterally and use the legs of one side either in trailing to actively push the animal to the opposite side, or in leading, to less forcefully pull the animal in that direction. Individual force-sensitive mechanoreceptors differed in their patterns of activity during trailing or leading according to their location on the dactyl. Units of proximal receptors fired more vigorously when used in trailing than in leading. Discharges in trailing were also increased by loading of the animal. In contrast, distal receptors near the dactyl tip fired equally intensely during walking in either direction. Proximal receptors thus encode forces and loads applied to the leg. Distal receptors do not encode loads but can signal leg contact and, potentially, exteroceptive vibrations. Sensory stimulation of force-sensitive mechanoreceptors was produced during walking by a device that imposed continuous mechanical bending of the dactyl and by electrical stimulation of dactyl nerves. Intra- and inter-segmental reflexes were evaluated by myographic recordings from leg muscles. Continuous mechanical deformation of the dactyl increased the activity of the levator and decreased firing in the depressor muscles of the homonymous leg during walking. The same stimulus produced enhanced activity in depressor muscles of adjacent legs. The latter effect was not due to simple mechanical coupling resulting from reflexes in the stimulated leg. These reflexes can function to limit forces applied to a leg and provide compensatory adjustments in other legs. Brief low-threshold electrical stimuli applied to nerves in which the activities of force-sensitive mechanoreceptors were recorded produced reflex effects similar to those obtained by mechanical stimulation. These stimuli also reset the rhythm of motor neuron bursting in both homonymous and adjacent legs during walking. These studies confirm the importance of force-sensitive mechanoreceptors in adapting walking patterns and in determining leg coordination in locomotion.

Temporal and Spatial Spread of an Intersegmental Reflex in Crayfish

Abstract An intersegmental reflex initiated by flexing a crayfish leg at the mero-carpal joint was examined by recording reflex response latencies of cephalic, thoracic and abdominal muscles. The first response was an intrasegmental resistance reflex in the extensor muscle of the stimulated leg. Spread of the intersegmental reflex occurred in both cephalic and caudal directions. Activation of the cephalic appendages occurred first (antennal levators, with latencies of 14–18 ms) while the abdominal musculature was activated last (superficial extensors, with latencies of 51–62ms). Shift of the stimulus site from the second to the fifth leg resulted in shorter latencies of the fifth leg and abdominal muscle responses while the latency for second leg extensor muscle discharge increased. Low correlation coefficients between the response latencies of pairs of cephalic and abdominal muscles, and thoracic and abdominal muscles, indicate that reflex pathways which initiate the abdominal responses are different from those that evoke the cephalic and thoracic responses. High correlation coefficients indicate common reflex pathways for activating either ipsilateral or contralateral pairs of extensors or flexors in the second and fifth legs. High correlations suggesting common reflex pathways or cross-coupling were also obtained for bilateral pairs of abdominal extensors. Low correlation coefficients for the response latencies of paired muscles indicate separate reflex pathways for (1) bilaterally homologous leg muscles and (2) first–fifth segment abdominal extensors. Surgical isolation of the supraoesophageal ganglion from the ventral nerve cord eliminated the responses of the antennal levators while producing a substantial increase in the response latencies of both maxilliped extensors and the contralateral second leg extensor and flexor, as well as a small but significant decrease in the contralateral first abdominal extensor. The synaptic input zones of the interneurones that mediate the thoracic and abdominal responses are located in the ventral nerve cord and not in the supraoesophageal ganglion.

An intersegmental reflex between the copulatory swimmerets of the male squat lobster,Galathea strigosa

The structure of the sexually modified 1st 2 pairs of swimmerets of the male squat lobster Galathea strigosa are described, and a reflex involving these swimmerets is characterised. The endopodite of the 1st swimmeret forms a partially rolled lamina which hooks around the “bottle brush” end of the endopodite of the 2nd swimmeret. Mechanical stimulation of a sensitive region on the endopodite of each 1st swimmeret causes retraction of both 2nd swimmerets, inducing the “bottle brush” to push up within the endopodite of the 1st swimmeret. The reflex is thought to be involved in sperm transfer during copulation. Neural information travels between the 1st and 2nd swimmerets in the interganglionic connective ipsilateral to the stimulus.

Reversal of an Intersegmental Reflex Elicited by A Muscle Receptor Organ

ABSTRACT One of the most common reflexes observed in invertebrates is the resistance reflex, in which a proprioceptor at a given joint excites the motor neurones innervating the muscles controlling the joint so as to resist imposed movement (Bush, 1962, 1963, 1965; Barnes, Spirito & Evoy, 1972). As well as these intrasegmental reflexes, proprioceptive reflexes in which sensory information is used to control muscles at joints other than the one spanned by a given proprioceptor have been reported (Ayers & Davis, 1977; Clarac, Vedel & Bush, 1978). These intersegmental reflexes may also control the state of excitation of other receptors (Moody, 1970; Clarac et al. 1978). Resistance reflexes and intersegmental reflexes are presumed to have a role in postural maintenance and load compensation (op. cit.; for review see Mill, 1976). However, resistance reflexes can be suppressed during locomotion (Barnes et al. 1972) and intersegmental reflexes may be modified during walking (Ayers & Davis, 1977). In addition, we have recently shown that a resistance reflex elicited by the thoracic-coxal muscle receptor organ (TCMRO) in the crab can be reversed to become a positive feedback assistance reflex (DiCaprio & Clarac, 1981). In this report we demonstrate that an intersegmental reflex activation of the basipodite levator and depressor motor neurones mediated by the TCMRO can also be reversed with respect to movement of the thoracic-coxal (TC) joint.

Abdominal Motoneurone Responses Elicited by Flexion of a Crayfish Leg

ABSTRACT Flexion of the mero-carpal joint of the leg of a partially dissected Pro-cambarus initiated an intersegmental reflex in the superficial extensor (SEMNs) and flexor (SFMNs) abdominal motoneurones. When flexion induced a full extension of the abdomen, as in intact crayfish, there was a discharge of the 5 SEMN exciters and the SFMN peripheral inhibitor throughout the extension. The extension antagonists -the SEMN peripheral inhibitor and the five SFMN exciters-discharged one or two spikes immediately following the stimulus, which suggests that more than one inter-ganglionic interneurone must be excited to activate the neuronal pathway which mediates the abdominal extension.