Organization Of Reflexes Research Articles

Estimation of Self-Motion for Gaze and Flight Stabilization in Flying Insects

: The stunning maneuverability of flying insects has attracted much attention from biologists and engineers over past decades. Biologists, fascinated by insect flight performance, have taken several different approaches when investigating how the insect nervous system computes signals in powerful closed–loop motor control circuits. So far, quantitative behavioral experiments, the measurement of electrical activity in the nervous system, and modeling studies have mainly been focusing on individual sensory mechanisms contributing to the functional organization of stabilization reflexes. Recently it became obvious, however, that it is the orchestration of several sensory mechanisms, operating in parallel, which enables motor control over an extended dynamic range. Current research aims at discovering general principles in multisensor fusion and sensor-rich feedback control that flying insects have evolved to master stabilization tasks during flight. Engineers follow the latest progress with excitement wondering whether biological control systems may inspire the design of technical applications in man-made devices.

Studies of the organization of the human nociceptive withdrawal reflex*†

Acta PhysiologicaVolume 189, Issue s654 p. 1-35 Studies of the organization of the human nociceptive withdrawal reflex*† Focus on sensory convergence and stimulation site dependency O. K. Andersen, O. K. Andersen Department of Health Science and Technology, Center for Sensory-Motor Interaction (SMI), Aalborg University, DenmarkSearch for more papers by this author O. K. Andersen, O. K. Andersen Department of Health Science and Technology, Center for Sensory-Motor Interaction (SMI), Aalborg University, DenmarkSearch for more papers by this author First published: 13 April 2007 https://doi.org/10.1111/j.1748-1716.2007.01706.xCitations: 52 * Throughout the dissertation ‘reflex’ denotes the nociceptive withdrawal reflex when nothing else is mentioned. ‡ †This dissertation is in part based on the following peer-reviewed papers, which are referred to as I–VIII in the text: I. Andersen, O.K., Jensen, L.M., Brennum, J. & Arendt-Nielsen, L. 1994. Evidence for central summation of C and A nociceptive activity in man. Pain59, 273–280. II. Andersen, O.K., Sonnenborg, F.A. & Arendt-Nielsen, L. 1999. Functional organization of human leg withdrawal reflexes elicited by electrical stimulation of the foot sole. Muscle Nerve22, 1520–1530. III. Andersen, O.K., Graven-Nielsen, T., Matre, D., Arendt-Nielsen, L. & Schomburg, E.D. 2000. Interaction between cutaneous and muscle afferent activity in polysynaptic reflex pathways – a human experimental study. Pain84, 29–36. IV. Arendt-Nielsen, L., Sonnenborg, F.A. & Andersen, O.K. 2000. Facilitation of the withdrawal reflex by repeated transcutaneous electrical stimulation: an experimental study on central integration in humans. Eur J Appl Physiol81, 165–173. V. Andersen, O.K, Sonnenborg, F.A. & Arendt-Nielsen, L. 2001. Reflex receptive fields for human withdrawal reflexes elicited by non-painful and painful electrical stimulation of the foot sole. Clin Neurophysiol112, 641–649. VI. Andersen, O.K., Sonnenborg, F., Matjacic, Z. & Arendt-Nielsen, L. 2003. Reflex receptive fields for human withdrawal reflexes in symmetrical standing position elicited by painful electrical stimulation of the foot sole. Exp Brain Res152, 434–443. VII. Andersen, O.K., Finnerup, N.B., Spaich, E.G., Jensen, T.S. & Arendt-Nielsen, L. 2004. Expansion of nociceptive withdrawal reflex receptive fields in spinal cord injured humans. Clin Neurophysiol115, 2798–2812. VIII. Andersen, O.K., Spaich, E.G., Madeleine, P. & Arendt-Nielsen, L. 2005. Gradual enlargement of human withdrawal reflex receptive fields following repetitive painful stimulation. Brain Res1042, 194–204. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume189, Issues654April 2007Pages 1-35 RelatedInformation

Exogenous overexpression of nerve growth factor in the urinary bladder produces bladder overactivity and altered micturition circuitry in the lumbosacral spinal cord

BackgroundExogenous NGF or saline was delivered to the detrusor smooth muscle of female rats for a two-week period using osmotic mini-pumps. We then determined: (1) bladder function using conscious cystometry; (2) organization of micturition reflexes using Fos protein expression in lumbosacral (L5-S1) spinal cord neurons; (3) calcitonin gene-related peptide (CGRP)-immunoreactivity (IR) in lumbosacral spinal cord segments.MethodsAn osmotic pump infused 0.9% NaCl (n = 6) or NGF (n = 6)(2.5 μg/μl solution; 0.5 μl/hr) for two weeks into the bladder wall. NGF bladder content was determined by enzyme-linked immunoassays. Bladder function was assessed with conscious cystometry. Immunohistochemical and imaging techniques were used to determine the distribution of Fos-IR cells and CGRP expression in the L5-S1 spinal cord in saline and NGF-treated rats two hours after intravesical saline distention. Fos expression and CGRP-IR in NGF-treated rats with bladder distention was compared to that observed in cyclophosphamide (CYP; 75 mg/kg; i.p.) treated rats with bladder distention.ResultsTwo-week infusion of NGF into the bladder wall increased bladder weight, reduced bladder capacity (60%), reduced the intercontraction interval (60%) and increased the amplitude of non-voiding contractions. NGF treatment and intravesical saline distention (2 hr) increased expression of Fos protein in L6-S1 spinal cord and altered the distribution pattern of Fos-IR cells. CGRP-IR in the lumbosacral spinal cord was also increased after NGF treatment.ConclusionThese data suggest that NGF infusion into the bladder wall induces bladder overactivity, can reveal a "nociceptive" Fos expression pattern in the spinal cord in response to a non-noxious bladder stimulus and increases CGRP-IR in the lumbosacral spinal cord.

Nociceptive withdrawal reflexes evoked by uniform-temperature laser heat stimulation of large skin areas in humans

Nociceptive withdrawal reflexes (NWR) were evoked by brief (200 ms) painful CO 2 laser stimulation at five intensities (1.2, 1.4, 1.6, 1.8, and 2.0 × pain threshold) applied to nine sites (2 cm 2) separated by 1.7 cm on the dorsal side of the foot and anterior part of the lower leg of 14 healthy volunteers. The purpose of the study was to investigate the characteristics of NWRs evoked by a natural stimulation modality. The reflexes were measured as the electromyographic response from the iliopsoas (ILI), quadriceps vastus lateralis (QVL), biceps femoris (BF), tibialis anterior (TA), and soleus (SOL) muscles. Stimulus–response relationships between heat intensity and the reflex magnitude and correlation between perceived pain intensity and reflex magnitude were observed in the ILI, QVL, BF, and TA but not the SOL. No significant differences in reflex magnitude were found between the stimulation sites. NWRs were evoked more often in flexor muscles than extensor muscles, indicating a non-site-specific reflex organization. The paper presents a new method to evoke NWRs by uniform-temperature laser heat stimulation of large skin areas in humans. These heat evoked reflexes had a stimulus–response relationship.

Transcranial Magnetic Stimulation over Sensorimotor Cortex Disrupts Anticipatory Reflex Gain Modulation for Skilled Action

Skilled interactions with new environments require flexible changes to the transformation from somatosensory signals to motor outputs. Transcortical reflex gains are known to be modulated according to task and environmental dynamics, but the mechanism of this modulation remains unclear. We examined reflex organization in the sensorimotor cortex. Subjects performed point-to-point arm movements into predictable force fields. When a small perturbation was applied just before the arm encountered the force field, reflex responses in the shoulder muscles changed according to the upcoming force field direction, indicating anticipatory reflex gain modulation. However, when a transcranial magnetic stimulation (TMS) was applied before the reflex response to such perturbations so that the silent period caused by TMS overlapped the reflex processing period, this modulation was abolished, while the reflex itself remained. Loss of reflex gain modulation could not be explained by reduced reflex amplitudes nor by peripheral effects of TMS on the muscles themselves. Instead, we suggest that TMS disrupted interneuronal networks in the sensorimotor cortex, which contribute to reflex gain modulation rather than reflex generation. We suggest that these networks normally provide the adaptability of rapid sensorimotor reflex responses by regulating reflex gains according to the current dynamical environment.

The cerebellum may implement the appropriate coupling of sensory inputs and motor responses: Evidence from vestibular physiology

Starting from a survey of current ideas on the role of the cerebellum in sensorimotor transformations, the present review summarizes the results of recent experiments showing that (a) somatosensory signals modify the spatial organization of the postural reflexes, thus leading to body stability, and (b) otolith input changes the plane of reflex eye movements, by keeping it perpendicular to the gravito-inertial vector. Evidence will be given that both transformations require the integrity of specific cerebellar regions. These data indicates that the cerebellum allows an optimal input-output coupling in relation to the ultimate behavioural goal of the motor activity.

Reflex reciprocal facilitation of antagonist muscles in spinal cord injury.

Electromyographic study in complete and incomplete spinal cord injury (SCI). To examine the changes in the pattern of reciprocal inhibition between agonist and antagonist muscles in SCI. Sensory Motor Performance Program, Rehabilitation Institute of Chicago, IL, USA. Tendon taps were delivered manually with an instrumented hammer to the tendons of the tibialis anterior and soleus muscle in positions of full-ankle dorsiflexion and plantarflexion in eight subjects with complete SCI and eight subjects with incomplete SCI. Electromyographic activity (EMG) was recorded from ankle dorsiflexor and plantarflexor muscles. Tapping force was also recorded by a force sensor mounted to the tendon hammer, indicating the stimulus onset. Measures of reflex EMG magnitude and reflex latency were obtained for both agonist and antagonist muscles. The ratio of antagonist to agonist EMG was computed based on normalized EMG. Substantial reflex responses occurred in both the stretched muscle and in its antagonist. The reflex in antagonist, which we term 'reciprocal facilitation (RF)', was most evident in subjects with incomplete SCI. The magnitude of RF was consistently greater than reflex responses in agonist muscles under all test conditions. The latency of the RF was comparable to that of monosynaptic reflex response. Following SCI, reciprocal organization of segmental reflexes at the ankle is often partially or completely suppressed, allowing reflex activation in antagonist muscles to be manifested. Possible mechanisms underlying these changes in neural organization are discussed. This study was supported by Spinal Cord Research Foundation, the Paralyzed Veterans of America.

Neuromotor Issues in Human Performance: Introduction

Two current approaches frequently implemented to understand mechanisms involved in motor control are presented in a series of papers. One approach aims at understanding what specific neural mechanisms are responsible for motor behavior. Such neural mechanisms might be operative at any of several sites in the nervous system, including spinal sites capable of complex reflex organization, as well as supraspinal sites involved in integrating multiple sensory and motor processes. Alternative approaches involve the assessment of kinematic and other variables used to describe the behavior using dynamical systems theory. Such an approach allows the researcher to explore relationships among groups of variables in, for example, multijoint control. In the series of papers that follow, the value of both of these approaches is discussed using examples from tasks that involve both rhythmic activities (running and cycling) and discrete movement (weight lifting and golf).

Spinal interneurons infected by renal injection of pseudorabies virus in the rat

The potency of spinal sympathetic reflexes is increased after spinal injury, and these reflexes may result in life-threatening hypertensive crises in humans. Few, if any, primary afferents project directly to sympathetic preganglionic neurons (SPN). Therefore, spinal sympathetic interneurons (IN) must play a major role in generating dysfunctional sympathetic activity after spinal cord injury. Furthermore, these IN are potentially aberrant targets, either for ascending and descending axons that may sprout after spinal cord injury or for axons that regenerate after spinal cord injury. We identified IN via the transsynaptic retrograde transport of pseudorabies virus (PRV) injected into the kidneys of rats. The proportion of infected IN ranged from approximately 1/3 to approximately 2/3 of the number of infected SPN. IN were heavily concentrated among the SPN in spinal lamina VII. However, IN were located in all lamina of the dorsal horn. The longitudinal distribution of infected IN was closely correlated with the longitudinal distribution of infected SPN. Few infected IN were found rostral or caudal to the longitudinal range of infected SPN. Infected IN were heterogeneous in both their sizes and the extent of their dendritic trees. The strong correlation between longitudinal distributions of infected IN and SPN supports physiological data demonstrating a segmental organization of spinal sympathetic reflexes. The paucity of infected IN in segments distant from SPN suggests that multisegmental sympathetic reflexes are mediated by projections onto IN rather than onto SPN themselves. The morphological heterogeneity of IN probably manifests the variety of systems that affect spinal sympathetic regulation.

Nociceptive EMG suppression in triceps brachii muscle in humans

Inhibitory spinal reflexes in human hand muscles mediated by cutaneous afferents (=cutaneous silent periods, CSPs) serve to protect the hand from injury. Proximal muscles are included in a complex protective pattern implementing both excitatory and inhibitory reflexes. We investigated the functional organization of CSPs in the triceps brachii muscle (TB) - the prime elbow extensor - assessing different stimulus intensities and elbow positions. Thirteen healthy subjects underwent recurrent electrical index finger tip stimulation with different intensities while volitionally activating TB against resistance. The rectified and averaged electromyogram (EMG) was recorded from TB with surface electrodes while the elbow joint was held in full flexion, full extension, and at an angle of 90 degrees. Digit II stimulation resulted in distinct CSPs in TB. Increasing stimulus intensities caused a more profound EMG suppression. Different elbow positions had a significant influence on CSP onset and end latency, and duration. The present findings are consistent with a functional organization of protective reflexes in the proximal human upper limb across several metameric segments. Spinal inhibitory neurons serving to rapidly suppress basic muscle synergies may compete with neural circuitry involved in postural control.

Male Wistar rats show uniform wind-up responses in carrageenan-induced inflammation but not in the normal situation.

The technique of recording spinal cord withdrawal reflexes as single motor units (SMUs) does not require intense preparatory surgery and allows the study of the nociceptive system in physiological conditions. It has been used to show that the wind-up phenomenon depends on the level of excitability of spinal cord neurones, the integrity of the spinal cord and the parameters of the stimulation used. We have now used SMU recordings to assess whether wind-up is also an heterogeneous phenomenon depending on the muscle studied, and, if so, how the presence of hyperalgesia affects its generation. The experiments were performed in normal and carrageenan-induced inflammation in male Wistar rats anesthetized with alpha-chloralose. Wind-up was recorded in units from peroneus longus, tibialis anterior and extensor digitorum longus. The results showed that in normal animals, the curves of C-fibre mediated wind-up reached saturation at different times and the shape of the curves was different depending on the muscle studied and on the intensity of stimulation used. In inflammation, however, C-fibre mediated wind-up became very uniform in the muscles studied, with a similar shape and saturation point. A-fibre mediated wind-up was only observed in animals with inflammation and no differences were observed between muscles. We conclude that in the absence of preparatory surgery and inflammation, C-fibre wind-up is heterogeneous, and supports a modular organization of nociceptive spinal reflexes. In hyperalgesia, however, wind-up curves are similar in units from different muscles, confirming a loss of modular organization that also affects the generation of wind-up.

Heat nociception is severely reduced in a mutant mouse deficient for the L1 adhesion molecule

Recent findings indicate that the spatial organization of the spinal nociceptive reflex system is adjusted postnatally through experience-dependent mechanisms. The cellular and molecular mechanisms underlying this tuning are not known. Because the adhesion molecule L1 is known to play an important role in neural development and synaptic plasticity, we studied the nociceptive withdrawal reflexes in awake adult mutant mice deficient in L1. Withdrawal reflexes were elicited by a CO 2 laser (heat stimulation) and von Frey monofilaments (tactile stimulation). L1-deficient mice ( n=10) had an abnormally high nociceptive heat-reflex threshold compared with wild-type mice ( n=11), except for the nose. Other behavioral signs of heat pain, such as vocalization, were either absent or strongly reduced in L1-deficient mice. Tactile thresholds for withdrawal reflexes were increased in L1-deficient mice when compared with wild-types except for the tail. By contrast, the spatial organization of the withdrawal reflexes appeared normal indicating that the L1 adhesion molecule is not essential for the spatial adjustments of reflex connections during development. The termination patterns of thin primary afferent fibers in the superficial dorsal horn, visualized using intra-plantar injections of WGA-HRP, were normal, suggesting that decreased nociceptive heat sensitivity in L1-deficient mice is mainly due to altered central processing. In view of the known interactions between L1 and some of the NMDA-receptor subtypes, and the prominent role of NMDA receptors in nociception and plasticity, it is conceivable that the hypoalgesia seen in L1 mutants is due, in part, to disturbed NMDA-receptor function.

Descending spinal projections from the rostral gigantocellular reticular nuclei complex.

Electrophysiological and physiological studies have suggested that the ventral medullary gigantocellular reticular nuclei (composed of the gigantocellular ventralis and pars alpha nuclei as well as the adjacent lateral paragigantocellular nucleus; abbreviated Gi-LPGi complex) provide descending control of pelvic floor organs (Mackel [1979] J. Physiol. (Lond.) 294:105-122; Hubscher and Johnson [1996] J. Neurophysiol. 76:2474-2482; Hubscher and Johnson [1999] J. Neurophysiol. 82:1381-1389; Johnson and Hubscher [1998] Neuroreport 9:341-345). Specifically, this complex of paramedian reticular nuclei has been implicated in the inhibition of sexual reflexes. In the present study, an anterograde fluorescent tracer was used to investigate direct descending projections from the Gi-LPGi complex to retrogradely labeled pudendal motoneurons (MN) in the male rat. Our results demonstrated that, although a high density of arborizations from Gi-LPGi fibers appears to be in close apposition to pudendal MNs, this relationship also applies to other MNs throughout the entire spinal cord. The Gi-LPGi also projects to spinal autonomic regions, i.e., both the intermediolateral cell column and the sacral parasympathetic nucleus, as well as to regions of the intermediate gray, which contain interneurons involved in the organization of pelvic floor reflexes. Lastly, throughout the length of the spinal cord, numerous neurons located primarily in laminae VII-X, were retrogradely labeled with Fluoro-Ruby after injections into the Gi-LPGi. The diffuse descending projections and arborizations of this pathway throughout the spinal cord suggest that this brainstem area is involved in the direct, descending control of a variety of spinal activities. These results are in contrast with our observations of the discrete projections of the caudal nucleus raphe obscurus, which target the autonomic and somatic MNs involved specifically in sexual and eliminative functions (Hermann et al. [1998] J. Comp. Neurol. 397:458-474).

Chapter 34 Cajal's prophetic functional considerations on respiratory reflexes: new questions about old answers

In the "Histology of the Nervous System" (Histologie, Spanish edition, 1899, 1904; French translation, 1909, 1911; all citations are from the American translation, 1995) Cajal did not only describe the origins and central pathways of cranial nerves but his detailed observations led him to numerous conclusions about the functional organization of brainstem reflexes. From studies of vagal and glossopharyngeal afferents he proposed a structural organization of the nucleus tractus solitarii (NTS). His view has been considerably changed by several authors on the basis of modern tracing studies. However, detailed histological examinations of functionally identified sensory fibers provided new understanding of a functional organization of the solitary nucleus that is very well in line with Cajal's original descriptions. The prophetic character of Cajal's concepts of structural-functional relations becomes even more evident by a reconsideration of his explanations of the reflexes underlying respiration, coughing and vomiting. Recent electrophysiological studies of spontaneously rhythmically active in vitro preparations have provided us with new insights in respiratory control. However, it appears that quite a number of Cajal's key questions concerning respiratory reflexes are still not solved. Therefore, a reconsideration of old and partly forgotten concepts might indeed provide a novel understanding of the structural and functional organization of brainstem reflexes.

Principles of linear and angular vestibuloocular reflex organization in the frog.

We compared the spatial organization patterns of linear and angular vestibuloocular reflexes in frogs by recording the multiunit spike activity from cranial nerve branches innervating the lateral rectus, the inferior rectus, or the inferior obliquus eye muscles. Responses were evoked by linear horizontal and/or vertical accelerations on a sled or by angular accelerations about an earth-vertical axis on a turntable. Before each sinusoidal oscillation test in darkness, the static head position was systematically altered to determine those directions of horizontal linear acceleration and those planes of angular head oscillation that were associated with minimal response amplitudes. Inhibitory response components during angular accelerations were clearly present, whereas inhibitory response components during linear accelerations were absent. Likewise was no contribution from the vertical otolith organs (i.e., lagena and saccule) observed during vertical linear acceleration. Horizontal linear acceleration evoked responses that originated from eye muscle-specific sectors on the contralateral utricular macula. The sectors of the inferior obliquus and lateral rectus muscles on the utricle had an opening angle of 45 and 60 degrees, respectively and overlapped to a large extent in the laterorostral part of the utricle. Both sectors were coplanar with the horizontal semicircular canals. The sector of the inferior rectus muscle was narrow (opening 5 degrees), laterocaudally oriented, and slightly pitched up by 6 degrees. Angular acceleration evoked maximal responses in the inferior obliquus muscle nerve that originated from the ipsilateral horizontal and the contralateral anterior vertical canals in a ratio of 50:50. Lateral rectus excitation originated from the contralateral horizontal and anterior vertical semicircular canals in a ratio of 80:20. The excitatory responses of the inferior rectus muscle nerve originated exclusively from the contralateral posterior vertical canal. Measured data and known semicircular canal plane vectors were used to calculate the spatial orientation of maximum sensitivity vectors for the investigated eye muscle nerves in semicircular canal coordinates. Comparison of the directions of maximal sensitivity vectors of responses evoked by linear or angular accelerations in a given eye muscle nerve showed that the two vector directions were oriented about orthogonally with respect to each other. With this arrangement the linear and the angular vestibuloocular reflex can support each other dynamically whenever they are co-activated without a change in the spatial response characteristics. The mutual adaptation of angular and linear vestibuloocular reflexes as well as the differences in their organization described here for frogs may represent a basic feature common for vertebrates in general.

Neck muscle responses to abrupt vertical acceleration in the seated human.

The control of neck muscle during marked changes in "g" loading must be to protect head-trunk orientation. However, little is known about the organization of reflexes. We therefore investigated the shortest latency in neck muscle evoked by abrupt ascending and descending vertical acceleration with a stroke of 20 cm and peak acceleration 0.4xg in six healthy subjects. The subjects were seated upright and restrained on a chair driven by a hydraulic servo system. Ascent induced small responses in sternocleidomastoid muscles (SCMs) with a latency of 24.0 ms (SE 1.7) from onset of head acceleration, followed by larger responses of 100 ms in duration. In comparison the responses in SCMs evoked by descent were significantly delayed, with greater interindividual variations at 44.1 ms (SE 3.1) and smaller in amplitude than responses in ascent. Latencies were consistent and showed no habituation. In order to eliminate stretch components, we measured the neck responses to vertical acceleration with the head fixed by cervical collar. The latency of the fast response of SCM evoked by ascent was not significantly different from the latency of SCMs without the collar. These results may indicate that the fast responses of SCMs to sudden ascent may be composed of a vestibular-collic reflex for making the neck and head rigid for defense to sudden gravitational change.

Modular organization of excitatory and inhibitory reflex receptive fields elicited by electrical stimulation of the foot sole in man

Objectives: The present study aimed to investigate how the inhibitory and excitatory reflex components of the human (polysynaptic) withdrawal reflex are organized depending on the stimulation site. The reflexes were elicited during a voluntary pre-contraction (between 10 and 20% of maximum voluntary contraction) of two antagonistic muscles. Methods: Inhibitory and excitatory reflex receptive fields to tibialis anterior (TA) and soleus (SO) were mapped in 14 healthy subjects using randomized electrical stimulation at 16 sites of the foot sole. Low, non-painful (3× perception threshold), and high, painful (1.5× pain threshold), stimulus intensities were used. Results: The inhibitory reflex receptive fields were organized in a highly functional manner supporting the action of the excitatory reflex. Together the two reflexes result in an optimal withdrawal from the stimulus. Low stimulation intensity was found sufficient to elicit the inhibitory reflex. High stimulation intensity caused a reversal of the inhibition to excitation in tibialis anterior. In soleus the inhibition was facilitated for stronger intensities. Conclusion: In conclusion, findings in animals of a modular organization of inhibitory reflexes are reproduced in humans.

Reflex patterns in preganglionic sympathetic neurons projecting to the superior cervical ganglion in the rat

Reflex patterns in preganglionic neurons projecting in the cervical sympathetic trunk (CST) were analyzed in response to stimulation of various afferent systems. We focused on the question whether these preganglionic neurons can be classified into functionally distinct subpopulations. Reflex responses were elicited by stimulation of trigeminal and spinal nociceptive, thermoreceptive as well as baroreceptor and chemoreceptor afferents. Multi- and single fiber preparations were studied in baroreceptor intact and sino-aortically denervated animals. Spontaneous activity of 36 preganglionic single neurons ranged from 0.2 to 3.5 imp/s (median=1.11 imp/s). The degree of cardiac rhythmicity (CR) in the activity of sympathetic neurons was 69.5±13% (mean±S.D.; N=52; range=39–95%). Noxious stimulation of acral skin activated the majority (67%) of sympathetic preparations by 37±25% ( N=35) above pre-stimulus activity; 15% were inhibited. In these neurons the response to noxious stimulation of acral skin was significantly correlated with the degree of CR ( P<0.001, N=52) in that neurons showing the strongest excitation to noxious stimulation displayed the strongest CR. Noxious mechanical stimulation of body trunk skin ( N=60) inhibited the majority (80%) of fiber preparations tested (by 34±18% of pre-stimulus activity, N=48); an activation was not observed. Cold stimulation of acral ( N=9) and body trunk skin ( N=42) activated most fiber preparations. Trigeminal stimulation evoked a uniform reflex activation of preganglionic neurons (+79±73% of pre-stimulus activity, N=32). Chemoreceptor stimulation by systemic hypercapnia elicited inhibitory (−31±19%, N=8) as well as excitatory (+59±5%, N=4) responses. These results show that preganglionic sympathetic neurons projecting to target organs in the head exhibit distinct reflex patterns to stimulation of various afferent systems; however, a clear classification into different functional subgroups did not emerge. Furthermore, reflex patterns showed a segmental organization to noxious cutaneous stimulation of acral parts and body trunk reflecting a differential central integration of spinal afferent input. Compared with the cat the reflex organization of sympathetic neurons projecting to the head seems to be less differentiated in the anesthetized rat.

Trigemino‐facial reflex inhibitory responses in some lower facial muscles

The effects of electrical trigeminal stimulation on activated facial muscles were studied in 20 normal subjects in order to evaluate whether excitatory or inhibitory responses are present and to investigate whether the reflex organization is similar in all the facial muscles. No inhibition was observed in frontalis, orbicularis oculi, orbicularis oris, and mentalis muscles. By contrast, a clear suppression of electromyographic (EMG) activity (late silent period or SP2) was present in the levator labii superioris, depressor anguli oris, and depressor labii inferioris muscles, with a mean latency ranging from 41.8 to 50.2 ms, and a mean duration ranging from 27.5 to 40.9 ms. An early suppression of EMG activity (early silent period or SP1) was observed, with a latency of 16 to 20 ms and a duration of 10 ms, mainly in inferior perioral muscles. Our findings show a selective trigeminal inhibitory influence upon some specific lower facial muscles. © 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 939–945, 2000

Trigemino-facial reflex inhibitory responses in some lower facial muscles

The effects of electrical trigeminal stimulation on activated facial muscles were studied in 20 normal subjects in order to evaluate whether excitatory or inhibitory responses are present and to investigate whether the reflex organization is similar in all the facial muscles. No inhibition was observed in frontalis, orbicularis oculi, orbicularis oris, and mentalis muscles. By contrast, a clear suppression of electromyographic (EMG) activity (late silent period or SP2) was present in the levator labii superioris, depressor anguli oris, and depressor labii inferioris muscles, with a mean latency ranging from 41.8 to 50.2 ms, and a mean duration ranging from 27.5 to 40.9 ms. An early suppression of EMG activity (early silent period or SP1) was observed, with a latency of 16 to 20 ms and a duration of 10 ms, mainly in inferior perioral muscles. Our findings show a selective trigeminal inhibitory influence upon some specific lower facial muscles.