Organization Of Reflexes Research Articles

A survey of spinal dorsal horn neurones encoding the spatial organization of withdrawal reflexes in the rat.

The withdrawal reflex pathways to hindlimb muscles have an elaborate spatial organization in the rat. In short, the distribution of sensitivity within the cutaneous receptive field of a single muscle has a spatial pattern that is a mirror image of the spatial pattern of the withdrawal of the skin surface ensuing on contraction in the respective muscle. In the present study, a search for neurones encoding the specific spatial input-output relationship of withdrawal reflexes to single muscles was made in the lumbosacral spinal cord in halothane/nitrous oxide-anaesthetized rats. The cutaneous receptive fields of 147 dorsal horn neurones in the L4-5 segments receiving a nociceptive input and a convergent input from A and C fibres from the hindpaw were studied. The spatial pattern of the response amplitude within the receptive fields of 118 neurones was quantitatively compared with those of withdrawal reflexes to single muscles. Response patterns exhibiting a high similarity to those of withdrawal reflexes to single muscles were found in 27 neurones located in the deep dorsal horn. Twenty-six of these belonged to class 2 (responding to tactile and nociceptive input) and one belonged to class 3 (responding only to nociceptive input). None of the neurones tested (n = 20) with reflex-like response patterns could be antidromically driven from the upper cervical cord, suggesting that they were spinal interneurones. With some overlap, putative interneurones of the withdrawal reflexes to the plantar flexors of the digits, the plantar flexors of the ankle, the pronators, the dorsiflexors of the ankle, and a flexor of the knee, were found in succession in a mediolateral direction.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence of positive force feedback among hindlimb extensors in the intact standing cat

1. The functional organization of heterogenic reflexes produced by activation of extensor force receptors (Golgi tendon organs) was studied in intact cats during stationary stance. Intramuscular stimulation (200 Hz, 20 ms) of hindlimb extensor muscles via chronically implanted electrodes was used to evoke weak muscle contractions and naturally activate Golgi tendon organ Ib afferents while cats stood unrestrained with each paw on a moveable triaxial force plate. 2. Intramuscular stimulation of every hindlimb extensor muscle tested in this study evoked excitatory responses that were widely distributed among hindlimb extensor muscles. Source and target specializations in the functional organization of this positive force feedback system were also observed. For example, stimulation of ankle extensors typically excited extensors and flexors at the ankle and hip (but not knee), whereas stimulation of hip extensors typically excited only extensors at all three joints. In addition, intramuscular stimulation of either lateral (LG) or medial (MG) gastrocnemius consistently inhibited soleus while exciting other extensors at the ankle and more proximal joints. 3. The electromyographic (EMG) reflex responses described above are attributed to the natural (via muscle contraction) activation of extensor group Ib afferents. Direct activation of intramuscular afferents by the stimulus was unlikely because there was no evidence that Ia afferents, which have the lowest electrical thresholds, were activated. Both the observed inhibition of the synergist, soleus, and the excitation of the antagonist, tibialis anterior, produced by gastrocnemius stimulation are opposite to the reflex effects that would be produced at the ankle by activation of gastrocnemius Ia afferents.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatocardiovascular reflexes in anesthetized rats with the central nervous system intact or acutely spinalized at the cervical level

The effects of noxious mechanical stimulation of various segmental areas on heart rate and mean arterial blood pressure (MAP), as well as cardiac and renal sympathetic nerve activities were examined in anesthetized rats with the central nervous system (CNS) intact or acutely spinalized at the cervical level. In CNS-intact rats, pinching for 20 s applied to any segmental skin area, but particularly that of the paw, produced an increase in heart rate, blood pressure and the sympathetic nerve activities. In acutely spinalized rats, pinching the chest, abdomen and back of the body produced large increases, while hindlimb and perineum stimulation induced only a small increase or no increase in heart rate, blood pressure and the sympathetic nerve activities. Stimulation of the right side produced particularly large responses in heart rate and stimulation of the ipsilateral side produced large responses in cardiac and renal sympathetic nerve activities in spinalized rats. These results suggest the existence of the two types of reflex responses, supraspinal and propriospinal, in the somatocardiovascular reflex. The supraspinal one has characteristics of diffuse reflex organization, while; the propriospinal one has strong segmental and lateral organization.

Role of dopaminoreactive systems of the cortex and the neostriatum in the organization of situational conditioned reflexes.

The results of experiments on dogs with dysfunction of the dopaminoreactive system of the brain suggest the nonidenticality of its different divisions (cortical, striatal, mesencephalic) in the organization of situational conditioned reflexes. It was demonstrated that the nigrostriatal system is involved to a greater degree in the spatial analysis of signals, while the mesocortical system is more involved in the analysis of their biological significance. The dopaminoreactive system of the caudate nucleus is associated to a greater degree with the realization of cognitive, while that of the putamen is associated with the realization of motor programs of situational conditioned reflexes. The thesis of the necessity of the coordinated functioning of the DA-reactive systems for the organization of goal-directed behavior is substantiated.

Role of 5-hydroxytryptamine in gastrointestinal chemosensitivity

The present electrophysiological investigation examines the effect of 5-hydroxytryptamine (5-HT) on gastrointestinal afferent fiber discharge. 5-HT markedly and specifically stimulated vagal mucosal chemosensitive afferents. The response was mediated by 5-HT3 receptors as demonstrated by the action of 2-methyl-5-HT and antagonism by granisetron. At doses of granisetron that completely block the response to 5-HT, the afferent fibers still responded to both mechanical and chemical stimulation of the mucosa. This sensitivity of extrinsic afferents is in marked contrast to that reported for intrinsic afferents, suggesting fundamental differences in the organization of enteric and vagal reflexes.

Reinnervated muscles fail to produce stretch reflexes.

1. We studied the stretch-evoked reflex organization of hind limb muscles in two decerebrate cats 36 mo after unilateral section and immediate surgical repair of the common nerve supplying the lateral gastrocnemius (LG) and soleus (S) muscles. 2. The production of considerable reflex force by reinnervated muscles in response to electrical stimulation of uninjured nerves indicated substantial functional recovery of motor units. However, reduction in the responsiveness of reinnervated muscles to stretch of the untreated medial gastrocnemius (MG) muscle indicated some deficit in recovery of normal synaptic integration. 3. Stretch failed to elicit autogenic excitation of the reinnervated S and LG. This failure was observed whether the reinnervated muscles were quiescent or contracting in other reflexes. 4. The heterogenic reflex organization of reinnervated muscles was abnormal. Stretch of the reinnervated S failed to evoke heterogenic reflexes both in the untreated MG and in the reinnervated LG. Stretch of the reinnervated LG failed to produce excitation of MG. 5. These findings demonstrate deficiencies in proprioceptive feedback from reinnervated muscles and lead us to expect incomplete recovery of motor function after nerve section.

Computational modeling of neuronal dynamics for systems analysis: application to neurons of the cardiorespiratory NTS in the rat

The study constructs computational models of neurons in order to examine the contribution that their response dynamics may make to functional properties at the system level. As described in the accompanying study, neurons in the cardiorespiratory nucleus tractus solitarii (NTS) of the rat were recorded in vitro. When these cells were intracellularly injected with a constant current pulse, spike discharge patterns and subthreshold voltage trajectories were observed that were time- and voltage-dependent. The accompanying manuscript describes these dynamic responses in 4 classes of putative second-order cells that appear to receive direct primary afferent input, and a previous paper described two populations of rhythmically firing interneurons, one of which is intrinsically auto-active. In the present manuscript experimental neuronal voltage response data was collected across a current injection series for the S3 neuron type described in the accompanying study and for the auto-active neuron described previously. Using this data, computational model neurons have been constructed for these two neurons by using membrane ion channels to produce and match the observed neuronal voltage behavior. The channels were those implicated in the dynamic responses observed in the companion study, and include gNa fast , gK dr , gK A , gK Ca , gK AHP , gK M , gCa T and gCa L . The description of channel kinetics follows the Hodgkin-Huxley form. Different neuronal sources from the literature of channel kinetics were investigated and assembled into a ‘channel kinetics library’ from which both neuron models were tuned, primarily by adjusting the maximum channel densities, g¯, and time-dependence of kinetics. Methods are described for tuning the channel kinetics library to match various physiological responses. This approach created neuron models that were able to closely replicate the observed complex voltage and spiking responses of the two very different cardiorespiratory NTS neurons. The interaction of voltage- and calcium-dependent conductances were analyzed for their functional contributions by tuning their kinetics. Specific parameters are given that account for the behavior of each model. Sensitivity analyses by perturbing K Ca and K A are are shown for both neurons, and I/F curves are presented for the auto-active neuron's simulated and recorded responses. The potential systems-level functional implications resulting from the different kinetics is demonstrated by driving the S3 model neuron in simulation with the pattern of input produced by model primary baroreceptor afferents. The limitations and significance of this approach are discussed. The present study of model neurons are being extended to the larger family of neurons found in the cardiorespiratory NTS (e.g. S1, S2 and S4), are being related to the baroreceptor vagal reflex by in vivo studies, and are being used to explore systems level computation, for example by creating networks reflecting baroreceptor reflex organization. The present kinetics library in principle could be used in this way for other neuronal systems.

Wolff Award 1992. Exteroceptive suppression of temporalis muscle activity in patients with chronic headache and in normal volunteers: methodology, clinical and pathophysiological relevance.

Exteroceptive suppression of temporalis muscle activity was studied in patients with chronic headache and in healthy controls. Among different methods of recording, averaging 10 full-wave rectified EMG responses produces results with acceptable variability and discomfort. The late temporalis exteroceptive suppression period (ES2) is reduced on average in patients with chronic tension-type headache; this finding has been reproduced by several independent laboratories. Mean duration of temporalis ES2 is also diminished, but to a lesser degree, in daily drug abuse headache and, as shown by others, in episodic tension-type headache. It is normal in migraine between attacks, cluster headache and various types of symptomatic headaches. Temporalis ES2 may be decreased in untreated patients with major depression. In healthy volunteers, temporalis ES2 duration is reduced by a short-lasting painful stimulus to peripheral limbs after a delay of 50 to 60 ms, and by a sub-motor threshold electromagnetic stimulation to the contralateral cerebral cortex after a delay of 20 to 30 ms. In contrast, long-lasting trains of peripheral painful stimuli have no effect. Various pharmacological agents are able to modify temporalis ES2. Its duration is increased by 5-HT antagonists, but decreased by 5-HT uptake blockers. Pharmacological effects may differ between controls and patients. Considering these results and available data on the anatomo-functional organization of masticatory reflexes, we postulate that temporalis ES2 is a marker of the excitability of interneuronal nets in the ponto-medullary reticular formation. In chronic tension-type headache, excitability of these interneurons is decreased because of inadequate control by the serotonergic raphe magnus nucleus and the periaqueductal gray matter. Dysfunctioning of the latter structures might be caused by abnormal limbic inputs to the brain stem. Some steps of this pathophysiological hypothesis can be verified by modern neurophysiological techniques.

Neuronal specificity and plasticity in the autonomic nervous system

The autonomic nervous system is divided into the sympathetic, parasympathetic and enteric subdivisions. The present review is focussed upon the highly specialized reflex organization and neurochemistry of sympathetic parasympathetic neurons. The currently available informations allow to conclude that autonomic control of each peripheral target tissue is specifically regulated under normal conditions but nevertheless able to respond to altered conditions by changes in neural activity and mediator expression.

Functional organization of the nociceptive withdrawal reflexes

The spatial organization of the cutaneous input to hindlimb withdrawal reflexes was studied in spinalized, decerebrated, unanesthetized rats. Reflex activity in plantar flexors of the digits, pronators of the foot, dorsiflexors of the digits, and/or the ankle and flexors of the knee was recorded with electromyographic techniques for up to 12 h after spinalization. Graded mechanical (pinch) and thermal stimulation (CO2 laser) of the skin were used. Reflexes were absent ("spinal shock") during approximately 10-20 min after spinalization. The reflex thresholds for pinch and CO2 laser stimulation then decreased considerably during the following 5-8 h. After this time, even mild pressure (less than 0.1 N/mm2) on the skin was sufficient to evoke a reflex in most muscles. During the period from about 0.5-3 h after spinalization, the nociceptive receptive field of each muscle usually corresponded to the area of the skin withdrawn by the muscle. Maximal responses were evoked from the area of the receptive field maximally withdrawn. During this period, responses to innocuous pinch were evoked mainly from the most sensitive area of the receptive fields. Concomitant with the decrease in reflex thresholds, the nociceptive receptive fields expanded for all muscles, often to include areas of the skin not withdrawn by the muscles. For most muscles, reflexes on tactile stimuli were eventually elicited from the entire receptive fields. The receptive fields for thermonociceptive and mechanonociceptive inputs were similar in most muscles. The interossei muscles were exceptional in that they responded very weakly to thermal stimulation. It is concluded that there are neuronal networks in the spinal cord that translate cutaneous nociceptive and tactile input into a withdrawal. However, the control exerted by descending pathways is necessary to maintain a functionally adequate excitability in these reflex pathways and an appropriate size for their receptive fields.

Segmental reflex organization in endurance-trained athletes and untrained subjects

In an effort to investigate the effects of training on spinal reflex pathways in humans, we measured the isometric force-time curve of the patellar (PTR) and Achilles (ATR) tendon-tap reflex in 12 endurance-trained (ET) athletes and 12 control (C) subjects. We also conditioned the tendon jerk with a contralateral or ipsilateral tendon-tap stimulus, to ascertain the effects of segmental inputs on crossed-spinal reflex activity. The conditioning stimulus preceded the test reflex by 25, 40, 55, 70, 85, 100, 115, 130, or 145 ms. The results demonstrated significant differences in control reflexes and conditioned reflexes between the two groups. A contralateral patellar tendon-tap produced a significantly greater excitatory effect to the contralateral quadriceps motoneurons for the ET group, whereas a contra- or ipsilateral conditioning caused a significantly greater inhibitory effect to the triceps surae motoneurons for the ET athletes. These results demonstrate that motoneuron excitability changes can be produced as a result of ipsi- and contralateral segmental inputs, and raise the possibility that trained athletes demonstrate different reflex recovery profiles. Several neurophysiological mechanisms are proposed to contribute to these changes.

Participation of glutamatergic and dopaminergic systems of the neostriatum in the organization of alimentary conditioned reflexes.

In this study the results of behavioral, neurophysiological, and morphological investigations in relation to the participation of the corticostriatonigral system in the organization of conditioned reflexes are presented. It was demonstrated in experiments on dogs that blockade of N-methyl-D-aspartate receptors of the caudate nucleus disrupts the realization of consolidated conditioned reflexes and renders their development more difficult. The blockade of quisqualate receptors facilitates the process of differentiation. Switching off of the dopaminergic input makes the development of positive conditioned reflexes more difficult. The reversible switching off of the substantia nigra leads to the reorganization of the neuronal activity of the caudate nucleus in response to the presentation of the conditional signal. Inhibitory nigral influences are directed primarily to the ventromedial divisions of the nucleus, while activating influences are directed to its dorsal segments. The topically organized connections of the motor regions of the cortex with the dorsal region of the caudate nucleus, and of the limbic regions with its ventromedial divisions were studied in morphological investigations on cats. A certain distinctiveness was identified of the spatial organization of the nigrostriatal projections. The data obtained are discussed from the point of view from the systemic organization of behavior.

Spatial organization of linear vestibuloocular reflexes of the rat: responses during horizontal and vertical linear acceleration

1. The spatial properties of linear vestibuloocular reflexes (LVOR) were studied in pigmented rats in response to sinusoidal linear acceleration on a sled. The orientation of the animal on the sled was altered in 15 degrees steps over the range of 360 degrees. Horizontal, vertical, and torsional components of eye movements were recorded with the magnetic field search coil technique in complete darkness. Conjugacy of the two eyes was studied in the horizontal movement plane. 2. Acceleration along the optic axis of one eye (approximately 50 degrees lateral) induced maximal vertical responses in the ipsilateral eye and, at the same time, maximal torsional responses in the contralateral eye. These vertical and torsional responses of the LVOR coincide with those obtained when the respective coplanar vertical semicircular canals are stimulated. Such a congruence suggests a common reference frame for LVOR and angular vestibuloocular reflexes (AVOR), with the result that direct combination of signals indicating apparent and real head tilt is facilitated. 3. Transformations of vertical and torsional responses into head coordinates (pitch and roll) show that these movements are compensatory in direction for any combination of apparent head tilt in pitch and roll planes. 4. Gain (rotation of the eye/apparent rotation of the gravity direction) was approximately 0.3 at 0.1 Hz and decreased to approximately 0.1 at 1.0 Hz. Vertical responses tended to have a larger gain than torsional responses. Phase lag relative to peak acceleration increased from about -9 degrees to about -47 degrees over the same frequency range. 5. Vertical linear acceleration evoked only vertical eye movements at a frequency of 1.0 Hz. 6. Horizontal responses of both eyes were symmetric or asymmetric in amplitude and in-phase (conjugate) or out-of-phase (disconjugate) with respect to each other, depending on the direction of linear acceleration. Translation in the transverse direction evoked conjugate compensatory horizontal responses. Forward-backward translation evoked movements of both eyes that were symmetric in amplitude, but 180 degrees out-of-phase. Translation along diagonal axes evoked almost no horizontal responses in the eye facing in the direction of linear motion but maximal horizontal responses in the eye facing away from the direction of linear motion. These disconjugate movements resulted in a modulation of the vergence angle of the eyes. 7. Disconjugate horizontal responses in darkness are best explained by the assumption that part of the visual consequences of a translational head displacement (i.e., change of viewing distance in light) is taken into account centrally.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential synaptic effects on physiological flexor hindlimb motoneurons from cutaneous nerve inputs in spinal cat

1. We previously demonstrated in the spinal cat that superficial peroneal cutaneous nerve stimulation produced strong reflex contraction in tibialis anterior (TA) and semitendinosus (St) muscles but unexpectedly produced mixed effects in another physiological flexor muscle, extensor digitorum longus (EDL). The goal of the present study was to further characterize the organization of ipsilateral cutaneous reflexes by examining the postsynaptic potentials (PSPs) produced in St, TA, and EDL motoneurons by superficial peroneal and saphenous nerve stimulation in decerebrate, spinal cats. 2. In TA and St motoneurons, low-intensity cutaneous nerve stimulation that activated only large (A alpha) fibers [i.e., approximately 2-3 times threshold (T)], typically produced biphasic PSPs consisting of an initial excitatory phase and subsequent inhibitory phase (EPSP, IPSP). Increasing the stimulus intensity to activate both large (A alpha) and small (A delta) myelinated cutaneous fibers supramaximally (15-45 T) tended to enhance later excitatory components in TA and St motoneurons. 3. In EDL motoneurons, 2-3 T stimulation of the superficial peroneal nerve evoked initial inhibition (of variable magnitude) in 7/10 EDL motoneurons tested, with either excitation (n = 2) or mixed effects (n = 1) observed in the remaining EDL motoneurons. Saphenous nerve stimuli produced excitation either alone, or preceded by an inhibitory phase in EDL. Increasing the stimulus intensity enhanced later inhibitory influences from superficial peroneal and excitatory influences both from superficial peroneal and saphenous nerve inputs in EDL motoneurons. 4. Short-latency (less than 1.8 ms) EPSPs were observed in a few motoneurons in all reflex pathways examined, except for EPSPs in EDL motoneurons evoked by saphenous stimulation. IPSPs with central latencies less than 1.8 ms were also produced by both saphenous (TA, n = 1; EDL, n = 2) and superficial peroneal (EDL, n = 4) nerve stimulation. 5. The results, in comparison with other reports employing spinal and nonspinal preparations, suggest that removal of influences from higher centers reveals inhibitory circuits from the superficial peroneal and saphenous nerves to EDL motoneurons in the spinal preparation. The inhibitory inputs observed are thought to reflect the activation of "specialized" reflex pathways. Additionally, the demonstration of short-latency EPSPs and IPSPs suggest that the minimal linkage in both the excitatory and inhibitory cutaneous reflex pathways examined is disynaptic. The results are discussed in relation to previous studies on classically conditioned flexion reflex facilitation in spinal cat.

Organization of Segmental Reflexes in Trained Dancers

Unilateral and conditioned Achilles tendontap reflex (ATR) characteristics were examined in a group of skilled dancers and a group of sedentary, untrained subjects (n = 7/group). For the conditioned reflex, the right ATR was conditioned by a tap to the left Achilles tendon using intervals of 10, 40, 70, 100, 130, 160 and 190 ms. Peak isometric force, contraction time and half-relaxation time were examined on each trial. The results indicated that the trained dancers exhibited less unilateral isometric force and longer half-relaxation times (p less than 0.05) than the untrained subjects. Moreover, the contralateral conditioning stimulus caused a more marked short-latency facilitation as well as a long-latency inhibition in the reflex force characteristics for the trained dancers when compared with the untrained subjects. These differences in both simple and conditioned reflexes in individuals trained for dance activities may reflect differences in muscle stiffness, tissue compliance or neural organization.

Plasticity of sympathetic reflex organization following cross-union of inappropriate nerves in the adult cat.

1. The present study has investigated the reflex organization of sympathetic neurones and its control of autonomic effector organs following nerve injury and repair. A well-defined population of vasoconstrictor neurones supplying blood vessels of the hairy skin was forced to innervate a territory that contained some appropriate, but mainly inappropriate autonomic effector organs. For this purpose the central stump of the cut sural nerve was sutured to the peripheral stump of the cut tibial nerve 11-12 months prior to the terminal experiment. 2. The activity of postganglionic sympathetic neurones was recorded from fine strands of the sural nerve proximal to the nerve lesion. Using a laser-Doppler device cutaneous blood flow was measured in the hairless skin of the hindpaw that was now reinnervated by the sural nerve. The results show a qualitative change of the reflex organization of sympathetic neurones following cross-union of these nerves. 3. Stimulation of arterial chemoreceptors by ventilating the animals with a hypoxic gas mixture (8% O2 in N2 for 3-8 min) increased the activity in twelve out of thirteen strands containing postganglionic sympathetic fibres. The increase of sympathetic activity contrasts with results from normal animals where systemic hypoxia causes a reflex decrease of activity in postganglionic fibres of the sural nerve. 4. Reflex changes of sympathetic activity were closely followed by corresponding changes of cutaneous blood flow. Systemic hypoxia produced vasoconstriction in operated animals in contrast to the vasodilatation observed in normal animals. 5. We conclude that the reflex organization of sympathetic neurones can change qualitatively following nerve lesion when sympathetic neurones regenerate and supply inappropriate target tissues. This long-lasting change reflects the plasticity of the autonomic nervous system and can produce a sustained abnormal control of reinnervated autonomic effector organs.

Functional organization of the nociceptive withdrawal reflexes

1. The organization of the nociceptive hindlimb withdrawal reflexes was investigated in 93 halothane/nitrous oxide anesthetized rats. Electromyographical techniques were used to record reflex activity in single motor units. 2. Most of the hindlimb muscles were activated by noxious mechanical stimulation of the skin of the ipsilateral hindlimb. These were the plantar flexors of the digits, the pronators of the paw, the dorsiflexors and the plantar flexors of the ankle, the flexors of the knee, the flexors of the hip and the adductors. By grading the stimulus intensity it was shown that all these muscles received input from cutaneous nociceptors. 3. Noxious stimulation of the skin failed to activate the obturator, knee extensors and m. tibialis posterior and, in most rats tested, m. semimembranosus and m. adductor magnus. The plantar flexors of the ankle, while exhibiting a clear nocireceptive field in all rats tested, had a high threshold and responded much more weakly than the dorsiflexors of the ankle. Thus, responses in muscles which oppose gravity in the standing position were either very weak or absent. 4. The present study shows that each of the activated hindlimb muscles has a highly organized nocireceptive field on the skin, which is related to the withdrawal movement caused by the muscle itself. Each of the muscles normally causes the withdrawal of its receptive field when the foot is on the ground. The skin area most effectively withdrawn, in this situation, corresponds to the most sensitive area of the nocireceptive field. However, with the exception of the plantar flexors of the digits and/or the ankle, each of the hindlimb muscles also withdraws the major parts of their receptive fields when the foot is off the ground. The locations of the nocireceptive fields were independent of the position of the hindlimb. These characteristics of the nociceptive withdrawal reflexes are the basis for their "local sign" (Sherrington 1906). 5. The threshold and the time course of reflex activation were different in different muscles. However, muscles with a similar action; the plantar flexors of the digits, the pronators of the paw, the dorsiflexors of the digits, the flexors of the knee and the adductors, respectively, had similar thresholds and time courses. Furthermore, the threshold and latency of activation of each muscle increased towards the border of its nocireceptive field, reflecting a decreasing sensitivity. These findings explain the progressive recruitment of muscles during increasing strength of noxious stimulation, termed "irradiation" (Sherrington 1906).(ABSTRACT TRUNCATED AT 400 WORDS)

Neuronal influence on intestinal transport

Reflex activation of the enteric nervous system (ENS) from the intestinal lumen and also from the serosa induces intestinal secretion. Thus mechanical distention, cholera toxin, heat-stable enterotoxin from E. coli, bile acids, mucosal inflammation and chemical peritonitis all induce an intestinal secretion that is inhibited by 60-100% by nerve-blocking agents. As a result of a large number of in vitro and in vivo studies, a picture of the organization of the secretory enteric nervous reflexes is now emerging. In secretory states with preserved intact intestinal epithelium, it is proposed that the reflex activation occurs via stimulation of receptor cells, i.e. epithelial endocrine cells such as EC and N-cells, which release peptides/amines into the interstitial space and thereby activate nerves close to the epithelium. The afferent neurones appear to transfer the reflex to the myenteric plexus, probably by using tachykinins as transmitters. This is in agreement with a superior and co-ordinating role for the myenteric plexus in the control of intestinal function by the ENS. Interneurones in turn mediate the transmission of the nerve signal to the submucosal plexus and the efferent neurones via cholinergic, nicotinic postganglionic receptors. The transmitters at the effector cells are acetylcholine and probably VIP.

Effects of flexor reflex afferent stimulation on the soleus H reflex in patients with a complete spinal cord lesion: evidence for presynaptic inhibition of Ia transmission

The effects of electrically stimulating the Flexor Reflex Afferent (FRA) on the soleus H reflexes were investigated in 34 paraplegic patients having a clinically complete spinal cord lesion. Conditioning stimuli (5-50 mA) were applied to the ipsilateral or contralateral sural nerve. The conditioning-test interval ranged from 20 to 1000 ms. A late ipsilateral flexor reflex (EMG) was found in all patients. A late contralateral extension reflex was sporadically observed in only 3 patients. The excitability curves usually showed two phases of ipsilateral H reflex inhibition and contralateral H reflex facilitation, one between 50 and 130 ms and the other after over 200 ms. These intervals correspond to early and late flexion reflexes. With high intensity stimulation the early and late ipsilateral inhibition fused. An early low threshold ipsilateral facilitation occurred in 9 patients. The contralateral late facilitation was followed by prolonged inhibition in 10 patients. Changes in presynaptic inhibition were assessed by measuring the heteronymous monosynaptic Ia facilitation from quadriceps to soleus. For methodological reasons, it was only possible to investigate the effect of contralateral conditioning volleys which was performed in 5 patients. A significant and regular reduction of the heteronymous Ia facilitation was found in 4 patients. The reduction is taken to indicate that the FRA evokes presynaptic inhibition of Ia transmission to alpha motoneurones. Presynaptic inhibition was also indicated by the enhancement of a vibratory stimulus induced inhibition in 2 subjects. These results are consistent with the hypothesis that the reflex organization in patients with a spinal cord section is similar to that of the acute spinal cat injected with DOPA.

The participation of mediator and peptidergic systems of the brain in conditioned reflex mechanisms

New data on the significance of mediator and peptidergic systems of the striatal level in the organization of alimentary conditioned reflexes are presented in this report. The role of acetylcholine-, dopamine-, GABA-and P-ergic systems of the caudate nucleus and the amygdala in the realization of positive and negative conditioned reflexes was investigated. The experiments were carried out on dogs with chemotrodes and microelectrodes implanted in subcortical structures. The results of the experiments with microinjections of the relevant substances into individual subcortical structures showed that activation of the same mediator system in various structures may lead to both unidirectional and multidirectional behavioral effects. On the other hand, the activation of various subcortical mediator systems can lead to identical changes in conditioned reflex activity. The effect of the administration of activators or blockers of a subcortical mediator system depends in many ways on the functional state of the nervous system at the moment of administration and on the localization of the microinjection. It is difficult to predict beforehand the role of various subcortical structures in the organization of integrated behavioral acts. The question of the necessity of studying mediator and peptidergic systems of each subcortical structure in order to understand their significance in the mechanisms of the conditioned reflex is raised.