Reflex mechanisms of interlimb interrelationships displayed in lumbar flexor centers of the cat spinal cord]

Interaction of segmental, propriospinal and spino-bulbo-spinal components of the lumbar flexor reflexes evoked by activation of the hind-and forelimb afferents with paired stimuli was studied in anesthetized cats. Coincidence in time of a reflex discharge evoked by stimulation of the forelimb afferent nerves with monosynaptic hindlimb flexor reflex causes considerable facilitation of the latter. The monosynaptic reflex increases for 40-50 ms. tthe polysynaptic flexor reflexes of segmental, propriospinal and spino-bulbo-spinal origin act upon each other in both a facilitatory and an inhibitory manner. Facilitation takes place only during the period of coincidence of the responses, inhibition when the responses are separated in time. Three types of inhibition with duration of 7-15, 40-150, 300-500 ms were observed. Possible neuronal mechanisms of interaction of the above-mentioned responses and their role in the inter limb interrelations are discussed     

Somato-vesical reflexes in chronic spinal cats

The effects of afferent volleys in hindlimb cutaneous and muscle nerves on vesical tone and contractility and on the discharges in pelvic nerves to the bladder were measured in anesthetized CNS-intact and 2-19 months chronic spinal cats. In chronic spinal cats volleys in group III and IV fibers increased the tone of the quiet, empty bladder (excitatory somato-vesical reflex). The same volleys inhibited the slow, large, rhythmic micturition contractions of the expanded bladder (inhibitory somato-vesical reflex). In CNS intact cats single or short tetanic volleys induced a reflex discharge in pelvic vesical nerve branches with 3 distinct components. These reflexes could be observed during micturition contractions, not markedly between the contractions or when the bladder was empty and quiet. The latencies of the 3 components were 90, 320 and 770 ms, respectively. The two early components (AI- and A2-reflex) were evoked by volleys in group II and III hindlimb afferents. The late component (C-reflex) was induced by group IV volleys. In chronic spinal cats a group II and III-induced A-reflex (latency 90 ms) and a group IV-induced C-reflex (latency 340 ms) were observed. The central pathways and the physiological significance of the various somato-vesical reflexes are discussed.     

Functional organization of the spinal reflex pathways from forelimb afferents to hindlimb motoneurons in the cat. II. Conditions of the interneuronal connections

The interneuronal conditionsof the descending pathways from forelimb afferents to hindlimb motoneurones were investigated by testing spatial interactions in these pathways and between these pathways and segmental lumbar reflex pathways. In high spinal unanaesthetized cats hindlimb motoneuroneswere intracellularly recorded and spatial interactions were tested between effects evoked by stimulation of pairs of ipsi- and contralateral forelimb nerves or pairs of a forelimb and an ipsilateral hindlimb nerve. The excitatory and late inhibitory pathways from forelimb afferents projecting to most of the hindlimb motoneurone pools, showed an interactive pattern which was distinctly different to the fast inhibitory pathway projecting specifically for ipsilateral forelimb afferents to flexor digitorum and hallucis longus (FDHL) motoneurones. Stimulation of homonymous or heteronymous pairs of two forelimb nerves of both sides evoked generally a distinct spatial facilitation of the excitatory and late inhibitory effects, while the specific early IPSPs to FDHL motoneurones were not facilitated. Paired stimulation of two forelimb nerves of one side only produced spatial facilitation of EPSPs or late IPSPs if low strength stimuli were used, using higher strength which induced larger effects, generally caused occlusion instead. In case of large IPSPs this may be due to the vicinity to the equilibrium potential. Except for an inhibition of cutaneous reflex pathways, the spatial interaction of the excitatory and late inhibitory pathways onto segmental lumbar reflex pathways was weak and variable. The fast inhibitory pathway to FDHL motoneurone showed a partial spatial facilitatory interaction with lumbar reflex pathways from cutaneous and group II muscle afferents. The second IPSP wave evoked by this pathway was inhibited by antidromic stimulation of the ventral root L7S1 and of the α-efferents of the antagonistic peroneal nerve. From the results conclusions are drawn on the interneuronal organization of the descending pathways from forelimb afferents to hindlimb motoneurones.     

Functional organization of the spinal reflex pathways from forelimb afferents to hindlimb motoneurones in the cat. II. Conditions of the interneuronal connections

The interneuronal conditions of the descending pathways from forelimb afferents to hindlimb motoneurones were investigated by testing spatial interactions in these pathways and between these pathways and segmental lumbar reflex pathways. In high spinal unanaesthetized cats hindlimb motoneurones were intracellularly recorded and spatial interactions were tested between effects evoked by stimulation of pairs of ipsi- and contralateral forelimb nerves or pairs of a forelimb and an ipsilateral hindlimb nerve. The excitatory and late inhibitory pathways from forelimb afferents projecting to most of the hindlimb motoneurone pools, showed an interactive pattern which was distinctly different to the fast inhibitory pathway projecting specifically from ipsilateral forelimb afferents to flexor digitorum and hallucis longus (FDHL) motoneurones. Stimulation of homonymous or heteronymous pairs of two forelimb nerves of both sides evoked generally a distinct spatial facilitation of the excitatory and late inhibitory effects, while the specific early IPSPs to FDHL motoneurones were not facilitated. Paired stimulation of two forelimb nerves of one side only produced spatial facilitation of EPSPs or late IPSPs if low strength stimuli were used, using higher strength which induced larger effects, generally caused occlusion instead. In case of large IPSPs this may be due to the vicinity to the equilibrium potential. Except for an inhibition of cutaneous reflex pathways, the spatial interaction of the excitatory and late inhibitory pathways onto segmental lumbar reflex pathways was weak and variable. The fast inhibitory pathway to FDHL motoneurones showed a partial spatial facilitatory interaction with lumbar reflex pathways from cutaneous and group II muscle afferents. The second IPSP wave evoked by this pathway was inhibited by antidromic stimulation of the ventral root L7S1 and of the alpha-efferents of the antagonistic peroneal nerve. From the results conclusions are drawn on the interneuronal organization of the descending pathways from forelimb afferents to hindlimb motoneurones.     

Influence of L-DOPA on transmission in long ascending propriospinal pathways in the cat

In high spinal cats the influence of an intravenous injection ofl-3,4,-dihydroxyphenylalanine (DOPA) has been investigated on the transmission of long ascending propriospinal pathways to certain groups of forelimb motoneurones. The early discharge evoked in pectoralis major and deep radial motoneurones on electrical stimulation of hindlimb afferents, which may be obtained in some high spinal preparations, is facilitated after DOPA. A late discharge (30–80 msec) appears after DOPA in the same forelimb motoneurones and may often last up to 600 msec or more. Facilitation by hindlimb nerves of forelimb mono- and polysynaptic reflexes is similarly prolonged. Ipsilateral hindlimb nerves are more effective than contralateral. Late discharges have also been evoked in forelimb motoneurones on stimulation of forelimb afferents after DOPA and it is concluded that a somewhat similar organization of late reflexes exists in brachial segments as previously reported by Jankowskaet al. in the lumbar cord.The influence of DOPA on long ascending propriospinal and forelimb reflexes is ascribed to excitation of the terminals of noradrenergic reticulospinal fibres. The reflex changes are considered to reflect activity in neuronal systems involved in the control of stepping in the cat.A further system modifying long ascending propriospinal transmission could be excited by stimulation of the ventral quadrant of the spinal cord at C₁. The effects on propriospinal transmission could outlast the stimulus by several tens of minutes.     

Functional organization of long ascending propriospinal pathways linking lumbo-sacral and cervical segments in the cat

In high spinal cats propriospinal pathways ascending from lumbo-sacral levels of the spinal cord can mediate strong excitatory and inhibitory changes in reflexes to different groups of motoneurones supplying muscles of the forelimb. Discharges evoked by electrical stimulation of hindlimb nerves could be evoked in 41% of experiments in the motoneurones of pectoralis major and minor. The latency of the discharge (8–18 msec) could be shortened by increasing the repetition frequency of the stimulus, the greatest reduction occurring in the range 1–4 Hz. Contralateral hindlimb nerves were less effective and the discharge generally occurred at a latency 1–2 msec longer than for ipsilateral nerves.Monosynaptic reflexes to pectoralis major and deep radial motoneurones supplying the physiological flexor muscles were strongly facilitated by hindlimb nerve stimulation, ipsilateral nerves being more effective than contralateral. Monosynaptic reflexes to latissimus dorsi showed a reciprocal pattern of conditioning, being depressed by ipsilateral and facilitated by contralateral hindlimb extensor nerves, the flexor nerves giving the reverse pattern. Monosynaptic reflexes to median and ulnar nerves supplying physiological extensor muscles were not significantly affected by hindlimb nerve conditioning.Polysynaptic reflexes to pectoralis major and deep radial motoneurones received initial strong facilitation followed by prolonged depression, ipsilateral hindlimb nerves being more effective than contralateral. In latissimus dorsi a reciprocal pattern similar to that for monosynaptic reflex testing was found. Polysynaptic reflexes to median and ulnar motoneurones received only prolonged depression.The hindlimb afferent nerves responsible for the discharge in forelimb motoneurones and for the facilitation and depression of forelimb reflexes include groups II and II muscle afferents and group II skin afferents, especially from quadriceps and sartorius muscles, and sural and superficial peroneal nerves, respectively.The ascending long propriospinal pathways are influenced bilaterally from hindlimb nerves and are located in the lower thoracic segments in the ventrolateral funiculus. The pathways mediate effects on ipsilateral and contralateral forelimb reflex systems, the ipsilateral projections being dominant. Part of the long ascending projection terminates monosynaptically on the motoneurones of pectoralis major. It is likely that group II afferents from ipsilateral quadriceps muscle activate the ascending tract monosynaptically and those from contralateral quadriceps disynaptically.The hypothesis is suggested that long propriospinal paths primarily represent intrinsic links between hindlimb and forelimb ‘motor centres’. The pattern of long ascending influences to groups of forelimb motoneurones corresponds closely to the sequences of hindlimb and forelimb stepping observed in normal cats. A functional role in stepping is therefore proposed for long ascending propriospinal pathways.     

Efferent activity in the phrenic nerve during the startle reflex in chloralose-anesthetized cats

Reflex activity in the phrenic nerve was studied in chloralose anesthetized cats during development of somatic startle reflexes in limb and lower intercostal nerves. It was shown that the main component of this activity during low-threshold reflexes evoked by acoustic, tactile and low-threshold somatic afferent stimulation was depression of phrenic inspiratory activity. The following reflex discharges were prevalent components of phrenic responses to high-threshold afferent stimulation: early, propriospinal (intercostal-to-phrenic reflex) and late, suprasegmental ones. The latter were of two types: inspiratory (observed mainly during inspiration in about 75% of experiments) and expiratory (observed during expiration in 25% of experiments) which could be classified as "phrenic startle reflexes". Modulation of all responses during the respiratory cycle was described. Structural characteristics of reflex responses evoked in the phrenic nerve by stimulation of various respiratory and nonrespiratory bulbar sites as well as their respiratory modulation have been analyzed. Organization of possible neurophysiological mechanisms of phrenic responses during startle reflexes is discussed.     

Cutaneous inputs from the back abolish locomotor-like activity and reduce spastic-like activity in the adult cat following complete spinal cord injury

Spasticity is a condition that can include increased muscle tone, clonus, spasms, and hyperreflexia. In this study, we report the effect of manually stimulating the dorsal lumbosacral skin on spontaneous locomotor-like activity and on a variety of reflex responses in 5 decerebrate chronic spinal cats treated with clonidine. Cats were spinalized 1 month before the terminal experiment. Stretch reflexes were evoked by stretching the left triceps surae muscles. Crossed reflexes were elicited by electrically stimulating the right tibial or superficial peroneal nerves. Wind-up of reflex responses was evoked by electrically stimulating the left tibial or superficial peroneal nerves. We found that pinching the skin of the back abolished spontaneous locomotor-like activity. We also found that back pinch abolished the rhythmic activity observed during reflex testing without eliminating the reflex responses. Some of the rhythmic episodes of activity observed during reflex testing were consistent with clonus with an oscillation frequency greater than 3 Hz. Pinching the skin of the back effectively abolished rhythmic activity occurring spontaneously or evoked during reflex testing, irrespective of oscillation frequency. The results are consistent with the hypothesis that locomotion and clonus are produced by common central pattern-generators. Stimulating the skin of the back could prove helpful in managing undesired rhythmic activity in spinal cord-injured humans.     

Supraspinal regulation of spinal reflex discharge into cardiac sympathetic nerves

(1) In chloralose anaesthetized cats, reflex responses were recorded in inferior cardiac nerves following stimulation of intercostal nerves and hind limb afferent nerves. (2) In 80% of cats, a long latency reflex response alone was recorded, whereas, in the others, a short and long latency response was present to intercostal nerve stimulation. (3) In cats displaying only a long latency somatocardiac reflex response, damage to the ventral quadrant of the ipsilateral cervical spinal cord, through which runs a bulbospinal inhibitory pathway, resulted in the appearance of shorter latency reflexes to intercostal nerve stimulation. Lesions elsewhere in the cervical cord did not do this. (4) The characteristics of the early responses indicated that they were somatosympathetic reflexes and not dorsal root reflexes. (5) The early reflexes remained and the late reflex disappeared on subsequent complete transection of the spinal cord. The early reflexes were therefore spinal reflexes, and suppressed in the animal with cord intact. (6) Lesions at C4, which included a contralateral hemisection and a section of dorsal columns extending into the dorsal part of the lateral funiculus, abolished the inhibition of a sympathetic reflex that followed stimulation of some somatic afferent nerve fibres. These sections did not release the spinal reflex. Therefore, this reflex inhibition was not responsible for the suppression of the spinal somatosympathetic reflex. (7) The descending inhibitory influence on the segmental reflex pathway was not antagonized by strychnine, bicuculline or picrotoxin. (8) The possibility is discussed that the spinal reflex pathway into cardiac sympathetic nerves is tonically inhibited by a bulbospinal pathway originating from the classical depressor region of the ventromedial reticular formation.     

Distal hind-limb reflex responses in cats with largely intact spinal reflex circuits

Reflex responses to single shocks to peripheral nerves were studied in the small muscles of the hind limb of the decerebrated and subsequently spinalized cat. Monosynaptic and high threshold polysynaptic reflexes of plantar muscles evoked by tibial nerve shocks were significantly more active in preparations that had extensive dissection of nerves and muscles. Monosynaptic reflexes were more active in the plantar flexor portion than in other parts of the interosseus. Compared with proximal limb muscles, this muscle showed features of reflex behavior that were neither consistently flexor nor extensor. In spinal animals the threshold of the tibialis anterior to tibial nerve shocks was often less than the threshold for other muscles, suggesting a function other than nociceptive flexion reflex, probably tactile influence in gait. Extensor digitorum brevis reflexes did not exhibit the flexor reflex pattern typified by those of the tibialis anterior muscle. The data further suggest activation of these reflexes by Ib interosseus muscle afferents and plantar cutaneous afferents and tonic inhibition from Ia receptors.     

Analysis of reflex activity in cardiac sympathetic nerve induced by myelinated phrenic nerve afferents

Electrical stimulation of the phrenic nerve afferents evoked excitatory responses in the right inferior cardiac sympathetic nerve in chloralose-anaesthetized cats. The reflex was recorded in intact and spinal cats. The latency and threshold of the volley recorded from the phrenic nerve as well as of the cord dorsum potentials evoked by electrical stimulation of the phrenic nerve indicated that group III afferents were responsible for this reflex. The phrenicocardiac sympathetic reflex recorded in intact cats was followed by a silent period. The maximum amplitude of the reflex discharges was 800 microV, the latency was 83 ms and the central transmission time 53 ms. Duration of the silent period lasted up to 0.83 s. In spinal cats the reflex was recorded 5.5-8 h after spinalization. The maximum amplitude of the spinal reflex discharges ranged from 22 to 91 microV and the latency from 36 to 66 ms.     

Reflex effects evoked by stimulation of hypoglossal afferent fibers

In pentobarbitone-anesthetized cats, electrical stimulation of the central ends of the main trunks of transected hypoglossal nerves evoked vascular (pressor or depressor) reactions, mydriasis, slow and deep breathing, and reflex activation of laryngeal and facial muscles. Stimulation of the central end of the transected ramus descendens hypoglossi also provoked reflex contraction of cricothyroideus. These reflexes may be elicited also after intracranial section of hypoglossal nerve roots, but not after intracranial section of ipsilateral vagal roots. The above reflexes were abolished by acute section of the ipsilateral hypoglossonodosal branch, but they may be reproduced by electrical stimulation of the central end of this anastomotic branch between hypoglossal nerve and nodose ganglion. Stimulation of the central end of one transected hypoglossus evoked reflex efferent discharges in contralateral hypoglossus and contraction of contralateral tongue muscles. Stimulation of the central end of one transected hypoglossal end-branch inhibited efferent discharges in another end-branch. The crossed hypoglossohypoglossal reflex and the ipsilateral reflex inhibition were abolished by section of the hypoglossonodosal branch or vagal roots at the stimulated side. We conclude that reflexes evoked by stimulation of peripheral hypoglossal nerve in cats are mediated by afferent fibers directed to the nodose ganglion and entering the brain stem via vagal roots.     

Hoffmann reflex from foreleg flexor nerves in cats: lateralization, picrotoxin, strychnine, crossed flexor reflex

Hoffmann (H) reflexes from foreleg flexor nerves were studied in cats. The right and left flexor nerves were stimulated and H reflexes were recorded from the same nerves. Paw preference was assessed by a food reaching test. Stimulation of the right median nerve elicited mono- and polysynaptic reflexes from the left ulnar nerve (crossed flexor nerve). Picrotoxin depressed, and strychnine increased H reflexes from both sides without affecting the spinal motor asymmetry. H reflexes were found to be larger on the left than the right side in right-preferent cats and vice versa in left-preferent cats. The right H-reflex recovery curve was higher than left in right-preferent cats. The inhibitory period of the recovery cycle disappeared after picrotoxin and changed to facilitation for the nonpreferred side. Strychinine caused bilateral, nearly-synchronous motoneuronal discharges from the right and left flexor nerves; the discharges originating from the left side preceded those from the right side in a right-preferent cat. These results indicate that spinal motor activity predominates on the nonpreferred side, which would be a prerequisite for postural adjustments during paw use in cats. This asymmetric motor organization in the forelegs of cats having quadrpedal locomotion seems to be similar to asymmetric motor organization in legs in humans.     

Effect of magnesium ions on presynaptic inhibition of monosynaptic reflexes

In experiments on spinal narcotized cats perfusion of lumbosacral spinal cord through central canal with artificial cerebrospinal fluid containing high concentration (20-46 mM) of magnesium ions led to reversible depression of negative DRP as well as to depression of prolonged "presynaptic" inhibition of extensor monosynaptic reflexes produced by repetitive impulse volleys in group I flexor muscle afferents. Magnesium did not cause a depression of monosynaptic reflex discharges in spinal ventral roots.     

Role of vesical afferent nerve fibres involved in the control of internal anal sphincter motility

The neural pathways involved in the interactions between urinary bladder and internal anal sphincter (IAS) were studied in anaesthetized spinal cats. Activation of vesical afferents produced in the IAS a reflex increase in the electrical activity and a reflex inhibition of the excitatory responses evoked by stimulation of one hypogastric nerve. Both reflexes are achieved partly in the lumbar spinal cord and partly within the inferior mesenteric ganglion.     

Changes in the postsynaptic responses of spinal cord motor neurons against a background of rhythmic stimulation of the locus coeruleus

Influences of locus coeruleus rhythmical stimulation on the postsynaptic reactions of spinal motoneurons were studied in chloralose anesthetized cats. IPSPs evoked by flexor reflex afferent (FRA) stimulation were inhibited, but EPSPs evoked by FRA and PSPs evoked by low-threshold muscle afferents stimulation were unchanged under these conditions. The inhibition of IPSPs disappeared in reserpine-pretreated animals. Both IPSPs and EPSPs evoked by FRA stimulation were diminished also during rhythmical stimulation of nucleus reticularis pontis oralis. However this effect was not of monoaminergic nature because it was present in reserpine-pretreated animals.     

There is an inverse relationship between the reflex size from wrist flexors and paw preference in spinal cats

The relationship between paw preference and reflex size from wrist flexors was studied in spinal cats. Paw preference was assessed by a food-reaching test. The monsynaptic H reflex and the polysynaptic reflexes were recorded from the median or ulnar nerves following stimulation of the same nerves electrically. The mono- and polysynaptic reflexes were found to be significantly larger on the left side than the right side in right-preferent spinal cats and vice versa in left-preferent spinal cats.     

Plasticity of urinary bladder reflexes evoked by stimulation of pudendal afferent nerves after chronic spinal cord injury in cats

Bladder reflexes evoked by stimulation of pudendal afferent nerves (PudA-to-Bladder reflex) were studied in normal and chronic spinal cord injured (SCI) adult cats to examine the reflex plasticity. Physiological activation of pudendal afferent nerves by tactile stimulation of the perigenital skin elicits an inhibitory PudA-to-Bladder reflex in normal cats, but activates an excitatory reflex in chronic SCI cats. However, in both normal and chronic SCI cats electrical stimulation applied to the perigenital skin or directly to the pudendal nerve induces either inhibitory or excitatory PudA-to-Bladder reflexes depending on stimulation frequency. An inhibitory response occurs at 3–10 Hz stimulation, but becomes excitatory at 20–30 Hz. The inhibitory reflex activated by electrical stimulation significantly (P < 0.05) increases the bladder capacity to about 180% of control capacity in normal and chronic SCI cats. The excitatory reflex significantly (P < 0.05) reduces bladder capacity to about 40% of control capacity in chronic SCI cats, but does not change bladder capacity in normal cats. Electrical stimulation of pudendal afferent nerves during slow bladder filling elicits a large amplitude bladder contraction comparable to the contraction induced by distension alone. A bladder volume about 60% of bladder capacity was required to elicit this excitatory reflex in normal cats; however, in chronic SCI cats a volume less than 20% of bladder capacity was sufficient to unmask an excitatory response. This study revealed the co-existence of both inhibitory and excitatory PudA-to-Bladder reflex pathways in cats before and after chronic SCI. However our data combined with published electrophysiological data strongly indicates that the spinal circuitry for both the excitatory and inhibitory PudA-to-Bladder reflexes undergoes a marked reorganization after SCI.     

Spontaneous activity of cat spinal ganglion neurons in vivo

Recordings were made from L4-S1 spinal ganglion neurons of anesthetized cats while their associated dorsal root and the sciatic nerve were left intact, locally anesthetized, or locally anesthetized and sectioned. In all three experimental conditions spontaneous discharges were recorded. These discharges occurred in the absence of any electrical stimulation of the dorsal root or sciatic nerve, and were not due to peripheral exploration of receptive fields or sustained firing in joint or muscle afferents. The spontaneous discharges were relatively rhythmic, and their firing frequency ranged from 5 to 100 impulses per s. Interactions between spontaneous and electrically evoked discharges were observed that depended on the impulse's frequency of firing. High frequency discharges always abolished low frequency impulses regardless of whether these latter were spontaneous or evoked. Extra spikes and postspike events that followed impulses evoked by stimulation of the dorsal root or sciatic nerve were also recorded from some spinal ganglion neurons. These results suggest that spontaneous discharges may originate within the spinal ganglion itself, and that they can occur under normal circumstances.     

L-dopa-induced locomotor-like activity in ankle flexor and extensor nerves of chronic and acute spinal cats

The ability of L-DOPA and nialamide to produce locomotor-like rhythmic discharges (fictive locomotion) in hind limb nerves of acute and chronically spinalized and paralyzed cats was examined. Ankle flexor and extensor nerves of chronic cats exhibited pharmacologically induced alternate bursts of activity that had significantly shorter cycle times and burst durations than those produced in ankle flexor and extensor nerves of acutely prepared cats. Furthermore, prior to pharmacologic activation, both ankle flexor and extensor nerves of chronic preparations frequently exhibited spontaneous alternate bursts of activity. Neuronal discharges from nerves of chronic preparations, both prior to and after pharmacologic activation, exhibited much greater variability in both cycle time and burst duration compared with those observed in acute preparations.