Analysis of moving supernumerary limbs of Xenopus laevis.

Behavioral, electrophysiological, and histological observations were made of adult Xenopus laevis with grafted supernumerary hindlimbs which were innervated by lumbar spinal cord segments. The supernumerary hindlimb moved in a coordinated manner in apparent perfect synchrony with the normal ipsilateral hindlimb. Frogs which had received a grafted limb at a younger tadpole stage (49 or 50) exhibited better homologous movements than did frogs which received a limb at an older stage (52 or 53). We investigated a pair of area-specific reflex responses evoked by natural mechanical stimulation of the limbs while recording activity in nerves supplying knee flexor and knee extensor muscles of the two limbs simultaneously. Appropriate, synchronous reflex responses were recorded in these homologous muscle nerves of the two limbs whether or not the knee moved. An important condition was that the frog had received its grafted limb before a critical stage (54). Some electrophysiological evidence was obtained suggesting that motor neurons do not branch to supply homologous muscles of the two limbs. Our data are consistent with the assumption of an underlying neuronal basis for the behaviorally observed homologous movements, but we can only speculate about the level of neural organization responsible for the coordination of the limbs.Histological studies confirmed an increase in the number of lateral motor column neurons on the experimental side in all cases (ranging from +3.7% to +28.1%). A significant increase in cell size (nuclear cross-sectional area) was shown in three cases. The age of the host tadpole when it receives its grafted supernumerary limb may determine the degree of the two types of cellular responses observed (increase in cell number vs. increase in cell size).     

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.     

Electro-acupuncture stimulation to a hindpaw and a hind leg produces different reflex responses in sympathoadrenal medullary function in anesthetized rats

The effects of electro-acupuncture stimulation (EAS) of two different areas of a hindlimb with different stimulus intensities on sympathoadrenal medullary functions were examined in anesthetized artificially ventilated rats. Two needles of 160 microm diameter and about 5 mm apart were inserted about 5 mm deep into a hindpaw (Chungyang, S42) or a hind leg (Tsusanli, S36) and current of various intensities passed to excite various afferent nerve fiber groups at a repetition rate of 20 Hz and pulse duration of 0.5 ms for 30-60 s. Fiber groups of afferent nerves stimulated in a hindlimb were monitored by recording evoked action potentials from the afferents innervating the areas stimulated. The sympathoadrenal medullary functions were monitored by recording adrenal sympathetic efferent nerve activity and secretion rates of catecholamines from the adrenal medulla. EAS of a hindpaw at a stimulus strength sufficient to excite the group III and IV somatic afferent fibers produced reflex increases in both adrenal sympathetic efferent nerve activity and the secretion rate of catecholamines. EAS of a hind leg at a stimulus strength sufficient to excite the group III and IV afferent fibers produced reflex responses of either increases or decreases in sympathoadrenal medullary functions. All responses of adrenal sympathetic efferent nerve activity were lost after cutting the afferent nerves ipsilateral to the stimulated areas, indicating that the responses are the reflexes whose afferents nerve pathway is composed of hindlimb somatic nerves. It is concluded that electro-acupuncture stimulation of a hindpaw causes an excitatory reflex, while that of a hind leg causes either excitatory or inhibitory reflex of sympathoadrenal medullary functions, even if both group III and IV somatic afferent fibers are stimulated.     

Contribution of unmyelinated afferents from the sural nerve to spinal reflex activity

Ipsilateral ventral root reflexes evoked from electrical stimulation of the sural nerve were studied in an attempt to determine if the C or unmyelinated afferent fibers give rise to motor reflex responses because uncertainties in this area have persisted. Appropriate blocking techniques were utilized to isolate C fiber afferent barrages. Evidence was produced that a component of ipsilateral ventral root reflexes (including flexor reflexes) can be evoked solely with a C fiber afferent volley.     

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.     

Convergence of trigeminal input with visceral and phrenic inputs on primate C1-C2 spinothalamic tract neurons.

Trigeminal, spinal and vagal afferent fibers overlap in C1-C2 segments. We hypothesized that trigeminal input from the superior sagittal sinus (SSS) can excite C1-C2 spinothalamic tract (STT) neurons receiving thoracic visceral or phrenic inputs. Effects of SSS stimulation were evenly divided among cells responding to each nerve stimulus; magnitude of responses to ipsilateral vagal input was greater in neurons excited by SSS input. Somatic fields of 80% of neurons responding to SSS stimulation included face areas innervated by the trigeminal nerve, whereas somatic fields of 89% of neurons unaffected by SSS stimulation were located only on areas innervated by cervical spinal nerves. Results are consistent with the idea that pain referred to trigeminal areas could originate in thoracic organs.     

Convergence of trigeminal input with visceral and phrenic inputs on primate C1–C2 spinothalamic tract neurons

Trigeminal, spinal and vagal afferent fibers overlap in C1–C2 segments. We hypothesized that trigeminal input from the superior sagittal sinus (SSS) can excite C1–C2 spinothalamic tract (STT) neurons receiving thoracic visceral or phrenic inputs. Effects of SSS stimulation were evenly divided among cells responding to each nerve stimulus; magnitude of responses to ipsilateral vagal input was greater in neurons excited by SSS input. Somatic fields of 80% of neurons responding to SSS stimulation included face areas innervated by the trigeminal nerve, whereas somatic fields of 89% of neurons unaffected by SSS stimulation were located only on areas innervated by cervical spinal nerves. Results are consistent with the idea that pain referred to trigeminal areas could originate in thoracic organs.     

The cutaneous contribution to the hamstring flexor reflex in the rat: an electrophysiological and anatomical study

The location and properties of the cutaneous receptive fields responsible for detecting the flexor withdrawal reflex in the posterior head of biceps femoris (pBF) and semitendinosus (ST) components of the hamstring muscle have been examined in unanaesthetized decerebrate rats, spinalized at T10-T11. Single alpha-motoneurone efferents were recorded from the nerve to pBF and the principal head of ST and their responses to ipsi- and contralateral hindlimb skin stimulation investigated. The efferents to both muscles characteristically had a low or absent background discharge and they all had mechanoreceptive fields on the ipsilateral foot. The mechanical threshold of these fields was high with no response to light touch or brush. Fifty-four percent of these units also had a smaller and weaker contralateral mechanoreceptive field. The only apparent difference between ST and pBF efferents was that more ST efferents had contralateral fields than pBF units. Noxious, hot and cold thermal stimuli applied to the ipsilateral foot activated 56% of the efferents. Mustard oil, a chemical irritant, produced a long-lasting flexor response when applied to the ipsilateral foot. The responses of these efferents to stimulation of A beta, A delta and C cutaneous afferents in the sural nerve were also studied. Short latency reflexes were elicited in all efferents by A beta inputs, longer latency reflexes were elicited in 64% by A delta inputs and very long latency responses with long afterdischarges were found in 73% of the units to C inputs. Retrograde labelling of the hamstring motoneurones with WGA-HRP indicated that they lay in ventrolateral lamina IX extending from the caudal portion of the third lumbar segment to the junction of the 5th and 6th lumbar segments. Transganglionic labelling of small diameter primary afferent terminals in the dorsal horn of cutaneous nerves innervating the foot revealed that the longitudinal distribution corresponded closely with that of the hamstring motor nucleus. The flex-or reflex in the spinal rat provides a useful model therefore, for studying how the input in nociceptive afferents is processed and transformed within the spinal cord, to produce appropriate outputs.     

The critical importance of stimulus intensity in intraoperative monitoring for partial dorsal rhizotomy

During partial lumbosacral dorsal rhizotomy (PDR), intraoperative dorsal rootlet stimulation (drs) evokes motor responses, presumed to be reflexes, which are used to select rootlets for section. However, dr stimuli may also costimulate ventral root (vr) and evoke an M rather than a reflex response, the two being distinguishable only by comparison of response latencies after drs at two separate sites. In 15 consecutive spastic cerebral palsy patients undergoing PDR, we asked whether reflex and M responses were distinguishable on the basis of stimulus intensity (SI). For soleus H reflexes evoked by percutaneous tibial nerve stimulation, the SI for reflex afferents was usually subthreshold for exciting motor fibers. Similarly, for nerve roots, reflexes were evoked by drs at SIs generally less than that for M responses evoked by vr stimulation (vrs). In contrast, M responses evoked by drs required SIs that were on average 20 times greater. Finally, costimulation of contralateral vr after ipsilateral vrs occurred at SIs shown to evoke M responses after drs. We conclude that: (1) reflex and M responses evoked by drs are distinguishable on the basis of the required SI; and (2) drs employing SIs greater than that required for vrs evokes M rather than reflex responses due to costimulation of ipsilateral and contralateral vr. © 1996 John Wiley & Sons, Inc.     

A comparison of the reflex organization of thoracic and lumbar segments in the frog spinal cord.

Both lumbar dorsal root (DR) primary afferents and descending fibers in the lateral column (LC) make monosynaptic connections with ipsilateral lumbar motoneurons in the frog spinal cord. We have determined that LC fibers also make monosynaptic connections with thoracic motoneurons, while thoracic primary afferents do not. The central reflex time (CRT) for the lumbar DR-VR pathway was 2.5 +/- 0.3 msec, but the CRT for the thoracic DR-VR pathway was 8.5 +/- 2.6 msec. By using a conditioning-test paradigm we have been able to determine that the earliest sign of segmental synaptic transmission in thoracic motoneurons occurs only after a delay of 6.1 +/- 0.9 msec. These results correlate very well with the different morphological characteristics of lumbar and thoracic segments. We have also investigated the central organization of lumbar and thoracic segments and found that the segmental polysynaptic input to motoneurons is more diffuse in thoracic than in lumbar segments. The intersegmental reflexes between thoracic and lumbar segments provide additional evidence for a more diffuse organization in thoracic segments.     

Intercentral relations in rat spinal cord with local depression of the inhibitory processes]

The changes in certain reflex responses of the rat spinal cord after local depression of inhibitory processes by tetanus toxin (the so-called phenomenon of "determinative dispatch station") were studied. It is shown that the tonic and rhythmic activity generated by this locus in the lumbar part of the spinal cord evokes generalized activity of all spinal motoneurons with similar time characteristics. The depression of its neurons by glycine removes this phenomenon. The excitation of "determinative dispatch station" neurons in cervical segments causes a pathologically enhanced scratch reflex in the ipsilateral hind limb. The enhancing of the scratch reflex is not connected with the depression of inhibitory processes of lumbar motoneurons. The formation of the "determinative dispatch station" in cervical segments produces both excitatory and inhibitory influences on monosynaptic reflexes of the lumbar flexor motoneurons. The role of local inhibitory processes depression in the functioning of the nervous system is discussed.     

Axon reflexes in axolotl limbs: evidence that branched motor axons reinnervate muscles selectively.

Numerous axon reflexes were found in grafted forelimbs, regenerated forelimbs, and forelimbs with regenerated nerves in the axolotl Ambystoma mexicanum. They were not seen in normal limbs. Each reflex was due to a single motor axon which branched, generally at a point central to the limb. In most cases several consecutive electrical stimuli were necessary to cause a visible contraction or a muscle action potential in the motor units concerned. I observed a total of 13 axon reflexes between the supernumerary limb and the ipsilateral host limb. All but one could be stimulated in either direction. In other animals I demonstrated 13 axon reflexes by cutting a small nerve in the distal limb and stimulating its proximal stump. In at least five, and possibly as many as 14 of these 26 axon reflexes, the two muscles involved were synonymous. In 20 of the 26, the muscles involved were situated in the same limb region and were synergistic or synonymous. Only in five axon reflexes were the muscles in widely different parts of the limb and clearly unrelated in function. Random innervation or mechanical guidance alone cannot account for these muscle-specific axon reflexes. Axon branches innervated muscles selectively, although the mechanism remains unclear. The selectivity was not perfect, though, because axon reflexes between dissimilar muscles did occur occasionally. Although it has been proposed that an axon may remain in an inappropriate muscle but be functionally “repressed,” no evidence of such repressed synapses was found.     

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.     

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     

Ascending and descending effects of joint afferent discharge on forelimb and hindlimb flexion reflex excitability in decerebrate cats

In decerebrate cats with intact innervation of the fore- and hindlimbs, flexion reflexes are most easily elicited in forelimb muscles when the hindlimb is extended, and hindlimb flexion reflexes are most easily elicited when the forelimbs are extended. After intra-articular injection of local anaesthetic, this modulation of reflex excitability is abolished. Thus, in addition to their known segmental effects, joint afferents also exert significant ascending and descending effects on motoneurone excitability.     

Announcement

The purpose of this study was to investigate innervation of transplanted supernumerary hindlimbs in the frog (Xenopus laevis). Motoneurons innervating identified muscles in normal and supernumerary limbs were located by the method of retrograde transport of HRP after intramuscular injection. In the lumbar spinal cord of normal Xenopus, motoneurons supplying medial hindlimb muscles, which are derived from the ventral muscle mass during development, are located at the medial end of the motor column; those innervating lateral, dorsallyderived muscles, lie at the lateral end of the motor column. In animals with supernumerary limbs, motoneurons supplying the transplant usually occupied the same mediolateral position as those supplying the same muscle in the normal limb. However, the rostrocaudal location of these motor pools exhibited greater flexibility. When the transplant was innervated by a rostral nerve of the lumbar plexus, motoneurons supplying gastrocnemius could be located in a region of the spinal cord whose motoneurons do not normally innervate this muscle. There is thus no rigid requirement that gastrocnemius motoneurons be located at specific segmental levels. Motoneurons supplying gastrocnemius in the normal limb on the experimental side showed normal rostrocaudal distributions, indicating little rearrangement of these motor pools. Dorsal root ganglion cells labeled after HRP injection could be concentrated in a ganglion which normally supplies little or no innervation to the injected muscle. The location of these cells confirmed the segmental source of sensory innervation of the extra limb; i.e., there was no stray innervation. Animals with supernumerary limbs exhibited little or no increase in the number of motoneurons on the extra limb side. In contrast, dorsal root ganglion cell populations exhibited a large increase on the experimental side.     

Innervation and behaviour of ectopic limbs in Xenopus

The hindlimb bud of Xenopus tadpoles was replaced with a forelimb bud, or vice versa, prior to axon invasion of the limb. Ectopic hindlimbs supported 94% as many brachial motoneurons as the remaining forelimb, and ectopic forelimbs supported 46% as many lumbar motoneurons as the remaining hindlimbs, on average, after the period of motoneuron death. The patterns of movement of ectopic limbs were characteristic of the innervating spinal cord segments, and not the limbs. The anatomical patterns of nerve trunks were characteristic of the ectopic limbs, and not the sources of innervation. HRP transport studies showed a resemblance between the locations of lumbar motoneurons supplying ectopic forelimb muscles and those supplying the homologous muscles of the hindlimb. It was concluded that motoneurons could survive the period of cell death following connection to muscles for which their patterns of activity were inappropriate, and the projections to ectopic limb muscles were specific although the nerve paths within the limbs were different.     

Patterns of cortical projection to hindlimb muscle motoneurone pools.

This study was undertaken to examine the organization of the hindlimb area of the motor cortex. Two specific questions were posed. The first was: are the cortical neurones which control the excitability of a given motoneurone pool localized in a small zone of corjex or are they diffuse? The second question was: does microstimulation in the hindlimb area of the motor cortex activate spinal motoneurones in a reciprocal fashion, i.e., is cortically elicited facilitation of a muscle accompanied by inhibition of the antagonist? Intracortical microstimulation was used to condition monosynaptic reflexes of the cat hindlimb to study the organization of a cortical projection to lumbar motoneurone pools. Cortical neurones which produced facilitation or inhibition of a given monosynaptic reflex were localized within a small zone of the cortex. Facilitatory and inhibitory effective zones were found to have similar shape and size. Intracortical microstimulation elicited facilitation or inhibition of individual monosynaptic reflexes without eliciting reciprocal effects on the antagonists. The pyramidal tract was shown to play an important role in the mediation of cortically elicited facilitation as well as inhibition of the monosynaptic reflexes in the lumbar cord.     

Submodality-Selective Hyperalgesia Adjacent to Partially Injured Sciatic Nerve in the Rat is Dependent on Capsaicin-Sensitive Afferent Fibers and Independent of Collateral Sprouting or a Dorsal Root Reflex

We studied submodality dependence of sensory changes produced by unilateral ligation of the sciatic or the saphenous nerve in the rat. We focused especially on sensory changes in the skin area adjacent to the innervation area of the injured nerve. Moreover, we examined the roles of capsaicin-sensitive nociceptive fibers, collateral sprouting and a dorsal root reflex in sensory changes observed behaviorally. Assessment of sensory changes was performed by a pattern of behavioral tests: hot-plate test and hindlimb withdrawal responses induced by radiant heat, hot-water bath, innocuous mechanical stimuli, and noxious mechanical stimuli. In one group, the saphenous nerve ipsilateral to the sciatic ligation was topically treated with capsaicin (1%) at the time of the surgery. A proximal stump of a saphenous nerve strand was orthodromically stimulated to induce a dorsal root reflex (an antidromic volley) in nociceptive fibers of the saphenous nerve trunk. For visualization of plasma extravasation induced by a dorsal root reflex, a dye-labeling (Evans blue) technique was used. A collateral sprouting of nociceptive fibers of the uninjured saphenous nerve was evaluated by determining the plasma extravasation response induced by antidromic stimulation of the saphenous nerve. Three and 10 days following the sciatic constriction injury, the hindlimb withdrawal threshold evoked by noxious mechanical stimulation of the medial side of the paw (the innervation are of the intact saphenous nerve) was significantly decreased. There was no corresponding thermal hyperalgesia adjacent to the injured sciatic nerve. Chronic constriction of the saphenous nerve did not produce any significant hyper- or hypoalgesia to mechanical or thermal stimulation of the uninjured sciatic nerve area. Topical treatment of the ipsilateral (intact) saphenous nerve at the time of the sciatic nerve ligation completely prevented the development of mechanical hyperalgesia in the medial side of the paw (the innervation area of the saphenous nerve). No dorsal root reflex in nociceptive fibers mediating the adjacent hyperalgesia could be evoked. No collateral sprouting of the uninjured nociceptive fibers of the saphenous nerve was observed. The results indicate that the constriction injury of the sciatic nerve produced a selective hyperalgesia to mechanical stimulation in the innervation area of the neighboring saphenous nerve. At the peripheral level, the mechanical hyperalgesia adjacent to the innervation area of the injured nerve was mediated by capsaicin-sensitive nociceptive fibers. Collateral sprouting of nociceptive fibers from the uninjured to the injured innervation area did not contribute to the present sensory findings. The sciatic nerve injury did not induce a dorsal root reflex in nociceptive fibers innervating the hyperalgesic saphenous nerve area.     

The functional subdivisions of the nucleus tractus solitarii of the cat in relation to the carotid sinus nerve reflex

The field potentials evoked by electrical stimulation of the afferent A delta fibers of the ipsilateral carotid sinus nerve (CSN) were surveyed in all the regions of the nucleus tractus solitarii of the cat (NTS responses). Pressor and inspiratory responses, like the CSN chemoreceptor reflex, are elicited by electrical stimulation of the site of the NTS responses in the rostral regions, the lateral portions of the intermediate regions and the commissure regions. On the other hand, depressor and apneic responses, like the CSN baroreceptor reflex, are elicited by electrical stimulation of the site of the NTS responses in the medial portions of the intermediate regions and the dorsal portions of the commissure regions.