Somatotopic organization of the dorsal horn in the lumbosacral enlargement of the spinal cord in the neonatal cat

The somatotopic organization of the light touch receptive fields of single unidentified dorsal horn neurons in the lumbosacral spinal cord has been studied in the neonatal cat anesthetized with chloralose. Satisfactory recordings were obtained from single dorsal horn neurons in kittens aged 3-6 days. Reconstruction of recording tracks from pontamine blue dye spots and comparisons of the depths of recording sites with Nissl-stained sections of cord showed that most single-unit recordings were obtained from laminae III and IV of Rexed. In animals of all ages neurons were found which responded briskly to light cutaneous mechanical stimulation. Their receptive fields varied widely in size, being smallest on the distal digits and largest on proximal skin. Receptive field areas were similar in proportion to the size of the hindlimb to those seen in the equivalent region in the adult cat. Because of the shape of the dorsal horn and the relatively narrow dorsal columns in neonatal kittens it proved difficult to locate units with receptive fields on proximal skin. Nevertheless the main features of the somatotopic organization of the dorsal horn were similar to those in the adult cat. Thus the somatotopic map of the kitten showed a medial representation of glabrous skin that was bounded laterally by the representation of the hairy skin of the toes. Proximal skin was represented in the lateral parts of the dorsal horn, a region which was not easily accessible for microelectrode recording. The individual toes were represented in a rostral to caudal sequence such that toe 2 was represented rostrally and toe 5 caudally. Around the toe representation the medial surface of the foot was represented rostrally, the ventrolateral surface caudally, and the dorsal surface laterally. The results indicate that the mature organization of light touch receptive fields of dorsal horn neurons in the lumbosacral cord of the cat is already largely present at birth.     

Increased receptive field size of dorsal horn neurons following chronic spinal cord hemisections in cats

The somatotopic organization of the 17 dorsal horn was studied using extracellular recordings in normal cats, and in cats with acute or chronic spinal cord hemisection at T13, sparing the dorsal columns. Based on data concerning recovery of function and collateral sprouting of afferents following hemisections, we predicted that the lesion would result in increases in receptive field size and decreases in the specificity of the somatotopic map. In normal animals, the usual mediolateral, rostrocaudal and dorsoventral somatotopic sequences were found. Following acute hemisections (6 h–5 days), there were changes in spontaneous and evoked activity, but receptive field sizes and somatotopic organization remained unchanged. Following chronic hemisections (88–174 days), proximal hindlimb receptive fields in the lateral dorsal horn ipsilateral to the lesion increased dramatically in size and were significantly larger than similar receptive fields on the contralateral side. The largest of these fields extended from the dorsal midline to the middle of the foot. Receptive field sizes elsewhere in the dorsal horn remained unchanged, as did somatotopic organization in general. These findings indicate that hemisections result in a complex series of changes consisting of an early stage of anatomically generalized changes in excitability and a later stage of highly localized changes in receptive field size. Possible mechanisms for these changes, as well as their relationship to recovery of function, are discussed.     

Effects of capsaicin on receptive fields and on inhibitions in rat spinal cord

The dorsal horn of the lumbar enlargement of the spinal cord is somatopically arranged such that the medial half contains cells with receptive fields on the distal parts of the leg and the cells in the lateral half have proximal receptive fields. After chronic sciatic nerve transection that removes input from the distal limb, a substantial number of cells in the medial dorsal horn begin to respond to proximal cutaneous stimulation. We attempted to discover the mechanisms responsible for this expansion of receptive fields following deafferentation. In these series of experiments we used capsaicin, a C-fiber neurotoxin that either destroys C fibers when administered neonatally or produces a functional blockade of C input to the cord when administered topically to a peripheral nerve. After both neonatal or topical capsaicin treatment there was disorganization of the somatopic map of the dorsal horn similar to that produced by nerve transection. Neonatal capsaicin treatment also produced a decrease in primary afferent depolarization and of A-afferent-mediated inhibitions in the dorsal horn, similar to that observed after nerve transection. Local capsaicin treatment, however, did not alter primary afferent depolarization or A-afferent inhibitions. It is unlikely, therefore, that these forms of inhibitions were responsible for controlling receptive field size. The actions of capsaicin, however, did imply some role for C fibers in determining the organization of receptive fields in the dorsal horn.     

Effect of peripheral nerve injury on receptive fields of cells in the cat spinal cord

When the sciatic and saphenous nerves are cut and ligated in adult cats, the immediate effect is the production of a completely anesthetic foot and a region in medial lumbar dorsal horn where almost all cells have lost their natural receptive fields (RFs). Beginning at about 1 week and maturing by 4 weeks, some 40% of cells in the medial dorsal horn gain a novel RF on proximal skin, that is, upper and lower leg, thigh, lower back, or perineum. This new RF is supplied by intact proximal nerves and not by sciatic and saphenous nerve fibers that sprouted in the periphery. During the period of switching of RFs from distal to proximal skin there was no gross atrophy of dorsal horn grey matter and no Fink-Heimer stainable degeneration of central arbors and terminals of peripherally axotomized afferents. In intact animals medial dorsal horn cells showed no sing of response to mechanical stimulation of proximal skin. RFs of some of the cells had spontaneous variations in size and sensitivity, but these were not nearly sufficient to explain the large shifts observed after chronic nerve section. Tetanic electrical stimulation of skin or peripheral nerves often caused RFs to shrink, but never to expand. Although natural stimuli of proximal skin would not excite medial dorsal horn cells in intact or acutely deafferented animals, it was found that electrical stimulation of proximal nerves did excite many of these cells, often at short latencies. In the discussion we justify our working hypothesis that the appearance of novel RFs is due to the strengthening or unmasking of normally present but ineffective afferent terminals, rather than to long-distance sprouting of new afferent arbors within the spinal cord.     

Cells of origin of the spinocervical tract in the monkey

The responses of cells of the spinocervical tract were recorded from the lumbosacral spinal cord in anesthetized monkeys. The neurons were identified by antidromic activation following stimulation of the dorsal part of the lateral funiculus at C₃. Recordings were also made in a few experiments from neurons of the lateral cervical nucleus. These cells were identified by by antidromic activation following stimulation of the contralateral medial lemniscus and by demonstration of their receptive fields on the skin of the trunk or hind limb. Most of the cells of origin of the spinocervical tract were in the region of the dorsal horn comparable to laminae IV and V in the cat. However, some were more ventral and one was in lamina I. The conduction velocities of the axons ranged from 7.1 to 60 m/sec (mean of 27.8 m/sec). The receptive fields of the spinocervical tract neurons were on the ipsilateral hind limb. Many of the cells were activated by hair movement or by gentle tactile stimulation of the skin. Others were excited not only by comparable stimuli but, in addition, by more intense mechanical stimulation of the skin. One cell required a noxious stimulus for its activation. A strong thermal stimulus caused an increased discharge of some of the cells. There was a somatotopic organization of the cells within the dorsal horn. Laterally situated neurons were associated with peripheral receptive fields on the dorsal surface of the limb, while medially located neurons had receptive fields on the ventral surface of the limb. The rostrocaudal somatotopic organization was dermatomal. The neurons of the lateral cervical nucleus were activated by hair movement or by tactile stimulation. It is concluded that the monkey somatosensory system includes a spinocervicothalamic pathway which is comparable to that found in the carnivore.     

Morphology and somatotopic organization of the central terminals of hindlimb hair follicle afferents in the rat lumbar spinal cord

The morphology of the central collateral arborizations of 24 A-beta hair follicle afferents (HFAs) innervating different regions of the skin of the hindlimb were studied by the intra-axonal injection of horseradish peroxidase (HRP) in adult rats. A total of 236 collaterals were recovered. These fell into three classes--complex, simple, and blind-ending--based on numbers of boutons and terminal branch patterns. The morphology of the HFA central arbors innervating the lateral and medial leg and dorsum of the foot was flame-shaped. Afferents with receptive fields on the glabrous-hairy skin border consistently had extra terminal branches running ventromedially into laminae IV/V. Differences in the width of terminal arbors were found. HFA terminals innervating the lateral leg formed narrower sheets than those innervating the dorsum of the foot and toes. The somatotopic organization of the collaterals and terminal arborizations of individual afferents were analyzed both by considering all the collaterals along an axon's rostrocaudal extent and by only examining arbors with boutons (the complex and simple arbors). Thirty-seven percent of blind-ending and 18% of simple collaterals were found to overlap in the rostrocaudal direction with the complex arborizations of afferents whose receptive fields were in a different cutaneous nerve territory. There was no overlap between complex arborizations of afferents from different nerve territories. However, the complex arbors of afferents with receptive fields within a particular nerve territory showed considerable terminal overlap even if they had nonadjacent peripheral receptive fields. The topographical organization of the central terminals of HFAs, forms a coarse somatotopic map of overlapping terminals whereby a particular region of dorsal horn has a maximal, but not exclusive, input from a particular area of skin.     

Crossed and uncrossed projections to cat sacrocaudal spinal cord: I. Axons from cutaneous receptors

Intra-axonal recording and horseradish peroxidase staining techniques were used to map terminal fields of primary afferent fibers from cutaneous receptors within the cat sacrocaudal spinal cord. It was hypothesized that projection patterns of cutaneous afferent fibers mirror the known somatotopic organization of sacrocaudal dorsal horn cells. Forty-three primary afferent fibers, innervating either slowly adapting type I receptors, hair follicles, or slowly adapting type II receptors, all on the tail, were recovered. All collaterals (N = 372) branched from parent axons in the dorsal columns. Most collaterals coursed rostromedially to the ipsilateral gray matter, penetrated the medial dorsal horn, and arborized within laminae III, IV, and to a lesser extent, V. Ipsilateral projections to dorsal horn were as follows: axons with dorsal or dorsolateral receptive fields (RFs; n = 20) to the lateral portion, axons with lateral RFs (n = 4) to the central portion, and axons with ventral or ventro-lateral RFs (n = 19) to the medial portion. Most axons (16 of 20) with dorsal or dorsolateral RFs also had contralateral projections to lateral dorsal horn and most axons (15 of 19) with ventral or ventrolateral RFs also had contralateral projections to medial dorsal horn. No axons with lateral RFs had crossed projections. These data represent the first complete mapping of the somatotopic organization of primary afferent fiber projection patterns to a spinal cord level. The findings demonstrate that ipsilateral projection patterns of sacrocaudal primary afferent fibers are in register with the somatotopic organization of the dorsal horn. Our earlier suggestion that crossed projections of primary afferent fibers give rise to crossed components of dorsal horn RFs spanning the midline is supported by these results.     

Cutaneous receptive fields of somatic and viscerosomatic neurones in the thoracic spinal cord of the cat

Extracellular single-unit recordings were made from 121 neurones in the thoracic spinal cord of the cat. All neurones could be driven by electrical stimulation of dorsal root afferent fibres. The neurones were classified, according to the absence or presence of inputs from the ipsilateral splanchnic nerve, as "somatic" or "viscerosomatic", respectively. Cutaneous receptive fields were identified for 75 of the neurones: 31 were somatic and 44 viscerosomatic. Only two of the somatic cells received cutaneous nociceptive inputs, compared with 33 of the viscerosomatic cells. Sixty-four percent of the whole sample of neurones had receptive fields which included three or more dermatomes. Viscerosomatic cells tended to have larger receptive fields than the somatic neurones, and six of them had fields which did not include the corresponding (T11) dermatome. Neurones with receptive fields in the dorsal one-third of the dermatome tended to be located in the lateral one-third of the dorsal horn, but those with receptive fields in the ventral two-thirds of the dermatome showed no differential distribution within the gray matter. This is discussed with respect to the results of anatomical studies on the dorsal horn projections of cutaneous afferent fibres from different regions of the dermatome. Preliminary results from intracellular staining with horseradish peroxidase reveal extensive branching of primary afferents in the dorsal horn, and large dendritic fields of dorsal horn neurones. Our physiological and morphological results indicate that the somatotopic organisation of the thoracic spinal cord is less well defined than that of the lumbosacral region.     

Somatotopic organization of cutaneous afferent terminals and dorsal horn neuronal receptive fields in the superficial and deep laminae of the rat lumbar spinal cord

The somatotopic organization of A- and C-afferent fibre terminals in the dorsal horn of the rat lumbar spinal cord was compared with the spatial location of second-order dorsal horn neuronal mechanoreceptive fields. The central terminal fields of the sural, saphenous, and tibial nerve were mapped by labelling the nerves with horseradish peroxidase (HRP). A previous study used the transganglionic transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) to produce a somatotopic map of high-threshold C-fibre terminal fields in lamina II (Swett and Woolf: J. Comp. Neurol. 231:66-77, '85). In the present study the terminal fields of low-threshold A beta afferents that terminate in laminae III and IV were mapped by using unconjugated HRP at prolonged survival times (72 hours). Unfixed tissue was used to increase the sensitivity of the tetramethylbenzidine reaction, thus allowing these afferent terminals to be clearly seen. The general spatial arrangement of the terminal fields in laminae III/IV closely resembled that found in lamina II in the mediolateral and rostrocaudal planes but because of a dorsoventral obliquity of the afferent terminals, the superficial and deeper fields are not in strict vertical register. The input to laminae II-IV of the dorsal horn may therefore be viewed as two horizontally arranged sheets of afferent terminals both accurately representing the skin surface, the more superficial sheet representing the high-threshold C-afferents and the deeper sheet, low-threshold A-beta afferents. The spatial organization of high-threshold A-delta afferents in laminae I and V appears to be quite different, with a transverse rather than a longitudinal orientation. To study dorsal horn cell receptive field organization two single units with mechanoreceptive fields were recorded extracellularly in each of 87 vertical tracks in the lumbar spinal cord, one unit in the superficial dorsal horn and the second in the deep dorsal horn. In general the somatotopic organization of the receptive fields of both sets of units followed that of the afferent terminal fields but there were cells with receptive fields that were anomalous relative to the recording site. No evidence of any vertical relation or columnar arrangement in receptive field size, threshold, or location on the body surface was found when comparing the two units in a pair. Furthermore, no laminar functional specialization was found, the majority of neurones having both low- and high-threshold inputs.(ABSTRACT TRUNCATED AT 400 WORDS)     

Chronic peripheral nerve injuries alter the somatotopic organization of the cuneate nucleus in kittens

The effect of chronic peripheral nerve injuries on the somatotopic organization of the cuneate nucleus was examined in kittens, using electrophysiological techniques. In normal kittens, most cells in the dorsal part of the nucleus possessed small receptive fields on the ipsilateral front paw. Several weeks after paw denervation in young kittens, however, many cells in the corresponding dorsal part of the nucleus responded to tactile stimulation of the wrist, forearm, or trunk. Consistent with this change in receptive fields, the neurons in the dorsal part of the nucleus were more responsive to electrical stimulation of the medial cutaneous nerve, which innervates part of the forearm, in kittens after paw denervation than in control kittens. These somatotopic changes were not an artifact of severe atrophy of the dorsal part of the nucleus. This experiment confirms that after chronic peripheral nerve injuries, central somatosensory neurons can begin to respond to ascending afferent volleys originating from other undamaged peripheral axons, which were previously incapable of exciting the cells. Moreover, this change in functional connectivity is evident at the first synapse central to the injury site.     

The cutaneous sensitivity of units in laminae VII and VIII of the cat

The cutaneous sensitivity of units in laminae VII and VIII was compared to that of dorsal horn units in the same cats. There appeared to be a reversal of somatotopic organization between the dorsal and ventral horns. When this reversal was taken into account, it was apparent that most ventral horn units have localized receptive fields. They responded almost exclusively to intense, presumably noxious, stimulation of these discrete skin regions.     

Timecourse for receptive field plasticity following spinal cord hemisection

Previously, we demonstrated that between 5 days and 3 months following a partial spinal cord hemisection, proximal hindlimb receptive fields of neurons in the ipsilateral L7 dorsal horn of cats become enlarged. In this study, we used somatotopic mapping procedures, applied bilaterally, to demonstrate that this change in receptive field size occurs between 10 and 14 days postoperatively.     

Absence of mediolateral reorganization of dorsal horn somatotopy after peripheral deafferentation in the cat

The effect of chronic transection of the sciatic and saphenous nerves on the receptive fields of dorsal horn neurons in the L7 segment has been reinvestigated in six cats anesthetized with chloralose. Following nerve transection only a narrow lateral band of dorsal horn contained neurons with light touch receptive fields; these were situated on the proximal part of the hind limb. Dorsal horn neurons situated more than about 0.25 mm medial of the lateral edge (at the level of lamina IV) of the dorsal horn lost their light touch receptive fields, and did not acquire new light touch RFs on the proximal part of the hind limb for as long as 49 days after nerve transection. There was thus no sign of the extensive mediolateral reorganization of somatotopy described by some previous workers. Many affected neurons throughout laminae IV to VI became phasically responsive to mechanical stimulation of unidentified mechanoreceptors in deep tissue (e.g., muscle, tendon, joints, and fasciae) of the proximal part of the limb. Some of these neurons had quite low thresholds to mechanical distortion. A small proportion of neurons in medial lamina V and VI may acquire large, high-threshold cutaneous mechanoreceptive fields on the proximal part of the limb. The relation of these time-dependent changes to the known distribution of primary afferent fibers within the dorsal horn is discussed.     

The immediate shift of afferent drive of dorsal column nucleus cells following deafferentation: A comparison of acute and chronic deafferentation in gracile nucleus and spinal cord

The somatotopic map of the gracile nucleus was determined using tungsten electrodes in anesthetized adult cats. Following deafferentation of the hind leg by cutting all dorsal roots caudal to L3, the nucleus was remapped. The total number of points in the map where abdomen responses were recorded doubled immediately following deafferentation. The latency of responses of cells responding to brush of the abdomen was not different after deafferentation. Some of the cells which began responding to abdominal stimulation had one or more of the following characteristics: (i) a rapid flick of the hair was required to fire the cell, (ii) habituation, and (iii) widespread inhibitory fields. To confirm that individual cells had switched the afferents which excite them, we examined the respone of single cells before, during, and after a reversible cold block of all the afferents from the hind leg. Of 40 single cells examined, 11 which had receptive fields on the leg switched their receptive fields to the abdomen as soon as the block of leg afferents was complete. Mapping the gracile nucleus 8 months following deafferentation still showed an increase in abdominal representation. Examination of the dorsal horn in the L6–7 segment of these chronically deafferented cats showed that abdominal afferents excited cells in a region normally responding to leg afferents. These results suggest that deafferentation results in the unmasking of normally ineffective connections. Unmasking could be a mechanism which explains many of the observed changes in the responses of central nervous system neurons following lesions.     

The somatotopic organization of primary afferent terminals in the superficial laminae of the dorsal horn of the rat spinal cord

Transganglionic transport of wheatgerm agglutinin conjugated horse-radish peroxidase (WGA-HRP) was used to reveal the central distribution of terminals of primary afferent fibers from peripheral nerves innervating the hind leg of the rat. In separate experiments the sizes and locations of cutaneous peripheral receptive fields were determined by electrophysiological recording techniques for each of the nerves that had been labeled with WGA-HRP. By using digital image analysis, the sizes and positions of the peripheral receptive fields were correlated with the areas of superficial dorsal horn occupied by terminals of primary afferents from each of these receptive fields. Data were obtained from the posterior cutaneous nerve of the thigh, lateral sural, sural, saphenous, superficial peroneal, and tibial nerves. The subdivisions of the sciatic nerve, the sural, lateral sural, superficial peroneal, and tibial nerves each projected to a separate and distinct region of the superficial dorsal horn and collectively formed a "U"-shaped zone of terminal labeling extending from lumbar spinal segments L2 to the caudal portions of L5. The gap in the "U" extended from L2 to the L3-4 boundary and was occupied by terminals from the saphenous nerve. Collectively, all primary afferents supplying the hindlimb occupied the medial 3/4 of the superficial dorsal horn with terminals from the tibial nerve lying most medially and occupying the largest of all the terminal fields. Afferents from the superficial peroneal lay in a zone between the medially situated tibial zone and the more laterally placed sural zone. Afferents from the posterior cutaneous nerve were located most caudally and laterally. Terminal fields from the posterior cutaneous and saphenous nerves differed from the others in having split representations caused presumably by their proximity to the mid-axial line of the limb. Comparisons between the peripheral and the central representations of each nerve revealed that 1 mm2 of surface area of the superficial dorsal horn serves approximately 600-900 mm2 of hairy skin and roughly 300 mm2 of glabrous skin. The vast majority of terminal labeling observed in the dorsal horn was found in the marginal layer and substantia gelatinosa, suggesting that small diameter afferents have an orderly somatotopic arrangement in which each portion of the skin surface is innervated by afferent fibers that terminate in preferred localities within the dorsal horn.     

Muscle Afferents Innervating Skin Form Somatotopically Appropriate Connections in the Adult Rat Dorsal Horn

We have studied the somatotopic reorganization in dorsal horn neurons after a disruption in the normal spatial arrangement of primary sensory axons in adult rats. Muscle afferents were redirected to skin by cutting and cross-anastomosing the hindlimb gastrocnemius nerve (GN) and sural nerve (SN). It has previously been shown that after 10 – 12 weeks GN afferents innervate the hairy skin of the lateral ankle and calf (previously innervated by SN afferents) and become potentially capable of relaying information on the location and intensity of stimuli applied to the skin. We determined the receptive field and response properties of dorsal horn neurons in the lumbar spinal cord, in regions where the lower hindlimb is normally represented. In control animals (with intact or self-anastomosed sural nerves) very few neurons (<8%) received any synaptic input from the GN as assessed by electrical stimulation of the nerve. In contrast, when this nerve innervated skin, many cells responded to GN stimulation, and these nearly all had receptive field components in the former SN territory. Moreover, in animals with cross-anastomosed nerves, cells without GN inputs all had receptive fields outside the former SN skin territory. We have shown that in all likelihood GN afferents substituted for SN afferents in subserving the low and high threshold receptive fields of dorsal horn neurons. Furthermore, for many neurons, receptive fields were formed from inappropriately regrown GN afferents and adjacent intact cutaneous afferents (in the tibial or common peroneal nerves). Therefore, when GN afferents innervate skin in adult animals, they alter their central connectivity in an appropriate manner for their new peripheral terminations, so that an orderly somatotopic representation of the hind limb skin is maintained. We suggest that this plasticity of dorsal horn somatotopy is driven in part by activity-dependent mechanisms.     

Altered responses of nociceptive cat lamina I spinal dorsal horn neurons after chronic sciatic neuroma formation

The activity of lumbar spinal dorsal horn lamina I neurons with afferent drive from the sciatic nerve was studied in intact cats and in cats with acute sciactic nerve transection or chronic sciatic nerve transection with neuroma formation. The majority (51 of 75) of neurons recorded in lamina I ipsilateral to a neuroma had no receptive field and could only be identified by their responses to electrical stimulation of the sciatic nerve. The remainder could be activated by the sciatic nerve, but their responses to mechanical stimulation were irregular in comparison to the stable responses of cells recorded in control animals and to the responses of cells contralateral to chronic nerve lesions. Animals with acute nerve transections demonstrated as loss sciatic nerve-innvervated cells with receptive fields except for those cells located on the lateral edge of the dorsal horn, which had normal, proximal receptive fields and response characteristics. In addition, the characteristic somatotopy of lamina I cells was not observed in some cats with chronic neuromata. The mediolateral distribution of cell types indicated that some cells had altered receptive fields following chronic nerve transection. The data presented for lamina I neurons agrees with the observation of spinal cord plasticity first presented for cat dorsal horn cells. Since there is no evidence for a redistribution of intact afferent fibers following chronic nerve transection in adult mammals, the mechanism of altered somatotopy may involved alterations in synaptic efficacy at existing synapses.     

The organization of the seventh lumbar spinal ganglion of the cat

The organization of the seventh lumbar dorsal root ganglion (DRG) of the cat has been investigated both anatomically and electrophysiologically. In the first two series of experiments an attempt was made to relate the topographic location of identified groups of cells in the ganglion with the rostro-caudal position of their central processes in the filaments of the dorsal root. ³H-proline was injected into various sectors of the ganglion and the distribution of the axonically transported proteins, in individual dorsal rootlets, was determined by means of liquid scintillation spectroscopy and the location of the injections was determined by autoradiography of the sectioned ganglia. The projection pattern was also determined by antidromically activating DRG cells in various parts of the ganglion by sequentially stimulating each of six dorsal root filaments. The results of both groups of experiments indicate that cells located in the medial (caudal) parts of the ganglion project into the most caudal rootlets of the dorsal root; cells in the most lateral (rostral) parts of the ganglion project into the most rostral rootlets, while cells in the intermediate parts of the ganglion project into the middle rootlets. In a third series of experiments, a shifting pattern of overlapping receptive fields was demonstrated for a series of recordings that traversed the ganglion from medial to lateral. This pattern was shown to be nearly equivalent to the organization of receptive fields previously demonstrated by Kuhn ('53) for a rostral to caudal sequence of dorsal rootlets, i.e., foot and leg preaxial fields predominated in the lateral sectors, while postaxial fields were found in the medial sectors of the ganglion.     

Distribution of Cutaneous Nociceptive and Tactile Climbing Fibre Input to Sagittal Zones in Cat Cerebellar Anterior Lobe

Climbing fibres projecting to the cerebellar C3 zone (and the related C1 and Y zones) receive spatially well organized tactile and nociceptive inputs from the skin. In the present study, cutaneous tactile and nociceptive input to climbing fibres projecting to the X, B, C2 and D1 zones in lobule V were investigated in pentobarbitone-anaesthetized cats. From the present results and previous studies, it is concluded that the X, C1, CX, C3 and Y zones receive cutaneous nociceptive climbing fibre input. By contrast, climbing fibres to the B, C2 and D1 zones lack cutaneous nociceptive input. Tactile input was found in all zones. The spatial organization of receptive fields of climbing fibres projecting to the X and D1 zones was similar to that in the C3 zone. They were located on the ipsilateral forelimb, mainly its lateral and distal parts, and their proximal borders were located close to joints. In the B zone, more than half of the receptive fields of climbing fibres were confined to the ipsilateral hind- or forelimb. However, frequently more than one limb and parts of the trunk were included. In the C2 zone, the majority of climbing fibres had distal ipsi- or bilateral receptive fields on the forelimbs, often also including the head/face. Some of the bilateral forelimb receptive fields additionally included the hindlimbs ipsi- or bilaterally. The results indicate that each zone has a characteristic set of climbing fibre receptive fields, which is probably related to its efferent control functions.     

Central distribution of trigeminal and upper cervical primary afferents in the rat studied by anterograde transport of horseradish peroxidase conjugated to wheat germ agglutinin

Injections of WGA-HRP were made in the rat trigeminal ganglion and C1-3 dorsal root ganglia (DRGs) to study the central projection patterns and their relations to each other. Trigeminal ganglion injections resulted in heavy terminal labeling in all trigeminal sensory nuclei. Prominent labeling was also observed in the solitary tract nucleus and in the medial parts of the dorsal horn at C1-3 levels, but labeling could be followed caudally to the C7 segment. Contralateral trigeminal projections were found in the nucleus caudalis and in the dorsal horn at C1-3 levels. The C1 DRG was found to be inconstant in the rat. When it was present, small amounts of terminal labeling were found in the external cuneate nucleus (ECN) and the central cervical nucleus (CCN). No dorsal horn projections were seen from the C1 DRG. Injections in the C2 DRG resulted in heavy labeling in the ECN, nucleus X, CCN, and dorsal horn, where it was mainly located in lateral areas. Labeling could be followed caudally to the Th 7 segment. C2 DRG projections also appeared in the cuneate nucleus (Cun), in all the trigeminal sensory nuclei, and in the spinal, medial, and lateral vestibular nuclei. A small C2 DRG projection was observed in the ventral cochlear nucleus. C3 DRG injections resulted in heavy labeling in both medial middle and lateral parts of the dorsal horn, in the ECN, and in nucleus X, whereas the labeling in the CCN was somewhat weaker. Smaller projections were seen to trigeminal nuclei, Cun, and the column of Clarke. Comparisons of the central projection fields of trigeminal and upper cervical primary afferents indicated a somatotopic organization but with a certain degree of overlap.