Responses of spinocervical tract neurones to noxious stimulation of the skin.

1. Activity of single spinocervical tract neurones has been recorded in the lumbar spinal cord of chloralose anaesthetized or decerebrated cats. Reversible spinalization was produced by cold block at L3. Sensitivity of these neurones to noxious stimulation was studied by heating their cutaneous receptive fields above 40-45 degrees C. 2. Most of the units were located in lamina IV of the dorsal horn and had their receptive fields in the ipsilateral foot. All but one of the studied neurones were excited by moving hairs or by gentle mechanical stimulation of the skin. 3. Eighty-four % of the units were affected by noxious stimuli and three kinds of response were obtained: (i) 61% were excited (E-cells) by noxious heat; (ii) 19% were inhibited (I-cells); and (iii) 19% gave a mixed response reversing from excitatory to inhibitory (EI-cells). 4. E-cells had axons with a wider range of conduction velocities than the rest and also received the strongest descending inhibition from supraspinal structures. 5. The recording sites of EI-cells were located in the medial third of the dorsal horn whereas E- and I-cells were distributed over the full width of the dorsal horn. 6. The possible role of the spinocervical tract in nociception is discussed.     

基于Sihler’s技术的踝和足背皮神经的整体分布模式研究

目的 揭示踝及足背皮神经的整体分布模式,为皮瓣移植感觉重建提供形态学指导。 方法 成年尸体24具,紧贴肌表面摘取含皮下脂肪的踝及足背皮肤,用改良的Sihler’s染色法显示并观察皮神经整体分布模式。 结果 在Sihler’s染色的标本中,肉眼可见隐神经支配踝前区（40.01±7.6）%、踝后区（30±6.7）%、以及部分足背内侧缘。腓浅神经支配踝前区（60.03±6.8）%,其足背内侧皮神经支配足背内侧区、第1、2趾背及第3趾背内侧半;95.83%的足背中间皮神经分布到第3趾背外侧半、第4、5趾背。腓肠神经支配踝后区（70±5.3）%,其足背外侧皮神经支配足背外侧缘皮肤。腓深神经分布到第1、2趾背相对面。初级神经支密度以踝前区最高,次级及以下神经支密度和总的神经支密度均以足背内侧区最高。 结论 在踝或足背的皮瓣移植中,建议把踝前区或足背内侧区设计为利于感觉重建的首选供区或感觉需求较高的受区。     

The detailed somatotopic organization of the dorsal horn in the lumbosacral enlargement of the cat spinal cord

The somatotopic organization of spinocervical tract cells and unidentified dorsal horn neurons that lie in the same depth range as the spinocervical tract cells has been examined in detail in the lumbosacral enlargement of cats anesthetized with alpha-chloralose. Only gentle hair movement or light touch of glabrous skin were used as stimuli. Within the region of the dorsal horn containing these neurons there is a precise somatotopic organization. However, there is considerable variation between animals in the relationship between the somatotopic map and the lumbosacral segmental boundaries. The somatotopic map described here is considered to be restricted to a 300- to 500-micron thick lamina. In the medial half to two-thirds of this lamina in the L6 and L7 segments the toes are represented in a rostrocaudal sequence from toe 2 to toe 5. Over the most medial 200-500 micron of this part of the dorsal horn are found cells that respond to stimulation of the glabrous skin of the toe pads and the central pad. The toe representation is surrounded by a strip of foot representation, which is in turn surrounded by a strip of leg representation. The most lateral part of the lamina curves ventrally in the L6 and L7 segments and contains a continuous rostrocaudal representation of the skin of the thigh. In this region are found both spinocervical tract cells and unidentified dorsal horn neurons with receptive fields on the thigh. The skin of the hindlimb is represented such that a line of discontinuity runs down the posteromedial thigh, leg, and foot. Skin lateral to this line is represented caudally, while skin medial to it is represented rostrally.     

Ascending tract neurones processing information from group II muscle afferents in sacral segments of the feline spinal cord.

1. Ascending tract neurones located in the dorsal horn of sacral segments of the spinal cord have been investigated by extracellular and intracellular recording in the anaesthetized cat. The aim was to determine whether information from group II afferents that terminate within the sacral segments is conveyed to supraspinal structures and which types of neurones are involved. 2. A considerable proportion of ascending tract neurones found in the dorsal horn in the same segments as the pudendal (Onuf's) motor nucleus were excited by group II muscle afferents. The great majority (93%) of these neurones had axons ascending in ipsilateral funiculi. Spinocervical tract neurones constituted the largest proportion (82%) of such neurones, while very few spinocerebellar tract and propriospinal neurones and no postsynaptic dorsal column neurones were found among them. 3. In addition to activation by group II muscle afferents all of the neurones were strongly excited by cutaneous afferents. The most potent excitation was evoked by afferents of the posterior biceps-semitendinosus and gastrocnemius muscle nerves and by afferents of the cutaneous femoris, sural and pudendal nerves. The latencies of intracellularly recorded excitatory potentials were indicative of a high incidence of monosynaptic coupling between the afferents and ascending tract neurones. 4. The highly effective monosynaptic excitation of spinocervical tract neurones in the sacral segments by group II afferents is in contrast to the weak disynaptically mediated actions of group II afferents on such neurones in the L6-L7 segments but comparable to the actions of group II afferents on ascending tract neurones in the midlumbar segments. 5. Both the patterns of peripheral input and the latencies of synaptic actions in ascending tract neurones were similar to those in interneurones at the same locations (accompanying report). Similar information is therefore likely to be processed by both categories of neurones. 6. The role of sacral spinocervical tract neurones as a system for transmitting information from group II muscle afferents to supraspinal centres and the potential contribution of this system to the perception of limb position are discussed.     

Ascending projections of nociceptor-driven Lamina I neurones in the cat

Summary Single unit activity has been recorded from nociceptor-driven Lamina I neurones in the lumbar spinal cord of chloralose anaesthetized and gallamine paralysed cats. Ninety-four nociceptor-driven Lamina I neurones were identified by their superficial location in the dorsal horn and their ability to respond only to noxius stimulation of their cutaneous receptive fields. One-third of the Lamina I neurones responded only to noxious mechanical stimulation of the skin (Class 3a) und two-thirds responded to both mechanical and thermal noxious stimulation (Class 3b). Lissauer's tract was stimulated electrically two and three segments rostral to the recording sites. Ninety percent of the neurones tested showed a post-synaptic excitation mediated by fibres conducting at a mean velocity of 5.2 m/s (range 0.9–13.3 m/s). It is concluded that A and C afferent fibres running in Lissauer's tract excite nociceptor-driven Lamina I neurones. Ninety-six percent of the neurones tested showed a long period of inhibition (100–200 ms) following stimulation of large afferent fibres in the dorsal column. This inhibition was increased when the intensity of stimulation recruited Lissauer's tract fibres. Fifteen percent of the neurones tested were antidromically activated by Lissauer's tract stimulation from up to 3 segments rostal to their origin. A further 18.5% were antidromically excited by stimulation of deeper tracts. The mean conduction velocity of the axons of these projecting neurones was 8.6 m/s (range 3.8–16.5 m/s) and thus are small myelinated axons. The Class 3b neurones exhibited a significantly lower conduction velocity (7.5±2.8 (S.D.) m/s) than the Class 3a neurones (10.7±3.7 (S.D.) m/s).It is concluded that at least two-thirds of the population of nociceptor-driven Lamina I neurones are segmental interneurones.     

Functional organization of long,second-order afferents in the dorsal funiculus

Summary Second-order neurones activated from forelimb nerves and ascending in the deep part of the dorsal funiculus from the eighth to the first cervical segentm were investigated in the cat by axonal recording. These neurones form a previously unknown tract denoted the ascending dorsal funiculus tract, ADFT. The ADFT neurones receive excitation from cutaneous afferents as well as high threshold afferents in deep nerves. The excitation is supplied by afferents from hair, touch, and possibly also pain receptors in the skin, and from receptors in deep connective tissue. There is no excitation from muscle spindles or from specific joint receptors. The cutaneous receptive fields are small and lack inhibitory surround.     

Functional properties of crossed spinocerebellar tract neurones with cell bodies in the S1 segment.

Functional properties of a crossed spinocerebellar tract with cell bodies located in laminae VII and IX of the S1 segment were investigated using intracellular recording. The neurones were found to be excited by group I and II muscle afferents and afferents of skin, joint and interosseus nerves. Volleys from group II muscle afferents and cutaneous afferents evoked inhibition in these cells. It is concluded that S1 spinocerebellar neurones convey a similar type of information to that of dorsal spinocerebellar tract and ventral spinocerebellar tract neurones but integrate it in a different way.     

The time course and specificity of the changes in the behavioural and dorsal horn cell responses to noxious stimuli following peripheral nerve capsaicin treatment in the rat

Capsaicin, a neurotoxin which acts specifically on sensory primary afferent C-fibres was applied locally to one sciatic nerve of a group of rats. One to sixteen days following this a series of behavioural and electrophysiological studies were performed. The latency of foot withdrawal of the rats to a controlled thermal noxious stimuli was significantly elevated (200%). The peak increase occurred on day 1 after treatment; the response then fell to a steady but elevated level for up to 16 days. Responses to noxious mechanical stimuli were unaffected by capsaicin treatment. Single unit analysis of the dorsal horn of the spinal cord showed that the number of neurones in deep laminae (4, 5 and 6) responding to a C peripheral volley was normal (60%) for the first 2 days after treatment. On day 3 post treatment, the number of cells with a C input began to fall reaching a maximal decrease on day 7 (25%), where it remained up to day 16. In contrast to this delayed effect on C-evoked responses, the number of cells responding to noxious heating of the skin fell from control levels of 60% down to 20% on day 1 and remained decreased for up to 16 days. The onset of thermal analgesia following local, capsaicin treatment, therefore, closely parallels the time course of the decrease of noxious heat-evoked responses in the dorsal horn. Since at early pretreatment times, the electrically C-evoked activity is normal these effects are likely to be due to action on peripheral C-fibre nociceptors in the skin. At a later stage capsaicin also appears to act on the central terminals of fibres reducing transmission to second order dorsal horn neurones.     

Responses of identified spinal neurones to acetylcholine applied by micro-electrophoresis.

1. The responses of identified cells in the cat Clarke's column and dorsal horn to micro-electrophoretically applied cholinomimetics and anti-cholinergic substances have been investigated. 2. Both antidromically identified (DSCT neurones) and synaptically activated neurones from the region of the Clarke's column of the spinal cord were excited by ACh. However, the proportion of ACh excited cells was greater in units synaptically activated by ipsilateral dorsolateral funiculus stimulation (78%) than in DSCT neurones (50%). In addition, about 55% of neurones activated either antidromically or synaptically by ipsilateral dorsal column stimulation were excited by ACh. 3. In contrast to a relatively weak excitatory potency on the DSCT neurones (maximum firing frequency did not exceed 130% of the control activated by ipsilateral dorsolateral funiculus stimulation (maximum firing frequency reached 430% of the control level). 4. ACh has a relatively quick and rapidly reversible excitatory effect on Clarke's column neurones and some types of dorsal horn interneurones, which can be obtained also with nicotine. However, the action of nicotine is frequently delayed in onset and recovery. This excitatory action of ACh can be blocked or markedly depressed by dihydro-beta-erythroidine. These results and those obtained with acetyl-beta-methylcholine and atropine seem to suggest that the receptors mediating excitation of the cholinoceptive spinal cells activated either antidromically or synaptically by ipsilateral dorsolateral funiculus stimulation besides predominantly nicotinic have also weak muscarinic properties. 5. Desensitization with repeated applications of ACh and nicotine has been observed in both DSCT neurones and units antidromically activated by ipsilateral dorsal column stimulation. 6. About 11% of units antidromically activated by ipsilateral dorsolateral funiculus stimulation were depressed by ACh. In addition, the depressant effect of ACh was more frequently encountered in the cells unresponsive either to the dorsolateral funiculus or dorsal column stimulation. ACh depression was also seen in units activated either antidromically or synaptically by ipsilateral dorsal column stimulation. In contrast, none of the units synaptically activated by the ipsilateral dorsolateral funiculus stimulation were depressed by ACh. The same was true for spinal neurones receiving convergent peripheral inputs activated either antidromically or synaptically by ipsilateral dorsolateral or dorsal column stimulation. 7. The findings that ACh depression of all tested DSCT neurones is blocked by atropine and readily evoked by acetyl-beta-methylcholine indicates that receptors mediating the effect are of muscarinic type.     

Convergence of skin reflex and corticospinal effects in segmental and propriospinal pathways to forelimb motoneurones in the cat

The organization of facilitatory convergence from cutaneous afferents (Skin) and the corticospinal tract (pyramidal tract, Pyr) in pathways to forelimb motoneurones of mainly distal muscles was studied in anaesthetized cats by analysing postsynaptic potentials (PSPs), which were spatially facilitated by combinations of stimuli to the two sources at different time intervals. Conditioning Pyr volleys facilitated Skin-evoked PSPs of fixed (1.2–3.6 ms) central latencies (Skin PSPs), suggesting that disynaptic and polysynaptic skin reflex pathways are facilitated from the pyramidal tract. The shortest latencies (1.2–1.7 ms) of pyramidal facilitation suggested direct connection of pyramidal fibres with last order neurones of skin reflex pathways. Conditioning Skin volleys facilitated Pyr-evoked PSPs of fixed, mostly disynaptic latencies (1.0–2.5 ms; Pyr PSPs), suggesting that pyramido-motoneuronal pathways are facilitated from Skin at a premotoneuronal level. The shortest pathway from skin afferents to the premotor neurones appeared to be monosynaptic. Although Pyr and Skin volleys were mutually facilitating, the facilitation curve of Pyr PSPs and that of Skin PSPs were discontinuous to each other, with the peak facilitation at different Skin-Pyr volley intervals. Transection of the dorsal column (DC) at the C5/C6 border had little effect on the latencies or amplitudes evoked by maximal stimulation and the pyramidal facilitation of Skin PSPs. In contrast, the facilitation of Pyr PSPs by Skin stimulation was greatly decreased after the DC transection, and the facilitation curve of Pyr PSPs was continuous to that of Skin PSPs, with no separate peak. Latencies of Pyr PSPs ranged similarly to those in DC intact preparations. More rostral DC transection (C4/C5 border) reduced Skin-facilitated Pyr excitatory PSPs (EPSPs) less than C5/C6 lesions, suggesting that the C5 segment also contains neurones mediating Skin-facilitated Pyr EPSPs. The results show that convergence from skin afferents and the corticospinal tract occurs at premotor pathways of different cervical segments. We suggest that corticospinal facilitation of skin reflex occurs mostly in the brachial segments and Skin facilitation of cortico-motoneuronal effects takes place largely in the rostral cervical segments and partly in the brachial segments.     

Evidence for a role of GABA interneurones in the cortical modulation of midbrain 5-hydroxytryptamine neurones.

Recent electrophysiological studies demonstrate that the ventral medial prefrontal cortex has a powerful inhibitory influence on 5-hydroxytryptamine (5-HT) neurones in the dorsal raphe nucleus. Here we utilised a combination of anatomical and electrophysiological methods to characterise the cellular substrate underlying this effect.Anterograde tracing (Phaseolus vulgaris leucoagglutinin) using electron microscopy demonstrated a pathway from the ventral medial prefrontal cortex that makes neuronal contacts throughout the dorsal raphe nucleus. These contacts were predominantly asymmetrical synapses adjoining GABA immunoreactive dendrites and spines.In vivo extracellular recordings were made in the dorsal raphe nucleus of the anaesthetised rat from a subpopulation of non-5-HT neurones. These neurones were fast-firing, irregular and with short spike width, properties strongly reminiscent of immunochemically identified GABA interneurones in other brain regions. Recordings of classical 5-HT neurones were also included. Electrical stimulation of the ventral medial prefrontal cortex elicited a rapid onset (16 ms latency), orthodromic excitation of the non-5-HT neurones (13/25 neurones). This stimulation also caused a pronounced inhibition of most 5-HT neurones tested, with a longer latency (30 ms), and this was partially blocked by locally applied bicuculline.These data provide the first evidence that the ventral medial prefrontal cortex influences the activity of large numbers of raphe 5-HT neurones by targeting a local network of GABA neurones. This circuitry predicts that physiological and pathological changes in the ventral medial prefrontal cortex will impact on significant parts of the forebrain 5-HT system.     

Localization and function of the Kv3.1b subunit in the rat medulla oblongata: focus on the nucleus tractus solitarii

The voltage-gated potassium channel subunit Kv3.1 confers fast firing characteristics to neurones. Kv3.1b subunit immunoreactivity (Kv3.1b-IR) was widespread throughout the medulla oblongata, with labelled neurones in the gracile, cuneate and spinal trigeminal nuclei. In the nucleus of the solitary tract (NTS), Kv3.1b-IR neurones were predominantly located close to the tractus solitarius (TS) and could be GABAergic or glutamatergic. Ultrastructurally, Kv3.1b-IR was detected in NTS terminals, some of which were vagal afferents. Whole-cell current-clamp recordings from neurones near the TS revealed electrophysiological characteristics consistent with the presence of Kv3.1b subunits: short duration action potentials (4.2 ± 1.4 ms) and high firing frequencies (68.9 ± 5.3 Hz), both sensitive to application of TEA (0.5 m m ) and 4-aminopyridine (4-AP; 30 μ m ). Intracellular dialysis of an anti-Kv3.1b antibody mimicked and occluded the effects of TEA and 4-AP in NTS and dorsal column nuclei neurones, but not in dorsal vagal nucleus or cerebellar Purkinje cells (which express other Kv3 subunits, but not Kv3.1b). Voltage-clamp recordings from outside-out patches from NTS neurones revealed an outward K⁺ current with the basic characteristics of that carried by Kv3 channels. In NTS neurones, electrical stimulation of the TS evoked EPSPs and IPSPs, and TEA and 4-AP increased the average amplitude and decreased the paired pulse ratio, consistent with a presynaptic site of action. Synaptic inputs evoked by stimulation of a region lacking Kv3.1b-IR neurones were not affected, correlating the presence of Kv3.1b in the TS with the pharmacological effects.     

Paresthesia and hypesthesia in the dorsum of the foot as the presenting complaints of a ganglion cyst of the foot

Although ganglion cysts of the foot represent a substantial amount of lumps in this region, they rarely cause peripheral nerve symptoms. We describe the clinical case of a 43‐year‐old female with complaints in the previous three months of hypesthesia and paresthesia in the anterior portion of the medial half of the dorsum of her left foot that extended into the first interdigital cleft. She associated the start of her neurological symptoms to the appearance of a lump in the dorsum of the foot. A presumptive diagnosis of compression of the medial branch of the deep fibular nerve and of the medial dorsal cutaneous nerve in the dorsum of the foot by a ganglion cyst was made. Ultrasonography confirmed the cystic nature of the lesion and surgery allowed complete excision of a mass arising from the joint between the medial and intermediate cuneiform bones that was compressing the deep fibular nerve and the medial dorsal cutaneous nerve. Pathological examination confirmed that the lesion was a cystic ganglion. As far as the authors know, the simultaneous compression of the medial branch of the deep fibular nerve and of the medial dorsal cutaneous nerve in the dorsum of the foot by a ganglion cyst has not been described before. Clin. Anat. 23:606–610, 2010. © 2010 Wiley‐Liss, Inc.     

Afferent G Units Responding to Mechanical,Thermal and Chemical Stimuli in Human Non-Glabrous Skin

C unit activity was recorded with microelectrodes from intact sensory fascicles in the human peroneal nerve. The analysis includes 46 afferent units with receptive fields predominantly on the dorsum of the foot and ankle. 16 units were tested quantitatively. Another 30 units were tested qualitatively by a combination of electrical and natural stimuli in the skin. This method was valuable for a reliable identification of activity in individual afferent C elements, when several C units with similar potential amplitudes responded to testing in the skin. The units were not spontaneously active at normal skin temperatures but one unit showed a low frequency discharge at a skin temperature of 22^o C. Cooling by ether evaporation was an inefficient stimulus except for 2 units. Gentle mechanical stimuli did not activate any of the units, whereas afferent C unit impulses were induced by moderately intense mechanical stimuli, noxious heat and various chemical irritants. The sensations produced by stimuli inducing intense afferent C unit activity were reported as “burning or delayed pain”, whereas stimuli eliciting low frequency activity often were reported as “itch”. It is concluded that polymodal C receptors, similar with “polymodal nociceptors” in the cat and monkey, are numerous in skin areas sparsely covered with hairs on the dorsum of the foot and ankle in man, whereas no low threshold C mechanoreceptors were identified. The experiments do not exclude the possibility that both delayed pain and burning itch sensations may be mediated by different impulse patterns from polymodal C receptors.     

Activity evoked from the mesencephalic tegmentum in descending pathways other than the rubrospinal tract

Summary Discharges evoked by mesencephalic stimulation have been recorded from the contralateral dissected dorsal and ventral quadrants in the lower thoracic region of the spinal cord in cats. The effect of this activity on different spinal cord mechanisms was analysed.After interruption of the rubrospinal tract in the lateral part of the medulla, stimulation just dorsal to the red nucleus still evokes a discharge in the contralateral dorsal quadrant. The discharge which requires repetitive stimulation is probably mediated by a two-neurone pathway. Since the stimuli giving this dorsal discharge produces inhibition of interneuronal transmission from the flexor reflex afferents to motoneurones, which is the characteristic effect of activity in the dorsal reticulospinal system (Engberg et al., 1968) it is suggested that the second order neurones belong to this pathway.Stimulation just dorsal to the red nucleus also evokes a synchronized discharge in the contralateral ventral quadrant, mediated by a two-neurone pathway. The first order neurones are at least partly of tectal origin; the second order neurones originate from the brain stem and their axons descend in the medial longitudinal fasciculus. Activity in these fibres has no detectable effect on spinal cord mechanism controlling hindlimb muscles but produces monosynaptic EPSPs in motoneurones of the upper lumbar segments.Some observations are reported regarding long propriospinal excitatory and inhibitory connexions to upper lumbar motoneurones.This work was supported by the Swedish Medical Research Council (Project No. 14X-94-07C).     

Proliferation of protease-enriched mast cells in sarcoptic skin lesions of raccoon dogs

Skin sites, tongue, lung, liver, jejunum and rectum from two raccoon dogs with Sarcoptes scabiei infestation and five normal (control) raccoon dogs were examined in terms of the distribution, proteoglycan properties and protease activity of mast cells. Infestation with S. scabiei caused a significant increase in the number of dermal mast cells. While the number of mast cells (average +/- standard deviation) in specimens of skin from the dorsum, dorsal neck, dorsal hind foot and dorsal fore foot was 40.0 +/- 19.8/mm2 in control animals, it was 236.1 +/- 58.9/mm2 in the skin of mange-infested animals. Histochemical analysis revealed the glycosaminoglycan, heparin, within the mast cells of all organs examined in both control and affected animals. Enzyme-histochemical detection of serine proteases demonstrated an increase in mast-cell-specific protease activity (i.e., chymase and tryptase) in the skin of infested animals. The percentage of mast cells demonstrating chymase activity was 53.0 +/- 27.4% in control animals and 73.8 +/- 19.4% in mite-infested animals. The corresponding results for tryptase activity were 53.5 +/- 25.2% and 89.4 +/- 9.8%. Increases in mast cell chymase or tryptase activity, or both, were also observed within other organs of the infected animals, but the total number of mast cells found at such sites (with the exception of liver and ventrolateral pinna) did not differ from those of control animals.     

The morphology of spinocervical tract neurones in the cat.

1. The morphology of physiologically identified spinocervical tract (SCT) neurones was studied using the intracellular injection of Procion dyes in anesthetized and decerebrate cats. 2. Extracellular recordings were made from SCT neurones at depths between 1000 and 2850 mum from the cord surface but neurones were only stained at depths between 1100 and 2400 mum. 3. The dendritic trees of stained SCT neurones were reconstructed in the transverse plane of the spinal cord. All SCT neurones had well developed dorsal dendrites but despite this it is not possible to consider the twenty-two SCT cells in out sample as consituting a morphologically homogenous population. 4. There was no correlation between the form of the dendritic trees and the depth of SCT neurones in the dorsal horn as determined both from measurements from the dorsal grey-white border and the position of cells with respect to the border between Rexed's laminae II and III. 5. Six types of SCT neurones were identified on the basis of the form of their dendritic trees as viewed in the transverse plane: (1) radially symmetrical, (2) semicircular, (3) large elliptical, (4) bilobed, (5) triangular, (6) small elliptical. Each of these types was found only in a certain region across the dorsal horn although any one region could contain more than one type. 6. Spinocervical tract neurones with small elliptical dendritic trees always had receptive fields encompassing part of the hip or thigh and were unique in being located in the lateral portions of the horn. 7. There was no correlation between the morphology of SCT neurones and their excitatory cutaneous inputs, receptive field size, axonal conduction velocity or depth in the dorsal horn.     

Indications for coupling between feline spinocervical tract neurones and midlumbar interneurones

The possibility of collateral segmental actions of spinocervical tract (SCT) neurones upon interneurones with input from cutaneous and group II muscle afferents was investigated in deeply anaesthetized cats. To this end, intracellular and/or extracellular recordings were made from 35 dorsal horn and 15 intermediate zone interneurones in midlumbar segments of the spinal cord and effects of stimulation of the ipsilateral dorso-lateral funiculus (DLF) at C3 and C1 levels, i.e. below and above the lateral cervical nucleus where axons of SCT cells terminate, were compared. The stimuli applied at the C3 segment were within the range of stimuli (50–100 μA) required for antidromic activation of SCT neurones in the same experiment. Those applied at the C1 segment (200–500 μA) were at least 3 times stronger than C3 stimuli. Under the same experimental conditions, long ascending and descending tract neurones (dorsal spino-cerebellar and rubro-spinal tract neurones) with axons in the DLF were activated at similar thresholds from the C1 and C3 segments. Intracellular recordings were made from 29 interneurnoes of which 19 (65%) were dorsal horn and 10 (35%) were intermediate zone interneurones. Excitatory postsynaptic potentials (EPSPs) evoked by single stimuli applied at the C3 segment, but not the C1 segment, were found in 14 (48%) of those interneurones; their latencies (3.0–5.7 ms) and frequency following with only minimal temporal facilitation were as required for potentials being evoked monosynaptically by the fastest conducting SCT neurones. Extracellular recordings were made from 30 interneurones (24 dorsal horn and 6 intermediate zone interneurones), and in these neurones spike potentials induced from the C3, but not from the C1 segment, were evoked only by short trains of stimuli. However, their latencies from the first effective stimulus (4.3–5.4 ms) were compatible with mono- or oligosynaptically mediated collateral actions of SCT neurones. They were found in 10 (33%) of the 30 investigated interneurones. Similar effects of C3 stimuli were found in similar proportions of dorsal horn interneurones and intermediate zone interneurones. Indications were also found for synaptic actions evoked by C3 stimuli that could not be attributed to direct collateral actions of SCT neurones. In some intracellularly recorded dorsal horn interneurones, short-latency EPSPs were evoked from the C3 segment by the 2nd or 3rd stimulus in the train, but not by single stimuli. In other dorsal horn and intermediate zone interneurones, inhibitory postsynaptic potentials (IPSPs) were evoked from the C3 segment at minimal latencies (2.7–3.2 ms), which might be too short to allow their mediation via SCT neurones. We conclude that SCT neurones might be used to forward information from muscle group II and cutaneous afferents not only to neurones in the lateral cervical nucleus and via them to thalamus and cerebral cortex but also to interneurones in spinal reflex pathways. Thereby reflex actions evoked from group II and cutaneous afferents might be co-ordinated with responses mediated by supraspinal neurones. We conclude also that dorsal horn and intermediate zone mid-lumbar interneurones might contribute to the previously reported di-and poly-synaptic excitation or inhibition of postsynaptic dorsal column (PSDC), spinothalamic tract (STT) and spinomesencephalic tract (SMT) neurones by collateral actions of SCT cells. Thereby these interneurones might contribute to the co-ordination of responses mediated by various populations of supraspinal neurones. Received: 18 November 1996 / Accepted: 1 September 1997     

Methamphetamine increases the hippocampal alpha(2A)-adrenergic receptor and Galpha(o) in mice

Simultaneous recordings of cortical activity, recorded as the cortical local field potential (CLFP) in the contralateral posterior sigmoid gyrus, and the spinal activity, recorded as the cord dorsum potential (CDP) of the L6 lumbar segment, were made in the anaesthetized cat. The electrodes were positioned in somatosensory regions where the largest spontaneous negative CLFPs and CDPs were recorded. We found that spontaneous negative CLFPs were preceded by spontaneous negative CDPs with a mean latency of 14.4+/-3.5 ms. Amplitude of these spontaneous negative CLFPs was abolished after section of the dorsal columns and ipsilateral dorsolateral funiculus. It is concluded that the neurones of the primary somatosensory cortex can be driven by dorsal horn spinal neurones producing the spontaneous negative CDPs. This suggests very strongly that spontaneous neuronal activity in somatosensory regions of the brain is generated not only by ongoing activity of neurones located at supraspinal sites, but also by ongoing activity of spinal neurones.