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PubMed1977

The ventral spino-olivocerebellar system in the cat. III. Functional characteristics of the five paths.

1. Five spino-olivocerebellar paths ascending through the ventral funiculus (VF-SOCPs) with different projection zones in the cerebellar cortex have been distinguished (Oscarsson and Sjöuld, 1977). The paths are denoted the a-, b1-, b2-, c1- and c3-VF-SOCPs according to the labelling of the projection zones. The functional organization of these paths has now been investigated. 2. All five paths are activated by the flexor reflex afferents from wide receptive fields (one or more limbs). Distal nerves are more effective in evoking responses than proximal nerves. 3. The a-, c1- and c3-paths are activated from the ipsilateral hindlimb only. The b1- and b2-paths are activated bilaterally from the forelimbs and hindlimbs, respectively. 4. The a-, b1- and b2-paths have long segmental delays indicating a polysynaptic linkage between the primary afferents and the tract neurones, whereas the c1- and c3-paths have short delays demonstrating a monosynaptic linkage. 5. The neurones giving origin to the paths are situated within a few segments of the dorsal root entrance. The axons cross the midline, ascend through the contralateral ventral funiculus, and activate the olivary neurones monosynaptically. 6. The spino-olivary tract of the c3-path has an upper conduction velocity of 30 m/s, whereas the other paths have upper conduction velocities of 40--45 m/s. 7. The segmental delay of the b1-VF-SOCP is much longer (mean 8.7 ms) than that of the b2-VF-SOCP (mean 3.9 ms). As a result simultaneous stimuli to the hindlimbs and forelimbs are signalled to reach the cerebellar cortex at the same time. 8. It is suggested that the information carried by the different paths is concerned with the segmental motor control.

Animals↗
PubMed2006

Multiple pathways for noxious information in the human spinal cord.

To investigate the pathways of noxious information in the spinal cord in humans, we recorded cortical potentials following the stimulation of A-delta fibers using a YAG laser applied to two cutaneous points on the back at the C7 and Th10 level, 4cm to the right of the vertebral spinous process. A multiple source analysis showed that four sources were activated; the primary somatosensory cortex (SI), bilateral parasylvian region (Parasylvian), and cingulate cortex. The activity of the cingulate cortex had two components (N2/P2). The mean peak latencies of the activities obtained by C7 and Th10 stimulation were 166.9 and 186.0 ms (SI), 144.3 and 176.8 ms (contralateral Parasylvian), 152.7 and 185.5 ms (ipsilateral Parasylvian), 186.2 and 215.8 ms (N2), and 303.0 and 332.3 ms (P2). Estimated spinal conduction velocities (CVs) of the respective activities were 16.8, 9.3, 8.7, 10.1 and 10.7 m/s. CV of SI was significantly faster than the others (P<0.05). Therefore, our results suggested that noxious signals were conveyed through at least two distinct pathways of the spinal cord probably reaching distinct groups of thalamic nuclei. Further studies are required to clarify the functional significance of these two pathways.

Adult↗
PubMed1999

Paradoxical heat sensation in healthy subjects: peripherally conducted by A delta or C fibres?

Paradoxical heat sensation upon cooling of the skin has been reported in central as well as in peripheral neurological conditions. In our study, we examined this phenomenon in 35 naive healthy test subjects, of whom 23 experienced paradoxical heat sensation under test conditions. We measured the peripheral conduction velocities of cold sensation, warm sensation and of paradoxical heat sensation by using a quantitative sensory testing model of indirect peripheral conduction velocity measurement. This was based on comparison of measurements at a proximal and a distal site using two measurement methods, one inclusive and the other exclusive of reaction time. We found that the conduction velocity of paradoxical heat sensation (0.70 m/s) was similar to that of warm sensation (0.68 m/s), and that the conduction velocity of cold sensation (7.74-8.01 m/s) was considerably faster. Thus, we conclude that paradoxical heat sensation in healthy subjects is conducted peripherally via slow unmyelinated C fibres and not via the faster A delta fibres. Consequently, we propose that paradoxical heat sensation is encoded via the heat sensing pathway, in accordance with the labelled-line code theory. The mechanisms proposed suggest a malfunctioning cold-sensing pathway disinhibiting the heat-sensing pathway, at peripheral, central or both levels, thus facilitating a paradoxical heat sensation.

Adolescent↗
PubMed1995

Ventrostriopallidal functional interconnections with cortical and quasi-cortical regions.

A total of 287 neurons were antidromically driven in quasi-cortical regions, i.e., anterior olfactory nucleus (24%), basolateral amygdala (13%), main olfactory bulb (4%), prefrontal cortex (37%), and in the hippocampal formation (22%) following macro- and microstimulation of the rat's ventrostriopallidal region (VSPR). In addition, a substantial number of units (n = 175) were also transynaptically affected in all these structures by shocks delivered to the VSPR. Excitatory effects were detected in 50 neurons (56.1% of responsive cells), 36 cells (40.4%) responding with inhibition of spontaneous discharges. Conversely, stimulation of cortical and quasi-cortical regions antidromically discharged (n = 37) or transynaptically affected (n = 151) units in the VSPR; 168 neurons were not responsive to VSPR stimulation. Axon collateralization (branching) of 14 neurons in anterior olfactory nucleus, basolateral amygdala, and hippocampal formation was revealed with the use of the reciprocal collision test. Conduction properties of 35 neurons, evaluated by paired-pulse stimulation, indicated that only 26% showed a significant increase in conduction velocity and a decrease in threshold during the supernormal phase. The present findings confirm and extend previous neuroanatomical studies that have, first, described strong interconnections between the neocortex and striatal structures, and second, that the VSPR as suggested by previous structural, hodological, and histochemical studies, seems to maintain a more close relationship with olfactory related structures than hitherto suspected.

Animals↗
PubMed1994

Multiple sclerosis: assessment of lesional levels by means of transcranial stimulation.

Conduction in the Pyramidal Tracts (PTs) was studied in 30 healthy volunteers and 17 patients with definite Multiple Sclerosis. Central motor conduction time (CMCT) was assessed employing unipolar electrical transcranial stimulation and studies of the peripheral conduction time. Fourteen out of the seventeen studied patients showed CMCT abnormalities. No significative correlation was found between the intensity of muscle weakness and the slowness of conduction in the corresponding PTs. Subclinical abnormalities were detected in more than half of the studied patients. CMCT slowness showed a good correlation with the time course of the disease in the cortico-cervical (CCT) but not in the cortico-lumbar (CLT) tracts. Evidence favoring the existence of two different lesional levels along the PSs was found in 9 out of the 14 patients studied with recordings in the hand and leg muscles. Two patterns of abnormalities gave support to this conclusion. The first consisted of slowed conduction or inexcitability in both the CCT and CLT at one side, while only one of the contralateral PTs was impaired. In the second one, the 4 explored PTs showed a slowed conduction, but in addition, CMCT difference between the CLT and CCT was longer than normal. Both patterns suggest that one lesional level could be situated between the internal capsula and the lower cervical cord and the other in the spine below the 8th cervical methamera or in the corona radiata.

Adolescent↗
PubMed1987

Neurons (presumably A1-cells) projecting from the caudal ventrolateral medulla to the region of the supraoptic nucleus respond to baroreceptor inputs in the rabbit.

Extracellular recordings were made in the caudal ventrolateral medulla from 29 neurons that could be antidromically activated from the region of the supraoptic nucleus in the rabbit. The median axonal conduction velocity was 0.8 m/s. Of 15 cells tested only one did not respond to some form of baroreceptor input. Fourteen were inhibited by experimentally increasing arterial pressure and 8 were excited by decreasing arterial pressure. Stimulation of the aortic depressor nerve decreased the discharge rate of 8 out of 12 cells tested. The location and projections of these neurons suggest that they were A1 noradrenaline-synthesizing cells.

Action Potentials↗
PubMed2003

Model of song selectivity and sequence generation in area HVc of the songbird.

In songbirds, nucleus HVc plays a key role in the generation of the syllable sequences that make up a song. Auditory responses of neurons in HVc are selective for single syllables and for combinations of syllables occurring in temporal sequences corresponding to those in the bird's own song. We present a model of HVc that produces syllable- and temporal-combination-selective responses on the basis of input from recorded bird songs filtered through spectral temporal receptive fields similar to those measured in field L, a primary auditory area. Normalization of the field L outputs, similar to that proposed in models of visual processing, plays an important role in the generation of syllable-selective responses in the model. For temporal-combination-selective responses, N-methyl-d-aspartate (NMDA) conductances provide a memory that allows inhibitory neurons to gate responses to a final syllable in a sequence on the basis of responses to earlier syllables. When the same network that produces temporal-combination-selective responses is excited by a nonspecific timing signal, it generates a similar pattern of output as it does in response to auditory song input. Thus the same model network can perform both sensory and motor functions.

Algorithms↗
PubMed1981

Evaluation of somatosensory pathway by short latency evoked potentials in patients with end-stage renal disease maintained on hemodialysis.

Somatosensory evoked potentials and peripheral nerve conduction velocity were studied on 10 patients with end-stage renal failure maintained on hemodialysis treatment. None of the patients had symptomatic neuropathy and the only abnormal finding on neurological examination was absent ankle jerk in 7 of the 10 patients. Nerve conduction velocities and intercomponent conduction times of the somatosensory evoked potential were determined using electrical stimulation of nerve trunks and mechanical stimulation of the finger. Nerve ending conduction times was determined using a combination of the two stimuli and found to be abnormal in 8 patients. All 10 patients had slowed sensory conduction velocities at some segment of the tested peripheral nerve. Intercomponent time differences in the somatosensory evoked potentials could not be defined in the majority of our patients due to the absence of many of the components, making it impossible to distinguish whether the changes in somatosensory evoked potentials were due to impaired peripheral input, or to changes in the somatosensory pathway.

Adult↗
PubMed1990

Private inhibitory systems for the X and Y pathways in the dorsal lateral geniculate nucleus of the cat.

1. Inhibitory connections of X- and Y-type principal cells in the cat's dorsal lateral geniculate nucleus were studied with intracellular recording techniques in barbiturate-anaesthetized animals. Cells were identified as principal cells by antidromic activation from the visual cortex and as X or Y types by their responses to visual stimulation. 2. Graded electrical stimulation was used to obtain selective activation of X and Y ganglion cell axons. The optic nerves were stimulated through ring electrodes behind the eye bulbs and the evoked nerve volley was monitored by an optic tract electrode. The nerve volley consisted of two well-segregated components, an early, low-threshold Y component and a late, high-threshold X component. 3. All principal cells received monosynaptic excitation and disynaptic feed-forward inhibition from optic nerve fibres. The excitatory and inhibitory postsynaptic potentials were evoked by Y axons in Y cells and by X axons in X cells. Thus, the feed-forward inhibitory pathway to principal cells is type selective. 4. Recurrent inhibition was evoked in all cells by antidromic activation of principal cell axons in the visual cortex. The recurrent inhibitory potentials had significantly shorter latencies in Y than in X cells but with considerable overlap between the two samples. This overlap presumably reflects a similar overlap in antidromic conduction times for X and Y principal cell axons. 5. Recurrent inhibitory potentials evoked in the orthodromic direction by optic nerve stimulation originated from Y axons in Y principal cells and from X axons in X cells as would be expected for a type-selective recurrent inhibitory pathway. 6. It is concluded that X and Y principal cells in the dorsal lateral geniculate nucleus have similar but functionally separate inhibitory circuits.

Animals↗
PubMed2000

Responses of reticulospinal neurons in intact lamprey to vestibular and visual inputs.

A lamprey maintains the dorsal-side-up orientation due to the activity of postural control system driven by vestibular input. Visual input can affect the body orientation: illumination of one eye evokes ipsilateral roll tilt. An important element of the postural network is the reticulospinal (RS) neurons transmitting commands from the brain stem to the spinal cord. Here we describe responses to vestibular and visual stimuli in RS neurons of the intact lamprey. We recorded activity from the axons of larger RS neurons with six extracellular electrodes chronically implanted on the surface of the spinal cord. From these multielectrode recordings of mass activity, discharges in individual axons were extracted by means of a spike-sorting program, and the axon position in the spinal cord and its conduction velocity were determined. Vestibular stimulation was performed by rotating the animal around its longitudinal axis in steps of 45 degrees through 360 degrees. Nonpatterned visual stimulation was performed by unilateral eye illumination. All RS neurons were classified into two groups depending on their pattern of response to vestibular and visual stimuli; the groups also differed in the axon position in the spinal cord and its conduction velocity. Each group consisted of two symmetrical, left and right, subgroups. In group 1 neurons, rotation of the animal evoked both dynamic and static responses; these responses were much larger when rotation was directed toward the contralateral labyrinth, and the dynamic responses to stepwise rotation occurred at any initial orientation of the animal, but they were more pronounced within the angular zone of 0-135 degrees. The zone of static responses approximately coincided with the zone of pronounced dynamic responses. The group 1 neurons received excitatory input from the ipsilateral eye and inhibitory input from the contralateral eye. When vestibular stimulation was combined with illumination of the ipsilateral eye, both dynamic and static vestibular responses were augmented. Contralateral eye illumination caused a decrease of both types of responses. Group 2 neurons responded dynamically to rotation in both directions throughout 360 degrees. They received excitatory inputs from both eyes. Axons of the group 2 neurons had higher conduction velocity and were located more medially in the spinal cord as compared with the group 1 neurons. We suggest that the reticulospinal neurons of group 1 constitute an essential part of the postural network in the lamprey. They transmit orientation-dependent command signals to the spinal cord causing postural corrections. The role of these neurons is discussed in relation to the model of the roll control system formulated in our previous studies.

Action Potentials↗
PubMed1982

Central somatosensory conduction time from 10 to 79 years.

Somatosensory evoked potentials were recorded simultaneously from the neck and scalp following stimulation of the median nerve at the wrist in 83 normal subjects aged 10-79 years. The central somatosensory conduction time was measured by subtracting the peak latency of the major response from the upper cervical area (N14) from that of the primary cortical response (N20). The central conduction time remained constant between 10 and 49 years but increased abruptly by approximately 0.3 msec between the fifth and sixth decades. Following this increase there was no further change in the central conduction time. Changes with age in the amplitude of N14 and N20 differed both from the changes in latency and from each other. The amplitude of N14 was stable between 10 and 39 years but then declined progressively. The amplitude of N20 deceased between 10 and 39 years and then increased until the end of the seventh decade.

Adolescent↗
PubMed1988

Contrasting properties of medial septal neurons projecting to hippocampus or interpeduncular nucleus in the rat.

The properties of neurons of the medial septal nucleus and of the nucleus of the diagonal band of Broca which project to hippocampus or to interpeduncular nucleus were compared in rats anesthetized with urethane. Neurons projecting to the interpeduncular nucleus had a slower conduction velocity and a lower spontaneous discharge rate. In contrast, their responses to various putative neurotransmitters (glutamate, GABA, acetylcholine) were similar. In a few cases, neurons projecting to both structures (i.e., with branched axons) were observed. Both septohippocampal and septointerpeduncular pathways are known to be partly cholinergic. Our results show that they originate from two independent populations of medial septal-nucleus of the diagonal band of Broca neurons with different physiologic properties.

Animals↗
PubMed1976

Intracellular responses from granule cell layer in slices of rat hippocampus: perforant path synapse.

Intracellular responses were recorded in vitro from the denate granule cell layer of hippocampal slices prepared from adult rats. Spontaneous activity of granule cells in vitro consisted of action potentials and small, graded depolarizations, presumably of synaptic origin. Granule cells could be activated by injection of depolarizing current or release of hyperpolarizing current. Individual granule cells spatially summed input from the perforant path and fired multiple action potentials in vitro following strong presynaptic volleys. Depolarization decreased and hyperpolarization increased the EPSP amplitude, which is consistent with a conductance-increase mechanism. Although we could demonstrate postexcitatory inhibition in some cells, granule cells in vitro appeared to receive less inhibitory feedback than in vivo, EPSP amplitude and spike output of granule cells showed frequency potentiation and posttetanic potentiation to perforant path stimulation. These intracellular responses in vitro complement some of the findings from field-potential analyses of the dentate gyrus in intact animals.

Action Potentials↗
PubMed1975

The mode of synaptic linkage in the cerebro-ponto-cerebellar pathway of the cat. II. Responses of single cells in the pontine nuclei.

Extracellular and intracellular recordings were made from single cells in the pontine nuclei (PN) of the cat. PN cells were identified by antidromic invasion from the cerebellum by stimulating either the brachium pontis (BP) or the white matter near the cerebellar nuclei. The cerebrally-induced impulses excited PN cells postsynaptically with a monosynaptic latency. Both fast and slow conducting cortical fibres contributed to the corticopontine excitation, so that the latency varied over a wide range. Measurements of the latencies for antidromic and corticopontine excitation and of the distances between stimulated sites permitted the calcuation of conduction velocities of PN cell axons and of their cortical input fibres. PN cells with fast conducting axons received convergence from both fast and slow cortical fibres, whereas PN cells with slow axons were innervated only by slow cortical fibres. The majority of PN cells were also excited by stimulating the medullary pyramid through collaterals of the pyramidal tract. Evidence of abundant pyramidal collaterals was provided by the collision technique. The functional role of the PN is discussed in connection with the cerebro-cerebellar loop circuits.

Animals↗
PubMed2005

Chronically implanted electrodes for repeated stimulation and recording of spinal cord potentials.

We have recorded and characterized the spinal cord evoked potentials (SCEPs) from the epidural space in the halothane-anesthetized rats. A group of 11 adult Wistar male rats was chronically implanted with two pairs of epidural electrodes. SCEPs were repeatedly elicited by applying electrical stimuli via bipolar U-shaped electrodes to the dorsal aspect of the spinal cord at C3-4 or Th11-12 levels, respectively. Responses were registered with the other pair of implanted electrodes, thus allowing us to monitor the descending (stimulation cervical/recording thoracic) and ascending SCEPs (stimulation thoracic/recording cervical). We studied the time-dependent changes of several SCEP parameters, among them the latency and amplitude of two major negative waves N1 and N2. During 4-weeks' survival, all major components of recordings remained stable and only minor changes in some parameters of the SCEPs were detected. We concluded that this technique enables repeated quantitative analysis of the conductivity of the spinal cord white matter in the rat. Our results indicate that SCEPs could be used in long-term experiments for monitoring progressive changes (degeneration/regeneration) in long projection tracts, primarily those occupying the dorsolateral quadrants of the spinal cord. These include projections that are of interest in spinal cord injury studies, i.e. ascending primary afferents, and important descending pathways including corticospinal, rubrospinal, reticulospinal, raphespinal and vestibulospinal tracts.

Action Potentials↗
PubMed1985

Identification of two populations of corticothalamic neurons in cat primary somatosensory cortex.

Extracellular and intracellular recordings of corticothalamic (CT) cells were performed in the primary somatosensory cortex of the cat. CT neurons were antidromically activated by electrically stimulating the ventroposterior lateral (VPL) nucleus of the thalamus and were classified into two types according to their physiological properties. Type 1 had no spontaneous activity and no identifiable somatic receptive field. Type 2 fired action potentials spontaneously and responded to mechanical stimulation of the skin or underlying tissues. Axonal conduction velocities were slower for type 1 cells and their cell bodies were located slightly deeper in the cortex than those of type 2 cells. Both types of CT neurons exhibited inhibitory postsynaptic potentials in response to VPL stimulation but an early synaptic excitation and rebound discharge was observed almost exclusively in type 2 cells. These results suggest that only type 2 CT cells can modify the activity of thalamic neurons through a corticothalamic feedback loop.

Action Potentials↗
PubMed1986

Integration in descending motor pathways controlling the forelimb in the cat. 14. Differential projection to fast and slow motoneurones from excitatory C3-C4 propriospinal neurones.

The projection of C3-C4 propriospinal neurones (PNs) to alpha-motoneurones of forelimb muscles has been analysed with the aid of antidromic stimulation of the ascending branch of the PNs to the lateral reticular nucleus (LRN). A single stimulus of 500 microA applied in the caudo-dorsal part of the LRN evoked a maximal or greater than 90% maximal monosynaptic EPSP in the motoneurones. Systematic mapping of EPSPs evoked by stimulation of 500 microA in and around the LRN revealed that at this strength there was hardly any co-activation of a medial system (Peterson et al. 1979) which evoked small monosynaptic EPSPs with shorter latency and faster time course. The LRN EPSP amplitude was positively correlated with the homonymous group Ia EPSP amplitude, the input resistance and the afterhyperpolarization (AHP) duration. It is therefore postulated that the LRN EPSP amplitude is correlated with motor unit type (Burke 1967, 1968; Burke et al. 1973) with the largest EPSPs in slow (S), the smallest in fast, fatiguable (FF) and possibly intermediate sized in fast, fatigue resistant (FR) units. There was only a small difference in latency of the LRN EPSP in fast and slow motoneurones, while the time course was considerably slower in the latter. It is suggested that slow motoneurones receive projection both from fast and slowly conducting PNs but fast motoneurones mainly from fast PNs. Comparison of the disynaptic pyramidal EPSPs and the LRN EPSPs revealed a positive correlation, but the amplitude ratio pyramidal EPSP: LRN EPSP was smaller in slow than in fast motoneurones. A negative correlation was found between this amplitude ratio and the latency of the disynaptic pyramidal EPSP. It is suggested that this correlation reflects the excitability level in the PNs and that low excitability is due to inhibition of the PNs.

Animals↗
PubMed1990

Magneto-electrical stimulation of central motor pathways compared with percutaneous electrical stimulation.

The central motor conduction to the relaxed muscles was studied in 30 normal volunteers using magneto-electrical stimulation (MES) of the central motor pathways. The results were compared with those obtained by the percutaneous electrical stimulation technique (PES) described previously. None of the cortical and spinal latencies (Lcor and Lsp, respectively) and the central motor conduction time were different between MES and PES in the upper limb muscles. In some lower limb muscles, however, the Lsps of MES were significantly shorter than those of PES. This was probably because the magnetic stimulation over the lumbar spinal column activated the motor roots at their exit from the spinal canal rather than the level of conus medullaris, at which activation occurs in the electrical stimulation.

Adult↗