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PubMed1973

Efferent control of arterial chemoreceptors mediated by glossopharyngeal fibres and artifacts introduced by stimulation techniques.

1. In anaesthetized cats, stimulation of the cut carotid sinus nerve generally caused a reduction in discharge in afferent fibres peeled from the nerve distal to the stimulating electrodes, though this was somewhat variable. In four out of five fibres the inhibition was reduced or abolished by close intra-arterial injection of atropine. Only single fibres were used.2. There was a risk of adventitious excitation of the afferent fibre by stimulus escape. Some of the features of this excitation and the ease with which it occurred were investigated using an isolated length of vagus, baroreceptor fibres and chemoreceptor fibres. Low concentrations of local anaesthetic could raise the threshold for adventitious excitation whilst not affecting the normal passage of impulses.3. During stimulation of the efferent components of the sinus nerve, a continuous check for adventitious excitation was kept, utilizing the fact that chemoreceptor fibres show a minimum inter-spike interval of about 10 msec.4. The true inhibition of discharge would seem to be vasomotor in origin.

Action Potentials↗
PubMed1973

Activation of descending control of the spinocervical tract by impulses ascending the dorsal columns and relaying through the dorsal column nuclei.

1. Micro-electrode recordings were made from axons of the spinocervical tract in unanaesthetized decerebrate cats.2. Orthodromic activation of the dorsal columns and dorsal column nuclei was used to condition responses evoked in spinocervical tract neurones from cutaneous nerves. Such conditioning produced inhibition of transmission through the tract. The inhibition had a time course of 200 msec or more with maximal action at 30-70 msec and was most effective against polysynaptic responses.3. After removal of the cerebellum or section of the cerebellar peduncles the degree of inhibition was reduced but inhibition could still be evoked by activation of the dorsal columns and dorsal column nuclei.4. Transection of the brain stem just rostral to the dorsal column nuclei removed the inhibitory effects although segmental inhibition was not affected.5. It is concluded that impulses ascending the dorsal columns and relaying through the dorsal column nuclei can lead to activation of descending control of the spinocervical tract. Parts of the pathways involved include the cerebellum and the brain stem. It is unlikely that the cells in the dorsal column nuclei which have descending axons are concerned with the control of transmission through the spinocervical tract.

Animals↗
PubMed1974

Evidence for the involvement in the baroreceptor reflex of a descending inhibitory pathway.

1. The onset and time course of baroreceptor inhibition of pre- and post-ganglionic sympathetic reflex activity has been examined in the anaesthetized cat.2. The shortest time to the onset of inhibition of an intercostal evoked reflex response in cardiac and renal nerve was less than 90 msec following a rise in pressure in a carotid sinus blind sac, and around 55 msec following stimulation of the ipsilateral sinus nerve. The cardiac nerve response was completely inhibited before the renal nerve response.3. Because of the long delays in the somato-sympathetic reflex pathway it is argued that these minimum times will be much less than the real central delay of baroreceptor inhibition. These were estimated by adding on the central times for the somato-sympathetic reflexes to give latencies of 94-143 msec for the inhibition.4. A spinal sympathetic reflex was inhibited by 30-75% following a rise in pressure in a carotid sinus blind sac or sinus nerve stimulation. The minimum time for this inhibition was around 100 msec.5. The baroreceptor inhibition of the spinal sympathetic reflex was abolished following section of a restricted region in the dorsolateral part of the lateral funiculus of the cervical spinal cord.6. Both pre- and post-ganglionic reflexes could be inhibited when stimulating within three regions of the medulla oblongata. The latency to inhibition elicited from the ventromedial reticular formation was short, some 5-30 msec, whereas that elicited from a ventrolateral region or the mid line raphe nucleus was long, some 90-160 msec.7. The possibility is discussed that the baroreceptor inhibition of both the pre- and post-ganglionic reflexes examined in this study is occurring at the spinal level via a pathway from either the raphe nuclei or ventrolateral medulla.

Animals↗
PubMed1975

Corticofugal effects from sensorimotor area I and somatosensory area II on neurones of the pontine nuclei in the cat.

1. The objective of the present experiments was to study the cortical influence from sensorimotor area I (SM I) and from somatosensory area II (S II) on single neurones of the pontine nuclei (PN) in cats under N2--thiamylal anaesthesia. 2. Extracellular single unit recordings revealed a considerable convergence from S II and SM I. Out of ninety-one PN neurones (identified as ponto-cerebellas neurones by antidromic stimulation of the contralateral brachium pontis), fifty-seven neurones were influenced by stimulation of at least one cortical site. Slightly less than half of these neurones (twenty-five) had a convergent input from SM I and S II; twenty-three PN neurones were excited by SM I only and nine PN neurones by S II only. The proportion of PN neurones excited via collaterals of cortico-spinal neurones was small and restricted to those neurones which had an input from SM I. 3. Sixty per cent of the ponto-cerebellar neurones were reliably activated by natural stimulation such as tapping or passive manipulations of limbs of various joints. The vast majority (thirty-three out of thirty-six PN neurones) which had receptive fields were also influenced by electrical stimulation of one or both cortical areas. The long latency and low probability of discharge to peripheral nerve stimulation suggest a complex, probably transcortical, pathway from the periphery to the PN. 4. The distribution of latencies to both cortical and brachium pontis stimulation indicates that the PN are a relay for fast and slow cerebro-cerebellar connexions. 5. The convergence from cortical areas on PN indicates that the neurones influenced from somatic areas SM I and S II transmit integrated patterns of activity to the cerebellum.

Animals↗
PubMed1975

Effects of afferent volleys from the limbs on the discharge patterns of interpositus neurones in cats anaesthetized with alpha-chloralose.

1. In cats anaesthetized with alpha-chloralose, micro-electrodes have been used to record the discharge patterns of single neurones in the region of the nucleus interpositus. 2. Almost all cells tested could be antidromically invaded following electrical stimulation of the contralateral red nucleus, showing that they were cerebellar efferent neurones. 3. A little over half of the interpositus neurones were spontaneously active, usually at rates of less than 20 impulses/sec. 4. About 40% of the cells had no spontaneous activity, although they gave brisk responses to electrical stimulation of cutaneous nerves. Such silent units were encountered most frequently in the earlier stages of an experiment, but a number were found more than 15 hr after the beginning of an experiment. 5. Stimulation of cutaneous and mixed nerves of the fore and hind limbs provoked impulse discharges of the cells and also produced phases of deceleration of the resting discharge of spontaneously firing cells. 6. The typical response of an interpositus neurone consisted of a short latency (6-35 msec) discharge, usually separated from a long latency (50-500 msec) discharge by a period of inhibition or return to the resting discharge rate. The two phases of excitation appeared to be independently generated, since in a number of cells one phase appeared without the other. In addition, the later phase of excitation was abolished in all cells tested by a small dose of pentobarbitone which produced very little effect on the earlier phase. The long latency response was quantitatively much greater, sometimes consisting of 50 or more impulses in a response which lasted several hundred msec, but was very variable from one trial to another. 7. The long latency discharge and sometimes the preceding inhibition could readily be mimicked by single shock stimulation of the region of the contralateral inferior olive. Short latency discharges were, however, rarely evoked by olivary stimulation. 8. It is suggested that the short latency responses of the interpositus neurones were a result of synaptic excitation via cerebellar afferents, while the ensuing inhibition was a result of post-synaptic inhibition resulting from the Purkinje cell excitation due to the afferent volleys. It is suggested that the long latency excitation is due to the afferent volleys. It is suggested that the long latency excitation is due at least in part to disinhibition resulting from long pauses in Purkinje cell firing following their activation by climbing fibre afferents. 9. The possibility that these long latency responses have a physiological significance in relation to locomotion is discussed.

Action Potentials↗
PubMed1975

Depression in the excitability of relay cells of lateral geniculate nucleus following saccadic eye movements in the cat.

1. The excitability of relay cells of the lateral geniculate nucleus during a saccadic eye movement was studied in alert cats. Excitability was assessed by the firing probability of the cells in response to electrical stimulation of the optic chiasm. Modifications in the excitability were evaluated during the period following eye movements, by triggering a stimulator from potential shifts in electro-oculogram and altering delays in the stimulus pulse. 2. The cells were classified into S and T cells, based on their response properties and the latencies to chiasmatic stimulation. With a saccade in a stationary patterned field, T cells showed a burst discharge, while the discharges of S cells were completely suppressed. 3. The excitability was depressed in both S and T cells for 150-200 msec after a saccade, when the eye movement occurred in light. However, the depression did not occur in complete darkness. 4. The depression occurred also in the absence of eye movement, when the patterned visual field was moved in a saccadic fashion. 5. The depression in S cells occurred during an inhibitory period. Since S cells do not receive signals on image movement directly from the retina, the depression was due to a recurrent inhibition by signals transferred through the T ganglion-relay cell channel. 6. The depression in T cells occurred concomitantly with the burst discharge. Since the recurrent inhibition was operating less effectively during the period, the depression may be due to a phasic occlusion of the test impulse by coincident high-rate firings in the same cell. 7. The impairment in transmission of visual information through the lateral geniculate nucleus during the period following eye movements has been discussed in connexion with a neurophysiological basis for saccadic suppression.

Animals↗
PubMed1975

Synaptic actions on mitral and tufted cells elicited by olfactory nerve volleys in the rabbit.

1. A unitary study has been carried out of mitral and tufted cell responses to olfactory nerve volleys in the olfactory bulb of rabbits lightly anaesthetized with urethane-chloralose. 2. With volleys of different strengths, some mitral cells responded with a spike whose latency decreased considerably as the strength increased (elastic response); other cells responded at an invariant latency (inelastic response). The former may reflect diffuse olfactory nerve inputs to the dendritic tufts in the olfactory glomeruli, while tha latter may reflect input from discrete bundles of fibres. 3. The shortest spike latencies are consistent with monosynaptic excitation by the olfactory nerves; longer latencies may be due to longer pathways through the nerves, or polysynaptic pathways within the glomerular layer. 4. Facilitation, in terms of lower threshold and shorter spike latency, was found when testing with paired volleys of weak intensity at relatively short intervals (less than 40 msec). Suppression, in terms of raised threshold, longer latency and briefer repetitive discharges, was found at intervals up to several hundred msec. The facilitation and suppression are consistent with the hypothesis of synaptic excitation and inhibition, respectively, mediated through interneurones in the olfactory bulb. 5. Presumed tufted cells were similar in response properties to identified mitral cells. 6. Intracellular recordings revealed long-lasting hyperpolarization and in some cases, an initial depolarization leading to spike initiation, in response to an olfactory nerve volley.

Action Potentials↗
PubMed1976

Activation and inhibition of the lateral hypothalamic neurones elicited by medial forebrain bundle stimulation.

1. Single neurone discharges were recorded from the lateral hypothalamus (LH) at the level of the ventromedial nucleus. Single stimulation of the medial forebrain bundle (MFB) at the level of the mesodiencephalic junction elicited a strong inhibition lasting for 100-300 msec in these neurones. 2. However, by the use of multiple stimulating electrodes, it was possible to find a circumscribed locus in the MFB which gave rise to an initial activation of firing discharges with a latency of 1-15 msec (in different neurones) preceding the period of inhibition. 3. One class of the LH neurones was antidromically activated, and was thought to give off axons into the descending MFB. The other was activated orthodromically through a highly efficient synaptic connexion, and was viewed as 'relay' neurones of the ascending MFB. 4. Although the former could also be activated orthodromically, the efficacy of driving was distinctly lower than that observed in the latter. Presumably they integrate the messages from the visceral centres of the medulla and pons, thus participating in the viscero-motor outflow from the hypothalamus. 5. Intracellularly recorded spike potentials of these neurones deteriorated rapidly leaving only hyperpolarization which corresponded in its time course to the suppression of extracellular spike discharges following MFB stimulation. It was suggested that the inhibition was elicited via recurrent routes localized within the hypothalamus.

Action Potentials↗
PubMed1977

Properties of vestibular neurones projecting to neck segments of the cat spinal cord.

1. Vestibular neurones projecting to the upper cervical grey matter (vestibulocollic neurones) were identified by localized microstimulation in the C3 segment of the cat spinal cord.2. The neurones were found in the lateral (Deiters'), medial and descending nuclei bilaterally and projected to the spinal cord in the lateral and medial vestibulospinal tracts (LVST and MVST). Ipsilateral axons of Deiters' neurones were mostly in the LVST, axons of medial and descending neurones in the MVST; a few Deiters' neurones had axons in the MVST; some descending neurones had axons in the LVST. Most axons of contralateral neurones were in the MVST.3. The axons of 62% of ipsilateral vestibulocollic Deiters' neurones not only gave off a collateral to C3, but also extended as far as the cervical enlargement (;branching'); some of these neurones projected as far as the upper thoracic cord, almost none to the lumbar cord. Ipsilateral descending nucleus neurones branch in the same fashion, but there is no branching in the relatively small medial nucleus population.4. A large majority of vestibulocollic neurones receive monosynaptic excitation from the ipsilateral labyrinth and a number are inhibited by stimulation of the contralateral labyrinth (commissural inhibition). It is possible that commissural inhibition acts on a broad population of vestibular neurones involved in the control of eye, head and trunk movement.5. Vestibulocollic neurones do not make up a homogeneous population acting only on the neck. Instead it is likely that subpopulations, for example branching and non-branching neurones, have different functions.

Animals↗
PubMed1977

The carotid chemoreceptor input to the respiratory neurones of the nucleus of tractus solitarus.

1. An investigation has been made into the connexions between the carotid body chemoreceptors and the dorsal respiratory neurones of the cat's medulla.2. In confirmation of previous work these neurones were found to be all inspiratory in firing pattern and to fall into two categories, Ralpha (forty-four units) which fire only with the central inspiratory rhythm and Rbeta (thirty-two neurones) that are also excited by lung inflation. Both categories were shown to be excited by stimuli delivered to the carotid bodies during inspiration but, with a single exception, not during expiration.3. When Rbeta neurones were made to fire tonically in expiration by maintained lung inflation, chemoreceptor activation inhibited this discharge in 7/11 cases, the remainder being unaffected.4. Iontophoretically applied DL-homocysteic acid or glutamate made both Ralpha and Rbeta neurones fire tonically in expiration. Chemoreceptor stimulation during expiration inhibited this activity in all neurones tested (nine Ralpha and three Rbeta cells).5. Using the measurement of the antidromic latency to spinal stimulation as an index of membrane potential, evidence was obtained that any subthreshold influence of the chemoreceptors on dorsal respiratory neurones during expiration was inhibitory (9/18 cases).6. It is concluded that chemoreceptors do not even subliminally excite dorsal inspiratory neurones during expiration; such influence as they have then is inhibitory. Possible reasons for this difference in chemoreceptor influence during inspiration and expiration are discussed. It is suggested that chemoreceptor excitation reaches them only as part of an enhanced central inspiratory drive from an as yet unknown source.

Action Potentials↗
PubMed1977

Post-tetanic potentiation, habituation and facilitation of synaptic potentials in reticulospinal neurones of lamprey.

1. Synaptic potentials evoked by electrical stimulation of cranial nerves were recorded in giant reticulospinal neurones (Müller cells) of lamprey. A variety of patterns of stimulation was employed to explore further the functional properties of the pathways intervening between the cranial nerve fibres and Müller cells.2. Simultaneous low intensity stimulation of two different cranial nerves produced excitatory short-latency synaptic potentials whose amplitudes summed linearly.3. Tetanic (10/sec) stimulation of a cranial nerve depressed the evoked short-latency synaptic response, but following the tetanus the synaptic response was potentiated above control amplitude for several minutes. Tetanic stimulation of one cranial nerve had no effect upon the synaptic responses evoked by stimulation of other cranial nerves.4. Low-frequency stimulation (1/sec to 1/20 sec) of a cranial nerve produced a progressive decrease in the amplitude of the evoked short-latency synaptic response. This phenomenon was termed synaptic habituation because its characteristics were functionally similar to behavioural habituation in animals.5. Habituation of the synaptic response to stimulation of one cranial nerve had no effect on the synaptic responses produced by stimulation of other cranial nerves.6. Synaptic afterdischarges lasting from several seconds to several minutes were recorded in Müller cells. They occurred both spontaneously and in response to strong electrical stimulation of cranial nerves. For several minutes following an afterdischarge the amplitudes of short-latency synaptic potentials produced by stimulation of any one of the cranial nerves were increased as much as twofold. This facilitation occurred equally well whether the short-latency synaptic responses had been habituated or not.7. A theoretical cell-wiring diagram is proposed to account for the properties of short-latency evoked synaptic responses and synaptic afterdischarges and for the facilitation of short-latency responses by afterdischarges.

Animals↗
PubMed1977

Responses of directional ganglion cells in the pigeon retina.

1. Extracellular single-unit records were taken from ganglion cells in the pigeon retina, and average response histograms were recorded, with base line spike counts. 2. Movements in the preferred direction in directional cells produce discharge peaks. Movements in the null direction produce spike deletion suggesting there is an inhibitory patch offset from the field centre, towards the start of the null sweep. 3. Bi-directional responses can be obtained from the preferred side of the field centre; bi-directional inhibition can be obtained at the null side. Scans orthogonal to the null-preferred direction passing through the inhibitory patch can produce deletions. 4. The latency of deletions from the inhibitory patch is slightly greater than of excitation from the field centre, judged by flashed or moving stimuli.

Action Potentials↗
PubMed1977

Brain stem stimulation and the acetylcholine-evoked inhibition of neurones in the feline nucleus reticularis thalami.

1. In cats anaesthetized with halothane and nitrous oxide, the responses to iontophoretically applied acetylcholine (ACh) and to high-frequency stimulation of the mid-brain reticular formation (MRF) were tested on spontaneously active neurones in the nucleus reticularis thalami and underlying ventrobasal complex.2. The initial response to MRF stimulation of 90% of the ACh-inhibited neurones found in the region of the dorsolateral nucleus reticularis was an inhibition. Conversely, the initial response of 82% of the ACh-excited neurones in the ventrobasal complex was an excitation. Neurones in the rostral pole of the nucleus reticularis were inhibited by both ACh and RMF stimulation.3. The mean latency (and s.e. of mean) for the MRF-evoked inhibition was 13.7 +/- 3.2 ms (n = 42) and that for the MRF-evoked excitation, 44.1 +/- 4.2 ms (n = 35).4. The ACh-evoked inhibitions were blocked by iontophoretic atropine, in doses that did not block amino acid-evoked inhibition. In twenty-four ACh-inhibited neurones the effect of iontophoretic atropine was tested on MRF-evoked inhibition. In all twenty-four neurones atropine had no effect on the early phase of MRF-evoked inhibition but weakly antagonized the late phase of inhibition in nine of fourteen neurones.5. Interspike-interval histograms showed that the firing pattern of neurones in the nucleus reticularis was characterized by periods of prolonged, high-frequency bursting. Both the ACh-evoked inhibitions and the late phase of MRF-evoked inhibitions were accompanied by an increased burst activity. In contrast, iontophoretic atropine tended to suppress burst activity.6. The possibility is discussed that electrical stimulation of the MRF activates an inhibitory cholinergic projection to the nucleus reticularis. Since neurones of the nucleus reticularis have been shown to inhibit thalamic relay cells, activation of this inhibitory pathway may play a role in MRF-evoked facilitation of thalamo-cortical relay transmission and the associated electrocortical desynchronization.

Acetylcholine↗
PubMed1977

Properties of different functional types of neurones in the cat's rostral trigeminal nuclei responding to sinus hair stimulation.

1. Properties of neurones in the trigeminal nuclei principalis and oralis responding to movements of facial sinus hairs were studied in cats anaesthetized by I. V. infusion of pentobarbitone.2. Using electrophysiological methods trigeminal neurones were classified into primary afferent fibres, trigeminothalamic relay neurones, interneurones and other unspecified higher order neurones.3. When receptive fields of synaptically activated neurones were compared with those of primary afferent fibres, an often extensive convergence from first order on to higher order neurones was established. Out of 119 relay neurones six received input from one sinus hair only. Spontaneous activity was encountered about twice as often in synaptically activated neurones than in primary afferent fibres.4. The responsiveness of single neurones was unstable over time in about one fifth of the population and then the total number of impulses discharged in successive responses could vary by as much as 500%. Unstable responsiveness occurred sometimes alone but was often accompanied by marked changes in the size or the configuration of the receptive field. Such instabilities were observed in all kinds of synaptically activated neurones but not in primary afferent fibres.5. Afferent inhibition in relay neurones could be elicited from within the excitatory receptive field and appeared to be related to the activation of distinct receptor populations responding to specific stimulus parameters. Inhibition was also seen in interneurones following both mechanical stimulation of the skin and electrical stimulation of lemniscal fibre terminals in the contralateral ventromedial thalamus.6. The results are discussed and compared with previous findings about sinus hair representation in the trigeminal nucleus and the ascending lemniscal projection. The findings indicate that the concept of the ;static properties' of relay neurones is not adequate for all trigeminothalamic relay neurones and may require a critical reconsideration.7. It is suggested that the afferent input from sinus hairs is effectively controlled at the level of the rostral trigeminal nuclei. This control may affect the spatial input to relay neurones, the temporal components of their responses and the intensity dimension of their transmission capacity. It is postulated that by these mechanisms tactile information from the sinus hair system is modulated according to the instantaneous sensory requirements of the behaving cat.

Animals↗
PubMed1978

Field potentials, inhibition and the effect of pentobarbitone in the rat olfactory cortex slice.

1. Field potentials were evoked in slices of rat olfactory cortex by stimulating the lateral olfactory tract. In addition to previously described components of the wave-form, a further distinct surface-negative potential of low amplitude and long duration (I-wave) has been described. 2. Pentobarbitone, at concentrations of 10(-5) M and above, markedly enhanced enhanced the amplitude and duration of the I-wave with only minimal effect on other components of the field potential. 3. The I-wave was reversibly reduced by the GABA antagonists bicuculline and picrotoxin and was also attenuated at rapid rates of stimulation. Low chloride medium usually caused a transient increase in amplitude of the I-wave followed by a gradual reduction, suggesting that a chloride-mediated depolarization was involved. 4. Evoked inhibition, which was most probably post-synaptic, occurred in parallel with the I-wave. This was monitored as a suppression of, or increase in latency of the population spike evoked by a second stimulus at appropriate intervals after the first. Pentobarbitone substantially increased the duration of the post-synpatic inhibition, without obvious changes in the presynaptic inhibitory phenomenon associated with antidromic firing in the lateral olfactory tract. 5. It is proposed that the I-wave is the field potential representation of a population depolarizing i.p.s.p. and that the main action of pentobarbitone is to enhance this inhibition.

Action Potentials↗
PubMed1978

Neurones in cat gracile nucleus with both local and widefield inputs.

1. Forty-three neurones were isolated in the cat gracile nucleus that could be driven by electrical stimulation of the ipsilateral forefoot or the contralateral hind food as well as having a normal low threshold localized receptive field on the ipsilateral hind limb. 2. Twenty-five (58%) of the cells were found to have axons projecting to the contralateral ventrobasal thalamus. 3. Most of the cells could only be driven from the 'widefield' receptive field on the forefoot or contralateral hindfoot by percutaneous electrical stimulation. 4. These results are discussed in the context of a model of the gracile nucleus in whick these occasional 'widefield' connexions are considered to be errors in connectivity which are not normally effective due to the patterns of excitation and inhibition in the normally functioning nucleus. 5. In this model, electrical stimulation is an abnormal type of stimulation that can drive cells through these erroneous connexions.

Animals↗
PubMed1978

Crossed disynaptic inhibition of sacral motoneurones.

1. Intracellular recording was made from motoneurones in lower sacral (S2 and S3) segments of the spinal cord in cats, to analyse the neuronal organization of the inhibition evoked in these motoneurones from contralateral afferents. 2. It was confirmed that stimulation of the lowest threshold afferents of contralateral dorsal roots evokes i.p.s.p.s with latencies similar to those of disynaptic i.p.s.p.s. evoked from group Ia muscle spindle afferents in limb motoneurones. 3. The crossed disynaptic i.p.s.p.s in sacral motoneurones were found to be mediated by interneurones which are themselves inhibited by Renshaw cells, these interneurones and Renshaw cells being activated from the dorsal and ventral roots respectively, on the side of the body opposite to the location of the inhibited motoneurones. 4. In unanaesthetized decerebrate preparations crossed recurrent facilitation of sacral motoneurones was evoked with a time course similar to that of recurrent facilitation of lumbar motoneurones. It was taken to indicate a tonic inhibition of sacral motoneurones by interneurones responsible for their crossed disynaptic inhibition, and a disinhibition following stimulation of contralateral ventral roots. 5. In anaesthetized preparations crossed recurrent inhibition appeared, instead of the recurrent facilitation, in more than one half of the tested motoneurones. 6. A comparison of the input from ipsilateral and contralateral afferents to identified motoneurones of tail muscles with the input to pudendal motoneurones led to the conclusion that crossed disynaptic inhibition is evoked specifically in tail motoneurones. 7. Intracellular staining of sacral motoneurones with horseradish peroxidase revealed that the tail motoneurones and others with crossed disynaptic inhibition differ from the pudendal motoneurones in their location and in a number of morphological features; tail motoneurones are larger, they have differently directed dendrites and they show more extensively branched initial axon collaterals which appeared to ramify only within the ventral and lateral parts of the ipsilateral ventral horn. 8. One Renshaw cell which was stained with horseradish peroxidase was found to project contralaterally, after giving a number of axon collaterals ipsilaterally.

Animals↗
PubMed1979

Segmental and supraspinal input to cells of origin of non-primary fibres in the feline dorsal columns.

1. The synaptic input to ascending tract cells with axons in the dorsal columns was investigated using intracellular recording. 2. E.p.s.p.s evoked by stimulation of the lateral funiculus were analysed to test for the possibility of collateral connexions between spino-cervical tract cells and dorsal column cells. Three groups of fibres were found to contribute to such e.p.s.p.s: fibres which terminated or originated between spinal segments C3-4 and C1, or Th9 and C3-4 and cortico-spinal tract fibres. The latencies and thresholds of e.p.s.p.s evoked by stimulation of the first group of fibres were compatible with their origin via axon collaterals of spino-cervical tract cells. The occurrence of these e.p.s.p.s in dorsal column cells which were disynaptically excited from cutaneous afferents further corroborated this possibility. 3. E.P.S.P.S of specifically cervical origin were also found in some other neurones in the dorsal horn, probably segmental interneurones, but were absent in spinocervical tract cells. 4. Convergence of group I muscle afferents (possibly both group Ia and group Ib) and cutaneous afferents was found in about 50% of the dorsal column cells. The shortest latency e.p.s.p.s from cutaneous and group I afferents were evoked with segmental delays indicating monosynaptic and disynaptic coupling. 5. I.p.s.p.s were evoked from cutaneous and group I muscle afferents in either the same or different nerves as those from which the e.p.s.p.s were elicited. Excitatory potentials were, however, dominating.

Animals↗