The source and mechanisms of inhibition in the lateral cervical nucleus of the cat

145

SUMMARY1. Intra-and extracellular recordings were made from cells of the spinocervical tract in the lumbosacral spinal cord. A convergence of monosynaptic excitatory post-synaptic potentials (EPSPs) and disynaptic inhibitory post-synaptic potentials (IPSPs) was a general pattern of effects from the low threshold cutaneous fibres. Unitary IPSPs, probably mediated via the same disynaptic path, were evoked by light touch of hairs, which was also the adequate stimulus for exciting the cells. The receptive field for unitary IPSPs was closely related to the excitatory receptive field but was eccentric, not of a surround type.2. EPSPs, IPSPs, or both, were evoked from the flexor reflex afferents in the great majority of neurones. Disynaptic IPSPs may be evoked from the interosseous nerve. No effects were produced by volleys in group I muscle afferents.3. It is suggested, on the basis of the spatial organization of the excitatory and inhibitory receptive skin fields, that the spinocervical tract may give information regarding the direction of tactile stimuli.

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

post‐synaptic excitation and inhibition from primary afferents in neurones of the spinocervical tract

Hongo¹,

Jankowska²,

Lundberg³

1968

145

“…There is no indication of an excitatory input to the l.c.n. from the contralateral side (Horrobin, 1966) but there is evidence for an inhibitory one (Fedina, Gordon & Lundberg, 1968). It is possible that the contralateral cells contribute to this pathway.…”

Section: Location Of Sct Neurosesmentioning

confidence: 99%

The density, distribution and topographical organization of spinocervical tract neurones in the cat

Brown¹,

Fyffe²,

Noble³

et al. 1980

110

1. In acute experiments, detailed grids of micro-electrode recordings were made from spinocervical tract (s.c.t.) cells in the lumbosacral cord of anaesthetized cats. These grids provided electrophysiological data on the location, distribution, density and somatotopic organization of s.c.t. neurones.2. In acute experiments lasting up to 48 hr, retrograde labelling of s.c.t. cells was carried out by injecting horseradish peroxidase into the lateral cervical nucleus in anaesthetized cats. The aim was to flood the nucleus with the enzyme so that all s.c.t. neurones would be labelled in order to provide an independent check on the location, density and distribution data obtained in the electrophysiological experiments.3. The electrophysiological and the anatomical experiments were sometimes performed on the same animal.4. The electrophysiological and anatomical results were in excellent agreement. (a) S.c.t. cells are located mainly in ipsilateral laminae III, IV and V. About 25% are in lamina III, 60% in lamina IV and 10% in lamina V. There are a few cells in laminae I, II and VI making up the remaining 5%. (b) There are about 550-800 s.c.t. cells in the lumbosacral enlargement (L4-S2 inclusive) on each side of the cord. Most cells are in L7-S1 where there are twenty to forty s.c.t. neurones in each millimetre length of cord.5. Many marginal (lamina I) cells were labelled with the retrograde horseradish peroxidase method and a few cells on the contralateral side in laminae III-V and VII-VIII were also labelled. The marginal cells formed 12-18% of labelled cells on the side of injection and, in addition, a similar absolute number of marginal cells was labelled on the side contralateral to the injection. The possible identity of these neurones is discussed.6. S.c.t. cells form a sheet of neurones across the dorsal horn. The sheet is organized somatotopically in a way which resembles the representation of the hind limb dermatomes in the dorsal columns (Werner & Whitsel, 1967). There is a relative enlargement of the L6-S1 dermatomes which encroach upon their neighbouring cord segments. The gradient of the map is very steep in the mediolateral direction but gradual in the rostrocaudal direction. The detailed somatotopic maps generated in the present work have revealed that s.c.t. cells are arranged so that their receptive fields form longitudinal columns and cells within the columns have overlapping fields.

“…Oswaldo-Cruz & Kidd, 1964;Horrobin, 1966;Craig & Tapper, 1978;Metherate, da Costa, Herron & Dykes, 1986) had shown, mainly, that the only obvious difference between SCT and LCN neurones, apart from the above mentioned absence of responses to noxious stimuli, was an increase in the sizes of excitatory receptive fields. Furthermore, previous workers, except Fedina, Gordon & Lundberg (1968), had made little comment on the presence of inhibitory receptive fields for LCN neurones. Fedina et al (1968), who used chloralose as the anaesthetic, had shown both postsynaptic and presynaptic inhibition at the level of the LCN.…”

mentioning

confidence: 99%

Receptive fields and in‐field afferent inhibition of neurones in the cat's lateral cervical nucleus.

Brown

Maxwell

Short

1989

SUMMARY1. Extracellular microelectrode recordings were made from projection neurones of the lateral cervical nucleus (LCN) in cats anaesthetized with chloralose and paralysed with gallamine triethiodide.2. The receptive fields of eighty-five units were analysed. Most units had excitatory receptive fields similar in size and shape to those of spinocervical tract (SCT) cells. A few (14 %) had either very large fields or 'stocking-like' fields. The majority of the LCN neurones (fifty-five, 65 %) were excited by hair movement and, in addition, by noxious rnechanical stimulation within the skin area responding to hair movement. Twenty-five units (29 %) were excited by hair movement alone. For seven of these twenty-five neurones, noxious mechanical stimulation within the excitatory receptive field produced inhibition of the background discharge. One unit was excited by noxious mechanical stimulation and for the remaining four units no receptive field could be found. In six units inhibitory receptive fields outside the excitatory field were found.3. Air-jet stimuli were used to define the excitatory profiles of the units' receptive fields to hair movement. In general, receptive fields had single regions of greatest sensitivity usually at or near the centre of the field, where that was oval in shape, with the sensitivity declining towards the field's circumference. In some units with very large fields that included parts of one or two limbs and the trunk there could be more than one highly sensitive region.4. Pairs of air-jet stimuli were used to investigate in-field afferent inhibition in LCN cells. One jet was used to condition the responses to another jet located at a different position within the excitatory receptive field and occurring 200 ms later. Sixteen units were tested and significant in-field inhibition was observed in all sixteen.5. The in-field afferent inhibition was organized spatially in the sense that inhibition was generally strongest when the conditioning and testing stimuli were close together and became weaker as they were moved apart. The afferent inhibition was not simply a function of the response produced by the conditioning stimulus.Furthermore, increasing the strength of the stimuli did not in general lead to larger areas from which the inhibition could be produced. The inhibitory areas defined in these experiments were generally less than 120 mm in length in units with receptive fields much longer than 100 mm.A. G. BROWrN, D. J. AIAXIVELLANDA. D. SHORT 6. We conclude that: (1) neurones of the LCN that project through the medial lemniscus have the same classes of excitatory inputs as neurones of the SCT that excite them -there is no convergence from different classes of SC(T cells onto LCN projection neurones; (2) the major, and perhaps the only. operation carried out at the level of the LCN is a considerable degree of spatial summation for a small subpopulation of neurones, although most LCN neurones have receptive fields no larger than those of SCT cells; (3) the in-field afferent inhibitio...