The dorsal column projection of muscle afferent fibres from the cat hindlimb.

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SUMMARY1. Evidence has been sought for crossed actions on midlumbar propriospinal neurones activated by ipsilateral group II muscle afferents, with particular emphasis on those neurones with projections to the ipsilateral hindlimb motor nuclei.2. A large majority of group II-activated midlumbar neurones were influenced by stimulation of contralateral group II afferents. The most frequent and most powerful actions were from those nerves which most effectively influenced ipsilateral midlumbar neurones. Crossed actions from group I afferents were rare.3. In the great majority of neurones the pattern of actions was similar from both limbs, the neurones being bilaterally excited, bilaterally inhibited or had both EPSPs and IPSPs from both sides.4. The latencies of crossed actions suggest that the earliest crossed EPSPs from group II afferents were evoked disynaptically (i.e. via a single commissural neurone) and that the crossed IPSPs were evoked trisynaptically.5. The pattern of crossed actions suggests a strong bilateral interaction between midlumbar neurones. The possible role of these neurones in postural control and the production of co-ordinated movements of the hindlimbs is discussed.

Section: Resultsmentioning

confidence: 99%

Crossed actions on group II‐activated interneurones in the midlumbar segments of the cat spinal cord.

Bajwa¹,

Edgley²,

Harrison³

1992

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“…Although impulses in group II afferents of these nerves are less delayed than those of group I afferents because of the shorter peripheral conduction path (see Table 1, far right column, of Edgley & Jankowska, 1987a), they enter the spinal cord about 20 mm more rostrally than afferents of PBST. The additional conduction time between the L6 and sacral segments may amount to about 0-6 ms since the intraspinal conduction velocity of ascending collaterals of group II afferents is 30-60% of that in peripheral nerves Fern, Harrison & Riddell, 1988) and may be even lower in descending collaterals. Three further observations are also of relevance to the estimates of the ranges of monosynaptic actions of Q afferents in the sacral segments.…”

Section: Methods Preparationmentioning

confidence: 99%

Interneurones in pathways from group II muscle afferents in sacral segments of the feline spinal cord.

Jankowska

Riddell

1994

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1. Properties of dorsal horn interneurones that process information from group II muscle afferents in the sacral segments of the spinal cord have been investigated in the cat using both intracellular and extracellular recording. 2. The interneurones were excited by group II muscle afferents and cutaneous afferents but not by group I muscle afferents. They were most effectively excited by group II afferents of the posterior biceps, semitendinosus, triceps surae and quadriceps muscle nerves and by cutaneous afferents running in the cutaneous femoris, pudendal and sural nerves. The earliest synaptic actions were evoked monosynaptically and were very tightly locked to the stimuli. 3. EPSPs evoked monosynaptically by group II muscle afferents and cutaneous afferents of the most effective nerves were often cut short by disynaptic IPSPs. As a consequence of this negative feedback the EPSPs gave rise to single or double spike potentials and only a minority of interneurones responded with repetitive discharges. However, the neurones that did respond repetitively did so at a very high frequency of discharges (08-1P2 ms intervals between the first 2-3 spikes). 4. Sacral dorsal horn group II interneurones do not appear to act directly upon motoneurones because: (i) these interneurones are located outside the area within which last order interneurones have previously been found and (ii) the latencies of PSPs evoked in motoneurones by stimulation of the posterior biceps and semitendinosus, cutaneous femoris and pudendal nerves (i.e. the main nerves providing input to sacral interneurones) are compatible with a tri-but not with a disynaptic coupling. Spatial facilitation of EPSPs and IPSPs following synchronous stimulation of group II and cutaneous afferents of these nerves shows, however, that sacral interneurones may induce excitation or inhibition of motoneurones via other interneurones. 5. Comparison of the properties of group II interneurones in the sacral segments with those of previously studied group II interneurones in the midlumbar segments leads to the conclusion that these two populations of neurones are specialized for the processing of information from different muscles and skin areas. In addition, equivalents of only one of the two subpopulations of midlumbar interneurones have been found at the level of the pudendal nucleus: neurones with input from group II but not from group I muscle afferents. Neurones integrating information from group I and II muscle afferents and in direct contact with motoneurones thus seem to be scarce in the sacral segments. 6. On the basis of the patterns of input to sacral group II interneurones it is hypothesized that these interneurones are involved in postural adjustments associated with the defecation and grooming reflexes, as well as some labyrinthine reflexes.We have recently reported that neurones relaying segments, several types of neurones have input from group information from group II muscle afferents are located not II afferents; these include last order interneurones wit...

“…The present sample of group II fibres was therefore selected on the basis of both their peripheral thresholds (.> 2 T) and conduction time between the intraspinal stimulation site and the peripheral nerve recording electrode. Taking into account the slowing of conduction velocity of hind limb muscle afferents ascending in the dorsal columns to the L4/L5 level (Fern, Harrison & Riddell, 1988), impulses evoked with latencies of 3 7 ms or more were considered to originate in group II fibres (see Edgley & Jankowska, 1987a;Harrison & Jankowska, 1989). …”

Section: The Sample Of Afferent Fibresmentioning

confidence: 99%

Depolarization of group II muscle afferents by stimuli applied in the locus coeruleus and raphe nuclei of the cat.

Riddell

Jankowska

Eide

1993

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SUMMARY1. Electrical stimuli applied in the locus coeruleus/subcoeruleus (LC/SC) and raphe nuclei produce a profound depression of transmission in reflex pathways from group II muscle afferents. The present experiments were performed to determine whether presynaptic inhibitory mechanisms contribute to these effects.2. Changes in the excitability of afferent terminals to electrical stimuli have been used as an indication of primary afferent depolarization (PAD) produced by conditioning stimuli applied within the LC/SC and raphe nuclei and, for comparison, in the nucleus ruber. Group II afferents originating from ankle flexor muscles and terminating in the midlumbar segments were used for testing.3. Clear changes in excitability were observed in fourteen of nineteen group II fibres in which the effects of conditioning stimuli applied in the LC/SC were tested and in twelve of seventeen fibres in which the effects of stimuli applied within the raphe nuclei were tested. By comparison, only one of the twelve fibres tested with conditioning stimuli applied to the nucleus ruber was found to be influenced. These effects matched those of the same conditioning stimuli on field potentials evoked by group II afferents at the location at which the terminals of group II fibres were stimulated.4. Stimuli applied in the LC/SC and in the raphe nuclei both produced a mean decrease in threshold stimulus current of 19 %. These effects are comparable to those produced by the most effective volleys in peripheral afferents which, in the same fibres, produced a mean decrease in threshold stimulus current of 24%.5. In all cases (twelve) in which the effects of stimuli applied in the LC/SC and raphe nuclei were tested on the same group II fibre, either both or neither were found to be effective. This strengthens previous indications that some populations of neurones might be activated by stimuli applied in each of these regions of the brain.6. In contrast to group II afferents, group I a afferents investigated in the same experiments were only exceptionally affected. Of seven fibres tested with stimuli applied in the LC/SC, six with stimuli applied in the raphe nuclei and seven with stimuli applied in the nucleus ruber, only one fibre showed any clear change in