Characteristics and Distribution of Spinal Focal Synaptic Potentials Generated by Group II Muscle Afferents

1994

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...

Section: Methods Preparationmentioning

confidence: 99%

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

1994

“…However, interneurones of midlumbar segments mediate only some of the actions of groupII afferents; they are the main (though not exclusive; Cavallari & Pettersson, 1991) relay neurones from group II actions originating from quadriceps, sartorius and pretibial flexors while group II afferents of other muscles (e.g. hamstring and triceps surae) have their interneuronal relay in more caudal segmenits (see Fu, Santini & Schomburg, 1974;. Since the effects of conditioning stimuli have so far only been investigated in the midlumbar segments the degree to which neurones in other spinal segments would be affected was unknown.…”

Section: Introductionmentioning

confidence: 99%

Gating of transmission to motoneurones by stimuli applied in the locus coeruleus and raphe nuclei of the cat.

Skoog

et al. 1993

SUMMARY1. Neuronal systems activated by stimulation in the region of the locus coeruleus/subcoeruleus (LC/SC) and raphe nuclei have previously been shown to depress transmission from group II muscle afferents in regions of the midlumbar spinal segments in which premotor interneurones are located. The aim of the present investigation was to determine the extent to which such depression is paralleled by depression of the reflex actions of group II afferents on motoneurones.2. The effects of short trains of conditioning electrical stimuli applied within the LC/SC and raphe nuclei were examined on postsynaptic potentials (PSPs) evoked by group I and group II muscle afferents in hindlimb motoneurones. The effects were examined over a wide range of conditioning-test intervals but particular emphasis was placed on the effects produced at long intervals (> 100 ms) since such effects are more likely to be mediated by the descending noradrenergic and serotonergic neurones of the LC/SC and raphe nuclei which are of slow conduction velocity. In addition, conditioning stimuli alone evoked PSPs in motoneurones (with latencies of 7-15 ms and a duration of 50-80 ms) and effects evoked at short conditioning-test intervals might therefore have been secondary to changes in motoneurone membrane properties.3. At conditioning-test intervals between 100 and 350 ms synaptic actions of group II origin were strongly and consistently depressed. Both EPSPs and IPSPs were affected, two-thirds of those tested being reduced in amplitude by 50 % or more. A similar depression was exerted on PSPs evoked from the quadriceps and deep peroneal nerves mediated predominantly by interneurones located in the midlumbar segments and on PSPs evoked from the hamstring and triceps surae nerves mediated by interneurones located in more caudal segments. It is thus concluded that neuronal systems activated by stimuli applied in the LC/SC and raphe nuclei are capable of gating transmission in all those interneuronal pathways which mediate the reflex actions of group II afferents on motoneurones in anaesthetized animals.

“…For instance, single muscle spindle secondaries labelled by intra-axonal injection of horseradish peroxidase have been found to terminate within laminae IV-IX of the L6 and L7 segments (Fyffe, 1979;Hongo, Kudo, Yamashita, Ishizuka & Mannen, 1981;Ishizuka, Hongo, Kudo, Sasaki, Yamashita & Mannen, 1985;Hoheisel, LehmannWillenbrock & Mense, 1989;Hongo, 1992) and group II muscle afferent fibres have been activated by intraspinal stimuli applied at segmental levels from S1 to Thl3 (Eccles, Schmidt & Willis, 1963;Carpenter, Lundberg & Norrsell, 1963;Fern, Harrison & Riddell, 1988;Jimenez, Rudomin & Solodkin, 1988;Harrison & Jankowska, 1989;Riddell, Jankowska & Eide, 1992). Group II muscle afferent fibres have also been found to have direct contacts with neurones within the dorsal horn, the intermediate zone, Clarke's column and motor nuclei within the S1 to L3 segments (Coombs, Curtis & Landgren, 1956;Eccles, Oscarsson & Willis, 1961;Fu, Santini & Schomburg, 1974;Kirkwood & Sears, 1975;Stauffer, Watt, Taylor, Reinking & Stuart, 1976;Lundberg, Malmgren & Schomburg, 1977Munson, Fleshman & Sypert, 1980;b, 1988Jankowska & Noga, 1990; for review see Jankowska, 1992).…”

Section: Introductionmentioning

confidence: 99%

A relay for input from group II muscle afferents in sacral segments of the cat spinal cord.

1993

SUMMARY1. A neuronal relay for input from group II afferents of hindlimb muscle nerves has been found in the previously little explored sacral segments of the cat spinal cord.2. Electrical stimulation of group II muscle afferents of a number of nerves evoked negative potentials on the surface (cord dorsum potentials) and population postsynaptic potentials (field potentials) within the sacral segments. The largest potentials were evoked by stimulation of the posterior biceps-semitendinosus and triceps surae nerves which evoke much smaller potentials in other segments. Group II afferents of other nerves, notably those which have their main relay within the middle lumbar segments, were much less effective.3. The sites at which cord dorsum and field potentials evoked by group II muscle afferents were recorded varied in relation to the external topography of the L7-S2 spinal segments but were consistent in their location relative to the pudendal motor nucleus (Onuf's nucleus). Potentials evoked by group II afferents of the posterior biceps and semitendinosus nerves peaked at a level corresponding to the rostral half of Onuf's nucleus and potentials evoked by afferents of the gastrocnemius nerves peaked just rostral to this nucleus. The largest field potentials (of 05-lO mV) were recorded within the dorsal horn. Field potentials in the intermediate zone were much smaller ( < 0 3 mV) and were seen less frequently.4. Evidence was obtained that the dorsal horn field potentials are to a great extent evoked monosynaptically by the fast conducting fraction of group II muscle afferents: (i) they were evoked at short latencies (2A4-2-7 ms from the stimulus; 1P3-1H7 ms from group I components of afferent volleys and 05-07 ms from group II components of these volleys), (ii) the conduction times of impulses in the fastest conducting fraction of group II afferents, between the sacral segments (where these impulses were induced by intraspinal stimuli) and the peripheral nerves, were only about 0 5 ms shorter than the latencies of field potentials recorded at the site of intraspinal stimulation and evoked by stimulation of the same peripheral nerves and, (iii) the field potentials followed repetitive stimuli without temporal facilitation. * Present address: Institute of Physiology, University of Glasgow, Glasgow G12 8QQ, Scotland.MS 1701 E. JANKOWSKA AND J. S. RIDDELL 5. Negative cord dorsum and field potentials were also evoked by small stretches of the semitendinosus and triceps surae muscles. Although they were smaller than potentials evoked by electrical stimulation of sensory fibres and appeared at longer latencies, their presence is consistent with a contribution of muscle spindle afferents to the actions of group II muscle afferents within the sacral segments.6. The study leads to the conclusion that there are neurones within the sacral segments that mediate the actions of group II afferents primarily of posterior biceps and semitendinosus and gastrocnemius-soleus. Together with previous observations on the actions of group ...