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

Abstract

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.

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

“…(2) These effects were produced by the same conditioning stimuli that produced depression of field potentials evoked by group II afferents in the same region of the spinal cord. (3) The conditioning-test intervals over which PAD was produced by stimuli in supraspinal sites are consistent with the time course of the depression of midlumbar field potentials and postsynaptic potentials in motoneurones evoked by group II afferents (Noga et al 1992;Jankowska et al 1993). (4) Stimuli in the nucleus ruber which have little effect on the midlumbar field potentials produced by group II afferents are also largely without effect on the excitability of the terminals of group II muscle afferents in this region.…”

“…The aim of the present investigation was to look for evidence that the depressive actions of stimuli applied in the LC/SC and raphe nuclei on transmission from group II muscle afferents (Noga et al 1992;Jankowska et al 1993) might involve a presynaptic mechanism of action. Several observations from the present study are consistent with this possibility.…”

“…Full details of the method of placement of stimulating electrodes are given in the companion paper (Jankowska et al 1993). The location of all brain stimulation sites was verified histologically by relating the positions of electrolytic lesions made at the end of the experiment to clearly identifiable stained structures and are shown in Fig.…”

“…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 INTRODUCTION Neuronal systems activated by electrical stimuli applied in the locus coeruleus/ subcoeruleus (LC/SC) and raphe nuclei induce a profound depression of transmission in group II reflex pathways (Noga, Bras & Jankowska, 1992;Jankowska, Riddell, Skoog & Noga, 1993). This depression is exerted on both the excitatory and inhibitory reflex actions of group II afferents and actions originating from group II afferents in a variety of hindlimb muscle nerves are depressed with similar effectiveness.…”

Spatial and temporal patterns of serotonin release in the rat’s lumbar spinal cord following electrical stimulation of the nucleus raphe magnus

“…These times and distances are not well suited for conveying rapid, specific commands, but can serve to set up segmental circuits to respond with specific motor patterns to descending glutamatergic motor commands under a particular state of peripheral input (Jankowska et al, 1993). On the sensory side, these scales imply that monoamines modulate ascending transmission of information over longer times and larger somatotopic regions than encompassed in the typical dynamics of afferent input.…”