Common interneurones in reflex pathways from group 1a and 1b afferents of knee flexors and extensors in the cat.

Abstract

SUMMARY1. Input from group I afferents of knee flexors and extensors to interneurones in Rexed's laminae V-VI in the cat spinal cord was analysed by use of intracellular recording and electrical stimulation ofthe nerves to differentiate between group I a and and I b synaptic actions. The aim was to find out if these interneurones may mediate synaptic actions of both group I a and Ib afferents.2. 28% of the forty-nine neurones analysed were excited by both group Ia and group Ib afferents; 32 % were inhibited by both and 35 % were excited by the one and inhibited by the other. Taking into account all of these actions, input from both subgroups of group I afferents was found in nearly 60 % of neurones. Most were also excited and/or inhibited by group I afferents of ankle and toe extensors.3. Selective (excitatory and/or inhibitory) input from Ia afferents was found in 18 % and from I b afferents in 22 % of the neurones.4. Excitation was evoked from I a afferents of either knee flexors or extensors but not from both. In several of the neurones Ia i.p.s.p.s were, however, evoked from both posterior biceps-semitendinosus and quadriceps.5. Intracellular staining with horseradish peroxidase revealed axonal projections of laminae V-VI interneurones to motor nuclei as well as to the intermediate zone, ipsilateral as well as contralateral. No correlation was found between patterns ofinput from group I afferents and axonal projections, and interneurones co-excited by I a and I b afferents were among those with different axonal projections.

Medullary reticulospinal tract mediating the generalized motor inhibition in cats: Parallel inhibitory mechanisms acting on motoneurons and on interneuronal transmission in reflex pathways

“…It has been shown that Ib interneurons mediate postsynaptic inhibition of MNs, 5,36,38,54 a variety of interneurons 9,11,28,36 and spinocerebellar tract neurons. 32 They also produce PAD.…”

Medullary reticulospinal tract mediating a generalized motor inhibition in cats: iii. functional organization of spinal interneurons in the lower lumbar segments

“…In this condition the spinal reflexes and the excitability of motoneurons are profoundly depressed (Glenn and Dement 1981a, 1981b, 1981cMorales and Chase, 1978). But supraspinal neurons arising from the cerebral cortex, the red nucleus, and the vestibular nucleus have been shown to be active during REM sleep (Arduini et al, 1963;Bizzi et al, 1964).…”

“…Interneurons in reflex pathways from Ib afferents are co-excited by group Ia and Ib afferents and consequently some of this group are known as interneurons mediating group I non-reciprocal inhibition (Jankowska, 1992;Jankowska et al, 1981a;Czarkowska et al, 1981). In this study we defined the cells without recurrent inhibition as group I interneurons.…”

Genetically Defined Inhibitory Neurons in the Mouse Spinal Cord Dorsal Horn: A Possible Source of Rhythmic Inhibition of Motoneurons during Fictive Locomotion

“…However, the group II inhibitory interneurons that project to motoneurons are in intermediate to ventral laminae, are primarily glycinergic, and do not project to Clarke's column. In the region where GFPϩ neurons are located in these GAD65::GFP mice, medial laminae V/VI, there have been two prominent populations of inhibitory neurons previously identified: (1) those responsible for presynaptic inhibition of group Ia afferent synapses on motoneurons (Hughes et al, 2005) and (2) those responsible for nonreciprocal inhibition (Czarkowska et al, 1981;Jankowska et al, 1981;Brink et al, 1983).…”

“…In addition to RCs and IaINs, at least two classes of inhibitory interneurons have been defined in intermediate laminae, including medial laminae V/VI (Czarkowska et al, 1981;Jankowska et al, 1981;Brink et al, 1983;Rudomin et al, 1987). These populations receive low-threshold primary afferent input and are comprised of both GABAergic and glycinergic neurons, with some projecting to Clarke's column (Hongo et al, 1983a,b;Rudomin et al, 1990).…”