Convergence on interneurones mediating the reciprocal Ia inhibition of motoneurones. I. Disynaptic Ia inhibition of Ia inhibitory interneurones.

Interneurones identified as mediating the disynaptic reciprocal Ia inhibition of motoneurones (referred to as "Ia inhibitory interneurones") were recorded in the lumbar spinal cord of the cat. It was revealed that the Ia inhibitory interneurones themselves receive disynaptic Ia inhibition. The muscles from which this inhibition is evoked are strictly antagonistic to those supplying their Ia excitation. Similar to the Ia inhibition in motoneurones the Ia inhibition in the Ia inhibitory interneurones is decreased when preceded by an antidromic stimulation of ventral roots. Furthermore, transmission of Ia inhibition to the Ia inhibitory interneurones is facilitated from ipsilateral and contralateral primary afferents as well as several supraspinal pathways analogous to earlier findings for the Ia inhibition of motoneurones. The pattern and control of the Ia inhibition of motoneurones and of Ia inhibitory interneurones display so striking similarities that it is suggested that identical interneurones are responsible. The conclusion thus emerges that "opposite" Ia inhibitory interneurones (i.e. interneurones monosynaptically connected to antagonistic muscles) are mutually inhibiting each other. The functional significance of this organization is discussed.

[1]  E Jankowska,et al.  Recurrent inhibition from motor axon collaterals of transmission in the Ia inhibitory pathway to motoneurones , 1971, The Journal of physiology.

[2]  Convergence of large muscle spindle (Ia) afferents at interneuronal level in the reciprocal Ia inhibitory pathway to motoneurones. , 1972, Acta physiologica Scandinavica.

[3]  G. Orlovsky,et al.  Activity of interneurons mediating reciprocal 1a inhibition during locomotion , 1975, Brain Research.

[4]  H. Hultborn,et al.  Relative contribution from different nerves to recurrent depression of Ia IPSPs in motoneurones , 1971, The Journal of physiology.

[5]  E Jankowska,et al.  Synaptic actions of single interneurones mediating reciprocal Ia inhibition of motoneurones , 1972, The Journal of physiology.

[6]  J. Eccles,et al.  Analysis of the fast afferent impulses from thigh muscles , 1953, The Journal of physiology.

[7]  B. Gustafsson,et al.  Recurrent control from motor axon collaterals of Ia inhibitory pathways to ventral spinocerebellar tract neurones. , 1973, Acta physiologica Scandinavica.

[8]  H. Hultborn,et al.  Convergence on interneurones mediating the reciprocal Ia inhibition of motoneurones. II. Effects from segmental flexor reflex pathways. , 1976, Acta physiologica Scandinavica.

[9]  H Hultborn,et al.  Convergence on interneurones in the reciprocal Ia inhibitory pathway to motoneurones. , 1972, Acta physiologica Scandinavica. Supplementum.

[10]  H. Hultborn,et al.  Convergence on interneurones mediating the reciprocal Ia inhibition of motoneurones. III. Effects from supraspinal pathways. , 1976, Acta physiologica Scandinavica.

[11]  E. Jankowska,et al.  Morphology of interneurones mediating Ia reciprocal inhibition of motoneurones in the spinal cord of the cat , 1972, The Journal of physiology.

[12]  H. Hultborn,et al.  Facilitation from ipsilateral primary afferents of interneuronal transmission in the Ia inhibitory pathway to motoneurones. , 1972, Acta physiologica Scandinavica.

[13]  A. Lundberg,et al.  Integrative pattern of Ia synaptic actions on motoneurones of hip and knee muscles , 1958, The Journal of physiology.

[14]  J. Eccles,et al.  Synaptic actions on motoneurones in relation to the two components of the group i muscle afferent volley , 1957, The Journal of physiology.

[15]  H. Hultborn,et al.  Recurrent inhibition of interneurones monosynaptically activated from group Ia afferents , 1971, The Journal of physiology.

[16]  E. Jankowska,et al.  An electrophysiological demonstration of the axonal projections of single spinal interneurones in the cat , 1972, The Journal of physiology.