Summary
Extra- and intracellular recording was made from cells in the C3-C4 segments with the aim of finding interneurones of previously described inhibitory pathways to the C3-C4 propriospinal neurones, which may mediate descending feed-forward inhibition and feed-back inhibition from the forelimb, respectively. The lateral interneurones were found in the lateral part of lamina VII interspersed among the C3-C4 PNs and like them they receive convergent monosynaptic EPSPs and disynaptic IPSPs from the cortico-, rubro-, tecto- and reticulospinal tracts. Disynaptic IPSPs, but only rarely monosynaptic EPSPs, are evoked in them from forelimb nerves. The lateral interneurones do not project to the lateral reticular nucleus (LRN). The medial interneurones were found medially in laminae V and VI in a region where volleys in forelimb nerves evoke extracellular monosynaptic focal potentials (Rosén 1969). There is somatotopic organization of the projection from the forelimb to this region. Many neurones are strongly monosynaptically excited from group I muscle or/and cutaneous forelimb afferents. In addition, late discharges are evoked in many cells from cutaneous afferents and high threshold muscle afferents. Corticospinal volleys evoked monosynapic excitation in the great majority of these cells and usually also late EPSPs or IPSPs. Typically, rubrospinal and tectospinal volleys evoked neither monosynaptic excitation nor late effects as those elicited from corticospinal fibres. In some of the interneurones, IPSPs were evoked from forelimb nerves. About 20% of the medial “interneurones” have an ascending projection to the caudal brain stem. Threshold mapping for antidromic stimulation revealed termination in the main cuneate nucleus, the external cuneate nucleus and/or the LRN and also a branch projecting to more rostral levels in the brain. A few of the neurones in the medial region are PNs projecting to the forelimb segments. It is postulated that interneurones both of the lateral and medial type are inhibitory and project to the C3-C4 PNs. It is further postulated that the former are intercalated in the descending feed-forward inhibitory pathway to the C3-C4 PNs and the latter in the feed-back inhibitory pathway from the forelimb to these PNs. The role of feed-forward and feed-back inhibition of transmission from the brain to forelimb motoneurones via the C3-C4 PNs is discussed.
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Alstermark B, Lindström S, Lundberg A, Sybirska E (1981) Integration in descending motor pathways controlling the forelimb in the cat. 8. Ascending projection to the lateral reticular nucleus from C3-C4 propriospinal neurones also projecting to forelimb motoneurones. Exp Brain Res 42: 282–298
Alstermark B, Lundberg A, Sasaki S (1984a) Integration in descending motor pathways controlling the forelimb in the cat. 10. Inhibitory pathways to forelimb motoneurones via C3-C4 propriospinal neurones. Exp Brain Res 56: 279–292
Alstermark B, Lundberg A, Sasaki S (1984b) Integration in descending motor pathways controlling the forelimb in the cat. 11. Inhibitory pathways from higher motor centres and forelimb afferents to the C3-C4 propriospinal neurones. Exp Brain Res 56: 293–307
Alstermark B, Pinter M, Sasaki S (1983) Brainstem relay of disynaptic pyramidal EPSPs to neck motoneurons in the cat. Brain Res 259: 147–150
Andersen P, Eccles JC, Oshima T, Schmidt RF (1964) Mechanisms of synaptic transmission in the cuneate nucleus. J Neurophysiol 27: 1096–1116
Baldissera F, Lundberg A, Udo M (1972) Stimulation of pre- and postsynaptic elements in the red nucleus. Exp Brain Res 15: 151–167
Brink E, Jankowska E, McCrea DA, Skoog B (1983) Inhibitory interactions between interneurones in reflex pathways from group Ia and group Ib afferents in the cat. J Physiol (Lond) 343: 361–373
Carstens E, Trevino DL (1978) Anatomical and physiological properties of ipsilaterally projecting spinothalamic neurons in the second cervical segment of the cat's spinal cord. Exp Comp Neurol 182: 167–184
Clendenin M, Ekerot C-F, Oscarsson O (1974) The lateral reticular nucleus in the cat. III. Organization of component activated from ipsilateral forelimb tract. Exp Brain Res 21: 501–513
Cooke JD, Larson B, Oscarsson O, Sjölund B (1971a) Origin and termination of cuneocerebellar tract. Exp Brain Res 13: 339–358
Cooke JD, Larson B, Oscarsson O, Sjölund B (1971b) Organization of afferent connections to cuneocerebellar tract. Exp Brain Res 13: 359–377
Ekerot C-F, Oscarsson O (1975) Inhibitory spinal paths to the lateral reticular nucleus. Brain Res 99: 157–161
Gordon G, Grant G (1982) Dorsolateral spinal afferents to some medullary sensory nuclei. Exp Brain Res 46: 12–23
Grant G, Illiert M, Tanaka R (1980) Integration in descending motor pathways controlling the forelimb in the cat. 6. Anatomical evidence consistent with the existence of C3-C4 propriospinal neurones projecting to forelimb motornuclei. Exp Brain Res 38: 87–93
Grantyn A, Grantyn R (1982) Axonal patterns and sites of termination of cat superior colliculus neurons projecting in the tecto-bulbo-spinal tract. Exp Brain Res 46: 243–256
Hongo T, Jankowska E, Lundberg A (1969) The rubrospinal tract. II. Facilitation of interneuronal transmission in reflex paths to motoneurones. Exp Brain Res 7: 365–391
Hongo T, Jankowska E, Ohno T, Sasaki S, Yamashita M, Yoshida K (1983a) Inhibition of dorsal spinocerebellar tract cells by interneurones in upper and lower lumbar segments in the cat. J Physiol (Lond) 342: 145–159
Hongo T, Jankowska E, Ohno T, Sasaki S, Yamashita M, Yoshida K (1983b) The same interneurones mediate inhibition of dorsal spinocerebellar tract cells and lumbar motoneurones in the cat. J Physiol (Lond) 342: 161–180
Illert M, Jankowska E, Lundberg A, Odutola A (1981) Integration in descending motor pathways controlling the forelimb in the cat. 7. Effects from the reticular formation on C3-C4 propriospinal neurones. Exp Brain Res 42: 269–281
Illert M, Lundberg A, Padel Y, Tanaka R (1978) Integration in descending motor pathways controlling the forelimb in the cat. 5. Properties of and monosynaptic excitatory convergence on C3-C4 propriospinal neurones. Exp Brain Res 33: 101–130
Imai Y, Kusama T (1969) Distribution of the dorsal root fibers in the cat. An experimental study with the Nauta method. Brain Res 13: 338–359
Molenaar I (1978) The distribution of propriospinal neurons projecting to different motoneuronal cell groups in the cat's brachial cord. Brain Res 158: 203–206
Rosén I (1969) Localization in caudal brain stem and cervical spinal cord of neurones activated from forelimb group I afferents in the cat. Brain Res 16: 55–71
Rustioni A (1974) Non-primary afferents to the cuneate nucleus in the brachial dorsal funiculus of the cat. Brain Res 75: 247–259
Rustioni A, Kaufmann AB (1977) Identification of cells of origin of nonprimary afferents to the dorsal column nuclei of the cat. Exp Brain Res 27: 1–14
Rustioni A, Molenaar I (1975) Dorsal column nuclei afferents in the lateral funiculus of the cat. Distribution pattern and absence of sprouting after chronic deafferentation. Exp Brain Res 23: 1–12
Uddenberg N (1968) Functional organization of long, secondorder afferents in the dorsal funiculi. Exp Brain Res 4: 377–382
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This work was supported by the Swedish Medical Research Council (project no. 94)
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Alstermark, B., Lundberg, A. & Sasaki, S. Integration in descending motor pathways controlling the forelimb in the cat. Exp Brain Res 56, 308–322 (1984). https://doi.org/10.1007/BF00236286
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DOI: https://doi.org/10.1007/BF00236286