Integration in descending motor pathways controlling the forelimb in the cat
An analysis has been made of the ascending projection to the lateral reticular nucleus (LRN) from the previously described C3-C4 “propriospinal” neurones (PNs) which are monosynaptically activated from several higher motor centres and project caudally, some of them directly to forelimb motoneurones (Illert et al. 1977, 1978).
Extra- and intracellular recording was made from cells in the C3-C4 segments which could be antidromically activated both from the lateral funicle in C7 and from the ipsilateral LRN. The ascending projection to LRN was found in 84% of the PNs terminating rostral to Th9 but at the most in 11% of the PNs projecting beyond Th9. Threshold mapping in and around the LRN showed that the stem axons of the ascending collaterals enter the nucleus from a position dorsomedial to its caudal part and terminate at different levels, along the entire rostrocaudal extent of the nucleus. Termination was not restricted to the forelimb region (the A-zone, Clendenin et al. 1974a) but was found also in the ventral part of the LRN. The conduction velocity was generally slower in the ascending than in the descending branch (mean values 26 and 44 m/s). The conduction velocity was higher in the PNs projecting beyond Th9 (mean value 101 m/s).
Stimulation in the LRN evoked large monosynaptic EPSPs in forelimb motoneurones as would be expected from the double projection of C3-C4 PNs. These EPSPs are elicited from the regions where the collaterals from C3-C4 PNs ascend and terminate. Their latency and time course are those expected for EPSPs mediated by the bifurcating axons of C3-C4 PNs. It is concluded that they are produced by antidromic activation of ascending neurones also projecting to forelimb motoneurones. The monosynaptic EPSPs from the LRN were found in all motor nuclei tested but were larger in motoneurones to elbow flexors than to elbow extensors (mean values 4.5 and 2.9 mV). Motoneurones classified as fast or slow from the duration of the afterhyperpolarization received EPSPs from the LRN even if pyramidal volleys evoked excitation in the former and inhibition in the latter. Double stimuli in the LRN revealed considerable frequency potentiation of the EPSPs.
Stimulation in the LRN gives marked facilitation of transmission in the reciprocal Ia inhibitory pathway to motoneurones. The effective LRN region, threshold strength and time course is the same as for the monosynaptic EPSPs in motoneurones. The Ia inhibitory interneurones receive a direct projection from C3-C4 PNs (Illert and Tanaka 1978) and it is postulated that these PNs also have an ascending collateral to the LRN which antidromically mediate monosynaptic excitation to the Ia inhibitory interneurones.
It is suggested that the ascending collaterals are a link in an intrinsic feed-back by which the brain controls how the C3-C4 PNs govern forelimb movements. This mode of ascending information — a mirror of the activity reaching forelimb motoneurones and Ia inhibitory interneurones — is discussed in relation to the more complex information in other ascending systems signalling intrinsic spinal activity.
Key wordsC3-C4 propriospinal neurones Bifurcating descending, ascending projection Motoneurones LRN
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- Alstermark B, Lundberg A (1980) Do corticospinal fibres send collaterals to the lateral reticular nucleus? Acta Physiol Scand 108: C4Google Scholar
- Alstermark B, Lundberg A, Norrsell U, Sybirska E (1981) Integration in descending motor pathways controlling the forelimb in the cat. 9. Differential behavioural defects after spinal cord lesions interrupting defined pathways from higher centres to motoneurones. Exp Brain Res 42: 299–318PubMedGoogle Scholar
- Anderson ME, Yoshida M, Wilson VJ (1972) Tectal and tegmental influences on cat forelimb and hindlimb motoneurons. J Neurophysiol 35: 462–470Google Scholar
- Brodal A (1943) The cerebellar connections of the nucleus reticularis lateralis in rabbit and cat. Experimental investigations. Acta Psychiatr Scand 18: 171–233Google Scholar
- Brodal P, Marsala J, Brodal A (1967) The cerebral cortical projection to the lateral reticular nucleus in the cat, with special reference to the sensorimotor cortical areas. Brain Res 6: 252–274Google Scholar
- Clendenin M, Ekerot C-F, Oscarsson O, Rosén I (1974a) The lateral reticular nucleus in the cat. I. Mossy fibre distribution in cerebellar cortex. Exp Brain Res 21: 473–486Google Scholar
- Clendenin M, Ekerot C-F, Oscarsson O (1974b) The lateral reticular nucleus in the cat. II. Organization of component activated from bilateral ventral flexor reflex tract (bVFRT). Exp Brain Res 21: 487–500Google Scholar
- Clendenin M, Ekerot C-F, Oscarsson O (1974c) The lateral reticular nucleus in the cat. III. Organization of component activated from ipsilateral forelimb tract. Exp Brain Res 21: 501–513Google Scholar
- Corvaja N, Grofova I, Pompeiano O, Walberg F (1977) The lateral reticular nucleus in the cat. I. An experimental anatomical study of its spinal and supraspinal afferent connections. Neuroscience 2: 537–553Google Scholar
- Ekerot C-F, Oscarsson O (1975) Inhibitory spinal paths to the lateral reticular nucleus. Brain Res 99: 157–161Google Scholar
- Grant G, Illert 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: 87–93Google Scholar
- Hirai N, Hongo T, Yamaguchi T (1978) Spinocerebellar tract neurones with long descending axon collaterals. Brain Res 142: 147–151Google Scholar
- Illert M, Lundberg A (1978) Collateral connections to the lateral reticular nucleus from cervical propriospinal neurones projecting to forelimb motoneurones in the cat. Neurosci Lett 7: 167–172Google Scholar
- 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: 101–130Google Scholar
- Illert M, Lundberg A, Tanaka R (1976a) Integration in descending motor pathways controlling the forelimb in the cat. 1. Pyramidal effects on motoneurones. Exp Brain Res 26: 509–519Google Scholar
- Illert M, Lundberg A, Tanaka R (1976b) Integration in descending motor pathways controlling the forelimb in the cat. 2. Convergence on neurones mediating disynaptic cortico-motoneuronal excitation. Exp Brain Res 26: 521–540Google Scholar
- Illert M, Lundberg A, Tanaka R (1977) Integration in descending motor pathways controlling the forelimb in the cat. 3. Convergence on propriospinal neurones transmitting disynaptic excitation from the corticospinal tract and other descending tracts. Exp Brain Res 29: 323–346Google Scholar
- Illert M, Tanaka R (1978) Integration in descending motor pathways controlling the forelimb in the cat. 4. Corticospinal inhibition of forelimb motoneurones mediated by short propriospinal neurones. Exp Brain Res 31: 131–141Google Scholar
- Kawamura K, Brodal A, Hoddevik G (1974) The projection of the superior colliculus onto the reticular formation of the brain stem. An experimental anatomical study in the cat. Exp Brain Res 19: 1–19Google Scholar
- Kuypers HGJM (1958) An anatomical analysis of corticobulbar connexions to the pons and lower brain stem in the cat. J Anat 92: 198–218Google Scholar
- Kuypers HGJM, Maisky VA (1975) Retrograde axonal transport of horseradish peroxidase from spinal cord to brain stem cell groups in the cat. Neurosci Lett 1: 9–14Google Scholar
- Ladpli R, Brodal A (1968) Experimental studies of commissural and reticular formation projections from the vestibular nuclei in the cat. Brain Res 8: 65–96Google Scholar
- Lindström S (1973) Recurrent control from motor axon collaterals of Ia inhibitory pathways in the spinal cord of the cat. Acta Physiol Scand [Suppl] 392: 1–43Google Scholar
- Lundberg A (1971) Function of the ventral Spinocerebellar tract — a new hypothesis. Exp Brain Res 12: 317–330Google Scholar
- Lundberg A (1979) Integration in a propriospinal motor centre controlling the forelimb in the cat. In: Asanuma H, Wilson VJ (eds) Integration in the nervous system. Igaku-Shoin, Tokyo New York, pp 47–64Google Scholar
- Tohyama M, Sakai K, Salvert D, Touret M, Jouvet M (1979) Spinal projections from the lower brain stem in the cat as demonstrated by the horseradish peroxidase technique. I. Origins of the reticulospinal tracts and their funicular trajectories. Brain Res 173: 383–403Google Scholar
- Walberg F (1958) Descending connections to the lateral reticular nucleus. An experimental study in the cat. J Comp Neurol 109: 363–389Google Scholar
- Walberg F, Pompeiano O (1960) Fastigiofugal fibers to the lateral reticular nucleus; an experimental study in the cat. Exp Neurol 2: 40–53Google Scholar
- Wilson VJ, Uchino Y, Maunz RA, Susswein A, Fukushima K (1978) Properties and connections of cat fastigiospinal neurones. Exp Brain Res 32: 1–17Google Scholar
- Wilson VJ, Yoshida M (1969) Comparison of effects of stimulation of Deiter's nucleus and medial longitudinal fasciculus on neck, forelimb and hindlimb motoneurones. J Neurophysiol 32: 743–758Google Scholar
- Zangger P, Wiesendanger M (1973) Excitation of lateral reticular nucleus neurones by collaterals of the pyramidal tract. Exp Brain Res 17: 144–151Google Scholar