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Integration in descending motor pathways controlling the forelimb in the cat

7. Effects from the reticular formation on C3-C4 propriospinal neurones

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Summary

Effects of stimulation in the medullary reticular formation (RF) on C3-C4 propriospinal neurones (PNs) were investigated in two series of experiments: (1) indirectly by analyzing how propriospinal transmission to forelimb motoneurones is modified by reticular stimuli; (2) directly by intracellular recording from C3-C4 neurones, which were identified as propriospinal by their antidromic activation from the C6 segment.

Propriospinally mediated disynaptic EPSPs evoked in motoneurones from the pyramid (Pyr) and the red nucleus (NR) were effectively facilitated by conditioning stimulation in the RF with a time course of facilitation indicating monosynaptic linkage to the PNs. Propriospinally mediated trisynaptic IPSPs were facilitated less regularly and sometimes instead depressed by conditioning stimulation in the RF. The depression is at least partly due to inhibition of the first order PNs.

Recording from C3-C4 PNs revealed that many of them were excited or inhibited by single stimuli in the RF. The brief latency of the EPSPs evoked in these neurones shows monosynaptic linkage from fast reticulospinal fibres. Some IPSPs were similarly monosynaptically evoked from fast fibres and observations are presented suggesting that longer latency IPSPs are monosynaptically mediated by slower fibres. Facilitation of propriospinal transmission to motoneurones as well as the EPSPs and IPSPs in PNs were evoked from a region within or close to the nucleus reticularis gigantocellularis.

Convergence of monosynaptic EPSPs from Pyr, NR, tectum, and RF was common in C3-C4 PNs. Linear summation of the EPSPs from RF with those evoked from cortico-, rubro-, or tectospinal tracts shows that the former are not due to stimulation of collaterals which the latter tracts may have in RF. Mediation of the EPSPs and IPSPs by descending, rather than by antidromically activated ascending fibres, was indicated by temporal facilitation produced by RF stimuli, subliminal for evoking monosynaptic PSPs in the PNs. Stimulation of the labyrinth did not evoke disynaptic PSPs in any of the PNs investigated.

It is concluded that the C3-C4 PNs projecting to forelimb motoneurones can be excited not only from the cortico-, rubro-, and tectospinal tracts (Illert et al. 1977, 1978) but also by reticulospinal fibres.

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Abbreviations

LF:

lateral funiculus

MLF:

medial longitudinal fasciculus

NR:

nucleus ruber

PNs:

propriospinal neurones

Pyr:

pyramids

T:

tectum

RF:

reticular formation

i:

ipsilateral

co:

contralateral

Bi:

biceps

Br:

brachialis

DR:

deep radial

Tri:

triceps

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Author notes

  1. M. Illert

    Present address: Department of Physiology, University of Munich, Pettenkoferstr. 12, D-8000, Munich 2, Federal Republic of Germany

  2. A. Odutola

    Present address: Department of Anatomy, University of Ibadan, Ibadan, Nigeria

Authors and Affiliations

  1. Department of Physiology, University of Göteborg, Box 33031, S-400 33, Göteborg, Sweden

    M. Illert, E. Jankowska,  A. Lundberg & A. Odutola

Authors
  1. M. Illert
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  2. E. Jankowska
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  3. A. Lundberg
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  4. A. Odutola
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Additional information

This work was supported by the Swedish Medical Research Council (Project No. 94)

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Illert, M., Jankowska, E., Lundberg, A. et al. Integration in descending motor pathways controlling the forelimb in the cat. Exp Brain Res 42, 269–281 (1981). https://doi.org/10.1007/BF00237494

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