Factors responsible for multiple discharge of neurons in Clarke's column.

1. Clarke's column neurons of the dorsal spinocerebellar tract (DSCT) were recorded intracellularly in anaesthetized cats during weak sustained contractions of triceps surae (TS) produced by direct electrical stimulation of the muscle. 2. Of 145 DSCT neurons, 77 (53%) were contraction sensitive suggesting that information about weak contraction of a limited number of muscles is widely distributed among DSCT neurons. Four types of effects were observed in individual neurons during TS contractions. 3. In the first group of 11 DSCT neurons (14% of the contraction-sensitive cells), the effect was excitation persisting throughout the duration of contractions. These responses were ascribed to actions of afferents from contraction-activated tendon organs. 4. In a second group of 15 neurons (20% of the contraction-sensitive cells), quickly declining excitatory potentials were recorded during sustained TS contractions. By analogy with previous observations of contraction-induced effects in motoneurons, the decline of excitation might be explained by contraction-induced presynaptic inhibition of group I afferents in Clarke's column. 5. Declining inhibitions, resembling those previously observed in homonymous and synergic motoneurons, were recorded in 49 % of contraction-sensitive DSCT neurons. This appears in keeping with the fact that interneurons mediating I b inhibition to motoneurons project axon collaterals to DSCT neurons. Presynaptic inhibition of I b fibres might therefore cause parallel reductions of inhibitory potentials in motoneurons and in DSCT neurons. 6. In a final group of 13 neurons, mixed excitatory and inhibitory effects were observed during TS contractions. Such DSCT neurons might monitor the excitability of Ib interneurons by integration of information about input to and output from these neurons. 7. The non-uniform patterns of DSCT responses to TS contractions suggest complex processing of information on ankle extensor activity in cerebellum. Phasic signalling of contraction onset is observed in many DSCT neurons while others carry messages about duration and strength of contraction.

mentioning

confidence: 77%

Heterogeneity of contraction‐induced effects in neurons of the cat dorsal spinocerebellar tract.

Zytnicki

Lafleur

Kouchtir

et al. 1995

“…One example is provided by the branches of Ia afferent fibres which have characteristically different effects at two different synapses. One branch causes a large, powerful, excitatory potential in the neurones of Clarke's column while another evokes only a small subthreshold potential in spinal motoneurones (Kuno & Miyahara, 1968). It is not yet known how these synapses behave with trains of impulses.…”

Section: Discussionmentioning

confidence: 99%

Different properties of synapses between a single sensory neurone and two different motor cells in the leech C.N.S

Muller¹,

Nicholls²

1974

SUMMARYIn leech ganglia, an individual sensory cell that responds specifically to noxious mechanical stimulation of the skin (N cell) excites two different motoneurones. One raises the annuli of the skin into ridges (the AE cell), while the other innervates longitudinal muscles and thereby shortens the body segment (L cell). A comparison has been made of the way in which these two synapses behave when their common presynaptic cell is stimulated in various conditions. 1. Using previously described criteria, N sensory cells have been shown to make monosynaptic chemical connexions with both the AE and L motoneurones (Nicholls & Purves, 1972). Following a single stimulus, the excitatory synaptic potential recorded in the AE motoneurone was only about one tenth the size of that in the L cell (approximately 0 5 mV compared to 5 mV). Trains of impulses in the same N sensory cell gave rise to synaptic potentials in the AE and the L motoneurones that underwent phases of facilitation and depression; the facilitation, however, was characteristically greater and longer lasting at synapses upon the AE motoneurone.2. The differences between the two synapses were accentuated in Ringer fluid containing increased concentrations of Ca and also in the cold. Under both of these conditions repetitive firing by the N sensory cell could give rise to synaptic potentials in the AE motoneurone which progressively increased in amplitude, while those in the L motoneurone became smaller.3. The results suggest that the differences in synaptic transmission can be accounted for by variations in the amount of transmitter released at the presynaptic N cell terminals, rather than by differences in the

“…Maximum electrical stimuli applied to such monosynaptic paths often produce large excitatory post-synaptic potentials (e.p.s.p.s) in DSCT neurones which range up to 30-65 mV in amplitude (Kuno & Miyahara, 1968; Eide, Fedina, Jansen, Lundberg & Vyklick', 1969a). This contrasts with synaptic action on spinal motoneurones in which the maximum monosynaptic e.p.s.p.s rarely exceed 12 mV (Eccles, Eccles & Lundberg, 1957).…”

Section: Introductionmentioning

confidence: 99%

Synaptic action on Clarke's column neurones in relation to afferent terminal size

Kuno¹,

Muñoz-Martínez²,

Randić³

1973

SUOMMARY1. Excitatory post-synaptic potentials (e.p.s.p.s) were recorded intracellularly from Clarke's column neurones (DSCT neurones) of the cat in response to adequate stimuli applied to a variety of sensory receptors.2. The amplitude of e.p.s.p.s so produced varied from less than 0-2 mV to more than 2-3 mV. The M. KUNO AND OTHERS and motoneurones were examined with the electron microscope after chronic section of the dorsal roots.7. Dendritic degenerating terminals showed no significant difference in size between motoneurones and DSCT neurones. Degenerating 'giant' terminals were found on DSCT neurones, but they were located only on or very close to the cell body.8. It is concluded that the major factor responsible for a large number of 'quanta' of transmitter released at synapses on DSCT neurones is the number of multiple synaptic contacts formed by one afferent fibre rather than the size of individual synapses.