Excitation of Renshaw cells in relation to orthodromic and antidromic excitation of motoneurons.

Inhibition of human motoneurones, probably of Renshaw origin, elicited by an orthodromic motor discharge

“…The activation by the conditioning stimulus of inhibitory afferent fibres (essentially Tb) is not responsible for this inhibition of the test reflex, since it has been demonstrated that this inhibition is only related to the size of HI (at least when the time interval separating the SI conditioning stimulus from the SM test stimulus is between 10 and 25 msec). This reduction of the fraction of the motoneurones involved in HI which is recruited by the SM test stimulus can be explained very well by recurrent inhibition, the amount of which depends upon the size of the conditioning discharge (Ryall et al 1972). However, one must consider another explanation based on the differences in susceptibility of the motoneurones undergoing after-hyperpolarization to the Ia test volley.…”

“…The smallest interval explored was 6 msec, since it has been shown in a previous paper (Pierrot-Deseilligny et al 1976 belong to the fraction of the soleus a motoneurone pool which has already discharged in response to the conditioning volley (see above). In these motoneurones, the excitatory post-synaptic potentials resulting from the conditioning Ia afferent volley are eliminated by the action potentials they have elicited (Coombs, Eccles & Fatt, 1955b (Coombs, Eccles & Fatt, 1955a); (2) enhancement of the 324 B. BUSSEL AND E. PIERROT-DESEILLIGNY recurrent inhibition caused by the increased reflex discharge (H 1) in response to the SI conditioning volley (Ryall, Piercey, Polosa & Goldfarb, 1972); (3) activation, when the intensity of the conditioning stimulus is increased, of a larger number of either Ib fibres disynaptically inhibiting the homonymous motoneurones (Laporte & Lloyd, 1952), or of Ia fibres giving presynaptic inhibition of the test volley (Barnes & Pompeiano, 1970). Intensity of SI (mA) Fig.…”

Primary Afferent Synapses on Developing and Adult Renshaw Cells

“…Monosynaptic dorsal root activation of Renshaw cells (responses evoked with latencies Ͻ1 ms) was later proposed by Frank and Fuortes (1956) in decerebrated cats. However, subsequent work using barbiturate-or chloraloseanesthetized cats failed to find monosynaptic connections (Curtis and Ryall, 1966;Ryall and Piercey, 1971;Ryall et al, 1972). These latter studies suggested that Ia afferent inputs do influence Renshaw cell activity but via disynaptic (through motoneurons) or polysynaptic pathways.…”

Patterns of recurrent excitation and mutual inhibition of cat Renshaw cells.

“…It seems likely that one function of mutual inhibition could be to suppress liminal excitation of Renshaw cells so as to sharpen the focus of convergent excitation and improve the selectivity of excitatory transmission to the Renshaw cells. It is noteworthy that far less convergence of excitation onto individual Renshaw cells is observed when they are disynaptically excited via the motoneurones (Ryall et al 1972b). Under more physiological conditions, when motoneurones of differing functional groups are co-activated, mutual inhibition may improve the selectivity and modulate the convergent excitation of Renshaw cells.…”