After-Potentials and Excitability of Spinal Motoneurones Following Antidromic Activation

Intracellular recording from antidromically activated motoneurones

“…Figs. 9 and 11; Brooks et al 1950;, and presumably it also causes the concurrent depression of the synaptically evoked discharge from the motoneurone (Brooks et al 1950;. Thus the SD spike is again identified with the synaptically activated membrane of the motoneurone.…”

“…(iv) Brooks et al (1950) reported that, a few milliseconds after antidromic activation of a motoneurone pool, some at least of those motoneurones were more excitable than at the depth of depression about 10 msec later; this was confirmed by Lloyd (1951a). In part at least this effect was attributed to a brief waning phase of supernormal excitability in motoneurones which had been partly depolarized by antidromic impulses that had been blocked at their axon-soma junctions.…”

The refractory period of the sensory synapses of the lateral geniculate nucleus

“…Together they place an upper limit of about 0-85 msec for the absolutely refractory period of oculomotor and geniculate synapses. The absolutely refractory period of the synapses on spinal motoneurones has been shown by Lloyd (1943) and Brooks, Downman & Eccles (1950a) to be rather longer than this, probably about 1-5 msec. These investigators used an antidromic conditioning volley followed by an orthodromic testing volley, but allowance had to be made for the failure of some of the antidromic impulses to invade the cell body.…”

“…particularly Brooks, Downman & Eccles, 1950a, b;Eccles, 1955;Lloyd, 1951) and brain stem (Lorente de No, 1935b;). The present study, which is concerned with the sensory synapses of the dorsal nucleus of the lateral geniculate body, is limited to the recovery from the refractory state.…”

The recovery of responsiveness of the sensory synapses in the lateral geniculate nucleus

“…It is possible that the cell body spike may persist for a brief interval after the spike in the initial segment sufficient to provide a powerful catelectrotonic effect upon the latter. Brooks et al (1950a) have put forward a similar explanation to account for the recurrent discharge in motor axons. (2) Freygang (1958) and similar unpublished observations from this laboratory provide evidence which suggests that, while most of the post-synaptic membrane may be excited synaptically to produce a post-synaptic potential, the dendritic membrane and possibly also part of the cell body membrane are not excited electrically and do not produce a propagating spike.…”