The effects of disuse and of activity on mammalian spinal reflexes

Disuse enhances synaptic efficacy in spinal mononeurones.

“…Post-tetanic potentiation of monosynaptic e.p.s.p.s in response to stimulation of sectioned afferent fibres is known to be significantly increased in both amount and duration (Eccles et al 1959). This behaviour has been considered to be indicative of partial restoration of the efficiency of disused central synapses by intense activation (Eccles et al 1959; also, see Eccles & McIntyre, 1953). In the present study, attempts were made to examine whether a similar augmentation of post-tetanic potentiation may occur at synapses disused for 2 weeks because of the application of TTX.…”

“…It is well known that the cell body of a sensory neurone shows a chromatolytic reaction to section of its peripheral process (Anderson, 1902;Ranson, 1914;Hare & Hinsey, 1940;Carmel & Stein, 1969). This reaction is associated with a decrease in axonal conduction velocity of both the peripheral (Eccles & McIntyre, 1953;Eccles et al 1959;Kiraly & Krnjevi6, 1959; Cz6h, Kudo & Kuno, 1977) and central (dorsal root) processes (Cz6h et al 1977). Thus, reaction of sensory neurones to peripheral axotomy apparently spreads centrally beyond the cell bodies.…”

“…Eccles & McIntyre (1953) have shown that spinal monosynaptic reflexes are strikingly depressed after 3 weeks of total disuse induced by section of the dorsal roots just distal to the ganglia. Similarly, following section of a muscle nerve in the hind leg, monosynaptic excitatory post-synaptic potentials (e.p.s.p.s) recorded from the homonymous and heteronvmous motoneurones are significantly reduced in amplitude within 2 weeks (Eccles, Krnjevi6 & Miledi, 1959).…”

Changes in conduction velocity and fibre size proximal to peripheral nerve lesions

“…Numerous observers have noted that fibre diameter in the central stump becomes reduced during regeneration (Greenman, 1913;Gutmann & Sanders, 1943;Weiss, Edds & Cavanaugh, 1945;Sanders & Young, 1946;Sanders, 1948;Gutmann & Holubar, 1951;Eccles & McIntyre, 1953). These investigators confined their examination to distances not greater than 2 cm above the lesion, or did not specify the level of examination.…”

Disuse in the lateral geniculate nucleus of the cat

“…Some support for this theory is provided by the demonstration of 'post-tetanic potentiation' at many synapses, although the duration of this effect, a few minutes at most, is clearly W. BURKE AND W. R. HAYHOW inadequate to account for the relatively permanent changes which must accompany learning. It has also been argued by Eccles & McIntyre (1953) and by Eccles, Krnjevic' & Miledi (1959) that disuse of a synapse should produce depression of synaptic function. By disuse here is meant an absence of impulses in presynaptic nerve fibres.…”