The occurrence and function of collateral sprouting in the sympathetic nervous system of the cat

Abstract

It is now established that surviving axons in incompletely denervated striated muscle extend their existing fields of innervation by a process of collateral sprouting, thereby accounting for the functional recovery which occurs (for review see Edds, 1953). A similar process also occurs in skin partly deprived of its sensory nerve supply (Weddell, Guttmann & Gutmann, 1941). Although the phenomenon has not been directly observed in the sympathetic nervous system, there is evidence of remarkable recovery of function after incomplete denervation (Simeone, Cannon & Rosenblueth, 1938;Geohegan & Aidar, 1942).In the present work, partial denervation of the superior cervical ganglion in the cat was performed by severing rami communicantes from their respective thoracic nerves. Subsequently, sprouts arise within the ganglion from the remaining intact preganglionic fibres and form synapses with ganglion cells denervated by the preliminary operation. This spatial increment in the field of innervation of the remaining preganglionic fibres results in an almost complete functional recovery of the ganglion even when as many as 90 % of the fibres have been divided. Experiments have been performed so as to correlate the histological and functional changes within the ganglion, including the time course of the sprouting process and its effect on the acetylcholine release, electrical and pharmacological responses. It seems most likely that under similar conditions post-ganglionic fibres also respond by collateral sprouting.The factors responsible for the efficiency of the sprouting process in the sympathetic nervous system are discussed. A preliminary account of this work has already been published (Murray & Thompson, 1956).

Monosynaptic excitatory action on motoneurones regenerated to antagonistic muscles

“…Since the cross-union operation resulted in the chromatolytic death of about two thirds of the spinal ganglion cells, their degenerating central terminals may have stimulated sprouting of adjacent Ia afferent fibres which then established the aberrant synaptic connexions on the Per motoneurones. This effect of degenerating nerve fibres was first demonstrated in partial muscle denervation (Hoffman, 1950(Hoffman, , 1951Edds, 1950Edds, , 1953, and it has also been found in the partially denervated sympathetic ganglion (Murray & Thompson, 1957) and in the spinal cord when spinal cord section caused degeneration of the descending tracts (McCouch, Austin, Liu & Liu, 1958).…”

Selective synapse formation during sprouting after partial denervation of the guinea‐pig superior cervical ganglion.

“…The responses that remain were due to preganglionic axons running in the an~za8ubclavia. of selected spinal cord segments (Murray & Thompson, 1957;Guth & Bailey, 1961;Guth & Bernstein, 1961).…”

“…However, if the ganglion is partially denervated by interrupting the sympathetic rami T1-T3, the residual preganglionic axons, arising from T4-T7, will sprout and establish new synaptic connexions with ganglion cells that are obviously inappropriate to them. Thus several weeks after partial denervation, stimulation of the residual preganglionic axons elicits an abnormally wide range of peripheral sympathetic effects, including dilatation of the pupil, a response which is normally elicited only by preganglionic axons arising from T1-T3 (Murray & Thompson, 1957;Guth & Bailey, 1961;Guth & Bernstein, 1961). This loss ofspecificity might be a consequence ofthe complete removal ofpreganglionic axons arising from particular spinal levels.…”

Reflex reciprocal facilitation of antagonist muscles in spinal cord injury

“…Evidence accumulated from experimental work has shown that, following a partial lesion in the nervous system, terminals with injured fibers degenerate and intact afferent fibers progressively sprout collaterally to occupy the evacuated regions. [18][19][20][21][22] Reorganization of the nervous system comprises degenerative and regenerative changes in the afferent neurons distal to the lesion sites, disorganization and reorganization of the whole network, and ultimately the new growth. [22][23][24][25][26][27][28][29] It is suggested that the process of degeneration, reorganization and sprouting results in an alteration of the 'synaptic zone', which is the very element of the nervous system transmitting information from one neuron to another, forming the basis of the reflex behavior.…”