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

Abstract

SUMMARY1. The synaptic connexions established by sprouting of intact preganglionic sympathetic axons were examined by intracellular recording in vitro and by observing the sympathetic end organ responses to ventral root stimulation in vivo.2. The superior cervical ganglion of the guinea-pig was partially denervated (70-85 %) by crushing the cervical sympathetic trunk at the level of the subclavian artery, leaving the ansa subclavia intact. The intact nerve carried some preganglionic axons arising from each of the eight spinal cord segments (C8-T7) contributing innervation to the ganglion. 3. During the first 4 weeks after the operation, there was a two-to threefold increase in the number of steps in the synaptic response elicited in individual ganglion cells by graded stimulation of the ansa subclavia. There was also an increase in the amplitude of the synaptic potential elicited by each preganglionic axon.4. This increase in the synaptic contribution of the intact nerve to neurones in the superior cervical ganglion after partial denervation was attributed to sprouting of residual preganglionic axons. A major contribution from collateral connexions between ganglion cells was ruled out by intracellular recording from neurones during antidromic stimulation of their axons in the inferior post-ganglionic nerve.5. After sprouting, the specificity of the sympathetic end organ responses elicited by stimulation of the ventral roots of spinal segments TI and T4 in vivo was indistinguishable from normal, although the strength of these responses increased from just perceptible acutely after partial denervation to near normal 3-6 weeks after the operation, when sprouting was largely complete.6. These results show that intact preganglionic axons arising from different spinal levels established selective connexions with different classes of ganglion cells during sprouting.

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“…Because 3 weeks is very early for a complete re‐innervation to occur, it might be possible that synaptic connections occur between the damaged CTN fibers and the cutaneous somatosensory fibers. A similar observation has been made by Maehlen and Nja 17 . They observed synapse formation during sprouting after partial denervation of the guinea‐pig superior cervical ganglion.…”

Chronic block of the cervical trunk increases synaptic efficacy in the superior and stellate ganglia of the guinea‐pig.

“…One week after partial denervation of the superior cervical ganglion, there is some degree of sprouting from the remaining preganglionic axons (Maehlen & Nja, 1981), thus it is possible that the increase in e.p.s.p. amplitude observed by us could be due to an increase in the number of synaptic connexions from non-injured axons if the TTX capillary produced some degree of axon damage.…”

“…The fibres forming the ansa subclavia constitute about 17 0 of the fibres in the superior cervical trunk (Maehlen & Nja, 1981) and the rest form the subelavian trunk.…”

Trophic interactions between rat nerves and blood vessels in denervated peripheral arteries and in anterior eye chamber transplants.

“…58, No. 5, May 1986 sidual processess following partial denervation of the superior cervical ganglion in the guninea pig (Maehlen and Nja, 1981). Skeletal muscle in culture has been shown to secrete nerve growth factor (Murphy et al, 1979), and Chamley et al (1973b) suggested that nerve growth factor may account for the specificity of sympathetic innervation of various tissues in culture.…”