The formation of synapses in mammalian sympathetic ganglia reinnervated with preganglionic or somatic nerves

Abstract

SUMMARY -1. A study has been made of the formation of synapses in the superior cervical ganglion of the guinea-pig, during reinnervation either with axons of the cervical sympathetic trunk, or with somatic axons of the nerve to the sternohyoid muscle.2. No significant changes in either the geometry or electrical parameters of sympathetic motorneurones were detected following denervation for periods of 3-6 weeks, or after reinnervation with either preganglionic or somatic axons.3. The post-ganglionic action potential reappeared about 4 weeks after preganglionic trunk section (eighteen of eighteen ganglia); its amplitude increased progressively and was almost normal by more than 10 weeks after nerve section. A very small response was detected from thirteen of eighteen ganglia after periods longer than 8 weeks after cross-reinnervation with somatic axons. 4. Regenerated preganglionic or somatic nerve terminals were demonstrated around the ganglion cells using ZIO impregnation and electronmicroscopy; the structure of these terminals was unchanged following regeneration into the ganglia, although many more synapses were formed by preganglionic terminals than by somatic terminals.5. The facilitation of evoked synaptic potentials which occurs during repetitive stimulation of preganglionic axons was retained following their regeneration, whereas most synapses formed on ganglion cells by regenerating somatic axons showed facilitation of transmitter release during trains of stimuli, rather than the normal depression.6. These observations suggest that the structure and electrical properties of adult mammalian autonomic motorneurones are not under neural control, but that these neurones do show some selectivity in the type of nerve which they will permit to form synapses on them.

Apportionment of the terminals from single preganglionic axons to target neurones in the rabbit ciliary ganglion.

“…However, for a response of approximately 29 mV (the average amplitude of responses in singly innervated neurones) to be reduced to the size of many responses in multiply innervated neurones (2-4 mV), the synapses would have to be about two space constants from the cell body. Such an electrically remote location seems unlikely given what is known about the passive properties of autonomic ganglion cells (see McLachlan, 1974;Henon, Brown & McAfee, 1981).…”

Changes in the dendritic geometry of mouse superior cervical ganglion cells following postganglionic axotomy

“…In some neuronal systems, removal of afferent inputs curtails the very survival of postsynaptic cells in the course of normal development (Oppenheim, 198 1;Okado and Oppenheim, 1984;Clarke, 1985). Nevertheless, the absence of afferent input has little influence on the dendritic differentiation of spinal neurons (Brown et al, 1983;Sedivec et al, 1986;see, however, Brown et al, 1979) or of sympathetic ganglion cells (Hamlyn, 1954;McLachlan, 1974;Smolen and BeastonWimmer, 1986;Voyvodic, 1987) (although afferent input is necessary for the biochemical differentiation of sympathetic ganglion cells; see Black, 1978Black, , 1982. Therefore, it is quite unlikely that axotomy of the superior cervical ganglion first induces a loss of afferent synapses, which then results in a secondary dendritic atrophy.…”

Neural units in the superior cervical ganglion of the guinea‐pig.

“…The separation of the micro-electrodes was measured with an eye-piece graticule. Since these ganglion cells receive synapses on dendrites which radiate from the cell body (McLachlan, 1974;Purves, 1975) Lichtman, 1980 Fig. 1.…”