Development and Ongoing Regulation of Synaptic Connections and Neuronal Morphology in Autonomic Ganglia
The development of synaptic connections in autonomic ganglia is closely correlated with the development of ganglion cell dendritic geometry. There is now considerable evidence that this correlation is due to preganglionic inputs adjusting their synapses according to the geometry of their target ganglion cells. Ganglion cell geometry, in turn, is regulated not by preganglionic innervation but by the relative size of the ganglion cells peripheral target. Ganglion cell regulation of preganglionic synapses depends upon the ganglion cells receiving continuous retrograde signals from peripheral targets, implying a multistep pathway of retrograde trophic signalling. Furthermore, this target regulation of innervation is apparently an active process continuing throughout life, a conclusion supported by direct in situ observations of continuously rearranging pre- and postganglionic structures in normal adult ganglia. That ongoing trophic interactions regulate geometry and innervation suggests several possible consequences for the control of ganglionic function.
