Maintenance of cholinergic neurones and synapses in the ciliary ganglion of aged rats.

The ciliary ganglion has been examined in young adult (1.5-2 months) and aged rats (24-28 months). In young adult rats the ganglion contains about 200 neurones, each of which is innervated by 1-4 preganglionic axons (mean, 2.2). In these animals about 2-3 X 10(3) synaptic boutons were observed per square millimetre in thin sections of the ganglion; synapses were located mainly on finger-like extensions of cell bodies and on dendrites. The size of the ganglion cell population, the number of inputs per ganglion cell, the density of synaptic boutons and the amplitude of post-synaptic potentials recorded intracellularly did not differ significantly between the young and aged animals. It thus appears that the neuronal population of the ciliary ganglion and the cholinergic synapses received by ganglion cells are remarkably stable well into old age.