The elimination of redundant preganglionic innervation to hamster sympathetic ganglion cells in early post-natal life.

The superior cervical ganglion of adult and neonated hamsters has been studied with intracellular recording. 1. Neurones in adult hamster ganglia are innervated by an average of 6-7 preganglionic axons. During the first week of post-natal life, however, these cells are innervated by at least eleven to twelve axons. Ganglion cells in animals 2-3 weeks old are innervated to an intermediate degree, indicating that these neurones lose a substantial portion of their initial synaptic contacts during the first weeks after birth. 2. The over-all innervation of the superior cervical ganglion in adult hamsters arises from thoracic segments T1-T5; no additional segments contribute significantly to the innervation of neonatal ganglia. 3. The average number of segments innervating each adult ganglion cell is 2 . 8 compared to 3 . 7 segments innervating neonatal neurones. Throughout post-natal development the innervation of individual neurones arises from a contiguous subset of the spinal segments that innervate the ganglion as a whole. 4. We conclude that the elimination of redundant innervatin in early life is not limited to those nerve and muscle cells contacted by a sigle axon in maturity, but also occurs in sympathetic ganglia where adult neurones remain multiply innervated. Moreover, the loss of some synaptic contacts during development refines the selective innervation of individual neurones.