Neonatal Nerve Research Articles

Ultrastructural observations on synapse elimination in neonatal rabbit skeletal muscle.

Electron microscopic techniques were used to investigate two main questions about mammalian neuromuscular development. One, does neonatal synapse elimination proceed by the degeneration of synaptic terminals and preterminal axons, or are the terminals retracted into the parent axon, in a process analogous to the resorption of axonal growth cones? Two, is there any discernible relationship between the elimination of supernumerary synapses and the myelination of preterminal axons? Examination of several hundred sections through endplates fixed at the peak time of synapse elimination revealed no signs of degeneration. This result is not consistent with the proposal that the major mechanism of synapse elimination is terminal degeneration, according to calculations based on the time course of terminal degeneration following neonatal nerve transection. Serial and semi-serial reconstruction of terminals and preterminal axons suggest that myelination of intramuscular axons lags behind synapse elimination and that elimination can proceed while axons bear an immature relationship to Schwann cells. In addition, reconstruction of serial sections through neonatal synapses revealed that their three-dimensional configuration is more complex than that of mature neuromuscular synapses; this feature may be indicative of a dynamic relationship between nerve and muscle at early stages.

Axonal transport in the optic system of neonatal and adult hamsters

The axonal transport of [ 3H]proline-labeled protein was determined in the optic system of neonatal and adult hamsters. Proline was injected intravitreally at three stages of visual development: before eye opening (10 days), early functional (16, 21, and 30 days), and adult. The rate of fast axonal transport increased with age from 140 to 220 mm/day. There were two peaks of slowly transported radioactivity in neonatal optic nerve (∼8 and 1.4 mm/day), the earlier being the dominant component. With maturation, the later slow component became larger. There were also two slow-transport peaks in the optic nuclei of adults. The earlier of these turned over rapidly and was apparently produced by the later of the two slow-transport components in the optic nerve. The ratio of radioactivity in optic nerve to that in nerveending samples was much higher in adult than in neonatal nerve, possibly reflecting a larger diameter of adult axons. Slowly transported radioactivity disappeared more slowly from adult than from neonatal nerve endings, although there was no difference in optic nerve samples. Possible explanations for slower decay in the adult include increased stability of nerve-ending proteins, enhanced reutilization of proline, and diminished retrograde transport and/or transneuronal transfer.

Paradoxical decrease in norepinephrine content of adult mouse spleen and heart after neonatal nerve growth factor treatment

Paradoxical decrease in norepinephrine content of adult mouse spleen and heart after neonatal nerve growth factor treatment

Neonatal Electromyography and Nerve Conduction Studies in Myelomeningocele

Neonatal Electromyography and Nerve Conduction Studies in Myelomeningocele