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Volume 17, Number 21, Issue of November 1, 1997 pp. 8402-8407
Copyright ©1997 Society for Neuroscience

Developmental Synaptic Depression Underlying Reorganization of Visceral Reflex Pathways in the Spinal Cord

Received May 5, 1997; revised Aug. 18, 1997; accepted Aug. 20, 1997.

Isao Araki and William C. de Groat

Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261

During development, neuronal connectivity has a remarkable plasticity. Synaptic refinement in the spinal autonomic nucleus might be involved in the elimination of primitive segmental reflexes and the emergence of mature spinobulbospinal reflexes, which occurs a few weeks after birth. To address this possibility, we examined the postnatal changes of segmental excitatory synaptic transmission by applying the whole-cell recording technique to parasympathetic preganglionic neurons in slice preparations of the rat lumbosacral spinal cord. The mean magnitude of unitary excitatory synaptic currents evoked in preganglionic neurons by stimulation of single interneurons remained unchanged during the first two postnatal weeks but was reduced by 50% during the third postnatal week. This reduction in synaptic efficacy was associated with a decrease in the amount of transmitter release from interneurons. Moreover, this developmental depression of segmental synaptic transmission was prevented by spinal cord transection at the thoracic level on postnatal day 14. Thus, developmental modification of excitatory synapses on preganglionic neurons appears to be attributable to competition between segmental interneuronal and descending bulbospinal inputs, which results in the developmental reorganization of parasympathetic excretory reflex pathways.

Key words: synaptic plasticity; developmental synaptic depression; glutamatergic excitatory synaptic currents; spinal autonomic nucleus; parasympathetic preganglionic neurons; micturition reflex; chronic spinal transection; quantal analysis

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