Synaptic organisation of lumbar sympathetic ganglia of guinea pigs: Serial section ultrastructural analysis of dye-filled sympathetic final motor neurons

Ian L. Gibbins, Helen F. Rodgers, Sue E. Matthew, Susan M. Murphy

    Research output: Contribution to journalArticlepeer-review

    25 Citations (Scopus)

    Abstract

    The authors serially sectioned seven dye-filled neuronal somata and more than 1.6 mm of their dendrites from the lumbar sympathetic ganglia of guinea pigs and examined them ultrastructurally to determine the distribution of preganglionic synaptic inputs to their dendrites and cell bodies. Most of the surface of the neurons was covered with Schwann cells. Apposing boutons were rare, with an average density of one axosomatic bouton per 125 μm2 of somatic membrane and one axodendritic bouton per 25 μm of dendrite. Many dendritic segments that were more than 50 μm long completely lacked any apposing boutons. Although the average density of apposing boutons was low, local densities could be high, so that clusters of up to four adjacent boutons occurred on cell bodies and dendrites alike. The spatial arrangement of the apposing boutons for each of the cells examined here was not significantly different from a random distribution. Consequently, the number of apposing boutons observed for any neuron was simply proportional to the amount of neuronal surface sampled in the serial section run. About 50% of boutons directly apposing the neurons lacked any detectable presynaptic specialisations. When they were present, the presynaptic densities had a mean length of about 220 nm, with no difference between boutons that made axosomatic or axodendritic appositions. By applying these data to complete reconstructions of the dendritic trees of dye-filled sympathetic neurons at the light microscopic level, the authors estimated that few neurons in the lumbar sympathetic chain of guinea pigs would receive more than 200 synapses or apposing boutons and that many of them would receive less than 100 synapses. Up to 50% of these boutons would be predicted to make axosomatic contacts. These new observations provide a strong morphological framework for a better understanding of how sympathetic final motor neurons process their preganglionic synaptic inputs.

    Original languageEnglish
    Pages (from-to)285-302
    Number of pages18
    JournalJournal of Comparative Neurology
    Volume402
    Issue number3
    DOIs
    Publication statusPublished - 12 Dec 1998

    Keywords

    • Convergence
    • Dendrite
    • Preganglionic
    • Schwann cells
    • Synaptic strength

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