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A semi-quantitative electron-microscopic study of neuronal cell bodies, nerve profiles and synapses in the anterior pelvic ganglia of the guinea-pig has been carried out following in vivo labelling of adrenergic nerve endings with 5-hydroxydopamine. Ganglion cells of three main types have been distinguished: 1) the majority (about 70%) not containing granular vesicles, probably cholinergic elements; 2) those containing large granular vesicles of uniform size (80-110 nm), with granules of medium density and prominent halos; and 3) those containing vesicles of variable size (60-150 nm), with very dense eccentrically placed granular cores. Some non-neuronal 'granule-containing' cells were present, mainly near small blood vessels. Some 95% of the total axon profiles within the ganglia were cholinergic, the remaining 5% were adrenergic. However, 99% of synapses (i.e. axons within 50 nm of nerve cell membrane with pre- and post-synaptic specialisations) were cholinergic, and 1% were adrenergic. Only three examples of nerve cell bodies exhibiting both cholinergic and adrenergic synapses were observed. Unlike the para- and prevertebral ganglia, the pelvic ganglia contained large numbers of axo-somatic synapses. As many as 20% of the nucleated neuronal cell profiles displayed two distinct nuclei.

The dermal melanocytes in the lesions of nevus of Ito and Mongolian spot were shown to possess the extracellular sheath composed of both fine filaments and granules (2-5 nm in diameter). In the case of nevus of Ito, the granular component appeared to predominate in the shealth, which measured up to 3 micrometers in width and was estimated to cover about 97% of the total surface of dermal melanocytes. No ultrastructural changes were appreciable on the melanocyte shealth in nevus of Ito according to the difference in the age of patients (39 and 64 years), or in the lasting period of the dermal melanocytosis. By contrast, the melanocyte sheath in the case of Mongolian spot was much less developed than in nevus of Ito, predominantly filamentous in texture, and showed a marked decline with advance of the age of infants (from 2 mo to 6 yr). Many of the dermal melanocytes in Mongolian spot showed a partial disruption of their cytolemma, resulting in discharges of melanosomes free into the connective tissue matrix. Significance of these findings was discussed in relation to the differtial fate of melanocytes within the human dermis.

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An electron-microscopic study has been made of adrenergic and cholinergic nerve fibres and synapses in the pelvic ganglion of the guinea-pig at intervals of up to 60 days following section of the hypogastric and pelvic nerves. Transection of the hypogastric nerves led to degeneration of 80-90% of the cholinergic nerve profiles and synapses in the ganglion. The small number of adrenergic nerves and synapses did not change, but 30-60 days after section, this number increased 8-10 times. Transection of the pelvic nerves led to degeneration of about 15% of the cholinergic nerve terminals, but no change in adrenergic terminals. After transection of both hypogastric and pelvic nerves, only about 1% of cholinergic nerves survived, but after 30-60 days, the number of adrenergic nerves increased 8-10 times. It is concluded that following cholinergic nerve degeneration in the ganglion, adrenergic nerves, probably originating as collateral sprouts from postganglionic neurones and granule-containing cells, can replace them to some extent.