Vergleichende elektronenmikroskopische Untersuchungen an sympathischen und parasympathischen Ganglien des Goldhamsters

The fine structure of the ganglia of the guinea-pig trachea

The parasympathetic ganglia of the guinea-pig trachea have been investigated by scanning and transmission electron microscopy. They are covered by a continuous perineurium and connective tissue is found between the neural elements. Blood vessels inside the ganglia have continuous endothelia and are sometimes accompanied by pericytes and a sheath of perineurial cells. Individual neuronal cell bodies and large processes are almost completely covered by a thin layer of satellite cells, except for very small areas that directly face the basal lamina and connective tissue space. Nerve fibres are also completely and individually ensheathed by Schwann cell processes; naked fibres are not found. In some regions of the nerve cell body, there are complex interdigitations between short neuronal processes and satellite cells. Large differences in the size of neurons may indicate the presence of different neuronal populations. Nerve endings containing mainly small clear vesicles are the most common type, and these form synapses on dendrites, but some profiles have many large granular vesicles. These ganglia resemble other parasympathetic, sympathetic and sensory ganglia and not the enteric ganglia. However, an unusual feature of the cytoplasm of the satellite and Schwann cells is the abundance of 10 nm intermediate filaments.

Nerve fiber synapses on spiral ganglion cells in the human cochlea

Nerve fiber synapses were observed on the small myelinated and unmyelinated spiral ganglion cells of the human cochlea. The nerve fibers penetrated the junctions of the ensheathing satellite cells and myelin lamellae, and partly invaginated into the perikarya to establish axosomatic synapses. One small myelinated neuron with a nerve fiber synapse demonstrated multipolar cell processes. However, most small neurons with identical ultrastructural characteristics did not show these synapses. Axodendritic synapses were also seen on the dendritic processes of the small neurons and between varicose nerves and unmyelinated nerve fibers some distance from the small neurons. While these observations conform in some aspects with the concept of parasympathetic nerve fibers and neurons in the cochlea, they are also compatible with the idea that the small neurons may have an auditory function influenced by the synaptic contacts of efferent fibers from the olivocochlear bundle.

Nature and nurture in development of the autonomic neuron

Arguments are presented for the hypothesis that during an early stage of development the cells which become principal neurons of the autonomic nervous system possess information regarding the positions they will occupy within the body. A second stage of development, during which a decision is made regarding which neurotransmitter to employ, is delayed until each neuron has assumed its permanent position in the body and has sampled, presumably via its growing axons, the peripheral field which it will innervate. The development of cholinergic mechanisms takes precedence; adrenergic neurons may develop only when cholinergic sites have been occupied. An extended period during which the differentiation of transmitter mechanisms may be modulated permits the neuron to adequately sample the periphery prior to commitment to a specific transmitter economy.