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Ultrastructural localization of cholinesterase activity in the trigeminal ganglion of the rat.

The cholinesterases are of considerable importance in the function of the neuron, through their involvement with the neurotransmitter substance, acetylcholine, generally accepted as a chemical transmitter for neuromuscular junctions and for those nerve cells and fibres traditionally classified as cholinergic (Gerebtzoff, 1959; Koelle, 1963; Hebb, 1972). However, the role of the enzyme acetylcholinesterase at neuronal locations other than synaptic sites, as well as in non-nervous tissues, such as the placenta and erythrocyte, is still uncertain (Potter, 1970). Several authors have discussed the light microscopic localization of cholinesterase activity in spinal and trigeminal ganglia (Koelle, 1955; Gerebtzoff, 1959; Tewari & Bourne, 1962, 1963; Cauna & Naik, 1963; Kokko, 1966; Matsuura, Mori & Kawakatsu, 1969). In general, acetylcholinesterase activity was found in nerve cell bodies and some nerve fibres, while butyrylcholinesterase activity, if observed at all, was confined to capsular structures around the neuronal perikarya. It was not possible to determine the precise subcellular locations of the enzymes from these histochemical studies. The fine structure of the trigeminal ganglion was the topic of earlier papers (Dixon, 1963 a, b; Peach & Dixon, 1968; Peach, 1972). Other investigators (Matsuura & Fujita, 1968; Kalina & Bubis, 1969) have described some of the ultrastructural features of cholinesterase activity in the rat trigeminal ganglion. Their somewhat conflicting results with respect to enzyme location, as well as indications of inadequate fixation, prompted our use of Lewis & Shute's (1966) method for the electron microscopic localization of cholinesterase activity, which gave promising results in a preliminary investigation (Dixon, 1968). The purpose of the present paper is to describe the ultrastructural localization and identification of cholinesterases in trigeminal ganglia from adult rats, with a view to obtaining a greater understanding of the occurrence and distribution of cholinesterases in the peripheral trigeminal system.