Expression of Choline Acetyltransferase of the Peripheral Type in the Primary Sensory Neurons of the Guinea Pig Trigeminal Ganglion

The fact that the splice variant form of choline acetyltransferase (pChAT) is expressed in peripheral organs, including sensory ones, preferentially than the common type (cChAT) is well known. In the current study the possible functional significance of this variant in sensory neurons has been characterized immunohistochemically by investigating the pChAT-immunoreactivity (IR) in the trigeminal ganglia (TG) of the guinea pig. We documented an almost uniform distribution and a considerable number of pChAT-immunoreactivity of all trigeminal neurons. The size of pChAT-IR neurons varied from small to medium-size, although large-sized neurons also observed. Most pChAT reactivity was mainly in the cytoplasm with few number of pChAT-IR neurons had nuclear staining. Double immunofluorescent study showed that a great proportion of substance P (SP)- and calcitonin gene-related peptide (CGRP)-positive trigeminal cells showed pChAT-immunoreactivity, although those with SP outnumbered those with CGRP. The intracellular expression of pChAT (which differs from that of cChAT) probably reflecting a difference in the physiological roles between pChAT and cChAT in ACh production in distinct intracellular compartments. The present data suggest also that pChAT may play roles other than nociception and may be involved in the sensory functions of the TG neurons.