Expression of a splice variant of choline acetyltransferase in magnocellular neurons of the tuberomammillary nucleus of rats

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A splice variant of choline acetyltransferase mRNA has recently been identified in rat pterygopalatine ganglion. An antiserum against this variant protein (pChAT) stained peripheral cholinergic neurons. In the present study, we examined the immunohistochemical localization of pChAT in rat brain. Although the antiserum failed to stain known cholinergic neurons in the brain, magnocellular neurons in the tuberomammillary nucleus (TMN) of the posterior hypothalamus were stained with the antiserum. RT- PCR experiments confirmed the expression of pChAT mRNA in rat posterior hypothalamus. The distribution pattern of pChAT-positive neurons in the nucleus was similar to that positive for histidine decarboxylase (HDC) and adenosine deaminase (ADA). Double immunohistochemical staining in rats pretreated with colchicine indicated mat virtually all pChAT-positive cells contained ADA. Some pChAT-positive cells in the nucleus were retrogradely labeled following the injection of cholera-toxin B subunit into the cerebral cortex. These results suggest the existence of a presumed corticipetal cholinergic pathway ascending from the TMN.