Evidence that cell bodies in the arcuate nucleus of the hypothalamus are not cholinergic

Central cholinergic pathways have been implicated in the control of pituitary hormone release. Based on studies using acetylcholinesterase (AChE) histochemistry, it has been proposed that the cholinergic neurons controlling hormone release originate in neurons of the arcuate nucleus (AH). Although AChE histochemistry has been widely utilized to map central cholinergic pathways, AChE is not an unequivocal marker for cholinergic neurons. A more precise method for determining that neurons are cholinergic is the immunocytochemical labeling of choline acetyltransferase (CAT). In order to determine if the AChE-positive neurons in the AH are cholinergic, we double-labeled tissue sections for CAT and AChE using a combined immunocytochemical and AChE-histochemical method. Although neurons in several areas of the brain could be labeled for both CAT and AChE, neurons in the AH were only AChE-positive. We concluded that the AChE-positive neurons in the AH may be cholinoceptive but are not likely to be the source of cholinergic neurons controlling hormone release from the pituitary gland.