Rebaudioside A (RebA) is a steviol glycoside used for production of sweeteners. It was shown
that the glycosides affect memory and learning processes. The aim of the study was to investigate
neurons immunoreactive for acetylcholinesterase (AChE) and M1 muscarinic receptors
(mAChRs-M1) of the hippocampal CA1 and CA3 fields and striatal caudateputamen (CP)
and globus pallidus (GP) in rats receiving RebA. RebA was administrated to adult rats for 45 days
in dilutions of 1 mg and 2 mg RebA/ml water. Indirect peroxidase-antiperoxidase immunohistochemical reaction was conducted on frontal sections containing the hippocampus and striatum
with use of antibodies against AChE and mAChRs-M1. Immunoreactive for the studied proteins
neurons were morphologically and morphometrically assessed in hippocampal CA1 and CA3
fields and in CP and GP. Microscopic observations did not reveal significant changes in morphology of immunoreactive neurons, which suggests no neurotoxic effect of the studied glycoside
on these cells. Morphometric analyses revealed an increase in the density of AChE and
mAChRs-M1 immunoreactive neurons. A decrease in reaction intensity of AChE-positive
neurons was also demonstrated in the hippocampal CA1 field and in GP. In contrast, an increase
in reaction intensity of mAChRs-M1-positive neurons was found in CA1, CA3 fields and in CP
and GP. The results of our preliminary studies indicate that RebA administrated to rats has
an impact on cholinergic neurons in the studied area. The results suggest a possible increase
in the activity of the cholinergic system, responsible for memory and learning processes, after
administration of RebA.