You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Reversible effect of developmental exposure to chlorpyrifos on late-stage neurogenesis in the hippocampal dentate gyrus in mouse offspring. The effect of developmental exposure to chlorpyrifos (CPF) on hippocampal neurogenesis was examined in male mice after maternal dietary exposure to CPF at 0, 4, 20, or 100ppm from gestation day 10 to postnatal day (PND) 21. Cholinesterase activity was dose-dependently decreased in red blood cells at ≥4ppm and in the brain at 100ppm both in dams and offspring on PND 21. Immunohistochemically, doublecortin(+) cells were decreased at ≥20ppm in the subgranular zone (SGZ) of the dentate gyrus, and NeuN(+)-expressing mature neurons were decreased at 100ppm in the hilus on PND 21. There were no differences in the numbers of progenitor populations expressing Tbr2 or M1 muscarinic acetylcholine receptors. Transcript levels of Dcx also decreased at ≥20ppm, and those of Pcna, Casp3, Bax, Bcl2, Pax6 and Tbr2 were unchanged in the dentate gyrus by real-time RT-PCR. At PND 77, hippocampal neurogenesis was unchanged. These results suggest that developmental CPF exposure directly but transiently suppresses maturation of late-stage granule cell lineages in the SGZ and affects interneuron populations in the hilus.
{"Chemical": ["acetylcholine", "chlorpyrifos", "CPF"]}