title: D1 dopamine receptor agonist-induced Fos-like immunoreactivity occurs in basal forebrain and mesopontine tegmentum cholinergic neurons and striatal neurons immunoreactive for neuropeptide Y.
abstract: The present study sought to determine whether the D1 dopamine receptor agonist CY 208-243 increases Fos-like immunoreactivity in neurochemically distinct populations of interneurons in the 6-hydroxydopamine-denervated striatum. In vivo microdialysis studies indicate that cholinergic interneurons in the striatum are excited by the administration of CY 208-243 and that this effect is potentiated by dopaminergic deafferentation. Since Fos is considered to be a marker of neuronal activity, we examined the overlap between CY-208-243-induced Fos-like immunoreactivity and striatal cholinergic interneurons labelled with the cholinergic marker enzyme choline acetyltransferase. Unexpectedly, cholinergic interneurons in the striatum were not found to express Fos-like immunoreactivity. However, D1 agonist-induced Fos-like immunoreactivity was found in neurons immunoreactive for neuropeptide Y. Consequently, the failure of cholinergic neurons in the striatum to express D1 agonist-induced Fos-like immunoreactivity does not appear to be a general property of striatal interneurons. Indeed, CY 208-243 increased Fos-like immunoreactivity in choline-acetyltransferase-positive neurons in the basal forebrain and lateral dorsal tegmental nucleus. In the case of cholinergic basal forebrain neurons, administration of CY 208-243 has been shown to enhance the release of acetylcholine from their terminals located in the frontal cortex. Thus, unlike cholinergic interneurons in the striatum, the expression of Fos-like immunoreactivity in cholinergic basal forebrain neurons is correlated with an increase in transmitter release. Choline acetyltransferase immunoreactivity was markedly reduced in cholinergic basal forebrain neurons ipsilateral to the 6-hydroxydopamine lesion. This decrease in choline acetyltransferase immunoreactivity was confined to a pocket of cortically projecting neurons located in the posterior part of the horizontal limb of the diagonal band which included the medial preoptic nucleus. Interestingly, D1 agonist-induced Fos-like immunoreactivity was located predominantly in those cholinergic neurons which displayed depressed choline acetyltransferase immunoreactivity. Since Fos is often induced as a consequence of increased activity, it is tempting to speculate that those neurons which stained weakly for choline acetyltransferase had been excited by the D1 agonist administration. Accordingly, the destruction of mesencephalic dopaminergic neurons with 6-hydroxydopamine may have deprived these cholinergic neurons of an excitatory D1 receptor-mediated drive, resulting in a reduction of choline acetyltransferase immunoreactivity. These results suggest that the degeneration of nigrostriatal dopamine neurons may contribute to the loss of cholinergic basal forebrain function in Parkinson's disease.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, University of Ottawa, Ontario, Canada.
authors.forename: G S
authors.initials: GS
authors.lastname: Robertson
authors.forename: W A
authors.initials: WA
authors.lastname: Staines
mesh_terms: D000109:Acetylcholine / Q000378:metabolism; D000110:Acetylcholinesterase / Q000032:analysis; D000818:Animals; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002795:Choline O-Acetyltransferase / Q000032:analysis / Q000378:metabolism; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015259:Dopamine Agents / Q000494:pharmacology*; D007150:Immunohistochemistry; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009478:Neuropeptide Y / Q000032:analysis*; D016627:Oxidopamine / Q000633:toxicity; D010617:Phenanthridines / Q000494:pharmacology*; D011149:Pons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D016548:Prosencephalon / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis / Q000096:biosynthesis*; D051381:Rats; D017447:Receptors, Dopamine D1 / Q000187:drug effects / Q000502:physiology*
chemical_list: D015259:Dopamine Agents; D007211:Indoles; D009478:Neuropeptide Y; D010617:Phenanthridines; D016760:Proto-Oncogene Proteins c-fos; D017447:Receptors, Dopamine D1; C054531:CY 208-243; D016627:Oxidopamine; D002795:Choline O-Acetyltransferase; D000110:Acetylcholinesterase; D000109:Acetylcholine