Striatal neurochemical changes in transgenic models of Huntington's disease.
Transgenic mouse models of Huntington's disease (HD) were examined following the onset of overt behavioral symptoms. The HD transgenic mice demonstrated profound striatal losses in D1, D2, and D3 dopamine (DA) receptor proteins in comparison with their nonsymptomatic, age-matched littermate controls. In parallel, a robust increase in the striatal D5 DA receptor subtype occurred in the transgenic compared with the wild-type control mice. This receptor elevation was accompanied by heightened cyclic AMP levels, which may be induced by the adenylyl cyclase-linked D5 receptor. This is a unique result; normal striatal D5 protein levels are modest and not thought to contribute substantially to cyclic AMP-mediated DA signaling mechanisms. Simple compensatory up-regulation of D5 DA receptors in response to D1 receptor subtype loss does not explain our findings, because genetic inactivation of the D1 DA receptor does not alter levels of D5 DA receptor expression. Immunofluorescent detection of tyrosine hydroxylase showed that nigrostriatal DA containing terminals were reduced, further supporting that disturbances in DA signaling occurred in HD transgenic models. The substance P-containing striatal efferent pathway was more resistant to the HD mutation than met-enkephalin-producing striatal projection neurons in the transgenics, based on neuropeptide immunofluorescent staining. Analogous findings in multiple transgenic models suggest that these changes are due to the presence of the transgene and are not dependent on its composition, promotor elements, or mouse strain background. These findings suggest modifications in the striatal DA system and that its downstream signaling through cyclic AMP mechanisms is disrupted severely in HD following onset of motor symptoms.
Department of Neuroscience, The Chicago Medical School, North Chicago, Illinois 60064, USA. arianom@finchcms.edu
Marjorie A
MA
Ariano
Neil
N
Aronin
Marian
M
Difiglia
Danilo A
DA
Tagle
David R
DR
Sibley
Blair R
BR
Leavitt
Michael R
MR
Hayden
Michael S
MS
Levine
D000818:Animals; D003342:Corpus Striatum / Q000737:chemistry*; D000242:Cyclic AMP / Q000032:analysis; D015536:Down-Regulation; D004744:Enkephalin, Methionine / Q000032:analysis; D005455:Fluorescent Antibody Technique; D006816:Huntington Disease / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D010766:Phosphorylation; D011954:Receptors, Dopamine / Q000032:analysis*; D017447:Receptors, Dopamine D1 / Q000032:analysis; D017448:Receptors, Dopamine D2 / Q000032:analysis; D050637:Receptors, Dopamine D3; D050641:Receptors, Dopamine D5; D015398:Signal Transduction; D013373:Substance P / Q000032:analysis; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis; D015854:Up-Regulation
C493594:Drd3 protein, mouse; C493606:Drd5 protein, mouse; D011954:Receptors, Dopamine; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D050641:Receptors, Dopamine D5; D013373:Substance P; D004744:Enkephalin, Methionine; D000242:Cyclic AMP; D014446:Tyrosine 3-Monooxygenase