title: Alterations in serotonin signalling are involved in the hyperactivity of Pitx3-deficient mice.
abstract: Pitx3 deficiency in mice causes a dramatic loss of dopaminergic neurones located in the substantia nigra pars compacta during development. This early disruption of the nigrostriatal pathway in Pitx3-deficient mice is characterized by increased spontaneous home-cage activity levels during the habitual sleep phase of these animals. These findings are reminiscent of the spontaneous hyperactivity in mice neonatally lesioned with 6-hydroxydopamine, which is caused by an extensive serotonergic hyperinnervation of the striatum. The present study investigated whether an imbalance between dopamine (DA) and serotonin (5-HT) signalling is involved in the behavioural phenotype of Pitx3-deficient mice. Serotonergic hyperinnervation was demonstrated by increased [3H]-citalopram autoradiographic binding specifically in the dorsal striatum of adult Pitx3-deficient mice, indicating alterations in 5-HT transporter levels that correlated to DA dysfunction in Pitx3 deficiency. In addition, stimulus-induced release of DA and 5-HT indicated an altered balance between these neurotransmitters in the dorsal striatum of Pitx3-/- mice. To determine whether the increased 5-HT signalling was involved in the spontaneous hyperactivity during the light phase observed in Pitx3 deficiency, we treated Pitx3-deficient and control mice with the selective irreversible tryptophan hydroxylase inhibitor p-chlorophenylalanine to decrease 5-HT levels. Reduction of 5-HT levels in Pitx3-deficient mice decreased their locomotor activity to normal levels, whereas the same treatment increased the locomotor activity levels of control mice. Taken together, our results indicate alterations in 5-HT signalling in Pitx3-deficient mice that underlie their spontaneous hyperactivity.
authors.affiliation: Rudolf Magnus Institute of Neuroscience, Department of Neuroscience and Pharmacology, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands. m.p.smidt-2@umcutrecht.nl
authors.forename: Simone M
authors.initials: SM
authors.lastname: Smits
authors.forename: Cornelle W
authors.initials: CW
authors.lastname: Noorlander
authors.forename: Martien J H
authors.initials: MJ
authors.lastname: Kas
authors.forename: Geert M J
authors.initials: GM
authors.lastname: Ramakers
authors.forename: Marten P
authors.initials: MP
authors.lastname: Smidt
mesh_terms: D000818:Animals; D005260:Female; D018398:Homeodomain Proteins / Q000235:genetics; D006948:Hyperkinesis / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011485:Protein Binding / Q000502:physiology; D012701:Serotonin / Q000235:genetics / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors / Q000172:deficiency* / Q000235:genetics
chemical_list: D018398:Homeodomain Proteins; D050486:Serotonin Plasma Membrane Transport Proteins; C493231:Slc6a4 protein, mouse; D014157:Transcription Factors; C433629:homeobox protein PITX3; D012701:Serotonin