Serotonin hyperinnervation abolishes seizure susceptibility in Otx2 conditional mutant mice.
The homeobox-containing transcription factor Otx2 is crucially involved in fate determination of midbrain neurons. Mutant mice, in which Otx2 was conditionally inactivated by a Cre recombinase expressed under the transcriptional control of the Engrailed1 (En1) gene (En1(cre/+); Otx2(flox/flox)), show a reduced number of dopaminergic neurons and an increased number of serotonergic neurons in the ventral midbrain. Despite these developmental anatomical alterations, En1(cre/+); Otx2(flox/flox) adult mice display normal motor function. Here, we further investigated the neurological consequences of Otx2 inactivation in adult En1(cre/+); Otx2(flox/flox) mice. Adult En1(cre/+); Otx2(flox/flox) mice showed increased serotonin (5-HT) levels in the pons, ventral midbrain, hippocampus (CA3 subfield), and cerebral cortex, as indicated by HPLC and immunohistochemistry. Conversely, SERT (5-HT transporter) levels were decreased in conditional mutant brains. As a consequence of this increased 5-HT hyperinnervation, En1(cre/+); Otx2(flox/flox) mice were resistant to generalized seizures induced by the glutamate agonist kainic acid (KA). Indeed, prolonged pretreatment of En1(cre/+); Otx2(flox/flox) mice with the 5-HT synthesis inhibitor para-chlorophenylalanine (pCPA) restored brain 5-HT content to control levels, fully reestablishing KA seizure susceptibility. Accordingly, c-fos mRNA induction after KA was restricted to the hippocampus in En1(cre/+); Otx2(flox/flox) mice, whereas a widespread c-fos mRNA labeling was observed throughout the brain of En1(cre/+); Otx2(flox/flox) mice pretreated with pCPA. These results clearly show that increased brain 5-HT levels are responsible for seizure resistance in En1(cre/+); Otx2(flox/flox) mice and confirm the important role of 5-HT in the control of seizure spread.
Tripathi
Prem Prakash
PP
Istituto di Neuroscienze del Consiglio Nazionale delle Ricerche, Laboratorio di Neurobiologia della Scuola Normale Superiore, 56100 Pisa, Italy.
Di Giovannantonio
Luca Giovanni
LG
Viegi
Alessandro
A
Wurst
Wolfgang
W
Simeone
Antonio
A
Bozzi
Yuri
Y
D000704:Analysis of Variance; D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D010134:Fenclonine / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics; D007608:Kainic Acid; D008636:Mesencephalon / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation; D051857:Otx Transcription Factors / Q000235:genetics*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D012640:Seizures / Q000139:chemically induced / Q000235:genetics*; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology; D050486:Serotonin Plasma Membrane Transport Proteins / Q000378:metabolism; D013997:Time Factors
C080330:En1 protein, mouse; D004791:Enzyme Inhibitors; D018398:Homeodomain Proteins; D051857:Otx Transcription Factors; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D050486:Serotonin Plasma Membrane Transport Proteins; D012701:Serotonin; D010134:Fenclonine; D007608:Kainic Acid
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