title: Arterial chemoreceptor activation reduces the activity of parapyramidal serotonergic neurons in rats.
abstract: The parapyramidal (ppy) region targets primarily the intermediolateral cell column and is probably involved in breathing and thermoregulation. In the present study, we tested whether ppy serotonergic neurons respond to activation of central and peripheral chemoreceptors. Bulbospinal ppy neurons (n=30) were recorded extracellularly along with the phrenic nerve activity in urethane/α-chloralose-anesthetized, paralyzed, intact (n=7) or carotid body denervated (n=6) male Wistar rats. In intact animals, most of the ppy neurons were inhibited by hypoxia (n=14 of 19) (8% O2, 30s) (1.5 ± 0.03 vs. control: 2.4 ± 0.2 Hz) or hypercapnia (n=15 of 19) (10% CO2) (1.7 ± 0.1 vs. control: 2.2 ± 0.2 Hz), although some neurons were insensitive to hypoxia (n=3 of 19) or hypercapnia (n=4 of 19). Very few neurons (n=2 of 19) were activated after hypoxia, but not after hypercapnia. In carotid body denervated rats, all the 5HT-ppy neurons (n=11) were insensitive to hypercapnia (2.1 ± 0.1 vs. control: 2.3 ± 0.09 Hz). Biotinamide-labeled cells that were recovered after histochemistry were located in the ppy region. Most labeled cells (90%) showed strong tryptophan hydroxylase immunocytochemical reactivity, indicating that they were serotonergic. The present data reveal that peripheral chemoreceptors reduce the activity of the serotonergic premotor neurons located in the ppy region. It is plausible that the serotonergic neurons of the ppy region could conceivably regulate breathing automaticity and be involved in autonomic regulation.
authors: Department of Pharmacology, Institute of Biomedical Science, University of São Paulo, 05508-000 São Paulo, SP, Brazil.
authors: A C
authors: AC
authors: Takakura
authors: T S
authors: TS
authors: Moreira
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology; D000818:Animals; D062186:Arterial Pressure / Q000187:drug effects / Q000502:physiology; D001710:Biotin / Q000031:analogs & derivatives / Q000378:metabolism; D002245:Carbon Dioxide / Q000494:pharmacology; D002452:Cell Count; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D006935:Hypercapnia / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology; D008297:Male; D046529:Microscopy, Electron, Transmission; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D010791:Phrenic Nerve / Q000166:cytology* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D059326:Serotonergic Neurons / Q000502:physiology*; D017552:Solitary Nucleus / Q000166:cytology*; D014364:Tryptophan / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide; C095117:tryptophanhydroxamate; C093086:biotinamide; D001710:Biotin; D014364:Tryptophan