Critical role of B3 serotonergic cells in baroreflex inhibition during the defense reaction triggered by dorsal periaqueductal gray stimulation.
The present study was designed to identify the serotonergic pathway causing baroreflex inhibition associated with the defense reaction in rats. Under conditions that produce physiological responses typical of the defense reaction, electrical stimulation of the dorsal periaqueductal gray (dPAG) was found to double c-Fos immunoreactive serotonergic neurons within the mid-rostrocaudal extent of the B3 group (which comprises the raphe magnus and the lateral paragigantocellular reticular nuclei) in anesthetized rats. Local blockade of neuronal activity by microinjection of muscimol (a GABA(A) receptor agonist) directly into the B3 region prevented the inhibitory effect of dPAG activation on the cardiac baroreflex. Conversely, neuron activation by local application of D,L-homocysteic acid into B3 region caused baroreflex inhibition that was suppressed by microinjection of granisetron (a 5-HT(3) antagonist) into the nucleus tractus solitarius. These results show that activation of serotonergic cells in the mid-portion of B3 group is critical to trigger baroreflex inhibition occurring during the defense reaction evoked by dPAG stimulation.
Bernard
Jean-François
JF
Université Pierre et Marie Curie - Paris 6, Faculté de Médecine Pierre et Marie Curie, Site Pitié-Salpêtrière, IFR 70 des Neurosciences, UMR S677, Paris, F-75013, France. jfbernar@ext.jussieu.fr
Netzer
Florence
F
Gau
Rémi
R
Hamon
Michel
M
Laguzzi
Raùl
R
Sévoz-Couche
Caroline
C
D000818:Animals; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D003674:Defense Mechanisms; D004558:Electric Stimulation; D018755:GABA Agonists / Q000494:pharmacology; D017829:Granisetron / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006710:Homocysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D009118:Muscimol / Q000494:pharmacology; D009433:Neural Inhibition / Q000502:physiology*; D009434:Neural Pathways; D010487:Periaqueductal Gray / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley / Q000502:physiology*; D012701:Serotonin / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017552:Solitary Nucleus / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D014630:Vagus Nerve / Q000166:cytology / Q000502:physiology
D018755:GABA Agonists; D017829:Granisetron; D006710:Homocysteine; D009118:Muscimol; D016760:Proto-Oncogene Proteins c-fos; D012701:Serotonin; D012702:Serotonin Antagonists; C007956:homocysteic acid