title: [A receptors in the locus ceruleus involved in attenuating the intracerebroventricular histamine-induced carotid baroreflex resetting in rats].
abstract: OBJECTIVE
  To investigate the effects of alpha1 and alpha2 receptors in the locus ceruleus (LC) on carotid baroreflex (CBR) resetting induced by intracerebroventricular injection (ICV) of histamine (HA).
  
  
  METHODS
  The left and right carotid sinus regions were isolated from the systemic circulation in 23 Sprague-Dawley rats anesthetized with pentobarbital sodium. The intracarotid sinus pressure (ISP) was altered in a stepwise manner. ISP-mean arterial pressure (MAP) relationship curve and its characteristic parameters were constructed by fitting to the logistic function with five parameters. The changes in CBR performance induced by ICV HA and the effects of pretreatment with alpha1 or alpha2 receptor antagonist into the LC on the responses of CBR to HA were examined.
  
  
  RESULTS
  ICV HA (60 micromol x L(-1) in 5 microl) significantly shifted the ISP-MAP relationship curve upwards (P < 0.05) and reduced the MAP range and maximum gain (P < 0.05). The pretreatment with phenoxybenzamine (PBZ, a selective antagonist of alpha1 receptor, 3 micromol x L(-1) in 500 nl) or yohimbine (YOH, a selective antagonist of alpha2 receptor, 2.5 micromol x L(-1) in 500 nl) into the LC could obviously intensify the above-mentioned changes in CBR performance induced by HA, but the intensive effect of PBZ was less remarkable than that of YOH (P < 0.05).
  
  
  CONCLUSIONS
  The intracerebroventricular administration of HA results in a rapid resetting of CBR and a decrease in reflex sensitivity, and the functions of alpha1 and alpha2 receptors in the LC may attenuate CBR resetting induced by ICV HA. Furthermore, alpha2 receptor in the LC might play a more important role in regulating the responses of CBR to HA.
authors.affiliation: Department of Physiology, Medical School, Soochow University, Suzhou 215007, China.
authors.forename: Guo-Qing
authors.initials: GQ
authors.lastname: Wang
authors.forename: Xi-Ping
authors.initials: XP
authors.lastname: Zhou
mesh_terms: D000818:Animals; D017704:Baroreflex / Q000187:drug effects* / Q000502:physiology; D002346:Carotid Sinus; D006632:Histamine / Q000494:pharmacology*; D008125:Locus Coeruleus; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D017981:Receptors, Neurotransmitter
chemical_list: D017981:Receptors, Neurotransmitter; D006632:Histamine