title: Angiotensin 1A receptors transfected into caudal ventrolateral medulla inhibit baroreflex gain and stress responses.
abstract: OBJECTIVE
  The caudal ventrolateral medulla (CVLM) is important for autonomic regulation and is rich in angiotensin II type 1A receptors (AT(1A)R). To determine their function, we examined whether the expression of AT(1A)R in the CVLM of mice lacking AT(1A)R (AT(1A)(-/-)) alters baroreflex sensitivity and cardiovascular responses to stress.
  
  
  RESULTS
  Bilateral microinjections into the CVLM of AT(1A)(-/-) mice of lentivirus with the phox-2 selective promoter (PRSx8) were made to express either AT(1A)R (Lv-PRSx8-AT(1A)) or green fluorescent protein (Lv-PRSx8-GFP) as a control. Radiotelemetry was used to record mean arterial pressure (MAP), heart rate (HR), and locomotor activity. Following injection of Lv-PRSx8-GFP, robust neuronal expression of GFP was observed with ∼60% of the GFP-positive cells also expressing the catecholamine-synthetic enzyme tyrosine hydroxylase. After 5 weeks, there were no differences in MAP or HR between groups, but the Lv-PRSx8-AT(1A)- injected mice showed reduced baroreflex sensitivity (-25%, P = 0.003) and attenuated pressor responses to cage-switch and restraint stress compared with the Lv-PRSx8-GFP-injected mice. Reduced MAP mid-frequency power during cage-switch stress reflected attenuated sympathetic activation (Pgroup × stress = 0.04). Fos-immunohistochemistry indicated greater activation of forebrain and hypothalamic neurons in the Lv-PRSx8-AT(1A) mice compared with the control.
  
  
  CONCLUSIONS
  The expression of AT(1A)R in CVLM neurons, including A1 neurons, while having little influence on the basal blood pressure or HR, may play a tonic role in inhibiting cardiac vagal baroreflex sensitivity. However, they strongly facilitate the forebrain response to aversive stress, yet reduce the pressor response presumably through greater sympatho-inhibition. These findings outline novel and specific roles for angiotensin II in the CVLM in autonomic regulation.
authors.affiliation: Neuropharmacology Laboratory,  Baker IDI Heart and Diabetes Research Institute, 75 Commercial Road, PO Box 6492 St Kilda Road Central, Melbourne, VIC 8008,  Australia.
authors.forename: Kesia
authors.initials: K
authors.lastname: Palma-Rigo
authors.forename: Jaspreet K
authors.initials: JK
authors.lastname: Bassi
authors.forename: Thu-Phuc
authors.initials: TP
authors.lastname: Nguyen-Huu
authors.forename: Kristy L
authors.initials: KL
authors.lastname: Jackson
authors.forename: Pamela J
authors.initials: PJ
authors.lastname: Davern
authors.forename: Daian
authors.initials: D
authors.lastname: Chen
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Elghozi
authors.forename: Walter G
authors.initials: WG
authors.lastname: Thomas
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Allen
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Head
mesh_terms: D000818:Animals; D001345:Autoradiography; D017704:Baroreflex; D001794:Blood Pressure; D018014:Gene Transfer Techniques; D006339:Heart Rate; D007150:Immunohistochemistry; D016086:Lentivirus; D008297:Male; D008526:Medulla Oblongata / Q000378:metabolism*; D051379:Mice; D009043:Motor Activity; D011401:Promoter Regions, Genetic; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism*; D012149:Restraint, Physical; D013315:Stress, Psychological; D019076:Transgenes
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D044140:Receptor, Angiotensin, Type 1