title: GABAergic control of arteriolar diameter in the rat retina.
abstract: OBJECTIVE
  To investigate the role of γ-aminobutryic acid (GABA) in the regulation of arteriolar diameter in the rat retina.
  
  
  METHODS
  The actions of GABA on arteriolar diameter were examined using ex vivo retinal whole-mount preparations and isolated vessel segments. In most experiments, arterioles were partially preconstricted with endothelin (Et)-1. The expression levels of GABAA and GABAB receptors on isolated rat retinal Müller cells were assessed by immunohistochemistry.
  
  
  RESULTS
  GABA (0.1-1 mM) evoked vasodilation or vasoconstriction of arterioles in whole-mount preparations. No such effects were observed with isolated vessel segments. In whole mount samples, the GABAA receptor agonist muscimol caused vasomotor responses in only a small proportion of vessels. In contrast, arteriolar responses to the GABAB receptor agonists baclofen and SKF97541 more closely resembled those observed with GABA. No responses were seen with the GABAC receptor agonist 5-methylimidazoleacetic acid. GABA-induced vasodilator responses were, for the most part, repeatable in the presence of the GABAA receptor antagonist bicuculline. These responses, however, were completely blocked in the presence of the GABAB receptor inhibitor 2-hydroxysaclofen. Strong immunolabeling for both GABAA and GABAB receptors was detected in isolated Müller cells. In the absence of Et-1-induced preconstriction, most vessels were unresponsive to bicuculline or 2-hydroxysaclofen.
  
  
  CONCLUSIONS
  GABA exerts complex effects on arteriolar diameter in the rat retina. These actions appear largely dependent upon the activation of GABAB receptors in the retinal neuropile, possibly those located on perivascular Müller cells. Despite these findings, endogenous GABA appears to contribute little to the regulation of basal arteriolar diameter in the rat retina.
authors.affiliation: Centre for Vision and Vascular Science, School of Medicine, Dentistry and Biomedical Sciences, Queen's University of Belfast, Belfast, United Kingdom.
authors.forename: Kevin
authors.initials: K
authors.lastname: Hinds
authors.forename: Kevin P
authors.initials: KP
authors.lastname: Monaghan
authors.forename: Bente
authors.initials: B
authors.lastname: Frølund
authors.forename: J Graham
authors.initials: JG
authors.lastname: McGeown
authors.forename: Tim M
authors.initials: TM
authors.lastname: Curtis
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001160:Arterioles / Q000033:anatomy & histology / Q000187:drug effects*; D063928:Ependymoglial Cells; D018682:GABA Agents / Q000378:metabolism / Q000494:pharmacology*; D018755:GABA Agonists / Q000494:pharmacology; D007150:Immunohistochemistry; D023421:Models, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000378:metabolism; D018080:Receptors, GABA-B / Q000378:metabolism; D012161:Retinal Artery / Q000033:anatomy & histology / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D018682:GABA Agents; D018755:GABA Agonists; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D005680:gamma-Aminobutyric Acid
keywords: GABA; retinal arterioles; vascular tone