title: The effect of strenuous exercise and beta-adrenergic blockade on the visual performance of juvenile rainbow trout, Oncorhynchus mykiss.
abstract: It is hypothesised that the visual performance of rainbow trout, Oncorhynchus mykiss, will be impaired by strenuous exercise as a result of metabolic stress (blood lactacidosis) that activates the Root effect and limits the oxygen-carrying capacity of blood flowing to the eye. The ability to resolve high contrast objects on a moving background, as a measure of visual performance, was quantified pre- and post-exercise using the optomotor response. Strenuous exercise induced a metabolic acidosis (8.0 mmol l(-1) blood lactate) and a significant red cell swelling response but no change in the optomotor response threshold (120 min of arc) was observed. Beta-adrenergic blockade (propranolol) abolished post-exercise red cell swelling but optomotor response thresholds were still maintained at 120 min of arc despite a significant blood lactate load (7.8 mmol l(-1)). The choroid rete mirabile of the trout is extremely well developed (rete area:eye area = 0.39) and may maintain visual performance by ensuring a relatively direct supply of oxygen to the central regions of the avascular retina. Exercised fish under beta-adrenergic blockade exhibited an enhanced optomotor response at 240-300 min of arc. Assuming that these responses reflect "tunnel vision", adrenergic regulation of red cell function may preserve a high ocular PO(2) gradient that satisfies the oxygen demand of peripheral retinal cells.
authors.affiliation: School of Biological Sciences, The University of Auckland, New Zealand. n.herbert@niwa.cri.nz
authors.forename: N A
authors.initials: NA
authors.lastname: Herbert
authors.forename: R M G
authors.initials: RM
authors.lastname: Wells
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D001808:Blood Vessels / Q000033:anatomy & histology; D002829:Choroid / Q000098:blood supply; D004909:Erythrocyte Indices; D019344:Lactic Acid / Q000097:blood; D009043:Motor Activity / Q000502:physiology*; D017686:Oncorhynchus mykiss / Q000033:anatomy & histology / Q000097:blood / Q000502:physiology*; D010807:Physical Endurance; D011433:Propranolol / Q000494:pharmacology*; D014785:Vision, Ocular / Q000187:drug effects* / Q000502:physiology*
chemical_list: D000319:Adrenergic beta-Antagonists; D019344:Lactic Acid; D011433:Propranolol