Intracerebroventricular injections of noradrenaline affect brain energy metabolism of rainbow trout.

To assess the role of noradrenaline (NA) as a possible regulator of brain energy metabolism in teleost fish, the impact of increased noradrenaline levels within the brain on several parameters of energy metabolism was assessed in rainbow trout brain. Accordingly, two different doses of noradrenaline, producing increases in brain NA levels comparable to those occurring in several physiological processes in nature, were selected. In a subsequent set of three different experiments, fish were intracerebroventricularly injected with 1 microL 100 g(-1) body weight of Cortland saline alone (control) or containing NA (5 nmol NA and 10 nmol NA); after 30 min, brain and plasma samples were taken to assess changes in parameters of energy metabolism due to NA treatment. The results obtained clearly show dose-dependent changes in NA-treated fish in several parameters, including decreased glycogen and ATP levels, increased lactate and pyruvate levels, decreased fructose 1,6-bisphosphatase activity, and increased pyruvate kinase and lactate dehydrogenase activities. Altogether, the present experiments show for the first time in a teleost fish evidence supporting that increased noradrenaline levels in the brain elicit metabolic changes in the brain (enhanced glycogenolysis and glycolysis), resulting in an increased energy demand. These metabolic changes may be related to those occurring under several physiological conditions in nature such as hypoxia, in which increased energy demand and increased noradrenaline levels occur in the brain simultaneously.