title: Histochemical profiles of motoneurons innervating muscle fibres with different activity patterns in the zebrafish, Brachydanio rerio.
abstract: Enzyme histochemical profiles of spinal motoneurons in the zebrafish were determined. Five enzymes of glucose metabolism were chosen: glucose-6-phosphate dehydrogenase (G6PDH), hexokinase (HK), phosphofructokinase (PFK), succinate dehydrogenase (SDH) and NADH tetrazolium reductase (NADH-TR). Motoneurons were traced with Fluorogold and classified as those that innervate white muscle fibres (W-MNs) and those that innervate red and intermediate muscle fibres (R/I-MNs). The average enzyme activities per volume of tissue in the somata of both populations differed at most by 25%. Both the average soma volume and the average number of muscle fibres innervated are three times larger for the W-MNs than for the R/I-MNs. This suggests that the total amount of enzyme activity within a neuron soma matches target size. In the R/I-MNs, the activities of SDH and NADH-TR were closely correlated (correlation coefficient, r = 0.99; p less than 0.05) and HK activity correlated well with G6PDH activity (r = 0.94; p less than 0.05), but not with PFK (r = 0.64; p greater than 0.05). In the W-MNs, there was no correlation between SDH and NADH-TR (r = -0.59; p greater than 0.05) or between HK and G6PDH (r = 0.50; p greater than 0.05) and the correlation coefficient between HK and PFK activity was close to zero (r = 0.04; p greater than 0.05). It was concluded that in the R/I-MNs, which are continuously active, firing activity is fuelled by oxidative metabolism. We suggest that in the W-MNs glucose is stored in the form of glycogen and that, despite high levels of NADH-TR present, the energy for intermittent firing activity is provided by glycolysis.
authors.affiliation: Department of Experimental Zoology, University of Amsterdam, The Netherlands.
authors.forename: F
authors.initials: F
authors.lastname: De Graaf
authors.forename: W
authors.initials: W
authors.lastname: Van Raamsdonk
authors.forename: E
authors.initials: E
authors.lastname: Van Asselt
authors.forename: P C
authors.initials: PC
authors.lastname: Diegenbach
mesh_terms: D000818:Animals; D002451:Cell Compartmentation; D005954:Glucosephosphate Dehydrogenase / Q000032:analysis; D006019:Glycolysis; D006593:Hexokinase / Q000032:analysis; D009046:Motor Neurons / Q000201:enzymology / Q000378:metabolism*; D009132:Muscles / Q000294:innervation*; D009243:NAD / Q000032:analysis; D010084:Oxidation-Reduction; D010732:Phosphofructokinase-1 / Q000032:analysis; D013116:Spinal Cord / Q000033:anatomy & histology / Q000378:metabolism; D013385:Succinate Dehydrogenase / Q000032:analysis; D013778:Tetrazolium Salts; D015027:Zebrafish
chemical_list: D013778:Tetrazolium Salts; C042207:4-anisyltetrazolium blue; D009243:NAD; D005954:Glucosephosphate Dehydrogenase; D013385:Succinate Dehydrogenase; D006593:Hexokinase; D010732:Phosphofructokinase-1