CROLL, R.P.; FINNEY, J.L.; SMITH, F.M.; Dalhousie Univ.; Dalhousie Univ.; Dalhousie Univ.: Innervation of the Swimbladder in the Zebrafish, Danio rerio

The zebrafish has emerged as an important model organism used to understand basic principles of development. However, while much work has focussed on the development of the central nervous system, little is known about the development of the autonomic nervous system or even of the general patterns of innervation of visceral organs in this species. We address this deficiency by examining the development of the swimbladder and the neural circuitry used to control buoyancy. The swimbladder develops from the esophagus, and its inflation in other cyprinid fish is controlled both by secretion of gases into the swimbladder from the blood and by exchange of gases via a pneumatic duct connecting the swimbladder with the esophagus. We describe the patterns of autonomic innervation of the swimbladder and its associated vasculature in the adult zebrafish. Antibodies against choline acetyltransferase (ChAT), an enzyme involved in acetylcholine synthesis, and tyrosine hydroxylase (TH), an enzyme involved in synthesis of norepinephrine, were used to label parasympathetic and sympathetic neuronal elements, respectively. In addition, we also examined immunoreactivities to neuropeptide Y (NPY), vasointestinal peptide (VIP) and substance P (SP), which are associated with the peripheral nervous system. Finally, we have supplemented these studies with histochemical procedures for labelling catecholamines (using glyoxylate-induced fluorescence), NO synthetase (NADPH diaphorase) and acetylcholinesterase. These visualization techniques produce complementary data suggesting that the swimbladder and associated vasculature are richly innervated by both intrinsic and extrinsic autonomic and sensory neurons which together form a complex control system. Subsequent work will examine how this system develops and how it functions to control buoyancy in this species.