ELSEVIER Neuroscience Letters 198 (1995) 87-90 HiUROSCIEHC[ IEIT[BS Dendritic morphology of neurons in sympathetic ganglia of the goldfish, Carassius auratus Paul Karila a,*, Ian Gibbins b, Sue Matthew b aDepartment of Zoophysiology, GOteborg University, Medicinaregatan 18, S-413 90 GOteborg, Sweden bDepartment of Anatomy and Histology and Centrefor Neuroscience, Flinders University of South Australia, Bedford Park, SA 5042, Australia Received 24 July 1995; revised version received 14 August 1995; accepted 21 August 1995 Abstract We used intracellular dye injection to examine the dendritic morphology of postganglionic neurons in the coeliac ganglion of gold- fish. About 80% of the neurons had at least one dendrite, with the mean number of dendrites per cell being 7.8 ± 5.5 (±SD, n = 37 cells). Dendrites varied in length from a few/xm to more than 400/~m. Around 37% of the neurons possessed axon collaterals in addi- tion to dendrites. These results show that postganglionic sympathetic neurons of goldfish can have a complex morphology, more like the sympathetic neurons of small mammals than those of amphibians. This raises the possibility that at least some sympathetic ganglion cells of teleost fish receive multiple convergent preganglionic inputs, suggesting a hitherto unsuspected level of complexity in these pathways. Keywords: Teleost; Autonomic nervous system; Coeliac ganglion; Dye injection; Axon collaterals Postganglionic neurons of the autonomic nervous sys- tem have a varying morphology depending on species and target tissue innervated [14-16]. Generally, in mammals, the cell body size of the neurons increases and the den- dritic arborization becomes more complex in larger ani- mals. In any individual animal, the dendritic complexity is related to the volume of the target tissue [14-16, 19]. With increasing dendritic complexity, the number of con- verging preganglionic axons also increases [15]. A similar type of organisation also seems to occur in the sympa- thetic ganglia of birds [ 1,2,5]. However, the postgangli- onic sympathetic neurons of amphibians are monopolar and totally lack dendrites, regardless of their target tissue. There is a correspondingly small number of convergent preganglionic inputs to these neurons [5,6,13,18]. Given the stark contrast in ganglionic organisation between anu- ran amphibians and amniotes, such as mammals and birds, it is of great interest to know if the simple synaptic arrangement of amphibian sympathetic ganglia reflects the primitive vertebrate condition, or whether it represents an evolutionary specialisation peculiar to this group of * Corresponding author. Tel.: +46 31 7733628; fax: +46 31 7733807; e-mail: p.karila@zool.gu.se. animals. In order to answer this question, we need to know more about the dendritic structure and synaptic organisation of autonomic ganglia from a much wider range of vertebrate species. Modern teleost fish provide a good comparison with amphibians on the one hand and amniotes on the other. Most teleosts have well developed sympathetic chains with sympathetic innervation of a range of target tissues similar to those in other vertebrates (see [5,12] for review). However, there is only scanty and inconclusive information regarding the morphology of autonomic ganglion cells in fish, but it seems that at least some postganglionic neurons of teleosts may bear den- drites [1,5,9]. Consequently, the primary aim of this study was to use intracellular dye injection to examine the den- dritic morphology of postganglionic sympathetic neurons in one species of teleost fish, the goldfish, Carassius au- ratus, to address the question of whether or not these neu- rons bear dendrites. We concentrated on neurons in the coeliac ganglion since it is relatively large, it is the most extensively studied sympathetic ganglion in fish, and it supplies well defined target tissues in the gastrointestinal tract (see [12] for a review). Fifteen goldfish, Carassius auratus, ranging from 18- 75 g were used in the study. They were kept in aerated 0304-3940/95/$09.50 © 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0304-3940(95)1 1970-5