Aminergic and peptidergic elements and actions in a cardiac parasympathetic ganglion" LUKASZ k!. KQNOPKA~, LAURA A. MERNAM, JEAN C. HARDWICK, AND RODNEY L. PARSONS' Department of Anufonty and Neumbiology, University of Vermont College of Medicine, Burlington, VT 05405, Uo SS A. Received September 23, 1991 KONOPKA, L, ,M., MERRIAM, L. A., HARDWICK, J. C., and PARSONS, R. L. 1992. Aminergic and peptidergic elements and actions in a cardiac parasympathetic ganglion. Can. J. Physiol. Pharmacol. '$0: S32-S43. Correlated histochemical, immunocytochemical, and electroghysiological experiments have been undertaken to identify putative neurotransmitter - neuromodulator substances in cells and fibers in the parasympathetic cardiac ganglion of the mud- puppy, Necfums ~ C ~ ~ ~ O S U S , and to determine the action of these agents on the properties of the parasympatheticpostganglionic neurons. The mudpuppy cardiac ganglion contains two neuron types: large parasympathetic postganglionic neurons and smaller intrinsic neurons initially identified as small intensely fluorescent cells. We have shown that the postganglionic neurons contain both acetylcholine and a gahnin-like neuropeptide. Also, we have demonstrated that the intrinsic neurons contain a number of different bisgenic arnines such as doparnine and serotonin, as well as neuropeptides including a substance P-like peptide and a gdanin-like peptide. The results of these studies indicate that the anatomical and histochemical organiza- tion of the mudpuppy cardiac ganglion is more complex than that seen in other amphibians and is very similar to that found in most mammalian species. Previously, we showed that galanin has actions that make it of interest as a potential inhibitory neurotransmitter in the mudpugpy cardiac ganglion. Galanin hyperpolarizes and decreases membrane excitability in mast parasympathetic neurons. Here we show that galanin initiates membrane hypepolarization by activating a voltage- and time- dependent potassium conductance. We also present the initial results of ongoing studies which indicate that calcitonin gene- related peptide can depolarize some of the parasympathetic neurons as well as evidence that serotonin initiates depolarization in many parasympathetic neurons. This serotonin-induced depolarization consists of an initial transient depolarization fol- lowed by a longer, more slowly developing depolarization. Action potential activity is stimulated during the initial period of depolariaatisn, but depressed during the later, slow depolarization. The results of these eBectraphysiologica1 experiments suggest that many of the bioactive substances that have been identified in the different cells and nerve fibers within the cardiac ganglion affect the excitability of the postganglionic neurons. In concIusion, we suggest that the results of the studies summa- rized in this review demonstrate that eke cardiac ganglion in the mudpuppy is not simply 8 relay station. Rather, the cardiac ganglion has a complex organization and exhibits a diversity sf physiological responses, indicating that it very likely is another site of integration for control sf cardiac function. Key words: parasympathetic neurons, cardiac ganglion, neuropeptides, kiogenic amines, galanin, serotonin. KONOPKA, L. M., MERRHAM, L. A., HARDWICK, J. C., et PARSONS, R. L. 1992. Aminergic and peptidergic elements and actions in a cardiac parasympathetic ganglion. Can. 9. Physiol. Pharrnacol. 70 : S32-S43. On a eu recours B des expkriences ClectrophysiologiqPles, immunocytochimicpes ee kistochimiques parallkles pour identifier les substances meurotransmettrices - neurornsdulatrices putatives dans les cellules et les fibres du ganglion cardiaque parasym- pathique de la salarnandre, N~CPUP~S wctelosees, et pour dkterrniner l'action de ces substances sur les proprietes des neuroanes post-ganglionnaires parasympathiques. Le ganglion cardiaque de la salamandre contient deux types de neurones : de gras neurones post-ganglionnaires parasympathiques et des neurones intrinsbques plus petits, indentifks cornme de petites cellules intenstrnent fluorescentes. Nous avons constat6 que les neurones post-ganglionnaires contiennent de l'acktylchsline et un neuropeptide semblable 21 la galanine. De plus, nous avons demontre que les neurones intrinsbques contiennent diverses ami- nes biogtniques, telles que la dopamine et H a ~Crotonine, et des neuropeptides, dont un peptide semblable B la substance P et un autre sernblable A la galanine. Les rCsultats de ces etudes indiquent que l'organisation histochimique et anatomique du ganglion cardiaque de la salamndre est plus cornplexe que celle observke chez d'autres amphibiens et qu'elle s9apparente Ctroi-siternent ii celle de la plupart des rnamifkres. Antkrieurernent, nous avons dCmontrC qu'en raisan de ses actions, la gala- nine prQente un intCret en termes de neurotransmetteur iralaibiteur potentiel dans Ie ganglion cardiaque de la salamandre. La gdanine hyperpolarise et diminue l'excitabilitd mnembranaire dans la plupart des neurones parasympathiques. Ici, nous mntrons que la galanine dCclenche l'hypeqmlarisation rnembranaire en activamt une conductance potassique dependante du temps et da la tension. Nsus pr6sentons aussi les premiers rksultats des ttudes en cours, qui indiquent que Be peptide lit au gkne de la calcitonine pourrait dkpolariser certains neuronaes parasympathiques, ainsi que les faits dkrnontrant que la serotonine provoque une dkpolarisatisn dam plusieurs neurones parasympathiques. Cetge dtpolarisation induite par la ~Crotonine consiste en une dkpolarisation transitoire initiale suivie d'une dkpolarisation plus Isngue se dtveloppant plus lentement. k'activite du potentiel d'action est accrue durant la ptriode initiale de deplarisation, mais est diminute durant la dtpolarisation lente. Les resultats de ces experiences 6lectrophysiologiques suggbrent que plusieurs des substances bioactives, qui ont kt6 identifikes clans les diffkrentes sellules et fibres nerveuses du ganglion cardiaque, influencent I'excitabilitC des neurones post-gangliomaires. En conclusion, wous suggkrons que les rCsultats des ktaades rCsum&s dans me article dtmontrent que, chez Isr salamandre, le ganglion cardiaque n'est pas simplement une relais. Au contraire, le ganglion cardiaque a une organisation cornplexe et prCsente une diversit6 de r6ponses physidogiques, indiquant qu'il est vraisemblablernent un autre site Q'intCgration pour le contrble de la fonction cardiaque. MOPS ckds : neurones parasympathiques, ganglions cardiaques, neuropeptides, amines biogtniques, galanine, skrotonine. 'This paper was presented at the satellite symposium of the International Brain Research Organization meeting held August 12- 14, 2991, at the University of Alberta, Edmonton, Alta., Canada, entitled The Physiology, Phamacolsgy , and Biophysics of Ganglionic Transmission, and has undergone the Journal's usual peer review. 2Present address: Section of Biological Psychiatry, 1 14A19, Veterans Administration Hines Medical Center, Hines, IL 60 14 1, U .S .A. 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