Postganglionic nerve cell bodies and neurotransmitter localization in the teleost heart.

A studywasundertakentodeterminethedistributionofspecifictypesofautonomic
nerves andthepresenceofvarioustransmittersubstancesintheheartoftwoteleost
species: themullet(Mugil cephalus) andtheNilecatfish(Synodontis nigriventris).
Large nervetrunksinthesinusvenosuswereshowntocontaintyrosinehydroxylase
immunoreactivity andindicatethelocationofadrenergicnervefibers,whichare
also associatedwithacoronarycirculationtotheventricularmyocardiuminthe
mullet heart.Fluorescenceimmunolabellingmethodsrevealedthattheatriumand
the outerandinnercompactmuscleoftheventriclehavenervesinwhichsubstance
P andgalanin(GA)arelocalized.Itseemslikelythatthecellbodies(perikarya)of
the substancePandGA-immunopositiveaxonsarelocatedatsitesoutsidetheheart.
The GA-immunopositivenervefibersmayrepresentapopulationofaxonsof
intramural postganglionicnervecellbodies.Mostintracardiacnervecellbodiesare
located inthesinusvenosusandinthesinoatrialjunctionandrevealimmunor-
eactivity tosubstanceP,GA,neuronalnitricoxidesynthase(nNOS),vasoactive
intestinal peptide(VIP)andpituitaryadenylatecyclase-activatingpeptide(PACAP).
Furthermore, substancePimmunoreactivityispresentinthecardiaccells
intermingled withthesubstanceP-immunopositivenervefibers.Anerveplexus
consisting ofawell-developednetworkofnervefibersandnervecellbodiesmay
possibly correspondtoacardiacpacemaker,butitsfunctioninfishcardiac
regulation isunknownandremainstobeelucidated.