MULTIPLE POPULATIONS OF NEUROPEPTIDE-CONTAINING INTRINSIC NEURONS IN THE GUINEA-PIG HEART

Recent studies of autonomic ganglia have shown that specific combinati ons of neuropeptides and other potential neurotransmitters distinguish different functional types of neurons. In the present paper the patte rns of coexistence of neurochemicals in guinea-pig cardiac ganglion ce lls was examined, using multiple-labelling immunohistochemistry. Many neurons were found to contain somatostatin immunoreactivity with vario us combinations of immunoreactivity for dynorphin B, substance P, neur opeptide Y and nitric oxide synthase. There were several small populat ions of neurons without somatostatin immunoreactivity, which contained combinations of immunoreactivity for vasoactive intestinal peptide, n europeptide Y, dynorphin B, substance P and nitric oxide synthase. Pos sible synaptic inputs to these populations of ganglion cells were iden tified using multiple-labelling immunohistochemistry combined with lon g-term organ culture. These experiments demonstrated that cardiac gang lia contain prominent pericellular baskets of varicose nerve terminals of sympathetic and sensory origin. In addition, populations of intrin sic intraganglionic nerve terminals were identified which were immunor eactive for vasoactive intestinal peptide, neuropeptide Y or both pept ides. These terminals presumably originate from intrinsic neurons, wit h the same combinations of neuropeptides, located in other cardiac gan glia. These results have demonstrated that there are diverse populatio ns of cardiac ganglion cells in the guinea-pig and that some of these neurons may act as interneurons within the intrinsic cardiac plexuses. Therefore it is highly likely that vagal transmission in the heart is modified by sympathetic, sensory and intrinsic neurons and that cardi ac ganglia are complex integrators of convergent neuronal activity rat her than simple relays.