DISTRIBUTION OF SYNAPTIC BOUTONS AROUND IDENTIFIED NEURONS LYING IN THE CARDIAC PLEXUS OF THE GUINEA-PIG

Neurones in the cardiac plexus of the guinea-pig were subdivided into three groups according to their electrophysiological properties and su bsequently labelled with neurobiotin. Preparations were counterstained with antibodies to synaptophysin to reveal boutons containing synapti c vesicles. Two of the three groups of cells which, in the electrophys iological studies were found to receive excitatory synaptic inputs wer e associated with numerous synaptophysin positive boutons. Cells of th e other group, which did not appear to receive any synaptic inputs wer e associated with fewer synaptophysin positive boutons. Wholemount pre parations were double stained with antibodies to Protein Gene Product 9.5 and synaptophysin. This revealed most neurones, along with vesicle filled boutons. Ganglia generally contained less than 10 neurones wit h a range between one and over 30. In wholemount preparations it was f ound that about 90% of the cells were associated with a large number o f synaptophysin positive boutons whilst the remaining cells were assoc iated with very few synaptophysin positive boutons. These results are consistent with the idea that a proportion of cardiac ganglion cells f ail to receive a synaptic input and suggest that by staining wholemoun t preparations of guinea-pig cardiac plexus with antibodies to synapto physin it is possible to differentiate between groups of cells which r eceive a synaptic input and those which fail to receive a synaptic inp ut. Approximately 10% of intrinsic cardiac neurones appear to lack a s ynaptic input. (C) 1997 Elsevier Science B.V.