NEUROPEPTIDE Y-IMMUNOREACTIVE INTRACARDIAC NEURONS, GRANULE-CONTAINING CELLS AND NERVES ASSOCIATED WITH GANGLIA AND BLOOD-VESSELS IN RAT AND GUINEA-PIG HEART

Intrinsic neuropeptide Y-containing neurones in rat and guinea-pig hea rts were studied at the ultrastructural level by the pre-embedding per oxidase-antiperoxidase immunocytochemical technique. Intracardiac neur onal cell bodies were often weakly or moderately immunostained, and th e labelling was usually pronounced in the Golgi complex, multivesicula r bodies, some cisterns of granular endoplasmic reticulum and large gr anular vesicles. Neuropeptide Y-immunoreactive nerve fibres were also observed in association with intracardiac neurones. A subpopulation of neuropeptide Y-immunoreactive granule-containing cells in the rat hea rt are described for the first time and were very heavily labelled; ot her granule-containing cells were non-immunoreactive, but were contact ed by neuropeptide Y-containing nerves. Preterminal regions of nerve f ibres that were located in nerve bundles were only weakly neuropeptide Y-immunoreactive, in contrast to the heavy labelling observed in vari cosities that contained many synaptic vesicles. Many neuropeptide Y-im munoreactive nerve fibres were associated with the coronary vasculatur e and were particularly prominent in the walls of small arteries and a rterioles where labelled nerve varicosities were present close to the smooth muscle cells. Immunoreactive nerves were also seen in the myoca rdium, usually near to capillaries. In axonal varicosities, the centra l core of large granular vesicles was immunolabelled, and electron-den se immunoreactive material outlined the membranes of small and large c lear vesicles. The significance of neuropeptide Y-immunoreactive intra cardiac neurones and granule-containing cells and the origin of associ ated labelled nerve fibres in the heart are discussed.