Intrinsic connections of caudate neurons. II. Fluorescence and electron microscopy following chronic isolation

‘En passant’ terminals, small axospinous junctions, and synapses having an interrupted junction remained viable following isolation of the caudate nucleus, and therefore could be identified as boutons of intrinsic neurons. Both symmetrical and asymmetrical junctions were found. The presynaptic boutons usually contained a mixture of ovoid and rounded vesicles, but sometimes one or the other predominated. Large granular vesicles were commonly found in terminals ‘en passant’. Since catecholamine fluorescence was absent in the surrounding tissue, it is unlikely that the large granular vesicles in these axons contained dopamine.