Neuropeptide Y-immunoreactive terminals form axo-axonic synaptic arrangements in the substantia gelatinosa (lamina II) of the cat spinal dorsal horn.

The ultrastructural organization of nerve terminals containing neuropeptide Y-immunoreactivity was studied in the substantia gelatinosa of the cat spinal dorsal horn. Seventy immunoreactive boutons were examined through serial sections and 67 of them were found to form between one and five synaptic junctions with dendrites (59.5% of synapses), somata (3% of synapses) and other axon terminals (37.5% of synapses). The postsynaptic axon terminals were often the central boutons of glomeruli. These findings suggest that neuropeptide Y regulates spinal sensory transmission through both a postsynaptic action upon dorsal horn neurons and a presynaptic action upon primary afferent terminals.