Relationship of corticoclaustral axon terminals to neurons of the claustrum in the cat.

A dark type degeneration of axon terminals was observed in the dorsocaudal part of the claustrum following lesions of the visual cortex. Most of the degenerating axon terminals had synapses mainly with dendritic spines (64.1%) and small dendrites (25.1%). Only 5.8% of degenerating axon terminals formed synaptic contacts with medium-sized dendrites, 1.0% with large dendrites and 0.5%--with other parts of the claustral neurons. 3.5% of degenerating axon terminals were observed to form a contact with more than one postsynaptic structure. Degenerating axon terminals displayed synaptic contacts exclusively of asymmetrical type with clearly identifiable postsynaptic densities which suggest corticoclaustral afferents to be excitatory. Our data strongly support the notion that there are direct synaptic contacts between the ascending arm of the corticoclaustral neuronal loop.