Synaptic relationships of Golgi type II cells in the medial geniculate body of the cat.

A combined analysis with the Golgi and silver-degeneration methods and electron microscopy in the ventral nucleus of the medial geniculate body has confirmed that the Golgi type II neuron forms dendro-dendritic synapses with the principal neuron in terminal aggregates called synaptic nests. Both types of neurons receive synaptic contacts from the afferent axons that ascend from the posterior colliculus and from those that descend from the auditory cortex. Only the principal neuron projects to the auditory cortex. The Golgi type II cells that receive endings from afferent axons send presynaptic processes to principal cells that are also contacted by the very same afferent axons. The axons of Golgi type II cells project to synaptic nests other than those supplied by the dendrites of the parent cell and link the Golgi type II cells with each other. On the surface of the Golgi type II cell there is a segregation of the different types of synaptic endings and a consistent sequence in their synaptic relationships. The endings of colliculogeniculate and Golgi type II axons predominate on the distal dendrites in the synaptic nests. Corticogeniculate endings congregate more on the soma and proximal dendrites. In the synaptic nests the Golgi type II dendrites are presynaptic to the principal cell dendrites, whereas both kinds of dendrites are postsynaptic to the very same axons, which project either from the posterior colliculus or from Golgi II cells...