Neuronal and synaptic structure of the specific thalamic nuclei.

1. Neuronal organization of the specific thalamic nuclei is rather uniform. The ratio of thalamocortical relay neuron and Golgi II type interneuron is 2:1, as well as 3:1. 2. Interneurons show GABA-immunoreactivity. The presynaptic dendrites (F2-profiles) modify the intrathalamic transmission of the specific afferent impulses. 3. The two principal types of synaptic arrangements were observed in the specific thalamic nuclei: the synaptic glomeruli and the general neuropil. 4. Three different types of axon-terminals could be distinguished in the neuropil of all specific thalamic nuclei: the large RL-boutons are terminals of the specific afferents, the small RS-boutons are mainly the terminals of cortical afferents and the F1-boutons are probably axon-terminals of the Golgi II type interneurons, as well as axon-endings originating from the reticular nucleus of thalamus. 5. Synaptic contacts of the specific afferent fibers have basic importance in the relay nuclei. 6. In associative and anterior thalamic nuclei the RS- and F1-boutons have a significant modification effect on the interneurons (inhibition-disinhibition).