Ultrastructure and distribution of axon terminals from the reticular thalamic nucleus to the anteroventral thalamic nucleus of the rat

Ultrastructure of axon terminals projecting to the anteroventral thalamic nucleus (AV) from the reticular thalamic nucleus (RTN) of the rat was studied by using the anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP). Anterogradely labeled fibers were distributed in ventral and caudal parts in AV following WGA-HRP injections into the medial part of rostral RTN, whereas labelings were found in the anterodorsal thalamic nucleus (AD) and dorsal part of AV following injections into the dorsal part of rostral RTN. The main labeled terminals were small to medium in size, containing pleomorphic vesicles, and made symmetrical contacts on wide range of neuronal surfaces, including cell bodies, dendritic shafts and their spines. Majority of these terminals made a single synaptic contact, whereas some labeled terminals had two synaptic contacts on two different postsynaptic profiles, such as on both soma and large dendrite, on both soma and small dendrite, on both soma and dendritic spine, and on both large and small dendrites.