The Globus Pallidus Sends Axons to the Thalamic Reticular Nucleus Neurons Projecting to the Centromedian Nucleus of the Thalamus: A Light and Electron Microscope Study in the Cat

Abstract

We examined whether light and electron microscopically projection fibers from the globus pallidus (GP) of the cat might terminate on neurons of the thalamic reticular nucleus (RT) sending axons to the centromedian thalamic nucleus (CM). In the first group of experiments, wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) was injected into the GP, and anterogradely labeled preterminal and terminal-like elements were seen in the anterior part of RT. At the anterior pole of RT, these labeled elements were localized in its lateral portion. In the second group of experiments, the retrograde labeling method with WGA-HRP was combined with the degeneration method using kainic acid. In each cat, lesion was placed stereotaxically in the GP by kainic acid injection, and WGA-HRP was then injected into the CM ipsilateral to the kainic acid injection. In the rostral part of RT, a considerable number of degenerated axon terminals deriving from GP were seen to establish synaptic contact with dendritic and somatic profiles, which were retrogradely labeled by WGA-HRP injections in CM. The results indicate that GP innervates directly RT nucleus neurons projecting to CM.