COLLATERAL PROJECTIONS OF SINGLE NEURONS IN THE POSTERIOR THALAMIC REGION TO BOTH THE TEMPORAL CORTEX AND THE AMYGDALA - A FLUORESCENT RETROGRADE DOUBLE-LABELING STUDY IN THE RAT

It has been reported that the acoustic thalamus of the rat sends proje ction fibers to both the temporal cortical areas and the lateral amygd aloid nucleus to mediate conditioned emotional responses to an acousti c stimulus. In the present study, fluorescent retrograde double labeli ng with Fast Blue and Diamidino Yellow has been used in the rat to exa mine whether single neurons in the posterior thalamic region send axon collaterals to both the temporal cortical areas and lateral amygdaloi d nucleus. One of the tracers was injected into the lateral amygdaloid nucleus and the other into the temporal cortical areas close to the r hinal sulcus. Neurons double-labeled with both tracers were found main ly in the posterior intralaminar nucleus and suprageniculate nucleus, and to a lesser extent in the subparafascicular nucleus and medial div ision of the medial geniculate nucleus. No double-labeled neurons were seen in either the dorsal or ventral division of the medial geniculat e nucleus. When one of the tracers was injected into the lateral amygd aloid nucleus and the other into either the dorsal portion of the temp oral cortex, the dorsal portion of the entorhinal cortex, or the poste rior agranular insular cortex, no double-labeled neurons were found in the posterior thalamic region. The present results indicate that a su bstantial number of single neurons in the acoustic thalamus project to both the limbic cortical areas and lateral amygdaloid nucleus by way of axon collaterals. These neurons may be implicated in affective and autonomic components of responses to multi-sensory stimuli, including acoustic ones. (C) 1997 Wiley-Liss, Inc.