VISCERAL AFFERENT PATHWAYS TO THE THALAMUS AND OLFACTORY TUBERCLE - BEHAVIORAL-IMPLICATIONS

The goal of this study was to support the hypothesis that visceral sig nals may integrate and influence behavior by way of direct pathways fr om the nucleus tractus solitarii (NTS) to the olfactory tubercle and t he midline/intralaminar thalamus. An anterograde tracer, biotinylated dextran amine (BDA) was iontophoresed bilaterally into the caudal NTS to optimize terminal labeling. NTS-cortical projections traversed both limbs of the diagonal bands providing heavy innervation, and terminat ed lightly within layer 3 of the olfactory tubercle. NTS-thalamic proj ections terminated within anterior and, as previously shown, posterior divisions of nucleus paraventricularis thalami and avoided the adjoin ing mediodorsal thalamic nucleus. Heretofore unrecognized projections were traced to the parafascicular and reuniens thalamic nuclei, and th e peripeduncular nucleus. Control experiments identified the nucleus g racilis as the principal source of ascending projections to ventropost erior lateral, posterior and intralaminar thalamic nuclei. Our data co rroborate the supposition that olfactory signals may integrate with vi sceral stimuli in the striatal compartment of olfactory tubercle. NTS projections encompass thalamic nuclei that project topographically to the prefrontal cortex, hippocampus and ventral (limbic) striatum, regi ons activated by visceral stimulation. Structural data support the ide a that compartments of the non-discriminative thalamus may contribute to perception and behavioral responses to visceral stimulation. (C) 19 98 Published by Elsevier Science B.V. All rights reserved.