Interrelationship between the cortical and amygdaloid outputs within the forebrain region in the control of the autonomic function.

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We demonstrated possible pathways from the infralimbic cortex(ILC), the insular cortex(IC) and the central nucleus of the amygdala(ACe), to the nucleus of the solitary tract(NST) via the lateral hypothalamus(LH) using combined anterograde and retrograde tracing method. Prominent overlapping distributions of these cortical or amygdaloid fibers and NST-projecting neurons were observed in the lateralmost part of the posterior LH. In this region, both cortical fibers formed asymmetrical synapses with dendrites and spines of the NST-projecting neurons, whereas the amygdaloid fibers made symmetrical synapses with dendrites and cell bodies of the NST-projecting neurons. We also revealed the synaptic organization between and among the fibers originating from the IC and ACe, and the LH neurons using double anterograde labeling. Prominent overlapping distributions of the IC and ACe fibers were found in the lateralmost part of the posterior LH. In this area, some of single dendrite or spine received convergent synaptic inputs from both sets of terminals. Using anterograde tracing combined with immunohistochemistry for GABA, we further showed that most of the amygdaloid fibers were GABAergic and that they contained not only clear vesicles but also dense-cored vesicles, suggesting the co-localization of GABA and peptides. Taken together, these results suggest possible pathways from the ILC, IC and ACe to the NST via the LH. Moreover, excitatory inputs from the ILC and IC, and inhibitory inputs from the Ace might be integrated in the NST-projecting neurons in the LH for the control of the autonomic function