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Zusammenfassung:
The large spindle-shaped von Economo neuron (VEN) occurs in a specific architectonic area (‘VEN-area’) in the macaque anterior insula (Evrard et al., Neuron, 2012, 74:482-9). Given its relatively large size and localization in layer 5a, the VEN likely projects to distant brain regions. We recently reported that one of this target is the midbrain periaqueductal gray (PAG). Here we examined the insular projections to another key homeostatic center, the parabrachial nucleus (PBN) using injections of anterograde tracers in AIC and of retrograde tracers in PBN. Injections of biotin-dextran-amine (BDA) in the insular area containing VENs produced sparse but consistent anterograde labeling in both the medial and lateral aspects of the PBN. Injections of retrograde cholera toxin b (CTb) or fluorescent dextran in PBN invariably labeled cortical projections neurons on both side of the neocortex. However, unlike for our prior injections in PAG, the AIC, including the VEN area, was almost the only cortical region labeled. The retrogradely labeled neurons included pyramidal neurons as well as VENs and their companion Fork neurons (FNs). These results are consistent with our microstimulation works showing activation of both left and right PBN with microstimulation of either the left or right AIC (see Smuda et al, this meeting). They are also consistent with our recent collaborative evidence that the human VEN area is strongly functionally connected with PBN and that this functional connection is massively altered in coma patients with a brainstem lesion (Fischer et al., Neurology, 2016, 90:143-51). Finally, they suggest that the relatively large VEN and FN might provide rapid cortical efferent projections for the regulation of brainstem autonomic processing both at the afferent (PBN) and efferent (PAG) stages.
