Three-Dimensional Structure And Association With Blood Vessels Of Chemosensitive And Nonchemosensitive Locus Coeruleus Neurons From Neonatal Rats

We studied the 3 dimensional structure of LC neurons from neonatal rats. Neurons were identified as either chemosensitive or nonchemosensitive based on their firing rate response to hypercapnia, studied using whole‐cell patch clamping. Chemosensitive neurons have less rounded soma than nonchemosensitive neurons and they have dendrites arising from two poles to produce a fusiform appearance. The dendritic branches extend a greater distance from the soma of chemosensitive than nonchemosensitive neurons. Chemosensitive LC neurons have at least one projection that makes a closer approach to the floor of the 4th ventricle than nonchemosensitive neurons, but on average this closest approach is still greater than 50 microns. Nothing about the 3 dimensional structure of chemosensitive neurons appears to be correlated with the neuron being chemosensitive. Interestingly,however, the dorsal and intermediate zones of the LC have a very high percentage of chemosensitive neurons while the ventral zone has mostly nonchemosensitive neurons. Based on Image J analysis of LC regions stained for neurons (Neu‐N) and blood vessels (isolectin), there is a higher density of blood vessels in the chemosensitive dorsal and intermediate regions of the LC compared to the nonchemosensitive ventral region, suggesting greater perfusion of chemosensitive neurons. Finally, we found that capillaries make direct contacts with the soma of chemosensitive neurons but not with the soma of nonchemosensitive neurons. Our findings are consistent with chemosensitive signaling being based in the soma of LC neurons and provide anatomical information for the construction of multi‐compartment computational models of chemosensitive neurons. We are currently comparing our findings in LC neurons with chemosensitive and nonchemosensitive neurons from the nucleus of the solitary tract (NTS). Grant Funding Source : Supported by NIH Grant HL56683