QUANTITATIVE ANALYSIS OF SUPERFICIAL DORSAL HORN NEURON AXONS IN RATS
Éva Kókai1, 2, Liliana L. Luz3, 4, Elisabete C. Fernandes3, 4, Boris V. Safronov3, 4, Péter Szücs1, 2
3 Instituto de Investigacao e Inovacao em Saude, Universidade do Porto, Porto, Portugal; 4Neuronal Networks Group, Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Porto, Portugal
Little is known about the organization principles of neuronal circuits in the dorsal horn (DH), where initial sensory processing occurs. While there is substantial data on the somatodendritic morphology of DH neurons, the distribution pattern of their axons is almost unknown. In a recent work we started to analyse the axon distribution of lamina III neurons to provide anatomical basis for the claim that they are capable of relaying non-noxious stimuli towards lamina I. In the present study we used Neurolucida to fully reconstruct 10 lamina I projection neurons (PNs) along with 15 lamina I interneurons (INs) in 3-D to extend the morphometrical analysis and to compare these axons with those of lamina III interneurons. In line with our earlier observations we found that lamina I interneurons in the lateral aspect of the DH send dense axon collaterals towards the medial part of the DH and occupy laminae I-III with occasional deeper collateral branches. Interestingly only a few axons presented collaterals that reached the most medial part of the DH while the majority of the axons did not extend further then the mediolateral span of the corresponding dendritic tree. We also found that axon collaterals projecting contralaterally almost exclusively belong to PNs. Thus the dorsal commissural axons reported to originate from the lateral part of the DH do not seem to belong to lamina I interneurons. In summary, lamina I neurons have distinct local axon collateral distribution patterns that might be linked to their role in the DH circuitry.