Neurons in the lateral part of the lumbar spinal cord show distinct novel axon trajectories and are excited bz short propriospinal ascending inputs

Antal, Zsófia and Luz, Liliana L. and Safronov, Boris V. and Antal, Miklós and Szücs, Péter (2015) Neurons in the lateral part of the lumbar spinal cord show distinct novel axon trajectories and are excited bz short propriospinal ascending inputs. Brains Structure and Function. ISSN 1869-2653

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Abstract

The role of spinal dorsal horn propriospinal connections in nociceptive processing is not yet estab- lished. Recently described, rostrocaudally oriented axon collaterals of lamina I projection and local-circuit neurons (PNs and LCNs) running in the dorsolateral funiculus (DLF) may serve as the anatomical substrate for interseg- mental processing. Putative targets of these axons include lateral dendrites of superficial dorsal horn neurons, in- cluding PNs, and also neurons in the lateral spinal nucleus (LSN) that are thought to be important integrator units receiving, among others, visceral sensory information. Here we used an intact spinal cord preparation to study intersegmental connections within the lateral part of the superficial dorsal horn. We detected brief monosynaptic and prolonged polysynaptic excitation of lamina I and LSN neurons when stimulating individual dorsal horn neurons located caudally, even in neighboring spinal cord seg- ments. These connections, however, were infrequent. We also revealed that some projection neurons outside the dorsal grey matter and in the LSN have distinct, previously undescribed course of their projection axon. Our findings indicate that axon collaterals of lamina I PNs and LCNs in the DLF rarely form functional connections with other lamina I and LSN neurons and that the majority of their targets are on other elements of the dorsal horn. The unique axon trajectories of neurons in the dorsolateral aspect of the spinal cord, including the LSN do not fit our present un- derstanding of midline axon guidance and suggest that their function and development differ from the neurons inside lamina I. These findings emphasize the importance of un- derstanding the connectivity matrix of the superficial dorsal horn in order to decipher spinal sensory information processing.

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