Multisegmental Aδ- and C-Fiber Input to Neurons in Lamina I and the Lateral Spinal Nucleus

Abstract

Spinal lamina I and the lateral spinal nucleus (LSN) receive and integrate nociceptive primary afferent inputs to project through diverse ascending pathways. The pattern of the afferent supply of individual lamina I and LSN neurons through different segmental dorsal roots is poorly understood. Therefore, we recorded responses of lamina I and LSN neurons in spinal segments L4 and L3 to stimulation of six ipsilateral dorsal roots (L1-L6). The neurons were viewed through the overlying white matter in the isolated spinal cord preparation using the oblique infrared LED illumination technique. Orientation of myelinated fibers in the white matter was used as a criterion to distinguish between the LSN and lamina I. Both types of neurons received mixed (monosynaptic and polysynaptic) excitatory A␦-and C-fiber input from up to six dorsal roots, with only less than one-third of it arising from the corresponding segmental root. The largest mixed input arose from the dorsal root of the neighboring caudal segment. Lamina I and LSN neurons could fire spikes upon the stimulation of up to six different dorsal roots. We also found that individual lamina I neurons can receive converging monosynaptic A␦-and/or C-fiber inputs from up to six segmental roots. This study shows that lamina I and LSN neurons function as intersegmental integrators of primary afferent inputs. We suggest that broad monosynaptic convergence of A␦-and C-afferents onto a lamina I neuron is important for the somatosensory processing.

Long and Short Multifunicular Projections of Sacral Neurons Are Activated by Sensory Input to Produce Locomotor Activity in the Absence of Supraspinal Control

“…They had small somata and relatively un-branched dendritic trees. These DLF neurons were located only in the dorsal laminae of the gray matter and in the dorsolateral white matter (the latter is consistent with the lateral spinal nucleus of rodents Waldron, 1968, 1969;Jiang et al, 1999;Olave and Maxwell, 2004;Dutton et al, 2006;Pinto et al, 2010). Few neurons were found in lamina VII.…”

Heterosynaptic Long-Term Potentiation at GABAergic Synapses of Spinal Lamina I Neurons

“…Previous work indicates that most neurons located in lamina I of the spinal cord, being either excitatory or inhibitory, receive monosynaptic input from either A␦-fibers and/or C-fibers (Yoshimura and Jessell, 1990;Dahlhaus et al, 2005;Yasaka et al, 2007;Pinto et al, 2010), and many also express group I mGluRs (Alvarez et al, 2000). In the present study, we recorded from unidentified lamina I neurons and showed that LTP GABA could Figure 7.…”

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

“…Nevertheless, this is still higher than the success rate of recovering biocytin filled cells in our previous work on LSN neurons (30%, Pinto et al, 2010). Probably due to the same reason, we could not achieve presynaptic labelling to an extent that would have allowed identification of synaptic connections in the initial trials, thus, later we excluded biocytin from the cell-attached pipette to reduce contamination of the preparation that would have made it difficult to trace the axon trajectories.…”

“…In terms of functionality, these ultra-short propriospinal connections are of questionable importance, but may increase the complexity of intraspinal divergence and convergence (Pinto et al, 2010) of primary afferent inputs. Synaptic delay in the recorded monosynaptic connections showed a large variation, but even the longest observed latencies would be compatible with putative long axodendritic pathways and recording conditions at room temperature .…”