Biology subjects

Baumbauer, K. M.

Publications and source records attributed to Baumbauer, K. M..

2 recordsLinked to original sources

bioRxiv2021

Comprehensive Phenotyping of Cutaneous Afferents Reveals Rapid-Onset Alterations in Nociceptor Response Properties Following Spinal Cord Injury

Spinal cord injury (SCI) is a complex syndrome that has profound effects on patient well-being, including the development of medically-resistant chronic pain. The mechanisms underlying SCI pain have been the subject of thorough investigation but remain poorly understood. While the majority of the research has focused on changes occurring within and surrounding the site of injury in the spinal cord, there is now a consensus that alterations within the peripheral nervous system, namely sensitization of nociceptors, contribute to the development and maintenance of chronic SCI pain. Here we demonstrate that thoracic spinal contusion injury results in the emergence of autotomy and spasticity, both indicators of spontaneous pain, in areas below the level of the injury within 24 hr of SCI. These behaviors were associated with hindpaw edema and elevated cutaneous calcitonin gene-related peptide (CGRP) concentration. Electrophysiological recordings using an ex vivo skin/nerve/DRG/spinal cord preparation demonstrated that SCI increased mechanical and thermal sensitivity, as well as the incidence of spontaneous activity (SA) and afterdischarge (AD), in below-level C-fiber nociceptors 24 hr following injury. Interestingly, the distribution of nociceptors that exhibit SA and AD are not identical, and the development of SA was observed more frequently in nociceptors with low thermal thresholds, while AD was found more frequently in nociceptors with high thermal thresholds. These results demonstrate that SCI causes the rapid-onset of peripheral inflammation-like processes that sensitize nociceptors, which may contribute to the early emergence and persistence of chronic SCI pain.

neuroscience↗

bioRxiv2020

Optogenetic evaluation of the ability of different cutaneous C-fiber afferents to evoke aversive behaviors

Most cutaneous C-fibers, including both peptidergic and non-peptidergic subtypes are presumed to be nociceptors and respond to noxious input in a graded manner. However, mechanically sensitive, non-peptidergic C-fibers also respond to mechanical input in the innocuous range, and so the degree to which they contribute to nociception remains unclear. To address this gap, we investigated the function of non-peptidergic afferents using the MrgprdCre allele. In real time place aversion studies, we found that low frequency optogenetic activation of MrgrpdCre lineage neurons was not aversive in naive mice, but became aversive after spared nerve injury (SNI). To address the underlying mechanisms of this allodynia, we recorded from lamina I spinoparabrachial (SPB) neurons using the semi-intact ex vivo preparation. Following SNI, innocuous brushing of the skin gave rise to abnormal activity in lamina I SPB neurons, consisting of an increase in the proportion of recorded neurons that responded with excitatory post synaptic potentials or action potentials. This increase was likely due, at least in part, to an increase in the proportion of lamina I (LI) SPB neurons that received input upon optogenetic activation of MrgprdCre lineage neurons. Intriguingly, in SPB neurons there was a significant increase in the EPSC latency from MrgprdCre lineage input following SNI, consistent with the possibility that the greater activation post SNI could be due to the recruitment of a new polysynaptic circuit. Together, our findings suggest MrgprdCre lineage neurons can provide mechanical input to the dorsal horn that is non-noxious before injury but becomes noxious afterwards due the engagement of a previously silent polysynaptic circuit in the dorsal horn.

neuroscience↗