Presentation Authors: Luke Grundy*, Andrea Harrington, Ashlee Caldwell, Joel Castro, Vladimir Zagorodnyuk, Simon Brookes, Nick Spencer, Stuart Brierley, Adelaide, Australia
Introduction: Primary afferent neurons transduce distension of the bladder wall into action potentials that are relayed into the spinal cord and brain, where autonomic reflexes necessary for maintaining continence are coordinated with pathways involved in sensation. However, the relationship between spinal circuits involved with physiological and nociceptive signalling from the bladder have only been partially characterised. The aim of this study to was to investigate the spinal cord circuits processing bladder afferent input and how the sub-classes of high and low threshold bladder mechanosensitive afferents feed into these spinal circuits.
Methods: We used ex-vivo bladder afferent recordings to characterise mechanosensitive afferent responses to graded distension (0-60mmHg) and retrograde tracing from the bladder wall to identify central axon projections within the dorsal horn of the lumbosacral spinal cord. Labelling of dorsal horn neurons with phosphorylated-MAP-Kinase (pERK), combined with labelling for neurochemical markers (calbindin, calretinin, GABA, parvalbumin) following in-vivo bladder distension (20-60mmHg) was used to identify spinal cord circuits processing bladder afferent input.
Results: Ex-vivo bladder distension evoked an increase in primary afferent output, and the recruitment of both low and high-threshold mechanosensitive afferents characterised by distinct pressure response profiles. In-vivo bladder distension evoked a stimulus dependent activation of pERK-immunoreactive dorsal horn neurons. Retrograde tracing revealed bladder afferent projections that localised with pERK- immunoreactive dorsal horn neurons within the superficial laminae (SDH), dorsal grey commissure (DGC) and within lateral collateral tracts of the lumbosacral spinal cord. Populations of pERK-immunoreactive neurons co-labelled with calbindin, calretinin, or GABA, but not parvalbumin. Noxious distension that activated high-threshold mechanosensitive afferents increased the percentage of pERKimmunoreactive neurons co-labelled with calretinin.
Conclusions: We identified LS spinal circuits supporting autonomic and nociceptive reflexes responsible for maintaining continence and bladder sensations. Our findings show for the first time that low and high-threshold bladder afferents relay into similar dorsal horn circuits, with nociceptive signalling recruiting a larger number of neurons.
Source of Funding: Stuart Brierley is a National Health and Medical Research Council of Australia (NHMRC) R.D Wright Biomedical Research Fellow (APP1126378) and is funded by NHMRC Australia Project Grants #1083480, #1139366 and #1140297. Andrea Harrington received funding v