Proceedings of The Physiological Society
Cardiff University (2009) Proc Physiol Soc 17, PC15
Properties of neuronal networks linked to nociceptive and non-nociceptive sensory processing in the rat spinal dorsal horn: a study using micro-electrode array technology
R. Chapman1, D. Ursu2, E. Sher2, A. E. King1
1. IMSB, University of Leeds, Leeds, United Kingdom. 2. Eli Lilly & Co., Windlesham, United Kingdom.
Spinal cord dorsal horn neurones (DHNs) are important for local processing and modulation of somatosensory inputs of peripheral origin. DHN output is determined by the complex interplay of cell biophysical properties, synaptic and network-based mechanisms. Single microelectrode techniques have provided much data on DHN firing patterns and synaptic transmission but little is known about how DHNs are organized and operate as networks to support sensory processing. Multisite-microelectrode array (MEA) technology enables simultaneous recordings from spatially distinct regions within the superficial and deep DH thereby enabling analysis of spatio-temporal characteristics of activity across DH laminae. We have used 4-aminopyridine (4-AP), which triggers network-based activity within the substantia gelatinosa (Chapman et al., 2009, J. Physiol. 587.11: 2499-2510), and MEA technology to generate a map of 4-AP-induced activity and characterise more fully the patterns of network behaviour emergent from nociceptive and non-nociceptive circuitry in vitro. Transverse lumbar spinal slices (250μm), cut from terminally anaesthetized (urethane, 2g/kg I.P.) Wistar rats, were mounted onto 8 x 8 arrays of 3-D microelectrodes (40μm diameter; 35-45μm height; 100 or 200μm spaced; Ayanda Biosystems) and recordings were performed at 10000 KHz using the Multichannel MEA system. All animal procedures accord with current UK legislation. A digital image of the spinal slice was captured and superimposed onto the 8 x 8 array to indicate precise recording localizations. Spinal cord slices were superfused with oxygenated ACSF at 34oC, and in ACSF containing 4-AP (50μM, n = 28). In control ACSF, little activity was recorded although spontaneous single unit activity (amplitude 25-35μV) was observed in 9 slices at ~8% of recording sites, increasing to ~15% after 4-AP. Superfusion of 4-AP induced widespread excitation that manifest as large amplitude extracellular population field potentials (amplitude range 20-150μV, duration ~407s, peak frequency ~0.8Hz) spatio-temporally distributed throughout the DH. Auto- and cross-correlation analysis respectively revealed a) a rhythmic characteristic to 4-AP-induced activity, as indicated by a narrow range of inter-spike intervals (1.5-4s) and b) a high degree of unilateral synchrony between superficial and deep DH laminae within each hemicord. These data indicate the potential of MEA technology to describe in more detail the spatial patterns of multi-cell activity in DH networks that support sensory processing including nociception.
Where applicable, experiments conform with Society ethical requirements