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This Article Full Text Full Text (PDF) All Versions of this Article: 562/1/183    most recent jphysiol.2004.076398v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Asghar, A. U. R. Articles by King, A. E. Search for Related Content PubMed PubMed Citation Articles by Asghar, A. U. R. Articles by King, A. E.

¹ School of Biomedical Sciences, University of Leeds, Leeds, LS2 9JT, UK
² Department of Biological Sciences and Hull York Medical School, University of Hull, Hull, HU6 7RX, UK

Abstract

Although rhythmic behaviour of mammalian spinal ventral horn networks has been extensively studied little is known about oscillogenesis in the spinal dorsal horn. The aims of this in vitro study were to record and determine the underlying mechanisms of potassium-evoked network field oscillations in the substantia gelatinosa of the neonatal rat dorsal horn, a lamina involved in nociceptive processing. Transient pressure ejection of a potassium solution evoked reproducible rhythmic activity in discrete areas of the substantia gelatinosa which lasted for 5–15 s with a single prominent peak in the 4–12 Hz frequency band (7.7 ± 0.1 Hz, n = 60). Oscillations of similar frequency and amplitude were also observed in isolated dorsal horn quadrants. Application of CNQX (10 µM) reduced peak power amplitude and integrated power area (from 4 to 12 Hz) of the power spectrum, whereas D-AP5 (50 µM) had no effect on the potassium-evoked rhythm. Bicuculline (30 µM) or strychnine (10 µM) reduced the power amplitude and area. On combination of bicuculline (30 µM) and strychnine (10 µM) the reductions in power amplitude and area were not significantly different (P > 0.05) when compared with application of either drug alone. The gap junction blockers carbenoxolone (100 µM) or octanol (1 mM) significantly reduced power amplitude and area. Although TTX (1 µM) or a calcium-free perfusate both caused reductions in the power amplitude and area, potassium-evoked rhythmic activity persisted. However, this persistent rhythm was further reduced on combination of calcium-free perfusate with octanol (1 mM) and was abolished using a cocktail of drugs. Blockade of the potassium delayed rectifier current by tetraethylammonium (5 mM) or the hyperpolarization-activated current (I_h) by ZD7288 (10 µM) disrupted the synchronization of the potassium-induced oscillation. The frequency of potassium-induced rhythms was unaffected by any of the drugs tested. These novel findings demonstrate that transient pressure ejection of potassium evokes oscillatory activity in the substantia gelatinosa in vitro. This rhythm is partly dependent upon various receptors (AMPA/kainate, GABA_A and glycine), ion channels (potassium delayed rectifier and I_h) and gap junctions. Oscillatory behaviour in the substantia gelatinosa could potentially play a role in the processing of nociceptive signals.

(Received 30 September 2004; accepted after revision 2 November 2004; first published online 4 November 2004)
Corresponding author A. Asghar: Department of Biological Sciences, Hull York Medical School, University of Hull, Hull HU6 7RX, UK. Email: aziz.asghar{at}hyms.ac.uk

The authors dedicate this publication to the late Professor Eberhard H. Buhl who made a substantive intellectual contribution and advised on the methodologies used in the study.

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