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The effects of 5-HT receptor activation on sympathetic rhythms in rat spinal cord slices
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Dr Michelle Pierce
Pierce ML, Deuchars J, Deuchars S
Conference Proceedings (inc. Abstract)
Proceedings of The Physiological Society
University College London, UK
Year of Conference
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The outflow of the sympathetic nervous system has long been known to contain rhythmic activity in the intact organism (see
for review). Interestingly, rhythmic sympathetic nerve discharges are also observed in an
mouse spinal cord preparation
, suggesting that some of this activity is spinally generated. We used spinal cord slices to investigate rhythmic activity in the intermediolateral cell column (IML), the main source of sympathetic outflow from the spinal cord. The effects of 5-HT receptor activation (which is known to enhance oscillatory activity in a variety of neural networks, e.g.
) on this rhythmic activity were determined. 10-12 day old Wistar rats were deeply anaesthetised with urethane (2g/kg I.P.) and transcardially perfused with ice cold buffer. The thoracic spinal cord was removed and transverse slices (500μm) were cut. Extracellular field recordings were made from the IML in the presence and absence of 5-HT receptor agonists, using glass micropipettes filled with a saline solution containing (in mM): NaCl (124), NaHCO
(26), glucose (10), KCl (3), NaH
O (2), CaCl
(2). Traces were amplified, filtered and digitised before being analysed offline using Spike2 software. Oscillations were considered to be present if the trace had a sinusoidal autocorrelogram and a defined peak in the power spectrum. The degree of oscillatory activity was quantified by the area under the power spectrum peak normalised to the total power at all frequencies (“normalised power”) expressed as a percentage. 12 of 27 slices (44.4%) displayed oscillatory activity (spontaneous or drug-induced) at a peak frequency of 8-17Hz (median=8.9Hz) in the region of the IML. Slices that did not oscillate under any conditions were not studied further. 10μM 5-HT significantly (paired t-test, n=6, p<0.05) enhanced the normalised power of the spontaneous oscillations to 41.3±16.9% compared to 27.8±13.4% in control. Furthermore, application of the specific 5-HT
agonist α-methyl-5-HT (10μM) mimicked this effect (n=3), increasing the power of the oscillations to 55.4±21.8% compared to 28.3±23.6% in control conditions. The oscillations could be attenuated by blocking synaptic transmission with 1μM TTX (normalised power= 18.0% in control, 4.3% in TTX, n=1) and also by the gap junction blocker carbenoxolone (100μM, normalised power=16.8% in control, 9.4% in drug, n=1). Our results demonstrate that oscillatory activity can be recorded from the IML of rat spinal cord slices in the 8-17Hz band. Furthermore, these oscillations can be enhanced by 5-HT, probably via the 5-HT
receptor, although a contribution from other subtypes cannot be ruled out. Preliminary data implicate roles for both chemical and electrical synaptic transmission in generating this activity.
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