Proceedings of The Physiological Society

University of Leeds (2002) J Physiol 544P, S009

Communications

Activation of adenosine A2A receptors in the intermediolateral cell column (IML) enhances inhibitory but not excitatory synaptic transmission

R.E. Brooke, J. Deuchars and S.A. Deuchars

School of Biomedical Sciences, University of Leeds, Leeds LS2 9NQ, UK


Adenosine is an important neuromodulator in the CNS. Its actions are mediated via G-protein-coupled receptors classified as A1, A2A, A2B and A3. When administered intrathecally, agonists at the A1R (Koh et al. 1996) and A2AR (Koh et al. 2000) decrease blood pressure and heart rate. Deuchars et al. (2001) determined the presence and function of A1Rs in the IML but since the neuronal circuitry mediating the A2AR effect is unclear we studied the distribution and role of A2ARs in the spinal cord.

For immunohistochemical studies, rats (100-150 g) were injected intraperitoneally with 0.1 ml 1 % Fluorogold and 7 days later were humanely killed by Sagatal (60 mg kg-1 I.P.) and perfused transcardially with 4 % paraformaldehyde/0.1-0.5 % glutaraldehyde. Thoracic spinal cord slices (50 mm) were cut and incubated in anti-A2AR antibody (Santa Cruz, Biotechnology) followed by a Cy3 conjugated secondary antibody. A2AR immunoreactivity was observed throughout the spinal cord. Intense punctate staining was observed in a compact region of the IML. These punctate structures, suggestive of terminals, apposed Fluorogold labelled sympathetic preganglionic neurones (SPNs). For electro-physiology, thoracic spinal cord slices (250 mm) from terminally urethane-anaesthetised (2 g kg-1 I.P.) 10- to 12-day-old rats were submerged in ACSF equilibrated with 95 % O2 and 5 % CO2 at 20°C. Whole-cell recordings were made from SPNs and interneurones in the IML, identified by electrophysiology and histology. Bath application of the A2AR agonist CGS-21680 (1 mM) had no significant effect (Student's paired t test) on EPSPs evoked by stimulation of the lateral funiculus but significantly enhanced the amplitude of bicuculline and strychnine sensitive IPSPs (control 5.1 ± 0.6 mV, CGS-21680 7.2 ± 0.8 mV, mean ± S.E.M., n = 19, P

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