Expression of adenosine A2a receptor gene in rat dorsal root and autonomic ganglia Alain Kaelin-Lang*, Theres Lauterburg, Jean-Marc Burgunder Neuromorphological Laboratory, Department of Neurology, University Hospital, Inselspital, CH-3010 Bern, Switzerland Received 23 February 1998; accepted 2 March 1998 Abstract The adenosine A2a receptors (A2aR) play an important role in the purinergic mediated neuromodulation. The presence of A2aR in the brain is well established. In contrast, little is known about their expression in the periphery. The purpose of this study was to investigate the expression of A2aR gene in the autonomic (otic, sphenopalatine, ciliary, cervical superior ganglia and carotid body) and in the dorsal root ganglia of normal rat. Hybridization histochemistry with S 35 -labelled radioactive oligonucleo- tide probes was used. An expression of A2aR gene was found in the large neuronal cells of the rat dorsal root ganglia. The satellite cells showed no expression of A2aR gene. In the superior cervical ganglion, isolated ganglion cells expressed A2aR. In the carotid body clusters of cells with a strong A2aR gene expression were found. In contrast, the ciliary and otic ganglia did not expressed A2aR gene, and only few small sized A2aR expressing cells were demonstrated in the sphenopalatine ganglion. The discrete distribution of A2aR gene expression in the peripheral nervous system speaks for a role of this receptor in the purinergic modulation of sensory information as well as in the sympathetic nervous system.  1998 Published by Elsevier Science Ireland Ltd. Keywords: Adenosine; A2a receptors; Rat; Peripheral nervous system; Autonomic ganglia; Spinal ganglia The extracellular nucleoside adenosine (A) plays a role in the pre- and postsynaptic modulation of neuronal activity through several membrane receptors. Four receptors-sub- types have been cloned: the A1, A2a, A2b and A3 receptors [9]. The presence of high affinity A2a adenosine receptors (A2aR) in the central nervous system, particularly in the striatum is well known. In contrast, little is known about the presence of the A2a receptors in the peripheral nervous system, although pharmacological and physiological studies suggest a function of A2a receptors in the transmission of nociception [2] as well as in the control of vegetative func- tions [10]. In the developing rat nervous system a wide- spread, partly transient distribution of A2aR was found [15] and a RT-PCR study on tissue homogenates [7] has shown the presence of A2aR mRNA in several peripheral tissue. However, the cellular localisation of the A2a receptors in the peripheral nervous system is not known. The aim of the present study was to investigate the expres- sion of A2aR gene in peripheral ganglia. Tissue samples included both sympathetic (superior cervical ganglion) and parasympathetic ganglia (otic, ciliary and sphenopala- tine ganglia) as well as primary sensory ganglia (dorsal root ganglia). Adult female Wistar rats were killed by decapitation under carbon dioxide anaesthesia. The dorsal root ganglia were rapidly removed, frozen on dry ice or in nitrogen- cooled isopentane and kept at -70°C until further proces- sing. Seven other adult male Wistar rats (200–250 g) were anaesthetized with intraperitoneal injection of sodium pen- tobarbital (50 mg/kg). They were killed by bleeding. Otic, sphenopalatine, ciliary and cervical superior ganglia were quickly removed and frozen in nitrogen-cooled isopentane. They were kept at -70°C until further use. The in situ hybri- dization histochemistry was done according to [16]. Briefly, series of 12 mm adjacent sections were mounted onto gela- tin-coated slides. After fixation with 4% formaldehyde in phosphate buffered saline (PBS), the sections were washed twice in PBS. They were then placed in 0.25% acetic anhy- Neuroscience Letters 246 (1998) 21–24 0304-3940/98/$19.00  1998 Published by Elsevier Science Ireland Ltd. All rights reserved PII S0304-3940(98)00216-X * Corresponding author. Tel.: +41 31 6322111; fax: +41 31 6329679; e-mail: alain.kaelin@dkf6.unibe.ch