THE EFFECTS OF ADENINE DINUCLEOTIDES ON EPILEPTIFORM ACTIVITY IN THE CA3 REGION OF RAT HIPPOCAMPAL SLICES F. M. ROSS,* M. J. BRODIE† and T. W. STONE*‡ *Institute of Biomedical and Life Sciences, Division of Neuroscience and Biomedical Systems, West Medical Building, University of Glasgow, Glasgow G12 8QQ, U.K. †Epilepsy Unit, Department of Medicine and Therapeutics, Western Infirmary, Glasgow G11 6NT, U.K. Abstract––Alpha, omega-adenine dinucleotides (Ap n A) consist of two adenosine molecules linked at the 5 position by phosphate groups, the number of which is denoted by n and can range from 2 to 6. The aim of this study was to investigate the effect of Ap 4 A and Ap 5 A on the rate of epileptiform activity. Hippocampal slices (450 μm), when perfused with a medium containing no added magnesium and 4-aminopyridine (50 μM), generate epileptiform activity of an interictal nature. Ap 4 A and Ap 5 A at 1 μM depressed the discharge rate to a significant extent. At this concentration adenosine (1 μM) did not produce any effect. However at 10 μM adenosine, Ap 4 A and Ap 5 A all decreased the burst frequency. Adenosine deaminase (0.2 U/ml) totally annulled the inhibition of epileptiform activity produced by 10 μM adenosine or 1 μM Ap 4 A and Ap 5 A. Adenosine deaminase did not significantly change the maximum depression of activity produced by 10 μM Ap 4 A and Ap 5 A. 8-cyclopentyl-1,3- dimethylxanthine, an A 1 , receptor antagonist, increased the basal rate of epileptiform activity and prevented the depression of burst discharges by Ap 4 A. 5-adenylic acid deaminase converts AMP into IMP which is inactive. 5-adenylic acid deaminase did not prevent the inhibitory effects of Ap 4 A. The results suggests that in the CA3 region of the hippocampus, Ap 4 A and Ap 5 A act partly by stimulating xanthine-sensitive receptors directly and partly through the formation of the metabolite, adenosine.  1998 IBRO. Published by Elsevier Science Ltd. Key words: ATP, purines, adenosine, adenine dinucleotides, dinucleotides, epileptiform activity. Alpha, omega-adenine dinucleotides (Ap n A) or dinu- cleoside polyphosphates consist of two adenosine molecules linked at their 5 region by a number of phosphate groups, with n denoting the number of phosphates. Diadenosine diphosphate (Ap 2 A) through to diadenosine hexaphosphate (Ap 6 A) are known to exist naturally. Since the first demonstra- tion that dinucleotides could influence tissue function by inducing contraction of smooth muscles 44 a role in extracellular communication has been established 4,13 with effects also being shown on platelet aggregation 15,23 and neuronal firing. Several reports exist describing the actions of dinucleotides in different regions of the CNS. The frequency of spontaneous action potentials in locus coeruleus neurons recorded from pontine slices was increased by diadenosine triphosphate (Ap 3 A), diadenosine teraphosphate (Ap 4 A) and diadenosine pentaphosphate (Ap 5 A). 10 Similarly Ap 4 A and Ap 5 A raised the level of excitation in nodose ganglion neurons. 25 In contrast the rate of firing of rat cortical neurons was depressed by Ap 5 A 45 and within the hippocampus Ap 4 A and Ap 5 A both depressed extra- cellular postsynaptic field potentials and intracellular postsynaptic currents to a similar extent. 20 However, in hippocampal CA3 neurons and whole brain synaptosomes Ap 5 A produced a reversible increase in the current through calcium channels. 31 This ability to increase intracellular calcium levels was also reported in deermouse brain 37 and midbrain synaptosomes. 35 In a previous study we have investigated the effect of nucleotides on a model of epileptiform activity (Ross et al., unpublished observations). 40 Due to the evidence that adenosine dinucleotides can exert an effect within the brain including the hippocampus, it was a natural progression to investigate whether Ap 4 A and Ap 5 A could influence the frequency of epileptiform activity in slices of rat hippocampus. EXPERIMENTAL PROCEDURES Male Wistar rats (180–250 g) (Harlan Olac) were anaes- thetized with urethane (1.3 g/kg) prior to being killed by ‡To whom correspondence should be addressed. A bbreviations: ACSF, artificial cerebrospinal fluid; AM- Pase, 5-adenylic acid deaminase; 4-AP, 4-aminopyridine; Ap 2 A, diadenosine diphosphate; Ap 3 A, diadenosine tri- phosphate; Ap 4 A, diadenosine teraphosphate; Ap 5 A, dia- denosine pentaphosphate; Ap 6 A, diadenosine hexaphos- phate; CPT, 8-cyclopentyl-1,3-dimethylxanthine; HPLC, high performance liquid chromatography; PPADS, pyridoxal-6-azophenyl-2,4-disulphonic acid. Pergamon N euroscience Vol. 85, No. 1, pp. 217–228, 1998 Copyright  1998 IBRO. Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved 0306–4522/98 $19.00+ 0.00 PII: S0306-4522(97)00619-2 217