BRAIN RESEARCH ELSEVIER Brain Research 679 (1995) 184-187 Short communication Inhibition of nitric oxide synthase dramatically potentiates seizures induced by kainic acid and pilocarpine in rats Roberto Maggio a,*, Fabio Fumagalli h, Eugenio Donati h Pascaline Barbier a Giorgio Racagni b, Giovanni U. Corsini c, Marco Riva d a Institute of Pharmacology, School of Medicine, University ofPisa, Vta Roma 55, 56100 Pisa, Italy b Center for Neuropharmacology, Institute of Pharmacological Sciences, University of Milan, Milan, Italy c Associazione 'Anni Verdi', Via Q. Maiorana 145, 00152 Rome, Italy d DIBIT, San Raffaele Hospital, Milan, Italy Accepted 7 February 1995 Abstract We investigated whether the severity of convulsions evoked by kainic acid and pilocarpine is modified in nitric oxide synthase inhibitor-treated rats. We found that chronic treatment (4 days) with Nw-nitro-L-arginine greatly potentiates seizures induced by both convulsants suggesting a potential role for nitric oxide in mechanisms regulating seizure induction and propagation. Keywords: Nitric oxide; Seizure; Pilocarpine; Kainic acid; N-Methyl-D-aspartate receptor; Nitro-L-arginine Nitric oxide (NO) is regarded as one of the major neuronal messengers in brain and peripheral tissues [10]. NO is generated by the enzyme NO-synthase which, by histochemical studies, was shown to occur widely in the central nervous system [15]. Within the brain NO can act as a neurotransmitter by stimulating the soluble guanylate cyclase to form cyclic guanosine 3',5'-monophosphate (cGMP) [10]. NO has been implicated in some forms of synaptic plasticity as well as in pathological conditions involving an overstimulation of glutamate receptors, mainly of the NMDA type [5,15]. Epilepsy is one of the diseases in which excitatory aminoacids are implicated and NO could be an important pathogenetic component in the mechanisms that regulate seizure induction, propaga- tion and progression. The enzyme NO-synthase can be blocked by argi- nine analogues such as nitro-L-arginine and these drugs can be used as a tool to investigate the role of nitric oxide in different cellular mechanisms [6,10]. In the present report we have therefore investigated whether inhibition of NO-synthase would affect limbic motor seizures induced by intraperitoneal injection of kainic acid or pilocarpine. * Corresponding author. Fax: (39) (50) 55-1434. 0006-8993/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0006-8993(95)00217-0 Animals. Adult male Sprague-Dawley albinos rats (Charles River, Italy), weighing 200-250 g were used. The animals were housed in groups of 5 per cage under environmentally controlled conditions (12 h light/dark cycle with light on between 08.00 and 20.00 h, ambient temperature 21-23 ° C), with food and water ad libitum. All experiments were conducted during the light cycle in awake freely moving animals. Drug administration. NwNitro-L-arginine (nitro-L- arginine) was dissolved in saline and injected intraperi- toneally (i.p.) in doses of 5, 25 or 50 mg/kg, twice daily (12 h apart), for four days. Kainic acid and pilocarpine were dissolved in saline and injected i.p. The doses used were 10 mg/kg of kainic acid and 200 or 400 mg/kg of pilocarpine. Control rats were treated with saline. Animals injected with pilocarpine were pretreated with atropine in order to reduce the peripheric symp- toms. Atropine was dissolved in distilled water and injected subcutaneously in a dose of 1 mg/kg, 30 min before pilocarpine treatment. All products were purchased by Sigma. Seizure testing. The kainic acid model of seizures was scored as follows: 0.5 = facial myoclonus and forepaw myoclonus; 1 = clonic seizures, lasting at least 15 s with forelimb clonus, rearing and occasionally falling; 2 = explosive clonic seizures with wild running;