Behavioural and neurochemical interactions of the AMPA antagonist GYKI 52466 and the non-competitive NMDA antagonist dizocilpine in rats. M. Bubser 1,*, T.
Journalof J Neural Transm [Gen Sect] (1995) 101:115-126
Neural Transmission 9 Springer-Verlag 1995 Printed in Austria
Behavioural and neurochemical interactions of the A M P A antagonist GYKI 52466 and the non-competitive N M D A antagonist dizocilpine in rats M. Bubser 1,*, T. Tzschentke 1, and W. Hauber 2 1Department of Neuropharmacology, Zoological Institute, University of T0bingen, Ttibingen, and 2Department of Animal Physiology, Biological Institute, University of Stuttgart, Stuttgart, Federal Republic of Germany Accepted December 12, 1994
Summary. The behavioural and neurochemical effects of the N-methyl-Daspartate (NMDA) antagonist dizocilpine and the a-amino-3-hydroxy-5methylisoxazole-4-propionic acid (AMPA) antagonist GYKI 52466, given alone or in combination, were investigated in rats. Locomotor activity was increased by dizocilpine (0.2 mg/kg), but not by GYKI 52466 (2.4 mg/kg). Dizocilpine-induced hyperlocomotion was reduced by co-administration of GYKI 52466. In dizocilpine-treated rats dopamine (DA) metabolism (measured as D O P A C [dihydroxyphenylacetic acid] or D O P A C / D A in post mortem brain tissue) was increased in the prefrontal cortex and nucleus accumbens. In GYK152466-treated rats serotonin was reduced in the prefrontal cortex and nucleus accumbens while D A metabolism was not affected. In rats treated with dizocilpine plus GYKI 52466, D A metabolism was increased only in the prefrontal cortex, but not in the nucleus accumbens, when compared with vehicle-treated animals. These data confirm that A M P A and N M D A antagonists do not have synergistic effects on locomotor activity. A differential role of N M D A and A M P A antagonists in the control of mesolimbic D A neurons will be discussed here. Keywords: GYKI 52466, dizocilpine, locomotion, dopamine, serotonin Introduction Glutamate is the major excitatory neurotransmitter in the brain and acts through at least five subclasses of receptors referred to as N M D A (N-methylD-aspartate), kainate (2-carboxy-4-isopropenyl-3-pyrolidine acetate), A M P A
*Present address: Netherlands Institute for Brain Research, Amsterdam, The Netherlands
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(o~-amino-3-hydroxy-5-methyl-4-isoxazolepropionate), trans-ACPD (trans-1amino-cyclopentyl-l,3-dicarboxylate) and L-AP4 (2-amino-4-phosphobutyrate) receptors (see Nicholls, 1993, for review). Blockade of the NMDA subtype of glutamate receptors by the non-competitive antagonist dizocilpine produces in rats a behavioural syndrome consisting of locomotor stimulation, stereotyped sniffing and, in higher doses, ataxia (see Schmidt et al., 1992, for review). As dizocilpine enhances mesocortical and mesolimbic DA metabolism (Rao et al., 1990; L6scher et al., 1991; Bubser et al., 1992) and it also increases burst firing of A10 dopaminergic neurons (French and Ceci, 1990), its stimulant actions may be mediated via ascending dopaminergic systems. In contrast to the pharmacological actions of NMDA antagonists, the behavioural and neurochemical effects of selective AMPA antagonists, such as NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)-quinoxaline) (Honor6 et al., 1988) or the 2,3-benzodiazepine GYKI 52466 (1-(4aminophenyl)-4-methyl-7,8-methylene-dioxy-5H-2,3-benzodiazepine) (Tarnawa et al., 1989) have been rarely investigated. Evidence from electrophysiological and ligand binding studies shows that both compounds potently block AMPA and kainate receptors without interacting with NMDA receptors (Honor6, 1991; Ouardouz and Durand, 1991). Like NMDA antagonists, AMPA antagonists are cerebroprotective and anticonvulsant (for review see Rogawski, 1993). However, in some behavioural models in which NMDA antagonists produce motor stimulation and antagonize neuroleptic-induced catalepsy (Schmidt and Bubser, 1989; Carlsson and Carlsson, 1990) AMPA antagonists are ineffective: AMPA antagonists fail to stimulate locomotion in naive rats (Hauber and Andersen, 1993) and in reserpine-treated mice (Starr and Starr, 1993) and they do not reverse (Zadow and Schmidt, 1994) or even increase neuroleptic-induced catalepsy (Papa et al., 1993). The neurochemical actions underlying these differential effects of NMDA and AMPA antagonists are largely unknown. To this end we studied the effects of a blockade of NMDA and AMPA receptors by dizocilpine and GYKI 52466, respectively, on spontaneous locomotor activity and on DA and serotonin (5-HT) metabolism in the medial prefrontal cortex, the nucleus accumbens and in the anterior and posterior striatum, i.e. in areas that have been implicated in the motor-stimulant actions of dizocilpine (L6scher et al., 1991; Bubser et al., 1992). Since GYKI 52466 has been shown to reduce dizocilpine-induced locomotion (Hauber and Andersen, 1993) we also investigated the effects of combined NMDA and AMPA receptor blockade. Materials and methods
Animals Subjects were 39 male Sprague-Dawley rats (Interfauna, Tuttlingen), weighing 190-210 g, which were habituated to the housing conditions (12 h light/dark cycle, lights on at 6.00 h, 20-22~ for 2 weeks. They were fed with commercial rat chow (12 g/animal per day) and received water ad lib. Experiments were carried out in the light phase (8-15 h).
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Drugs GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylene-dioxy-5H-2,3-benzodiazepine hydrochloride) was dissolved in sterile distilled water. (+)-Dizocilpine maleate was purchased from Biotrend (Cologne, Germany) and dissolved in 0.9% sterile saline. Sterile distilled water (H20) and saline served as vehicles for GYKI 52466 and dizocilpine, respectively. Drug doses refer to the respective salt.
Experimental design Rats were randomly divided into 4 groups that received one of the following treatments: a) H20 + saline (n = 10), b) H20 + dizocilpine (0.2 mg/kg) (n = 9), c) GYKI 52466 (2.4 mg/kg) + saline (n = 10), or d) GYKI 52466 (2.4 mg/kg) + dizocilpine (0.2 mg/kg) (n = 10). All drugs were administered intraperitoneally 30 minutes before behavioural testing in a volume of 1 ml/kg (Schmidt and Bubser, 1989; Hauber and Andersen, 1993). In higher doses both N M D A and AMPA antagonists induce muscle relaxation and ataxia (Willetts et al., 1990; Ornstein et al., 1993; Browne and McCulloch, 1994; Danysz et al., 1994) which may interfere with locomotor activity. Therefore GYKI 52466 and dizocilpine were used in doses not causing visible signs of ataxia or muscle relaxation when administered alone or in combination (Yamaguchi et al., 1993; Hauber and Andersen, 1993), but high enough to induce neurochemical effects detectable in post-mortem tissue.
Adaptation and behavioural testing Behavioural experiments were carried out in an open field (69 • 69 cm) surrounded by a wooden box. The open field was divided by lines into 9 squares and it was dimly illuminated by two red bulbs (2 • 20 W). A fan was used to mask external noise. One day before the experiment, rats were familiarised with the open field for 10 minutes in groups of 5 animals. On the following day, the rats received drug injections or the respective vehicles. Thirty minutes later, they were placed individually into the open field and their behaviour during a 5-minute-session was recorded on video tape. After the experiment, behavioural parameters were manually typed into a microcomputer for detailed analysis of locomotor activity (number of line crossings) and rearing.
Monoamine measurements Rats were decapitated immediately after the open field experiment. Subsequently, their brains were removed from the skull and placed into ice-cold saline for 60 s. A cooled cutting block was used to prepare brain slices for the dissection of prefrontal cortex, nucleus accumbens, anterior striatum and posterior striatum (Heffner et al., 1980; Bubser et al., 1992). Tissue samples were rapidly dissected, weighed and stored in liquid nitrogen until chromatographic analysis. The tissue content of DA, 5-HT and some of their metabolites (dihydroxyphenylacetic acid [DOPAC], homovanillic acid [HVA] and 5-hydroxyindoleacetic acid [5-HIAA]) was determined by high-performance liquid chromatography with electrochemical detection as described previously (Kilpatrick et al., 1986; Bubser and Koch, 1994).
Statistics Data are presented as means + S.E.M. Statistical analyses were made by one-way analysis of variance (ANOVA) followed by Tukey's protected t-test and by simple correlation analysis. A p-value
