Pharmacological Reports Copyright © 2013 2013, 65, 11941203 by Institute of Pharmacology ISSN 1734-1140 Polish Academy of Sciences
Contribution of the mGluR7 receptor to antiparkinsonian-like effects in rats: a behavioral study with the selective agonist AMN082
Jolanta Konieczny, Tomasz Lenda
Department of Neuropsychopharmacology, Institute of Pharmacology, Polish Academy of Sciences, Smêtna 12, PL 31-343 Kraków, Poland
Correspondence: Jolanta Konieczny, e-mail address: [email protected]
Abstract: Background: Metabotropic glutamate receptors (mGluRs) have been shown to be potential targets for numerous neurological dis- eases, including Parkinson’s disease (PD). We previously reported that ACPT-1, a non-selective group III mGluRs agonist, injected locally into the globus pallidus, striatum or substantia nigra pars reticulata (SNr), significantly attenuated the haloperidol-induced catalepsy in rats. N,N’-dibenzhydryl-ethane-1,2-diamine dihydrochloride (AMN082) is a potent, brain penetrating mGluR7 agonist, selective over other mGluRs. Methods: The aim of the present study was to determine whether (1) activation of mGluR7 by systemic administration of AMN082 may produce antiparkinsonian-like effects in the haloperidol-induced catalepsy and reserpine-induced akinesia models in rats; (2) striatal and nigral mGluR7 is likely to contribute to such an effect. Results: We found that AMN082 (1 and 3 mg/kg) decreased the haloperidol (0.25 mg/kg)-induced catalepsy, but was not efficient in attenuating the reserpine (2.5 mg/kg)-induced akinesia. When given locally, AMN082 also significantly diminished catalepsy in rats; however, its effective striatal doses were 10-fold lower than those used in the SNr (2.5 and 7.5 pmol/0.5 µl/ side vs. 25 and 75 pmol/0.5 µl/side, respectively). Conclusion: The above findings support the idea that the activation of mGluR7 can produce antiparkinsonian-like effects in rats. Furthermore, our results indicate contribution of both striatal and nigral mGluR7 to the anticataleptic effects of AMN082.
Key words: Parkinson’s disease, metabotropic glutamate receptor, AMN082, basal ganglia, catalepsy, akinesia
Abbreviations: AMN082 – N,N’-dibenzhydryl-ethane-1,2- Introduction diamine dihydrochloride, BG – basal ganglia, DA – dopamine, DAT – dopamine transporter, Met-1 – N-benzhydryleth- ane-1,2-diamine, mGluRs – metabotropic glutamate receptors, Glutamate is the main excitatory neurotransmitter in a-MT – a-methyl-p-tyrosine, NET – norepinephrine trans- porter, 6-OHDA – 6-hydroxydopamine, PD – Parkinson’s dis- the central nervous system, its action being mediated ease, SERT – serotonin transporter, SNr – substantia nigra pars by both ionotropic and metabotropic glutamate recep- reticulata tors (mGluRs). To date, eight subtypes of mGluRs
1194 Pharmacological Reports, 2013, 65, 11941203 Antiparkinsonian-like effects of AMN082 in rats Jolanta Konieczny and Tomasz Lenda
(mGluR1–8) have been cloned and subdivided into SNr. Only one study showed an antiakinetic effect of three groups (I–III) on the basis of their sequence ho- intranigral administration of AMN082 in a reserpine mology, pharmacological profile and signal transduc- model [7]; however, it has not yet been ascertained tion mechanism [38]. Group III mGluRs (mGluR4, 6, whether beneficial effects are observed after periph- 7, 8) are localized mainly presynaptically at glutama- eral administration of AMN082. Therefore, the aim of tergic and GABAergic terminals [4–6, 14, 18] where the present study was to compare (1) potential they regulate the release of glutamate and GABA [23, antiparkinsonian-like effects of systemic administra- 35, 40, 43]. A growing body of evidence suggests that tion of AMN082 in two animal models of PD, i.e., the group III mGluRs may be potential targets for the haloperidol-induced catalepsy and reserpine-induced treatment of Parkinson’s disease (PD). In fact, three akinesia in rats; (2) the effects of mGluR7 activation members of group III mGluRs (mGluR4, 7, 8) are in the striatum and SNr in the haloperidol-induced widely expressed in the basal ganglia (BG), a group model of catalepsy in rats. Part of these data were of brain nuclei which are involved in the control of previously presented in the form of an abstract [15]. motor functions and are critical to the motor deficits observed in PD. Like other group III mGluRs, mGluR7 is located mainly presynaptically at the active zone of glutama- tergic and GABAergic terminals [4, 14, 28, 38]. Be- Materials and Methods cause of the low affinity of mGluR7 for glutamate, this receptor needs a high concentration of glutamate for its activation [14, 37]. The density of mGluR7 Animals within the BG is the highest in the striatum and sub- stantia nigra pars reticulata (SNr) [18, 24], i.e., struc- The experiment was performed on male Wistar rats tures which receive glutamatergic inputs from the (250–320 g). The animals were kept in a well- cortex and subthalamic nucleus, respectively. Since ventilated room on an artificial 12-h light/dark cycle glutamatergic corticostriatal and subthalamonigral (the light on from 7 a.m. to 7 p.m.) at a room tempera- pathways are thought to be overactive in parkinsonian ture of 21–22°C, with free access to food and water. condition, the reduction of glutamate release by acti- All experiments were carried out in compliance with vation of mGluR7 at the terminals of these pathways the Animal Protection Act of August 21, 1997 (pub- may be of significant importance in attenuating PD lished in Poland’s Current Legislation Gazette [Dzien- symptoms. So far, however, this receptor has been the nik Ustaw] no. 111/197, item 724), and according to least frequently studied target for potential antiparkin- the National Institutes of Health Guide for the Care sonian drugs because of the lack of highly selective and Use of Laboratory Animals, and were approved ligands. by the Institute’s Local Bioethics Commission. N,N’-dibenzhydrylethane-1,2-diamine dihydrochlo- ride (AMN082) is a very potent and brain penetrating mGluR7 agonist. This compound (< 10 µM) fails to Drugs show appreciable effects at other mGluRs [25]. Thanks to its binding site within the transmembrane Haloperidol (Polfa, Warszawa, Poland; ampoules of domain of mGluR7, AMN082 acts like an allosteric 5 mg/1 ml) was diluted to a concentration of 0.25 mg/ agonist. A previous study showed some antiparkinso- kg with distilled water. Reserpine (Polfa, Warszawa, nian-like effects of the systemically and intrastriatally Poland) was dissolved in a solution containing administered AMN082 [10]. However, there are still a 0.25% citric acid, a 2% benzyl alcohol and a 10% some controversies regarding the involvement of Tween 80; a-methyl-p-tyrosine (a-MT; Sigma- Aldrich, nigral mGluR7 in the therapeutic effects of mGluR7 St. Louis, MO, USA) was dissolved in distilled water. agonists. Using high doses of non-selective group III AMN082 (Ascent Scientific, Bristol, UK) was dis- agonists, most of the studies have indirectly demon- persed in a suspension of a 0.5% methylcellulose for strated either anti-parkinsonian [2, 22] or pro-parkin- systemic administration, or was dissolved in a 50% sonian-like effects [21] of mGluR7 activation in the DMSO for intracerebral injection.
Pharmacological Reports, 2013, 65, 11941203 1195 Fig. 1. Localization of cannula tips in the striatum (A) and the SNr (B) on the coronal section of the rat brain. Each symbol (x) in- dicates cannula placement in one animal on one side
Surgery and intracranial injection Higher doses of the drug induced the maximal cata- lepsy in our test, which made it impossible to evaluate The animals were operated under pentobarbital anes- the conceivable procataleptic effect of AMN082. thesia (Vetbutal; 30 mg/kg ip; Biowet, Pu³awy, Po- The animals were divided into three groups. The land). Two guide cannulae (11.9 mm long; 0.4 mm first group (66 animals) was given AMN082 (1–10 mg/ o.d.) were bilaterally implanted in the striatum or SNr. kg ip) or solvent systemically, and the second (47 ani- Intracerebral injections of the drug were made to con- mals) and third groups (64 animals) were locally in- scious animals using Hamilton microsyringes con- jected with AMN082 or solvent into the striatum nected, via polyethylene tubing, to two inner cannulae (0.5–2.5 nmol/0.5 µl/side) or SNr (2.5–75 pmol/0.5 µl/ (0.3 mm o.d.) which protruded by 0.7 mm (striatum) side), respectively, 60 min after haloperidol admini- or 2.1 mm (SNr) from the guide cannulae. Cannulae stration. Each animal received only one injection and tips were placed in the rostral striatum (A/P = +1.6; was tested only once. Since the experiment with sys- L = ±2.4 mm; D/V = –6.0 from the bregma) or SNr temic administration of the highest dose of AMN082 (A/P = –5.6; L = ±2.0; D/V = –8.4 from the bregma) (10 mg/kg) was performed at a different time than that (Figs. 1A, B) [32]. The injections (0.5 µl/side) lasted with the other doses, we used a separate haloperidol- 60 s, and the cannulae were left in place for another treated group for that study. 60 s to allow diffusion. Localization of all the cannula Catalepsy was determined using a 9-cm cork test. tips was checked histologically on frozen coronal Both forepaws of a rat were put on a cork and descent slices of the brain. All the rats used for the data analy- latency was measured 3 times at most, for up to 300 s ses had injection cannula tips located bilaterally in the each time. The longest time of keeping at least one striatum or SNr. forepaw on the cork was accepted as a catalepsy score. The test was evaluated twice: at 30 and 60 min Behavioral experiments after systemic administration of AMN082 (90 and 120 min after haloperidol), or at 15 and 30 min after Catalepsy intracerebral injection of that compound (75 and 90 min after haloperidol). A total of 177 rats were included in this study. Cata- lepsy was induced with haloperidol (0.25 mg/kg ip) in Locomotor activity all the animals tested. The dose of haloperidol was se- lected on the basis of our earlier findings, because it A total of 34 rats were included in this study. To induce produced catalepsy below the cut-off time (300 s). akinesia, the rats were treated systemically with
1196 Pharmacological Reports, 2013, 65, 11941203 Antiparkinsonian-like effects of AMN082 in rats Jolanta Konieczny and Tomasz Lenda
Fig. 2. The influence of systemic administration of AMN082 in doses of 1 and 3 mg/kg (A) or 10 mg/kg (B) on the haloperidol-induced catalepsy in rats. AMN082 (1–10 mg/kg ip) was administered 60 min after haloperidol (0.25 mg/kg ip). Catalepsy was estimated twice: at 30 and 60 min after AMN082. The values are the mean ± SEM. Statistics: the Kruskal-Wallis and the Mann-Whitney U tests. Symbols indicate the significance of differences in the Mann-Whitney U test: * p < 0.05, ** p < 0.01, *** p < 0.001 vs. control; ^ p < 0.05, ^^ p < 0.01 vs. haloperidol. The number of animals per group is given in parentheses
Fig. 3. The influence of local administration of AMN082 on the haloperidol-induced catalepsy. AMN082 was administered bilaterally into (A) the striatum (0.5 pmol to 25 pmol/0.5 µl/side) or (B) SNr (2.5 to 75 pmol/0.5 µl/side) 60 min after haloperidol (0.25 mg/kg ip). Catalepsy was esti- mated twice: at 15 and 30 min after AMN082 (doses higher than 75 pmol/0.5 µl/side are not shown in the figure). The values are the mean ± SEM. Statistics: the Kruskal-Wallis and the Mann-Whitney U tests. Symbols indicate the significance of differences in the Mann-Whitney U test: * p < 0.05, ** p < 0.01, *** p < 0.001 vs. control (group which locally received solvent instead of AMN082); ^ p < 0.05 vs. haloperidol & + 0.25 mg/kg (group which locally received solvent instead of AMN082); p < 0.05 vs. haloperidol + AMN082 25 pmol/0.5 µl/side; p < 0.05 vs. haloperidol + AMN082 2.5 pmol/0.5 µl/side. The number of animals per group is given in parentheses
Pharmacological Reports, 2013, 65, 11941203 1197 reserpine (2.5 mg/kg ip), and 16 h later with a-MT For the statistical evaluation of locomotor activity, (125 mg/kg ip). AMN082 (1 and 3 mg/kg ip) was a one-way ANOVA was used, followed – when the given 19.5 h after reserpine (3.5 h after a-MT). Control F-ratio was significant (p < 0.05) – by the Tukey rats received solvents instead of reserpine or AMN082. post-hoc test. Akinesia was recorded in Opto-Varimex cages (Co- lumbus Instruments, Columbus, OH), linked on-line to a compatible IBM computer. Each cage (43 × 44 × 25 cm) was surrounded with a 15 × 15 array of photo- cell beams located 3 cm above the floor surface. Results Three parameters were estimated: the distance trav- elled, which expressed horizontal locomotor activity (in cm); the ambulation time, and the resting time (in s). The effect of systemic administration of The rats were injected with AMN082 in their home AMN082 on the haloperidol-induced catalepsy cages. Thirty min later, the animals were individually placed in locomotor activity chambers. Immediately Haloperidol (0.25 mg/kg) injected ip to rats induced afterwards, the locomotor activity was recorded every moderate catalepsy, measured 90 and 120 min after its 15 min and measured for 60 min. The obtained data administration (Fig. 2A, B). AMN082 (3 mg/kg), ad- were analyzed using Auto-Track software (Columbus ministered systemically, markedly decreased the Instruments). haloperidol-induced catalepsy at the time points of 30 and 60 min (Fig. 2A). The effect of its lower dose Statistical analysis (1 mg/kg) was weaker and disappeared after 60 min. In contrast, the highest dose of AMN082 (10 mg/kg) The statistical analysis of catalepsy was carried out by produced no effect at all (Fig. 2B). AMN082 alone the Kruskal-Wallis and the Mann-Whitney U tests. (10 mg/kg) did not induce catalepsy in rats (Fig. 2B).
Fig. 4. The influence of systemic admini- stration of AMN082 on the reserpine- induced akinesia. The rats were treated systemically with reserpine (2.5 mg/kg ip) and 16 h later with a-MT (125 mg/kg ip). AMN082 (1 and 3 mg/ kg ip) was given 19.5 h after reserpine. Measurements started 30 min after AMN082 administration and locomotor activity was recorded for 60 min. The values are the mean ± SEM. Statistics: a one-way ANOVA, followed, when the F-ratio was significant (p < 0.05), by the Tukey post- hoc test. Symbols indi- cate the significance of differences in the Tukey post-hoc test: * p < 0.05 vs. control. The number of animals per group is given in parentheses
1198 Pharmacological Reports, 2013, 65, 11941203 Antiparkinsonian-like effects of AMN082 in rats Jolanta Konieczny and Tomasz Lenda
The effect of local administration of AMN082 parkinsonian effects of the AMN082-induced selec- on the haloperidol-induced catalepsy in rats tive mGluR7 activation. It was found that AMN082 attenuated the haloperidol-induced catalepsy after Catalepsy was measured in two groups of rats 75 and both systemic and local administration. In contrast, 90 min after haloperidol injection. Interestingly, the in- AMN082 was not effective in reducing the reserpine- tensity of catalepsy differed between the groups: the induced akinesia following systemic administration. group with cannulae implanted in the striatum showed These data are consistent with our earlier findings catalepsy twice as strong as that when cannulae were showing anticataleptic effects of the non-subtype- implanted in the SNr (Figs. 3A, B). However, the latter results were not surprising, since a similar effect was selective group III mGluR agonist ACPT-1 given into observed in our earlier study [18]. AMN082 (2.5 and rat striatum, GP or SNr [17], and with other authors 7.5 pmol/0.5 µl/side) injected into the striatum mark- studies demonstrating antiparkinsonian-like effects of edly attenuated the haloperidol-induced catalepsy (Fig. group III agonists, given systemically or intracere- 3A). A potent effect of AMN082 was observed only 15 brally, in various animal PD models [2, 3, 22, 40]. min after its administration, but a tendency to reduce The potent anticataleptic effect of AMN082 (1 and catalepsy was still present at 30 min after injection. 3 mg/kg) observed in our study is in line with the ob- The lowest (0.5 pmol/0.5 µl/side) and higher doses (25 servations of Greco et al. [10], who found a similar ef- pmol, 0.25 nmol and 2.5 nmol/0.5 µl/side) of AMN082 fect after oral administration of AMN082. Although did not wholly abolish catalepsy in animals (the data on we did not confirm our findings using knock-out doses higher than 25 pmol/0.5 µl/side are not shown). models, it was shown that the anticataleptic effect of Similarly, local administration of AMN082 into the SNr AMN082 was absent in mGluR7 knockout mice [10], decreased the haloperidol-induced catalepsy in rats which clearly demonstrates involvement of the recep- (Fig. 3B); however, 10-fold higher doses of AMN082 tor in these effects. In contrast, the higher dose of (25 and 75 pmol/0.5 µl/side) than those effective in the AMN082 (10 mg/kg) used in our study was not effec- striatum were necessary to evoke an anticataleptic ef- tive in attenuating catalepsy and it decreased locomo- fect. AMN082 administered alone into the striatum (2.5 tor activity in both wild-type [31] and knock-out mice pmol/0.5 µl/side) or the SNr (2.5 and 25 pmol/0.5 [30]; hence other mechanisms, unrelated to mGluR7, µl/side) did not evoke catalepsy in rats (Figs. 3A, B). may actually participate in these effects. Direct inhibi- tion of dopamine (DA) nigrostriatal transmission can The effect of systemic administration of AMN082 be excluded, since AMN082 at doses up to 20 mg/kg on the reserpine-induced akinesia in rats failed to alter extracellular DA levels in the striatum or nucleus accumbens [19, 20]. On the other hand, Reserpine (2.5 mg/kg) administered in combination with AMN082 is rapidly metabolized to a major metabo- a-MT (125 mg/kg) induced strong akinesia in rats, lite, N-benzhydrylethane-1,2-diamine (Met-1), in rat measured as a marked decrease in the distance travelled liver [40]. Although Met-1 shows appreciable affinity and the ambulation time, and as a distinct increase in the for the serotonin transporter (SERT), DA transporter resting time (Fig. 4). AMN082 given in doses that ef- (DAT) and norepinephrine transporter (NET) (323, fectively attenuated the haloperidol-induced catalepsy 3020 and 3410 nM, respectively) [40], involvement of (1 and 3 mg/kg) did not change any parameters meas- SERT and NET blockade in the beneficial effect of ured. AMN082 (3 mg/kg) given alone had no influence AMN082 seems doubtful, given that selective SERT on locomotor activity in comparison with control rats. and NET inhibitors fail to reverse locomotor deficits Since AMN082 given systemically did not affect any in MPTP-treated marmosets [11]. In contrast, selec- akinesia symptoms, the effects of local administration tive DAT inhibitors abolish akinesia in this model [11, were not examined in the reserpine model. 33]; however, since the affinity of Met-1 for DAT is ca. 10 times lower than for SERT, a potential benefit of DAT inhibition may be masked by the effects in- duced by SERT blockade. Furthermore, DAT inhibi- Discussion tors are known to elevate extracellular DA levels in the striatum and to potentiate locomotion [13, 26]. In the present study, we used rat haloperidol and re- Since AMN082 is unable to increase either striatal serpine models of PD to investigate potential anti- DA release [20] or locomotion (our study), its effect
Pharmacological Reports, 2013, 65, 11941203 1199 related to DAT inhibition also seems questionable. observed in the application site of AMN082, i.e., the Moreover, it should be stressed that peak concentra- rostral part of the ventrolateral striatum in our study tions of AMN082 in the brain were observed at vs. the more caudal dorsolateral area in the experi- 30 min after treatment [39], i.e., when the anticatalep- ment of Greco et al. It is noteworthy that 6- tic effect was the strongest. Given that the brain levels hydroxydopamine (6-OHDA) administered into the of AMN082 and Met-1 were similar at that time [39], ventrolateral striatum dramatically increased the re- and that the agonistic potency of AMN082 at mGluR7 sponse initiation time in a lever pressing paradigm was about 100-fold higher than that of Met-1 (EC50 of even in animals with mild DA depletion [9], which 66–81 nM and 5936 nM, respectively) [25, 39], these may suggest that the examined region is particularly findings strongly suggest that AMN082 is responsible responsible for such deficits. for the above-described effect. However, it cannot be Outside the striatum, immunocytochemical studies excluded that the decrease in locomotion after doses gathered evidence for the presence of mGluR7 on ter- of AMN082 higher than those effective in attenuating minals of GABA-ergic striatopallidal or glutamatergic catalepsy, or the antidepressant-like effects visible subthalamonigral projections [5, 18] which seem to a few hours after AMN082 administration [31] may be hyperactive in the parkinsonian condition. Hence, be off-target effects (e.g., they may be due to the ac- activation of pallidal and nigral mGluR7 should de- tion of Met-1 on SERT or NET). crease parkinsonian-like symptoms by reducing The anticataleptic effects of AMN082, observed GABA or glutamate release, respectively. On the after local administration of the compound, strengthen other hand, activation of mGluR7 localized on termi- the hypothesis that striatal and nigral mGluR7 con- nals of the GABAergic striatonigral pathways [18], tribute to the effect of the systemically administered whose activity seems to be decreased in PD, may AMN082. In fact, mGluR7 is the most abundant in counteract antiparkinsonian effects by stimulating the the striatum [18, 24], being located mostly on termi- SNr [43]. Participation of the pallidal mGluR7 in nals of the glutamatergic corticostriatal pathway antiparkinsonian-like effects seems rather doubtful, where its activation may inhibit glutamate release. In- since AMN082 administered directly into the GP does terestingly, the U-shaped dose-dependence and the in- not decrease the haloperidol-induced catalepsy in rats efficiency of higher doses of AMN082 to attenuate [10]. On the other hand, the existing studies with high catalepsy have been observed after both systemic and doses of non-selective group III agonists suggest ei- intrastriatal injection of the compound, which is gen- ther anti-parkinsonian [2, 22] or pro-parkinsonian-like erally attributed to the receptor desensitization due to effects [21] of mGluR7 activation in the SNr. Hence, prolonged agonist exposure. In fact, several studies it is of vital importance to verify the results concern- with orthosteric agonists of group III mGluR have ing participation of nigral mGluR7 in the beneficial shown similar effects [2, 40, 41]. Hence, our findings effects of group III mGluR agonists in view of such confirm a previous in vitro study [34] that AMN082 conflicting reports. may produce potent mGluR7 internalization. This It is likely that the SNr is very sensitive to any may be related to the ability of AMN082 to fully acti- pharmacological manipulations, since even applica- vate mGluR7 through an allosteric site [25] in con- tion of physiological saline to this structure may in- trast to most allosteric modulators which do not di- duce stereotyped behavior in rats [8]. In fact, the in- rectly activate the receptor but rather enhance the ef- tensity of catalepsy in rats injected with the solvent fects of endogenous agonists. These results may be of into the SNr was twice as weak compared to the ani- basic clinical significance, since they suggest that mals injected with the solvent into the striatum. On long-term treatment with mGluR7 agonists, even the other hand, the intranigral doses of AMN082 and those acting via an allosteric site, may decrease their ACPT-1 [17] effective in decreasing catalepsy were effectiveness. Surprisingly, the effective anticataleptic much higher than those efficient in the striatum. It is doses of the intrastriatally administered AMN082 (2.5 likely that the pro-parkinsonian-like effects of low and 7.5 pmol/0.5 µl/side) were much lower than its ef- doses (compared to the intrastriatal ones) of the intra- fective doses (0.1 and 0.5 nmol/0.5 µl/side), as re- nigrally administered AP4 and ACPT-1, regarded as ported by Greco et al. [10]. Such a discrepancy may potentiation of motor impairment in the reaction-time be due to the higher dose of haloperidol used by the task in 6-OHDA-treated rats [21], may be caused by latter authors. Furthermore, some differences were the dominant influence on the striatonigral pathway.
1200 Pharmacological Reports, 2013, 65, 11941203 Antiparkinsonian-like effects of AMN082 in rats Jolanta Konieczny and Tomasz Lenda
In line with the above assumption, an electrophysio- model, reversed by the nonselective group III antago- logical study with high concentrations of L-AP4 nist CPPG [7]. The above results also confirm the hy- showed that inhibition of glutamatergic transmission pothesis that under conditions of DA deficiency, in the SNr required a higher concentration of L-AP4 group III agonists may preferentially act on receptors than did reduction of GABAergic transmission in that localized on subthalamonigral terminals. However, structure [43]. Another cause of the discrepancy be- the extremely high effective doses of AMN082 used tween the present and the above-mentioned study may in the study (100–300 nmol) can activate other group lie in different PD models used in the two experi- III mGluRs, e.g., mGluR4. Indeed, in contrast to ments, i.e., a haloperidol vs. a 6-OHDA model. It has mGluR7, mGluR4 is fairly sparse at the striatonigral been demonstrated that nigral tonic DA levels may synapse [4, 18], which indicates that mGluR4 can modulate the function of presynaptic group III more selectively modulate the subthalamonigral path- mGluRs in the SNr [44]. Importantly, DA depletion way. Accordingly, studies with some more selective by reserpine or the blockade of DA receptors by ha- positive allosteric modulators of mGluR4 given sys- loperidol decreases the ability of group III mGluR temically, icv or into the SNr demonstrated a potent agonists to attenuate the inhibitory GABA-ergic tran- antiakinetic effect in reserpine-treated rats [7, 23, 27]. simission, but not the glutamatergic one, in the SNr, However, it cannot be excluded that the lack of effi- which, in turn, may enhance the therapeutic effect of cacy of AMN082 in the present study results from an group III agonists in DA deficiency conditions. How- almost complete DA depletion, since – in contrast to ever, the 6-OHDA model used by Lopez et al. repre- Broadstock et al. – we administered reserpine to- sents an early stage of PD, evoking only partial gether with a-MT which further inhibits de novo DA (50–60%) depletion of striatal DA [1]. In such condi- synthesis. Besides, unlike haloperidol which inhibits tions, the extracellular DA content in the SNr remains fairly selectively DA receptors, reserpine also de- at a normal level [36]. In line with the above findings, pletes other biogenic amines; hence, this model may potentiation of the motor impairment induced by in- reflect a late phase of the disease with more severe tranigral administration of group III agonists was ob- symptoms, when AMN082 can no longer be effective. served in both 6-OHDA-treated and sham-operated Summing up, our study demonstrates that AMN- animals [21]. 082 has a beneficial effect on the haloperidol-induced In contrast to the anticataleptic effect of the sys- catalepsy, but not on the reserpine-induced akinesia. It temically administered AMN082, the compound was seems that the anticataleptic effect of AMN082 de- completely ineffective in reversing the reserpine- pends on the reversal of the impaired initiation of a induced akinesia. The main difference between these movement rather than on the decrease in muscle rigid- two models lies in the fact that reserpine (given in ity. Our data imply that the effects of the systemically combination with a-MT) evokes strong muscle rigid- administered AMN082 are related to activation of ity [16] and produces an almost complete DA deple- both striatal and nigral mGluR7; however, intranigral tion [45], while a moderate dose of haloperidol in- injections require much higher doses of the compound duces catalepsy related to deficits in limb movement to obtain a beneficial effect. It is also proposed that initiation [12] rather than to muscle rigidity [29, 42]. the off-target effects of the systemically administered In accordance with the above results, systemically ad- AMN082 may be connected with its doses higher than ministrated AMN082 was found to reverse deficits in movement initiation in 6-OHDA-lesioned rats with anticataleptic ones, and with a longer period of time a partial depletion of striatal DA in a reaction-time elapsing after its administration. On the other hand, task [1]. Since parkinsonian symptoms appear when since AMN082 can easily produce mGluR7 desensiti- 80% of the striatal DA is lost, it is unlikely that mus- zation, long-term treatment with mGluR7 agonists cle rigidity should be produced at such a moderate may reduce their efficacy. level of DA depletion. Although we did not study the impact of local administration of AMN082 on the reserpine-induced akinesia because of the lack of ef- Acknowledgments: fects of this compound after systemic administration, This study was supported by statutory funds from the Institute of Pharmacology, Polish Academy of Sciences in Kraków (Poland). a most recent study showed an antiakinetic effect of The authors wish to express their thanks to Mrs. E. Smolak, M.A., the intranigrally administrated AMN082 in that for the linguistic supervision of the paper.
Pharmacological Reports, 2013, 65, 11941203 1201 References: a light and electron microscopic study. J Comp Neurol, 1998, 393, 332–352. 15. Konieczny J, Lenda T: Contribution of the mGluR7 re- 1. Amalric M, Moukhles H, Nieoullon A, Daszuta A: Com- ceptor to antiparkinsonian-like effects in rats: a behav- plex deficits on reaction time performance following bi- ioral study with the new selective agonist AMN082. lateral intrastriatal 6-OHDA infusion in the rat. Eur Pharmacol Rep, 2007, 59, 807. J Neurosci, 1995, 7, 972–980. 16. Konieczny J, Przegalinski E, Pokorski M: N-oleoyl- 2. Austin PJ, Betts MJ, Broadstock M, O’Neill MJ, dopamine decreases muscle rigidity induced by reserpine Mitchell SN, Duty S: Symptomatic and neuroprotective in rats. Int J Immunopathol Pharmacol, 2009, 22, 21–28. effects following activation of nigral group III meta- 17. Konieczny J, Wardas J, Kuter K, Pilc A, Ossowska K: botropic glutamate receptors in rodent models of Parkin- The influence of group III metabotropic glutamate recep- son’s disease. Br J Pharmacol, 2010, 160, 1741–1753. tor stimulation by (1S,3R,4S)-1-aminocyclo-pentane- 3. Beurrier C, Lopez S, Révy D, Selvam C, Goudet C, -1,3,4-tricarboxylic acid on the parkinsonian-like akine- Lhérondel M, Gubellini P et al.: Electrophysiological and sia and striatal proenkephalin and prodynorphin mRNA behavioral evidence that modulation of metabotropic expression in rats. Neuroscience, 2007, 145, 611–620. glutamate receptor 4 with a new agonist reverses experi- 18. Kosinski CM, Risso Bradley S, Conn PJ, Levey AI, mental parkinsonism. FASEB J, 2009, 23, 3619–3628. Landwehrmeyer GB, Penney JB Jr, Young AB, Standaert 4. Bradley SR, Levey AI, Hersch SM, Conn PJ: Immuno- DG: Localization of metabotropic glutamate receptor 7 cytochemical localization of group III metabotropic glu- mRNA and mGluR7a protein in the rat basal ganglia. tamate receptors in the hippocampus with subtype- J Comp Neurol, 1999, 415, 266–284. specific antibodies. J Neurosci, 1996, 16, 2044–2056. 19. Li X, Gardner EL, Xi ZX: The metabotropic glutamate re- 5. Bradley SR, Marino MJ, Whittmann M, Rouse ST, ceptor 7 (mGluR7) allosteric agonist AMN082 modulates Levey AI, Conn PJ: Physiological roles of presynapti- nucleus accumbens GABA and glutamate, but not dopa- cally localized type 2, 3 and 7 metabotropic glutamate mine, in rats. Neuropharmacology, 2008, 54, 542–551. receptors in the basal ganglia. Soc Neurosci Abstr, 1999, 20. Li X, Li J, Gardner EL, Xi ZX: Activation of mGluR7s 25, 176.16. inhibits cocaine-induced reinstatement of drug-seeking 6. Bradley SR, Standaert DG, Rhodes KJ, Rees HD, Testa behavior by a nucleus accumbens glutamate-mGluR2/3 CM, Levey AI, Conn PJ: Immunohistochemical localiza- mechanism in rats. J Neurochem, 2010, 114, 1368–1380. tion of subtype 4a metabotropic glutamate receptors in 21. the rat and mouse basal ganglia. J Comp Neurol, 1999, Lopez S, Turle-Lorenzo N, Acher F, De Leonibus E, 407, 33–46. Mele A, Amalric M: Targeting group III metabotropic 7. Broadstock M, Austin P, Betts M, Duty S: Antiparkin- glutamate receptors produces complex behavioral effects sonian potential of targeting group III metabotropic glu- in rodent models of Parkinson’s disease. J Neurosci, tamate receptor subtypes in the rodent substantia nigra 2007, 27, 6701–6711. 22. pars reticulata. Br J Pharmacol, 2012, 165, 1034–1045. MacInnes N , Messenger MJ, Duty S: Activation of 8. Costall B, Naylor RJ, Olley JE: Stereotypic and anticata- group III metabotropic glutamate receptors in selected leptic activities of amphetamine after intracerebral injec- regions of the basal ganglia alleviates akinesia in the tions. Eur J Pharmacol, 1972, 18, 83–94. reserpine-treated rat. Br J Pharmacol, 2004, 141, 15–22. 23. 9. Cousins MS, Salamone JD: Involvement of ventrolateral Marino MJ, Williams DL Jr, O’Brien JA, Valenti O, striatal dopamine in movement initiation and execution: McDonald TP, Clements MK, Wang R et al.: Allosteric a microdialysis and behavioral investigation. Neurosci- modulation of group III metabotropic glutamate receptor ence, 1996, 70, 849–859. 4: a potential approach to Parkinson’s disease treatment. 10. Greco B, Lopez S, van der Putten H, Flor PJ, Amalric M: Proc Natl Acad Sci USA, 2003, 100, 13668–13673. Metabotropic glutamate 7 receptor subtype modulates 24. Messenger MJ, Dawson LG, Duty S: Changes in meta- motor symptoms in rodent models of Parkinson’s dis- botropic glutamate receptor 1–8 gene expression in the ro- ease. J Pharmacol Exp Ther, 2010, 332, 1064–1071. dent basal ganglia motor loop following lesion of the ni- 11. Hansard MJ, Smith LA, Jackson MJ, Cheetham SC, Jen- grostriatal tract. Neuropharmacology, 2002, 43, 261–271. ner P: Dopamine, but not norepinephrine or serotonin, 25. Mitsukawa K, Yamamoto R, Ofner S, Nozulak J, Pescott reuptake inhibition reverses motor deficits in 1-methyl- O, Lukic S, Stoehr N et al.: A selective metabotropic glu- 4-phenyl-1,2,3,6-tetrahydropyridine-treated primates. tamate receptor 7 agonist: activation of receptor signal- J Pharmacol Exp Ther, 2002, 303, 952–958. ing via an allosteric site modulates stress parameters in 12. Hauber W, Schmidt WJ: The NMDA antagonist dizocil- vivo. Proc Natl Acad Sci USA, 2005, 102, 18712–18717. pine (MK-801) reverses haloperidol-induced movement 26. Nakachi N, Kiuchi Y, Inagaki M, Inazu M, Yamazaki Y, initiation deficits. Behav Brain Res, 1990, 41, 161–166. Oguchi K: Effects of various dopamine uptake inhibitors 13. Kelley AE, Lang CG: Effects of GBR 12909, a selective on striatal extracellular dopamine levels and behaviours dopamine uptake inhibitor, on motor activity and operant in rats. Eur J Pharmacol, 1995, 281, 195–203. behavior in the rat. Eur J Pharmacol, 1989, 167, 385–395. 27. Niswender CM, Johnson KA, Weaver CD, Jones CK, 14. Kinoshita A, Shigemoto R, Ohishi H, van der Putten H, Xiang Z, Luo Q, Rodriguez AL et al.: Discovery, charac- Mizuno N: Immunohistochemical localization of meta- terization, and antiparkinsonian effect of novel positive botropic glutamate receptors, mGluR7a and mGluR7b, allosteric modulators of metabotropic glutamate receptor in the central nervous system of the adult rat and mouse: 4. Mol Pharmacol, 2008, 74, 1345–1358.
1202 Pharmacological Reports, 2013, 65, 11941203 Antiparkinsonian-like effects of AMN082 in rats Jolanta Konieczny and Tomasz Lenda
28. Ohishi H, Nomura S, Ding YQ, Shigemoto R, Wada E, 38. Shigemoto R, Kinoshita A, Wada E, Nomura S, Ohishi H, Kinoshita A, Li JL et al.: Presynaptic localization of Takada M, Flor PJ et al.: Differential presynaptic localiza- a metabotropic glutamate receptor, mGluR7, in the pri- tion of metabotropic glutamate receptor subtypes in the rat mary afferent neurons: an immunohistochemical study in hippocampus. J Neurosci, 1997, 17, 7503–7522. the rat. Neurosci Lett, 1995, 202, 85–88. 39. Sukoff Rizzo SJ, Leonard SK, Gilbert A, Dollings P, 29. Ossowska K, Konieczny J, Wolfarth S, Pilc A: MTEP, Smith DL, Zhang MY, Di L et al.: The metabotropic glu- a new selective antagonist of the metabotropic glutamate tamate receptor 7 allosteric modulator AMN082: receptor subtype 5 (mGluR5), produces antiparkin- a monoaminergic agent in disguise? J Pharmacol Exp sonian-like effects in rats. Neuropharmacology, 2005, 49, Ther, 2011, 338, 345–352. 447–455. 40. Valenti O, Marino MJ, Wittmann M, Lis E, DiLella AG, 30. Pa³ucha A, Klak K, Branski P, van der Putten H, Flor PJ, Kinney GG, Conn PJ: Group III metabotropic glutamate Pilc A: Activation of the mGlu7 receptor elicits receptor-mediated modulation of the striatopallidal syn- antidepressant-like effects in mice. Psychopharmacology apse. J Neurosci, 2003, 23, 7218–7226. (Berl), 2007, 194, 555–562. 41. Vernon AC, Zbarsky V, Datla KP, Dexter DT, Croucher 31. Pa³ucha-Poniewiera A, Brañski P, Lenda T, Pilc A: MJ: Selective activation of group III metabotropic gluta- The antidepressant-like action of metabotropic glutamate mate receptors by L-(+)-2-amino-4-phosphonobutryic 7 receptor agonist N,N’-bis(diphenylmethyl)-1,2- acid protects the nigrostriatal system against 6-hydroxy- ethanediamine (AMN082) is serotonin-dependent. dopamine toxicity in vivo. J Pharmacol Exp Ther, 2007, J Pharmacol Exp Ther, 2010, 334, 1066–1074. 320, 397–409. 32. Paxinos G, Watson C: The rat brain in stereotactic coor- 42. Wardas J, Konieczny J, Lorenc-Koci E: SCH 58261, dinates. Academic Press, San Diego,1986. an A2A adenosine receptor antagonist, counteracts park- 33. Pearce RK, Smith LA, Jackson MJ, Banerji T, Scheel- insonian-like muscle rigidity in rats. Synapse, 2001, 41, Krüger J, Jenner P: The monoamine reuptake blocker 160–171. brasofensine reverses akinesia without dyskinesia in 43. Wittmann M, Marino MJ, Bradley SR, Conn PJ: Activa- MPTP-treated and levodopa-primed common marmo- tion of group III mGluRs inhibits GABAergic and gluta- sets. Mov Disord, 2002, 17, 877–886. matergic transmission in the substantia nigra pars reticu- 34. Pelkey KA, Yuan X, Lavezzari G, Roche KW, McBain lata. J Neurophysiol, 2001, 85, 1960–1968. CJ: mGluR7 undergoes rapid internalization in response 44. to activation by the allosteric agonist AMN082. Neuro- Wittmann M, Marino MJ, Conn PJ: Dopamine modulates pharmacology, 2007, 52, 108–117. the function of group II and group III metabotropic glu- 35. Pisani A, Calabresi P, Centonze D, Bernardi G: Activa- tamate receptors in the substantia nigra pars reticulata. tion of group III metabotropic glutamate receptors de- J Pharmacol Exp Ther, 2002, 302, 433–441. 45. presses glutamatergic transmission at corticostriatal syn- Yuan J, Callahan BT, McCann UD, Ricaurte GA: Evi- apse. Neuropharmacology, 1997, 36, 845–851. dence against an essential role of endogenous brain do- 36. Sarre S, Yuan H, Jonkers N, Van Hemelrijck A, Ebinger pamine in methamphetamine-induced dopaminergic neu- G, Michotte Y: In vivo characterization of somatoden- rotoxicity. J Neurochem, 2001, 77, 1338–1347. dritic dopamine release in the substantia nigra of 6-hydroxydopamine-lesioned rats. J Neurochem, 2004, 90, 29–39. 37. Schoepp DD: Unveiling the functions of presynaptic me- tabotropic glutamate receptors in the central nervous sys- Received: April 5, 2012; in the revised form: April 25, 2013; ac- tem. J Pharmacol Exp Ther, 2001, 299, 12–20. cepted: May 13, 2013.
Pharmacological Reports, 2013, 65, 11941203 1203