Effects of adenosine receptor agonists and antagonists in a genetic animal model of primary paroxysmal dystonia

Abstract

1. Recent studies have shown beneficial effects of an adenosine A(2A) receptor agonist in dt(sz) mutant hamsters, an animal model of paroxysmal dystonia, in which stress and consumption of coffee can precipitate dystonic attacks. This prompted us to examine the effects of adenosine receptor agonists and antagonists on severity of dystonia in dt(sz) hamsters in more detail. 2. The non-selective adenosine A(1)/A(2A) receptor antagonists, caffeine (10 - 20 mg kg(-1) i.p.) and theophylline (10 - 30 mg kg(-1) s.c.), worsened the dystonia in dt(sz) hamsters. 3. Aggravation of dystonia was also caused by the selective adenosine A(1)/A(2A) antagonist CGS 15943 (9-chloro2-2-furyl)[1,2,4]triazolo[1,5-c]quinazolin-5-amine) at a dose of 30 mg kg(-1) i.p. and by the adenosine A(1) antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine; 20 - 30 mg kg(-1) i.p.), while the A(2) antagonist DMPX (3,7-dimethyl-1-propargylxanthine; 2 - 4 mg kg(-1) i.p.) and the highly selective A(2A) antagonist ZM 241385 (4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol; 2 - 5 mg kg(-1) i.p.) failed to exert any effects on dystonia. 4. In contrast to the antagonists, both the adenosine A(1) receptor agonist CPA (N(6)-cyclopentyladenosine; 0.1 - 1.0 mg kg(-1) i.p.) and the A(2A) agonist CGS 21680 (2p-(2carboxyethylphen-ethylamino-5'-N-ethylcarboxamindoadenosine; 0.1 - 2.0 mg kg(-1) i.p.) exerted a striking improvement of dystonia. 5. These data suggest that the precipitating effects of methylxanthines are, at least in part, related to their adenosine receptor antagonistic action. 6. Although adenosine receptor agonists can be regarded as interesting candidates for the therapy of paroxysmal dystonia, adverse effects may limit the therapeutic potential of adenosine A(1) agonists, while beneficial effects of the adenosine A(2A) agonist CGS 21680 were already found at well tolerated doses.

Figure 1

Effects of the methylxanthines caffeine (10.0 and 20.0 mg kg⁻¹ i.p.) and theophylline (10.0, 20.0 and 30.0 mg kg⁻¹ s.c.) on severity of dystonia in mutant hamsters. Usually, the individual maximum severity of dystonia is reached within 3 h after induction of dystonia by triple stimulation including the injection of drugs (black bars) or vehicle for pre- and post-drug controls (open bars). The figure shows the average of the maximum individual severity scores of dystonia reached within the first, second and third hour after administration of the methylxanthine or vehicle, reflecting the progression of dystonia in dt^sz hamsters after treatment with the active compound and during control recordings. Control recordings were undertaken 2 days before (pre-drug control) and 2 days after (post-drug control) the drug trial. Asterisks indicate significant aggravation of dystonia in comparison to the pre- and post-drug control (^*P<0.05, ^**P<0.01). Data are shown as means±s.e. of seven (20 mg kg⁻¹ caffeine), eight (10 and 20 mg kg⁻¹ theophylline), nine (30 mg kg⁻¹ theophylline) or 10 (10 mg kg⁻¹ caffeine) dystonic hamsters. Absence of s.e. bars indicates that all hamsters had reached the same severity.

Figure 2

Effect of the adenosine A_1/2A receptor antagonist CGS 15943 on severity of dystonia in mutant hamsters after administration of 20 and 30 mg kg⁻¹ i.p. The figure shows the average of the maximum individual severity scores of dystonia reached within the first, second and third hour after administration of CGS 15943. Control recordings were taken 2 days before (pre-drug control) and 2 days after (post-drug control) the drug trial. Asterisks indicate significant aggravation of dystonia in comparison to the pre- and post-drug control (^*P<0.05). Data are shown as means±s.e. of 11 (20 mg kg⁻¹) or nine (30 mg kg⁻¹) hamsters. For further explanation see Figure 1 legend.

Figure 3

Effect of the adenosine A₁ receptor antagonist DPCPX (10 and 20 mg kg⁻¹ i.p.), of the A₂ receptor antagonist DMPX (2 mg kg⁻¹ i.p.) and of the A_2A antagonist ZM 241385 (5 mg kg⁻¹ i.p.) on severity of dystonia in mutant hamsters. The figure shows the average of the maximum individual severity scores of dystonia reached within the first, second and third hour after drug administration. Control recordings were taken 2 days before (pre-drug control) and 2 days after (post-drug control) the drug trial. Asterisks indicate significant aggravation of dystonia in comparison to the pre- and post-drug control (*P<0.05). Data are shown as means±s.e. of seven (ZM 241385), nine (10 mg kg⁻¹ DPCPX) or 10 (2 mg kg⁻¹ DMPX, 20 mg kg⁻¹ DPCPX) mutant hamsters. For further explanation see Figure 1 legend.

Figure 4

Effect of the adenosine A₁ receptor agonist CPA on severity of dystonia in mutant hamsters after administration of 0.1, 0.25, 0.5 and 1.0 mg kg⁻¹ i.p. The figure shows the average of the maximum individual severity scores of dystonia reached within the first, second and third hour after administration of CPA. Control recordings were taken 2 days before (pre-drug control) and 2 days after (post-drug control) the drug trial. Asterisks indicate significant reduction of dystonia in comparison to the pre- and post-drug control (^*P<0.05; ^**P<0.01). Data are shown as means±s.e. of seven (0.25 – 1.0 mg kg⁻¹) or nine (0.1 mg kg⁻¹) dt^sz hamsters. For further explanation see Figure 1.

Figure 5

Effect of the adenosine A_2A receptor agonist CGS 21680 on severity of dystonia in mutant hamsters after administration of 0.1, 0.25, 0.5, 1.0 and 2.0 mg kg⁻¹ i.p. Note that CGS 21680 already exerts antidystonic effects at lower doses of 0.1 and 0.25 mg kg⁻¹ than at those described recently (0.5 – 2.0 mg kg⁻¹; Richter et al., 2000). The figure shows the average of the maximum individual severity scores of dystonia reached within the first, second and third hour after administration of CGS 21680. Control recordings were taken 2 days before (pre-drug control) and 2 days after (post-drug control) the drug trial. Asterisks indicate a significant reduction of dystonia in comparison to the pre- and post-drug control (^*P<0.05; ^**P<0.01). Data are shown as means±s.e. of eight (2 mg kg⁻¹), nine (1 mg kg⁻¹) or 10 (0.1, 0.25 mg kg⁻¹) hamsters. For further explanation see Figure 1 legend.

Figure 6

Effect of the adenosine A₁ receptor agonist CPA (0.5 mg kg⁻¹ i.p.) and of the adenosine A_2A receptor agonist CGS 21680 (0.5 mg kg⁻¹ i.p.) on rectal temperature in a group of dt^sz mutant hamsters. The figure shows the average body temperature prior (0 min) and after drug administrations (30 – 150 min) in comparison to a control group treated with the vehicle (Tween 80). Data are shown as means±s.e. of five (CPA and CGS 21680) or six (vehicle control) mutant hamsters. Asterisks indicate significant differences after injections of vehicle or CPA versus prior treatment in the same group of animals (^*P<0.05, ^*P<0.01). Circles indicate a significant decrease in comparison to the vehicle control group (^•P<0.05; ^••P<0.01).

Figure 7

Pretreatments with the adenosine A_2A receptor agonist CGS 21680 (0.25 mg and 0.5 kg⁻¹ i.p.) or with the A₁ receptor agonist CPA (0.25 and 0.5 mg kg⁻¹ i.p.) 10 min prior i.p. injections of 20 mg kg⁻¹ caffeine. The figure shows the average of the maximum individual severity scores of dystonia reached within the first, second and third hour after caffeine alone and after pretreatments. Asterisks indicate significant differences of the severity of dystonia in comparison to the pre- and post-drug control (^*P<0.05). Circles indicate a significant reduction of the differences of severity score (caffeine vs control data) in animal groups pretreated with CPA (^•P<0.05; ^••P<0.01). Data are shown as means±s.e. of seven (20 mg kg⁻¹ caffeine), nine (caffeine after pretreatment with 0.5 mg kg⁻¹ CPA or CGS 21680) or 10 (caffeine after 0.25 mg kg⁻¹ CPA or CGS 21680) mutant hamsters. For further explanation see Figure 1 legend.