Differential prevention of morphine amnesia by antisense oligodeoxynucleotides directed against various Gi-protein alpha subunits

Abstract

The effect of the i.c.v. administration of pertussis toxin (PTX) and antisense oligodeoxynucleotide directed against the alpha subunit of different Gi-proteins (anti-Gialpha1, anti-Gialpha2, anti-Gialpha3) on amnesia induced by morphine was evaluated in the mouse passive avoidance test. The administration of morphine (6 - 10 mg kg(-1) i.p.) immediately after the training session produced amnesia that was prevented by PTX (0.25 microg per mouse i.c.v.) administered 7 days before the passive avoidance test. Anti-Gialpha1 (6.25 microg per mouse i.c.v.) and anti-Gialpha3 (12.5 microg per mouse i.c.v.), administered 18 and 24 h before the training session, prevented the morphine amnesia. By contrast, pretreatment with anti-Gialpha2 (3.12 - 25 microg per mouse i.c.v.) never modified the impairment of memory processes induced by morphine. At the highest effective doses, none of the compounds used impaired motor coordination, as revealed by the rota rod test, nor modified spontaneous motility and inspection activity, as revealed by the hole board test. These results suggest the important role played by Gi1 and Gi3 protein subtypes in the transduction mechanism involved in the impairment of memory processes produced by morphine.

Figure 1

Dose-response curve of morphine in the mouse passive avoidance test. Morphine (6 – 10 mg kg⁻¹ i.p.) and scopolamine (1.5 mg kg⁻¹ i.p.) were administered immediately after the training session. Vertical lines represent s.e.mean; between 19 and 25 mice were tested; the dose administered is reported in each column. ^*P<0.05 in comparison with saline-treated mice.

Figure 2

Prevention by pertussis toxin (PTX; 0.25 μg per mouse i.c.v.) pretreatment on morphine-induced (10 mg kg⁻¹ i.p.) amnesia in the mouse passive avoidance test. The test was performed 7 days after a single i.c.v. injection of vehicle or PTX. Vertical lines represent s.e.mean; between 11 and 16 mice were tested. ^*P<0.05 in comparison with vehicle-saline treated mice; ^∧P<0.05 in comparison with vehicle-morphine treated mice.

Figure 3

Prevention by pretreatment with an antisense oligonucleotide (aODN) to the α subunit of Gi₁-protein gene (1.56 – 12.5 μg per mouse i.c.v.) of morphine-induced (10 mg kg⁻¹ i.p.) amnesia in the mouse passive avoidance test. The test was performed 18 – 24 h after the i.c.v. injection of degenerate ODN (dODN; 12.5 μg per mouse i.c.v.) or aODN. Vertical lines represent s.e.mean; between 12 and 16 mice were tested; the dose administered is reported in each column. ^**P<0.01 in comparison with dODN+morphine group.

Figure 4

Lack of effect of pretreatment with an antisense oligonucleotide (aODN) to the α subunit of Gi₂-protein gene (3.12 – 25 μg per mouse i.c.v.) on morphine-induced (10 mg kg⁻¹ i.p.) amnesia in the mouse passive avoidance test. The test was performed 18 – 24 h after the i.c.v. injection of degenerate ODN (dODN; 25 μg per mouse i.c.v.) or aODN. Vertical lines represent s.e.mean; between 11 and 16 mice were tested; the dose administered is reported in each column. ^*P<0.05 in comparison with dODN+saline group.

Figure 5

Prevention by pretreatment with an antisense oligonucleotide (aODN) to the α subunit of Gi₃-protein gene (3.12 – 25 μg per mouse i.c.v.) of morphine-induced (10 mg kg⁻¹ i.p.) amnesia in the mouse passive avoidance test. The test was performed 18 – 24 h after the i.c.v. injection of degenerate ODN (dODN; 25 μg per mouse i.c.v.) or aODN. Vertical lines represent s.e.mean; between 13 and 18 mice were tested; the dose administered is reported in each column. ^*P<0.05 in comparison with dODN+saline group; ^∧P<0.05 in comparison with dODN+morphine-treated mice.

Figure 6

Lack of effect of pretreatment with an antisense oligonucleotide (aODN) to the α subunit of Gi₁- (12.5 μg per mouse i.c.v.), Gi₂- (25 μg per mouse i.c.v.) and Gi₃- (25 μg per mouse i.c.v.) protein gene on motor coordination in the mouse rota rod test. The test was performed 18 – 24 h after the i.c.v. injection of degenerate ODN (dODN; 25 μg per mouse) or aODN. Vertical lines represent s.e.mean; 12 mice per group were tested.

Figure 7

Lack of effect of pretreatment with an antisense oligonucleotide (aODN) to the α subunit of Gi₁- (12.5 μg per mouse i.c.v.), Gi₂- (25 μg per mouse i.c.v.) and Gi₃- (25 μg per mouse i.c.v.) protein gene on spontaneous motility (A) and inspection activity (B) in the mouse hole board test. The test was performed 18 – 24 h after the i.c.v. injection of degenerate ODN (dODN; 25 μg per mouse) or aODN. Vertical lines represent s.e.mean; 12 mice per group were tested. Veh: vehicle (DOTAP 13 μM); amphet: D-amphetamine 1 mg kg⁻¹ i.p. ^*P<0.05 in comparison with saline group.