Pd 168077

The DR1 agonist SKF-81297 (1 μM), the D2-like receptor agonist quinpirole (10 μM), the selective DR3 agonist pramipexole (10 μM), the DR4 agonist PD-168077 (200 nM), the selective DR4 antagonist L-745870 (500 nM), the dopamine (200 μM), the n-methy-d-aspartate (NMDA) receptor antagonist D-AP5 (50 μM) and CCH (5 μM) were purchased from Tocris Bioscience. Stock solutions, at thousand times the final concentration, were made up in water or in DMSO, and stored in individual aliquots at 20°C. Final solutions were prepared freshly on the day of the experiment. Drugs were applied to the recording ACSF 15 min after steady-state γ power was reached. The dead volume and bath volume was kept such that final concentration was reached in the bath in about 5 min.

Animals received a single intraperitoneal injection (i.p.) of either morphine sulphate (10 mg/kg; supplied by Ministerio de Sanidad, Política Social y Consumo (Spanish Government)), PD168,077 (1 mg/kg; Tocris Bioscience, UK) or both drugs, which were dissolved in 2% DMSO within 0.9% NaCl (vehicle). Animals were sacrificed by decapitation at 1 h or 2 h after treatment (n = 6 per group) (Table 2).Table 2

Experimental groups of the study.

Time point (h)	Treatment	Group	Dose (mg/kg)
1h	vehicle	C1h
	morphine	M1h	10 mg/kg
	PD168,077	PD1h	1 mg/kg
	morphine + PD168,077	MPD1h	10 mg/kg + 1 mg/kg
2 h	vehicle	C2h
	morphine	M2h	10 mg/kg
	PD168,077	PD2h	1 mg/kg
	morphine + PD168,077	MPD2h	10 mg/kg + 1 mg/kg

Groups were based on the drug treatment and time of sample extraction (n = 6 per group). RNA from three animals were pooled to perform the analysis (n = 2 pools per experimental group).

Dopamine receptor agonist cocktail contained D1 receptor agonist (SKF38393; Abcam, Cambridge, UK) and D4 receptor agonist (PD168077; Tocris, Bristol, UK) dissolved in saline. Mice kept under SD conditions were i.p. injected with dopamine agonist cocktail (1 mg/kg) 1 h before the ERG recording under dim red light, as described previously^{18 (link)}. Dopamine receptor antagonist cocktail contained D1 receptor antagonist (SCH 23390; Tocris) and D4 receptor antagonist (L-745870; Abcam) (1 mg/kg each) dissolved in saline. Mice kept under LD conditions were i.p. injected with dopamine antagonist cocktail 1 h before ERG recording under dim red light. Based on previous reports^{46 (link),47 (link)}, modafinil (M6940; Sigma-Aldrich, St. Louis, MO, USA), dissolved in 0.1% DMSO/saline, was injected by gavage (64 mg/kg, 4 h apart, three times each day during daytime for 3 days). Forskolin (66575-29-9; Wako, Osaka) dissolved in saline (1%) was administered to the eyes (2 µl each) as eye-drops using a pipet (4 h apart, three times each day during daytime for 3 days). The effects of topical administration of Forskolin were examined twice by different experimenters, and consistent results were obtained in both experiments.