Animal experiment:

Rats: Nalfurafine is given to male Sprague-Dawley rats at volume of 1 mL/kg. After collecting control samples for 80 min, PCP (10 mg/kg, i.p.) is administered to the rats, and then the collection of dialysate is continued for 180 min. Pre-treatment with TRK-820 or vehicle is performed subcutaneously 5 min before the administration of PCP. Dopamine and serotonin levels in the dialysate are quantified by high-performance liquid chromatography[2]. Mice: Chronic dry skin on the nape of the neck is induced on the C57BL/6 mice. Nalfurafine (20 μg/kg) or saline is administered. Then alloknesis testing is conducted[1].

Nalfurafine hydrochloride is a κ-opioid agonist and an anti-itch drug approved in Japan.

In mice with experimental dry skin, nalfurafine abolished spontaneous scratching but had no effect on alloknesis[1]. A single administration of subcutaneous TRK-820 significantly increased spontaneous ipsilateral rotational behavior of hemi-parkinsonian rats at 30 μg/kg though the efficacy is moderate and also significantly inhibited L-DOPA-induced dyskinesia at 10 and 30 μg/kg; this inhibition is reversed in the presence of nor-binaltorphimine, a kappa opioid receptor antagonist[2]. TRK-820 dose-dependently inhibited phencyclidine-induced rat hyperlocomotion. TRK-820 dose-dependently attenuated the biochemical changes of both dopamine and serotonin in the prefrontal cortex of rats treated with phencyclidine without affecting their basal levels in normal rats[3].

[1]. Akiyama T, et al. Nalfurafine suppresses pruritogen- and touch-evoked scratching behavior in models of acute and chronic itch in mice. Acta Derm Venereol. 2015 Feb;95(2):147-50. [2]. Ikeda K, et al. TRK-820, a selective kappa opioid receptor agonist, could effectively ameliorate L-DOPA-induced dyskinesia symptoms in a rat model of Parkinson's disease. Eur J Pharmacol. 2009 Oct 12;620(1-3):42-8. [3]. Yoshikawa S, et al. Effects of TRK-820, a selective kappa opioid receptor agonist, on rat schizophrenia models. Eur J Pharmacol. 2009 Mar 15;606(1-3):102-8.