Temporary Inactivation of Dopamine Receptors in the Dorsolateral Striatum

After 1 week of individual housing, continuously free-fed (FF) mice were implanted with stainless-steel guide cannulas unilaterally in the left dorsolateral striatum (DLS) as previously described (Colelli et al., 2014; Campus et al., 2015). Briefly, mice were anesthetized with Zoletil 100, Virbac, Milano, Italy (tiletamine HCl 50 mg/ml+zolazepam HCl 50 mg/ml) and Rompun 20, Bayer S.p.A Milano, Italy (xylazine 20 mg/ml) purchased commercially, and mounted on a stereotaxic apparatus (David Kopf Instruments, Tujunga, CA, United States). A single stainless-steel guide cannula (Unimed, Geneva, Switzerland: 7 mm in length, 0.50 mm in external diameter) was inserted in the left DLS (+0.8 mm anterior to bregma, ± 2.3 mm lateral to midline, -2.5 mm ventral from the skull according to Franklin and Paxinos, 2001). One week later, drugs were infused (total volume 0.4 μl, flow rate of 0.2 μl/min) through a stainless-steel injection cannula (Unimed, Geneva, Switzerland, 0.11 mm in internal diameter) connected by polyethylene catheter tubing to a 1 μl Hamilton micro-syringes (Hamilton, Co., Reno, NV, United States), as previously described (Colelli et al., 2014; Campus et al., 2015). Infusions were performed immediately after the firs FSt experience and behavioral test was performed 24 h later.

Doses of dopamine agonists were chosen in preliminary experiments. The D1 dopamine receptor antagonist SCH 23390 (Sigma Aldrich) was dissolved in a 0.90% saline solution and infused at one of two doses (0.5 or 1 μg/mouse); the D2/D3 dopamine receptor antagonist sulpiride (Sigma Aldrich) was first dissolved in 100% dimethyl sulfoxide (DMSO) and then diluted in 0.90% saline up to reaching two different final concentrations (0.5 or 1 μg/mouse). The final DMSO concentration never exceeded 10%; 0.90% saline or 0.90% saline +10% DMSO were infused in control (0) groups.