**7. Technical procedures**

### **7.1 Animals**

Male Wistar rats (Iffa-Credo France) weighing 250 g were used in the studies reported here. They were maintained and sacrificed in accordance with the European Communities Council Directive (86/609/EEC). The animals were anesthetized with 1.5% isoflurane in pure oxygen in air or were injected with chloral hydrate (400 mg/kg) and spontaneously inspired (Leviel et al., 1989; Olivier et al., 1995). When necessary they were placed in a stereotaxic device. For the short interventions (less than 1 hour), a mixture of ketamine/rompun was used (150/10 mg/Kg). Rectal temperature was maintained at 38 °C. Cardiac and respiratory rhythms were continuously monitored.

#### **7.2 Lesions of the lateral SN**

The lateral part of the SN was unilaterally injected with a solution of 6-OHDA (3 µg free base in 1 µl isotonic saline containing 0.2% ascorbic acid, pH 4). The stereotaxic coordinates were, in mm: Ant.: 3.5, Lat.: 2.5 and Ht.: 3.4. The horizontal plane passed through the interaural axis and incisor bar. Unlesioned rats were only submitted to nigral injection of the vehicle (Dentresangle et al., 2001; Dzahini et al., 2010).

#### **7.3 Surgery and procedures for recurrent ventricular injections**

Animals were anesthetized with ketamine (150 mg/Kg; Panpharma), maintained in a stereotaxic device and implanted with a cannula (0.71 mm o.d. with a removable mandrel) in the anterior part of the left lateral ventricle. The head of the cannula was sealed with acrylic cement, embedding screws set in the cranial bone. The stereotaxic coordinates were the following (in mm): AP: 0.48; LM: 1; H: 6 from the bregma (following Paxinos and Watson, 1986). Rats were allowed to recover for 2 weeks. In order to inject 6-OHDA (30 min after administering 25 mg/kg imipramine i.p. to protect noradrenergic neurons), the mandrel of the cannula was removed and replaced by an injector connected, through a thin catheter, to a microsyringe. Weekly injections of 10 µl of a solution (0.1% ascorbic acid in 0.9% NaCl) with or without 35 µg of 6-OHDA were given to awake and freely moving animals. Four groups of 12 animals received 2, 4, 6 or 8 weekly injections of the toxin (n=6) or the toxin vehicle only (n=6). A fifth group (n=6) of rats received 8 weekly injections of the toxin and a daily injection of 2 mg/kg MK801 (i.p.).
