Figure 5.

Behavioral consequences of challenging bulbar DAergic interneurons. A, Mean latency before falling down for the rotarod test are shown for mice injected with vehicle or 6-OHDA into the right SN or the two OBs at day 7 and day 30 after lesion (n = 8–23 per group). Mice injected into the SN exhibited shorter latencies compared with the control groups (i.e., vehicle-injected mice and mice treated with bilateral injection of 6-OHDA into the OB), indicating motor deficits. B, Representative tracing of mouse locomotion at 7 d after lesion, during a 3 min exposure to the tested odorant and to its vehicle. Panels represent the third stage of one session of the innate olfactory test habituation: exposure to the tested odorant in zone 1 and to its vehicle in zone 3. Top, Tracings of a vehicle-injected mouse (“vehicle mice”). Bottom, Tracings of a 6-OHDA-injected mouse (“6-OHDA mice”). The position of the mouse was quantified in the cage test by measuring the time spent in zone 1 and zone 3. The tested odorants were MO, TMT, 2-MB acid, Coco Pop cereals, and pool of female urines (“female urine”). Vehicle odorants were MO, water, or Parafilm as appropriate. Odorants were positioned in the middle of zone 1, except for Coco Pop cereals, which were exposed in the left part of zone 1. Whereas vehicle mice avoid aversive olfactory cues (TMT and 2-MB acid), 6-OHDA-treated mice showed no interest in these odorants. Moreover, whereas female urine attracted the vehicle mice, the 6-OHDA mice showed no interest to this social scent. C, Preference index values for mice injected into the two OBs by vehicle (black columns) or 6-OHDA (white columns) at 7 d after lesion (n = 14–20 mice per group, per odorants). Olfactory cues were chosen to be neutral (water, MO, Parafilm), aversive (2-MB acid, TMT), or attractive (Coco Pop cereals, female urine). Preference index = time spent in zone 1 during odorant trial − time spent in zone 1 during vehicle trial. Positive values indicate attraction and negative value repulsion. Female urine was strongly attractive for vehicle male mice but not for 6-OHDA-injected mice. 2-MB acid and TMT elicited robust aversion for vehicle mice, but not for 6-OHDA-injected mice. D, Preference index values for mice injected into the two OBs by vehicle (black) or 6-OHDA (white) at 1 week, 1 month, and 2 months after lesion (n = 15–18 mice per group). The tested odorant is the aversive odorant TMT. Whereas TMT induces a strong avoidance for vehicle mice, the response to this olfactory cue was altered in 6-OHDA-treated mice but restored at 2 months after lesion. E, Minocycline treatment blocks the strong neuroinflammation induced by 6-OHDA lesion. Top, Design of the experimental procedure. Minocycline or saline was administered during 8 d, starting 1 d before 6-OHDA lesion of the OB. A 6-OHDA-containing solution, or vehicle alone, was infused into the dorsal part of each OB. Bottom, CD68 staining in the dorsal lesioned OB at 1 week after 6-OHDA injection in vehicle (left), 6-OHDA-lesioned (center), and minocycline-treated lesioned (right) mice. F, Preference index values for mice treated with saline or minocycline (gray) for 1 week and injected at day 1 into the two OBs by vehicle (black) or 6-OHDA (white) at 1 month after lesion (n = 7–10 mice per group). The response to TMT is unchanged by minocycline treatment. *p < 0.05. **p < 0.01. ***p < 0.001. ****p < 0.0001. Scale bar, 10 μm.