Table 2.

Available and potential treatments.

HUMAN HD
Tetrabenazine	Well-supported antichoreatic effects but frequent adverse reactions limit its usefulness (Huntington Study Group, 2006).
D2 antagonists	Haloperidol: a traditional D2 antagonist; improves chorea, but does not increase functional capacity (Bonelli and Wenning, 2006). Olanzapine and risperidone: atypical antipsychotic drugs with D2 antagonist properties; improve chorea and behavioral disturbances (Squitieri et al., 2001; Duff et al., 2008).
D2 agonists	Bromocriptine: effects are both positive and negative (Frattola et al., 1977; Caraceni et al., 1980). Lisuride: limited positive effects (Caraceni et al., 1980; Frattola et al., 1983). Aripiprazole: a partial D2 agonist; improves chorea but not cognitive function (Brusa et al., 2009).
Other DA drugs	Pridopidine: a DA stabilizer; produces slight improvements in motor dysfunction (De Yebenes et al., 2011). L-DOPA: possibly useful for treatment of rigidity (Racette and Perlmutter, 1998).
ANIMAL MODELS
Tetrabenazine	Alleviates motor alterations and reduces striatal loss in both early and late stages (Tang et al., 2007; Wang and Morris, 2010; André et al., 2011a).
D1 antagonist	SCH23390: rescues electrophysiological changes in excitatory and inhibitory synaptic transmission in direct pathway MSNs (André et al., 2011a).
D1 agonist	SKF38393: reverses impaired LTP in the medial prefrontal cortex of presymptomatic R6/1 mice (Dallerac et al., 2011).
D2 antagonist	Haloperidol: early and chronic treatment significantly reduces striatal toxicity in the tgHD rat model (Charvin et al., 2008).
D2 agonist	Quinpirole: restores the ability of transgenic cortical slices to support LTD (Cummings et al., 2006).