Subchronic administration of tetrabenazine as a mouse model for depression

1. Subchronic administration of tetrabenazine as a mouse model for depression Zsuzsanna Callaerts-Vegh, Sam Willems, Rudi D’Hooge Laboratory of Biological Psychology, Department of Psychology, KU Leuven, B-3000 Leuven, Belgium Zsuzsanna.Vegh@psy.kuleuven.be Results Introduction Clinical depression is considered to be one of the most prevalent psychopathologies that may affect up to 20% of our active population at some point in life. DSM-IV criteria include pathognomonic symptoms of depressed mood and loss of interest (including anhedonia) as well as various cognitive changes that may also contribute to intractability and relapse of the disorder. Hypo-dopaminergic (DA) function has been implicated in the pathogenesis of depression1, while modulation of DA signaling is a successful tool in treating depression2, and interference with DA signaling in VTA has been shown to have antidepressant effects3,4. Induction of hypo-DA function via catecholamine depletion by tetrabenazine (TBZ) has been shown to induce depression-like behaviors in rats and has been used as a preclinical model for depression 5-7. Clinically, TBZ has been promoted as a useful antichorea drug in Huntington’s patients, but its severe side effects include depression8. We have treated C57BL/6 mice subchronically with TBZ and investigated the longterm effect in a series of depression-related tests. Time line: Animals were injected with TBZ for 7 days and body weight and general behavior was recorded. 7 days after last injection, behavioral tests were performed acoording to the indicated schedule. No changes in body weight or general behavior (grooming, activity) were observed. Methods: Animals: Female C57BL/6 (6 weeks of age) were injected daily with TBZ (1mg/kg i.p. in saline) or vehicle (n=10 for each group) for 7 days. Behavioral testing started 1 week after last injection. Behavioral despair: The Porsolt forced swim test (FST) gives indication to the amount of escape behavior when placed in an uncomfortable situation9-12. FST has been validated as preclinical model to screen for novel antidepressant drugs. Mice are placed for 6 min in a water tank and escape behavior (e.g. swimming, climbing) as well as despair behavior (immobility) was quantified. Anhedonia: Sucrose preference were assessed using the modified anhedonia (ANH) test13. After pre-exposure (reduction of neophobia) mice were exposed to a choice of water or 2.5% sucrose solution for 48h. A preference for sucrose below 65% indicated anhedonic behavior. Social preference test (SP): Mice are exposed to one unknown mouse in a three compartment setup14,15. Approach and exploration behaviour towards the stranger mice was quantified. Spontaneous alternation in T-maze (SA): Working memory was measured using a T-shaped maze by counting the number of alternation of arm visits16. Appetitive conditioning (AC): Mice were conditioned in sequential schedules to obtain food pellets when activating a nose poke device. Increasingly demanding schedules were presented to evaluate motivational drive. Conclusion Subchronic injections with tetrabenazine induced depression-like behavior up to 2 weeks after cessation of drug injections. In particular, we observed increased behavioral despair, anhedonia, impaired working memory and social exploration. In contrast, we observed no effect on body weight (general well being and feeding behavior), neuromotor activity (rotarod, grip, 24h activity, data not shown) and appetitive conditioning. Subchronic TBZ injections might be a useful tool to induce pharmacologically depression-like behavior in mice. The presented result are part of a pilot study to evaluate and validate TBZ injections as a possible pharmacological tool and we will expand our findings including additional behavioral, electrophysiological and molecular approaches to understand the etiology of hypodopaminergic function in depression. SOCIAL PREFERENCE When presented with the choice to explore a wire cage with a stranger mouse (STR1) or an empty wire cage, control mice (black bars) prefered STR1 by spending more time sniffing it (p<0.05), while TBZ treated mice (orange bars) showed no preference. FORCED SWIM TEST Behavioral despair in modified forced swim test: TBZ treated mice showed significantly longer immobility time than saline treated mice. (**P<0.01) ANHEDONIA Animals treated with TBZ show a sucrose preference that was not different from anhedonic threshold of 65% (blue line), while saline treated animals display a sucrose preference that was significantly different from anhedonia threshold (*P<0.05) SPONTANEOUS ALTERNATIONS TBZ treated mice show a reduced number of alternations in the T maze (P<0.05, Student’s test) compared to saline treated animals (black bars). Alternating visits (left-right-left right..) has been identified as a form of working memory in rodents. APPETITIVE CONDITIONING In food deprived animals (~85% free feeding bw) both groups learned to use the nose poke device to obtain food rewards. Increasing schedule demand from fixed ratio (FR3, FR5, FR10) to variable ratio (VR10) to variable interval (VI30) increased the response rate in both groups in the same rate.