Anti-anhedonic activity of long-term lithium treatment in rats exposed to repeated unavoidable stress.
Behavioural and neurochemical responses to palatable food exposure represent an index of hedonic competence. In rats, a palatable meal increases extra-neuronal dopamine levels in the nucleus accumbens shell (NAcS) that confers to it incentive salience and reinforcing value. Repeated stress exposure decreases dopamine output and impairs the NAcS dopaminergic response to palatable food and the competence to acquire a vanilla sugar (VS)-reinforced instrumental behaviour [VS-sustained appetitive behaviour (VAB)]. Moreover, chronic stress exposure disrupts reactivity to aversive stimuli. A 3-wk treatment with lithium, the gold-standard treatment in bipolar disorder, tonically reduces NAcS dopamine output and the reactivity to aversive stimuli. However, it does not affect the dopaminergic response to VS and the competence to acquire VAB. This study investigated whether repeated lithium administration is endowed with anti-anhedonic activity. The NAcS dopaminergic response to VS and the competence to acquire VAB and sucrose self-administration (SA), in terms of fixed-ratio (FR)1, FR5 and progressive ratio schedules of reinforcement, were studied in saline or lithium-treated groups of non-food-deprived rats exposed or not to repeated unavoidable stress. Chronic stress exposure impaired the NAcS dopaminergic response to VS, acquisition of VAB and sucrose SA, in terms of FR1 and FR5 schedules of reinforcement and breaking point score. Repeated lithium treatment restored these parameters to control group values, even when treatment began in rats already showing an anhedonia-like condition. Since the breaking point defines the reinforcement efficacy of a hedonic stimulus, the present data suggest that lithium treatment is endowed with anti-anhedonic activity in rats.
Department of Molecular and Developmental Medicine, University of Siena, Italy.
Giovanna
G
Marchese
Simona
S
Scheggi
Maria Elena
ME
Secci
Maria Graziella
MG
De Montis
Carla
C
Gambarana
D000704:Analysis of Variance; D000818:Animals; D018692:Antimanic Agents / Q000627:therapeutic use*; D001070:Appetitive Behavior / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D004298:Dopamine / Q000378:metabolism; D004334:Drug Administration Schedule; D018021:Lithium Chloride / Q000627:therapeutic use*; D008297:Male; D017551:Microdialysis; D009714:Nucleus Accumbens / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012054:Reinforcement, Psychology; D013315:Stress, Psychological / Q000188:drug therapy*; D013549:Sweetening Agents / Q000008:administration & dosage
D018692:Antimanic Agents; D013549:Sweetening Agents; D018021:Lithium Chloride; D004298:Dopamine