Chronic lithium attenuates dopamine D1-receptor mediated increases in acetylcholine release in rat frontal cortex

The effects of chronic lithium treatment on methylphenidate-, D₁ dopamine receptor agonist (A-77636)-, and tactile stimulation-induced increases in frontal cortical acetylcholine release were studied in the rat using in vivo brain microdialysis. Cortical acetylcholine release in control rats was maximally stimulated by methylphenidate (1.25 and 2.5 mg/kg) to 173% and 212% above baseline, respectively. The effect of methylphenidate (2.5 mg/kg) was blocked by pretreatment with the dopamine D₁ receptor antagonist SCH 23390 (0.3 mg/kg). Chronic treatment with lithium chloride (3–4 weeks) produced plasma lithium concentrations of 0.45±0.02 meq/l. Chronic lithium significantly reduced increases in cortical acetylcholine release produced by methylphenidate. Stimulation of dopamine D₁ receptors with the full D₁ receptor agonist A-77636 (0.73 mg/kg) increased cortical acetylcholine release. Chronic lithium significantly reduced this effect of A-77636. In contrast, lithium failed to influence the increases of cortical acetylcholine release produced by tactile stimulation. These results suggest that while lithium does not influence normal, arousal-related increases in cortical acetylcholine release, this ion selectively attenuates dopamine mediated increases and/or abnormally large increase, which in the present circumstances were pharmacologically induced. The relevance of these findings to the antimanic actions of lithium is discussed.