Effects of lithium carbonate on apomorphine-induced sniffing behaviour in rats

Effects of lithium carbonate (Li2CO3) on sniffing induced by apomorphine have been tested in rats. Intraperitoneal administration of different doses of apomorphine (0.25, 0.5 and 1 mg/kg) induced a dose-dependent sniffing response. Chronic Li2CO3 exposure (0.1% in drinking water for 30-35 days) but not acute administration of the drug (320 mg/kg, intraperitoneally) decreased the response of apomorphine. The response to chronic Li2CO3 exposure was observed when apomorphine was injected 60 min., 24 hr or 72 hr after Li2CO3withdrawal, with maximum effect observed when the drug was administered 72 hr after withdrawal of Li2CO3. Blockade of sniffing induced by apomorphine by the D1 dopamine receptor antagonist, SCH23390 (0.005 mg/kg, intraperitoneally) or the D2 dopamine receptor antagonist, sulpiride (25 mg/kg, intraperitoneally) was not increased in acute Li2CO3-treated animals. In animals which were treated chronically with Li2CO3, the blockade of apomorphine response by sulpiride but not by SCH23390 was potentiated. It is concluded that chronic treatment of animals with Li2CO3 is able to alter D2 dopamine receptors response.