Increased S(-)-apomorphine-induced vacuous chewing and attenuated effect of chronic haloperidol treatment in streptozotocin-induced diabetic rat

The incidence of S(-)-apomorphine-induced vacuous chewing movements (VCMs) as a model for tardive dyskinesia was investigated in streptozotocin (STZ)-induced diabetic rats. A single dose STZ (65 mg/kg, intravenously) caused a diabetic state (hyperglycemia, 480-490 vs. 116-118 mg/dl in naive rats). S(-)-apomorphine (250 μg/kg, subcutaneously)-induced VCMs were significantly intensified in diabetic rats which had received STZ 9 weeks previously. The enhancement of VCMs was also observed in nondiabetic rats which received subsequent treatment with depot haloperidol (4 mg/kg, intramuscularly, once a week, every week for 4 weeks) followed by a 2-week washout period. The ability of haloperidol to enhance VCMs was attenuated in diabetic rats. The implications of these results in relation to altered neurotransmissions in STZ induced diabetes are discussed.