Changes in ambulatory activity and dopamine turnover in streptozotocin-induced diabetic rats

We have observed the acute effects of streptozotocin (STZ) on ambulatory activity by employing the automatic apparatus for continuous and direct measurement of drinking and ambulation. Ambulatory activity (counts) in the control periods was 298.2 +/- 20.1 in the dark, 35.6 +/- 9.4 in the light, and 343.9 +/- 24.1 over 24 h. After administration of STZ (60 mg/kg, ip), the ambulatory activity gradually decreased [at 3 days: 165.0 +/- 12.3 in the dark (P less than 0.001), 34.0 +/- 10.5 in the light (P = NS), and 199.0 +/- 10.5 over 24 h (P less than 0.001). For determination of statistical significance, values were compared with those at the same time in the control groups. We observed decreased ambulatory activity in STZ-induced diabetic rats during the dark, but not the light, cycle. Moreover, ambulatory activity in STZ-induced diabetic rats gradually decreased, while the blood glucose level rose. Ambulatory activity correlated inversely with blood glucose level (r = -0.76; P less than 0.05). We measured the ratio of dopamine (DA) to 3,4-dihydroxyphenylacetic acid (nanograms per g) in the striatum. The turnover rate of DA was significantly lower in the diabetic rats than in the control group [diabetic, 0.102 +/- 0.003; control, 0.112 +/- 0.001 (mean +/- SE); P less than 0.05]. A negative correlation between the 3,4-dihydroxyphenylacetic acid to DA ratio and blood glucose level was observed (r = -0.693; P less than 0.01). The present study suggests that there are metabolic abnormalities in the striatum dopaminergic neurons of STZ-induced diabetic rats associated with decreased ambulatory activity.