Impact of Tetrahydropyrido[2,1-b][1,3,5]thiadiazines on L-DOPA Effects in the Tail Suspension Test

Aim. Evaluation of the impact of tetrahydropyrido[2,1-b][1,3,5]thiadiazine derivatives on L-DOPA effects in the tail suspension test.

Materials and methods. Some tetrahydropyrido[2,1-b][1,3,5]thiadiazines exhibit a pronounced antidepressant and adaptogenic activity. We selected compounds that demonstrated the most potent antidepressant effect in the Porsolt’s forced swim test. We chose to combine two approaches in the study: estimation of the antidepressant drug impact on levodopa effects and the tail suspension test. Caffeine sodium benzoate, amitriptyline and fluoxetine were chosen as the reference compounds. Studies of the 1,3,5-thiadiazine effects on levodopa activity were undertaken to ground detailed downstream analyses of associated responses in the dopaminergic neurotransmitter system. We measured the rectal temperature in laboratory rats prior to and after tail suspension and the total active time during 5 min in the test.

Results. Administration of levodopa at a dose of 150 mg/kg led to a reduction in rectal temperature and the total time of physical activity in rats in the tail suspension test. The dosage of 500 mg/kg led to a temperature increase of 0.7°C prior to and after the stress and a longer maintenance of physical activity. Rats exhibited exophthalmos and polyuria.

Levodopa at a 150 mg/kg dosage in combination with caffeine sodium benzoate did not cause a significant increase in the body temperature and prolonged physical activity by 69% in the test vs. the control group. Amitriptyline in combination with levodopa at a dose of 150 mg/kg triggered a temperature increase of 1.3°C prior to and 1.85°C after tail suspension, thus leading to a prolonged physical activity. Levodopa at a dose of 150 mg/kg in combination with fluoxetine led to elevation of the body temperature by 0.6°C prior to and 0.55°C after the stress. The total active time exhibited a declining trend.

The substance TD-0348 reveals an antidepressant activity. Physical active time increased by 32% in the test vs. the control group. Temperature elevation by 1.15°C prior to and 1.25°C after the stress suggests activation of the autonomic nervous system. TD-0470 in combination with levodopa (150 mg/kg) led to a rectal temperature elevation by 0.4°C prior to and 0.7°C after tail suspension. Physical activity was prolonged compared to the levodopa-treated group (150 mg/ kg). TD-0479 led to a temperature elevation by 0.85°C prior to and 0.95°C after the stress and caused polyuria. Treatment with TD-0164 did not provide sufficient data to suggest an impact on dopamine metabolism.

Conclusions. The compounds TD-0348, TD-0470 and TD-0479 affect physiological processes in experimental rats in response to treatment with L-DOPA at a dose of 150 mg/kg, which suggests the autonomic nervous system (ANS) activation. TD-0470 exhibits antidepressant properties. Treatment with TD-0164 does not provide sufficient data to evaluate its dopamine-related effects.