AIM: To investigate the involvement of L-type Ca2+ channels in antinociceptive action induced by the 5-HT precursor,5-hydroxytryptophan (5-HTP). METHODS: Female Kunming mice were treated with either 5-HTP (20-80 mg/kg,ip) alone, or the combination of 5-HTP and fluoxetine (2-8 mg/kg, ip), pargyline (15-60 mg/kg, ip), nimodipine (2.5-10 mg/kg, ip), nifedipine (2.5-10 mg/kg, ip), verapamil (2.5-10 mg/kg, ip), CaCl2 (5-20 mmol/L, icv), or EGTA(0.5-3 mmol/L, icv) prior to the hot-plate test (55 C, hind-paw licking latency). In addition, locomotor activity inmice treated with 5-HTP alone was measured using an ambulometer with five activity boxes. RESULTS: Ipinjection of 5-HTP alone had no influence on the spontaneous locomotor activity, whereas dose-dependently in-creased the latency to licking hind-paw in the hot-plate test in mice. The inhibitory effects of 5-HTP on nociceptiveresponse were significantly enhanced by fluoxetine in the mouse hot-plate test. At a sub-effective dose, pargylinecould cause a leftward shift in the dose-response curve of 5-HTP-induced antinociception. Co-administration with5-HTP and nimodipine, nifedipine, or verapamil obviously potentiated the antinociceptive effects elicited by 5-HTP.Interestingly, 5-HTP-induced antinociception was antagonized by CaCl2 and enhanced by EGTA injected icv in themouse hot-plate test. CONCLUSION: These findings suggest that systemic administration of 5-HTP may yield theantinociceptive effects, which are related to Ca2+ influx from extracellular fluid through L-type Ca2+ channels. AIM: To investigate the involvement of L-type Ca 2+ channels in antinociceptive action induced by the 5-HT precursor, 5-hydroxytryptophan (5-HTP). METHODS: Female Kunming mice were treated with either 5-HTP kg, ip) alone or in combination with 5-HTP and fluoxetine (2-8 mg / kg ip) pargyline (15-60 mg / kg ip) verapamil (2.5-10 mg / kg, ip), CaCl2 (5-20 mmol / L, icv), or EGTA (0.5-3 mmol / L, icv) prior to The hot-plate test (55 C, hind-paw licking latency). In addition, locomotor activity in mice treated with 5-HTP alone was measured using an ambulometer with five activity boxes. the spontaneous locomotor activity, but dose-dependently in-creased the latency to licking hind-paw in the hot-plate test in mice. The inhibitory effects of 5-HTP on nociceptive responses were significantly enhanced by fluoxetine in the mouse hot-plate test. At a sub-effective dose, parg Co-administration with 5-HTP and nimodipine, nifedipine, or verapamil apparent potentiated the antinociceptive effects elicited by 5-HTP. Interrestingly, 5-HTP-induced CONCLUSION: These findings suggest that systemic administration of 5-HTP may yield theantinociceptive effects, which are related to Ca2 + influx from extracellular fluid through L-type Ca2 + channels .