Printed in Great Britain Effec t of penty l ene te trazo l on the carbaryl - induced changes of serotonin metabol i sm in rat - brain hypothalamus

Carbaryl (200 mg/kg or #00 mg/kg, p.o.) significantly elevated serotonin (5-HT) (57-109%) and 5-hydroxyindoleacetic acid (5-HIAA) (60-7g%) levels at t.0 h in the hypothalamic region of adult male rat brain. Further, administration of carbaryl (200 mg/kg, p.o.) for different time intervals (0.5 h, 1.0 h, and 2.0 h) revealed that both 5-HT and 5-HIAA levels elevated maximally at 0.5 h in hypothalamus. These regional 5-HT and 5-HIAA levels were not significantly affected with pen ty lene te t r azo l (PTZ) at any time after its t rea tment . But simultaneous administration of carbaryl (200 mg/kg, p.o.) and PTZ (60 mg/kg, s.c.) reduced the carbaryl-induced elevation of both 5-HT and 5-HIAA leveis . Measurement of (i) probenecid-induced (200 mg/kg 9 i .p.) accumula t ion and (ii) pargyline-induced (75 mg/kg, i.p.) depletion of hypothalamic 5-HIAA level in the absence or presence of carbaryl (200 mg/kg, p.o.) and/or PTZ (60 mg/kg, s .c . ) r evea led that (a) ca rba ry l enhanced the synthesis as well as the breakdown of 5-HT, (b) PTZ had no ef fec t on either of these processes of 5-HT9 and (c) carbaryl-induced increased catabolism of 5-HT became normal in the presence of PTZ.