| OBJECTIVETo explore the effects of exposure of Sprague-Dawley (SD) rats to organophosphate pesticide chlorpyrifos (CPF) at low dosage on their neurobehavior and substantia nigra pars compacta(SNpc) tyroxine hydroxylase (TH).METHODS56 neonate SD rats were divided randomly into experiment group (Goup A), vehicle control group (Group B) and naive control group (Group C). 24 animals in Group A were administrated with CPF (3mg/kg/d, i.p.) to establish CPF exposure model of neonate SD rats at ages of PN1-7d (Subgroup A1, n=8), PNS-14d(Subgroup A2, n=8) and PN1-21d (Subgroup A3, n=8), respectively. The animals in Group B (n=24) were injected with vehicle of dimethylsulfoxide intraperitoneally. The animals in Group C (n=8) were used as the naive. Group A animals were monitored for their weights dynamically and observed whether or not they present acually poinsoning symptoms within 6 hours following CPF administration, and their neurobehavior were estimated at PN30d and PN60d, including emotion level measured by rating scals, locomotor and cognitive ability measured by Open Field Test and anxious leve measured by Elevated-Plus Maze Test. For Subgroup A3 animals, SNpc TH expression were assayed via immnohistochemisty. Each of the measures or observations of Group A correspondingly had their controls.RESULTS1. There were significant difference in neruobehavour at PN60d between Group A and Group B as well as Group C (p＜0.05). Emotion leves of A1 (2.75±0.50), A2 (2.75±1.50) and A3 (2.67±1.63) were all significantly lower that that of B1 (3.33±1.75), B2 (3.83±1.17) and B3 (3.75±1.71) as well as that of Group C (4.33±0.52). A1, A2 and A3 showed impaired cognition and their spending time (5.50±3.32,8.00±3.37, 6.83±2.79) in certal aquares of Open Field were significantly longer compared with B1, B2, B3 and C (1.33±0.80, 1.67±1.21, 1.75±0.87, 0.33±0.12, p＜0.05). A1, A2 and A3 demontrated obviously lower locomotion (34.00±9.13,31.75±6.13,18.50±7.39 ) than did B1, B2 , B3 and C (59.17±12.80, 57.17±11.13, 58.00±19.30, 63.17±19.17, p＜0.05). In terms with the time spent in the open arms and closed arms, and the entries into the open arms and closed arms of the Elevated-Plus Maze, the animals significantly increased anxious level in A1, A2 and A3 compared with their corresponding controls (p＜0.05). No significant difference existed parewise in neurobehavior among A1, A2 and A3(P＞0.05). There was no significant difference in neurobehaviour at PN3 0d between A and the variant controls (P＞0.05).2. There were significant difference in the SNpc expression at PN60d between A3 (159.20±9.64) and B3 (96.48±6.91) as well as C (95.94±2.45) (P＜005).3. Group A didn't significantly differ from the controls in weight gain (P＞0.05).4. Actual poinsoning symptoms didn't occur during the observation period.CONCLUSIONExposure of Neonate SD rats to low dose of CPF can lead to decreased SNpc expression and altered neurobehavior, including decreased emotion level, impaired cognition, decreased locomotion and increased anxious level at PN60d.
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