Neurotoxicology and Teratology, Vol. 19. No. 5, pp. 355-362,1997 Published by Elsevier Science Inc. Printed in the USA. All rights reserved 0892-0362/97 $17.00 + .OO ELSEVIER PII SO892-0362(97)00041-X Behavioral Effects of Low-Dose Gestational Day 11-13 Retinoic Acid Exposure R. ROBERT HOLSON,* RUSSELL A. GAZZARA,” SHERRY A. FERGUSON” AND JANE ADAMS? zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML *Division of Reproductive and Developmental Toxicology, National Cetiter for Toxicological Research, Jefferson, AR 72079 iDepartment of Psychology, University of Massachusetts, Boston Harbour Campus, Boston, MA 02125 Received 18 November 1996; Accepted 25 March 1997 HOLSON, R. R., R. A. GAZZARA, S. A. FERGUSON, AND J. ADAMS. Behavioral effects of low-dose gestational day II-13 retinoic acid exposure. NEUROTOXICOL TERATOL 19(.5) 355-362, 1997.-In a companion article we report that maternal PO exposure to 2.5 mg/kg all-truns retinoic acid (RA) daily for 3 consecutive days over gestational days (CD) 11-13 produces a 10% reduction in weight of cerebellum at 4 weeks of age, not accompanied by other malformations. Here we report the results of a preliminary behavioral analysis of offspring exposed gestationally to RA as above. Exposed dams were allowed to deliver normally, and litters were culled to eight pups (4 + 1 of each sex) at birth. Both male and female off- spring were tested prior to weaning on CD 21. Thereafter females were killed on postnatal day (PND) 28 for verification of RA effects on regional brain weight, and all subsequent behavioral testing was conducted on males. Preweaning tests were re- stricted to negative geotaxis (PND 8-9) and open field activity (PND 22). Postweaning tests included open field activity (PND 43). auditory startle response (three times, on PNDs 22, 43, and 84), 2-week activity in residential running wheels (PNDs 62-76), complex maze performance for 5 consecutive days (PND 83-87) emergence latency (PND 106), and assess- ment of the behavioral response to an amphetamine challenge (PND 107). Males were then killed on PND 108 for verifica- tion of RA effects on regional brain weights. In this study, RA reduced weight of cerebellum but not striatum. Cerebellar weight was 92% of control values in PND 28 females, and this weight difference had diminished to 95% of control weight by PND 108 in males. There were no treatment effects on negative geotaxis, activity in a small open field, auditory startle ampli- tude, or latency to enter an illuminated alley from a dark chamber. Maze learning occurred at levels equal to or slightly better than controls. Running wheel activity was enhanced by RA exposure, whereas activity in response to an amphetamine chal- lenge was reduced by such exposure. We conclude that RA doses low enough to produce mild weight reductions in cerebel- lum, without attendant malformations, can alter behavior. The precise nature of these alterations remains to be elucidated, but the findings reported here suggest that effects may be more pronounced on activity than on learning. Published by Elsevier Science Inc. Retinoids All-trans retinoic acid Brain Development Cerebellum Behavior Learning Activity IT is now evident that children exposed to isotretinoin early in pregnancy often have reduced intelligence, and this impair- ment is not always accompanied by other detectable malfor- mations (4). The malformations caused by retindid exposure in animals are developmental stage specific (20,25,26,30), and it is probable that the same is true for retinoid effects on the brain. Because the occasional early gestational exposure in humans cannot shed much light on the question of the age- specific neurological effects of retinoid exposure, it is neces- sary to examine this question in laboratory animals. In two companion articles we have begun an investigation of this problem by assessing the effects of RA exposure in rats at three separate gestational periods: GD 8-10 or 11-13 or 1416 (13,14). In these studies we report a marked sensitive period on GD 11-13 for all-truns retinoic acid effects on lethality, body weight, weight of cerebellum, and volume of cerebellar relay nuclei. In this article we further examine the effects of GD 11-13 RA exposure on behavioral measures. Requests for reprints should be addressed to R. Robert Holson, National Center for Toxicological Research. Division of Reproductive and Developmental Toxicology, 3900 NCTR Rd., Jefferson, AR 72079. Tel: (501) 543-7050; Fax: (501) 543-7682. 355