Neurotoxicology and Teratology. Vol. 13, pp. 471-474. ©Pergamon Press plc, 1991. Printed in the U.S.A. 0892-0362/91 $3.00 + .00 BRIEF COMMUNICATION Prenatal Valproic Acid Exposure Decreases Neuronal Membrane Order in Rat Offspring Hippocampus and Cortex CHARLES V. VORHEES,* SCOTT L. RAUCHt AND ROBERT J. HITZEMANNf *Institute for Developmental Research, Children's Hospital Research Foundation and Department of Pediatrics University of Cincinnati, Cincinnati, OH 45229 ?Department of Psychiatry, Massachusetts General Hospital, Boston, MA 02114 SDepartment of Psychiatry and Behavioral Science, State University of New York at Stony Brook Stony Brook, NY 11794 Received 15 January 1991 VORHEES, C. V., S. L. RAUCH AND R. J. HITZEMANN. Prenatal valproic acid exposure decreases neuronal membrane order in rat offspring hippocampus and cortex. NEUROTOXICOL TERATOL 13(4) 471--474, 1991.--Sprague-Dawley rats were administered 0 or 200 mg/kg of valproic acid (VPA) on days 7-18 of gestation. Controls were pair-fed. On postnatal day 28, analyses of brain tissues were performed on enriched neuronal membrane fractions from cerebellum, hippocampus, and cortex for anisotropy using the membrane probe 1,6-diphenyl-l,3,5-hexatriene (DPH). No significant differences in membrane anisotropy were noted in the cerebellum, but a significant reduction in anisotropy in the hippocampus and cortex was observed. This change corresponds to a 3-5°C increase in temperature or that produced by other membrane disordering agents (ethanol, phenytoin), An association between membrane anisotropy and functional effects of prenatal VPA exposure is discussed. Synaptic membrane order Prenatal valproic acid Anisotropy in hippocampus Anisotropy in cortex In utero valproic acid and membrane anisotropy Valproate-induced reduction in membrane order Rats PERLMAN and Goldstein (10) have demonstrated that the po- tency of valproic acid and structurally related fatty acids to de- crease synaptic membrane order in vitro parallels their anticonvulsant activity against pentylenetetrazol-induced sei- zures. We have recently found that prenatal exposure of rats to another anticonvulsant, phenytoin, decreases in vivo hippocam- pal synaptic membrane order 28 days postnatally (19). VPA has also been found to be behaviorally teratogenic in rats (16). These data suggest that a) anticonvulsants may share one or more common mechanisms of action on neuronal membranes and b) one such common mechanism may be decreased neuronal membrane order. We propose to extend the theme of a common mechanism of action on embryonic development to other anti- convulsants. This would be consistent with the observation that, despite the fact that children have been described as having de- velopmental impairments related to different maternal anticon- vulsant exposures, all of the syndromes exhibit a high degree of symptom overlap (1). Indeed, it has been suggested that sepa- rate syndromes do not exist, but rather that there may be a ge- neric fetal anticonvulsant syndrome (3). The present experiment was designed to determine the effects of prenatal valproic acid exposure on postnatal synaptic plasma membrane order development in specific brain regions. Synaptic plasma membrane order is a tightly regulated marker of neuronal development (12,15). Membrane order increases ontogenetically and shows differential temporal and regional changes which par- allel synaptic maturation (6,11). An increase in cholesterol rela- tive to phospholipid biosynthesis appears to be primarily respons- ible for the developmental increase in membrane order. We hy- pothesized that valproic acid would delay synaptic membrane ontogeny, and we were particularly interested in effects on the hippocampus, based on our previous neuronal anisotropy (19) and behavioral teratogenic findings with phenytoin (17,20). METHOD Nulliparous female Sprague-Dawley CD rats (Charles River, Portage, MI) and their offspring served as subjects. Females were acclimated to the laboratory for 2--4 weeks prior to breed- ing. Rats were maintained in facilities fully accredited by the American Association for the Accreditation of Laboratory Ani- mal Care. Housing was in rooms with regulated temperature (22-4-2°C) and humidity (50 _+ 10%) and automatic lighting (12-h light/dark cycle), and rats were provided with Purina 5001 rat chow and filtered water. 471