Neurotoxicologyand Teratology, Vol. 15, pp. 139-144,1993 0892-0362/93$6.00 + .00 Printedin the U.S.A. All rightsreserved. Copyright © 1993Pergamon Press Ltd. Effects of Perinatal Diazepam Exposure on the Sexually Dimorphic Rat Locus Coeruleus M. RODRIGUEZ-ZAFRA, M. R. DE BLAS, C. PEREZ-LASO, J. M. CALES, A. GUILLAMON AND S. SEGOVIA l Departamento de Psicobiolog/a, Universidad Nacional de Educaci6n a Distancia, Ciudad Universitaria, 28040-Madrid, Spain Received 27 March 1992; Accepted 7 January 1993 RODRIGUEZ-ZAFRA, M., M. R. DE BLAS, C. PEREZ-LASO, J. M. CALES, A. GUILLAMON AND S. SEGOVIA. F_Jfectsof perinatal diazepam exposure on the sexually dimorphic locus coeruleus of the rat. NEUROTOXI- COL TERATOL 15(2) 139-144, 1993.-Diazepam (DZ) administration over prenatal, postnatal, and pre plus postnatal periods altered the normal expression of the morphological sex differences of the LC. Males were affected only by the prenatal exposure and the effect of this exposure produced an increase in the volume and neuron number of male's LC. By contrast, females were affected by both pre and postnatal treatments and the effect of this exposure resulted in a decrease in the volume and neuron number of female's LC. However, pre plus postnatal treatment did not affect female's LC. Sex differences Diazepam Neuroteratology Locus coeruleus IT has been shown that benzodiazepines (BDZ), anxiolytic compounds widely used in clinical practice (24,25), are able to induce long-lasting neural and behavioral effects (13-17,22- 25,42,48). We have reported (44) that early postnatal DZ ad- ministration, from the day of birth (P0) to day 16 (PI6) alters the sexual differentiation of the locus coeruleus (LC). This period overlaps the time in which the maximal concentration of BDZ receptors is reached in the rat brain (4). In the LC, a brainstem cellular group that supplies the main norepineph- rine (NE) source to the brain (2,12,45), female presented greater volume and neuron number than male rats (8,18,44). After P0-P16 DZ treatment both volume and neuron number were decreased in the LC of the females but not of the males (44). This teratogenic effect of the DZ on the sexual dimor- phism of the LC is similar that those found after the andro- genization of the female rat on the day of birth (8,18). The noradrenergic system has been described as being al- tered by DZ administration during pregnancy (23,24,42). The hypothalamic levels of NE were decreased in adult rats after the prenatal exposure to DZ and this treatment prevented the decrease of NE hypothalamic levels that occurs after restraint stress and attenuated the stress-induced increase of plasma corticosterone levels (23). Moreover, prenatal DZ treatment affects the brainstem NE levels in a gender-related manner, because this treatment induced higher NE levels in treated males, as compared to control males, but not in treated female rats when they were adult (42). However, there is no information about the influence of DZ exposure during different periods of the early develop- ment on the sexual differentiation of LC. Therefore, the aim of the present work is to elucidate the possible long-lasting effects of prenatal (EI4-E21), postnatal (P0-PI6) and pre plus postnatal (EI4-E21 plus P0-PI6) DZ exposure on the development of sex differences in the size and neuron number of the dorsal and ventral regions of the rat LC (28,29,45,46). METHOD Subjects Sixteen pregnant rats of the Wistar strain (Sepal, Madrid, Spain) were weighed on gestational day (GD) 14 and randomly assigned to DZ or control groups. On the day of birth, the litters were cross-fostered, and in any one group, animals from a minimum of three litters were included. So, male and female rat pups were randomly divided into the following groups: (a) Prenatal Groups (PRE): 7 males and 7 females were exposed to DZ daily over GD 14-21. They were injected postnatally over days 0 to 16 with vehicle; (b) Postnatal Groups (POST): 7 males and 7 females were exposed prena- tally over GD 14-21 to vehicle and exposed to DZ on a daily basis postnatally (Days 0 to 16); (c) Pre Plus Postnatal Groups (PP): 7 males and 7 females were exposed to DZ pre and postnatally GD 14 to 21 plus postnatal days 0 to 16); (d) Vehicle Groups (VEH): 7 males and 5 females were exposed to vehicle pre and postnatally (GD 14-21 plus postnatal days 0-16). LRequests for reprints should be addressed to S. Segovia, Depanamento de Psicobiologta, Universidad Nacional de Educaci6n a Distancia, Ciudad Universitaria, P.O. Box 50487, 28040-MADRID, Spain. 139