Psychoneuroendocrinology, Vol. 23, No. 7, pp. 701 – 712, 1998 © 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0306-4530/98 $19.00 +0.00 PII: S0306-4530(98)00035-3 EFFECT OF DIAZEPAM AND SEX HORMONES ON EEG OF GONADECTOMIZED MALE AND FEMALE RATS E. Ugalde 1 , I.Y. Del Rı ´o-Portilla 1 , J. Jua ´rez 2 , A. Rolda ´n 1 , M.A. Guevara 1,2 and M. Corsi-Cabrera 1 1 Facultad De Psicologı ´a, Posgrado, Universidad Nacional Auto ´noma de Me ´xico, Av. Universidad 3004 Copilco-Universidad Me ´xico, D.F. 04510, Mexico 2 Instituto de Neurociencias, Universidad de Guadalajara, Rayo 2611, Guadalajara, Jalisco, Mexico (Receied 3 December 1997; in final form 19 July 1998) SUMMARY Waking EEG was recorded from left and right parietals in 60 adult Wistar rats gonadectomized after puberty during 5 days, 1 as baseline, 1 with vehicle and 1 with 10 mg/kg i.m. of diazepam with hormonal treatment (either testosterone propionate, 5- -dihydrotestosterone or vehicle in males and progesterone, estradiol benzoate or vehicle in females). Quantitative EEG analysis showed that: diazepam in gonadectomized males increased absolute power of ,  1 and  2, increased interparietal correlation of  and decreased interparietal correlation of slow , fast  and  1, whereas in gonadectomized females, diazepam additionally decreased slow and fast  absolute power. EEG effects were not modified by testosterone propionate or 5- -dihydrotestosterone treatment in males. Diazepam plus estradiol rendered the female EEG response similar to the gonadectomized or testosterone-treated males response; diazepam plus progesterone induced the same response in females as in gonadectomized females and additionally induced interparietal asymmetry and de- creased interparietal correlation of all EEG bands. Present results add information on the effects of diazepam on interparietal coupling of EEG and demonstrate that the EEG response to diazepam in adult rats is sexually dimorphic and depends on sex as well as on activational effects of gonadal steroids. © 1998 Elsevier Science Ltd. All rights reserved. Keywords — Waking EEG; Gonadectomy; Sex differences; Hormonal treatment; Benzodiazepines. INTRODUCTION Quantitative analysis of electroencephalographic activity (EEG) from parietal cortex in intact adult rats has shown the existence of sex differences in the waking EEG. Males show higher  relative power, as well as, higher interparietal coupling (IPC), as assessed by interhemispheric correlation than females (Jua ´rez and Corsi-Cabrera, 1995). These sex differences are dependent on the organizational actions of sex steroids during the critical prenatal period of brain sex differentiation. Exposure of females fetuses to testosterone propionate during 14 – 19 days of gestation masculinize their EEG: the values of  relative Address correspondence and reprint requests to: Dra. Marı ´a Corsi-Cabrera, Facultad de Psicologı ´a Posgrado, Av. Universidad 3004, Copilco-Universidad, Me ´xico, D.F. 04510, Me ´xico (Tel: +52 5 6222251; Fax: +52 5 5502560; E-mail: corsi@servidor.unam.mx). 701