40 Brain Research, 422 (1987) 40- 51 Elsevier BRE 12899 Sex steroid effects on extrahypothalamic CNS. I. Estrogen augments neuronal responsiveness to iontophoretically applied glutamate in the cerebellum Sheryl S. Smith, Barry D. Waterhouse and Donald J. Woodward* Department of Physiology and Biophysics, Hahnemann University, Philadelphia, PA 19102-1192 (U.S.A.) (Accepted 24 February 1987) Key words: Estrogen; Cerebellar Purkinje cell; Glutamate; Evoked excitation; Neuromodulation The purpose of this study was to test whether 17fl-estradiol (E2) could alter neuronal activity or responsiveness to iontophoretically applied amino acid neurotransmitters in an area not reported to contain classical E 2 receptors. Such a region is the cerebellum, which was selected as a model system for these studies because it has been well characterized electrophysiologically. Extracellular activity of cerebellar Purkinje neurons was recorded from urethane-anesthetized, adult, ovariectomized rats using multibarrel glass micropipets. Spontaneous firing rate and responses of single units to microiontophoretic pulses (10 s pulses every 40 s) of GABA (10-50 nA) or glu- tamate (GLUT, 3-40 nA) were examined before, during and after iontophoretic (0.25 mM 17fl-estradiol hemisuccinate) or jugular i.v. (100, 300 or 1000 ng/kg 17fl-estradiol) administration of E 2. Both modes of E 2 administration resulted in a significant increase in Purkinje cell excitatory responses to GLUT, independent of the direction of change in spontaneous firing rate. This effect was seen as early as one minute after iontophoretic application of E 2 and 10-40 min following i.v. E 2. In all cases, recovery to the control level of response was not observed by 2 h following E 2 administration. 17a-E2 (300 ng/kg) resulted in a less pronounced, transient increase in GLUT response, while a lower dose (I00 ng/kg) did not have any effect. Prior administration of the anti-estrogen tamoxifen did not prevent any of the observed E 2 effects. In addition, estrogen-priming did not alter E2-induced potentiation of GLUT responses. In contrast to the effect of E 2 on GLUT responsiveness, GABA-mediated inhibition of Purkinje cells was either increased, antagonized or unchanged following E 2 application. In summary, this study suggests the hypothesis that circulating levels of E 2 may alter neuronal sensitivity to specific neurotransmitter substances within the cerebellar circuitry. INTRODUCTION Although the classic function of estrogen is to act at the level of the hypothalamo-pituitary-gonadal axis and uterus to promote full reproductive func- tion, recent reports by numerous investigators indi- cate effects of estrogen on a variety of parameters in extrahypothalamic regions of the CNS. Both endoge- nous and exogenously administered estrogen have also been shown to exert global activational effects on sensorimotor function in the rat 2 and human ~4, en- hance seizure activity 28 and alter affect 8. In addition, estrogen has been demonstrated to stimulate dopa- mine release and neuronal excitability in the stria- tum 3,5, and alter receptor and synthetic/degradative enzyme systems for amino acid neurotransmitters in extrahypothalamic areas 26. Local effects of 17fl-es- tradiol (E2) on membrane permeability have also been demonstrated recently 39, suggesting the possi- bility that this steroid may act directly at the mem- brane level. A pertinent question to be asked at this stage is whether estrogen can alter neuronal physiology in an intact, local circuit of the extrahypothalamic CNS. The Purkinje neuron, the major output cell of the cere- bellum, was chosen as a test site because it is well * Present address: Dept. of Cell Biology and Anatomy, Univ. of Texas Health Science Center, Dallas, TX 75235, U.S.A. Correspondence: S.S. Smith, Department of Physiology and Biophysics, Hahnemann University, Broad and Vine, Philadelphia, PA 19102-1192, U.S.A. 0006-8993/87/$03.50 (~) 1987 Elsevier Science Publishers B.V. (Biomedical Division)