IMPLICATIONS OF IMMEDIATE-EARLY GENE INDUCTION IN THE BRAIN FOLLOWINGSEXUAL STIMULATION OF FEMALE AND MALE RODENTS

Induction of immediate-early genes (IEGs), such as c-fos, has been wid ely used to mark the activation of brain regions following different t ypes of sexual stimulation and behavior, A relatively common set of ho rmone-concentrating basal forebrain and midbrain structures in female and male rodents is activated by copulatory stimulation, in particular , stimulation of sensory nerves that innervate the penis or vagina/cer vix, olfactory or pheremonal stimuli, and conditioned sexual incentive s. These regions include the preoptic area, lateral septum, bed nucleu s of the stria terminalis, paraventricular hypothalamus, ventromedial hypothalamus, medial amygdala, ventral premammillary nuclei, ventral t egmentum, central tegmental field, mesencephalic central gray, and per ipeduncular nuclei. Regions that do not contain classic intracellular steroid receptors, such as the ventral and dorsal striatum or cortex, are also activated. IEGs have also been colocalized with cytoplasmic p roteins like GnRH and oxytocin, and have been used in conjunction with retrograde tracers to reveal functional pathways associated with diff erent sexual behaviors, Steroid hormones can also alter the ability of sexual stimulation to induce IEGs, Despite the many similarities, som e differences in IEG induction between sexes have also been found. We review these findings and raise the question of what IEG induction in the brain actually means for sexual behavior, that is, whether it indi cates the perception of sexual stimulation, commands for motor output, or the stimulation of a future behavioral or neuroendocrine event rel ated to the consequences of sexual stimulation. To understand the role of a particular activated region, the behavioral or neuroendocrine ef fects of lesions, electrical stimulation, drug or hormone infusions, m ust also be known. (C) 1997 Elsevier Science Inc.