C-FOS IMMUNOREACTIVITY IN THE SEXUALLY DIMORPHIC AREA OF THE HYPOTHALAMUS AND RELATED BRAIN-REGIONS OF MALE GERBILS AFTER EXPOSURE TO SEX-RELATED STIMULI OR PERFORMANCE OF SPECIFIC SEXUAL BEHAVIORS

The sexually dimorphic area of the gerbil hypothalamus is essential fo r male sex behavior. To determine which aspects of mating activate its cells, or cells near or connected to it, we visualized c-Fos in the b rains of male gerbils that had been exposed to various types of sex-re lated stimuli or that had displayed various aspects of sex behavior. F ive groups of males were placed in familiar arenas containing sex-rela ted odors. All subjects had previously mated in these arenas. For four groups, a female was introduced and remained with the male until he e jaculated, intromitted, mounted or sniffed her. Males in the fifth gro up remained in the arena alone. Males in a sixth group were placed in a dean arena in another room. These males were also familiar with this arena but had never encountered a female there. The seventh group rem ained in their home cages. The posterodorsal preoptic nucleus, the lat eral part of the posterodorsal medial amygdala, the medial part of the sexually dimorphic area and the parvicellular part of the subparafasc icular nucleus of the thalamus expressed c-Fos after ejaculation. Whet her these cells triggered ejaculation or responded to it is not clear. The latter two areas also expressed c-Fos whenever males were exposed to the sex arena, but the sexually dimorphic area pars compacta did n ot express c-Fos under any condition. The medial core of the nucleus a ccumbens, the ventrolateral septum, the caudomedial bed nucleus of the stria terminalis, the medial/central part of the posterodorsal medial amygdala and the lateral part of the sexually dimorphic area also exp ressed c-Fos when males entered the sex arena. The ventrolateral part of the ventromedial nucleus of the hypothalamus expressed c-Fos whenev er males were with females. None of the 31 areas studied responded to mounting or intromission, but the zona incerta, the amygdalohippocampa l area, the lateral part of the sexually dimorphic area and the area l ateral to the medial part of the sexually dimorphic area showed progre ssive increases in c-Fos expression as mating progressed. The area dor sal to the medial part of the sexually dimorphic area, the paraventric ular nucleus of the hypothalamus, the ventral premammillary nucleus an d the retrorubral field showed the same level of c-Fos expression when males were exposed to the non-sexual context as when they were expose d to the sexual one. While a projection to the retrorubral field from the sexually dimorphic area is critical for male sex behavior, the ret rorubral field did not show a sex-related c-Fos response. The data sug gest that brain regions involved in male sex behavior are involved in different aspects of it and that this can also apply to different subs ets of cells in each area. The data also indicate that cells involved in mating do not necessarily show mating-related patterns of c-Fos exp ression. Thus, while c-Fos is useful for identifying areas involved in mating, or other behaviors, its characteristics could cause relevant areas to be overlooked.