Rat as model for studying behavior effects of hCG

The demonstration of receptors for luteinizing hormone (LH)/human chorionic gonadotropin (hCG) in several parts of rat brain suggested their novel functional role. Subsequent studies tested the effect of hCG (intraperitoneally or intracerebroventricularly) on brain arousal and different types of stress situations in an intact female rat model on the day of proestrus. Treatment resulted in changes of activity and several other behavioral patterns associated with sites of brain hCG/LH receptors. hCG given peripherally caused a longer sleeping time and a decreased activity level. Whereas administration of indomethacin alone had no effect, coadministration inhibited the effects of hCG. hCG increased immunoreactive prostaglandin D2 (PGD2) and decreased PGE2 in brain areas controlling activity and sleep. hCG effects were probably mediated via prostaglandin pathways. After central hCG treatment, animals were less active and showed less exploratory behavior in an open-field box than the control animals. Taste and odor neophobias were dramatically decreased following central injection of hCG. hCG-treated rats were less anxious and exhibited a higher level of maternal interest than the controls. hCG treatment also had a beneficial effect against stress ulcer, which was prevented by pretreatment with antisense receptor oligonucleotide, suggesting a direct hCG receptor-mediated effect. In summary, because hCG can cross the blood-brain barrier, both peripheral administration and central administration affect several behavioral patterns. This effect is similar to treatment with anxiolytics and suggests the functional relevance of brain LH/hCG receptors. Some observed behavioral changes have parallels in pregnant women.