Hippocampus, amygdala and dorsal raphe nucleus are the cerebral main structures involved in learning, memory and anxiety. Ghrelin increases the level of several hormones in these structures and affects learning, memory and anxiety-like behaviors. This study was performed to investigate the effect of ghrelin agonist on passive avoidance learning and anxiety in adult female rats in the presence and absence of ovary hormones. Five groups of rats, including control group with no injections, ovariectomized groups; one group receiving normal saline and other group receiving ghrelin agonist solution, surgery shocked (sham operated) groups; one group receiving saline and other group ghrelin agonist solution, were tested. Inside stereotaxis apparatus, two sided CA1 cannulae were used and 1 microL of saline or ghrelin agonist solution, at 3 nmol microL(-1) concentration, was injected into each cannula. Passive avoidance learning was measured by using shuttle box and anxiety by elevated plus- maze. Ghrelin agonist increased the level of learning in surgery shocked group in comparison with control group. Anxiety-like behavior was seen in both ovariectomized and surgery shocked groups. Ghrelin agonist binds its own receptors in the hippocampus, thereby increases learning capability and induces anxiety-like behaviors. Proper management of these behaviors might be useful in controlling some forms of nervous system diseases in humans.

The relative expression of renin, angiotensin converting enzyme (ACE) and angiotensin II type 1 receptor (AT1R) was performed using quantitative real-time PCR on tissue from the heart ventricles to investigate the effect of 3,5,3'-l-triiodothyronine (T3)-induced pulmonary hypertension syndrome (PHS) in broiler chickens at 12 and 42 d of age. Plasma angiotensin II was also measured using enzyme immunoassay at 12, 21, 28, 32 and 42 d. Renin transcript in the right ventricle of the treated group was significantly increased at 12 d and decreased at 42 d of age compared to controls. ACE transcript in the left ventricle of the treated group was significantly increased at 42 d of age compared to controls. In the right ventricle, the expression of this gene was significantly increased at 12 d while decreased at 42 d of age in the treated group compared to control. AT1R transcript in the right ventricle of the treated group was significantly increased at 12 and 42 d of age compared to control. In the left ventricle of the treated group, the transcript of this gene was only higher at 12 d of age than control. Plasma angiotensin II was significantly increased in pulmonary hypertensive chickens at 28 d of age compared to control. It is concluded that gene expression of renin, ACE and AT1R was relatively upregulated in the heart of chickens developing pulmonary hypertension. The right ventricle of hearts from pulmonary hypertensive chickens showed considerable reductions of renin/ACE and elevation of AT1R which may provide evidence of diminished responsiveness of the renin-angiotensin system.