The Relation between Increasing Anxiety and Prolactin-Releasing Peptide in Rats

PrRP, also known as prolactoliberin, is a bovine hypothalamic extract neurohormone that stimulates prolactin synthesis in a rat pituitary adenoma cell line and lactating rat pituitary cells. PrRP has been shown to control the intake of food and energy expenditure, but it may also have a role in stress sensitivity, reproduction, cardia productivity, secretion of endocrine components, and lately, neuroprotective characteristics, among others. The current study was performed to identify if prolactin-releasing peptide (PrRP) had any effect in increasing anxiety clinical features in rats as an animal model. The study included 114 Wistar handling-acclimated male rats (160 gm, 2 months old); divided randomly into three major groups. The rats were divided randomly into three major groups (38-control animals (38C), and 38-PrRP animals (38P), both were examined using the EPM test to test for stress-related signs, such as fear of height (5 mins duration for each rat). The maze was cleaned with water to eliminate the previous rat odor after the experiment for each rat was completed. The tests were performed between 13:00 to 17:00 of the day. Then, a week later, 38 (19-PrRP animals (19P) and 19-control animals (19C)) were examined using the SP test conducted between 13:00 to 16:00 of the day. Fifteen minutes before EPM, the 38C received intranasal 0.9%-10µl NaCl (per nostril), and 38P received intranasal 10^-10mol/l-10 µl PrRP (per nostril), and the anxiety-related signs, such as time spent in open arms (less time means more anxious), during the EPM test were recorded. The 19P and 19C received 10^-10mol/l-10µl PrRP and 0.9%-10µl NaCl, respectively, (intranasal, per nostril, and 15 minutes before the SP test, where a stranger rat was placed in a specific cage in front of each of the 19P and 19C animals in a separate cage, in which both cages provided visual and olfactory but no confrontational contact). The results showed that PrRP significantly (P<0.05) decreased the time spent by the treated rats on the open arms. In addition, PrRP revealed significant (P<0.05) decreases in the time spent close to the stranger rat, which means increased anxiety levels. The current findings revealed that prolactin-releasing peptide increases anxiety and decreases sociality in the studied male rats.