Research paperEffects of activation and blockade of orexin A receptors in the medial preoptic area on food intake in male rats

- MPOA is a site implicated in orexin A induced feeding.
- Orexin A increased feeding 2 and 8 h after injection into the MPOA.
- The stimulating effect of orexin receptors into the MPOA on appetite is time dependent and can be removed one day after injection.
- The blocking of orexin type 1 receptors into the MPOA has no effect on rat's food intake.

It has been shown that activation of type 1 orexinergic receptors (ORX1) in several parts of the hypothalamus stimulate food intake. Orexin A receptive sites for food intake exist primarily in a narrow band of the hypothalamus that is known to be involved in control of energy homeostasis. The present study aimed to investigate the role of orexin receptors in the medial preoptic area (MPOA) on food intake in rats. Twenty-four male rats weighing 200-250 g were divided into three groups (n = 8 in each group). Rats were cannulated using stereotaxic coordinates above the MPOA. Normal saline was microinjected into the MPOA in the control group. Another group received intra MPOA microinjection of SB334867, a selective antagonist for ORX1 receptors. In the other group, orexin A was microinjected (0.5 μl of 1 μmol) into the MPOA. Food intake was measured in metabolic cages. The statistical significance of differences between groups was detected by a one way ANOVA. A value of p < 0.05 was considered significant. There was no significant difference in food consumption between saline and SB334867 treated groups. However, activation of the orexin receptor in the MPOA significantly increased food intake during the 2 and 8 h after orexin A microinjection. Our results showed that during ad libitum access to food, activation but not blockade of the MPOA ORX1 receptor can increase food intake in a time-dependent manner. The role of these receptors in hunger and appetite stimulation requires further study.