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Co‐Expression of Leptin and Oestrogen Receptors in the Preoptic‐Hypothalamic Area

The interaction between the reproductive axis and energy balance suggests that leptin acts as a possible mediator. This hormone acts in the regulation of metabolism, feeding behaviour and reproduction. Animals homozygous for the gene ‘ob’ (ob/ob) are obese and infertile, and these effects are reversed after systemic administration of leptin. Thus, the present study aimed to determine: (i) whether cells that express leptin also express oestrogen receptors of type‐α (ER‐α) or ‐β (ER‐β) in the medial preoptic area (MPOA) and in the arcuate (ARC), dorsomedial (DMH) and ventromedial hypothalamic nucleus and (ii) whether there is change in the gene and protein expression of leptin in these brain areas in ovariectomised (OVX) animals when oestrogen‐primed. Wistar female rats with normal oestrous cycles or ovariectomised oestrogen‐primed or vehicle (oil)‐primed were utilised. To determine whether there was a co‐expression, immunofluorescence was utilised for double staining. Confocal microscopy was used to confirm the co‐expression. The technique of real‐time polymerase chain reaction and western blotting were employed to analyse gene and protein expression, respectively. The results obtained showed co‐expression of leptin and ER‐α in the MPOA and in the DMH, as well as leptin and ER‐β in the MPOA, DMH and ARC. However, we did not detect leptin in the MPOA, ARC and DMH using western blotting and there was no statistical difference in leptin gene expression in the MPOA, DMH, ARC, pituitary or adipose tissue between OVX rats treated with oestrogen or vehicle. In conclusion, the results obtained in the present study confirm that the brain is also a source of leptin and reveal co‐expression of oestrogen receptors and leptin in the same cells from areas related to reproductive function and feeding behaviour. Although these data corroborate the previous evidence obtained concerning the interaction between the action of brain leptin and reproductive function, the physiological relevance of this interaction remains uncertain and additional studies are necessary to elucidate the exact role of central leptin.