title: Different amounts of ejaculatory activity, a natural rewarding behavior, induce differential mu and delta opioid receptor internalization in the rat's ventral tegmental area.
abstract: Opioid receptors internalize upon specific agonist stimulation. The in vivo significance of receptor internalization is not well established, partly due to the limited in vivo models used to study this phenomenon. Ejaculation promotes endogenous opioid release which activates opioid receptors at the brain, including the mesolimbic system and medial preoptic area. The objective of the present work was to analyze if there was a correlation between the degree of in vivo mu (MOR) and delta opioid receptor (DOR) internalization in the ventral tegmental area and the execution of different amounts of ejaculatory behavior of male rats. To this aim, we analyzed the brains of rats that ejaculated once or six successive times and of sexually exhausted rats with an established sexual inhibition, using immunofluorescence and confocal microscopy. Results showed that MOR and DOR internalization increased as a consequence of ejaculation. There was a relationship between the amount of sexual activity executed and the degree of internalization for MOR, but not for DOR. MOR internalization was larger in rats that ejaculated repeatedly than in animals ejaculating only once. Significant DOR internalization was found only in animals ejaculating once. Changes in MOR, DOR and beta arrestin2 detection, associated to sexual activity, were also found. It is suggested that copulation to satiety might be useful as a model system to study the biological significance of receptor internalization.
authors.affiliation: Departamento de Farmacobiología, Cinvestav Sede Sur, Calzada de los Tenorios 235, Col Granjas Coapa, Delegación Tlalpan, C.P. 14330, México D.F., México; Departamento de Neuromorfología Funcional, Dirección de Neurociencias, Instituto Nacional de Psiquiatría "Ramón de la Fuente Muñiz", Av. México-Xochimilco 101, Col. San Lorenzo Huipulco, C.P. 14370, México, D.F., México.
authors.forename: René
authors.initials: R
authors.lastname: Garduño-Gutiérrez
authors.forename: Martha
authors.initials: M
authors.lastname: León-Olea
authors.forename: Gabriela
authors.initials: G
authors.lastname: Rodríguez-Manzo
mesh_terms: D000818:Animals; D004542:Ejaculation / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D008297:Male; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D017465:Receptors, Opioid, delta / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D012201:Reward; D017557:Ventral Tegmental Area / Q000378:metabolism*
chemical_list: D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu
keywords: Ejaculation; Endogenous opioids; In vivo mu and delta opioid receptor internalization; Sexual exhaustion; Ventral tegmental area; β-Arrestin2