RESUMEN
We previously identified KEPI as a morphine-regulated gene using subtractive hybridization and differential display PCR. Upon phosphorylation by protein kinase C, KEPI becomes a powerful inhibitor of protein phosphatase 1. To gain insights into KEPI functions, we created KEPI knockout (KO) mice on mixed 129S6xC57BL/6 genetic backgrounds. KEPI maps onto mouse chromosome 10 close to the locus that contains the mu-opioid receptor (Oprm1) and provides a major quantitative trait locus for morphine effects. Analysis of single nucleotide polymorphisms in and near the Oprm1 locus identified a doubly-recombinant mouse with C57BL/6 markers within 1 Mb on either side of the KEPI deletion. This strategy minimized the amount of 129S6 DNA surrounding the transgene and documented the C57BL/6 origin of the Oprm1 gene in this founder and its offspring. Recombinant KEPIKO mice displayed (a) normal analgesic responses and normal locomotion after initial morphine treatments, (b) accelerated development of tolerance to analgesic effects of morphine, (c) elevated activity of protein phosphatase 1 in thalamus, (d) attenuated morphine reward as assessed by conditioned place preference. These data support roles for KEPI action in adaptive responses to repeated administration of morphine that include analgesic tolerance and drug reward.
Asunto(s)
Analgésicos Opioides/farmacología , Tolerancia a Medicamentos/genética , Morfina/farmacología , Dolor/tratamiento farmacológico , Proteínas/genética , Eliminación de Secuencia , Animales , Condicionamiento Clásico/efectos de los fármacos , Condicionamiento Clásico/fisiología , Tolerancia a Medicamentos/fisiología , Péptidos y Proteínas de Señalización Intracelular , Locomoción/efectos de los fármacos , Locomoción/fisiología , Proteínas de la Membrana , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos , Ratones Noqueados , Dolor/genética , Dolor/metabolismo , Polimorfismo de Nucleótido Simple , Proteína Fosfatasa 1/metabolismo , Proteínas/metabolismo , Receptores Opioides mu/genética , Recompensa , Percepción Espacial/efectos de los fármacos , Percepción Espacial/fisiología , Tálamo/enzimologíaRESUMEN
Pineal melatonin synthesis (serotonin --> N-acetylserotonin --> melatonin) is severely compromised in most inbred strains of mice, in many cases because serotonin is not acetylated by serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase, AANAT). We have found that in the C57BL/6J strain, AANAT mRNA encodes a severely truncated AANAT protein, because a pseudo-exon containing a stop codon is spliced in. This is the first identification of a natural mutation which knocks down melatonin synthesis. The decrease in melatonin signaling may have been a selective factor in the development of laboratory strains of mice because melatonin can inhibit reproduction and modify circadian rhythmicity.