RESUMEN
An enriched environment protects dopaminergic neurons from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neuronal injury, but the underlying mechanism for this is not clear. Growth associated protein-43 (GAP-43) is closely associated with neurite outgrowth and axon regeneration during neural development. We speculate that an enriched environment can reduce damage to dopaminergic neurons by affecting the expression of GAP-43. This study is designed to test this hypothesis. Three-month-old female senescence-accelerated mouse prone 8 (SAMP8) mice were housed for 3 months in an enriched environment or a standard environment. These mice were then subcutaneously injected in the abdomen with 14 mg/kg MPTP four times at 2-hour intervals. Morris water maze testing demonstrated that learning and memory abilities were better in the enriched environment group than in the standard environment group. Reverse-transcription polymerase chain reaction, immunohistochemistry and western blot assays showed that mRNA and protein levels of GAP-43 in the substantia nigra were higher after MPTP application in the enriched environment group compared with the standard environment group. These findings indicate that an enriched environment can increase GAP-43 expression in SAMP8 mice. The upregulation of GAP-43 may be a mechanism by which an enriched environment protects against MPTP-induced neuronal damage.
RESUMEN
Senescence-accelerated mouse prone 8 (SAMP8) has an early onset of senility and a shorter life span, providing with cognitive impairment. Contrasted with C57BL/6 mouse, which is most commonly used in the study of Parkinson's disease (PD), SAMP8 needs shorter period of breeding and might be good candidate for the investigation of cognitive impairment in PD. Studies had shown the increase of sensibility to 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) with aging in C57BL/6 mouse. However, the sensitivity of MPTP neurotoxicity depends on the strains of animal and the exact mechanisms of the progression of PD promoted by aging is lack of consensus. Here, we showed after MPTP injection, the spontaneous activity of both young (3-month-old) and old (6-month-old) SAMP8 decreased dramatically, and the old mice required longer recovery time. Immunohistochemical and immunoblot analysis revealed that old mice displayed significant reductions in the dopaminergic neuron numbers and tyrosine hydroxylase (TH) protein. Microglia protein (CD11b) in the striatum of old mice increased more pronouncedly than that in the young mice from 24 h to 3 days. Inducible nitric oxide synthase (iNOS) in the striatum remarkably increased, however, no discernible difference between the two groups was found. These results suggested that the sensibility to MPTP increased with aging in SAMP8. A greater increase of microglial activation in old mice may be a possible mechanism to explain how advancing age predisposes the dopamine system to parkinsonism. The MPTP-SAMP8 model will start a new consideration for the study of PD.
Asunto(s)
Envejecimiento/metabolismo , Encéfalo/metabolismo , Dopamina/metabolismo , Microglía/metabolismo , Neuronas/metabolismo , Trastornos Parkinsonianos/metabolismo , 1-Metil-4-fenil-1,2,3,6-Tetrahidropiridina , Animales , Encéfalo/patología , Antígeno CD11b/metabolismo , Recuento de Células , Cuerpo Estriado/metabolismo , Cuerpo Estriado/patología , Masculino , Mesencéfalo/metabolismo , Mesencéfalo/patología , Ratones , Ratones Mutantes , Microglía/patología , Actividad Motora , Degeneración Nerviosa/inducido químicamente , Degeneración Nerviosa/metabolismo , Degeneración Nerviosa/patología , Neuronas/patología , Óxido Nítrico Sintasa de Tipo II/metabolismo , Trastornos Parkinsonianos/inducido químicamente , Trastornos Parkinsonianos/patología , Factores de Tiempo , Tirosina 3-Monooxigenasa/metabolismoRESUMEN
Neuroprotective effects of enriched environment (EE) have been well established. Recent study suggests that exposure to EE can protect dopaminergic neurons against MPTP-induced Parkinsonism. After 64 female SAMP8 mice were reared in EE and standard environment (SE) for 3 months, the effects of EE and SE were compared on behavioural change, tyrosine hydroxylase (TH) immunoreaction positive neuron and dopaminetransporter (DAT) expression in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP)-treated SAMP8. EE mice showed decreased spontaneous activity compared with SE mice. But EE+MPTP mice showed less decreased spontaneous activity compared with SE+MPTP mice. Otherwise, EE mice showed increased percentage of entries into the open arms and percentage of time spent in the open arms. Furthermore, EE mice demonstrated reduced neurotoxicity, with less decreased TH mRNA and protein expression in Substantia Nigra (SN) after MPTP administration compared with SE mice. SE mice showed a 53.77% loss of TH-positive neurons, whereas EE mice only showed a 42.28% loss. Moreover, EE mice showed decreased DAT mRNA and protein expression compared with SE mice. These data demonstrate that EE can protect dopaminergic neurons against MPTP-induced neuronal damage, which suggest that the probability of developing Parkinson's disease (PD) may be related to life environment.
Asunto(s)
Encéfalo/patología , Ambiente , Trastornos Parkinsonianos/etiología , Trastornos Parkinsonianos/patología , Animales , Conducta Animal/fisiología , Encéfalo/metabolismo , Encéfalo/fisiopatología , Recuento de Células , Proteínas de Transporte de Dopamina a través de la Membrana Plasmática/biosíntesis , Femenino , Inmunohistoquímica , Ratones , Degeneración Nerviosa/patología , Neuronas/metabolismo , Neuronas/patología , Trastornos Parkinsonianos/metabolismoRESUMEN
Application of aged animals to studies of Parkinson's disease (PD) will be beneficial to improve the understanding of its pathogenesis. The senescence-accelerated mouse prone8 (SAMP8) mouse has an early onset of senility and a short life span, characterized by learning and memory impairment, and affective disturbance in the aging process. There is no animal currently being used as a PD model that exhibits these characteristics. Application of the SAMP8 mouse to PD research may have several merits. For the first time, we have investigated damage of the nigrostriatal system in the SAMP8 mouse induced by 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). Male SAMP8 mice (12 weeks) were treated with four subcutaneous injections of MPTP (20mg/kg at 2h intervals): spontaneous activity decreased significantly after the third injection, and recovered 48h after the first injection. In MPTP-SAMP8 mice, the tyrosine hydroxylase (TH)-positive neuronal loss at 6h (7.06%), 24h (12.79%), 3 days (22.49%), and 8 days (42.39%), while striatal dopamine (DA) levels decreased at 6h by 79.09%, at 24h by 80.33%, at 3 days by 83.86%, and at 8 days by 80.14%. These results indicated that there were marked decreases in striatal DA levels and a loss of dopaminergic neurons in the substantia nigra, with the behavior change following shortly thereafter, in MPTP-SAMP8 mice. On the basis of the current findings, the SAMP8 mouse is also vulnerable to neurotoxic effects of MPTP. These data suggest that the SAMP8 mouse may be utilized in PD research.