Spontaneous physical activity and mediators of energy homeostasis in the hypothalamus of mice from 4 to 10 months of age.

NEW FINDINGS: What is the central question of this study? Is the initial decline of spontaneous physical activity (SPA) in mice related to impaired insulin and leptin signalling or brain-derived neurotrophic factor expression in the hypothalamus? What is the main finding and its importance? We showed that SPA started to decline at an early stage, concomitantly with an impairment of hypothalamic leptin signalling. Consequently, energy expenditure decreased and glucose tolerance worsened. Our results demonstrate the need to counteract the initial decline in SPA to avoid metabolic impairments and indicate the possible involvement of central leptin in the reduction in SPA with age. The biological control of physical activity is poorly understood. Age decreases insulin, leptin and brain-derived neurotrophic factor (BDNF) signalling in the hypothalamus, and all have been shown to modulate spontaneous physical activity (SPA). We investigated the age at which SPA starts to decline and whether this is associated with the emergence of hypothalamic insulin and leptin resistance and reduced BDNF expression. Spontaneous physical activity (and other parameters of locomotion) and energy expenditure were determined monthly in mice from the 4th to the 10th month of age. Metabolic and hypothalamic analyses were performed in 4-, 6- and 10-month-old mice. Spontaneous physical activity, distance travelled and speed of locomotion started to decrease in 6-month-old mice. The reduction in SPA became more evident from 8 months of age. Energy expenditure decreased from the 8th month. Hypothalamic BDNF protein expression and insulin signalling did not change throughout the time span studied. Leptin signalling decreased at 6 and 10 months compared with 4 months. Also, compared with 4 months, 6- and 10-month-old mice were glucose intolerant. In conclusion, SPA begins to decline in parallel with reduced hypothalamic leptin signalling. Metabolic impairment also manifests as SPA decreases, highlighting the need to understand the regulation of SPA in order to combat its decline.

Behavioural changes observed in demyelination model shares similarities with white matter abnormalities in humans.

Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating disease of the central nervous system (CNS). Further to the symptoms resulting from demyelination, new studies point to the involvement of neuroinflammation and white matter abnormalities in psychiatric disorders and neurodegenerative diseases. Cuprizone, a model of MS, produces consistent demyelination and elicits behavioural, morphological and inflammatory changes in animals that share some similarities with those observed in humans. In this study, we used the cuprizone model in Lewis rats to evaluate clinical signs triggered by the demyelination process which could be comparable with the symptoms seen in white matter abnormalities in human beings. To induce the demyelination process, 0.6% cuprizone was added to the Lewis rats' diet for 4 weeks. We proceeded with behavioural, morphological and immunological analyses. Animals fed with cuprizone exhibited behavioural changes: higher scores in the neurotoxicity test, reduced exploratory and locomotion behaviour, and also an increase of permanency in the closed arm of the elevated plus maze test, were observed. In these analyses, the animals showed motor coordination impairment and anxiety-like behaviour. Demyelination also triggered changes in discrimination of objects identified by an increase in the time spent close to a familiar object. These behavioural alterations were associated with a significant increase in the levels of TNF-alpha and corticosterone, consistent with the activation of microglia and astrocytes. Taken together, the results of this work show the cuprizone/Lewis rat model demyelination as an attractive paradigm for studying the correlation between white matter abnormalities and behaviour.