PPARα is involved in high-fat diet-induced risk avoidance impairment via the regulation of hippocampal BDNF.

Risk avoidance behaviors are essential for survival. "Uncontrollable" risk-taking behaviors in animals or humans may have severe adverse consequences. In humans, a large proportion of psychiatric disorders are accompanied by impairments in risk avoidance. Obesity is associated with psychiatric disorders. Peroxisome proliferator-activated receptor α (PPARα) takes part in regulating lipid metabolism and neuronal function. Here, we investigated the effect of high-fat diet (HFD)-induced obesity on risk avoidance and the role of PPARα in this behavior. Male PPARα-null (KO) mice and wild-type (WT) mice were assigned to four different groups: WT-CON and KO-CON (normal diet); WT-HFD and KO-HFD (high fat diet). The HFD began at week 6 and was continued until sampling. A series of behavioral tests were performed at week 11. We found that WT but not KO mice fed with a HFD exhibited weight gain and risk avoidance impairment, compared with the mice fed with a normal diet. The staining of c-Fos revealed that the hippocampus was the main brain region involved in risk avoidance behavior. Moreover, biochemical analysis suggested that the decreased levels of the brain-derived neurotrophic factor (BDNF) in the hippocampus might contribute to risk avoidance impairment induced by a HFD. These results indicated that PPARα is involved in HFD-induced risk avoidance impairment via the regulation of hippocampal BDNF.

Lateral septal nucleus, dorsal part, and dentate gyrus are necessary for spatial and object recognition memory, respectively, in mice.

Introduction: Cognitive impairment includes the abnormality of learning, memory and judgment, resulting in severe learning and memory impairment and social activity impairment, which greatly affects the life quality of individuals. However, the specific mechanisms underlying cognitive impairment in different behavioral paradigms remain to be elucidated. Methods: The study utilized two behavioral paradigms, novel location recognition (NLR) and novel object recognition (NOR), to investigate the brain regions involved in cognitive function. These tests comprised two phases: mice were presented with two identical objects for familiarization during the training phase, and a novel (experiment) or familiar (control) object/location was presented during testing. Immunostaining quantification of c-Fos, an immediate early gene used as a neuronal activity marker, was performed in eight different brain regions after the NLR or NOR test. Results: The number of c-Fos-positive cells was significantly higher in the dorsal part of the lateral septal nucleus (LSD) in the NLR and dentate gyrus (DG) in the NOR experiment group than in the control group. We further bilaterally lesioned these regions using excitotoxic ibotenic acid and replenished the damaged areas using an antisense oligonucleotide (ASO) strategy. Discussion: These data reinforced the importance of LSD and DG in regulating spatial and object recognition memory, respectively. Thus, the study provides insight into the roles of these brain regions and suggests potential intervention targets for impaired spatial and object recognition memory.

Reduced Synaptic Transmission and Intrinsic Excitability of a Subtype of Pyramidal Neurons in the Medial Prefrontal Cortex in a Mouse Model of Alzheimer's Disease.

BACKGROUND: Abnormal morphology and function of neurons in the prefrontal cortex (PFC) are associated with cognitive deficits in rodent models of Alzheimer's disease (AD), particularly in cortical layer-5 pyramidal neurons that integrate inputs from different sources and project outputs to cortical or subcortical structures. Pyramidal neurons in layer-5 of the PFC can be classified as two subtypes depending on the inducibility of prominent hyperpolarization-activated cation currents (h-current). However, the differences in the neurophysiological alterations between these two subtypes in rodent models of AD remain poorly understood. OBJECTIVE: To investigate the neurophysiological alterations between two subtypes of pyramidal neurons in hAPP-J20 mice, a transgenic model for early onset AD. METHODS: The synaptic transmission and intrinsic excitability of pyramidal neurons were investigated using whole-cell patch recordings. The morphological complexity of pyramidal neurons was detected by biocytin labelling and subsequent Sholl analysis. RESULTS: We found reduced synaptic transmission and intrinsic excitability of the prominent h-current (PH) cells but not the non-PH cells in hAPP-J20 mice. Furthermore, the function of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels which mediated h-current was disrupted in the PH cells of hAPP-J20 mice. Sholl analysis revealed that PH cells had less dendritic intersections in hAPP-J20 mice comparing to control mice, implying that a lower morphological complexity might contribute to the reduced neuronal activity. CONCLUSION: These results suggest that the PH cells in the medial PFC may be more vulnerable to degeneration in hAPP-J20 mice and play a sustainable role in frontal dysfunction in AD.