Microglia is considered the central nervous system (CNS) resident macrophages that establish an innate immune response against pathogens and toxins. However, the recent studies have shown that microglial gene and protein expression follows a circadian pattern; several immune activation markers and clock genes are expressed rhythmically without the need for an immune stimulus. Furthermore, microglia responds to an immune challenge with different magnitudes depending on the time of the day. This review examines the circadian control of microglia function and the possible physiological implications. For example, we discuss that synaptic prune is performed in the cortex at a certain moment of the day. We also consider the implications of daily microglial function for maintaining biological rhythms like general activity, body temperature, and food intake. We conclude that the developmental stage, brain region, and pathological state are not the only factors to consider for the evaluation of microglial functions; instead, emerging evidence indicates that circadian time as an essential aspect for a better understanding of the role of microglia in CNS physiology.

Seizure-mediated oxidative stress is a crucial mechanism in the pathophysiology of epilepsy. This study evaluated the antioxidant effects of daytime-restricted feeding (DRF) and the role of the Nrf2 signaling pathway in a lithium-pilocarpine model seizure model that induces status epilepticus (SE). We performed a lipoperoxidation assay and dihydroethidium fluorescence to measure oxidative stress markers in the hippocampus (malondialdehyde and reactive oxygen species). The protein content of Nrf2 and its downstream protein SOD2 was evaluated using Western blotting. The cellular distribution of the Nrf2 and SOD2 proteins in the pyramidal cell layer of both the CA1 and CA3 hippocampal subfields and astrocytes (GFAP marker) were quantified using immunofluorescence and immunohistochemistry, respectively. Our results indicate that DRF reduced the malondialdehyde levels and the production of reactive oxygen species. Furthermore, a significant increase in Nrf2 and SOD2 protein content was observed in animals subjected to restrictive diet. In addition, DRF increased the relative intensity of the Nrf2 fluorescence in the perinuclear and nuclear compartments of pyramidal neurons in the CA1 subfield. Nrf2 immunoreactivity and the astrocyte marker GFAP also increased their colocalization under DRF conditions. Additionally, SOD2 immunoreactivity was increased in CA1 pyramidal neurons but not in the CA3 region. Our findings suggest that DRF partially prevents oxidative stress by increasing the Nrf2 transcriptional factor and the SOD2 enzyme during the development of SE.

Background. Adiponectin (APN) is an adipocyte-derived hormone that has peripheral beneficial effects. Although its receptors AdipoR1 and AdipoR2 are expressed in the brain, their function in neurons is poorly understood. The aims of this work were to describe the distribution of APN receptors in the olfactory bulb (OB) as well as the possible effects of APN injection on the insulin receptor (InsR) content and Akt kinase. Method. We performed the double immunofluorescence technique to describe the distribution of AdipoRs and the cellular type they were expressing. mRNA transcript and protein content were assessed by RT-PCR and Western blot, respectively. APN injection was performed to analyze its possible effect on the insulin pathway. Results. We found that AdipoRs were localized in all cell layers and in both neurons and astrocytes. We observed the presence of mRNA transcripts and immunoblot analysis confirmed the protein on the intact OB; APN injection in the OB resulted in a slight decrease of the total InsR and Akt phosphorylation and a reduction of phopho-InsR content. Conclusions. These data demonstrated that AdipoRs are expressed in OB regions, and APN injection could act as an insulin pathway modulator in the OB and thus possibly contribute to olfaction physiology.

It has been proposed that interictal epileptiform discharges observed in epilepsy-related structures, such as the hippocampus contributes to epileptogenesis. Intermittent fasting (IF) produces anticonvulsant effects protecting against experimentally induced seizures. It has been suggested that protective effects could be associated with astrocytic metabolic changes. However, it is unknown whether IF modifies the epileptogenic process. Therefore, this work aimed to analyze the impact of IF on interictal epileptiform discharges in the rat hippocampus and their possible correlation with astrocytic activation. Male Wistar rats were divided into two groups: one group had free access to food, while the other group was subjected to IF (food was provided for 2 h a day). Both groups underwent a hippocampal electrical kindling protocol with 36 stimulations. Our results showed that IF inhibited the incidence of generalized seizures induced by kindling and significantly reduced the total spectral power of interictal epileptiform discharges in the hippocampus. Furthermore, IF prevented the rise in fasting blood glucose and reduced seizure-induced astrogliosis by preventing the GFAP expression and the morphological complexity of astrocytes in the hippocampal CA3 region. These results support the notion that IF modifies epileptogenesis by modulating hippocampal hyperexcitability during the interictal stage, which could be associated with reductions in glucose metabolism and astrogliosis. Graphical Abstract

Seizure-mediated oxidative stress is a crucial mechanism in the pathophysiology of epilepsy. This study evaluated the antioxidant effects of daytime-restricted feeding (DRF) and the role of the Nrf2 signaling pathway in a lithium-pilocarpine model seizure model that induces status epilepticus (SE). We performed a lipoperoxidation assay and dihydroethidium fluorescence to measure oxidative stress markers in the hippocampus (malondialdehyde and reactive oxygen species). The protein content of Nrf2 and its downstream protein SOD2 was evaluated by Western blot. Cellular distribution of the Nrf2 and SOD2 proteins in the pyramidal cell layer of both CA1 and CA3 hippocampal subfields and astrocytes (GFAP marker) were quantified by immunofluorescence and immunohistochemistry respectively. Our results indicate that DRF reduced malondialdehyde levels and the production of reactive oxygen species. Furthermore, a significant increase in Nrf2 and SOD2 protein content was observed in animals subjected to restrictive diet. In addition, DRF increased the relative intensity of the Nfr2 fluorescence in the perinuclear and nuclear compartments of pyramidal neurons in the CA1 subfield. Nfr2 immunoreactivity and the astrocyte marker GFAP also increased their colocalization in DRF conditions. Also, SOD 2 immunoreactivity was increased in CA1 pyramidal neurons but not in CA3 region. Our findings suggest that DRF partially prevents oxidative stress by increasing the Nrf2 transcriptional factor and the SOD2 enzyme during the development of SE.