Methylene blue and photobiomodulation recover cognitive impairment in hepatic encephalopathy through different effects on cytochrome c-oxidase

From functional neuroimaging to neurostimulation: fNIRS devices as cognitive enhancers

Functional near-infrared spectroscopy (fNIRS) relies on near-infrared (NIR) light for changes in tissue oxygenation. For decades, this technique has been used in neuroscience to measure cortical activity. However, recent research suggests that NIR light directed to neural populations can modulate their activity through "photobiomodulation" (PBM). Yet, fNIRS is being used exclusively as a measurement tool. By adopting cognitive tests sensitive to prefrontal functioning, we show that a 'classical' fNIRS device, placed in correspondence of the prefrontal cortices of healthy participants, induces faster RTs and better accuracy in some of the indexes considered. A well-matched control group, wearing the same but inactive device, did not show any improvement. Hence, our findings indicate that the 'standard' use of fNIRS devices generates PBM impacting cognition. The neuromodulatory power intrinsic in that technique has been so far completely overlooked, and future studies will need to take this into account.

The removal and addition of cues does not impair spatial retrieval and leads to a different metabolic activity of the limbic network in female rats

The retrieval of spatial memories does not always occur in an environment with the same stimuli configuration where the memory was first formed. However, re-exposure to a partial portion of the previously encountered cues can elicit memory successfully. Navigation with contextual changes has received little attention, especially in females. Thus, we aimed to assess memory retrieval using the Morris Water Maze spatial reference protocol in female adult Wistar rats. Rats were trained with five allocentric cues, and retrieval was explored one week later either with the same cues, or with four removed, or with three added cues. We studied the underlying brain oxidative metabolism of the hippocampus, prefrontal, parietal, retrosplenial, entorhinal, and perirhinal cortices through cytochrome c oxidase (CCO) histochemistry. Neither cue removal nor cue addition impaired retrieval performance. Retrieval with a degraded subset of cues led to increased prefrontal, hippocampal, retrosplenial, parietal, and perirhinal CCO activity. Retrieval with extra cues led to an enhancement of CCO activity in the hippocampus and retrosplenial cortex. Different patterns of network intercorrelations were found. The cue-removal group presented a closed reciprocal network, while the group with extra cues had separate parallel networks. Both groups showed a simpler network than the group with no cue modifications. Future research is needed to delve into behavioral and brain-related functions of spatial memory processes under modified environmental conditions.

No Effects of Photobiomodulation on Prefrontal Cortex and Hippocampal Cytochrome C Oxidase Activity and Expression of c-Fos Protein of Young Male and Female Rats

The role of light in our biological processes and systems is extensively known. In addition, the use of light devices has been introduced in the field of healthcare as an opportunity to administer power light at specific wavelengths to improve our body functions and counteract light deficiency. One of these techniques is photobiomodulation (PBM), which uses red to infrared light in a non-invasive way to stimulate, heal, regenerate, and protect tissue. The main proposed mechanism of action is the stimulation of the cytochrome c oxidase (CCO), the terminal enzyme in the mitochondrial electron transport chain. PBM has achieved positive effects on brain activity and behavioral function of several adult animal models of health and disease, the potential use of this technique in developing stages is not surprising. This research aims to examine the effects of PBM on the prefrontal cortex and hippocampus of 23 day-old healthy male (n = 31) and female (n = 30) Wistar rats. Three groups of each sex were used: a PBM group which received 5 days of PBM, a device group submitted to the same conditions but without light radiation, and a control basal group. CCO histochemistry and c-Fos immunostaining were used to analyze brain metabolic activity and immediate early genes activation, respectively. Results displayed no metabolic differences between the three groups in both sexes. The same results were found in the analysis of c-Fos positive cells, reporting no differences between groups. This research, in contrast to the PBM consequences reported in healthy adult subjects, showed a lack of PBM effects in the brain markers we examined in young healthy rat brains. At this stage, brain function, specifically brain mitochondrial function, is not disturbed so it could be that the action of PBM in the mitochondria may not be detectable using the analysis of CCO activity and c-Fos protein expression. Further studies are needed to examine in depth the effects of PBM in brain development, cognitive functions and postnatal disorders, along with the exploration of the optimal light parameters.