Whole blood serotonin levels in healthy elderly are negatively associated with the functional activity of emotion-related brain regions

Common synaptic inputs and persistent inward currents of vastus lateralis motor units are reduced in older male adults

Although muscle atrophy may partially account for age-related strength decline, it is further influenced by alterations of neural input to muscle. Persistent inward currents (PIC) and the level of common synaptic inputs to motoneurons influence neuromuscular function. However, these have not yet been described in the aged human quadriceps. High-density surface electromyography (HDsEMG) signals were collected from the vastus lateralis of 15 young (mean ± SD, 23 ± 5 y) and 15 older (67 ± 9 y) men during submaximal sustained and 20-s ramped contractions. HDsEMG signals were decomposed to identify individual motor unit discharges, from which PIC amplitude and intramuscular coherence were estimated. Older participants produced significantly lower knee extensor torque (p < 0.001) and poorer force tracking ability (p < 0.001) than young. Older participants also had lower PIC amplitude (p = 0.001) and coherence estimates in the alpha frequency band (p < 0.001) during ramp contractions when compared to young. Persistent inward currents and common synaptic inputs are lower in the vastus lateralis of older males when compared to young. These data highlight altered neural input to the clinically and functionally important quadriceps, further underpinning age-related loss of function which may occur independently of the loss of muscle mass.

Shedding light on neurofilament involvement in cognitive decline in obstructive sleep apnea and its possible role as a biomarker

Obstructive sleep apnea is one of the most common sleep disorders with a high estimated global prevalence and a large number of associated comorbidities in general as well as specific neuropsychiatric complications such as cognitive impairment. The complex pathogenesis and effects of the disorder including chronic intermittent hypoxia and sleep fragmentation may lead to enhanced neuronal damage, thereby contributing to neuropsychiatric pathologies. Obstructive sleep apnea has been described as an independent risk factor for several neurodegenerative diseases, including Alzheimer's disease and all-cause dementia. The influence of obstructive sleep apnea on cognitive deficits is still a topic of recent debate, and several mechanisms, including neurodegeneration and depression-related cognitive dysfunction, underlying this correlation are taken into consideration. The differentiation between both pathomechanisms of cognitive impairment in obstructive sleep apnea is a complex clinical issue, requiring the use of multiple and costly diagnostic methods. The studies conducted on neuroprotection biomarkers, such as brain-derived neurotrophic factors and neurofilaments, are recently gaining ground in the topic of cognition assessment in obstructive sleep apnea patients. Neurofilaments as neuron-specific cytoskeletal proteins could be useful non-invasive indicators of brain conditions and neurodegeneration, which already are observed in many neurological diseases leading to cognitive deficits. Additionally, neurofilaments play an important role as a biomarker in other sleep disorders such as insomnia. Thus, this review summarizes the current knowledge on the involvement of neurofilaments in cognitive decline and neurodegeneration in obstructive sleep apnea patients as well as discusses its possible role as a biomarker of these changes.

Emotional intelligence scores in children and adolescents with subclinical hypothyroidism-correlation with serum serotonin and thyroid-stimulating hormone (TSH) concentrations

INTRODUCTION

Thyroxine is essential for nervous system development. Subclinical hypothyroidism (SCH), also known as mild thyroid failure, is associated with impaired cognitive function in children and mood disorders in adults. Serotonin is also involved in brain development as well as in mood and behavior modulation. The possible interaction between thyroid function tests, serum serotonin concentrations, and emotional intelligence (EI) was studied.

METHODS

A total of 224 schoolchildren from the Peloponnese, Greece, aged 11-19, were included in the study, of whom 26.3% had SCH. Emotional quotients (EQ), such as well-being, self-control, emotionality, and sociability, were assessed using the TEIQue-ASF questionnaire, and TSH, fT4, and serum serotonin concentrations were also evaluated.

RESULTS

Children and adolescents with SCH had a lower EQ total score (p < 0.001), EQ well-being score (p = 0.025), EQ self-control score (p = 0.029), EQ emotionality score (p = 0.029), and EQ sociability score (p = 0.010) and lower serum serotonin concentrations (p < 0.001).

CONCLUSIONS

Children and adolescents with SCH exhibited lower EI scores and lower serum serotonin concentrations when compared with age-matched healthy controls.

Age-Associated Gut Dysbiosis, Marked by Loss of Butyrogenic Potential, Correlates With Altered Plasma Tryptophan Metabolites in Older People Living With HIV

BACKGROUND

Imbalance in tryptophan (TRP) metabolism and its neuroactive metabolites, serotonin and kynurenine (KYN), is a known pathogenic mechanism underlying neurocognitive impairment. Gut microbiota plays an important role in TRP metabolism, and the production of these neuroactive molecules affects neurocognitive function. Although both HIV infection and normal aging independently induce gut dysbiosis and influence TRP metabolism, their interactive effects on compositional/functional changes in gut microbiota and consequent alterations in TRP metabolites remain largely undetermined.

METHODS

Older people living with HIV infection (PLWH, aged 50-70 years, n = 22) were enrolled in this cross-sectional pilot study. Metagenomic analysis of fecal microbiome using 16S Ribosomal ribonucleic acid gene sequencing and metabolomics analysis of plasma using mass spectrometry with a reverse-phase iquid chromatography tandem mass spectrometry were performed. Statistical analyses included the univariate linear regression and Spearman correlation analyses.

RESULTS

Age-associated changes in plasma levels of key neuroactive TRP metabolites, serotonin and KYN, were seen in PLWH. Specifically, we observed age-dependent decreases in serotonin and increases in KYN and KYN-to-TRP ratio, indicative of dysfunctional TRP metabolism. Furthermore, the gut dysbiosis seen in older PLWH is characterized by a reduction of Firmicutes/Bacteroidetes ratio and butyrate-producing microbial families Lachnospiraceae and Lactobacillaceae. Of importance, correspondent with gut dysbiosis, increasing age was significantly associated with decreased plasma butyrate levels, which in turn correlated positively with serotonin and negatively with KYN/TRP ratio.

CONCLUSIONS

Age-dependent gut microbial dysbiosis distinguished by a decrease in butyrogenic potential is a key pathogenic feature associated with the shift in TRP metabolism from serotonin to KYN in older PLWH.