Increased homocysteine-induced release of excitatory amino acids in the striatum of spontaneously hypertensive stroke-prone rats

The Role of Amino Acids in Neurotransmission and Fluorescent Tools for Their Detection

Neurotransmission between neurons, which can occur over the span of a few milliseconds, relies on the controlled release of small molecule neurotransmitters, many of which are amino acids. Fluorescence imaging provides the necessary speed to follow these events and has emerged as a powerful technique for investigating neurotransmission. In this review, we highlight some of the roles of the 20 canonical amino acids, GABA and β-alanine in neurotransmission. We also discuss available fluorescence-based probes for amino acids that have been shown to be compatible for live cell imaging, namely those based on synthetic dyes, nanostructures (quantum dots and nanotubes), and genetically encoded components. We aim to provide tool developers with information that may guide future engineering efforts and tool users with information regarding existing indicators to facilitate studies of amino acid dynamics.

The relationship between associative learning, transfer generalization, and homocysteine levels in mild cognitive impairment

Previous studies have shown that high total homocysteine levels are associated with Alzheimer's disease (AD) and mild cognitive impairment (MCI). In this study, we test the relationship between cognitive function and total homocysteine levels in healthy subjects (Global Dementia Rating, CDR = 0) and individuals with MCI (CDR = 0.5). We have used a cognitive task that tests learning and generalization of rules, processes that have been previously shown to rely on the integrity of the striatal and hippocampal regions, respectively. We found that total homocysteine levels are higher in MCI individuals than in healthy controls. Unlike what we expected, we found no difference between MCI subjects and healthy controls in learning and generalization. We conducted further analysis after diving MCI subjects in two groups, depending on their Global Deterioration Scale (GDS) scores: individuals with very mild cognitive decline (vMCD, GDS = 2) and mild cognitive decline (MCD, GDS = 3). There was no difference among the two MCI and healthy control groups in learning performance. However, we found that individuals with MCD make more generalization errors than healthy controls and individuals with vMCD. We found no difference in the number of generalization errors between healthy controls and MCI individuals with vMCD. In addition, interestingly, we found that total homocysteine levels correlate positively with generalization errors, but not with learning errors. Our results are in agreement with prior results showing a link between hippocampal function, generalization performance, and total homocysteine levels. Importantly, our study is perhaps among the first to test the relationship between learning (and generalization) of rules and homocysteine levels in healthy controls and individuals with MCI.

Homocysteine, neural atrophy, and the effect of caloric restriction in rhesus monkeys

Higher serum homocysteine (Hcy) levels in humans are associated with vascular pathology and greater risk for dementia, as well as lower global and regional volumes in frontal lobe and hippocampus. Calorie restriction (CR) in rhesus monkeys (Macaca mulatta) may confer neural protection against age- or Hcy-related vascular pathology. Hcy was collected proximal to a magnetic resonance imaging (MRI) acquisition in aged rhesus monkeys and regressed against volumetric and diffusion tensor imaging indexes using voxel-wise analyses. Higher Hcy was associated with lower white matter volume in pons and corpus callosum. Hcy was correlated with lower gray matter volume and density in prefrontal cortices and striatum. CR did not influence Hcy levels. However, control monkeys exhibited a strong negative correlation between Hcy and global gray matter, whereas no relationship was evident for the CR monkeys. Similar group differences were also seen across modalities in the splenium of the corpus callosum, prefrontal cortices, hippocampus, and somatosensory areas. The data suggest that CR may ameliorate the influence of Hcy on several important age-related parameters of parenchymal health.