RESUMO
Altered autonomic input to the heart plays a major role in atrial fibrillation (AF). Autonomic neurons termed ganglionated plexi (GP) are clustered on the heart surface to provide the last point of neural control of cardiac function. To date the properties of GP neurons in humans are unknown. Here we have addressed this knowledge gap in human GP neuron structure and physiology in patients with and without AF. Human right atrial GP neurons embedded in epicardial adipose tissue were excised during open heart surgery performed on both non-AF and AF patients and then characterised physiologically by whole cell patch clamp techniques. Structural analysis was also performed after fixation at both the single cell and at the entire GP levels via three-dimensional confocal imaging. Human GP neurons were found to exhibit unique properties and structural complexity with branched neurite outgrowth. Significant differences in excitability were revealed between AF and non-AF GP neurons as measured by lower current to induce action potential firing, a reduced occurrence of low action potential firing rates, decreased accommodation and increased synaptic density. Visualisation of entire GPs showed almost all neurons are cholinergic with a small proportion of noradrenergic and dual phenotype neurons. Phenotypic distribution differences occurred with AF including decreased cholinergic and dual phenotype neurons, and increased noradrenergic neurons. These data show both functional and structural differences occur between GP neurons from patients with and without AF, highlighting that cellular plasticity occurs in neural input to the heart that could alter autonomic influence on atrial function. KEY POINTS: The autonomic nervous system plays a critical role in regulating heart rhythm and the initiation of AF; however, the structural and functional properties of human autonomic neurons in the autonomic ganglionated plexi (GP) remain unknown. Here we perform the first whole cell patch clamp electrophysiological and large tissue confocal imaging analysis of these neurons from patients with and without AF. Our data show human GP neurons are functionally and structurally complex. Measurements of action potential kinetics show higher excitability in GP neurons from AF patients as measured by lower current to induce action potential firing, reduced low firing action potential rates, and decreased action potential accommodation. Confocal imaging shows increased synaptic density and noradrenergic phenotypes in patients with AF. Both functional and structural differences occur in GP neurons from patients with AF that could alter autonomic influence on atrial rhythm.
RESUMO
The heat stability of levamisole was investigated. Results obtained indicated that the drug was stable in boiling water at 100 degrees C, but unstable at 260 degrees C in cooking oil, with a half-life of about 5 minutes. The effect of cooking (microwaving, boiling, roasting, grilling and frying) on levamisole residues in a range of fortified and incurred tissue was studied. No evidence of instability was obtained in any of the cooking methods investigated. Most observed net changes fell within the limits of the precision of the method once allowance for weight loss during cooking was made to counter an apparent increase in concentration. Roasting was the only method of cooking where a net loss of levamisole was observed. Insufficient juices were produced to permit analysis in this instance. The net loss of levamisole in the cooked tissue was similar to that found with other cooking methods, where the levamisole lost was found in the cooking liquid or juices. An assessment of homogeneity of the incurred tissue used in the investigation was made. The pig muscle was found not to be homogeneous with larger differences seen between different areas of the animal than within the same muscle. The findings of this investigation showed that data obtained from measurements on raw tissue are suitable for use in consumer exposure estimates and dietary intake calculations.
