Activities of pineal N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase, involved in the biosynthesis of melatonin from serotonin, were assessed over 24 h in the pineal organ of pikes (Esox lucius, L.; teleosts) entrained to natural (winter) environmental conditions. Only NAT activity exhibited daily changes, rising at the onset of darkness and resuming low values shortly before the end of the scotophase. The rhythm was damped under constant darkness, lower and higher values being shifted towards intermediate ones. NAT activity was lowered under constant light; however, a significant increase was seen at the end of the subjective night, suggesting the existence of a low-amplitude rhythm. Illumination of the pikes at the middle of the scotophase induced inactivation of roughly half of the maximal NAT activity, possibly indicating the existence of one photolabile and one photostable enzymatic component. Under natural conditions, radioassayable melatonin of the pike pineal organ displayed daily variations which paralleled those of NAT activity. Melatonin production thus appears to reflect the daily changes of NAT, synchronized to the light/dark cycle.
In 2008 a fatal case of primary amoebic meningoencephalitis, due to the amoeboflagellate Naegleria fowleri, occurred in Guadeloupe, French West Indies, after a child swam in a bath fed with geothermal water. In order to improve the knowledge on free-living amoebae in this tropical part of France, we investigated on a monthly basis, the presence of Naegleria spp. in the recreational baths, and stream waters which feed them. A total of 73 water samples, 48 sediments and 54 swabs samples were collected from 6 sampling points between June 2011 and July 2012. The water samples were filtered and the filters transferred to non-nutrient agar plates seeded with a heat-killed suspension of Escherichia coli while sediment and swab samples were placed directly on these plates. The plates were incubated at 44°C for the selective isolation of thermophilic Naegleria. To identify the Naegleria isolates the internal transcribed spacers, including the 5.8S rDNA, were amplified by polymerase chain reaction and the sequence of the PCR products was determined. Thermophilic amoebae were present at nearly all collection sites. The pathogenic N. fowleri was the most frequently encountered thermophilic species followed by N. lovaniensis. The concentration of N. fowleri was rather low in most water samples, ranging from 0 to 22 per liter. Sequencing revealed that all N. fowleri isolates belonged to a common Euro-American genotype, the same as detected in the human case in Guadeloupe. These investigations need to be continued in order to counsel the health authorities about prevention measures, because these recreational thermal baths are used daily by local people and tourists.
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