Endogenous circadian and circannual rhythms may exist in the metabolism, ventilation, and breathing pattern of turtles that could further prolong dive times during daily and seasonal periods of reduced activity. To test this hypothesis, turtles were held under seasonal or constant environmental conditions over a 1-yr period, and in each season, V(O)(2) and respiratory variables were measured in all animals under both the prevailing seasonal conditions and the constant conditions for 24 h. Endogenous circadian and circannual rhythms in metabolism and ventilation occurred independent of ambient temperature, photoperiod, and activity, although long-term entrainment to daily and seasonal changes in temperature and photoperiod were required for them to be expressed. Metabolism and ventilation were always higher during the photophase, and the day-night difference was greater at any given temperature when the photoperiod was provided. When corrected for temperature, turtles had elevated metabolic and ventilation rates in the fall and spring (corresponding to the reproductive seasons) and suppressed metabolism and ventilation during winter. The strength of the circadian rhythm varied seasonally, with proportionately larger day-night differences in colder seasons. Daily and seasonal cycles in ventilation largely followed metabolism, although daily and seasonal changes did occur in the breathing pattern independent of levels of total ventilation. These endogenous circadian and circannual changes in metabolism, ventilation, and breathing pattern prolonged dive times at night and in winter and may serve to reduce the costs of breathing and transport and risk of predation.

Peripheral arterial chemoreceptors have been located previously in the carotid labyrinth, the aortic arch, and the pulmocutaneous artery of frogs. In the present study we used cholera toxin B neuronal tract tracing and immunohistochemical markers for cholinergic cells (vesicular acetylcholine transporter [VAChT]), tyrosine hydroxylase (TH), and serotonin (5HT) to identify putative O2-sensing cells in Rana catesbeiana. We found potential O2-sensing cells in all three vascular areas innervated by branches of the vagus nerve, whereas only cells in the carotid labyrinth were innervated by the glossopharyngeal nerve. Cells containing either 5HT or TH were found in all three sites, whereas cells containing both neurotransmitters were found only in the carotid labyrinth. Cell bodies containing VAChT were not found at any site. The morphology and innervation of putative O2-sensing cells were similar to those of glomus cells found in other vertebrates. The presence of 5HT- and TH-immunoreactive cells in the aorta, pulmocutaneous artery, and carotid labyrinth appears to reflect a phylogenetic transition between the major neurotransmitter seen in the putative O2-sensing cells of fish (5HT) and those found in the glomus cells of mammals (acetylcholine, adenosine, and catecholamines).

In Colombia, the epidemiology and circulating genotypes of Clostridium difficile have not yet been described. Therefore, we molecularly characterized clinical isolates of C.difficile from patients with suspicion of C.difficile infection (CDI) in three tertiary care hospitals. C.difficile was isolated from stool samples by culture, the presence of A/B toxins were detected by enzyme immunoassay, cytotoxicity was tested by cell culture and the antimicrobial susceptibility determined. After DNA extraction, tcdA, tcdB and binary toxin (CDTa/CDTb) genes were detected by PCR, and PCR-ribotyping performed. From a total of 913 stool samples collected during 2013–2014, 775 were included in the study. The frequency of A/B toxins-positive samples was 9.7% (75/775). A total of 143 isolates of C.difficile were recovered from culture, 110 (76.9%) produced cytotoxic effect in cell culture, 100 (69.9%) were tcdA+/tcdB+, 11 (7.7%) tcdA-/tcdB+, 32 (22.4%) tcdA-/tcdB- and 25 (17.5%) CDTa+/CDTb+. From 37 ribotypes identified, ribotypes 591 (20%), 106 (9%) and 002 (7.9%) were the most prevalent; only one isolate corresponded to ribotype 027, four to ribotype 078 and four were new ribotypes (794,795, 804,805). All isolates were susceptible to vancomycin and metronidazole, while 85% and 7.7% were resistant to clindamycin and moxifloxacin, respectively. By multivariate analysis, significant risk factors associated to CDI were, staying in orthopedic service, exposure to third-generation cephalosporins and staying in an ICU before CDI symptoms; moreover, steroids showed to be a protector factor. These results revealed new C. difficile ribotypes and a high diversity profile circulating in Colombia different from those reported in America and European countries.

SUMMARYThe purpose of the present study was to determine whether the daily and seasonal changes in ventilation and breathing pattern previously documented in red-eared sliders resulted solely from daily and seasonal oscillations in metabolism or also from changes in chemoreflex sensitivity. Turtles were exposed to natural environmental conditions over a one year period. In each season, oxygen consumption, ventilation and breathing pattern were measured continuously for 24 h while turtles were breathing air and for 24 h while they were breathing a hypoxic-hypercapnic gas mixture (H-H). We found that oxygen consumption was reduced equally during the day and night under H-H in all seasons except spring. Ventilation was stimulated by H-H but the magnitude of the response was always less at night. On average, it was also less in the winter and greater in the reproductive season. The data indicate that the day-night differences in ventilation and breathing pattern seen previously resulted from daily changes in chemoreflex sensitivity whereas the seasonal changes were strictly due to changes in metabolism. Regardless of mechanism, the changes resulted in longer apneas at night and in the winter at any given level of total ventilation, facilitating longer submergence at times of the day and year when turtles are most vulnerable.

Peripheral arterial chemoreceptors have been isolated to the common carotid artery, aorta, and pulmonary artery of turtles. However, the putative neurotransmitters associated with these chemoreceptors have not yet been described. The goal of the present study was to determine the neurochemical content, innervations, and distribution of putative oxygen-sensing cells in the central vasculature of turtles and to derive homologies with peripheral arterial chemoreceptors of other vertebrates. We used tract tracing together with immunohistochemical markers for cholinergic cells (vesicular acetylcholine transporter [VAChT]), tyrosine hydroxylase (TH; the rate-limiting enzyme in catecholamine synthesis), and serotonin (5HT) to identify putative oxygen-sensing cells and to determine their anatomical relation to branches of the vagus nerve (Xth cranial nerve). We found potential oxygen-sensing cells in all three chemosensory areas innervated by branches of the Xth cranial nerve. Cells containing either 5HT or VAChT were found in all three sites. The morphology and size of these cells resemble glomus cells found in amphibians, mammals, tortoises, and lizards. Furthermore, we found populations of cholinergic cells located at the base of the aorta and pulmonary artery that are likely involved in efferent regulation of vessel resistance. Catecholamine-containing cells were not found in any of the putative chemosensitive areas. The presence of 5HT- and VAChT-immunoreactive cells in segments of the common carotid artery, aorta, and pulmonary artery appears to reflect a transition between cells containing the major neurotransmitters seen in fish (5HT) and mammals (ACh and adenosine).