Dynamics of aggregation and emergence of cooperation.

Aggregation is one of the most basic social phenomena, and many activities of social insects are linked to it. For instance, the selection of a valuable site and the spatial organization of the population are very often by-products of amplifications based on the local density of nestmates. The patterns of aggregation are very diverse, ranging from the gathering of all animals in a unique site to their splitting between several ones. One might question how these multiple patterns emerge. Do ants actively initiate the formation of such patterns by modulating the emission of an attracting signal such as the trail pheromone? Alternatively, do patterns result from quantitative changes in the duration of interaction between animals once they have reached the gathering site, without any active modulation of the communications? To discuss these questions, we present two empirical studies: the gregarious behavior of cockroaches (Blatella) and self-assembly in the weaver ant (Oecophylla). Through experimental and theoretical studies, we show how a single behavior-the resting time-leads to a collective choice in both species. This behavior is a response to the density of conspecifics and can also be modulated by heterogeneities in the environment. In weaver ants, it allows the colony to focus the formation of chains in a given area among several potential sites. In cockroaches, it allows the gathering of individuals in particular shelters, depending on the proximity between strains. These results are discussed with emphasis on the role of aggregation processes in the emergence of cooperativity and task allocation.

Model of droplet dynamics in the Argentine ant Linepithema Humile (Mayr).

The formation of droplets of ants Linepithema humile (Mayr) is observed under certain experimental conditions: a fluctuating aggregate forms at the end of a rod and a droplet containing up to 40 ants eventually falls down. When the flux of incoming ants is sufficient, this process can continue for several hours, leading to the formation and fall of tens of droplets. Previous work indicates that the time series of drop-to-drop intervals may result from a nonlinear low-dimensional dynamics, and the interdrop increments exhibit long-range anticorrelations. A model of aggregation and droplet formation, based on experimental observations, is introduced and shown to reproduce these properties.

Efficacy of ondansetron treatment with different timing schedules: a randomized double-blind study.

The purpose of this study was to determine whether preloading administration of ondansetron given 12.5 h before cisplatin therapy, every 6 h, is better in controlling acute cisplatin-induced emesis than a standard dose every 8 h. All patients had previously received three cycles of CDDP-based chemotherapy in a dose of 100 mg/m2. Ondansetron was given according to two schedules: in group A (40 patients) at a dose of 8 mg in 100 ml normal saline over 10 min by intravenous infusion before the infusion of CDDP continued with 1 tablet of 8 mg after 8 and 16 h; in group B (40 patients) it was administered in six intravenous doses (every 6 h) starting 12.5 h before cisplatin administration. During the following 3 days, patients from both groups continued with tablets of 8 mg orally, every 8 h in group A and every 6 h in group B. The only difference in terms of the antiemetic response noticed between the two groups was in the number of patients that presented with nausea, which was increased in group A (32) in comparison to group B (25; p < 0.022). No difference was found in the number of vomiting episodes, retches or control of emesis, during the 3-day evaluation period after cisplatin infusion, and in secondary side effects. In conclusion the total dose of 24 mg ondansetron during the acute phase of emesis is as effective as preloading and increasing the total dose to 32 mg.

Comparison of ondansentron versus ondansentron plus methylprednisolone as antiemetic prophylaxis during cisplatin-containing chemotherapy.

We compared the antiemetic efficacy of ondansentron versus ondansentron and corticosteroids in cisplatin-induced emesis. None of our patients had received prior chemotherapy. All patients received chemotherapy including cisplatin 100 mg/m2. Forty patients received ondansentron alone (Group A) and 40 the combination of ondansentron and methylprednisolone (Group B). Ondansentron was given at a dose of 8 mg in 100 mL N/S over 10 min by intravenous infusion. The initial dose was administered before the cisplatin and was followed by 8 mg orally in the afternoon and before sleeping the first day of chemotherapy. During the next 2 days, the patients received 8 mg orally 3 times daily. Methylprednisolone was given as an intravenous bolus of 40 mg before chemotherapy and then together with each dose of ondansentron at a dose of 16 mg orally. Group A had significantly longer duration of nausea after chemotherapy than group B (117 +/- 111 min, 62 +/- 71 min, P < 0.013). The response on emesis was also improved in group B, especially the day of chemotherapy [treatment failure: group A: 13 patients (30%) versus group B: 5 patients (11.6%), P < 0.03] and the next day [complete response: group A: 17 patients (39.5%) versus group B: 30 patients (69.7%), P < 0.005]. Patients in group B presented more sedative effects (P < 0.001) and better appetite (P < 0.02) than patients in group A. There were no other significant differences in side effects (activity, headache, constipation, etc). We conclude that corticosteroids improve the antiemetic efficacy of ondansentron in cisplatin-induced chemotherapy, and should be included in antiemetic regimens.