Nematic fluctuations in the cuprate superconductor Bi2Sr2CaCu2O8+δ.

Establishing the presence and the nature of a quantum critical point in their phase diagram is a central enigma of the high-temperature superconducting cuprates. It could explain their pseudogap and strange metal phases, and ultimately their high superconducting temperatures. Yet, while solid evidences exist in several unconventional superconductors of ubiquitous critical fluctuations associated to a quantum critical point, in the cuprates they remain undetected until now. Here using symmetry-resolved electronic Raman scattering in the cuprate [Formula: see text], we report the observation of enhanced electronic nematic fluctuations near the endpoint of the pseudogap phase. While our data hint at the possible presence of an incipient nematic quantum critical point, the doping dependence of the nematic fluctuations deviates significantly from a canonical quantum critical scenario. The observed nematic instability rather appears to be tied to the presence of a van Hove singularity in the band structure.

Sarcoplasmic reticulum: a key factor in cardiac contractility of sea bass Dicentrarchus labrax and common sole Solea solea during thermal acclimations.

This study investigated the effects of acclimation temperature upon (i) contractility of ventricular strips (ii) calcium movements in ventricular cardiomyocytes during excitation-contraction coupling (ECC), and (iii) the role of the sarcoplasmic reticulum (SR) in myocardial responses, in two marine teleosts, the sea bass (Dicentrarchus labrax) and the common sole (Solea solea). Because of the different sensitivities of their metabolism to temperature variation, both species were exposed to different thermal ranges. Sea bass were acclimated to 10, 15, 20, and 25 °C, and common sole to 6, 12, 18, and 24 °C, for 1 month. Isometric tension developed by ventricular strips was recorded over a range of physiological stimulation frequencies, whereas the depolarization-induced calcium transients were recorded on isolated ventricular cells through hyperpotassic solution application (at 100 mM). The SR contribution was assessed by ryanodine (RYAN) perfusion on ventricular strips and by caffeine application (at 10 mM) on isolated ventricular cells. Rates of contraction and relaxation of ventricular strip, in both species, increased with increasing acclimation temperature. At a low range of stimulation frequency, ventricular strips of common sole developed a positive force-frequency relationship at high acclimation temperature. In both the species, SR Ca(2+)-cycling was dependent on fish species, acclimation temperature and pacing frequency. The SR contribution was more important to force development at low acclimation temperatures in sea bass but at high acclimation temperatures in common sole. The results also revealed that high acclimation temperature causes an increase in the maximum calcium response amplitude on ventricular cells in both the species. Although sea bass and common sole occupy similar environments and tolerate similar environmental temperatures, this study indicated that sea bass and common sole can acclimatize to new thermal conditions, adjusting their cellular process in a different manner.

Role of the cerebellum in an avoidance conditioning task in the rat.

Adult DA/HAN strain male rats were submitted to an avoidance conditioning procedure. They were divided into two experimental groups, the animals being either conditioned (COC group) or not (NOC group) before cerebellectomy, and two control groups, the animals being either intact (C group) or sham-operated (SO group). Although the NOC rats could be conditioned successfully and the cerebellum is not absolutely necessary for the avoidance conditioning achievement, their scores were significantly lower than the preoperative scores of COC rats. Moreover, the scores of NOC rats (postoperative scores) were significantly lower than the postoperative scores of COC animals, suggesting that the preoperative conditioning makes the postoperative conditioning easier. At last, comparing postoperative scores of COC rats with those obtained by C and SO rats when given the retrieval test and comparing preoperative and postoperative scores in COC animals show that retention of the initial (preoperative) conditioning is partly abolished by the cerebellectomy. Histological controls demonstrated that the entire cerebellum except for the flocculus and the nodulus was removed. These results strongly suggest that the cerebellum is involved in the memory processes that sustain the avoidance conditioning.

Effects of cerebellectomy at day 15 on the ontogenesis of the equilibrium behavior in the rat.

Young cerebellectomized and control (sham-operated) DA/HAN strained rats, 1 day to 1 month old, were submitted to an equilibrium test consisting for the animals in maintaining their equilibrium when placed on a horizontal mast rotating around its longitudinal axis at 10 or 20 rpm (slow and fast rotation rates, respectively). Cerebellectomized animals, operated when 15 days old, were either naive (tested at one given day) or trained; these last ones were trained before and after the operation, or only before, or only after, according to a slow or a fast rotation rate. Control rats were also either naive or trained in conditions similar to those given to operated animals. Relevant comparisons show that: (1) rats cerebellectomized at day 15 which have not been trained before the operation are unable to learn a given motor pattern. (2) When trained before the operation, the animals learn the motor patterns that they use to maintain their equilibrium upon the rotating mast as well as controls. (3) Postoperative training is inefficient in the acquisition of the equilibrium behavior whether the animals were trained preoperatively or not. (4) Compared to the slow rotation rate (10 rpm), the evolution of the equilibrium behavior in cerebellectomized rats is not altered when the rotation rate is increased to 20 rpm, that is when the task is more difficult.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the cerebellum in the ontogenesis of the equilibrium behavior in the young rat: a behavioral study.

Young cerebellectomized and control DA/HAN strained rats, one day to 1 month old, were submitted to an equilibrium test. Cerebellectomized animals, operated when 10-, 20- or 24-day-old, were either trained-operated-trained (trained every day before and after cerebellectomy), naïve-operated-trained (cerebellectomized while naïve and trained every day after the operation), or naïve-operated-naïve (tested at one given day after the operation). Control rats were either trained-controls (trained every day) or naïve-controls (tested at a given day). Relevant comparisons show that (1) in control rats, the maturation of the equilibrium behavior does not depend on a specific training, at least to a great extent; however, training increases the rate of acquisition of the maximal score. (2) Rats cerebellectomized at day 10 and trained after cerebellectomy only are not able to learn a given motor pattern, while rats cerebellectomized by the 20th or 24th day are; however, their scores are always lower than those of control animals trained from the same age. Cerebellectomy alters the ontogenesis of the equilibrium behavior more especially as the operation is early. (3) Impairments of the equilibrium behavior after cerebellectomy can be explained by both motor disorders and learning processes deficiency. (4) Preoperative training counterbalances the effects of cerebellectomy in improving postoperative scores only when the cerebellum is removed at day 24. From these results it can be concluded that, in the rat, the cerebellum is involved in the learning processes that sustain the ontogenesis of the equilibrium behavior as it is in other motor learning mechanisms.