Shrinking of silicon nanocrystals embedded in an amorphous silicon oxide matrix during rapid thermal annealing in a forming gas atmosphere.

We report the effect of hydrogen on the crystallization process of silicon nanocrystals embedded in a silicon oxide matrix. We show that hydrogen gas during annealing leads to a lower sub-band gap absorption, indicating passivation of defects created during annealing. Samples annealed in pure nitrogen show expected trends according to crystallization theory. Samples annealed in forming gas, however, deviate from this trend. Their crystallinity decreases for increased annealing time. Furthermore, we observe a decrease in the mean nanocrystal size and the size distribution broadens, indicating that hydrogen causes a size reduction of the silicon nanocrystals.

Effects of Ginkgo biloba extract (EGb 761) on learning and possible actions on aging.

A study of the effect of Ginkgo biloba extract (EGb 761) has shown enhancing effects on training in adult and aged Swiss mice. An analysis of inbred mice has confirmed this sensitivity to EGb 761, but depending on the strains, with different effects at different ages. The most interesting results are related to improvements in performances observed with aged mice of the DBA/2J strain. The results obtained with inbred strains in the study of the mossy fibers of the hippocampus make it possible to suggest a link between the improvements in training and the histological structure of the hippocampus. This possibility, which can be confirmed by further studies, is presented here.

Zolpidem in insomnia: a 3-year post-marketing surveillance study in Switzerland.

A multicentre post-marketing surveillance study was conducted in Switzerland in routine practice and involved 1972 insomniac patients treated with zolpidem, an imidazopyridine hypnotic agent. The patients were representative of the general insomniac population (65% women; mean age 55 years; 29% over 65). Of the patients, 87% were treated with a zolpidem dosage of 10 mg/day and the median treatment duration was 30 days. All adverse events were collected through spontaneous reporting. A total of 175 patients (8.9%) reported 343 adverse events, and 102 (5.2%) of them discontinued treatment. CNS (central nervous system)-related adverse events accounted for 66% of the total, the most common events being residual daytime sedation and insufficient efficacy in 3.7% and 1.6%, respectively; confusion, disorientation, nervousness, nightmares, amnesia, impaired concentration and anxiety were observed in a lower proportion. Gastro-intestinal symptoms, headache and skin reactions were the most frequent non-CNS related effects. No serious adverse event was reported and no new risk factors or at-risk populations were identified. The safety profile of zolpidem is thus consistent with its known pharmacological properties, the results of previous clinical trials, and the cumulative international experience gained with this short-acting hypnotic drug.

Similar effects of a beta-carboline and of flumazenil in negatively and positively reinforced learning tasks in mice.

Methyl beta-carboline-3-carboxylate (beta-CCM) and flumazenil (Ro15-1788) are known to be respectively an inverse agonist and an antagonist of the central benzodiazepine-receptor. Surprisingly, these two drugs have shown a similar enhancing effect in a negatively reinforced multiple-trial brightness discrimination task in mice. Thus, to evaluate the role of anxiety in this task, the action of these two drugs were compared in the same learning task with a positive or a negative reinforcement. Mice were trained for sessions of ten trials per day for six consecutive days. The sessions during the first three days took place after administration of beta-CCM (0.3 mg/kg), flumazenil (15 mg/kg) or vehicles of these drugs. A negative reinforcement (electric foot-shock) was used in a first experiment, and a positive one (food reward) in a second experiment. Results showed that, whatever the reinforcement, the two drugs enhance learning in a brightness discrimination task. The hypothesis is that flumazenil could have an inverse agonist profile in learning tasks. The question remains as to whether the flumazenil enhancing learning process results from increased arousal and/or anxiogenic factors, or from a negative modulatory influence of endogenous diazepam-like ligands for benzodiazepine receptors.

Methyl beta-carboline-3-carboxylate enhances performance in a multiple-trial learning task in mice.

In contrast to diazepam, a benzodiazepine receptor (BZ-R) ligand, which impairs memory processing, methyl beta-carboline-3-carboxylate (beta-CCM), another BZ-R ligand, administered before a training session, enhances performance in a retention test. This action, however, has only been demonstrated in single trial or single session learning protocols. The present report extends these results to a multiple-trial learning procedure in mice (brightness discrimination in a T-maze with negative reinforcement). The animals were trained for sessions of ten trials per day for six consecutive days. In a first experiment, the sessions during the first three days took place after administration of beta-CCM (0.3 mg/kg), diazepam (2.5 mg/kg) or saline. In a second experiment, especially designed to study the effects of beta-CCM, during the first three days animals received beta-CCM (0.3 mg/kg), Ro 15-1788 (15 mg/kg), beta-CCM + Ro 15-1788, vehicles of these drugs or saline. In the first experiment, performance was improved by beta-CCM and impaired by diazepam in the first three sessions as well as in the final three. In the second experiment, beta-CCM alone, as well as Ro 15-1788 improved performance, and the simultaneous administration of the two drugs suppressed these effects. These results suggest that the performance enhancing effects of beta-CCM observed in single trial learning protocols, during the retention test, can already be observed during drug treatment. They confirm that beta-CCM has an action on acquisition (learning). As the effects of beta-CCM are suppressed by the simultaneous administration of Ro 15-1788, our results could suggest a role for benzodiazepine receptors in learning. This question is discussed.