Participation of the dorsal hippocampus in stimulus discrimination with scopolamine.

Stimulus discrimination is the capacity of an organism to differentiate between stimuli and emit associated responses. The administration of the muscarinic antagonist scopolamine can be used as a stimulus by mammals in a discrimination task. The present study analyzes the contribution of the hippocampus in scopolamine discrimination and generalization. Male Wistar rats, weighing 250-300 g at the beginning of the experiment, were trained to discriminate between scopolamine (1.0 mg/kg, i.p.) and saline administration using a two-lever operant task; rats had to respond differentially to each lever depending on the preceding drug or saline administration. Once stimulus control was attained, rats were tested with different scopolamine doses (0.0, 0.056, 0.091, 0.16, 0.31 and 1.0 mg/kg, i.p.) in order to obtain generalization curves. After generalization the rats were randomly assigned to hippocampal CA1 lesion or control groups. Hippocampus impairment produced a transient decrease in the capacity to discriminate between scopolamine and saline conditions; nonetheless, scopolamine correct responses were rapidly recovered after a few sessions and even maintained after 90 days. Correct responses for saline condition were never recovered. The generalization curve obtained after hippocampus lesion showed a response gradient severely flattened. Results suggest that the hippocampus participates as a neural system supporting the sensitivity to detect discrete changes in stimulus properties and relational memory, more than on the capacity to recall for simple associative responses.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in Majorcan hospitals: high prevalence of the epidemic clone EMRSA-15.

Clinical isolates (n = 389) of methicillin-resistant Staphylococcus aureus (MRSA) recovered from 371 patients between January 2003 and June 2004 at the three major public hospitals on the island of Majorca, Spain were studied. The clonal relatedness of MRSA isolates was determined by pulsed-field gel electrophoresis (PFGE) after digestion with SmaI. During the study period, MRSA was found in 31% of patients with S. aureus-positive cultures. PFGE analysis identified three predominant clones, affecting 94% of the patients. The three clones had been detected since 1999 in one hospital, and were designated as clones A, B and C. Whereas clones A and B (multidrug-resistant) were related to the two most prevalent clones in Spain at this time, clone C was identical to EMRSA-15, currently one of the most common MRSA clones in UK hospitals and also detected in other countries, but rarely in Spanish hospitals. This imported epidemic clone was detected in c. 10% of patients admitted to one of the three hospitals in 2002, but its prevalence has increased significantly (32% of the patients investigated in the three hospitals in the present study), and this clone also accounted for 44% of the isolates from non-hospitalised patients. Even though EMRSA-15 showed the least multidrug resistance of the three major clones, it was apparently more virulent, since it was associated significantly (p 0.001) with bacteraemia, and positive blood cultures were documented for 21% of the patients infected by this clone, compared with only 10% and 7% of patients infected with clones A and B, respectively.