Ultrastructural development of the dorsal lateral geniculate nucleus of genetically microphthalmic mice

Summary The ultrastructure of the dorsal lateral geniculate nucleus (dLGN) of microphthalmic mice is described in affected white homozygotes (mi/mi) and their apparently normal grey littermates. In the dLGN of mi/mi animals populations of apparently normal axon terminals were observed, including some with flattened synaptic vesicles and other small terminals with round vesicles and dark mitochondria (RSD), possibly of cortico-thalamic origin, just as in normal mice. However, no typical large retinal endings with round vesicles and pale mitochondria (RLP) are visible. Instead they appear to be replaced by other large boutons with round vesicles and dark mitochondria (RLD). Eye enucleation does not cause degeneration of these RLD terminals. In apparently normal grey littermates RLP terminals are present and they degenerate when an eye is enucleated. But RLD endings are also found in these animals, and never degenerate after enucleation. The origin of the RLD terminals is unclear but seems not to be cortical. These findings are compared with those of Cullen and Kaiserman-Abramof (1976) in a different strain (ZRDCT-An) of anophthalmic mouse in which they found large replacement terminals similar to our RLD boutons.     

Golgi and Nissl studies of the visual cortex of the bottlenose dolphin

Nissl, Golgi and fibre preparations were made of the cerebral cortex of the lateral gyrus of the bottlenose dolphin (Tursiops truncatus) in the region where visual evoked potentials have been reported (Sokolov et al., '72; Ladygina et al., '78). In the adult the visual cortex is relatively thin (average about 1,300 micron) for so large a brain (fixed brain weight for a typical adult in our series was 1,330 g). Layers I, III, and VI are wide and represent three-quarters of the total cortical thickness. Layer I contains few cell bodies, while III and VI have a variety of pyramidal and nonpyramidal neurons. Layers II and V are narrow and contain striking palisades of darkly staining pyramidal cells that are particularly large in layer V. No clearly demarcated layer IV is present in the adult dolphin visual cortex. Many of the neurons identified with the Golgi technique are typical of pyramids in other mammals, with a single apical dendrite and a bouquet of basal dendrites, mostly highly spiny. Others are unusual in having bifurcated or oblique apical dendrites. Typical large and small spiny and nonspiny stellates are also found, mainly in layers III and VI. In addition various forms of spindle-shaped, bipolar and multipolar neurons are found in most layers. An 18-day-old brain shows signs of immaturity in its visual cortex. It is thinner (970 micron) and on average its neurons are smaller, paler, and more densely packed. Especially the pyramids of layer V are much smaller than in the adult. Also, a distinct "granular" band occurs between layers III and V and seems to be a rudimentary layer IV. At 3 years of age most of the adult features have developed, but layer IV is still detectable. No striking differences were observed in cell and fibre architecture between the cortex of the lateral gyrus and that of the so-called "calcarine" area that has also been considered as "visual." We concluded that, although different in many respects from other mammalian visual cortices, that of the dolphin is apparently well developed and differentiated.     

Outcomes of bacteremia due to Pseudomonas aeruginosa with reduced susceptibility to piperacillin-tazobactam: implications on the appropriateness of the resistance breakpoint.

BACKGROUND: Bacteremia due to Pseudomonas aeruginosa is associated with grave clinical outcomes. Recent studies have emphasized the importance of appropriate empirical therapy, but controversy arises when piperacillin-tazobactam is used against isolates with reduced susceptibility. METHODS: We performed a retrospective cohort study of pseudomonal bacteremia from 2002 to 2006. Patients were identified by the microbiology laboratory database, and pertinent clinical data (demographic characteristics, baseline Acute Physiology and Chronic Health Evaluation [APACHE] II scores, source of bacteremia, and therapy) were retrieved from the electronic medical records. All patients received appropriate empirical therapy within 24 h of positive culture results. Patients receiving piperacillin-tazobactam were compared with those receiving other agents (control subjects). The primary outcome was 30-day mortality from the first day of bacteremia. RESULTS: A total of 34 bacteremia episodes were identified involving isolates with reduced susceptibility to piperacillin-tazobactam (minimum inhibitory concentration, 32 or 64 mg/L, reported as susceptible); piperacillin-tazobactam was empirically given in 7 episodes. There was no significant difference in baseline characteristics between the 2 groups. Thirty-day mortality was found to be 85.7% in the piperacillin-tazobactam group and 22.2% in the control group (P = .004). Time to hospital mortality was also found to be shorter in the piperacillin-tazobactam group (P < .001). In the multivariate analysis, 30-day mortality was found to be associated with empirical piperacillin-tazobactam therapy (odds ratio, 220.5; 95% confidence interval, 3.8-12707.4; P = .009), after adjustment for differences in age and APACHE II score. CONCLUSIONS: In P. aeruginosa bacteremia due to isolates with reduced piperacillin-tazobactam susceptibility, empirical piperacillin-tazobactam therapy was associated with increased mortality. Additional studies are warranted to examine the appropriateness of the current Clinical Laboratory Standards Institute resistance breakpoint of piperacillin-tazobactam.     

Prevalence of AmpC over-expression in bloodstream isolates of Pseudomonas aeruginosa

This study examined the contribution of AmpC over-expression to beta-lactam resistance in clinical isolates of Pseudomonas aeruginosa obtained from a hospital in Houston, TX, USA. Seventy-six non-repeat bloodstream isolates obtained during 2003 were screened for ceftazidime resistance in the presence and absence of clavulanic acid 4 mg/L. AmpC was identified by isoelectric focusing (with and without cloxacillin inhibition); stable derepression was ascertained phenotypically by a spectrophotometric assay (with and without preceding induction by imipenem) using nitrocefin as the substrate, and was confirmed subsequently by quantitative RT-PCR of the ampC gene. The clonal relatedness of the AmpC-over-expressing isolates was assessed by pulsed-field gel electrophoresis. In addition, the ampC and ampR gene sequences were determined by PCR and sequencing. For comparison, two standard wild-type strains (PAO1 and ATCC 27853) and three multidrug-susceptible isolates were used as controls. AmpC over-expression was confirmed in 14 ceftazidime-resistant isolates (overall prevalence rate, 18.4%), belonging to seven distinct clones. The most prevalent point mutations in ampC were G27D, V205L and G391A. Point mutations in ampR were also detected in eight ceftazidime-resistant isolates. AmpC over-expression appears to be a significant mechanism of beta-lactam resistance in P. aeruginosa. Understanding the prevalence and mechanisms of beta-lactam resistance in P. aeruginosa may guide the choice of empirical therapy for nosocomial infections in hospitals.     

Pharmacokinetic/pharmacodynamic antimicrobial individualization and optimization strategies

Effective antimicrobial chemotherapy integrates pharmacology and microbiology to achieve the most favorable clinical and microbiologic outcomes. Understanding such relationships allows us to select the optimal drug dose in a rational manner. The difficulty lies in translating the research findings to clinicians at the bedside. Current clinical practices have not embraced fully many advances in pharmacokinetic/pharmacodynamic research. This article summarizes what we have learned over the past decades and highlights some of the barriers to translating these results into clinical practice. Reducing these barriers would help to bring clinically relevant laboratory work to the bedside and would emphasize evidence-based medicine. It may also improve patient outcomes and minimize the emergence of resistance.