Optimization of antibiotic dosing schedules in the light of increasing antibiotic resistance.

The development of antibiotic-resistant bacteria is an increasing problem throughout the world and is, without doubt, due to the increasing use of antibiotics themselves. As organisms become more resistant, treatment options become more limited and treatment failures increasingly likely. The need to reverse, or at least minimize this pattern of increasing resistance is therefore essential. Numerous strategies to achieve this have been postulated and there is no doubt that a combination of these will ultimately prove to be most effective. Among them, using antibiotic dosing regimens that may be less likely to promote resistance is one measure which could be beneficial, and this will be the focus of this review. Individual antibiotics will be discussed under the headings of the patterns of killing activity that they produce. Namely whether they exhibit concentration-dependent killing with prolonged persistent effects, time-dependent killing with minimal or no persistent effects, or time-dependent killing with prolonged persistent effects. The available evidence for optimal dosing regimens, as far as minimizing antibiotic resistance is concerned, will be reviewed. Where possible, recommendations relating to clinical practice will be made, or failing that, an indication of where further research would be of benefit.

Sex-related differences in neuronal cell survival and signaling in rats.

While substantial and compelling evidence exists for sex-related differences in gross and microscopic brain structure, our understanding of the cellular mechanisms that give rise to these sexual dimorphisms is in its infancy. To investigate possible underlying mechanisms for sex-related differences in neuronal development, we examined neuronal survival and transductional signaling in male and female rat primary cortical neuronal cultures. We found that following 14 days in culture, the total number of surviving neurons was significantly higher in female cultures derived from either cortical plate (cp) or ventricular zone (vz), the regions where differentiating (cp) and proliferating (vz) cells are located. In addition, sex-related differences in the levels of phospho-ERK1 and Akt were also observed. Female cortical cultures had significantly higher levels of ERK1 in both cp and vz and higher levels of Akt in cp. No sex-related differences in Bcl-2 were observed. These data suggest that dimorphisms in cell survival may underlie enhanced neuronal survival (or decreased apoptosis) in female brain. Further, the appearance of sex-related differences at cellular and signaling levels in cortical neuronal cultures demonstrates that the effects of gender are not limited to parts of the brain mediating reproduction.

Functional properties of ryanodine receptors in hippocampal neurons change during early differentiation in culture.

6-((4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-propionyl)amino)hexanoic acid ryanodine (BODIPY-ryanodine) binding and Ca(2+) imaging were used to study the properties of ryanodine receptors (RyRs) and cytoplasmic Ca(2+) (Ca) changes in neurons cultured from the embryonic rat hippocampus during the earliest stages of differentiation. Baseline Ca levels declined from 164 +/- 5 (SD) nM at early stages to 70 +/- 4 nM in differentiated neurons. Fluorescent BODIPY-ryanodine binding signals identified activated RyRs in somata, which were eliminated by removal of external Ca(2+) or by blockage of Ca(2+) entry through L-type but not N-type Ca(2+) channels. The GABA synthesis inhibitor 3-mercaptopropionic acid completely abolished ryanodine binding. Caffeine or K(+)-depolarization inhibited the activity of RyRs at very early stages of differentiation but had stimulatory effects at later stages after a network of processes had formed. BayK-8644 stimulated RyRs throughout all regions of all differentiating cells. The results suggest that in differentiating embryonic hippocampal neurons the activity of RyRs is maintained via Ca(2+) entering through L-type Ca(2+) channels. The mode of activation of L-type voltage-gated Ca(2+) channels with either membrane depolarization or specific pharmacological agents affects the coupled activity of RyRs differently as neurons differentiate processes and networks.

Allopregnanolone activates GABA(A) receptor/Cl(-) channels in a multiphasic manner in embryonic rat hippocampal neurons.

Although 3alpha-substituted metabolites of progesterone are well established to interact with GABA(A) receptor/Cl(-) channels, the nature of the interaction(s) remains uncertain. We used patch-clamp recording to study the interaction with GABA(A) receptor/Cl(-) channels expressed by embryonic hippocampal neurons differentiating in culture and nonneuronal cells transfected with GABA(A) receptor subunits. Allopregnanolone primarily induced multiphasic current responses in neurons, which were eliminated by bicuculline, an antagonist of GABA at GABA(A) receptor/Cl(-) channels. Similar multiphasic responses blocked by bicuculline were induced by allopregnanollone in nonneuronal cells transfected with alpha(1) and gamma(2) subunits, indicating that the steroid activation of GABA(A) receptor/Cl(-) channels occurred independently of GABA. Fluctuation analyses of current responses to allopregnanolone and GABA revealed underlying channel activities with similar estimated unitary properties. However, although both agonists activated Cl(-) channels with similar estimated short and long burst-length durations, most of those stimulated by the steroid were short, while most of those opened by GABA were long. Allopregnanolone potentiated GABA-evoked Cl(-) currents in nonneuronal cells transfected with alpha(1) and beta(2) or beta(3) subunits, which did not exhibit multiphasic responses to the steroid, indicating another, independent action of the steroid at activated receptors. Pertussis toxin treatment eliminated the low-amplitude current and attenuated the high-amplitude current induced by allopregnanolone in a reversible manner. Mastoparan, which activates G proteins directly, triggered a high-amplitude current after a delay, which was blocked by bicuculline. The results indicate that allopregnanolone interacts with GABA(A) receptor/Cl(-) channels expressed by embryonic hippocampal neurons in multiple ways, some of which are mediated by G proteins.