Representation of acoustic communication signals by insect auditory receptor neurons.

Despite their simple auditory systems, some insect species recognize certain temporal aspects of acoustic stimuli with an acuity equal to that of vertebrates; however, the underlying neural mechanisms and coding schemes are only partially understood. In this study, we analyze the response characteristics of the peripheral auditory system of grasshoppers with special emphasis on the representation of species-specific communication signals. We use both natural calling songs and artificial random stimuli designed to focus on two low-order statistical properties of the songs: their typical time scales and the distribution of their modulation amplitudes. Based on stimulus reconstruction techniques and quantified within an information-theoretic framework, our data show that artificial stimuli with typical time scales of >40 msec can be read from single spike trains with high accuracy. Faster stimulus variations can be reconstructed only for behaviorally relevant amplitude distributions. The highest rates of information transmission (180 bits/sec) and the highest coding efficiencies (40%) are obtained for stimuli that capture both the time scales and amplitude distributions of natural songs. Use of multiple spike trains significantly improves the reconstruction of stimuli that vary on time scales <40 msec or feature amplitude distributions as occur when several grasshopper songs overlap. Signal-to-noise ratios obtained from the reconstructions of natural songs do not exceed those obtained from artificial stimuli with the same low-order statistical properties. We conclude that auditory receptor neurons are optimized to extract both the time scales and the amplitude distribution of natural songs. They are not optimized, however, to extract higher-order statistical properties of the song-specific rhythmic patterns.

Bacterial translocation during graft-versus-host disease after small bowel transplantation is reduced following inhibition of inducible nitric oxide synthesis.

BACKGROUND: Increased nitric oxide (NO) production may contribute to intestinal barrier dysfunction and increased bacterial translocation (BT). Since BT may play a major role in graft-versus-host disease (GVHD) after small bowel transplantation (SBTx), we evaluated the role of NO production in GVHD after SBTX in the rat. METHODS: Using the standard model of semiallogeneic SBTx in the rat, we prepared three experimental groups. Recipients in group 1 received LBNF1-LBNF1 transplants and were treated with aminoguanidine (AG) (200 mg/kg), recipients in group 2 received Lewis-LBNF1 grafts and were injected with saline, and recipients in group 3 received Lewis-LBNF1 transplants and AG (200 mg/kg). Urine nitrite/nitrate levels were measured daily, and BT was determined by culturing peritoneal swabs, mesenteric lymph nodes, spleen, liver, and blood. RESULTS: In group 1 we detected indefinite survival with normal histology. In group 2 a survival of 10.5 +/- 1.1 days was reached, and the typical histological features of acute GVHD were observed. The animals in group 3 showed a mean survival of 14.8 +/- 0.6 days (P<0.02 compared with group 2) and the histological features of acute GVHD, although with a prolonged time course. Comparing NO production and BT between groups 2 and 3 we detected significantly reduced NO production on postoperative days 2-9 (P<0.03) and significantly decreased BT on postoperative days 3 and 9 (P<0.03). CONCLUSION: Inhibition of inducible NO synthesis with AG reduces NO production, decreases BT, and prolongs survival during GVHD after SBTx and therefore may be a useful addition to standard treatment protocols for GVHD.

A randomized, placebo-controlled trial with anti-interleukin-2 receptor antibody for immunosuppressive induction therapy after liver transplantation.

The introduction of quadruple induction therapy after liver transplantation with the murine anti-interleukin-2 receptor (IL-2R) antibody (BT563) has decreased the incidence of serious side effects, such as tachycardia, hypertension, rash, fever and nausea since it does not lyse its target cell. To investigate the immunosuppressive efficacy of BT563, a placebo-controlled trial was performed and BT563 was added to the standard triple induction after liver transplantation. Forty consecutive recipients of primary orthotopic liver transplants (OLT) (median age 47 yr [range 18-65]) were randomized. All patients received triple immunosuppression with cyclosporine A (CyA), prednisolone (PRED) and azathioprine (AZA). In addition, 19 patients received BT563 (Biotest, Dreieich, Germany) at a dose of 10 mg/d from day 0 until day 12. The remaining 21 patients received a placebo infusion at the same days after transplantation. Minimal follow-up for all patients was 3 yr. Patient survival at 3 yr was 74% in the BT563 group and 90% in placebo group. Similar results were observed for graft survival. Two acute rejection episodes were detected in the BT563 group and 9 acute rejections (5 steroid-resistant) were observed in the placebo group (p < 0.034). The incidences of sepsis, pneumonia, cholangitis, urinary tract infections as well as cytomegalo-virus (CMV) infections were similar in both groups. Side effects of the BT563 therapy and/or post-transplant lymphoproliferative disease (PTLD) were not detected. Quadruple induction therapy with BT563 significantly reduces the incidence of rejection episodes after liver transplantation, while infectious complications and/or PTLD is not increased. Therefore, the anti-IL2 receptor antibody BT563 constitutes a safe and efficient addition to the immunosuppressive induction regimen following OLT.