Nutritional insult and recovery in the neonatal rat cerebellum: Insulin-like growth factors (IGFs) and their binding proteins (IGFBPs)

Alterations in growth caused by neonatal malnutrition may be mediated in part by changes in insulin-like growth factor (IGF) and IGF binding protein (IGFBP) expression. Since the neonatal rat cerebellum undergoes a transient, proliferative growth phase in the first two weeks of life, this structure was used to determine whether alterations in circulating and tissue IGFs and IGFBPs may mediate effects of impaired nutrition on the developing central nervous system. Gravid rats were placed on a 4% (protein-calorie deprived, D) or 20% (control, C) protein diets one day prior to delivery and allowed to nurse their pups postpartum. Pups nursing from D mothers received a limited volume of milk and were calorically deprived. Some litters of D pups were foster fed by C mothers from day 8 to day 13 to constitute a recovery group (R). Cerebellar weight, protein, and DNA content in D pups were less than C, p<0.001. In R pups, DNA and protein returned to C levels by day 13. Between days 6 and 13, serum IGF-I levels rose from 158±18 to 210±18 ng/ml in C but remained low in D (47±6 ng/ml and 25±3 ng/ml), respectively. In R pups, serum IGF-I partially recovered during this time, and increased from 49±5 to 110±7 ng/ml. In cerebellar extracts, IGF-I levels in both C and D were lower at 13 days than at 6 days, p<0.05 and p<0.005, respectively. IGF-I levels in C were similar at day 9 and day 11 and were consistently higher than D (11.84±0.83 vs 8.56±0.92 ng/g, p<0.02 C vs D). In R, IGF-I was reduced on day 11, but was similar to C on day 13. Serum IGF-II in D was lower than C, p<0.01, and did not increase in the R group. Cerebellar IGF-II was virtually undetectable in either group. Immunoprecipitation and ligand blotting studies of serum demonstrated that circulating levels of 32–34 K IGFBPs were increased 3–4 fold in D vs C, reflecting high levels of IGFBP-1 and/or-2, while levels of 24 K IGFBP-4 were lower in D vs C. By contrast, immunoprecipitation and ligand blotting of cerebellar extracts detected IGFBP-2 and-4, but did not detect IGFBP-1. Further, tissue levels of IGFBP-2 were not increased in D vs C, and levels of IGFBP-4 also were not markedly affected by nutritional deprivation. These results suggest that alterations in tissue content and the availability of IGF-I only modestly contributed to the effects of impaired nutrition in the developing central nervous system.     

Computer simulation and analysis of the reaction pathway of triosephosphate isomerase

A theoretical approach designed for chemical reactions in the condensed phase is used to determine the energy along the reaction path of the enzyme triosephosphate isomerase. The calculations address the role of the enzyme in lowering the barrier to reaction and provide a decomposition into specific residue contributions. The results suggest that, although Lys-12 is most important, many other residues within 16 A of the substrate contribute and that histidine-95 as the imidazole/imidazolate pair could act as an acid/base catalyst.     

Inspiratory resistive load detection in conscious dogs

The physiological mechanisms mediating the detection of mechanical loads are unknown. This is, in part, due to the lack of an animal model of load detection that could be used to investigate specific sensory systems. We used American Foxhounds with tracheal stomata to behaviorally condition the detection of inspiratory occlusion and graded resistive loads. The resistive loads were presented with a loading manifold connected to the inspiratory port of a non-rebreathing valve. The dogs signaled detection of the load by lifting their front paw off a lever. Inspiratory occlusion was used as the initial training stimulus, and the dogs could reliably respond within the first or second inspiratory effort to 100% of the occlusion presentations after 13 trials. Graded resistances that spanned the 50% detection threshold were then presented. The detection threshold resistances (delta R50) were 0.96 and 1.70 cmH2O.l-1.s. Ratios of delta R50 to background resistance were 0.15 and 0.30. The near-threshold resistive loads did not significantly change expired PCO2 or breathing patterns. These results demonstrate that dogs can be conditioned to reliably and specifically signal the detection of graded inspiratory mechanical loads. Inspiration through the tracheal stoma excludes afferents in the upper extrathoracic trachea, larynx, pharynx, nasal passages, and mouth from mediating load detection in these dogs. It is unknown which remaining afferents (vagal or respiratory muscle) are responsible for load detection.     

Effect of inspiratory muscle strength training on inspiratory motor drive and RREP early peak components.

This study investigated the effect of inspiratory muscle strength training (IMST) on inspiratory motor drive [mouth occlusion pressure at 0.1 s (P(0.1))] and respiratory-related evoked potentials (RREP). It was hypothesized that, if IMST increased inspiratory muscle strength, inspiratory motor drive would decrease. If motor drive were related to the RREP, it was further hypothesized that an IMST-related decrease in drive would change RREP latency and/or amplitude. Twenty-three subjects received IMST at 75% of their maximal inspiratory pressure (Pi(max)) with the use of a pressure threshold valve. IMST consisted of four sets of six breaths daily for 4 wk. P(0.1) and the RREP were recorded before and after IMST. Posttraining, Pi(max) increased significantly by 36.0 +/- 2.7%. P(0.1) decreased significantly by 21.9 +/- 5.2%. The increase in Pi(max) was significantly correlated to the decrease in P(0.1). RREP peaks P(1a), N(f), P(1), and N(1) were identified pre- and post-IMST, and there was no difference in either amplitude or latency for those peaks. These results demonstrate that high-intensity IMST significantly increased Pi(max), decreased P(0.1), but did not change the RREP.