Behavioral measurement of axonal thresholds

A behavioral method for measuring the electrical sensitivity of directly stimulated elements in the brain is described and applied to the medial forebrain bundle (MFB) reward path and the tectospinal circling path. Equations are derived from which threshold current densities may be calculated from knowledge of the electrode tip dimensions and the current required to produce criterion behavior, which is a function of electrode size. Four different sizes of electrode were implanted in the MFB of rats and self-stimulation rates plotted against stimulating current. The mean currents for criterion bar-pressing rates of 25% and 55% of maximum rate were determined for each electrode size and the values used to calculate average threshold current densities. Two sizes of electrode were implanted in the tectospinal tract of rats and the average currents to produce circling at 0.2 and 0.4 turns/s were measured. The threshold current densities for self-stimulation axons were about 5 times as large as those for circling, in accordance with other evidence that tectal circling path axons are larger than those of the MFB reward path.     

Greater efficacy of pulsatile insulin in type I diabetics critically depends on plasma glucagon levels

The aim of this study was to investigate the role of plasma glucagon levels on the blood glucose response to intravenous insulin administered continuously or in a pulsatile manner. Six type I diabetic patients proven to have no residual insulin secretion were investigated. Endogenous glucagon secretion was inhibited by a continuous intravenous infusion of somatostatin (100 micrograms/h) and replaced by exogenous infusions of the hormone at three different rates (7.5, 4.5, and 2.5 micrograms/h), resulting in three different plasma glucagon steady-state levels (i.e., approximately equal to 200, approximately equal to 130, and approximately equal to 75 pg/ml, respectively). Each subject, in random order and on different days, was infused intravenously with regular human insulin either continuously (0.17 mU X kg-1 X min-1) or with the same amount of insulin infused in a pulsatile manner (0.85 mU X kg-1 X min-1 during 2 min followed by 8 min during which no insulin was infused). At plasma glucagon levels approximately equal to 200 pg/ml, blood glucose rose from approximately 10 to approximately 13 mM without any difference between the two modalities of insulin infusion. For plasma glucagon levels approximately equal to 130 pg/ml, plasma glucose remained steady throughout the experiments, but during the last 40 min, plasma glucose levels were significantly lower when insulin was administered intermittently. This greater blood glucose-lowering effect of pulsatile insulin occurred earlier and was more pronounced for plasma glucagon levels averaging 75 pg/ml. We conclude that the greater hypoglycemic effect of insulin administered intravenously in a pulsatile manner in type I diabetics critically depends on plasma glucagon circulating levels.     

The late results after axillo-femoral bypass grafts in patients with leg ischaemia

The late results--up to six years--after axillo-femoral bypass reconstruction are reported for 85 patients with leg ischaemia who were regarded as poor-risk patients for aortic bypass surgery, or who had aortic graft infection. Velour-Dacron grafts and expanded polytetrafluoroethylene (PTFE, Gore-Tex)--grafts have been used. The cumulative patency rate (life table) six years after graft implantation was 64% (PTFE-grafts) and 58% (Velour-Dacron grafts). The corresponding cumulative limb salvage rate six years after graft implantation was 88% when PTFE grafts were used and 77% when Velour-Dacron grafts were used. Our results demonstrate that axillo-femoral reconstruction is a useful procedure with a good patency rate 6 years after implantation. This procedure should be considered when dealing with poor risk patients with severe leg ischaemia.     

Central and peripheral changes in catecholamine-synthesizing enzyme activities after systemic administration of the neurotoxin DSP-4

In brain regions containing noradrenergic (NA) cell bodies or terminals, DSP-4 induces changes in the activity of catecholamine-synthesizing enzymes which suggest that central NA neurons are lesioned by this neurotoxin. In contrast, the lack of change in the same enzymatic activities in an area containing mostly adrenergic (A) neurons (C2 region), favors the hypothesis of a resistance of the A neurons to DSP-4. Furthermore, the enzymatic changes observed in peripheral organs suggest a peripheral activation of the NA cell bodies in response to lesioning of the sympathetic terminals by DSP-4.     

Aging pathways for organophosphate-inhibited human butyrylcholinesterase, including novel pathways for isomalathion, resolved by mass spectrometry.

Some organophosphorus compounds are toxic because they inhibit acetylcholinesterase (AChE) by phosphylation of the active site serine, forming a stable conjugate: Ser-O-P(O)-(Y)-(XR) (where X can be O, N, or S and Y can be methyl, OR, or SR). The inhibited enzyme can undergo an aging process, during which the X-R moiety is dealkylated by breaking either the P-X or the X-R bond depending on the specific compound, leading to a nonreactivatable enzyme. Aging mechanisms have been studied primarily using AChE. However, some recent studies have indicated that organophosphate-inhibited butyrylcholinesterase (BChE) may age through an alternative pathway. Our work utilized matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry to study the aging mechanism of human BChE inhibited by dichlorvos, echothiophate, diisopropylfluorophosphate (DFP), isomalathion, soman, sarin, cyclohexyl sarin, VX, and VR. Inhibited BChE was aged in the presence of H2O18 to allow incorporation of (18)O, if cleavage was at the P-X bond. Tryptic-peptide organophosphate conjugates were identified through peptide mass mapping. Our results showed no aging of VX- and VR-treated BChE at 25 degrees C, pH 7.0. However, BChE inhibited by dichlorvos, echothiophate, DFP, soman, sarin, and cyclohexyl sarin aged exclusively through O-C bond cleavage, i.e., the classical X-R scission pathway. In contrast, isomalathion aged through both X-R and P-X pathways; the main aged product resulted from P-S bond cleavage and a minor product resulted from O-C and/or S-C bond cleavage.