Dexter M. Easton

Garfish Olfactory Nerve: Easily Accessible Source of Numerous Long, Homogeneous, Nonmyelinated Axons

The olfactory nerve of the garfish, Lepisosteus, is about 1 millimeter in diameter and about 20 centimeters long, depending on the size of the fish; it is easily prepared by breaking off successive scored segments of the rostrum. It consists of a relatively homogeneous population of about 107 nonmyelineated nerve fibers, each about 0.24 micrometer in diameter. In most other nerves each fiber is separated from all others by an enfolding Schwann cell, but in the olfactory nerve the fibers are directly in contact with one another in groups of several hundred fibers. The Schwann cell, not directly concerned with propagation of the nerve impulse, forms a thin layer at the periphery of the group and makes up a small proportion of the total cellular material. The volume of axon cytoplasm is about five times greater than that of Schwann cell cytoplasm, and the axon surface is about 30 times the Schwann cell surface. The ratio of surface to volume for axons of a typical olfactory nerve is about 5400 times that for the squid axon of the same diameter. The large proportion of axonal membrane recommends this nerve for use in chemical and physical studies of properties of axon membranes.

Oxyhemoglobin dissociation curve as expo-exponential paradigm of asymmetric sigmoid function☆

Abstract From the assumption that the fractional increase of HbO2 as a function of pO2 is proportional to HbO2, and that the proportionality coefficient of that relation decreases exponentially with pO2, an equation can be derived that gives an excellent fit to the full range of the oxyhemoglobin dissociation curve. To generate this asymmetric sigmoid curve, only one rate constant is required. In addition, the initial and final conditions specify an intermediate constant B, the “shift factor” that determines the horizontal displacement of the curve. The rate constant K specifies the rate of change of the specific rate of increase of HbO2 with respect to O2. Governing the slope of the curve, K decreases as temperature and acidity increase, while the B factor remains constant. For Hb in solution, B decreases with decrease of concentration, but K appears to be unchanged. The expo-exponential constants provide convenient specification of the full course and position of the oxyhemoglobin dissociation curve.

Major lipids of non-myelinated (olfactory) and myelinated (trigeminal) nerve of garfish, Lepisosteus osseus

Abstract 1. 1. Densitometry of spots developed by thin-layer chromatography, showed the following approximate percentages of total lipids in non-myelinated olfactory nerve and in myelinated trigeminal nerve of garfish: cholesterol 14, 22; phosphatidyl choline 31, 22; phosphatidyl ethanolamine 19, 22; phosphatidyl serine 11, 12; sphingomyelin 7.5, 7.5; cerebroside 0,1; sulfatide 0,5; phosphatidyl inositol 0.7, 0.2. 2. 2. Three uncharacterized lipids were present in greater concentration in the non-myelinated than in the myelinated nerve. 3. 3. Phospholipids of the non-myelinated nerve generally ran ahead of those from the myelinated nerve. 4. 4. The densitometric method may allow subtler discriminations than phosphorus analysis for phospholipids, but discrepancies may arise because of non-identity of nerve lipids compared to standards.

Autotomy of walking legs in the Pacific Shore crab Hemigrapsus oregonesis

The ease of autotomy in Hemigrapsus oregonensis was tested by crushing the propodite of each walking leg. Individual curves of percent autotomy in groups of 18–21 animals were drawn for six different sequences of stimulation. Lumped data show peaks in ease of autotomy for the third anatomical leg of each side and for the second leg stimulated regardless of anatomical position. Later autotomies are more severely depressed when the stimulation sequence is from posterior to anterior. Segmental and lateral interaction and the characteristics of individual responses suggest that autotomy of legs in the crab, while depending upon specific structural features of the legs, is less a unisegmental reflex, than an accident occurring during escape.

Nerve-End Recording in Conducting Volume

When the end of a freshly cut nerve is drawn into a tube by means of a hydraulic device that serves as a holder and as an electrode, monophasic positive records of action potentials are recorded. A trailing positive phase develops, with time, after the cut. After-potentials can also be recorded by this method.

Fluorescence monitoring of unstained protein bands in acrylamide gel

Abstract A general method for detecting and quantitation of unstained protein bands in an electrophoretic supporting gel is described. The fluorescence emission of the aromatic amino acids is monitored with the aid of a simple mechanism for advancing the tube of gel past the slit of a fluorometer. This procedure is presently being utilized for the routine surveying of protein separations. It should also lend itself to the automatic clinical analysis of serum proteins.

Temperature-induced changes in fatty acid composition of myelinated and non-myelinated axon phospholipids

The olfactory (non-myelinated) and trigeminal (myelinated) nerve axons of garfish show changes in phospholipid fatty acid composition when these fish are acclimated to temperatures ranging from 11 to 35 degrees C. Myelinated and non-myelinated nerve axons show similar changes in the percent saturated, percent 16-carbon, percent 18-carbon, and percent 20-carbon-and-greater unsaturated fatty acids. The observed changes in phospholipid fatty acid composition fit a linear regression model suggesting a gradual change in axonal phospholipid fatty acid composition with temperature. The temperature-induced changes in garfish nerve phospholipid fatty acid composition are consistent with the general observation of increased saturated fatty acid residues in plasma membrane phospholipids of organisms acclimated to higher environmental temperatures. The garfish data are similar to data previously obtained for goldfish tissues and Tetrahymena.

For prediction of elder survival by a Gompertz model, number dead is preferable to number alive

The standard Gompertz equation for human survival fits very poorly the survival data of the very old (age 85 and above), who appear to survive better than predicted. An alternative Gompertz model based on the number of individuals who have died, rather than the number that are alive, at each age, tracks the data more accurately. The alternative model is based on the same differential equation as in the usual Gompertz model. The standard model describes the accelerated exponential decay of the number alive, whereas the alternative, heretofore unutilized model describes the decelerated exponential growth of the number dead. The alternative model is complementary to the standard and, together, the two Gompertz formulations allow accurate prediction of survival of the older as well as the younger mature members of the population.

Gompertz Pharmacokinetic Model for Drug Disposition

AbstractPurpose. Disposition of drugs among compartments of the body usually occurs at changing rates that are commonly modeled as sums of exponential terms with different rate constants. This paper describes an alternative, Gompertz kinetics, in which the rates can change systematically. Methods. Differential equations were developed and solved that fit typical examples taken from the literature. The three or four constants required for a visually satisfactory fit to data could readily be found by successive adjustment “by hand,” but strategies and results are presented for computer fitting of the data. Results. In four examples, the amount remaining in the blood decreases as an exponentially declining fraction of the amount present at any moment, but the antecedent processes responsible for that amount differ as follows: (a) In simple i.v. disposition (e.g., lidocaine) concentration falls as a decelerated exponential decay. (b) Delayed i.v. disposition (e.g., hexobarbital) requires, as well, a decelerated exponential growth function. (c) In simple disposition after oral administration, the concentration in the blood initially increases at a decelerating rate. (d) In biphasic oral disposition (e.g., Li+ carbonate), the initial Gompertz growth is followed by decelerated exponential decay. Conclusions. Gompertz kinetics provides an accurate and parsimonious mathematical model describing drug disposition.

Efflux of endogenous protein from non-myelinated olfactory nerve as monitored by tryptophan fluorescence.

Endogenous protein was lost from the olfactory nerve of the garfish (Lepisosteus osseus) when the excised but excitable nerve was bathed with normal physiological solution. The protein could be detected by its fluorescence at 340 nm when excited at 280 nm. The relative concentrations were expressed in terms of an equivalent fluorescence from a standard solution of tryptophan. From an initial fluorescence, equivalent to 5 × 10−10 mol of tryptophan/mg of nerve washed out during each 10 min, the efflux may decline slowly in rate to 10−11 mol/mg per 10 min. Depolarizing direct current or a several‐fold increase of the concentration of KCl in the bathing solution might transiently double the rate of efflux above the resting rate during continuous monitoring of the fluorescence intensity. Changes in concentrations of external KCl, glucose or sucrose, in ionic strength (at constant osmolality), or in osmolality all produced a transient increase of fluorescence in the effluent from the nerve. An increase followed both introduction of the experimental solution and the return to the control solution. We interpreted the increase in intensity of fluorescence of the washout solution to indicate an increase in concentration of an intrinsic specific protein washed from the nerve. By electrophoresis, a single acidic fluorescent protein band was observed travelling with the marking dye. Chromatographic fractionation on Sephadex suggested a mol. wt. in excess of 100,000.