Concentrating Engines and the Kidney: II. Multisolute Central Core Systems

The analysis of the central core model of the renal medulla is extended to multisolute systems. It is shown that total solute concentration obeys the same differential equations for core and ascending limb as in a single solute system. Equations are derived for the concentration of individual solutes. Application of these equations to a two solute system shows that a central core system can concentrate with all transport being down a concentration gradient. This analysis applied to the renal medulla shows that mixing of urea from the collecting duct (CD) and salt from the loop of Henle in the central core of the inner medulla contributes to the concentration of urine during antidiuresis. It also sets criteria for completely passive function of the loop in the inner medulla, but whether these are satisfied cannot be determined from present experimental data.     

Aldehyde dehydrogenase isozymes in rat hepatoma-mouse fibroblast hybrids

A study of aldehyde dehydrogenase in rat hepatoma cells and rat hepatoma-mouse fibroblast hybrids revealed that the hepatoma cells had activity comparable to that found in whole rat liver and that the enzyme activity was suppressed in early hybrids and reappeared following chromosome loss. Starch gel electrophoresis and heat inactivation studies showed that a new form of enzyme was produced in the hybrids, possibly a heteropolymorphic combination between the HTC enzyme and a previously repressed mouse form. Staining methods for starch gel electrophoresis and histochemical detection of aldehyde dehydrogenase are described.This work was supported by grants from the Damon Runyon Foundation (DRG 1088s) and the Public Health Service (1-R01-Ca 12310-02).     

Branch Input Resistance and Steady Attenuation for Input to One Branch of a Dendritic Neuron Model

Mathematical solutions and numerical illustrations are presented for the steady-state distribution of membrane potential in an extensively branched neuron model, when steady electric current is injected into only one dendritic branch. Explicit expressions are obtained for input resistance at the branch input site and for voltage attenuation from the input site to the soma; expressions for AC steady-state input impedance and attenuation are also presented. The theoretical model assumes passive membrane properties and the equivalent cylinder constraint on branch diameters. Numerical examples illustrate how branch input resistance and steady attenuation depend upon the following: the number of dendritic trees, the orders of dendritic branching, the electrotonic length of the dendritic trees, the location of the dendritic input site, and the input resistance at the soma. The application to cat spinal motoneurons, and to other neuron types, is discussed. The effect of a large dendritic input resistance upon the amount of local membrane depolarization at the synaptic site, and upon the amount of depolarization reaching the soma, is illustrated and discussed; simple proportionality with input resistance does not hold, in general. Also, branch input resistance is shown to exceed the input resistance at the soma by an amount that is always less than the sum of core resistances along the path from the input site to the soma.     

SURVIVAL,PAIR BOND RETENTION AND NEST-SITE TENACITY IN BULLER'S MOLLYMAWK*

Adult Buller's Mollymawks Diomedea bulleri banded in 1948 and 1961 at the Snares Islands south of New Zealand have been recovered between 1961 and 1971. Survival curves are presented which indicate the existence of a constant annual mortality rate of not more than 11.1 % with a mean expectation of further life at the time of banding of not less than 8.5 years. Breeding birds show a strong tendency to retain both the pair bond and the nest-site. One pair was still breeding in 1971 at the same nest at which it bred 23 years earlier. No re-matings were recorded while the original partner was known to be still alive. The dimensions of eggs laid over the years by particular females are presented. These enable some general indications to be given of the effects of the age of the female on the dimensions of the eggs which she lays.     

A re-evaluation of polypodium bradeorum and P. Colysoides

During field studies on the pteridophytes of Costa Rica, a peculiarly dimorphic polypodioid fern was found in the rain-forests of the Atlantic lowlands near Puerto Viejo. The variation in the fertile frond, ranging from simple and short petiolate to pinnatisect and long petiolate, coupled with peculiarly elongate and irregular sori, prompted further investigations. Additional herbarium specimens from localities in Mexico, British Honduras, Nicaragua, and Costa Rica showed intermixed variations between plants with all leaves simple (typified byPolypodium bradeorum Rosenstock) to plants with all leaves lobed or pinnatisect (typified byP. colysoides Maxon & Copeland). Other characters were judged sufficiently homogeneous to consider these individuals as conspecific underP. bradeorum. Morphological studies indicate parallel evolution of several characters in the Asiatic generaColysis, Microsorium, andLeptochilus on the one hand and the New World members ofMicro gramma, Pleopeltis, andPolypodium bradeorum on the other     

MORPHOLOGY OF CHAETOMIUM ERRATICUM

Development of perithecia from single, uninucleate ascospores disclosed a homothallic condition for Chaetomium erraticum. This species was found to produce sessile ascogonial coil initials from uninucleate vegetative cells that become enveloped by hyphae formed at the base of the ascogonium. The ascogonium consists of several cells that are uninucleate or binucleate. A perithecium forms from numerous divisions and enlargement of the surrounding uninucleate cells. Differentiation of the perithecial cells results in the formation of a carbonaceous wall, perithecial hairs, and an ostiole lined with periphyses. A convex hymenial cluster of ascogenous cells forms in the lower half of the centrum from which typical croziers develop. Asci push up into the pseudoparenchyma cells of the centrum. The growth of the ascogenous system is in part responsible for increase in perithecial size. The breakdown of the pseudoparenchyma cells around the developing asci results in the formation of a central cavity in which ascospores are released when the asci deliquesce. No paraphyses are present. The type of development and features of the centrum of C. erraticum and other species of Chaetomium indicate a distinct Xylaria-type centrum.