Physiological characteristics of the tympanic organ in noctuoid moths

Summary The tympanic organ ofSpodoptera frugiperda, Mocis latipes, Erebus odorata (Noctuidae) andMaenas jussiae (Arctiidae) was stimulated with acoustic stimuli of 20 kHz, 45 ms and 5 s duration, and intensities ranging from 30 to 100 dB. The electric activity of the auditory receptors was recorded at the tympanic nerve with a stainless steel hook electrode. In all of these moth species there is an intensity range (ca. 20 dB) in which the response of each auditory receptor (A₁ and A₂ cells) to 45 ms pulses varies in a linear relation to the logarithm of stimulus intensity. For intensities higher than this value, depending on the species and the cell analysed, the spike discharge may continue to increase, may saturate or may diminish (Fig. 2). InE. odorata andM. latipes the A₁-cell response shows a decrease for stimulus intensities higher than 30 dB above the threshold. In the former species there is a statistically significant linear relation between the A₂-cell response and the decrease of the A₁-cell response, but this is not the case inM. latipes (Fig. 3). The similarity of the responses ofE. odorata to those described inEmpyreuma pugione (Coro and Pérez 1984) suggest that also in this noctuid species one may assume that the A₂ cell inhibits the A₁ receptor. In all of these moth species there is a maximum firing rate of the auditory cells at the beginning of the response to pure tones of 5 s and an exponential decrease of their discharge frequency with the course of time (Fig. 5). The analysed species differ in the adaptation rates of their auditory receptors. In all of these species the A₂ cell adapts more rapidly than the A₁ cell. In most of these species the stimulus intensity influences the adaptation rate of the auditory receptors (Fig. 7). These results are compared with data obtained by other authors, and it is concluded that there are more interspecific differences in the physiological characteristics of the auditory receptors in noctuoid species than those reported so far.Abbreviation AP action potential     

Asexual propagation and reproductive strategies in aquatic Oligochaeta

A great variety of asexual reproductive modes are known among aquatic oligochaetes. The main types of these modes are shortly described. Based upon observations on natural populations, the possible genetical and ecological implications of asexual reproduction are discussed. The following points are emphasized: (1) The often expressed expectations of a strong predominance of one particularly adaptive genotype is not born out. (2) In most cases, a number of genetically distinct clones are present in each population, and they show a strong differential distribution in heterogeneous environments, indicating an effective exploitation of the available resources. (3) Most cases of asexual propagation are reproductive strategies of their own and not escape mechanisms. (4) The mechanisms underlying asexual propagation are complex and involve many aspects of the life history. The great variety of types among aquatic oligochaetes offer particularly useful models for the study of these problems.     

Organic ion transport during seven decades. The amino acids

The amino acids are ions of various charge combinations, and one can argue that historically they were the first ions for which the ongoing problem of membrane transport was presented; also that among transported ions these may undergo a highly detailed molecular recognition. Furthermore, the distribution of charge on the amino acid molecule determines by what route or routes it is conducted across the biological membrane, with what directional and structural specificity, and therefore what regulation is imposed, and where. Cases where a presumably charged chemical group behaves as if it were somehow absent from the amino acid have been observed to fall into several categories: Straightforward cases where the pH has been low enough or high enough to remove the charge by protonation or deprotonation, even in free solution. Cases where that protonation or deprotonation is facilitated at the binding site, and perhaps by the total transport process. The cystine molecule can apparently thus be rendered either a tripolar anion or a tripolar cation for transport. Cases where an otherwise co-transported Na+ is omitted to redress charge, or where a Na+ serves as a surrogate for a missing charged group on the amino acid molecule. A case where the protonation occurs reversibly at the receptor site rather than on the amino acid molecule.     

Trypanosoma brucei-induced blockage of expulsion of Echinostoma revolutum and of homologous E. revolutum resistance in mice

Experiments were designed to study the effect of Trypanosoma brucei on the expulsion of Echinostoma revolutum and on the development and maintenance of homologous E. revolutum resistance in the mouse. T. brucei given 3, 2, and 1 wk before and 1 wk after infection with E. revolutum completely inhibited the expulsion of the E. revolutum worm burden for a period of at least 6 wk following infection, and T. brucei given 2 or 3 wk after infection with E. revolutum conferred a significant delay in the expulsion of the E. revolutum worm burden. T. brucei given 1 wk before and 1 wk after a primary E. revolutum infection blocked completely the resistance of the mouse to a homologous E. revolutum challenge given 2 wk after the primary infection. A similar blockage of resistance to a homologous challenge was experienced by mice given T. brucei 3 wk after the primary E. revolutum infection and challenged following another 2 wk. The mechanisms underlying the T. brucei-induced interference with the expulsion of E. revolutum and with the development and maintenance of homologous E. revolutum resistance in mice are presumably immunologically mediated.     

Evidence for X-Linkage of Steroid Sulfatase in the Mouse: Steroid Sulfatase Levels in Oocytes of XX and XO Mice

The steroid sulfatase (STS) levels in mature oocytes of XX and XO mice were assayed along with lactate dehydrogenase (LDH), an autosomal marker, and glucose-6-phosphate dehydrogenase (G6PD), a known X-linked gene. LDH levels in XX and XO oocytes were equal, whereas STS and G6PD levels were approximately twice as high in XX oocytes as in XO oocytes. These results indicate that the STS gene is X-linked in the mouse just as it is in humans. Assays of STS in kidney tissue of XX and XO mice indicated dosage compensation for the gene, which is different from that observed in humans.     

Effect of dextran and dextran modifications on the thermal and proteolytic stability of conjugated bovine testis beta-galactosidase and human serum albumin

In order to study carbohydrate-induced protein stabilization bovine testis beta-galactosidase and human serum albumin were conjugated with dextran, partially acetylated dextran and partially methylated dextran. The conjugates and the free proteins were compared with respect to thermal stability at 50 degrees C and resistance to proteolytic digestion by subtilopeptidase A. Both beta-galactosidase and serum albumin were stabilized by conjugation with polysaccharide. However, higher stability was achieved by conjugating the proteins with the hydrophilic polysaccharides, dextran and acetylated dextran, than by conjugation with the hydrophobic polysaccharide, methylated dextran. The results are discussed in relation to possible explanations of carbohydrate-induced protein stabilization.     

A subcortical, pigment-containing structure in Xenopus eggs with contractile properties

An accumulation of insoluble, finely granular material has been observed under the pigmented surface of Xenopus eggs by a specialized "dry fracture" technique and scanning electron microscopy. Cortical granules and pigment granules can be recognized with the techniques and can be seen to be embedded in the material. Thin sections show that the region also contains mitochondria and membranous vesicles or reticula. Yolk platelets are largely excluded from the heaviest accumulations of the material. The substance is most dense just under the cortex and grades off gradually into the more diffuse, yolk-containing network of the endoplasm. The accumulation of material is much thicker in the animal hemisphere of the egg than in the vegetal hemisphere, and the pigment embedded in it defines the pigmented area of the animal hemisphere. In the pigmented area the material excludes yolk for a thickness of 3-7+ microns from the surface. In the vegetal hemisphere there is no such accumulation and yolk platelets can be found almost touching the plasmalemma. Cortical contractions have been experimentally induced in eggs. Their relative strength correlates with the relative thickness of the finely granular, subcortical material. During contraction the material accumulates to much greater thicknesses, excluding yolk from thicknesses of 15-30+ microns from the surface. The contracting entity is, or is in, the finely granular material. Injection of cytochalasins into the eggs inhibits cleavage furrow operation but does not inhibit the induced cortical contractions. The thus do not seem to be dependent on actin microfilamentogenesis as is the operation of the contractile ring of the cleavage furrow. The differential sensitivity to cytochalasins of the contractile ring and the system responding in the induced cortical contractions, suggests a two-component system for cortical contractions in the egg. A model is presented which accommodates the available data.