Spectral mechanisms in the tree squirrel retina

Summary The retina of the gray squirrel (Sciurus carolinensis) contains rods and cones in a ratio of about 23. The spectral mechanisms in this retina were examined in behavioral and electrophysiological experiments. Tests of color vision revealed that this animal has a spectral neutral point at about 500 nm and, thus, dichromatic color vision. Recordings made from single optic nerve fibers and results obtained from an analysis of the flicker photometric electroretinogram (ERG) indicated that vision in the gray squirrel is based on three spectral mechanisms. One of these, presumably rod-based, has peak sensitivity at about 502 nm. The other two mechanisms reflect the presence of two classes of cone having average peak sensitivity of about 444 nm and 543 nm.     

Acoustic orientation in adult, female crickets (Gryllus bimaculatus de Geer) after unilateral foreleg amputation in the larva

Summary InGryllus bimaculatus females one foreleg was amputated at the coxa-trochanter joint in the 2nd, 4th or 8th/9th larval instar. A leg of up to normal length is regenerated (Fig. 1) but it lacks a functional ear. In spite of the, usually shorter, regenerated foreleg, the adult one-eared crickets show no impairments in walking when tested on a locomotion compensator. Without sound they walk erratically and most of them weakly circle towards the intact side (Fig. 2).With calling song presentation three response types can be distinguished:tracking (Fig. 3A), hanging on (Fig. 3B) or continuouscircling towards the intact side (Fig. 3C, D). Turning tendencies in monaurals increase with song intensity and exceed those of intact and bilaterally operated animals (Fig. 4). Course deviations towards the intact side also slightly increase with intensity (Fig. 5). Course stability is reduced compared to that of intact animals but exceeds that of bilaterally operated crickets (Figs. 5, 6). It is best at 60 dB and deteriorates at higher sound intensities (Fig. 6). The percentage of monaurals tracking or hanging on decreases with increasing intensity (Fig. 7B). Tracking is established in most animals but it is limited to a narrow intensity range (Fig. 7A, C). Apart from an increased percentage of tracking after early operations (Fig. 7D), there are no prominent changes in orientational parameters with the date of foreleg amputation.Reamputation of the regenerated leg in the adult monaurals does not significantly impair acoustic orientation (Figs. 8, 9), but occlusion of the ipsilateral prothoracic spiracle does (Figs. 10, 11).An attempt is made to correlate the behavioral performance with the activity of auditory interneurons which have undergone morphological and physiological changes (Fig. 12).     

Enzymatic dehalogenation of 4-chlorobenzoate by 4-chlorobenzoate dehalogenase from Pseudomonas sp. CBS3 in organic solvents

Summary 4-Chlorobenzoate dehalogenase from Pseudomonas sp. CBS3 showed dehalogenating activity in various organic solvents. In alcohols like methanol (150%) or ethanol (120%) higher activities than in water (100%) were obtained. In apolar solvents like petroleum ether (5%) and nhexane (5%) only trace activities were observed. The solvents did not increase the stability of the enzyme. 4-Chlorobenzoic acid methylester, a substance not soluble in water, was not dehalogenated in organic solvents.     

The relationship between RNA catalytic processes

Proposals that an RNA-based genetic system preceeded DNA, stem from the ability of RNA to store genetic information and to promote simple catalysis. However, to be a valid basis for the RNA world, RNA catalysis must demonstrate or be related to intrinsic chemical properties which could have existed in primordial times. We analyze this question by first classifying RNA catalysis and related processes according to their mechanism. We define: (A) thedisjunct nucleophile class which leads to 5-phosphates. These include Group I and II intron splicing, nuclear mRNA splicing and RNase P reactions. Although Group I introns and its excision mechanism is likely to have existed in primordial times, present-day examples have arisen independently in different phyla much more recently. Comparative methodology indicates that RNase P catalysis originated before the divergence of the major kingdoms. In addition, alldisjunct nucleophile reactions can be interrelated by a proposed mechanism involving a distant 2-OH nucleophile. (B) theconjunct nucleophile class leading to 3-phosphates. This class is composed of self-cleaving RNAs found in plant viruses and the newt. We propose that tRNA splicing is related to this mechanism rather than the previous one. The presence of introns in tRNA genes of eukaryotes and archaebacteria supports the idea that tRNA splicing predates the divergence of these cell types.     

Depletion of Brain Glutathione in Preweanling Mice by L-Buthionine Sulfoximine

Previous studies indicated that DL-buthionine sulfoximine (DL-BSO), an agent that inhibits the biosynthesis of GSH in liver and other peripheral organs, fails to suppress levels of GSH in the CNS. In the current study, preweanling mice responded to repeated injections of L-BSO with marked declines (79.6-86.5%) of GSH content in brain and spinal cord. In adult mice, the same treatment schedule produced only modest declines (17.8-29.2%) of GSH content in brain and a 55.9% decline in spinal cord. Pretreatment of preweanling mice with L-BSO represents a tool for studying the role of GSH in the CNS.     

The structure of toxic protein, the mistletoe lectin, at different pH: the study using intrinsic fluorescence method

The effects of pH on the conformation of mistletoe lectin I and its isolated A- and B-subunits has been investigated by using the methods of intrinsic fluorescence. By the denaturating action of guanidine hydrochloride and the influence of the quenchers (I-, Cs+, acrylamide) the structural stability of the native protein and its isolated subunits was estimated. Treatment of the protein with the denaturant and quenchers revealed its different structure at pH 7.0 and 4.0. At pH 4.0 tryptophan residues become more accessible to quenchers, positive charge of the surrounding area increases and the protein becomes more stable to the action of denaturant. The structure of the isolated A- and B-chains of mistletoe lectin I differs considerably from that of the whole protein: a) its stability to the action of guanidine hydrochloride is lower; b) it depends on the ionic strength of the solvent; c) it is characterized by increased accessibility of tryptophan residues to quenchers (for B-chain). Differences between the conformations of the isolated chains at pH 7.0 and 4.0 are marked more strongly; moreover, at pH 4.5 the B-chain undergoes structural transition. The possible relationship between structural peculiarities of mistletoe lectin I and the mechanism of its transmembrane transfer is discussed.     

Contribution of midbody channels to embryogenesis in the mouse

Summary We have examined the persistence of midbody channels during the second, third, and fourth cleavage cycles of the mouse using immunofluorescence to map the distribution of midbody microtubule bundles in intact embryos. Electron microscopy showed these bundles to be a characteristic feature of midbodies throughout the interphase period. In recently-divided embryos at each cleavage stage the number of midbodies was half the number of blastomeres, and declined towards zero as the next cleavage approached. This indicated to us that the only midbodies present in each stage were those which had arisen in the immediately-preceding division. Of those blastomeres which were in mitosis at the time of fixation, less than 4% were connected via a midbody to another blastomere, demonstrating that persistence of midbodies beyond a single cleavage cycle is a rare event. We conclude that midbody channels in our embryos are likely to connect only pairs of sister blastomeres because midbodies do not persist through multiple cleavage cycles. Midbody channels cannot, therefore, be regarded as providing extensive cell coupling in advance of the onset of gap junctional communication.