The effect of pulse repetition rate on the delay sensitivity of neurons in the auditory cortex of the FM bat,Myotis lucifugus

1. Echo delay is the primary cue used by echolocating bats to determine target range. During target-directed flight, the repetition rate of pulse emission increases systematically as range decreases. Thus, we examined the delay tuning of 120 neurons in the auditory cortex of the bat, Myotis lucifugus, as repetition rate was varied. 2. Delay sensitivity was exhibited in 77% of the neurons over different ranges of pulse repetition rates (PRRs). Delay tuning typically narrowed and eventually disappeared at higher PRRs. 3. Two major types of delay-sensitive neurons were found: i) delay-tuned neurons (59%) had a single fixed best delay, while ii) tracking neurons (22%) changed their best delay with PRR. 4. PRRs from 1-100/s were represented by the population of delay-sensitive neurons, with the majority of neurons delay-sensitive at PRRs of at least 10-20/s. Thus, delay-dependent neurons in Myotis are most active during the search phase of echolocation. 5. Delay-sensitive neurons that also responded to single sounds were common. At PRRs where delay sensitivity was found, the responses to single sounds were reduced and the responses to pulse-echo pairs at particular delays were greater than the single-sound responses. In facilitated neurons (53%), the maximal delay-dependent response was always larger than the best single-sound responses, whereas in enhanced neurons (47%), these responses were comparable. The presence of neurons that respond maximally to single sounds at one PRR and to pulse-echo pairs with particular echo delays at other PRRs suggests that these neurons perform echo-ranging in conjunction with other biosonar functions during target pursuit.     

New chromosome 21 DNA markers isolated by pulsed field gel electrophoresis from an ETS2-containing Down syndrome chromosomal region

To generate new chromosome 21 markers in a region that is critical for the pathogenesis of Down syndrome (D21S55-MX1), we used pulsed field gel electrophoresis (PFGE) to isolate a 600-kb NruI DNA fragment from the WA17 hybrid cell line, which has retained chromosome 21 as the only human material. This fragment, which contains the oncogene ETS2, was used to construct a partial genomic library. Among the 14 unique sequences that were isolated, 3 were polymorphic markers and contained sequences that are conserved in mammals. Five of these markers mapped on the ETS2-containing NruI fragment and allowed us to define an 800-kb high-resolution PFGE map.     

Variants of the anti-Müllerian hormone gene in a compound heterozygote with the persistent Müllerian duct syndrome and his family

Summary The human genome contains a large number of interspersed simple repeat sequences that are variable in length and can therefore serve as highly informative, polymorphic markers. Typing procedures include conventional multilocus and single locus probing, and polymerase chain reaction aided analysis. We have identified simple sequences in a cosmid clone stemming from the human Y chromosome and consisting of (gata)_n repeats. We have compared these with two equivalent simple repeat loci from chromosome 12. After amplifying the tandemly repeated motifs, we detected between four and eight different alleles at each of the three loci. Codominant inheritance of the alleles was established in family studies and the informativity of the simple repeat loci was determined by typing unrelated individuals. The polymorphisms are suitable for application in linkage studies, practical forensic case work, deficiency cases in paternity determination, and for studying ethnological questions. The mutational mechanisms that bring about changes in simple repeats located both on the autosomes and on the sex chromosomes, are discussed.Professor Dr. Otto Prokop (Humboldt-Universität Berlin) on the occasion of his 70th birthday     

Glucocorticoid regulation of phenylethanolamine N-methyltransferase in vivo.

In vivo, supraphysiological doses of glucocorticoids are required to restore adrenal medullary phenylethanolamine N-methyltransferase (PNMT, E.C. 2.1.1.28) activity after hypophysectomy. However, in vitro, phenylethanolamine N-methyltransferase gene expression appears normally glucocorticoid-responsive. To explore this paradox, rats were given dexamethasone or the type II-specific glucocorticoid RU28362 (1-1000 micrograms/day), and adrenal phenylethanolamine N-methyltransferase activity and mRNA levels were determined. At low doses (1-30 micrograms/day), neither steroid altered mRNA whereas at higher doses (100-1000 micrograms/day), mRNA rose 10- to 20-fold, with dexamethasone approximately 3 times as potent as RU28362. In contrast, enzyme activity fell with low doses of either steroid, consistent with suppression of ACTH and endogenous steroidogenesis. At higher doses of RU28362, enzyme activity remained low and unchanged despite increased mRNA expression, whereas higher doses of dexamethasone progressively restored the enzyme to normal. These findings suggest 1) that glucocorticoid regulation of phenylethanolamine N-methyltransferase activity occurs largely independent of gene expression; 2) that glucocorticoid effects on enzyme activity are primarily indirect, probably through cosubstrate regulation and/or enzyme stabilization; and 3) that these effects are not mediated via a classical (type II) glucocorticoid receptor mechanism, given the high doses of dexamethasone and corticosterone required and the inability of RU28362 to mimic the effects of these less selective steroids.     

The effect of rigid fixation on growth of the neurocranium

The effects on skull growth of plating the coronal suture and frontal bone were studied in New Zealand White rabbits. Three-dimensional coordinate landmarks were digitized and analyzed to determine the differences in form between operated and unoperated animals using Euclidian distance matrix analysis. This method compares sets of interlandmark distances in three dimensions and was used to demonstrate changes induced by plating. We interpret these changes in morphology to be the result of differences in growth between the operated and unoperated groups. Periosteal elevation alone (n = 6) resulted in a minimal local growth increase. Coronal suture plating (n = 8) resulted in local growth restriction with contralateral and adjacent size increases. Frontal bone plating (n = 6) without crossing a suture line also resulted in local growth restriction and adjacent bone size increases. The timing of intervention in relation to the completion of bone growth may explain the magnitude of clinically apparent effects. Changes in bones adjacent to those directly manipulated may be an attempt to maintain a normal skull volume.     

Immunocytochemical Localization of Glutamine Synthetase in Organs of Phaseolus vulgaris L

Glutamine synthetase was localized in nodules, roots, stems, and leaves of red kidney bean (Phaseolus vulgaris L.) by immunocytochemistry. Affinity purified antibodies reactive with glutamine synthetase were prepared using purified nodule-enhanced glutamine synthetase. Immunogold labeling was observed in the cell cytoplasm in each plant organ. In nodules, the labeling was more intense in the infected cells than in the uninfected cells. No labeling was observed in nodule bacteroids, peribacteroid spaces, or in peribacteroid membranes, while previous reports of glutamine synthetase immunolabeling of legume nodules showed labeling in the bacteroid fraction. Significant labeling was observed in nodule proplastids which contained starch granules. Substantial labeling was also observed in leaf chloroplasts. No labeling was observed in other organelles including mitochondria, peroxisomes, and endoplasmic reticulum. Preimmune IgGs did not bind to any structure in the tissues examined.     

Antiport mediated rounding and endocytosis are enhanced by sulphate

Rapid cell detachment concomitant with the flat-to-round (FTR) change that is mediated by an upshifted Na+/H+ antiporter via HCO3(-)-dependent H+ pumping, is significantly enhanced by the addition of Na2SO4 (FTR + SO4): (1) a faster and greater reduction in cell surface area and perimeter, and (2) a higher level of macromolecular internalization which is also amiloride sensitive. At a fixed 1 mg/ml extracellular FITC-dextran (FDx) concentration, the intracellular FDx load is similar irrespective of the particle size, in the range from 4400 to 2 million mol.wt which is a 455-fold diversity. This is inconsistent with entry via limited sized portals which would discriminate against the larger molecular weight species, such as the 2 million mol.wt species that measures up to 5 microns in width. Two million mol.wt FDx loads linearly in direct proportion to the extracellular FDx concentration, simulating simple diffusion. Large-channel endocytosis is considered to be a characteristic of specialized cell types such as phagocytes and macrophages. However, the antiporter mediated endocytosis (AME) shown here is demonstrated in two different cell types which are not known for their endocytic prowess, viz. epitheloid human Chang liver cells (ATCC CCL 13) and human lung fibroblasts (ATCC CCL 202). The rounded cells with internalized FDx start reverting back to their flat and protracted form upon flooding with warm growth medium, a round-to-flat (RTF) change. However the cell surface reversion is not associated with efflux of FDx which are sorted out into 'granular patches', the later stage endosomes without membrane outlines in AME. FDx-loaded cells grow as well as trypsinized cells without FDx loaing and they maintain a significant FDx load even after nearly 4 cell divisions. Toad sperms internalized into Chang cells via antiporter activation are also sorted into granular patches. AME provides (a) distinctive access to large particles, simulating small ion influx, and (b) an alternate membrane recycling capability where granular patches are instrumental in sorting. It appears to be not a simple endocytosis-exocytosis pathway.     

The role of the pro-sequence in the processing and secretion of the thermolysin-like neutral protease from Bacillus cereus

The Bacillus cereus cnp gene coding for the thermolysin-like neutral protease (TNP) has been cloned, sequenced, and expressed in Bacillus subtilis. The protease is first produced as a pre-pro-protein (M(r) = 61,000); the pro-peptide is approximately two-thirds of the size of the mature protein. The pro-sequence has been compared with those of six other TNPs, and significant homologies have been found. Additionally, the TNP pro-sequences are shown to be homologous to the pro-sequence of Pseudomonas aeruginosa elastase. A mutant has been constructed from cnp, in which 23 amino acids upstream from the pro-protein processing site have been deleted. This region has no homologous analogue in any of the other TNP pro-sequences. The deletion results in a delay of six to eight hours in detection of active protease in the growth medium, as well as a 75% decrease in maximum protease production. N-terminal analysis of the mutant mature protein demonstrates that the processing site is unaltered by the pro-sequence deletion. The deletion must, therefore, modulate the kinetics of processing and/or secretion of the pro-protein.