Frequency selectivity of hearing in the green treefrog,Hyla cinerea

Frequency selectivity of hearing was measured in the green treefrog, Hyla cinerea. A psychophysical technique based on reflex modification was used to obtain masked threshold estimates for pure tones (300-5,400 Hz) presented against two levels of broadband masking noise. A pure tone (S-1) presented 200 ms prior to a reflex-eliciting stimulus (S-2) inhibited the motor reflex response to S-2. The magnitude of this reflex modification effect varied systematically with the sound pressure level (SPL) of S-1, and threshold was defined as the SPL of S-1 at which the reflex modification effect disappeared. Masked thresholds were used to calculate critical ratios, an index of the auditory system's frequency selectivity. The frequency selectivity of the treefrog's hearing is greatest and critical ratios are lowest (22-24 dB) at about 900 and 3,000 Hz, the two spectral regions dominant in the male treefrog's species-specific advertisement call. These results suggest that the treefrog's auditory system may be specialized to reject noise at biologically-relevant frequencies. As in other vertebrates, critical ratios remain constant when background noise level is varied; however, the shape of the treefrog's critical ratio function across frequencies differs from the typical vertebrate function that increases with increasing frequency at a slope of about 3 dB/octave. Instead, the treefrog's critical ratio function resembles its pure tone audiogram. Although the shape of the treefrog's critical ratio function is atypical, the critical ratio values themselves are comparable to those of many other vertebrates in the same frequency range. Critical ratio values here measured behaviorally do not match critical ratio values previously measured physiologically in single eighth nerve fibers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Foraging site use and interspecific competition between bluegills and golden shiners

Synopsis Laboratory experiments examined the foraging performances of a dietary generalist, bluegill,Lepomis macrochirus, and a dietary specialist, golden shiner,Notemigonus crysoleucas, as they fed from devices simulating four foraging sites (bottom substrate, water column, submerged macrophytes, and water surface). Fishes foraged in monospecific and mixed-species groups of two and four individuals. For monospecific groups, foraging rates of bluegills did not differ among the four sites, but golden shiners had significantly higher rates on bottom and midwater sites than on plant and surface sites. The size of monospecific groups did not affect foraging rates of either species. In mixed-species trials, bluegills removed more food items than golden shiners from plant and surface sites in two- and four-fish groups and from bottom sites in two-fish groups. Bluegills' foraging performances improved with experience, golden shiners' performances did not. Experimental results are discussed with respect to interactions between bluegills and golden shiners in natural assemblages.     

The effect of L-canavanine and L-canaline on the hemolymph amino acid composition of the tobacco hornworm,Manduca sexta (L.) (Sphingidae)

Tobacco hornworm larvae, Manduca sexta (L.) (Sphingidae), were administered L-canaline either by parenteral injection or by dietary consumption. The overt toxicity and the alteration of hemolymph amino acids caused by these nonprotein amino acids were evaluated. The LD₅₀ value for parenterally administered canavanine and canaline is 1.0 and 2.5 mg/g fresh body weight, respectively. A dietary concentration of 5.2 mM for canavanine and over 20 mM for canaline represent the respective LC₅₀ values. A large percentage of the larvae reared on diets supplemented with additional arginine, ornithine, or 2,4-diaminobutyric acid in addition to canavanine or canaline were unable to complete larval-pupal ecdysis. These toxic effects were associated with a decreased glutamic acid hemolymph titer and dramatically elevated ornithine. On the other hand, larvae administered canavanine or canaline alone, either by dietary consumption or parenteral injection, experienced less drastic developmental aberrations. These symptoms were in some cases correlated with increased ornithine and glutamic acid titers. Evidence is presented that even a canavanine- and canaline-sensitive insect such as M. sexta has a marked ability to eliminate these protective allelochemicals.     

Ontogeny of endocrine responses to methadone in rats

The effects of methadone (METH) on serum levels of prolactin (PRL), growth hormone (GH), corticosterone (CS) and TSH were determined in developing rats. METH increased PRL, GH and CS and decreased TSH at all ages tested, but the time course and magnitude of these effects changed during ontogeny. METH effects on day 10 were lower in magnitude than those observed in adults. In 20 day old pups, METH effects on GH and CS were comparable to those of adults, but TSH effects were still blunted. METH effects on hormone secretion in both 10 and 20 day old pups lasted longer than those observed in adults. Naloxone blocked all hormonal responses in adults, but did not completely block METH effects on CS secretion in 10 day old pups.     

Hypermagnesaemia in Presence of Magnesium Depletion in Acute-on-chronic Renal Failure

A patient with renal failure developed hypermagnesaemia, with confusion, drowsiness, and dysarthria. Nevertheless, the dietary magnesium content was low, and investigation showed actual intracellular depletion of magnesium. The cause of this state is not known, though it is presumably connected with a failure to maintain the normal concentration gradient of magnesium across the cell wall. The clinical state and the serum magnesium level returned to normal after treatment with calcium gluconate.     

Causes of Hypertension in the Young

Of 127 hypertensive patients aged 12 to 40 investigated by intravenous pyelography, abdominal aortography, and renal biopsy an underlying cause was found in 57%. The proportion with secondary hypertension was higher in young patients and in those with severe hypertension. Primary arteritis of the aorta was an important cause of renovascular hypertension in an Asian population.     

Essential function in chloroplast recognition of the ferredoxin transit peptide processing region

Molecular Genetics and Genomics - Plant ferredoxin is a nuclear-encoded chloroplast protein that is synthesized in the cytoplasm as a transit peptide-containing precursor molecule. To identify...     

Characterization of a Nerve Growth Factor-Stimulated Protein Kinase in PC12 Cells Which Phosphorylates Microtubule-Associated Protein 2 and pp250

Treatment of PC12 cells with nerve growth factor (NGF) resulted in the rapid, but transient, activation of a protein kinase which specifically phosphorylated an endogenous 250-kDa cytoskeletal protein (pp250). We report that the microtubule-associated protein, MAP2, is an alternative substrate for the NGF-activated kinase. NGF treatment maximally activated the kinase within 5 min; however, the activity declined with longer exposure to NGF. The enzyme was localized predominantly in microsomal and soluble fractions and phosphorylated MAP2 on serine and threonine residues. The soluble enzyme was fractionated by DEAE chromatography and gel filtration and had an apparent Mr of 45,000. The enzyme was purified to near homogeneity by chromatofocussing and had a pI of 4.9. Kinetic analysis revealed that NGF treatment caused a sevenfold increase in Vmax for MAP2. The Km with respect to the MAP2 substrate was approximately 50 nM and was not altered by NGF treatment. A novel feature of the NGF-stimulated enzyme was its sharp dependence on Mn2+ concentration. The active enzyme is likely to be phosphorylated, because inclusion of phosphatase inhibitors was required for recovery of optimal activity and the activity was lost on treatment of the enzyme with alkaline phosphatase. Histones, tubulin, casein, bovine serum albumin, and the ribosomal subunit protein S-6 were not phosphorylated by this enzyme. The NGF-stimulated kinase was distinct from A kinase, C kinase, or other NGF-stimulated kinases. The rapid and transient activation of the protein kinase upon NGF treatment suggests that the enzyme may play a role in signal transduction in PC12 cells.     

A serum-free system for culturing human placental trophoblasts

Summary We have compared hormone production by early gestation and term human placental trophoblasts cultured in Ham's F10 medium containing 10% fetal bovine serum with that by cells cultured in serum-free HB102 medium. Mean daily production of progesterone on Days 3 to 7 was approximately 25% less by both early gestation and term cells cultured in HB102 as compared to Ham's F10, but production was maintained at a stable level for at least 7 d longer than the cells in Ham's. Estradiol production from 10⁻⁶ M dehydroepiandrosterone by both early gestation and term cells was comparable in both media. Human placental lactogen production on Days 3 to 7 was 40% less by cells cultured in HB102. Human chorionic gonadotropin (hCG) output by early gestation cells was also 50% less in HB102 but term cells in HB102 produced twice as much hCG as those in Ham's F10. 3B-Hydroxysteroid dehydrogenase (3BHSD) activity in early gestation and term cells and 11B-hydroxysteroid dehydrogenase (11BHSD) activity of early gestation cultures was comparable in the two media. 11BHSD activity was decreased in the term cultures, and this decrease was more marked in Ham's than in HB102. Sulfatase and aromatase activities in the early gestation cultures were comparable in both media; sulfatase activity was comparable and aromatase activity only 20% less in the term cells cultured in HB102. These results indicate that serum-free HB102 supports differential function of human trophoblast cells and is useful for studies of placental activity for as long as 14 d in culture.     

Cytogenetic characterization of 20 lymphoblastoid lines derived from human individuals differing in bleomycin sensitivity

Summary Forty lymphoblastoid (lymphoid) lines were established from 42 volunteer blood donors, including healthy individuals and patients with head and neck carcinomas. Each peripheral blood sample was split into two portions, one for the establishment of a lymphoid line and the other for short-term culture, which was used to estimate bleomycin sensitivity by cytogenetic procedures. Twenty lymphoid lines were selected at random to compare bleomycin sensitivity with data obtained from short-term lymphocyte cultures. In each set, bleomycin sensitivity of lymphoid cells was similar to that of the lymphocytes. The lymphoid lines, which can be propagated for an unlimited supply of relatively homogeneous cellular material, will be useful for a variety of future investigations. This investigation was supported by grants from the John S. Dunn Foundation, Houston, TX, the Esther Knispel Fund administered by The University of Texas M. D. Anderson Cancer Center, Houston, TX, and Department of Health and Human Services PHS grant DE 07007.