First Report of Tomato yellow leaf curl virus in South Carolina

Tomato yellow leaf curl virus (TYLCV), a begomovirus in the family Geminiviridae, causes yield losses in tomato (Lycopersicon esculentum Mill.) around the world. During 2005, tomato plants exhibiting TYLCV symptoms were found in several locations in the Charleston, SC area. These locations included a whitefly research greenhouse at the United States Vegetable Laboratory, two commercial tomato fields, and various garden centers. Symptoms included stunting, mottling, and yellowing of leaves. Utilizing the polymerase chain reaction (PCR) and begomovirus degenerate primer set prV324 and prC889 (1), the expected 579-bp amplification product was generated from DNA isolated from symptomatic tomato leaves. Another primer set (KL04-06_TYLCV CP F: 5'GCCGCCG AATTCAAGCTTACTATGTCGAAG; KL04-07_TYLCV CP R: 5'GCCG CCCTTAAGTTCGAAACTCATGATATA), homologous to the Florida isolate of TYLCV (GenBank Accession No. AY530931) was designed to amplify a sequence that contains the entire coat protein gene. These primers amplified the expected 842-bp PCR product from DNA isolated from symptomatic tomato tissues as well as viruliferous whitefly (Bemisia tabaci) adults. Expected PCR products were obtained from eight different samples, including three tomato samples from the greenhouse, two tomato plants from commercial fields, two plants from retail stores, and a sample of 50 whiteflies fed on symptomatic plants. For each primer combination, three PCR products amplified from DNA from symptomatic tomato plants after insect transmission were sequenced and analyzed. All sequences were identical and generated 806 nucleotides after primer sequence trimming (GenBank Accession No. DQ139329). This sequence had 99% nucleotide identity with TYLCV isolates from Florida, the Dominican Republic, Cuba, Guadeloupe, and Puerto Rico. In greenhouse tests with a total of 129 plants in two separate experiments, 100% of the tomato plants became symptomatic as early as 10 days after exposure to whiteflies previously fed on symptomatic plants. A low incidence (<1%) of symptomatic plants was observed in the two commercial tomato fields. In addition, two symptomatic tomato plants obtained from two different retail garden centers tested positive for TYLCV using PCR and both primer sets. Infected plants in both retail garden centers were produced by an out-of-state nursery; this form of "across-state" distribution may be one means of entry of TYLCV into South Carolina. To our knowledge, this is the first report of TYLCV in South Carolina. Reference: (1) S. D. Wyatt and J. K. Brown. Phytopathology 86:1288, 1996.

Metamorphic development of the bronchial columella of the larval bullfrog (Rana catesbeiana)

Histological and immunohistochemical analyses of head and respiratory structures in bullfrog (Rana catesbeiana) tadpoles were undertaken to address the hypothesis that the bronchial columella (BC) is the primary sound conduction pathway in these larval anurans. In postembryonic tadpoles, the BC is composed of fibroblasts surrounded by a Type I collagen matrix, with Type II collagen located in basement membranes at the distal ends. It provides a highly flexible tendon-like attachment between the round window and the membranous sac of the primary bronchus of the ipsilateral lung. As the animals approach metamorphic climax stages, the fibroblasts decrease in number and the BC becomes almost exclusively collagenous. During metamorphic climax, the BC degenerates and is completely resorbed by the time the animal becomes a postmetamorphic froglet. At all larval stages examined, the BC is structurally and immunohistochemically different from both the opercularis muscle of tadpoles and the tympanic columella (stapes homolog) of postmetamorphic animals. These observations suggest that the BC may not be rigid enough to provide an effective coupling between the lungs and the round window. An alternative hypothesis for the function of the BC, based on its structure, is presented.

Development and differentiation of the anuran auditory brainstem during metamorphosis: an acetylcholinesterase histochemical study

The time course of cell differentiation and the presence of histochemically defined areas in brainstem auditory nuclei were examined in developing bullfrogs, Rana catesbeiana, using cresyl violet staining and acetylcholinesterase (AChE) histochemistry. In the medulla, the dorsolateral nucleus (DLN) can be seen as a distinct structure in its adult location only at Gosner stage 40 and beyond. The majority of cells in the DLN are not fully differentiated until late metamorphic climax (stages 45-46) and early postmetamorphosis. The more ventral vestibular nucleus differentiates earlier (stage 37) than the DLN. Adult-like organization of auditory nuclei in the torus semicircularis (TS) of the midbrain cannot be reliably discerned until metamorphic climax stages. Cellular masses in the brainstem reveal AChE from the earliest stage examined (stage 27) but the intensity of staining differs among cell groups. Staining intensity in the DLN is at a peak in recently metamorphosed froglets. The time course of cell differentiation in the DLN precedes slightly or is coincident with the increased, transient presence of AChE. Staining of the superior olive stabilizes at a moderate level in early postmetamorphic stages. Ventral regions of the principal nucleus in the TS stain more intensely than dorsal regions beginning at stage 40. This dorsal-ventral gradient in staining persists in adult stages. There is a transient decline in staining of the laminar nucleus in metamorphic climax stages. Staining intensity in the magnocellular nucleus peaks during stages 40-46 and in early postmetamorphic froglets and then declines in adults, paralleling the pattern seen in the DLN. These data suggest that metamorphic climax and early froglet periods are an important developmental window for major differentiation and maturational events in the auditory brainstem.

Effects of planting pattern of collards on resistance to whiteflies (Homoptera: Aleyrodidae) and on parasitoid abundance

Fourteen collard entries, Brassica oleraceae L., Acephala group, were evaluated for resistance to natural populations of Bemisia argentifolii Bellows & Perring in replicated field plots in Charleston, SC. Glossy-leaf phenotypes ('SC Glaze', 'SC Landrace,' 'Green Glaze') were the most resistant collard entries and had fewer whiteflies than the nonglossy, open-pollinated cultivars. Also, two F1 hybrid cultivars with normal, nonglossy leaves ('Blue Max' and 'Top Bunch') were resistant. In laboratory experiments, there were no differences in the intrinsic rate of growth (rs) of B. argentifolii populations on either glossy or nonglossy collard phenotypes. Over a 2-yr period, there were no differences in the abundance of whiteflies on the glossy phenotype of Green Glaze when it was planted in solid 20-plant plots or when it was alternated (every other plant) with the nonglossy phenotype of Green Glaze. In a similarly designed experiment, there was no difference in the resistance of Blue Max in either solid or mixed planting scheme compared with the susceptible 'Morris Heading'. Higher numbers of whiteflies and parasitoids (primarily Eretmocerus spp.) were collected on yellow sticky cards in the solid plantings of the nonglossy phenotype of Green Glaze than were collected in the solid plantings of the glossy Green Glaze phenotype. Counts on sticky cards in the mixed plots were intermediate. These data show that planting pattern of collard entries is relatively unimportant in the deployment of these sources of host plant resistance. The data also suggest that nonpreference is the primary mode of resistance to whiteflies for certain collard entries.

Perception of mistuned harmonics in complex sounds by the bullfrog (Rana catesbeiana)

The ability of 73 male bullfrogs (Rana catesbeiana) to detect single mistuned harmonics in an otherwise periodic signal was studied. Bullfrogs in their natural environment were presented with playbacks of synthetic signals, resembling their species advertisement calls, that differed in the frequency of 1 harmonic component (out of 22). There were significant differences in the number and latency of the males' evoked vocal responses to these stimuli, suggesting that males were sensitive to the differences between the sounds. Differences in envelope shape (rate and depth of amplitude modulation) produced by the harmonic mistunings may underlie the differences in response. Frogs, like birds and humans, can discriminate sounds on the basis of harmonic structure, indicating that this is a general perceptual trait shared among vertebrates.

Representation of waveform periodicity in the auditory midbrain of the bullfrog, Rana catesbeiana

The period of complex signals is encoded in the bullfrog's eighth nerve by a synchrony code based on phase-locked responding. We examined how these arrays of phase-locked activity are represented in different subnuclei of the auditory midbrain, the torus semicircularis (TS). Recording sites in different areas of the TS differ in their ability to synchronize to the envelope of complex stimuli, and these differences in synchronous activity are related to response latency. Cells in the caudal principal nucleus (cell sparse zone) have longer latencies, and show little or no phase-locked activity, even in response to low modulation rates, while some cells in lateral areas of the TS (magnocellular nucleus, lateral part of principal nucleus) synchronize to rates as high as 90-100 Hz. At midlevels of the TS, there is a lateral-to-medial gradient of synchronization ability: cells located more laterally show better phaselocking than those located more medially. Pooled all-order interval histograms from short latency cells located in the lateral TS represent the waveform periodicity of a biologically relevant complex harmonic signal at different stimulus levels, and in a manner consistent with behavioral data from vocalizing male frogs. Long latency cells in the caudal parts of the TS (cell sparse zone, caudal magnocellular nucleus) code stimulus period by changes in spike rate, rather than by changes in synchronized activity. These data suggest that neural codes based on rate processing and time domain processing are represented in anatomically different areas of the TS. They further show that a populationbased analysis can increase the precision with which temporal features are represented in the central auditory system.

Nymphal survival and movement of crawlers of Bemisia argentifolii (Homoptera: Aleyrodidae) on leaf surfaces of selected vegetables

Bemisia argentifolii Bellows & Perring generally feeds and develops on the under leaf surface of most host plants, but in excess of 50% of the immature population may be found on the upper surface of some host species. This study determined the influence of leaf surface on survival of immature B. argentifolii and the likelihood of movement by the crawler (1st instar) from the upper (adaxial) leaf surface on selected vegetable hosts. Laboratory, tests were conducted on 5 vegetables: cantaloupe, Cucumis melo L.; collard, Brassica oleracea ssp. acephala de Condolle: cowpea, Vigna unguiculata (L.) Walpers ssp. unguiculata; pepper, Capsicum annuum L. ssp. annuum; and tomato, Lycopersicon esculentum Miller. Survival to the 1st instar was high (85-95%) on the upper leaf surface on all hosts. Survival to the adult stage was similar between whitefly nymphs on the upper and lower leaf surfaces within each host crop, except more survived on the lower surface of cowpea compared with the upper surface. Movement of the crawlers from the upper to the lower surface was high on pepper (approximately 80%), cantaloupe (approximately 55%), and cowpea (approximately 55%). Conversely, less movement to the lower surface was observed on collard (approximately 18%) and tomato (approximately 30%). The impetus to move from the upper surface appears primarily a response to feeding and tactile cues instead of responses to geotropic or phototropic stimuli.

Coding of amplitude modulation in the auditory midbrain of the bullfrog (Rana catesbeiana) across metamorphosis

The functional development of the auditory system across metamorphosis was examined by recording neural activity from the torus semicircularis of larval and postmetamorphic bullfrog froglets in response to amplitude-modulated sound. Multiunit activity in the torus semicircularis during early larval stages showed significant phase-locking to the envelopes of amplitude-modulated noise bursts, up to modulation rates as high as 250 Hz. Beginning at metamorphic climax and continuing into the froglet period, phase locking was restricted to the more limited frequency range characteristic of adult frogs. The onset of operation of the tympanic pathway does not reinstate the highly synchronous neural activity characteristic of the operation of the fenestral pathway. Modulation transfer functions based on spike count did not show tuning for modulation rate in early stage tadpoles, but a greater variety of shapes of these functions emerged as development proceeded. Most of the different kinds of modulation transfer functions seen in adult frogs were also observed in froglets, but band-pass functions were not as sharply peaked. These data suggest that different neural codes for processing of the periodicity of complex signals operate in early stage tadpoles than in postmetamorphic froglets.

Transient "deafness" accompanies auditory development during metamorphosis from tadpole to frog

During metamorphosis, ranid frogs shift from a purely aquatic to a partly terrestrial lifestyle. The central auditory system undergoes functional and neuroanatomical reorganization in parallel with the development of new sound conduction pathways adapted for the detection of airborne sounds. Neural responses to sounds can be recorded from the auditory midbrain of tadpoles shortly after hatching, with higher rates of synchronous neural activity and lower sharpness of tuning than observed in postmetamorphic animals. Shortly before the onset of metamorphic climax, there is a brief "deaf" period during which no auditory activity can be evoked from the midbrain, and a loss of connectivity is observed between medullary and midbrain auditory nuclei. During the final stages of metamorphic development, auditory function and neural connectivity are restored. The acoustic communication system of the adult frog emerges from these periods of anatomical and physiological plasticity during metamorphosis.

Ectoparasitic acugutturid nematodes of adult lepidoptera

Noctuidonema guyaneme is an interesting ectoparasite of adult Lepidoptera that feeds on hosts from at least five families with its long stylet. Noctuidonema guyanense spends its entire life on the adult moth and is sustained as it is passed from moth to moth during host mating. Overlapping host generations are essential for parasite survival. This nematode occurs throughout tropical and subtropical America and is transported by at least one of its hosts, Spodoptera frugiperda, during migration to northern sites in the United States each spring. Noctuidonema guyanense debilitates its hosts. Research conducted to help determine the biological control importance of this nematode is reviewed. Two additional species, N. daptria and N. dibolia, are now known for Noctuidonema.

MYC family DNA amplification in 126 tumor cell lines from patients with small cell lung cancer

We identified 126 tumor cell lines established from patients with small cell cancer at the NCI-Navy Medical Oncology Branch from 1977 through 1992. Extensive clinical information was available on 96 patients from whom these cell lines were established. These patients comprised approximately one fourth of the 407 patients treated on prospective therapeutic clinical trials during the same time period. The proportion of tumor cell lines established from previously untreated patients with both limited and extensive stage small cell lung cancer increased during the 16 years of the study (P = 0.008). MYC family DNA amplification was present in 16 of 44 (36%) tumor cell lines established from previously treated patients compared to 7 of 52 (11%) of tumor cell lines established from untreated patients (P = 0.009). MYC DNA amplification in tumor cell lines established from patients previously treated with chemotherapy continued to be associated with shortened survival (P = 0.001). The initiation of a policy to obtain tumor tissue for the purpose of selecting chemotherapeutic agents given to individual patients was associated with an increase in the proportion of patients from whom tumor cell lines could be established for both extensive and limited stage patients (P = 0.0001 and 0.05, respectively).

Postmetamorphic changes in auditory sensitivity of the bullfrog midbrain

During metamorphosis, the lateral line system of ranid frogs (Rana catesbeiana) degenerates and an auditory system sensitive to airborne sounds develops. We examined the onset of function and developmental changes in the central auditory system by recording multi-unit activity from the principal nucleus of the torus semicircularis (TSp) of bullfrogs at different postmetamorphic stages in response to tympanically-presented auditory stimuli. No responses were recorded to stimuli of up to 95 dB SPL from late-metamorphic tadpoles, but auditory responses were recorded within 24 hours of completion of metamorphosis. Audiograms from froglets (SVL < 5.5 cm) were relatively flat in shape with high thresholds, and showed a decrease in most sensitive frequency (MSF) from about 2500 Hz to about 1500 Hz throughout the first 7-10 days after completion of metamorphosis. Audiograms from frogs larger than 5.5 cm showed continuous downward shifts in MSF and thresholds, and increases in sharpness around MSF until reaching adult-like values. Spontaneous activity in the TSp increased throughout postmetamorphic development. The torus increased in volume by approximately 50% throughout development and displayed changes in cell density and nuclear organization. These observations suggest that the onset of sensitivity to tympanically presented airborne sounds is limited by peripheral, rather than central, auditory maturation.

Specific inhibition of poly(ADP-ribose) glycohydrolase by adenosine diphosphate (hydroxymethyl)pyrrolidinediol

Adenosine diphosphate (hydroxymethyl)pyrrolidinediol (ADP-HPD), an NH analog of ADP-ribose, was chemically synthesized and shown to be a potent and specific inhibitor of poly-(ADP-ribose) glycohydrolase. The synthetic starting material was the protected pyrrolidine, (2R,3R,4S)-1-(benzyloxycarbonyl)-2-(hydroxymethyl)pyrrolidine-3,4-diol 3,4-O-isopropylidene acetal. This starting pyrrolidine was phosphorylated, coupled to adenosine 5'-monophosphate, and deprotected, yielding the title inhibitor ADP-HPD. ADP-HDP was shown to inhibit the activity of poly(ADP-ribose) glycohydrolase by 50% (IC50) at 0.12 microM, a value 1000-times lower than the IC50 of the product, ADP-ribose. The NAD glycohydrolase from Bungarus fasciatus venom was less sensitive to inhibition by ADP-HPD, exhibiting an IC50 of 260 microM. ADP-HPD did not inhibit either poly(ADP-ribose) polymerase or NAD:arginine mono(ADP-ribosyl)-transferase A at inhibitor concentrations up to 1 mM. At low ADP-HPD concentration, inhibition was therefore shown to be highly specific for poly(ADP-ribose) glycohydrolase, the hydrolytic enzyme in the metabolism of ADP-ribose polymers.

Perception of complex sounds by the green treefrog, Hyla cinerea: envelope and fine-structure cues

1. The envelope periodicity of communication signals is an important feature distinguishing advertisement and aggressive calls for the green treefrog (Hyla cinerea). Envelope periodicity, a cue for periodicity pitch perception in humans, is affected by the fine-structure of the signal, a cue for timbre perception in humans. The present study examined perception of two acoustic features affecting waveform fine-structure--harmonic structure and phase structure--in male green treefrogs. 2. We analyzed evoked vocal responses of male green treefrogs living in laboratory arenas to playbacks of digitally-generated signals resembling either conspecific advertisement or aggressive calls in their first harmonic periodicity. Systematic changes in the harmonic structure of these signals were achieved by varying the harmonic relations between frequency components in the signals, and changes in phase structure were achieved by varying the starting phases of harmonically-related components. 3. Calling was significantly influenced by the first harmonic periodicity of the signals. Males vocalized more to signals with the periodicity of the advertisement than the aggressive call. There were no differences in response to harmonic and inharmonic signals with similar spectral content. Phase structure did not significantly influence vocal responses. 4. These results suggest that the fine-structure ("timbre") of complex acoustic signals is not a significant feature guiding behavior tested using a communication response in this species.

Periodicity extraction in the anuran auditory nerve. II: Phase and temporal fine structure

Discharge patterns of single eighth nerve fibers in the bullfrog, Rana catesbeiana, were analyzed in response to signals consisting of multiple harmonics of a common, low-amplitude fundamental frequency. The signals were chosen to reflect the frequency and amplitude spectrum of the bullfrog's species-specific advertisement call. The phase spectrum of the signals was manipulated to produce envelopes that varied in their shapes from impulselike (sharp) to noiselike (flattened). Peripheral responses to these signals were analyzed by computing the autocorrelation functions of the spike trains and their power spectra, as well as by constructing period histograms over the time intervals of the low-frequency harmonics. In response to a phase aligned signal with an impulsive envelope, most fibers, regardless of their characteristic frequencies or place of origin within the inner ear, synchronize to the fundamental frequency of the signal. The temporal patterns of fiber discharge to these stimuli are not typically captured by that stimulus harmonic closet to the fiber characteristic frequency, as would be expected from a spectral coding mechanism for periodicity extraction, but instead directly reflect the periodicity of the stimulus envelope. Changing the phase relations between the individual harmonics constituting the signal produces changes in temporal discharge patterns of some fibers by shifting predominant synchronization away from the fundamental frequency to the low-frequency spectral peak in the complex stimuli. The proportion of fibers whose firing is captured by the fundamental frequency decreases as the waveform envelope becomes less impulselike. Fiber characteristic frequency is not highly correlated with the harmonic number to which synchronization is strongest. The higher-harmonic spectral fine structure of the signals is not reflected in fiber temporal response, regardless of the shape of the stimulus envelope, even for those harmonics within the range of phase locking to simple sinusoids. Increasing stimulus intensity also shifts the synchronized responses of some fibers away from the fundamental frequency to one of the low-frequency harmonics in the stimuli. These data suggest that the synchronized firing of bullfrog eighth nerve fibers operates to extract the waveform periodicity of complex, multiple-harmonic stimuli, and this periodicity extraction is influenced by the phase spectrum and temporal fine structure of the stimuli. The similarity in response patterns of amphibian papilla and basilar papilla fibers argues that the frog auditory system employs primarily a temporal mechanism for extraction of first harmonic periodicity.

Synthesis of [35S]thiophosphoryl adenylic acid, utilizing a general procedure for [35S]thiophosphoryl chloride production

Elemental [35S]sulfur was shown to equilibrate with the sulfur of thiophosphoryl chloride when these materials are heated together. This isotopic exchange reaction is the basis of a convenient, microscale synthesis of high specific activity [35S]PSCl3. [35S]Thiophosphoryl chloride is otherwise not commercially available except through custom synthesis. The labeled thiophosphoryl chloride was used in a novel procedure for the preparation of [35S]adenosine 5'-phosphorothioate. This isotopic exchange method should find wide application in the synthesis of many radiolabeled thiophosphoryl esters which utilize PSCl3 as the source of the thiophosphoryl group.

Periodicity extraction in the anuran auditory nerve. I. "Pitch-shift" effects

1. Activity of individual eight nerve fibers in the bullfrog, Rana catesbeiana, was measured in response to complex, multiple-frequency stimuli differing in both frequency composition and harmonic structure. Stimuli were chosen to parallel types of stimuli producing "pitch-shift" effects in humans. 2. The fundamental frequency of harmonic stimuli can be extracted from the autocorrelation of fiber firing, whether the fundamental is physically present in the stimulus or is a "missing" fundamental. The spectral fine-structure of harmonic stimuli is not robustly represented in fiber temporal response. These effects are seen in both AP and BP fibers. 3. The pseudoperiod of inharmonic stimuli is represented by synchronization to successive high-amplitude peaks in the stimulus envelope. Temporal responses to stimuli with high center frequencies are similar regardless of whether their frequency components are harmonically or inharmonically related. Responses remain dominated by the envelope periodicity, and no "pitch-shift" is signaled. In response to stimuli with low center frequencies, temporal responses signal a "pitch-shift" between harmonic and inharmonic complexes. Both AP and BP fibers show these effects. 4. These data suggest that bullfrog peripheral fibers extract the periodicity of complex stimuli by time-domain rather than frequency-domain coding.

myc family DNA amplification in 107 tumors and tumor cell lines from patients with small cell lung cancer treated with different combination chemotherapy regimens

We studied 107 specimens (38 tumors and 69 tumor cell lines) from 90 patients with small cell lung cancer to determine the characteristics and clinical situations of patients from whom tumor cell lines could be established and the myc family DNA copy number. The proportion of extensive stage small cell lung cancer patients from whom a tumor cell line could be established prior to the initiation of therapy increased during the 10 years of the study (P less than 0.001). Amplification of one of the myc family genes occurred in 3 of 40 (8%) of the untreated patient specimens compared to 19 of 67 (28%) of the treated patient specimens (P = 0.01). The myc family DNA amplification occurred in 17 of 54 (31%) of the specimens from patients treated with cyclophosphamide-based combinations and 2 of 13 (15%) of the specimens from patients treated with etoposide/cisplatin (P = 0.25). Both tumors and tumor cell lines were obtained from 17 patients with small cell lung cancer and the myc family DNA copy number was similar in 16 of the 17 patients. We conclude that: (a) myc family DNA amplification occurs more commonly in specimens from treated than untreated patients (b) there are no prominent differences in the frequency of amplification following treatment with different chemotherapy regimens; and (c) myc family DNA amplification is similar in tumors and tumor cell lines from the same patients.

Synthesis and properties of photoaffinity labels for the pyridine dinucleotide binding site of NAD glycohydrolase

Two new photoactive analogues of oxidized nicotinamide adenine dinucleotide (NAD+) which are resistant to cleavage by NAD glycohydrolase were synthesized and characterized. The beta-D-ribonucleotide ring of the nicotinamide riboside moiety of NAD+ was replaced with a 2,3-dihydroxycyclopentane ring forming a carbocyclic dinucleotide analogue. Photoreactivity was achieved by the incorporation of an azido group at the 8-position of the adenosyl ring. The previously published synthesis of carbocyclic pyridine dinucleotide analogues [Slama, J. T., & Simmons, A. M. (1988) Biochemistry 27, 183] was modified by resolving the carbocyclic 1-aminoribose analogues and producing optically pure (+)-(1S)- or (-)-(1R)-4 beta-amino-2 alpha,3 alpha-dihydroxy-1 beta-cyclopentanemethanol. Each of these was converted to the corresponding carbocyclic nicotinamide 5'-nucleotide analogue and coupled with 8-azidoadenosine 5'-monophosphate. Two photoactive and isomeric NAD+ analogues were thus prepared. 8-Azidoadenosyl carba-NAD is the analogue in which D-dihydroxycyclopentane is substituted for the D-ribose of the nicotinamide nucleoside moiety. 8-Azido-adenosyl pseudocarba-NAD contains the L-carbocycle in place of the D-ribotide ring. 8-Azidoadenosyl carba-NAD was shown to inhibit the NAD glycohydrolase from Bungarus fasciatus venom competitively with an inhibitor dissociation constant of 187 microM. 8-Azidoadenosyl pseudocarba-NAD was shown to inhibit the same enzyme competitively with a Ki of 73 microM. The superior NADase inhibitor, 8-azidoadenosyl pseudocarba-NAD, was characterized kinetically and shown to fulfill the criteria required of a specific active site directed photoaffinity probe. Irradiation of mixtures of the photoprobe and NAD glycohydrolase with short-wave ultraviolet light resulted in the rapid and irreversible loss of enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Encoding of a spectrally-complex communication sound in the bullfrog's auditory nerve

1. A population study of eighth nerve responses in the bullfrog, Rana catesbeiana, was undertaken to analyze how the eighth nerve codes the complex spectral and temporal structure of the species-specific advertisement call over a biologically-realistic range of intensities. Synthetic advertisement calls were generated by Fourier synthesis and presented to individual eighth nerve fibers of anesthetized bullfrogs. Fiber responses were analyzed by calculating rate responses based on post-stimulus-time (PST) histograms and temporal responses based on Fourier transforms of period histograms. 2. At stimulus intensities of 70 and 80 dB SPL, normalized rate responses provide a fairly good representation of the complex spectral structure of the stimulus, particularly in the low- and mid-frequency range. At higher intensities, rate responses saturate, and very little of the spectral structure of the complex stimulus can be seen in the profile of rate responses of the population. 3. Both AP and BP fibers phase-lock strongly to the fundamental (100 Hz) of the complex stimulus. These effects are relatively resistant to changes in stimulus intensity. Only a small number of fibers synchronize to the low-frequency spectral energy in the stimulus. The underlying spectral complexity of the stimulus is not accurately reflected in the timing of fiber firing, presumably because firing is 'captured' by the fundamental frequency. 4. Plots of average localized synchronized rate (ALSR), which combine both spectral and temporal information, show a similar, low-pass shape at all stimulus intensities. ALSR plots do not generally provide an accurate representation of the structure of the advertisement call. 5. The data suggest that anuran peripheral auditory fibers may be particularly sensitive to the amplitude envelope of sounds.

Inhibition of NAD glycohydrolase and ADP-ribosyl transferases by carbocyclic analogues of oxidized nicotinamide adenine dinucleotide

Analogues of oxidized nicotinamide adenine dinucleotide (NAD+) in which a 2,3-dihydroxycyclopentane ring replaces the beta-D-ribonucleotide ring of the nicotinamide riboside moiety of NAD+ have recently been synthesized [Slama, J. T., & Simmons, A. M. (1988) Biochemistry 27, 183]. Carbocyclic NAD+ analogues have been shown to inhibit NAD glycohydrolases and ADP-ribosyl transferases such as cholera toxin A subunit. In this study, the diastereomeric mixture of dinucleotides was separated, and the inhibitory capacity of each of the purified diastereomers was defined. The NAD+ analogue in which the D-dihydroxycyclopentane is substituted for the D-ribose is designated carba-NAD and was demonstrated to be a poor inhibitor of the Bungarus fasciatus venom NAD glycohydrolase. The diastereomeric dinucleotide pseudo-carbocyclic-NAD (psi-carba-NAD), containing L-dihydroxycyclopentane in place of the D-ribose of NAD+, was shown, however, to be a potent competitive inhibitor of the venom NAD glycohydrolase with an inhibitor dissociation constant (Ki) of 35 microM. This was surprising since psi-carba-NAD contains the carbocyclic analogue of the unnatural L-ribotide and was therefore expected to be a biologically inactive diastereomer. psi-Carba-NAD also competitively inhibited the insoluble brain NAD glycohydrolase from cow (Ki = 6.7 microM) and sheep (Ki = 31 microM) enzyme against which carba-NAD is ineffective. Sensitivity to psi-carba-NAD was found to parallel sensitivity to inhibition by isonicotinic acid hydrazide, another NADase inhibitor. psi-Carba-NAD is neither a substrate for nor an inhibitor of alcohol dehydrogenase, whereas carba-NAD is an efficient dehydrogenase substrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Selectivity for harmonic structure in complex sounds by the green treefrog (Hyla cinerea)

1. A psychophysical technique based on reflex modification was used to study the detection of two-tone complexes in background noise by the green treefrog (Hyla cinerea). Three different two-tone complexes were synthesized and presented to measure detection thresholds--a harmonic complex of 900 + 3000 Hz (periodicity of 300 Hz, mimicking the structure of the natural advertisement call); an inharmonic complex of 830 + 3100 Hz; and a second harmonic complex of 828 + 2760 Hz (periodicity of 276 Hz). 2. Masked thresholds and 'critical ratios' (signal-to-noise ratios at threshold) were lowest for the two harmonic complexes (900 + 3000 Hz, mean 'critical ratio' of 16 dB; 828 + 2760 Hz, mean 'critical ratio' of 14 dB). For the inharmonic complex, for which there is no stable first-harmonic periodicity, the mean 'critical ratio' was 24 dB. These data suggest that the green treefrog is sensitive to the harmonic structure of complex sounds as a specific acoustic feature. 3. Because of the unique structure of the treefrog's inner ear, the heightened behavioral sensitivity to harmonic complexes must be due to processing in the central, rather than peripheral, auditory system.

Carbanicotinamide adenine dinucleotide: synthesis and enzymological properties of a carbocyclic analogue of oxidized nicotinamide adenine dinucleotide

The dinucleotide carbanicotinamide adenine dinucleotide (carba-NAD), in which a 2,3-dihydroxycyclopentane ring replaces the beta-D-ribonucleotide ring of the nicotinamide ribonucleoside moiety of NAD, has been synthesized and characterized enzymologically. The synthesis begins with the known 1-aminoribose analogue (+/-)-4 beta-amino-2 alpha,3 alpha-dihydroxy-1 beta-cyclopentanemethanol. The pyridinium ring is first introduced and the resultant nucleoside analogue specifically 5'-phosphorylated. Coupling the racemic carbanicotinamide 5'-mononucleotide with adenosine 5'-monophosphate produces two diastereomeric carba-NAD analogues which are chromatographically separable. Only one diastereomer is a substrate for alcohol dehydrogenase and on this basis is assigned a configuration analogous to D-ribose. The reduced dinucleotide carba-NADH was characterized by fluorescence spectroscopy and found to adopt a "stacked" conformation similar to that of NADH. The analogue is reduced by both yeast and horse liver alcohol dehydrogenase with Km and Vmax values for the analogue close to those observed for NAD. Carba-NAD is resistant to cleavage by NAD glycohydrolase, and the analogue has been demonstrated to noncovalently inhibit the soluble NAD glycohydrolase from Bungarus fasciatus venom at low concentrations (less than or equal to 100 microM).

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)