Biomedical subjects

A B Smit

Publications and source records attributed to A B Smit.

63 records · Page 4Linked to original sources

PubMed1989

Some effects of variations in response time latency on speech rate, interruptions, and fluency in children's speech.

The present study was designed to examine adult-child interactions during conversation with respect to the effects of adult paralinguistic speech variations on the speech production of children. Four 4-year-old children served as subjects. A single-subject A-B-A design with counterbalancing and replication was implemented. Each subject participated in three 15-min conversations with an experimenter. The independent variable was the interspeaker pause time--the response time latency (RTL). During the 15-min conversations, the experimenter used either a 1-s or a 3-s RTL when responding to the child. RTL was measured for each subject in each condition. Data analysis revealed that each child's RTL was significantly longer when the experimenter's RTL was 3 s than when it was 1 s, and all differences between all conditions reached significance for these subjects. Other dependent variables included speech rate, the frequency of disfluencies, and the frequency of interruptions produced by the subjects within each condition. All 4 subjects varied the frequency of disfluencies and interruptions. However, each child varied rate and disfluencies in a highly individualistic manner.

Child, Preschool↗

PubMed1989

Detection of mRNA molecules coding for neuropeptide hormones of the pond snail Lymnaea stagnalis by radioactive and non-radioactive in situ hybridization: a model study for mRNA detection.

To develop and optimize non-radioactive in situ hybridization techniques for mRNA detection, we used the neuropeptidergic system of the pond snail Lymnaea stagnalis as a biological model system. First, we investigated the in situ hybridization procedure using radioactive-labeled cDNA and synthetic oligonucleotide probes specific for egg-laying hormone (ELH) mRNA and molluscan insulin-like peptide (MIP) mRNA. The results show an intense grain deposit above the caudodorsal cells and light-green cells expressing, respectively, ELH mRNA and MIP mRNA. Good results with relation to signal strength and tissue morphology were obtained with freeze-dry paraformaldehyde vapor fixation. The necessity to perform tissue pre-treatment appeared to be dependent on the cell type of interest. The optimized in situ hybridization protocol proved to be applicable using probes that are either sulfonated/transaminated or labeled with acetylaminofluorene (AAF). In situ hybridization of such haptenized probes led to intense and specific staining of the cytoplasm of the caudodorsal cells. Egg-laying hormone mRNA appeared not to be homogeneously distributed in the cytoplasm but showed a "patch-like" pattern. Nuclear and axoplasmic staining for mRNA was also observed.

2-Acetylaminofluorene↗

PubMed1989

Central and peripheral expression of genes coding for egg-laying inducing and insulin-related peptides in a snail.

Egg laying in the hermaphrodite freshwater snail Lymnaea stagnalis is a highly complex activity, including a series of internal activities (ovulation, egg and egg mass formation) which are closely correlated to a pattern of behaviours (alteration of locomotion and feeding, specific postures, oviposition). In this snail egg laying is induced by the neuroendocrine caudodorsal cells (CDCs), consisting of two homogeneous clusters at a total of 100 neurons. At egg laying these neurons release their products during a 60 min period of firing. The genes coding for these products have been cloned and characterized. There are two genes, CDCH-I and -II. Each gene codes for 12 peptides; one of these is the ovulation hormone (CDCH). The genes display over 90% homology. The most striking difference is a 17 bp deletion near the carboxy-terminal region. With immunocytochemistry and in situ hybridization both CDCH genes appeared to be expressed in the CDC and in paired groups of ectopic CDC-like neurons in the pleural ganglia, while a group of small neurons in the cerebral ganglia expresses the CDCH-I gene only. In addition, a widespread expression of the CDCH genes has been demonstrated in peripheral tissues. In the female part of the reproductive tract neurons were found to express the CDCH-I gene. In the male part of the tract exocrine secretory cells express the CDCH-I or -II gene. The gene products are secreted into the male tract and transferred to the female partner during copulation. Finally, sensory neurons in the head skin and mantle edge were found to express the CDCH-I gene. The presence of insulin-related peptides has been demonstrated in the brain as well as the digestive system of Lymnaea. The brain insulin-related peptides are produced in 4 groups of 50 giant neurons each (Light green cells, LGC). These neurons are involved in various physiological activities, related to body growth and glycogen metabolism. The major gene products expressed in the LGC have been cloned and characterized. It appeared that the predicted proteins represent three types of insulin-related molecules (MIP, molluscan insulin-related peptide). In these MIPs, those elements important in the determination of the tertiary structure, have been conserved. The MIP of the digestive system has been characterized up to now only at the peptide level. The snail gut MIP is more hydrophobic compared to bovine insulin. Cells containing MIP have been identified immunocytochemically in the gut epithelium.

Animals↗

PubMed1988

Growth-controlling molluscan neurons produce the precursor of an insulin-related peptide.

Insulin and related peptides are key hormonal integrators of growth and metabolism in vertebrates. There is little biochemical evidence for insulin-related peptides in invertebrates, apart from insects for which definitive structural information on these peptides (prothoracicotropic hormone, PTTH) has recently been obtained. We report here the first complete complementary DNA-derived primary structure of a preproinsulin-related protein from identified neurons in an invertebrate, the mollusc Lymnaea stagnalis. We have demonstrated by in situ hybridization that transcription of the gene for this molluscan insulin-related peptide (MIP) occurs in the cerebral light-green cells, giant neuroendocrine cells involved in the control of growth, as well as in a pair of neuroendocrine cells called the canopy cells. The insulin-related peptide precursor has the same overall structure as its vertebrate counterparts. The discovery of insulin-related peptides in invertebrates substantiates the evidence for a widespread and early evolutionary origin of the insulin superfamily.

Amino Acid Sequence↗

PubMed1988

Isolation, characterization, and evolutionary aspects of a cDNA clone encoding multiple neuropeptides involved in the stereotyped egg-laying behavior of the freshwater snail Lymnaea stagnalis.

The cerebral neurosecretory caudodorsal cells (CDCs) of the freshwater pulmonate snail Lymnaea stagnalis control egg laying, an event that involves a pattern of stereotyped behaviors. The CDCs synthesize and release multiple peptides, among which is the ovulation hormone (CDCH). It is thought that each peptide controls a specific aspect of the processes involved in egg laying. We isolated and characterized a CDC-specific cDNA clone that encodes the ovulation hormone (CDCH). RNA blot analysis and in situ hybridization experiments demonstrated that the CDCs are the major cell groups in the cerebral ganglia that transcribe the CDCH gene. In addition to CDCH, the 259-amino acid-long CDCH preprohormone contains 11 other predicted peptides. The overall homology of the CDCH preprohormone with the egg-laying hormone (ELH) preprohormones of the marine opisthobranch snails Aplysia californica and A. parvula is very low (29 and 26%, respectively). However, a more detailed comparison revealed a highly differential pattern of conservation of peptide regions. Significant homology was found between the regions containing (1) CDCH and ELH, (2) repeated pentapeptides, (3) alpha-caudodorsal cell peptide and alpha-bag cell peptide, and (4) 2 regions representing as yet unidentified peptides. Insignificant homology was found when comparing regions containing the other predicted peptides. The conserved peptides probably control similar aspects of the egg-laying fixed action patterns in these distantly related gastropod species. The pentapeptide region exhibits the highest level of homology (75%); in addition, an extra pentapeptide has been generated on the CDCH precursor. This indicates a vital function of these peptides in Aplysia, as well as in Lymnaea species.

Amino Acid Sequence↗

PubMed1986

Conserved sequence elements upstream of the gene encoding yeast ribosomal protein L25 are involved in transcription activation.

Previous studies have revealed the occurrence of two closely linked conserved sequence elements, designated as HOMOL 1 and RPG box, in front of most yeast ribosomal protein genes examined. To investigate whether these conserved nucleotide elements play a role in the regulation of ribosomal protein gene expression, we performed deletion analysis of the DNA region upstream of the gene encoding ribosomal protein L25. To that end we constructed a hybrid gene consisting of the pertinent 5'-flanking sequence and the Escherichia coli galK marker gene. The effects on the transcription of this fusion gene of Bal31-generated deletions were measured by Northern analysis of RNA isolated from the respective transformed yeast cells. The results demonstrate that removal of one box has a detrimental effect on the level of transcription, whereas after the deletion of both boxes hardly any transcription can be observed. Subsequently we inserted synthetic oligonucleotides in the upstream region of an L25 gene from which the original boxes had been removed. Expression of the inactivated hybrid gene turned out to be restored even by insertion of one RPG element. Moreover, the RPG box functions in both orientations, though not with equal efficiency.

Base Sequence↗

PubMed1983

Performance of articulation-disordered children on language and perception measures.

Five-year-old articulation-disordered children were classified as syllable reducers or as substituters. They were compared to each other and to normal controls on measures of expressive and receptive language and on preception of word-initial and word-final voicing contrasts. There were significant differences among the groups on several imitative expressive language measures, with the syllable reducers making both deletion and substitution errors and the substituters making substitution errors for functors. There were no significant differences on a receptive language measure, nor in perception of final voicing contrasts, but the articulation-disordered groups performed more poorly than the controls in perception of initial voicing contrasts. Children's familiarity with the stimulus words of the perception task was related to their performance on language measures. Word familiarity appeared to interact with the intrinsic difficulty of stimulus pairs in the case of word-final voicing contrasts.

Articulation Disorders↗

PubMed1983

Voicing contrasts and their phonological implications in the speech of articulation-disordered children.

Five-year-old articulation-disordered children, some classified as substituters and some as syllable reducers, were compared with normal child and adult controls in their production of voicing contrasts. These contrasts occurred in minimal pairs containing word-final obstruents and in minimal triples containing word-initial stops and /s/-plus-stop clusters in initial position. Measures of vowel duration, voice onset time (VOT), and frequency of use of phonetic voicing were made from spectrograms. In every comparison the substituters' performance resembled that of the normal controls, as did the syllable reducers' use of VOT in stop singles. The syllable reducers used larger vowel duration ratios than the normal controls in a few minimal pairs and used phonetic voicing less often in word-initial /b d g/. The production data and previously reported perception data were examined for evidence that individual syllable reducers had voicing contrasts in underlying phonological form despite their deletions of obstruents in which these contrasts occurred. Most of the syllable reducers appeared to recognize underlying voicing contrasts in at least a few final obstruents and in some of the initial stop singles.

Articulation Disorders↗

PubMedDate not supplied

Structural and functional characterization of neuropeptides involved in the control of male mating behavior of Lymnaea stagnalis.

Mating as a male in the simultaneous hermaphrodite freshwater snail, Lymnaea stagnalis, comprises a series of complex behaviors that are a prelude to copulation. Copulatory behavior itself is assumed to be controlled by various types of peptidergic neurons as well as serotonergic cells. Here we report the primary structure of two peptides that were extracted from a cluster of neurons that innervates the penial complex and that is located in the anterior lobe of the right cerebral ganglion. The sequences of the peptides were determined as: Ala-Pro-Gly-Trp-amide and Ser-Gly-Ser-Asp-Tyr-Cys-Glu-Thr-Leu-Lys-Glu-Val-Ala-Asp-Glu-Tyr-Ile-Leu- Leu- Ser-Tyr-Lys-Ile-Glu-Glu-Gln-Arg-Ala-Ala-Asp-Cys-Gly-Gly-Glu-Pro-Pro-Asn- Ser- Gln(amide), respectively. The longer peptide is a homodimer. Both peptides are processed from the recently identified Ala-Pro-Gly-Trp-amide prohormone, which is expressed in the neurons of the anterior lobe of the right cerebral ganglion. Ala-Pro-Gly-Trp-amide could also be recovered from the penial complex. This peptide, when applied in vitro, inhibits the contractions of the penis retractor muscles evoked by serotonin in a dose-dependent fashion.

Amino Acid Sequence↗