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J R Coleman

Publications and source records attributed to J R Coleman.

At least 55 records · Page 3Linked to original sources
PubMed1992

Rate and frequency interactions in the auditory brainstem response of the adult rat.

Tone pip stimuli were used at different repetition rates to examine influences upon auditory brainstem response components. Rate increases to 80.1/s result in significant latency increases in waves IV and V at all test frequencies. Rate effects occur in rostral brainstem response components which show frequency related latencies different from wave I. Amplitude measures decline at higher repetition rates for waves I and IV at most test frequencies. Rate effects are most pronounced at 8 kHz stimulation which is around the optimal behavioral frequency in rat. At higher rates the second peak of wave I is enhanced at 8 kHz, whereas the third peak of wave I at 40 kHz disappears. These results demonstrate that tone-specific stimuli provide sensitive measures of latency, amplitude and wave morphology of components of the auditory brainstem response as a function of stimulus repetition.

Acoustic Stimulation↗
PubMed1992

Identification, characterization and sequence analysis of the gene encoding phosphoenolpyruvate carboxylase in Anabaena sp. PCC 7120.

The gene (ppc) encoding phosphoenolpyruvate carboxylase (PEPCase) in the cyanobacterium Anabaena sp. PCC 7120 has been isolated, characterized and its nucleotide sequence determined. Heterologous hybridization using the Synechococcus sp. PCC 7942 ppc gene as a probe of an Anabaena genomic DNA library identified an 8.2 kb HindIII DNA fragment that contained a 3.08 kb open reading frame encoding the cyanobacterial PEPCase. Deletion analysis of the 8.2 kb DNA fragment was used to determine sequences required for expression of enzyme activity in Escherichia coli cells. Primer extension data have been used to identify the cyanobacterial transcription initiation site and the position of the ppc start codon. Comparisons of the Anabaena deduced amino acid sequence with the Synechococcus sp. PCC 6301, E. coli and higher-plant ppc sequences have also been performed and the data are discussed with respect to conservation of specific regions of the protein.

Amino Acid Sequence↗
PubMed1992

Association of Carbonic Anhydrase Activity with Carboxysomes Isolated from the Cyanobacterium Synechococcus PCC7942.

The development of a simple method for the isolation of purified carboxysomes from the cyanobacterium Synechococcus PCC7942 has made it possible to identify a specific and inducible, intracellular carbonic anhydrase (CA) activity that is strongly associated with carboxysomes. This was shown, in part, through enzyme recovery experiments that indicated that a clear majority of a CA activity that is sensitive to the CA inhibitor ethoxyzolamide (I(50) = 4 mum) copurifies with a majority of the cell's ribulose-1,5-bisphosphate carboxylase/oxygenase activity in a highly purified pelletable fraction. Electron microscopy of this pelletable fraction revealed the presence of carboxysomes that were physically intact. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of carboxysome proteins showed that the large and small subunits of ribulose-1,5-bisphosphate carbosylase/oxygenase were clearly prominent and that several other minor proteins could be distinguished. The specific location of this carboxysomal CA activity is further reinforced by the finding that a previously isolated high CO(2)-requiring mutant, Type II/No. 68 (G.D. Price, M.R. Badger [1989] Plant Physiol 91: 514-525), displayed a 30-fold reduction in carboxysome-associated CA activity when tested under optimal conditions. Carboxysomal CA has the unusual property of being inactivated by dithiothreitol. The enzyme also requires 20 mm Mg(2+) (as MgSO(4)) for near maximum activity; other divalent cations, such as Ca(2+) and Mn(2+), also stimulate carboxysomal CA activity, but to a lesser extent than Mg(2+). Results are discussed in relation to the role of carboxysomes in the CO(2)-concentrating mechanism in cyanobacteria and the role that carboxysomal CA activity appears to play in this process.

Journal Article↗
PubMed1991

Structural features of neurons in whole grafts of the rat inferior colliculus.

The inferior colliculus (IC) is a midbrain structure that receives ascending auditory input from brainstem nuclei via the lateral lemniscus, sends efferent fibers to the medial geniculate body of thalamus and receives descending projections from auditory cortex. In the rat, the IC consists of dorsal and external cortices surrounding the central nucleus of IC (CNIC) which is populated by discoid and stellate neurons; the CNIC has a laminar appearance arising from organization of lemniscal fibers and processes of discoid cells. The IC of adult rats was chosen for implantation of whole grafts of E16-17 caudal tectum into unilateral lesion sites. Dendritic and somal architecture of graft neurons was examined 1 to 4.5 months following implantation using rapid Golgi, HRP and Nissl methods. The CNIC of rat is dominated by principal neurons with relatively flattened dendritic fields. In grafts of caudal tectum the most common neuron class observed possesses flattened dendritic arbors which often parallel one another. These neurons also resemble CNIC neurons of host tissue adjacent to the graft border. Spine formations appear on both proximal and distal dendrites of this neural type in both normal and implanted tissues. In addition, comparable somal features of graft neurons include ovoid or fusiform shapes with regular nuclear membranes as found in the normal colliculus. In Golgi stained material fewer stellate class neurons appear as in the normal CNIC, although stellate cell classes are more abundant in the pericentral areas of normal tissue. Both neuron populations are retrogradely labelled in graft and normal IC after HRP injection into the medial geniculate body. These features suggest that the graft core typically consists of prototypic CNIC cells. Other features of neuron and glial cell density vary in graft material which also shows a complex network of vasculature. These results demonstrate that whole grafts of caudal tectum placed into the inferior colliculus can form organized neural architecture similar to the normal CNIC. The somal, dendritic and spine features of these neurons form a potential substrate for connectional and functional properties which establish this preparation as suitable for further investigation as a model for development and recovery of function in the central auditory system.

Animals↗
PubMed1991

Isolation and characterization of a cDNA coding for pea chloroplastic carbonic anhydrase.

Using a polyclonal antibody generated against the purified pea (Pisum sativum) carbonic anhydrase (CA) monomeric species, we have isolated and characterized a cDNA coding for this enzyme. Protein sequence analysis was used to confirm the identity of the clone. The presence of a large transit peptide suggests that CA is transported into the chloroplast and then processed to the mature size of approximately 26 kilodaltons. Northern hybridization, using the CA cDNA as a probe of total leaf RNA, revealed a single transcript of 1.45 kilobase pairs. This transcript was not detected in RNA extracted from root or etiolated leaf tissue. Comparison of the deduced amino acid sequence with that of spinach CA showed approximately 68% identity over the length of the nascent protein but with greater similarity observed within the mature protein sequences. In addition, regions of the pea and spinach CA proteins were found to be significantly similar to the Escherichia coli cyanate permease.

Journal Article↗
PubMed1991

Identification and localization of carbonic anhydrase in two chlorella species.

Carbonic anhydrase (CA) activity and localization have been examined in two species of the eukaryotic green alga Chlorella. Mass spectrometric and potentiometric assays of CA activity indicate that C. ellipsoidea contains very little extracellular CA activity whereas C. saccharophila exhibits significant extracellular activity when grown at alkaline pH values. Extracellular CA activity appears to be correlated with the presence of a 36 kilodalton polypeptide that was detected immunologically using a polyclonal antibody directed against the 37 kilodalton Chlamydomonas CA monomer. Both Chlorella species and enzymatically isolated C. ellipsoidea chloroplasts also contain an immunologically similar 38 kilodalton polypeptide that may be a cytosolic or chloroplastic form of CA.

Journal Article↗
PubMed1990

Distinct vascular and intestinal smooth muscle myosin heavy chain mRNAs are encoded by a single-copy gene in the chicken.

We examined whether the gizzard MHC gene is expressed in other smooth muscle tissues and, if so, whether there exist any smooth muscle MHC isoforms at the mRNA level. Northern blot analysis showed that the gizzard MHC gene was also expressed in the aorta and jejunum, but not in the pectoralis muscle or in fibroblasts. This indicates that striated muscle and non-muscle MHC isoforms are encoded in genes distinct from the smooth muscle MHC gene. Further, nuclease S1 mapping showed that the aortic smooth muscle MHC mRNA was distinct from the gizzard mRNA in the 5'-terminal coding region. Both of these mRNA species are expressed in the jejunum. These observations suggest that there exist at least two chicken smooth muscle MHC isoforms, vascular-type and intestinal-type, and that these isoforms are generated from a single-copy gene, probably by an alternative mRNA processing mechanism.

Animals↗
PubMed1990

Anatomy of the rat medial geniculate body: I. Cytoarchitecture, myeloarchitecture, and neocortical connectivity.

The cytoarchitecture, myeloarchitecture, and neocortical connectivity of the rat medial geniculate body (MGB) were comprehensively studied in adult and immature rats to define major anatomical divisions and nuclei. The MGB is a highly intricate structure composed of the ventral (MGv), dorsal (MGd), and medial (MGm) divisions and component nuclei, each having reciprocal connections with auditory neocortex. The MGv lies inferior to the midgeniculate bundle and extends to the rostral, but not caudal MGB tip. The MGv is composed of ventral and ovoid nuclei bounded by a marginal zone, each region containing dark staining small and medium sized, densely packed neurons shown to have tufted dendritic morphology; in contrast to the MGd, but similar to the dorsal lateral geniculate nucleus, only the perikarya of MGv neurons stain for Nissl in early postnatal material. Ventral nucleus cells align with afferent brachial axons, which penetrate the nucleus in a dorsoventral direction, whereas rostrocaudal cellular arrays are retrogradely labeled after injections of horseradish peroxidase (HRP) into auditory cortex. The ovoid nucleus is a double spiraled structure encircled and penetrated by afferent fibers that determine the orientation of constituent perikarya. Neurons in the transition zone align with a spray of axons emanating from the juncture of the ovoid and midgeniculate bundles. Marginal zone neurons are oriented in parallel to the free geniculate wall. The MGd resides within and superior to the midgeniculate bundle, and is composed of several nuclei that stain palely for myelin. In immature material, both dendritic processes and somata in the MGd stain for Nissl with our protocol; many of these cells show a stellate arborization pattern that distinguishes this region from the MGv, but is similar to the staining pattern of immature neurons of the lateral posterior nucleus. The adult dorsal nucleus has medium-sized, loosely packed neurons. The deep dorsal nucleus is situated among the fibers of the midgeniculate bundle and contains loosely packed round and fusiform cells; the latter cell type constitutes a minor proportion of the adult neuronal population but the major cell type in immature animals. The caudodorsal nucleus, which occupies the caudal tip of the MGB and rostrally courses superior to the dorsal nucleus, contains small, dark staining multipolar cells; the ventrolateral nucleus courses inferior to the MGv. The suprageniculate and limitans nuclei are included in the auditory thalamus on the basis of connections with auditory neocortex; the former has medium to dark staining mixed-sized cells, and the latter has densely packed cells which form a vertical column.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Anatomy of the rat medial geniculate body: II. Dendritic morphology.

The medial geniculate body (MGB) of the rat was studied with Golgi methods to determine the distribution of neurons identified by dendritic morphology. These findings were compared with major divisions and constituent nuclei established by somatic and fiber architectonics, and by connections with temporal neocortex (Clerici et al.: Society of Neuroscience Abstracts 12:1272, 1986; 13:325, 1987; Anatomical Record 218:23, 1987; Winer and Larue: Journal of Comparative Neurology 257:282-315, 1987; Clerici and Coleman: Journal of Comparative Neurology 297:14-31, 1990). It was found that an elaboration of the prototypical scheme proposed by Morest (Journal of Anatomy 98:611-630, 1964) for partitioning the mammalian MGB is valid for characterizing the rat MGB. Two predominant categories of principal neuron dendritic patterning were identified: a bushy cell having tufted dendritic fields and a stellate cell with a radiate dendritic domain. Tufted neurons have large caliber dendritic trunks that divide profusely into daughter branches close to the soma with intertwining higher order branches that maintain a relatively restricted dendritic field. Stellate neurons typically emit primary dendrites in all directions that then divide dichotomously at wide angles at subsequent orders of branching to produce a somewhat spheroidal dendritic field. In the present study, the rat MGB is found to be a tripartite structure composed of ventral (MGv), dorsal (MGd), and medial (MGm) divisions, each uniquely characterized by constituent dendritic morphology. The paramount neuronal class of the MGv is the tufted principal cell. In the ventral and ovoid nuclei of the MGv the neuronal orientation of highly oriented bitufted cells is in register with afferent brachial axons. In the ventral nucleus, this arrangement approximates vertical with a dorsomedial tilt most prominent rostrally; in the ovoid nucleus, tufted cells adhere to the double spiraled course of afferent axons. The transition zone between ventral and ovoid nuclei contains tufted neurons that align with radially oriented fibers issuing from the junction of the ovoid and midgeniculate bundles. Bitufted neurons of the marginal zone parallel fibers at the lateral margin of the geniculate. Within the MGd the dorsal and caudodorsal nuclei are characterized by stellate cells with extensive dendritic arbors and busy neurons with dendritic branches less tufted than those observed in the MGv. The deep dorsal nucleus contains bitufted neurons that polarize with the long axis of the midgeniculate bundle and intermingle with stellate neurons. The suprageniculate nucleus includes neurons with large somata and long, sparsely branched and dorsoventrally oriented dendrites orthagonal to corticothalamic axons, as well as smaller neurons and classical stellate cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Fetal tectum grafted as a cell suspension into the adult rat inferior colliculus.

The known structural and functional features of the inferior colliculus provided an advantageous substrate for examining the outcome of neural transplantation. In the present study, tissue from the midbrain tectum of Sprague-Dawley rat fetuses was removed at 15, 16 and 19 days of gestation (E15, E16 and E19), incubated as a dissociated cell suspension for 12 to 15 h in a medium containing True Blue for prelabeling, and injected into the central nucleus of the inferior colliculus (CNIC) of 28 normal male adult conspecifics. Viable tectal grafts were found in 57.5% of host animals with 65.2% located in CNIC. Grafts of E16 tissue had a survival rate of 84.2%, which was twice that of E15 or E19 donors, and there was no difference in graft survival rate in hosts sacrificed up to 6 months after the implantation procedure. Neurons prelabeled with True Blue and counterstained with thionin were identified as uniquely green stained cells in brightfield illumination and brilliant opaque cells in darkfield microscopy. Grafts were organized in tightly packed clusters of cells including large rounded polygonal and smaller cells similar in size to normal CNIC large and small multipolar neurons. Cell morphology of the larger ovoid and fusiform grafted neurons most closely resembled that of typical adult CNIC cell populations; other implanted cell types appeared immature even when host post-implant survival was extended. At longer post-implant intervals graft and host cells further intermingled, and both cellular and fibrous bridges were observed at the interface between host and graft tissue. The present work demonstrates the viability and development of homotypic cells grafted into a central auditory structure utilizing a simple method of prelabeling donor tissue with a fluorescent dye.

Animals↗
PubMed1990

Auditory brainstem responses to tonal stimuli in young and aging rats.

The auditory brain stem response (ABR) was studied in young adult and aged rats using 3,8 and 40 kHz tone pips. The expected inverse relationship between frequency and latency was observed in the younger group for waves I, II and III, while the response to the highest frequency stimulus had the longest latency at wave V. Absolute latencies for waves I through V each showed age-related increments with more pronounced changes occurring to 3 and 40 kHz stimuli than to the frequency of maximum sensitivity (8 kHz). Threshold increases with age for the highest frequency approximately doubled those for the lower frequencies. Examination of interpeak intervals (IPI) I-III, III-V and I-V revealed aging effects. The largest IPI I-V increment occurred to 3 kHz stimulation which reflects changes at both I-III and III-V sub-intervals. These results demonstrate electrophysiological correlates of aging due to transformations in the peripheral auditory system coupled with alterations in brainstem auditory pathways.

Acoustic Stimulation↗
PubMed1989

Regulation of expression and nucleotide sequence of the Anabaena variabilis recA gene.

The expression of the cyanobacterial recA gene, isolated from Anabaena variabilis, has been examined at the levels of transcript and protein abundance. Exposure of the cyanobacterium to a variety of DNA-damaging agents, including mitomycin C, methyl methanesulfonate, and UV irradiation, results in a rapid increase in the abundance of the recA transcript above basal levels as determined by Northern (RNA) blot analysis. A concomitant increase in the abundance of a 37- to 38-kilodalton polypeptide was also detected by Western (immuno-) blot analysis of soluble cyanobacterial polypeptides using polyclonal antiserum directed against the Escherichia coli recA protein. The cyanobacterial polypeptide is of the same molecular mass as that synthesized by an in vitro, DNA-directed procaryotic transcription-translation system primed with an A. variabilis genomic fragment containing the recA gene. Nucleotide sequence analysis of the cyanobacterial gene revealed a protein of 358 amino acids with a molecular weight of 38,403 daltons. The A. variabilis and E. coli recA genes share similarity at 58% of the amino acid residues; however, an E. coli-like lexA repressor-binding site is not present in the A. variabilis promoter region. The similarities of A. variabilis and E. coli recA expression and gene sequence are discussed.

Amino Acid Sequence↗
PubMed1988

Aging and presbycusis: effects on 2-deoxy-D-glucose uptake in the mouse auditory brain stem in quiet.

Autoradiography was used to assess the incorporation of [2-14C]deoxy-D-glucose by the auditory brain stem of young and aging mice of the C57BL/6 strain (which demonstrates progressive chronic sensorineural hearing loss) and the CBA strain (which maintains good hearing until late in life). Animals were injected with labeled 2-deoxyglucose and placed in quiet for 45 min; brain stem sections were prepared for autoradiography. The amounts of 2-deoxyglucose incorporated into the anterior ventral cochlear nucleus (AVCN), inferior colliculus (IC), and trigeminal nerve (TN) were densitometrically analyzed. Within each subject, the densities of the three structures were statistically compared. In every mouse, inferior colliculus density was greater than that of the anterior ventral cochlear nucleus, which was greater than trigeminal nerve density. To compare subject groups, relative densities (inferior colliculus and anterior ventral cochlear nucleus re: trigeminal nerve) were used; no significant differences were found between groups. Thus, aging, with or without severe loss of hearing, is not associated with altered incorporation of 2-deoxyglucose (and presumably glucose) in quiet.

Aging↗
PubMed1988

Effect of CO(2) Concentration on Protein Biosynthesis and Carbonic Anhydrase Expression in Chlamydomonas reinhardtii.

The effect of external inorganic carbon (C(i)) concentrations on protein biosynthesis and carbonic anhydrase (CA) mRNA abundance were examined in the eukaryotic alga Chlamydomonas reinhardtii. Transfer of high CO(2) (5%) grown algae to air levels of CO(2) resulted in the transitory synthesis of two polypeptides of approximately 49,000 and 52,000 daltons as well as prolonged synthesis and accumulation of the 37,000 dalton CA monomer and an unidentified 20,000 dalton polypeptide. The gene coding for carbonic anhydrase was isolated from a genomic expression library and subjected to restriction endonuclease analysis. Southern blot analysis of chromosomal DNA indicates that only a single copy of the gene is present. The 2.5 kilobase DNA fragment hybridizes specifically to a 1.4 kilobase transcript in RNA isolated from air-grown cells and from cells grown on 5% CO(2) that have been exposed to air levels of CO(2). Maximum mRNA abundance was observed after 1 to 3 hours of exposure to air. Transfer of air-grown cells to a high CO(2) environment resulted in the elimination of the CA transcript after 60 minutes of exposure. Changes in CA transcript abundance in response to external C(i) concentrations occurred in the presence or absence of light.

Journal Article↗
PubMed1987

Sources of projections to subdivisions of the inferior colliculus in the rat.

Brainstem and forebrain projections to major subdivisions of the rat inferior colliculus were studied by using retrograde and anterograde transport of horseradish peroxidase. Retrograde label from injection into the external cortex of the inferior colliculus appears bilaterally in cells of the inferior colliculus, as well as in other brainstem auditory groups including the ipsilateral dorsal nucleus of the lateral lemniscus and contralateral dorsal cochlear nucleus. The external cortex is the only collicular subdivision where an injection labels cells in the contralateral cuneate nucleus, gracile nucleus, and spinal trigeminal nucleus. Other projecting cells to the external cortex are found in the lateral nucleus of substantia nigra, the parabrachial region, the deep superior colliculus, the midbrain central gray, the periventricular nucleus, and area 39 of auditory cortex. Injection of the dorsal cortex of inferior colliculus heavily labels pyramidal cells of areas 41, 20, and 36 of the ipsilateral neocortex. Anterograde label from a large injection of auditory cortex is densely distributed in the dorsal cortex, lesser so in the external cortex, and only slightly in the central nucleus. Labelled cells appear in the central nucleus, dorsal cortex, and external cortex, primarily ipsilaterally, following dorsal cortex injection. Relatively few cells from other brainstem auditory groups show projections to the dorsal cortex. Injection of the central nucleus of the inferior colliculus results in robust labelling of nuclei of the ascending auditory pathway including the anteroventral, posteroventral, and dorsal cochlear nuclei (mainly contralaterally), and bilaterally the lateral superior olive, lateral nucleus of the trapezoid body, dorsal nucleus of the lateral lemniscus, and the central nucleus, dorsal cortex, and external cortex of the colliculus. The medial superior olive, superior paraolivary nucleus, and ventral nucleus of the trapezoid body essentially show ipsilateral projections to the central nucleus. The differential distribution of afferents to the inferior colliculus provides a substrate for functional parcellation of collicular subdivisions.

Animals↗
PubMed1987

Development of auditory brainstem response to tone pip stimuli in the rat.

The course of development of the auditory brainstem response (ABR) in rat was examined. Pure tone pip stimuli of 3, 8 and 40 kHz at intensities up to 106 dB sound pressure level peak equivalent were presented to anesthetized rats on postnatal days (PND) 9, 10, 12, 14, 16, 20, 24, 36, 70 and 96. The peak-to-peak amplitude and the order of appearance of each wave was examined at each stimulus parameter. The first response to presentation of an auditory stimulus was observed on PND 12. This response was demonstrated to be of non-neural origin and presumed to be a summating potential representing hair cell function in the cochlea. The first neural responses, observed on PND 14, to 3- and 8-kHz tones only, appeared as two or more waves. High-frequency (40 kHz) tones did not elicit any substantive neural response on PND 14, but neural activity to this stimulus was observed consistently by PND 16. By PND 20, 4 waves were present consistently at all test frequencies, and by PND 36 the full adult complement of 5 vertex positive waves was recorded. The frequency-dependent sequential appearance of waves during development lends support to data charting the development of frequency mapping in the cochlea. The amplitude of waves I and II at 8 kHz decreased as the animal matured, while waves III-V generally showed an initial increase in amplitude at all test frequencies through PND 24 followed by a gradual amplitude decrease to adult levels. Possible sources for developmental changes in amplitude are discussed.

Animals↗