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Biomedical subjects

D D Hunter

Publications and source records attributed to D D Hunter.

At least 19 recordsLinked to original sources
PubMed2001

Neurotrophins and asthma.

The neurotrophins are a family of peptides that promote survival, growth, and differentiation of neurons. Neurotrophins may also influence the function of nonneuronal cell types, including immune cells. The development and maintenance of asthma is thought to involve the nervous system and the immune system, but the role that neurotrophins play in asthma is unknown. The cellular sources of the neurotrophins include mast cells, lymphocytes, macrophages, epithelial cells, smooth muscle cells, and eosinophils. The activation of neurotrophin receptors in immune cells and neurons involves ligand-induced homodimerization, which leads to activation of intrinsic Trk receptor kinase. The exact consequences of activating these receptors on immune cells is unknown, but rather than having unique actions on immune cells, the neurotrophins appear to act in concert with known immune regulating factors to modulate the maturation, accumulation, proliferation, and activation of immune cells. Neurotrophins can modulate afferent nerve function by stimulating the production of neuropeptides within airway afferent neurons. These neuropeptides may be released from the central terminals of airway afferent neurons, which leads to heightened autonomic reflex activity, and increased reactivity in the airways.

Animals↗
PubMed2000

A novel member of the netrin family, beta-netrin, shares homology with the beta chain of laminin: identification, expression, and functional characterization.

The netrins are a family of laminin-related molecules. Here, we characterize a new member of the family, beta-netrin. beta-Netrin is homologous to the NH(2) terminus of laminin chain short arms; it contains a laminin-like domain VI and 3.5 laminin EGF repeats and a netrin C domain. Unlike other netrins, this new netrin is more related to the laminin beta chains, thus, its name beta-netrin. An initial analysis of the tissue distribution revealed that kidney, heart, ovary, retina, and the olfactory bulb were tissues of high expression. We have expressed the molecule in a eukaryotic cell expression system and made antibodies to the expressed product. Both in situ hybridization and immunohistochemistry were used to describe the cellular source of beta-netrin and where beta-netrin is deposited. beta-Netrin is a basement membrane component; it is present in the basement membranes of the vasculature, kidney, and ovaries. In addition, beta-netrin is expressed in a limited set of fiber tracts within the brain, including the lateral olfactory tract and the vomeronasal nerve. Functional studies were performed and show that beta-netrin promotes neurite elongation from olfactory bulb explants. Together, these data suggest that beta-netrin is important in neural, kidney, and vascular development.

Amino Acid Sequence↗
PubMed2000

Laminin expression in adult and developing retinae: evidence of two novel CNS laminins.

Components of the extracellular matrix exert myriad effects on tissues throughout the body. In particular, the laminins, a family of heterotrimeric extracellular glycoproteins, have been shown to affect tissue development and integrity in such diverse organs as the kidney, lung, skin, and nervous system. Of these, we have focused on the roles that laminins play in the differentiation and maintenance of the nervous system. Here, we examine the expression of all known laminin chains within one component of the CNS, the retina. We find seven laminin chains-alpha3, alpha4, alpha5, beta2, beta3, gamma2, and gamma3-outside the retinal basement membranes. Anatomically, these chains are coexpressed in one or both of two locations: the matrix surrounding photoreceptors and the first synaptic layer where photoreceptors synapse with retinal interneurons. Biochemically, four of these chains are coisolated from retinal extracts in two independent complexes, confirming that two novel heterotrimers-alpha4beta2gamma3 and alpha5beta2gamma3-are present in the retinal matrix. During development, all four of these chains, along with components of laminin 5 (the alpha3, beta3, and gamma2 chains) are also expressed at sites at which they could exert important effects on photoreceptor development. Together, these data suggest the existence of two novel laminin heterotrimers in the CNS, which we term here laminin 14 (composed of the alpha4, beta2, and gamma3 chains) and laminin 15 (composed of the alpha5, beta2, and gamma3 chains), and lead us to hypothesize that these laminins, along with laminin 5, may play roles in photoreceptor production, stability, and synaptic organization.

Adult↗
PubMed2000

Neural integration and allergic disease.

Changes in neural activity play a key role in many symptoms of allergic disease, including sneezing, coughing, itching, and ocular irritation, among others. The mechanisms underlying allergen-induced changes in neural activity (reflexes) are largely unknown and under active investigation. Allergic inflammation can affect neural activity on a variety of levels, including at the primary afferent sensory nerve, integrative centers of the central nervous system, autonomic ganglia, and autonomic neuroeffector junction. At the level of the afferent sensory nerve, mediators released after allergen exposure either directly or indirectly increase neuronal firing. At the level of sensory ganglia, which contain cell bodies that innervate a variety of organs, changes in neuronal excitability may lead to a generalization of allergic symptoms. In the central nervous system, where afferent inputs from throughout the body converge, allergic inflammation may be associated with central sensitization, leading to the modulation of the neural reflexes. Finally, at the autonomic ganglia and neuroeffector junction, allergic inflammation appears to be associated with enhanced ganglionic transmission and neurotransmitter release, respectively. Mechanisms by which allergen challenge affects neuronal activity at various levels of the nervous system are reviewed, with a primary emphasis on studies of airway physiologic factors.

Central Nervous System↗
PubMed2000

Toluene diisocyanate enhances substance P in sensory neurons innervating the nasal mucosa.

Inhalation of irritants, such as toluene diisocyanate (TDI), stimulates substance P (SP) release from peripheral processes of sensory neurons innervating the airways. The purpose of this study was to determine if TDI inhalation affects intraneuronal levels of SP and preprotachykinin (PPT) messenger RNA (mRNA) in the sensory neurons of the trigeminal ganglion (TG) which innervate the nasal epithelium. The nasal cavity of Fisher-344 rats was instilled with rhodamine-labeled latex microspheres. Ten days later, the rats were exposed to 60 ppb of 2,4-2,6-TDI vapor for 2 h. The TG were removed 1, 12, 24, 48, 72, and 96 h after TDI treatment and prepared for SP immunocytochemistry and PPT in situ hybridization. SP nerve fiber density in nasal epithelium was significantly increased 12, 24, and 48 h after TDI exposure. The proportion of microsphere-labeled cell bodies expressing high levels of SP immunoreactivity was decreased at 24 h but was increased above controls at 48 and 72 h. The proportion of microsphere-labeled cell bodies expressing high levels of PPT mRNA was increased above control levels at 24 and 48 h. The percentage of leukocytes observed in nasal lavage fluid was significantly increased 12, 24, 48, and 72 h after inhalation. These studies indicate that SP production in TG neurons projecting to the nasal epithelium is transiently increased after TDI exposure, suggesting that TDI inhalation not only causes SP release but also increased intraneuronal neuropeptide levels. Increased neuronal SP levels may be involved in maintaining neurogenic inflammation or the development of airway hyperresponsiveness.

Animals↗
PubMed2000

Nerve growth factor-induced phenotypic switch in guinea pig airway sensory neurons.

Immunohistochemistry was combined with retrograde tracing techniques to characterize the effect of nerve growth factor (NGF) on substance P (SP) producing vagal neurons innervating the guinea pig trachea. Fast blue dye instilled into the trachea retrogradely labeled nerve cell bodies located in the nodose and jugular ganglia. In untreated guinea pigs > 99% of the SP-containing neurons labeled with fast blue were located in the jugular ganglia. The SP-positive neurons were small in diameter (23 +/- 1 microm) and were negative for neurofilament immunoreactivity. The fast-blue-positive neurons in the nodose ganglia, by contrast, were large in diameter (40 +/- 3 microm) and were negative for SP immunoreactivity and positive for neurofilament immunoreactivity. After NGF-beta injections into the tracheal wall, approximately 10% of the large-diameter nodose neurofilament-positive neurons projecting fibers to the trachea became SP-positive (p < 0.05). We previously demonstrated that nodose nerve endings supplying the trachea are exquisitely mechanically sensitive, but capsaicin- and bradykinin-insensitive. These results suggest that NGF not only increases SP expression in airway neurons, but changes the neuronal phenotype such that large, capsaicin-insensitive nodose neurons with fast-conducting "Adelta" fibers provide a component of the tachykinergic innervation.

Airway Resistance↗
PubMed1999

Disruption of laminin beta2 chain production causes alterations in morphology and function in the CNS.

From the elegant studies of Ramon y Cajal (1909) to the current advances in molecular cloning (e.g., Farber and Danciger, 1997), the retina has served as an ideal model for the entire CNS. We have taken advantage of the well described anatomy, physiology, and molecular biology of the retina to begin to examine the role of the laminins, one component of the extracellular matrix, on the processes of neuronal differentiation and synapse formation in the CNS. We have examined the effect of the deletion of one laminin chain, the beta2 chain, on retinal development. The gross development of retinas from laminin beta2 chain-deficient animals appears normal, and photoreceptors are formed. However, these retinas exhibit several pathologies: laminin beta2 chain-deficient mice display abnormal outer segment elongation, abnormal electroretinograms, and abnormal rod photoreceptor synapses. Morphologically, the outer segments are reduced by 50% in length; the outer plexiform layer of mutant animals is disrupted specifically, because only 7% of observed rod invaginating synapses appear normal, whereas the inner plexiform layer is undisturbed; finally, the rate of apoptosis in the mutant photoreceptor layer is twice that of control mice. Physiologically, the electroretinogram is altered; the amplitude of the b-wave and the slope of the b-wave intensity-response function are both decreased, consistent with synaptic disruption in the outer retina. Together, these results emphasize the prominence of the extracellular matrix and, in particular, the laminins in the development and maintenance of synaptic function and morphogenesis in the CNS.

Animals↗
PubMed1999

An olfactory sensory neuron line, odora, properly targets olfactory proteins and responds to odorants.

The site for interactions between the nervous system and much of the chemical world is in the olfactory sensory neuron (OSN). Odorant receptor proteins (ORPs) are postulated to mediate these interactions. However, the function of most ORPs has not been demonstrated in vivo or in vitro. For this and other reasons, we created a conditionally immortalized cell line derived from the OSN lineage, which we term odora. Odora cells, under control conditions, are phenotypically similar to the OSN progenitor, the globose basal cell. After differentiation, odora cells more closely resemble OSNs. Differentiated odora cells express neuronal and olfactory markers, including components of the olfactory signal transduction pathway. Unlike other cell lines, they also efficiently target exogenous ORPs to their surface. Strikingly, differentiated odora cells expressing ORPs respond to odorants, as measured by an influx of calcium. In particular, cells expressing one ORP demonstrate a specific response to only one type of tested odorant. Odora cells, therefore, are ideal models to examine the genesis and function of olfactory sensory neurons.

Animals↗
PubMed1999

Characterization and expression of the laminin gamma3 chain: a novel, non-basement membrane-associated, laminin chain.

Laminins are heterotrimeric molecules composed of an alpha, a beta, and a gamma chain; they have broad functional roles in development and in stabilizing epithelial structures. Here, we identified a novel laminin, composed of known alpha and beta chains but containing a novel gamma chain, gamma3. We have cloned gene encoding this chain, LAMC3, which maps to chromosome 9 at q31-34. Protein and cDNA analyses demonstrate that gamma3 contains all the expected domains of a gamma chain, including two consensus glycosylation sites and a putative nidogen-binding site. This suggests that gamma3-containing laminins are likely to exist in a stable matrix. Studies of the tissue distribution of gamma3 chain show that it is broadly expressed in: skin, heart, lung, and the reproductive tracts. In skin, gamma3 protein is seen within the basement membrane of the dermal-epidermal junction at points of nerve penetration. The gamma3 chain is also a prominent element of the apical surface of ciliated epithelial cells of: lung, oviduct, epididymis, ductus deferens, and seminiferous tubules. The distribution of gamma3-containing laminins on the apical surfaces of a variety of epithelial tissues is novel and suggests that they are not found within ultrastructurally defined basement membranes. It seems likely that these apical laminins are important in the morphogenesis and structural stability of the ciliated processes of these cells.

Amino Acid Sequence↗
PubMed1999

Association of adhesive macromolecules with terminal sprouts at the neuromuscular junction after botulinum treatment.

Small quantities of botulinum toxin (BTX) are useful in the treatment of certain movement disorders, such as laryngeal spasmodic dysphonia, blepharospasm, and cervical dystonia. However, the corrective paralytic effects of BTX are only temporary, in part because of the formation of remodeled neuromuscular junctions. Here, we questioned whether various factors within and near the neuromuscular junction could contribute to the remodeling seen after BTX treatment. BTX was injected subcutaneously in the region of the levator auris longus muscle. At 1-week intervals, levator auris longus muscles were removed and examined histochemically. As previously described, BTX treatment results in a progressive elongation of end plates. The neural cell adhesion molecule was not associated with the elongated end plates but was associated with the BTX-induced nerve sprouts after long intervals (3 to 4 weeks). Similarly, after BTX, laminin-1 (composed of alpha 1, beta 1, and gamma 1 chains) reactivity was associated with the nerve sprouts, but not with the end plates. Laminin beta 2 reactivity at the end plate dispersed somewhat within 1 week but remained diffusely associated with the elongating end plates for up to 5 weeks. Together these results suggest that neural cell adhesion molecule and laminins may participate in the sprouting observed after BTX treatment and that alterations in laminin beta 2 expression may participate in initial loss of contacts.

Animals↗
PubMed1999

Identification and substance P content of vagal afferent neurons innervating the epithelium of the guinea pig trachea.

Both the nodose and jugular vagal ganglia provide sensory innervation to the airways. The purpose of this study was to localize and characterize the substance P (SP) content of vagal afferent neurons that project specifically to the tracheal epithelium. A retrograde neuronal tracer, fast blue dye or rhodamine-labeled latex microspheres, was instilled into the guinea pig trachea. After 7 d, the nodose and jugular ganglia were removed, sectioned, and prepared for immunocytochemistry. Sections of tracheal mucosa demonstrated that fast blue dye diffused throughout the airway wall, whereas the rhodamine-labeled microspheres, as expected, did not penetrate the basement membrane and were thus localized to the epithelium. When the diffusible fast blue dye was used, approximately 60% of the labeled neurons were found in the nodose ganglia and 40% in the jugular ganglia. By contrast, when the beads were used to label only epithelial nerve fibers, 97 +/- 1% of the tracheal neurons taking up the dye were derived from jugular neurons, 60 +/- 6% of which contained SP immunoreactivity. These studies demonstrate that, in contrast to the submucosa, nerve fibers innervating the epithelium of the trachea are derived nearly exclusively from neurons with cell bodies in the jugular ganglia.

Amidines↗
PubMed1998

Girk2 expression in the ventral midbrain, cerebellum, and olfactory bulb and its relationship to the murine mutation weaver.

The mouse mutant weaver exhibits developmental deficits and cell death in several neuronal classes. weaver is almost certainly a mutation in the potassium channel, Girk2. In some vulnerable neurons, including those in the midbrain, it is not known whether weaver expression is the primary defect, or whether deficits are secondary to weaver expression elsewhere. In wild-type mice, our results point to subsets of dopamine-containing cells of the midbrain as primary targets of weaver. In the midbrain, all Girk2-positive cells examined in A9 (substantia nigra), A10, and A8 (retrorubral nucleus) are tyrosine hydroxylase-positive. The expression of Girk2 varies among and within these regions. Girk2-positive cells are most numerous in the substantia nigra, pars compacta, a region badly affected in homozygous weavers; in this region, Girk2 expression is found in cell somata and dendrites. In addition, in homozygous weavers, the remaining neuronal processes in A9 (as well as A8) are stunted. Within A10, a region largely spared in weaver homozygotes, Girk2 expression is undetectable in the most medially placed nuclei and is present in the nuclei that border A9. In the cerebellum, Girk2 immunoreactivity was also found in somata and dendrites of populations vulnerable to weaver, including the deep cerebellar nuclei. In a region not previously known to be affected, the olfactory bulb, Girk2 protein is detectable only in processes. The expression of mutated Girk2 has consequences for the olfactory bulb where ectopic cells are present in the external plexiform layer of the homozygous weaver. Our results emphasize that the Girk2 mutation may act to alter the development and maintenance of cell processes and that defects may be present in all Girk2-containing regions in weaver mutants.

Animals↗
PubMed1998

Effects of silica exposure on substance P immunoreactivity and preprotachykinin mRNA expression in trigeminal sensory neurons in Fischer 344 rats.

Trigeminal sensory neurons innervate the nasal cavity and may release substance P (SP) upon exposure to inhaled irritants. The purpose of this study was to determine if silica dust, an occupational irritant causing inflammation, activates sensory neurons supplying the nasal cavity. Male Fischer 344 rats were placed in inhalation chambers and exposed daily to 2 mg/m3 of fresh silica (average diameter 1 microm) for 6 mo. Following exposure, the trigeminal ganglia (TG) were removed and prepared for SP immunocytochemistry and for preprotachykinin (PPT) autoradiographic in situ hybridization. The SP-like immunofluorescence in TG neurons was subjectively categorized as high, moderate, or low (background) intensity. In situ hybridization autoradiographs were quantified on the basis of grain density using digital imaging analysis. The SP immunoreactivity and PPT mRNA expression in the TG neurons were significantly increased after silica inhalation. The proportion of highly positive SP-immunoreactive neurons shifted from 1.30 +/- 0.58% in controls to 11.30 +/- 1.15% after silica treatment. The neurons exhibiting high grain density for PPT mRNA increased from 1.50 +/- 0.87% in controls to 11.67 +/- 0.58% in the silica group. Thus, inhalation of silica causes upper airway irritation resulting in increased levels of immunoreactive neuronal SP and PPT mRNA. These findings suggest that silica activates sensory pathways that may be involved in nasal inflammation.

Air Pollutants↗
PubMed1998

Identification and neuropeptide content of trigeminal neurons innervating the rat nasal epithelium.

Trigeminal ganglia provides sensory innervation to the rat nasal cavity. The purpose of this study was to identify the location and characterize the neuropeptide content of trigeminal neurons that project specifically to the rat nasal epithelium. The right nasal cavity was instilled with 4 microliters of rhodamine-labelled latex microspheres. Seven, 10 or 14 days after tracer instillation, both trigeminal ganglia were removed and prepared for substance P and calcitonin gene-related peptide immunocyto-chemistry. neurons labelled with microspheres were located in the trigeminal ganglia at the division of the ophthalmic and maxillary nerves and were only found on the side ipsilateral to the instillation. The percentage of labelled cell body profiles in the right trigeminal ganglia averaged 1.61 +/- .04% at seven days. 1.54 +/- .01% at 10 days, and 1.65 +/- .02% at 14 days after instillation. These values were not statistically different, but the fluorescence intensity in labelled neurons was increased after 14 days. The right trigeminal ganglia contained a mean of 166 +/- 13.81 labelled cell body profiles representing 1.60 +/- .09% of the total. Of the labelled profiles, 81.6 +/- 3.27% were immunoreactive for substance P and 35.2 +/- 4.00% for calcitonin gene-related peptide. Sections of nasal mucosa showed that the microspheres were localized only in the epithelial layer and did not enter the lamina propria indicating that the microsphere transport was confined to nerve fibres present in the epithelial layer. These studies have identified specific neurons in the trigeminal ganglia that project to the nasal epithelium. Most of the neurons retrogradely labelled from the nasal cavity contained substance P but some contained calcitonin gene-related peptide, suggesting that the nasal epithelium is predominantly targeted by substance P-containing neurons.

Animals↗
PubMed1997

Identification of the cellular source of laminin beta2 in adult and developing vertebrate retinae.

The interphotoreceptor matrix (IPM) is a specialized extracellular matrix that surrounds the inner and outer segments of photoreceptors. This matrix contains molecules that may be important in directing photoreceptor differentiation and survival. For example, one molecule that we have previously identified as a component of the IPM, laminin beta2 (formerly known as s-laminin), is implicated in the differentiation of rod photoreceptor cells. Developmentally, laminin beta2 is present before rod birth in a position that is consistent with a role in directing rod differentiation; it is found, in both the rat and skate, in the ventricular space that ultimately becomes the IPM. In this study, we identify the source of laminin beta2 in the adult and developing retina. Both immunohistochemistry in the adult skate retina and in situ hybridizations in the adult rat retina reveal that laminin beta2 is produced by Müller cells. In addition, in the skate but not the rat retina, retinal pigment epithelial cells may be an alternative source of laminin beta2. During development, however, laminin beta2 is present before the birth of Müller glial cells; at this stage of development, laminin beta2 RNA is present within the neuroepithelial layer in a pattern that is consistent with its production by neuroepithelial cells.

Animals↗
PubMed1997

Beta 2 laminins modulate neuronal phenotype in the rat retina.

The production of cell types in the vertebrate retina follows a stereotyped time course. We have focused on a component of the extracellular matrix that may guide this schedule: the laminin beta 2 chain. Here, we have asked directly whether heterotrimeric laminins containing the laminin beta 2 chain can promote the production of presumptive rod photoreceptors ("rods") and have correlated changes in rod production with changes in the production of other cell types. In cultures in which few rods, but many Müller and bipolar cells, are produced, the production of rods can be enhanced sixfold and that of bipolar cells can be reduced by 66%, by exposing cells to a laminin beta 2-rich matrix. Substitution of a laminin beta 2-depleted matrix (created with antisense RNA) returns the density of rods and bipolar cells to control levels. These linked alterations in phenotype expression suggest that laminins may control the choice between rod photoreceptor and rod bipolar cell fates.

Animals↗