Search PubMed⌕ Search

Biomedical subjects

M R Quinn

Publications and source records attributed to M R Quinn.

At least 37 records · Page 2Linked to original sources
PubMed1986

Differentiation of a cell line from olfactory epithelium is induced by dibutyryladenosine 3',5'-cyclic monophosphate and 12-O-tetradecanoylphorbol-13-acetate.

Olfactory receptor neurons undergo continual replacement with new cells differentiating from a population of basal cells located in the olfactory epithelium. We have previously described the isolation of a cell line from murine olfactory epithelium (MOE CL1) which is now shown to be sensitive to two differentiation promoting agents, dibutyryladenosine 3',5'-cyclic monophosphate (db-cAMP) and 12-O-tetradecanoylphorbol-13-acetate (TPA). Cells grown in the presence of db-cAMP or TPA, after a lag phase of 72-96 h, became bipolar, with long neurite-like processes. Cells conditioned for at least one passage in db-cAMP or TPA, or cells exposed to a mixture of db-cAMP and TPA, attained a bipolar morphology within 24 h. Cultures grown with db-cAMP, TPA or db-cAMP + TPA showed significant increases in the percentage of process-bearing cells. An increase in population doubling time and decrease in saturation density were also observed in cultures exposed to db-cAMP. Cells exposed to TPA continued to divide at the same rate as control cells, while those treated with db-cAMP + TPA underwent terminal differentiation. Peripheral-type benzodiazepine binding sites, which within the olfactory epithelium are localized on the receptor neurons, were present in homogenate membranes of undifferentiated cells. Cells differentiated by exposure to db-cAMP + TPA for 7 days showed a 65% increase in the density (Bmax) of peripheral-type benzodiazepine binding sites. Undifferentiated cells in control cultures showed no spontaneous changes in membrane potential or regenerative responses during current injection. Small, bipolar cells in morphologically differentiated cultures, however, were capable of generating several types of spontaneous changes in membrane potential including slow, regular oscillations; irregular, slow and fast depolarizations; and trains of action potentials.

Action Potentials↗
PubMed1986

Chloride-dependent binding sites for L-[3H]glutamate on dendrodendritic synaptosomal membranes of rat olfactory bulb.

Dendrodendritic synapses occur between granule cell dendrites and secondary dendrites of mitral cells within the olfactory bulb and are attainable in a subcellular fraction (DDS). Since the mitral cells are thought to utilize an excitatory amino acid as a neurotransmitter, we determined the pharmacologic specificity of Na+-independent L-[3H]glutamate binding to fresh membranes of DDS in 50 mM Tris-HCl, pH 7.1. Binding of L-glutamate to membranes of DDS was specific, Cl(-)-dependent, and saturable. Scatchard plots were analyzed by nonlinear regression analyses using the computer program LIGAND, and the data was best-fitted to a one-site model with KD of 0.56 +/- 0.04 microM and an apparent Bmax of 48 +/- 5 pmol/mg protein. Hill plots also indicated the presence of one site and no cooperativity (nH = 0.99 +/- 0.03). However, the relative effectiveness of several compounds in inhibiting L-glutamate binding to membranes of DDS clearly demonstrated the presence of more than one site. Electrophysiological studies suggest that 2-amino-4-phosphonobutyrate (APB) is a potent antagonist of evoked responses elicited by stimulation of mitral cell axons and that quisqualate is a potent agonist; both of these compounds were highly effective inhibitors of L-glutamate binding to DDS membranes. APB displaced about 70% of the sites labeled with 200 nM L-glutamate with a KI of 1.6 microM, whereas quisqualate inhibition of L-glutamate binding yielded a line that was curvilinear in the Scatchard plot and was resolved into two sites of relatively high affinity (KI values of 0.02 and 0.65 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Aminobutyrates↗
PubMed1984

Decreased high-affinity binding of [3H]muscimol to cerebral synaptic membranes of scrapie-infected mice.

Scrapie is a transmissible disease that results in progressive degeneration of the central nervous system and death. Although scrapie has been studied histopathologically, relatively little is known concerning neurotransmitter alterations. Specific [3H]muscimol binding to whole brain crude synaptic membranes (CSM) from mice clinically affected with scrapie was significantly (p less than 0.01) reduced, to approximately 73% of that of the controls. Of the brain regions examined, binding to only cerebral CSM was significantly (p less than 0.0001) decreased. Scatchard analyses of saturation curves revealed that the high-affinity (KD = 8 +/- 3 nM) site for muscimol was abolished in cerebral CSM from scrapie-infected mice, while the low-affinity site was unaffected. Binding of [3H]flunitrazepam to cerebral CSM was unaffected by scrapie and was stimulated by GABA to the same extent in both scrapie and control mice. These results suggest that scrapie agent 139A in C57BL/6J mice manifests a portion of its CNS pathology via a high-affinity GABA binding site that is unassociated with the benzodiazepine receptor.

Animals↗
PubMed1984

Effects of dietary salt, fat, and carbohydrate on fluid and salt consumption of rats.

Studies were conducted to investigate the influence of dietary sodium chloride (NaCl), fat, and carbohydrate on NaCl preferences of rats. Both long-term (48 hr) and short-term (20 min) two-bottle preference tests were used. Rats were fed either a basal salt (1.17%) diet or high salt (8.37 to 8.59%) diets in which the level of sucrose was modified by substitution with either corn oil or cornstarch. Water and NaCl consumption was measured in 48-hr two-bottle preference tests using various concentrations (0.005 to 0.5 M) of NaCl paired with water. The results of these studies suggest that changes in fluid consumption were accounted for by an increase in water consumption which was inversely related to the sucrose to starch ratio and directly related to the NaCl content of the diets. A reduction in NaCl consumption was observed only during the short-term (20 min) tests.

Animals↗
PubMed1982

High specific binding of [3H]GABA and [3H]muscimol to membranes from dendrodendritic synaptosomes of the rat olfactory bulb.

Olfactory bulbs contain dendrodendritic synapses, which occur between granule cells and mitral cells, and gamma-aminobutyric acid (GABA) is thought to act as an inhibitory neurotransmitter at these synapses. Synaptosomes derived from the dendrodendritic synapses of the olfactory bulb were shown previously to contain considerable L-glutamate decarboxylase activity. The subcellular distribution and binding parameters of [3H]GABA and [3H]muscimol binding sites have now been determined in the rat olfactory bulb. Of all fractions examined, crude synaptic membranes (CSM) prepared from the dendrodendritic synaptosomes were shown to have the highest specific binding activity and accounted for nearly all of the total binding activity for both ligands. The specific binding activities for [3H]GABA and for [3H]muscimol were greatly increased after treating the CSM with 0.05% Triton X-100. Binding was shown to be Na+-independent, reversible, pharmacologically specific, and saturable. High- and low-affinity sites were detected for both ligands, and both classes of sites had appreciably lower KD values for muscimol (KD1 = 3.1 nM, KD2 = 25.1 nM) than for GABA (KD1 = 8.6 nM; KD2 = 63.7 nM). The amounts of the high-affinity binding sites for muscimol and GABA were similar (Bmax = 1.7 and 1.5 pmol/mg protein, respectively). The results of the present experiments indicate that the GABA and muscimol binding sites represent the GABA postsynaptic receptor, presumably on mitral cell dendrites, and provide further support for the hypothesis that GABA functions as a neurotransmitter at the dendrodendritic synapses in the olfactory bulb.

Animals↗
PubMed1981

Diet-induced changes in NaCl preference and blood pressure in rats.

The interrelationship between diet, blood pressure and the acceptability of salt solutions was examined. Sprague-Dawley rats were fed high carbohydrate (5% corn oil), all unsaturated fat (20% corn oil) or all saturated fat (20% coconut oil) diets containing either basal (0.15% NaCl) or high (8.0% NaCl) levels of salt. Systolic blood pressure was determined indirectly using an electro-sphygmomanometer. Percent acceptance was determined using a two-bottle preference test. Results from this experiment suggest that postingestional feedback mechanisms rather than blood pressure play an important role in determining the acceptability of salt solutions by the Sprague-Dawley rat.

Animals↗
PubMed1980

Subcellular distribution of glutamate decarboxylase in rat olfactory bulb: high content in dendrodendritic synaptosomes.

The olfactory bulbs in the CNS contain reciprocal dendrodendritic synapses between the granule cells and the secondary dendrites of mitral cells. Based on pharmacologic and electrophysiologic evidence, these synapses are believed to utilize GABA as an inhibitory neurotransmitter. A dendrodendritic synaptosomal fraction has been isolated from rat olfactory bulbs. The upper portion (PB) of the crude nuclear pellet contains 30-40% of the GAD (glutamate decarboxylase) activity of the olfactory bulb homogenate. When PB is purified on a discontinuous sucrose density gradient, 78-85% of the GAD activity is localized to the region containing the dendrodendritic synaptosomes, which were identified by transmission electron microscopy. The presence of a substantial proportion of GAD, the enzyme that catalyzes synthesis of GABA, in the DDS provides neurochemical support for the hypothesis that GABA functions at the reciprocal dendrodendritic synapses in the olfactory bulb.

Animals↗