Biomedical subjects

N Mizuno

Publications and source records attributed to N Mizuno.

At least 145 records · Page 8Linked to original sources

PubMed1995

Hyperresponse in calcium-induced insulin release from electrically permeabilized pancreatic islets of diabetics GK rats and its defective augmentation by glucose.

In spontaneously diabetic GK rats, insulin secretion from pancreatic beta cells in response to glucose is selectively impaired, probably due to deficient intracellular metabolism of glucose and impaired closure of KATP channels during glucose stimulation. By using electrically permeabilized islets of GK rats, we explored the functional modulations in exocytotic steps distal to the rise in [Ca2+]i in the diabetic condition. At 30 nmol/l Ca2+ (basal conditions) insulin release was similar between GK and non-diabetic control Wistar rats. In response to 3.0 mumol/l Ca2+ (maximum stimulatory conditions), insulin release was significantly augmented in permeabilized GK islets (p < 0.01). Raising glucose concentrations from 2.8 to 16.7 mmol/l further augmented insulin release induced by 3.0 mumol/l Ca2+ from permeabilized control islets (p < 0.001), but had no effect on that from permeabilized GK islets. The stimulatory effect of glucose on insulin release from permeabilized control islets was partly inhibited by 2,4-dinitrophenol, an inhibitor of mitochondrial oxidative phosphorylation (p < 0.01). The hyperresponse to Ca2+ in GK islets may play a physiologically compensatory role on the putative functional impairment both in [Ca2+]i rise and energy state in response to glucose in diabetic beta cells, and may explain the relative preservation of insulin release induced by non-glucose depolarizing stimuli, such as arginine, from pancreatic islets in non-insulin-dependent diabetes mellitus.

2,4-Dinitrophenol↗

PubMed1995

Colocalization of vasoactive intestinal polypeptide and nitric oxide in penis-innervating neurons in the major pelvic ganglion of the rat.

By using a combination of fluorescent retrograde labeling and double immunofluorescence histochemistry, the present study revealed in the rat that the vast majority of major pelvic ganglion neurons innervating penile erectile tissue contained both vasoactive intestinal polypeptide (VIP) and nitric oxide synthase. The result suggests that VIP and nitric oxide may exert a cooperative action in penile erection.

Amino Acid Oxidoreductases↗

PubMed1995

An anterograde-retrograde labeling study of the carotid sinus nerve of the Japanese monkey (Macaca fuscata).

The sites of origin and termination of efferent and afferent fibers in the carotid sinus nerve (CSN) were investigated in the Japanese monkey. After application of a mixture of horseradish peroxidase (HRP) and wheat germ aggulutinin-conjugated HRP to the central cut end of the CSN, sensory ganglion neurons were labeled in the jugular ganglion of the vagus nerve, as well as in the superior and petrosal ganglia of the glossopharyngeal nerve. Many sympathetic ganglion neurons were also labeled retrogradely in the superior cervical ganglion. In the brain, many labeled terminals were seen ipsilaterally in the lateral division of the nucleus of the solitary tract (NST). A few neuronal cell bodies were also labeled ipsilaterally in a reticular region dorsomedial to the caudal one-third of the facial nucleus. The results indicate that the CSN of the Japanese monkey is composed mainly of afferent fibers terminating in the NST, that the afferent fibers in the CSN originate not only from the superior and petrosal ganglia of the glossopharyngeal nerve but also from the jugular ganglion of the vagus nerve, and that efferent fibers contained in the CSN arise from the medullary reticular formation and superior cervical ganglion.

Animals↗

PubMed1995

Trigeminoparabrachial projection neurons showing substance P receptor-like immunoreactivity in the rat.

By means of substance P receptor (SPR) immunofluorescence histochemistry combined with Fluoro-Gold fluorescent retrograde labeling, SPR-like immunoreactive neurons in the caudal subnucleus of the spinal trigeminal nucleus of the rat were observed to send their axons to the nucleus of Kölliker-Fuse and ventrolateral part of the lateral parabrachial nucleus bilaterally with a clear ipsilateral dominance. These neurons were distributed mainly in lamina I, and additionally in lamina III.

Animals↗

PubMed1995

Effects of the ester moiety on stereoselective hydrolysis of several propranolol prodrugs in rat tissues.

The stereochemical characteristics of the hydrolysis of several ester-type prodrugs of propranolol, O-acetyl, O-propionyl, O-butyryl, O-pivaloyl and succinyl esters, were studied in phosphate buffer (pH 7.4), rat plasma and rat tissue homogenates. In phosphate buffer, no differences were observed in the hydrolysis rate between the esters of (R)- and (S)-propranolol. The effects of the ester moieties on the hydrolysis rate in phosphate buffer were in the following order: acetate > propionate > butyrate > succinate > pivalate. In rat plasma and tissue homogenates, the hydrolysis of the esters was accelerated, and stereoselective hydrolysis was observed. In plasma, the hydrolysis of the (R)-isomer was faster than that of the (S)-isomer except for the succinate ester. On the other hand, in the liver and intestine homogenates, the (S)-isomer was hydrolyzed faster than the (R)-isomer except for the succinate and pivalate esters in the liver homogenate. Also, the ratio of the hydrolysis rates (S/R) changed with the type of prodrug. As the length of the alkyl chain of the ester increased, the S/R ratio approached unity in liver and intestine homogenates but stayed almost constant in plasma. For the pivalate ester, stereoselective hydrolysis was observed in plasma and intestine homogenate but not in liver homogenate. The stereoselective hydrolysis of the succinate ester was observed only in intestine homogenate, but the S/R ratio was almost 1 in plasma, liver and intestine homogenates. No interconversion between (R)- and (S)-isomer was observed during the hydrolysis of any of the ester prodrugs. These results indicate that hydrolysis of ester-type prodrugs of propranolol occurs stereoselectively in rat tissues, and that its selectivity is dependent on the kind of tissue and prodrug.

Adrenergic beta-Antagonists↗

PubMed1995

Effect of vehicles on diclofenac permeation across excised rat skin.

The in vitro percutaneous permeation of diclofenac from various vehicles was examined using rat abdominal skin as a model membrane. The oleaginous vehicles used in this study consisted of three components: i.e. fatty acid, fatty acid ester and nonpolar oil. The solubilities of sodium diclofenac in formulated vehicles were above 0.2 M. The effect of each oleaginous component in the vehicle on the permeation of diclofenac across the skin was in the following order: oleic acid > isostearic acid, diisopropyl adipate = diethyl sebacate > Panasate 875 and squalane > liquid paraffin. To clarify the reason for the differences in permeation among the fatty acid esters, the release of diclofenac through either porous or lipoidal membranes from these vehicles in vitro and the solubility of sodium diclofenac in the vehicles were studied. However, no relationship was observed between the release rate or solubility and skin permeability. The skin permeation of diclofenac increased following pretreatment with diisopropyl adipate or diethyl sebacate, but not with middle chain triglyceride (Panasate 875). These results suggested that the main reason may be the enhancement effect of fatty acid esters. Emulsions and creams containing 3% sodium diclofenac were prepared using the above oleaginous vehicles. A large flux and short lag time were observed in these preparations compared with an aqueous suspension of sodium diclofenac. The incorporation of urea significantly enhanced the permeation of diclofenac from these preparations. These results suggest that the emulsion and cream prepared in this study are useful for development for practical purposes.

Animals↗

PubMed1995

A monitor of secretion from single pancreatic beta-cells.

ATP is known to be coreleased with insulin from pancreatic beta-cells. To monitor insulin secretion from single beta-cells, a single beta-cell was surrounded in culture by Fura 2-loaded calf pulmonary artery endothelium (CPAE) cells, which can detect the ATP. CPAE cells did not respond with an elevation in cytoplasmic calcium concentration ([Ca2+]i) to either tolbutamide (100 mumol/l) or kainate (1 mmol/l) but did respond with an elevation in [Ca2+]i to ATP (0.1-10 mumol/l) without desensitization and in a dose-dependent manner. A brief application of tolbutamide (10 mumol/l) increased [Ca2+]i in both the beta-cell and the adjacent CPAE cells in co-culture. Suramin (100 mumol/l), an ATP-receptor blocker, inhibited the tolbutamide-induced elevation in [Ca2+]i in the CPAE cells but did not inhibit the elevation in [Ca2+]i in the beta-cell, confirming that the insulin secretagogue-induced Ca2+ response in CPAE cells in co-culture is mediated by ATP released from the beta-cell. When co-culture of the beta-cell and CPAE cells was stimulated by kainate (1 mmol/l) and then tolbutamide (10 mumol/l), the CPAE cells showed elevations in [Ca2+]i in response to kainate and tolbutamide during elevation in [Ca2+]i in the beta-cell. This strongly suggests that insulin secretion as well as an increase in [Ca2+]i in response to different agents, i.e., kainate and tolbutamide, occurs in a single beta-cell. A long exposure of tolbutamide (100 mumol/l, 4 min) resulted in a long-lasting elevation in [Ca2+]i in the beta-cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1995

Glutaminase-positive and glutaminase-negative pyramidal cells in layer VI of the primary motor and somatosensory cortices: a combined analysis by intracellular staining and immunocytochemistry in the rat.

Pyramidal neurons in layer VI of the primary motor and somatosensory cortices were examined by a combined method of intracellular recording, biocytin injection, and immunocytochemistry using in vitro slice preparations of rat brain immunofluorescence staining revealed that biocytin-injected pyramidal cells in layer VI were separated into glutaminase (PAG)-immunopositive and PAG-immunonegative cells. Although the two groups of pyramidal cells showed no statistically significant differences in passive membrane properties and spike characteristics, a clear difference was found in spike afterpotentials. Ten of 12 PAG-positive pyramidal cells showed no or a small fast afterhyperpolarization (fAHP), whereas 10 of 11 PAG-negative pyramidal cells displayed a large fAHP. Depolarizing afterpotentials were observed only in PAG-positive pyramidal cells than in PAG-negative cells. In contrast, the arborization of basal dendrites was more developed in PAG-positive pyramidal cells than in PAG-negative cells. The main axons of all the pyramidal cells entered the subcortical axons of all the pyramidal cells entered the subcortical white matter. The local axon collaterals of PAG-positive pyramidal cells were widely spread in the horizontal direction, whereas those of PAG-negative cells were distributed vertically along the dendritic tree. Since PAG is considered to be a marker of glutamatergic neurons in the cerebral cortex, the present results indicate that layer VI pyramidal cells are separated into glutamatergic and nonglutamatergic neurons that have different electrical properties and input-output organizations. Thus, cortical outputs from layer VI are suggested to use at least two distinct systems.

Animals↗

PubMed1994

Induction of c-fos-like protein in the spinoparabrachial tract-neurons locating within the sacral parasympathetic nucleus in the rat.

Immunoreactivity against c-fos-like protein (FOS) was induced in many neuronal cell bodies within the sacral parasympathetic nucleus (SPN) in urethane-anesthetized rats by chemical irritation of the urinary bladder with formalin. More than half of these FOS-immunoreactive neurons were retrogradely labeled with Fluoro-Gold injected into the lateral parabrachial nucleus (PBN1). The results indicate that some neurons within the SPN may transmit noxious information from the urinary bladder to the PBN1.

Animals↗

PubMed1994

Immunohistochemical localization of substance P receptor in the central nervous system of the adult rat.

In an attempt to reveal the function sites of substance P (SP) in the central nervous system (CNS), the distribution of SP receptor (SPR) was immunocytochemically investigated in adult rat and compared with that of SP-positive fibers. SPR-like immunoreactivity (LI) was mostly localized to neuronal cell bodies and dendrites. Neurons with intense SPR-LI were distributed densely in the cortical amygdaloid nucleus, hilus of the dentate gyrus, locus ceruleus, rostral half of the ambiguus nucleus, and intermediolateral nucleus of the thoracic cord; moderately in the caudatoputamen, nucleus accumbens, olfactory tubercle, median, pontine, and magnus raphe nuclei, laminae I and III of the caudal subnucleus of the spinal trigeminal nucleus, and lamina I of the spinal cord; and sparsely in the cerebral cortex, basal nucleus of Meynert, claustrum, gigantocellular reticular nucleus, and lobules IX and X of the cerebellar vermis. Neurons with weak to moderate SPR-LI were distributed more widely throughout the CNS. The regional patterns of distribution of SPR-LI were not necessarily the same as those of SP-positive fibers. The entopedunucular nucleus, substantia nigra, and lateral part of the interpeduncular nucleus showed intense SP-LI but displayed almost no SPR-LI. Conversely, the hilus of the dentate gyrus, anterodorsal thalamic nucleus, central nucleus of the inferior colliculus, and dorsal tegmental nucleus showed intense to moderate SPR-LI but contained few axons with SP-LI. These findings confirmed the presence of the "mismatch" problem between SP and SPR localizations. However, the distribution of SPR-LI was quite consistent with that of the SP-binding activity, which has been studied via autoradiography. This indicates that the sites of SPR-LI revealed in the present study represent most, if not all, sites of SP-binding activity.

Animals↗

PubMed1994

Differential expression of five N-methyl-D-aspartate receptor subunit mRNAs in the cerebellum of developing and adult rats.

Five N-methyl-D-aspartate (NMDA) receptor subunits have been identified thus far: NR1, NR2A, NR2B, NR2C, and NR2D. Here, we have analyzed the expression patterns of mRNAs for the NMDA receptor subunits in the developing and adult rats by in situ hybridization. The developmental changes of the expression patterns were most salient in the cerebellum. In the external granular layer, hybridization signals of mRNAs for NR1, NR2A, NR2B, and NR2C appeared by postnatal day 3, but no NR2D mRNA was expressed at any developmental stage examined. The NR1 mRNA was expressed in all cerebellar neurons at all developmental stage examined. The NR1 mRNA was expressed in all cerebellar neurons at all developmental stages examined. The signals for the NR2A mRNA appeared in Purkinje cells and granule cells during the second postnatal week. The signals for the NR2B mRNA in granule cells were seen transiently during the first 2 weeks after birth. The signals for NR2C mRNA appeared in granule cells and glial cells during the second postnatal week. The signals for NR2D mRNA appeared transiently in Purkinje cells during the first 8 postnatal days; in adult rats, these were seen in stellate and Golgi cells. In the cerebellar nuclei, mRNAs for NR1, NR2A, NR2B, and NR2D were more or less expressed on postnatal day 0, while expression signals for the NR2C mRNA were first detected in postnatal day 14. Thus, the most conspicuous changes of expression patterns were observed in the cerebellar cortex during the first 2 weeks after birth, when development and maturation of the cerebellum proceed most rapidly.

Animals↗

PubMed1994

Single retinal ganglion cells projecting bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals in the cat.

In most mammals with frontalized eyes, retinal ganglion cells in the nasal or temporal retina send their axons to the contralateral or ipsilateral half, respectively, of the brain. Previous studies in the cat, however, have indicated a retinal region of "nasotemporal overlap" from which arise the retinal projections to both the contralateral and ipsilateral halves of the brain. The present study thus examined in the cat whether any retinal ganglion cells give rise to bifurcating axons that innervate both halves of the brain. By employing fluorescent retrograde double labeling, we investigated whether or not single retinal ganglion cells project bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals. After Fast Blue was injected into the lateral geniculate nucleus on one side and Diamidino Yellow was injected contralaterally into the lateral geniculate nucleus, 100-200 ganglion cells in each retina were double labeled with both tracers. These double-labeled cells were distributed primarily in the temporal retina, including the region around the vertical meridian and, additionally, in the nasal retina. About 60-80% of the double-labeled cells had large cell bodies (more than 25 microns in diameter), and the others had medium-sized ones (15-25 microns in diameter). The pattern of distribution of double-labeled cells, which was observed after the combined injection into both superior colliculi, was similar to that seen after the combined injection into both lateral geniculate nuclei; more than 90% of double-labeled cells, however, were large.(ABSTRACT TRUNCATED AT 250 WORDS)

Amidines↗

PubMed1994

Functional neuronal ionotropic glutamate receptors are expressed in the non-neuronal cell line MIN6.

We report that a non-neuronal cell line, MIN6, derived from insulin-secreting pancreatic beta-cells, naturally expresses functional ionotropic glutamate receptors. Electrophysiological recordings show that kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), and N-methyl-D-aspartate (NMDA) depolarize single MIN6 cells and evoke inward ionic currents. These agents also increase the intracellular calcium concentration in MIN6 cells. Furthermore, insulin secretion from MIN6 cells is stimulated by kainate, AMPA, and NMDA. The presence of AMPA/kainate and NMDA receptor subtypes is confirmed by reverse transcriptase-polymerase chain reaction. These results demonstrate that ionotropic glutamate receptors with properties similar to those in neuronal cells are expressed in a non-neuronal cell line, MIN6. Thus, MIN6 provides a useful and valuable model system for biochemical, pharmacological, and physiological studies of ionotropic glutamate receptors.

Animals↗

PubMed1994

Developmentally regulated postsynaptic localization of a metabotropic glutamate receptor in rat rod bipolar cells.

The retinal bipolar cell receiving glutamate transmission from photoreceptors mediates a key process in segregating visual signals into ON center and OFF center pathways. This transmission involves a G protein-coupled metabotropic glutamate receptor (mGluR). Immunocytochemical and immunoelectron microscopic studies indicate that restricted localization of a specific mGluR subtype, mGluR6, at the postsynaptic site of the rat rod bipolar cell. This specialization is developmentally regulated: mGluR6 is initially distributed in both the soma and dendrites and is finally concentrated on the postsynaptic site. The mGluR6 localization is reversed when photoreceptors degenerate in the mutant rat with retinal dystrophy. Evidence is thus presented indicating specialized, developmentally regulated receptor distribution in the central nervous system and the crucial role of mGluR6 in photoreceptor-bipolar cell synaptic transmission.

Amino Acid Sequence↗

PubMed1994

Expression of mRNAs of L-AP4-sensitive metabotropic glutamate receptors (mGluR4, mGluR6, mGluR7) in the rat retina.

Expression patterns of mRNAs of L-AP4-sensitive metabotropic glutamate receptors (mGluR4, mGluR6, mGluR7) in the rat retina were examined by northern blot analysis and in situ hybridization histochemistry. Expression patterns of mGluR4 and mGluR7 mRNAs were quite different from that of mGluR6 mRNA which was expressed at the outer part of the inner nuclear layer. The mGluR4 mRNA was expressed on the cell bodies of the ganglion cells, but not in the inner or outer nuclear layer. The expression of mGluR7 mRNA was observed throughout the entire region of the inner nuclear layer and on the cell bodies of the ganglion cells.

Aminobutyrates↗

PubMed1994

Direct projections from the entopeduncular nucleus to the lower brainstem in the rat.

The present study reports the existence of projection fibers from the entopeduncular nucleus to the superior colliculus and lateral parts of the pontobulbar tegmental regions (so-called lateral tegmental field) in the rat, suggesting that the entopeduncular nucleus may control eye-head and orofacial movements via these projection fibers. The anterograde axonal tracing with Phaseolus vulgaris-leucoagglutinin has revealed that the entopedunculotectal fibers terminate, bilaterally, with an ipsilateral predominance, in the deep layers of the superior colliculus through its rostral one-third level and that the entopedunculotegmental fibers terminate, bilaterally, with an ipsilateral predominance, in the parabrachial area, reticular formation surrounding the trigeminal motor nucleus, and parvicellular, dorsal, and ventral reticular nuclei. The cells of origin of the entopedunculotectal and entopedunculotegmental projections have been identified by retrograde axonal tracing with Fluoro-Gold and cholera toxin B subunit. The entopedunculotectal or entopedunculotegmental fibers originate, respectively, from the dorsal or ventral part of the entopeduncular nucleus. Additionally, a series of fluorescent retrograde double-labeling experiments with Fast Blue and Diamidino Yellow have indicated that single entopeduncular nucleus neurons projecting to the superior colliculus or lateral tegmental field often send their axon collaterals to the lateral habenular nucleus. The entopedunculotectal fibers are assumed to control head movements, which may be provoked via the tectospinal fibers, and further to participate in eye movements as the nigrotectal fibers that have been known to arise from the substantia nigra pars reticulata to end in the deep layers of the superior colliculus primarily through its caudal two-thirds level. The entopedunculotegmental fibers are presumed to be involved in control of orofacial movements, because the sites of termination of the entopedunculotegmental fibers correspond well with the reported areas of distribution of premotor interneurons for the trigeminal motor, facial, and hypoglossal nuclei.

Amidines↗

PubMed1994

Cloning and functional characterization of a third pituitary adenylate cyclase-activating polypeptide receptor subtype expressed in insulin-secreting cells.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide belonging to the vasoactive intestinal polypeptide/glucagon/secretin family. It is widely distributed in the body, and a variety of biological actions have been reported. PACAP exerts its biological effects by binding to specific receptors that are coupled to GTP-binding proteins. Recent studies have shown that there is a family of PACAP receptors (PACAPRs), and two members of this family have been identified. We report here the cloning, functional expression, and tissue distribution of a third PACAPR subtype, designated PACAPR-3. The cDNA encoding PACAPR-3 has been isolated from a mouse insulin-secreting beta-cell line MIN6 cDNA library. Mouse PACAPR-3 is a protein of 437 amino acids that has 50% and 51% identity with rat PACAP type I and type II receptors, respectively. Expression of recombinant mouse PACAPR-3 in mammalian cells shows that it binds to vasoactive intestinal polypeptide as well as PACAP-38 and -27, with a slightly higher affinity for PACAP-38, and is positively coupled to adenylate cyclase. The expression of PACAPR-3 in Xenopus oocytes indicates that calcium-activated chloride currents are evoked by PACAP and vasoactive intestinal polypeptide, suggesting that PACAPR-3 can also be coupled to phospholipase C. RNA blot analysis studies reveal that PACAPR-3 mRNA is expressed at high levels in MIN6, at moderate levels in pancreatic islets and other insulin-secreting cell lines, HIT-T15 and RINm5F, as well as in the lung, brain, stomach, and colon, and at low levels in the heart. Furthermore, insulin secretion from MIN6 cells is significantly stimulated by PACAP-38. These results suggest that the diverse biological effects of PACAP are mediated by a family of structurally related proteins and that PACAPR-3 participates in the regulation of insulin secretion.

Amino Acid Sequence↗

PubMed1994

Distribution of primary afferent fibers projecting from hindlimb cutaneous nerves to the medulla oblongata in the cat and rat.

The dorsal column nuclear complex, one of the most important relays for tactile perception, has well been known to be somatotopically organized. Topographical arrangements of terminal sites of individual cutaneous nerves within the dorsal column nuclei, however, have not been examined systematically, although many studies have been done upon primary afferents to the medulla oblongata, including the dorsal column nuclear complex. Thus, in the present study, distribution of primary afferent fibers projecting from the hindlimb cutaneous nerves to the medulla oblongata was examined in the cat and rat by means of the transganglionic transport method with horseradish peroxidase. Cutaneous primary afferent fibers projecting from the hindlimb to the medulla oblongata were distributed mainly in the ipsilateral gracile nucleus. Terminal labeling in the gracile nucleus was seen at all rostrocaudal levels of the nucleus, occasionally including the nuclear part straddling the midline (the median or accessory nucleus). The labeled axon terminals in the gracile nucleus were more densely distributed in the middle and caudal parts of the nucleus than in the rostral part. Although the fields of termination of the hindlimb cutaneous nerves overlapped in the gracile nucleus, the foci of the terminal labeling of the nerves innervating the distal parts of the hindlimb were located more medially or dorsomedially than those of the nerves innervating the proximal parts. Terminal labeling was further found in a small zone immediately medial to the rostromedial border of the external cuneate nucleus. This hitherto undescribed zone (U zone) contained a small cluster of medium-sized neurons in the cat. Although no particular cell cluster was found in the U zone of the rat, convergence of the primary afferent fibers of the cutaneous nerve from the hindlimb appeared to occur as in the U zone of the cat.

Animals↗