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Biomedical subjects

E Shen

Publications and source records attributed to E Shen.

At least 19 recordsLinked to original sources
PubMed2001

Microphase separation in bioerodible copolymers for drug delivery.

This research examines the microstructure of bioerodible polyanhydrides with an eye towards precise design of drug delivery devices. Our main hypothesis is that the bioerodible copolymer poly(1,6-bis-p-carboxyphenoxyhexane-co-sebacic anhydride) (CPH : SA) undergoes micro-phase separation at certain copolymer compositions due to differences in relative hydrophobicity of the co-monomers, resulting in thermodynamic partitioning of drugs incorporated into these copolymers. We investigate the thermal properties, degree of crystallinity, and surface microstructure of several compositions of CPH : SA using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and atomic force microscopy (AFM). We observe that the degree of crystallinity decreases, while the crystal lamellar thickness increases with CPH content. Phase-imaging using AFM indicates the presence of micro-domains in 20 : 80 and 80 : 20 CPH : SA, while poly(SA) and 50 : 50 CPH : SA show no micro-phase separation. Finally, drug-polymer interactions are studied by loading the polymers with different amounts of brilliant blue (hydrophilic) and p-nitroaniline (hydrophobic). DSC and WAXD analysis shows that loading hydrophobic drugs into relatively hydrophobic polymers (poly(SA)) lowers melting point that becomes more pronounced with increased drug loading.

Biodegradation, Environmental↗
PubMed1998

Intracerebroventricularly injected L-arginine-induced vasopressin release is mediated by cGMP in rats.

AIM: To study the possible role of cGMP in the effect of L-arginine-induced arginine-vasopressin (AVP) release. METHODS: In anesthetized rats, saline, L-arginine, 8-Br-cGMP, L-arginine + methylene blue (an inhibitor of guanylyl cyclase) were injected intracerebroventricularly (icv) and the plasma vasopressin level was detected with radioimmunoassay. RESULTS: Both 8-Br-cGMP 2.53 g.L-1 and L-arginine 100 g.L-1 increased plasma AVP level [from (2.6 +/- 0.3) to (6.6 +/- 0.4) ng.L-1, and from (3.2 +/- 0.5) to (5.8 +/- 1.4) ng.L-1, respectively; P < 0.01] 5 min after the icv injection; methylene blue (3.74 g.L-1) + L-arginine (100 g.L-1) did not change plasma AVP level. CONCLUSION: cGMP was a mediator of the effect of L-arginine-induced AVP release.

Animals↗
PubMed1997

Hrp1, a sequence-specific RNA-binding protein that shuttles between the nucleus and the cytoplasm, is required for mRNA 3'-end formation in yeast.

In yeast, four factors (CF I, CF II, PF I, and PAP) are required for accurate pre-mRNA cleavage and polyadenylation in vitro. CF I can be separated further into CF IA and CF IB. Here we show that CF IB is the 73-kD Hrp1 protein. Recombinant Hrp1p made in Escherichia coli provides full CF IB function in both cleavage and poly(A) addition assays. Consistent with the presence of two RRM-type motifs, Hrp1p can be UV cross-linked to RNA, and this specific interaction requires the (UA)6 polyadenylation efficiency element. Furthermore, the CF II factor enhances the binding of Hrp1p to the RNA precursor. A temperature-sensitive mutant in HRP1 yields mRNAs with shorter poly(A) tails when grown at the nonpermissive temperature. Genetic analyses indicate that Hrp1p interacts with Rna15p and Rna14p, two components of CF 1A. The HRP1 gene was originally isolated as a suppressor of a temperature-sensitive npl3 allele, a gene encoding a protein involved in mRNA export. Like Npl3p, Hrp1p shuttles between the nucleus and cytoplasm, providing a potential link between 3'-end processing and mRNA export from the nucleus.

Amino Acid Sequence↗
PubMed1997

[Characteristics of synaptic responses of motoneurons to ventrolateral funiculus stimulation in vitro].

By using the intracellular recording techniques, the electrophysiological characteristics of fast excitatory postsynaptic potentials (EPSP) evoked by ventrolateral funiculus (VLF) stimulation were analyzed in neonate rat motoneurons (MN) of spinal cord slices. The incidences of VLF-EPSPs was 80% (n = 28), among which 2 is preceded by inhibitory postsynaptic potential and 6 followed by slow EPSPs. Considering the distribution skewness of VLF-EPSP latency histogram, it was suggested that short- and long-latency EPSPs correspond respectively to mono- and poly-synaptic transmission respectively. The possible neurotransmitters mediating VLF-EPSPs were excitatory amino acids and non-NMDA receptors were critically involved in these synaptic transmissions, for both VLF-EPSP and glutamate-induced response were similarly and almost completely abolished by kynurenic acid and DNQX. Typical spatial summation of VLF-EPSPs and EPSPs evoked by ventral root stimulation were observed in the same recorded MNs. Most importantly, VLF-EPSPs were found to increase with hyperpolarizing and decreased with depolarizing the membrane, indicating that the descending fibers in the VLF may terminate on the soma or proximal dendrites of MNs, while the EPSPs evoked by the dorsal or ventral root stimulation were insensitive to membrane potential changes, indicating that the primary sensory afferents in the dorsal and ventral roots may contact the distal dendrites of the MNs. The results imply that the commanding signals conducting along the descending fibers in the VLF may directly modulate the MN's activities, whereas messages from the periphery may cause fine changes of the membrane potential subject to integration of the MNs.

Animals↗
PubMed1996

Nitric oxide stimulates both the basal and reflex release of vasopressin in anesthetized rats.

In view of the fact of the high concentration of neuronal nitric oxide synthase (NOS) in the supraoptic and paraventricular nuclei as well as the posterior pituitary, it has been supposed that nitric oxide (NO) may be involved in the regulation of hormone secretion from these sites. In the present study, L-arginine, the precursor of NO, and N(omega)-nitro-L-arginine methyl ester (L-NAME), the NOS inhibitor, were intracerebroventricularly (i.c.v.) administered into the pentobarbital anesthetized rats. The results showed that plasma arginine vasopressin (AVP) concentration increased after the injection of L-arginine (1.0 mg in microliters, i.c.v.) and decreased after the L-NAME (270 micrograms in 5 microliters, i.c.v.). The elevated plasma AVP level in response to short-term hypotension induced by intravenous infusion of sodium nitroprusside was also significantly reduced by i.c.v. administration of L-NAME. The results indicate that NO acts as a stimulating factor to both the basal and reflex release of AVP, opposing the view that NO plays an inhibitory role in the regulation of AVP secretion.

Anesthesia↗
PubMed1996

Genetic analysis of macromolecular transport across the nuclear envelope.

Numerous factors that promote movement of macromolecules in and out of the nucleus have now been identified. These include both soluble cytoplasmic and nucleoplasmic proteins and proteins of the nuclear pore complex (NPC). Genetic analyses of the nuclear transport process in the model organism, the budding yeast Saccharomyces cerevisiae, have revealed remarkable conservation of all of these factors. In addition, important clues as to how these factors promote the unique bidirectional movement across the NPC have emerged from studies of yeast. We summarize the characterization and genetic interactions of the soluble transport factors and present data to illustrate how genetic experiments can be used to further define the import and export pathways.

Biological Transport, Active↗
PubMed1995

Endogenous acetylcholine-induced Fos expression in magnocellular neurosecretory neurons in the supraoptic nucleus of the rat hypothalamus.

Induction of c-Fos expression in the supraoptic nucleus (SON) of the rat hypothalamus by endogenous acetylcholine was examined by microinfusion of neostigmine, a cholinesterase inhibitor, into the nucleus to locally accumulate the spontaneously released acetylcholine from the cholinergic terminals in the SON. Double staining of the neurosecretory neurons with antiserum to Fos, the protein product of c-Fos, and antiserum to vasopressin or oxytocin was performed. Fos-like immunoreactivity was manifested in both the vasopressin neurons and oxytocin neurons following the microinfusion of neostigmine. Microinfusion of nicotinic agonist, nicotine, to the SON also induced Fos expression, but mainly in the vasopressin neurons. Microinfusion of muscarinic agonist, carbachol, induced Fos expression as well, but mostly in the oxytocin neurons.

Acetylcholine↗
PubMed1995

[The distribution of tumor suppressor gene APC mRNA in guinea pig brain].

The APC gene was identified in 1991 at chromosome 5 q 21, which is responsible for the familial adenomatous polyposis (FAP). The gene has been classified as one of the tumor suppressor genes. The APC gene mutations were suggested to initiate sporadic as well as inherited colorectal neoplasia and to be related to mental retardation. The different forms of APC gene expression and their association to carcinogenesis have been carefully studied. However, the function of APC gene in the central nervous system has not been known. In this study, on the basis of the cDNA cloning of APC homologue in the guinea pig by Dr. Fan Meng, we rescued this fragment including the full length encoding region from plasmid pMe 18s and then subcloned it into the polylink site of the plasmid pBluscript KS. Both digoxigenin labeled sense and anti-sense RNA were synthesized by in vitro transcription. RNase protection assay and in situ hybridization enable us to examine the distribution of APC transcripts in guinea pig brain. Strong signals were detected in hippocampus. APC mRNA was mainly localized in the pyramidal neurons of CA 1, CA 3, as well as in the dentate granule cells; the cerebellum granular cells also showed strong staining; in the cerebrum, the parietal and primary olfactory cortex showed stronger signals than the frontal cortex; in olfactory bulb, positive cells with strong signals were observed: the brain stem showed a relatively weaker staining. Very similar expression pattern was also shown in embryonic guinea pig brain; except that the expression of APC gene in frontal cortex and olfactory bulb was stronger than that in adult animals. The results suggest that the APC transcripts in brain may play an important role during the early development of the central nervous system. Further study may enable us to take a deeper insight into the mechanism underlying inherited mental deficiency.

Animals↗
PubMed1994

Spontaneous and transmitter-induced rhythmic activity in neonatal rat sympathetic preganglionic neurons in vitro.

1. Intracellular recordings were made from sympathetic preganglionic neurons (SPNs) in transverse thoracolumbar spinal cord slices of 12- to 16-day-old rats. 2. A population of SPNs exhibited spontaneous, rhythmic activities that can be grouped into regular firing, bursting, or tonic oscillatory mode; the spikes were interspersed with subthreshold afterdepolarizing potentials (ADPs). 3. Spontaneous activities were not abolished by the excitatory amino acid antagonists 6-cyano-7-nitroquinoxoline-2,3-dione (CNQX, 10-20 microM) and D-2-amino-5-phosphonovaleric acid (APV, 10-20 microM) nor by the inhibitory amino acid antagonists bicuculline (10-30 microM) and strychnine (1 microM). 4. Stimulation of lateral funiculus elicited a CNQX-sensitive excitatory postsynaptic potential (EPSP) in the majority of spontaneously active SPNs tested. Moreover, rhythmic activities could be triggered by stimulation of lateral funiculus in 8 of the 80 otherwise quiescent SPNs tested. 5. Spontaneous spikes and ADPs were abolished by either Na(+)-free or tetrodotoxin (TTX, 0.5 microM)-containing Krebs solution. 6. The spontaneous spike afterhyperpolarization (AH) consisted of two components: a fast AHf and a slower AHS with a mean half decay time of 74.5 +/- 10.2 and 153.8 +/- 15.4 (SD) ms, respectively. 7. Superfusing the slices with a Ca(2+)-free Krebs solution or Krebs solution containing tetraethylammonium (TEA, 10-30 mM) preferentially blocked the AHS, thereby increasing the spontaneous discharge frequency. 8. Caffeine (3 mM) initially prolonged the AHS, thereby slowing the discharge frequency; the spontaneous discharges were eventually obliterated in the continuous presence of caffeine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Differential amino-terminal anchors for peptide binding to H-2M3a or H-2Kb and H-2Db.

We previously established that H-2M3a, the H chain of the maternally transmitted Ag (Mta), is specialized for presentation of N-formylated peptides. We hypothesized that the N-formyl group might prevent or limit the presentation of peptide Ag by H-2K and H-2D molecules. We now show by Mta- and OVA-specific CTL assays, peptide competition, and immunofluorescence analyses that N-formyl modification of four antigenic peptides inhibited their binding by either H-2Kb (OVAMet258-264, VSVNP52-59, and SVNP324-332) or H2-Db (SVNP324-332, and IVNP366-374). In contrast, N-formyl-OVAMet258-264 did bind to H2-M3a. The data imply lack of an N-formyl-binding pocket in classical MHC class I molecules and are consistent with a specialized role for H2-M3a in presentation of N-formylated peptides such as derived from intracellular prokaryotic parasites.

Alkylation↗
PubMed1993

Protein-DNA interactions at a dioxin-responsive enhancer. Analysis of six bona fide DNA-binding sites for the liganded Ah receptor.

The DNA upstream of the dioxin-inducible CYP1A1 gene contains six distinct sites to which the liganded Ah receptor binds in intact mouse hepatoma cells. Here, we have analyzed these six bona fide receptor-binding sites in order to study the relationships between DNA sequence, receptor binding, and dioxin responsiveness. Gel retardation studies reveal that the sites vary by about 7-fold in their relative affinities for the liganded receptor. Within this range, there is no obvious association between the strength of receptor binding and the degree of dioxin responsiveness, as measured in transfection experiments. In fact, one site binds the receptor well but fails to respond to dioxin. This observation implies that the receptor-DNA binding event per se is not sufficient to confer dioxin responsiveness upon a linked gene. Comparison of the DNA sequences of the six receptor-binding sites permits the derivation of a "functional consensus" recognition sequence, which is more extended in length than the "core"-binding sequence previously described. In corroboration of these results, protein-DNA cross-linking studies indicate that the liganded receptor contacts base pairs beyond the core sequence. Our observations also indicate that the liganded receptor can tolerate limited sequence heterogeneity at its DNA-binding site and still elicit a response to dioxin. This finding might reflect corresponding heterogeneity in the amino acid sequence of the liganded receptor's DNA-binding domain.

Animals↗
PubMed1993

Contralateral projections of thoracic respiratory interneurones in the cat.

1. Retrograde neuronal transport following small iontophoretic injections of horseradish peroxidase was used to investigate the location of neurones projecting to the thoracic ventral horn of the cat. 2. A concentration of labelled neurones was seen in the contralateral medial ventral horn at the immediately opposite rostrocaudal position. 3. The participation of respiratory interneurones in the projection was investigated by means of spike-triggered averaging, as follows. 4. Spike trains of single interneurones whose firing patterns were related to the central respiratory cycle were recorded extracellularly in the thoracic ventral horn of anaesthetized, paralysed cats. Firing patterns were defined by the construction of cycle-triggered histograms. 5. Spike-triggered averaging of the signal from an extracellular tungsten microelectrode in the opposite ventral horn was performed to test for the presence of axonal, terminal or focal synaptic potentials. 6. At least one of these types of potential was found for 34/55 units. Terminal potentials were found for thirty-one units, accompanied by focal synaptic potentials for twenty-seven units. Potentials were found for units with all types of firing patterns. Units whose activity elicited these potentials were generally located in the medial half of the ventral horn. 7. We conclude that at least 60% of the respiratory interneurones project to the immediately opposite ventral horn.

Action Potentials↗
PubMed1993

Putative transmitter systems of mammalian sympathetic preganglionic neurons.

The sympathetic nervous system evokes complex effects at multiple target organs in response to external, internal as well as mental stimuli. This output involves an interplay between the actions of a number of transmitters and modulators and at the postsynaptic and presynaptic sites of the autonomic ganglia and the sympathetic preganglionic neurons (SPNs). This review concerns particularly the SPNs of the cat and neonatal rat, studied by means of electrophysiological and immunohistochemical methods. Four types of responses may be elicited, the fast EPSP and IPSP, and their currents, and the slow EPSPs and IPSPs, and their currents. Glutamate and glycine appear to mediate the fast excitatory and inhibitory responses, respectively; peptides and amines seem to be responsible for generating the slow excitatory response, while the slow inhibitory response, found so far only in the cat, appears to be mediated by norepinephrine. Finally, glutamate, enkephalin and GABA, but not glycine attenuate the release of the inhibitory and excitatory transmitters from the nerve terminals abutting on the SPNs. The supraspinal efferent and afferent projections which may release the transmitters and modulators in question are discussed, as well the mechanisms that ensure appropriate programming and moment-to-moment regulation of the autonomic output.

Animals↗
PubMed1992

Hypotension preferentially induces c-fos immunoreactivity in supraoptic vasopressin neurons.

Immunoreactivity to Fos protein (Fos-IR) was detected in rat hypothalamic neurons within 1 h of onset of hemorrhage by withdrawing 4-5 ml of blood, which lowered the arterial blood pressure to 50-70 mm Hg. About 70% of vasopressin (AVP)-containing neurons in the supraoptic nucleus (SON) and 20% in the paraventricular nucleus (PVN) expressed Fos-IR. In contrast, 5% of oxytocin (OXY)-containing neurons in the SON and < 1% in PVN were Fos-IR. Intravenous infusion of the vasodilating agent, nitroprusside, which lowered the blood pressure to levels comparable to that attained by hemorrhage, induced Fos-IR in greater than 65% of AVP-containing neurons in the SON, while relatively few AVP neurons in the PVN were Fos positive. These results suggest that hemorrhage or hypotension preferentially induces c-fos expression in supraoptic AVP-containing neurons.

Animals↗
PubMed1992

Hypovolemia induces Fos-like immunoreactivity in neurons of the rat supraoptic and paraventricular nuclei.

Immunoreactivities to Fos proteins were detected in numerous neurons in the supraoptic, paraventricular and accessory neurosecretory nuclei 1 h following withdrawal of 4-5 cc of blood from the rat femoral arteries. Few or no positive cells were observed in the same nuclei in sham-operated or control animals. It is concluded that hypovolemia induces c-fos expression in hypothalamic neurons known to be associated with blood volume/pressure regulation.

Animals↗
PubMed1992

Synaptic mechanisms in sympathetic preganglionic neurons.

Intracellular recordings from sympathetic preganglionic neurons (SPNs) in adult cat and neonatal rat spinal cord slices reveal four types of synaptic potentials, namely, excitatory postsynaptic potentials (EPSPs), inhibitory postsynaptic potentials (IPSPs), and slow EPSPs in both preparations, and a slow IPSP in cat SPNs. Pharmacological studies show that glutamate or a related excitatory amino acid and glycine are the probable mediators of EPSPs and IPSPs. There may be heterogenous mediators of slow EPSPs; substance P, serotonin, norepinephrine, and epinephrine are all probable mediators of slow EPSPs in subpopulations of SPNs. In the case of slow IPSPs, norepinephrine appears to be the likely transmitter. Finally, stimulation of ventral roots elicits a synaptic potential that appears to be caused by glutamate released from afferent fibers in the ventral roots. Our results indicate that a multitude of synaptic mechanisms exist in the rat SPNs by means of which inputs arising from sensory and supraspinal neurons are processed in a timely and orderly manner, thus ensuring highly organized but differentiated outputs to multiple peripheral target cells.

Animals↗