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Biomedical subjects

R K Mishra

Publications and source records attributed to R K Mishra.

At least 37 records · Page 2Linked to original sources
PubMed2000

L-prolyl-l-leucyl-glycinamide and its peptidomimetic analog 3(R)-[(2(S)-pyrrolidylcarbonyl)amino]-2-oxo-1-pyrrolidineacetamide (PAOPA) attenuate haloperidol-induced c-fos expression in the striatum.

Acute treatment of rats with haloperidol results in a rapid and transient increase in striatal c-fos mRNA and Fos immunoreactivity. The induction of immediate early genes by haloperidol may be involved in the development of extrapyramidal side effects. L-Prolyl-L-leucyl-glycinamide (PLG, or MIF-1) has been observed to antagonize the development of haloperidol-induced D(2) receptor supersensitivity in rats. We investigated the modulatory effects of PLG on haloperidol-induced c-fos and Fos protein expression in the rat striatum. We report that coadministration of either PLG or the potent analog of PLG, 3(R)-[(2(S)-pyrrolidylcarbonyl)amino]-2-oxo-1-pyrrolidineacetam ide (PAOPA), attenuated haloperidol-induced c-fos and Fos expression. Haloperidol induced [2 mg/kg, intraperitoneally (i.p.)] c-fos and Fos expression by 500% and 100%, respectively. These responses were attenuated by 170% and 75%, respectively, when coadministered with PLG (20 mg/kg, i.p.) or by 79% by PAOPA (10 microg/kg, i.p.).

Animals↗
PubMed1999

Synthesis and dopamine receptor modulating activity of unsubstituted and substituted triproline analogues of L-prolyl-L-leucyl-glycinamide (PLG).

Triprolines Pro-Pro-Pro-NH2 (4), Pro-Pro-D-Pro-NH2 (5), Pro-Pro(trans-3-Me)-D-Pro-NH2 (6), and Pro-Pro(cis-3-Me)-D-Pro-NH2 (7) were made as conformationally constrained analogues of Pro-Leu-Gly-NH2. Triprolines 4-6 produced significant increases in the high- and low-affinity state ratio (RH/RL) of the dopamine receptor, but only 4 was found to increase apomorphine induced rotations in 6-hydroxydopamine-lesioned rats.

Animals↗
PubMed1999

Synthesis and dopamine receptor modulating activity of substituted bicyclic thiazolidine lactam peptidomimetics of L-prolyl-L-leucyl-glycinamide.

6-Substituted bicyclic thiazolidine lactam peptidomimetics of Pro-Leu-Gly-NH(2) (1) were synthesized to test the hypothesis that incorporation of a hydrophobic side chain into the bicyclic thiazolidine lactam scaffold would further enhance the dopamine receptor modulating activity of such peptidomimetics. The substituents employed were the isobutyl, butyl, and benzyl groups to give peptidomimetics 3-5, respectively. These peptidomimetics were evaluated in vivo as modulators of apomorphine-induced rotational behavior in the 6-hydroxydopamine-lesioned rat model of hemiparkinsonism and were compared with the unsubstituted bicyclic thiazolidine lactam Pro-Leu-Gly-NH(2) peptidomimetic 2. Peptidomimetics 3-5 each affected rotational behavior in a bell-shaped dose-response relationship producing maximal increases of 44% (1 microgram/kg,ip), 56% (0.1 microgram/kg,ip), and 30% (1 microgram/kg, ip), respectively. In comparison, unsubstituted peptidomimetic 2 increased rotational behavior by only 23% at a dose of 0.1 microgram/kg, ip.

Animals↗
PubMed1999

Modulation of agonist stimulated adenylyl cyclase and GTPase activity by L-pro-L-leu-glycinamide and its peptidomimetic analogue in rat striatal membranes.

L-prolyl-L-leucyl-glycinamide (PLG), also known as melanocyte-stimulating hormone release inhibiting factor (MIF-1), is an endogenous brain tripeptide. Previous studies have shown that PLG, and its peptidomimetic analogues, render dopamine D2 receptors more responsive to agonists by maintaining the high-affinity binding state of the receptors. In the present study, we examined the effect PLG and its analogue 3(R)-[(2(S)-pyrrolidylcarbonyl)amino]-2-oxo-1-pyrrolidineacetam ide (PAOPA) on dopamine-stimulated adenylyl cyclase and NPA-stimulated GTPase activity in rat striatal membranes. Dopamine-stimulated adenylyl cyclase activity was inhibited by both PLG and PAOPA in a dose-dependent manner, whereas R(-)-propylnorapomorphine (NPA)-stimulated low Km GTPase activity was significantly increased by 1 microM PLG or 1 nM PAOPA. These results suggest that PLG and PAOPA maintain the high affinity state of the D2 receptor by increasing GTP hydrolysis through stimulation of agonist-induced GTPase activity.

Adenylyl Cyclases↗
PubMed1999

Synthesis and dopamine receptor modulating activity of novel peptidomimetics of L-prolyl-L-leucyl-glycinamide featuring alpha,alpha-disubstituted amino acids.

In the present study, L-prolyl-L-leucyl-glycinamide (1) peptidomimetics 3a-3d and 4a-4d were synthesized utilizing alpha, alpha-disubstituted amino acids. These analogues were designed to explore the conformational effects of constraints at the phi3 and psi3 torsion angles. Constrained conformations were verified by the use of X-ray crystallography and circular dichroism. The effects of Pro-Leu-Gly-NH2 analogues 3a-3d and 4a-4d on enhancing rotational behavior induced by apomorphine in the 6-hydroxydopamine-lesioned animal models of Parkinson's disease were studied. The ability of these peptidomimetics to increase the binding of agonist N-propylnorapomorphine (NPA) to the dopamine D2 receptor was also examined. Extended analogue Pro-Leu-Deg-NH2 was the most active compound of this series. It was 10 times more potent and almost 2 times more effective than 1 in increasing apomorphine-induced rotations (56 +/- 15% at 1.0 mg/kg ip) and in enhancing [3H]NPA specific binding (40%).

Animals↗
PubMed1999

Design, synthesis, and dopamine receptor modulating activity of spiro bicyclic peptidomimetics of L-prolyl-L-leucyl-glycinamide.

In the present study, the synthesis of the 5.5.6. and 5.6.5. spiro bicyclic lactam PLG peptidomimetics, compounds 3 and 4, respectively, was undertaken. These peptidomimetics were designed to examine the following: (1) the effect that changing the size of the thiazolidine and lactam ring systems would have on the ability of these systems to mimic the type-II beta-turn and (2) the effect that these structural perturbations would have on the ability of the peptidomimetics to modulate dopamine receptors. Through the use of the [3H]spiroperidol/N-propylnorapomorphine (NPA) dopamine D2 receptor competitive binding assay, 3 and 4, at a concentration of 100 nM, decreased the dissociation constant of the high-affinity state of the dopamine receptor for the agonist. These effects were observed when either Gpp(NH)p was absent or present and they were comparable to those produced by PLG at a concentration of 1 microM. Peptidomimetics 3 and 4 also increased the percentage of D2 receptors that existed in the high-affinity state. Even with Gpp(NH)p present, 3 and 4 were able to return the RH/RL ratios to values observed in the respective controls where Gpp(NH)p was absent. Furthermore, both peptidomimetics were able to attenuate the Gpp(NH)p-induced shift to the low-affinity state to a greater extent than PLG. Peptidomimetics 3 and 4 were evaluated in vivo as modulators of apomorphine-induced rotational behavior in the 6-hydroxydopamine-lesioned rat model of hemiparkinsonism, and each affected the rotational behavior in a bell-shaped dose-response relationship producing increases of 95 +/- 31% (0.01 mg/kg, ip) and 88 +/- 14% (0.001 mg/kg, ip), respectively. In comparison, the previously reported 5.5.5. spiro bicyclic lactam 2 increased rotational behavior by 25 +/- 11% (0.01 mg/kg, ip).

Animals↗
PubMed1999

Modulatory effects of PLG and its peptidomimetics on haloperidol-induced catalepsy in rats.

A behavioral model of dopaminergic function in the rat was used to examine the anticataleptic effects of L-prolyl-L-leucyl-glycinamide (PLG) and peptidomimetic analogs of PLG. Administration of 1 mg/kg PLG intraperitoneally significantly attenuated haloperidol (1 mg/kg)-induced catalepsy (as measured by the standard horizontal bar test), whereas doses of 0.1 and 10 mg/kg PLG did not. Eight synthetic PLG peptidomimetics (Calpha, alpha-dialkylated glycyl residues with lactam bridge constraint [1-4] and without [5-8]) were tested in the same manner (at a dose of 1 microg/kg) and categorized according to their activity, i.e. very active (5), moderately active (2, 3, 4, and 6), and inactive (1, 7, and 8). The catalepsy-reversal action of the diethylglycine-substituted peptidomimetic 5 was examined further and found to exhibit a U-shaped dose-response effect with an optimal dose of 1 microg/kg. The similarity between the effects of PLG and the synthetic peptidomimetics suggests a common mechanism of action. Finally, the synthetic peptidomimetics examined here, particularly peptidomimetic 5, were more effective than PLG in attenuating haloperidol-induced catalepsy.

Animals↗
PubMed1998

Selective inhibition of cell-free translation by oligonucleotides targeted to a mRNA hairpin structure.

Using an in vitro selection approach we have previously isolated oligodeoxy aptamers that can bind to a DNA hairpin structure without disrupting the double-stranded stem. We report here that these oligomers can bind to the RNA version of this hairpin, mostly through pairing with a designed 6 nt anchor. The part of the aptamer selected against the DNA hairpin did not increase stability of the RNA-aptamer complex. However, it contributed to the binding site for Escherichia coli RNase H, leading to very efficient cleavage of the target RNA. In addition, a 2'- O -methyloligoribonucleotide analogue of one selected sequence selectively blocked in vitro translation of luciferase in wheat germ extract by binding to the hairpin region inserted upstream of the initiation codon of the reporter gene. Therefore, non-complementary oligomers can exhibit antisense properties following hybridization with the target RNA. Our study also suggests that in vitro selection might provide a means to extend the repertoire of sequences that can be targetted by antisense oligonucleotides to structured RNA motifs of biological importance.

Binding Sites↗
PubMed1998

Chromatin domain boundaries in the Bithorax complex.

Eukaryotic chromosomes are thought to be organized into a series of discrete higher-order chromatin domains. This organization is believed to be important not only in the compaction of the chromatin fibre, but also in the utilization of genetic information. Critical to this model are the domain boundaries that delimit and segregate the chromosomes into units of independent gene activity. In Drosophila, such domain boundaries have been identified through two different approaches. On the one hand, elements like scs/scs' and the reiterated binding site for the SU(HW) protein have been characterized through their activity of impeding enhancer-promoter interactions when intercalated between them. Their role of chromatin insulators can protect transgenes from genomic position effects, thereby establishing independent functional domains within the chromosome. On the other hand, domain boundaries of the Bithorax complex (BX-C) like Fab-7 and Mcp have been identified through mutational analysis. Mcp and Fab-7, however, may represent a specific class of boundary elements; instead of separating adjacent domains that contain separate structural genes. Mcp and Fab-7 delimit adjacent cis-regulatory domains, each of which interacts independently with their target promoters. In this article, we review the genetic and molecular characteristics of the domain boundaries of the BX-C. We describe how Fab-7 functions to confine activating as well as repressive signals to the flanking regulatory domains. Although the mechanisms by which Fab-7 works as a domain boundary remain an open issue, we provide preliminary evidence that Fab-7 is not a mere insulator like scs or the reiterated binding site for the SU(HW) protein.

Animals↗
PubMed1998

Protection against MPTP treatment by an analog of Pro-Leu-Gly-NH2 (PLG, MIF-1)

3(R)-[(2(S)-Pyrrolidinyl-carbonyl)amino]-2-oxo-1-pyrrolidineacetamide (PAOPA) is a peptidomimetic analog of Pro-Leu-Gly-NH2 (PLG or MIF-1) that has previously been demonstrated to be more potent and efficacious that MIF-1 in enhancing dopamine receptor activity. Given the ability of MIF-1 to protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesioning in C57 BL/6 mice, the present study was undertaken to evaluate the neuroprotective effect of PAOPA in this model. PAOPA was found to be more potent and efficacious that MIF-1 in sparing dopamine and its metabolite levels following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine administration. Whether the enhanced neuroprotective effect of PAOPA is due to dopamine receptor stimulation, or a result of reduced oxidative stress through normalization of dopamine turnover, remains to be determined.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1998

Modulation of dopamine D2 receptor expression by an NMDA receptor antagonist in rat brain.

The expression of dopamine D2 receptor mRNA was studied in rat brain following micro-injection of a competitive N-methyl D-aspartate (NMDA) receptor antagonist at the prefrontal cortex. Male Sprague-Dawley rats cannulated bilaterally into the medial prefrontal cortex were injected with a competitive NMDA receptor antagonist (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP). The levels of mRNA for NMDA-R1 and dopamine D2 receptors were measured by reverse transcriptase-polymerase chain reaction (RT-PCR), and D2 receptor density was quantified by [3H]spiperone binding in the cortex and striatum of these animals. In the prefrontal cortex, the levels of NMDA-R1 receptor mRNA showed significant decrease in CPP-treated animals compared to control animals. However, NMDA-R1 mRNA levels in striatum remained unchanged in any of the experimental groups. The D2 receptor mRNA levels and [3H]spiroperidol binding in prefrontal cortical membranes showed no significant difference between the CPP-treated and control groups of animals. In the striatum, a significant increase in striatal dopamine D2 receptor mRNA levels was shown in animals treated with CPP. The increase in D2 mRNA level was correlated with an increase in the D2 receptor binding sites in the striatal membranes. These results suggest a possible interaction between prefrontal cortical NMDA receptors and striatal dopamine receptors.

Animals↗
PubMed1997

Design, synthesis, and dopamine receptor modulating activity of diketopiperazine peptidomimetics of L-prolyl-L-leucylglycinamide.

The diketopiperazine "C5" conformational mimic has been incorporated into the L-prolyl-L-leucylglycinamide (PLG, 1) structure and into the bicyclic lactam PLG peptidomimetic structure 3 to give compounds 5 and 6, respectively. These analogues were designed to explore the idea that the N-terminal "C5" conformation, which was found in the crystal structure of 2 and which was mimicked in 4 by the diketopiperazine function, was a factor in the high potency of these two agents. Through the use of the [3H]spiroperidol/N-propylnorapomorphine (NPA) D2 receptor competitive binding assay, both 5 and 6 were found to increase the affinity of the dopamine receptor for agonists and both were found to increase the percentage of D2 receptors which existed in the high-affinity state. These effects were observed when Gpp(NH)p was either absent or present, and they were analogous to the effects observed previously for PLG and the PLG peptidomimetics 2 and 4. However, the potency seen with 5 and 6 was less than that seen for 2 and 4, suggesting that while the N-terminal "C5" conformation may play a role in the potency of the gamma-lactam peptidomimetics of PLG, it does not appear to be the primary factor. In the 6-hydroxydopamine-lesioned animal model of Parkinson's disease, 5 altered apomorphine-induced rotational behavior in a dose-dependent manner. The maximum effect occurred at a dose of 0.01 mg/kg i.p. and resulted in a 52.27 +/- 13.96% (p < 0.001, n = 7) increase in rotations compared to apomorphine administered alone.

Animals↗
PubMed1997

Three small nucleolar RNAs that are involved in ribosomal RNA precursor processing.

Three small nucleolar RNAs (snoRNAs), E1, E2 and E3, have been described that have unique sequences and interact directly with unique segments of pre-rRNA in vivo. In this report, injection of antisense oligodeoxynucleotides into Xenopus laevis oocytes was used to target the specific degradation of these snoRNAs. Specific disruptions of pre-rRNA processing were then observed, which were reversed by injection of the corresponding in vitro-synthesized snoRNA. Degradation of each of these three snoRNAs produced a unique rRNA maturation phenotype. E1 RNA depletion shut down 18 rRNA formation, without overaccumulation of 20S pre-rRNA. After E2 RNA degradation, production of 18S rRNA and 36S pre-rRNA stopped, and 38S pre-rRNA accumulated, without overaccumulation of 20S pre-rRNA. E3 RNA depletion induced the accumulation of 36S pre-rRNA. This suggests that each of these snoRNAs plays a different role in pre-rRNA processing and indicates that E1 and E2 RNAs are essential for 18S rRNA formation. The available data support the proposal that these snoRNAs are at least involved in pre-rRNA processing at the following pre-rRNA cleavage sites: E1 at the 5' end and E2 at the 3' end of 18S rRNA, and E3 at or near the 5' end of 5.8S rRNA.

Animals↗
PubMed1997

Modulation of dopamine receptor agonist-induced rotational behavior in 6-OHDA-lesioned rats by a peptidomimetic analogue of Pro-Leu-Gly-NH2 (PLG).

The present study was undertaken to determine if the previously reported in vitro interactions of the Pro-Leu-Gly-NH2 (PLG) peptidomimetic analogue 3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-2-oxo-1-pyrrolidineacet amide (PAOPA) with the dopaminergic system could be exhibited in an in vivo animal model using 6-hydroxydopamine (6-OHDA)-lesioned rats. In this model, PAOPA was found to potentiate the contralateral rotational behavior induced by either apomorphine or L-DOPA. PAOPA was 100-fold more potent than PLG, and produced a fourfold greater response than PLG when administered i.p. PAOPA also potentiated contralateral rotations induced by SKF-38393 and quinpirole. In summary, the results of this study indicate that PAOPA, a conformationally constrained peptidomimetic analogue of PLG, can modulate dopaminergic activity in vivo with higher potency and efficacy than PLG.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1997

Non-traumatic coma--profile and prognosis.

Two hundred consecutive patients of non-traumatic coma, were investigated to establish its aetiology. Neurologic profile of these patients included assessment of Glasgow Coma Scale (GCS) score and evaluation of brainstem reflexes. 102 patients died and only 54 patients could make good recovery. Cerebrovascular diseases (33%), CNS infections (21%), and hepatic encephalopathy (18%) were the frequent causes of non-traumatic coma, with the first two carrying relatively poor prognosis. Poor outcome was also associated with low GCS score and absence of brainstem reflexes specially absent pupillary, oculocephalic and oculovestibular responses and decerebrate posture.

Adolescent↗
PubMed1996

NMDA and dopamine D2L receptor interaction in human neuroblastoma SH-SY5Y cells involves tyrosine kinase and phosphatase.

Blockade of N-methyl-D-aspartate (NMDA) receptors by the specific antagonists dizocilpine and (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid on human neuroblastoma SH-SY5Y cells expressing human D21 receptors resulted in a significant increase in the density of D2L receptors. In order to understand the mechanism of dopamine D2L receptor induction following NMDA receptor blockade we used specific protein tyrosine kinase and phosphatase inhibitors to demonstrate their involvement in this interaction. The induction of dopamine D2L receptor was measured by radioreceptor binding assay. The density of the dopamine D2L receptor was increased to 109% by the inhibition of protein tyrosine kinase and prevented by the inhibition of phosphatase 1 or 2A. Inactivation of NMDA receptors might effect the phosphorylation-dephosphorylation states of the regulatory proteins and lead to the induction of the D2L receptor gene.

Cell Line↗
PubMed1996

Modulation of dopaminergic neurotransmission in the 6-hydroxydopamine lesioned rotational model by peptidomimetic analogues of L-prolyl-L-leucyl-glycinamide.

Melanocyte stimulating hormone release inhibiting factor (MIF-1), also known as L-prolyl-L-leucyl-glycinamide (PLG), has previously been found to have the ability to modulate dopamine D2-receptor agonist binding both in the striatum and limbic regions. In the present study the 6-hydroxydopamine unilateral lesion model of apomorphine-induced rotational behaviour, in Wistar rats, was used to assess the dopaminergic modulatory activity of PLG and two novel analogues, L-prolyl-L-prolyl-L-prolinamide (analogue A) and (2S, 5R, 7R)-1-Aza-7[3'(S)-1-(2',5'-dioxo-pyrrolidino[2,1-c]piperazino++ +)] -8-oxo-4-thiabicyclo[3.30]octane-2-carboxamide (analogue B). PLG and the two novel analogues showed a bell-shaped dose-response relationship, suggesting that analogue A, B and PLG all manifest their effect through a similar mechanism and exhibit a window of therapeutic efficacy. Analogue A was a 100 times, while analogue B was 10 times, more potent than PLG in increasing the contralateral rotational response when given in combination with apomorphine. Analogue A was also more efficacious than PLG or analogue B at increasing apomorphine-induced contralateral rotations. Intrastriatal administration of either analogue A or B resulted in a greater increase in apomorphine-induced rotations than the most efficacious intraperitoneally delivered dose. The results of the present study suggest that PLG and its two novel analogues are able to modulate dopamine receptor activity and may be possible therapeutic agents for the treatment of Parkinsonian symptoms as well as tardive dyskinesia.

Animals↗