Prolyl-leucyl-glycinamide (PLG): inhibition of offensive aggression in mice

The effects on offensive aggression of the endogenous peptide-leucyl-glycinamide (PLG, MIF-1) and the exogenous opiate antagonist, naloxone, were examined in male mice. PLG (0.01-10 mg/Kg) reduced, in a dose-dependent manner, the incidence and intensity of offensive aggression in dominant resident mice. PLG was more potent than naloxone (1.0 mg/Kg). In a number of cases, PLG completely eliminated the display of offensive aggression towards intruder mice. These results raise the possibility that PLG may function as an "anti-aggressive" peptide whose actions may include antagonistic and/or modulatory influences on both opioid and non-opioid systems.     

Linkage of plasminogen (PLG) and apolipoprotein(a) (LPA) in baboons.

Four allelic forms of serum plasminogen (PLG) were detected in baboons (Papio hamadryas Linneaus 1758) by isoelectric focusing and were determined to be inherited as autosomal codominant traits. Linkage analysis of data from 179 progeny and their parents revealed that PLG is tightly linked (lod score = 30.20) to the gene encoding apolipoprotein(a) (LPA), as in humans. No recombinant individuals were identified. This is the first linkage detected between PLG and LPA in any species other than humans and is the first genetic linkage identified in a nonhuman primate species by family studies.     

Seasonal variation of morphine physical dependence

The characteristics of morphine physical dependence in ground squirrels ($\text{Citellus lateralis}$) were examined during each of the four annual seasons. The results showed that this rodent hibernator exhibits a strong and characteristic naloxone-precipitated abstinence syndrome during its non-hibernation state, irrespective of the season. Although qualitatively unchanged throughout the year, the abstinence syndrome showed clear quantitative seasonal differences. These differences were evident in terms of both the number of occurences of particular signs and the percentage of the morphine-dependent population exhibiting them.     

Rat brain proteome in morphine dependence

The aim of this study was to reveal potential markers associated with drug dependence, using the proteomic approach. Gels containing samples derived from morphine-treated and control animals were compared and analyzed. Inspection of protein profiles, following TCA/acetone precipitation and the use of nano-scale liquid chromatography coupled to tandem mass spectrometry, allowed for identification of eleven potential dependence markers, mainly cytoplasmic and mitochondrial enzymes, e.g. proteins that belong to GTPase and GST superfamilies, ATPase, asparaginase or proteasome subunit p27 families.     

Pharmacological manipulation of gamma-aminobutyric acid (GABA) in morphine analgesia,tolerance and physical dependence

The findings from our laboratory indicated that pharmacological manipulations of GABA system modified morphine analgesia, tolerance and physical dependence. Elevating brain levels of GABA by slowing its destruction with aminooxyacetic acid not only antagonized the analgesic action of morphine in both non-tolerant and tolerant mice, but also enhanced the development of tolerance and physical dependence. On the other hand, blockade of postsynaptic sites of GABA receptors by bicuculline resulted in an inhibition of tolerance and dependence development. Administration of 2,4-diaminobutyric acid, an inhibitor of GABA uptake in the neurons, antagonized morphine analgesia in both non-tolerant and tolerant mice. However, it did not modify naloxone precipitated withdrawal jumping. On the contrary, β-alanine, an inhibitor of the GABA uptake process in glial cells, potentiated naloxone precipitated withdrawal jumping in morphine dependent mice, but it had no effect on morphine antinociception in both non-tolerant and tolerant mice.     

Linkage between the loci for the Lp(a) lipoprotein (LP) and plasminogen (PLG)

Summary A locus, LP, that determines quantitative variation of Lp(a) lipoprotein phenotypes is linked to the plasminogen (PLG) locus (peak lod score =12.73). This linkage relationship assigns a locus with alleles that have an affect on risk for coronary artery disease to the long arm of chromosome 6.     

Inhibition of morphine dependence by a lipopolysaccharide from Pantoea agglomerans.

A lipopolysaccharide from Pantoea agglomerans (LPSp) was purified and examined for relief of morphine dependence by observing its inhibition of the jumping of mice on naloxone-precipitate withdrawal. Administration of LPSp either intravenously or intradermally showed marked inhibition of the jumping. Beta-endorphin in mouse serum and brain tissue were recognized to be in synchrony with the time course of the relief. Administration of TNF-alpha gave similar effect, suggesting that LPSp induces a cytokine cascade to produce endogenous TNF followed by ACTH/beta-LPH gene products and beta-endorphin. The effect of LPSp was better than that of LPS from E. coli or Bordetella pertussis, and thus is considered to be applicable for clinical use.     

Physical dependence in rats after low morphine doses

The minimum level of morphine administration necessary to produce physical dependence in rats was investigated. Rats received low doses of morphine (10 mg/kg) intraperitoneally once daily for 1, 3, or 5 days. Naloxone given intraperitoneally 1 hr. after the last morphine injection produced significant withdrawal signs after only three days.     

Antagonism of morphine tolerance and dependence by metoclopramide

Metoclopramide produced significant analgesic activity when tested by acetic acid induced writhing assay. Repeated injections of metoclopramide did not result in the development of tolerance to its analgesic activity. Pretreatment with metoclopramide antagonised acute morphine tolerance and suppressed the withdrawal signs (both in acute dependence type and abrupt withdrawal type). It is suggested that metoclopramide may be a useful tool in the management of morphine dependence.     

Attenuation of morphine tolerance and dependence by alpha-melanocyte stimulating hormone(alpha-MSH).

Repeated administration of morphine resulted in significant reduction of its analgesic potency. If 0.1 mg/kg α-MSH was coadministered, the tolerance development was attenuated, 1 mg/kg MIF (MSH release inhibiting factor), given simultaneously with morphine, did not affect tolerance. Injecting, however, MIF 1 hour prior to the daily opiate treatment resulted in accelerated development of tolerance supposedly by lowering the plasma α-MSH level at the time of morphine administration. Of the morphine abstinence symptoms the naloxone-induced jumping in morphine pretreated mice could not be modified either by α-MSH coadministration or by MIF pretreament, but the withdrawal body weight loss was found to be diminished by the former and increased by the latter peptide. The possible role of α-MSH in preventing the development of tolerance to the analgesic effect of endogenous opioid peptides is discussed.     

Inhibition by L-Prolyl-L-Leucyl-Glycinamide (PLG) of Alpha-melanocyte stimulating hormone release from hypothalamic slices

Release of -MSH from male rat hypothalamic slices was studied using a sensitive bioassay (1–2 pg). Addition of 60 mM KC1 to superfusion medium resulted in a twofold increase in -MSH release compared to spontaneous release. Both spontaneous and potassium- induced release were inhibited in a dose-response manner by the tripeptide Pro-Leu-Gly-NH₂ (PLG, or MIF-1); 0.04 μg to 1 μg PLG inhibited the -MSH release but the lowest dose demonstrated a greater inhibitory effect; high concentrations of PLG, on the other hand, did not modify either spontaneous or potassium-evoked -MSH release from the slices. Contrarily, DA did not modify either spontaneous or potassium- induced -MSH release at any of the doses tested. These findings demonstrate that the inhibitory behavior of PLG and DA in the central nervous system (CNS) differs from their behavior towards -MSH release in the pituitary. This suggests differences in the regulation of -MSH release from the pituitary and the CNS.     

In-vitro evaluation of morphine dependence. III. Response of the rat ileum to ACh

The kinetic of cholinergic receptor systems was studied in an in vitro model for opiate tolerance and dependence. The isolated ileum of rate chronically treated with morphine and sacrificed at different time intervals and in different conditions (with and without abstinence signs) was used. In evaluating the response of this preparation to doses of ACh ranging from 5.5 x 10(-10) to 5.5 x 10(-7), no statistically significant response was found to the cholinergic receptor system in conditions of abstinence and non-abstinence in vivo and in vitro. On the other hand, statistically significant differences are related to duration of treatment in vivo. The pattern for these responses is similar to the one observed in the fundus (Note I) and it can be considered as an expression of morphine-induced tolerance.     

Rapid analysis of gene expression (RAGE) facilitates universal expression profiling.

Current techniques for analysis of gene expression either monitor one gene at a time, for example northern hybridization or RT-PCR methods, or are designed for the simultaneous analysis of thousands of genes, for example microarray hybridization or serial analysis of gene expression. To provide a flexible, intermediate scale alternative, a PCR-based method for the rapid analysis of gene expression has been developed which allows expression changes to be determined in either a directed search of known genes, or an undirected survey of unknown genes. A single set of reagents and reaction conditions allows analyses of most genes in any eukaryote. The method is useful for assaying on the order of tens to hundreds of genes in multiple samples. Control experiments indicate reliable detection of changes in gene expression 2-fold and greater, and sensitivity of detection better than 1 in 10 000. Analyses of over 400 genes in a mouse system transgenic for the E2F1 gene have identified several new downstream targets of E2F1, including Brca1 and Cdk7, in addition to several unidentified genes that are upregulated in the transgenic mice. Changes in expression of several genes related to apoptosis suggest a possible potentiation of apoptotic pathways in the transgenic keratinocytes.     

Morphinome--a meta-analysis applied to proteomics studies in morphine dependence

This review is a meta-analysis of data describing proteins regulated by morphine influence studied worldwide across last years administration. Up to date (July 2010), 15 studies concerning this subject have been published. Animal models, examined brain structures, the route of morphine administration and proteomic platforms used for identification of differentially expressed proteins were described. Standardization of obtained results allowed for creation of database of proteins, whose expression was altered by morphine administration (www.addiction-proteomics.org). Their analysis by tools available in Celera Panther Database was possible too. Proteins, which seem to be the most promising candidates for further research, due to their consistent appearance in different studies, were indicated. Created database may facilitate further studies by providing a possibility to compare results obtained during different experiments. At the end, dynamic picture of proteome after morphine administration, which emerges from the obtained results, is discussed and need for standardization of proteomics experiments is stressed. As meta-analysis is a very powerful tool for evaluation and comparison of multiple data. We believe this approach will be useful in the nearest future to extract vital information from a vast number of similar publications. Morphinome database created already by our group is a comfortable tool for validation and verification of new data received after morphine influence on proteomes investigations. It gives a chance for fast comparison of results without hours spent on life science literature mining.     

Down-regulation of haloperidol-induced striatal dopamine receptor supersensitivity by active analogues of L-prolyl-L-leucyl-glycinamide (PLG)

Tardive dyskinesia, a clinical syndrome, is one of the major side effects of protracted treatment with neuroleptics in schizophrenic patients. Functional supersensitivity of striatal dopamine receptors is believed to contribute to the pathogenesis of schizophrenia and tardive dyskinesia. In a rodent model of neuroleptic-induced dopamine receptor supersensitivity, we investigated the efficacy of structurally modified analogues of PLG to down-regulate the striatal dopamine receptor supersensitivity as determined by alterations in [³H]spiroperidol binding to striatal membranes in vitro. The PLG analogue, L-prolyl-L-leucyl-(+)-thiazolidine-2-carboxamide-HCl, when given at the dose of 10 mg/kg IP for 5 days prior to haloperidol (3 mg/kg IP 21 days) significantly prevented the up-regulation of striatal dopamine receptor supersensitivity, thus demonstrating a prophylactic effect. Two other analogues, L-prolyl-L-leucyl-5-aminomethyltetrazole and L-prolyl-L-leucyl-glycine-dimethylamide at a dose of 10 mg/kg IP when given concurrently with haloperidol for 21 days, suppressed the development of dopamine receptor supersensitivity. None of the analogues tested in the post-haloperidol session reversed the haloperidol-induced increase in the density of striatal dopamine receptors. Active PLG analogues hold promise as potential therapeutic agents for the amelioration of tardive dyskinesia.     

An opiate cocktail that reduces morphine tolerance and dependence

Morphine is an exceptionally effective analgesic whose utility is compromised by the development of tolerance and dependence to the drug. Morphine analgesia and dependence are mediated by its activity at the mu opioid peptide (MOP) receptor [1]. The MOP receptor is activated not only by morphine, but also by other opiate drugs such as methadone and endogenous opioids such as endorphins. Morphine, however, is a unique opioid agonist ligand because it fails to induce endocytic trafficking of the MOP receptor [2], whereas the endogenous ligands and methadone do facilitate endocytosis [3]. Using the unique pharmacology of the MOP receptor and its proposed existence as an oligomeric structure [4], we designed a pharmacological cocktail that facilitates endocytosis of the MOP receptor in response to morphine. This cocktail consists of morphine and a small dose of methadone. Importantly, this cocktail, while retaining full analgesic potency, does not promote morphine dependence. We further demonstrate that dependence is reduced, at least in part, because endocytosis of the MOP receptor in response to morphine prevents the upregulation of N-methyl-D-aspartate (NMDA) receptors.