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Biomedical subjects

R Maldonado

Publications and source records attributed to R Maldonado.

At least 55 records · Page 3Linked to original sources
PubMed1998

Behavioural and biochemical evidence for signs of abstinence in mice chronically treated with delta-9-tetrahydrocannabinol.

Tolerance and dependence induced by chronic delta-9-tetrahydrocannabinol (THC) administration were investigated in mice. The effects on body weight, analgesia and hypothermia were measured during 6 days of treatment (10 or 20 mg kg(-1) THC twice daily). A rapid tolerance to the acute effects was observed from the second THC administration. The selective CB-1 receptor antagonist SR 141716A (10 mg kg(-1)) was administered at the end of the treatment, and somatic and vegetative manifestations of abstinence were evaluated. SR 141716A administration precipitated several somatic signs that included wet dog shakes, frontpaw tremor, ataxia, hunched posture, tremor, ptosis, piloerection, decreased locomotor activity and mastication, which can be interpreted as being part of a withdrawal syndrome. Brains were removed immediately after the behavioural measures and assayed for adenylyl cyclase activity. An increase in basal, forskolin and calcium/calmodulin stimulated adenylyl cyclase activities was specifically observed in the cerebellum of these mice. The motivational effects of THC administration and withdrawal were evaluated by using the place conditioning paradigm. No conditioned change in preference to withdrawal associated environment was observed. In contrast, a conditioned place aversion was produced by the repeated pairing of THC (20 mg kg(-1)), without observing place preference at any of the doses used. This study constitutes a clear behavioural and biochemical model of physical THC withdrawal with no motivational aversive consequences. This model permits an easy quantification of THC abstinence in mice and can be useful for the elucidation of the molecular mechanisms involved in cannabinoid dependence.

Analysis of Variance↗
PubMed1998

Field trial of a vaccine against New World cutaneous leishmaniasis in an at-risk child population: safety, immunogenicity, and efficacy during the first 12 months of follow-up.

The safety, immunogenicity, and efficacy of a vaccine against cutaneous leishmaniasis in rural Ecuadorian children was assessed in a randomized, controlled, double-blinded study. Vaccine group subjects received 2 intradermal doses of a whole, killed promastigote vaccine cocktail plus bacille Calmette-Guérin (BCG) adjuvant. Control subjects got 2 doses of BCG only. The subjects who received both vaccination doses, 438 in the vaccine group (79.3%) and 406 in the control group (83.4%), were followed for 12 months. No serious adverse side effects were identified in either group. Significantly more vaccine group subjects than controls converted to a positive Montenegro skin test (85.1% vs. 20.1%; chi2 = 279; P < .001). The incidence of cutaneous leishmaniasis was significantly reduced in the vaccine compared with the control group (2.1% vs. 7.6%; chi2 = 8.95; P < .003). The protective efficacy of the vaccine was 72.9% (95% confidence interval = 36.1%-88.5%).

Child↗
PubMed1998

Efficiency of T4 gene 60 translational bypassing.

Ribosomes translating bacteriophage T4 gene 60 mRNA bypass 50 noncoding nucleotides from a takeoff site at codon 46 to a landing site just upstream of codon 47. A key signal for efficient bypassing is contained within the nascent peptide synthesized prior to takeoff. Here we show that this signal is insensitive to the addition of coding information at its N terminus. In addition, analysis of amino-terminal fusions, which allow detection of all major products synthesized from the gene 60 mRNA, show that 50% of ribosomes bypass the coding gap while the rest either terminate at a UAG stop codon immediately following codon 46 or fail to resume coding. Bypassing efficiency estimates significantly lower than 50% were obtained with enzymatic reporter systems that relied on comparing test constructs to constructs with a precise excision of the gap (gap deletion). Further analysis showed that these estimates are distorted by differences between test and gap deletion functional mRNA levels. An internal translation initiation site at Met12 of gene 60 (which eliminates part of the essential nascent peptide) also distorts these estimates. Together, these results support an efficiency estimate of approximately 50%, less than previously reported. This estimate suggests that bypassing efficiency is determined by the competition between reading signals and release factors and gives new insight into the kinetics of bypassing signal action.

Amino Acid Sequence↗
PubMed1997

Absence of opiate rewarding effects in mice lacking dopamine D2 receptors.

Dopamine receptors have been implicated in the behavioural response to drugs of abuse. These responses are mediated particularly by the mesolimbic dopaminergic pathway arising in the ventral tegmental area and projecting to the limbic system. The rewarding properties of opiates and the somatic expression of morphine abstinence have been related to changes in mesolimbic dopaminergic activity that could constitute the neural substrate for opioid addiction. These adaptive responses to repeated morphine administration have been investigated in mice with a genetic disruption of the dopaminergic D2 receptors. Although the behavioural expression of morphine withdrawal was unchanged in these mice, a total suppression of morphine rewarding properties was observed in a place-preference test. This effect is specific to the drug, as mice lacking D2 receptors behaved the same as wild-type mice when food is used as reward. We conclude that the D2 receptor plays a crucial role in the motivational component of drug addiction.

Animals↗
PubMed1997

The attenuation of morphine-conditioned place preference following chronic mild stress is reversed by a CCKB receptor antagonist.

Chronic exposure to mild unpredictable stress has been found to abolish the acquisition of preference for a distinctive environment paired with morphine, whereas morphine induced conditioning place preference in non-stressed rats. Chronic treatment for 21 days with the tricyclic antidepressant imipramine reversed the motivational effects produced by chronic mild stress, and animals showed a place preference for the morphine-paired compartment. When the CCKB receptor antagonist PD-134,308 was co-administered with morphine in stressed animals during the conditioning period, the preference for the morphine-paired compartment was also re-established. The CCKB receptor antagonist given alone did not induce rewarding effects in this paradigm. These findings indicate that the administration of a CCKB receptor antagonist reversed the effects of chronic mild stress on opiate rewarding properties.

Animals↗
PubMed1997

CCK-B receptors in the limbic system modulate the antidepressant-like effects induced by endogenous enkephalins.

Systemic administration of RB 101, a complete inhibitor of enkephalin catabolism, has been reported to induce antidepressant-like responses in mice which were potentiated by an ineffective dose of a CCK-B antagonist. The aim of this study was to investigate the neuroanatomical substrate involved in the facilitatory effects induced by CCK-B antagonists on RB 101 behavioural responses. Thus, the CCK-B antagonist PD-134,308 was locally administered into different brain structures (anterior nucleus accumbens, central amygdala and caudate nucleus) and its effects on the antidepressant-like response induced by systemic administration of RB 101 were evaluated in the conditioned suppression of motility (CSM) test in rats. RB 101 administered alone by the IV route decreased the CSM in rats, as previously obtained in mice. Systemic administration of a non effective dose of PD-134,308 facilitated the antidepressant-like effect induced by RB 101. Local injection of PD-134,308 into the anterior nucleus accumbens, the central amygdala or the caudate nucleus did not modify CSM. The antidepressant-like effects elicited by RB 101 in this test were potentiated by PD-134,308 after microinjection in the anterior nucleus accumbens and central amygdala, but not in the caudate nucleus. All these effects were observed only in shocked animals. The present results suggest that the mesolimbic system, particularly the anterior nucleus accumbens and the central amygdala, seems to play an important role in the interaction occurring between the endogenous CCK and opioid system in the control of behavioural responses.

Amygdala↗
PubMed1997

Participation of noradrenergic pathways in the expression of opiate withdrawal: biochemical and pharmacological evidence.

Several lines of biochemical and pharmacological evidence provide support for the involvement of the noradrenergic system in the expression of the somatic symptoms of opiate withdrawal. Early studies reported changes in brain noradrenaline and metabolite levels during opiate dependence. The significance of these changes has been clarified in recent microdialysis studies indicating that acute morphine decreases the extraneuronal levels of noradrenaline, whereas an increase in release of the neurotransmitter occurs during opiate withdrawal in several brain areas. Changes in the sensitivity and density of alpha 2- and beta-adrenoceptors have also been reported, probably as a consequence of the decreased presynaptic noradrenergic activity induced during morphine dependence. In addition, the administration of alpha 2-agonists, such as clonidine, or beta-antagonists, such as propranolol, has been reported to attenuate some manifestations of opiate withdrawal. The noradrenergic structure mediating the expression of opioid abstinence seems to be the locus coeruleus. However, the activation of the locus coeruleus during morphine withdrawal seems to be primarily due to the afferent projections containing excitatory amino acids and derived from the nucleus paragigantocellularis, although intrinsic modifications, consisting of an up-regulation of the cAMP pathway, seem also to be involved in this activation. The participation of the mesolimbic dopaminergic system in opiate dependence and its relation with the changes produced in the noradrenergic system are also discussed.

Adrenergic Fibers↗
PubMed1997

Initial experience with reuse of coronary angioplasty catheters in the United States.

OBJECTIVES: We sought to evaluate the performance of angioplasty catheters, restored under a strict manufacturing process, in patients with coronary artery disease. BACKGROUND: Most countries outside the United States routinely reuse disposable medical equipment, resulting in significant cost savings. Because of quality and legal concerns, reuse in the United States has been limited. We investigated the reuse of percutaneous transluminal coronary angioplasty (PTCA) balloon catheters, restored by a process strictly controlled for bioburden and sterility, in patients undergoing PTCA. METHODS: Used PTCA balloon catheters were shipped to a central facility and were decontaminated, cleaned and tested for endotoxin using the limulus amebocyte lystate (LAL) gel clot method. Physical testing and quality assurance were performed. The products were packaged and sterilized with ethylene oxide. Catheter performance was assessed in a pilot study powered to detect a 5% difference in the angiographic failure rates of new and reused balloons (beta 0.8). RESULTS: The study enrolled 107 patients. The indication for PTCA was stable angina pectoris in 69 patients, unstable angina in 22 and acute myocardial infarction in 16. Of the 107 patients enrolled, 106 had a successful laboratory outcome, and 1 required coronary artery bypass graft surgery after failed rescue stenting. There were 122 lesions attempted (American College of Cardiology/American Heart Association classification A, n = 32; B1, n = 43; > or = B2, n = 35; C, n = 12). Of the 110 lesions initially approached with restored PTCA catheters, 108 were crossed and dilated. Sixty-four required no further procedures. Stenting was performed in 37 patients (29 planned, 8 rescue). Thus, the angiographic failure rate was 7% (10 of 108, 95% confidence interval 2% to 12%), comparable to the 10% rate seen with new balloons in other studies. CONCLUSIONS: Restoration of disposable coronary angioplasty catheters using a highly controlled process appears to be safe and effective, with success rates similar to those of new products and no detectable sacrifice in performance. Cost analysis suggests that implementation of reuse technology for expensive disposable equipment may offer cost savings for U.S. hospitals, without sacrifice of quality.

Angioplasty, Balloon, Coronary↗
PubMed1996

Loss of morphine-induced analgesia, reward effect and withdrawal symptoms in mice lacking the mu-opioid-receptor gene.

Despite tremendous efforts in the search for safe, efficacious and non-addictive opioids for pain treatment, morphine remains the most valuable painkiller in contemporary medicine. Opioids exert their pharmacological actions through three opioid-receptor classes, mu, delta and kappa, whose genes have been cloned. Genetic approaches are now available to delineate the contribution of each receptor in opioid function in vivo. Here we disrupt the mu-opioid-receptor gene in mice by homologous recombination and find that there are no overt behavioural abnormalities or major compensatory changes within the opioid system in these animals. Investigation of the behavioural effects of morphine reveals that a lack of mu receptors abolishes the analgesic effect of morphine, as well as place-preference activity and physical dependence. We observed no behavioural responses related to delta- or kappa-receptor activation with morphine, although these receptors are present and bind opioid ligands. We conclude that the mu-opioid-receptor gene product is the molecular target of morphine in vivo and that it is a mandatory component of the opioid system for morphine action.

Analgesics↗
PubMed1996

Similar involvement of several brain areas in the antinociception of endogenous and exogenous opioids.

The complete inhibitor of the enkephalin degrading enzymes, RB 101, N-{(R,S)-2-benzyl-3[(S)-(2-amino-4-methylthio)butyldithio]-1- oxopropyl}-L-phenylalanine benzyl ester, which crosses the blood-brain barrier, induced antinociceptive effects similar to those of exogenous opiates. The almost complete absence of tolerance and dependence after chronic administration of RB 101 is therefore due to limited stimulation of opioid receptors by 'protected' endogenous enkephalins. In order to clarify the mechanisms involved in these response, we have investigated the participation of several brain structures in the antinociceptive effects induced by systemic administration of morphine or RB 101. Rats were implanted with bilateral cannulae into the ventro-basal thalamus, central amygdala and periaqueductal gray matter, or with a cannula into the raphe magnus nucleus. The antinociceptive responses induced by systemic morphine or RB 101 were measured by using the tail-electrical stimulation test, where three different thresholds were determined: motor response, vocalization and vocalization post-discharge. The ability of the opioid receptor antagonist methylnaloxonium to block these antinociceptive responses was evaluated after local injection into the different brain structures. The blockade of morphine- and RB 101-induced antinociception was similar, and was stronger when methylnaloxonium was injected into the periaqueductal gray matter and raphe magnus nucleus than when it was injected into the ventro-basal thalamus and amygdala. These results suggest that brain structures related to the control of pain seem to be the same for the antinociception induced by exogenous opiates and endogenous opioids.

Analgesia↗
PubMed1996

Cyclic AMP regulates basement membrane heparan sulfate proteoglycan, perlecan, metabolism in rat glomerular epithelial cells.

Perlecan, the basement membrane heparan sulfate proteoglycan (HSPG), has been fully cloned from mouse and human tissues. When a cRNA probe of murine perlecan cDNA was employed in RNase protection assay to test whether rat glomerular epithelial cells (GEC) constitutively express perlecan, several bands of hybridization were seen, suggesting that sequences between rat and murine perlecan may not be identical. Using primers based on published cDNA sequences of murine and human perlecan and poly A+ RNA of rat GEC, we synthesized a 497 bp product (RPD-I) by RT-PCR. The deduced aminoacid sequence showed an 85% and 88% homology with domain I of murine and human perlecan, respectively. The three putative sites containing the consensus sequence SGD for attachment of heparan sulfate chains were fully conserved in the rat perlecan as was a site (NFT) for attachment of N-linked oligosaccharide. RPD-I detected a > 9.5 kb transcript of perlecan in RNA of GEC, similar in size to that present in rat glomeruli. Employing a riboprobe synthesized from RPD-I in RNase protection assay we examined whether dbcAMP regulated perlecan expression in the GEC. At 1, 6, 24 and 48 h of incubation, 1 mM dbcAMP caused 43%, 32%, 47% and 40% reduction in mRNA abundance of perlecan, respectively. Immunoprecipitation showed a corresponding reduction of 61%, 70% and 65% in the synthesis of 35SO4 labeled basement membrane HSPG by the GEC following 12, 24 and 48 h of incubation with dbcAMP. Following incubation for 1 and 24 h prostaglandins, PGE1 and PGE2 (1 uM), known activators of glomerular adenylate cyclase, reduced perlecan mRNA abundance to a similar extent as dbcAMP on northern analysis. Our results show that glomerular basement membrane HSPG synthesized by the GEC belongs to the perlecan family. Decrease of GEC perlecan gene expression and synthesis by cAMP and prostaglandins may be of relevance to proteinuric states characterized by activation of these mediators.

Alprostadil↗
PubMed1996

Reduction of morphine abstinence in mice with a mutation in the gene encoding CREB.

Chronic morphine administration induces an up-regulation of several components of the cyclic adenosine 5'-monophosphate (cAMP) signal transduction cascade. The behavioral and biochemical consequences of opiate withdrawal were investigated in mice with a genetic disruption of the alpha and Delta isoforms of the cAMP-responsive element-binding protein (CREB). In CREBalphadelta mutant mice the main symptoms of morphine withdrawal were strongly attenuated. No change in opioid binding sites or in morphine-induced analgesia was observed in these mutant mice, and the increase of adenylyl cyclase activity and immediate early gene expression after morphine withdrawal was normal. Thus, CREB-dependent gene transcription is a factor in the onset of behavioral manifestations of opiate dependence.

Adenylyl Cyclases↗
PubMed1996

The CCKB antagonist PD-134,308 facilitates rewarding effects of endogenous enkephalins but does not induce place preference in rats.

The interaction between cholecystokinin and endogenous opioid systems on rewarding responses was examined. Motivational effects induced by peripheral administration of a complete inhibitor of enkephalin catabolism, RB 101 or the CCKB antagonist PD-134,308, and by both compounds in combination were evaluated in the conditioned place preference test in rats. RB 101 (5, 10, 20, 40 and 80 mg/kg, IP, and 20 mg/kg, IV) given alone produced a bell-shaped dose-effect function. A significant increase of the preference for the drug-associated compartment was only observed at doses of 10 and 20 mg/kg (IP). The effect observed with morphine was stronger, and all the doses used of this compound (1.25, 2.5 and 5 mg/kg, SC) were found to be active. These results suggest that the inhibitor of enkephalin catabolism has weak rewarding properties. Pretreatment with the CCKB antagonist PD-134,308 (0.1, 0.3, 1 and 3 mg/kg, IP) alone failed to produce a reliable aversion or preference on the paradigm studied. When PD-134,308 (0.3 mg/kg, IP) was coadministered with a subthreshold dose of morphine (0.6 mg/kg, SC) or RB 101 (5 mg/kg, IP), a conditioned place preference was observed, indicating that the CCKB antagonist facilitated the motivational responses induced by endogenous enkephalins as compared to morphine. This suggests that endogenous cholecystokinin, acting through CCKB receptors, modulates the rewarding effects of endogenous enkephalins.

Animals↗
PubMed1996

Protein kinases in the rat nucleus accumbens are involved in the aversive component of opiate withdrawal.

The specific participation of protein kinases in the expression of the somatic signs of morphine withdrawal has been previously demonstrated, suggesting that changes in intracellular signalling systems are involved in opioid addiction. In the present study, the involvement of protein kinases in the aversive/dysphoric effects of morphine abstinence has been investigated in the nucleus accumbens, because of the critical role played by the mesolimbic system in the rewarding effects of opioids. Rats were chronically treated with morphine, twice a day for 5 days, with doses progressively increased from 5 to 30 mg/kg (i.p.). In addition, microinjections into the nucleus accumbens of the serine-threonine kinase inhibitors H7 or H8 (1 or 10 nmol per side) or saline once daily were also given, both in control and in morphine-treated animals. After these chronic treatments, withdrawal syndrome was induced by naloxone administration (0.1 mg/kg, s.c.), and the motivational component of morphine abstinence was studied using the place aversion paradigm. When administered at the highest dose (10 nmol), H7 and H8 strongly reduced the place aversion induced by naloxone in morphine dependent animals. Protein kinase inhibitors did not induce significant behavioural responses in non-dependent animals. Chronic morphine treatment induced a selective up-regulation of adenylate cyclase activity in the amygdala, without affecting other brain regions. The morphine-increased adenylate cyclase activity in amygdala was reversed by the chronic intra-accumbens microinjections of H7 and H8. These results suggest that serine-threonine kinases in the nucleus accumbens play an important role in the emotional/dysphoric properties which characterize opiate withdrawal.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1996

Similar decrease in spontaneous morphine abstinence by methadone and RB 101, an inhibitor of enkephalin catabolism.

1. The dual inhibitor of enkephalin degrading enzymes, RB 101, is able to block endogenous enkephalin metabolism completely, leading to potent antinociceptive responses potentiated by blockade of CCKB receptors. In this study we have investigated the effects induced by RB 101 given alone, or with the CCKB antagonist, PD-134,308, on a model of spontaneous morphine withdrawal and substitutive maintenance in rats. 2. Animals were chronically treated with morphine for 7 days followed, 36 h after the interruption of drug administration, by a maintenance treatment for 5 days with methadone (2 mg kg-1, i.p.), clonidine (0.025 mg kg-1, i.p.), RB 101 (40 mg kg-1, i.p.), PD-134,308 (3 mg kg-1, i.p.) or a combination of RB 101 plus PD-134,308. Several behavioural observations were made during this period in order to evaluate the acute effects as well as the consequence of chronic maintenance induced on spontaneous withdrawal by the different treatments. 3. Methadone was the most effective compound in decreasing the spontaneous withdrawal syndrome after acute administration. Both, methadone and RB 101 had similar effectiveness in reducing opiate abstinence during the period of substitutive treatment. PD-134,308 did not show any effect when administered alone and did not modify the effect of RB 101. 4. Naloxone (1 mg kg-1, s.c.) failed to precipitate any sign of withdrawal when injected at the end of the chronic maintenance treatment suggesting that, under the present conditions, methadone and RB 101 did not induce significant physical opiate-dependence. 5. The mildness of the side effects induced by chronic RB 101, suggests that systemically active inhibitors of enkephalin catabolism could represent a promising treatment in the maintenance of opiate addicts.

Analgesics↗