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J A García-Sevilla

Publications and source records attributed to J A García-Sevilla.

At least 19 recordsLinked to original sources
PubMed2004

Neurofilament proteins and cAMP pathway in brains of mu-, delta- or kappa-opioid receptor gene knock-out mice: effects of chronic morphine administration.

Opiate addiction is associated with abnormalities of neurofilament (NF) proteins and upregulation of cAMP signaling in the brain, which may modulate neuronal plasticity. This study investigated, using gene-targeted mice lacking mu-, delta- or kappa-opioid receptors, the role of these receptors in modulating the basal activity and the chronic effects of morphine on both intracellular targets. In WT mice, chronic treatment (5 days) with morphine (20-100 mg/kg) resulted in decreases in the immunodensity of neurofilament (NF)-L in the cerebral cortex (14-23%). In contrast, chronic morphine did not decrease NF-L in cortices of mu-, delta-, and kappa-KO mice, suggesting the involvement of the three types of opioid receptors in this effect of morphine. Also, the marked increase in phosphorylated NF-H induced by chronic morphine in WT mice (two-fold) was abolished in mu -KO mice. In cortex and/or striatum of mu-, delta- and kappa-KO mice, the basal immunodensities of Galphai1/2 proteins, the catalytic isoform (Calpha) of protein kinase A (PKA) and the total content of cAMP response element-binding protein (CREB, the nuclear target of PKA) were not different from those of WT mice. In contrast, phosphorylated CREB (the active form of this transcription factor) was reduced in cortex and/or striatum (23-26%) of mu- and delta-KO mice, but not in kappa-KO animals. These results suggest that the endogenous opioid tone acting on mu-/delta-receptors tonically stimulate CREB activation in the brain. In cortex and/or striatum of WT mice, chronic morphine did not induce upregulation of the main components of the cAMP signaling pathway. In contrast, chronic morphine treatment in mu-KO mice, but not in delta- or kappa-KO, resulted in a paradoxical upregulation of Galphai1/2 (12-19%), PKA (19-21%,) and phosphorylated CREB (21-73%), but not total CREB, in cortex and/or striatum. The induction of heterologous receptor adaptations in mu-KO mice may explain this paradoxical effect of morphine.

Animals↗
PubMed2004

Long-term regulation of signalling components of adenylyl cyclase and mitogen-activated protein kinase in the pre-frontal cortex of human opiate addicts.

Opiate addiction involves the development of chronic adaptive changes in micro -opioid receptors and associated pathways (e.g. cAMP signalling) which lead to neuronal plasticity in the brain. This study assessed the status of cAMP and mitogen-activated protein kinase (MAPK) pathways in brains (pre-frontal cortex) of chronic opiate addicts. In these subjects (n = 24), the immunodensities of adenylyl cyclase-I, PKA Calpha, total and phosphorylated CREB were not different from those in sex-, age- and PMD-matched controls. Moreover, the ratio pCREB/tCREB was similar in opiate addicts (0.74) and controls (0.76), further indicating that opiate addiction in humans is not associated with an upregulation of several key components of cAMP signalling in the pre-frontal cortex. In contrast, the components of MAPK cascade (Ras/c-Raf-1/MEK/ERK) were decreased in the same brains. Notably, pronounced downregulations of phosphorylated MEK (85%) and ERK1/2 (pERK1: 81%; pERK2: 80%) were quantitated in brains of opiate addicts. Chronic morphine treatment in rats (10-100 mg/kg for 5 days) was also associated with decreases of pERK1/2 (59-68%) in the cortex. In SH-SY5Y cells, morphine also stimulated the activity of pERK1/2 (2.5-fold) and the MEK inhibitor PD98059 blocked this effect (90%). The abnormalities of MAPK signalling might have important consequences in the long term development of various forms of neural plasticity associated with opiate addiction in humans.

Adenylyl Cyclases↗
PubMed2002

Acute treatment with the cyclic antidepressant desipramine, but not fluoxetine, increases membrane-associated G protein-coupled receptor kinases 2/3 in rat brain.

The homologous regulation of receptors is mediated by G protein-coupled receptor kinases (GRKs) which phosphorylate the agonist-activated receptor. This study was designed to assess the in vivo indirect activation of adrenoceptors or 5-HT receptors by the reuptake blocker desipramine or fluoxetine on the cellular distribution of GRK 2/3 in rat brain. Immunoblot analysis (frontal cortex) with a GRK 2 antibody revealed a unique 80 kDa protein (mixed GRK 2/3) in total homogenate (H) and in membrane (P2) and cytosolic (S2) fractions. The proportion of GRK 2/3 in each fraction, relative to that of H, was: P2/H=0.11 and S2/H=0.45. Acute desipramine (noradrenaline reuptake blocker) increased in a dose- (1-30 mg/kg, i.p.) and time- (1-6 h) dependent manner the content of GRK 2/3 in the membrane (P2/H ratios increased by 37-164%). This effect vanished with a prolonged desipramine (30 mg/kg) exposure (24 h). Desipramine did not alter the content of GRK 2/3 in the cytosol (S2/H ratios). Chronic desipramine (10 mg/kg every 24 h) for 14 days did not change significantly the immunodensity of GRK 2/3 in the membrane or the cytosol. The acute administration (2 h) of fluoxetine (5-HT reuptake blocker; 3-30 mg/kg) did not induce significant changes in the content of GRK 2/3 in the membrane (P2/H ratio) or cytosol (S2/H ratio). The results indicate that the in vivo activation of adrenoceptors by desipramine is associated with a time-dependent modulation of membrane-associated GRK 2/3 (i.e. an acute increase in the kinase content which is followed by a return to the basal expression upon repeated treatment). In contrast, the acute in vivo activation of 5-HT receptors induced by fluoxetine does not result in modulation of GRK 2/3.

Animals↗
PubMed2002

Neurotransmitter receptor-mediated activation of G-proteins in brains of suicide victims with mood disorders: selective supersensitivity of alpha(2A)-adrenoceptors.

Abnormalities in the density of neuroreceptors that regulate norepinephrine and serotonin release have been repeatedly reported in brains of suicide victims with mood disorders. Recently, the modulation of the [(35)S]GTPgammaS binding to G-proteins has been introduced as a suitable measure of receptor activity in postmortem human brain. The present study sought to evaluate the function of several G-protein coupled receptors in postmortem brain of suicide victims with mood disorders. Concentration-response curves of the [(35)S]GTPgammaS binding stimulation by selective agonists of alpha(2)-adrenoceptors, 5-HT(1A) serotonin, mu-opioid, GABA(B), and cholinergic muscarinic receptors were performed in frontal cortical membranes from 28 suicide victims with major depression or bipolar disorder and 28 subjects who were matched for gender, age and postmortem delay. The receptor-independent [(35)S]GTPgammaS binding stimulation by mastoparan and the G-protein density were also examined. The alpha(2A)-adrenoceptor-mediated stimulation of [(35)S]GTPgammaS binding with the agonist UK14304 displayed a 4.6-fold greater sensitivity in suicide victims than in controls, without changes in the maximal stimulation. No significant differences were found in parameters of 5-HT(1A) serotonin receptor and other receptor-mediated [(35)S]GTPgammaS binding stimulations. The receptor-independent activation of G-proteins was similar in both groups. Immunoreactive densities of G(alphai1/2)-, G(alphai3)-, G(alphao)-, and G(alphas)-proteins did not differ between suicide victims and controls. In conclusion, alpha(2A)-adrenoceptor sensitivity is increased in the frontal cortex of suicide victims with mood disorders. This receptor supersensitivity is not related to an increased amount or enhanced intrinsic activity of G-proteins. The new finding provides functional support to the involvement of alpha(2)-adrenoceptors in the pathogenesis of mood disorders.

Adult↗
PubMed2001

Acute and chronic effects of morphine and naloxone on the phosphorylation of neurofilament-H proteins in the rat brain.

Increased amounts of phosphorylated neurofilaments (pNF-H and pNF-M) are found in postmortem brains of opioid addicts. Because of the potential relevance of aberrant pNF in opioid addiction (alterations of neuronal cytoskeleton and associated functions), the effects of opiate drugs on pNF-H were investigated in rat brain. Acute morphine (30 mg/kg, 2 h) induced a marked increase in the immunodensity of pNF-H in the cerebral cortex (93%). Chronic morphine (10-100 mg/kg for 5 days) followed by opiate withdrawal resulted in a time-dependent decline in pNF-H (induction of tolerance). Thus, 2 h after the last dose of morphine, the abundance of pNF-H was still increased (27%), which was followed (6-24 h) by down-regulation of pNF-H (5% increase at 6 h; 5% decrease at 12 h, and 29% decrease at 24 h). The acute (10 mg/kg for 2 h) and chronic (2 x 10 mg/kg for 14 days) treatments with naloxone, an opioid receptor antagonist, did not alter pNF-H in the cerebral cortex, suggesting that the opioid receptors (probably the mu-type) modulating the phosphorylation state of NF-H are not tonically activated by endogenous opioids. The results indicate that morphine addiction is associated with an aberrant hyperphophorylation of NF-H in the rat brain.

Animals↗
PubMed2001

Cyclic AMP-mediated signaling components are upregulated in the prefrontal cortex of depressed suicide victims.

The components of cyclic AMP signaling cascade (catalytic (Calpha) subunit of cyclic AMP-dependent protein kinase (PKA) and cyclic AMP response element binding protein (CREB)) were quantitated by Western blotting in the prefrontal cortex of depressed suicide victims (n=23) and their matched controls (n=14). There was a significant increase in the levels of CREB, both in total (tCREB; 121+/-8% (mean+/-S.E.M.), P<0.02) and phosphorylated (pCREB; 128+/-9%, P<0.01) forms, but not in PKA Calpha levels (109+/-9%, ns), in brains of depressed suicides compared to those in control subjects. The increases in CREB were specifically observed in antidepressant drug-free subjects (tCREB: 137+/-11%, P<0.01; pCREB: 136+/-12%, P<0.02; n=9), but not in the antidepressant-treated subjects (tCREB: 108+/-18%, ns; pCREB: 111+/-17%, ns; n=8). There were significant correlations between the levels of PKA and those of tCREB and pCREB in the prefrontal cortex of depressed suicides. These results indicate that the components of cyclic AMP signaling are upregulated in a coordinated manner in brains of depressed suicides and that this alteration is not related to antidepressant treatment.

Adult↗
PubMed2001

Relationships between beta- and alpha2-adrenoceptors and G coupling proteins in the human brain: effects of age and suicide.

Interactions between brain alpha2- and beta-adrenoceptors are of interest in physiological (aging) and pathological (major depression) processes involving both receptors. In this study, total beta-adrenoceptors and beta1/2-subtypes were quantitated in postmortem human brains to investigate their relationships with alpha2A-adrenoceptors and specific G proteins during the process of aging and in brains of suicide victims. Analysis of [3H]CGP12177 binding, in the presence of CGP20712A (beta1-antagonist), indicated that the predominant beta-adrenoceptor in the frontal cortex is the beta1-subtype (65-75%). The density of total beta- (r=-0.60, n=44) or beta1-adrenoceptors (r=-0.78, n=22), but not the beta2-subtype, declined with aging (3-80 years). The density of total beta- or beta1-adrenoceptors, but not the beta2-subtype, correlated with the number of alpha2-adrenoceptors quantitated in the same brains with the agonist [3H]UK14304 (r=0.71-0.81) or the antagonist [3H]RX821002 (r=0.61-0.66). Interestingly, the ratios alpha2/beta- or alpha2/beta1-adrenoceptors did not correlate with the age of the subject at death, indicating that the proportion of alpha2/beta-adrenoceptors in brain remains rather constant during the process of aging. The density of beta-adrenoceptors correlated with the immunodensity of G(alpha)s (r=0.55) and Gbeta (r=0.61) proteins, and that of alpha2-adrenoceptors with those of G(alpha)i1/2 (r=0.88) and Gbeta (r=0.65). In brains of suicides, compared to controls, the ratio between alpha2- and beta- or beta1-adrenoceptors (alpha2-full agonist sites/beta-sites) was greater (1.3- to 2.0-fold; P<0.05). The results demonstrate a close interdependence between brain alpha2- and beta-adrenoceptors during aging, and in brains of suicides. The quantitation of the alpha2A/beta-adrenoceptor ratio could represent a relevant neurochemical index in the study of brain pathologies in which both receptors are involved.

Adolescent↗
PubMed2001

The imidazoline receptor ligand 2-(2-benzofuranyl)-2-imidazoline is a dopamine-releasing agent in the rat striatum in vivo.

2-BFI (2-(2-benzofuranyl)-2-imidazoline) is a prototypical I2-imidazoline receptor ligand. In vivo, however, 2-BFI (1-20 mg/kg) decreased the synthesis of dopa/dopamine (DA) in rat striatum through mechanisms not related to interaction with I2-imidazoline receptors or to inhibition of the enzyme monoamine oxidase. The aim of this study was to unravel the mechanism underlying this potent effect of 2-BFI in brain. In vitro 2-BFI showed very low affinity for D2-dopamine receptors (K(i)=47 microM), and in vivo the drug (7 mg/kg) decreased the synthesis of striatal dopa/DA similarly in control rats (43%) and in rats pre-treated with alpha-methyl-para-tyrosine (50%) or cocaine (51%), indicating that this effect was not the result of D2-dopamine autoreceptor direct stimulation, inhibition of the enzyme tyrosine hydroxylase or blockade of neuronal DA reuptake. In DA-depleted (reserpine-treated) rats, however, 2-BFI did not inhibit significantly (11%), the synthesis of dopa/DA in the striatum, indicating that the effect of 2-BFI was indirectly mediated by endogenous DA through the activation of D2-dopamine autoreceptors. In conclusion, the I2-imidazoline receptor ligand 2-BFI is also a DA releasing agent in brain, and consequently a DA indirect agonist in vivo.

Adrenergic Uptake Inhibitors↗
PubMed2001

Brain alpha(2)-adrenoceptors in monoamine-depleted rats: increased receptor density, G coupling proteins, receptor turnover and receptor mRNA.

1. This study was designed to assess the molecular and cellular events involved in the up-regulation (and receptor supersensitivity) of brain alpha(2)-adrenoceptors as a result of chronic depletion of noradrenaline (and other monoamines) by reserpine. 2. Chronic reserpine (0.25 mg kg(-1) s.c., every 48 h for 6 - 14 days) increased significantly the density (B(max) values) of cortical alpha(2)-adrenoceptor agonist sites (34 - 48% for [(3)H]-UK14304, 22 - 32% for [(3)H]-clonidine) but not that of antagonist sites (11 - 18% for [(3)H]-RX821002). Competition of [(3)H]-RX821002 binding by (-)-adrenaline further indicated that chronic reserpine was associated with up-regulation of the high-affinity state of alpha(2)-adrenoceptors. 3. In cortical membranes of reserpine-treated rats (0.25 mg kg(-1) s.c., every 48 h for 20 days), the immunoreactivities of various G proteins (Galphai(1/2), Galphai(3), Galphao and Galphas) were increased (25 - 34%). Because the high-affinity conformation of the alpha(2)-adrenoceptor is most probably related to the complex with Galphai(2) proteins, these results suggested an increase in signal transduction through alpha(2)-adrenoceptors (and other monoamine receptors) induced by chronic reserpine. 4. After alpha(2)-adrenoceptor alkylation, the analysis of receptor recovery (B(max) for [(3)H]-UK14304) indicated that the increased density of cortical alpha(2)-adrenoceptors in reserpine-treated rats was probably due to a higher appearance rate constant of the receptor ((Delta)r=57%) and not to a decreased disappearance rate constant ((Delta)k=7%). 5. Northern- and dot-blot analyses of RNA extracted from the cerebral cortex of saline- and reserpine-treated rats (0.25 mg kg(-1), s.c., every 48 h for 20 days) revealed that reserpine markedly increased the expression of alpha(2a)-adrenoceptor mRNA in the brain (125%). This transcriptional activation of the receptor gene expression appears to be the cellular mechanism by which reserpine induces up-regulation in the density of brain alpha(2)-adrenoceptors.

Adrenergic Uptake Inhibitors↗
PubMed2001

Chronic morphine induces up-regulation of the pro-apoptotic Fas receptor and down-regulation of the anti-apoptotic Bcl-2 oncoprotein in rat brain.

1. This study was designed to assess the influence of activation and blockade of the endogenous opioid system in the brain on two key proteins involved in the regulation of programmed cell death: the pro-apoptotic Fas receptor and the anti-apoptotic Bcl-2 oncoprotein. 2. The acute treatment of rats with the mu-opioid receptor agonist morphine (3-30 mg x kg(-1), i.p., 2 h) did not modify the immunodensity of Fas or Bcl-2 proteins in the cerebral cortex. Similarly, the acute treatment with low and high doses of the antagonist naloxone (1 and 100 mg x kg(-1), i.p., 2 h) did not alter Fas or Bcl-2 protein expression in brain cortex. These results discounted a tonic regulation through opioid receptors on Fas and Bcl-2 proteins in rat brain. 3. Chronic morphine (10-100 mg x kg(-1), 5 days, and 10 mg x kg(-1), 13 days) induced marked increases (47-123%) in the immunodensity of Fas receptor in the cerebral cortex. In contrast, chronic morphine (5 and 13 days) decreased the immunodensity of Bcl-2 protein (15-30%) in brain cortex. Chronic naloxone (10 mg x kg(-1), 13 days) did not alter the immunodensities of Fas and Bcl-2 proteins in the cerebral cortex. 4. The concurrent chronic treatment (13 days) of naloxone (10 mg x kg(-1)) and morphine (10 mg x kg(-1)) completely prevented the morphine-induced increase in Fas receptor and decrease in Bcl-2 protein immunoreactivities in the cerebral cortex. 5. The results indicate that morphine, through the sustained activation of opioid receptors, can promote abnormal programmed cell death by enhancing the expression of pro-apoptotic Fas receptor protein and damping the expression of anti-apoptotic Bcl-2 oncoprotein.

Animals↗
PubMed2000

Regulation of nonphosphorylated and phosphorylated forms of neurofilament proteins in the prefrontal cortex of human opioid addicts.

The neurofilament (NF) proteins (NF-H, NF-M, and NF-L for high, medium, and low molecular weights) play a crucial role in the organization of neuronal shape and function. In a preliminary study, the abundance of total NF-L was shown to be decreased in brains of opioid addicts. Because of the potential relevance of NF abnormalities in opioid addiction, we quantitated nonphosphorylated and phosphorylated NF in postmortem brains from 12 well-defined opioid abusers who had died of an opiate overdose (heroin or methadone). Levels of NF were assessed by immunoblotting techniques using phospho-independent and phospho-dependent antibodies, and the relative (% changes in immunoreactivity) and absolute (changes in ng NF/microg total protein) amounts of NF were calculated. Decreased levels of nonphosphorylated NF-H (42-32%), NF-M (14-9%) and NF-L (30-29%) were found in the prefrontal cortex of opioid addicts compared with sex, age, and postmortem delay-matched controls. In contrast, increased levels of phosphorylated NF-H (58-41%) and NF-M (56-28%) were found in the same brains of opioid addicts. The ratio of phosphorylated to nonphosphorylated NF-H in opioid addicts (3.4) was greater than that in control subjects (1.6). In the same brains of opioid addicts, the levels of protein phosphatase of the type 2A were found unchanged, which indicated that the hyperphosphorylation of NF-H is not the result of a reduced dephosphorylation process. The immunodensities of GFAP (the specific glial cytoskeletol protein), alpha-internexin (a neuronal filament related to NF-L) and synaptophysin (a synapse-specific protein) were found unchanged, suggesting a lack of gross changes in glial reaction, other intermediate filaments of the neuronal cytoskeletol, and synaptic density in the prefrontal cortex of opioid addicts. These marked reductions in total NF proteins and the aberrant hyperphosphorylation of NF-H in brains of opioid addicts may play a significant role in the cellular mechanisms of opioid addiction.

Adult↗
PubMed2000

I2-Imidazoline receptors and monoamine oxidase B enzyme sites in human brain: covariation with age.

An association between monoamino oxidase B enzyme (MAO-B) sites and I(2)-imidazoline receptors (I(2)-IR) has been established in human brain on the basis of correlational studies of radiolabelled binding sites. Because both MAO-B and I(2)-IR densities increase with aging, the age at death could be partially involved in the observed correlations. The evaluation of two independent but similar datasets demonstrated that the linear correlation between MAO-B and I(2)-IR densities dropped from 0.70 (P=0.02) and 0.41 (P=0.14) in the crude analyses to the negligible values of 0.07 (P=0.84) and 0.09 (P=0.75) when the age at death was controlled for in the statistical analyses. The results lead to conclude, contrary to former interpretations, that there is not any statistical association linking both MAO-B catalytic unit sites and I(2)-IR densities in the human brain.

Adolescent↗
PubMed2000

Chronic clorgyline induces selective down-regulation of alpha2-adrenoceptor agonist binding sites in rat brain.

Inactivation of alpha2-adrenoceptors by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) has been shown to induce an increase in brain regulatory G alpha(i1/2) proteins, which was related to biphasic recovery of agonist binding sites. To investigate further the nature of this phenomenon, the chronic effects of clorgyline (a monoamine oxidase inhibitor antidepressant) on the recovery of alpha2-adrenoceptors after EEDQ and on EEDQ-induced up-regulation of G alpha(i1/2) proteins were assessed in rat brain. Clorgyline (1 mg kg(-1) for 7-35 days) induced a time-dependent down-regulation (20% to 55%) of the density of cortical alpha2-adrenoceptor agonist sites ([3H]UK 14304/bromoxidine binding) but not of antagonist sites ([3H]RX 821002/2-methoxy idazoxan binding). However, chronic clorgyline did not alter the immunoreactive levels of G alpha(i1/2), G alpha(i3), and G alpha(o) proteins in cortex. In clorgyline-treated rats, the turnover functions for agonist and antagonist binding sites (receptor recovery after EEDQ) were different and indicated that the reduced density of alpha2-adrenoceptor agonist sites induced by clorgyline was due to a greater rate of receptor disappearance. The recovery of [3H]UK 14304 binding in clorgyline-treated rats did not fit a biphasic recovery model and the turnover parameters were very similar to those obtained for the second phase of recovery (biphasic model) of agonist binding sites in naive rats. This suggested that clorgyline down-regulated only the alpha2-adrenoceptors of rapid turnover which is associated with the increases in the expression of G alpha(i1/2) proteins induced by EEDQ. In this context, clorgyline (1 mg kg(-1) for 7 days) fully prevented the up-regulation (50%) of brain G alpha(i1/2) proteins induced by EEDQ. The results indicate that one relevant mechanism involved in the in vivo desensitization of brain alpha2-adrenoceptors is an effective impairment of receptor-G protein coupling.

Adrenergic alpha-Agonists↗
PubMed2000

Activation of I(2)-imidazoline receptors enhances supraspinal morphine analgesia in mice: a model to detect agonist and antagonist activities at these receptors.

This work investigates the receptor acted upon by imidazoline compounds in the modulation of morphine analgesia. The effects of highly selective imidazoline ligands on the supraspinal antinociception induced by morphine in mice were determined. 2. Intracerebroventricular (i.c.v.) or subcutaneous (s.c.) administration of ligands selective for the I(2)-imidazoline receptor, 2-BFI, LSL 60101, LSL 61122 and aganodine, and the non selective ligand agmatine, increased morphine antinociception in a dose-dependent manner. Neither moxonidine, a mixed I(1)-imidazoline and alpha(2)-adrenoceptor agonist, RX821002, a potent alpha(2)-adrenoceptor antagonist that displays low affinity at I(2)-imidazoline receptors, nor the selective non-imidazoline alpha(2)-adrenoceptor antagonist RS-15385-197, modified the analgesic responses to morphine. 3. Administration of pertussis toxin (0.25 microg per mouse, i.c.v.) 6 days before the analgesic test blocked the ability of the I(2)-imidazoline ligands to potentiate morphine antinociception. 4. The increased effect of morphine induced by I(2)-imidazoline ligands (agonists) was completely reversed by idazoxan and BU 224. Identical results were obtained with IBI, which alkylates I(2)-imidazoline binding sites. Thus, both agonist and antagonist properties of imidazoline ligands at the I(2)-imidazoline receptors were observed. 5. Pre-treatment (30 min) with deprenyl, an irreversible inhibitor of monoamine oxidase B (IMAO-B), produced an increase of morphine antinociception. Clorgyline, an irreversible IMAO-A, given 30 min before morphine did not alter the effect of the opioid. At longer intervals (24 h) a single dose of either clorgyline or deprenyl reduced the density of I(2)-imidazoline receptors and prevented the I(2)-mediated potentiation of morphine analgesia. 6. These results demonstrate functional interaction between I(2)-imidazoline and opioid receptors. The involvement of G(i)-G(o) transducer proteins in this modulatory effect is also suggested.

Analgesia↗
PubMed2000

Induction of reactive astrocytosis and prevention of motoneuron cell death by the I(2)-imidazoline receptor ligand LSL 60101.

I(2)-imidazoline receptors are mainly expressed on glial cells in the rat brain. This study was designed to test the effect of treatment with the I(2)-imidazoline selective receptor ligand LSL 60101 [2-(2-benzofuranyl)imidazole] on the morphology of astrocytes in the neonate and adult rat brain, and to explore the putative neuroprotective effects of this glial response. Short-term (3 days) or chronic (7-10 days) treatment with LSL 60101 (1 mg kg(-1), i.p. every 12 h) enhanced the area covered by astroglial cells in sections of facial motor nucleus from neonate rats processed for glial fibrillary acidic protein (GFAP) immunostaining. Facial motoneurons surrounded by positive glial cell processes were frequently observed in sections of LSL 60101-treated rats. A similar glial response was observed in the parietal cortex of adult rats after chronic (10 days) treatment with LSL 60101 (10 mg kg(-1), i.p. every 12 h). Western-blot detection of the specific astroglial glutamate transporter GLT-1, indicated increased immunoreactivity after LSL 60101 treatment in the pons of neonate and in the parietoccipital cortex of adult rats. In the facial motor nucleus of neonate rats, the glial response after LSL 60101 treatment was associated to a redistribution of the immunofluorescence of the basic fibroblast growth factor (FGF-2) from the perinuclear area of motoneurons to cover most of their cytoplasm, suggesting a translocation of this mitogenic and neurotrophic factor towards secretion pathways. The neuroprotective potential of the above effects of LSL 60101 treatment was tested after neonatal axotomy of facial motor nucleus. Treatment with LSL 60101 (1 mg kg(-1), i.p. every 12 h from day 0 to day 10 after birth) significantly reduced (38%) motoneuron death rate 7 days after facial nerve axotomy performed on day 3 after birth. It is concluded that treatment with the I(2)-imidazoline selective receptor ligand LSL 60101 provokes morphological/biochemical changes in astroglia that are neuroprotective after neonatal axotomy.

ATP-Binding Cassette Transporters↗
PubMed2000

mu-opioid receptor and alpha2-adrenoceptor agonist stimulation of [35S]GTPgammaS binding to G-proteins in postmortem brains of opioid addicts.

Repeated opioid administration has been associated in human brain with unaltered density of mu-opioid receptors (agonist radioligand binding sites and immunodetected receptor protein). These receptors are coupled to Gi/Go-proteins, which are increased in brain of heroin addicts. To assess the activity of G-proteins and their coupling to receptors after chronic opioid abuse, [35S]GTPgammaS binding was quantified in postmortem prefrontal cortices of 15 opioid-dependent subjects and 15 matched controls. The stimulation of [35S]GTPgammaS binding by the mu-opioid receptor agonist DAMGO or the alpha2-adrenoceptor agonist UK14304 was used as a functional measure of the status of the receptor-G-protein coupling. [35S]GTPgammaS binding basal values were similar in opioid addicts (819+/-83 fmol mg-1 of protein) and controls (918+/-106 fmol mg(-1) of protein). In opioid addicts, [35S]GTPgammaS binding stimulation by DAMGO showed a maximal effect (62+/-8%) and a potency (EC50 = 1.09+/-0.26 microM) that did not differ from the maximal effect (60+/-12%) and potency (EC50 = 2.01+/-0.58 microM) in controls. In opioid addicts, [35S]GTPgammaS binding stimulation by UK14304 was not different in maximal effect (28+/-3%) from controls (32+/-8%), but the potency of the agonist was decreased (EC50 = 4.36+/-1.81 microM) when compared with controls (EC50 = 0.41+/-0.15 microM). The results provide a direct evidence of an apparent normal functional activity of brain mu-opioid receptors (Gi/Go-protein coupling) during the opioid dependence process in humans. The data also demonstrate a functional uncoupling of alpha2-adrenoceptors from G-proteins, which indicates a heterologous desensitization of these receptors. This finding could represent an adaptive mechanism against the decreased noradrenergic activity induced by the chronic presence of opioid drugs.

Adrenergic alpha-2 Receptor Agonists↗
PubMed1999

Pharmacologic characterization of imidazoline receptor proteins identified by immunologic techniques and other methods.

Biochemical and pharmacologic evidence supports the heterogeneous nature of imidazoline receptors (IRs). However, only monoamine oxidase (MAO) (55- and 61-kD) isozymes have been identified as imidazoline binding site-containing proteins. Idazoxan-binding proteins of approximately 70- and approximately 45-kD of unknown amino acid sequences have been isolated from chromaffin cells and rat brain, respectively. Other proteins of approximately 27-30 to > 80 kD have been visualized by immunologic and photoaffinity labeling techniques in different tissues and species. The specific antiserum that recognizes the approximately 70-, approximately 45-, and approximately 29-kD IR proteins, but not MAO, was used to quantitate these proteins in the rat brain cortex. Treatments (7 days) with the I2-selective imidazoline drugs idazoxan (10 mg/kg), cirazoline (1 mg/kg), and LSL 60101 ([2-(2-benzofuranyl) imidazole; 10 mg/kg]) induced differential changes in these proteins: levels of the approximately 29-kD IR were increased by idazoxan and LSL 60101 (23%), levels of the approximately 45-kD protein only by cirazoline (44%), and those of the approximately 66-kD protein only by idazoxan (50%). These treatments also increased the densities of [3H]-idazoxan (I2) binding sites (32-42%). Chronic treatment with efaroxan, RX821002, and yohimbine (10 mg/kg), which possess very low affinity for I2-IRs, did not alter either their immunoreactivities or the density of I2 sites. Chronic treatment with MAO inhibitors clorgyline and phenelzine (10 mg/kg) and acute treatment with EEDQ (1.6 mg/kg, 6 h) induced decreases in the levels of these IR proteins (17-47%) and I2 sites (31-57%). Significant correlations were found when the mean percentage changes in immunoreactivity of IR proteins were related to the mean percentage changes in the density of I2 sites after treatment with the foregoing drug (r = 0.92, r = 0.69, and r = 0.75 for the approximately 29-, approximately 45-, and approximately 66-kD proteins, respectively). These results indicate that in the rat cerebral cortex, the I2 sites labeled by [3H]idazoxan are heterogeneous and that the related immunoreactive IR proteins contribute differently to the modulation of I2 sites after drug treatment.

Animals↗