Younjoo Park

The effect of PARP inhibitor on ischaemic cell death, its related inflammation and survival signals

Poly(ADP‐ribose) polymerase (PARP) plays an important role in ischaemic cell death, and 3‐aminobenzamide (3‐AB), one of the PARP inhibitors, has a protective effect on ischaemic stroke. We investigated the neuroprotective mechanisms of 3‐AB in ischaemic stroke. The occlusion of middle cerebral artery (MCA) was made in 170 Sprague–Dawley rats, and reperfusion was performed 2 h after the occlusion. Another 10 Sprague–Dawley rats were used for sham operation. 3‐AB was administered to 85 rats 10 min before the occlusion [3‐AB group (n = 85) vs. control group without 3‐AB (n = 85)]. Infarct volume and water content were measured, brain magnetic resonance imaging, terminal deoxynucleotidyltransferase (TdT)‐mediated dUTP‐biotin nick end‐labelling (TUNEL) and Cresyl violet staining were performed, and immunoreactivities (IRs) of poly(ADP‐ribose) polymer (PAR), cleaved caspase‐3, CD11b, intercellular adhesion molecule‐1 (ICAM‐1), cyclooxygenase‐2 (COX‐2), phospho‐Akt (pAkt) and phospho‐glycogen synthase kinase‐3 (pGSK‐3) were compared in the peri‐infarcted region of the 3‐AB group and its corresponding ischaemic region of the control group at 2, 8, 24 and 72 h after the occlusion. In the 3‐AB group, the infarct volume and the water content were decreased (about 45% and 3.6%, respectively, at 24 h), the number of TUNEL‐positive cells was decreased (about 36% at 24 h), and the IRs of PAR, cleaved caspase‐3, CD11b, ICAM‐1 and COX‐2 were significantly reduced, while the IRs of pAkt and pGSK‐3 were increased. These results suggest that 3‐AB treatment could reduce the infarct volume by reducing ischaemic cell death, its related inflammation and increasing survival signals. The inhibition of PARP could be another potential neuroprotective strategy in ischaemic stroke.

Increased dopamine D2 receptor binding and enhanced apomorphine-induced locomotor activity in μ-opioid receptor knockout mice

Previous studies from our laboratory have indicated possible interactions between opioidergic and dopaminergic neurons in the central nervous system. In this study, apomorphine-induced locomotor activity and the D1 and D2 subtype dopamine receptor binding were examined in mice lacking the mu-opioid receptor genes. The ambulatory time, vertical time and total motor distance of locomotor activity were measured after administration of apomorphine (2mg/kg, i.p.) for a period of 90min. The autoradiographic studies of D1 and D2 dopamine receptors were conducted using [3H] SCH23390 and [3H] raclopride as ligand, respectively. In wild type mice that received apomorphine, 2mg/kg, i.p., the locomotor activity such as ambulatory time, vertical time and total motor distance were not significantly altered as compared with that of the saline control group. However, the locomotor activity measured was significantly increased in the same dose of apomorphine treated mu-opioid receptor knockout mice between 5 and 40min after administration. The results obtained also show that the binding of D2 dopamine receptor in mu-opioid receptor knockout mice was significantly higher than that of the wild type in the caudate putamen. However, the binding of the D1 dopamine receptor in mu-opioid receptor knockout mice was not significantly different from that of the wild type. It appears that the apomorphine treated mu-opioid receptor knockout mice showed enhancement in locomotor activity. The enhanced locomotor activity may be related to the compensatory up-regulation of D2 dopamine receptors in mice lacking mu-opioid receptor genes.

Region specific increase of dopamine receptor D1/D2 mRNA expression in the brain of μ-opioid receptor knockout mice

Previous pharmacological studies have indicated the possible existence of functional interactions between opioidergic and dopaminergic neurons in the CNS. In this study, the expression of mRNAs encoding dopamine receptor D1/D2 was examined to investigate whether there is a change in the dopamine pathway of mice lacking the mu-opioid receptor by in situ hybridization technique. In the mu-opioid receptor knockout mice, the expression of dopamine receptor D1 mRNA was increased in the olfactory tubercle, nucleus accumbens, caudate putamen, and the layer VI of the neocortex compared with that of wild-type mice. The expression of dopamine receptor D2 mRNA was also increased in the olfactory tubercle, caudate putamen, and the nucleus accumbens of mu-opioid receptor knockout mice. These results indicate that there are compensational changes in the dopaminergic systems of mu-opioid receptor knockout mice.

Comparison of G-protein activation in the brain by μ-, δ-, and κ-opioid receptor agonists in μ-opioid receptor knockout mice

Mice lacking the μ-opioid receptor gene have been developed by a gene knockout procedure. In this study, the activity of opioid receptor coupled G-proteins was examined to investigate whether there is a change in the extent of coupling for μ-, δ-, and κ-opioid receptors in μ-opioid receptor knockout mice. Selective agonists of μ- (DAMGO), δ- (DPDPE), and κ- (U-69,593) opioid receptors stimulated [35S]GTPγS binding in the caudate putamen and cortex of wild-type mice. In contrast, only U-69,593 stimulated [35S]GTPγS binding in these regions of μ-opioid receptor knockout mice. These results confirmed the absence of G-protein activation by a μ-opioid receptor agonist in μ-opioid receptor knockout mice, and demonstrated that coupling of the κ-opioid receptor to G-proteins is preserved in these mice. However, G-protein activation by the δ-opioid receptor agonist, DPDPE, was reduced in the μ-opioid receptor knockout mice, at least in the brain regions studied using autoradiography.

Autoradiographic study of NMDA-displaceable [3H]glutamate and [3H]MK-801 binding during butorphanol withdrawal in the rat brain.

Influences of continuous administration of butorphanol on the autoradiography of [3H]glutamate binding and [3H]MK-801 binding were investigated to study the effects of butorphanol withdrawal on NMDA receptors. Rats were administered butorphanol (26 nmol microl(-1) h(-1)) by continuous intracerebroventricular (i.c.v.) infusion through pre-implanted cannula connected to osmotic mini-pumps for 3 days. Rats were then sacrificed at 2, 7, and 24 h after discontinuation of butorphanol infusion. [3H]MK-801 binding was slightly increased in the cortical area, hippocampus, and cerebellum in 2, 7, and 24 h withdrawal groups and was shown most significant increase in the 7 h withdrawal group. NMDA-displaceable [3H]glutamate binding was markedly increased in the cortical area, striatum, septum, hippocampus, thalamus, and cerebellum in 7 h withdrawal group and was significantly increased in the striatum, hippocampus, and thalamus in 24 h withdrawal group. These results demonstrate that the development of butorphanol withdrawal is more prominent by 7 h after discontinuation of butorphanol infusion and suggest that NMDA binding sites at NMDA receptors may play more important role in the development of butorphanol withdrawal than that of channel blocking sites.

Involvement of μ-opioid receptors in potentiation of apomorphine-induced climbing behavior by morphine: studies using μ-opioid receptor gene knockout mice

The present study examined the hypothesis that μ-opioid receptors contribute to a behavioral stimulation produced by stimulation of dopamine receptors by comparing responses in μ-opioid receptor knockout and wild type mice. Apomorphine-induced climbing behavior was augmented by 65%, in wild type mice, but not in μ-knockout, following subcutaneous administration of morphine (15 mg/kg). Moreover, pretreatment with either naloxone (an opioid receptor antagonist) or haloperidol (a mixed D1/D2 receptor antagonist) eliminated the enhancement by morphine of climbing behavior in wild type mice. These results indicate that expression of μ-opioid receptors plays an important role in the enhancement of climbing behavior induced by the dopamine receptor agonist, apomorphine. Furthermore, this augmentation is mediated by interaction between dopamine and μ-opioid receptors.

Differential effects of morphine, DPDPE, and U-50488 on apomorphine-induced climbing behavior in μ-opioid receptor knockout mice

The present study examined the hypothesis whether the opioid receptors (mu, delta, and kappa) contribute to a behavioral dopaminergic activation produced by dopamine receptor agonist, apomorphine, by comparing responses in wild type and mu-opioid receptor knockout mice. The data suggest that expression of mu-opioid receptors plays an important role in the enhancement of climbing behavior induced by apomorphine. Compared to wild type mice, a response in the dopaminergic behavior by treatment with delta-receptor agonist, DPDPE, is more sensitive to the mice lacking mu-opioid receptor. Treatment with kappa-receptor agonist, U-50488, is potentiated the apomorphine-induced climbing behavior in wild type and mu-opioid receptor knockout mice. These responses may be independent of that through mu-opioid receptors. Therefore, the our results show that dopaminergic activation measured by climbing behavior in mu-opioid receptors knockout mice are differently regulated by mu-, delta-, and kappa-opioid receptor agonists.

Regional specific increases of [3H]AMPA binding and mRNA expression of AMPA receptors in the brain of μ-opioid receptor knockout mice

Previous pharmacological studies have indicated the possible existence of functional interactions between opioidergic and glutamatergic neurons in the CNS. In the present study, [(3)H]AMPA binding and the expression of mRNAs encoding flip and flop variants of three subtypes of AMPA glutamate receptor GluR1-3 were examined by in situ hybridization technique in order to investigate whether there is a change in the AMPA receptor system of mice lacking the mu-opioid receptor. In the mu-opioid receptor knockout mice, [(3)H]AMPA binding was increased in the hippocampal CA1 and dentate gyrus, cortex, and caudate putamen compared with that of the wild-type animals. The expression of GluR1 flip mRNA was increased in the cortex and caudate putamen of mu-opioid receptor knockout mice. The expression of GluR1 flop mRNA was increased in the cortex, caudate putamen, and hippocampal CA1 layer of mu-opioid receptor knockout mice. The expression of GluR2 flip mRNA was decreased in the hippocampal dentate gyrus of mu-opioid receptor knockout mice. The expression of GluR2 flop was not altered in any regions studied. The expression of GluR3 flip was increased in the cortical area and caudate putamen of mu-opioid receptor knockout mice. The expression of GluR3 flop was increased in the cortical area, hippocampal CA3 area, and caudate putamen of mu-opioid receptor knockout mice. These results indicate that [(3)H]AMPA binding and the expression of GluR1-3 mRNA were increased in a region and subunit specific manner, and suggest that changes in the AMPA receptor system are accompanied by the absence of mu-opioid receptor gene.

κ-opioid agonist stimulated regional distribution of [35S]GTPγs binding in butorphanol continuously infused rat

Abstract Butorphanol is a mixed agonist/antagonist opioid analgesic agent, which exerts its effects mainly by interaction with the κ-opioid receptor. Opioid receptors are coupled to G proteins of G i /G o family, and recently a decrease in μ-opioid activation of G proteins has been reported in specific brainstem nuclei after chronic morphine administration. The influence of centrally administered butorphanol on agonist-stimulated G protein coupling was examined in the rat brain, using in situ guanylyl-5′-O-(γ-[ 35 S]thio)-triphosphate (GTPγS) binding autoradiography. Rats were treated with butorphanol (26 nmol/μl/h) by intracerebroventricular infusion via osmotic minipumps for 3 days. The distribution of [ 35 S]GTPγS binding in the brain 7 h after the termination of butorphanol infusion was measured in the presence or absence of the selective κ-opioid agonist, U-50,488. This agonist significantly increased [ 35 S]GTPγS binding in the parietal cortex, caudate putamen, thalamus, and central gray of control rats, but not in those regions of the butorphanol-infused animals. These results suggest that chronic administration of butorphanol developed tolerance and abolished U-50,488 activation of G proteins in these brain areas.

Effects of morphine on pentobarbital-induced responses in μ-opioid receptor knockout mice

Effects of morphine on the potentiation of pentobarbital-induced responses were investigated using mu-opioid receptor knockout mice. The duration of loss of righting reflex, hypothermia, and loss of motor coordination induced by pentobarbital were measured after pretreatment with either morphine or saline. Morphine pretreatment failed to show potentiation of both pentobarbital-induced loss of righting reflex and hypothermia in mu-opioid receptor knockout mice, while it significantly potentiated these responses in the wild-type controls. For motor incoordination test, morphine potentiated pentobarbital-induced motor incoordination in the wild-type mice. However, morphine may have opposite effects in the mu-opioid receptor knockout mice. These results demonstrate that synergism between morphine and pentobarbital is not detected in mu-opioid receptor knockout mice and that potentiation of pentobarbital-induced loss of righting reflex and hypothermia by morphine is mediated through mu-opioid receptor. It was interesting to note that pentobarbital-induced decrease in body temperature was less severe in mu-opioid receptor knockout mice than in wild-type mice.