kaushal patel - Academia.edu (original) (raw)
Papers by kaushal patel
Pharmacology Biochemistry and Behavior, 2003
Chronic opioid antagonist treatment increases the density of m-opioid receptors (mOR) in many mod... more Chronic opioid antagonist treatment increases the density of m-opioid receptors (mOR) in many model systems. In previous studies, naltrexone treatment produced an increase in mOR density accompanied by decreases in GRK-2 and DYN-2 protein abundance. To examine the relationship between changes in receptor density and proteins involved in receptor trafficking, the dose-dependent effect of chronic naloxone infusion was determined. Dose-dependent antagonism of morphine analgesia was also examined. Mice were infused with naloxone (0.1, 1.0, 5.0 mg/kg/day sc) for 7 days via osmotic pump. Controls were treated with placebo pellets. On the 7th day, morphine doseresponse studies were determined using the tail flick. Other mice were sacrificed at the end of the treatment and spinal cords were collected for determination of mOR density and GRK-2 and DYN-2 protein abundance. Naloxone infusion dose-dependently increased spinal mOR density with no change in affinity. The increases in m-receptor density were proportional to dose-dependent decreases in GRK-2 and DYN-2 protein levels. Furthermore, naloxone dose-dependently antagonized morphine. These data suggest that opioid antagonist-induced mOR upregulation in mouse spinal cord is associated with regulation of proteins involved in receptor trafficking and support suggestions that opioid antagonist-induced receptor up-regulation is due to reduced constitutive internalization of opioid receptors. D
European Journal of Pharmacology, 2004
Opioid agonists and antagonists can regulate the density of A-opioid receptors in whole animal an... more Opioid agonists and antagonists can regulate the density of A-opioid receptors in whole animal and in cell culture. High intrinsic efficacy agonists (e.g., etorphine), but not lower intrinsic efficacy agonists (e.g., morphine), produce A-opioid receptor down-regulation and can alter the abundance of A-opioid receptor mRNA. Conversely, opioid antagonists substantially increase the density of A-opioid receptors without changing its mRNA. A-Opioid receptor up-regulation has been associated with decreases in the trafficking protein dynamin-2, whereas Aopioid receptor down-regulation produces an increase in dynamin-2 abundance. To probe the differences between opioid agonist and antagonist-induced A-opioid receptor regulation, the current study determined changes in A-opioid receptor density using a combined radioligand binding ([ 3 H] DAMGO) and quantitative Western blotting approach in mouse spinal cord. Furthermore, the differences between intermittent and continuous dosing protocols were evaluated. Continuous (7-8 days) s.c. infusions of naloxone (5 mg/kg/day) or naltrexone (15 mg s.c. implant pellet) increased A-opioid receptor density in radioligand binding assays (c+80%) in mouse spinal cord and downregulated dynamin-2 abundance (cÀ30%), but had no effect on the abundance of immunoreactive A-opioid receptor. Continuous (7 days) s.c. infusion of etorphine (200 Ag/kg/day) decreased immunoreactive A-opioid receptor (cÀ35%) and [ 3 H] DAMGO binding (cÀ30%), and concurrently increased dynamin-2 abundance (c+40%). Continuous (7 days) morphine infusion (40 mg/kg/day plus 25 mg s.c. implant pellet) had no effect on any outcome measure. Delivery of the same daily dose of etorphine or naloxone using intermittent (every 24 h for 7 days) s.c. administration had no effect on immunoreactive A-opioid receptor, [ 3 H] DAMGO binding or dynamin-2 abundance. These data indicate that A-opioid receptor density, determined in radioligand binding assays, and immunoreactive dynamin-2 abundance are regulated by continuous, but not intermittent, opioid ligand treatment. Furthermore, the differential regulation of A-opioid receptor abundance by agonists and antagonists in immunoblotting assays contrasts with changes in [ 3 H] DAMGO binding. Taken together, these results suggest that etorphine-induced down-regulation may depend upon A-opioid receptor degradation and changes in dynamin-2-mediated receptor trafficking. Conversely, antagonist-induced up-regulation does not require an increase in A-opioid receptor synthesis and may entail conversion of receptors to an appropriate conformation to bind ligand, as well as changes in receptor trafficking. D
Synapse, 2003
Chronic opioid antagonist treatment produces functional supersensitivity and μ-opioid receptor (μ... more Chronic opioid antagonist treatment produces functional supersensitivity and μ-opioid receptor (μOR) upregulation. Studies suggest a role for G-protein receptor kinases (GRKs) and dynamin (DYN), but not signaling proteins (e.g., Giα2), in regulation of μOR density following opioid treatment. Therefore, this study examined μOR density, agonist potency, and the abundance and gene expression of GRK-2, DYN-2, and Giα2 in mouse spinal cord after opioid antagonist treatment. Mice were implanted with a 15 mg naltrexone (NTX) or placebo pellet and 8 days later pellets were removed. At 24 and 192 h following NTX treatment, mice were tested for spinal DAMGO analgesia. Other mice were sacrificed at 0 or 192 h following NTX treatment and Giα2, GRK-2, and DYN-2 protein and mRNA levels determined. [3H] DAMGO binding studies were also conducted. Immediately following NTX treatment (0 h), μOR density was increased (+ ≈135%), while 192 h following NTX treatment μOR density was unchanged. NTX increased DAMGO analgesic potency (3.1-fold) 24 h following NTX treatment, while there was no effect at 192 h. NTX decreased protein and mRNA abundance of GRK-2 (−32%; −48%) and DYN-2 (−25%; −29%) in spinal cord at 0 h. At 192 h following 8-day NTX treatment, GRK-2 protein and mRNA were at control levels, while DYN-2 protein remained decreased (–31%) even though DYN-2 mRNA had returned to control levels. Giα2 was unaffected by NTX treatment. These data suggest that opioid antagonist-induced μ-receptor upregulation is mediated by changes in abundance and gene expression of proteins implicated in receptor trafficking, which may decrease constitutive receptor cycling. Synapse 50:67–76, 2003. © 2003 Wiley-Liss, Inc.
European Journal of Pharmacology, 2004
Pharmacology Biochemistry and Behavior, 2003
Chronic opioid antagonist treatment increases the density of m-opioid receptors (mOR) in many mod... more Chronic opioid antagonist treatment increases the density of m-opioid receptors (mOR) in many model systems. In previous studies, naltrexone treatment produced an increase in mOR density accompanied by decreases in GRK-2 and DYN-2 protein abundance. To examine the relationship between changes in receptor density and proteins involved in receptor trafficking, the dose-dependent effect of chronic naloxone infusion was determined. Dose-dependent antagonism of morphine analgesia was also examined. Mice were infused with naloxone (0.1, 1.0, 5.0 mg/kg/day sc) for 7 days via osmotic pump. Controls were treated with placebo pellets. On the 7th day, morphine doseresponse studies were determined using the tail flick. Other mice were sacrificed at the end of the treatment and spinal cords were collected for determination of mOR density and GRK-2 and DYN-2 protein abundance. Naloxone infusion dose-dependently increased spinal mOR density with no change in affinity. The increases in m-receptor density were proportional to dose-dependent decreases in GRK-2 and DYN-2 protein levels. Furthermore, naloxone dose-dependently antagonized morphine. These data suggest that opioid antagonist-induced mOR upregulation in mouse spinal cord is associated with regulation of proteins involved in receptor trafficking and support suggestions that opioid antagonist-induced receptor up-regulation is due to reduced constitutive internalization of opioid receptors. D
European Journal of Pharmacology, 2004
Opioid agonists and antagonists can regulate the density of A-opioid receptors in whole animal an... more Opioid agonists and antagonists can regulate the density of A-opioid receptors in whole animal and in cell culture. High intrinsic efficacy agonists (e.g., etorphine), but not lower intrinsic efficacy agonists (e.g., morphine), produce A-opioid receptor down-regulation and can alter the abundance of A-opioid receptor mRNA. Conversely, opioid antagonists substantially increase the density of A-opioid receptors without changing its mRNA. A-Opioid receptor up-regulation has been associated with decreases in the trafficking protein dynamin-2, whereas Aopioid receptor down-regulation produces an increase in dynamin-2 abundance. To probe the differences between opioid agonist and antagonist-induced A-opioid receptor regulation, the current study determined changes in A-opioid receptor density using a combined radioligand binding ([ 3 H] DAMGO) and quantitative Western blotting approach in mouse spinal cord. Furthermore, the differences between intermittent and continuous dosing protocols were evaluated. Continuous (7-8 days) s.c. infusions of naloxone (5 mg/kg/day) or naltrexone (15 mg s.c. implant pellet) increased A-opioid receptor density in radioligand binding assays (c+80%) in mouse spinal cord and downregulated dynamin-2 abundance (cÀ30%), but had no effect on the abundance of immunoreactive A-opioid receptor. Continuous (7 days) s.c. infusion of etorphine (200 Ag/kg/day) decreased immunoreactive A-opioid receptor (cÀ35%) and [ 3 H] DAMGO binding (cÀ30%), and concurrently increased dynamin-2 abundance (c+40%). Continuous (7 days) morphine infusion (40 mg/kg/day plus 25 mg s.c. implant pellet) had no effect on any outcome measure. Delivery of the same daily dose of etorphine or naloxone using intermittent (every 24 h for 7 days) s.c. administration had no effect on immunoreactive A-opioid receptor, [ 3 H] DAMGO binding or dynamin-2 abundance. These data indicate that A-opioid receptor density, determined in radioligand binding assays, and immunoreactive dynamin-2 abundance are regulated by continuous, but not intermittent, opioid ligand treatment. Furthermore, the differential regulation of A-opioid receptor abundance by agonists and antagonists in immunoblotting assays contrasts with changes in [ 3 H] DAMGO binding. Taken together, these results suggest that etorphine-induced down-regulation may depend upon A-opioid receptor degradation and changes in dynamin-2-mediated receptor trafficking. Conversely, antagonist-induced up-regulation does not require an increase in A-opioid receptor synthesis and may entail conversion of receptors to an appropriate conformation to bind ligand, as well as changes in receptor trafficking. D
Synapse, 2003
Chronic opioid antagonist treatment produces functional supersensitivity and μ-opioid receptor (μ... more Chronic opioid antagonist treatment produces functional supersensitivity and μ-opioid receptor (μOR) upregulation. Studies suggest a role for G-protein receptor kinases (GRKs) and dynamin (DYN), but not signaling proteins (e.g., Giα2), in regulation of μOR density following opioid treatment. Therefore, this study examined μOR density, agonist potency, and the abundance and gene expression of GRK-2, DYN-2, and Giα2 in mouse spinal cord after opioid antagonist treatment. Mice were implanted with a 15 mg naltrexone (NTX) or placebo pellet and 8 days later pellets were removed. At 24 and 192 h following NTX treatment, mice were tested for spinal DAMGO analgesia. Other mice were sacrificed at 0 or 192 h following NTX treatment and Giα2, GRK-2, and DYN-2 protein and mRNA levels determined. [3H] DAMGO binding studies were also conducted. Immediately following NTX treatment (0 h), μOR density was increased (+ ≈135%), while 192 h following NTX treatment μOR density was unchanged. NTX increased DAMGO analgesic potency (3.1-fold) 24 h following NTX treatment, while there was no effect at 192 h. NTX decreased protein and mRNA abundance of GRK-2 (−32%; −48%) and DYN-2 (−25%; −29%) in spinal cord at 0 h. At 192 h following 8-day NTX treatment, GRK-2 protein and mRNA were at control levels, while DYN-2 protein remained decreased (–31%) even though DYN-2 mRNA had returned to control levels. Giα2 was unaffected by NTX treatment. These data suggest that opioid antagonist-induced μ-receptor upregulation is mediated by changes in abundance and gene expression of proteins implicated in receptor trafficking, which may decrease constitutive receptor cycling. Synapse 50:67–76, 2003. © 2003 Wiley-Liss, Inc.
European Journal of Pharmacology, 2004