Amitriptyline attenuates astrocyte activation and morphine tolerance in rats: role of the PSD-95/NR1/nNOS/PKCγ signaling pathway.
The tricyclic antidepressant amitriptyline binds with high affinity to N-methyl-d-aspartate receptors (NMDARs) and inhibits NMDAR-mediated events. Activation of the postsynaptic density protein-95 (PSD-95)/NMDAR-mediated downstream signaling cascade, including neuronal nitric oxide synthase (nNOS) and protein kinase gamma (PKCγ), has been shown to be involved in morphine tolerance. The present study examined the potential effect of amitriptyline on chronic morphine infusion-induced spinal PSD-95/NMDAR/nNOS/PKCγ signaling in morphine tolerance. Male Wistar rats were implanted with an intrathecal catheter and received an intrathecal infusion of saline or amitriptyline (15 μg/h), morphine+saline (tolerance induction, 15 μg/h), or morphine+amitriptyline for 5 days. Co-administration of amitriptyline with morphine not only preserved the antinociceptive effect of morphine, but also attenuated astrocyte activation in the rat spinal cord dorsal horn. On day 5 after drug infusion, increased expression and phosphorylation of spinal membrane NMDAR NR1 subunit and expression of PSD-95 were observed following chronic morphine infusion and these effects were attenuated by amitriptyline co-infusion. Upregulation of NMDAR-induced intracellular nNOS expression was also inhibited by amitriptyline co-infusion in chronic morphine-infused rats. Furthermore, amitriptyline co-infusion significantly inhibited morphine-induced PKCγ expression in both the cytosol and membrane of spinal neurons. These findings suggest that the attenuation of morphine tolerance caused by amitriptyline is due to downregulation of NMDAR NR1 subunit expression in the synaptosomal membrane accompanied by decreased expression of the scaffolding protein PSD-95. The effects of amitriptyline in attenuating astrocyte activation and reversing tolerance to morphine may be due, at least in part, to inhibition of the PSD-95/NMDAR NR1/nNOS/PKCγ signaling cascade.
Hsin Sheng College of Medical Care and Management, Taoyuan, Taiwan.
Ya-Ni
YN
Huang
Ru-Yin
RY
Tsai
Shinn-Long
SL
Lin
Chih-Cheng
CC
Chien
Chen-Hwan
CH
Cherng
Ching-Tang
CT
Wu
Chun-Chang
CC
Yeh
Chih-Shung
CS
Wong
D000639:Amitriptyline / Q000008:administration & dosage / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D000929:Antidepressive Agents, Tricyclic / Q000008:administration & dosage / Q000494:pharmacology; D001253:Astrocytes / Q000378:metabolism; D000076122:Disks Large Homolog 4 Protein; D016291:Dizocilpine Maleate / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D004347:Drug Interactions; D004361:Drug Tolerance / Q000502:physiology*; D007278:Injections, Spinal; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis*; D009020:Morphine / Q000008:administration & dosage / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D052248:Nitric Oxide Synthase Type I / Q000096:biosynthesis*; D011493:Protein Kinase C / Q000096:biosynthesis*; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000096:biosynthesis; D015398:Signal Transduction / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
D000701:Analgesics, Opioid; D000929:Antidepressive Agents, Tricyclic; D000076122:Disks Large Homolog 4 Protein; C501449:Dlg4 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D016194:Receptors, N-Methyl-D-Aspartate; D000639:Amitriptyline; D016291:Dizocilpine Maleate; D009020:Morphine; D052248:Nitric Oxide Synthase Type I; C087857:protein kinase C gamma; D011493:Protein Kinase C