Spinal cord thyrotropin releasing hormone receptors of morphine tolerant-dependent and abstinent rats.
The effect of chronic administration of morphine and its withdrawal on the binding of 3H-[3-MeHis2]thyrotropin releasing hormone (3H-MeTRH) to membranes of the spinal cord of the rat was determined. Male Sprague-Dawley rats were implanted with either 6 placebo or 6 morphine pellets (each containing 75-mg morphine base) during a 7-day period. Two sets of animals were used. In one, the pellets were left intact at the time of sacrificing (tolerant-dependent) and in the other, the pellets were removed 16 hours prior to sacrificing (abstinent rats). In placebo-pellet-implanted rats, 3H-MeTRH bound to the spinal cord membranes at a single high affinity binding site with a Bmax of 21.3 +/- 1.6 fmol/mg protein, and an apparent dissociation constant Kd of 4.7 +/- 0.8 nM. In morphine tolerant-dependent or abstinent rats, the binding constants of 3H-MeTRH to spinal cord membranes were unaffected. Previous studies from this laboratory indicate that TRH can inhibit morphine tolerance-dependence and abstinence processes without modifying brain TRH receptors. Together with the present results, it appears that the inhibitory effect of TRH on morphine tolerance-dependence and abstinence is probably not mediated via central TRH receptors but may be due to its interaction with other neurotransmitter systems.
Rahmani
N H
NH
Department of Pharmacodynamics (m/c 865), University of Illinois, Chicago, IL 60612.
Gulati
A
A
Bhargava
H N
HN
D000818:Animals; D004361:Drug Tolerance / Q000502:physiology; D008297:Male; D009021:Morphine Dependence / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D018025:Receptors, Thyrotropin-Releasing Hormone; D013116:Spinal Cord / Q000378:metabolism*; D013375:Substance Withdrawal Syndrome / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*; D014316:Tritium
D017981:Receptors, Neurotransmitter; D018025:Receptors, Thyrotropin-Releasing Hormone; D014316:Tritium; D013973:Thyrotropin-Releasing Hormone