Enhanced binding of nor-binaltorphimine to kappa-opioid receptors in rats dependent on butorphanol

Prodynorphin gene deficiency potentiates nalbuphine-induced behavioral sensitization and withdrawal syndrome in mice

Dynorphin is the presumed endogenous ligand for the kappa-opioid receptor. The dynorphin gene may play a role in psychotropic agent-mediated behavioral changes via dopaminergic modulation. Therefore, in this study, possible involvement of the dynorphin gene in nalbuphine-mediated behavioral responses was examined using prodynorphin (Pdyn) gene knock-out (-/-) mice. Pdyn gene deficiency potentiates nalbuphine-induced behavioral sensitization of locomotor activity and accumbal c-Fos expression. Administration of nalbuphine induced a significant increase in the dialysate dopamine level in the nucleus accumbens. This increase was more pronounced in the Pdyn (-/-) mice than in the wild-type (WT) mice. In addition, Pdyn (-/-) mice were more vulnerable to the naloxone-precipitated withdrawal syndrome (i.e., teeth chattering, wet dog shakes, forepaw tremors, jumping, weight loss, and global withdrawal score) after repeated treatment with nalbuphine than the WT mice. Consistently, nor-binaltorphimine, a kappa-opioid receptor antagonist, significantly potentiated nalbuphine-induced behavioral effects in WT mice, whereas U-50488H, a kappa-opioid receptor agonist, significantly attenuated these changes in Pdyn (-/-) mice in a dose-dependent manner. Our data suggest that the kappa-opioid receptor/dynorphin system is specifically modulated in response to behavioral sensitization and withdrawal signs induced by nalbuphine.

Butorphanol dependence increases hippocampal kappa-opioid receptor gene expression

Butorphanol is a synthetic opioid agonist/antagonist analgesic agent, which exerts its effects mainly via kappa-opioid receptors. Characterizations of the gene expression levels of the mRNA for and protein levels of the kappa-opioid receptor in different brain regions of rats are essential for investigating possible mechanisms in the development of physical dependence on and withdrawal from butorphanol. Animals were rendered dependent by intracerebroventricular (i.c.v.) infusion of butorphanol (26 nmol/microl/hr) via osmotic minipumps for 3 days. Rats were sacrificed immediately (dependent group) or 7 hr after discontinuation of i.c.v. butorphanol infusion (withdrawal group). Expression levels of the mRNA for the kappa-opioid receptor, as detected by reverse transcription-polymerase chain reaction followed by Southern blot analysis, were significantly increased in the cerebral cortex, striatum, and midbrain, including thalamus, hippocampus, and pons, in animals dependent on butorphanol. In both dependent and withdrawal groups, Western blot analysis of kappa-opioid receptor protein levels showed significant increases in the amygdaloid nucleus, paraventricular thalamus, and thalamus. However, in the withdrawal group, there were significant decreases in the hippocampus and cortical regions, including the frontal, parietal, and temporal cortex. Regional changes in the mRNA for and protein levels of the kappa-opioid receptor focus attention on highly special roles for this receptor in the development of physical dependence on and the expression of withdrawal from butorphanol dependence.

Kappa opioid antagonists: past successes and future prospects

Antagonists of the kappa opioid receptor were initially investigated as pharmacological tools that would reverse the effects of kappa opioid receptor agonists. In the years following the discovery of the first selective kappa opioid antagonists, much information about their chemistry and pharmacology has been elicited and their potential therapeutic uses have been investigated. The review presents the current chemistry, ligand-based structure activity relationships, and pharmacology of the known nonpeptidic selective kappa opioid receptor antagonists. This manuscript endeavors to provide the reader with a useful reference of the investigations made to define the structure-activity relationships and pharmacology of selective kappa opioid receptor antagonists and their potential uses as pharmacological tools and as therapeutic agents in the treatment of disease states.

Kappa opioid antagonists: past successes and future prospects

Antagonists of the kappa opioid receptor were initially investigated as pharmacological tools that would reverse the effects of kappa opioid receptor agonists. In the years following the discovery of the first selective kappa opioid antagonists, much information about their chemistry and pharmacology has been elicited and their potential therapeutic uses have been investigated. The review presents the current chemistry, ligand-based structure activity relationships, and pharmacology of the known nonpeptidic selective kappa opioid receptor antagonists. This manuscript endeavors to provide the reader with a useful reference of the investigations made to define the structure-activity relationships and pharmacology of selective kappa opioid receptor antagonists and their potential uses as pharmacological tools and as therapeutic agents in the treatment of disease states.

Kappa opioid antagonists: past successes and future prospects

Antagonists of the kappa opioid receptor were initially investigated as pharmacological tools that would reverse the effects of kappa opioid receptor agonists. In the years following the discovery of the first selective kappa opioid antagonists, much information about their chemistry and pharmacology has been elicited and their potential therapeutic uses have been investigated. The review presents the current chemistry, ligand-based structure activity relationships, and pharmacology of the known nonpeptidic selective kappa opioid receptor antagonists. This manuscript endeavors to provide the reader with a useful reference of the investigations made to define the structure-activity relationships and pharmacology of selective kappa opioid receptor antagonists and their potential uses as pharmacological tools and as therapeutic agents in the treatment of disease states.

Changes in the brain kappa-opioid receptor levels of rats in withdrawal from physical dependence upon butorphanol

Changes in kappa-opioid receptor levels have been implicated in the development of physical dependence upon and withdrawal from the mixed agonist-antagonist opioid, butorphanol. Immunoblotting analysis was performed to determine the levels of kappa- and mu-opioid receptors in brain regions of rats in withdrawal from dependence upon butorphanol or morphine. Physical dependence was induced by a 72 h i.c.v. infusion with either butorphanol or morphine (26 nmol/microl/h). Withdrawal was subsequently precipitated by i.c.v. challenge with naloxone (48 nmol/5 microl/rat), administered 2 h following cessation of butorphanol or morphine infusion. Immunoblotting analysis of kappa-opioid receptors from butorphanol-withdrawal rats showed significant increases in 11 of 21 brain regions examined, including the nucleus accumbens, amygdala, dorsomedial hypothalamus, hypothalamus, paraventricular thalamus, thalamus, presubiculum, and locus coeruleus, when compared with saline treated, non-dependent controls. In addition, significant reductions were found in the hippocampus and in cortical brain regions, including the parietal cortex and temporal cortex from butorphanol-withdrawal rats. These findings contrasted with those from morphine-withdrawal rats, in which the only changes noted were increases in the thalamus and paraventricular thalamus. Changes in the levels of the mu-opioid receptor protein were observed in 11 of 21 brain regions examined in morphine-withdrawal rats, but only in three of 21 in butorphanol-withdrawal rats. These results implicate a substantive and largely unique role for kappa-opioid receptors in mediation of the development of physical dependence upon, and the expression of withdrawal from, butorphanol, as opposed to the prototypical opioid analgesic, morphine.