benzofurans and Morphine-Dependence

Agmatine, an endogenous ligand for imidazoline receptor, has been shown to prevent opioid dependence, but not much is known about the mechanisms of the effect of agmatine. In the present study, we investigated the function of I1 imidazoline receptor and its candidate protein imidazoline receptor antisera-selected (IRAS)/Nischarin in morphine dependence as well as in the effect of agmatine inhibiting morphine dependence by pharmacological and molecular approaches. Results showed that inhibition of IRAS or Nischarin did not change the development of morphine dependence in vitro and in vivo under the basal condition. Agmatine could reduce the cyclic 3', 5' adenosine monophosphate (cAMP) overshoot at the concentration of 0.01-10 µM in the primary cultured rat hippocampal neurons and attenuated the withdrawal signals and the elevation of FosB and ΔFosB at the dose of 5 mg/kg in the morphine-dependent mice. The effect of agmatine was inhibited by efaroxan (I1 imidazoline receptor non-specific antagonist) and the RNA interference against IRAS or Nischarin. These findings indicate that I1 imidazoline receptor or IRAS/Nischarin mediates the effect of agmatine on morphine dependence and provide evidence that I1 imidazoline receptor may be a new target for treating morphine dependence.

Topics: Adenosine Monophosphate; Adrenergic alpha-Antagonists; Agmatine; Animals; Benzofurans; Cells, Cultured; Drug Interactions; Gene Knockdown Techniques; Hippocampus; Imidazoles; Imidazoline Receptors; Immune Sera; Intracellular Signaling Peptides and Proteins; Male; Mice; Mice, Inbred BALB C; Morphine Dependence; Neurons; Proto-Oncogene Proteins c-fos; RNA, Small Interfering; Substance Withdrawal Syndrome

This study was designed to determine the affinity and binding profile of beta-carbolines for imidazoline I2 receptors and catalytic sites of monoamine oxidase (MAO)-A/B in rat brain and liver. The aim was also directed to assess the in vivo effects of norharman (beta-carboline) and LSL 60101 (I2 ligand) on brain 3,4-dihydroxyphenylalanine (DOPA) synthesis in morphine-dependent rats. Competition experiments against [3H]2-BFI revealed that beta-carbolines recognize the high- and low-affinity components of the brain imidazoline I2 receptor with the rank order of potency (K(iH) in nM): noreleagnine (12)>norharman (20)>harmalol (82)>harmaline (177)>>harmine (630)>harman (700)>>FG-7142 (>100,000). In liver, this rank was different: harmine (51)>harmaline (103)=noreleagnine (103)>>harmalol (1290)>harman (2000)>>norharman (12,382)>>FG-7142 (>100,000). In brain and liver, competition curves for beta-carbolines against [3H]Ro41-1049 (MAO-A) and [3H]Ro19-6327 (MAO-B) were monophasic and resulted in different drug potencies for the two MAO isozymes (higher affinities for MAO-A) and in similar pharmacological profiles in both tissues. In morphine-dependent rats, naloxone (2 mg/kg, 2 h)-precipitated withdrawal increased the synthesis of DOPA in the cerebral cortex and hippocampus (50%). Pretreatment with norharman (20 mg/kg) or LSL 60101 (20 mg/kg) (30 min before naloxone) fully prevented the stimulatory effect of opiate withdrawal on DOPA synthesis. Norharman and LSL 60101 also attenuated the severity of the withdrawal syndrome. The results indicate that beta-carbolines bind with high affinity to imidazoline I2B receptors, and similarly to I2 ligands (LSL 60101) can block the behavioural and biochemical effects of opiate withdrawal.

Topics: Animals; Benzofurans; Binding, Competitive; Brain; Carbolines; Cerebral Cortex; Dihydroxyphenylalanine; Dose-Response Relationship, Drug; Harmine; Hippocampus; Imidazoles; Imidazoline Receptors; Liver; Male; Monoamine Oxidase; Morphine; Morphine Dependence; Naloxone; Norepinephrine; Picolinic Acids; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, Drug; Substance Withdrawal Syndrome; Thiazoles; Tritium; Tyrosine 3-Monooxygenase