AtT-20 cells, which make and release beta-endorphin, or AtT-20/hENK cells, an AtT-20 cell line transfected with the human proenkephalin gene and secreting enkephalin as well as presumably beta-endorphin, were implanted in mouse spinal subarachnoid space. Cell implants did not affect the basal response to thermal nociceptive stimuli. Administration of isoproterenol, believed to stimulate secreti...

Ingestion by rats of rat placenta or amniotic fluid enhances opioid-mediated, or partly opioid-mediated, antinociception produced by morphine injection, vaginal or cervical stimulation, late pregnancy, and foot shock. This phenomenon is believed to be produced by a placental opioid-enhancing factor (POEF). Ingestion by rats of human or dolphin placenta has also been shown to enhance opioid anti...

Nitric oxide (NO) plays pivotal roles in controlling physiological functions, participates in pathophysiological intervention, and is involved in mechanisms underlying beneficial or untoward actions of therapeutic agents. Endogenous nitric oxide is formed by three isoforms of nitric oxide synthase: endothelial, neurogenic and inducible. The former two are constitutively present mainly in the en...

Glycyl-glutamine (Gly-Gln; beta-endorphin(30-31)) is an endogenous dipeptide that is synthesized through the posttranslational processing of beta-endorphin in brain stem regions that control respiration and autonomic function. This study tested the hypothesis that Gly-Gln administration to conscious rats will prevent the respiratory depression caused by morphine without affecting morphine antin...

The effects of twice-daily injections of L-arginine or D-arginine (200 mg/kg i.p.) for 4 days on morphine-induced antinociception, brain nitric oxide synthase activity and brain and serum distribution of morphine and brain m-opioid receptors labeled with [H][D-Ala,MePhe,Gly-ol]enkephalin were determined in male Swiss-Webster mice. Chronic treatment with L-arginine, but not D-arginine, decreased...

BACKGROUND The pivotal role of glial activation and up-regulated inflammatory mediators in the opioid tolerance has been confirmed in rodents but not yet in humans. Here, the authors investigated the intraspinal cytokine and chemokine profiles of opioid-tolerant cancer patients; and to determine if up-regulated chemokines could modify opioid tolerance in rats. METHODS Cerebrospinal fluid samp...

BACKGROUND Lithium has been shown to relieve mania and induce antinociception. In the present study, swim stress at 8C induced antinociception in both phases of the formalin test. Intraperitoneal administration of lithium chloride (LiCl) (0.05, 0.25, and 0.5 mg/kg) also induced antinociception in both phases of the formalin test. METHODS Antinociception was assessed by the formalin test metho...

Ingestion by rats of rat placenta or amniotic fluid enhances opioid-mediated, or partly opioid-mediated, antinociception produced by morphine injection, vaginal or cervical stimulation, late pregnancy, and foot shock. This phenomenon is believed to be produced by a placental opioid-enhancing factor (POEF). Ingestion by rats of human or dolphin placenta has also been shown to enhance opioid anti...

Serotonin specific reuptake inhibitors (SSRI) may induce antinociception however, the mechanism of this effect is not clear. SSRls increase 5-HT levels in neuronal synapses and facilitate serotonergic activity. In this study, therefore, the activity of para-chlorophenylalanine (pCPA), which reduces 5-HT release, and 5- hydroxy tryptophan (5-HTP), a precursor of 5-HT, were examined on the a...