Three types of opioid receptors exist in the animals, each is encoded by a single gene, i.e., the mu opioid receptor gene, the delta opioid receptor gene, and the kappa opioid receptor gene. However, each opioid receptor gene produces multiple mRNA variants as a result of alternative promoter usages, splicing and/or polyadenylation. As such, a large reservoir of regulatory events has evolved fo...

Baseline nociception and opioid antinociception were compared in male and ovariectomized female rhesus monkeys. Females were studied without estradiol replacement or during treatment with estradiol benzoate at doses (0.002 and 0.01 mg/kg/day) designed to mimic 17beta-estradiol blood levels observed during different phases of the menstrual cycle and during pregnancy. Baseline sensitivity to ther...

Reductions in pain ratings when administered a placebo with expected analgesic properties have been described and hypothesized to be mediated by the pain-suppressive endogenous opioid system. Using molecular imaging techniques, we directly examined the activity of the endogenous opioid system on mu-opioid receptors in humans in sustained pain with and without the administration of a placebo. Si...

Chronic exposure of mu-and delta-opioid receptors to their agonists leads to different rates in receptor down-regulation. In order to analyze the role of the carboxyl terminus of mu-and delta-opioid receptors in the difference in the rate of down-regulation, two chimeras of these receptors were generated by swapping the carboxyl termini; MORTAGDT and DORTAGMT. These chimeras were tagged at the ...

The influence of naloxone (NAL), a competitive antagonist of mu, kappa, delta and sigma receptors; D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2) (CTOP), selective antagonist of mu-opioid receptors; nor-binaltorphimine (NOR-BNI), a potent and higly selective kappa opioid receptor antagonist; naltrindole (NTI), a delta-opioid receptor antagonist and naltriben (NTB), a highly selective delta(2)-opioid...

Opioid receptors were shown to modulate a variety of cellular processes in the vertebrate central nervous system, including synaptic transmission. While the effects of opioid receptors on chemically mediated transmission have been extensively investigated, little is known of their actions on gap junction-mediated electrical synapses. Here we report that pharmacological activation of mu-opioid r...

The analgesic effect of opioids varies widely among vertebrate species. This may be due to the distribution, number and type of opioid receptors within the brain. In general, distribution of opioid receptor types is conserved across species in brainstem and spinal cord areas but varies significantly in the forebrain [2]. In the pigeon forebrain 76% of the total opioid receptors are kappa [2]. E...

A nonisotopic, immunoelectrophoretic technique was used to analyze the characteristics of opioid-evoked activation of Gi2/ G(x/z) transducer proteins of mouse periaqueductal gray matter membranes. In the presence of picomolar concentrations of guanosine 5'-O-(3-thiotriphosphate), the opioid agonists promoted concentration-dependent increases of immunoreactivity associated with free Gi2alpha and...

Activation of neurons in the midbrain periaqueductal gray (PAG) inhibits spinal dorsal horn neurons and produces behavioral antinociception in animals and analgesia in humans. Although dorsal horn regions modulated by PAG activation contain all three opioid receptor classes (mu, delta, and kappa), as well as enkephalinergic interneurons and terminal fields, descending opioid-mediated inhibition...

(D-ALa2, NMePhe4, Gly-ol5) encephalin (DAMGO), a selective mu-opioid receptor agonist, has previously been demonstrated to inhibit the cholinergic and the noncholinergic contraction in guinea-pig airways. In contrast, opioids had no inhibitory effect on cholinergic neurotransmission in the upper trachea when stimulated at 8 Hz. We investigated whether DAMGO, a selective mu-opioid receptor agoni...