Localization of cb1 receptors in rat`s periaqueductal gray after immobilization stress and effects of peptide tyr-w-mif- 1. immunocytochemical study

Periaqueductal gray (PAG) is a midbrain structure closely involved in the stress-induced analgesia. It suppresses nociception by the descending efferent pathways to the dorsal horn of the spinal cord. Except stimulation of opioid receptors, the PAG is specialized to produce cannabinoid-mediated stress-induced analgesia. Attractive candidates for opiate modulators are neuropeptides from Tyr-MIF-1 family. These peptides also are involved in the development of stress. Based on behavioral and anatomical data about direct interactions of cannabinoid type 1 (CB1) receptors and μ-receptors in the PAG we decided to investigate the effects of the Tyr-W-MIF-1 neuropeptide on expression of CB1 immunoreactive neurons in rat`s PAG after immobilization stress. Light microscopic study was used to determine the distribution of CB1 receptor immunoreactivity. The obtained results showed that stress itself increased the expression of CB1 immunoreactive neurons in the PAG compared with intact animals, while Tyr-W-MIF-1 decreased stress-induced CB1 expression mentioned above probably by opioid/cannabinoid interaction. Further studies are needed to understand the exact role of Tyr-W-MIF-1 on CB1 receptors in response to immobilization stress

Involvement of the opioidergic and nociceptinergic systems in the analgesic effects of novel nociceptin analogues after acute and chronic immobilization stress

Stress is known to exert an influence on neuroendocrine, autonomic, hormonal functioning. Various stress models have been reported to induce analgesia. This is a phenomenon, referred to as stress-induced analgesia (SIA). Nociceptin/Orphanin FQ(N/OFQ) is a heptadecapeptide that has been found to play a direct role on pain perception. This study aimed to investigate the effects of novel nociceptin analogues on nociception after acute and chronic immobilization stress (CIS) and the involvement of the opioid and nociceptinergic systems in analgesic effects. Analgesic effects were examined by paw-pressure (PP) and hot-plate (HP) tests. Our data showed that acute immobilization stress induced hypoalgesia. The analgesic effect was more pronounced in pain caused by a mechanical stimulus than by a thermal one. CIS attenuated the hyperalgesic effect of naloxone and JTC-801 for mechanical and thermal stimulation. The effects of the opioid system are more pronounced in acute immobilization stress, while the nociceptin mechanisms predominate after chronic stress

Immunocytochemical Study Of Cb1 Receptors In Rat ‘s Periaqueductal Gray After Cold Stress And Effects Of Peptides Tyr -W-Mif -1 And Tyr -K-Mif -1

The immunohistochemical localization of cannabinoid type 1 (CB1) receptors in periaqueductal gray (PAG) of male rats after acute cold stress and effects of endogenous antiopiate peptides Tyr-W-MIF-1 and Tyr-KMIF-1 on nociception was studied. The nociception was measured by the paw pressure test. As control were used intact rats. Stress activates PAG as an important component of the descending inhibitory pain pathway and stress-induced analgesia. CB1 immunoreactivity appeared as puncta and was found in cell bodies, axons and dendrites. The morphometric analysis revealed that acute cold stress increases the density of CB1-immunoreactive neurons in PAG compared with expression in intact animals. Secund, the results showed that Tyr-K-MIF-1 and Tyr-W-MIF-1 decreased the density of CB1-immunoreactive neurons in PAG of control rats, acute cold stress and after acute cold stress and effects of endogenous antiopiate peptides Tyr-WMIF-1 and Tyr-K-MIF-on nociception

Involvement of the Nitricoxidergic System in the Analgesic Effects of Newly Synthesized Nociceptin Analogues After Chronic Immobilization Stress

Stress is known to exert an influence on neuroendocrine, autonomic, hormonal, and immune functioning. Various stress models have been reported to induce analgesia. This is a phenomenon referred to as stress-induced analgesia (SIA). Nociceptin and analogues are neuropeptides, neuromodulators, which are able to inhibit the expression of some forms of SIA. Nociceptin/orphanin FQ(N/OFQ) is a heptadecapeptide, which has been found to play a direct role on pain perception.Nitric oxide (NO) plays an important role in the initiation and maintenance of pain. It is also known that acute and chronic stress induce biochemical changes affecting both pain threshold and behaviour. Thus, endogenous opioid peptides and NO mediate a wide variety of physiological processes, including pain transmission and SIA.The aim of the present study was to investigate the effects of novel analogues of N/OFQ(1-13)NH2, where lysine (Lys) at position 9 and/or 13 was substituted by L-ornithine (Orn) on nociception after chronic immobilization stress (IS) and the involvement of the nitric oxideergic systems in these effects. Analgesic activity was examined by nociceptive test – paw-pressure (PP). All novel analogues of N/OFQ were injected at a dose of 10 μg/kg, NG-nitro-L-arginine methylester (L-NAME, 10 mg/kg) and L-arginine (L-arg, 1 mg/kg). All drugs were dissolved in saline and were injected intraperitoneally (i.p.). The nociceptive tests were performed 10 min after peptide injection. Antinociceptive effects were statistically accessed by ANOVA.In conclusion, we suggest that the nitricoxidergic system after chronic immobilization stress is involved in the analgesic effects of the novel analogues of nociceptin

Interactions between the endogenous cannabinoid system and the peptides of the Tyr-MIF-1 family modulate heat stress-induced analgesia

The present study aimed at evaluating whether an interaction between the endocannabinoid system (ECS) and peptides from the Tyr-MIF-1 family modulates heat stress-induced analgesia. For this purpose, adult male rats were subjected to 1 hour of heat stress. Pain perception was estimated in vivo by Paw pressure test. Immunohistochemical evaluation of CB1 receptors was also performed in the periaqueductal grey (PAG). Our results showed that the application of CB1-receptor agonist anandamide at the end of the stress led to a tendency of decrease in heat-SIA. We also found that each of the four Tyr-MIF-1 peptides interacted with the ECS after acute heat stress, resulting in changes in the PP-thresholds with different direction, degree, and duration. In particular, the administration of MIF-1 and Tyr-K-MIF-1 after CB1-receptor agonist anandamide increased heat stress-induced analgesia (heat-SIA) after the 10th min, while Tyr-MIF-1 and Tyr-W-MIF-1 produced only short-lasting analgesia. CB1-expression in the PAG was also estimated, showing an increase after Tyr-MIF-1 and Tyr-W-MIF-1 administration with anandamide pretreatment, and a decrease after Tyr-W-MIF-1 administration with the CB1-receptor antagonist AM251- or the opioid receptor antagonist naloxone pretreatment. In summary, it can be inferred that under heat stress conditions the peptides from the Tyr-MIF-1 family, interacting with opioid and non-opioid receptors, differently relate with the cannabinoid system and such an interaction modulates heat stress-induced analgesia. It also seems that Tyr-MIF-1 and Tyr-W-MIF-1 have a direct impact on CB1-expression in the PAG, while MIF-1 and Tyr-K-MIF-1 probably act via second messengers or the activation of additional neurotransmitter system(s)

Synthesis and analgesic effects of novel 2-tryptophan hexapeptide analogs

International audienceAiming to develop more potent analgesic substances a new series of hexapeptides containing b2-tryptophan analogues was synthesized. The Trp in position 4 and 5, respectively in Ac-Arg-Phe-Met-Trp-Met-Lys-NH2 (opioid receptor antagonist) and Ac-Arg-Tyr-Tyr-Arg-Trp-Lys- NH2 (highly potent and selective NOP-receptor agonist) was substituted by the (S)-2-(1-methyl-1H-indol-3-yl)propionic residue or the (S)-2-(5-methoxy-1H-indol-3-yl)propionic residue. The analgesic effect of the four newly synthesized compounds has been evaluated in male Wistar rats by PPand HP tests and compared to the native templates. Further estimation of the mechanisms of action of each compound was achieved using specific antagonists--naloxone for opioid and JTC801 for the NOP receptor. Replacement of Trp with b2-tryptophan analogues in 4th position (Ac-Arg-Phe-Met-Trp-Met-Lys-NH2) led to increased and longer lasting analgesic effect. The results obtained permit us to assume that both opioid and NOP receptors take part in the newly synthesized compounds analgesic effects