Effect of acute topical application of +-pentazocine on the mechanical allodynia in diabetic mice

Pharmacological Modulation of the Sigma 1 Receptor and the Treatment of Pain

There is a critical need for new analgesics acting through new mechanisms of action, which could increase the efficacy with respect to existing therapies and reduce their unwanted effects. Current preclinical evidence supports the modulatory role of sigma-1 receptors (σ1R) in nociception, mainly based on the pain-attenuated phenotype of σ1R knockout mice and on the antinociceptive effect exerted by σ1R antagonists on pains of different etiologies. σ1R is highly expressed in different pain areas of the CNS and the periphery (particularly dorsal root ganglia), and interacts and modulates the functionality of different receptors and ion channels . The antagonism of σ1R leads to decreased amplification of pain signaling within the spinal cord (central sensitization), but recent data also support a role at the periphery. σ1R antagonists have consistently demonstrated efficacy in neuropathic pain , but also in other types of pain including inflammatory, orofacial, visceral, and post-operative pain. Apart from acting alone, when combined with opioids, σ1R antagonists enhance opioid analgesia but not opioid-induced unwanted effects. Interestingly, unlike opioids, σ1R antagonists do not modify normal sensory mechanical and thermal sensitivity thresholds but they exert antihypersensitive effects in sensitizing conditions, enabling the reversal of nociceptive thresholds back to normal values. Accordingly, σ1R antagonists are not strictly analgesics; they are antiallodynic and antihyperalgesic drugs acting when the system is sensitized following prolonged noxious stimulation or persistent abnormal afferent input (e.g., secondary to nerve injury). These are distinctive features allowing σ1R antagonists to exert a modulatory effect specifically in pathophysiological conditions such as chronic pain .

Possible involvement of the Sigma-1 receptor chaperone in chemotherapeutic-induced neuropathic pain

Previous studies have shown that ligands of the sigma-1 receptor chaperone (Sig-1R) regulate pain-related behaviors. Clinical use of chemotherapeutics is often compromised due to their adverse side effects, particularly those related to neuropathy. Previous studies have shown that repeated administration of oxaliplatin and paclitaxel produces neuropathy in rodents. Therefore, the aim of the present study was to clarify the involvement of the Sig-1R in chemotherapeutic-induced neuropathy by examining the effects of oxaliplatin and paclitaxel on the Sig-1R levels in the spinal cord, and by examining the effects of Sig-1R agonist and antagonist on oxaliplatin- and paclitaxel-induced neuropathy in rats. Chemotherapeutic-induced neuropathic pain was accompanied by a significant reduction of the Sig-1R level in the spinal cord. Furthermore, the administration of paclitaxel to CHO cells that stably overexpressed Sig-1Rs induced the clustering of Sig-1Rs. We also found that the Sig-1R agonist SA4503 potently inhibited the neuropathy induced by oxaliplatin- and paclitaxel, whereas this action was abolished by the Sig-1R antagonist NE-100. These results suggest that the reduction of Sig-1R activity is involved in chemotherapeutic-induced neuropathy, and the Sig-1R agonist SA4503 could serve as a potential candidate for the treatment of chemotherapeutic-induced neuropathy.

Beneficial effects of levobupivacaine regional anaesthesia on postoperative opioid induced hyperalgesia in diabetic mice

Background

Diabetic neuropathy is one of the most common complications of diabetes and causes various problems in daily life. The aim of this study was to assess the effect of regional anaesthesia on post surgery opioid induced hyperalgesia in diabetic and non-diabetic mice.

Methods

Diabetic and non-diabetic mice underwent plantar surgery. Levobupivacaine and sufentanil were used before surgery, for sciatic nerve block (regional anaesthesia) and analgesia, respectively. Diabetic and non-diabetic groups were each randomly assigned to three subgroups: control, no sufentanil and no levobupivacaine; sufentanil and no levobupivacaine; sufentanil and levobupivacaine. Three tests were used to assess pain behaviour: mechanical nociception; thermal nociception and guarding behaviours using a pain scale.

Results

Sufentanil, alone or in combination with levobupivacaine, produced antinociceptive effects shortly after administration. Subsequently, sufentanil induced hyperalgesia in diabetic and non-diabetic mice. Opioid-induced hyperalgesia was enhanced in diabetic mice. Levobupivacaine associated to sufentanil completely prevented hyperalgesia in both groups of mice.

Conclusion

The results suggest that regional anaesthesia can decrease opioid-induced hyperalgesia in diabetic as well as in non-diabetic mice. These observations may be clinically relevant for the management of diabetic patients.

Sigma 1 receptor: a new therapeutic target for pain

Sigma 1 receptor (σ₁ receptor) is a unique ligand-regulated molecular chaperone located mainly in the endoplasmic reticulum and the plasma membrane. σ₁ receptor is activated under stress or pathological conditions and interacts with several neurotransmitter receptors and ion channels to modulate their function. The effects reported preclinically with σ₁ receptor ligands are consistent with a role for σ₁ receptor in central sensitization and pain hypersensitivity and suggest a potential therapeutic use of σ₁ receptor antagonists for the management of neuropathic pain as monotherapy. Moreover, data support their use in opioid adjuvant therapy: combination of σ₁ receptor antagonists and opioids results in potentiation of opioid analgesia, without significant increases in opioid-related unwanted effects. Results from clinical trials using selective σ₁ receptor antagonists in several pain conditions are eagerly awaited to ascertain the potential of σ₁ receptor modulation in pain therapy.

Sigma-1 receptor-mediated increase in spinal p38 MAPK phosphorylation leads to the induction of mechanical allodynia in mice and neuropathic rats

The direct activation of the spinal sigma-1 receptor (Sig-1R) produces mechanical allodynia (MA) and thermal hyperalgesia (TH) in mice. In addition, the blockade of the spinal Sig-1R prevents the induction of MA, but not TH in chronic constriction injury (CCI)-induced neuropathic rats. The present study was designed to investigate whether the increase in spinal p38 MAPK phosphorylation (p-p38 MAPK) mediates Sig-1R-induced MA or TH in mice and the induction of MA in neuropathic rats. MA and TH were evaluated using von Frey filaments and a hot-plate apparatus, respectively. Neuropathic pain was produced by CCI of the right sciatic nerve in rats. Western blot assay and immunohistochemistry were performed to determine the changes of p-p38 MAPK expression in the spinal cord. Intrathecal (i.t.) injection of PRE084, a selective Sig-1R agonist, into naïve mice time-dependently increased the expression of p-p38 MAPK, which was blocked by pretreatment with BD1047, a Sig-1R antagonist. I.t. pretreatment with SB203580, a p38 MAPK inhibitor also dose-dependently inhibited PRE084-induced MA, whereas TH induction was not affected. In CCI rats, i.t. injection of BD1047 during the induction phase (postoperative days 0 to 5) reduced the CCI-induced increase in p-p38 MAPK. In addition, i.t. SB203580 treatment during the induction phase also suppressed the development of CCI-induced MA, but not TH. Conversely, i.t. SB203580 treatment during the maintenance phase (postoperative days 15 to 20) had no effect on CCI-induced MA or TH. These results demonstrate that the increase in spinal p-p38 MAPK is closely associated with the induction of Sig-1R mediated MA, but not TH. Sigma-1 receptor modulation of p-p38 MAPK also plays an important role in the induction, but not the maintenance, of MA in neuropathic pain.

Endogenous opiates and behavior: 2010

This paper is the thirty-third consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2010 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).