Intrathecal antinociceptive interaction between the NMDA antagonist ketamine and the opioids, morphine and biphalin

The effect of topical ketamine administration on the corneal epithelium repair

The cornea is regarded as a sensitive organ to pain. Ketamine can effectively reduce postoperative neuropathic pain. We hypothesized that topical ketamine could mitigate postoperative corneal neuropathic pain. The aim of this study was to determine whether topical ketamine is safe for cornea and evaluate its effect on the repair procedure the damaged corneal tissue. Our study was performed on only the right eyes of 15 male rats. All animals underwent general anesthesia and the whole corneal epithelium was removed. All subjects were divided into two groups: group 1 (n = 8), one drop of ketamine, and group 2 (n = 7), one drop of 0.9% sodium chloride administered topically on the scraped cornea every 6 h for 7 days. The rats' s cornea was carefully monitored daily for the size of epithelial defects under a microscope and was photographed. On the eighth day, the eyes were sent for pathological examination. The eyes were examined for the amount of inflammation, neovascularization, keratinization, epithelial thickness and Descemet's membrane pathologies. The epithelial defect has healed completely on the sixth day in all rats in both groups. There was no significant difference in the speed of complete recovery between the two groups. No significant difference was observed between the two groups in terms of inflammation grade, neovascularization grade, and epithelial thickness. Our study showed that topical ketamine had no significant effect on corneal wound healing in a rat animal model and could be used safely for the management of postoperative chronic ocular pain.

Biphalin-A Potent Opioid Agonist-As a Panacea for Opioid System-Dependent Pathophysiological Diseases?

Biphalin, one of the opioid agonists, is a dimeric analog of enkephalin with a high affinity for opioid receptors. Opioid receptors are widespread in the central nervous system and in peripheral neuronal and non-neuronal tissues. Hence, these receptors and their agonists, which play an important role in pain blocking, may also be involved in the regulation of other physiological functions. Biphalin was designed and synthesized in 1982 by Lipkowski as an analgesic peptide. Extensive further research in various laboratories on the antinociceptive effects of biphalin has shown its excellent properties. It has been demonstrated that biphalin exhibits an analgesic effect in acute, neuropathic, and chronic animal pain models, and is 1000 times more potent than morphine when administered intrathecally. In the course of the broad conducted research devoted primarily to the antinociceptive effect of this compound, it has been found that biphalin may also potentially participate in the regulation of other opioid system-dependent functions. Nearly 40 years of research on the properties of biphalin have shown that it may play a beneficial role as an antiviral, antiproliferative, anti-inflammatory, and neuroprotective agent, and may also affect many physiological functions. This integral review analyzes the literature on the multidirectional biological effects of biphalin and its potential in the treatment of many opioid system-dependent pathophysiological diseases.

The opioid peptide biphalin modulates human corneal epithelial wound healing in vitro

PURPOSE

Analgesic drugs, including nonselective opioids and non-steroidal anti-inflammatory drugs, should be used with great precautions to relieve pain after trauma to the corneal epithelium because of their unfavorable effects on wound healing. Biphalin is a synthetic opioid peptide that has been demonstrated to possess a strong analgesic effect on rodents. The purpose of this study is to investigate the effects of biphalin on human corneal epithelial wound healing.

METHODS

An immortalized human corneal epithelial cell (HCEC) culture was used to analyze the effects of biphalin on wound healing. The toxicity of biphalin at various concentrations was measured by the MTT assay. The effects of 1μM and 10μM biphalin on wound closure, cell migration and proliferation were tested in an in vitro scratch assay of HCECs. Naloxone, a non-selective competitive opioid receptor antagonist, was also used to inhibit the effects of biphalin in all experiments.

RESULTS

Biphalin did not cause any toxic effect on HCECs at concentrations lower than 100μM at various incubation time points. Biphalin significantly increased wound healing at 1μM concentration in an in vitro scratch assay of HCECs (P<0.05). It also significantly increased migration of HCECs (P<0.01). There was no significant difference between the biphalin and control groups of HCECs in the Ki67 proliferation assay.

CONCLUSION

Biphalin, which is a synthetic opioid peptide, promotes corneal epithelial wound healing by increasing cell migration. This role should be evaluated in further in vivo and clinical studies.

Biphalin, a dimeric opioid peptide, reduces neonatal hypoxia-ischemia brain injury in mice by the activation of PI3K/Akt signaling pathway

Previous studies have demonstrated that the activation of delta opioid receptors is neuroprotective against neonatal hypoxia-ischemia (HI) brain injury. The aim of this study was to investigate the neuroprotective effects of biphalin, a dimeric opioid peptide, in a mouse model of neonatal HI and the underlying mechanisms. On postnatal day 10, mouse pups were subjected to unilateral carotid artery ligation followed by 1 h of hypoxia (10 % O₂ in N₂). For treatment, biphalin (5 mg/kg, 10 mg/kg, 20 mg/kg) was administered intraperitoneally immediately after HI. The opioid antagonist naloxone or phosphatidylinositol-3-kinase inhibitor Ly294002 was administered to determine the underlying mechanisms. Infarct volume, brain edema, phosphorylated Akt and apoptosis-related proteins levels were evaluated by using a combination of 2,3,5-triphenyltetrazolium chloride staining, brain water content and Western blotting at 24 h after HI. The long-term effects of biphalin were evaluated by brain atrophy measurement, Nissl staining and neurobehavioral tests at 3 weeks post-HI. Biphalin (10 mg/kg) significantly reduced the infarct volume and ameliorated brain edema. Biphalin also had long-term protective effects against the loss of ipsilateral brain tissue and resulted in improvements in neurobehavioral outcomes. However, naloxone or Ly294002 abrogated the neuroprotective effects of biphalin. Furthermore, biphalin treatment significantly preserved phosphorylated Akt expression, increased Bcl-2 levels, and decreased Bax and cleaved caspase 3 levels after HI. These effects were also reversed by naloxone and Ly294002 respectively. In conclusion, biphalin protects against HI brain injury in neonatal mice, which might be through activation of the opioid receptor/phosphatidylinositol-3-kinase/Akt signaling pathway.

Analgesic effects of low-dose ketamine after spinal fusion in adults: A protocol of prospective randomized trial

BACKGROUND

Patients with spinal fusion often have opioid tolerance and chronic pain, which makes it difficult to control postoperative pain. In this double-blind, randomized, prospective study, we assessed the safety and efficacy of intravenous low-dose ketamine for the treatment of pain in patients undergoing the lumbar spinal fusion.

METHODS

This randomized, prospective, double-blind and placebo-controlled study was approved via the hospital institutional review committee. Patients were registered with signed written consent. All the floor nurses, recovery room and surgeons, patients, statisticians as well as research assistants were unaware of the grouping. The patients were randomly divided into ketamine group and control group by random number table. Nausea, vomiting or vomiting, the intensity of pain, adverse events, cumulative morphine consumption, as well as the amount of extra antiemetics or analgesics were evaluated at 6 hours, 12 hours, 24 hours, 36 hours, and 48 hours after the operation. P < .05 was considered to be the statistically significant. The Statistical Package for the software of Social Sciences 20.0 was utilized for statistical analysis.

CONCLUSIONS

For the present trial, we assumed that intravenous ketamine could improve the satisfaction of patient by reducing the total consumption of morphine equivalent and the pain scores.

TRIAL REGISTRATION

This study protocol was registered in Research Registry (researchregistry5896).

In vitro and in vivo activity of cyclopeptide Dmt-c[d-Lys-Phe-Asp]NH2, a mu opioid receptor agonist biased toward β-arrestin

Morphine and related drugs, which are the most effective analgesics for the relief of severe pain, act through activating opioid receptors. The endogenous ligands of these receptors are opioid peptides which cannot be used as antinociceptive agents due to their low bioactivity and stability in biological fluids. The major goal of opioid research is to understand the mechanism of action of opioid receptor agonists in order to improve therapeutic utility of opioids. Analgesic effects of morphine are mediated mostly through activation of the mu opioid receptor. However, in the search for safer and more effective drug candidates, analogs with mixed opioid receptor profile gained a lot of interest. Recently, the concept of biased agonists able to differentially activate GPCR downstream pathways, became a new approach in the design of novel drug candidates. It is hypothesized that compounds promoting G-protein signaling may produce analgesia while β-arrestin recruitment may be responsible for opioid side effects. In this report we showed that replacement of the tyrosine residue in the mu-selective ligand Tyr-c[d-Lys-Phe-Asp]NH₂ with 2',6'-dimethyltyrosine (Dmt) produced a cyclopeptide Dmt-c[d-Lys-Phe-Asp]NH₂ with mu/delta opioid receptor agonist profile. This analog showed improved antinociception in the hot-plate test, probably due to the simultaneous activation of mu and delta receptors but also significantly inhibited the gastrointestinal transit. Using the bioluminescence resonance energy transfer (BRET) assay it was shown that this analog was a mu receptor agonist biased toward β-arrestin. β-Arrestin-dependent signaling is most likely responsible for the observed inhibition of gastrointestinal motility exerted by the novel cyclopeptide.

Biphalin, a Dimeric Enkephalin, Alleviates LPS-Induced Activation in Rat Primary Microglial Cultures in Opioid Receptor-Dependent and Receptor-Independent Manners

Neuropathic pain is relatively less responsive to opioids than other types of pain, which is possibly due to a disrupted opioid system partially caused by the profound microglial cell activation that underlines neuroinflammation. We demonstrated that intrathecally injected biphalin, a dimeric enkephalin analog, diminished symptoms of neuropathy in a preclinical model of neuropathic pain in rats (CCI, chronic constriction injury of the sciatic nerve) at day 12 postinjury. Using primary microglial cell cultures, we revealed that biphalin did not influence cell viability but diminished NO production and expression of Iba1 in LPS-stimulated cells. Biphalin also diminished MOP receptor level, as well as pronociceptive mediators (iNOS, IL-1β, and IL-18) in an opioid receptor-dependent manner, and it was correlated with diminished p-NF-κB, p-IκB, p-p38MAPK, and TRIF levels. Biphalin reduced IL-6, IL-10, TNFα, p-STAT3, and p-ERK1/2 and upregulated SOCS3, TLR4, and MyD88; however, this effect was not reversed by naloxone pretreatment. Our study provides evidence that biphalin diminishes neuropathy symptoms, which might be partially related to reduced pronociceptive mediators released by activated microglia. Biphalin may be a putative drug for future pain therapy, especially for the treatment of neuropathic pain, when the lower analgesic effects of morphine are correlated with profound microglial cell activation.

Acute and subchronic antinociceptive effects of nociceptin/orphanin FQ receptor agonists infused by intrathecal route in rats

Severe pain occurs in the context of many diseases and conditions and is a leading cause of disability. Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand of the N/OFQ peptide (NOP) receptor. This peptidergic system controls pain transmission and in particular spinally administered N/OFQ has robust antinociceptive properties. The aim of this study was to investigate the spinal antinociceptive properties of NOP peptide agonists after acute and subchronic treatment in rats. Doses unable to alter motor coordination were selected. UFP-112 (full NOP agonist) and UFP-113 (partial NOP agonist) were administered intrathecally (i.t.) by spinal catheterization. Acute injection of UFP-112 induced antinociceptive response at lower dosages (0.03-1nmol i.t.) compared to morphine and similar to N/OFQ. UFP-113 was effective in a 0.001-1nmol i.t. dose range. The antinociceptive effects of NOP ligands were no longer evident in rats knockout for the NOP gene, while those of morphine were maintained. The continuous spinal infusion (by osmotic pumps) of 0.1nmol/h UFP-112 and UFP-113 showed antinociceptive action comparable to 1-3nmol/h morphine or N/OFQ. The antinociceptive effect of morphine progressively decreased and was no longer significant after 6 days of treatment. Similar results were obtained with N/OFQ, UFP-112, and UFP-113. The acute i.t. injection of morphine in animals tolerant to N/OFQ and UFP-112 evoked analgesic effects. Neither morphine nor N/OFQ induced antinociceptive effects in morphine- and UFP-113-tolerant rats. In conclusion this study highlights the analgesic efficacy and potency of UFP-112 and UFP-113 underlining the relevance of NOP system in analgesia.

Biphalin analogs containing β(3)-homo-amino acids at the 4,4' positions: Synthesis and opioid activity profiles

Biphalin, a synthetic opioid octapeptide with a palindromic sequence has high analgesic activity. Biphalin displays a strong affinity for μ and δ-opioid receptors, and a significant to κ-receptor. The paper reports the synthesis of novel analogs of biphalin containing β(3)-homo-amino acid residues at the 4,4' positions and a hydrazine or 1,2-phenylenediamine linker. The potency and selectivity of the peptides were evaluated by a competitive receptor-binding assay in rat brain homogenate using [(3)H]DAMGO (a μ ligand) and [(3)H]DELT (a δ ligand). Analogs with β(3)-h-p-NO2Phe in positions 4 and 4' are the most active compounds. Selectivity depends on the degree of freedom between the two pharmacophore moieties. Analogs with a hydrazine linker show noticeable binding selectivity to μ receptors (IC50(μ)=0.72nM; IC50(δ)=4.66nM), while the peptides with a 1,2-phenylenediamine linker show slight δ selectivity (IC50(μ)=10.97nM; IC50(δ)=1.99nM). Tyr-d-Ala-Gly-β(3)-h-p-NO2PheNHNH-β(3)-h-p-NO2Phe (1) and (Tyr-d-Ala-Gly-β(3)-h-p-NO2PheNH)2 (2) produced greater antinociceptive effect compared to morphine after i.t. administration.

N-terminal guanidinylation of the cyclic 1,4-ureido-deltorphin analogues: the synthesis, receptor binding studies, and resistance to proteolytic digestion

The synthesis of a series of N-guanidinylated cyclic ureidopeptides, analogues of 1,4-ureido-deltorphin/dermorphine tetrapeptide is described. The δ- and μ-opioid receptor affinity of new guanidinylated analogues and their non-guanidinylated precursors was determined by the displacement radioligand binding experiments. Our results indicate that the guanidinylation of cyclic 1,4-ureidodeltorphin peptide analogues does not exhibit a uniform influence on the opioid receptor binding properties, similarly as reported earlier for some linear peptides. All analogues were also tested for their in vitro resistance to proteolysis during incubation with large excess of chymotrypsin, pepsin, and papain by means of mass spectroscopy. Guanidinylated ureidopeptides 1G-4G showed mixed μ agonist/δ agonist properties and high enzymatic stability indicating their potential as therapeutic agents for treatment of pain.

Calcium-permeable ion channels in pain signaling

The detection and processing of painful stimuli in afferent sensory neurons is critically dependent on a wide range of different types of voltage- and ligand-gated ion channels, including sodium, calcium, and TRP channels, to name a few. The functions of these channels include the detection of mechanical and chemical insults, the generation of action potentials and regulation of neuronal firing patterns, the initiation of neurotransmitter release at dorsal horn synapses, and the ensuing activation of spinal cord neurons that project to pain centers in the brain. Long-term changes in ion channel expression and function are thought to contribute to chronic pain states. Many of the channels involved in the afferent pain pathway are permeable to calcium ions, suggesting a role in cell signaling beyond the mere generation of electrical activity. In this article, we provide a broad overview of different calcium-permeable ion channels in the afferent pain pathway and their role in pain pathophysiology.

Antinociceptive profile of potent opioid peptide AM94, a fluorinated analogue of biphalin with non-hydrazine linker

AM94 is a fluorinated analog of biphalin with non-hydrazine linker that has an in vitro affinity for μ-opioid and δ-opioid receptors tenfold higher than biphalin. Furthermore, in vivo evaluation in rats showed that AM94 has in hot plate test - after both intracerebroventricular and intravenous administrations - a greater and more durable efficacy than biphalin. Here, the antinociceptive profile of AM94 is further evaluated by following two different administration routes, intrathecal and subcutaneous, and two different animal species, rats and mice. The analgesic potency of AM94 is compared with that of both the parent peptide biphalin and morphine. Results show that in rats (tail flick test) and in mice (formalin test), AM94 has a higher and more durable analgesic effect than biphalin after intrathecal and subcutaneous administrations. Conformational properties of biphalin and AM94 were also investigated by variable-temperature (1)H NMR and energy minimization.

Polyanalgesic Consensus Conference 2012: recommendations for the management of pain by intrathecal (intraspinal) drug delivery: report of an interdisciplinary expert panel

INTRODUCTION

The use of intrathecal (IT) infusion of analgesic medications to treat patients with chronic refractory pain has increased since its inception in the 1980s, and the need for clinical research in IT therapy is ongoing. The Polyanalgesic Consensus Conference (PACC) panel of experts convened in 2000, 2003, and 2007 to make recommendations on the rational use of IT analgesics based on preclinical and clinical literature and clinical experiences.

METHODS

The PACC panel convened again in 2011 to update the standard of care for IT therapies to reflect current knowledge gleaned from literature and clinical experience. A thorough literature search was performed, and information from this search was provided to panel members. Analysis of published literature was coupled with the clinical experience of panel members to form recommendations regarding the use of IT analgesics to treat chronic pain.

RESULTS

After a review of literature published from 2007 to 2011 and discussions of clinical experience, the panel created updated algorithms for the rational use of IT medications for the treatment of neuropathic pain and nociceptive pain.

CONCLUSIONS

The advent of new algorithmic tracks for neuropathic and nociceptive pain is an important step in improving patient care. The panel encourages continued research and development, including the development of new drugs, devices, and safety recommendations to improve the care of patients with chronic pain.

Nonopioid effect of β-endorphin

This review presents the generalized literature data and the results of our own research of the nonopioid effect of β-endorphin, an opioid neuropeptide interacting not only with opioid but also with nonopioid (insensitive to the opioid antagonist naloxone) receptors. The roles of the hormone and its receptors in regulation of the immune, nervous, and endocrine systems are discussed. The effect of neuromediator on the immune system mediated by both opioid and nonopioid receptors is considered in detail. The data on distribution and function of the nonopioid β-endorphin receptor in human and animal organisms are presented. All available data on the characteristics of the nonopioid β-endorphin receptor obtained by means of radioligand analysis are given. The discussed information is supposed to extend our conceptions of the role of β-endorphin in mammals and to be of extensive use in medicine and pharmacology.

Neuroprotective potential of biphalin, multireceptor opioid peptide, against excitotoxic injury in hippocampal organotypic culture

Biphalin is a dimeric opioid peptide that exhibits affinity for three types of opioid receptors (MOP, DOP and KOP). Biphalin is undergoing intensive preclinical study. It was recognized that activation of δ-opioid receptor elicits neuroprotection against brain hypoxia and ischemia. We compare the effect of biphalin and morphine and the inhibition of opioid receptors by naltrexone on survival of neurons in rat organotypic hippocampal cultures challenged with NMDA.

FINDINGS

(1) 0.025-0.1 μM biphalin reduces NMDA-induced neuronal damage; (2) biphalin neuroprotection is abolished by naltrexone; (3) reduced number of dead cells is shown even if biphalin is applied with delay after NMDA challenge.

Ketamine and remifentanil interactions on the sevoflurane minimum alveolar concentration and acute opioid tolerance in the rat

BACKGROUND

Ketamine is used at low doses for its analgesic and antihyperalgesic properties when combined with opioids but also when opioid-induced hyperalgesia and tolerance appear. In this study we determined the interaction of ketamine and remifentanil on the minimum alveolar concentration (MAC) of sevoflurane in rats and to determine whether ketamine may block acute opioid tolerance (AOT).

METHODS

Male Wistar rats were anesthetized with sevoflurane, and the MAC was determined before and after ketamine administration (10, 20, 40, and 80 mg kg(-1) or saline) alone or combined with remifentanil (120 and 240 μg kg(-1) h(-1), low and high doses, respectively). One additional group received the lowest ketamine dose after starting a remifentanil infusion. Finally, naloxone was administered to determine the potential action of ketamine on opioid receptors. MAC was determined from intratracheal gas samples, and tail clamping was used as a supramaximal stimulus. End-tidal anesthetic concentrations were assayed using a side stream gas analyzer. Statistical analysis was performed with an analysis of variance.

RESULTS

Ketamine and remifentanil dose-dependently reduced the MAC. Adding the low dose of remifentanil to ketamine did not improve the MAC reduction, whereas the high dose of remifentanil enhanced ketamine reduction in a subadditive fashion. Nevertheless, ketamine was unable to block the development of AOT to remifentanil at either dose. Finally, naloxone blocked the MAC reduction produced by ketamine.

CONCLUSIONS

A subadditive effect between ketamine and remifentanil was found on the sevoflurane MAC reduction rats. In addition, ketamine was unable to block AOT. The clinical relevance of these findings should be elucidated in future studies to reduce anesthetic requirements.

Ketamine for perioperative pain management in children: a meta-analysis of published studies

INTRODUCTION

Balanced analgesia, using both opioid and nonopioids agents, has become the standard care for postoperative pain management. Ketamine, a compound with analgesic and antihyperalgesic properties, has been shown to decrease postoperative pain and opioid requirements in adults. The goal of the present meta-analysis was to investigate postoperative analgesic properties of ketamine in pediatric patients.

MATERIAL AND METHODS

A comprehensive literature search was conducted to identify clinical trials that used ketamine as a perioperative analgesic compound in children and infants. Outcomes measured were postoperative analgesic consumption, pain intensity and duration of sensory block (when ketamine was used by caudal route) during the postoperative care unit (PACU) stay and the early postoperative period (6-24 h after leaving the operative room). The data from each trial were combined to calculate the pooled odds ratios or standard mean differences and their 95% confidence intervals.

RESULTS

Thirty-five randomized, blinded controlled studies were retrieved from the literature. Systemic ketamine was effective in decreasing PACU pain intensity and analgesic requirement but failed to influence early (6-24 h) pain intensity and analgesic requirement. Ketamine administered locally during tonsillectomy, decreased PACU and early (6-24 h) pain intensity and PACU analgesic requirements. Used as an adjuvant for caudal analgesia, ketamine increased the duration of sensory block and PACU analgesic requirement without impacting PACU pain intensity. Ketamine failed to exhibit a postoperative opioid-sparing effect.

CONCLUSIONS

This meta-analysis found that administration of ketamine was associated with decreased PACU postoperative pain intensity and nonopioid analgesic requirement. However, ketamine failed to exhibit a postoperative opioid-sparing effect.

Combining ketamine with astrocytic inhibitor as a potential analgesic strategy for neuropathic pain ketamine, astrocytic inhibitor and pain

BACKGROUND

Neuropathic pain is an intractable clinical problem. Intrathecal ketamine, a noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist, is reported to be useful for treating neuropathic pain in clinic by inhibiting the activity of spinal neurons. Nevertheless, emerging studies have disclosed that spinal astrocytes played a critical role in the initiation and maintenance of neuropathic pain. However, the present clinical therapeutics is still just concerning about neuronal participation. Therefore, the present study is to validate the coadministration effects of a neuronal noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine and astrocytic cytotoxin L-α-aminoadipate (LAA) on spinal nerve ligation (SNL)-induced neuropathic pain.

RESULTS

Intrathecal ketamine (10, 100, 1000 μg/kg) or LAA (10, 50, 100 nmol) alleviated SNL-induced mechanical allodynia in a dose-dependent manner respectively. Phosphorylated NR1 (pNR1) or glial fibrillary acidic protein (GFAP) expression was down-regulated by intrathecal ketamine (100, 1000 μg/kg) or LAA (50, 100 nmol) respectively. The combination of ketamine (100 μg/kg) with LAA (50 nmol) showed superadditive effects on neuropathic pain compared with that of intrathecal administration of either ketamine or LAA alone. Combined administration obviously relieved mechanical allodynia in a quick and stable manner. Moreover, down-regulation of pNR1 and GFAP expression were also enhanced by drugs coadministration.

CONCLUSIONS

These results suggest that combining NMDAR antagonist ketamine with an astrocytic inhibitor or cytotoxin, which is suitable for clinical use once synthesized, might be a potential strategy for clinical management of neuropathic pain.

A comparative study of morphine stimulation and biphalin inhibition of human glioblastoma T98G cell proliferation in vitro

Biphalin is a new type of opioid peptide analog with high analgesic potency that is over 1000-fold greater than morphine. Because of its less addictive nature, biphalin has been suggested as a prospective new analgesic drug. Its high analgesic activity may be related to synergic interaction with all three types of opioid receptors (mu, delta, and kappa). Earlier data implicating involvement of opioid receptors, particularly MOR (mu opioid receptor) and KOR (kappa opioid receptor), in cell cycle regulation prompted us to investigate the effect of biphalin and morphine on human glioma T98G cell proliferation in vitro. We have documented an inhibitory effect of biphalin on tumor cell growth related to a decreased proliferation rate, decline of cell ability to form colonies, and modulation of the Ki-67 proliferation index. Morphine displayed the opposite effect and triggered stimulation of T98G cell proliferation. Our experiments have shown that biphalin might constitute an alternative solution for morphine application in anti-pain and anti-cancer therapy.

Effects of intrathecal ketamine in the neonatal rat: evaluation of apoptosis and long-term functional outcome

BACKGROUND

Systemic ketamine can trigger apoptosis in the brain of rodents and primates during susceptible developmental periods. Clinically, spinally administered ketamine may improve the duration or quality of analgesia in children. Ketamine-induced spinal cord toxicity has been reported in adult animals but has not been systematically studied in early development.

METHODS

In anesthetized rat pups, intrathecal ketamine was administered by lumbar percutaneous injection. Changes in mechanical withdrawal threshold evaluated dose-dependent antinociceptive and carrageenan-induced antihyperalgesic effects in rat pups at postnatal day (P) 3 and 21. After intrathecal injection of ketamine at P3, 7, or 21, spinal cords were examined for apoptosis (Fluoro-Jade C and activated caspase-3), histopathologic change, and glial responses (ionized calcium-binding adapter molecule 1 and glial fibrillary acid protein). After maximal doses of ketamine or saline at P3 or P21, sensory thresholds and gait analysis were evaluated at P35.

RESULTS

Intrathecal injection of 3 mg/kg ketamine at P3 and 15 mg/kg at P21 reverses carrageenan-induced hyperalgesia. Baseline neuronal apoptosis in the spinal cord was greater at P3 than P7, predominantly in the dorsal horn. Intrathecal injection of 3-10 mg/kg ketamine in P3 pups (but not 15 mg/kg at P21) acutely increased apoptosis and microglial activation in the spinal cord and altered spinal function (reduced mechanical withdrawal threshold and altered static gait parameters) at P35.

CONCLUSIONS

Because acute pathology and long-term behavioral change occurred in the same dose range as antihyperalgesic effects, the therapeutic ratio of intrathecal ketamine is less than one in the neonatal rat. This measure facilitates comparison of the relative safety of spinally administered analgesic agents.

Endogenous opiates and behavior: 2008

This paper is the 31st consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2008 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 and thermoregulation (Section 16); and immunological responses (Section 17).