Ana González-Cuello

Increased Spinal Dynorphin Levels and Phospho-Extracellular Signal-Regulated Kinases 1 and 2 and c-Fos Immunoreactivity after Surgery under Remifentanil Anesthesia in Mice

In humans, remifentanil anesthesia enhances nociceptive sensitization in the postoperative period. We hypothesized that activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and the expression of c-Fos, prodynorphin (mRNA), and dynorphin in the spinal cord could participate in the molecular mechanisms underlying postoperative opioid-induced sensitization. In a mouse model of incisional pain, we evaluated thermal (Hargreaves test) and mechanical (von Frey) hyperalgesia during the first 21 postoperative days. Moreover, prodynorphin (mRNA, real-time polymerase chain reaction), dynorphin (enzymatic immunoassay), c-Fos expression, and ERK1/2 phosphorylation (both by immunohistochemistry) in the lumbar spinal cord were assessed. Surgery performed under remifentanil anesthesia induced a maximal decrease in nociceptive thresholds between 4 h and 2 days postoperatively (p < 0.001) that lasted 10 to 14 days compared with noninjured animals. In the same experimental conditions, a significant increase in prodynorphin mRNA expression (at 2 and 4 days) followed by a sustained increase of dynorphin (days 2 to 10) in the spinal cord was observed. We also identified an early expression of c-Fos immunoreactivity in the superficial laminae of the dorsal horn of the spinal cord (peak at 4 h; p < 0.001), together with a partial activation of ERK1/2 (4 h; p < 0.001). These findings suggest that activated ERK1/2 could induce c-Fos expression and trigger the transcription of prodynorphin in the spinal cord. This in turn would result in long-lasting increased levels of dynorphin that, in our model, could participate in the persistence of pain but not in the manifestation of first pain.

Activation of c-fos expression in the heart after morphine but not U-50,488H withdrawal.

In the present work we have studied in the heart the expression of Fos, the protein product of the c‐fos proto‐oncogene and the adaptive changes in noradrenergic neurons after naloxone or nor‐binaltorphimine (nor‐BNI) administration to morphine or U‐50,488H pretreated rats. Male rats were implanted with placebo (naïve) or morphine (tolerant/dependent) pellets for 7 days. On day 8 rats received saline s.c., naloxone (5 mg kg−1 s.c.) or nor‐BNI (5 mg kg−1 i.p.). Other groups of rats were rendered tolerant/dependent on U‐50,488H by injecting the drug twice daily (15 mg kg−1 i.p.) for 4 days. Control animals received saline. On day 5 the animals were injected with vehicle i.p. or nor‐BNI (5 mg kg−1 i.p.). Using immunohistochemical staining of Fos, present results indicate that morphine withdrawal induced marked Fos immunoreactivity (Fos‐IR) within the cardiomyocyte nuclei. Moreover, Western blots analysis revealed a peak expression of c‐fos in right and left ventricle after naloxone induced withdrawal in parallel with an increase in noradrenaline (NA) turnover. However, after nor‐BNI administration to rats chronically treated with U‐50,488H, we found a decrease in the NA turnover. In addition, the administration of nor‐BNI to rats chronically treated with U‐50,488H or morphine did not induce modifications in the Fos‐IR, in the heart. These results demonstrated that morphine withdrawal induces the expression of Fos protein, as well as an enhancement of noradrenergic activity in the heart. In contrast to morphine U‐50,488 withdrawal produces no changes in Fos‐IR in parallel with a decrease in NA turnover, indicating that the kappa–opioid receptors are not involved in the molecular adaptive mechanisms responsible for the development of opioid dependence in the heart.

Effects of rolipram and diazepam on the adaptive changes induced by morphine withdrawal in the hypothalamic paraventricular nucleus

A role for the cyclic AMP systems in the development of morphine dependence has been previously reported. In this study we investigated whether morphine dependence was inhibited by phosphodiesterase (PDE) 4 inhibitors rolipram and diazepam. Dependence on morphine was induced by a 7-day s.c. implantation of morphine pellets. On day 8, morphine withdrawal was precipitated by an injection of naloxone. In order to determine the effect of rolipram and diazepam rats were injected with these drugs once daily for seven days as well as 30 min before of naloxone injection. When opioid withdrawal was precipitated, an enhanced noradrenaline turnover and increased level of cyclic AMP and cyclic GMP in the hypothalamic paraventricular nucleus (PVN) were observed 30 min after naloxone administration. Moreover, c-Fos expression was induced in the PVN after naloxone-precipitated morphine withdrawal. Co-administration of rolipram or diazepam with morphine during the pre-treatment period, significantly reduced the signs of withdrawal, the enhancement of noradrenaline turnover and the increase in cyclic AMP. However, these inhibitors did not modify either levels of cyclic GMP or c-Fos expression in the PVN. These findings demonstrate that co-administration of rolipram or diazepam with morphine attenuate the withdrawal syndrome and suggest that these compounds may prevent the up-regulation of the cyclic AMP pathway and the associated increase in cyclic AMP level in morphine-withdrawn rats.

Memantine prevents reference and working memory impairment caused by sleep deprivation in both young and aged Octodon degus

Memory loss is one of the key features of cognitive impairment in either aging, Mild Cognitive Impairment (MCI) or dementia. Pharmacological treatments for memory loss are today focused on addressing symptomatology. One of these approved compounds is memantine, a partial NMDA receptor antagonist that has proved its beneficial effects in cognition. The Octodon degus (O. degus) has been recently proposed as a potential model relevant for neurodegenerative diseases. However, there are no previous studies investigating the effect of pharmacological treatments for age-related cognitive impairment in this rodent. In this work we aimed to evaluate the effect of memantine on sleep deprivation (SD)-induced memory impairment in young and old O. degus. Young and old animals were trained in different behavioral paradigms validated for memory evaluation, and randomly assigned to a control (CTL, n=14) or an SD (n=14) condition, and treated with vehicle or memantine (10-mg/Kg i.p.) before the SD started. We demonstrate that SD impairs memory in both young and old animals, although the effect in the old group was significantly more severe (P<0.05). Memantine pretreatment was able to prevent the cognitive impairment caused by SD in both age groups, while it had no negative effect on CTL animals. The positive effect of memantine in counteracting the negative effect of SD on the retrieval process even in the aged O. degus further supports the translational potential of both the challenge and the species, and will enable a better understanding of the behavioral features of memantine effects, especially related with reference and working memories.

Transcranial magnetic stimulation and aging: Effects on spatial learning and memory after sleep deprivation in Octodon degus

The benefits of neuromodulatory procedures as a possible therapeutic application for cognitive rehabilitation have increased with the progress made in non-invasive modes of brain stimulation in aged-related disorders. Transcranial magnetic stimulation (TMS) is a non-invasive method used to examine multiple facets of the human brain and to ameliorate the impairment in cognition caused by Alzheimers disease (AD). The present study was designed to evaluate how a chronic TMS treatment could improve learning and memory functions after sleep deprivation (SD) in old Octodon degus. SD was executed by gently handling to keep the animals awake throughout the night. Thirty young and twenty-four old O. degus females were divided in six groups (control, acute and chronic TMS treatment). Behavioral tests included; Radial Arm Maze (RAM), Barnes Maze (BM) and Novel Object Recognition (NOR). Although learning and memory functions improved in young animals with only one session of TMS treatment, a significant improvement in cognitive performance was seen in old animals after 4 and 7days of TMS, depending on the task that was performed. No side effects were observed following, which showed therapeutic potential for improving age-related cognitive performance.