Intrathecal L-arginine reduces the antinociception of sevoflurane in formalin-induced pain in rats.

The purpose of this study was to investigate the contribution of spinal nitric oxide (NO) to the antinociceptive effects of emulsified sevoflurane in rats. Formalin tests were used to assess the nociceptive response. Immunohistochemistry was performed to determine the effects of emulsified sevoflurane on formalin-induced changes of Fos-like immunoreactive (Fos-LI)-positive neurons in the spinal cord. We found that emulsified sevoflurane administered intraperitoneally at a dosage of 2.5 ml/kg did not impair motor performance in rats, but it significantly decreased the formalin-induced paw licking time. Furthermore, Fos-LI-positive neurons were mainly found in the ipsilateral dorsal horn after the injection of formalin. The administration of emulsified sevoflurane significantly decreased Fos-LI-labeled neurons. Finally, intrathecal L-arginine alone did not affect the basal pain threshold, but it significantly decreased the antinociceptive response of emulsified sevoflurane against formalin injection and the suppressive effects of sevoflurane on formalin-induced Fos protein expression (P<0.05). These data suggest that spinal cord NO is involved in the antinociception of sevoflurane in rats.

Effects of isoflurane inhalation on the male reproductive system in rats.

The 15-day intact adult male assay was used to evaluate effects of isoflurane on the testes and sexual hormones. Forty adult male Sprague-Dawley rats were divided into five groups exposed to air containing 0, 50, 300, 1800 or 10,800 ppm isoflurane. After the treatments, serum was collected for the hormones assay. The right testis was to be used for daily sperm production. The left testis was processed for histopathology and electron microscopy observation. Daily sperm productions were significantly decreased at doses of 300, 1800 and 10,800 ppm. Impaired seminiferous tubules were noted at doses of 300, 1800 and 10,800 ppm. Ultrastructural changes included nucleus agglutination of spermatocytes, big lipid drops and autophagosome in cytoplasm. The serum follicle-stimulating hormone and testosterone concentrations reduced significantly at doses of 1800 and 10,800 ppm. Isoflurane induced impairments of seminiferous tubules and spermatogenesis. The testicular damages caused by isoflurane can be related to the imbalances in the sexual hormones.

Involvement of kainate receptors in the analgesic but not hypnotic effects induced by inhalation anesthetics.

In the present study, the role of kainate (KA) receptors in hypnosis and analgesia induced by emulsified inhalation anesthetics was investigated. A mouse model of hypnosis and analgesia was established by an intraperitoneal injection of emulsified enflurane, isoflurane or sevoflurane. We intracerebroventricularly (icv) or intrathecally (it) administered KA, a KA receptor agonist to mice. The effects of the KA on the sleep time were observed using a hypnosis test, and the tail-withdrawal latency was analyzed using the tail-withdrawal test. In the hypnosis test, KA (2.5, 5 or 10 ng; icv administered) treatment had no distinctive effects on the sleep time of mice treated with emulsified inhalation anesthetics. In the tail-withdrawal test, KA (0.2, 0.4 or 0.8 ng; it administered) treatment significantly and dose-dependently decreased the tail-withdrawal latency of mice treated with emulsified anesthetics. These results suggested that KA receptors may modulate the analgesic but not hypnotic effects induced by emulsified enflurane, isoflurane or sevoflurane.

Nicotinic acetylcholine receptors mediate the hypnotic and analgesic effects of emulsified inhalation anesthetics.

This study was designed to investigate the role of nicotinic acetylcholine receptors (nAChRs) in hypnosis and analgesia induced by emulsified inhalation anesthetics. After having established the mice model of hypnosis and analgesia by intraperitoneal injections of appropriate doses of enflurane, isoflurane or sevoflurane, we intracerebroventricularly or intrathecally injected different doses of nicotine and then observed the effects on the sleeping time using awaken test and the pain threshold in hot-plate test (HPPT) using hot-plate test. In the awaken test, 10, 20 and 40 microg of nicotine (intracerebroventricularly) significantly decreased the sleeping time of the mice treated with the three emulsified inhalation anesthetics mentioned above (P < 0.05 or 0.01). In the HPPT, 5, 10 and 15 microg of nicotine (intrathecally) did not affect the HPPT in conscious mice (P > 0.05); in contrast, 5, 10 and 15 microg of nicotine (intrathecally) significantly decreased the HPPT of the mice treated with emulsified inhalation anesthetics (P < 0.05 or 0.01). The data presented in this study suggest that nAChRs may be important targets for the hypnotic and analgesic effects induced by emulsified enflurane, isoflurane and sevoflurane.

[Effects of combination of midazolam and propofol on anterograde amnesia in critical patients].

OBJECTIVE: To observe the effects of sedation with midazolam and propofol on anterograde amnesia in critical patients. METHODS: Sixty selected patients on mechanical ventilation in intensive care unit (ICU) were randomly divided into three subgroups (propofol, midazolam, and midazolam and propofol combination group), with 20 cases in each group. Patients who were awakened from sedation were showed with a card depicted with different colors, figures and numbers. When patients were totally conscious after weaning from mechanical ventilation,the influence of the different methods of sedation on anterograde amnesia of these critically ill patients was assessed. RESULTS: (1) 70%, 95% and 90% of patients manifested amnesia in propofol, midazolam and the combination group, respectively. All the patients recovered their memory immediately in 30 minutes after withdrawal of the sedatives. (2) When midazolam was compared with propofol and combination group, time of onset was obviously prolonged after an intravenous injection of a load dose in midazolam group [(2.7+/-1.1) minutes and (3.1+/-1.3) minutes vs. (5.1+/-2.8) minutes], also was time of extubation after regaining of consciousness [(0.7+/-0.2) hour and (1.2+/-0.6) hours vs. (2.7+/-0.3) hours, all P<0.01]. There was no significant difference between propofol group and the combination group in time of onset and extubation (both P>0.05). (3) Cost of propofol [(2,100+/-125) yuan] was 75% higher than that of midazolam [(1,200+/-112) yuan, P<0.01], but cost of sedatives in the combination group [(1,300+/-132) yuan] was similar to that in midazolam group (P>0.05). CONCLUSION: Combination of midazolam and propofol can not only ensure anterograde amnesia in critical patients, reduce drug dosage and adverse reactions, but also can help reduce the hospital expenses. This method may be a better sedation program in ICU.

[Effect of gamma-hydroxybutyric acid receptor on focal cerebral ischemia-reperfusion injury in rats].

This study is to investigate the effect of gamma-hydroxybutyric acid receptor (GHBR) on focal cerebral ischemia-reperfusion injury in rats and its mechanism. NCS-356 (the agonist of GHBR) and NCS-382 (the antagonist of GHBR) were adopted as the tool medicine. The ripe male Sprague-Dawley rats weighing 240 - 280 g were randomly divided into seven groups: sham operation group (sham), ischemia-reperfusion group (Isc/R), NCS-356 160 microg x kg(-1) group (N1), NCS-356 320 microg x kg(-1) group (N2), NCS-356 640 microg x kg(-1) group (N3), NCS-382 640 microg x kg(-1) + NCS-356 640 microg x kg(-1) group (NCS-382 + N3), and nimodipine (Nim) 600 microg x kg(-1) group. The middle cerebral artery occlusion (MCAO) model referring to Longa's method with modifications was adopted. The effect of GHBR on behavioral consequence of MCAO rats was studied after 2 h of ischemia-reperfusion. After 24 h of ischemia-reperfusion, part of animals were used to measure the cerebral infarction volume by TTC staining; ischemic cortex of another part of animals were used to measure the content of intracellular free calcium by flow cytometry, the tNOS, iNOS activity and the content of NO by spectrophotometric method, the content of cGMP by radioimmunoassay. The neurological function score and infarction volume rate in Isc/R group rats increased significantly than that in sham group; The content of intracellular calcium ([Ca2+]) of cortex neuron and cGMP, the activities of tNOS and iNOS, and the content of NO in Isc/R group were higher than that in sham group obviously (P < 0.01); These consequence we mentioned of N1, N2, N3 and Nim group were lower than that of Isc/R. NCS-382 + N3 group could significantly antagonize the above effect of N3. Thus, NCS-356 has protective effects against ischemia-reperfusion brain injury by activating GHBR. The neuroprotective effect of GHBR is related with decreasing the content of [Ca2+]i, NO, cGMP and tNOS, iNOS activity in MCAO rats.

Spinal alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors may mediate the analgesic effects of emulsified halogenated anaesthetics.

1. The present study was designed to investigate the relationship between spinal cord alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and the analgesic effects of emulsified halogenated anaesthetics. 2. After having established the mouse model of analgesia by intraperitoneal or subcutaneous injections of appropriate doses of emulsified enflurane, isoflurane or sevoflurane, we injected different doses of AMPA intrathecally and observed effects on the pain threshold using the hot-plate and acetic acid-induced writhing tests. 3. The results showed that intrathecal injection of AMPA (0.25, 0.5 and 1.0 ng) did not affect the pain threshold on the hot-plate test or the writhing times in conscious mice. In contrast, AMPA (0.25, 0.5 and 1.0 ng intrathecally) significantly and dose-dependently decreased the pain threshold on the hot-plate test and increased the writhing times in mice treated with emulsified anaesthetics. 4. These results suggest that spinal AMPA receptors may be important targets for the analgesic effects of emulsified enflurane, isoflurane and sevoflurane.

Involvement of local orphanin FQ in the tolerance induced by repeated microinjections of morphine into ventrolateral periaqueductal gray in rats.

The present study evaluated the role of ventrolateral periaqueductal gray (vlPAG)-located orphanin-FQ (OFQ) in the opioid tolerance induced by repeated microinjections of morphine (MOR) into vlPAG. Microinjection of MOR (5 microg/0.5 microl) into vlPAG caused antinociception as quantified with the tail flick and the hot plate tests. When MOR microinjection was repeated twice daily, the antinociceptive effect disappeared within 2 days (tolerance). However, if MOR microinjection was preceded by the OFQ receptor antagonist nocistatin (NST; 1 ng/0.5 microl), the microinjections of MOR did not induce tolerance. If NST microinjections were suspended, subsequent MOR microinjections induced tolerance. In MOR-tolerant rats, a single NST microinjection into vlPAG was enough to restore the antinociceptive effect of MOR. Furthermore, if OFQ (1 ng/0.5 microl) was microinjected into vlPAG, then a MOR microinjection administered 15 min later into vlPAG did not elicit antinociception. Finally, opioid tolerance induced by repeated systemic MOR injections (5 mg/kg, i.p.) was reversed by a single microinjection of NST into vlPAG. This emphasizes the central importance of vlPAG-located OFQ in the MOR tolerance.

Strychnine-sensitive glycine receptors mediate the analgesic but not hypnotic effects of emulsified volatile anesthetics.

The present study was designed to investigate the role of strychnine-sensitive glycine receptors in hypnosis and analgesia induced by emulsified volatile anesthetics. After having established the mice model of hypnosis and analgesia by intraperitoneally injecting (i.p.) appropriate doses of ether, enflurane, isoflurane or sevoflurane, we intracerebroventricularly (i.c.v.) or intrathecally (i.t.) injected different doses of strychnine and then observed the effects on the sleeping time using the awaken test and the pain index in hot-plate test (HPPI) using the hot-plate test. In the awaken test, strychnine 1, 2, 4 microg (i.c.v.) had no distinctive effect on the sleeping time of the mice treated with the four emulsified inhalation anesthetics mentioned above (p > 0.05); in the hot-plate test, strychnine 0.1, 0.2, 0.4 microg (i.t.) can significantly and dose-dependently decrease the HPPI of the mice treated with emulsified ether, enflurane and sevoflurane (p < 0.05, p < 0.01); strychnine 0.1 microg (i.t.) did not affect the HPPI of the mice treated with emulsified isoflurane (p > 0.05), but 0.2 and 0.4 microg (i.t.) can significantly decrease the HPPI of the mice treatedwith emulsified isoflurane (p < 0.05, p < 0.01). These results suggest that strychnine-sensitive glycine receptors may contribute to the analgesic but not to the hypnotic effects induced by ether, enflurane, isoflurane and sevoflurane.

Involvement of local orphanin FQ in the development of analgesic tolerance induced by morphine microinjections into the dorsal raphe nucleus of rats.

It is well known that dorsal raphe nucleus (DRN) is one of the key structures for the development of opioid analgesia and tolerance. An increased activity of 'antiopioids' like orphanin-FQ (OFQ) has been proposed as a possible mechanism for opioid tolerance. The present study evaluates the role of DRN-located OFQ in the opioid analgesic tolerance induced by repeated microinjections of morphine (MOR) into DRN. Male rats were implanted with chronic guide cannulae aimed at the DRN. Microinjection of MOR (0.5 microg in 0.5 microl) into DRN caused antinociception as quantified with the tail flick and the hot plate tests. When MOR microinjection was repeated twice daily, the antinociceptive effect disappeared within 2 days (tolerance). However, if each MOR microinjection was preceded (within 15 min) by a microinjection of the OFQ receptor antagonist nocistatin (NST) (1 ng in 0.5 microl) into the same DRN site, the microinjections of MOR always produced antinociception and did not induce tolerance. If NST microinjections were suspended, subsequent MOR microinjections induced tolerance. In MOR-tolerant rats, a single NST microinjection into the same DRN site was enough to restore the antinociceptive effect of MOR. On the other hand, if OFQ (1 ng in 0.5 microl) was microinjected into DRN, then MOR microinjection administered 15 min later into the same DRN site did not elicit antinociception. Finally, opioid tolerance induced by repeated systemic MOR injections (5 mg/kg, i.p.) was reversed by a single microinjection of NST into DRN. This emphasizes the central importance of DRN-located OFQ in the MOR analgesic tolerance.

Strychnine-sensitive glycine receptors mediate analgesia induced by emulsified inhalation anaesthetics in thermal nociception but not in chemical nociception.

The present study was designed to investigate the role of strychnine-sensitive glycine receptors in analgesia induced by emulsified inhalation anaesthetics. After having established the mice model of analgesia by intraperitoneal or subcutaneous injections of appropriate doses of ether, enflurane, isoflurane or sevoflurane, we injected different doses of strychnine intrathecally and then observed the effects on the tail-flick latency using the tail-withdrawal test and the writhing times and acetic acid-induced writhing test. In the tail-withdrawal test, all four emulsified inhalation anaesthetics (intraperitoneally) significantly increased the tail-flick latency (P < 0.01) compared with baseline, and the increase of tail-flick latency induced by four emulsified inhalation anaesthetics can be abolished by intrathecally injected strychnine. In the acetic acid-induced writhing test, writhing times inhibition induced by subcutaneous administration of four emulsified inhalation anaesthetics was not effected by intrathecal strychnine (0.1, 0.2 and 0.4 microg). The data presented in this study suggest that glycine receptors are specifically involved in mediating the analgesic effect of ether, enflurane, isoflurane and sevoflurane on thermal-induced nociception but not chemically induced nociception.

Spinal N-methyl-D-aspartate receptors may mediate the analgesic effects of emulsified halogenated anesthetics.

The present study was designed to investigate the relationship between spinal cord N-methyl-D-aspartate (NMDA) receptors and the analgesic effects of emulsified halogenated anesthetics. After having established the mouse model of analgesia by intraperitoneally or subcutaneously injecting appropriate doses of emulsified enflurane, isoflurane or sevoflurane, we intrathecally injected different doses of NMDA and then observed the effects on the pain threshold using the hot-plate test and the acetic acid-induced writhing test. The results showed that intrathecal injection of NMDA (2.5, 5 and 10 ng) did not affect the pain threshold on the hot-plate test or the writhing times in conscious mice (p > 0.05); in contrast, NMDA (2.5, 5 and 10 ng intrathecally) can significantly and dose dependently decrease the pain threshold on the hot-plate test (p < 0.05 or p < 0.01) and increase the writhing times (p < 0.05 or p < 0.01) in the mice treated with emulsified anesthetics. These results suggest that spinal NMDA receptors may be important targets for the analgesic effects of emulsified enflurane, isoflurane and sevoflurane.

GABAA receptor partially mediated propofol-induced hyperalgesia at superspinal level and analgesia at spinal cord level in rats.

AIM: To observe effects of propofol on nociceptive response at superspinal and spinal level in rats. METHODS: Two hundreds and fifty-eight Sprague-Dawley male rats were randomized into thirty-two groups. Propofol and bicuculline were microinjected into lateral ventricle (icv), ventrolateral periaqueductal gray (vlPAG), intrathecal (ith), and intraperitoneal (ip). The noxious responses were evaluated by hot plate and formalin test. RESULTS: In hot-plate test, systemic and superspinal administration of propofol (40 mg.kg(-1) ip, 100 microg in 10 microL, icv, and 4 microg in 0.4 microL vlPAG microinjection) produced hyperalgesia (P<0.01). Hyperalgesia induced by vlPAG microinjection of propofol was significantly antagonized by 69.8 %, 71.2 %, 98.8 % at 10, 20, and 30 min by microinjection of bicuculline (10 ng in 0.4 microL, vlPAG) (P<0.01). Analgesia induced by ith propofol (100 microg.10 microL(-1)) was antagonized about 81.3 %, 54.8 %, 80.8 %, and 97.4 % at 10, 20, 30 and 40 min by ith bicuculline (P<0.05). In formalin test, systemic and superspinal administration of propofol (40 mg.kg(-1) ip, 4 microg in 0.4 microL, vlPAG) also produced hyperalgesia (P<0.01). The increased formalin pain scores were antagonized about 57.1 % by bicuculline (10 ng, vlPAG) (P<0.05) at 60 min after formalin injection. The decreased formalin pain scores induced by ith propofol (100 microg in 10 microL) were antagonized about 66.7 % at 30 min by ith bicuculline (P<0.05) after formalin injection. Hyperalgesia produced by ip propofol in both hot plate and formalin test could not be antagonized by vlPAG administration of bicuculline. CONCLUSION: GABAA receptor partly mediated propofol-induced hyperalgesia at superspinal and analgesia at spinal cord in rats.

[Propofol depresses c -fos expression of NOS neurons in the spinal cord of rats with inflammatory pain].

In formalin pain model, the effect of propofol on Fos expression in the spinal cord was examined by means of c -fos oncogene immunohistochemistry and NADPH-d histochemistry. Fos-like immunoreactive (FLI) neurons were mainly found in the ipsilateral dorsal horn after injection of formalin, some of which were FLI/NOS double-labeled neurons. Most of the FLI or FLI/NOS double-labeled neurons were observed in the medial part of lamina and the outer lamina . Before or after injection of formain, i.p. injection of propofol significantly decreased the number of FLI and FLI/NOS double-labeled neurons in all laminae (P<0.05 or P<0.01). By single i.p. injection of propofol or normal saline, few FLI neurons were found in the spinal cord. The results suggest that the antinociceptive function of propofol is possibly involved in the depression of the NOS neurons in the spinal cord.

[The protective effects of melatonin on global cerebral ischemia-reperfusion injury in gerbils].

AIM: To investigate the effects of melatonin (MT) on histology and behavioral tests during global cerebral ischemia-reperfusion in gerbils. METHODS: Global cerebral ischemia was induced by occluding the bilateral common carotid arteries for 10 min in gerbils. Three doses of MT were administrated intraperitoneally 30 min prior to the onset of ischemia. Locomotor activity was measured by using the open field method 3 and 7 days after the ischemic episode. T maze test was carried out 4, 5 and 6 days after ischemia to assess the working memory of gerbils. Neuronal damage was assessed in CA1 pyramidal layer of gerbil hippocampus and evaluated 7 days after ischemia. RESULTS: MT significantly reversed the locomotor activity increases, ameliorated learning and working memory deficit, and reduced the extent of CA1 hippocampal pyramidal cells injury after transient global cerebral ischemia in the Mongolian gerbil. CONCLUSION: MT provides significantly protective effect against both histological and behavioral consequences of global cerebral ischemia-reperfusion injury in gerbils.