Propofol enhances GABA(A) receptor-mediated presynaptic inhibition in human spinal cord

Anesthetic Fade in Intraoperative Transcranial Motor Evoked Potential Monitoring Is Mainly due to Decreased Synaptic Transmission at the Neuromuscular Junction by Propofol Accumulation

BACKGROUND

 We previously reported that normalization of motor evoked potential (MEP) monitoring amplitude by compound muscle action potential (CMAP) after peripheral nerve stimulation prevented the expression of anesthetic fade (AF), suggesting that AF might be due to reduced synaptic transfer in the neuromuscular junction.

METHODS

 We calculated the time at which AF began for each of craniotomy and spinal cord surgery, and examined whether AF was avoided by CMAP after peripheral nerve stimulation normalization in each. Similar studies were also made with respect to the upper and lower limb muscles.

RESULTS

 AF was observed in surgery lasting 160 minutes for craniotomy and 260 minutes or more for spinal surgery, and 195 minutes in the upper limb muscles and 135 minutes in the lower limb muscles. In all the series, AF could be avoided by CMAP after peripheral nerve stimulation normalization.

CONCLUSION

 AF of MEP occurred in both craniotomy and spinal cord surgery, and it was also corrected by CMAP after peripheral nerve stimulation. AF is considered to be mainly due to a decrease in synaptic transfer of the neuromuscular junction due to the accumulation of propofol because of the avoidance by CMAP normalization. However, it may be partially due to a decrease in the excitability of pyramidal tracts and α-motor neurons, because AF occurred earlier in the lower limb muscles than in the upper limb muscles.

Effect of Compound Muscle Action Potential After Peripheral Nerve Stimulation Normalization on Anesthetic Fade of Intraoperative Transcranial Motor-Evoked Potential

PURPOSE

Anesthetic fade refers to the time-dependent decrease in the amplitude of the intraoperative motor-evoked potential. It is thought to be caused by the accumulation of propofol. The authors examined whether normalization by the compound muscle action potential (CMAP) after peripheral nerve stimulation could compensate for anesthetic fade.

METHODS

In 1,842 muscles in 578 surgeries, which did not exhibit a motor-neurologic change after the operation, the motor-evoked potential amplitude was normalized by the CMAP amplitude after peripheral nerve stimulation, and the CMAP amplitude and operation times were analyzed.

RESULTS

The amplitudes of both motor-evoked potential and CMAP increased over time after peripheral nerve stimulation because of the disappearance of muscle-relaxant action. Especially, after peripheral nerve stimulation, CMAP significantly increased from the beginning to the end of the operation. Anesthetic fade in transcranial motor-evoked potential monitoring seemed to occur at more than 235 minutes of surgery based on the results of a receiver operating characteristic analysis of the operation time and relative amplitudes. Although the mean amplitude without CMAP normalization at more than 235 minutes was significantly lower than that at less than 235 minutes, the mean amplitude with normalization by CMAP after peripheral nerve stimulation at more than 235 minutes was not significantly different from that at less than 235 minutes.

CONCLUSIONS

Compound muscle action potential after peripheral nerve stimulation normalization was able to avoid the effect of anesthetic fade. Anesthetic fade was seemed to be caused by a decrease in synaptic transmission at the neuromuscular junction because of propofol accumulation by this result.

Synergistic analgesic effect of propofol-alfentanil combination through detecting the inhibition of cAMP signal pathway

OBJECTIVE

The study aims to investigate the possible mechanism of the synergistic analgesic effect of propofol-alfentanil combination.

METHODS

The synergistic analgesic effects of propofol-alfentanil combination in Sprague-Dawley (SD) rats were analysed through the von Frey test. Then, we examined the activity of phospholipase C (PLC) and the intracellular levels of Ca(2+) and adenosine 3', 5'cyclic monophosphate (cAMP) in primary neuronal cells of fetal SD rats. We detected the intracellular Ca(2+) concentration by fluorescence and flow cytometry. The PLC activity of the primary neuronal cells was assayed using the EnzChek(®) Direct Phospholipase C Assay Kit. The cAMP content of the cells was assayed using the cAMP Direct Immunoassay Kit (Fluorometric).

KEY FINDINGS

Both propofol and alfentanil treatments depressed cAMP levels and PLC activity, but propofol-alfentanil combination decreased these parameters to a greater extent than alfentanil treatment alone. Propofol and alfentanil both inhibited Ca(2+) channel, but propofol-alfentanil combination suppressed this channel to a greater extent than alfentanil treatment alone. Fluorescent image analysis revealed that both propofol and alfentanil reduced the intracellular levels of Ca(2+) , and propofol-alfentanil combination showed weaker signals than alfentanil alone. Propofol-alfentanil combination significantly reduced intracellular Ca(2+) level, cAMP level and PLC activity.

CONCLUSION

Propofol and alfentanil exert synergistic analgesic effects through the adenylyl cyclase pathway.

Effects of docosahexaenoic acid on learning and memory impairment induced by repeated propofol anesthesia in young rats

The aim of the present study was to investigate the effects of docosahexaenoic acid (DHA) on the learning and memory ability of young rats exposed to propofol, and its underlying mechanisms. Sprague Dawley rats (n=60) were randomly divided into six groups: Control group (group A); solvent control group (group B); propofol group (group C); low-dose DHA + propofol group (group D); medium dose DHA + propofol group (group E); and high-dose DHA + propofol group (group F). The Morris water maze (MWM) test was performed to evaluate the rats' learning and memory ability, and tissue samples from the hippocampi of the rats were obtained for biochemical analysis. The results of the MWM test revealed that DHA supplementation administered to young rats led to an evident decrease in the latency to find the maze platform, and a significant increase in the number of platform crossings in groups E and F compared with group C (P<0.05). High-performance liquid chromatography indicated that glutamate concentration levels were significantly lower and γ-aminobutyric acid concentration levels were significantly higher in the hippocampi of group E and F rats treated with DHA compared with group C rats (P<0.05). Furthermore, DHA treatment alleviated the decrease in brain-derived neurotrophic factor levels (P<0.05), and superoxide dismutase (P<0.05) and glutathione peroxidase (P<0.05) activities induced by the administration of propofol. Additionally, DHA treatment decreased malondialdehyde levels in the hippocampi of rats (P<0.05). The aforementioned findings demonstrate that DHA was able to effectively improve learning and memory dysfunction induced by repeated propofol-induced anesthesia in young rats. This data suggests that DHA may be a potential candidate for further preclinical studies aimed at treating postoperative cognitive dysfunction.

Gastrointestinal delivery of propofol from fospropofol: its bioavailability and activity in rodents and human volunteers

BACKGROUND

Propofol is a safe and widely used intravenous anesthetic agent, for which additional clinical uses including treatment of migraine, nausea, pain and anxiety have been proposed (Vasileiou et al. Eur J Pharmacol 605:1-8, 2009). However, propofol suffers from several disadvantages as a therapeutic outside anesthesia including its limited aqueous solubility and negligible oral bioavailability. The purpose of the studies described here was to evaluate, in both animals and human volunteers, whether fospropofol (a water soluble phosphate ester prodrug of propofol) would provide higher propofol bioavailability through non-intravenous routes.

METHODS

Fospropofol was administered via intravenous, oral and intraduodenal routes to rats. Pharmacokinetic and pharmacodynamic parameters were then evaluated. Based on the promising animal data we subsequently conducted an oral and intraduodenal pharmacokinetic/pharmacodynamic study in human volunteers.

RESULTS

In rats, bioavailability of propofol from fospropofol delivered orally was found to be appreciable, in the order of around 20-70%, depending on dose. Availability was especially marked following fospropofol administration via the intraduodenal route, where bioavailability approximated 100%. Fospropofol itself was not appreciably bioavailable when administered by any route except for intravenous. Pharmacologic effect following oral fospropofol was confirmed by observation of sedation and alleviation of thermal hyperalgesia in the rat chronic constrictive injury model of neuropathic pain. The human data also showed systemic availability of propofol from fospropofol administration via oral routes, a hereto novel finding. Assessment of sedation in human volunteers was correlated with pharmacokinetic measurements.

CONCLUSIONS

These data suggest potential utility of oral administration of fospropofol for various therapeutic indications previously considered for propofol.

Synergistic antinociceptive interactions between fospropofol and alfentanil in mice

BACKGROUND

Combination therapy, which provides the opportunity to achieve optimal analgesia with reduced side effects at lower drug doses, is a valid approach for the treatment of pain. The analgesic interaction between fospropofol and alfentanil has not been investigated till date. We sought to determine the nature of the interaction between fospropofol and alfentanil in mice models of the formalin test, hot-plate test and the tail-flick test.

METHODS

The effects of fospropofol, alfentanil and their combinations were examined in the formalin-induced paw inflammatory hyperalgesia, the hot-plate test and the tail-flick test in mice. In the three models, dose-response curves were established and their respective ED50 (50% effective dose) values were determined separately for each agent. Fixed-ratio combinations of fospropofol and alfentanil were tested for their combined antinociceptive effects, and the type of interaction was determined by the isobolographic analysis.

RESULTS

Fospropofol, alfentanil and their combination produced a dose-dependent decrease in the number of flinches during phase 1 of the formalin test. In the hot-plate test and in the tail-flick test, fospropofol, alfentanil and their combination significantly and dose dependently prolonged the latency of withdrawal. In the three models, isobolographic analysis revealed a significant synergistic interaction between fospropofol and alfentanil. The ED50 value for the drug combination was significantly lower than the theoretical additive value (p<0.05).

CONCLUSIONS

The results demonstrate that fospropofol and alfentanil provide synergistic antinociceptive interactions in the formalin, hot-plate, and tail-flick tests. The observed synergistic interaction between fospropofol and alfentanil are indicative of the effectiveness of the combination treatment in pain management and should be explored further in patients undergoing minor surgical procedures.

Acute intrathecal baclofen withdrawal: a brief review of treatment options

BACKGROUND

Acute baclofen toxicity and withdrawal can present with a constellation of symptoms making differentiation between these two entities and other potential diagnoses challenging. Baclofen withdrawal is associated with numerous complications which may require neurocritical care expertise such as respiratory failure, refractory seizures, delirium, and blood pressure lability.

METHODS

Case report and literature review.

RESULTS

This case report discusses a case of intrathecal baclofen (ITB) withdrawal, focusing on the differential diagnosis for acute baclofen withdrawal and reviews the various options that exist to treat the symptoms of acute baclofen withdrawal such as benzodiazepines, propofol, skeletal muscle relaxants, and tizanidine.

CONCLUSIONS

Critical care practitioners should be prepared to treat this potentially devastating and often refractory complication of ITB therapy.

Effects of anesthetic propofol on release of amino acids from the spinal cord during visceral pain

As one of general anesthetics, propofol, has been used for surgical procedures of visceral organs. However, the mechanisms underlying the action of propofol on visceral nociception remain controversial. The aim of this study is to test whether the antinociception of systemic administration of propofol against visceral stimuli is related to the changes in release of excitatory and inhibitory amino acids in the spinal cord. The spinal microdialysis catheters were implanted subarachnoidally via the atlanto-occipital membrane in healthy SD rats. The rats received an intraperitoneal injection of acetic acid for visceral pain induction 10min after intraperitoneal pretreatment with vehicle or propofol (100mg/kg). The acetic acid-induced writhing assay was used to determine the degree of antinociception. Cerebrospinal fluid dialysate was collected by microdialysis from the spinal subarachnoid space before pretreatment and after visceral pain induction. Visceral pain-induced release of amino acids into the dialysate, including glutamate, aspartate, and γ-amino butyric acid was evaluated by measuring the changes in the concentrations of these amino acids. Acetic acid increased release of aspartate and glutamate, and decreased release of γ-amino butyric acid in the cerebrospinal fluid as measured by microdialysis. Pretreatment with propofol significantly decreased writhing responses induced by visceral pain, suppressed the visceral pain-induced aspartate and glutamate release, and reversed the decreased release of γ-amino butyric acid in the cerebrospinal fluid. These data provide evidence for a potential mechanism for the antinociceptive effects of propofol on visceral nociception.

Effects of general anesthetics on visceral pain transmission in the spinal cord

Current evidence suggests an analgesic role for the spinal cord action of general anesthetics; however, the cellular population and intracellular mechanisms underlying anti-visceral pain by general anesthetics still remain unclear. It is known that visceral nociceptive signals are transmited via post-synaptic dorsal column (PSDC) and spinothalamic tract (STT) neuronal pathways and that the PSDC pathway plays a major role in visceral nociception. Animal studies report that persistent changes including nociception-associated molecular expression (e.g. neurokinin-1 (NK-1) receptors) and activation of signal transduction cascades (such as the protein kinase A [PKA]-c-AMP-responsive element binding [CREB] cascade)-in spinal PSDC neurons are observed following visceral pain stimulation. The clinical practice of interruption of the spinal PSDC pathway in patients with cancer pain further supports a role of this group of neurons in the development and maintenance of visceral pain. We propose the hypothesis that general anesthetics might affect critical molecular targets such as NK-1 and glutamate receptors, as well as intracellular signaling by CaM kinase II, protein kinase C (PKC), PKA, and MAP kinase cascades in PSDC neurons, which contribute to the neurotransmission of visceral pain signaling. This would help elucidate the mechanism of antivisceral nociception by general anesthetics at the cellular and molecular levels and aid in development of novel therapeutic strategies to improve clinical management of visceral pain.

Depression of presynaptic excitation by the activation of vanilloid receptor 1 in the rat spinal dorsal horn revealed by optical imaging

In this study, we show that capsaicin (CAP) depresses primary afferent fiber terminal excitability by acting on vanilloid receptor 1 (TRPV1 channels) of primary afferent fibers in adenosine 5'-triphosphate (ATP)- and temperature-dependent manner using two optical imaging methods. First, transverse slices of spinal cord were stained with a voltage-sensitive dye and the net excitation in the spinal dorsal horn was recorded. Prolonged treatment (>20 min) with the TRPV1 channel agonist, CAP, resulted in a long-lasting inhibition of the net excitation evoked by single-pulse stimulation of C fiber-activating strength. A shorter application of CAP inhibited the excitation in a concentration-dependent manner and the inhibition was reversed within several minutes. This inhibition was Ca⁺⁺-dependent, was antagonized by the TRPV1 channel antagonist, capsazepine (CPZ), and the P₂X and P₂Y antagonist, suramin, and was facilitated by the P₂Y agonist, uridine 5'-triphosphate (UTP). The inhibition of excitation was unaffected by bicuculline and strychnine, antagonists of GABA_A and glycine receptors, respectively. Raising the perfusate temperature to 39°C from 27°C inhibited the excitation (-3%/°C). This depressant effect was antagonized by CPZ and suramin, but not by the P₂X antagonist, 2', 3'-O-(2,4,6-trinitrophenyl) adenosine 5'-triphosphate (TNP-ATP). Second, in order to record the presynaptic excitation exclusively, we stained the primary afferent fibers anterogradely from the dorsal root. CAP application and a temperature increase from 27°C to 33°C depressed the presynaptic excitation, and CPZ antagonized these effects. Thus, this study showed that presynaptic excitability is modulated by CAP, temperature, and ATP under physiological conditions, and explains the reported central actions of CAP. These results may have clinical importance, especially for the control of pain.

Intrathecal propofol has analgesic effects on inflammation-induced pain in rats

PURPOSE

Propofol is thought to act on gamma-aminobutyric acid receptors, which have some role in pain transmission in the spinal cord. In this study, we examined the effects of intrathecal propofol on acute thermally- or inflammation-induced pain in rats.

METHODS

Lumbar intrathecal catheters were implanted in Male Sprague-Dawley rats. The tail withdrawal response to thermal stimulation (tail flick test) or paw flinching and shaking response by sc formalin injection into the hind paw (formalin test) were tested. Propofol 1000, 300 or 100 microg or saline (control) was administered as 10 microL intrathecally. Motor disturbance and behavioural side effects were also monitored in the rats during the tail flick test. Eight rats were used for each dose in each test.

RESULTS

No analgesic effects were observed in the tail flick test. In the formalin test, 50% of effective doses were 449 mug (95% confidence interval, 80-3180 microg) in phase 1 and 275 microg (146-519 microg) in phase 2. Motor disturbance was observed in one rat with 100 microg and agitation and allodynia were seen in one rat with 300 microg. However, both were reversible in 120 min.

CONCLUSIONS

Intrathecal administration of propofol had analgesic effects on inflammation-induced acute and facilitated pain but not on thermally-induced acute pain. Transient motor and sensory disturbance could not rule out the possibility of neurotoxicity.