Suppression of cyclic guanosine monophosphate formation in rat cerebellar slices by propofol, ketamine and midazolam

Intravenous Anesthetic, Propofol Affects Synaptic Responses in Cerebellar Purkinje Cells

Objective

Propofol is an intravenously administered anesthetic that enhances γ-aminobutyric acid-mediated inhibition in the central nerve system. Other mechanisms may also be involved in general anesthesia. Propofol has been implicated in movement disorders. The cerebellum is important for motor coordination and motor learning. The aim of the present study was to investigate the propofol effect on excitatory synaptic transmissions in cerebellar cortex.

Methods

Excitatory postsynaptic currents by parallel fiber stimulation and complex spikes by climbing fiber stimulation were monitored in Purkinje cells of Wister rat cerebellar slice using whole-cell patch-clamp techniques.

Results

Decay time, rise time and amplitude of excitatory postsynaptic currents at parallel fiber Purkinje cell synapses and area of complex spikes at climbing fiber Purkinje cell synapses were significantly increased by propofol administration.

Conclusion

The detected changes of glutamatergic synaptic transmission in cerebellar Purkinje cell, which determine cerebellar motor output, could explain cerebellar mechanism of motor deficits induced by propofol.

Effects of methylene blue on propofol requirement during anaesthesia induction and surgery

Delayed emergence from anaesthesia and neurological disturbances have been reported in patients undergoing parathyroidectomy who received methylene blue (MB) pre-operatively. We hypothesised that MB would decrease propofol requirements. The Bispectral index (BIS) and a target-controlled infusion of propofol were used in two groups of 11 matched patients. Patients in one group were pretreated with MB. During induction, clinical sedation scores and BIS values were significantly lower at the predicted effect-site propofol concentration of 2 microg x ml(-1) in the MB compared with the control group. Intra-operatively, although similar BIS values were achieved in the two groups, patients pretreated with MB required a mean 50% lower dose of propofol compared with controls. In view of these findings, care should be taken to ensure an adequate depth of anaesthesia by titrating the administration of anaesthetic agents whenever MB is infused peri-operatively.

Synergistic depression of NMDA receptor-mediated transmission by ketamine, ketoprofen and L-NAME combinations in neonatal rat spinal cords in vitro

BACKGROUND AND PURPOSE

Spinal N-methyl-D-aspartate (NMDA) receptor/cyclooxygenase (COX) and nitric oxide synthase (NOS) pathways play a major role in nociceptive processing, and influencing them simultaneously may induce synergistic analgesia. This study determined the spinal antinociceptive interactions between ketamine (NMDA receptor channel blocker), ketoprofen (COX inhibitor) and L-NAME (NOS inhibitor) combinations.

EXPERIMENTAL APPROACH

Using an in vitro neonatal rat spinal cord preparation, two A-fibre-mediated reflexes, the monosynaptic reflex (MSR) and the low-intensity excitatory postsynaptic potential (epsp), and one C-fibre-mediated reflex, the high-intensity epsp, were evoked electrically. The effect of drugs and drug combinations on these reflexes was assessed and the type of interaction determined by isobolographic analysis.

KEY RESULTS

Infusion of ketamine alone decreased all three reflexes. That of ketoprofen decreased both the low and the high-intensity epsp only. Infusion of L-NAME alone produced no significant effects. Co-infusion of fixed ratios of IC(40) fractions of both (ketamine+ketoprofen) and (ketamine+L-NAME) were synergistic for depressing the low and the high-intensity epsps. The interaction was sub-additive for both combinations on the MSR. The only significant effect for the (ketoprofen+L-NAME) combination was synergism on the high-intensity epsp.

CONCLUSIONS AND IMPLICATIONS

All three combinations synergistically depressed nociceptive spinal transmission, and both ketamine and ketoprofen and ketamine and L-NAME combinations did so with potentially decreased motor side effects. If such combination profiles also occur in vivo, the present findings raise the possibility of ultimate therapeutic exploitation of increased analgesia with fewer side effects.

Characterization of a novel effect of serotonin 5-HT1A and 5-HT2A receptors: increasing cGMP levels in rat frontal cortex

Elucidating the mechanisms of action of hallucinogens has become an increasingly important area of research as their abuse has grown in recent years. Although serotonin receptors appear to play a role in the behavioral effects of the phenethylamine and indoleamine hallucinogens, the signaling pathways activated by these agents are unclear. Here it is shown that administration of serotonin (5-hydroxytryptamine, 5-HT) increased cyclic guanosine monophosphate (cGMP) production in frontal cortical slices of rat brain. The effect of 5-HT was greater than that of N-methyl-D-aspartate (NMDA), a stimulant of cGMP formation in the central nervous system. The 5-HT(2A/2C) receptor phenethylamine agonist, 2,5-dimethoxy-4-methylamphetamine (DOM), increased cGMP content in the slices. Additionally 8-hydroxy-2-(di-n-propylamino)tetralin (DPAT), a 5-(HT1A/7) receptor agonist also increased cGMP production. Stimulation of cGMP formation by DOM was prevented by a 5-HT(2A/2C) receptor antagonist, pirenperone, as well as by a 5-HT2A receptor selective antagonist, MDL100907. A 5-HT2C receptor antagonist, SB242084, did not block the effect of DOM. Stimulation of cGMP production by DPAT was blocked by the 5-HT1A receptor antagonist, WAY100635. Stimulation of cGMP formation by serotonin could be prevented by pirenperone or WAY100635. In summary, activation of serotonin 5-HT1A and 5-HT2A receptors increase brain cGMP levels.

Tumor necrosis factor-alpha reduces ketamine- and propofol-induced anesthesia time in rats

Tumor necrosis factor-alpha (TNFalpha) is a crucial neuromodulator in the brain. TNFalpha is involved in many physiological events including pain response and sleep. However, the interactions between TNFalpha and anesthetics have not been elucidated yet. In the present study, we investigated the effects of four intracerebroventricular (ICV) doses (1, 10, and 100 pg, and 1 ng) and two intraperitoneal (IP) doses (10 and 100 ng) of TNFalpha on anesthesia time of ketamine (100 mg/kg IP) and propofol (80 mg/kg IP) in rats. All ICV doses of TNFalpha reduced anesthesia time of ketamine and propofol compared with the saline ICV group (ketamine control group, 45.4 +/- 6.5 min; propofol control group, 43.5 +/- 11.0 min). The maximum effect was obtained after the ICV injection of 10 pg of TNFalpha (76% and 54% of ketamine and propofol control groups, respectively). Anesthesia time of ketamine or propofol was also decreased by IP injection of TNFalpha in a dose-dependent manner. Injection of 100 ng of TNFalpha IP reduced anesthesia time of ketamine and propofol by 67% and 64% of each control group, respectively. These data show that TNFalpha can modulate the anesthesia time of IV anesthetics, suggesting that anesthetic requirements might be altered in the presence of cerebral or systemic inflammation.

IMPLICATIONS

Tumor necrosis factor alpha (TNFalpha) regulates many physiological events in the brain. We investigated the effects of TNFalpha on anesthesia time in rats. Both central and peripheral administration of TNFalpha decreased anesthesia time induced by ketamine and propofol.