Propofol anesthesia significantly alters plasma blood levels of melatonin in rats.

BACKGROUND: General anesthesia combined with surgery has been shown to decrease the nocturnal peak of melatonin in patients. However, the role of anesthesia itself on melatonin secretion remains unknown. We previously showed that anesthesia induced by propofol modifies the circadian time structure in both rats and humans and phase advances the circadian rest-activity rhythm in rats. In this study, we examined the secretion of melatonin during 24 h after a 30-min propofol anesthesia in rats. METHODS: Rats were exposed to 12-h light/12-h dark alteration conditions and anesthetized with propofol (120 mg/kg intraperitoneally) around their peak of melatonin secretion (Zeitgeber time 16). Trunk blood samples were collected at seven subsequent Zeitgeber times to assess the effects of propofol on circadian melatonin secretion. RESULTS: Propofol modifies the peripheral melatonin by significantly decreasing its concentration ( approximately 22-28%) during the immediate 3 h after the wake up from anesthesia and then significantly increasing melatonin secretion 20 h after anesthesia ( approximately 38%). Cosinor analysis suggests that propofol induces a phase advance of the circadian secretion of peripheral melatonin. CONCLUSIONS: The results demonstrate the disturbing effects of propofol anesthesia on the circadian rhythm of plasma melatonin in rats under normal light conditions. These results parallel the desynchronization of the circadian rhythms of locomotor activity and temperature previously observed after propofol anesthesia.

Circadian disruption of body core temperature and rest-activity rhythms after general (propofol) anesthesia in rats.

BACKGROUND: General anesthesia is commonly associated with sleep disorders, fatigue, drowsiness, and mood alterations in patients. The authors examined whether general (propofol) anesthesia can impact the circadian temporal structure by disturbing circadian rest-activity and body temperature rhythms under normal light-dark conditions (light-dark 12:12 h) in rats. METHODS: A group of rats was anesthetized with propofol, and another was injected with 10% Intralipid, which was used as a control lipidic solution. The authors examined six groups of rats according to the Zeitgeber time of intraperitoneal administration (ZT6, ZT10, ZT16) and the substance injected (propofol or Intralipid). RESULTS: On the day after anesthesia, propofol induced a significant 60- to 80-min phase advance of both rest-activity and body temperature rhythms. A significant 45- to 60-min phase advance of body temperature and a significant 20-min phase advance of rest-activity were still observed on the second day after anesthesia. The amplitudes of both rest-activity and body temperature rhythms were decreased on the first and second days after anesthesia. The 24-h mean rest-activity rhythm was decreased on the day after anesthesia, whereas the 24-h mean body temperature rhythm was not modified. CONCLUSION: The results demonstrate the disturbing effects of propofol anesthesia on the circadian time structure in rats under normal light conditions.

Delayed aversive effects of high-dose fentanyl. Prevention by a polyamine-deficient diet.

The present study aimed to examine the effects of an acute administration of the mu-opioid receptor fentanyl on affect as assessed by place-conditioning procedure in rats. We determined the affective properties of fentanyl not only immediately following its administration, but also 24h later. Experiments were performed using the dose of fentanyl (240 gamma/kg; four injections of 60 gamma/(ml kg) every 15 min, subcutaneously) for which secondary hyperalgesia has been previously described. Our results show that the acute administration of fentanyl display biphasic affective properties, with early rewarding and 24-h delayed aversive components. The 24-h delayed aversive effects of fentanyl were not observed in animals submitted to a polyamine-deficient diet, suggesting an NMDA-dependent mechanism.

Involvement of the basal cholinergic forebrain in the mediation of general (propofol) anesthesia.

BACKGROUND: Recent studies have pointed out the involvement of the basal forebrain gamma-aminobutyric acid-mediated system in mediating the effects of general anesthesia. In this study, the authors asked whether the basal forebrain cholinergic system is also involved in mediating the effects of general anesthetics such as propofol. METHODS: Cholinergic lesions were produced by administration of the selective immunotoxin 192 immunoglobulin G-saporin into the lateral ventricles, the medial septum, or the nucleus basalis magnocellularis. The anesthetic potency of propofol was determined using an anesthetic score with a crossover counterbalanced design. Animals were given intraperitoneal propofol (25 or 50 mg/kg) repeatedly every 15 min to set up a subanesthetic (low-dose) or anesthetic (high-dose) state. The anesthetic score was assessed for each cumulative dose. Control of the cholinergic depletion was performed using histochemical acetylcholinesterase staining on brain slices. RESULTS: A shift from a subanesthetic state to an anesthetic state was observed mainly in the rats with the immunotoxin injected into the lateral ventricles or the medial septum and vertical diagonal band of Broca, compared with controls. In those rats, the density of acetylcholinesterase reaction products was normal in the striatum and the thalamus, but reduced in the cortex and the hippocampus. CONCLUSION: The anesthetic potency of propofol was increased in all rats with hippocampal lesions, whatever the injection sites, compared with controls. These results demonstrate that a cholinergic dysfunction in the basal forebrain potentiates the anesthetic effects of propofol.

Short-term propofol anaesthesia down-regulates clock genes expression in the master clock.

BACKGROUND: Propofol anesthesia triggers phase-advances of circadian rhythms controlled by the suprachiasmatic nuclei (SCN), the master clock. Besides, inhalational anesthesia has been associated with a subsequent reduction of Per2 mRNA levels in the whole brain of rodents. The acute effects of propofol anesthesia per se on the SCN molecular clockwork remain unclear. Here we aim to study the expression of Per1 and Per2 clock genes in the SCN of rats exposed to constant darkness after a single dose of propofol. METHODS: Thirty 2-months old rats were randomly divided into 2 groups receiving a single dose of either 120 mg/kg propofol 1% (n=15), or intralipid® 10% (n=15) in late day (projected circadian time (CT) 10, i.e., 10h after the expected time of lights on). Thereafter, rat brains were sampled in darkness 1h, 2h or 3h after the treatment (projected CT11, CT12 or CT13). Expression of Per1 and Per2 mRNA was analyzed by in situ hybridization in SCN coronal sections. RESULTS: Per1 expression was affected by time and treatment. Per1 expression in the SCN after propofol treatment decreased at CT11 and CT12 when compared to the vehicle group. For Per2 expression, we observed only a treatment effect. Observed in dark conditions without hypothermia or/and concomitant surgery, such down-regulation of clock genes Per is only correlated to propofol treatment. This may explain "jet-lag-like" symptoms described by patients after anesthesia. CONCLUSION: We show here for the first time that short-term propofol anesthesia leads to a transient down-regulation of Per1 and Per2 expression in the SCN.

Reciprocal relationships between general (Propofol) anesthesia and circadian time in rats.

Several common postdischarge symptoms, such as sleep disorders, headache, drowsiness or general malaise, evoke disturbances of circadian rhythms due to jet lag (ie crossing time zones) or shift work rotation. Considering that general anesthesia is associated with numerous effects on the central nervous system, we hypothesized that it may also act on the circadian timing system. We first determined the effects of the circadian timing on general anesthesia. We observed that identical doses of propofol showed marked circadian fluctuations in duration of effects, with a peak at the middle of the resting period (ie 7 h after lights on). Then, we examined the effects of general anesthesia on circadian timing, by analysing stable free-running circadian rhythms (ie in constant environmental conditions), an experimental approach used widely in circadian biology. Free-running rats were housed in constant darkness and temperature to assess possible phase-shifting effects of propofol anesthesia according to the time of the day. When administered around (+/-2 h) the daily rest/activity transition point, a 30-min propofol anesthesia induced a 1-h phase advance in the free-running rest-activity rhythm, while anesthesia had no significant resetting effect at other times of the day. Anesthesia-induced hypothermia was not correlated with the phase-shifting effects of propofol anesthesia. From our results, anesthesia itself can reset circadian timing, and acts as a synchronizing cue for the circadian clock.

Texture analysis of brain MRI evidences the amygdala activation by nociceptive stimuli under deep anesthesia in the propofol-formalin rat model.

Magnetic resonance images of rat brain were analyzed by texture analysis in order to study the effects of a nociceptive stimulation (formalin test) under propofol deep anesthesia. Changes of the texture in different cerebral brain areas acquired before and after stimulation were checked. Our statistical analysis of texture shows that these changes were present only in the amygdala, in agreement with the facts already known about the unconscious memorization of nociceptive stimuli.

Fos immunolabelling evidence for brain regions involved in the Pavlovian degraded contingency effect and in its disruption by atropine.

Using a fear conditioning preparation, [Carnicella, S., Pain, L., Oberling, P., 2005a. Cholinergic effects on fear conditioning I: The degraded contingency effect is disrupted by atropine but reinstated by physostigmine. Psychopharmacology 178, 524-532] showed that the muscarinic receptor antagonist atropine disrupted the degraded contingency effect (DCE) in the rat, that is, the processes by which contextual memory competes with cued memory for the control over conditioned responding. Here, we investigated neural substrates involved in the expression of normal and atropine-disrupted DCE, using the protein Fos as a marker of neuronal activity. Compared to contingent conditioning, the DCE was associated with a decrease of the amount of Fos immunoreactive neurons within the auditory system and the amygdala and an increase within the medial prefrontal cortex (mPFC). Compared to the normal DCE, atropine-induced disruption of the DCE was associated with an increase of the amount of Fos immunoreactive neurons within the central nucleus of the amygdala. When atropine-induced suppression of the DCE, Fos pattern was modified in the mPFC with a change in Fos immunoreactivity, but no longer associated with the DCE. However, the mPFC was the unique structure studied in which the amount of Fos immunoreactive neurons was differentially affected according to both the conditioning procedure and the pharmacological treatment. These results are discussed in the framework of the cholinergic modulation of context processing in the rat and are put in parallel with an emerging set of studies in humans regarding the role of the PFC in such processing.

Cholinergic effects on fear conditioning I: the degraded contingency effect is disrupted by atropine but reinstated by physostigmine.

RATIONALE: The cholinergic system has been shown to modulate contextual fear conditioning. However, with the exception of trace conditioning studies, most of the available data have focussed on independent context, i.e., context that do not compete with the conditioned stimulus to control for the conditioned response (interactive context). OBJECTIVE: In the present series of experiments, the effects of the muscarinic antagonist, atropine, were assessed when contextual fear memory interacts with cued fear memory to regulate conditioned response, using a Pavlovian degraded contingency preparation in rats. This preparation not only afforded an insight into simple Pavlovian associations but also enabled us to test for the processes of competition that made use of these associations to make an appropriate response to a stimulus [degraded contingency effect (DCE)]. METHODS: In experiment 1, three doses of atropine [2.5, 5.0, and 10.0 mg/kg, intraperitoneally (i.p.)] were evaluated on male Sprague-Dawley rats. In experiment 2, physostigmine (0.037-0.3 mg/kg, i.p.) was injected after the administration of 5 mg/kg of atropine. RESULTS: Experiment 1A and its partial replication (experiment 1B) showed that at asymptotic level of training, atropine did not alter contextual and cued fear memories when the subjects were directly tested for them, whereas it suppressed the DCE for a 5 mg/kg dose. Indeed, atropine-induced suppression of the DCE was found to be an inverted U-shaped dose-response curve. Experiment 2 showed that physostigmine caused a dose-dependent reversal of the atropine-induced alleviation of the DCE, without altering the expression of simple cued and contextual fear memories. CONCLUSION: These results evidence at asymptotic level of training a cholinergic modulation of the processing of interactive context, but not of independent ones. They are discussed in the framework of the mechanisms that are involved in both types of contextual processing.

Cholinergic effects on fear conditioning II: nicotinic and muscarinic modulations of atropine-induced disruption of the degraded contingency effect.

RATIONALE: In a companion study (Carnicella et al., 2005), we showed that the muscarinic antagonist atropine, when administered after extensive training during both conditioning and testing, affected neither cued nor contextual fear memories when both of them did not compete for the control of the overt behaviour. In contrast, atropine altered the degraded contingency effect (DCE), that is, the processes by which contextual fear memory competes with the cued one for the control of the conditioned response. Atropine-induced disruption of the DCE was fully reversed by the administration of the anticholinesterase inhibitor physostigmine, which suggests a direct cholinergic implication. OBJECTIVE: The present series of experiments was conducted in order to define more precisely the involvement of the cholinergic system in such an effect. METHODS: Oxotremorine (0.0, 0.0075, 0.015, or 0.03 mg/kg), pilocarpine (0.0, 0.3, 1, or 3 mg/kg), xanomeline (0.0, 2.5, 5.0, 10.0 or 20.0 mg/kg) and nicotine (0.0, 0.1, 0.2, or 0.4 mg/kg) were tested for reversal of the atropine-induced alteration of the DCE. RESULTS: Oxotremorine and pilocarpine did not reverse the atropine-induced alteration of the DCE. In contrast, xanomeline and nicotine reversed the effect of atropine on the DCE. CONCLUSION: The present series of experiments reveals complex pharmacological interactions within the cholinergic system when cued and contextual fear memories interact. Results are discussed in this connection and with regard to the relation between the properties of cholinergic agonists and their therapeutic values.

The anesthetics propofol and ketamine inhibit cocaine-induced egr-1 gene expression in rat forebrain.

Acute cocaine injection to rats is known to induce the expression of immediate early genes in the forebrain, the effect being primarily mediated by the dopaminergic system. We examined the effect of the anesthetics ketamine and propofol on cocaine-induced egr-1 mRNA expression. Using in situ hybridization, we show that both compounds did not induce egr-1 gene by themselves, but were able to dose-dependently reduce cocaine-induced egr-1 mRNA synthesis in the nucleus accumbens, caudate-putamen and cingulate cortex. Our data suggest that in addition to glutamate NMDA receptors, propofol may act via GABA(A) receptors or ion channels.

Disruption of the circadian system by environmental factors: Effects of hypoxia, magnetic fields and general anesthetics agents.

The biological clock of mammals is under the control of external factors, social life and the environment, and of internal genetic factors. When the biological clock of an individual is no longer in phase with its environment, either because there is no longer any harmony (desynchronization) between the two systems (shift work, night work, and transmeridian flights...) or because the perception of signals in the environment is defective (blindness) or because of a pathology, disorders of the biological clock occur resulting in persistent fatigue, sleep disorders leading to chronic insomnia and mood disturbances that can cause depression. We review here new groups of factors that have been recently studied and that can be considered as potential disruptors of the circadian time structure. These factors are hypoxia, magnetic fields and anesthetic agents whose importance has to be considered.

[Postanesthesia cognitive dysfunction]. / Fonctions cognitives après anesthesie.

The cognitive dysfunctions observed in patients after anesthesia are due not only to the effects of but also to the surgery, the disease requiring surgery, and post-operative treatment. Initial cognitive recovery from anesthetic agents is usually fast, from several hours to several days, but can be delayed by postoperative treatment (analgesia, for example) that have deleterious cognitive effects. During the initial period after surgery, acute impairment of cognitive functions is seen in some patients at risk (major surgery, aged patients, brain sensitivity, or sepsis), specifically transitory (1-3 days in most cases) postoperative delirium. This delirium or confusion requires follow-up at 3 months to check cognitive functions, especially in aged patients. Cohort studies show that cognitive impairment can be objectively identified at one week after surgery with general anesthesia in around 40% of patients, regardless of age. This risk is reduced slightly by the use of loco-regional anesthesia. Cognitive dysfunction is still observed at 3 months after surgery in about 10-15% of patients older than 60 years and in about 6% of younger patients. In patients with a pre-existing cerebral disease with cognitive symptoms, the incidence of long-lasting additional cognitive impairment remains unknown. The mechanisms of this long-term cognitive dysfunction remain to be elucidated.

Plasma corticosterone in rats is specifically increased at recovery from propofol anesthesia without concomitant rise of plasma ACTH.

General anesthesia combined with surgery is commonly associated with post-operative stress-response in humans. Effects on the hypothalamic-pituitary-adrenal axis (HPA) during and after anesthesia are correlated with the magnitude of surgery and choice of anesthetics. The aim of our study in rats was to characterize the effects of general anesthesia without any surgery on HPA regulation of corticosterone and adrenocorticotropic hormone (ACTH) secretions. First, to assess whether the acute effects of general anesthesia on corticosterone concentration depend on time of day, rats were anesthetized with propofol at three different Zeitgeber times (ZT6, ZT10, and ZT16; with lights-on and -off at ZT0 and ZT12, respectively). Second, to determine the prolonged effects of general propofol anesthesia on daily corticosterone and ACTH concentrations, rats were anesthetized at ZT16 (4 h after lights-off) and euthanized either 1, 4, 12, 16, 20, or 24 h later. Third, the effects of propofol anesthesia on corticosterone and ACTH secretion were studied in rats instrumented with intracarotid cannulation. This permitted us to examine the individual patterns of corticosterone responses to propofol anesthesia as compared to their respective baseline corticosterone secretion. All of the results obtained showed that general propofol anesthesia, independent of the time-of-day of its administration, induces a significant increase of corticosterone secretion during the early recovery period without effect on ACTH secretion (i.e., no pituitary mediated stress-response).

General anesthetics effects on circadian temporal structure: an update.

Disruptions of circadian and biological rhythms as well as general anesthesia can induce sleep disorders, resulting in an increase in sleepiness and drowsiness and a decrease in vigilance. It has been previously shown that circadian time can influence the pharmacologic sensitivity and the duration of action of general anesthetics. Studies on interactions between general anesthesia and circadian rhythms are few, but all of them suggest an important role of general anesthetics on circadian rhythms. General anesthesia is a particular wake-sleep state that could potentially alter circadian rhythms on the days following anesthesia. The aim of this review is to discuss the various effects of general anesthesia on animal and human circadian time structure. This topic is highly relevant to clinicians, especially those involved in that field of ambulatory practice responsible for post-operative patient care, including patient recovery and fatigue.

Effect of a nonsedative dose of propofol on memory for aversively loaded information in rats.

BACKGROUND: The effects of propofol on memory for aversive information are not well determined. The authors evaluated the effects of a minimal nonsedative dose of propofol or midazolam on memory in rats, using an apparatus composed of two compartments: a large bright anxiogenic one and a small dark neutral one. METHODS: Groups of rat received propofol (9 mg/kg, intraperitoneally) or midazolam (3 mg/kg). Anxiety was assessed in rats placed in the anxiogenic compartment as the time before the animals entered the neutral compartment. Memory for an aversive event was assessed in rats placed in the anxiogenic compartment as the time to enter the neutral one where they previously experienced foot shocks (fear conditioning). To assess the memory for a nonaversive event, rats were placed in the neutral compartment with no shocks (preexposure). The following day, rats were placed in it and they experienced foot shocks. As a result of the preexposure, rats exhibit less fear to enter it. RESULTS: Propofol and midazolam increased the time to enter the neutral compartment. Propofol or midazolam was given to rats before experiencing foot shocks in the neutral compartment. When later tested, the time to enter it was decreased. Propofol or midazolam was given to rats before the preexposure to the neutral compartment. When later tested, the latency to enter it was not modified by the preexposure. CONCLUSIONS: Propofol and midazolam impaired memory for aversive and for nonaversive experiences at equianxiolytic doses that do not produce locomotor impairment in rats.

In vivo dopamine measurements in the nucleus accumbens after nonanesthetic and anesthetic doses of propofol in rats.

UNLABELLED: There is growing evidence that propofol acts on affective and reward processes. We designed this study to assess the effect of propofol on the concentration of dopamine in the nucleus accumbens, a main component of the mesolimbic system. The concentration of dopamine in the nucleus accumbens was assessed by using in vivo brain microdialysis in freely moving rats. A microdialysis probe was placed within guide cannulae previously placed during stereotaxic surgery. Fluid was perfused through the probe, and samples were collected every 20 min for measuring concentrations by high-pressure liquid chromatography. All rats served as their own controls and were randomized to four different doses of propofol, injected intraperitoneally: 0, 9, 60, or 100 mg/kg, according to a within design. Compared with the baseline value, dopamine concentration was decreased at the smallest dose of 9 mg/kg, whereas concentration was largely increased at the subanesthetic (60 mg/kg) and anesthetic (100 mg/kg) doses. This increase was of the same magnitude (+90%) for subanesthetic and anesthetic doses but was more prolonged at the anesthetic dose. Data show that only subanesthetic and anesthetic doses of propofol increase the concentration of dopamine in the nucleus accumbens, as previously described with drugs of potential abuse. IMPLICATIONS: Depending on the dose, propofol either increased or decreased the concentration of dopamine in the nucleus accumbens, as assessed during microdialysis in freely moving rats. Only large doses which display a pharmacological profile, such as propofol, may show promise.

Fentanyl enhancement of carrageenan-induced long-lasting hyperalgesia in rats: prevention by the N-methyl-D-aspartate receptor antagonist ketamine.

BACKGROUND: Tissue damage may produce hyperalgesia, allodynia, and persistent pain. The authors recently reported that fentanyl elicits analgesia but also activates N-methyl-D-aspartate-dependent pain facilitatory processes opposing analgesia. In nonsuffering rats, this leads to a long-lasting enhancement in pain sensitivity. The current study assessed whether fentanyl could amplify carrageenan-induced hyperalgesia. METHODS: First, rats were injected once with carrageenan in a hind paw, with fentanyl (60 or 100 microg/kg each given four times at 15-min intervals [4 x 60 or 4 x100]) or saline. Second, rats were injected with carrageenan twice without fentanyl (7-day interval), with the second injection either in the previously injected paw or in the other paw. Third, rats were injected twice with carrageenan in the same hind paw: the first ketamine injection was given (10 mg/kg each given three times at 5-h intervals) with or without fentanyl (4 x 60 microg/kg), and second injection was given without ketamine or fentanyl. The consequences of treatments on long-term hyperalgesia were examined by the paw-pressure vocalization test. RESULTS: The long-lasting hyperalgesia induced by the first carrageenan injection was dose-dependently enhanced in both duration and magnitude in 4 x 60 or 4 x 100 microg/kg fentanyl-treated rats: 5 or 10 days, respectively, as compared with 2 days in saline-treated rats. Hyperalgesia observed in the hind paw contralateral to the first carrageenan injection was enhanced in fentanyl-treated rats. The second carrageenan injection, performed in any hind paw, induced an exaggerated hyperalgesia, especially in fentanyl-treated rats. Pretreatment with ketamine totally prevented the carrageenan- and fentanyl-induced enhancement of the long-lasting hyperalgesia. CONCLUSION: Central sensitization in inflammatory pain states is reinforced by an opiate treatment, which could be prevented by N-methyl-D-aspartate receptors blockade.