Anesth Analg 2001;92:1307-1315
© 2001 International Anesthesia Research Society
REGIONAL ANESTHESIA AND PAIN MEDICINE
The Antinociceptive and Sedative Effects of Carbachol and Oxycodone Administered into Brainstem Pontine Reticular Formation and Spinal Subarachnoid Space in Rats
Hai-Chun Ma, MD,
Shuji Dohi, MD, PhD,
Yan-Fen Wang, MD,
Yumiko Ishizawa, MD, PhD, and
Fumi Yanagidate, MD
Department of Anesthesiology and Critical Care Medicine, Gifu University School of Medicine, Gifu City, Gifu 500-8705, Japan
Address correspondence to Shuji Dohi, MD, PhD, Department of Anesthesiology and Critical Care Medicine, Gifu University School of Medicine, Tsukasamachi-40, Gifu city, Gifu 500-8705, Japan. Address e-mail to shu-dohi@cc.gifu-u.ac.jp.
 |
Abstract
|
|---|
To clarify the supraspinal and spinal actions of a cholinergic agonist, carbachol, and an opioid, oxycodone, we studied their antinociceptive and behavioral effects when administered into brainstem medial pontine reticular formation (mPRF) or spinal subarachnoid space with or without pretreatment of muscarinic receptor subtype antagonist. Sprague-Dawley rats were implanted with a 24-gauge stainless steel guide cannula into the mPRF and chronically implanted with a lumbar intrathecal catheter. Antinociception was tested using tail flick latency, motor coordination was evaluated by the rotarod test, and overt sedation was assessed using a behavioral checklist. Carbachol (0.5–4.0 µg) administered into the mPRF produced significant dose- and time-dependent antinociception, sedation, and motor dysfunction. These were completely blocked by pretreatment with atropine and the M2 muscarinic antagonist, methoctramine, and partially blocked by pretreatment with M1 pirenzepine but not with M3 p-fHHSiD. Oxycodone administered into the mPRF did not produce such effects. Spinal carbachol and oxycodone produced antinociception without any behavioral effects; their antinociceptive effects were completely blocked by pretreatment with atropine and M2 antagonist. These results suggest that the antinociceptive action of carbachol is mediated by muscarinic cholinergic receptor activation, especially by M2 receptor subtype in mPRF and spinal cord, and that although oxycodone seems unlikely to affect the cholinergic transmission of mPRF, spinal oxycodone-induced analgesia is at least partly mediated via the activation of M2 receptor subtype at the spinal cord.
Implications: Carbachol-induced antinociception and sedation is mediated with the activation of M2 muscarinic receptors. Oxycodone administered into brainstem medial pontine reticular formation did not cause any antinociceptive or behavioral effects, but its spinal administration produced a significant antinociception via M2 muscarinic receptor activation
|
Introduction
|
|---|
The cholinergic activation of the central nervous system is important in the arousal and perception of painful stimuli (1–4). Also, systemically and intrathecally administered cholinergic agonists will alter the pain response (5,6). Furthermore, cholinomimetic drugs such as carbachol, physostigmine, neostigmine, and acetylcholine (ACh), administered into the intracerebroventricular space (7) and the brainstem medial pontine reticular formation (mPRF) (8,9), produce significant changes in the nociceptive threshold. The main functions of brainstem mPRF are directed toward maintaining the conscious state and perceiving pain sensation (8–11). Besides antinociceptive effects, sedative effects could also be prominent central muscarinic receptor-dependent effects (3,10,11). In intact and unanesthetized animals, cholinergic activation through microinjection of cholinergic agonist (10) and acetylcholinesterase inhibitors (11) into the mPRF causes a rapid eye movement (REM) sleep-like state and induces the antinociceptive behaviors (8–11). Because the cholinergic receptors are widely distributed throughout the central nervous system (12–14) including mPRF (15), cholinergic agents that affect this region of mPRF could play a role in modulating nociceptive transmission of centrally acting drugs such as opioids. Electrical stimulation in the brainstem reticular formation inhibits the excitation of evoked neuronal activity of spinal dorsal horn neurons by noxious skin heating (16), and morphine significantly suppresses this activity (17), suggesting multiple roles for spinal dorsal horn neurons.
Oxycodone and morphine are two commonly used opioid analgesics recommended by the World Health Organization for the management of moderate to severe pain. Morphine decreases ACh in the pons (18), but stimulates ACh release in the spinal cord (19). Antinociception with opioids seems to occur via activation of muscarinic acetylcholine receptors (mAChRs) resulting from release of ACh via supraspinal and spinal µ-opioid receptors (2). In addition to suppressing nociceptive signaling, morphine also seems to suppress REM sleep through µ-opioid receptor activation (18). Opioids, as observed clinically, cause analgesic and sedative effects when given systemically as well as spinally. Thus, opioids may differentially affect supraspinal and spinal ACh, and thus opioid’s sedative effect may arise from its supraspinal action. However, although it has been in use for more than 80 yr, we know less about oxycodone than about morphine (20). Thus, to better understand the cholinergic mechanisms of opioids, we examined the hypothesis that the microinjection of carbachol and an old opioid oxycodone into the mPRF or into the spinal subarachnoid space would modulate the response of nociception and behavioral changes. Because several studies have also investigated which mAChR subtypes are involved in the antinociception evoked by muscarinic agonists, our aim was to identify the subtype of mAChR involved in the analgesic action of carbachol and oxycodone via central cholinergic activation.
|
Methods and Materials
|
|---|
All experimental procedures were approved by our animal care and use committee. Ninety-eight animals were used. Each animal was assigned to one of the following protocols: mPRF/tail flick test (n = 30), mPRF/rotarod (n = 24), mPRF/sedation (n = 24), or intrathecal/tail flick test (n = 20). Male Sprague-Dawley rats weighing 250 g (age, 8 wk) were anesthetized with 50 mg/kg IP of pentobarbital for surgical preparations.
Using the method described by Ishizawa et al. (9), the rat was positioned in a stereotaxic apparatus (Narishige, Japan). A 24-gauge stainless steel guide cannula was unilaterally implanted 1 mm above the mPRF using the following stereotaxic coordinates with bregma as reference: posterior = 8.4 mm, lateral = 1.0 mm, ventral = 6.4 mm from the dura mater (21). The guide cannula was then fixed to the skull with two steel screws and dental cement. The implanted guide cannula allowed repeated microinjections of compounds into the same region of the mPRF. The cannula was kept sealed except during the injection.
Using the method described previously (22), an intrathecal catheter (PE-10, 8.5 cm) was inserted through an opening in the cisterna magna to the lumber subarachnoid space. The catheter’s external arm was tunneled subcutaneously to emerge at the neck. After surgery, the rats were housed individually in a temperature-controlled (21 ± 1°C) room with a 12-h light/dark cycle, and they were given free access to water and food. The rats were allowed to recover for 1 wk before the experiments.
The antinociceptive effect was measured by the tail-flick latency (TFL) response ( Fig. 1A, C). Each animal was placed in an individual plastic cylinder with an opening to allow the tail to protrude. A high-intensity light was focused on the dorsal surface of the rat’s tail and the time for the rat to move its tail out of the light beam was automatically recorded (Thermal Analgesimeter KN-205E; Natume, Tokyo). A cut-off time of 10s was predetermined to minimize the risk of tissue damage. After baseline measurements for TFL had been obtained, each animal received the following mPRF pretreatment: atropine sulfate 5 µg, mecamylamine hydrochloride 1 µg, pirenzepine dihydrochloride 3 µg, methoctramine tetrahydrochloride 5 µg, p-fluoro-hexahydro-sila-difenidol (p-fHHSiD) 3 µg or saline, and the following intrathecal pretreatment: atropine 5 µg, methoctramine 5 µg or saline, respectively. Fifteen minutes later carbachol 0.5 µg, 1 µg, or 4 µg, oxycodone 15 µg or 30 µg, or saline into the mPRF and carbachol 1 µg 4 µg, oxycodone 1 µg, 5 µg, 10 µg, or 15 µg or saline into intrathecal were administered, and TFL was determined at 5, 10, 15, 20, 30, 40, 50, 60, 90, and 120 min after mPRF or intrathecal administration of drugs (Fig. 1A and 1C). Drugs were administered into the mPRF with a 30-gauge stainless steel needle connected via polyethylene tubing to a microinjection pump (CMA/100; Microdialysis, Action, MA) inserted through the guide cannula protruding 1.0 mm beyond the tip of the guide cannula at the same rate of 0.3 µL/60 s with a constant volume of 0.3 µL in the experiment. After microinjection, the needle was left in place at least for 30 s. Drugs administered intrathecally were in a volume of 10 µL, followed by 10 µL saline to flush the catheter. All drugs were purchased from Sigma Chemical Co. (St. Louis, MO). All experimental measurements were performed between 10:00 AM and 5:00 PM. Each animal was studied three or four times in an experimental series with 2–4 day intervals between studies.
View larger version (37K):
[in this window]
[in a new window]
|
Figure 1. Experimental protocols are shown for measurement of antinociception of carbachol and oxycodone through medial pontine reticular formation (mPRF) (A) and intrathecal (C) administration. The measurement of rotarod and sedation of carbachol were performed after mPRF administration (B). In each protocol, pretreatment with atropine, mecamylamine, pirenzepine, methoctramine, p-fHHSiD or saline (A, B) and atropine, methoctramine, or saline (C) was performed 15 min before carbachol, oxycodone, or saline injection, respectively.
|
|
Motor efficiency and motor coordination were evaluated by the rotarod test (Fig. 1B). The test apparatus (Rota-Rod treadmills for rats, Ugo Basile, Comeno, Varese, Italy) consisted of a horizontal rod (diameter, 6 cm) located 25 cm above the floor. A period of 60 s of continuous walking on the rotating rod was accepted as a criterion of the properly performed test. The speed of the rod was 14 rpm. The rats were subjected to a preliminary training every day for five consecutive days before stereotaxic surgery. On the second day after operation the training was continued. Six days after surgery only rats that were able to walk on the rod for 60 s were used for testing. Each animal received mPRF administration of atropine (5 µg), pirenzepine (3 µg), methoctramine (5 µg, 10 µg), p-fHHSiD (3 µg) or saline in a volume of 0.3 µL over 60s, 15 min after pretreatment, carbachol 4 µg, oxycodone 15 µg, 30 µg or saline was injected into mPRF. The tests were measured at 10, 20, 30, 60, 90, and 120 min after administration. The results were presented in seconds. These trials were performed in a separate group of rats from those for TFL tests.
Although TFL and rotarod tests provided the objective measurements, the degree of overt sedation was also measured for general behavior depression that was assessed by direct observation using a behavioral checklist as described by Drew et al. (23) (Fig. 1B). Briefly, pretreatment with atropine (5 µg), pirenzepine (3 µg), methoctramine (5, 10 µg), p-fHHSiD (3 µg), or saline mPRF was administered in a volume of 0.3 µL over 60 s, 15 min later carbachol 4 µg, oxycodone 15 µg, 30 µg, or saline was injected into the mPRF. Overt sedation was assessed by observing for gross differences from control rats. The assessment was performed by a person kept blinded as to the treatment. The following indices were used: ptosis, lowered body posture, slow gait, escape reflex (depressed response to light pressure between the finger and thumb placed on either side of the body), and passivity (assessed by whether or not the rat struggled when picked up gently by the dorsal fold of loose skin of the neck, held gently on its back, held suspended by a fore or hind limb). The sedation was scored on a 0 to 3 basis according to severity. A score of 0 indicates a normal animal and a score of 3 indicates complete sedation. A composite score of all the variables was added for each group at each time interval. The rat used for sedation assessment did not take part in the testing of TFL and rotarod measurement.
On completion of the experiments, the animals were deeply anesthetized with pentobarbital, and bromophenol blue 2.5% 1.0 µL was injected at the stereotaxic target. The brains were immediately soak-fixed in 10% neutral formaldehyde. The brain serially sectioned into 0.3 to 0.5-mm coronal slices. The microinjection sites were histologically localized with the use of the atlas of Paxinos and Watson (21). Furthermore, the sections that contained injection sites were embedded in paraffin and sectioned at 20-µm thickness. The sections were stained with Luxol fast blue. The target area was defined as the area of the mPRF at the level between 8.3 and 8.7 mm posterior from the bregma (9). Bromophenol blue 2.5% 10 µL was injected intrathecally to confirm the position of the catheter and the likely spread of the injectate (22).
Statistical Analysis
Data are presented as mean ± SEM. The response of the TFL test is expressed as the percentage of the maximum possible effect (% MPE) using the following formula: % MPE = (postdrug TFL - baseline TFL)/(cutoff time - baseline TFL) x 100. As to the effect of drugs on the TFL, Rotarod test and sedation, statistical differences were analyzed using two-way analysis of variance followed by Bonferroni’s correction for post hoc comparisons. Differences in the AUC were compared using one-way analysis of variance followed by Student-Newman-Keuls test to measure the significance. A probability value of <0.05 was considered statistically significant. In addition, the time courses for the effect expressed as the area under the time-response curve was calculated by a trapezoidal rule (24).
|
Results
|
|---|
Brainstem mPRF administration of carbachol (0.5 µg, 1 µg, 4 µg) produced a significant dose- and time-dependent antinociception in the TFL test ( Fig. 2A). The peak effects of carbachol were observed 5 min after drug administration. Longer antinociceptive time courses were observed after mPRF injection of larger doses of carbachol (4 µg). Oxycodone 15 µg and 30 µg administered into mPRF did not induce any antinociception as measured by TFL (Fig. 2B).
View larger version (27K):
[in this window]
[in a new window]
|
Figure 2. Time course of the antinociceptive effect (%MPE) of carbachol (A) and oxycodone (B) administered into the brainstem medial pontine reticular formation of rats in tail-flick tests. The results are expressed as the mean ± SEM from five or eight rats in each group. Asterisks indicate significant increases in carbachol-elicited antinociceptive behavior compared with saline (P < 0.05).
|
|
Intrathecal administration of carbachol (1 µg or 4 µg) or oxycodone (1 µg, 5 µg, 10 µg, or 15 µg) induced a significant dose- and time-dependent antinociception as measured by TFL, respectively ( Fig. 3A and B).
View larger version (28K):
[in this window]
[in a new window]
|
Figure 3. Time course of antinociceptive effect (%MPE) of intrathecally administered carbachol (A) and oxycodone (B) in tail-flick tests. The results are expressed as the mean ± SEM of six rats in each group. *P < 0.05 compared with saline; #P < 0.05 compared with carbachol 1 µg;  P < 0.05 compared with oxycodone 10 µg; ¶P < 0.05 compared with oxycodone 15 µg. Atro = atropine; meth = methoctramine; carb = carbachol.
|
|
To identify the characteristics of the receptor effect of a cholinergic agonist, we administered, into the mPRF, nonselective muscarinic and nicotinic receptor antagonists atropine and mecamylamine, 15 min before carbachol was given. The effects of mPRF carbachol 4 µg on the TFL test were significantly blocked by pretreatment of the rat with atropine 5 µg and mecamylamine 1 µg ( Fig. 4), whereas this dose of atropine and mecamylamine had no effect when administered alone. To further test the hypothesis that brainstem cholinergic mechanisms causally contribute to antinociceptive effect by which muscarinic receptor subtype, the M1 antagonist pirenzepine, M2 antagonist methoctramine, or M3 antagonist p-fHHSiD were microinjected into the mPRF 15 min before carbachol administration by the same route. The microinjection of pirenzepine, methoctramine, or p-fHHSiD into the mPRF did not produce any effect on the TFL test. However, mPRF microinjection of M2 subtype antagonist methoctramine (5 µg) completely blocked the effect of mPRF carbachol 4 µg ( Figs. 4, 5), whereas M1 antagonist pirenzepine (3 µg) partially blocked the effect time of antinociception of mPRF carbachol to 30 min (Fig. 5). In contrast, M3 receptor antagonist p-fHHSiD (3 µg) did not induce a significant change in the TFL test. Intrathecally administered atropine and methoctramine per se did not significantly affect the TFL at a dose of 5 µg, but pretreatment significantly antagonized the antinociception of intrathecal carbachol and oxycodone ( Fig. 6).
View larger version (32K):
[in this window]
[in a new window]
|
Figure 4. To examine pharmacologic antagonist on antinociceptive effects induced with carbachol (0.5 µg, 1.0 µg, and 4 µg), atropine (Atro) 5 µg, mecamylamine (Meca) 1 µg, pirenzepine (Pire) 3 µg, methoctramine (Meth) 5 µg, or p-fluro-hexahydro-sila-difenidol (p-fHHSiD) 3.0 µg was administered into mPRF 15 min before the administration of carbachol (Carb) 4.0 µg, respectively. Each antagonist does not induce any change in tail-flick test. Each bar represents the mean ± SEM from five rats. *P < 0.05 versus saline;  P < 0.05 versus carbachol 4.0 µg. AUC = area under the time-response curve.
|
|
View larger version (35K):
[in this window]
[in a new window]
|
Figure 5. The pharmacologic antagonism of the effects of cholinergic agonist and time course. Atropine 5 µg, pirenzepine 3 µg, methoctramine 5 µg, or p-fHHSiD 3 µg, was injected into the brainstem of medial pontine reticular formation 15 min before the administration of carbachol 4 µg in tail-flick tests, respectively. Each point represents the mean ± SEM. The asterisk shows the value of P < 0.05 compared with saline group.
|
|
Microinjection of atropine, pirenzepine, methoctramine, or p-fHHSiD into the mPRF did not affect the permanence of the rotarod test. However, impairment of the motor performance was observed in rats that were injected with carbachol (1 µg and 4 µg) into the mPRF ( Table 1). The maximal effect was observed 10 min after the application of carbachol and was dose dependent. The impairment was observed as late as 30 min after the largest dose of carbachol (4 µg) and they recovered thereafter. After pretreatment with atropine and M2 receptor subtype antagonist methoctramine, the impairment of the performance of the rotarod induced by carbachol was antagonized completely. Oxycodone administered into the mPRF did not affect the motor coordination as tested by rotarod (Table 1).
View this table:
[in this window]
[in a new window]
|
Table 1. Accelerating Rotarod Time in Animals Treated with Saline, Carbachol, Oxycodone Given into the Medial Pontine Reticular Formation With or Without Pretreatment of a mAChR Antagonist
|
|
Carbachol also produced a significant, dose-dependent, profoundly overt sedation as depicted by an increase in the observational test score ( Table 2). Oxycodone administered into the mPRF did not affect the sedation score. Atropine, pirenzepine, methoctramine, and p-fHHSiD alone were devoid of any effects; however, atropine or methoctramine significantly antagonized the sedation produced by carbachol (Table 2), whereas pirenzepine or p-fHHSiD never induced any significant changes on sedation produced by carbachol.
View this table:
[in this window]
[in a new window]
|
Table 2. Observational Rating of Sedation in Animals Treated with Saline, Oxycodone, Carbachol into the Medial Pontine Reticular Formation or With Pretreatment of mAChR Antagonist
|
|
The sites of microinjection of drugs are illustrated in Figure 7, which indicates that the drugs were administered into the mPRF. Not all experiments were included for the sites of injection in this figure.
View larger version (21K):
[in this window]
[in a new window]
|
Figure 7. Schematic drawing illustrates microinjection sites of the rat’s brain studied in the coronal section at 8.3 and 8.7 mm posterior with bregma as reference according to the atlas of Paxinos and Waton (21). IC, inferior colliculas; DR, dorsal raphy necleus; py, pyramidal tract; PPT, pedunculopontine tegmental nuclei; LDT, laterodosal tegmental nuclei; mPRF, medial pontine reticular formation.
|
|
|
Discussion
|
|---|
Our main findings are that microinjection of carbachol, a cholinergic agonist, into the mPRF produced a significant dose- and time-dependent antinociceptive action, sedation and motor suppression. However, oxycodone, an opioid, administered into the mPRF, did not produce any such action. The effects of mPRF carbachol were completely blocked by pretreatment with atropine and M2 antagonist methoctramine, and partially blocked with M1 antagonist pirenzepine, but not with M3 antagonist (p-fHHSiD). Although spinal administration of carbachol and oxycodone produced an antinociceptive effect in a dose-related manner without any behavioral effects, the M2 subtype antagonist, administered intrathecally, completely blocked their antionciceptive effects. Thus, carbachol-induced antinociception and sedation are mediated with the activation of M2 receptor subtype. Oxycodone seems to have no role in the activation of mPRF, but antinociception resulting from its spinal administration is, at least partly, via M2 muscarinic receptor activation of the spinal cord.
Members of mAChR family (M1-M5) are involved in a large number of important central and peripheral physiological and pathophysiological processes (3,4,14). They have well documented involvement in the regulation of heart rate, movement, and temperature controls as well as antinociceptive responses and are three of the most prominent central muscarinic receptor-dependent effects. The antinociception of carbachol administered into mPRF is mediated directly through cholinergic receptors but not through opioid mechanisms (8). In addition to its antinociceptive effect, carbachol injected into the mPRF, which receives the cholinergic input from more rostral laterodorsal region of the brain, produces a sedative effect and enhances REM sleep (8,18). Previously we also observed that microinjection of carbachol into the mPRF caused sedation and a generalized suppression of motor activity that lasted a very short time (9). M1 receptors are basically limited to the forebrain cholinergic projection fields and are quite distinct from M2 receptor distribution (13), which are consistently present in the rat brainstem. In the midbrain and brainstem, cholinergic terminals are not accompanied by M1 receptors, and in the cholinergic projections of thalamic and interpeduncular nucleus, only M2 receptors have been found (13). M2 muscarinic receptor subtype plays a key role in mediating muscarinic receptor-dependent antinociceptive responses (14). Our results indicate that mPRF treated with carbachol induces muscarinic signaling via activation of M2 subtype in mPRF. Because such actions of carbachol were also blocked with pretreatment of atropine or M2 antagonist, but not with M1 and M3 antagonist, carbachol-induced antinociception, sedation, and motor dysfunction seem to be mediated by activation of M2 mAChRs of the brainstem.
Cholinergic antinociceptive actions are also mediated by mAChR within the spinal cord (2–4,12–15). Carbachol, as a mAChR agonist, produces antinociceptive effects by interacting with mAChRs located in the spinal regions (5,24). Several studies have investigated which mAChR subtypes are involved in the spinal antinociception evoked by muscarinic agonists. The results are not in agreement (25–27). Two studies indicate that M1 subtype is involved in the muscarinic antinociception (26,27) and one study indicates that activity at the M1 subtype is not a requirement for antinociceptive activity in mice (28). Naguib and Yaksh (29) also found that spinal muscarinic agonists, such as carbachol and neostigmine, induce a potent analgesia that is likely mediated by spinal M1 and/or M3 subtype in rats. Using a neuropathic pain model, the antiallodynic action of cholinesterase inhibitors is probably mediated by a spinal muscarinic system, especially at the M1 receptor subtype (30). The present results provide evidence that the antinociceptive effect of carbachol administered into mPRF is likely mediated by M2 subtype and partly by M1, but M3 subtype is not involved in the antinociceptive effect of carbachol. It is important to note that muscarinic antagonists are only relatively selective, not exclusively specific, for individual subtype (31). Thus, because of the overlapping expression patterns of the M1-M5 mAChR subtypes and the lack of ligand endowed with sufficient subtype selectivity (3,31), the precise physiological functions of the individual mAChR subtypes remain to be elucidated in further studies. In addition to its action as a muscarinic agonist, carbachol exhibits nicotinic agonist properties for ACh receptors and resists hydrolysis by cholinesterase (32). Subtypes of nicotinic ACh receptors, which are present throughout the neuronal pathways that respond to pain, can also mediate analgesia in the spinal cord (33), both by direct mechanism and indirectly by stimulation of norepinephrine and ACh (33). Because carbachol-induced antinociception was also blocked with pretreatment of mecamylamine, a nicotinic receptor antagonist, we cannot exclude the possibility that activation of nicotinic receptors would be involved, at least partly, in carbachol-induced antinociception and perhaps in the sedative effect and motor impairment because of its microinjection into the mPRF.
Oxycodone and morphine are structurally related, strong opioid analgesics when administered both systemically as well as in the vicinity of the spinal cord. Antinociception with morphine seems to occur as a result of activation of mAChRs of the spinal cord or perhaps because of release of ACh via activation of supraspinal and spinal µ-opioid receptors (2). Although it is not known whether oxycodone affects ACh release by acting on cholinergic cell bodies or on cholinergic axon terminals, as an opioid µ-receptor agonist it may act similarly with morphine. Oxycodone administered into mPRF did not produce any antinociceptive and sedative effects. No antinociceptive effect has been reported with morphine into the mPRF (8). Because ACh in mPRF was not altered by remifentanil and was significantly decreased by fentanyl (18), we should also keep in mind that different opioids differently affect the mPRF, although morphine and oxycodone could similarly produce spinal antinociception (34). Morphine-induced analgesia and morphine-increased ACh release in spinal cord dorsal horn (19) are enhanced by intrathecal neostigmine injection (35). Oxycodone is unlikely to affect the mPRF via ACh release and thus could produce less sedative effect.
In summary, the present data confirm and extend past experiments describing the central antinociceptive effects of a cholinergic agonist carbachol, perhaps via the activation of M2 subtype, in rats. As compared with spinal antinociceptive action of opioids, their specific actions in the mPRF, a very sensitive site of cholinomimetics-induced antinociception and behaviors, is unclear. Although the present study can only partly clarify some differences in supraspinal and spinal effects of carbachol and oxycodone, the results do encourage future studies for understanding the roles of pontine cholinergic neurotransmission in antinociceptive behaviors and for elucidating the mechanism(s) for diverse supraspinal actions of opioids, especially via release or inhibition of ACh in the mPRF. Although oxycodone administered into the mPRF does not cause any effects related to unwanted opioid action, aside from the limited behavioral observations noted in the present study, our results suggest the widespread importance of this opioid, which has been reported to act as an intrinsic 
-opioid receptor, for clinical use (36).
|
Acknowledgments
|
|---|
Supported, in part, by research grants No. 11307027 and No. 12557129 from the Ministry of Education, Science and Culture of Japan.
|
Footnotes
|
|---|
Presented, in part, at the 11th Annual Meeting of the Japanese Society of PharmacoAnesthesiology, 1999, Tokyo, Japan.
|
References
|
|---|
-
Gillberg PG, Hartvig P, Gordh T, et al. Behavioral effects after intrathecal administration of cholinergic receptor agonists in the rat. Psychopharmacology 1990; 100: 464–9.[Medline]
-
Eisenach JC. Muscarinic-mediated analgesia. Life Sci 1999; 64: 549–54.[ISI][Medline]
-
Durieux ME. Muscarinic signaling in the central nervous system: recent developments and anesthetic implications. Anesthesiology 1996; 84: 173–89.[ISI][Medline]
-
Lambert DG, Appadu BL. Muscarinic receptor subtypes: do they have a place in clinical anesthesia? Br J Anaesth 1995; 74: 497–9.[Free Full Text]
-
Yaksh TL, Dirksen R, Harty GJ. Antinociceptive effects of intrathecally injected cholinomimetic drugs in the rat and cat. Eur J Pharmacol 1985; 117: 81–8.[ISI][Medline]
-
Petersson J, Gordh TE, Hartvig P, Wiklund L. A double blind trial of the analgesic properties of physostigmine in postoperative patients. Acta Anaesthesiol Scand 1986; 30: 283–8.[ISI][Medline]
-
Oliveira MA, Prado WA. Antinociception and behavioral manifestations induced by intracerebroventricular or intra-amygdaloid administration of cholinergic agonists in the rat. Pain 1994; 57: 383–91.[ISI][Medline]
-
Kshatri AM, Baghdoyan HA, Lydic R. Cholinomimetics, but not morphine, increase antinociceptive behavior from pontine reticular regions regulating rapid-eye-movement sleep. Sleep 1998; 21: 677–85.[ISI][Medline]
-
Ishizawa YM, Ma HC, Dohi S, Shimonaka H. Effects of cholinomimetic injection into the brain stem reticular formation on halothane anesthesia and antinociception in rats. J Pharmacol Exp Ther 2000; 293: 845–51.[Abstract/Free Full Text]
-
Baghdoyan HA, Rodrigo-Angulo ML, McCarley RW, Hobson JA. Site-specific enhancement and suppression of desynchronized sleep signs following cholinergic stimulation of three brainstem regions. Brain Res 1984; 306: 39–52.[Medline]
-
Baghdoyan HA, Monaco AP, Rodrigo-Angulo ML, et al. Microinjection of neostigmine into the pontine reticular formation of cats enhances desynchronized sleep signs. J Pharmacol Exp Ther 1984; 231: 173–80.[Abstract/Free Full Text]
-
Buckley NJ, Bonner TI, Brann MR. Localization of a family of muscarinic receptor mRNAs in rat brain. J Neurosci 1988; 8: 4646–52.[Abstract]
-
Spencer DG Jr, Horvath E, Traber J. Direct autoradiographic determination of M1 and M2 muscarinic acetylcholine receptor distribution in the rat brain: relation to cholinergic nuclei and projections. Brain Res 1986; 380: 59–68.[ISI][Medline]
-
Gomeza J, Shannon H, Kostenis E, et al. Pronounced pharmacologic deficits in M2 muscarinic acetylcholine receptor knockout mice. Proc Natl Acad Sci U S A 1999; 96: 1692–7.[Abstract/Free Full Text]
-
Vilaro MT, Wiederhold KH, Palacios JM, Mengod G. Muscarinic M2 receptor mRNA expression and receptor binding in cholinergic and non-cholinergic cells in the rat brain: a correlative study using in situ hybridization histochemistry and receptor autoradiography. Neuroscience 1992; 47: 367–93.[ISI][Medline]
-
Morton CR, Siegel J, Xiao H-M, Zimmermann M. Modulation of cutaneous nociceptor activity by electrical stimulation in the brain stem does not inhibit the nociceptive excitation of dorsal horn neurons. Pain 1997; 71: 65–70.[ISI][Medline]
-
Dohi S, Toyooka H, Kitahata LM. Effects of morphine sulfate on dorsal–horn neuronal responses to graded noxious thermal stimulation in the decerebrated cat. Anesthesiology 1979; 51: 408–13.[ISI][Medline]
-
Mortazavi S, Thompson J, Baghdoyan HA, Lydic R. Fentanyl and morphine, but not remifentanil, inhibit acetylcholine release in pontine regions modulating arousal. Anesthesiology 1999; 90: 1070–7.[ISI][Medline]
-
Bouaziz H, Tong CY, Yoon Y, et al. Intravenous opioids stimulate norepinephrine and acetylcholine release in spinal cord dorsal horn. Anesthesiology 1996; 84: 143–54.[ISI][Medline]
-
Leow KP, Smith MT. The antinociceptive potencies of oxycodone, noroxycodone and morphine after intracerebroventricular administration to rats. Life Sci 1994; 54: 1229–36.[ISI][Medline]
-
Paxinos G, Watson C. The rat brain in stereotaxic coordinates. 4th ed. San Diego: Academic Press, 1998.
-
Zeng WA, Dohi S, Shimonaka H, Asano T. Spinal antinociceptive action of Na+-K+ pump inhibitor ouabain and its interaction with morphine and lidocaine in rats. Anesthesiology 1999; 90: 500–8.[ISI][Medline]
-
Drew GM, Gower AJ, Marriott AS.
2-Adrenoceptors mediate clonidine-induced sedation in the rat. Br J Pharmacol 1979; 67: 133–41.[ISI][Medline]
-
Naguib M, Yaksh TL. Antinociceptive effects of spinal cholinesterase inhibition and isobolographic analysis of the interaction with µ and 2 receptor systems. Anesthesiology 1994; 80: 1338–48.[ISI][Medline]
-
Gillberg PG, Gordh T Jr, Hartvig P, et al. Characterization of the antinociception induced by intrathecally administered carbachol. Pharmacol Toxicol 1989; 64: 340–3.[ISI][Medline]
-
Iwamoto ET. Characterization of the antinociception induced by nicotine in the pedunculopontine tegmental nucleus and the nucleus raphe magnus. J Pharmacol Exp Ther 1990; 257: 120–33.[Abstract/Free Full Text]
-
Bartolini A, Ghelardini C, Fantelli L, et al. Role of muscarinic receptor subtypes in central antinociception. Br J Pharmacol 1992; 105: 77–82.[ISI][Medline]
-
Sheardown MJ, Shannon HE, Swedberg MD, et al. M1 receptor agonist activity is not a requirement for muscarinic antinociception. J Pharmacol Exp Ther 1997; 281: 868–75.[Abstract/Free Full Text]
-
Naguib M, Yaksh TL. Characterization of muscarinic receptor subtypes that mediate antinociception in the rat spinal cord. Anesth Analg 1997; 85: 847–53.[Abstract]
-
Hwang JH, Hwang KS, Leem JK, et al. The antiallodynic effects of intrathecal cholinesterase inhibitors in a rat model of neuropathic pain. Anesthesiology 1999; 90: 492–9.[ISI][Medline]
-
Caulfield MP. Muscarinic receptors: characterization, coupling, and function. Pharmacol Ther 1993; 58: 319–79.[ISI][Medline]
-
Gilman GA, Goodman LS, Gilman A. The pharmacological basis of therapeutics. In: Taylor P, ed. Cholinergic agonists. New York: Macmillan, 1980: 91–119.
-
Marubio LM, Mar Arroyo-Jimenez M, Cordero-Erausquin ME, et al. Reduced antinociception in mice lacking neuronal nicotinic receptor subunits. Nature 1999; 398: 805–10.[Medline]
-
Poyhia R, Kalso EA. Antinociceptive effects and central nervous system depression caused by oxycodone and morphine in rats. Pharmacol Toxicol 1992; 70: 125–30.[ISI][Medline]
-
Eisenach JC, Gebhart GF. Intrathecal amitriptyline: antinociceptive interactions with intravenous morphine and intrathecal clonidine, neostigmine, and carbamylcholine in rats. Anesthesiology 1995; 83: 1036–45.[ISI][Medline]
-
Ross FB, Smith MT. The intrinsic antinociceptive effects of oxycodone appear to be kappa-opioid receptor mediated. Pain 1997; 73: 151–7.[ISI][Medline]
Accepted for publication January 17, 2001.
This article has been cited by other articles:
|
|
|
|
 
H.-M. Zhang, D.-P. Li, S.-R. Chen, and H.-L. Pan
M2, M3, and M4 Receptor Subtypes Contribute to Muscarinic Potentiation of GABAergic Inputs to Spinal Dorsal Horn Neurons
J. Pharmacol. Exp. Ther.,
May 1, 2005;
313(2):
697 - 704.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
F. Yanagidate and S. Dohi
Epidural oxycodone or morphine following gynaecological surgery
Br. J. Anaesth.,
September 1, 2004;
93(3):
362 - 367.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Duttaroy, J. Gomeza, J.-W. Gan, N. Siddiqui, A. S. Basile, W. D. Harman, P. L. Smith, C. C. Felder, A. I. Levey, and J. Wess
Evaluation of Muscarinic Agonist-Induced Analgesia in Muscarinic Acetylcholine Receptor Knockout Mice
Mol. Pharmacol.,
November 1, 2002;
62(5):
1084 - 1093.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
Abstract
Introduction
