Fentanyl-induced Muscular Rigidity Research Articles

Inhibition by neuropeptide Y of fentanyl-induced muscular rigidity at the locus coeruleus in rats

The aim of this study was to evaluate the effects of centrally administered neuropeptide Y (NPY) on muscular rigidity induced by fentanyl in Sprague–Dawley rats. They were anesthetized with ketamine (120 mg/kg, i.p.) and their lungs were mechanically ventilated. Intravenous administration of fentanyl (100 μg/kg) consistently evoked a significant increase in the electromyographic activity (EMG) recorded from the sacrococcygeus dorsalis lateralis muscle. This implied muscular rigidity was appreciably attenuated by intracerebroventricular administration of NPY (4 nmol/2.5 μl). Microinjection of NPY (40 or 160 pmol/50 nl) into the bilateral locus coeruleus (LC) elicited an inhibition of the EMG activation induced by fentanyl in a dose-dependent manner. Microinjection of 160 pmol NPY plus antiserum against NPY (NPY Ab, 1:20) into the LC failed to suppress fentanyl-induced muscular rigidity. However, this implied muscular rigidity was not affected by NPY plus normal rabbit serum (NRS, 1:20). In addition, NPY Ab or NRS per se had no substantial effect on the rigidity. Microinjection of NPY (160 pmol) into the areas adjacent to the LC did not attenuate the rigidity. Our results suggest that the centrally administered NPY attenuated fentanyl-induced muscular rigidity by acting at the LC, but endogenous NPY may not be involved in this process.

Involvement of Cerulospinal Glutamatergic Neurotransmission in Fentanyl-induced Muscular Rigidity in the Rat

Investigators in the authors' laboratory previously established the critical participation of the cerulospinal noradrenergic pathway in muscular rigidity elicited by fentanyl. The identification of colocalization of glutamate with tyrosine hydroxylase in most locus ceruleus neurons suggests a role for cerulospinal glutamatergic neurotransmission in fentanyl-induced muscular rigidity. This suggestion and the subtype(s) of glutamate receptors involved were investigated here. Electromyographic signals activated by bilateral microinjection of 2.5 microg fentanyl into the locus ceruleus were recorded differentially from the left sacrococcygeus dorsi lateralis muscle of adult male Sprague-Dawley rats. The effect of intrathecal administration at the lower lumbar spinal cord of various N-methyl-D-aspartate (NMDA) and non-NMDA receptor antagonists or agonists on this index of muscular rigidity was studied. Rats were under mechanical ventilation, and intravenous infusion of ketamine (30 mg x kg(-1) x h(-1)) was maintained until 10 min before fentanyl was administered. Microinjection of fentanyl bilaterally into the locus ceruleus increased the root mean square and decreased the mean power frequency values of electromyographic signals. The efficacy of fentanyl to elicit muscular rigidity in this manner was significantly reduced by previous intrathecal administration of either 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801), D-(-)-2-amino-5-phosphonovaleric acid (AP5), or (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP). Intrathecal administration of kainic acid or NMDA also resulted in significant electromyographic activation. In addition to the cerulospinal noradrenergic mechanism, the cerulospinal glutamatergic pathway and both NMDA and non-NMDA receptors in the spinal cord may mediate fentanyl-induced muscular rigidity in the rat.

Involvement of spinal adenosine A 1 and A 2 receptors in fentanyl-induced muscular rigidity in the rat

In the present study, using hydrophilic adenosine antagonists either selective to A 1 or A 2 receptors, we investigated the central and spinal adenosinergic participation in fentanyl-induced muscular rigidity. Adult Sprague–Dawley rats were anesthetized with ketamine and were under mechanical ventilation. Fentanyl (100 μg/kg, i.v.) consistently elicited electromyographic (EMG) activation in the sacrococcygeal dorsalis lateralis muscle. This implied muscular rigidity was not blocked by i.c.v. administration of the adenosine A 1 antagonist, 1-allyl-3,7-dimethyl-8- p-sulfophenyl-xanthine (ADSPX; 20 or 40 nmol/2.5 μl), except at higher dose (80 nmol). Equimolar doses of the adenosine A 2 antagonist, 3,7-dimethyl-1-propargylxanthane (DMPX), did not exert any inhibitory effect on fentanyl-induced rigidity. Intrathecal (i.t.) administration of the same doses of ADSPX (20, 40 or 80 nmol/10 μl) appreciably suppressed the EMG activation. However, the rigidity was only inhibited by 40 or 80 nmol (i.t.) of DMPX, but not by the lowest dose. High-dose (80 nmol, i.t.) adenosine A 1 or A 2 antagonist per se did not induce motor impairment or hindlimb paralysis in conscious animals. These results suggest that adenosine A 1 and A 2 receptors in the spinal cord may play a more crucial role than those in the central nervous system (CNS) in fentanyl-induced muscular rigidity in rats.

Inhibition by intrathecal prazosin but not yohimbine of fentanyl-induced muscular rigidity in the rat

We evaluated the effect of intrathecally administered prazosin, α 1-adrenoceptor antagonist, or yohimbine, α 2-adrenoceptor antagonist, on fentanyl-induced muscular rigidity. Adult, male Sprague-Dawley rats were anesthetized with ketamine and were under mechanical ventilation. Fentanyl given intravenously (100 μg/kg) or microinjected into the bilateral locus coeruleus (LC) (2.5 μg/50 nl) consistently evoked a significant increase in the electromyographic activity recorded from the sacrococcygeus dorsalis lateralis muscle. This implied muscular rigidity was appreciably antagonized by prior intrathecal (10 μl) administration of prazosin (5 or 10 nmol), but not equimolar dose of yohimbine. These results suggest that the spinal α 1-adrenoceptors in the coerulospinal noradrenergic pathway play a key role in fentanyl-induced muscular rigidity.

Involvement of potassium and calcium channels at the locus coeruleus in fentanyl-induced muscular rigidity in the rat

Previous work from our laboratory suggested that Goα protein at the locus coeruleus (LC) may be involved in the signal transduction process that underlies muscular rigidity induced by fentanyl. The present study further evaluated the roles of K + and L-type Ca 2+ channels, gating of which is known to be associated with activation of Goa protein, in this process, using Sprague-Dawley rats anesthetized with ketamine. Bilateral microinjection into the LC of tetraethylammonium chloride (100 or 200 pmol), a K + channel blocker, and S(-)-Bay K 8644 (0.5 nmol), a Ca 2+ channel activator, produced significant antagonization of the EMG activation elicited by fentanyl (100 μg/kg, i.v.), as recorded from the sacrococcygeus dorsalis lateralis muscle. On the other hand, local application to the bilateral LC of diazoxide (10 or 20 nmol), an ATP-dependent K + channel activator, and nifedipine (0.25 or 0.5 pmol), a L-type Ca 2+ channel blocker, was ineffective in blunting fentanyl-induced muscular rigidity. These results suggest that activation of K + channels and/or inhibition of L-type Ca 2+ channels secondary to triggering of the Goa protein at the LC may underlie the signal transduction process in the mediation of fentanyl-induced muscular rigidity.

Subtypes of Guanine-Nucleotide-Binding Regulatory Proteins at the Locus coeruleus Involved in Fentanyl-Induced Muscular Rigidity in the Rat.

Previous results from our laboratory have established that the G(o) subtype of guanine nucleotide (GTP)-binding regulatory protein at the locus coeruleus (LC) may participate in the elicitation of muscular rigidity by fentanyl. The present study further examined the involvement of other subtypes of GTP-binding regulatory proteins at the LC in this process, using Sprague-Dawley rats anesthetized with ketamine (120 mg/kg, i.p., with 30 mg/kg/h i.v. infusion supplements) and under mechanical ventilation. Intravenous administration of fentanyl (100 &mgr;g/kg) induced a significant increase in electromyographic signals recorded from the sacrococcygeus dorsi lateralis muscle. Power spectral analysis revealed that this was accomplished by a decrease in the mean power frequency and an increase in the root mean square values of the signals. The above responses were appreciably antagonized by pretreating animals with bilateral microinjection into the LC of pertussis toxin (80 or 160 fmol), N-ethylmaleimide (16 pmol) or 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (100 or 200 fmol); but not by cholera toxin (120 or 240 fmol), forskolin (240 or 480 pmol) or N-ethylmaleimide at a higher dose (32 pmol). These results suggest that, in addition to G(o) protein, fentanyl-induced muscular rigidity may also involve other pertussis toxin-sensitive GTP-binding regulatory proteins, possibly G(i) and G(p) subtypes, in the signal transduction processes following activation of &mgr;-opioid receptors at the LC. Copyright 1995 S. Karger AG, Basel

Antagonization of fentanyl-induced muscular rigidity by neurotensin at the locus coeruleus of the rat

We evaluated the interaction between neurotensin (NT) and μ-opioid receptors at the locus coeruleus (LC), using fentanyl-induced muscular rigidity as our experimental index. Adult, male Sprague-Dawley rats anesthetized with ketamine (120 mg/kg, i.p., with 24 mg/kg/h i.v. infusion supplements) were used. Intravenous injection of fentanyl (100 μg/kg) consistently promoted a significant increase in the electromyographic activity recorded from the sacrococcygeus dorsalis lateralis muscle. This implied muscular rigidity was appreciably and dose-dependently antagonized by prior intracerebroventricular (i.c.v.) application of NT (15, 30 or 60 nmol/5 μl). Microinjection of the tridecapeptide (300 or 600 pmol/100 nl) into the bilateral LC produced similar results. This suppressive effect of NT on fentanyl-induced muscular rigidity was antagonized by simultaneously administered NT antiserum ( 1:80), or partially blocked by its antagonist, ( d-Trp 11)-NT (300 pmol), but not by normal rabbit serum ( 1:80). These results suggest that NT may interact with the μ-opioid receptors at the LC, resulting in the suppression of fentanyl-induced muscular rigidity in the rat.

Power spectral analysis of electromyographic and systemic arterial pressure signals during fentanyl-induced muscular rigidity in the rat

We have measured electromyographic (EMG) and systemic arterial pressure (SAP) signals during fentanyl-induced muscular rigidity in adult male Sprague-Dawley rats anaesthetized initially with ketamine 120 mg kg-1 i.p. during controlled ventilation. Fentanyl 100 micrograms kg-1 i.v. induced significant increase in EMG activity, recorded from the sacrococcygeus dorsi lateralis muscle. Power spectral analysis revealed that this was produced by an increase in the root mean square and a decrease in the mean power frequency values of the signals, signifying recruitment and synchronous activation of motor units. Together with transient hypotension and bradycardia, power spectral analysis of the SAP signals demonstrated a reduced but maintained power density of the frequency components that represent respiratory, baroreceptor and vasomotor activities. All these effects were only demonstrated unequivocally in rats maintained by i.v. infusion of ketamine until 10 min before the administration of fentanyl. We conclude that analysis of the temporal alterations in the spectral components of the EMG and SAP signals in rats during mechanical ventilation provides a sensitive method of measuring fentanyl-induced muscular rigidity and the accompanying alterations in haemodynamic variables.

Involvement of G oα subtype of guanine nucleotide-binding regulatory protein at the locus coeruleus in fentanyl-induced muscular rigidity in the rat

Previous work from our laboratory suggested that locus coeruleus (LC) and the coerulospinal noradrenergic pathway are intimately related to the elicitation of muscular rigidity by fentanyl. The present study attempted to identify the subtype of guanine nucleotide-binding regulatory protein that may participate in this process, using Sprague-Dawley rats anesthetized with ketamine and under mechanical ventilation. Immunofluorescent staining with a polyclonal antiserum directed against a 39-kDa protein that corresponds to the α subunit of G o revealed the presence of G oα immunoreactivity in neurons of the LC. Bilateral microinjection of the same G oα antiserum into the LC also significantly blunted the enhanced electromyographic activity recorded from the sacrococcygeus dorsalis lateralis muscle induced by intravenous administration of fentanyl (100 μg/kg). These results suggest that G oα protein at the LC may participate in the signal transduction process that underlies muscular rigidity induced by high-dose fentanyl.

Automated method for the measurement of fentanyl-induced muscular rigidity

An automated method is described that can accurately and reliably measure weight displacement resulting from hindlimb extension due to muscular rigidity following opioid administration in rats. IV administration of fentanyl (0.035 mg/kg) immediately induced rigidity. Rigidity was dose dependently reversed by the α 2-agonist clonidine with an ED 50 value equal to 0.011 mg/kg IV. Second, rigidity was restored following administration of the α 2-antagonist idazoxan (0.3 mg/kg, IV) thereby confirming an α 2-mediated mechanism of action. Previously, reversal of fentanyl-induced muscular rigidity was measured by subjective rating criteria not suitable for quantitative potency comparisons. The new automated rigidity model provides a simple yet precise measurement of the ability of α 2-agonist to attenuate opioid-induced muscular rigidity in rats.

Antagonization of fentanyl-induced muscular rigidity by denervation of the coerulospinal noradrenergic pathway in the rat

The present study examined the effect of denervating the coerulospinal noradrenergic pathway on the muscular rigidity elicited by fentanyl in Sprague-Dawley rats anesthetized with ketamine. We demonstrated that the dopamine-β-hydroxylase-positive nerve terminals arborizing on spinal motoneurons that innervate the sacrococcygeus dorsi lateralis (SCDL) muscle were significantly eliminated by DSP4 treatment. Unilateral microinjection of fentanyl ( 2.5 μ g 50 nl ) into the locus coeruleus of these animals also failed to evoke discernible increase in the electromyographic activity recorded from the SCDL muscle. These results lend further support for our previous finding that the coerulospinal noradrenergic neurotransmission is critically involved in fentanyl-induced muscular rigidity.

Spinal cord localization of the motoneurons innervating the sacrococcygeus dorsi lateralis muscle and their noradrenergic nerve terminals in rats

We examined in the present study the spinal cord localization of motoneurons innervating the caudal portion of the sacrococcygeus dorsi lateralis (SCDL) muscle and their noradrenergic nerve terminals in Sprague-Dawley rats, using horseradish peroxidase (HRP) and dopamine-β-hydroxylase (DBH) double-labeling techniques. Retrogradely HRP-labeled motoneurons innervating the caudal part of the SCDL muscle were located ipsilaterally in the ventromedial aspect of the ventral horn (lamina IX) in spinal segments of S 2–S 4. These cells were polygonal in shape, with an average soma diameter of 37.0 ± 1.1 μm (mean ± S.E.M., n = 95) and amounted to 33.6 ± 5.7 ( n = 7) in the horizontal plane. Of note was the presence of abundant DBH-positive nerve terminals arborizing on the soma and dendrites of HRP-labeled motoneurons. These results provided anatomical evidence to further support our previous findings that the coerulospinal noradrenergic neurotransmission is involved in the mediation of fentanyl-induced muscular rigidity.

Involvement of coerulospinal noradrenergic pathway in fentanyl-induced muscular rigidity in rats

Unilateral, site-specific microinjection of fentanyl ( 2.5 μ g 50 nl ) into the locus coeruleus (LC) in Sprague-Dawley rats anesthetized with ketamine evoked a significant increase in the electromyographic activity recorded from both caudal lateral extensor and gastrocnemius muscles. This correlate of opiate-induced muscular rigidity was appreciably antagonized by a pretreatment with the specific α 1-adrenoceptor blocker, prazosin (250 μg/kg, i.v.). On the other hand, an equimolar dose (0.65 μmol/kg) of the specific α 2-adrenoceptor blocker, yohimbine (0.23 mg/kg, i.v.) failed to prevent the occurrence of fentanyl-induced EMG activation. We suggest that the coerulospinal noradrenergic pathway may be directly involved in the elicitation of muscular rigidity by fentanyl, possibly via α 1-adrenoceptors in the spinal cord.

Differential effects of prazosin and yohimbine on fentanyl-induced muscular rigidity in rats

Whereas muscular rigidity is a well-known phenomenon that is related to anesthesia induced by large doses of narcotic drugs, the precise underlying mechanism(s) remain to be fully elucidated. This study investigated the possible role of noradrenergic neurotransmission and the participation of α-adrenoceptors in this phenomenon. Male Sprague-Dawley rats, under ketamine-induced anesthesia (120 mg/kg, i.p.) and with proper control of respiration, body temperature and end-tidal CO 2 were used. Intravenous administration of fentanyl (lOO g/kg) consistently caused a significant increase in the electromyographic (EMG) activity, recorded from both gastrocnemius and abdominal reetus muscles. This implied muscular rigidity was markedly antagonized by pretreatment with the specific α 1-adrenoceptor blocker, prazosin (50 or 250μg/kg, i.V.). This antagonism occurred in spite of a high level of fentanyl in the plasma, as determined by radioimmunoassay. The specific α 2-adrenoceptor blocker, yohimbine (1.15 or 2.3 mg/kg, i.V.), on the other hand, not only failed to prevent fentanyl-induced activation of the EMG, but actually potentiated the response. It is concluded that noradrenergic neurotransmission, possibly originating from the locus coeruleus, may participate in the elicitation of muscular rigidity by fentanyl. Furthermore, this process may involve an excitatory action through α 1-, and an inhibitory action through α 2-adrenoceptors, in the spinal cord.

Fentanyl increases catecholamine oxidation current measured by in vivo voltammetry in the rat striatum.

A proposed mechanism for fentanyl-induced muscular rigidity is the effect of opioids on dopaminergic transmission in the striatum. The objective of this study was to observe the effect of fentanyl on the rat striatal catechol oxidation current (CA.OC) which reflects extracellular DOPAC (3-4,dihydroxyphenylacetic acid) concentration (a major metabolite of dopamine), as measured by in vivo voltammetry. Male Sprague-Dawley rats, anaesthetized with halothane, were stereotaxically implanted with carbon fibre electrodes in the striatum and after an initial stabilization period of an hour were given a control saline IV injection followed 30 min later by fentanyl 10 micrograms.kg-1 IV over 10 min and at 70 min by the monoamine oxidase inhibitor pargyline 70 mg.kg-1 IP. Fentanyl produced a significant (P less than 0.05 Anova) increase in CA.OC in all animals. This reached a plateau 15 min following the administration of fentanyl and was at a maximum of 148 +/- 10.2 per cent of control 35 min after the administration of fentanyl. Pargyline produced a rapid decline in CA.OC peak height which went from 143 +/- 11.6 to 39 +/- 6.8 per cent of control over 30 min. There were no significant differences between the pH, PaO2 and PaCO2 during the saline and fentanyl injection periods and there was no significant variation of blood pressure throughout the experiment. This study shows that under stable physiological conditions, fentanyl produces a significant increase in CA.OC in the rat striatum.

Involvement of locus coeruleus and noradrenergic neurotransmission in fentanyl-induced muscular rigidity in the rat

Whereas muscular rigidity is a well-known side effect that is associated with high-dose fentanyl anesthesia, a paucity of information exists with regard to its underlying mechanism(s). We investigated in this study the possible engagement of locus coeruleus of the pons in this phenomenon, using male Sprague-Dawley rats anesthetized with ketamine. Under proper control of respiration, body temperature and end-tidal CO2, intravenous administration of fentanyl (50 or 100 micrograms/kg) consistently promoted an increase in electromyographic activity recorded from the gastrocnemius and abdominal rectus muscles. Such an induced muscular rigidity by the narcotic agent was significantly antagonized or even reduced by prior electrolytic lesions of the locus coeruleus or pretreatment with the alpha-adrenoceptor blocker, prazosin. Microinjection of fentanyl (2.5 micrograms/50 nl) directly into this pontine nucleus, on the other hand, elicited discernible electromyographic excitation. It is speculated that the induction of muscular rigidity by fentanyl may involve the coerulospinal noradrenergic fibers to the spinal motoneurons.