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R Lydic

Publications and source records attributed to R Lydic.

At least 19 recordsLinked to original sources
PubMed2006

Sleep and GABA levels in the oral part of rat pontine reticular formation are decreased by local and systemic administration of morphine.

Morphine, a mu-opioid receptor agonist, is a commonly prescribed treatment for pain. Although highly efficacious, morphine has many unwanted side effects including disruption of sleep and obtundation of wakefulness. One mechanism by which morphine alters sleep and wakefulness may be by modulating GABAergic signaling in brain regions regulating arousal, including the pontine reticular nucleus, oral part (PnO). This study used in vivo microdialysis in unanesthetized Sprague-Dawley rat to test the hypothesis that mu-opioid receptors modulate PnO GABA levels. Validation of the high performance liquid chromatographic technique used to quantify GABA was obtained by dialyzing the PnO (n=4 rats) with the GABA reuptake inhibitor nipecotic acid (500 microM). Nipecotic acid caused a 185+/-20% increase in PnO GABA levels, confirming chromatographic detection of GABA and demonstrating the existence of functional GABA transporters in rat PnO. Morphine caused a concentration-dependent decrease in PnO GABA levels (n=25 rats). Coadministration of morphine (100 microM) with naloxone (1 microM), a mu-opioid receptor antagonist, blocked the morphine-induced decrease in PnO GABA levels (n=5 rats). These results show for the first time that mu-opioid receptors in rat PnO modulate GABA levels. A second group of rats (n=6) was used to test the hypothesis that systemically administered morphine also decreases PnO GABA levels. I.v. morphine caused a significant (P<0.05) decrease (19%) in PnO GABA levels relative to control i.v. infusions of saline. Finally, microinjections followed by 2 h recordings of electroencephalogram and electromyogram tested the hypothesis that PnO morphine administration disrupts sleep (n=8 rats). Morphine significantly (P<0.05) increased the percent of time spent in wakefulness (65%) and significantly (P<0.05) decreased the percent of rapid eye movement (REM) sleep (-53%) and non-REM sleep (-69%). The neurochemical and behavioral data suggest that morphine may disrupt sleep, at least in part, by decreasing GABAergic transmission in the PnO.

Animals↗
PubMed2004

Carbachol in the pontine reticular formation of C57BL/6J mouse decreases acetylcholine release in prefrontal cortex.

The prefrontal cortex and brainstem modulate autonomic and arousal state control but the neurotransmitter mechanisms underlying communication between prefrontal cortex and brainstem remain poorly understood. This study examined the hypothesis that microdialysis delivery of carbachol to the pontine reticular formation (PRF) of anesthetized C57BL/6J (B6) mouse modulates acetylcholine (ACh) release in the frontal association cortex. Microdialysis delivery of carbachol (8.8 mM) to the PRF caused a significant (P<0.01) decrease (-28%) in ACh release in the frontal association cortex, a significant (P<0.01) decrease (-23%) in respiratory rate, and a significant (P<0.01) increase (223%) in time to righting after anesthesia. Additional in vitro studies used the [(35)S]guanylyl-5'-O-(gamma-thio)-triphosphate ([(35)S]GTPgammaS) assay to test the hypothesis that muscarinic cholinergic receptors activate guanine nucleotide binding proteins (G proteins) in the frontal association cortex and basal forebrain. In vitro treatment with carbachol (1 mM) caused a significant (P<0.01) increase in [(35)S]GTPgammaS binding in the frontal association cortex (62%) and basal forebrain nuclei including medial septum (227%), vertical (210%) and horizontal (165%) limbs of the diagonal band of Broca, and substantia innominata (127%). G protein activation by carbachol was concentration-dependent and blocked by atropine, indicating that the carbachol-stimulated [(35)S]GTPgammaS binding was mediated by muscarinic cholinergic receptors. Together, the in vitro and in vivo data show for the first time in B6 mouse that cholinergic neurotransmission in the PRF can significantly alter ACh release in frontal association cortex, arousal from anesthesia, and respiratory rate.

Acetylcholine↗
PubMed2004

M2 muscarinic receptors in pontine reticular formation of C57BL/6J mouse contribute to rapid eye movement sleep generation.

Microinjecting the acetylcholinesterase inhibitor neostigmine into the pontine reticular formation of C57BL/6J (B6) mouse causes a rapid eye movement (REM) sleep-like state. This finding is consistent with similar studies in cat and both sets of data indicate that the REM sleep-like state is caused by increasing levels of endogenous acetylcholine (ACh). Muscarinic cholinergic receptors have been localized to the pontine reticular formation of B6 mouse but no previous studies have examined which of the five muscarinic receptor subtypes participate in cholinergic REM sleep enhancement. This study examined the hypothesis that M2 receptors in pontine reticular formation of B6 mouse contribute to the REM sleep-like state caused by pontine reticular formation administration of neostigmine. B6 mice (n=13) were implanted with electrodes for recording states of sleep and wakefulness and with microinjection cannulae aimed for the pontine reticular formation. States of sleep and wakefulness were recorded for 4 h following pontine reticular formation injection of saline (control) or neostigmine. Experiments designed to gain insight into the muscarinic receptor subtypes mediating REM sleep enhancement involved pontine reticular formation administration of neostigmine after pertussis toxin, neostigmine after methoctramine, and neostigmine after pirenzepine. Pertussis toxin was used to block effects mediated by M2 and M4 receptors. Methoctramine was used to block M2 and M4 receptors, and pirenzepine was used to block M1 and M4 receptors. Pertussis toxin and methoctramine significantly decreased the neostigmine-induced REM sleep-like state. In contrast, pretreatment with pirenzepine did not significantly decrease the REM sleep-like state caused by neostigmine. These results support the interpretation that M2 receptors in the pontine reticular formation of B6 mouse contribute to the generation of REM sleep.

Action Potentials↗
PubMed2004

Acetylcholine release in the pontine reticular formation of C57BL/6J mouse is modulated by non-M1 muscarinic receptors.

Pontine acetylcholine (ACh) contributes to the regulation of electroencephalographic and behavioral arousal in all mammals so far investigated. The mouse is recognized as a powerful model for pharmacogenomics but the synaptic mechanisms regulating ACh release in mouse pontine reticular formation have not been characterized. Drug delivery by microdialysis was used in isoflurane-anesthetized C57BL/6J (B6) mice (n=33) to test the hypothesis that muscarinic autoreceptors modulate ACh release in the pontine reticular nucleus, oral part (PnO). Dialysis delivery of tetrodotoxin to the PnO significantly decreased ACh by 58% below control levels, confirming that measured ACh reflected neurotransmitter release. The muscarinic antagonist scopolamine increased ACh release in the PnO by 21% (3 nM), 48% (10 nM), 56% (30 nM), and 104% (100 nM). The muscarinic agonist bethanechol dialyzed into the PnO significantly decreased ACh release by 60% compared with control. Dialysis delivery of relatively subtype selective muscarinic antagonists to the PnO revealed the following order of potency for increasing ACh release: scopolamine (3 nM)>AF-DX 116 (100 nM)=pirenzepine (100 nM). These data support the conclusion that ACh release in PnO of B6 mouse is modulated by non-M1 muscarinic receptors.

Acetylcholine↗
PubMed2001

G protein activation in rat ponto-mesencephalic nuclei is enhanced by combined treatment with a mu opioid and an adenosine A1 receptor agonist.

STUDY OBJECTIVES: Opioids delivered to the pons inhibit REM sleep, whereas pontine administration of adenosine enhances REM sleep. In other brain areas opioids and adenosine interact to produce antinociception. Adenosine A1 receptors and mu opioid receptors each activate Gi/Go proteins. This study tested the hypothesis that combined treatment with the adenosine A1 receptor agonist SPA and the mu opioid agonist DAMGO would enhance G protein activation to a greater level than produced by either agonist alone. G protein activation was quantified in seven brainstem regions regulating sleep and nociception. This study also tested the hypothesis that G protein activation caused by SPA would be concentration dependent and blocked by the adenosine A1 receptor antagonist DPCPX. DESIGN: Activation of G proteins was assessed autoradiographically by agonist stimulation of [35S]GTPgammaS binding in slide-mounted sections of rat brainstem. G protein activation was quantified in nCi/g tissue for pontine reticular formation, dorsal raphe, ventrolateral and dorsomedial periaqueductal gray, and laterodorsal and pedunculopontine tegmental nuclei. SETTING: N/A. PATIENTS OR PARTICIPANTS: N/A. MEASUREMENTS AND RESULTS: Combined treatment with SPA and DAMGO caused a partially additive increase in G protein activation that was significantly (p<0.01) greater than G protein activation caused by either agonist alone. Treatment with SPA alone caused a concentration dependent (p<0.001) increase in [35S]GTPgammaS binding that was blocked by DPCPX. CONCLUSION: Agonist activation of adenosine A1 receptors stimulates G proteins in brainstem nuclei regulating sleep and nociception. In these same nuclei, G protein activation by combined treatment with DAMGO and SPA was partially additive, suggesting that mu opioid and adenosine A1 receptors activate some common G protein pools.

Analgesics, Opioid↗
PubMed2001

M2 muscarinic autoreceptors modulate acetylcholine release in prefrontal cortex of C57BL/6J mouse.

Muscarinic autoreceptors modulate cholinergic neurotransmission in animals ranging from insects to humans. No previous studies have characterized autoreceptor modulation of acetylcholine (ACh) release in prefrontal cortex of intact mouse. Data obtained from experiments in 45 mice considered ACh as a phenotype and tested the hypothesis that pharmacologically defined M2 receptors modulate ACh release in prefrontal cortex of C57BL/6J mouse. In vivo microdialysis quantified ACh release during delivery of Ringer's (control) or Ringer's containing muscarinic receptor antagonists. The lowest concentration of each antagonist [scopolamine, pirenzepine, or 11-2[(-[(diethylamino)methyl]-1-piperidinyl)-acetyl]-5,11-dihydro-6H-pyrido(2,3-b)(1,4)-benzodiazepine-one (AF-DX116)] that significantly increased ACh release was determined and defined as the minimum ACh-releasing concentration. Dialysis delivery of scopolamine caused a concentration-dependent increase in ACh release, consistent with the existence of muscarinic autoreceptors. The order of potency for causing increased ACh release was scopolamine = AF-DX116 > pirenzepine. Administration of pertussis toxin into prefrontal cortex blocked the AF-DX116-induced increase in ACh release. These findings support the conclusion that M2 receptors modulate ACh release in C57BL/6J mouse prefrontal cortex. Nearly every human gene has a mouse homolog and the appeal of mouse models is reinforced by the identification of mouse genes causing phenotypic deviants. The present data encourage comparative phenotyping of cortical ACh release in additional mouse strains.

Acetylcholine↗
PubMed1999

M2 muscarinic receptor subtype in the feline medial pontine reticular formation modulates the amount of rapid eye movement sleep.

Rapid eye movement (REM) sleep is generated, in part, by activating muscarinic cholinergic receptors (mAChRs) in the medial pontine reticular formation (mPRF). Molecular cloning has identified five mAChR subtypes, and this study tested the hypothesis that the M2 subtype in the mPRF modulates the amount of REM sleep. This hypothesis cannot be tested directly, due to lack of subtype selective muscarinic agonists. However, the amount of REM sleep can be enhanced by mPRF microinjection of a muscarinic agonist, and the relative potencies of muscarinic antagonists to block the REM sleep enhancement can be determined. Two muscarinic antagonists, methoctramine and 4-DAMP, were studied. Six concentrations of each antagonist were microinjected into the mPRF of conscious cat 15 min prior to the agonist bethanechol. Nonlinear regression analysis was used to calculate the dose of antagonist that caused a 50% inhibition (ID50) of bethanechol-induced REM sleep. Bethanechol significantly increased (442%) the amount of time spent in REM sleep. Both methoctramine and 4-DAMP significantly blocked the bethanechol-induced REM sleep increase, with an ID50 of 1.8 microM and 0.6 microM, respectively. The ID50 ratio for methoctramine-to-4-DAMP (3.0) was similar to the affinity ratio of methoctramine-to-4-DAMP only at the M2 subtype (3.5), suggesting that the M2 subtype in the mPRF modulates the amount of REM sleep. This study also tested the null hypothesis that sleep-dependent respiratory depression evoked by mPRF cholinomimetics would not be antagonized by pretreatment of the mPRF with muscarinic antagonists. Neither methoctramine nor 4-DAMP antagonized the bethanechol-induced decrease in respiratory rate.

Animals↗
PubMed1999

Fentanyl and morphine, but not remifentanil, inhibit acetylcholine release in pontine regions modulating arousal.

BACKGROUND: Opioids inhibit the rapid eye movement (REM) phase of sleep and decrease acetylcholine (ACh) release in medial pontine reticular formation (mPRF) regions contributing to REM sleep generation. It is not known whether opioids decrease ACh release by acting on cholinergic cell bodies or on cholinergic axon terminals. This study used in vivo microdialysis to test the hypothesis that opioids decrease ACh levels at cholinergic neurons in the laterodorsal tegmental nuclei (LDT) and LDT axon terminals in the mPRF. METHODS: Nine male cats were anesthetized with halothane, and ACh levels within the mPRF or LDT were assayed using microdialysis and high-pressure liquid chromatography (HPLC). ACh levels were analyzed in response to dialysis of the mPRF and LDT with Ringer's solution (control), followed by dialysis with Ringer's solution containing morphine sulfate (MSO4) or naloxone. ACh in the mPRF also was measured during either dialysis delivery or intravenous infusion of remifentanil and during dialysis delivery of fentanyl. RESULTS: Compared with dialysis of Ringer's solution, microdialysis with MSO4 decreased ACh by 23% in the mPRF and by 30% in the LDT. This significant decrease in ACh was antagonized by naloxone. MSO4 and fentanyl each caused a dose-dependent decrease in mPRF ACh when delivered by dialysis. Remifentanil delivered by continuous intravenous infusion or by dialysis into the mPRF did not alter mPRF ACh. CONCLUSIONS: Morphine inhibits ACh at the cholinergic cell body region (LDT) and the terminal field in the mPRF. ACh in the mPRF was not altered by remifentanil and was significantly decreased by fentanyl. Thus, MSO4 and fentanyl disrupt cholinergic neurotransmission in the LDT-mPRF network known to modulate REM sleep and cortical electroencephalographic activation. These data are consistent with the possibility that inhibition of pontine cholinergic neurotransmission contributes to arousal state disruption by opioids.

Acetylcholine↗
PubMed1998

Cholinomimetics, but not morphine, increase antinociceptive behavior from pontine reticular regions regulating rapid-eye-movement sleep.

Sleep disruption is a significant problem associated with the subjective experience of pain. Both rapid-eye-movement (REM) sleep and nociception are modulated by cholinergic neurotransmission, and this study tested the hypothesis that antinociceptive behavior can be evoked cholinergically from medial pontine reticular formation (mPRF) regions known to regulate REM sleep. The foregoing hypothesis was investigated by quantifying the effect of mPRF drug administration on tail flick latency (TFL) of cat during polygraphically defined sleep/wake states. The mPRF was microinjected with 0.25 ml saline, carbachol (4.0 microg), neostigmine (6.7 microg), or morphine sulfate (14.7 microg), and TFL measures were obtained in response to radiant heat. During wakefulness TFL (% increase) was not increased by morphine or saline, but was significantly increased by mPRF administration of carbachol (42.4%) and neostigmine (35.2%). Cortical somatosensory potentials (SSEPs) were reliably evoked by tail stimulation before and after mPRF microinjections of carbachol. The results show for the first time that mPRF administration of cholinomimetics significantly increased TFL. During NREM sleep and REM sleep, TFL was significantly increased compared to waking TFL (110% and 321%, respectively). The finding of sleep-dependent alterations in TFL demonstrates that mPRF regions known to regulate REM sleep can modulate supraspinal cholinergic antinociceptive behavior.

Analysis of Variance↗
PubMed1998

Opioids activate G proteins in REM sleep-related brain stem nuclei of rat.

Mu opioid receptors within the pontine reticular formation contribute to opioid-induced rapid eye movement (REM) sleep inhibition. Mu receptors are coupled to guanine nucleotide binding (G) proteins and this study tested the hypothesis that the micro opioid agonist [D-Ala2,N-Me-Phe4,Gly-ol5]enkephalin (DAMGO) would activate G proteins in rat brain stem nuclei known to regulate REM sleep. In vitro autoradiography of DAMGO-stimulated [35S]GTPgammaS binding showed that, compared with basal [35S]GTPgammaS binding, DAMGO significantly increased G protein activation in the nucleus pontis oralis (56.2%), nucleus pontis caudalis (57.3%), laterodorsal tegmental nucleus (75.8%), pedunculopontine tegmental nucleus (72.4%), nucleus locus coeruleus (77.2%) and dorsal raphe nucleus (73.4%). DAMGO stimulation of [35S]GTPgammaS binding in nuclei regulating REM sleep suggests that opioid-induced REM sleep inhibition involves activation of G proteins.

Animals↗
PubMed1998

Carbachol stimulates [35S]guanylyl 5'-(gamma-thio)-triphosphate binding in rapid eye movement sleep-related brainstem nuclei of rat.

Carbachol enhances rapid eye movement (REM) sleep when microinjected into the pontine reticular formation of the cat and rat. Carbachol elicits this REM sleep-like state via activation of postsynaptic muscarinic cholinergic receptors (mAChRs). The present study used in vitro autoradiography of carbachol-stimulated [35S]guanylyl-5'-O-(gamma-thio)-triphosphate ([35S]GTPgammaS) binding to test the hypothesis that carbachol activates mAChRs to induce stimulation of G-proteins in brainstem nuclei contributing to REM sleep generation. The results demonstrate a heterogeneous increase in carbachol-stimulated G-protein activation across rat brainstem. Binding of [35S]GTPgammaS in the presence of carbachol, compared with basal binding, was significantly increased in the laterodorsal tegmental nucleus (75.7%), caudal pontine reticular nucleus (68.9%), oral pontine reticular nucleus (64.5%), pedunculopontine tegmental nucleus (55.7%), and dorsal raphe nucleus (54.0%) but not in the nucleus locus coeruleus. The activation of G-proteins by carbachol was concentration-dependent and antagonized by atropine, demonstrating that G-proteins were activated via mAChR stimulation. The results provide the first direct measures of mAChR-activated G-proteins in brainstem nuclei known to contribute to REM sleep generation.

Animals↗
PubMed1998

M2 muscarinic autoreceptors modulate acetylcholine release in the medial pontine reticular formation.

Muscarinic autoreceptors regulate acetylcholine (ACh) release in several brain regions, including the medial pontine reticular formation (mPRF). This study tested the hypothesis that the muscarinic cholinergic receptor mediating mPRF ACh release is the pharmacologically defined M2 subtype. In vivo microdialysis was used to deliver muscarinic cholinergic receptor (MAChR) antagonists to the feline mPRF while simultaneously measuring endogenously released ACh. The lowest concentration of each antagonist that caused a significant increase in mPRF ACh release was determined and defined as the minimum ACh-releasing concentration. Data obtained from 41 mPRF dialysis sites in 10 animals showed that the order of potency (followed by the minimum ACh-releasing concentration) was scopolamine (1 nM) > AF-DX 116 (3 nM) > pirenzepine (300 nM). Comparison of these minimum ACh-releasing concentrations to the known affinities of the antagonists for the five mAChR subtypes is consistent with the conclusion that the autoreceptor regulating mPRF ACh release is the M2 subtype. Considerable evidence supports a role for cholinergic neurotransmission and postsynaptic M2 receptors in the mPRF in regulating levels of arousal. The present data suggest that presynaptic M2 receptors contribute to the regulation of arousal states by modulating mPRF ACh release.

Acetylcholine↗
PubMed1997

Vesicular acetylcholine transport inhibitor suppresses REM sleep.

The vesamicol-like compound (+/-)-4-aminobenzovesamicol (ABV) non-competitively inhibits vesicular packaging of acetylcholine (ACh) in presynaptic terminals. This study tested the hypothesis that microinjection of ABV into the medial pontine reticular formation (mPRF) of intact, unanesthetized cats would inhibit rapid eye movement (REM) sleep. Microinjection of ABV alone or before administration of the acetylcholinesterase inhibitor neostigmine was used to evaluate the effects of ABV on natural REM sleep and on the neostigmine-induced REM sleep-like state. ABV decreased (24.8%) REM sleep and significantly reduced (33.6%) the neostigmine-induced REM sleep-like state. The results show for the first time that REM sleep generation can be disrupted by blocking a synaptic vesicle protein that modulates ACh transport in localized regions of the mPRF.

Acetylcholine↗
PubMed1997

Pontine nitric oxide modulates acetylcholine release, rapid eye movement sleep generation, and respiratory rate.

Pontine cholinergic neurotransmission is known to play a key role in the regulation of rapid eye movement (REM) sleep and to contribute to state-dependent respiratory depression. Nitric oxide (NO) has been shown to alter the release of acetylcholine (ACh) in a number of brain regions, and previous studies indicate that NO may participate in the modulation of sleep/wake states. The present investigation tested the hypothesis that inhibition of NO synthase (NOS) within the medial pontine reticular formation (mPRF) of the unanesthetized cat would decrease ACh release, inhibit REM sleep, and prevent cholinergically mediated respiratory depression. Local NOS inhibition by microdialysis delivery of N(G)-nitro-L-arginine (NLA) significantly reduced ACh release in the cholinergic cell body region of the pedunculopontine tegmental nucleus and in the cholinoceptive mPRF. A second series of experiments demonstrated that mPRF microinjection of NLA significantly reduced the amount of REM sleep and the REM sleep-like state caused by mPRF injection of the acetylcholinesterase inhibitor neostigmine. Duration but not frequency of REM sleep epochs was significantly decreased by mPRF NLA administration. Injection of NLA into the mPRF before neostigmine injection also blocked the ability of neostigmine to decrease respiratory rate during the REM sleep-like state. Taken together, these findings suggest that mPRF NO contributes to the modulation of ACh release, REM sleep, and breathing.

Acetylcholine↗
PubMed1997

cAMP and protein kinase A modulate cholinergic rapid eye movement sleep generation.

Cholinergic neurotransmission in the medial pontine reticular formation (mPRF) modulates rapid eye movement (REM) sleep generation. Microinjection of cholinergic agonists and acetylcholinesterase inhibitors into the mPRF induces a REM sleep-like state, and microdialysis data reveal increased mPRF levels of acetylcholine during REM sleep. Muscarinic cholinergic receptors (mAChRs) participate in REM sleep generation, and data suggest that mAChRs of a non-M1 subtype modulate REM sleep generation. The signal transduction pathway activated by m2 and m4 mAChRs involves a pertussis toxin-sensitive G protein, adenylate cyclase (AC), adenosine 3',5'-cyclic monophosphate (cAMP), and protein kinase A (PKA). Therefore, the present study tested the hypothesis that cAMP and PKA within the mPRF modulate the carbachol-induced REM sleep-like state. To test this hypothesis, the mPRF was microinjected with compounds known to facilitate the effects of cAMP (dibutyryl cAMP and 8-bromo-cAMP), stimulate PKA (Sp-cAMP[S]), and inhibit PKA (Rp-cAMP[S]). The results showed that compounds that fostered the intracellular effects of cAMP significantly decreased cholinergic REM sleep, while having no effect on spontaneously occurring REM sleep. These data are consistent with the recent finding that within the mPRF, AC and a pertussis toxin-sensitive G protein modulate cholinergic REM sleep generation. These new data suggest a modulatory role for pontine cAMP and PKA in cholinergic REM sleep regulation.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

Pontine acetylcholine release is regulated by muscarinic autoreceptors.

Acetylcholine (ACh) in the medial pontine reticular formation (mPRF) originates from the laterodorsal and pedunculopontine tegmental (LDT/PPT) nuclei and contributes to generating rapid eye movement (REM) sleep. The mechanisms controlling mPRF ACh levels are incompletely understood. This study tested the hypothesis that mPRF ACh release is regulated, in part, by muscarinic autoreceptors. The mPRF of intact, halothane-anesthetized cats was dialyzed with Ringer's solution (control) or Ringer's containing the muscarinic antagonist scopolamine, Scopolamine caused a dose-dependent increase in mPRF ACh release and a concomitant decrease in the number of halothane-induced cortical EEG spindles. These data suggest that presynaptic muscarinic receptors, presumed to reside on cholinergic LDT/PPT terminals in the mPRF, play a role in regulating mPRF ACh release, REM sleep and EEG spindles.

Acetylcholine↗
PubMed1996

Pontine cholinergic mechanisms modulate the cortical electroencephalographic spindles of halothane anesthesia.

BACKGROUND: Halothane anesthesia causes spindles in the electroencephalogram (EEG), but the cellular and molecular mechanisms generating these spindles remain incompletely understood. The current study tested the hypothesis that halothane-induced EEG spindles are regulated, in part, by pontine cholinergic mechanisms. METHODS: Adult male cats were implanted with EEG electrodes and trained to sleep in the laboratory. Approximately 1 month after surgery, animals were anesthetized with halothane and a microdialysis probe was stereotaxically placed in the medial pontine reticular formation (mPRF). Simultaneous measurements were made of mPRF acetylcholine release and number of cortical EEG spindles during halothane anesthesia and subsequent wakefulness. In additional experiments, carbachol (88 mM) ws microinjected in the the mPRF before halothane anesthesia to determine whether enhanced cholinergic neurotransmission in the MPRF would block the ability of halothane to induce cortical EEG spindles. RESULTS: During wakefulness, mPRF acetylcholine release averaged 0.43 pmol/10 min of dialysis. Halothane at 1 minimum alveolar concentration decreased acetylcholine release (0.25 pmol/10 min) while significantly increasing the number of cortical EEG spindles. Cortical EEG spindles caused by 1 minimum alveolar concentration halothane were not significantly different in waveform, amplitude, or number from the EEG spindles of nonrapid eye movement sleep. Microinjection of carbachol into the mPRF before halothane administration caused a significant reduction in number of halothane-induced EEG spindles. CONCLUSIONS: Laterodorsal and pedunculopontine tegmental neurons, which provide cholinergic input to the mPRF, play a causal role in generating the EEG spindles of halothane anesthesia.

Acetylcholine↗