Acute interactive effects of MK-801 and morphine on cortical EEG and EEG power spectra in rats

The interaction between MK-801 and morphine-induced effects on cortical electroencephalography (EEG) was investigated. Rats were administered one of five MK-801 doses (IP) prior to morphine (IV). MK-801 dose-dependently increased morphine-induced global spectral power, duration of morphine-induced EEG bursts and latency to sleep onset, and decreased morphine-induced mean frequency, mobility, complexity, and edge frequency. MK-801 pretreatment shifted the relative distribution of total power to the left. Significant interaction effects were found for all spectral parameters except peak frequency. A second group of rats was administered MK-801 prior to an increasing cumulative morphine dose. MK-801 increased maximal morphine effects on all spectral parameters except peak frequency. The results are in agreement with those of recent analgesia and in vitro studies in spinal neurons, and support observations of a synergistic interaction between effects of NMDA antagonism and morphine. These data further suggest that the component of cortical EEG that is produced by mu-opioid- and NMDA-receptor interactive effects may be dominated by an inhibitory effect of morphine on NMDA receptor activity.     

Responses of raphe magnus neurons to systemic morphine in rats

The spontaneous firing rate of nucleus raphe magnus (NRM) neurons increased, decreased or were not altered in Wistar rats after various doses of morphine were administered intravenously. Dose-related changes were observed only in neurons which displayed increased firing frequency. Naloxone antagonized the morphine-induced effect more frequently in the excited neuron than in the inhibited one. These results suggest that morphine induced increases in discharge frequency is the more specific pharmacological effect, and that only the excited neuron might participate directly in the descending analgesic system of morphine.     

EEG effects of microinjection of naloxone in the region of the nucleus tractus solitarius of the rat

In recent years, we have carried out several studies on brainstem mechanisms associated with pain modulation. Of particular interest has been the region of the nucleus tractus solitarius (NTS) at the level of the area postrema (AP) in the dorsomedial medulla. This region has been found to be rich in opiate receptors and to be involved in pain modulation. Having previously demonstrated the EEG and behavioral effects of systemic administration of morphine, we initiated the present study to determine whether microinjection of naloxone directly into the region of the NTS will modify any or all of the EEG effects induced by subsequent systemic administration of morphine. Our results have shown that microinjections of naloxone into the region of the NTS block the cortical EEG synchronizing effects of systemically administered morphine. These results indicate that morphine-induced cortical EEG synchronization is mediated through the region of the NTS. This region may, therefore, comprise part of an opiate sensitive system which can influence cortical EEG activity.     

The effect of MK-801 and SCH23390 on the expression and sensitization of morphine-induced oral stereotypy

Repeated high doses of morphine sulfate, administered in a 24–36 h period, stimulates the expression of oral stereotypy in rats. Sensitization to this effect of morphine is demonstrated by the reexpression of the stereotypy by the administration of 4.0 mg/kg of morphine one week following the original exposure. To investigate the role ofN-methyl-d-aspartic acid (NMDA) and D₁ dopamine (DA) receptors in the acute expression and sensitization of morphine-induced oral stereotypy, rats were administered four injections of morphine (10.0 mg/kg) one injection every 12 h and observed for the expression of stereotyic behaviors following pretreatment with selective antagonists. Pretreatment with the NMDA antagonist, MK-801 (0.7 mg/kg), before each of the four morphine injections antagonized both the initial expression of oral stereotypy and the development of sensitization. In contrast, the DA D₁ receptor antagonist SCH23390 (40.0 μg/kg) administered during the four high-dose treatments with morphine antagonized the initial expression of oral stereotypy and not the development of sensitization. These findings implicate glutamate's action at the NMDA receptor in both the acute expression of morphine-induced oral stereotypy, and the development of sensitization of this morphine effect, whereas DA D₁ receptors may only be involved in the acute expression of the stereotypy.     

Relationships between quantitative EEG measures and pharmacodynamics of alfentanil in dogs

Intravenous alfentanil was administered as a constant 1 h infusion to 6 dogs. Before, during and up to 3 h after infusion, the effects of 3 doses (0.001, 0.004 and 0.016 mg/kg/min) on 6 quantitative EEG measures (zero-crossing frequency, root mean square (rms) amplitude, spectral edge, relative delta, alpha and beta power) were assessed in relation to plasma concentrations of alfentanil. All EEG measures, except zero-crossing frequency and rms amplitude, showed statistically significant dose-dependent changes in peak effect and duration. In addition, times-to-peak effect and return-to-baseline were sensitive to dose. The EEG effects of the low dose were smaller than those of the middle and high doses, whose peak effects did not statistically differ; but the high dose produced more persistent effects, which outlasted the infusion period for a longer time. Alfentanil-induced changes in rms amplitude and relative delta power showed the widest dynamic ranges. Measurable EEG changes occurred at low plasma concentrations, but EEG responses saturated at the middle dose. Significant correlations between plasma concentration and EEG effect were obtained for only the subperiod ranging from onset of infusion to peak EEG effect, indicating very short concentration-effect equilibration delays. On the other hand, clockwise concentration-effect loops were suggestive of acute tolerance: EEG responses peaked before peak plasma levels and they returned to baseline at dose-dependently higher plasma concentrations of alfentanil.     

A comparative study of morphine treatment regimen prior to mating and during late pregnancy

Pre-mating treatment of female rats with morphine may have long-term effects. In this study, we analyzed the effects of two types of morphine sulfate pre-treatment: during pre-mating (5.0 mg/kg on alternate days for a total of seven doses) and during pregnancy (3.5 mg/(kgday) for 5 days starting on day 17 of pregnancy during early lactation. In order to evaluate possible morphine-induced behavioral changes, dams were tested for maternal behavior and locomotor activity during early lactation, and striatal and hypothalamic concentrations of dopamine and their metabolites and serum levels of corticosterone were measured. Maternal behavior was disrupted only in animals treated with morphine sulfate during pregnancy and challenged acutely (1.5 mg/kg) during lactation. Pre-mating treatment with morphine sulfate-induced changes in responses with increased locomotor activity, striatal dopamine turnover and serum corticosterone levels. None of these parameters were affected by morphine sulfate pre-treatment during late pregnancy. These data suggest that morphine has specific long-term and sometimes addictive-like effects on actively reproductive female animals that vary with the pre-treatment period, late pregnancy being particularly sensitive for effects on maternal behavior.     

Seizure-like spreading depression in immature rabbit hippocampus in vitro

Cortical application of morphine (25, 100 and 400 micrograms) induced cortical spikes in a dose-related fashion and, at 400 micrograms, behavioral and electrographic seizures. These electrographic seizures were not opiate specific since this activity occurred undiminished in naltrexone-pretreated animals and was even potentiated in animals pretreated for 6 days with increasingly higher doses of systemic morphine. In contrast to the effects induced by morphine, the most consistent electrographic effect of cortically applied D-Ala2-methionine-enkephalin (DALA) and methadone was a depression of cortical EEG. These results support the hypothesis that the cortex and spinal cord together form the anatomical substrate of the documented nonspecific convulsive action of high systemically administered doses of morphine.     

Morphine effects in brainstem-transected cats: I. EEG and 'sleep-wakefulness' in the isolated forebrain

In order to examine the prosencephalic mechanisms that might sustain the effects of opiates on EEG and sleep-wakefulness, the actions of morphine sulfate on the EEG and the pupil size were examined in the chronically isolated forebrain of brainstem-transected cats. Single morphine doses (0.5, 2.0 or 3.0 mg/kg, i.p.) administered to these animals produced a long-lasting EEG desynchronization in the isolated forebrain which was associated with pupil mydriasis. The specificity of these morphine effects was shown by the fact that naloxone blocks both the EEG and pupillary effects of the drug. After morphine, spontaneous synchronized EEG with delta waves normally seen in the isolated forebrain preparation was suppressed for 6-18 h, followed by a strong rebound. Both the suppression and rebound in synchronization with delta waves occurred in a dose-dependent manner. The duration of these effects closely paralleled previously reported morphine effects on non-rapid eye movement (NREM) sleep in intact cats. Therefore, in relation to the effects of morphine on EEG and sleep-wakefulness in intact animals, this study suggests that: (1) Morphine suppression of NREM sleep and the subsequent arousal state of the animal are mediated by prosencephalic structures; (2) the generation of the typical neocortical EEG slow burst activity produced by opiates depends on lower brainstem structures.     

Glucocorticoids involvement in the control of CNS excitability

The effect of dexamethasone (DEX) and its interaction with psychostimulants agents (morphine, cocaine and amphetamine) has been studied on locomotor activity and straub reaction in mice: a) Morphine administration, (30-75-150 mg/kg,ip) induced a dose-related increase of the locomotor activity of mice, whereas DEX per se (0.1-1.0-10 mg/kg,ip) did not modify the activity of control mice. Pretreatment of mice with DEX 0.1 mg did not alter the hyperactivity produced by the three doses of morphine. In contrast, DEX administered at 1.0 mg reduced the morphine effects on locomotor activity, whereas DEX at 10 mg potentiated the morphine hypermotility. b) Cocaine (10 mg/kg/i.p.) and amphetamine (5 mg/kg/i.p.) increased markedly locomotor activity of mice whereas DEX per se (0.1-1.0-10 mg/kg/i.p.) did not modify the activity of control mice. DEX pretreatment decreased the stimulating effects induced by cocaine and amphetamine. DEX pretreatment 0, 15, 30, 60 and 120 min before amphetamine or cocaine strongly decreased both amphetamine and cocaine effects, but no dose-related effect was observed. The time-course study performed with DEX revealed differences in its reducing effect on cocaine and amphetamine hypermotility when the groups of animals treated with the steroid immediately before the cocaine (or amphetamine) injection when compared to those treated with the steroid later (15, 30, 60 and 120 min). Furthermore, actinomycin D was able to block the reducing effect of DEX on both amphetamine and cocaine hypermotility. c) When morphine was administered in doses of 7.5, 15 and 30 mg/kg/i.p, a dose-dependent straub reaction was produced. DEX per se (0.1-1.0-10 mg /kg,i.p.) did not modify the tail of control mice. Pre-treatment with DEX 120 min before morphine injection caused a dose-dependent reduction of straub reaction. Cycloheximide (15 mg/kg,i.p.) administered 2h before morphine did not change morphine-induced straub reaction, but was able to prevent the effects of DEX on morphine-induced straub reaction. The glucocorticoid receptor antagonist RU-38486 (15 mg/kg,i.p.) did not affect morphine-induced straub reaction, whereas it was able to block the effects of dexamethasone on morphine-induced straub reaction. Our results suggest that DEX may play an important regulatory role on the central effects of morphine, cocaine and amphetamine through a differential modulation of brain excitability systems indicating that DEX may play an important role on the stimulating effects of morphine, cocaine and amphetamine and that it may be of some utility in the clinical management of psychastimuants abuse. The ability of actinomicyn D and/or cycloheximide as well as of RU-38486 to block dexamethasone's effects indicates that the steroid's interference with psychostimulants-mediated effects involve a protein-synthesis-dependent mechanism via glucocorticoid receptors. The patents related to psychostimulant agent and glucocorticoids are also discussed in this article.     

Sleep spindles and spike–wave discharges in EEG: Their generic features, similarities and distinctions disclosed with Fourier transform and continuous wavelet analysis

Epileptic activity in the form of spike–wave discharges (SWD) appears in the electroencephalogram (EEG) during absence seizures. A relationship between SWD and normal sleep spindles is often assumed. This study compares time–frequency parameters of SWD and sleep spindles as recorded in the EEG in the WAG/Rij rat model of absence epilepsy. Fast Fourier transformation and continuous wavelet transformation were used for EEG analysis. Wavelet analysis was performed in non-segmented full-length EEG. A specific wavelet-based algorithm was developed for the automatic identification of sleep spindles and SWD.None of standard wavelet templates provided precise identification of all sleep spindles and SWD in the EEG and different wavelet templates were imperative in order to accomplish this task. SWD were identified with high probability using standard Morlet wavelet, but sleep spindles were identified using two types of customized adoptive ‘spindle wavelets’. It was found that (1) almost 100% of SWD (but only 50–60% of spindles) were identified using the Morlet-based wavelet transform. (2) 82–91% of sleep spindles were selected using adoptive ‘spindle wavelet 1’ (template's peak frequency 12.2 Hz), the remaining sleep spindles with ‘spindle wavelet 2’ (peak frequency 20–25 Hz). (3) Sleep spindles and SWD were detected by the elevation of wavelet energy in different frequencies: SWD, in 30–50 Hz band, sleep spindles, in 7–14 Hz. It is concluded that the EEG patterns of sleep spindles and SWD belong to different families of phasic EEG events with different time frequency characteristics.     

Nonspecific convulsions are induced by morphine but notd-Ala-methionine-enkephalinamide at cortical sites

Cortical application of morphine (25, 100 and 400 μg) induced cortical spikes in a dose-related fashion and, at 400 μg, behavioral and electrographic seizures. These electrographic seizures were not opiate specific since this activity occured undiminished in naltrexone-pretreated animals and was even potentiated in animals pretreated for 6 days with increasingly higher doses of systemic morphine. In contrast to the effects induced by morphine, the most consistent electrographic effect of cortically appliedd-Ala²-methionine-enkephalin (DALA) and methadone was a depression of cortical EEG. These results support the hypothesis that the cortex and spinal cord together form the anatomical substrate of the documented nonspecific convulsive action of high systematically administered doses of morphine.     

ACTH-like peptides and morphine: interaction at the level of the CNS.

(1) N-terminal fragments of ACTH antagonize morphine binding to opiate specific binding sites in vitro. (2) Morphine-induced analgesia in rats can be counteracted by administration (s.c.) of ACTH analogs. (3) ACTH-like peptides produce excessive grooming in rats when intraventricularly administered. (4) Excessive grooming can also be achieved by intraventricular administration of low doses of morphine or β-LPH_61–91. (5) Peptide- or morphine-induced excessive grooming can be blocked by administration (s.c.) of specific opiate antagonists (naloxone, naltrexone). (6) The structure activity requirements for ACTH-like peptides to (a) inhibit morphine binding to opiate receptors in vitro (b) produce excessive grooming behavior and (c) counteract morphine-induced analgesia, run fairly well parallel. (7) It is concluded that a common denominator exists in the action of ACTH-like peptides and opiates on the central nervous system.     

Histaminergic modulation of neocortical spindling and slow-wave activity in freely behaving rats

Summary Histaminergic H3 receptor antagonists stimulate neuronal histamine release and could consequently have a number of physiological effects in the brain. The effects of H3 receptor blockade, induced by systemically administered thioperamide, were assessed on the frontal cortex electroencephalographic (EEG) properties in freely behaving rats. The relationship of EEG activity variables to endogenous brain histaminergic markers was also examined, both in controls and in portocaval anastomosis (PCA)-operated rats (which show increased levels of brain histamine and t-methylhistamine). Thioperamide reduced the incidence of thalamusregulated EEG spindles, while it slightly increased their amplitude. It furthermore reduced the spectral power of low-frequency (1.5–5 Hz) EEG, which effect was equally distributed over the spindle and non-spindle EEG states. These EEG effects were accompanied by increased motor activity of the animals. Both the low-frequency EEG activity and spindle incidence correlated inversely with the histamine level of the brain (hypothalamus and cerebellum excluded) while t-methylhistamine level correlated with the degree of thioperamide-induced reduction of slow-wave EEG activity. The present results provide evidence for the involvement of endogenous brain histamine level, histamine release (as assessed by t-methylhistamine level) and H3 receptors in the histaminergic regulation of neocortical synchronization patterns assumed to be linked to arousal control.     

Ethanol effects on EEG spectra in monkeys: comparison to morphine and diazepam

The effects of oral administration of 3 doses of ethanol (0.75, 1.0 and 1.5 g/kg) and single doses of morphine (2.5 mg/kg) and diazepam (2.5 mg/kg) on spectral components of the EEG were investigated in the squirrel monkey Saimiri sciureus. Comparisons of mean spectral power in the 4 frequency bands (2-4 Hz, 4-8 Hz, 8-16 Hz, 16-32 Hz) revealed that the lowest dose of ethanol (0.75 g/kg) produced some increase in power in all 4 frequency bands with significant increases in the 8-16 Hz band. Morphine also produced some increase in power in all bands; however, significant increases were prominent in the 16-32 Hz range. Moderate doses of ethanol (1.0, 1.5 g/kg) produced dose-dependent decreases in the lower frequencies which were significant in the 2-4 Hz band. Diazepam also produced significant decreases in the lower frequencies (2-4, 4-8 Hz) but also produced significant decreases in 8-16 Hz and increases in the 16-32 Hz band. The distribution of these power changes as a function of time (power spectral band time series) was also studied. Evaluation of fluctuations in the 8-16 Hz band which is a measure of the periodic shifts in alertness demonstrated that ethanol and diazepam slowed the dominant frequency of the time series; whereas, morphine caused an increase in the frequency. This study suggests that two EEG measures, mean EEG spectral profiles and power spectral band time series analysis, can successfully discriminate the electrophysiological actions of ethanol, and that these markers may provide a means for uncovering ethanol's mechanisms of action.     

Spindle activity in children during cardiac surgery and hypothermic cardiopulmonary bypass.

Hypothermia has marked effects on the electrical activity of the brain, which has been shown in animals as well as in humans. The aim of this study was to investigate EEG spindle activity in children during cardiac surgery and hypothermic cardiopulmonary bypass. The authors obtained intraoperative 21-channel EEG recordings in 36 children (mean age, 22 months; range, 6 days to 69 months) with congenital heart disease. Bipolar EEG derivations were analyzed visually for rhythmic spindle activity based on morphology, frequency, duration, and amplitude. Linear regression analysis for duration, frequency, and amplitude versus rectal temperature was performed in each individual. Spindle activity was observed in 17 children (16 children < 12 months of age). Progressive slowing of spindle frequency with decreasing rectal temperature was found (mean decrease, 0.54 +/- 0.31 Hz/ degrees C). Spindle duration increased on average by 0.69 +/- 0.39 second/ degrees C during cooling procedures. Spindle amplitude did not show any correlation to changes in rectal temperature. The current study demonstrates spindle activity during hypothermic cardiopulmonary bypass with temperature-dependent spindle modifications of frequency and duration. Although the temperature-dependent changes in this study confirm temperature coefficients of other EEG studies, the reasons for the clear age relationship and the "nature" of these spindles remain unknown.     

Effects of somatosensory deafferentation on spectral characteristics of the sensorimotor EEG in the adult cat

A quantitative assessment of the sensorimotor EEG before and after transection of the dorsal columns at either a high (C1 to C3) or low (C5 to T1) cervical level was undertaken in unrestrained, adult cats. Electroencephalographic signals recorded unilaterally from postcruciate cortex (A:23) at medial (L:2 to 5) and lateral (L: 10 to 12) sites were subjected to bandpass frequency analysis. The incidence of 12- to 15-Hz sleep spindles and sensorimotor rhythm (SMR) activity was evaluated in comparable pre/postlesion EEG segments. Frequency analyses focused on the distribution of voltage in four bands (4 to 7, 8 to 11, 12 to 15, and 18 to 23 Hz). The findings showed that dorsal column transections markedly altered EEG spectral distributions. Most consistently affected was 8- to 15-Hz activity which increased significantly over sites corresponding to peripheral receptive fields below the level of the lesions. Observed increases in sleep spindles and SMR activity contributed to this finding. In prelesion recordings, voltage in all bands increased progressively over the course of slow-wave sleep to REM onset. Abrupt peaks in 12- to 15-Hz and 18- to 23-Hz activity preceded the REM stage. Dorsal column transections eliminated this sequence of frequency/voltage changes. These findings were interpreted in terms of the release of intrinsic rhythmic discharge patterns over ventrobasal thalamocortical projection pathways.     

Reptilian waking EEG: slow waves,spindles and evoked potentials

Signal spectral analysis procedures were used to compute the power spectrum of Gallotia galloti lizards EEG at different (5–35°C) body temperatures. EEG power spectra were mainly characterized by a low frequency peak between 0.5 and 4 Hz which was present at the different body temperatures. A second spectral peak, corresponding to spindles of similar pattern to the sleep spindles of mammals, also appears in the spectra. The peak frequency of the spindles increased with the body temperature. Flash evoked potentials were characterized by a slow triphasic component upon which a spindle was superimposed, adopting a morphology similar to the K complexes of mammalian sleep. The characteristics of this EEG and evoked potentials support the hypothesis of homology between the waking state of the reptiles and the slow wave sleep of mammals.     

Studies on the effects of intrathalamically injected DADL and morphine on nociceptive thresholds and electroencephalographic activity: a thalamic delta receptor syndrome

Bilateral microinjections of DADL (D-Ala2-D-Leu5-enkephalin) and morphine were carried out in rats in a systematic fashion at histologically identified medial and lateral thalamic sites. DADL produced a dose-dependent (1.5-15.0 nmol), naloxone-reversible (1 mg/kg, i.p.) increase in the hot-plate (HP), tail-flick (TF) and catalepsy (CAT) response latencies with a predominance of activity occurring at lateral as opposed to medial thalamic sites. These effects were seen within 5 min of microinjection. At a significant number of sites, DADL precipitated convulsive seizure activity. Equimolar doses of morphine had a negligible effect on nociceptive indices and were not productive of seizures even at sites where DADL was found to be active. To further examine seizure activity, rats were prepared with bilateral frontal cortical electrodes and microinjected also at medial and lateral thalamic sites with equimolar doses of DADL and morphine (15 nmol). DADL was found to produce electrographically defined seizures unaccompanied by convulsive motor behavior (cataleptic seizures), as well as convulsive seizures. All animals in this group exhibiting analgesia and catalepsy had electrographic evidence of a seizure with markedly abnormal EEG tracings showing postictal spiking and changes in baseline frequency and amplitude. These seizures appeared to be naloxone-reversible. Morphine on the other hand was not productive of seizures, but did produce changes in electroencephalographic activity including spindle bursting, high-voltage slow-frequency activity as well as spiking. As noted, these changes were not associated with any effects on nociceptive measures.     

Life-span changes in EEG spectral amplitude, amplitude variability and mean frequency.

OBJECTIVES: The objectives were to assess life-span alterations in intrasubject variability of EEG spectral amplitudes and in amplitude and mean frequency computed from spectral amplitude profiles. METHODS: EEG was recorded from the central and occipital scalp of 222 healthy males aged 4 to 90 years. Amplitude spectral profiles derived from FFT procedures provided data for the computation of amplitude variability (ampCV), absolute and relative amplitude and mean frequency for each of five spectral bands. Analysis of variance, coefficient of correlation and t test were employed in data analyses. RESULTS: The ampCV measure did not provide direct evidence of age-related intrasubject changes in EEG frequency but was useful for indexing the presence of rhythmic EEG activity. Marked decreases in absolute amplitude occurred during childhood with little change thereafter. Age changes in relative amplitude were more complex and differed for slow and fast EEG activity. We also report that an algorithm frequently used to estimate mean frequency can introduce consistent bias into mean frequency computations under some conditions. CONCLUSIONS: Life-span changes in measured EEG characteristics were generally consistent with those from earlier studies. It is important that investigators validate and describe procedures used to determine mean frequency of EEG spectral data.     

High resolution study of sleep spindles.

OBJECTIVE: Universal high-resolution time-frequency parameterization of sleep EEG structures. METHODS: A new algorithm called Matching Pursuit was used for the decomposition of sleep EEG into waveforms chosen from a large and redundant set of functions. As a result all signal structures were parameterized in terms of their frequency, time occurrence, time span and energy. Slow wave activity and sleep spindles were identified according to neurophysiological criteria and various distributions describing their time evolution, topographical and frequency characteristics were constructed. RESULTS: Two types of sleep spindles of different topological and spectral properties were identified. High time-frequency resolution made possible separation of superimposed spindles. Cross-correlation between high- and low-frequency components of superimposed spindles revealed a fixed time-delay between them, the high-frequency component preceding the low-frequency one. CONCLUSION: The results of our study suggest that processes of generation of both types of sleep spindles are weakly coupled.