PubMed Health⌕ Search

Biomedical subjects

H Szeto

Publications and source records attributed to H Szeto.

6 recordsLinked to original sources
PubMed1993

EEG changes with different levels of morphine self-administration.

Rats with chronically implanted jugular catheters and cortical EEG electrodes were allowed 24 hr per day access to morphine infusions (30 micrograms/kg) contingent on lever-pressing. Yoked control subjects received the same number and pattern of infusions as contingent subjects in an adjacent cage. Six subjects were studied, with data analyzed over 84 days of contingent and 63 days of yoked control (noncontingent) treatment. Self-administration rates were positively correlated with previous exposure to morphine. EEG total power was reduced in both contingent and yoked subjects during periods of self-administration. Averaging of trends in EEG power over time across multiple episodes of self-administration showed a greater reduction in power for contingent subjects that preceded the majority of morphine infusions. Desynchronization (diminished EEG amplitude) for contingent subjects at the onset of self-administration is probably related to lever-pressing activity. Ultradian describes biological rhythms in which the duration of one cycle (period) ranges from several minutes to values less than 24 hr. In both contingent and yoked subjects at intermediate or high levels of self-administration, increases occurred in the period and amplitude of ultradian cycles in EEG total power. Responsiveness to the light-dark cycle was also diminished at these levels of self-administration. In conclusion, morphine self-administration at intermediate or high levels disrupts both diurnal and ultradian rhythms in EEG total power for both contingent and yoked subjects. The ultradian EEG pattern associated with greater levels of morphine self-administration resembles diminished variation in EEG power that occurs normally during the inactive rest phase of the diurnal cycle.

Analysis of Variance↗
PubMed1992

Diurnal variation in continuous measures of the rat EEG power spectra.

EEG measures that vary on a continuous scale, without separating behavior into discrete states, may complement sleep staging as a means of characterizing diurnal variation in level of arousal. The object of the present study was to evaluate diurnal variation in the EEG power spectrum averaged independently of sleep state, and to determine which parameters best reflect this variation. The EEG from rats maintained with chronic cortical electrodes was continuously digitized at 256 Hz, and power spectra computed by fast Fourier transformation every four seconds. Artifact-free spectra occurring over one-hour periods were averaged. Spectral edge, calculated from 66 percent of the area of spectra, and relative power in delta and theta band-widths derived from averaged spectra vary in a consistent and highly significant diurnal pattern. The trend of relative delta power over the daytime, inactive period (when sleep occurs in nocturnal rodents) resembles that seen in human subjects during sleep, with peak levels occurring at the onset, followed by a steady decline during remaining hours of the daytime rest period.

Animals↗
PubMed1991

Naloxone causes a dose-dependent increase in total power and delta wave activity in the EEG of opioid-naive rats.

We studied the effect of opioid blockade with naloxone on the EEG of rats maintained chronically with i.v. catheters and cortical electrodes. EEG was analyzed on line by fast fourier transform, and drug was given as bolus injections during nighttime, active periods. Naloxone caused increases in EEG amplitude, reflected as increased total spectral power, for 60 to 90 min after injections. Power was increased primarily in the delta bandwidth, but spindles of large amplitude theta activity also occurred. An inverted "U" shaped dose-response relationship was obtained, with 1.0 mg/kg being the most effective dose. The appearance of enhanced slow wave activity in the EEG after blockade of opioid receptors suggests that endogenous opioid peptides may play a role in maintaining arousal during active periods in the rat.

Animals↗
PubMed1990

Altered diurnal pattern of arousal following naloxone administration in opioid-naive rats.

Heightened arousal occurring in response to physical or psychological stressors in associated with increased levels of endogenous opioid peptides in peripheral circulation and at binding sites in the central nervous system. When administered as a series of bolus injections during active periods, the opioid antagonist naloxone increased delta wave activity and total spectral power in the EEG of opioid-naive rats. A single 1.0 mg/kg injection of naloxone had a similar effect when given at the onset of night-time active periods, but not if administered during the day when rats are normally inactive. These results are consistent with a diminished level of arousal following blockade of endogenous opioid activity, and suggest an excitatory effect of opioid peptides in certain behavioral settings.

Animals↗