EEG effects of subcutaneous and intracerebroventricular injections of arginine vasopressin in the rat

Several studies have suggested that arginine vasopressin (AVP) may act centrally as a neurohormone or neuromodulator to produce electrophysiological and behavioral effects. However, there are few reports of EEG effects of AVP in unanesthetized, behaving animals. In the present study the EEG effects of "behaviorally relevant" subcutaneous (SC) doses of AVP (6 micrograms/kg) known to raise blood pressure were compared to "behaviorally relevant" intracerebroventricular (ICV) doses (0.1-1.0 ng) and multiple "toxic" ICV doses (1.0 microgram) of AVP. Central injections of toxic doses of AVP produced behavioral arrest, bodily barrel rolling, and EEG slowing, but did not induce electrographic signs of seizure activity. Comparison of the spectral characteristics of the EEG revealed some similarities in the distribution of power between SC and the 1.0 ng ICV dose; whereas ICV doses of 0.1 and 0.5 ng produced power distributions that were different from those seen following saline or SC doses of AVP. The similarities in EEG activity between SC injections and the 1.0 ng ICV dose suggest a common brain state may be induced by the two routes of administration in those dose ranges.

EEG spectra following phenytoin infusion in seizure patients

Diphenylhydantoin (DPH) kinetics were studied in five male patients with poorly controlled seizures. EEG recordings were taken on four of the patients immediately prior to and 30 minutes following a 60 minute i.v. infusion of phenytoin sodium. Mean phenytoin levels following post-infusion EEG recordings were 17.1 mg/L. Spectral analysis revealed that phenytoin produced a decrease in the variance of EEG spectral power as a function of time in frequencies between 8-18 Hz. This decrease in the variance of the time series of EEG spectra suggests increased EEG stability and may represent an electrographic marker of the anticonvulsant action of phenytoin.

Corticotropin releasing factor produces increases in brain excitability and convulsive seizures in rats

Corticotropin releasing factor (CRF) is a 41-residue peptide, capable of stimulating the secretion of corticotropin (ACTH)-like and beta-endorphin-like immunoreactivity from the adenohypophysis. Low doses of CRF (0.0015-0.15 nM) given intracerebroventricularly (i.c.v.) produced changes in electrographic activity suggestive of increased arousal. Higher doses of CRF (1.5-3.75 nM) induced, over a period of 3-7 h, electrographic and behavioral signs of seizure activity indistinguishable from those which occur following electrical 'kindling' of the amygdala.

Plasma measures of beta-endorphin/beta-lipotropin-like immunoreactivity in chronic pain syndrome and psychiatric subjects

This study compared basal concentrations of plasma beta-endorphin/beta-lipotropin-like immunoreactivity and dexamethasone suppression of cortisol in seven chronic pain patients, seven psychiatric disorder patients, and seven normal volunteers. Pain patients and psychiatric patients showed significantly higher basal concentrations of beta-endorphin/beta-lipotropin-like immunoreactivity compared to normal volunteers. Pain patients also had significantly higher beta-endorphin/beta-lipotropin-like immunoreactivity than psychiatric patients, even though there was no significant difference in severity of depressive symptomatology as assessed by Beck and Hamilton scores. Resistance to dexamethasone occurred in 57% of pain patients. These results may indicate that biological markers for depression occur in populations of chronic pain patients, or may reflect levels of central nervous system arousal in response to stress, pain, or nonaffective phenomena.

Amygdala kindling after ligation of the middle cerebral artery in the rat

Cerebral infarcts were produced in rats by ligation of the right or left middle cerebral artery. A significant increase in seizure threshold and in the number of days required to develop kindled seizures was found in rats stimulated in the amygdala contralateral to the infarct. However, no significant changes in threshold or kindling rates were found in animals kindled ipsilateral to the ligation. These results were found to be independent of whether the infarct was in the right or left cerebral cortex. These data suggest that contralateral frontoparietal cerebral infarct may have inhibitory influences on seizures originating from the amygdala.

The effect of single and repeated electroconvulsive shock (ECS) on locomotor activity in rats

Locomotor activity following administration of apomorphine (0.1 mg/kg), and amphetamine (1 mg/kg) was studied in rats receiving single and multiple electroconvulsive shock (ECS). Three groups of rats were utilized, one half of each group received sham treatment and the other half received either 1,5, or 10 daily ECS. Significant enhancement of the locomotor response to amphetamine, but not apomorphine, was seen in rats given repeated ECS as compared to controls. This study suggests that the number of ECS, is an important variable in ECS enhancement of locomotor response to amphetamine.

The effects of constant light on EEG and seizure activity in the epileptic baboon

The effects of a change from a standard photoperiod (12:12 LD, 45 fc) to that of constant low level illumination (LL, 5 fc) on electroencephalographic activity (EEG), photic seizures and urine cortisol excretion were investigated in the baboon Papio papio. Unlike the normal circadian cycle, in which maximal urine cortisol excretion occurred at 08.00 h and minimal at 20.00 h, rhythms in cortisol excretion were free running under constant light, shifting an average of 2 h/week toward an earlier time of day. The rhythms in seizure susceptibility and EEG spectral power, which were found to be roughly in phase with urine cortisol under conditions of 12:12 LD, were also altered. Average sensitivity to seizures was found to be increased throughout the 24h cycle, although no seizure responses were of the maximal severity obtained in 12:12 LD. A loss of rhythmicity and an overall decrease in total spectral power over the 1-60 c/sec range were observed in background EEG in the LL environment. An 'instability' in relative power within higher (15-30 c/sec) bands over time was also noted. These data suggesting loss of synchronizing cues may lead to disruption of background EEG and exacerbation of epileptic seizures.

Levonantradol potentiates the anticonvulsant effects of diazepam and valproic acid in the kindling model of epilepsy

The anticonvulsant effects of the cannabinoid derivative levonantradol and its ability to potentiate the anticonvulsant effects of diazepam and valproic acid were studied in rats with previously established amygdala-kindled seizures. Levonantradol administered in doses of 100 to 400 micrograms/kg did not block any components of the motor seizure. However, levonantradol did increase the latency of appearance of fully kindled seizures at the 400 micrograms/kg dose. Administration of diazepam at doses of 1 or 2 mg/kg or valproic acid at doses of 100 or 200 mg/kg produced seizure control as measured by a reduction in motor components of the seizure or a reduction in afterdischarge length or both. The anticonvulsant effects of diazepam and valproic acid were potentiated by administration of 100 microgram/kg levonantradol without apparent increases in sedation. Although the mechanism underlying this potentiation of the antiepileptic effects of valproic acid and diazepam remains unknown, levonantradol may have potential as adjunctive therapy in the treatment of complex partial seizures.

EEG and anticonvulsant effects of dipropylacetic acid and dipropylacetamide in the baboon Papio papio

The ability of dipropylacetic acid (DPA) and dipropylacetamide (DPM) to modify EEG and seizure activity was assessed in 4 female and 3 male Papio papio. Doses of 30-60 mg/kg of DPA given at intervals over an 8 h period produced blood levels of 19-44 micrograms/ml which were not protective against intermittent light stimulation (ILS). Administration of 150-200 mg/kg doses at intervals over a 36 h period produced blood levels greater than 150 micrograms/ml and were highly protective against ILS. Similar results were obtained following adminstration of DPM; however, DPM appeared to offer greater protection against ILS. A moderate amount of seizure control was obtained at blood levels of 60-91 micrograms/ml (DPA) and complete blockade occurred at levels greater than 100 micrograms/ml DPA. Background EEG changes were similar following either DPA or DPM and consisted of a striking increase in total spectral power with relative power changes in 10-20 c/sec range, the magnitude of which was related to blood levels of DPA. Both agents produced a quieting effect on behavior without severe depression.

Circadian periodicity of brain activity and urinary excretion in the epileptic baboon

A 24-H rhythm in the proclivity of the baboon Papio papio to exhibit a seizure response to intermittent light stimulation (ILS) has been uncovered. Seizure response to ILS was found to be greatest in the morning at about 0900 h, 2 h after lights on, and least severe in the evening at about 2000 h 1 h after lights off. Urine cortisol and potassium excretion rhythms followed the same pattern as seizure susceptibility and sodium rhythms were 3 or 4 delayed. Mean values for urine cortisol per 4 h ranged from 25 microgram/4 h at the maxima (0400 to 0800 h) to 2 microgram/4 h at the minima (2000 to 2400 h). Electrolyte rhythms ranged from 13 to 3 meq/4 h for potassium and 1 to 5 meq/4 h for sodium. Changes in electroencephalographic (EEG) activity also accompanied the change in urine cortisol and potassium, and seizure sensitivity, Changes in the EEG at the diurnal minima (2000 h) consisted of a decrease in slow waves concomitant with an increase in fast activity in the 18-25 Hz range,

The influence of cortisone on EEG and seizure activity in the baboon Papio papio

The ability of cortisone to modify EEG and seizure activity was investigated in the baboon, Papio papio. Acute intramuscular doses (0.5-4 mg/kg) caused a dose-dependent increase in seizure response to a flashing light stimulus. This increase in seizure response was apparent in both seizure duration and the spread of convulsive activity. Along with enhancement of seizures, cortisone was found to cause marked changes in the EEG, ranging from the appearance of interictal paroxysmal activity to alterations in spectral characteristics of the wave forms. Increases in slow waves appeared concomitant with a decrease in fast activity in the 18-25 c/sec range. Since previous studies have indicated that seizure proclivity in the Papio papio is maximal at the time of the day when cortisol excretion rates peak, these findings lend further evidence to the idea that corticosteroids may be involved in the thythmic variation of seizure activity in the baboon.