Analysis of electrical brain waves in neurotoxicology: γ-hydroxybutyrate.

Advances in computer technology have allowed quantification of the electroencephalogram (EEG) and expansion of quantitative EEG (qEEG) analysis in neurophysiology, as well as clinical neurology, with great success. Among the variety of techniques in this field, frequency (spectral) analysis using Fast Fourier Transforms (FFT) provides a sensitive tool for time-course studies of different compounds acting on particular neurotransmitter systems. Studies presented here include Electrocorticogram (ECoG) analysis following exposure to a glutamic acid analogue - domoic acid (DOM), psychoactive indole alkaloid - ibogaine, as well as cocaine and gamma-hydroxybutyrate (GHB). The ECoG was recorded in conscious rats via a tether and swivel system. The EEG signal frequency analysis revealed an association between slow-wave EEG activity delta and theta and the type of behavioral seizures following DOM administration. Analyses of power spectra obtained in rats exposed to cocaine alone or after pretreatment with ibogaine indicated the contribution of the serotonergic system in ibogaine mediated response to cocaine (increased power in alpha(1) band). Ibogaine also lowered the threshold for cocaine-induced electrographic seizures (increased power in the low-frequency bands, delta and theta). Daily intraperitoneal administration of cocaine for two weeks was associated with a reduction in slow-wave ECoG activity 24 hrs following the last injection when compared with controls. Similar decreased cortical activity in low-frequency bands observed in chronic cocaine users has been associated with reduced metabolic activity in the frontal cortex. The FFT analyses of power spectra relative to baseline indicated a significant energy increase over all except beta(2) frequency bands following exposure to 400 and 800 mg/kg GHB. The EEG alterations detected in rats following exposure to GHB resemble absence seizures observed in human petit mal epilepsy. Spectral analysis of the EEG signals combined with behavioral observations may prove to be a useful approach in studying chronic exposure to drugs of abuse and treatment of drug dependence.

Application of electrophysiological method to study interactions between ibogaine and cocaine.

The psychoactive indole alkaloid, ibogaine (IBO), has been investigated for over a decade concerning its reported anti-addictive properties for opioids as well as psychomotor stimulants. The mechanism for the anti-addictive action of IBO is still unclear. IBO interactions with opioid, NMDA, nicotinic, adrenergic, and serotonergic receptor sites have been suggested. The involvement of the dopaminergic system in IBO action is well documented. Increased or decreased levels of dopamine (DA) in specific brain regions following IBO pretreatment have been seen concomitantly with increased or decreased motor activity after subsequent amphetamine or cocaine administration. In this report, in vivo electrophysiological measures were monitored in awake adult male rats in order to investigate alterations of the electrocorticogram (ECoG) resulting from interactions between IBO and cocaine (COC). Rats were implanted bilaterally with bipolar ECoG electrodes. They were either injected with saline, COC alone (20 mg/kg, i.p.) or IBO (50 mg/kg, i.p.) and COC 1 hr later. The concentrations of DA, 5-HT, and their metabolites DOPAC, HVA, and 5-HIAA were assessed in the caudate nucleus in separate groups of saline-, COC-, and IBO/COC-treated rats. An alpha1 power increase was observed within 10 min after COC injection, which lasted for less than 20 min. A desynchronization over alpha2 and both beta power bands was observed throughout the recording. In IBO/COC-treated rats, a significant increase in delta, theta, and alpha1 power occurred within 20 min after COC injection (p <0.05). This effect lasted for up to an hour. DA levels significantly increased after COC only and decreased after IBO administration. A further decrease in levels of DA was observed in IBO/COC-treated rats. DA turnover increased significantly after IBO alone but was not observed after IBO/COC treatment. The alterations in ECoG and neurotransmitter levels suggest a decreased response to COC following IBO pretreatment.

Bioassays of shortened duration for drugs: statistical implications.

Declining survival rates in rodent carcinogenesis bioassays have raised a concern that continuing the practice of terminating such studies at 24 months could result in too few live animals at termination for adequate pathological evaluation. One option for ensuring sufficient numbers of animals at the terminal sacrifice is to shorten the duration of the bioassay, but this approach is accompanied by a reduction in statistical power for detecting carcinogenic potential. The present study was conducted to evaluate the loss of power associated with early termination. Data from drug studies in rats were used to formulate biologically based dose-response models of carcinogenesis using the 2-stage clonal expansion model as a context. These dose-response models, which were chosen to represent 6 variations of the initiation-promotion-completion cancer model, were employed to generate a large number of representative bioassay data sets using Monte Carlo simulation techniques. For a variety of tumor dose-response trends, tumor lethality, and competing risk-survival rates, the power of age-adjusted statistical tests to assess the significance of carcinogenic potential was evaluated at 18 and 21 months, and compared to the power at the normal 24-month stopping time. The results showed that stopping at 18 months would reduce power to an unacceptable level for all 6 submodels of the 2-stage clonal expansion model, with the pure-promoter and pure-completer models being most adversely affected. For the 21-month stopping time, the results showed that, unless pure promotion can be ruled out a priori as a potential carcinogenic mode of action, the loss of power is too great to warrant early stopping.

Alteration of electroencephalogram and monoamine concentrations in rat brain following ibogaine treatment.

Ibogaine (IBO) is a psychoactive indole alkaloid that has antiaddictive properties. However, treatment with IBO may lead to neurotoxicity, since IBO and its metabolites interact persistently with many neurotransmitter systems. Here, we recorded cortical electroencephalogram (EEG) signals from rats anesthetized with isoflurane. The heart rate (HR) was monitored via electrocardiogram (EKG) electrodes. After the baseline EEG was recorded, rats received one intraperitoneal (i.p.) dose of 50 mg/kg IBO. EEG signals were recorded for 2 hr. Rats were then sacrificed and brains dissected into frontal cortex (FC), caudate nucleus (CN), hippocampus (HIP), and brain stem (BS). The level of dopamine (DA), serotonin (5-HT), and their metabolites were determined by high-performance liquid chromatography with electrochemical detection (HPLC-ECD). Compared with baseline, a decrease in HR immediately after IBO injection and a decrease in delta, theta, alpha and beta power spectra frequency bands (1-4, 4-8, 8-13, 13-32 Hz) during the first 30 min after IBO administration was observed. EEG recovered within the next 15 min. In CN, the level of DA decreased and DA turnover rate increased significantly. The levels of 5-HT increased in FC. The pattern of EKG AND EEG response to IBO may be due to multiple receptor interactions of IBO.

Time-varying wall stress: an index of ventricular vascular coupling.

Previous work in the isolated heart and intact circulation has suggested that the relationship between wall stress and time during left ventricular (LV) ejection is linear and that the slope, which will be referred to as time-varying wall stress, increases in response to augmentation in afterload. However, the etiology of the increase in slope has not been determined in an intact animal. Magnetic resonance imaging coupled with high-fidelity LV pressure measurement using a nonferrous catheter-tip manometer generates a detailed assessment of wall stress in an animal model where the thorax and pericardium have never been disturbed. Accordingly, six anesthetized dogs were studied during autonomic blockade with atropine and propranolol during angiotensin infusion, producing three widely disparate left ventricular systolic pressures (87 +/- 7 vs. 124 +/- 13 vs. 152 +/- 10 mmHg, P less than 0.001). Time-varying wall stress did not change from low to medium load (-42.4 +/- 9.5 to -27.3 +/- 22.3 g.cm-2.ms-1) but increased significantly at high load (-21.7 +/- 14.9 g.cm-2.ms-1, P less than 0.05). Analysis of the relative contribution of pressure, chamber radius, wall thickness, and long-axis dimension to the changes in time-varying wall stress demonstrated only the pressure component to change its relative contribution at medium (P less than 0.001) and high load (P less than 0.001). Therefore, we conclude that the increase in time-varying wall stress results from augmentation of pressure in the latter one-half of systole that is incompletely offset by shortening and wall thickening.(ABSTRACT TRUNCATED AT 250 WORDS)

Epstein-Barr virus transformation of B lymphocytes from IgA nephropathy patients and first-degree relatives results in increased immunoglobulin synthesis not restricted to IgA.

In order to study B-cell activation patterns independent of T-cell regulation in patients with IgA nephropathy (IgAN), peripheral blood mononuclear cells from 67 patients with IgAN, 15 first-degree relatives of patients with familial disease, and 13 normal controls were transformed with Epstein-Barr virus (EBV). Culture supernatants of these transformed cells were assayed for levels of IgG, IgA, and IgM, and results obtained on the three populations were compared. EBV-transformed cells of IgAN patients, as well as the population of first-degree relatives, secreted significantly elevated levels of all three isotypes as compared with the normal controls. However, in comparing ratios of secreted isotypes, it was determined that more IgA relative to IgG and IgM was synthesized by cells of these two populations as compared with the normal controls. Our results imply that (1) the population of B cells susceptible to EBV activation is increased in IgAN patients; (2) this population of "activatable" B lymphocytes is polyclonal and not restricted to the IgA class; and (3) even though there may be a primary B-cell abnormality in IgAN, an additional defect(s) is probably operative in the pathogenesis, since cells of clinically unaffected relatives behaved in a pattern similar to that of patients.