Wolfgang Haschke

Postnatal conditioning for spreading cortical depression in the rat brain.

The cerebral cortex of anaesthetised 2- to 12-day-old rats was superfused with artificial cerebrospinal fluid containing 100 mM acetate substituted for chloride to condition the brain for spreading depression (SD). After such superfusion, the earliest SD-like events were found at day 9 and full blown SD at day 10, whereas in the unconditioned brain the first SD occurred between days 12 and 15. Acetate conditioning of the cerebral cortex may be used to unmask neuronal and glial properties that are hidden in early stages of development.

Initiation of spreading depression can be blocked by transcortical polarization of rat cerebral cortex.

Spreading depression (SD) was elicited in urethane anesthetized rats by pricking the cortical gray matter with a needle. The SDs were monitored by recording changes of direct current (DC) potentials and changes of extracellular potassium concentrations ([K+]e). Simultaneous recordings were made at cortical depths of 400 microns and 1200 microns by an array of two double-barrelled electrodes, one served to measure DC the other contained an ion-sensitive resin. An additional DC microelectrode was inserted in the gray matter near the point of SD elicitation at a depth of about 400 microns. An epicortical Ag-AgCl wire electrode surrounding the recording site and a remote Ag-AgCl electrode penetrating the cortex in the contralateral hemisphere were used for polarizing DC currents. These currents were applied 5 min before elicitation of SD by a needle prick and were sustained for a period ending 3 min after SD. Cathodic polarization of cortical surface with intensities of 30 microA and higher blocked the SD completely. Lower intensities of polarizing currents (10 or 20 microA) had no effect. After ending polarizations normal SDs could be elicited. The polarizing and restitution effects were replicable in the same animal. The results suggest that longer lasting DC polarization of the cortex blocks initiation of SD but not propagation.

Activation state of the cortex could be changed by reinforcement of low-amplitude visual evoked potentials in rabbits

Visually evoked potentials (VEP) were recorded chronically from occipital cortex in awake rabbits. The VEP typically consisted of a triphasic response (positive deflection P60--negative deflection N205--positive deflection P450) that was followed by a late negative shift starting about 750 ms after the eliciting flash. After computation of a discriminating amplitude value (200 or 250 microV) the VEP were divided for comparison in high- and low-amplitude groups. Significant differences between these groups existed in amplitudes and latencies of the early VEP components. High-amplitude VEP were followed by larger late negative shifts and had significantly (P less than 0.01) earlier second positive deflections. In these high-amplitude cases, the EEG-baseline was more negative than in the low-amplitude VEP. In addition, we found a more synchronized background EEG in the low-amplitude VEP group. We conclude that different VEP amplitudes depended on different activation states of the cortex which could be changed by reinforcement.

Reevaluation - A Systematic Approach by Means of Event-Related Potentials (EPRs)

An attempt was made to analyse the processing of reafferent information in man. 25 Ss solved arithmetical tasks, marked the confidence with which they found out the result and got a weak electric shock in one part of the experiments when the result was wrong (negative feedback), in the other part when the result was correct (positive feedback). The ERPs differed markedly between control and test conditions. The ERP-shape is not only influenced by the feedback conditions; motivational characteristics of the Ss and the subjective probability of stimulus occurrence are important, too.

Activation-induced changes in evoked and slow brain potentials: Effects of cocaine in awake rabbit

To study the interrelations between event-related potentials and brain activation, evoked responses to visual stimulation registered from occipital cortex and hippocampal CA1 region were investigated in awake animals administered cocaine (2 mg/kg, SC) or saline. Administration of COCA resulted in longterm significant changes in heart and breathing rates and spontaneous EEG (desynchronization in the occipital cortex and slow rhythmic theta activity in the hippocampus), inhibition of animal responses to noxious electroshock stimuli and modification in different amplitudes of evoked responses (mainly in the cortex, the enhancement of negativity and bidirectional changes in late slow phase). Principally identical but more or less changes were observed in response to administration of saline. Obtained results are discussed in respect to their interrelations with the general activation organisms response and the modification of brain metabolism induced by cocaine in restrained rabbits.

ERP analysis of reafferent information processing during the performance of an arithmetical task

Reafferent information processing accomplished by distributed cerebral systems was studied by analysing concomitant event-related potentials (ERPs) elicited by weak electrical stimulation of the skin of the hand. The subjects were instructed to interpret this stimulus as feedback information indicating whether their solution of an arithmetical task was correct or not. ERPs elicited by positive or negative feedback signals showed striking differences. ERPs were also influenced by the subjects confidence in the correctness of the solution, while probability of stimulus occurrence was less important in the design. Neurophysiological implications of ERP-disclosed influences on feedback processing are discussed.

Transcortical Polarization in Rat Inhibits Spreading Depression

In cerebral cortex of rats single spreading depressions (SD) were elicited by a slight needle prick. SDs were monitored by recording changes of direct current (DC) potential via an array of four glass microelectrodes providing a simultaneous depth profile. Using an epicortical Ag-AgCl wire electrode surrounding the recording site and a contralateral Ag-AgCl electrode penetrating the whole grey matter, a polarization current was applied starting 5 min before and ending 3 min after eliciting a SD. By anodic polarization of the cortical surface with intensities of 10 to 20 microA the SD was blocked in the whole grey matter. Restitution of SD in course and amplitudes was found only 45 min to 60 min after ending the polarization. Cathodic polarization of the cortical surface resulted in similar effects. Both polarizing and restitution effects were replicable in the same animal. The results are relevant for further investigations to discover the particular role of glial cells in regulation of extracellular potassium concentration during SD.

Changes of Slow Brain Potential Shifts Following Failure

The degree to which failure causes performance decrements or facilitates performance is of crucial practical importance. In this chapter we will report some neurophysiological data exploring the extent to which personality dispositions related to the ability of coping with failure are associated with specific slow brain potential shifts (SPS). We are specifically interested in achievement motivation (Heckhausen, 1989) and state orientation (Kuhl, 1983) as two reliable predictors of individual differences in coping styles.

Activation-induced changes in evoked and slow brain potentials: Effect of cocaine in rabbits previously subchronically treated by cocaine

To study the type of adaptive modification (tolerance vs. sensitization) in different organisms indices following intermittent cocaine (COC) administrations, acute COC (2 mg/kg, SC)-induced changes in heart and breathing rate, response to increasing noxious stimulation, spontaneous EEG and event-related evoked and slow brain potentials (ERP) registered from the occipital cortex and hippocampal CA1 region were investigated in naive rabbits and one subchronically treated with COC (6 injections at a same dose). Tolerance developed for bradycardia, depression of noxious responsiveness, cortical desynchronization and increase of main components of cortical ERP, typical to acute COC, while the changes in breathing and hippocampal ERP were stable. These changes as well as a significant increase due to COC administrations of the basal values of an animals noxious responsiveness and increase in relative changes in main component of cortical ERP (N205) are considered as a consequence of adaptive changes in neurophysiological/neurochemical substrate accepting COC action and mediating phenomena tolerance-sensitization and dependence typical to the drug.

Medial Septal Area Modulation of Sustained Negative Shifts in Awake Rabbits

Experiments were performed on rabbits with chronically implanted Ag-AgCl electrodes over occipital cortex and chrome-nickel stimulation electrodes in the medial septal area. Visual evoked potentials (VEP) were elicited by means of randomly occurring flashes. After measuring the N1-amplitude of the VEPs, responses with N1-1 amplitudes below a previously determined discriminative value were reinforced by a weak footshock 1.5 S1 after the flash. In the group of high-amplitude VEP we found longer negative shifts than in the group of low-amplitude VEP, starting 600-700 ms after flash and lasting up to the end of the observed time range. The stimulation of medial septal area (0.5 mA, 6 imp/s) during the normal flash application led to a delay of the maximum of this negative shift which returned now to baseline within the observed range. The amplitude of these sustained negative shifts was larger during septal stimulation. Larger negative shifts followed high-amplitude VEP than the low-amplitude ones. Repetition of usual flash application without septal stimulation after a 10 min break turned the negative shift to normal. After electrolytic destruction of medial septal area this late negative shift vanished without any restitution.