Fractal analysis of rat brain activity after injury.

With application of the Higuchi algorithm, fractal dimension (FD) values of the electrocortical activity of the rat parietal cerebral and paravermal cerebellar cortex were calculated, before and after unilateral discrete injury of the left parietal cortex. Immediately following the first acute injury, in a group of six rats, a reversible increase in mean FD was found at the left (ipsilateral side to the injury) cerebral cortex, from 1.38 to 1.59, and at the left cerebellar cortex from 1.51 to 1.73. In addition, an indication of plastic changes after repeated (third) injury was found as an irreversible increase in mean FD: 1.54 on the left and 1.48 on the right side of parietal cortex.

Pattern of glial fibrillary acidic protein expression following kainate-induced cerebellar lesion in rats.

In the present study glial fibrillary acidic protein (GFAP) expression was assessed following intravermian injection of kainic acid (KA) or physiological saline to adult rat cerebellum. After 2- to 30-day recovery period, free-floating sections cut with a microtome were obtained and were proccessed for immunocytochemistry against GFAP. Injection of both kainate and physiological saline elicited significant astrogliotic reaction, i.e. in the area around the lesion thick GFAP-positive Bergmann fibers with typical orientation appeared in the molecular and hypertrophied astrocytes abundantly appeared in the granular layer. However, following kainate intoxication lesion was not surrounded by typical demarcation glial scar during 30-day recovery period in contrast to the appearance of usual glial scar in the group injected with physiological saline, as early as 7-day postlesion. Preserved spatial organization of Bergmann fibers and the absence of typical demarcating glial scar after kainate-induced cerebellar lesion suggest distinct pattern of astrogliosis that presents an interesting model system to study the importance of glial scar in the recovery after ischemic brain insults.

Spatio-temporal changes in neurofilament proteins immunoreactivity following kainate-induced cerebellar lesion in rats.

1. Spatio-temporal changes in phosphorylated (pNFP) and nonphosphorylated (npNFP) neurofilament proteins were assessed immunocytochemicaly in adult rat cerebellum, 2-30 days following unilateral injection of kainic acid (KA) or physiological saline (s.c.). 2. Analysis of the staining intensity and pattern demonstrated that injection of both KA and physiological saline elicited significant and long-lasting increase of pNFP and npNFP immunoreactivity, at the ipsilateral, and to lesser extent at the contralateral side of lesion. 3. Kainate intoxication induced abundant expression of pNFP and npNFP in cerebellar white matter, as well as in all layers of perilesioned cortex. Higher pNFP expression was evidenced in the Purkinje cell layer, particularly at cell bodies, initial segments, and proximal dendrites, which normally do not contain pNFP. In addition, synaptophysin immunocytochemistry was used as a marker of synaptogenesis and plasticity. 4. Spatio-temporal pattern of NFP and synaptophysin expression suggests that perilesioned cortex undergoes dynamic changes following brain demage and possess a reparative capacity to abridge the consequences of brain trauma.

Interspike background activity in extracelullarly recorded Purkinje neurons: spectral analysis.

The aim of this study was to investigate the spectral characteristics of Purkinje cell interspike background activity caused by the occurrence of particular action potentials or by electrically induced enhancement of cerebellar inhibitory and excitatory input drive. Spontaneously active Purkinje neurons were extracellularly recorded in anesthetized rats before and after cessation of stimulation from the inferior olive (10) or locus coeruleus (LC). After A/D conversion (30 kHz), direct spectral analysis of extracted interspike background activity was done. Our results have shown that, in contrast to simple spikes, the occurrence of complex spikes induces changes in the spectra of interspike background activity. The different spectral changes of interspike background activity induced by LC and 10 stimulation also indicated the importance of this extracellularly recorded phenomenon.

Effect of early cortical lesion on the acute model of epilepsy.

The experiments were performed in order to investigate the sparing of function following early postnatal cortical lesion in the acute rat model of epilepsy. Sensorimotor cortex was unilaterally removed at 9 and 10 days of postnatal age in lesioned animals, while control animals were only sham operated (at the same early stage of life) or non-operated (before implantation of the electrodes). Seizure activity was recorded by means of electroencephalograms at adult stage of life induced by parenteral administration of penicillin (1,000,000 I.U./kg, i.p.). Our results showed that when the cortical lesion was performed in infancy (on the contrary to the lesion performed in adulthood) there was no prolongation of seizure activity in an acute model of epilepsy.

Effect of neurotoxin DSP4 on EEG power spectra in the rat acute model of epilepsy.

The effect of the adrenergic neurotoxin N-(chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) on electroencephalographic (EEG) activity was studied in the model of epilepsy induced by systemic application of penicillin (1,000,000 IU/kg, i.p). DSP4 (50 mg/kg, i.p.) was administrated to male Wistar rats, while the control animals were rats from the same litters. EEG activity was recorded in acute and chronic experiments 3 or 4 weeks after DSP4 treatment, before and after penicillin administration. Occasional locus coeruleus (LC) stimulation served as an electrophysiological test of DSP4 toxic effect. EEG power spectra in DSP4 treated animals showed a tendency to be greater in lower frequency bands than in controls before penicillin administration; there was almost no effect of electrical LC stimulation, regardless on penicillin treatment. In the model of epilepsy, the mean total EEG power spectra were greater in the period of 135-330 min after penicillin administration, as well as during 345-540 min, in DSP4 treated animals as compared to the controls. It seems that neurotoxin DSP4 is an optimal tool for studying the removal of LC influence in the acute model of epilepsy. It is also suggested that norepinephrine (NE) may have a modulatory role in the systemic penicillin epilepsy.

Changes in neuropeptide levels after brain damage in rats.

The physiological and pathophysiological roles of neuropeptides are still not clear. The aim of our study was to detect long lasting changes of vasoactive-intestinal peptide (VIP), somatostatin (SOM) and substance P (SP) contents in the rat cerebral cortex and hippocampus after brain lesion. The experiments were performed on groups of adult male Wistar rats. The first group consisted of animals with unilateral ablation of the sensorimotor cortex performed at the age of 60 days. The second group was a control one (rats of the same age but with an intact brain). Both groups of animals were sacrificed at the age of 90-105 days and radioimmunoassay was used to determine amounts of VIP, SOM and SP. The mean values of VIP levels were decreased significantly only in contralateral cortical areas, while there was an increase of SP in lesioned animals. Our results suggest that descrete changes in neuropeptide levels occur during restorative processes after brain lesion.

Amphetamine and haloperidol modulatory effects on Purkinje cell activity and on EEG power spectra in the acute rat model of epilepsy.

The modulation of cerebellar Purkinje cell activity and EEG from parietal cortex was studied in the rat model of epilepsy induced by penicillin under acute haloperidol and amphetamine treatment. The discharge pattern of Purkinje cells showed tendency towards inhibition and EEG power spectra increased after parenteral administration of penicillin (1000000 IU/kg, i.p.). Acute haloperidol treatment (1 mg/kg, i.p.), performed after the development of penicillin induced epileptic episodes, elicited a prominent excitation of Purkinje cell discharges associated with parallel increase in mean EEG power spectra. However, acute DL-amphetamine treatment induced marked suppression of Purkinje cell discharges as well as outstanding decrease of the mean EEG power spectra. These results indicate that cerebellar Purkinje cells may be important in the control of seizure activity and that noradrenergic influences are relevant.

Effect of cerebellar stimulation on EEG power spectra in the acute model of epilepsy.

Experiments were performed to investigate the effects of cerebellar stimulation on epilepsy induced by parenteral administration of penicillin, in rats without or with the lesion of sensorimotor cortex. There were no differences in the EEG activity of the same experimental animal after the first and subsequent penicillin treatments (at least 7 days later). The electrical stimulation (duration of 5-10 min) of the lateral cerebellar nucleus was applied repetitively 135-315 min after penicillin administration, when the EEG power spectra markedly increased. The cerebellar stimulation evoked the decrease of the mean total EEG power spectra, but the effects were temporary. The EEG power spectra were significantly lower (P < 0.05) during the period of 150-330 min after penicillin treatment in experimental sessions with applied cerebellar stimulation in comparison to the experimental sessions without such stimulation. The residual effects (if any) of cerebellar stimulation on the EEG activity in the later period, 345-600 after penicillin treatment were not significant (P > 0.05). Cerebellar stimulation had the same effect among unlesioned animals and animals with prior cortical lesion in the acute model of epilepsy.

The effect of cortical lesion on systemic penicillin epilepsy in rats.

There is a certain recovery of function following brain damage, due to neuronal plasticity. The experiments were performed in order to investigate the effects of cortical lesion on seizural activity in rats induced by systemic application of penicillin. The sensorimotor cortex was unilaterally removed in the lesioned animals, while the control animals were only sham operated or non-operated (before implantation of the electrodes). Seizural activity was recorded by means of electroencephalograms before and after penicillin treatment (1,000,000 I.U./kg, i.p). Testing of penicillin started at least 30 days after cortical lesion. Seizural activity was characterized by spike and wave complexes accompanied by vigilance reduction and sometimes by mild myoclonic jerks in both control and lesioned animals. The early period (about 2 h after penicillin administration) with appearance of the spike-wave discharges with relative increase of the mean total electroencephalogram powers as well as the succeeding period 2.5-5.5 h after penicillin administration) with maximum number of spike-wave discharges did not differ in the electroencephalogram of the control and lesioned animals. The late period of penicillin effect (from 6-11 h after penicillin administration) with frequent spike-wave discharges and still large mean total electroencephalogram powers was observed only in lesioned animals. It is concluded that a cortical lesion destabilizes the brain function in the rat model of epilepsy induced by parenteral administration of penicillin.

Activity of cat cerebellar neurons in penicillin epilepsy and amphetamine treatment.

The discharge pattern of cerebellar Purkinje cells and fastigial neurons was studied after acute amphetamine treatment in immobilized cats, as well as during generalized penicillin-induced epilepsy. There was a marked reversible decrease in spontaneous firing rate of Purkinje cells and an increase in spontaneous firing rate of fastigial neurons after acute d-1 amphetamine administration (5 mg/kg, s.c.). The discharge pattern of Purkinje cells showed tendency towards inhibition, while the fastigial neurons showed less clear tendency towards disinhibition in the course of epilepsy induced by parenteral administration of penicillin (400.000-500.000 I.U./kg, i.m.). Moreover, acute amphetamine treatment (5 mg/kg, s.c.) performed after the development of penicillin-induced epileptic episodes elicited a prominent suppression of Purkinje cell discharges associated with a parallel increase in discharges of fastigial neurons. These results suggest that the changes in discharge rate of cerebellar corticonuclear neurons induced by amphetamine contribute to suppression of seizural activity in the feline model of generalized epilepsy.

Effect of epidural spinal cord stimulation on the activity of lateral vestibular nucleus neurons in the cat.

The activity of neurons in Deiters' lateral vestibular nucleus was recorded in decerebrate cats before, during and after spinal cord stimulation. An almost equal number of units were inhibited and excited early during stimulation. Later during stimulation the majority of units was inhibited. Early after cessation of stimulation an ever larger number of units were inhibited to an even larger extent (for about 2 imp/s on the average). Later after stimulus cessation the predominant inhibitory effect could still be noted, as well as excitation in some units. The results could support the hypothesis that the inhibition of Deiters' neurons during and for some time after epidural cord stimulation may play a part in the decrease of limb spasticity. The mechanism of inhibitory and excitatory unitary responses, side effects during stimulation and differences between the experimental model and human state are discussed.