Kappa-opioid receptor changes and neurophysiological alterations during cerebral ischemia in rabbits

Endogenous opioids have been shown to produce beneficial effects in experimental stroke. To evaluate both neurophysiological and biochemical parameters, we induced massive cerebral ischemia in 11 rabbits according to the method standardized in our laboratory, using microspheres injected through the internal carotid artery. Binding studies were performed in the 11 embolized, in nine control, and in five sham-operated rabbits using the appropriate concentration of [3H]dynorphin A (1-8). Neurophysiological parameters were evaluated under baseline conditions and 1 hour after embolization, surgical preparation, or sham operation in 17 rabbits. Comparison of visual readings of the electroencephalograms and analyses of the quantified electroencephalograms under baseline conditions and after embolization indicated a marked and statistically significant (p less than 0.01) increase in bilateral delta activity; histologic examination confirmed bilateral brain edema. Binding studies on kappa-opioid receptors indicate that 1 hour after embolization there were significantly more (28%) kappa-opioid receptors (Bmax) in six embolized rabbits than in five sham-operated animals. No significant changes were observed in the affinity parameters, particularly in the dissociation constant (Kd). Our results indicate a role for endogenous dynorphin peptides in the pathogenesis of stroke.

[Spontaneous platelet aggregation after experimental focal ischemia in the rabbit. "Sensitivity", "specificity" and value of the test used]

Within the framework of an investigation at present under way at the Neurological Clinic of Pavia on experimental focal ischaemia, the peculiarities of platelet aggregation observed, have led to a more accurate assessment of both the phenomenon itself and the validity of the method used. In a group of 30 rabbits (17 of them submitted to embolization by means of microspheres introduced into the carotid and 13 used as controls), biohumoral electrical and histological parameters were examined. The spontaneous platelet aggregation test proved significantly related to the extent of changes taking place, as measured by PDS levels and QEEG "delta" activity (respectively, P less than 0.005 and P less than 0.05). Platelet aggregation, in relation to the occurrence or absence of focal ischaemia, revealed a "sensitivity" of 80% and a "specificity" of 92.3%. When not only the onset of but also the increase in aggregation is taken into account, the "sensitivity" figure appears to go up to 93.3%. Endothelial damage and "cascade" platelet aggregation appeared to be a prerequisite for the occurrence of the changes found. In these changes, the pathogenetic role of the regional vasospasm as opposed to mere mechanical obstruction seems to be confirmed. On the basis of these findings, it is concluded that the identification of spontaneous platelet aggregation using K. Breddin's method and its quantification based on Born's turbidimetric principle, may be usefully employed to assess the risk factor constituted by an abnormal tendency to platelet hyperaggregation.

Synchronization of the EEG and sedation induced by neuroleptics depend upon blockade of both D1 and D2 dopamine receptors

Blockade of dopamine (DA) receptors by neuroleptics tends to produce sedation, as shown by increased sleeping time, reduction of the arousal response to sensory stimuli and slowing of the electrical (EEG) activity of the brain. The EEG and behavioural effects of the selective compounds, SCH 23390 and raclopride, which block either D1 or D2 receptor subtypes, respectively were evaluated. Groups of rabbits were prepared for the measurement of EEG activity (neocortex and hippocampus). The EEG was analyzed visually and by spectral power analysis. Gross behaviour was also observed. The D1 antagonist, SCH 23390, by itself (0.03-0.3 mg/kg i.v.) produced small changes in the EEG and no evidence of sedation. Periods of slow waves occurred sporadically. Computerized EEG analysis showed moderate increases of total power density. The D2 receptor blocker, raclopride, alone (1-3 mg/kg i.v.) produced changes of the activity of the EEG, mostly, short periods of slow waves and slight increases of total power. No sedation was noted. Although both selective antagonists were studied at larger doses than those minimally effective, they produced slight EEG and behavioural changes which were not comparable with the marked actions produced by classical neuroleptics, such as haloperidol. However, when raclopride (1 mg/kg) was given after treatment with SCH 23390 (0.03 mg/kg) there was a marked synchronized activity in the EEG, associated with a state of sedation and diminished responsiveness to sensory stimuli. The data indicate that EEG synchronization and sedation, classically associated with treatment with neuroleptics, do not depend upon the selective blockade of either D1 or D2 receptors but, instead, require concurrent blockade of both subtypes of receptor.

Quantified EEG, somatosensory evoked potentials and cerebral blood flow in monitoring experimental brain ischemia

Cerebral ischemic lesions were induced in rabbits through internal carotid artery embolization by means of microspheres. Different models of stroke ranging from single focal cortical lesion to massive bilateral brain edema were reproduced and monitored up to the 24th hour by electroencephalogram (EEG and QEEG), somatosensory evoked potentials (SEPs), cerebral blood flow (CBF), platelet aggregation. The site and extent of the lesions were verified by histological examinations. Results obtained and physiopathological implications are discussed.

Influence of L-5-hydroxytryptophan and DL-p-chlorophenylalanine on neurophysiological profiles of serotonin reuptake inhibitors in rabbits

In a previous study we noted that some drugs, which exert their action by inhibiting serotonin (5-HT) reuptake, caused different EEGraphic, behavioural and autonomic patterns. These drugs (Alaproclate, Citalopram, Fluoxetine, Fluvoxamine, Indalpine, Zimelidine) have now been studied in two groups of animals pretreated with L-5-hydroxytryptophan (L-5-HTP), the 5-HT precursor, and with DL-p-chlorophenylalanine (PCPA), a 5-HT depletor. The administration of 5-HT reuptake inhibitors, after pretreatment with L-5-HTP, caused homogeneous changes, i.e. EEG cortical desynchronization and behavioural serotonergic syndrome. No significant modifications of the parameters examined were observed in the animals of the second group (pretreated with PCPA). The possible mechanisms of action of these drugs and some aspects of the role of serotonin in the central nervous system are discussed.

Neurophysiological changes induced by 5-HT reuptake inhibitors in rabbits

The EEGraphic, behavioural and autonomic changes induced by the administration of some inhibitors of serotonin (5-HT) reuptake were evaluated in the rabbit. The drugs examined were: Alaproclate (Ala), Citalopram (Cit), Fluoxetine (Fluo), Fluvoxamine (Fluvo), Indalpine (Ind), Zimelidine (Zim). It seems that all these drugs would act exclusively or prevalently on 5-HT uptake. The changes of the parameters studied were not homogeneous. Some of these drugs (Cit, Zim) induced an EEGraphic and behavioural "arousal" pattern, others (Fluo, Fluvo) a "slow wave sleep" one, others (Ala, Ind) a biphasic one (alteration of the two above-mentioned patterns). The possible hypotheses subtending these data are discussed.

Neuropharmacological profile of ketanserin

Eegraphic, behavioural, autonomic changes were studied in rabbits, after intravenous (i.v.) administration of L-5-hydroxytryptophan (L-5-HTP) and intracerebroventricular (i.c.v.) administration of ketanserin. The cerebral electrical activity on cortex and Cornu Ammonis dorsale (CAd) was evaluated by means of quantitative EEG analysis. The two drugs induced specific changes in all the parameters examined. L-5-HTP caused stereotyped movements typical of the serotoninergic syndrome and EEG "arousal" pattern. Ketanserin did not induce any behavioural change; quantitative EEG analysis showed an increase in those parameters typical of "slow sleep" pattern. The changes caused in guinea pigs by pretreatment with ketanserin, in the experimental model of myoclonus induced by L-5-HTP, were investigated. In the present study the possible mechanisms of action which subtend these results are discussed.

Synchronizing EEG effect of mianserin

The AA. report on the eegraphic, behavioral and neurovegetative effects caused by the i.v. administration of mianserin, in the rabbit. This substances induces behavioral sedation and EEG synchronization. In addition, these changes are partially reinforced with L-5-hydroxytryptophan (L-5HTP) and inhibited by pretreatment with DL-p-chlorophenylalanine (PCPA). In the light of these data, the AA. discuss the possible interactions between mianserin and neurotransmitter systems, particularly the serotoninergic one.

Behavioral and eegraphic changes induced by dopaminergic antidepressants in rabbits

Nomifensine, Bupropion and Amineptine, "second generation" antidepressants with dopaminergic effects, were studied in the rabbit with special regard to their action on somatic and autonomic behavior, and cerebral electrical activity. All three drugs induced an "alarm" reaction and typical dopaminergic behavioral responses including sniffing, jumping and chewing. Mydriasis was also observed especially at high dose levels. EEG showed an arousal pattern for each of these drugs. A marked increase in the hippocampal spiking resulted from the i.v. administration of 15 mg/kg of Bupropion.

Centrally administered N-terminal fragments of ACTH (1-10, 4-10, 4-9) display convulsant properties in rabbits

Electroencephalographic and behavioral effects of the following ACTH fragments: 1-4, 4-9, 4-11, 1-10, 4-10, 1-13, 1-17 and 1-24 were studied in rabbits. Sequences 4-9, 1-10 and 4-10 displayed some epileptic properties, i.e., they induced epileptic seizures (only electrographic or also behavioral) or increased hippocampal spiking. The 4-9 sequence seemed to be the common sequence responsible for these proconvulsant effects. The possible involvement of the enkephalinergic system is discussed.

EEG profile of the anticonvulsant action of viloxazine in the rabbit

The intravenous administration of the bicyclic antidepressant viloxazine, 0.5-2 mg/kg in rabbits, caused changes in the EEG profile with increased synchronous activity and shorter duration of the hippocampal afterdischarge following electrical stimulation. In animals exhibiting spontaneous epileptiform discharges, the injection of 1-2 mg/kg viloxazine was associated with disappearance of the paroxysmal EEG pattern that was substituted by a synchronous low frequency activity. This study also provided evidence of non-interactive effects of viloxazine (1-2 mg/kg i.v.) and alcohol (0.6 g/kg i.v.) on the EEG of normal rabbits.

Centrally administered VIP increases spindle activity in unanaesthetized rabbits

The action of VIP on structures responsible for cerebral electrical activity has been investigated in unanesthetized rabbits. VIP was given by slow infusion or bolus into the mesencephalic ventricle or the carotid artery, and topically applied on the motor or visual cortex. Both intracerebroventricular and intracarotid administration induced an increase of spindle activity of the cortex and an inhibition of the strychnine-transmitted spikes. These findings suggest a possible inhibitory role for VIP on certain CNS activity.

Neuropeptides and cerebral electric activity in rabbits

The effects of some neuropeptides infused into the cerebral ventricles on the spontaneous cerebral electric activity were studied in unanasthetized rabbits. The following peptides were investigated: physalaemin, caerulein, bombesin, litorin (supplied by Farmitalia). The rabbits were prepared according to Monnier and Gangloff's [10] method in order to record the spontaneous cortical activity. Each of these substances affects the electroencephalographic (EEG) records in a specific and dose-related way. Bombesin induces a biphasic pattern (synchronization followed by a partial activation), litorin is partially activating and physalaemin brings about a marked desynchronization. In spite of the marked structural analogy between bombesin and litorin, their EEG effects differ.

Effects of naloxone on ethanol and acetaldehyde-induced electroencephalographic changes in rabbits

Rabbits treated with a single IV dose of ethanol, 0.6 g/kg, exhibited rapid EEG synchronization and behavioral changes that were reversed and, in part, prevented by the opiate antagonist, naloxone, 40 micrograms/kg. The continuous intracerebroventricular infusion of acetaldehyde, 10 or 120 micrograms/min. caused biphasic changes with EEG activation and severe bradycardia followed by overt synchrony during the post-infusion period. The results of the present study provide further evidence for the ability of naloxone to counteract some acute effects of ethanol. Moreover, they do not support a role of acetaldehyde itself as mediator of EEG changes associated with mild alcohol intoxication.

Electroencephalographic effects of two short chain ACTH analogues

The effects of two short chain ACTH analogues, tetracosactide 1-24, eptadecapeptide 1-17, on EEG, behaviour and temperature of the rabbit are studied. The behaviour and temperature effects of two compounds are quite similar. The EEG synchronizing action is more evident when tetracosactide 1-24 is administered. This fact suggests that the aminoacids 18-24 might be important in affecting electric cerebral activity.

Lisuride and cerebral electrical activity in the rabbit

This study was meant to investigate the action of lisuride hydrogen maleate on somatic and visceral behaviour, and on cerebral electrical activity. With regard to the cortical and deep components of electrical activity, we recorded arousal and, at times, the onset of epileptic activity, mainly from the rhinencephalic area and sometimes spreading to other cerebral structures. We also report the results obtained in rabbits treated acutely and chronically by us with neuroleptics.

Behavioral and EEG effects of synthetic enkephalin analogue (FK 33-824)

The behavioral and eeg changes induced by i.c.v. administration of FK 33-824, an active synthetic met-enkephalin analogue, were studied. The Monnier and Gangloff stereotaxic method was used in order to record cortical and deep structures. The effects of an opiate antagonist (naloxone) were examined. The aim of this research was to verify two hypotheses: whether or not there were any relationships between sedation state and eeg findings, and if any interactions could be detected between FK 33-824 and serotoninergic mechanisms.

Antagonism between dopaminergic and neuroleptic drugs. I. Acute administration

In this paper we report our results concerning the antagonism between dopaminergic (bromocriptine, apomorphine, piribedil) and neuroleptic (haloperidol, chlorpromazine, reserpine, clotiapine) drugs on the eeg and behaviour of rabbits. The Monnier and Gangloff stereotaxic method was used in order to record cortical and deep structures. The use of neurophysiologic methods also enabled us to verify the magnitude and modes of the antagonism between the two types of drugs. Particularly, the dissociation between eeg and behavioural effects of this antagonism is discussed; this fact seems to confirm the hypothesis that dopaminergic drugs have a double point of attack in the CNS.

Antagonism between dopaminergic and neuroleptic drugs. II. Chronic administration

In this work the eeg and behavioural effects obtained after the administration of dopaminergic drugs (bromocriptine, apomorphine, piribedil) in rabbits chronically pretreated with haloperidol, chlorpromazine, clotiapine, are shown. The Monnier and Gangloff stereotaxic method was used. The aim of the study was to verify receptor supersensitivity by neurophysiologic methods. The neurophysiologic pattern of receptor supersensitivity induced by long-lasting treatment with neuroleptic drugs and its peculiarity are discussed.

Dopamine-agonist drugs and cerebral electrical activity in the rabbit

The eeg changes induced by acute administration in rabbits of dopamine-agonist drugs (bromocriptine, apomorphine, piribedil) were studied. We examined the spontaneous electric activity of cortex and deep structures, the electric excitability thresholds and the action of these drugs in "cerveau isolé" rabbit. Eeg findings were correlated with behavioural reactions. The modes of action and the probable double point of attack of the drugs at the CNS are discussed.

[Long-term treatment with lithium salts and cerebral electric activity. Experimental research]

An eeg study was carried out in rabbits to investigate the neurophysiological effects of chronic lithium clorure treatment. The Monnier and Gangloff's stereotaxic method was used for recording cortical and deep structure activity. Lithium clorure was administered i.p. at doses of 20 mg/Kg/die for 15-22 days (mean plasmatic levels: 0.04 mEq/l). The eeg changes consisted in synchronization of the cortical activity, slowing of the deep structure activity and increase of CAD spiking. The most interesting finding was the appearance of peculiar periodic spikes in the CAD and subcortical structures. A similar pattern has been previously described by us in rabbits treated with repeated ECT.