Midazolam suppresses spike-and-wave rhythm accompanying three different models of epileptic seizures

The action of a water-soluble benzodiazepine midazolam (0.1 and 1 mg/kg i.p.) was tested against three models of spike-and-wave rhythm in rats: rhythmic metrazol activity (a model of human absence seizures), minimal metrazol seizures, and epileptic afterdischarges induced by low-frequency cortical stimulation (probably models of human myoclonic seizures). Midazolam was able to reduce spike-and-wave activity in all three models, but there were quantitative differences: the lower dose was effective only against rhythmic metrazol activity, but its action against two other models was negligible, whereas the higher dose of midazolam resulted in significant effects in all three models. These quantitative differences are not sufficient to prove our hypothesis that the spike-and-wave rhythm represents different phenomena in various models. A spread of epileptic activity into brain structures other than the thalamocortical system determines the type of epileptic seizures.     

Influence of phenobarbital on ECoG phenomena induced by metrazol in rats during ontogenesis.

Effect of phenobarbital (PhB, 20 and/or 40 mg/kg) on epileptic ECoG phenomena induced by metrazol was studied in acute experiments in rats aged 7, 12, 18, 25 and 90 days. Fractionated administration of metrazol (20 mg/kg i.p. each 300 s) was used to quantify the effects of PhB. First signs of metrazol action (sharp elements and/or rhythmic metrazol activity) were not reliably influenced by PhB. On the contrary, the latency of the first EEG seizures as well as of the first generalized EEG seizures was prolonged and thus a dose necessary for their elicitation was increased in all age groups. These differences reached statistical significance in 12-, 18- and 25-day-old rats. A lack of effect of PhB against the rhythmic metrazol activity supports the adequacy of this activity as a model of human absences. Differences between the development of antiepileptic and hypnotic effects of PhB (described earlier) suggest two different mechanisms of action.     

Influence of propranolol on rhythmic electrocorticographic activity induced by metrazol in rats

Influence of propranolol (5 mg/kg i.p.) on rhythmic metrazol activity (RMA) was studied in 11 male albino rats with chronically implanted cortical as well as subcortical (thalamic ventrobasal complex and dorsal hippocampus) electrodes. Metrazol was injected subcutaneously at a low dose of 30 mg/kg. Another group of five rats was used to study the action of propranolol on spontaneously appearing episodes of rhythmic spikes as well as on vigilance. The incidence of both rhythmic metrazol activity and episodes was significantly increased by propranolol. The latency to the first burst of rhythmic metrazol activity and to the maximum of its incidence was significantly shortened by propranolol. Propranolol also increased the incidence of relaxed wakefulness and delayed the appearance of slow wave sleep. The facilitation of RMA and spontaneous episodes could not be explained only by the increased amount of relaxed wakefulness, i.e. the vigilance level necessary for these two phenomena, because these changes did not coincide in time. In two animals, the combination of propranolol and metrazol led to the appearance of ictal activity which was sometimes accompanied by partial clonic convulsions. This phenomenon was never seen after metrazol alone (30 mg/kg s.c.) in control recordings. Propranolol was found to potentiate the possible models of human absences--spontaneous episodes, RMA and minimal clonic seizures.     

Rhythmic metrazol activity and cortical spreading depression

The incidence of segments of rhythmic metrazol activity (RMA) in cortical leads and in the thalamus and hippocampus was studied in acute experiments on nine male albino laboratory rats. First of all we studied activity after administering metrazol in an i.p. dose of 50 mg/kg, without any further treatment, and then, after a control recording, we induced cortical spreading depression and observed its effect on the incidence and synchronization of RMA in the individual leads. We came to the conclusion that the thalamus is incapable of isolated production of RMA. The cortex is able to produce RMA without participation by the studied structures of the specific thalamus and hippocampus; RMA probably originates in the cortex itself. Generalization is impaired, but not eliminated, by a cortical block. The hippocampus independently produces another type of rhythmic activity.     

Anticonvulsant effects of clonazepam on chemically induced convulsions

The anticonvulsant effects of two doses of clonazepam (CZP, Rivotril Roche, 0.1 and 1 mg/kg i.p.) were studied on model motor seizures induced by strychnine, bicuculline, 3-mercaptopropionic acid and metrazol in male laboratory rats (Wistar strain). In the first part the effects of different doses of the convulsants were investigated and for interaction with CZP doses were chosen after which more than 70% of the animals displayed generalized tonic-clonic convulsions (a grand mal seizure). Strychnine induced this type of seizure only: two doses (2 and 3 mg/kg s.c.) were used. CZP reduced the incidence of convulsions only after the larger dose, but plain solvent (propylene glycol, ethanol, water) was equally effective. The other substances first induced a seizure of minimal (mainly clonic) convulsions and only later a grand mal seizure. CZP was highly effective against bicuculline (3 mg/kg s.c.) and metrazol (100 mg/kg s.c.), but was less so against 3-mercaptopropionic acid. The effect on grand mal seizures was more pronounced in every case than on minimal seizures. The decisive role in the anticonvulsant effect of CZP is played by the mechanisms by which the convulsants induce epileptic manifestations. CZP is most effective against substances acting on the supramolecular complex GABA receptor (benzodiazepine receptor) chloride ionophore (bicuculline and probably metrazol).     

Influence of a new antiepileptic drug ORG 6370 on metrazol-induced seizures in rats during ontogenesis

The anticonvulsant action of a new antiepileptic drug ORG 6370 (Organon International B.V.) was studied in 217 male albino rats aged 7, 12, 18, 25 and 90 days. Epileptic phenomena induced by a subcutaneous injection of a 100 mg/kg dose of metrazol (isolated myoclonic jerk, minimal metrazol seizures and major, generalized tonic-clonic metrazol seizures) were used as a model. ORG 6370 did not influence myoclonic jerks or minimal metrazol seizures in those age groups where they were regularly elicited. In 12-day-old rats pretreatment with ORG 6370 led to the appearance of minimal metrazol seizures, a phenomenon rarely seen under control conditions. Major seizures were suppressed only in adult rats with a 20 mg/kg dose; on the other hand, ORG 6370 exhibited a selective action against the tonic phase of major seizures at all stages of development. The profile of action of ORG 6370 is almost the same as that of phenytoin.     

Disruptive effects of lateral hypothalamic stimulation on the lick-interrupt cycle in rats

Consummatory licking at a water spout was compared with licking at a dry spout maintained by electrical hypothalamic stimulation in the same rats. Both forms of licking, recorded photoelectrically, were maintained on a fixed ratio 8 schedule. Duration of reinforcement delivery was equated [300 ms]. A computer analysis of the temporal distribution of licks in each 1024 ms period from onset of reinforcement revealed that lateral hypothalamic stimulation decreased the occurrence of licking and disrupted the normally synchronous pattern of this behaviour. An analysis of the effects of delivering lateral hypothalamic stimulation contingent on water-maintained licking revealed that this effect of stimulation was clearly current-dependent. It is proposed that differences in licking rates maintained by water and by electrical hypothalamic stimulation, respectively, are due to response interference in the latter case. This interference effect is also proposed to be a major factor underlying higher reward thresholds for self-stimulation when licking is the operant response.     

Disturbance of motivated behavior in rats by epileptic afterdischarges

Nearly all epileptic seizures in patients are characterized by deranged consciousness. We started to study changes in motivated behavior (drinking in thirsty rats) as a possible analogue of compromised consciousness during and after epileptic seizures. Epileptic afterdischarges (ADs) were elicited by stimulation of the dorsal hippocampus and/or thalamus. Rats with implanted electrodes (deprived of water for 24 hours) were trained to lick water from a narrow tube. After pretraining ADs were elicited eight times in each animal and access to water was allowed during different phases of the AD. Stimulation did not affect licking if no AD was induced. If stimulation was successful, licking was stopped in nearly 70 % of stimulations and modified (biting the tube) in 30 %. Hippocampal ADs (characterized by serrated waves in the EEG and by an arrest of behavior with subsequent automatisms) completely blocked licking, signs of recovery appeared during the interval between the AD and recurrent AD and it progressed during recurrent ADs. Thalamic ADs abolished licking in 82% of cases and immediately after ADs normal licking reappeared in 49 % of these observations. Our results suggest that changes in motivated behavior might serve as an analogue of compromised human consciousness.     

Level of vigilance influences licking frequency in rats

In rats, the basic licking rhythm is generated by the central pattern generator located in the brainstem. Nevertheless, the licking frequency can be regulated between about 7.5 and 4 Hz by changing the drinking conditions. If these conditions are kept constant, the licking frequency can be influenced only to a minor degree by factors such as deprivation level, type of solution, and phase of the session. The aim of our study was to compare the licking frequency of rats at different levels of vigilance. We investigated spontaneous licking of rats by an electrical lick sensor; parallel behavior monitoring was also performed. Animals kept in a stable environment and showing a lower level of vigilance licked at a rate of 5.96 Hz, fully vigilant rats licked significantly more rapidly at a frequency 6.57 Hz. The fastest rate of licking (6.49 Hz and 6.82 Hz, respectively) was encountered in alert rats under a mild stress caused by the presence of a second animal in the experimental box. The vigilance level is thus another factor affecting the licking rate of rats that should be taken into account in behavioral licking experiments.     

Muscimol infusions in the brain stem reticular formation reversibly block ingestion in the awake rat

Previous studies have localized a central pattern generator for mastication to the midline pontomedullary reticular formation (RF) based on cortically induced ororhythmic movements. The present study determined whether this same substrate mediated licking responses evoked by more natural stimuli. Licking in the awake rat was initiated either through an appetitive response to sucrose presented in a bottle or by intraoral (IO) infusions. Oral rejection responses also were obtained by IO infusions of quinine hydrochloride. Small volumes of the GABA(A) agonist muscimol bilaterally infused into the lateral medullary RF significantly reduced licking and oral rejection responses measured electromyographically from the anterior digastric and geniohyoid muscles. Other than the decrement or absence of ororhythmic activity, rats appeared normal and actively approached and probed the water bottle. The suppression was reversible and returned to baseline within 3 h. In contrast, midline infusions of muscimol did not affect licking or rejection responses. We postulate that the lateral medullary RF is an essential final common path for ingestive consummatory responses.     

Influence of ethosuximide on metrazol-induced seizures during ontogenesis in rats

Effects of metrazol (pentylenetetrazole and ethosuximide were studied in male albino rats aged 7, 12, 18 and 90 days. The 18-day-old rats exhibited the highest sensitivity to metrazol. CD50s in the remaining three age groups were nearly the same. Ethosuximide was reliably effective against metrazol only in adult rats; in young animals it did not significantly change CD50s. Metrazol induced in ethosuximide-pretreated young rats either modified (long-lasting minimal seizures in 18-day-old animals) or new seizure patterns (minimal seizures in 7- and 12-day-old rats).     

Effects of melanin-concentrating hormone on licking microstructure and brief-access taste responses

The effects of intracerebroventricular application of melanin-concentrating hormone (MCH) on licking for sucrose, quinine hydrochloride (QHCl), and water solutions were evaluated in two experiments. In experiment 1, rats received 90-min access to sucrose and water solutions after MCH or vehicle microinjection to the third ventricle (3V). MCH increased intake largely through increases in the rate of licking early in the meal and in the mean duration of lick bursts, suggesting an effect on gustatory evaluation. Therefore, in experiment 2, brief access tests were used with a series of sucrose and QHCl concentrations to behaviorally isolate the effects of intracerebroventricular MCH on gustatory evaluation. MCH uniformly increased licking for all sucrose solutions, water, and weak concentrations of QHCl; however, it had no effect on licking for the strongest concentrations of QHCl, which were generally avoided under control conditions. Thus MCH did not produce nonspecific increases in oromotor activity, nor did it change the perceived intensity of the tastants. We conclude that MCH enhanced the gain of responses to normally accepted stimuli at a phase of processing after initial gustatory detection and after the decision to accept or reject the taste stimulus. A comparison of 3V NPY and MCH effects on licking microstructure indicated that these two peptides increased intake via dichotomous behavioral processes; although NPY suppressed measures associated with inhibitory feedback from the gut, MCH appeared instead to enhance measures associated with hedonic taste evaluation.     

Electrophysiological analysis of retrieval of conditioned taste aversion in rats. Unit activity changes in critical brain regions.

Gustatory discrimination testing shows that rats with an overtrained conditioned taste aversion (CTA) to isotonic LiCl stop salt intake after 1 to 2 licks at the LiCl spout and move to the adjacent water spout within 0.7 s. Activity of 526 neurones from the nucleus of the solitary tract, gustatory thalamus, gustatory cortex, lateral and ventromedial thalamus, and amygdala was recorded in naive or CTA trained rats during the above gustatory discrimination. Post-stimulus histograms (PSH) triggered by water or salt licks or by spout switching were plotted for single units. Population responses of various regions were obtained by integration of the statistically significant excitatory and inhibitory intervals in the individual PSHs. Lick related changes of unit activity were orserved in 52% and 65% of neurones in control and CTA trained rats, respectively. The CTA training increased the incidence of units in which salt licking influenced the activity less than water licking. Presentation of the aversive fluid induced inhibition of unit activity in the gustatory cortex, ventromedial hypothalamus, and amygdala and excitation in the lateral hypothalamus. The changes started 100 to 150 ms after spout switching and culminated 100 ms later. Activity of the solitary tract nucleus and gustatory thalamus was affected less consistently. The results indicate that the gustatory cortex, amygdala and hypothalamus participate in CTA retrieval but a more specific identification of the electrical correlates of memory readout and of drinking control was not possible.     

Anti-metrazol action of R 57720 during postnatal development in rats

The effects of an experimental antiepileptic drug R 57720 (Janssen Pharmaceutica) on metrazol-induced seizures were studied in rats aged 7, 12, 18, 25 and 90 days. R 57720 exhibited a marked dose-dependent anticonvulsant effect against major, generalized tonic-clonic seizures in all the age groups studied. Similar action on minimal metrazol seizures (mMS) was present in rats aged 18 days and more. In the two youngest groups where metrazol did not induce mMS under control conditions, the combination of the 5- and 10-mg/kg doses of R 57720 and metrazol led to the appearance of mMS, whereas mMS failed to appear after the highest dose of R 57720 used (20 mg/kg).     

Role of licking and concomitant changes in the excitability of nerve centers in the elaboration of gustatory information in rats

The mechanism of nervous control of licking was studied in the frame work of the electrophysiological analysis of conditioned taste aversion. The licking rhythm is so stable that the rats are unable to slow it down by 20 percent. If the solution which was previously used for establishing the conditioned taste aversion, appears in the drinking spout, the rat stops drinking after one or two licks. Analysis of temporal relationships between afferent and efferent impulse activity of licking shows that the comparison of gustatory signals with memory traces and the corresponding decision occurs within 80 to 120 ms after lick onset. Electrical stimulation of the hypothalamic centres through implanted electrodes has shown that the amplitude of evoked responses and the impairment of licking increases, in proportion to the delay between lick onset and stimulus application. Isolated discharges of epileptic foci in the frontal cortex and the hypothalamus cause an omission of one or several licks, without interfering with the activity of the licking generator.     

Role of the striatum in the influence of serotoninergic substances on the course of corazole seizures in rats]

The effect of 5-oxytryptophane (5-OT) and of parachlor-phenylalanine (pCPA) on the behaviouristic EEG manifestations of metrazol convulsions in electrostimulation and destruction of the striatum was studied. The effect of the preparations on the myoclonia and the spike-wave rhythm caused by metrazol did not largely depend on the functional condition of the corpus striatum. The capacity of 5-OT to facilitate, and of pCPA to aggravate the course of generalized convulsions and of the postconvulsive state became enhanced in stimulation and was eliminated after the destruction of the striatum.     

Analgesic activity of leaf extracts of Culcasia scandens P. Beauv

Analgesic activity of methanol leaf extract of C. scandens obtained by column chromatography and its graded solvent fractions, was evaluated in mice using acetic acid-induced abdominal writhing and formalin-induced paw licking. The extract and fractions significantly inhibited abdominal writhing and two phases of formalin-induced paw licking in mice, indicating that antinociceptive activity may involve inhibition of pain by peripheral and central mechanisms.     

Antiepileptic effects of amphetamine may require GABA (benzodiazepine) activity

Secondary components of visual evoked potentials (slow negative wave-SNW, and photically-evoked sensory afterdischarge-SAD) are known to be precursors of experimentally activated wave-spike discharges, similar to wave-spikes of petit mal epilepsy. Both SNW and SAD may be potently suppressed wither by amphetamine or GABAergic compounds such as diazepam and sodium valproate. A hypothesis was tested in the present study, that amphetamine-induced suppression of wave-spike discharges may require GABA-benzodiazepine activity for its expression.Electrocortical activity was recorded and averaged in unrestrained albino rats with chronically implanted epicortical electrodes. SNW and SAD obtained in habituated rats in the predrug state were potently suppressed by amphetamine (1 mg/kg, i.p.). Fifteen minutes after amphetamine injection, a challenging drug (metrazol, picrotoxin, convulsant benzodiazepine, Ro 5-3663, or imidazodiazepine, Ro 15-1788) was administered intraperitoneally. Subconvulsive doses of metrazol (10 mg/kg) reversed amphetamine suppression; imidazodiazepine (20 mg/kg) and picrotoxin (1.5 mg/kg) reliably opposed the SNW suppression; convulsant benzodiazepine, Ro 5-3663 (2 mg/kg), showed modest and nonsignificant effect in the same direction. It is proposed that the antiepileptic potency of amphetamine may be associated with its ability, apparently via modulatory effect of norepinephrine, to facilitate the activation of benzodiazepine-GABA receptors.     

水鹿的群体结构和活动节律分析

水鹿是我国二级重点保护野生动物。2016年5月到2017年5月,利用红外相机技术在四川鞍子河自然保护区的非盐井生境和盐井生境(盐场)对水鹿的群体结构、日活动节律及舔盐活动节律进行了研究。基于设置的108个红外相机,共收集到水鹿在非盐井区域的独立照片620张,盐井区域的独立照片401张。水鹿日活动节律在不同季节具有较大差异：春季日活动高峰出现在17:00~20:00;夏季无明显日活动高峰;秋季日活动高峰出现在17:00~19:00;冬季日活动高峰分别出现在08:00~10:00、17:00~19:00、23:00~02:00。舔盐活动高峰出现在22:00~04:00,雌雄个体舔盐活动节律大致相同(重叠指数Δ=0.738)。水鹿有单独舔盐和集群舔盐两种方式,其中单独舔盐出现频率较高(占总访问频次的57.6%);舔盐的群体一般大小为2~7只,但以2只的群体居多(占总访问频次的21.5%)。在非盐井区域和盐井区域独立照片中水鹿的雌雄出现比例分别为2.05:1和2.66:1,表明雌鹿可能更需要补充盐分。本研究结果为保护区内水鹿的保护管理提供了基础的科学依据。     

Larval release rhythms and tidal exchange in the estuarine mudprawn, Upogebia africana

The mudprawn, Upogebia africana is common in intertidal regions of many South African estuaries. The life cycle is complex, incorporating a marine phase of development during the larval stages. Breeding peaks are in summer and first-stage larvae are released into the plankton at night. Maximum release activity and export to the marine environment follow a semi-lunar cycle synchronized to the time when high water in the estuary is crepuscular. This occurs after peak spring tidal amplitude. Estuarine reinvasion by postlarvae is also nocturnal, and maximum return occurs after neap's when low water at sea occurs around sunset. Rhythmic cycles of larval export and postlarval estuarine reinvasion are therefore asynchronous during the lunar cycle and are best explained by the timing of the change in light intensity relative to high and low water respectively. If maximum activity rhythms of Stage 1 and postlarvae are independent of tidal amplitude, then timing of maximum release and reinvasion during the lunar cycle would alter as the time of sunset shifts between solstices. Much of southern Africa experiences a semi-arid type climate and most estuaries close off from the sea for varying periods owing to sandbar development across tidal inlets. Larvae do not metamorphose if trapped in estuaries and recruitment ceases. Thus, mudprawn populations are directly affected by tidal inlet dynamics. In extreme cases populations become locally extinct if inlets remain closed for extended periods.