Effect of cannabidiol and of other Cannabis sativa compounds on hippocampal seizure discharges

The natural Cannabis sativa compounds, cannabidiol, cannabinol, ⁹- and ⁸-tetrahydrocannabinol, in that order of potency, decreased the susceptibility of rat dorsal hippocampus to seizure discharges caused by afferent stimulation. The drugs were effective following both intraperitoneal injection and topical application. They were more active, on a dose basis, than the well-known antiepileptic agents mysoline and diphenylhidantoin. Within the dose range effective in depressing hippocampal seizures, they had no effect on hippocampal evoked responses. This suggested that they might act by interfering with K⁺ release from hippocampal cells, which is known to be the causative factor in hippocampal seizures. This point was investigated using cannabidiol, which was found to effectively block the release of K⁺ from the hippocampus caused by afferent stimulation.With financial help from the Escola Paulista de Medicina, through a personal grant to one of us (I.I.), from the Consejo Nacional de Investigaciones Científicas y Técnicas of Argentina (grant N 3917), and from the Secretaría de Salud PÚblica de la Nación, Instituto Nacional de Farmacología of Argentina, through a special contract.     

A physiclogical difference in the hippocampus of rats with a low inborn learning ability

Rats with a low ability to learn conditioned avoidance responses in a shuttle-box were in-bred. After five or six generations, a fairly homogeneous population was obtained consisting of bad learners both in the shuttle-box and in a Lashley III maze. When the hippocampus of these bad-learner rats was perfused with high potassium solutions, it was observed that more stimuli were needed, under each potassium concentration, in order to elicit a seizure, than in normal animals. This was apparently the result of a lower release of potassium per stimulus into the extracellular space, in as much as other possibilities (low sensitivity to the epileptogenic effect of potassium, large extracellular space, high Na-K-Mg-ATPase activity) were excluded. This reduced potassium release by stimulation in the hippocampus of bad-learner rats was not due to a lower potassium gradient across cell membranes, and therefore, could in principle be attributed to a defect in the property of local neural membranes (pre- and/or postsynaptic) to increase potassium conductance when stimulated.The present data fit with the hypothesis advanced previously, that the hippocampus plays a role in learning through heterosynaptic interactions mediated by the release, and subsequent accumulation of potassium.Supported by grant No. 3917 from the Consejo Nacional de Investigaciones Científicas y Tícnicas, Argentina.     

Effects of chronic administration of diphenylhydantoin on learning and offspring behavior

An original parent group of 72 Sprague-Dawley albino rats was subdivided into four treatment groups that were administered 5, 10, or 15 mg/kg diphenylhydantoin and distilled water on days 5 to 55 after birth. At 85 days of age the drug females were bred to naive males to produce an F₁ generation. In similar fashion, the F₁ females were bred at maturity to produce an F₂ generation. Neither offspring group received any drug administrations or experimental treatments. All three groups were tested on avoidance conditioning at 75 days of age for a total of 150 trials. The results of statistical analysis indicated no significant differences in number of correct responses in the parent group, a significant Drug effect in the offspring groups and a significant Dose effect in the F₂ generation. This detrimental cross-generational effect on avoidance conditioning, caused by chronic diphenylhydantoin administration, is consistent with previously noted cross-generational effects of trifluoperazine, chlorpromazine, and methylphenidate.     

Effects of food deprivation,discrimination experience and physostigmine on choline acetylase and acetylcholine esterase in the dorsal hippocampus and frontal cortex of rats

The effects of food deprivation and preliminary training treatments on choline acetylase and acetylcholine esterase activity in the dorsal hippocampus and frontal cortex of rats have been investigated. In addition, blood sugar and adrenal epinephrine levels were examined. The activity of choline acetylase and the levels of blood sugar and adrenal epinephrine were significantly altered during various stages of preliminary training but all values were comparable to pre-experimental levels before discrimination commenced. In addition, rats were injected physostigmine salicylate (0.25 mg/kg) or saline i.p. each day immediately after receiving three training trials on a food-motivated black-white task. The physostigmine injected rats were significantly better than the controls in rate learning.No differences were observed in choline acetylase activity in the dorsal hippocampus and frontal cortex in discriminating rats treated with physostigmine or saline. However, choline acetylase activity is lower in treated and control rats which did not discriminate at the end of the 14th session.     

氯胺酮对大鼠学习记忆功能及海马神经元的影响

目的了解多次氯胺酮给药对学习记忆功能的影响及机制。方法SD大鼠30只随机分为高剂量组、低剂量组和1个对照组,高、低剂量组大鼠分别予以氯胺酮50和10 mg/kg腹腔注射给药,1次/d,连续7 d。对照组予以等量生理盐水。用水迷宫测试各组大鼠寻找隐匿台的逃避潜伏期和空间搜索能力,原位检测海马神经元凋亡情况,电子显微镜观察神经元超微结构变化。结果高剂量组逃避潜伏期显著延长(P<0.01),并且空间搜索能力明显降低(P<0.01);高剂量组海马神经元凋亡指数显著高于对照组(P<0.01);电子显微镜显示高剂量组海马神经元有明显变性。结论多次使用氯胺酮对学习记忆有损害,这种损害作用可能与海马神经元病变有关。     

The influence of diphenylhydantoin on intestinal glucose absorption in the rat

The influence of diphenylhydantoin (DPH) on intestinal glucose absoprtion was studied by perfusing an isolated jejunal loop of a rat under urethane anaesthesia. DPH produced dose dependent enhancement of glucose absorption. Since DPH also stimulates the absorption of 3-O-methylglucose, but not fructose, the stimulatory effect was considered to be primarily on facilitated transport.The highest concentration of DPH in the perfusate (10^{-4 M})stimulated the appearance of sodium in an originally sodium-free perfusate, while ouabain (1.25 mg/kg body wieght, i.v.) diminished this process. On the basis of these results an additional sodium pump, directed towards the lumen, is postulated in the brush border of the intestinal epithelial cell. The discrepancy between the results of in vitro experiments concerning the influence of sodium ions on intestinal glucose absorption, and the possible physiological role of the proposed apical sodium pump are discussed.     

盐酸甲氯芬酯联合尼莫地平对血管性痴呆大鼠学习记忆的影响

目的：研究盐酸甲氯芬酯与尼莫地平联合用药对血管性痴呆（V D ）大鼠学习记忆的影响。方法改良Pulsinelli四血管阻断法建立VD大鼠模型,造模后给予盐酸甲氯芬酯和尼莫地平治疗;Morris水迷宫检测大鼠学习记忆能力;HE染色观察海马脑区齿状回神经元的变化。结果经治疗后,VD大鼠海马齿状回细胞损伤减少,学习记忆能力明显提高。结论盐酸甲氯芬酯与尼莫地平联合用药能明显改善VD大鼠学习记忆能力,可能与其保护海马脑区神经元有关。     

The effect of diphenylhydantoin on the electrogenic component of the sodium pump in mammalian non-myelinated nerve fibres

A study has been made of the effect of diphenylhydantoin on the electrogenic component of the sodium pump in non-myelinated fibres of the desheathed rabbit vagus nerve. Acute or chronic administration of this drug did not affect the excitability, nor the membrane permeability, nor the activity of the sodium pump of the nerve fibres.     

Facilitation of avoidance learning by pentylenetetrazol as a function of task difficulty,deprivation and shock level

While the stimulant pentylenetetrazol produces strong and reliable facilitation of learning in appetitively motivated situation, its effects on avoidance learning have generally been small. The present study proposes that the apparent lack of facilitation in aversive situations is due to unfavorable interactions between particular doses of the drug with certain experimental variables.Male and female mice were trained in a wheel turn apparatus on both a simple and a discriminated avoidance task. Two level of shock were used. Half the subjects were deprived while the rest were fed ad libitum. Different groups of animals received injections of either normal saline or one of a range of doses of pentylenetetrazol immediately after each daily training session. Training was continued for twelve consecutive days.The results suggest that the magnitude and nature of the effects of pentylenetetrazol on learning are a function of the experimental conditions. Different doses of pentylenetetrazol were found to produce facilitation, disruption or no effect. The doses producing these effects varied with the complexity of the task, the level of shock, the degree of deprivation, and, in some instances, the sex of the subjects.The experiments reported were performed in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biological Sciences at the University of California, Irvine. The research was supported by Research Grant MH 12526 to Dr. J. L. McGaugh, Department of Psychobiology, School of Biological Sciences, University of California, Irvine. This support is gratefully acknowledged.     

Effects of cromakalim (BRL 34915) on potassium conductances in CA3 neurons of the guinea-pig hippocampus in vitro

Summary The action of the potassium channel activator, cromakalim (BRL 34915), on membrane potential, input resistance and current-voltage-relationship of CA3 neurons in a slice preparation of the guinea-pig hippocampus was investigated by means of intracellular recordings. In the presence of tetrodotoxin, cromakalim (30–100 mol/l) produced a hyperpolarization up to 4 mV associated with a decrease in input resistance up to 10 MOhms. Determination of the equilibrium potential of the cromakalim action revealed that the hyperpolarization is due to the activation of a potassium conductance. This cromakalim-activated potassium conductance was voltage-dependent, i.e. it increased with hyperpolarization. Among a number of potassium channel blockers tested, only Cs⁺ (2 mmol/l) and Ba²⁺ (0.5 mmol/1) were able to inhibit the cromakalim-induced effects. Simultaneously, both cations suppressed the hyperpolarizing inward rectification (anomalous rectification) in these neurons, indicating that cromakalim activated or potentiated an inwardly rectifying potassium conductance. In addition, cromakalim slightly enhanced both amplitude and duration of afterhyperpolarizations following single calcium-dependent action potentials, suggesting that cromakalim might have a weak facilitatory effect on calcium-dependent potassium conductances.Send offprint requests to C. Alzheimer at the above address     

Effects of infrasound on hippocampus-dependent learning and memory in rats and some underlying mechanisms

To investigate the effect of infrasound on the hippocampus-dependent spatial learning and memory as well as its underlying mechanisms, we measured the changes of cognitive abilities, brain-derived neurotrophic factor (BDNF)-tyrosine kinase receptor B (TrkB) signal transduction pathway and neurogenesis in the hippocampus of rats. The results showed that rats exposed to infrasound of 16 Hz at 130 dB for 14 days exhibited longer escape latency from day 2 and shortened time staying in the quadrant P in Morris water maze (MWM). It was found that mRNA and protein expression levels of hippocampal BDNF and TrkB were significantly decreased in real-time PCR and Western blot, and the number of BrdU-labeled cells in hippocampus was also reduced when compared to control. These results provided novel evidences that the infrasound of a certain exposure parameter can impair hippocampus-dependent learning and memory, in which the downregulation of the neuronal plasticity-related BDNF–TrkB signal pathway and less neurogenesis in hippocampus might be involved.     

Effect of diphenylhydantoin sodium and chlordiazepoxide alone and in combination on punishment behavior

Summary Punishment behavior was obtained in rats by simultaneously punishing and rewarding all lever presses made during the presentation of a non-aversive tone. When stable control performances were established, animals were given various doses of diphenylhydantoin or chlordiazepoxide. In addition, drug interaction studies were conducted with a non-effective dose of the former and selected doses of chlordiazepoxide. When diphenylhydantoin was given at effective anti-convulsant doses it did not diminish the suppressant effect of response produced shock. When the animals were given chlordiazepoxide after doses as low as 1.875 mg/kg, significant diminution was obtained in certain rats; and effects were dose-dependent until a clearly depressant dose was given. Both agents reduced variable interval responding after a dose of 15 mg/kg. Diphenylhydantoin did not enhance or antagonize the effects of chlordiazepoxide in the punishment phase of the schedule. However, some animals given non-depressant doses of each in combination did show a significant reduction in response rate in the variable interval component of the schedule.     

Influence of aminoglutethimide and spironolactone on the efficacy of carbamazepine and diphenylhydantoin against amygdala-kindled seizures in rats

Antagonists of steroid receptors may interfere with seizure phenomena. The present study deals with effects of aminoglutethimide and spironolactone on the action of carbamazepine and diphenylhydantoin in amygdala-kindled rats of both genders. Co-administration of the antimineralocorticoid with carbamazepine at their ineffective doses (50 and 15 mg/kg, respectively) led to significant reduction of the seizure and afterdischarge durations. No anticonvulsant effect was observed when spironolactone was combined with diphenylhydantoin. The concomitant treatment of aminoglutethimide and carbamazepine (both drugs at their subprotective doses of 5 and 15 mg/kg, respectively) resulted in antiseizure activity in respect of all measured parameters, including the afterdischarge threshold, seizure severity, seizure duration and afterdischarge duration. The similar combination of aminoglutethimide with diphenylhydantoin (2.5 mg/kg) significantly shortened the seizure and afterdischarge durations. The antiseizure effect of tested combinations was not sex-dependent and not reversed by hydrocortisone pretreatment. Pharmacokinetic events may be involved only in the interaction between spironolactone and carbamazepine. Among various chemoconvulsants, bicuculline reversed the action of aminoglutethimide on carbamazepine and diphenylhydantoin. The effect of aminoglutethimide on diphenylhydantoin was also abolished by N-methyl-d-aspartic acid and aminophylline. In conclusion, our results suggest that doses of carbamazepine and diphenylhydantoin should be modified in epileptic patients concomitantly treated with aminoglutethimide or spironolactone.     

The effect of diphenylhydantoin,diazepam and clonazepam on the activity of Purkinje cells in the rat cerebellum

Summary Spike discharges of single cerebellar Purkinje cells were recorded continuously with extracellular microelectrodes in unanaesthetized curarized rats. The intravenous injection of diphenylhydantoin in doses between 10 and 100 mg kg^–1 did not substantially alter the activity of Purkinje cells within 2–3 h. The two benzodiazepines, diazepam and clonazepam, already in low i.v. doses (0.03–0.1 mg kg^–1) consistently and reversibly depressed the firing rate. Our results do not support the previously advanced hypothesis that these drugs reduce epilepti-form activities by increasing the output from the cerebellar cortex. They rather point to the possibility that a reduced firing rate of cerebellar Purkinje cells mediates at least in part ataxia and muscular hypotonia observed after these drugs.     

Effects of diazepam and diphenylhydantoin on elicited and spontaneous seizures in kindled rats: a double dissociation

Diazepam (1 mg/kg) was more effective than diphenylhydantoin (100 mg/kg) in suppressing motor seizures elicited in kindled rats by amygdaloid stimulation; however, the effect of these drugs on the incidence of spontaneous motor seizures in rats kindled by amygdaloid stimulation was just the opposite. At the same doses, diphenylhydantoin effectively suppressed spontaneous motor seizures, but diazepam did not. This double dissociation suggests the need for caution in drawing inferences concerning spontaneously recurring seizures from studies of elicited seizures.     

Effects of intra-prelimbic prefrontal cortex injection of cannabidiol on anxiety-like behavior: Involvement of 5HT1A receptors and previous stressful experience

The prelimbic medial prefrontal cortex (PL) is an important encephalic structure involved in the expression of emotional states. In a previous study, intra-PL injection of cannabidiol (CBD), a major non-psychotomimetic cannabinoid present in the Cannabis sativa plant, reduced the expression of fear conditioning response. Although its mechanism remains unclear, CBD can facilitate 5HT_1A receptor-mediated neurotransmission when injected into several brain structures. This study was aimed at verifying if intra-PL CBD could also induce anxiolytic-like effect in a conceptually distinct animal model, the elevated plus maze (EPM). We also verified if CBD effects in the EPM and contextual fear conditioning test (CFC) depend on 5HT_1A receptors and previous stressful experience. CBD induced opposite effects in the CFC and EPM, being anxiolytic and anxiogenic, respectively. Both responses were prevented by WAY100,635, a 5HT_1A receptor antagonist. In animals that had been previously (24 h) submitted to a stressful event (2 h-restraint) CBD caused an anxiolytic, rather than anxiogenic, effect in the EPM. This anxiolytic response was abolished by previous injection of metyrapone, a glucocorticoid synthesis blocker. Moreover, restraint stress increased 5HT_1A receptors expression in the dorsal raphe nucleus, an effect that was attenuated by injection of metyrapone before the restraint procedure. Taken together, these results suggest that CBD modulation of anxiety in the PL depend on 5HT_1A-mediated neurotransmission and previous stressful experience.     

梓醇对血管性痴呆大鼠学习记忆能力及海马Bax、Bcl-2蛋白表达的影响

目的 考察梓醇对血管性痴呆(VD)大鼠学习记忆能力及海马Bax、Bcl-2蛋白表达的影响.方法 采用双侧颈总动脉结扎来制备VD大鼠模型,造模后第30天,将大鼠分成模型组、阳性组及梓醇高、中、低剂量组,连续给药30 d.采用Morris水迷宫法检测大鼠的学习记忆能力,HE染色法观察海马CA1区的病理组织形态,免疫组化法检测海马CA1区Bax和Bcl-2蛋白的表达.结果 与模型组相比,高、中剂量组大鼠第3、4天的逃避潜伏期明显缩短,高、中、低剂量梓醇组大鼠的站台穿越次数明显增加;梓醇能改善大鼠海马CA1区神经元的病理改变;梓醇高、中剂量能下调促凋亡蛋白Bax的表达,上调抑凋亡蛋白Bcl-2的表达.结论 梓醇能改善VD大鼠的学习记忆能力,其机制可能与抑制海马神经细胞凋亡有关.     

Nicotine and caffeine: Disruption of the long-term store of memory and proactive facilitation of learning in mice

The effects of nicotine and caffeine on the long-term store of memory in mice were determined for a wide range of dosages. Male F₁ mice (C57BL/6J×DBA/ 2J) were given two trials in an appetitive maze 24 h apart. Twenty-four hours after the second trial each animal was given the first of five daily injections of one of the dosages being tested. Beginning 48 h after the last injection, animals received one trial per day until a learning criterion was reached. Both nicotine and caffeine produced a dose-dependent disruption of performance in the trials following the injection series. In contrast, nicotine produced facilitation of performance in animals given a series of injections in the absence of previous training, and caffeine produced a strong trend in this direction. It was concluded that these drugs produced disruption of the long-term store of memory for the initial training and proactive facilitation of maze learning. The existence of separate and opposing effects of these drugs on different aspects of learning and memory was discussed.This investigation was supported by National Institute of Mental Health Grant MH20574 and National Institute of Mental Health Predoctoral Fellowship MH46975     

Perinatal food restriction impaired spatial learning and memory behavior and decreased the density of nitric oxide synthase neurons in the hippocampus of adult male rat offspring

Perinatal undernutrition has adverse effects on brain physiology as well as learning and memory activity. However, the mechanism is still incompletely understood. Nitric oxide (NO) synthesized by neuronal nitric oxide synthase (nNOS) has important roles in neuronal survival and synaptic plasticity as well as contributes to the learning and memory task. The aims of the present study were to investigate whether 50% perinatal food restriction (FR50) produced deleterious effects on the population of nNOS neurons in CA1 and CA3 and the dentate gyrus (DG) region of the hippocampus using ABC immunohistochemical method. The results showed FR50 reduced body weight of offspring on postnatal day (PD)1, PD7, PD10, PD14 and PD21, and this type of food restriction impaired learning and memory of adult male offspring rats (postnatal day 70) and decreased the density of nNOS-positive cells in the CA1, CA3 and DG region of the hippocampus. These findings suggest that perinatal undernutrition affects the activity of nNOS in hippocampus. Thus, these changes in the density of nNOS neurons may partly explain learning and memory disturbances commonly observed in undernourished rats and provide clues to the knowledge of malnutrition effects upon the brain.     

Interactive effects of chronic cigarette smoking and age on hippocampal volumes

Background

Previous cross-sectional MRI studies with healthy, young-to-middle-aged adults reported no significant differences between smokers and non-smokers on total hippocampal volume. However, these studies did not specifically test for greater age-related volume loss in the total hippocampus or hippocampal subregions in smokers, and did they did not examine relationships between hippocampal and subfield volumes and episodic learning and memory performance.

Methods

Healthy, young-to-middle-aged (45 ± 12 years of age) smokers (n = 39) and non-smokers (n = 43) were compared on total hippocampal and subfield volumes derived from high-resolution 4 Tesla MRI, emphasizing testing for greater age-related volume losses in smokers. Associations between hippocampal volumes and measures of episodic learning and memory were examined.

Results

Smokers showed significantly smaller volumes, as well as greater volume loss with increasing age than non-smokers in the bilateral total hippocampus and multiple subfields. In smokers, greater pack-years were associated with smaller volumes of the total hippocampus, presubiculum, and subiculum. In the entire cohort, performance on measures of learning and memory was related to larger total hippocampal and several subfield volumes, predominately in the left hemisphere.

Conclusions

Chronic cigarette smoking in this young-to-middle aged cohort was associated with smaller total hippocampal and subfield volumes, which were exacerbated by advancing age. Findings also indicated an adverse smoking dose/duration response (i.e., pack-years) with total hippocampal and select subfield volumes. These hippocampal volume abnormalities in smokers may be related to the deficiencies in episodic learning and memory in young-to-middle-aged smokers reported in previous studies.