Statistical parametric mapping reveals regional alterations in cannabinoid CB1 receptor distribution and G-protein activation in the 3D reconstructed epileptic rat brain

Purpose: The endocannabinoid system is known to modulate seizure activity in several in vivo and in vitro models, and CB₁‐receptor activation is anticonvulsant in the rat pilocarpine model of acquired epilepsy (AE). In these epileptic rats, a unique redistribution of the CB₁ receptor occurs within the hippocampus; however, an anatomically inclusive analysis of the effect of status epilepticus (SE)–induced AE on CB₁ receptors has not been thoroughly evaluated. Therefore, statistical parametric mapping (SPM), a whole‐brain unbiased approach, was used to study the long‐term effect of pilocarpine‐induced SE on CB₁‐receptor binding and G‐protein activation in rats with AE. Methods: Serial coronal sections from control and epileptic rats were cut at equal intervals throughout the neuraxis and processed for [³H]WIN55,212‐2 (WIN) autoradiography, WIN‐stimulated [³⁵S]GTPγS autoradiography, and CB₁‐receptor immunohistochemistry (IHC). The autoradiographic techniques were evaluated with both region of interest (ROI) and SPM analyses. Key Findings: In rats with AE, regionally specific increases in CB₁‐receptor binding and activity were detected in cortex, discrete thalamic nuclei, and other regions including caudate‐putamen and septum, and confirmed by IHC. However, CB₁ receptors were unaltered in several brain regions, including substantia nigra and cerebellum, and did not exhibit regional decreases in rats with AE. Significance: This study provides the first comprehensive evaluation of the regional distribution of changes in CB₁‐receptor expression, binding, and G‐protein activation in the rat pilocarpine model of AE. These regions may ultimately serve as targets for cannabinomimetic compounds or manipulation of the endocannabinoid system in epileptic brain.     

Spike–wave discharges are necessary for the expression of behavioral depression-like symptoms

Purpose:   The WAG/Rij strain of rats, a well-established model for absence epilepsy, has comorbidity for depression. These rats exhibit depression-like behavioral symptoms such as increased immobility in the forced swimming test and decreased sucrose intake and preference (anhedonia). These depression-like behavioral symptoms are evident in WAG/Rij rats, both at 3–4 and 5–6 months of age, with a tendency to aggravate in parallel with an increase in seizure duration. Here we investigated whether the behavioral symptoms of depression could be prevented by the suppression of absence seizures.
Methods:   Ethosuximide (ETX; 300 mg/kg/day, in the drinking water) was chronically applied to WAG/Rij rats from postnatal day 21 until 5 months. Behavioral tests were done before the cessation of the treatment. Electroencephalography (EEG) recordings were made before and after cessation of treatment to measure seizure severity at serial time-points.
Results:   ETX-treated WAG/Rij rats exhibited no symptoms of depression-like behavior in contrast to untreated WAG/Rij rats of the same age. Moreover, treated WAG/Rij rats did not differ from control age-matched Wistar rats. ETX treatment led to almost complete suppression of spike-wave discharges (SWDs) in 5–6 month old WAG/Rij rats. Discontinuation of chronic treatment was accompanied by a gradual emergence of SWDs; however, a persistent reduction in seizure activity was still present 47 days after discontinuation of the chronic treatment.
Discussion:   The results suggest that seizure activity is necessary for the expression of depression-like behavioral symptoms and confirm that epileptogenesis can be prevented by early and chronic treatment.     

The cannabinoid WIN 55,212‐2‐mediated protection of dentate gyrus granule cells is driven by CB1 receptors and modulated by TRPA1 and Cav2.2 channels

Cannabinoids regulate numerous physiological and pathological events like inflammation or neurodegeneration via CB₁ and CB₂ receptors. The mechanisms behind cannabinoid effects show a high variability and may also involve transient receptor potential channels (TRP) and N‐type voltage‐gated Ca²⁺ channels (Ca_v2.2). In the present study we investigated the neuroprotective effects of the synthetic cannabinoid WIN 55,212–2 (WIN) on dentate gyrus (DG) granule cells and elucidated the involvement of TRP and Ca_v2.2 that are shown to participate in inflammatory processes. Organotypic hippocampal slice cultures were excitotoxically lesioned using NMDA and subsequently incubated with different WIN concentrations (0.001–10 μM). WIN showed neuroprotective properties in an inverse concentration‐dependent manner, most effectively at 0.01 μM. The CB₁ receptor antagonist AM251 blocked neuroprotection mediated by WIN whereas the CB₂ receptor antagonist AM630 showed no effects. Application of the TRPA1 blocker HC‐030031 enhanced the neuroprotective efficacy of high (10 μM) WIN concentrations and the number of degenerating neurons became equal to that seen after application of the most effective WIN dose (0.01 μM). In contrast, the application of TRPA1 agonist icilin or allyl isothiocyanate (AITC) led to a stronger neurodegeneration. The use of TRPV1 blocker 6‐iodo‐nordihydrocapsaicin did not affect WIN‐mediated neuroprotection. The selective Ca_v2.2 blocker ω‐conotoxin (GVIA) completely blocked neuroprotection shown by 10 μM WIN. GVIA and HC‐030031 exerted no effects at WIN concentrations lower than 10 μM. Our data show that WIN protects dentate gyrus granule cells in a concentration dependent manner by acting upon CB₁ receptors. At high (10 μM) concentrations WIN additionally activates TRPA1 and Ca_v2.2 within the hippocampal formation that both interfere with CB₁ receptor‐mediated neuroprotection. This leads to the conclusion that physiological and pharmacological effects of cannabinoids strongly depend on their concentration and the neuroprotective efficacy of cannabinoids may be determined by interaction of activated CB₁ receptor, TRPA1, and Ca_v2.2. © 2010 Wiley‐Liss, Inc.     

Diminution of the NMDA receptor NR2B subunit in cortical and subcortical areas of WAG/Rij rats

Modulation of glutamatergic NMDA receptors affects the synchronization of spike discharges in in WAG/Rij rats, a valid genetic animal model of absence epilepsy. In this study, we describe the alteration of NR_2B subunit of NMDA receptors expression in WAG/Rij rats in different somatosensory cortical layers and in hippocampal CA1 area. Experimental groups were divided into four groups of six rats of both WAG/Rij and Wistar strains with 2 and 6 months of age. The distribution of NR_2B receptors was assessed by immunohistochemical staining in WAG/Rij and compared with age‐matched Wistar rats. The expression of NR_2B subunit was significantly decreased in different somatosensory cortical layers in 2‐ and 6‐month‐old WAG/Rij rats. In addition, the distribution of NR_2B in hippocampal CA1 area was lower in 6‐month‐old WAG/Rij compared with age‐matched Wistar rats. The reduction of NR_2B receptors in different brain areas points to disturbance of glutamate receptors expression in cortical and subcortical areas in WAG/Rij rats. An altered subunit assembly of NMDA receptors may underlie cortical hyperexcitability in absence epilepsy. Synapse 67:839–846, 2013 . © 2013 Wiley Periodicals, Inc.     

FMRI of brain activation in a genetic rat model of absence seizures

PURPOSE: EEG-triggered functional magnetic resonance imaging (fMRI) was used to identify areas of brain activation during spontaneous spike-and-wave discharges (SWDs) in an epileptic rat strain under awake conditions. METHODS: Spontaneous absence seizures from 10 WAG/Rij rats were imaged by using T2*-weighted echo planar imaging at 4.7 Tesla. fMRI of the blood-oxygenation-level-dependent (BOLD) signal was triggered based on EEG recordings during imaging. Images obtained during spontaneous SWDs were compared with baseline images. RESULTS: Significant positive BOLD signal changes were apparent in several areas of the cortex and several important nuclei of the thalamus. In addition, no negative BOLD signal was found in any brain area. CONCLUSIONS: We have shown that EEG-triggered BOLD fMRI can be used to detect cortical and thalamic activation related to the spontaneous SWDs that characterize absence seizures in awake WAG/Rij rats. These results draw an anatomic correlation between areas in which increased BOLD signal is found and those in which SWDs have been recorded. In addition, no negative BOLD signal was found to be associated with these spontaneous SWDs. We also demonstrated the technical feasibility of using EEG-triggered fMRI in a genetic rat model of absence seizure.     

Antibodies to cannabinoid type 1 receptor co‐react with stomatin‐like protein 2 in mouse brain mitochondria

Anti‐cannabinoid type 1 receptor (CB₁) polyclonal antibodies are widely used to detect the presence of CB₁ in a variety of brain cells and their organelles, including neuronal mitochondria. Surprisingly, we found that anti‐CB₁ sera, in parallel with CB₁, also recognize the mitochondrial protein stomatin‐like protein 2. In addition, we show that the previously reported effect of synthetic cannabinoid WIN 55,212‐2 on mitochondrial complex III respiration is not detectable in purified mitochondrial preparations. Thus, our study indicates that a direct relationship between endocannabinoid signaling and mitochondrial functions in the cerebral cortex seems unlikely, and that caution should be taken interpreting findings obtained using anti‐CB₁ antibodies.     

Thalamic lesions in a genetic rat model of absence epilepsy: Dissociation between spike-wave discharges and sleep spindles

Recent findings have challenged the traditional view that the thalamus is the primary driving source of generalized spike-wave discharges (SWDs) characteristic for absence seizures, and indicate a leading role for the cortex instead. In light of this we investigated the effects of thalamic lesions on SWDs and sleep spindles in the WAG/Rij rat, a genetic model of absence epilepsy. EEG was recorded from neocortex and thalamus in freely moving rats, both before and after unilateral thalamic ibotenic acid lesions. Complete unilateral destruction of the reticular thalamic nucleus (RTN) combined with extensive destruction of the thalamocortical relay (TCR) nuclei, resulted in the bilateral abolishment of SWDs and ipsilateral abolishment of sleep spindles. A suppression of both types of thalamocortical oscillations was found when complete or extensive damage to the RTN was combined with minor to moderate damage to the TCR nuclei. Lesions that left the rostral pole of the RTN and part of the TCR nuclei intact, resulted in an ipsilateral suppression of sleep spindles, but a large increase of bilateral SWDs. These findings demonstrate that the thalamus in general and the RTN in particular are a prerequisite for both the typical bilateral 7-11 Hz SWDs and natural occurring sleep spindles in the WAG/Rij rat, but suggest that different intrathalamic subcircuits are involved in the two types of thalamocortical oscillations. Whereas the whole RTN appears to be critical for the generation of sleep spindles, the rostral pole of the RTN seems to be the most likely part that generates SWDs.     

Cannabinoid agonist WIN55,212 in vitro inhibits interleukin‐6 (IL‐6) and monocyte chemo‐attractant protein‐1 (MCP‐1) release by rat pancreatic acini and in vivo induces dual effects on the course of acute pancreatitis

Background Cannabinoids (CBs) evoke their effects by activating the cannabinoid receptor subtypes CB1‐r and CB2‐r and exert anti‐inflammatory effects altering chemokine and cytokine expression. Various cytokines and chemokines are produced and released by rodent pancreatic acini in acute pancreatitis. Although CB1‐r and CB2‐r expressed in rat exocrine pancreatic acinar cells do not modulate digestive enzyme release, whether they modulate inflammatory mediators remains unclear. We investigated the CB‐r system role on exocrine pancreas in unstimulated conditions and during acute pancreatitis. Methods We evaluated in vitro and in vivo changes induced by WIN55,212 on the inflammatory variables amylasemia, pancreatic edema and morphology, and on acinar release and content of the cytokine interleukin‐6 (IL‐6) and chemokine monocyte chemo‐attractant protein‐1 (MCP‐1) in untreated rats and rats with caerulein ( CK ) ‐induced pancreatitis. Key Results In the in vitro experiments, WIN55,212 (10^?6 mol L^?1) inhibited IL‐6 and MCP‐1 release from acinar cells of unstimulated rats and after CK‐induced pancreatitis. In vivo, when rats were pretreated with WIN55,212 (2 mg kg^?1, intraperitoneally) before experimentally‐induced pancreatitis, serum amylase, pancreatic edema and IL‐6 and MCP‐1 acinar content diminished and pancreatic morphology improved. Conversely, when rats with experimentally‐induced pancreatitis were post‐treated with WIN55,212, pancreatitis worsened. Conclusions & Inferences These findings provide new evidence showing that the pancreatic CB1‐r/CB2‐r system modulates pro‐inflammatory factor levels in rat exocrine pancreatic acinar cells. The dual, time‐dependent WIN55,212‐induced changes in the development and course of acute pancreatitis support the idea that the role of the endogenous CB receptor system differs according to the local inflammatory status.     

Cortical and limbic excitability in rats with absence epilepsy

The classical cortico-reticular theory on absence epilepsy suggests that a hyperexcitable cortex is a precondition for the occurrence of absence seizures. In the present experiment seizure thresholds and characteristics of cortical and limbic epileptic afterdischarges (AD) were determined in a comparative cortical stimulation study in young and old adult genetically epileptic WAG/Rij, congenic ACI and Wistar rats. Fifteen-second series of 8Hz stimulation of the sensory-motor cortex were applied in 80- and 180-day-old rats with implanted electrodes. Strain differences were found for the threshold for movements directly induced by stimulation, low frequency spike-and-wave AD, maximal clonic intensity of seizures accompanying direct stimulation, and frequency characteristics of low frequency AD. None of these results agreed with a higher cortical excitability exclusively in WAG/Rij rats. However, WAG/Rij rats had the longest duration of the low frequency AD, and the lowest threshold for the transition to the limbic type of AD. The decrease of this threshold correlated with the increase of the incidence and total duration of spontaneous SWDs in WAG/Rij rats. It is concluded that the elevated excitability of the limbic system or pathways mediating the spread of the epileptic activity into this system can be attributed to the development of genetic epileptic phenotype in WAG/Rij rats.     

WIN55,212-2, a cannabinoid receptor agonist, protects against nigrostriatal cell loss in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson's disease

Parkinson’s disease (PD) is characterized by the progressive loss of nigrostriatal dopamine neurons leading to motor disturbances and cognitive impairment. Current pharmacotherapies relieve PD symptoms temporarily but fail to prevent or slow down the disease progression. In this study, we investigated the molecular mechanisms by which the non‐selective cannabinoid receptor agonist WIN55,212‐2 (WIN) protects mouse nigrostriatal neurons from 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induced neurotoxicity and neuroinflammation. Stereological analyses showed that chronic treatment with WIN (4 mg/kg, intraperitoneal), initiated 24 h after MPTP administration, protected against MPTP‐induced loss of tyrosine hydroxylase‐positive neurons in the substantia nigra pars compacta independently of CB₁ cannabinoid receptor activation. The neuroprotective effect of WIN was accompanied by increased dopamine and 3,4‐dihydroxyphenylacetic acid levels in the substantia nigra pars compacta and dorsal striatum of MPTP‐treated mice. At 3 days post‐MPTP, we found significant microglial activation and up‐regulation of CB₂ cannabinoid receptors in the ventral midbrain. Treatment with WIN or the CB₂ receptor agonist JWH015 (4 mg/kg, intraperitoneal) reduced MPTP‐induced microglial activation, whereas genetic ablation of CB₂ receptors exacerbated MPTP systemic toxicity. Furthermore, chronic WIN reversed MPTP‐associated motor deficits, as revealed by the analysis of forepaw step width and percentage of faults using the inverted grid test. In conclusion, our data indicate that agonism at CB₂ cannabinoid receptors protects against MPTP‐induced nigrostriatal degeneration by inhibiting microglial activation/infiltration and suggest that CB₂ receptors represent a new therapeutic target to slow the degenerative process occurring in PD.     

Endocannabinoid modulation of jejunal afferent responses to LPS

Background Endocannabinoids influence immune function and nociceptive signaling. This study examines cannabinoid modulation of sensory signaling from the GI tract following an acute inflammatory response triggered by systemic administration of bacterial lipopolysaccharide (LPS). Methods A segment of proximal jejunum was intubated, to measure intraluminal pressure, in anesthetized rats. Afferent impulse traffic was recorded from a single isolated paravascular nerve bundle supplying the jejunal loop. Drugs and LPS were administered intravenously and changes in afferent firing were determined. Key Results The non‐selective cannabinoid agonist, WIN55,212‐2 (1 mg kg^?1 i.v.) and the anandamide transport inhibitor, VDM11 (1 mg kg^?1 i.v.) but not the fatty acid amide hydrolase (FAAH) inhibitor, URB597 (0.3 mg kg^?1) caused a significant increase in afferent activity. The WIN55,212‐2‐induced afferent response was mediated by activation of CB₁ receptors whereas the VDM11 response was mediated by both CB₁ and CB₂ receptor mechanisms. LPS (10 mg kg^?1) evoked an increase in afferent activity which was significantly reduced in the presence of WIN55,212‐2 and VDM11 but not URB597. The inhibitory effect of WIN55,212‐2 was prevented by CB₁ but not CB₂ receptor antagonism. In contrast, the inhibitory effect of VDM11 remained unaltered after CB₁ or CB₂ receptor blockade. Conclusions & Inferences Endocannabinoids play a role in modulating afferent signaling and may represent a target for the treatment of visceral hypersensitivity. In contrast to the effects of blocking endocannabinoid uptake (VDM11), inhibiting breakdown of endocannabinoids (URB597) had no effect on baseline or LPS induced afferent firing. Therefore, uptake of cannabinoids rather than breakdown via FAAH terminates their action in the GI tract.     

Correlation of T-channel coding gene expression, IT, and the low threshold Ca2+ spike in the thalamus of a rat model of absence epilepsy

T-type Ca(2+) current-dependent burst firing of thalamic neurons is thought to be involved in the hyper-synchronous activity observed during absence seizures. Here we investigate the correlation between the expression of T-channel coding genes (alpha1G, -H, -I), T-type Ca(2+) current, and the T-current-dependent low threshold Ca(2+) spike in three functionally distinct thalamic nuclei (lateral geniculate nucleus; centrolateral nucleus; reticular nucleus) in a rat model of absence epilepsy, the WAG/Rij rats, and a non-epileptic control strain, the ACI rats. The lateral geniculate nucleus and centrolateral nucleus were found to primarily express alpha1G and alpha1I, while the reticular thalamic nucleus expressed alpha1H and alpha1I. Expression was higher in WAG/Rij when compared to ACI. The T-type Ca(2+) current properties matched the predictions derived from the expression pattern analysis. Current density was larger in all nuclei of WAG/Rij rats when compared to ACI and correlated with LTS size and the minimum LTS generating slope, while T-type Ca(2+) current voltage dependency correlated with the LTS onset potential.     

Midfrequency cortico-thalamic oscillations and the sleep cycle: genetic, time of day and age effects

WAG/Rij rats have various types of mid frequency cortico-thalamic oscillations, such as anterior and posterior sleep spindles and two types of spike-wave discharges (SWD). The generalized SWD (type I) preferentially occur at transitions from wake to sleep, type II can be found at the occipital cortex during quite wakefulness. In the present experiment sleep spindles, SWD and sleep cycle characteristics of 6-month-old WAG/Rij rats were studied and compared with those of younger WAG/Rij rats with much less SWD and age-matched control (ACI) rats. EEG recordings were made during the beginning (morning) and end (afternoon) of the light period in these four groups of rats. Quantitative characteristics of SWD, sleep spindles and the sleep cycle were determined. There were strain-related and age-dependent effects in the various cortico-thalamic oscillations, older WAG/Rij had more SWDs than younger WAG/Rij rats (both types I and II) and there were more type I SWDs at the end of the light period compared to the beginning. Large strain, age and time of day effects on the sleep cycle were found. The duration of non-REM sleep and the sleep cycle was shorter in WAG/Rij rats but only at the end of the light period and only in older WAG/Rij rats. It can be concluded that the various phasic events and the length of the sleep cycle are under genetic control, and that the sleep cycle length is also controlled by time of day, age and genetic factors. Non-REM sleep and the sleep cycle are disrupted by absence seizures but only in fragile periods when drowsiness and light slow wave sleep dominate.     

Changes in electroencephalographic characteristics and blood-brain barrier permeability in WAG/Rij rats with cortical dysplasia

PurposeThis study investigated the effects of cortical dysplasia (CD) on electrophysiology and blood-brain barrier (BBB) permeability in WAG/Rij rats with genetic absence epilepsy.MethodsPregnant WAG/Rij rats were exposed to 145 cGy of gamma-irradiation on embryonic day 17 to induce CD. An electroencephalogram was recorded from cortices subdurally in the offspring of the pregnant animals. Horseradish peroxidase (HRP) was used as determinant of BBB permeability.ResultsA massive tissue loss in the cerebral cortex was seen in WAG/Rij rats with CD (p < 0.05). There was a significant decrease in the number and duration of spike-and-wave discharges (SWDs) and an increase in the frequency of SWDs in the WAG/Rij rats with CD when compared with the properties of SWDs in intact WAG/Rij rats (p < 0.01). Ultrastructurally, the accumulation of HRP reaction products in the cerebral cortex and thalamus of WAG/Rij rats was significantly higher than that of control values (p < 0.01). The accumulation of HRP reaction products in the cerebral cortex and thalamus regions of WAG/Rij rats with CD increased and was higher than that of the control and WAG/Rij animals (p < 0.01).ConclusionIn our study, we showed that number and duration of SWDs decreased and SWD frequency increased in WAG/Rij rats with CD, suggesting a shift in seizure pattern. The association of these alterations with significant loss of cortical thickness and increased BBB permeability to HRP tracer may represent a causal relation of the EEG abnormalities with cerebral structural changes in these animals.     

Comparison of the antiepileptogenic effects of an early long‐term treatment with ethosuximide or levetiracetam in a genetic animal model of absence epilepsy

Purpose: Epilepsy is a heterogeneous syndrome characterized by recurrent, spontaneous seizures; continuous medication is, therefore, necessary, even after the seizures have long been suppressed with antiepileptic drug (AED) treatments. The most disturbing issue is the inability of AEDs to provide a persistent cure, because these compounds generally suppress the occurrence of epileptic seizures without necessarily having antiepileptogenic properties. The aim of our experiments was to determine, in the WAG/Rij model of absence epilepsy, if early long‐term treatment with some established antiabsence drugs might prevent the development of seizures, and whether such an effect could be sustained. Methods: WAG/Rij rats were treated for ～3.5 months (starting at 1.5 months of age, before seizure onset) with either ethosuximide (ETH; drug of choice for absence epilepsy) or levetiracetam (LEV; a broad‐spectrum AED with antiabsence and antiepileptogenic properties). Results: We have demonstrated that both drugs are able to reduce the development of absence seizures, exhibiting antiepileptogenic effects in this specific animal model. Discussion: These findings suggest that absence epilepsy in this strain of rats very likely follows an epileptogenic process during life and that early therapeutic intervention is possible, thereby opening a new area of research for absence epilepsy and AED treatment strategies.     

Anatomical characterization of the cannabinoid CB1 receptor in cell‐type–specific mutant mouse rescue models

Type 1 cannabinoid (CB₁) receptors are widely distributed in the brain. Their physiological roles depend on their distribution pattern, which differs remarkably among cell types. Hence, subcellular compartments with little but functionally relevant CB₁ receptors can be overlooked, fostering an incomplete mapping. To overcome this, knockin mice with cell‐type–specific rescue of CB₁ receptors have emerged as excellent tools for investigating CB₁ receptors’ cell‐type–specific localization and sufficient functional role with no bias. However, to know whether these rescue mice maintain endogenous CB₁ receptor expression level, detailed anatomical studies are necessary. The subcellular distribution of hippocampal CB₁ receptors of rescue mice that express the gene exclusively in dorsal telencephalic glutamatergic neurons (Glu‐CB₁‐RS) or GABAergic neurons (GABA‐CB₁‐RS) was studied by immunoelectron microscopy. Results were compared with conditional CB₁ receptor knockout lines. As expected, CB₁ immunoparticles appeared at presynaptic plasmalemma, making asymmetric and symmetric synapses. In the hippocampal CA1 stratum radiatum, the values of the CB₁ receptor‐immunopositive excitatory and inhibitory synapses were Glu‐CB₁‐RS, 21.89% (glutamatergic terminals); 2.38% (GABAergic terminals); GABA‐CB₁‐RS, 1.92% (glutamatergic terminals); 77.92% (GABAergic terminals). The proportion of CB₁ receptor‐immunopositive excitatory and inhibitory synapses in the inner one‐third of the dentate molecular layer was Glu‐CB₁‐RS, 53.19% (glutamatergic terminals); 2.30% (GABAergic terminals); GABA‐CB₁‐RS, 3.19% (glutamatergic terminals); 85.07% (GABAergic terminals). Taken together, Glu‐CB₁‐RS and GABA‐CB₁‐RS mice show the usual CB₁ receptor distribution and expression in hippocampal cell types with specific rescue of the receptor, thus being ideal for in‐depth anatomical and functional investigations of the endocannabinoid system. J. Comp. Neurol. 525:302–318, 2017. © 2016 Wiley Periodicals, Inc.     

In utero cannabinoid exposure alters breathing and the response to hypoxia in newborn mice

Cannabis is one of the most commonly used recreational drugs at ages highly correlated with potential pregnancy. Endocannabinoid signalling regulates important stages of neuronal development. When cannabinoid receptors, which are widely distributed through the nervous system, are activated by exogenous cannabinoids, breathing in adult rats is depressed. Here, we show that, in newborn mice, endocannabinoids, through the activation of cannabinoid receptor type 1 (CB₁R), participate in the modulation of respiration and its control. Blocking CB₁Rs at birth suppressed the brake exerted by endocannabinoids on ventilation in basal and in hypoxic conditions. The number of apnoeas and their duration were also minimized by activation of CB₁Rs in normoxic and in hypoxic conditions. However, prenatal cannabis intoxication, caused by a daily injection of WIN55,212‐2, in pregnant mice durably modified respiration of the offspring, as shown by hyperventilation in basal conditions, an altered chemoreflex in response to hypoxia, and longer apnoeas. When CB₁Rs were blocked in WIN55,212‐2 treated newborns, persistent hyperventilation was still observed, which could partly be explained by a perturbation of the central respiratory network. In fact, in vitro medullary preparations from WIN55,212‐2 treated pups, free of peripheral or of supramedullary structures, showed an altered fictive breathing frequency. In conclusion, the endocannabinoid pathway at birth seems to modulate breathing and protect the newborn against apnoeas. However, when exposed prenatally to an excess of cannabinoid, the breathing neuronal network in development seems to be modified, probably rendering the newborn more vulnerable in the face of an unstable environment.     

The WAG/Rij strain: a genetic animal model of absence epilepsy with comorbidity of depression [corrected

A great number of clinical observations show a relationship between epilepsy and depression. Idiopathic generalized epilepsy, including absence epilepsy, has a genetic basis. The review provides evidence that WAG/Rij rats can be regarded as a valid genetic animal model of absence epilepsy with comorbidity of depression. WAG/Rij rats, originally developed as an animal model of human absence epilepsy, share many EEG and behavioral characteristics resembling absence epilepsy in humans, including the similarity of action of various antiepileptic drugs. Behavioral studies indicate that WAG/Rij rats exhibit depression-like symptoms: decreased investigative activity in the open field test, increased immobility in the forced swimming test, and decreased sucrose consumption and preference (anhedonia). In addition, WAG/Rij rats adopt passive strategies in stressful situations, express some cognitive disturbances (reduced long-term memory), helplessness, and submissiveness, inability to make choice and overcome obstacles, which are typical for depressed patients. Elevated anxiety is not a characteristic (specific) feature of WAG/Rij rats; it is a characteristic for only a sub-strain of WAG/Rij rats susceptible to audiogenic seizures. Interestingly, WAG/Rij rats display a hyper-response to amphetamine similar to anhedonic depressed patients. WAG/Rij rats are sensitive only to chronic, but not acute, antidepressant treatments, suggesting that WAG/Rij rats fulfill a criterion of predictive validity for a putative animal model of depression. However, more and different antidepressant drugs still await evaluation. Depression-like behavioral symptoms in WAG/Rij rats are evident at baseline conditions, not exclusively after stress. Experiments with foot-shock stress do not point towards higher stress sensitivity at both behavioral and hormonal levels. However, freezing behavior (coping deficits) and blunted response of 5HT in the frontal cortex to uncontrollable sound stress, increased c-fos expression in the terminal regions of the meso-cortico-limbic brain systems and greater DA response of the mesolimbic system to forced swim stress suggest that WAG/Rij rats are vulnerable to some, but not to all types of stressors. We propose that genetic absence epileptic WAG/Rij rats have behavioral depression-like symptoms, are vulnerable to stress and might represent a model of chronic low-grade depression (dysthymia). Both 5HT and DAergic abnormalities detected in the brain of WAG/Rij rats are involved in modulation of vulnerability to stress and provocation of behavioral depression-like symptoms. The same neurotransmitter systems modulate SWDs as well. Recent studies suggest that the occurrence and repetition of absence seizures are a precipitant of depression-like behavior. Whether the neurochemical changes are primary to depression-like behavioral alterations remains to be determined. In conclusion, the WAG/Rij rats can be considered as a genetic animal model for absence epilepsy with comorbidity of dysthymia. This model can be used to investigate etiology, pathogenic mechanisms and treatment of a psychiatric comorbidity, such as depression in absence epilepsy, to reveal putative genes contributing to comorbid depressive disorder, and to screen novel psychotropic drugs with a selective and/or complex (dual) action on both pathologies.     

Cannabinoid receptor 1 signalling dampens activity and mitochondrial transport in networks of enteric neurones

Abstract Cannabinoid (CB) receptors are expressed in the enteric nervous system (ENS) and CB₁ receptor activity slows down motility and delays gastric emptying. This receptor system has become an important target for GI‐related drug development such as in obesity treatment. The aim of the study was to investigate how CB₁ ligands and antagonists affect ongoing activity in enteric neurone networks, modulate synaptic vesicle cycling and influence mitochondrial transport in nerve processes. Primary cultures of guinea‐pig myenteric neurones were loaded with different fluorescent markers: Fluo‐4 to measure network activity, FM1‐43 to image synaptic vesicles and Mitotracker green to label mitochondria. Synaptic vesicle cluster density was assessed by immunohistochemistry and expression of CB₁ receptors was confirmed by RT‐PCR. Spontaneous network activity, displayed by both excitatory and inhibitory neurones, was significantly increased by CB₁ receptor antagonists (AM‐251 and SR141716), abolished by CB₁ activation (methanandamide, mAEA) and reduced by two different inhibitors (arachidonylamide serotonin, AA‐5HT and URB597) of fatty acid amide hydrolase. Antagonists reduced the number of synaptic vesicles that were recycled during an electrical stimulus. CB₁ agonists (mAEA and WIN55,212) reduced and antagonists enhanced the fraction of transported mitochondria in enteric nerve fibres. We found immunohistochemical evidence for an enhancement of synaptophysin‐positive release sites with SR141716, while WIN55,212 caused a reduction. The opposite effects of agonists and antagonists suggest that enteric nerve signalling is under the permanent control of CB₁ receptor activity. Using inhibitors of the endocannabinoid degrading enzyme, we were able to show there is endogenous production of a CB ligand in the ENS.     

Effect of intracranial administration of ethosuximide in rats with spontaneous or pentylenetetrazol-induced spike-wave discharges

Purpose: Generalized absence seizures are characterized by bilateral spike‐wave discharges (SWDs), particularly in the frontoparietal cortical region. In WAG/Rij and GAERS rats with absence epilepsy, recent evidence indicates that SWDs arise first from the lateral somatosensory cortex (LSC), that is, the cortical focus theory. To further understand the cortical role in SWD generation, two epileptic rat models were assessed. Methods: Two models, Long‐Evans rats with spontaneous SWDs and Wistar rats with low‐dose pentylenetetrazol‐induced SWDs (20 mg/kg, i.p.), were administered intracortical or intrathalamic ethosuximide (ESM) or saline. Electroencephalographic recordings were analyzed before and after intracranial microinfusion to evaluate onset, frequency, and duration of SWDs. Key Findings: In both epileptic rat models, ESM in the LSC significantly reduced SWD number, shortened SWD duration, and delayed SWD onset compared to saline. By contrast, ESM in the medial somatosensory cortex had little effect compared to saline. Intrathalamic infusion of ESM only delayed SWD onset. Significance: These findings suggest that the LSC may be essential for the occurrence of SWDs. Our data support the cortical focus theory for the generation of absence seizures.