The odor span task (OST) infers working memory capacity (WMC) by requiring rodents to discriminate between previously presented and session-novel odors to obtain a hidden food reward. Here, rats' ...responses to session-novel odors and food rewards were assessed to determine whether rats use mitigating strategies in the OST. Rats accurately responded to session-novel odors but also reliably responded to the food reward alone and performed at chance when both a session-novel odor and food reward were presented in separate locations. The inclusion of unscented sand in the cups holding the food reward significantly reduced the rats' responses to the food reward alone. Collectively, these results demonstrate the need for rigorous tests of potential mitigating strategies and hold wide implications for rodent odor discrimination-based behavioral tasks.
The choroid plexus and cerebral ventricles are critical structures for the production of cerebral spinal fluid (CSF) and play an important role in regulating ion and metal transport in the brain, ...however many aspects of its roles in normal physiology and disease states, such as psychiatric illness, remain unknown. The choroid plexus is difficult to examine in vivo, and in situ ex vivo, and as such has typically been examined indirectly with radiolabeled tracers or ex vivo stains, making measurements of the endogenous K+, Cl-, and Ca+ distributions unreliable. In the present study, we directly examined the distribution of endogenous ions and biologically relevant transition metals in the choroid plexus and regions surrounding the ventricles (ventricle wall, cortex, corpus callosum, striatum) using X-ray fluorescence imaging (XFI). We find that the choroid plexus was rich in Cl- and Fe while K+ levels increase further from the ventricle as Cl- levels decrease, consistent with the known role of ion transporters in the choroid plexus CSF production. A polyI:C offspring displayed enlarged ventricles, elevated Cl- surrounding the ventricles, and intraventricular calcifications. These observations fit with clinical findings in patients with schizophrenia and suggest maternal treatment with polyI:C may lead to dysfunctional ion regulation in offspring. This study demonstrates the power of XFI for examining the endogenous elemental distributions of the ventricular system in healthy brain tissue as well as disease models.
The anterior retrosplenial cortex (aRSC) integrates multimodal sensory information into cohesive associative recognition memories. Little is known about how information is integrated during different ...learning phases (i.e., encoding and retrieval). Additionally, sex differences are observed in performance of some visuospatial memory tasks; however, inconsistent findings warrant more research. We conducted three experiments using the 1‐h delay object‐in‐place (1‐h OiP) test to assess recognition memory retrieval in male and female Long–Evans rats. (i) We found both sexes performed equally in three repeated 1‐h OiP test sessions. (ii) We showed infusions of a mixture of muscimol/baclofen (GABAA/B receptor agonists) into the aRSC ~15‐min prior to the test phase disrupted 1‐h OiP in both sexes. (iii) We assessed the role of aRSC ionotropic glutamate receptors in 1‐h OiP retrieval using another squad of cannulated rats and confirmed that infusions of either the competitive AMPA/Kainate receptor antagonist CNQX (3 mM) or competitive NMDA receptor antagonist AP‐5 (30 mM) (volumes = 0.50 uL/side) significantly impaired 1‐h OiP retrieval in both sexes compared to controls. Taken together, findings challenge reported sex differences and clearly establish a role for aRSC ionotropic glutamate receptors in short‐term visuospatial recognition memory retrieval. Thus, modulating neural activity in the aRSC may alleviate some memory processing impairments in related disorders.
Rats were bilaterally cannulated in anterior retrosplenial cortex (aRSC) and treatments were administered prior to the 1‐h object‐in‐place (OiP) test phase (a). Infusions of the glutamate antagonists CNQX (AMPA/Kainate) and AP‐5 (NMDA), significantly impaired OiP retrieval in both sexes (b).
Rationale
The nucleus accumbens (NAc) core gates motivationally relevant behavioral action sequences through afferents from cortical and subcortical brain regions. While the role of the NAc core in ...reward and effort-based decision making is well established, its role in working memory (WM) processes is incompletely understood. The odor span task (OST) has been proposed as a measure of non-spatial working memory capacity (WMC) as it requires rodents to select a novel odor from an increasing number of familiar odors to obtain a food reward.
Objective
To assess the role of the NAc core in the OST using (1) reversible chemical inactivation and (2) selective blockade of dopamine D1 and D2 receptors in the area.
Methods
Well-trained male rats were tested on the OST following intra-NAc core infusions of muscimol/baclofen, the D1 receptor antagonist SCH-23390 (1 μg/hemisphere) and the D2 receptor antagonist eticlopride (1 μg/hemisphere). Behavioral measurements included the average odor span, maximum odor span, choice latency, searching vigor, and patterns of responding during foraging that may relate to impulsivity.
Results
Chemical inactivation of the NAc core significantly decreased odor span relative to sham and vehicle conditions. Selective antagonism of D2, but not D1, receptors in the NAc core also produced deficits in odor span. We found that secondary behavioral measures of choice latency, searching vigor, and responding to the first odor stimulus encountered were largely unaffected by treatment.
Conclusions
These findings suggest that D2 receptors in the NAc core are required for OST performance.
Childhood Absence Epilepsy (CAE) accounts for approximately 10% of all pediatric epilepsies. Current treatments for CAE are ineffective in approximately 1/3 of patients and can be associated with ...severe side effects such as hepatotoxicity. Certain cannabinoids, such as cannabidiol (CBD), have shown promise in the treatment of pediatric epilepsies. However, CBD remains limited or prohibited in many jurisdictions, and has not been shown to have efficacy in CAE. Modulation of the type 1 cannabinoid receptor (CB1R) may provide more desirable pharmacological treatments. Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model many aspects of CAE, including cortical spike and wave discharges (SWDs). We have recently demonstrated that Δ9-tetrahydrocannabinol (THC) increases SWDs in GAERS whereas CBD decreases these events. Here, we characterized aspects of the endocannabinoid system in brain areas relevant to seizures in GAERS and tested whether positive allosteric modulators (PAMs) of CB1R reduced SWDs. Both female and male GAERS had reduced (>50%) expression of CB1R and elevated levels of the endocannabinoid 2-AG in cortex compared to non-epileptic controls (NEC). We then administered the CB1R PAMs GAT211 and GAT229 to GAERS implanted with cortical electrodes. Systemic administration of GAT211 to male GAERS reduced SWDs by 40%. Systemic GAT229 administration reduced SWDs in female and male GAERS. Intracerebral infusion of GAT229 into the cortex of male GAERS reduced SWDs by >60% in a CB1R-dependent manner that was blocked by SR141716A. Together, these experiments identify altered endocannabinoid tone in GAERS and suggest that CB1R PAMs should be explored for treatment of absence seizures.
•GAERS had sex-specific ECS differences compared to non-epileptic controls.•Injection of CB1R-PAMs GAT211 or GAT229 reduced spike and wave discharges in GAERS.•Cortical infusion of GAT229 reduced spike and wave discharges in GAERS.•The CB1R antagonist SR141716A blocked the effects of GAT229.•These data suggest CB1R-PAMs may have anticonvulsive properties in GAERS.
Abstract Childhood absence epilepsy (CAE) is often comorbid with behavioral and cognitive symptoms, including impaired visual memory. Genetic Absence Epilepsy Rats from Strasbourg (GAERS) is an ...animal model closely resembling CAE; however, cognition in GAERS is poorly understood. Crossmodal object recognition (CMOR) is a recently developed memory task that examines not only purely visual and tactile memory, but also requires rodents to integrate sensory information about objects gained from tactile exploration to enable visual recognition. Both the visual and crossmodal variations of the CMOR task rely on the perirhinal cortex, an area with dense expression of T-type calcium channels. GAERS express a gain-in-function missense mutation in the Cav3.2 T-type calcium channel gene. Therefore, we tested whether the T-type calcium channel blocker Z944 dose dependently (1, 3, 10 mg/kg; i.p.) altered CMOR memory in GAERS compared to the non-epileptic control (NEC) strain. GAERS demonstrated recognition memory deficits in the visual and crossmodal variations of the CMOR task that were reversed by the highest dose of Z944. Electroencephalogram recordings determined that deficits in CMOR memory in GAERS were not the result of seizures during task performance. In contrast, NEC showed a decrease in CMOR memory following Z944 treatment. These findings suggest that T-type calcium channels mediate CMOR in both the GAERS and NEC strains. Future research into the therapeutic potential of T-type calcium channel regulation may be particularly fruitful for the treatment of CAE and other disorders characterized by visual memory deficits.
T-type Ca
channels (Ca
3) represent emerging therapeutic targets for a range of neurological disorders, including epilepsy and pain. To aid the development and optimisation of new therapeutics, there ...is a need to identify novel chemical entities which act at these ion channels. A number of synthetic cannabinoid receptor agonists (SCRAs) have been found to exhibit activity at T-type channels, suggesting that cannabinoids may provide convenient chemical scaffolds on which to design novel Ca
3 inhibitors. However, activity at cannabinoid type 1 (CB
) receptors can be problematic because of central and peripheral toxicities associated with potent SCRAs. The putative SCRA MEPIRAPIM and its analogues were recently identified as Ca
3 inhibitors with only minimal activity at CB
receptors, opening the possibility that this scaffold may be exploited to develop novel, selective Ca
3 inhibitors. Here we present the pharmacological characterisation of SB2193 and SB2193F, two novel Ca
3 inhibitors derived from MEPIRAPIM.
The potency of SB2193 and SB2193F was evaluated
using a fluorometric Ca
flux assay and confirmed using whole-cell patch-clamp electrophysiology.
docking to the cryo-EM structure of Ca
3.1 was also performed to elucidate structural insights into T-type channel inhibition. Next,
pharmacokinetic parameters in mouse brain and plasma were determined using liquid chromatography-mass spectroscopy. Finally, anticonvulsant activity was assayed in established genetic and electrically-induced rodent seizure models.
Both MEPIRAPIM derivatives produced potent inhibition of Ca
3 channels and were brain penetrant, with SB2193 exhibiting a brain/plasma ratio of 2.7. SB2193 was further examined in mouse seizure models where it acutely protected against 6 Hz-induced seizures. However, SB2193 did not reduce spontaneous seizures in the
mouse model of Dravet syndrome, nor absence seizures in the Genetic Absence Epilepsy Rat from Strasbourg (GAERS). Surprisingly, SB2193 appeared to increase the incidence and duration of spike-and-wave discharges in GAERS animals over a 4 h recording period.
These results show that MEPIRAPIM analogues provide novel chemical scaffolds to advance Ca
3 inhibitors against certain seizure types.
Cannabis sativa has gained popularity as a "natural substance", leading many to falsely assume that it is not harmful. This assumption has been documented amongst pregnant mothers, many of whom ...consider Cannabis use during pregnancy as benign. The purpose of this study was to validate a Cannabis smoke exposure model in pregnant rats by determining the plasma levels of cannabinoids and associated metabolites in the dams after exposure to either Cannabis smoke or injected cannabinoids. Maternal and fetal cytokine and chemokine profiles were also assessed after exposure. Pregnant Sprague-Dawley rats were treated daily from gestational day 6-20 with either room air, i.p. vehicle, inhaled high-Δ
-tetrahydrocannabinol (THC) (18% THC, 0.1% cannabidiol CBD) smoke, inhaled high-CBD (0.7% THC, 13% CBD) smoke, 3 mg/kg i.p. THC, or 10 mg/kg i.p. CBD. Our data reveal that THC and CBD, but not their metabolites, accumulate in maternal plasma after repeated exposures. Injection of THC or CBD was associated with fewer offspring and increased uterine reabsorption events. For cytokines and chemokines, injection of THC or CBD up-regulated several pro-inflammatory cytokines compared to control or high-THC smoke or high-CBD smoke in placental and fetal brain tissue, whereas smoke exposure was generally associated with reduced cytokine and chemokine concentrations in placental and fetal brain tissue compared to controls. These results support existing, but limited, knowledge on how different routes of administration contribute to inconsistent manifestations of cannabinoid-mediated effects on pregnancy. Smoked Cannabis is still the most common means of human consumption, and more preclinical investigation is needed to determine the effects of smoke inhalation on developmental and behavioural trajectories.
•Olfactory working memory was tested in a rat model of maternal immune activation.•No differences were observed in a nonmatching-to-sample task.•PolyI:C offspring were impaired on acquisition and ...performance of the odor span task.•Increasing the delay between stimuli decreased performance of the odor span task.
Maternal immune activation during pregnancy is an environmental risk factor for psychiatric illnesses such as schizophrenia in the offspring. Patients with schizophrenia display an array of cognitive symptoms, including impaired working memory capacity. Rodent models have been developed to understand the relationship between maternal immune activation and the cognitive symptoms of schizophrenia. The present experiment was designed to test whether maternal immune activation with the viral mimetic polyinosinic:polycytidylic acid (polyI:C) during pregnancy affects working memory capacity of the offspring. Pregnant Long Evans rats were treated with either saline or polyI:C (4mg/kg; i.v.) on gestational day 15. Male offspring of the litters (2–3months of age) were subsequently trained on a nonmatching-to-sample task with odors. After a criterion was met, the rats were tested on the odor span task, which requires rats to remember an increasing span of different odors to receive food reward. Rats were tested using delays of approximately 40s during the acquisition of the task. Importantly, polyI:C- and saline-treated offspring did not differ in performance of the nonmatching-to-sample task suggesting that both groups could perform a relatively simple working memory task. In contrast, polyI:C-treated offspring had reduced span capacity in the middle and late phases of odor span task acquisition. After task acquisition, the rats were tested using the 40s delay and a 10min delay. Both groups showed a delay-dependent decrease in span, although the polyI:C-treated offspring had significantly lower spans regardless of delay. Our results support the validity of the maternal immune activation model for studying the cognitive symptoms of neurodevelopmental disorders such as schizophrenia.
There is significant interest in the use of cannabinoids for the treatment of many epilepsies including absence epilepsy (AE). Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model many aspects ...of AE including the presence of spike‐and‐wave discharges (SWDs) on electroencephalogram (EEG) and behavioral comorbidities, such as elevated anxiety. However, the effects of cannabis plant‐based phytocannabinoids have not been tested in GAERS. Therefore, we investigated how SWDs in GAERS are altered by the two most common phytocannabinoids, Δ9‐tetrahydrocannabinol (THC) and cannabidiol (CBD), and exposure to smoke from two different chemovars of cannabis. Animals were implanted with bipolar electrodes in the somatosensory cortex and EEGs were recorded for 2 hr. Injected THC (1–10 mg/kg, i.p.) dose‐dependently increased SWDs to over 200% of baseline. In contrast, CBD (30–100 mg/kg, i.p.) produced a ~50% reduction in SWDs. Exposure to smoke from a commercially available chemovar of high‐THC cannabis (Mohawk, Aphria Inc.) increased SWDs whereas a low‐THC/high‐CBD chemovar of cannabis (Treasure Island, Aphria Inc.) did not significantly affect SWDs in GAERS. Pre‐treatment with a CB1R antagonist (SR141716A) did not prevent the high‐THC cannabis smoke from increasing SWDs, suggesting that the THC‐mediated increase may not be CB1R‐dependent. Plasma concentrations of THC and CBD were similar to previously reported values following injection and smoke exposure. Compared to injected CBD, it appears Treasure Island did not increase plasma levels sufficiently to observe an anti‐epileptic effect. Together these experiments provide initial evidence that acute phytocannabinoid administration exerts the biphasic modulation of SWDs and may differentially impact patients with AE.
Genetic Absence Epilepsy Rats from Strasbourg (GAERS) spontaneously produce spike‐and‐slow wave discharges (SWDs). In the first experiments assessing cannabinoids in GAERS, injected tetrahydrocannabinol (Δ9‐THC) dose‐dependently increased SWDs, whereas injected cannabidiol (CBD) reduced these events. Furthermore, smoke exposure from high‐Δ9‐THC cannabis increased SWDs, but high‐CBD cannabis had no effect. These experiments show dissociable effects using two different exposure paradigms.
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