Insulin‐mediated signalling in the brain is critical for neuronal functioning. Insulin resistance is implicated in the development of some neurological diseases, although changes associated with ...absence epilepsy have not been established yet. Therefore, we examined the major components of PI3K/Akt‐mediated insulin signalling in cortical, thalamic, and hippocampal tissues collected from Genetic Absence Epilepsy Rats from Strasbourg (GAERS) and Non‐Epileptic Control (NEC) rats. Insulin levels were also measured in plasma and cerebrospinal fluid (CSF). For the brain samples, the nuclear fraction (NF) and total homogenate (TH) were isolated and investigated for insulin signalling markers including insulin receptor beta (IRβ), IR substrate‐1 and 2 (IRS1 & 2), phosphatase and tensin homologue (PTEN), phosphoinositide 3‐kinase phospho‐85 alpha (PI3K p85α), phosphatidylinositol 4,5‐bisphosphate, phosphatidylinositol (3,4,5)‐trisphosphate, protein kinase B (PKB/Akt1/2/3), glucose transporter‐1 and 4 (GLUT1 & 4) and glycogen synthase kinase‐3β (GSK3β) using western blotting. A significant increase in PTEN and GSK3β levels and decreased PI3K p85α and pAkt1/2/3 levels were observed in NF of GAERS cortical and hippocampal tissues. IRβ, IRS1, GLUT1, and GLUT4 levels were significantly decreased in hippocampal TH of GAERS compared to NEC. A non‐significant increase in insulin levels was observed in plasma and CSF of GAERS rats. An insulin sensitivity assay showed decreased p‐Akt level in cortical and hippocampal tissues. Together, altered hippocampal insulin signalling was more prominent in NF and TH compared to cortical and thalamic regions in GAERS. Restoring insulin signalling may improve the pathophysiology displayed by GAERS, including the spike‐and‐wave discharges that relate to absence seizures in patients.
•Parietal cortex inactivations do not impair the odour span task in rats.•Cross-modal object recognition memory depends on the parietal cortex.•There may be less parietal involvement in working ...memory in rats than in primates.•Parietal cortex may only mediate visuospatial working memory.
Working memory (WM) is the ability to temporarily store information for use and manipulation. Working memory is thought to depend on a distributed set of higher cortical areas including the prefrontal and parietal cortex in primates while relatively little research has been conducted in rodents to elucidate the exact role of the parietal cortex (PC) in WM, particularly in relation to the construct of WM capacity. Previous work in our lab demonstrates that performance of the odour span task (OST), an olfactory incremental delayed nonmatching-to-sample task, relies on the medial prefrontal cortex (mPFC). However, the effects of inactivating the PC on the OST have not been studied. Therefore, the present experiment assessed the effects of inactivating the PC with the GABA receptor agonists muscimol/baclofen on performance of the OST. Infusions of muscimol/baclofen did not disrupt working memory performance, assessed by the mean number of odours each rat could remember before making an error on each day of testing. In contrast, performance of a positive control task, spontaneous cross-modal object recognition, was impaired by inactivating the PC. These results suggest that performance of the OST does not depend on the PC in rats. Our results are notable given past research demonstrating the importance of the parietal cortex for attentional processes and working memory in other tasks.
Changes in brain activity can entrain cerebrovascular dynamics, though this has not been extensively investigated in pathophysiology. We assessed whether pathological network activation (i.e. ...seizures) in the Genetic Absence Epilepsy Rat from Strasbourg (GAERS) could alter dynamic fluctuations in local oxygenation. Spontaneous absence seizures in an epileptic rat model robustly resulted in brief dips in cortical oxygenation and increased spectral oxygen power at frequencies greater than 0.08 Hz. Filtering oxygen data for these fast dynamics was sufficient to distinguish epileptic vs. non-epileptic rats. Furthermore, this approach distinguished brain regions with seizures from seizure-free brain regions in the epileptic rat strain. We suggest that fast oxygen dynamics may be a useful biomarker for seizure network identification and could be translated to commonly used clinical tools that measure cerebral hemodynamics.
Dentine‐ and enamel‐forming cells secrete matrix in consistent rhythmic phases, resulting in the formation of successive microscopic growth lines inside tooth crowns and roots. Experimental studies ...of various mammals have proven that these lines are laid down in subdaily, daily (circadian), and multidaily rhythms, but it is less clear how these rhythms are initiated and maintained. In 2001, researchers reported that lesioning the so‐called master biological clock, the suprachiasmatic nucleus (SCN), halted daily line formation in rat dentine, whereas subdaily lines persisted. More recently, a key clock gene (Bmal1) expressed in the SCN in a circadian manner was also found to be active in dentine‐ and enamel‐ secretory cells. To probe these potential neurological and local mechanisms for the production of rhythmic lines in teeth, we reexamined the role of the SCN in growth line formation in Wistar rats and investigated the presence of daily lines in Bmal1 knockout mice (Bmal1−/−). In contrast to the results of the 2001 study, we found that both daily and subdaily growth lines persisted in rat dentine after complete or partial SCN lesion in the majority of individuals. In mice, after transfer into constant darkness, daily rhythms continued to manifest as incremental lines in the dentine of each Bmal1 genotype (wild‐type, Bmal+/–, and Bmal1−/−). These results affirm that the manifestation of biological rhythms in teeth is a robust phenomenon, imply a more autonomous role of local biological clocks in tooth growth than previously suggested, and underscore the need further to elucidate tissue‐specific circadian biology and its role in incremental line formation. Investigations of this nature will strengthen an invaluable system for determining growth rates and calendar ages from mammalian hard tissues, as well as documenting the early lives of fossil hominins and other primates.
Rats subject to SCN lesioning maintain incremental rhythms in dentine ranging from daily (5 lines over 5 days from labels 1–2) to subdaily (~13 lines over 7 days from labels 2–3, followed by ~11–12 lines over 4 days from label 3 to sacrifice). Furthermore, the lack of a local rhythmically expressed transcription factor, BMAL1, did not lead to the cessation of daily growth increments in Bmal1−/− mice after transfer to constant darkness. Biological rhythms in teeth are a robust and enigmatic phenomenon.
Childhood absence epilepsy (CAE) is associated with interictal co-morbid symptoms including abnormalities in social behaviour. Genetic Absence Epilepsy Rats from Strasbourg (GAERS) is a model of CAE ...that exhibits physiological and behavioural alterations characteristic of the human disorder. However, it is unknown if GAERS display the social deficits often observed in CAE. Sociability in rodents is thought to be mediated by neural circuits densely populated with T-type calcium channels and GAERS contain a missense mutation in the Cav3.2 T-type calcium channel gene. Thus, the objective of this study was to examine the effects of the clinical stage pan-T-type calcium channel blocker, Z944, on sociability behaviour in male and female GAERS and non-epileptic control (NEC) animals. Female GAERS showed reduced sociability in a three-chamber sociability task whereas male GAERS, male NECs, and female NECs all showed a preference for the chamber containing a stranger rat. In drug trials, pre-treatment with 5mg/kg of Z944 normalized sociability in female GAERS. In contrast, female NECs showed impaired sociability following Z944 treatment. Dose-dependent decreases in locomotor activity were noted following Z944 treatment in both strains. Treatment with 10mg/kg of Z944 altered exploration such that only 8 of the 16 rats tested explored both sides of the testing chamber. In those that explored the chamber, significant preference for the stranger rat was observed in GAERS but not NECs. Overall, the data suggest that T-type calcium channels are critical in regulating sociability in both GAERS and NEC animals. Future research should focus on T-type calcium channels in the treatment of sociability deficits observed in disorders such as CAE.
•Sociability was tested in a rat model of absence epilepsy.•Sociability was impaired in female rats with absence seizures.•The T-type calcium channel blocker Z944 reversed the sociability deficits.•Z944 produced sociability deficits in female animals of the control strain.
Perineuronal nets (PNNs) are specialized extracellular matrix structures that surround subsets of neurons throughout the central nervous system (CNS). They are made up of chondroitin sulfate ...proteoglycans (CSPGs), hyaluronan, tenascin-R, and many other link proteins that together make up their rigid and lattice-like structure. Modulation of PNNs can alter synaptic plasticity and thereby affect learning, memory, and cognition. In the present study, we degraded PNNs in the medial prefrontal (mPFC) and posterior parietal (PPC) cortices of Long-Evans rats using the enzyme chondroitinase ABC (ChABC), which cleaves apart CSPGs. We then measured the consequences of PNN degradation on spatial working memory (WM) with a trial-unique, non-matching-to location (TUNL) automated touchscreen task. All rats were trained with a standard 6 sec delay and 20 sec inter-trial interval (ITI) and then tested under four different conditions: a 6 sec delay, a variable 2 or 6 sec delay, a 2 sec delay with a 1 sec ITI (interference condition), and a 20 sec delay. Rats that received mPFC ChABC treatment initially performed TUNL with higher accuracy, more selection trials completed, and fewer correction trials completed compared to controls in the 20 sec delay condition but did not perform differently from controls in any other condition. Rats that received PPC ChABC treatment did not perform significantly differently from controls in any condition. Posthumous immunohistochemistry confirmed an increase in CSPG degradation products (C4S stain) in the mPFC and PPC following ChABC infusions while WFA staining intensity and parvalbumin positive neuron number were decreased following mPFC, but not PPC, ChABC infusions. These findings suggest that PNNs in the mPFC play a subtle role in spatial WM, but PNNs in the PPC do not. Furthermore, it appears that PNNs in the mPFC are involved in adapting to a challenging novel delay, but that they do not play an essential role in spatial WM function.
The posterior parietal cortex (PPC) participates in cognitive processes including working memory (WM), sensory evidence accumulation, and perceptually guided decision making. However, surprisingly ...little work has used temporally precise manipulations to dissect its role in different epochs of behavior taking place over short timespans, such as WM tasks. As a result, a consistent view of the temporally precise role of the PPC in these processes has not been described. In the present study, we investigated the temporally specific role of the PPC in the Trial‐Unique, Nonmatching‐to‐Location (TUNL) task, a touchscreen‐based, visuospatial WM task that relies on the PPC. To disrupt PPC activity in a temporally precise manner, we applied mild intracranial electrical stimulation (ICES). We found that intra‐PPC ICES (100 μA) significantly impaired accuracy in TUNL without significantly altering response latency. Moreover, we found that the impairment was specific to ICES applied during the delay and test phases of TUNL. Consistent with previous reports showing delay‐ and choice‐specific neuronal activity in the PPC, the results provide evidence that the rat PPC is required for maintaining memory representations of stimuli over a delay period as well as for making successful comparisons and choices between test stimuli. In contrast, the PPC appears not to be critical for initial encoding of sample stimuli. This pattern of results may indicate that early encoding of visual stimuli is independent of the PPC or that the PPC becomes engaged only when visual stimuli are spatially complex or involve memory or decision making.
A, Schematic showing the general progression of a TUNL trial. B, A representation of the interior of a touchscreen chamber used in the experiment. C, A schematic representation of example stimulus distances used in TUNL
Working memory (WM), the capacity for short-term storage of small quantities of information for immediate use, is thought to depend on activity within the prefrontal cortex. Recent evidence indicates ...that the prefrontal neuronal activity supporting WM is driven by thalamocortical connections arising in mediodorsal thalamus (mdThal). However, the role of these connections has not been studied using olfactory stimuli leaving open the question of whether this circuit extends to all sensory modalities. Additionally, manipulations of the mdThal in olfactory memory tasks have yielded mixed results. In the present experiment, we investigated the role of connections between the rat medial prefrontal cortex (mPFC) and mdThal in the odor span task (OST) using a pharmacological contralateral disconnection technique. Inactivation of either the mPFC or mdThal alone both significantly impaired memory performance in the OST, replicating previous findings with the mPFC and confirming that the mdThal plays an essential role in intact OST performance. Contralateral disconnection of the two structures impaired OST performance in support of the idea that the OST relies on mPFC-mdThal connections, but ipsilateral control infusions also impaired performance, complicating this interpretation. We also performed a detailed analysis of rats' errors and foraging behavior and found a dissociation between mPFC and mdThal inactivation conditions. Inactivation of the mdThal and mPFC caused a significant reduction in the number of approaches rats made per odor, whereas only mdThal inactivation or mPFC-mdThal disconnection caused significant increases in choice latency. Our results confirm that the mdThal is necessary for performance of the OST and that it may critically interact with the mPFC to mediate OST performance. Additionally, we have provided evidence that the mPFC and mdThal play dissociable roles in mediating foraging behavior.
•The effects of Cannabis smoke exposure were assessed using touchscreen tasks of executive function in adult male rats.•Acute high-THCCannabis smoke or THC injection impaired working memory in the ...TUNL task.•Neither acuteCannabissmoke exposure nor THC injection affected measures of attention or impulsivity in the 5-CSRTT.•Plasma levels of cannabinoids and their metabolites following all treatments are presented.•Results support the development of more ecologically valid rodent models of smoke exposure.
Executive functions including working memory (WM) and attention are altered following Cannabis exposure in humans. To test for similar effects in a rodent model, we exposed adult male rats to acute Cannabis smoke before testing them on touchscreen-based tasks that assess these executive processes. The trial-unique, delayed nonmatching-to-location (TUNL) task was used to evaluate WM, task performance at different spatial pattern separations, and response latencies. The five-choice serial reaction time task (5-CSRTT) was used to measure attention, impulsivity, perseveration, and response latencies. Rats were exposed acutely to high- Δ9-tetrahydrocannabinol (THC), low-CBD (Mohawk) and low-THC, high-CBD (Treasure Island) strains of Cannabis smoke using a chamber inhalation system. The effects of Cannabis smoke were directly compared to systemic Δ9-THC injection (3.0 mg/kg; i.p.). TUNL task performance was significantly impaired following acute high-THC smoke exposure or THC injections, but not low-THC smoke exposure, with no effects on response latencies. Fewer total trials and selection trials were also performed following THC injections. Performance was poorer for smaller separation distances in all groups. Neither acute smoke exposure, nor injected THC, impacted attentional processes, impulsivity, perseverations, or response latencies in the 5-CSRTT. Pharmacokinetic analysis of rat plasma revealed significantly higher THC levels following injections than smoke exposure 30 min following treatment. Exposure to low-THC, high-CBD Cannabis smoke significantly increased CBD in plasma, relative to the other treatments. Taken together, our results suggest that WM processes as measured by the TUNL task are more sensitive to THC exposure than the attentional and impulsivity measures assessed using the 5-CSRTT.
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