T-type calcium channels regulate the acquisition and recall of conditioned fear in male, Wistar rats.

The T-type calcium channel blocker, Z944, has been used as a pharmacological tool to assess T-type calcium channel function and examined for use as an anti-epileptic. As Z944 affects fear learning and memory in a rodent model of absence epilepsy, it is important to determine the effect of Z944 on learning and memory in a non-disease outbred rodent strain. This study examined the dose-dependent effects (5 mg/kg, 10 mg/kg, i.p.) of acute systemic treatment with Z944 on the learning and memory of fear conditioning and extinction in male Wistar rats. Z944 administered prior to the acquisition of fear conditioning significantly increased freezing prior to acquisition and extinction, during acquisition, and impaired recall of fear memory 24 h later. These findings suggest that T-type calcium channel activity may be required during associative learning for intact long-term memory. Enhanced fear behaviour observed prior to acquisition and extinction, and during acquisition could reflect an increase in anxiety, however, further testing is needed to determine the effect of Z944 on anxiety during fear conditioning and extinction. The use of Z944 for therapeutic purposes should consider the potential effects of Z944 on learning and memory in clinical populations.

Roles of the medial prefrontal cortex, mediodorsal thalamus, and their combined circuit for performance of the odor span task in rats: analysis of memory capacity and foraging behavior.

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.

Maternal Immune Activation during Pregnancy Alters the Behavior Profile of Female Offspring of Sprague Dawley Rats.

Sex differences are documented in psychiatric and neurological disorders, yet most preclinical animal research has been conducted in males only. There is a need to better understand of the nature of sex differences in brain disease in order to meet the needs of psychiatric patients. We present the behavior profile of adult female offspring produced using a maternal immune activation (MIA) model where pregnant rats receive an immune stimulant and the offspring typically show various abnormalities consistent with psychiatric illnesses such as schizophrenia and autism. The results in female offspring were compared to a previously published cohort of their male siblings (Lins et al., 2018). We examined prepulse inhibition (PPI), sociability, MK-801-induced locomotor activity, crossmodal object recognition (CMOR), and oddity discrimination; behaviors relevant to the positive, negative, and cognitive symptoms of schizophrenia. No between-treatment differences in PPI or locomotor activity were noted. Tactile memory was observed in the control and treated female offspring, visual recognition memory was deficient in the polyinosinic:polycytidylic acid (polyI:C) offspring only, and both groups lacked crossmodal recognition. PolyI:C offspring were impaired in oddity preference and had reduced preference for a stranger conspecific in a sociability assay. Systemic maternal CXCL1, IL-6, and TNF-a levels 3 h after polyI:C treatment were determined, but no relationship was found between these cytokines and the behavior seen in the adult female offspring. Overall, female offspring of polyI:C-treated dams display an array of behavior abnormalities relevant to psychiatric illnesses such as schizophrenia similar to those previously reported in male rats.

The T-type calcium channel blocker Z944 reduces conditioned fear in Genetic Absence Epilepsy Rats from Strasbourg and the non-epileptic control strain.

Genetic Absence Epilepsy Rats from Strasbourg (GAERS) are a rodent model of childhood absence epilepsy (CAE) that display a gain-of-function mutation in the gene encoding the Cav3.2 T-type calcium channel. GAERS demonstrate heightened learning and delayed extinction of fear conditioning. Our objective in the present study was to examine the effects of the pan-T-type calcium channel blocker Z944 on the acquisition, consolidation and extinction of conditioned fear in GAERS and the non-epileptic control (NEC) strain. Z944 (10 mg/kg; ip) was administered 15 min prior to either acquisition, extinction day 1 (24 hr later), acquisition and extinction day 1, or during the consolidation (post-acquisition) of tone-cued fear conditioning. Extinction was examined 24 and 48 hr after conditioning. In drug naïve GAERS, increased freezing during the acquisition and extinction phases of fear conditioning was found. Short-term effects of Z944 on performance were observed as Z944 increased freezing during testing on the day it was administered. Z944 administered prior to the acquisition phase had a long-term effect on extinction. Specifically, both GAERS and NECs showed a decrease in freezing during extinction relative to drug naïve GAERS and NEC rats respectively. Regardless of strain or treatment, female rats showed reduced extinction of fear relative to male rats. These results demonstrate that T-type calcium channels contribute to the neural systems that mediate the learning and memory of conditioned fear. Overall, these findings suggest that T-type calcium channel blockers show promise in the treatment of learning impairments observed in disorders such as CAE.

The T-type calcium channel antagonist, Z944, alters social behavior in Genetic Absence Epilepsy Rats from Strasbourg.

Abnormalities in social behavior are a co-morbid symptom of idiopathic generalized epilepsies such as childhood absence epilepsy. The Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model is a spontaneously occurring absence epilepsy phenotype closely correlated to that of human absence epilepsies. Similar to the human conditions, GAERS display social abnormalities. Previous studies have only demonstrated social abnormalities in female GAERS, whereas social problems are observed in male and female patients. Seizures in GAERS result in part due to a gain-of-function missense mutation in the Cav3.2 T-type calcium channel gene. This study examined the effects of the pan-T-type calcium channel antagonist, Z944, on social interaction behaviors in male and female GAERS using an open field social interaction test. A second objective of this study was to examine the effects of Z944 on anxiety-like behavior in an open field locomotion test and elevated plus maze. Results showed a decrease in social activity in GAERS relative to non-epileptic control (NEC) rats. Acute, systemic Z944 (5 mg/kg; i.p.) consistently reduced introductory and aggressive behaviors in both GAERS and NECs whereas strain effects were observed for over-and-under crawl behaviors. In the open field locomotion test and elevated plus maze, Z944 increased anxiety-like behaviors in GAERS, whereas, Z944 produced inconsistent effects on anxiety-like behaviors in NECs. The results of this study suggest that the regulation of T-type calcium channel activity may be a useful strategy for the development of new therapeutic approaches for the treatment of social and affective abnormalities observed in absence epilepsy disorders.

Prospective Analysis of the Effects of Maternal Immune Activation on Rat Cytokines during Pregnancy and Behavior of the Male Offspring Relevant to Schizophrenia.

Influenza during pregnancy is associated with the development of psychopathology in the offspring. We sought to determine whether maternal cytokines produced following administration of viral mimetic polyinosinic-polycytidylic acid (polyI:C) to pregnant rats were predictive of behavioral abnormalities in the adult offspring. Timed-pregnant Sprague Dawley rats received a single intravenous injection of 4-mg/kg polyI:C or saline on gestational day (GD)15. Blood was collected 3 h later for serum analysis of cytokine levels with ELISA. Male offspring were tested in a battery of behavioral tests during adulthood and behavior was correlated with maternal cytokine levels. Maternal serum levels of CXCL1 and interleukin (IL)-6, but not tumor necrosis factor (TNF)-α or CXCL2, were elevated in polyI:C-treated dams. PolyI:C-treated dams experienced post-treatment weight loss and polyI:C pups were smaller than controls at postnatal day (PND)1. Various behavior alterations were seen in the polyI:C-treated offspring. Male polyI:C offspring had enhanced MK-801-induced locomotion, and reduced sociability. PolyI:C offspring failed to display crossmodal and visual memory, and oddity preference was also impaired. Set-shifting, assessed with a lever-based operant conditioning task, was facilitated while touchscreen-based reversal learning was impaired. Correlations were found between maternal serum concentrations of CXCL1, acute maternal temperature and body weight changes, neonatal pup mass, and odd object discrimination and social behavior. Overall, while the offspring of polyI:C-treated rats displayed behavior abnormalities, maternal serum cytokines were not related to the long-term behavior changes in the offspring. Maternal sickness effects and neonatal pup size may be better indicators of later effects of maternal inflammation in the offspring.

Effects of the T-type calcium channel antagonist Z944 on paired associates learning and locomotor activity in rats treated with the NMDA receptor antagonist MK-801.

RATIONALE: Currently available antipsychotics are unsatisfactory given their side effects and limited efficacy for the cognitive symptoms of schizophrenia. Many currently available drugs, such as haloperidol, are T-type calcium channel antagonists in addition to their well-established antagonism of dopamine D2 receptors. Thus, preclinical research into the effects of T-type calcium channel antagonists/blockers in behavioral assays related to schizophrenia may inform novel therapeutic strategies. OBJECTIVES: We explored the effects of a recently developed highly selective T-type calcium channel antagonist, Z944 (2.5, 5.0, 10.0 mg/kg), on the MK-801 (0.15 mg/kg) model of acute psychosis. METHODS: To examine the effects of Z944 on behaviors relevant to schizophrenia, we tested touchscreen-based paired associates learning given its relevance to the cognitive symptoms of the disorder and locomotor activity given its relevance to the positive symptoms. RESULTS: Acute treatment with Z944 failed to reverse the visuospatial associative memory impairments caused by MK-801 in paired associates learning. The highest dose of drug (10.0 mg/kg) given alone produced subtle impairments on paired associates learning. In contrast, Z944 (5.0 mg/kg) blocked the expected increase in locomotion following MK-801 treatment in a locomotor assay. CONCLUSIONS: These experiments provide support that Z944 may reduce behaviors relevant to positive symptoms of schizophrenia, although additional study of its effects on cognition is required. These findings and other research suggest T-type calcium channel antagonists may be an alternative to currently available antipsychotics with less serious side effects.

T-type calcium channels in the orbitofrontal cortex mediate sensory integration as measured using a spontaneous oddity task in rats.

The roles of low-voltage-activated (T-type) calcium channels in brain diseases have been studied extensively. Less is known regarding the involvement of T-type channels in cognition and behavior. Sensory integration (SI) is a cognitive process whereby the brain uses unimodal or multimodal sensory features to create a comprehensive representation of the environment. The multisensory object oddity (MSO) task assesses SI using combinations of sensory features of objects, either in the same or different sensory modalities. The regulation of SI involves the orbitofrontal cortex (OFC), an area which shows high levels of T-type calcium channel expression. We tested the effects of blocking T-type calcium channels on the MSO task with the selective T-type antagonist, Z944 (5 mg/kg; i.p. systemic; 100 or 500 µM OFC infusion), in male Long Evans rats. With systemic treatment, Z944 impaired the visual and visual-olfactory versions of the task. Infusion of 100 and 500 µM Z944 produced deficits in the olfactory version of the task. In addition, only vehicle-infused, but not Z944-infused, rats showed significant performance above chance for all task variants. Thus, the present results suggest that T-type calcium channels in OFC are involved in SI of features in an oddity task. Given that unimodal SI was disrupted by OFC infusions of Z944, the deficits in the multimodal task must be interpreted with caution. As SI is disrupted in psychiatric disorders, further investigations elucidating the brain regions implicated in SI regulation by T-type calcium channels may help inform therapeutic development for those suffering from SI impairments.

Performance of the odour span task is not impaired following inactivations of parietal cortex in rats.

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.