Structural interhemispheric connectivity defects in mouse models of BBSOAS: Insights from high spatial resolution 3D white matter tractography.

White matter (WM) tract formation and axonal pathfinding are major processes in brain development allowing to establish precise connections between targeted structures. Disruptions in axon pathfinding and connectivity impairments will lead to neural circuitry abnormalities, often associated with various neurodevelopmental disorders (NDDs). Among several neuroimaging methodologies, Diffusion Tensor Imaging (DTI) is a magnetic resonance imaging (MRI) technique that has the advantage of visualizing in 3D the WM tractography of the whole brain non-invasively. DTI is particularly valuable in unpinning structural tract connectivity defects of neural networks in NDDs. In this study, we used 3D DTI to unveil brain-specific tract defects in two mouse models lacking the Nr2f1 gene, which mutations in patients have been proven to cause an emerging NDD, called Bosch-Boonstra-Schaaf Optic Atrophy (BBSOAS). We aimed to investigate the impact of the lack of cortical Nr2f1 function on WM morphometry and tract microstructure quantifications. We found in both mutant mice partial loss of fibers and severe misrouting of the two major cortical commissural tracts, the corpus callosum, and the anterior commissure, as well as the two major hippocampal efferent tracts, the post-commissural fornix, and the ventral hippocampal commissure. DTI tract malformations were supported by 2D histology, 3D fluorescent imaging, and behavioral analyses. We propose that these interhemispheric connectivity impairments are consistent in explaining some cognitive defects described in BBSOAS patients, particularly altered information processing between the two brain hemispheres. Finally, our results highlight 3DDTI as a relevant neuroimaging modality that can provide appropriate morphometric biomarkers for further diagnosis of BBSOAS patients.

Hyperactive and anxiolytic-like behaviors result from loss of COUP-TFI/Nr2f1 in the mouse cortex.

The nuclear receptor COUP TFI (also known as Nr2f1) plays major roles in specifying distinct neuronal subtypes during patterning of the neocortical motor and somatosensory cortex, as well as in regulating the longitudinal growth of the hippocampus during development. In humans, mutations in the NR2F1 gene lead to a global developmental delay and intellectual disabilities. While more than 30% of patients show behavioral features of autism spectrum disorder, 16% of haploinsufficient children show signs of hyperactivity and impulsivity. Loss of COUP-TFI in the cortical mouse primordium results in altered area organization and serotonin distribution, abnormal coordination of voluntary movements and learning and memory deficits. Here, we asked whether absence of COUP-TFI affects locomotor activity, anxiety, as well as depression. Mice mutant for COUP-TFI have normal motor coordination, but significant traits of hyperactivity, which does not seem to respond to N-Methyl-D-aspartate (NMDA) antagonists. However, no changes in anxiety, despite increased locomotor performances, were observed in the open field task. On the contrary, elevated plus maze and dark-light test explorations indicate a decreased anxiety-like behavior in COUP-TFI mutant mice. Finally, significantly reduced immobility in the forced swim test and no changes in anhedonia in the sucrose preference task suggest no particular depressive behaviors in mutant mice. Taken together, our study shows that loss of COUP-TFI leads to increased locomotor activity but less anxiety and contributes in further deciphering the pathophysiology of patients haploinsufficient for NR2F1.

Hippocampal neurogenesis protects against cocaine-primed relapse.

Accumulating evidence demonstrates a functional role for the hippocampus in mediating relapse to cocaine-seeking behavior and extinction-induced inhibition of cocaine seeking, and dentate gyrus neurogenesis in the hippocampus may have a role. Here, we tested the hypothesis that disruption of normal hippocampal activity during extinction alters relapse to cocaine-seeking behavior as a function of dentate gyrus neurogenesis. Adult rats were trained to self-administer cocaine on a fixed-ratio schedule, followed by extinction and cocaine-primed reinstatement testing. Some rats received low-frequency stimulation (LFS; 2 Hz for 25 minutes) after each extinction session in the dorsal or ventral hippocampal formation. All rats received an injection of the mitotic marker 5-bromo-2'-deoxyuridine (BrdU) to label developing dentate gyrus neurons during self-administration, as well as before or after extinction and LFS. We found that LFS during extinction did not alter extinction behavior but enhanced cocaine-primed reinstatement. Cocaine self-administration reduced levels of 24-day-old BrdU cells and dentate gyrus neurogenesis, which was normalized by extinction. LFS during extinction prevented extinction-induced normalization of dentate gyrus neurogenesis and potentiated cocaine-induced reinstatement of drug seeking. LFS inhibition of extinction-induced neurogenesis was not due to enhanced cell death, revealed by quantification of activated caspase3-labeled cells. These data suggest that LFS during extinction disrupts hippocampal networking by disrupting neurogenesis and also strengthens relapse-like behaviors. Thus, newly born dentate gyrus neurons during withdrawal and extinction learning facilitate hippocampal networking that mediates extinction-induced inhibition of cocaine seeking and may play a key role in preventing relapse.

Prefrontal high-frequency stimulation prevents sub-conditioning procedure-provoked, but not acute stress-provoked, reemergence of extinguished fear.

We have recently shown that post-extinction exposure of rats to a sub-conditioning procedure (SCP, i.e., retraining with a shock intensity that is too weak to induce by itself significant fear conditioning) or to acute stress provokes reemergence of extinguished fear. Furthermore, this SCP effect can be abolished by high-frequency stimulation (HFS) of the medial prefrontal cortex (mPFC), when applied following the SCP. The aim of the present study was to test whether HFS of the mPFC is effective in preventing both SCP-induced and acute stress-provoked fear reemergence. Rats implanted with stimulating electrodes in the mPFC were trained to acquire high levels of freezing to conditioned auditory cue. This fear response was then extinguished. Three weeks later, no spontaneous recovery was observed, but rats exposed to either the SCP or acute stress again exhibited high levels of freezing. HFS of the mPFC, applied before provoking fear reemergence, prevented the effects of SCP, but not acute stress. These data suggest that acute stress may have more impact on functions of the mPFC and/or associated structures than a situational reminder of fear conditioning.

Post-extinction fluoxetine treatment prevents stress-induced reemergence of extinguished fear.

RATIONALE: The post-extinction exposure of rats to a sub-conditioning procedure (SCP; i.e., retraining with a shock intensity that is too weak to induce by itself significant fear conditioning) has been reported to provoke the reemergence of extinguished fear. This phenomenon can be prevented by chronic fluoxetine treatment. OBJECTIVES: We sought to examine another potential inducer of fear reemergence, acute stress, in rats and determine whether fluoxetine prevents this phenomenon. METHODS: Because in previous studies fluoxetine was administered before extinction, we first analyzed its effect on the SCP-associated reemergence of auditory-cued conditioned fear in rats injected after extinction to avoid any interaction between fluoxetine and extinction learning. Next, we used the same protocol but replaced the SCP with acute stress. RESULTS: We found that the SCP and acute stress, which were carried out 3 weeks after fear extinction, similarly provoked the reemergence of extinguished fear in rats injected with vehicle during the 3-week period. In contrast, the animals treated with fluoxetine during this period behaved similarly to those not exposed to an inducer of fear reemergence. CONCLUSIONS: Our data establish acute stress as an inducer of fear reemergence. The results provide further support for the hypothesis that fluoxetine interfered with mechanisms that reactivated extinguished fear, even when administered after fear extinction.

Decreased daytime motor activity associated with apathy in Alzheimer disease: an actigraphic study.

OBJECTIVE: Across all stages of Alzheimer disease (AD), apathy is the most common neuropsychiatric symptom. Studies using the Neuropsychiatric Inventory (NPI) have found that apathy is present in up to 70% of individuals with Alzheimer disease. One of the main difficulties in assessing apathy and other neuropsychiatric symptoms is the absence of reliable, objective measures. Motor activity assessment using ambulatory actigraphy could provide an indirect, objective evaluation of apathy. The aim of our study was to assess the relationship between apathy and daytime motor activity in AD, using ambulatory actigraphy. METHODS: One hundred seven AD outpatients wore a wrist actigraph (Motionlogger) during seven consecutive 24-hour periods to evaluate motor activity. Participants were divided into two subgroups according to their apathy subscores on the NPI: individuals with apathy (NPI-apathy subscores >4) and those without. Daytime mean motor activity scores were compared between the two subgroups. RESULTS: Individuals with AD who had symptoms of apathy (n = 43; age = 79 ± 4.7 years; Mini-Mental State Examination = 20.9 ± 4.8) had significantly lower daytime mean motor activity than AD patients without apathy (n = 64; age = 76.3 ± 7.7; Mini-Mental State Examination = 21.5 ± 4.7), while nighttime mean motor activity did not significantly differ between the two subgroups. CONCLUSIONS: Ambulatory actigraphy could be added to currently used questionnaires as a simple, objective technique for assessing apathy in the routine assessment of AD patients.

Re-emergence of extinguished auditory-cued conditioned fear following a sub-conditioning procedure: effects of hippocampal and prefrontal tetanic stimulations.

Post-extinction exposure of rats to a sub-conditioning procedure can evoke conditioned fear, which may correspond to fear return and/or fear learning potentiation. The aim of the present study was to clarify this issue and examine the effects of tetanic stimulation of the hippocampus (HPC) and medial prefrontal cortex (mPFC), two brain regions implicated in post-extinction modulation of conditioned fear. Rats were initially submitted to five tone-shock pairings with either a 0.7-mA or 0.1-mA shock. Tone-evoked freezing was observed only with the higher shock intensity, indicating that the 0.1-mA shock corresponded to a sub-conditioning procedure. All conditioned rats underwent fear extinction with 20 tone-alone trials. When retrained with the sub-conditioning procedure, they displayed again tone-evoked freezing, except when the initial tone was unpaired or a new tone was paired with the 0.1-mA shock, demonstrating fear return rather than fear learning potentiation. We also found that HPC and mPFC tetanic stimulations, applied 24h after the sub-conditioning procedure, similarly reduced this fear return. However, mPFC inactivation abolished temporary HPC tetanus effect, whereas HPC inactivation did not interfere with mPFC tetanus effect. These data confirm our previous findings and reveal the nature of HPC-mPFC interactions in post-extinction modulation of conditioned fear.

Chronic treatment with fluoxetine prevents the return of extinguished auditory-cued conditioned fear.

RATIONALE: We have recently shown that post-extinction exposure of rats to a sub-threshold reminder shock can reactivate extinguished context-related freezing and found that chronic treatment with fluoxetine before fear extinction prevents this phenomenon. OBJECTIVES: In the present study, we examined whether these findings would be confirmed with auditory fear conditioning. METHODS: Rats were initially submitted to a session of five tone-shock pairings with either a 0.7- or 0.1-mA shock and underwent, 3 days later, a session of 20 tone-alone trials. RESULTS: At the beginning of this latter session, we observed cue-conditioned freezing in rats that received the strong, but not the weak, shock. At the end, both groups (strong and weak shocks) displayed similar low levels of freezing, indicating fear extinction in rats exposed to the strong shock. These rats exhibited again high levels of cue-evoked freezing when exposed to three tone-shock pairings with 0.1-mA shock. This reemergence of cue-conditioned fear was completely abolished by chronic (over a 21-day period) fluoxetine treatment which spared, when administered before the initial fear conditioning, the original tone-shock association. CONCLUSIONS: These data extend our previous findings and suggest that chronic fluoxetine treatment favor extinction memory by dampening the reactivation of the original tone-shock association.

Comparing three morningness scales: age and gender effects, structure and cut-off criteria.

OBJECTIVE: To add to the validity of the French version of the Composite Scale of Morningness (CSM) by comparing its structure with that of the Morningness-Eveningness Questionnaire (MEQ), the most widely used scale to measure circadian typology. Second, to compare the cut-off criteria used to transform the continuous scores into categorical chronotypes. Third, to further test the effects of age and gender on morningness scores. The rMEQ, a shortened version of the MEQ, is also considered. METHODS: Four hundred and fifty-six students served as volunteer subjects and filled the CSM and the MEQ. RESULTS: There was no effect of gender, and the CSM and MEQ scores correlated above (+) 0.90 in both genders. Regarding age, morningness was stable before age 35 and increased afterwards. We replicated the three-factor structure of the CSM previously reported in five different cultures. The MEQ is longer and counted a fourth factor while the first three factors were quite identical to those extracted from the CSM. This comparative study emphasizes the recurrent problem of cut-off scores: the available values for both instruments result in a very poor concordance of chronotypes. CONCLUSIONS: Belonging to the evening-type is regarded as a risk factor for sleep disorders and its positive predictive value should be correctly assessed. Hence, normative scores standardized in such a way they reflect the effects of age, gender and culture are needed for the total score and the factor scores. To this extent, T-scores (with a mean of 50 and standard deviation of 10) would be suitable, and normative tables for French subjects (N = 1598) are given as supplemental data.

Hippocampal low-frequency stimulation and chronic mild stress similarly disrupt fear extinction memory in rats.

Disruptions of fear extinction-related potentiation of synaptic efficacy in the connection between the hippocampus (HPC) and the medial prefrontal cortex (mPFC) have been shown to impair the recall of extinction memory. This study was undertaken to examine if chronic mild stress (CMS), which is known to alter induction of HPC-mPFC long-term potentiation, would also interfere with both extinction-related HPC-mPFC potentiation and extinction memory. Following fear conditioning (5 tone-shock pairings), rats were submitted to fear extinction (20 tone-alone presentations), which produced an increase in the amplitude of HPC-mPFC field potentials. HPC low-frequency stimulation (LFS), applied immediately after training, suppressed these changes and induced fear return during the retention test (5 tone-alone presentations). CMS, delivered before fear conditioning, did not interfere with fear extinction but blocked the development of extinction-related potentiation in the HPC-mPFC pathway and impaired the recall of extinction. These findings suggest that HPC LFS may provoke metaplastic changes in HPC outputs that may mimic alterations associated with a history of chronic stress.

Hippocampal train stimulation modulates recall of fear extinction independently of prefrontal cortex synaptic plasticity and lesions.

It has been shown that long-term potentiation (LTP) develops in the connection between the mediodorsal thalamus (MD) and the medial prefrontal cortex (mPFC) and between the hippocampus (HPC) and the mPFC following fear extinction, and correlates with extinction retention. However, recent lesion studies have shown that combined lesions of the MD and mPFC do not interfere with extinction learning and retention, while inactivation of the dorsal HPC disrupts fear extinction memory. Here we found in rats that immediate post-training HPC low-frequency stimulation (LFS) suppressed extinction-related LTP in the HPC-mPFC pathway and induced difficulties in extinction recall. HPC tetanus, applied several hours later, failed to re-establish mPFC LTP but facilitated recall of extinction. Delayed post-training HPC LFS also provoked mPFC depotentiation and difficulties with extinction recall. HPC tetanus abolished these two effects. We also found that damage to the mPFC induced fear return only in rats that received HPC LFS following extinction training. HPC tetanus also reversed this behavioral effect of HPC LFS in lesioned rats. These data suggest that the HPC interacts with the mPFC during fear extinction, but can modulate fear extinction independently of this interaction.

Influence of a GABA(B) and GABA(C) receptor antagonist on sleep-waking cycle in the rat.

This study tested the influence of CGP 36742, a both gamma-aminobutyric acid(B) (GABA(B)) and GABA(C) receptor antagonist, on sleep and waking. The compound was injected intraperitoneally at 1, 10, 30, 100, 300 and 500 mg/kg to rats which were recorded during 6 h. Only at 500 mg/kg, total waking was increased during third and fourth hours and total duration of recording by a specific enhancement of quiet waking (without hippocampal theta activity). Slow wave sleep was decreased at 100, 300, 500 mg/kg during the third and fourth hours, and during total recording time at 500 mg/kg. Paradoxical sleep was not affected. While it was not possible to distinguish already known GABA(B) and GABA(C) identical influence on waking and slow wave sleep, their previously shown opposite effect on paradoxical sleep seemed to nullify each other.

Fluoxetine reverses stress-induced fimbria-prefrontal long-term potentiation facilitation.

Stress has been reported to disrupt the induction of synaptic plasticity in different fimbria target structures. The aim of the present study was to investigate whether chronic mild stress may also affect synaptic plasticity in the medial prefrontal cortex, a fimbria target structure. Fimbria tetanus (100 Hz) did not produce any changes in medial prefrontal cortex synaptic efficacy in non-stressed rats. Rats exposed to chronic mild stress, however, developed significant long-term potentiation. Treatment with fluoxetine (10 mg/kg, intraperitoneal) suppressed long-term potentiation induction in the chronic mild stress group. These data demonstrate that stress not only inhibits long-term potentiation development, as often demonstrated, but can also facilitate long-term potentiation development in certain brain circuits.

Postextinction infusion of a mitogen-activated protein kinase inhibitor into the medial prefrontal cortex impairs memory of the extinction of conditioned fear.

We investigated whether postextinction training infusion of PD098059, a selective inhibitor of mitogen-activated protein kinase (MAPK) activation, into the medial prefrontal cortex, would impair retention of extinction learning in rats. We found that immediate, but not late (2 or 4 h), postextinction infusion of PD098059 provoked a full return of conditioned freezing. These results suggest that activation of prefrontal MAPK in early stages of postextinction training participates in processes that protect against spontaneous recovery of aversive responses.

Mixed cocaine agonist/antagonist properties of (+)-methyl 4beta-(4-chlorophenyl)-1-methylpiperidine-3alpha-carboxylate, a piperidine-based analog of cocaine.

The present study investigated the pharmacological properties of a piperidine-based novel cocaine analog, namely, (+)-methyl 4beta-(4-chlorophenyl)-1-methylpiperidine-3alpha-carboxylic acid [(+)-CPCA]. Like cocaine, (+)-CPCA inhibited rat synaptosomal dopamine and norepinephrine uptake with high affinity, but was 33-fold less potent than cocaine in inhibiting serotonin uptake. Like cocaine, (+)-CPCA is a locomotor stimulant, although it was less potent and efficacious than cocaine. Importantly, pretreatment with (+)-CPCA dose dependently blocked the locomotor stimulant effects of cocaine in rats. (+)-CPCA completely substituted for cocaine in drug discrimination tests, although it was about 3 times less potent than cocaine. It was also self-administered by rats. Unexpectedly, (+)-CPCA did not enhance cocaine-induced convulsions in mice. As expected from rodent studies, rhesus monkeys readily self-administered (+)-CPCA. However, compared with cocaine, (+)-CPCA showed limited reinforcing properties in rats as assessed by both fixed and progressive ratio intravenous drug self-administration tests. These results collectively suggest that (+)-CPCA has an atypical pharmacological profile having both cocaine-like "agonist" and some cocaine "antagonist" properties. These properties of (+)-CPCA suggest that it may have utility in the treatment of cocaine craving and dependence.