Comparison of the spatial-cognitive functions of dorsomedial striatum and anterior cingulate cortex in mice

Anterior Cingulate Cortex Contributes to the Hyperlocomotion under Nitrogen Narcosis

Nitrogen narcosis is a neurological syndrome that manifests when humans or animals encounter hyperbaric nitrogen, resulting in a range of motor, emotional, and cognitive abnormalities. The anterior cingulate cortex (ACC) is known for its significant involvement in regulating motivation, cognition, and action. However, its specific contribution to nitrogen narcosis-induced hyperlocomotion and the underlying mechanisms remain poorly understood. Here we report that exposure to hyperbaric nitrogen notably increased the locomotor activity of mice in a pressure-dependent manner. Concurrently, this exposure induced heightened activation among neurons in both the ACC and dorsal medial striatum (DMS). Notably, chemogenetic inhibition of ACC neurons effectively suppressed hyperlocomotion. Conversely, chemogenetic excitation lowered the hyperbaric pressure threshold required to induce hyperlocomotion. Moreover, both chemogenetic inhibition and genetic ablation of activity-dependent neurons within the ACC reduced the hyperlocomotion. Further investigation revealed that ACC neurons project to the DMS, and chemogenetic inhibition of ACC-DMS projections resulted in a reduction in hyperlocomotion. Finally, nitrogen narcosis led to an increase in local field potentials in the theta frequency band and a decrease in the alpha frequency band in both the ACC and DMS. These results collectively suggest that excitatory neurons within the ACC, along with their projections to the DMS, play a pivotal role in regulating the hyperlocomotion induced by exposure to hyperbaric nitrogen.

Kappa Opioid Receptor Antagonism Restores Phosphorylation, Trafficking and Behavior induced by a Disease Associated Dopamine Transporter Variant

Aberrant dopamine (DA) signaling is implicated in schizophrenia, bipolar disorder (BPD), autism spectrum disorder (ASD), substance use disorder, and attention-deficit/hyperactivity disorder (ADHD). Treatment of these disorders remains inadequate, as exemplified by the therapeutic use of d-amphetamine and methylphenidate for the treatment of ADHD, agents with high abuse liability. In search for an improved and non-addictive therapeutic approach for the treatment of DA-linked disorders, we utilized a preclinical mouse model expressing the human DA transporter (DAT) coding variant DAT Val559, previously identified in individuals with ADHD, ASD, or BPD. DAT Val559, like several other disease-associated variants of DAT, exhibits anomalous DA efflux (ADE) that can be blocked by d-amphetamine and methylphenidate. Kappa opioid receptors (KORs) are expressed by DA neurons and modulate DA release and clearance, suggesting that targeting KORs might also provide an alternative approach to normalizing DA-signaling disrupted by perturbed DAT function. Here we demonstrate that KOR stimulation leads to enhanced surface trafficking and phosphorylation of Thr53 in wildtype DAT, effects achieved constitutively by the Val559 mutant. Moreover, these effects can be rescued by KOR antagonism of DAT Val559 in ex vivo preparations. Importantly, KOR antagonism also corrected in vivo DA release as well as sex-dependent behavioral abnormalities observed in DAT Val559 mice. Given their low abuse liability, our studies with a construct valid model of human DA associated disorders reinforce considerations of KOR antagonism as a pharmacological strategy to treat DA associated brain disorders.

Neutrophil-specific deletion of Syk results in recruitment-independent stabilization of the barrier and a long-term improvement in cognitive function after traumatic injury to the developing brain

While traumatic brain injury (TBI) is the leading cause of death and disability in children, we have yet to identify those pathogenic events that determine the extent of recovery. Neutrophils are best known as "first responders" to sites of infection and trauma where they become fully activated, killing pathogens via proteases that are released during degranulation. However, this activational state may generate substantial toxicity in the young brain after TBI that is partially due to developmentally regulated inadequate antioxidant reserves. Neutrophil degranulation is triggered via a downstream signaling pathway that is dependent on spleen tyrosine kinase (Syk). To test the hypothesis that the activational state of neutrophils is a determinant of early pathogenesis and long-term recovery, we compared young, brain-injured conditional knockouts of Syk (sykf/fMRP8-cre+) to congenic littermates (sykf/f). Based upon flow cytometry, there was an extended recruitment of distinct leukocyte subsets, including Ly6G+/Ly6C- and Ly6G+/Ly6Cint, over the first several weeks post-injury which was similar between genotypes. Subsequent assessment of the acutely injured brain revealed a reduction in blood-brain barrier disruption to both high and low molecular weight dextrans and reactive oxygen species in sykf/fMRP8-cre+ mice compared to congenic littermates, and this was associated with greater preservation of claudin 5 and neuronal integrity, as determined by Western blot analyses. At adulthood, motor learning was less affected in brain-injured sykf/fMRP8-cre+ mice as compared to sykf/f mice. Performance in the Morris Water Maze revealed a robust improvement in hippocampal-dependent acquisition and short and long-term spatial memory retention in sykf/fMRP8-cre+ mice. Subsequent analyses of swim path lengths during hidden platform training and probe trials showed greater thigmotaxis in brain-injured sykf/f mice than sham sykf/f mice and injured sykf/fMRP8-cre+ mice. Our results establish the first mechanistic link between the activation state of neutrophils and long-term functional recovery after traumatic injury to the developing brain. These results also highlight Syk kinase as a novel therapeutic target that could be further developed for the brain-injured child.

Red raspberry (Rubus ideaus) supplementation mitigates the effects of a high-fat diet on brain and behavior in mice

OBJECTIVES

Research has shown that berries may have the ability to reverse, reduce, or slow the progression of behavioral dysfunction associated with aging and neurodegenerative disease. In contrast, high-energy and high-fat diets (HFD) may result in behavioral deficits like those seen in aging animals. This research examined whether red raspberry (Rubus ideaus) mitigates the effects of HFD on mouse brain and behavior.

METHODS

Eight-week-old mice consumed a HFD (60% calories from fat) or a control diet (CD) with and without 4% freeze-dried red raspberry (RB). Behavioral tests and biochemical assays of brain tissue and serum were conducted.

RESULTS

After 12 weeks on the diets, mice fed CD and HFD had impaired novel object recognition, but mice on the RB-supplemented diets did not. After approximately 20 weeks on the diets, mice fed HFD + RB had shorter latencies to find the escape hole in the Barnes maze than the HFD-fed mice. Interleukin (IL)-6 was significantly elevated in the cortex of mice fed HFD; while mice fed the CD, CD + RB, and HFD + RB did not show a similar elevation. There was also evidence of increased brain-derived neurotrophic factor (BDNF) in the brains of mice fed RB diets. This reduction in IL-6 and increase in BDNF may contribute to the preservation of learning and memory in HFD + RB mice.

CONCLUSION

This study demonstrates that RB may protect against the effects HFD has on brain and behavior; however, further research with human subjects is needed to confirm these benefits.

The anterior cingulate cortex projection to the dorsomedial striatum modulates hyperalgesia in a chronic constriction injury mouse model

INTRODUCTION

The aim of the study was to study the role of the anterior cingulate cortex (ACC)-dorsal midbrain striatum (DMS) in neuropathic pain in mice.

MATERIAL AND METHODS

Optogenetics has been increasingly used in neuroscience research to selectively and precisely control the activity of a defined group of central neurons to determine their roles in behavioral functions in animals. The most important opsins are blue-sensitive ChR2 and yellow-sensitive NpHR. Calcium-calmodulin dependent protein kinase Iiα (CaMKIIα) is mostly expressed in the pyramidal excitatory neurons. Mice were injected with AAV2/9-CamKII-ChR2-mCherry, AAV2/9-CamKII-eNpHR3.0-GFP or AAV2/9-CamKII-mCherry virus in the ACC region, and the optical fiber implantation was performed in the ACC or DMS region. Mice were then followed up for 2 to 8 weeks and behavioral tests were carried out in the presence or absence of the blue/yellow light (473 nm/589 nm). Pain behavioral tests with or without the blue/yellow light at the same time were performed on the third and the seventh day after the chronic constriction injury of sciatic nerve model (CCI) was established. The pain thresholds of left and right hind limbs of mice in all groups were measured.

RESULTS

No matter whether activating the neurons in ACC or DMS, compared with normal mice in the ChR2-off-right group, and the mCherry-on-right group, the thermal pain threshold and mechanical pain threshold of the normal mice in the ChR2-on-right group were significantly lower. When inhibiting the neurons in the ACC or DMS, on day 3 and day 7 after CCI operation, the thermal pain threshold and mechanical pain threshold of the CCI mice of the NpHR-on-right group were significantly higher compared with the NpHR-off-right and mCherry-on-right groups.

CONCLUSIONS

The anterior cingulate cortex-dorsal midbrain striatum may be involved in the regulation of neuropathic pain in mice.

Acquisition of Spatial Search Strategies and Reversal Learning in the Morris Water Maze Depend on Disparate Brain Functional Connectivity in Mice

Learning has been proposed to coincide with changes in connections between brain regions. In the present study, we used resting-state fMRI (rsfMRI) to map brain-wide functional connectivity (FC) in mice that were trained in the hidden-platform version of the Morris water maze. C57BL6 mice were investigated in a small animal MRI scanner following 2, 10, or 15 days of acquisition learning, or 5 days of reversal learning. Spatial learning coincided with progressive and changing FC between telencephalic regions that have been implemented in spatial learning (such as hippocampus, cingulate, visual, and motor cortex). Search strategy assessment demonstrated that the use of cognitively advanced spatial strategies correlated positively with extensive telencephalic connectivity, whereas non-spatial strategies correlated negatively with connectivity. FC patterns were different and more extensive after reversal learning compared with after extended acquisition learning, which could explain why reversal learning has been shown to be more sensitive to subtle functional defects.

Multiscale Imaging Reveals Aberrant Functional Connectome Organization and Elevated Dorsal Striatal Arc Expression in Advanced Age

The functional connectome reflects a network architecture enabling adaptive behavior that becomes vulnerable in advanced age. The cellular mechanisms that contribute to altered functional connectivity in old age, however, are not known. Here we used a multiscale imaging approach to link age-related changes in the functional connectome to altered expression of the activity-dependent immediate-early gene Arc as a function of training to multitask on a working memory (WM)/biconditional association task (BAT). Resting-state fMRI data were collected from young and aged rats longitudinally at three different timepoints during cognitive training. After imaging, rats performed the WM/BAT and were immediately sacrificed to examine expression levels of Arc during task performance. Aged behaviorally impaired, but not young, rats had a subnetwork of increased connectivity between the anterior cingulate cortex (ACC) and dorsal striatum (DS) that was correlated with the use of a suboptimal response-based strategy during cognitive testing. Moreover, while young rats had stable rich-club organization across three scanning sessions, the rich-club organization of old rats increased with cognitive training. In a control group of young and aged rats that were longitudinally scanned at similar time intervals, but without cognitive training, ACC-DS connectivity and rich-club organization did not change between scans in either age group. These findings suggest that aberrant large-scale functional connectivity in aged animals is associated with altered cellular activity patterns within individual brain regions.

Muscarinic activity in hippocampus and entorhinal cortex is crucial for spatial and fear memory retrieval

BACKGROUND

Hippocampus and entorhinal cortex are key players of learning and memory. Despite their established role in memory processes, the contribution of muscarinic receptor activity in these brain regions during memory retrieval remains elusive. This study was aimed to assess the role of hippocampal CA1 and medial entorhinal cortex muscarinic receptors in memory retrieval.

METHOD

Mice were implanted with bilateral cannulas in the hippocampus CA1 and medial entorhinal cortex. After recovery they were trained for Morris water maze test, novel object recognition test and contextual fear conditioning. Scopolamine was infused 10 min prior to retrieval test.

RESULTS

Pre-test scopolamine infusion in hippocampal CA1 and medial entorhinal cortex significantly reduced overall exploration of objects (p<0.001). Similarly, pre-retrieval inactivation dorsal hippocampal CA1 and medial entorhinal cortex muscarinic activity caused significant impairment of spatial and fear memories retrieval (p<0.05).

CONCLUSION

These findings showed vital role of muscarinic activity in retrieving hippocampal and entorhinal cortex dependent memories and suggest a possible target for treating retrograde amnesia.

Sucrose Abstinence and Environmental Enrichment Effects on Mesocorticolimbic DARPP32 in Rats

Dopamine- and cAMP-regulated neuronal phosphoprotein 32 kDa (DARPP32) is a signaling molecule that could serve as a molecular switch, promoting or restraining sucrose seeking. We measured DARPP32 and pThr34 DARPP32 in the brains of male Long-Evans rats with a history of sucrose self-administration followed by 1 or 30 days of abstinence and exposure to either overnight (acute) or one month (chronic) environmental enrichment (EE). Brains were extracted following a 1 h cue reactivity test or no exposure to the test environment. Micropunches (prelimbic, infralimbic, and anterior cingulate areas of the medial prefrontal cortex, orbitofrontal cortex, dorsal striatum, nucleus accumbens, and ventral tegmental area) were then processed using Western blot. Abstinence increased, while EE decreased, sucrose seeking. DARPP32 and pThr34 DARPP32 levels were affected by testing, abstinence, and/or EE in most regions. Especially salient results were observed in the nucleus accumbens core, a region associated with relapse behaviors. Both acute and chronic EE reduced DARPP32 in the nucleus accumbens core and acute EE increased the ratio of phosphorylated to total DARPP32. Degree of DARPP32 phosphorylation negatively correlated with sucrose seeking. These findings demonstrate a potential role for DARPP32 in mediating the “anti-craving” effect of EE.

Microbiota influence the development of the brain and behaviors in C57BL/6J mice

We investigated the contributions of commensal bacteria to brain structural maturation by magnetic resonance imaging and behavioral tests in four and 12 weeks old C57BL/6J specific pathogen free (SPF) and germ free (GF) mice. SPF mice had increased volumes and fractional anisotropy in major gray and white matter areas and higher levels of myelination in total brain, major white and grey matter structures at either four or 12 weeks of age, demonstrating better brain maturation and organization. In open field test, SPF mice had better mobility and were less anxious than GF at four weeks. In Morris water maze, SPF mice demonstrated better spatial and learning memory than GF mice at 12 weeks. In fear conditioning, SPF mice had better contextual memory than GF mice at 12 weeks. In three chamber social test, SPF mice demonstrated better social novelty than GF mice at 12 weeks. Our data demonstrate numerous significant differences in morphological brain organization and behaviors between SPF and GF mice. This suggests that commensal bacteria are necessary for normal morphological development and maturation in the grey and white matter of the brain regions with implications for behavioral outcomes such as locomotion and cognitive functions.

Volumetric changes in the aging rat brain and its impact on cognitive and locomotor functions

Impairments in cognitive and locomotor functions usually occur with advanced age, as do changes in brain volume. This study was conducted to assess changes in brain volume, cognitive and locomotor functions, and oxidative stress levels in middle- to late-aged rats. Forty-four male Sprague-Dawley rats were divided into four groups: 14, 18, 23, and 27months of age. ¹H magnetic resonance imaging (MRI) was performed using a 7.0-Tesla MR scanner system. The volumes of the lateral ventricles, medial prefrontal cortex (mPFC), hippocampus, striatum, cerebellum, and whole brain were measured. Open field, object recognition, and Morris water maze tests were conducted to assess cognitive and locomotor functions. Blood was taken for measurements of malondialdehyde (MDA), protein carbonyl content, and antioxidant enzyme activity. The lateral ventricle volumes were larger, whereas the mPFC, hippocampus, and striatum volumes were smaller in 27-month-old rats than in 14-month-old rats. In behavioral tasks, the 27-month-old rats showed less exploratory activity and poorer spatial learning and memory than did the 14-month-old rats. Biochemical measurements likewise showed increased MDA and lower glutathione peroxidase (GPx) activity in the 27-month-old rats. In conclusion, age-related increases in oxidative stress, impairment in cognitive and locomotor functions, and changes in brain volume were observed, with the most marked impairments observed in later age.