In vivo two‐photon imaging of structural dynamics in the spinal dorsal horn in an inflammatory pain model

Two‐photon microscopy imaging has recently been applied to the brain to clarify functional and structural synaptic plasticity in adult neural circuits. Whereas the pain system in the spinal cord is phylogenetically primitive and easily exhibits behavioral changes such as hyperalgesia in response to inflammation, the structural dynamics of dendrites has not been analysed in the spinal cord mainly due to tissue movements associated with breathing and heart beats. Here we present experimental procedures to prepare the spinal cord sufficiently to follow morphological changes of neuronal processes in vivo by using two‐photon microscopy and transgenic mice expressing fluorescent protein specific to the nervous system. Structural changes such as the formation of spine‐like structures and swelling of dendrites were observed in the spinal dorsal horn within 30 min after the multiple‐site injections of complete Freund's adjuvant (a chemical irritant) to a leg, and these changes continued for 5 h. Both AMPA and N‐methyl‐D‐aspartate receptor antagonists, and gabapentin, a presynaptic Ca²⁺ channel blocker, completely suppressed the inflammation‐induced structural changes in the dendrites in the spinal dorsal horn. The present study first demonstrated by in vivo two‐photon microscopy imaging that structural synaptic plasticity occurred in the spinal dorsal horn immediately after the injection of complete Freund's adjuvant and may be involved in inflammatory pain. Furthermore, acute inflammation‐associated structural changes in the spinal dorsal horn were shown to be mediated by glutamate receptor activation.     

Delayed in vitro development of Up states but normal network plasticity in Fragile X circuits

A broad range of neurophysiological phenotypes have been reported since the generation of the first mouse model of Fragile X syndrome (FXS). However, it remains unclear which phenotypes are causally related to the cognitive deficits associated with FXS. Indeed, because many of these phenotypes are known to be modulated by experience, a confounding factor in the interpretation of many studies is whether some phenotypes are an indirect consequence of abnormal development and experience. To help diminish this confound we first conducted an in vitro developmental study of spontaneous neural dynamics in cortical organotypic cultures. A significant developmental increase in network activity and Up states was observed in both wild‐type and Fmr1^?/y circuits, along with a specific developmental delay in the emergence of Up states in knockout circuits. To determine whether Up state regulation is generally impaired in FXS circuits, we examined Up state plasticity using chronic optogenetic stimulation. Wild‐type and Fmr1^?/y stimulated circuits exhibited a significant decrease in overall spontaneous activity including Up state frequency; however, no significant effect of genotype was observed. These results demonstrate that developmental delays characteristic of FXS are recapitulated during in vitro development, and that Up state abnormalities are probably a direct consequence of the disease, and not an indirect consequence of abnormal experience. However, the fact that Fmr1^?/y circuits exhibited normal homeostatic modulation of Up states suggests that these plasticity mechanisms are largely intact, and that some of the previously reported plasticity deficits could reflect abnormal experience or the engagement of compensatory mechanisms.     

Memory traces of long‐range coordinated oscillations in the sleeping human brain

Cognition involves coordinated activity across distributed neuronal networks. Neuronal activity during learning triggers cortical plasticity that allows for reorganization of the neuronal network and integration of new information. Animal studies have shown post‐learning reactivation of learning‐elicited neuronal network activity during subsequent sleep, supporting consolidation of the reorganization. However, no previous studies, to our knowledge, have demonstrated reactivation of specific learning‐elicited long‐range functional connectivity during sleep in humans. We here show reactivation of learning‐induced long‐range synchronization of magnetoencephalography power fluctuations in human sleep. Visuomotor learning elicited a specific profile of long‐range cortico‐cortical synchronization of slow (0.1 Hz) fluctuations in beta band (12–30 Hz) power. The parieto‐occipital part of this synchronization profile reappeared in delta band (1–3.5 Hz) power fluctuations during subsequent sleep, but not during the intervening wakefulness period. Individual differences in the reactivated synchronization predicted postsleep performance improvement. The presleep resting‐state synchronization profile was not reactivated during sleep. The findings demonstrate reactivation of long‐range coordination of neuronal activity in humans, more specifically of reactivation of coupling of infra‐slow fluctuations in oscillatory power. The spatiotemporal profile of delta power fluctuations during sleep may subserve memory consolidation by echoing coordinated activation elicited by prior learning. Hum Brain Mapp, 36:67–84, 2015. © 2014 Wiley Periodicals, Inc.     

Cripto-1 as a novel therapeutic target for triple negative breast cancer

Triple-negative breast cancer (TNBC) presents the poorest prognosis among the breast cancer subtypes and no current standard therapy. Here, we performed an in-depth molecular analysis of a mouse model that establishes spontaneous lung metastasis from JygMC(A) cells. These primary tumors resembled the triple-negative breast cancer (TNBC) both phenotypically and molecularly. Morphologically, primary tumors presented both epithelial and spindle-like cells but displayed only adenocarcinoma-like features in lung parenchyma. The use of laser-capture microdissection combined with Nanostring mRNA and microRNA analysis revealed overexpression of either epithelial and miRNA-200 family or mesenchymal markers in adenocarcinoma and mesenchymal regions, respectively. Cripto-1, an embryonic stem cell marker, was present in spindle-like areas and its promoter showed activity in primary tumors. Cripto-1 knockout by the CRISPR-Cas9 system inhibited tumor growth and pulmonary metastasis. Our findings show characterization of a novel mouse model that mimics the TNBC and reveal Cripto-1 as a TNBC target hence may offer alternative treatment strategies for TNBC.     

Lipopolysaccharide-Induced Depressive-Like Behavior is Associated with α1-Adrenoceptor Dependent Downregulation of the Membrane GluR1 Subunit in the Mouse Medial Prefrontal Cortex and Ventral Tegmental Area

Background:

Chronic stress-induced depressive-like behavior is relevant to inflammatory immune activation. However, the neurobiological alterations in the brain following the central inflammatory immune activation remain elusive.

Methods:

Therefore, we investigated the neurobiological alterations during depressive-like behavior induced in mice by systemic administration of lipopolysaccharide (LPS; 1.2mg/kg administered twice at a 30-min interval via intraperitoneal injection).

Results:

At 24h after the second administration of LPS, an increased immobility time in the tail suspension test and the forced swimming test were observed, as well as reduced sucrose preference. Protein levels of the AMPA receptor GluR1 were significantly decreased at the plasma membrane in the medial prefrontal cortex (mPFC) and ventral tegmental area (VTA), while levels of the GluR2 were increased at the plasma membrane in the nucleus accumbens (NAc) at 24h after LPS. However, total GluR1 and GluR2 protein levels in the mPFC, VTA, and NAc were not affected by LPS. Moreover, LPS facilitated release of noradrenaline in the mPFC and VTA, but not in the NAc. Consistently, systemic administration of prazosin, an α₁-adrenoceptor antagonist, blocked the LPS-induced downregulation of the membrane GluR1 subunit in both the mPFC and VTA and also blocked the upregulation of the membrane GluR2 subunit in the NAc. Intracerebroventricular administration of prazosin 30min before LPS injection abrogated the LPS-induced depressive-like behaviors. In opposition, administration of propranolol, a β-adrenoceptor antagonist, did not affect the LPS-induced downregulation of GluR1, the upregulation of GluR2, or the depressive-like behavior.

Conclusions:

These results suggest that LPS-activated α₁-adrenoceptor-induced downregulation of membrane GluR1 in the mPFC and VTA is associated with inflammation-induced depressive-like behavior.     

Increased Excitability of Lateral Habenula Neurons in Adolescent Rats following Cocaine Self-Administration

Background:

The lateral habenula is a brain region that has been critically implicated in modulating negative emotional states and responses to aversive stimuli. Exposure to addictive drugs such as cocaine negatively impacts affective states, an effect persisting longer than acute drug effects. However, the mechanisms of this effect are poorly understood. We hypothesized that drugs of abuse, such as cocaine, may contribute to drug-induced negative affective states by altering the firing properties of lateral habenula neurons, thus changing the signaling patterns from the lateral habenula to downstream circuits.

Methods:

Using whole-cell current-clamp recording of acutely prepared brain slices of rats after various periods of withdrawal from cocaine self-administration, we characterized an important heterogeneous subregion of the lateral habenula based on membrane properties.

Results:

We found two major relevant neuronal subtypes: burst firing neurons and regular spiking neurons. We also found that lateral habenula regular spiking neurons had higher membrane excitability for at least 7 days following cocaine self-administration, likely due to a greater membrane resistance. Both the increase in lateral habenula excitability and membrane resistance returned to baseline when tested after a more prolonged period of 45 days of withdrawal.

Conclusion:

This is the first study to look at intrinsic lateral habenula neuron properties following cocaine exposure beyond acute drug effects. These results may help to explain how cocaine and other drugs negatively impact affect states.     

Transcriptome response to infraorbital nerve transection in the gonadally intact male rat barrel cortex: RNA‐seq

The effects of infraorbital nerve (ION) transection on gene expression in the adult male rat barrel cortex were investigated using RNA sequencing. After a 24‐hour survival duration, 98 genes were differentially regulated by ION transection. Differentially expressed genes suggest changes in neuronal activity, excitability, and morphology. The production of mRNA for neurotrophins, including brain‐derived neurotrophin factor (BNDF), was decreased following ION transection. Several potassium channels showed decreased mRNA production, whereas a sodium channel (Na_Vβ4) associated with burst firing showed increased mRNA production. The results may have important implications for phantom‐limb pain and complex regional pain syndrome. Future experiments should determine the extent to which changes in RNA result in changes in protein expression, in addition to utilizing laser capture microdissection techniques to differentiate between neuronal and glial cells. J. Comp. Neurol. 524:152–159, 2016. © 2015 Wiley Periodicals, Inc.     

Neural correlates of context‐dependent feature conjunction learning in visual search tasks

Many perceptual learning experiments show that repeated exposure to a basic visual feature such as a specific orientation or spatial frequency can modify perception of that feature, and that those perceptual changes are associated with changes in neural tuning early in visual processing. Such perceptual learning effects thus exert a bottom‐up influence on subsequent stimulus processing, independent of task‐demands or endogenous influences (e.g., volitional attention). However, it is unclear whether such bottom‐up changes in perception can occur as more complex stimuli such as conjunctions of visual features are learned. It is not known whether changes in the efficiency with which people learn to process feature conjunctions in a task (e.g., visual search) reflect true bottom‐up perceptual learning versus top‐down, task‐related learning (e.g., learning better control of endogenous attention). Here we show that feature conjunction learning in visual search leads to bottom‐up changes in stimulus processing. First, using fMRI, we demonstrate that conjunction learning in visual search has a distinct neural signature: an increase in target‐evoked activity relative to distractor‐evoked activity (i.e., a relative increase in target salience). Second, we demonstrate that after learning, this neural signature is still evident even when participants passively view learned stimuli while performing an unrelated, attention‐demanding task. This suggests that conjunction learning results in altered bottom‐up perceptual processing of the learned conjunction stimuli (i.e., a perceptual change independent of the task). We further show that the acquired change in target‐evoked activity is contextually dependent on the presence of distractors, suggesting that search array Gestalts are learned. Hum Brain Mapp 37:2319–2330, 2016. © 2016 Wiley Periodicals, Inc.