Journal of Neuroscience Research

Traumatic brain injury (TBI), particularly sports- and recreational activity related mild TBI (mTBI), is common in young adults and can be followed by persistent attentional and executive complaints. This study investigated chronic ([≥]6 months post-injury) structural brain alterations in gray matter (GM) and white matter (WM) and their associations with self-reported inattentive and hyperactive/impulsive symptoms, with a focus on sex-differentiated patterns. Structural brain properties in gray matter (GM) and white matter (WM) were acquired from 44 subjects with TBI and 45 matched controls, by utilizing structural MRI and diffusion tensor imaging techniques. Behavioral measures assessing severities of post TBI inattentive and hyperactive/impulsive symptoms were collected from each participant. Between-group and sex-specific differences of these brain and behavioral measures were conducted. Interactions among the TBI-induced significant brain- and behavioral-alterations, and their sex-specific patterns, were assessed as well. Male-dominated pattern of increased cortical thickness in superior parietal lobule (SPL) and female-dominated pattern of higher superior longitudinal fasciculus and superior fronto-occipital fasciculus (sFOF) fractional anisotropy (FA) were observed in the TBI group, when compared to controls. In males with TBI, greater SPL cortical thickness was significantly correlated with increased inattentive behaviors. In females with TBI, higher FA of sFOF was significantly correlated with decreased hyperactive/impulsive behaviors. Findings suggest that TBI-induced superior parietal cortical GM abnormalities may significantly cause attention deficits in patients with TBI, especially in males; while optimal post-TBI WM recovery in sFOF significantly contributes to maintenance of inhibitive control in patients with TBI, especially in females.

Accumulating evidence supports sex differences in traumatic brain injury (TBI) outcomes, however the underlying processes that lead to sex differences are not well understood. TBI results in the initiation of molecular and cellular responses that facilitate the progression of neurodegeneration. Importantly, little is known about how the circulating hormone profile is altered in response to TBI, and whether sex differences in endocrine responses might shape secondary injury pathologies. Using intact male and female mice in a preclinical TBI model, we assessed changes in plasma hormone concentrations and cortical gene expression at 24 and 72 hours after TBI. We demonstrate that males and females exhibit sex-specific alterations in circulating levels of progesterone, testosterone, androstenedione, estradiol and dehydroepiandrosterone (DHEA) in response to TBI. We also identified sex differences in the expression of genes that are involved in immune responses and tissue remodeling after injury. Moreover, we report divergent circulating hormone and gene expression correlations between sexes.

Acute stress activates the immune system, leading to the release of pro-inflammatory cytokines, such as interleukin-6 (IL-6). Chronic alcohol consumption alters the physiological stress systems and is associated with increased chronic inflammation. However, it remains unclear how IL-6 responds to acute stress in individuals with alcohol use disorder (AUD). Forty patients with AUD during early abstinence and 37 healthy controls (HC) completed two study visits. On one day, an acute stress induction task was performed, and on the other, a non-stressful control task, with the order of tasks being balanced. Plasma IL-6 and C-reactive protein (CRP) were measured as inflammatory markers at baseline and changes in IL-6 were assessed 90 minutes after the experimental manipulation. Patients with AUD showed significantly elevated baseline IL-6 and CRP compared to HC. In HC, inflammatory parameters were positively correlated with age and BMI, whereas in patients with AUD, they were correlated with the amount of consumed alcohol. IL-6 responses to the stress intervention did not differ between groups. Increases in IL-6 were observed on stress and control days and were larger when samples were collected via an indwelling catheter than with a butterfly needle. These findings suggest that heavy chronic alcohol use may mask the typical associations between inflammatory markers and physiological factors. However, IL-6 responses to acute stress do not differ between AUD and HC, despite increased baseline inflammation. Furthermore, the results indicate that blood collection methods can influence IL-6 measurements and highlight the importance of methodological considerations.

Torpor is a hypometabolic state employed by many mammalian and non-mammalian species to cope with harsh environments. When exposed to a short photoperiod, Djungarian hamsters (Phodopus sungorus) enter daily torpor with body temperatures dropping to as low as 15{degrees}C. Despite the widely-held notion that torpor is a form of deep sleep, torpid animals are not completely inactive but exhibit occasional movements reflected in an increase in EMG tone. Little is known about these EMG events during torpor and whether they have a functional role during the torpid state. We here analysed EEG, EMG, and brain temperature data from Djungarian hamsters, and used an automatic detection algorithm to identify periods of EMG activation during spontaneous daily torpor. The hamsters exhibited regular periods of motility that were invariably initiated during a decline in brain temperature and were followed by a brain temperature increase. The frequency of EMG events exhibited a negative correlation with brain temperature, such that lower brain temperature was associated with a higher frequency of EMG events. In addition, EMG events were associated with a pronounced increase in EEG power, especially between 9.5-15.5 Hz, which often started with an EEG pattern similar to an evoked potential preceding the increase in the EMG activity. On the contrary, micro-arousals during normothermic NREM sleep were associated with a decrease in EEG power, a decrease in brain temperature and were of shorter duration than torpor EMG events, indicating that the two phenomena may serve different purposes. We speculate that periodic motility associated with increased brain activity during torpor may play a role in thermoregulation, and help retain vigilance to potentially mitigate predation risk during this hypometabolic state.

Traumatic brain injuries (TBIs) result from impact to or rapid displacement of the brain and can lead to various neurological deficits involving working memory, decision-making, and anxiety. While large-scale effects of brain damage are well-described for more severe TBIs, less is known about the extent and duration of cognitive deficits at the mild level. Interval timing can provide a helpful window into cognition in mice and humans. Interval-timing behavior is impaired in a wide range of neuropsychiatric disease states, such as Parkinsons disease. Furthermore, novel object recognition (NOR) and the Barnes maze (BM) tests are valuable assays for evaluating spatial learning, working memory, and anxiety-like behavior in mice. Here, we employed a weight-drop model of mild TBI (mTBI) to investigate changes in internal cognitive states resulting from mTBI treatment. mTBI mice were not significantly impaired in either interval timing or NOR, but they demonstrated impaired spatial memory in the Barnes Maze. Interestingly, within-sex comparisons revealed impairments in male mTBI mice in the interval-timing task and the NOR, suggesting that male and female mice may be differently affected by mTBIs.

Accurate and efficient memory processing is essential for survival. Recent work in human subjects and animal models has suggested that memory processing may differ in meaningful ways between males and females. In mice, contextual fear memory (CFM) encoding, consolidation, and recall have been well studied, and the mouse hippocampus and amygdala have been implicated in these processes. The present study addresses how the specific contribution of these brain regions to each stage CFM processing in female vs. male mice. We find that male and female mice show no differences in CFM recall, nor in sleep behavior in the hours following single-trial contextual fear conditioning (CFC), which is essential for CFM consolidation. However, females - but not males - show significantly increased expression of cFos in dorsal hippocampal CA1 and CA2 neurons during CFM encoding. On the other hand, males - but not females - show increased cFos expression among DG granule cells during CFM consolidation. These findings highlight the fact that the neurobiological underpinnings of memory processing may differ between males and females, even when recall performance is identical. Scope statementHistorically, research on the neurobiological basis of memory processing has been carried out mainly in male subjects. Thus, our understanding of these mechanisms is biased towards male brain neurophysiology. Recent studies have variously reported performance differences for episodic memory tasks, in which male subjects perform better, worse, or the same as females. Here, we find that male and female mice perform similarly on a well-studied experimental memory task but nonetheless have differences in the relative activity of different brain structures during sequential stages of memory processing. This emphasizes the importance of including both males and females in memory studies, due to potential sex differences in the neurobiological substrates of memory.

An increasing number of epidemiological and experimental studies have demonstrated a bidirectional relationship between mood disorders and the circadian system, with disrupted circadian rhythms contributing to depressive states, and their restoration playing a key role in antidepressants effects. In this context, we sought to examine whether key molecular targets of antidepressants exhibit diurnal regulatory patterns. Naive adult male and female C57BL/6 mice were euthanized at 3-hour intervals beginning at Zeitgeber Time 0 (ZT0), and hippocampal (HC) and medial prefrontal cortex (mPFC) tissues were collected for RT-qPCR and western blot analyses. We observed statistically significant diurnal rhythmicity in all analyzed transcripts (cFos, Arc, Nr4a1, Dusp1, Dusp5, and Dusp6) in both HC and mPFC samples, with peak expression occurring during the dark (active) phase (ZT15-18). Phosphorylation levels of TrkBY816 (tropomyosin-related kinase) and GSK3{beta}S9 (glycogen synthase kinase 3{beta}) also showed periodic rhythmicity, peaking during the light (inactive) phase. Levels of p-ERK2T185/Y187 (extracellular-signal regulated kinase) did not display rhythmicity, but peaked during the light phase in the HC, especially in males. Collectively, these findings demonstrate that antidepressant targets are subject to diurnal regulation, highlighting the importance of integrating circadian biology and time-of-day as relevant variables in the development of translationally relevant antidepressant research. HighlightsO_LIKey molecular targets of antidepressants exhibit diurnal regulation in adult mice C_LIO_LIDiurnal patterns were conserved across targets, sexes, and brain regions (HC&PFC) C_LIO_LIcFos, Arc, Nr4a1, Dusp1,5,6 mRNAs display peak expression during the dark phase C_LIO_LITrkBY816 and GSK3{beta}S9 phosphorylation peak during the light (inactive) phase C_LIO_LIAntidepressant mechanisms may be linked with circadian and sleep-wake dynamics C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=102 SRC="FIGDIR/small/716906v1_ufig1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@1e65e60org.highwire.dtl.DTLVardef@13e302corg.highwire.dtl.DTLVardef@1ccc25forg.highwire.dtl.DTLVardef@1ed10d3_HPS_FORMAT_FIGEXP M_FIG C_FIG

BackgroundThe three-chamber test (3CT) is widely used to assess social behaviour in mice, based on the assumption that time spent near a conspecific reflects motivation for social contact. However, the design of the task constrains interpretation, as behaviour may reflect exploration, novelty seeking, or territorial investigation rather than affiliative social motivation. In addition, key biological factors such as sex differences and social hierarchy are often overlooked. AimsWe hypothesised that the 3CT overestimates sociability and used a direct-interaction phase to investigate motivation for affiliative social contact. We also integrated social status to determine if this modulated behavioural patterns and interacted with sex. MethodsAdult male and female C57BL/6 mice (n = 32) were tested in a standard 3CT, followed by removal of the cage barrier to permit direct contact. Behavioural parameters were quantified, and social status was determined using the tube test. ResultsMales exhibited higher social interest index scores than females. Once the barrier was removed, both sexes displayed a negative direct sociability index, indicating greater environmental exploration than social engagement. Correlation analysis revealed no association between indirect and direct measures. Sex differences emerged primarily among submissive mice, with submissive males showing greater social investigation than submissive females. ConclusionThese findings suggest that standard 3CT indices reflect exploratory rather than affiliative social motivation. The modified paradigm incorporating direct interaction provides a more realistic assessment of social behaviour and challenges assumptions about intrinsic sociability in mice.

BackgroundGrowing evidence suggests that sleep plays an important role in PTSD outcomes, potentially due to its influence on emotional memory consolidation, though these mechanisms remain unknown. This study sought to test the hypotheses that sleep neurophysiology, PTSD status, and sex moderates the degree to which the late positive potential (LPP) mediates memory accuracy for affective visual stimuli. MethodsN = 39 participants (18 female) viewed 75 negative and 75 neutral IAPS images while EEG was recorded. After viewing the images, participants took a two-hour long nap which was followed by a memory assessment. Memory accuracy was measured using d = Z(hit rate) - Z(false alarm rate), where hit rate refers to the proportion of images seen during the memory assessment that are correctly identified as being previously seen, false alarm rate refers to the proportion of images seen during the memory assessment that are incorrectly identified as being previously seen, and Z() is the inverse cumulative distribution function of the standard normal distribution function. ResultsThe early (300 - 1000 ms) and late (1000 - 1500 ms) LPP mediated enhanced discrimination accuracy for emotional compared to neural stimuli (d) (ps < 0.001). The association between the late LPP and d was moderated by sleep such that the association was stronger when participants spent proportionately more time in N3 and REM (p = 0.02). The differences in reactivity between emotional and neutral images for both the early and late LPP were attenuated in PTSD+ individuals vs. controls (ps < 0.001). Despite mediation results showing greater d for emotional compared to neutral stimuli, women showed overall worse memory accuracy for negative compared to neutral stimuli (p < 0.001) whereas men showed no difference (p = 0.64). ConclusionsN3 and REM sleep play a critical role for memory of stimuli that produce large and sustained neural responses. PTSD is marked by a diminished ability to distinguish between negative and neutral information. More research is critical to understand sex effects on emotional memory.

While a history of TBI is associated with an increased risk of neurodegenerative disease, associated mechanisms remain largely unknown. Neuroinflammation is commonly implicated as playing a role in progressive neurodegeneration in general, yet little is known about the adaptive response of neuroinflammation in TBI or how it may contribute to progressive pathologies. To parse out components of the adaptive response, we assessed for intraparenchymal T-cell infiltration in two different translational large animal (swine) models of TBI, inertial injury and focal contusion. We characterized the extent and distribution of T cells post-injury and their association with blood-brain barrier disruption and axonal pathology. T-cell infiltration following focal TBI followed a spatiotemporal progression from gray matter at 72 hours to both gray and white matter at 6 months post-injury, consistent with recruitment into the parenchyma and then white matter. Inertial injury did not lead to substantial T-cell infiltration despite BBB breakdown and axonal pathology. We did not find a spatial correlation between blood-brain barrier breakdown or axonal pathology and T-cell infiltration in focal TBI. These data suggest that there is an active adaptive response to TBI, particularly in tissue proximal to contusions. A large animal model that reproducibly demonstrates chronic T-cell infiltration may allow for examination of the downstream effects of the adaptive response to TBI, and whether targeting this adaptive response may reduce chronic inflammation and improve recovery.

Astrocytes are the most abundant glial cells in the brain and an integrative component of the neural network. Studies have shown that ethanol altered expression of an astrocyte marker, i.e., glial fibrillary acidic protein (GFAP), in two key corticolimbic regions, the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc). These regions comprise anatomically and functionally different subregions, i.e., the prelimbic (PL) and infralimbic (IL) cortex of the mPFC, the shell and core subregions of the NAc. However, ethanol effects on GFAP expression within these subregions remain largely unknown. In addition, effects of pharmacological manipulation of astrocytes on alcohol drinking have been understudied. Western blot was conducted to determine GFAP expression in subregions of the mPFC and NAc after chronic ethanol drinking. Fluorocitrate, an astrocyte-specific metabolic inhibitor, was administered to inhibit astrocytes and was tested on ethanol drinking. Ethanol drinking enhanced GFAP protein expression in the PL cortex and NAc core, but not in the IL cortex or NAc shell. Intra-ventricular administration of fluorocitrate reduced ethanol intake and preference, but increased water consumption during choice ethanol drinking. In addition, fluorocitrate did not affect total fluid consumption or basal locomotor activity. These results indicate that chronic ethanol drinking induced GFAP elevation in a subregion-specific manner within the mPFC and NAc, and that metabolic inhibition of astrocytes selectively attenuated ethanol drinking without non-specific effects on water drinking or general activity. Together, these results suggest that astrocytes may play an important role in ethanol drinking. HighlightsO_LIEthanol drinking enhanced GFAP levels in the PL cortex and NAc core. C_LIO_LIFluorocitrate inhibition of astrocytes reduced intermittent ethanol drinking. C_LIO_LIFluorocitrate did not alter total fluid consumption or basal locomotor activity. C_LI

Previous research has demonstrated that children exhibit superior - as compared to adults - consolidation of newly acquired motor sequences across post-learning periods of wakefulness. Given that consolidation is thought to be supported by the reactivation of learning-related patterns of brain activity during the rest periods following active task practice, we hypothesized that the childhood advantage in offline consolidation may be linked to greater reactivation during post-learning wakefulness. Twenty-two children (7-11 years) and 23 adults (18-30 years) completed two sessions of a motor sequence learning task, separated by a 5-hour wake interval. Multivoxel analyses of task-related and resting-state functional magnetic resonance imaging data were employed to assess the persistence of learning-related patterns of neural activity into post-task rest epochs, reflective of reactivation processes. Behavioral results demonstrated the previously reported childhood advantage in offline consolidation over a post-learning wake interval. Imaging results revealed that children exhibited greater persistence of task-related hippocampal - but not putaminal - activity into post-learning rest as compared to adults. These findings suggest that the childhood advantage in awake motor memory consolidation may be supported, at least partially, by enhanced reactivation of task-dependent hippocampal activity patterns during offline epochs.

Highly aggressively proliferating immortalized (HAPI) cells were initially described as a spontaneously immortalized rat cell line isolated from a mixed neonatal rat glial population. It was demonstrated that HAPI cells are phagocytic, stain for macrophage-/microglia-specific markers like CD11b and GLUT5, and exhibit lipopolysaccharide (LPS)-induced nitric oxide (NO) and tumor necrosis factor-alpha (TNF-) release. These characteristics led to their widespread use as a rat microglial cell line. Here, we report that HAPI cells are mouse cells, not rat cells, but further establish that they have a microglia-like identity and properties useful for in vitro modeling. Cell line authentication by short tandem repeat (STR) profiling, a method that detects identifying DNA signatures, indicates that HAPI cells are a 100% match for SIM-A9 cells, a mouse microglial cell line reported to be spontaneously immortalized from primary cell culture. We find that both HAPI cells and SIM-A9 cells express the microglia-selective gene Tmem119, as well as the microglia-/macrophage-selective marker Cx3cr1, supporting a microglial origin. Like primary rodent microglia or macrophages, HAPI cells respond to combined stimulation with LPS and the Type II interferon, interferon-gamma (IFN-{gamma}), with a pro-inflammatory morphology, NO production, NO-dependent suppression of mitochondrial oxygen consumption, and increased extracellular acidification (an indicator of glycolysis). The Type I interferon, interferon-alpha (IFN-), also reduces mitochondrial oxygen consumption when administered alone or in combination with LPS. Overall, results indicate that HAPI cells are SIM-A9-related mouse cells of microglial origin and support their continued use to study microglial behavior in vitro, including immunometabolism.

Chronic short sleep (CSS) is an emerging public health issue that frequently begins in adolescence and is common among healthcare professionals and others engaged in shift work. Epidemiological studies associate CSS and sleep disruption with metabolic disorders, cardiovascular disease, cognitive decline, and heightened Alzheimers disease risk. Building on our prior findings that sleep deprivation perturbs proteostasis and activates endoplasmic reticulum (ER) stress pathways, we investigated the long-term consequences of CSS in young adult wild-type mice over the course of one year. Mice exposed to CSS displayed impaired cognition in hippocampal dependent tasks by 28 weeks of age, indicating emerging memory deficits. At the molecular level, CSS disrupted hippocampal proteostasis--particularly protein folding processes--and triggered ER stress and activation of the unfolded protein response (UPR). Importantly, disrupted proteostasis preceded the behavioral decline, with diminution of the key chaperone and UPR regulator BiP occurring at 20-22 weeks of age. CSS also increased markers of cellular stress and neuroinflammation while reducing the expression of proteins associated with memory function. Age also seemed to be a cellular stressor, causing a longitudinal increase in UPR, ISR, and neuroinflammation markers. Together, these results indicate that both chronic short sleep and age compromise proteostasis and promote neuroinflammation, contributing to progressive cognitive dysfunction.

Cerebellar communication with the prefrontal cortex (PFC) may play a significant role in cognitive functions. Our previous studies found that rule-based (RB) category learning depends on the PFC in humans and rats. The PFC is also crucial for behavioral flexibility following rule-changes in various tasks. Very little is known regarding the role of the cerebellum in RB category learning. The current study was designed to determine whether the cerebellum plays a role in RB category learning, and in categorization following a rule switch. Female and male rats were given bilateral lesions of the lateral cerebellar nuclei (LCN) or a control surgery and trained on an RB category learning task followed by a category rule switch. A subset of rats was trained on a control discrimination task with the same trial procedures as the categorization task. Rats with LCN lesions took significantly longer to learn both the first and second category rules but were not impaired on the control task. Computational modeling revealed less task engagement and increased switching between engaged and non-engaged states in the LCN lesion group. Several measures of task performance indicated that the category learning deficit was not caused by a motor impairment, response bias, or an inability to discriminate the stimuli. The category learning deficits with LCN lesions were related to reduced accuracy of stimulus classification, an inability to maintain task engagement, and loss of flexibility. The results show, for the first time, that the cerebellum plays a crucial role in category learning and category rule-switching.

The brain continuously integrates information from the external environment (exteroception) and the internal bodily milieu (interoception). How the balance between these two processing streams shifts across vigilance states with differing levels of environmental responsiveness, however, remains poorly understood. Here, we examined neural responses to external auditory and internal cardiac signals across wakefulness and REM sleep microstates - tonic and phasic REM - which are characterized by progressively reduced responsiveness to external stimulation. High-density EEG was recorded in healthy participants (n=25). Auditory evoked potentials (AEPs) and heartbeat evoked potentials (HEPs) served as indices of exteroception and interoception, respectively, and were compared across vigilance states. AEPs progressively decreased from wakefulness to tonic REM and were most attenuated during phasic REM. In contrast, HEPs were preserved across REM microstates and were enhanced relative to wakefulness, indicating sustained - and even amplified - processing of cardiac signals during REM sleep. To quantify the relative weighting of external and internal signals, we introduce an exteroceptive-interoceptive index, defined as the ratio of auditory to cardiac neural responses. This index decreased systematically across vigilance states, revealing a graded shift from externally oriented processing during wakefulness to internally oriented processing during phasic REM, with tonic REM occupying an intermediate position. Together, these findings demonstrate that while responsiveness to external stimuli diminishes during phasic REM, the brain continues to prioritize physiologically relevant internal signals. The exteroceptive-interoceptive balance may thus provide a novel, mechanistically grounded marker of altered consciousness, particularly informative in contexts where behavioural responsiveness cannot be assessed. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/712081v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@1e46a9borg.highwire.dtl.DTLVardef@112f050org.highwire.dtl.DTLVardef@5f5249org.highwire.dtl.DTLVardef@135cc4_HPS_FORMAT_FIGEXP M_FIG C_FIG

BackgroundTraumatic brain injury (TBI) together with non-cerebral injuries characterizes the TBI-polytrauma (P-TBI) constellation, which is associated with acute neurological deterioration, delirium and unfavourable prognosis. It is hypothesized that systemic inflammatory mediators my enhances the focal, cerebral neuroimmune reaction with overall detrimental consequences, in particular in terms of acute microglial reactivity. MethodsWe explored the role of the Complement factor 3 (C3) and of the TLR-co receptor cluster of differentiation (CD14) in a murine polytrauma model that involves a mild TBI together with femur fracture, blunt thorax trauma and resuscitated haemorrhagic shock, making use of mice genetically lacking either C3, CD14 or both. ResultsWe show that P-TBI results in a rapid (4h) and brain-wide induction of inflammatory cytokines, although with distinct profiles (TNF and CCL2 having brain-wide involvement and IL-1{beta} restricted to ipsilateral cortex and striatum). TNF and CCL2 mRNA as well as protein synthesis were upregulated in microglia upon P-TBI in cortex, hippocampus and striatum which was fully abolished in the C3-/-CD14-/-animals. The analysis of single-KO animals revealed that induction of TNF and CCL2 was prevented in animals lacking C3, but not CD14, in the contralateral cortex and striatum, with an abolishment in hippocampus in mice lacking both C3 and CD14. In the cortical area of focal lesion neither C3 nor CD14 affected the induction of pro-inflammatory cytokines. ConclusionThus, C3 and CD14 are dispensable for the acute cytokine response to P-TBI in the site of injury but play differential roles across the cortex, hippocampus and striatum for the induction of cytokines in the non-injured parenchyma and in particular in microglia. Thus, interventions on C3 (mainly) and/or CD14 may reduce the encephalopathy risk associated with P-TBI but not the acute response in the injury site, where additional DAMP signalling may offer redundant activation pathways.

Traumatic brain injury (TBI) causes sex-specific memory deficits, yet the underlying mechanisms are not fully understood. Using a mouse TBI model, we investigated the role of reactive astrocytes in sex-specific outcome. TBI provoked long-term contextual memory impairment in males and ovariectomized females, but not in intact females. The synthetic steroid tibolone preserved memory and cFos+ neuronal density in the hippocampus of ovariectomized females. Hormone deprivation upregulated astrocytic GFAP and S100B, reduced Homer1, and impaired myelin phagocytosis by astrocytes in females. These effects were counteracted by tibolone. In Four-Core-Genotype mice, memory loss correlated with reduced astrocytic myelin uptake and neuronal activity in XX males and XY female animals. Astrocyte transplantation showed that female astrocytes exhibit superior myelin clearance capacity, especially in female brain environments, though they outperform male astrocytes in both sex contexts. These findings identify astrocyte-mediated myelin phagocytosis as a key mechanism for memory preservation after TBI, governed by both hormonal and chromosomal sex factors.

Traumatic Brain Injury (TBI) patients may suffer from a number of long-term complications after injury such as impaired motor skills, cognitive decline, and sensory abnormalities including chronic pain. Disruption of endogenous pain modulatory pathways likely contributes to development of chronic pain in a wide range of conditions including TBI. Aerobic exercise has been shown to impact pain syndromes. Here we investigate the effect of exercise on pain outcome measures after TBI using a lateral fluid percussion (LFP) model and voluntary running wheels in male and female rats. We tested mechanical nociceptive reactivity with von Frey fibers and descending control of nociception (DCN) using hindpaw sensitization with PGE2 followed by a capsaicin-test stimulus to the forepaw. Pharmacological studies employed the administration of noradrenergic (NA) and serotoninergic receptor blockers. Neuropathological studies quantified neuroinflammatory changes and axonal damage. We found that exercise decreased the duration of the acute phase of pain from [~]5 weeks to 2-3 weeks in female and male TBI rats respectively, gains that could be reversed using the 1-adrenoceptor (1AR) antagonist, prazosin. Exercise also prevented the loss of DCN for at least 180 days post-injury in both male and female TBI rats. The intact DCN response in male and female TBI rats provided by exercise could be blocked using prazosin. Surprisingly, exercise-mediated restoration of the DCN response in male TBI rats was not blocked by the 5-HT7 receptor antagonist, SB-267790, the receptor system through which serotonin reuptake inhibitors restore DCN after TBI in male rats. Therefore, the transition from a noradrenergic to a serotonergic inhibitory pain pathway that we typically see in male TBI rats, was blocked by exercise. Assessment of neuropathology, acutely after TBI, reveals that both the astrocyte and microglial response to injury is significantly greater in male TBI compared to female TBI, regardless of exercise. The effect of exercise on the extent of neuroinflammation after injury was minimal in TBI rats of both sexes. In contrast, exercise significantly decreased the amount of axonal loss in the corpus callosum in both male and female TBI rats compared to sedentary TBI rats. However, the extent of axonal loss after TBI in both exercise and sedentary male rats was greater than in female exercise and sedentary groups respectively. These results demonstrate that exercise is a promising treatment for chronic pain after TBI in both male and females. It also highlights that dysfunction of the endogenous pain modulatory pathways observed in male rats after TBI can be prevented by exercise, possibly by reducing axonal loss.

The circadian clock controls a vast array of cellular and organismal functions, from the molecular scale to behavior. While each cell is regimented by a cell-autonomous clock, few studies in the brain have dissected the circuit and behavioral contributions of cell-specific clocks. Relatedly, astrocytes are now known to play key roles in regulating synaptic function, circuit activity and behavior, but whether these functions are guided by astrocyte-autonomous clocks is unknown. Here, we report that post-natal deletion of the critical circadian clock gene Bmal1 in astrocytes, which abrogates core clock function in a cell type specific manner, induced expression of genes related to extracellular matrix (ECM) production, maintenance, and remodeling. Circadian variations have been shown in a specific ECM structure, perineuronal nets (PNNs), which are implicated in synaptic function and plasticity. In astrocyte-specific Bmal1 knockouts, hippocampal PNN abundance was decreased, and the circadian rhythm of these structures was also abolished. In line with evidence implicating PNNs, and the ECM in general, in synaptic function and plasticity, we found that astrocyte-specific Bmal1 KO mice had increased synaptic strength but blunted long term potentiation (LTP), as well as impaired learning and memory performance in a novel object recognition task. Taken together, these findings suggest that the astrocyte circadian clock regulates circadian rhythms in perineuronal net abundance as well as synaptic plasticity and behavioral learning and memory.