Cognitive impairment in a classical rat model of chronic migraine may be due to alterations in hippocampal synaptic plasticity and N-methyl-D-aspartate receptor subunits

Orofacial pain models induce impairment in spatial learning and working memory in rodents: A systematic review and meta-analysis

Orofacial pain is one of the most common causes of chronic pain leading to physical and cognitive disability. Several clinical and pre-clinical studies suggest that chronic pain results in cognitive impairment. However, there is a lack of meta-analyses examining the effects of orofacial pain models on behavioral learning and memory in rodents. Thus, this study aimed to evaluate whether orofacial pain models can impair learning and memory in rodents. The protocol was registered in PROSPERO (CRD42023355502). We used CAMARADES and SYRCLE to estimate the quality and the publication bias by using Egger's and Begg's test. Here, 21 studies were included in this systematic review and meta-analysis. We included 12 studies with trigeminal neuralgia models, 4 with migraine-like pain models, 4 with tooth nociception, and 1 with acute orofacial pain model. Spontaneous nociception and facial mechanical allodynia were observed in orofacial pain models. Regarding spatial learning we detected that latency to find the platform in the Morris water maze (MWM) was increased in orofacial pain models (related to facial mechanical allodynia or spontaneous nociception). Although the mean quality of the articles was high, we identify publication bias in the Begg's test for the time in the quadrant in the MWM. Our findings revealed that spontaneous nociception and facial mechanical allodynia in orofacial pain models contribute to the working memory and spatial learning dysfunction. Therefore, further studies are still needed to evaluate the influence of sex, age, social isolation, and environmental enrichment in orofacial pain-related learning and memory.

Molecular assessment of NMDAR subunits and neuronal apoptosis in the trigeminal ganglion in a model of male migraine-induced rats following Moringa oleifera alcoholic extract administration

INTRODUCTION

Migraine, a common disorder marked by severe and repetitive headaches, has been linked to the involvement of the NMDA receptor (NMDAR), a receptor responsible for glutamate signaling. Moringa oleifera (M. oleifera), recognized for its anti-inflammatory properties and therapeutic potential in various conditions, has been investigated. This study aims to assess the efficacy and precise mechanisms of M. oleifera for the treatment of migraine, for which evidence is limited.

METHODS

Rats were stratified into four distinct groups. The control group did not undergo the migraine-induction protocol. Post-induction, the "sumatriptan" group was administered sumatriptan injections, the "treatment" group received oral M. oleifera extract, and the "vehicle" group was provided with oral solvent treatment. Behavioral evaluations encompassing Von Frey's and hot plate assessments, in addition to qPCR analysis targeting Nr2a, Nr2b, Bax, Bcl-2, and Caspase-3, were conducted.

RESULTS

Von Fery's and hot plate tests revealed a notable decrease in triggering pressure and temperature within the vehicle group when compared to the other groups (both ps < 0.001). The Nr2a expression levels in both the vehicle and treatment cohorts exhibited significantly higher values than those observed in the control group (p < 0.001, p = 0.001) and the sumatriptan group (p < 0.001, p = 0.002). Conversely, no substantial alterations in Nr2b or Bcl-2 expression levels were observed across the study groups (p = 0.404, p = 0.976). Notably, heightened expressions of Caspase-3 and Bax were evident in the vehicle group relative to the other groups (p = 0.013, p = 0.010).

CONCLUSIONS

Moringa oleifera extract appears to mitigate symptoms of migraine by inhibiting apoptosis, suggesting potential efficacy in migraine treatment; however, additional research investigating a wider range of pathways is necessary.

CLINICAL TRIAL NUMBER

Not applicable.

Diabetes exerts a causal impact on the nervous system within the right hippocampus: substantiated by genetic data

INTRODUCTION

Diabetes and neuronal loss in the hippocampus have been observed to be correlated in several studies; however, the exact causality of this association remains uncertain. This study aims to explore the potential causal relationship between diabetes and the hippocampal nervous system.

METHODS

We utilized the two-sample Mendelian randomization (MR) analysis to investigate the potential causal connection between diabetes and the hippocampal nervous system. The summary statistics of Genome-wide association study (GWAS) for diabetes and hippocampus neuroimaging measurement were acquired from published GWASs, all of which were based on European ancestry. Several two-sample MR analyses were conducted in this study, utilizing inverse-variance weighted (IVW), MR Egger, and Weight-median methods. To ensure the reliability of the results and identify any horizontal pleiotropy, sensitivity analyses were undertaken using Cochran's Q test and the MR-PRESSO global test.

RESULTS

Causal associations were found between diabetes and the nervous system in the hippocampus. Type 1 and type 2 diabetes were both identified as having adverse causal connections with the right hippocampal nervous system. This was supported by specific ranges of IVW-OR values (P < 0.05). The consistency of the sensitivity analyses further reinforced the main findings, revealing no significant heterogeneity or presence of horizontal pleiotropy.

CONCLUSIONS

This study delved into the causal associations between diabetes and the hippocampal nervous system, revealing that both type 1 and type 2 diabetes have detrimental effects on the right hippocampal nervous system. Our findings have significant clinical implications as they indicate that diabetes may play a role in the decline of neurons in the right hippocampus among European populations, often resulting in cognitive decline.

Hippocampal connectivity dynamics and volumetric alterations predict cognitive status in migraine: A resting-state fMRI study

The etiology of cognitive decline linked to migraine remains unclear, with a growing recurrence rate and potential increased dementia risk among sufferers. Cognitive dysfunction has recently gained attention as a significant problem among migraine sufferers that can be related to alterations in hippocampal function and structure. This study explores hippocampal subfield connectivity and volume changes in migraine patients. We recruited 90 individuals from Alanya University's Neurology Department, including 49 migraine patients and 41 controls, for functional and anatomical imaging. Using the CONN toolbox and FreeSurfer, we assessed functional connectivity and subfield volumes, respectively. Montreal Cognitive Assessment (MOCA) was used to assess cognition in the entire sample. As a result, migraine patients exhibited significantly lower MOCA scores compared to controls (p<.001). Also, we found significant differences in hippocampal subfields between migraine patients and control groups in terms of functional connectivity after adjusting for years of education; here we showed that the left CA3 showed higher connectivity with right MFG and right occipitolateral cortex. Furthermore, the connectivity of left fimbria with the left temporal lobe and hippocampus and the connectivity of the right hippocampal-tail with right insula, heschl's gyrus, and frontorbital cortex were lower in the migraineurs. Additionally, volumes of specific hippocampal subfields were significantly lower in the migraineurs (whole hippocampus p = 0.004, whole hippocampus head p = 0.003, right CA1 head p = 0.006, and right HATA p = 0.005) compared to controls. In conclusion, these findings indicate that migraine-associated cognitive impairment involves significant functional and structural brain changes, particularly in the hippocampus, which may heighten dementia risk. This pioneering study unveils critical hippocampal alterations linked to cognitive function in migraine sufferers, underscoring the potential for these changes to impact dementia development.

Neural Plasticity in Migraine Chronification

Chronic migraine (CM) is the ultimate and most burdensome form of the transformation from episodic migraine (EM), called chronification. The mechanism behind migraine chronification is poorly known and difficult to explore as CM has the same spectrum of pathogenesis as EM and the EM-CM transition is bidirectional. Central sensitization (CS) is a key phenomenon in migraine: its mechanisms include disturbed neural plasticity, which is the ability of the nervous system to adapt to endo- and exogenous changes. Cutaneous allodynia, a maker of central sensitization, may be an easy-to-determine marker of the EM-CM transition. Pituitary adenylate cyclase-activating peptide, a pro-inflammatory, vasodilatory and pain-producing neuropeptide, which has been proposed as an alternative to CGRP target in migraine, was shown to improve CS by regulating synaptic plasticity in the trigeminal nucleus caudalis in CM rats. Oxytocin and its receptor were found to influence CS through modulating synaptic plasticity in CM mice. Similar results were obtained for ephrin type-B receptor and its ligands. These and other studies suggest that neural plasticity may be important in CM pathogenesis. Still, its involvement in migraine chronification requires further studies which should include patients/animals with EM and CM. In this narrative/hypothesis paper, we review the current literature on the molecular mechanisms of CM pathogenesis and try to link them with neural plasticity and central sensitization to support the hypothesis that it is a key element in migraine chronification.

Animal Models of Chronic Migraine: From the Bench to Therapy

PURPOSE OF REVIEW

Chronic migraine is a disabling progressive disorder without effective management approaches. Animal models have been developed and used in chronic migraine research. However, there are several problems with existing models. Therefore, we aimed to summarize and analyze existing animal models to facilitate translation from basic to clinical.

RECENT FINDINGS

The most commonly used models are the inflammatory soup induction model and the nitric oxide donor induction model. In addition, KATP openers have also been used in model induction. Based on the above models, some molecular targets have been identified, such as glutamate receptors. However, each model has its shortcomings and characteristics, and there are still some common problems that need to be solved, such as spontaneous headache, evaluation criteria after model establishment, and identification methods. In this review, we summarized and highlighted the advantages and limitations of the currently commonly used animal models of chronic migraine with a special focus on drug discovery and current therapeutic strategies, and discussed the directions that can be worked on in the future.

Chronic pain exacerbates memory impairment and pathology of Aβ and tau by upregulating IL-1β and p-65 signaling in a mouse model of Alzheimer's disease

BACKGROUND

Chronic pain is linked to cognitive impairment; however, the underlying mechanisms remain unclear. In the present study, we examined these mechanisms in a well-established mouse model of Alzheimer's disease (AD).

METHODS

Neuropathic pain was modeled in 5-month-old transgenic APPswe/PS1dE9 (APP/PS1) mice by partial ligation of the sciatic nerve on the left side, and chronic inflammatory pain was modeled in another group of APP/PS1 mice by injecting them with complete Freund's adjuvant on the plantar surface of the left hind paw. Six weeks after molding, the animals were tested to assess pain threshold (von Frey filament), learning, memory (novel object recognition, Morris water maze, Y-maze, and passive avoidance), and depression-like symptoms (sucrose preference, tail suspension, and forced swimming). After behavioral testing, mice were sacrificed and the levels of p65, amyloid-β (residues 1-42) and phospho-tau in the hippocampus and cerebral cortex were assayed using western blotting, while interleukin (IL)-1β levels were measured by enzyme-linked immunosorbent assay.

RESULTS

Animals subjected to either type of chronic pain showed lower pain thresholds, more severe deficits in learning and memory, and stronger depression-like symptoms than the corresponding control animals. Either type of chronic pain was associated with upregulation of p65, amyloid-β (1-42), and IL-1β in the hippocampus and cerebral cortex, as well as higher levels of phosphorylated tau.

CONCLUSIONS

Chronic pain may exacerbate cognitive deficits and depression-like symptoms in APP/PS1 mice by worsening pathology related to amyloid-β and tau and by upregulating signaling involving IL-1β and p65.

Alleviation of migraine related pain and anxiety by inhibiting calcium-stimulating AC1-dependent CGRP in the insula of adult rats

BACKGROUND

Recent animal and clinical findings consistently highlight the critical role of calcitonin gene-related peptide (CGRP) in chronic migraine (CM) and related emotional responses. CGRP antibodies and receptor antagonists have been approved for CM treatment. However, the underlying CGRP-related signaling pathways in the pain-related cortex remain poorly understood.

METHODS

The SD rats were used to establish the CM model by dural infusions of inflammatory soup. Periorbital mechanical thresholds were assessed using von-Frey filaments, and anxiety-like behaviors were observed via open field and elevated plus maze tests. Expression of c-Fos, CGRP and NMDA GluN2B receptors was detected using immunofluorescence and western blotting analyses. The excitatory synaptic transmission was detected by whole-cell patch-clamp recording. A human-used adenylate cyclase 1 (AC1) inhibitor, hNB001, was applied via insula stereotaxic and intraperitoneal injections in CM rats.

RESULTS

The insular cortex (IC) was activated in the migraine model rats. Glutamate-mediated excitatory transmission and NMDA GluN2B receptors in the IC were potentiated. CGRP levels in the IC significantly increased during nociceptive and anxiety-like activities. Locally applied hNB001 in the IC or intraperitoneally alleviated periorbital mechanical thresholds and anxiety behaviors in migraine rats. Furthermore, CGRP expression in the IC decreased after the hNB001 application.

CONCLUSIONS

Our study indicated that AC1-dependent IC plasticity contributes to migraine and AC1 may be a promising target for treating migraine in the future.

Hippocampal synaptic plasticity injury mediated by SIRT1 downregulation is involved in chronic pain-related cognitive dysfunction

AIMS

Cognitive dysfunction associated with chronic pain may be caused by impaired synaptic plasticity. Considering the impact of silent information regulator 1 (SIRT1) on synaptic plasticity, we explored the exact role of SIRT1 in cognitive impairment caused by chronic pain.

METHODS

We evaluated the memory ability of mice with the fear conditioning test (FCT) after spared nerve injury (SNI) model. Western blotting and immunofluorescence were used to analyze the expression levels of SIRT1. Hippocampal synaptic plasticity was detected with Golgi staining, transmission electron microscopy, and long-term potentiation (LTP). In the intervention study, AAV9-CaMKIIα-Cre-EGFP was injected to SIRT1flox/flox mice to knockdown the expression levels of SIRT1. Besides, SNI mice were injected with AAV2/9-CaMKIIα-SIRT1-3*Flag-GFP or SRT1720 to increase the expression levels or enzymatic activity of SIRT1.

RESULTS

Our current results indicated that cognitive function in SNI mice was impaired, SIRT1 expression in glutaminergic neurons in the hippocampal CA1 area was downregulated, and synaptic plasticity was altered. Selective knockdown of SIRT1 in hippocampus damaged synaptic plasticity and cognitive function of healthy mice. In addition, the impaired synaptic plasticity and cognitive dysfunction of SNI mice could be improved by the upregulation of SIRT1 expression or enzyme activity.

CONCLUSIONS

Reduced SIRT1 expression in hippocampus of SNI mice may induce cognitive impairment associated with chronic pain by mediating the impaired synaptic plasticity.

Arc-Mediated Synaptic Plasticity Regulates Cognitive Function in a Migraine Mouse Model

Previous clinical and basic studies have shown that migraine is associated with cognitive impairment, anxiety, and depression. It severely affects the quality of life. In this study, C57BL/6 mice were randomly divided into four groups: IS group, IS+M group, and IS+S group with repeated application of dural inflammatory soup (IS) stimulation to establish a migraine model, followed by PBS, memantine, and sumatriptan interventions, respectively; the blank control group underwent the same treatment procedure but with PBS instead of IS and intervention drugs. The cognitive function of the mice was used as the main outcome indicator. After application of the IS, mice showed reduced pain threshold for mechanical stimulation, decreased learning memory capacity, attention deficit, a reduced number of dendritic spines in hippocampal neurons, and altered synaptic ultrastructure. The cognitive function indexes of mice in the IS+M group recovered with changes in Arc protein expression to a level not statistically different from that of the Control group, while the IS and IS+S groups remained at lower levels. The present results suggest that Arc-mediated synaptic plasticity may be an essential mechanism of cognitive dysfunction in migraine.

Preventive treatment can reverse cognitive impairment in chronic migraine

Objective

To study the impact of chronic migraine (CM) on the cognition and quality of life (QoL) of patients in the interictal period, and to analyse the degree of reversibility of any observed alterations following the use of preventive treatment.

Background

CM is a highly disabling disease, and migraineurs often have associated comorbidities, such as subjective memory problems, that are involved in the development of cognitive impairment. Our hypotheses are that patients suffering from chronic migraine experience objective cognitive alterations that are not only due to the pain that they suffer or their current emotional state. Furthermore, preventive treatment should be capable of reversing, or at least reducing, the impact of CM on the cognition and QoL of migraineurs.

Methods

The cognition and QoL of 50 control subjects and 46 patients with CM were assessed using a battery of tests, prior to the use of preventive treatment based on botulinum toxin or oral drugs and after 3 months of this treatment.

Results

Compared with controls, patients with CM had lower scores on the assessment of cognitive performance (Rey-Osterrieth Complex Figure test [ROCF] (p<0.05), Trail Making Test [TMT] B) (p < 0.05) and QoL (p < 0.05). Three months after the use of preventive treatment, improvement was observed in all cognitive parameters (p < 0.05) and QoL (p < 0.05), except the ROCF copy task (p = 0.79). No statistically significant differences were observed when these outcomes were compared based on treatment.

Conclusions

This study confirms poor cognitive performance that is not explained by migraine pain itself, as it occurs in the interictal period, irrespective of the patient’s emotional status. Our findings show that these effects are reversible in some cases with preventive treatment of CM, reaffirming the important impact of this condition on the QoL of these patients, and the need to establish preventive treatment guidelines.

Resveratrol Ameliorates Trigeminal Neuralgia-Induced Cognitive Deficits by Regulating Neural Ultrastructural Remodelling and the CREB/BDNF Pathway in Rats

Chronic pain often leads to cognitive impairment. Resveratrol (Res), a natural polyphenol existing in Polygonum cuspidatum, has been widely investigated for its antinociceptive, anti-inflammatory, and neuroprotective properties. Our aim was to explore the ameliorating effects of resveratrol on pain-related behaviors and learning and memory deficits induced by cobra venom-induced trigeminal neuralgia (TN). The TN model of rats was established by injecting cobra venom solution beneath the epineurium of the infraorbital nerve. Resveratrol was intragastrically administered at a dose of 40 mg/kg twice daily beginning on postoperative day 15. CREB inhibitor 666-15 was intraperitoneally administered at a dose of 10 mg/kg from POD 35-42 after morning resveratrol treatment. Mechanical allodynia was measured via von Frey filaments. Rat free movement was videotaped and analyzed. Spatial learning and memory were evaluated via the Morris water maze test. Ultrastructures of the hippocampal DG region and infraorbital nerve were observed by transmission electron microscopy. We found that resveratrol alleviated TN-induced allodynia, ameliorated learning and memory deficits, restored the ultrastructure of hippocampal neurons and synapses, repaired the damaged myelin sheath of the infraorbital nerve, and activated the CREB/BDNF pathway in the hippocampus of TN rats. CREB inhibitor administration suppressed the resveratrol-rescued abnormal hippocampal ultrastructural changes and aggravated spatial learning and memory impairment by inhibiting CREB/BDNF pathway activation in the hippocampus. Our findings indicated that resveratrol alleviated pain and improved cognitive deficits, probably by regulating neural ultrastructure remodelling and the CREB/BDNF pathway.

Differential synaptic mechanism underlying the neuronal modulation of prefrontal cortex, amygdala, and hippocampus in response to chronic postsurgical pain with or without cognitive deficits in rats

Chronic Postsurgical Pain (CPSP) is well recognized to impair cognition, particularly memory. Mounting evidence suggests anatomic and mechanistic overlap between pain and cognition on several levels. Interestingly, the drugs currently used for treating chronic pain, including opioids, gabapentin, and NMDAR (N-methyl-D-aspartate receptor) antagonists, are also known to impair cognition. So whether pain-related cognitive deficits have different synaptic mechanisms as those underlying pain remains to be elucidated. In this context, the synaptic transmission in the unsusceptible group (cognitively normal pain rats) was isolated from that in the susceptible group (cognitively compromised pain rats). It was revealed that nearly two-thirds of the CPSP rats suffered cognitive impairment. The whole-cell voltage-clamp recordings revealed that the neuronal excitability and synaptic transmission in the prefrontal cortex and amygdala neurons were enhanced in the unsusceptible group, while these parameters remained the same in the susceptible group. Moreover, the neuronal excitability and synaptic transmission in hippocampus neurons demonstrated the opposite trend. Correspondingly, the levels of synaptic transmission-related proteins demonstrated a tendency similar to that of the excitatory and inhibitory synaptic transmission. Furthermore, morphologically, the synapse ultrastructure varied in the postsynaptic density (PSD) between the CPSP rats with and without cognitive deficits. Together, these observations indicated that basal excitatory and inhibitory synaptic transmission changes were strikingly different between the CPSP rats with and without cognitive deficits.

Could Experimental Inflammation Provide Better Understanding of Migraines?

Migraines constitute a common neurological and headache disorder affecting around 15% of the world’s population. In addition to other mechanisms, neurogenic neuroinflammation has been proposed to play a part in migraine chronification, which includes peripheral and central sensitization. There is therefore considerable evidence suggesting that inflammation in the intracranial meninges could be a key element in addition to calcitonin gene-related peptide (CGRP), leading to sensitization of trigeminal meningeal nociceptors in migraines. There are several studies that have utilized this approach, with a strong focus on using inflammatory animal models. Data from these studies show that the inflammatory process involves sensitization of trigeminovascular afferent nerve terminals. Further, by applying a wide range of different pharmacological interventions, insight has been gained on the pathways involved. Importantly, we discuss how animal models should be used with care and that it is important to evaluate outcomes in the light of migraine pathology.

Amitriptyline Decreases GABAergic Transmission in Basal Forebrain Neurons Using an Optogenetic Model of Aging

The antidepressant drug amitriptyline is used in the treatment of clinical depression and a variety of neurological conditions such as anxiety, neuropathic pain disorders and migraine. Antidepressants are associated with both therapeutic and untoward effects, and their use in the elderly has tripled since the mid-1990s. Because of this widespread use, we are interested in testing the acute effects of amitriptyline on synaptic transmission at therapeutic concentrations well below those that block voltage-gated calcium channels. We found that 3 μM amitriptyline reduced the frequency of spontaneous GABAergic inhibitory postsynaptic currents (IPSCs) and reduced quantal content in mice at ages of 7-10 mo. and 23-25 mo., suggesting a presynaptic mechanism of action that does not diminish with age. We employed a reduced synaptic preparation of the basal forebrain (BF) and a new optogenetic aging model utilizing a bacterial artificial chromosome (BAC) transgenic mouse line with stable expression of the channelrhodopsin-2 (ChR2) variant H134R specific for GABAergic neurons [VGAT-ChR2(H134R)-EYFP]. This model enables optogenetic light stimulation of specific GABAergic synaptic terminals across aging. Age-related impairment of circadian behavior was used to confirm predictable age-related changes associated with this model. Our results suggest that low concentrations of amitriptyline act presynaptically to reduce neurotransmitter release and that this action is maintained during aging.

Cognition in the Chronic Pain Experience: Preclinical Insights

Acutely, pain is protective. It promotes escape from, and future avoidance of, noxious stimuli through strong and often lifetime associative memories. However, with persistent acute pain or when pain becomes chronic, these memories can promote negative emotions and poor decisions often associated with deleterious behaviors. In this review, we discuss how preclinical studies can provide insights into the relationship between cognition and chronic pain. We also discuss the concept of pain as a cognitive disorder and new strategies for treating chronic pain that emphasize inhibiting the formation of pain memories or promoting 'forgetting' of established pain memories.