Noxious tooth pulp stimulation suppresses c-fos expression in the rat hippocampal formation

Heat stroke-induced cerebral cortex nerve injury by mitochondrial dysfunction: A comprehensive multi-omics profiling analysis

In recent years, global warming has led to frequent instances of extremely high temperatures during summer, arousing significant concern about the adverse effects of high temperature. Among these, heat stroke is the most serious, which has detrimental effects on the all organs of human body, especially on brain. However, the comprehensive pathogenesis leading to brain damage remains unclear. In this study, we constructed a mouse model of heat stroke and conducted multi-omics profiling to identify relevant pathogenesis induced by heat stroke. The mice were placed in a constant temperature chamber at 42 °C with a humidity of 50 %, and the criteria for success in modeling were that the rectal temperature reached 42 °C and that the mice were trembling. Then the mice were immediately taken out for further experiments. Firstly, we conducted cFos protein localization and identified the cerebral cortex, especially the anterior cingulate cortex as the region exhibiting the most pronounced damage. Secondly, we performed metabolomics, transcriptomics, and proteomics analysis on cerebral cortex. This multi-omics investigation unveiled noteworthy alterations in proteins and metabolites within pathways associated with neurotransmitter systems, heatstroke-induced mitochondrial dysfunction, encompassing histidine and pentose phosphate metabolic pathways, as well as oxidative stress. In addition, the cerebral cortex exhibited pronounced Reactive Oxygen Species (ROS) production, alongside significant downregulation of the mitochondrial outer membrane protein Tomm40 and mitochondrial permeability transition pore, implicating cerebral cortex mitochondrial dysfunction as the primary instigator of neural impairment. This study marks a significant milestone as the first to employ multi-omics analysis in exploring the molecular mechanisms underlying heat stroke-induced damage in cerebral cortex neurons. It comprehensively identifies all potentially impacted pathways by heat stroke, laying a solid foundation for ensuing research endeavors. Consequently, this study introduces a fresh angle to clinical approaches in heatstroke prevention and treatment, as well as establishes an innovative groundwork for shaping future-forward environmental policies.

Recent Progress in Therapeutic Strategies for Ischemic Stroke

Possible strategies for treating stroke include neuroprotection in the acute phase of cerebral ischemia and stem cell therapy in the chronic phase of cerebral ischemia. Previously, we have studied the temporal and spatial expression patterns of c-fos, hypoxia inducible factor-1α (HIF-1α), heat shock protein 70 (HSP70), and annexin V after 90 min of transient middle cerebral occlusion in rats and concluded that there is a time window for neuroprotection from 12 to 48 h after ischemia. In addition, we have estimated the neuroprotective effect of glial cell line-derived neurotrophic factor (GDNF) by injecting Sendai viral vector containing the GDNF gene into the postischemic brain. This Sendai virus-mediated gene transfer of GDNF showed a significant neuroprotective effect in the ischemic brain. Additionally, we have administered GDNF and hepatocyte growth factor (HGF) protein into the postischemic rat brain and estimated the infarct size and antiapoptotic and antiautophagic effects. GDNF and HGF significantly reduced infarct size, the number of microtubule-associated protein 1 light chain 3 (LC3)-positive cells, and the number of terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick-end labeling (TUNEL)-positive cells, indicating that GDNF and HGF were greatly associated with not only the antiapoptotic effect but also the antiautophagic effects. Finally, we have previously transplanted undifferentiated iPSCs into the ipsilateral striatum and cortex at 24 h after cerebral ischemia. Histological analysis was performed at 14 and 28 days after cell transplantation, and we found that iPSCs could supply a great number of doublecortin-positive neuroblasts but also formed tridermal teratoma in the ischemic brain. Our results suggest that iPSCs have a potential to provide neural cells after ischemic brain injury if tumorigenesis is properly controlled. In the future, we will combine these strategies to develop more effective therapies for the treatment of strokes.

Dendritic inhibition in the hippocampus supports fear learning

Fear memories guide adaptive behavior in contexts associated with aversive events. The hippocampus forms a neural representation of the context that predicts aversive events. Representations of context incorporate multisensory features of the environment, but must somehow exclude sensory features of the aversive event itself. We investigated this selectivity using cell type-specific imaging and inactivation in hippocampal area CA1 of behaving mice. Aversive stimuli activated CA1 dendrite-targeting interneurons via cholinergic input, leading to inhibition of pyramidal cell distal dendrites receiving aversive sensory excitation from the entorhinal cortex. Inactivating dendrite-targeting interneurons during aversive stimuli increased CA1 pyramidal cell population responses and prevented fear learning. We propose subcortical activation of dendritic inhibition as a mechanism for exclusion of aversive stimuli from hippocampal contextual representations during fear learning.

The role of area postrema neurons expressing H-channels in the induction mechanism of nausea and vomiting

The area postrema is one of the circumventricular organs, lacks a blood-brain barrier, and is well known as the chemoreceptor trigger zone for emesis. Area postrema neurons are sensitive to emetic chemical substances carried in the blood plasma. Our previous study demonstrated the presence of 3 types of neurons characterized by different ion channels expressed in each cell type, but the type or types of area postrema neurons involved in the induction of nausea and/or emesis have remained unclear. To clarify the role of the most populous cells, which express the hyperpolarization-activated cation channel (H-channel), in induction of nausea and/or emesis, we investigated the effects of ZD7288 (an H-channel inhibitor) on apomorphine-induced conditioned taste aversion (CTA) to saccharin and c-Fos expression in the area postrema. We found that ZD7288 inhibited the acquisition of CTA and reduced apomorphine-induced c-Fos expression in the area postrema, indicating the involvement of the cells expressing H-channels in the induction of nausea and/or emesis. Finally, we discuss the role of cells expressing H-channels in the mechanism of nausea and/or vomiting.

Temporal and spatial differences of multiple protein expression in the ischemic penumbra after transient MCAO in rats

Temporal and spatial differences and relationships of proteins relating to the ischemic penumbra were examined at 1, 3, 12, 24, and 48 h after 90 min of transient middle cerebral artery occlusion (tMCAO) in rats. 2, 3, 5-triphenyltetrazolium chloride (TTC) staining showed that the apparent infarction focus first appeared at 1h after tMCAO, which then largely matured at 24h. Immunohistochemistry and Western blot indicated no or trace levels of c-fos, hypoxia inducible factor-1 alpha (HIF-1 alpha), heat shock protein 70 (HSP70), and annexin V (A5) positive cells in the sham control brain. Expression of c-fos increased quickly and widely within and outside of the affected arterial territory (peak at 1h), and that of HIF-1 alpha reached the maximum at 12h in a smaller area than c-fos. HSP70 began to be induced during the first few hours after tMCAO, peaked at 24h, then decreased within 48 h, while A5 was slightly expressed at 3h, then gradually increased until 48 h. Double immunofluorescent analyses showed that the colocalization rates of c-fos/HIF-1 alpha, HIF-1 alpha/HSP70, HSP70/A5, and A5/TUNEL were 40.6%, 58.4%, 42.1% and 61.0%, respectively. These data suggest that multiple molecular penumbra exist after 90 min of tMCAO in the rat brain where several different proteins participate in different temporal and spatial expression patterns. Thus, there is a window for rescue of ischemic neural cells from 12 to 48 h after injury.

Roles of the hippocampal formation in pain information processing

Pain is a complex experience consisting of sensory-discriminative, affective-motivational, and cognitive-evaluative dimensions. Now it has been gradually known that noxious information is processed by a widely-distributed, hierarchically- interconnected neural network, referred to as neuromatrix, in the brain. Thus, identifying the multiple neural networks subserving these functional aspects and harnessing this knowledge to manipulate the pain response in new and beneficial ways are challenging tasks. Albeit with elaborate research efforts on the cortical responses to painful stimuli or clinical pain, involvement of the hippocampal formation (HF) in pain is still a matter of controversy. Here, we integrate previous animal and human studies from the viewpoint of HF and pain, sequentially representing anatomical, behavioral, electrophysiological, molecular/biochemical and functional imaging evidence supporting the role of HF in pain processing. At last, we further expound on the relationship between pain and memory and present some unresolved issues.

Antinociceptive effect of intra-hippocampal CA1 and dentate gyrus injection of MK801 and AP5 in the formalin test in adult male rats

Previous research has shown that the hippocampus processes pain related-information, probably through hippocampal neurons that respond exclusively to painful stimulation. In the current experiments we tested whether blocking NMDA receptors in the hippocampal CA1 region and dentate gyrus could reduce nociceptive behaviors in rats. The competitive and noncompetitive NMDA receptor antagonists 2-amino-5-phosphonopentanoic acid (AP5; 3.75 microg/0.75 microl) and MK801 (1.5, 3, 6 microg/0.5 microl) were injected into the dentate gyrus and CA1 area of behaving rats 5 min before subcutaneous injection of formalin irritant. Pain behaviors in both acute and tonic phases of the formalin test were significantly reduced by AP5 (3.75 microg/0.75 microl) and MK801 (3 microg/0.5 microl, but not 1.5 and 6 microg/0.5 microl) injection to the dentate gyrus. In the CA1, injection of AP5 had no effect while injection of the effective dose of MK801 (3 microg/0.5 microl) had a significant antinociceptive effect. This effect was apparent only during the late phase of the formalin test. These results support the hypothesis that NMDA-sensitive mechanisms are involved in acute and persistent pain-related processing in the dentate gyrus and with tonic pain processing in the hippocampal CA1 region.

Microinjection of ritanserin into the dorsal hippocampal CA1 and dentate gyrus decrease nociceptive behavior in adult male rat

Prenatal 5HT depletion causes a significant decrease in the level of nociceptive sensitivity during the second phase of the formalin test behavioral response. These experiments were designed to test whether blocking 5HT2A/2c receptors in the CA1 region of the hippocampus and dentate gyrus would decrease nociceptive behaviors induced by a peripheral noxious stimulus formalin as an animal model of unremitting human being. The 5HT2A/2c receptor antagonist ritanserin (2, 4 and 8 microg/0.5 microl) was injected into the CA1 area and dentate gyrus of behaving rats 5 min before subcutaneous injection of formalin irritant. Nociceptive behaviors in both phases of the formalin test were significantly decreased by ritanserin (4 and 8 microg/0.5 microl) and ritanserin had no effect at 2 microg/0.5 microl. These results support the hypothesis that the hippocampal formation may modify the processing of incoming nociceptive information and that 5HT2A/2c receptor-sensitive mechanisms in the hippocampus may play a role in nociception and/or the expression of related behaviors.

Hippocampal theta state in relation to formalin nociception

In the present study using extracellular electrophysiological recording techniques, we explored the temporal characteristics of hippocampal theta activation in relation to formalin nociception. Results indicate that, compared to hind paw injection of saline, formalin injection in behaving rat evoked biphasic increase in duration of dorsal CA1 theta. Such an increase broadly paralleled animal biphasic behavioral activation, especially lick and moment-to-moment agitated behaviors. Correspondingly, theta-modulated cell firing was observed following formalin injection in anesthetized rat. The formalin-induced theta activation in behaving rat was most marked during peak of theta activation in the 2nd theta state (11-40 min post-injection) comprising 73% of the time in the 5 min block. An increase in theta peak frequency was also observed with respect to pre-injection control. However, the peak of theta in the 2nd theta state mostly preceded the peak of lick and flinch of the affected paw. In the 41-60 min, following formalin injection while the animals displayed robust nociceptive flinching and lifting, the theta activity approached control levels. Furthermore, the theta peak frequency at peak of theta was higher than the corresponding values of sustained theta observed in correlation with the nociceptive behaviors; in contrast, high frequency theta rhythm was observed during formalin-induced other moment-to-moment agitated behaviors. These findings favor the notion that in the formalin model the theta state of the hippocampus reflects a neural drive that is dissociated from the duration of nociceptive experience and is not selective to the typical nociceptive indices of lick, flinch, and lift of the injured paw.

Nociception-driven decreased induction of Fos protein in ventral hippocampus field CA1 of the rat

To test the hypothesis that the hippocampus field CA1 is recruited in nociceptive intensity-dependent fashion in the formalin model of inflammatory pain, we determined the effect of injection of formalin (0.625-2.5%) on the induction of Fos protein along the length of the hippocampus. Compared to injection of saline, injection of formalin (0.625-2.5%) evoked a concentration-dependent increase in nociceptive behavior and a significant linear increase in the number of Fos-positive cells in the spinal cord, especially in the deeper laminae. Injection of saline also increased induction of Fos along the length of hippocampus. On the other hand, injection of formalin decreased the number of Fos-positive cells in whole CA1, CA3 and dentate gyrus, with a greater significant effect in the posterior-ventral regions of the hippocampus. Indeed, a formalin concentration-dependent decrease was observed in the ventral CA1. A systematic pattern of change in Fos induction was not observed in the medial septum region. Of the regions examined, only the formalin-induced changes in Fos cell counts in the posterior and ventral CA1 were tightly correlated with the changes observed in the spinal cord. The foregoing findings suggest that nociceptive information is processed in distributed fashion by the hippocampus, and at least the ventral CA1 is implicated in nociceptive intensity-dependent integrative functions.

Dependence of rat hippocampal c-Fos expression on intensity and duration of exercise

The expression of c-Fos, an immediately early gene, is a marker of neural activity. In the present study, the effect of treadmill exercise on c-Fos expression was investigated in various regions of the rat hippocampus via immunohistochemistry. The first part of the experiment was aimed at determining the dependence of c-Fos expression on the intensity of treadmill exercise. In most of the hippocampal regions studied, increasing c-Fos expression was observed with increasing exercise intensity. In the second part of the experiment, the dependence of c-Fos expression on the duration of treadmill exercise was investigated. The c-Fos expression induced by mild-intensity exercise increased until the 7th day of exercise and subsequently decreased. Results of the present study suggest that the effect of treadmill exercise on neuronal activity in the hippocampus is intensity-and duration-dependent.

Long-lasting changes in central nervous system responsivity to colonic distention after stress in rats

BACKGROUND & AIMS

The highly prevalent functional gastrointestinal disorders involve visceral pain and disturbed bowel habit and are associated with preceding stressful experiences, although causality and biological mechanisms remain unclear. The aim of the present study was to establish whether stress can directly and lastingly alter central nervous system responsivity to colonic distention in the rat as well as which neural pathways are likely to be involved.

METHODS

Rats were treated with a brief session of stressful foot shocks known to induce long-term behavioral and autonomic sensitization. Two weeks later, after induction of inhalation anesthesia, a balloon catheter was inserted in the distal colon and repeatedly inflated with brief, constant-pressure air pulses.

RESULTS

Reflex decreases in blood pressure and heart rate indicative of visceral afferent activation were greater in previously shocked rats than in controls. Colonic distention increased the expression of Fos, a marker of neuronal activation, in the sacral spinal cord and caudal brain stem. In the central amygdala and several cortical areas (prelimbic, infralimbic, agranular insular, cingulate), previously shocked rats showed reduced Fos expression following colonic distention compared with relevant controls.

CONCLUSIONS

The results indicate that a brief but intense stressful experience causes long-lasting alterations in higher-order central nervous system responsivity to colonic distention even in the absence of conscious affective responses, pointing to basic alterations in the neural pathways involved.

Exacerbation of pain by anxiety is associated with activity in a hippocampal network

It is common clinical experience that anxiety about pain can exacerbate the pain sensation. Using event-related functional magnetic resonance imaging (FMRI), we compared activation responses to noxious thermal stimulation while perceived pain intensity was manipulated by changes in either physical intensity or induced anxiety. One visual signal, which reliably predicted noxious stimulation of moderate intensity, came to evoke low anxiety about the impending pain. Another visual signal was followed by the same, moderate-intensity stimulation on most of the trials, but occasionally by discriminably stronger noxious stimuli, and came to evoke higher anxiety. We found that the entorhinal cortex of the hippocampal formation responded differentially to identical noxious stimuli, dependent on whether the perceived pain intensity was enhanced by pain-relevant anxiety. During this emotional pain modulation, entorhinal responses predicted activity in closely connected, affective (perigenual cingulate), and intensity coding (mid-insula) areas. Our finding suggests that accurate preparatory information during medical and dental procedures alleviates pain by disengaging the hippocampus. It supports the proposal that during anxiety, the hippocampal formation amplifies aversive events to prime behavioral responses that are adaptive to the worst possible outcome.

Jun, Fos and Krox in the hippocampus after noxious stimulation: simultaneous-input-dependent expression and nuclear speckling

Stimulation of sensory C-fibres produces extensive expression of the Fos, Jun and Krox families of inducible transcription factors (ITFs) in many nociceptive CNS areas [28]. In the hippocampus, however, c-Fos is only weakly induced by such stimulation, and expression of the other ITFs has not been studied. Here we examine the effects of single, repeated and simultaneous C-fibre inputs on ITF expressions in the rat hippocampus. A brief, strong electrical stimulation of sciatic nerve C-fibres induced little or no expression of c-Fos or Krox-20. In contrast, FosB was induced and continued to rise in all areas, whereas the basal expressions of c-Jun and Krox-24 were initially reduced but then returned during the subsequent 36 h. A weak noxious cutaneous stimulus applied to one hindpaw induced only weak expressions of the ITFs. However, if the sciatic stimulation was applied contralaterally and 6 h beforehand, this weak stimulus strongly induced Krox-24, but not other ITFs, i.e. there was a potentiation of Krox-24 expression. When these two stimuli were applied simultaneously a few c-Fos labelled cells did appear, and there was and an increased Krox-24 expression. There was also a strong potentiation of FosB and a strong reduction in c-Jun expression. This simultaneous stimulation was the only type of stimulation to induce expression of Krox-20. Also after simultaneous stimulation the majority of the nuclear labelling for FosB, but not of the other ITFs, had a speckled appearance. MK-801 blocked these changes in ITF expressions, but it could also cause the C-fibre stimulations to induce c-Fos and c-Jun in specific areas of the hippocampus. Thus C-fibre stimulation does affect transcription factor activity in the hippocampus; and the strong responses of some ITFs to simultaneous inputs points to their having a role as 'genetic coincidence detectors' in the hippocampus.

Role of EGR1 in hippocampal synaptic enhancement induced by tetanic stimulation and amputation

Hippocampal neurons fire spikes when an animal is at a particular location or performs certain behaviors in a particular place, providing a cellular basis for hippocampal involvement in spatial learning and memory. In a natural environment, spatial memory is often associated with potentially dangerous sensory experiences such as noxious or painful stimuli. The central sites for such pain-associated memory or plasticity have not been identified. Here we present evidence that excitatory glutamatergic synapses within the CA1 region of the hippocampus may play a role in storing pain-related information. Peripheral noxious stimulation induced excitatory postsynaptic potentials (EPSPs) in CA1 pyramidal cells in anesthetized animals. Tissue/nerve injury caused a rapid increase in the level of the immediate-early gene product Egr1 (also called NGFI-A, Krox24, or zif/268) in hippocampal CA1 neurons. In parallel, synaptic potentiation induced by a single tetanic stimulation (100 Hz for 1 s) was enhanced after the injury. This enhancement of synaptic potentiation was absent in mice lacking Egr1. Our data suggest that Egr1 may act as an important regulator of pain-related synaptic plasticity within the hippocampus.