Visual and noxious electrical stimulus-evoked membrane-potential responses in anterior cingulate cortical neurons

The anterior cingulate cortex (ACC) is critically involved in processing the affective component of pain sensation. Visceral hypersensitivity is a characteristic of irritable bowel syndrome. Electrophysiological activity of the ACC with regard to visceral sensitization has not been characterized. Single ACC neuronal activities in response to colorectal distension (CRD) were recorded in control, sham-treated rats and viscerally hypersensitive (EA) rats (induced by chicken egg albumin injection, i.p). The ACC neurones of controls failed to respond to 10 or 30 mmHg CRD; only 22% were activated by 50 mmHg CRD. Among the latter, 16.4% exhibited an excitatory response to CRD and were labelled 'CRD-excited' neurones. In contrast, CRD (10, 30 and 50 mmHg) markedly increased ACC neuronal responses of EA rats (10%, 28% and 47%, respectively). CRD produced greater pressure-dependent increases in ACC spike firing rates in EA rats compared with controls. Splanchnicectomy combined with pelvic nerve section abolished ACC responses to CRD in EA rats. Spontaneous activity in CRD-excited ACC neurones was significantly higher in EA rats than in controls. CRD-excited ACC neurones in control and EA rats (7 of 16 (42%) and 8 of 20 (40%), respectively) were activated by transcutaneous electrical and thermal stimuli. However, ACC neuronal activity evoked by noxious cutaneous stimuli did not change significantly in EA rats. This study identifies CRD-responsive neurones in the ACC and establishes for the first time that persistence of a heightened visceral afferent nociceptive input to the ACC induces ACC sensitization, characterized by increased spontaneous activity of CRD-excited neurones, decreased CRD pressure threshold, and increased response magnitude. Enhanced ACC nociceptive transmission in viscerally hypersensitive rats is restricted to visceral afferent input.

Lower urinary tract (LUT) function is controlled by the central nervous system, including higher-order cognitive brain regions. The anterior cingulate cortex (ACC) is one of these regions, but the role of its activity in LUT function remains poorly understood. In the present study, we conducted optogenetic experiments to manipulate neural activity in mouse ACC while monitoring bladder pressure to elucidate how the activity of ACC regulates LUT function. Selective optogenetic stimulation of excitatory neurons in ACC induced a sharp increase in bladder pressure, whereas activation of inhibitory neurons in ACC prolonged the interval between bladder contractions. Pharmacological manipulation of ACC also altered bladder contractions, consistent with those observed in optogenetic experiments. Optogenetic mapping of the cortical area responsible for eliciting the increase in bladder pressure revealed that stimulation to ACC showed more potent effects than the neighboring motor cortical areas. These results suggest that ACC plays a crucial role in initiating the bladder pressure change and the micturition reflex. Thus, the balance between excitation and inhibition in ACC may regulate the reflex bidirectionally.

A variety of studies have implicated the anterior cingulate cortex (ACC) in fear, including permanent storage of fear memory. Recent pharmacological and genetic studies indicate that early synaptic plasticity in the ACC may also contribute to certain forms of fear memory at early time points. However, no study has directly examined the possible changes in neuronal activity of ACC neurons in freely behaving mice during early learning. In the present study, we examined the neural responses of the ACC during trace fear conditioning. We found that ACC putative pyramidal and nonpyramidal neurons were involved in the termination of fear behavior ("un-freezing"), and the spike activity of these neurons was reduced during freezing. Some of the neurons were also found to acquire un-freezing locked activity and change their tuning. The results implicate the ACC neurons in fear learning and controlling the abolition of fear behavior. We also show that the ACC is important for making cue-related fear memory associations in the trace fear paradigm as measured with tone-evoked potentials and single-unit activity. Collectively, our findings indicate that the ACC is involved in predicting future aversive events and terminating fear during trace fear.

IntroductionThe aim of the study was to study the role of the anterior cingulate cortex (ACC)-dorsal midbrain striatum (DMS) in neuropathic pain in mice.Material and methodsOptogenetics has been increasingly used in neuroscience research to selectively and precisely control the activity of a defined group of central neurons to determine their roles in behavioral functions in animals. The most important opsins are blue-sensitive ChR2 and yellow-sensitive NpHR. Calcium-calmodulin dependent protein kinase Iiα (CaMKIIα) is mostly expressed in the pyramidal excitatory neurons. Mice were injected with AAV2/9-CamKII-ChR2-mCherry, AAV2/9-CamKII-eNpHR3.0-GFP or AAV2/9-CamKII-mCherry virus in the ACC region, and the optical fiber implantation was performed in the ACC or DMS region. Mice were then followed up for 2 to 8 weeks and behavioral tests were carried out in the presence or absence of the blue/yellow light (473 nm/589 nm). Pain behavioral tests with or without the blue/yellow light at the same time were performed on the third and the seventh day after the chronic constriction injury of sciatic nerve model (CCI) was established. The pain thresholds of left and right hind limbs of mice in all groups were measured.ResultsNo matter whether activating the neurons in ACC or DMS, compared with normal mice in the ChR2-off-right group, and the mCherry-on-right group, the thermal pain threshold and mechanical pain threshold of the normal mice in the ChR2-on-right group were significantly lower. When inhibiting the neurons in the ACC or DMS, on day 3 and day 7 after CCI operation, the thermal pain threshold and mechanical pain threshold of the CCI mice of the NpHR-on-right group were significantly higher compared with the NpHR-off-right and mCherry-on-right groups.ConclusionsThe anterior cingulate cortex-dorsal midbrain striatum may be involved in the regulation of neuropathic pain in mice.

Patients with chronic pain often report being sensitive to pain at night before falling asleep, a time when the synchronization of cortical activity is initiated. However, how cortical activity relates to pain sensitivity is still unclear. Because sleep is characterized by enhanced cortical delta power, we hypothesized that enhanced cortical delta power may be an indicator of intensified pain. To test this hypothesis, we used pain thresholds tests, EEG/electromyogram recordings, c-Fos staining, and chemogenetic and pharmacological techniques in mice. We found that sleep deprivation or pharmacologic enhancement of EEG delta power by reserpine and scopolamine dramatically decreased mechanical pain thresholds, but not thermal withdrawal latency, in a partial sciatic nerve ligation model of neuropathic pain mice. On the contrary, suppression of EEG delta power using a wake-promoting agent modafinil significantly attenuated mechanical allodynia. Moreover, when EEG delta power was enhanced, c-Fos expression decreased in most regions of the cortex, except the anterior cingulate cortex (ACC), where c-Fos was increased in the somatostatin- and parvalbumin-positive GABAergic neurons. Chemogenetic activation of GABAergic neurons in ACC enhanced EEG delta power and lowered mechanical pain thresholds simultaneously in naive mice. However, chemogenetic inhibition of ACC GABAergic neurons could not block mechanical allodynia. These results provided compelling evidence that elevated EEG delta power is accompanied with aggravated neuropathic pain, whereas decreased delta power attenuated it, suggesting that enhanced delta power can be a specific marker of rising chronic neuropathic pain and that wake-promoting compounds could be used as analgesics in the clinic.

Different subregions of the anterior cingulate cortex differentially regulate acute itch-scratching behavior in rats.

Zingiber officinale Roscoe has been shown to possess analgesic properties. Zingerone (ZO), a bioactive compound derived from Zingiber officinale Roscoe, exhibits a range of pharmacological effects, including anti-inflammatory, anti-cancer, antioxidant, antibacterial, and anti-apoptotic activities. However, the analgesic properties of zingerone remain unclear. Complete Freund's adjuvant (CFA) was administered to the left hind paw of C57BL/6 mice to induce a model of inflammatory pain. The analgesic effects of zingerone were assessed using the Von Frey and Hargreaves tests. In vivo fiber photometry and whole-cell patch clamp techniques were employed to investigate the potential mechanisms. Both acute and long-term treatment with zingerone resulted in a significant increase in mechanical and thermal pain thresholds in mice experiencing CFA-induced inflammatory pain. Mechanical stimulation led to a pronounced increase in calcium levels within the anterior cingulate cortex (ACC) neurons of the inflammatory pain model, which was alleviated by zingerone administration. Furthermore, zingerone was found to modify synaptic transmission to ACC neurons and decrease their intrinsic excitability by prolonging the refractory period of these neurons. Zingerone demonstrates potential for alleviating CFA-induced inflammatory pain by reducing the intrinsic excitability of ACC neurons in a mouse model.

The anterior cingulate cortex (ACC) processes the affective component of pain, whereas the primary somatosensory cortex (S1) is involved in its sensory-discriminative component. Injection of morphine in the ACC has been reported to be analgesic, and endogenous opioids in this area are required for pain relief. Mu opioid receptors (MORs) are expressed in both ACC and S1; however, the identity of MOR-expressing cortical neurons remains unknown. Using the Oprm1-mCherry mouse line, we performed selective patch clamp recordings of MOR+ neurons, as well as immunohistochemistry with validated neuronal markers, to determine the identity and laminar distribution of MOR+ neurons in ACC and S1. We found that the electrophysiological signatures of MOR+ neurons differ significantly between these 2 areas, with interneuron-like firing patterns more frequent in ACC. While MOR+ somatostatin interneurons are more prominent in ACC, MOR+ excitatory neurons and MOR+ parvalbumin interneurons are more prominent in S1. Our results suggest a differential contribution of MOR-mediated modulation to ACC and S1 outputs. We also found that females had a greater density of MOR+ neurons compared with males in both areas. In summary, we conclude that MOR-dependent opioidergic signaling in the cortex displays sexual dimorphisms and likely evolved to meet the distinct function of pain-processing circuits in limbic and sensory cortical areas.

The Best Laid Plans: Computational Principles of Anterior Cingulate Cortex.

Nicotine improves attention and processing speed in individuals with schizophrenia. Few studies have investigated the effects of nicotine on cognitive control. Prior functional magnetic resonance imaging (fMRI) research demonstrates blunted activation of dorsal anterior cingulate cortex (dACC) and rostral anterior cingulate cortex (rACC) in response to error and decreased post-error slowing in schizophrenia. Participants with schizophrenia (n = 13) and healthy controls (n = 12) participated in a randomized, placebo-controlled, crossover study of the effects of transdermal nicotine on cognitive control. For each drug condition, participants underwent fMRI while performing the stop signal task where participants attempt to inhibit prepotent responses to "go (motor activation)" signals when an occasional "stop (motor inhibition)" signal appears. Error processing was evaluated by comparing "stop error" trials (failed response inhibition) to "go" trials. Resting-state fMRI data were collected prior to the task. Participants with schizophrenia had increased nicotine-induced activation of right caudate in response to errors compared to controls (DRUG × GROUP effect: p corrected < 0.05). Both groups had significant nicotine-induced activation of dACC and rACC in response to errors. Using right caudate activation to errors as a seed for resting-state functional connectivity analysis, relative to controls, participants with schizophrenia had significantly decreased connectivity between the right caudate and dACC/bilateral dorsolateral prefrontal cortices. In sum, we replicated prior findings of decreased post-error slowing in schizophrenia and found that nicotine was associated with more adaptive (i.e., increased) post-error reaction time (RT). This proof-of-concept pilot study suggests a role for nicotinic agents in targeting cognitive control deficits in schizophrenia.

The ability to recognize emotions in others and adapt one's behavior accordingly is critical for functioning in any social context. This ability is impaired in several psychiatric disorders, such as autism and psychopathy. Recent work has identified the anterior cingulate cortex (ACC) among other brain regions involved in this process. Neural recording studies have shown that neurons in ACC are modulated by reward or shock when delivered to a conspecific and when experienced first-hand. Because previous studies do not vary reward and shock within the same experiment, it has been unclear whether the observed activity reflects how much attention is being paid to outcomes delivered to a conspecific or the valence associated with those stimuli. To address this issue, we recorded from ACC as rats performed a Pavlovian task that predicted whether reward, shock, or nothing would be delivered to the rat being recorded from or a conspecific located in the opposite chamber. Consistent with previous reports, we found that the firing of ACC neurons was modulated by aversive stimuli delivered to the recording rat and their conspecific. Activity of some of these neurons genuinely reflected outcome identity (i.e., reward or shock); however, the population of neurons as a whole responded similarly for both reward and shock, as well as for cues that predicted their occurrence (i.e., reward > neutral and shock > neutral; attention). These results suggest that ACC can process information about outcomes (i.e., identity and recipient) in the service of promoting attention in some social contexts.

Although the cortex has been extensively studied in long-term memory storage, less emphasis has been placed on immediate cortical contributions to fear memory formation. AMPA receptor plasticity is strongly implicated in learning and memory, and studies have identified calcium permeable AMPA receptors (CP-AMPARs) as mediators of synaptic strengthening. Trace fear learning engages the anterior cingulate cortex (ACC), but whether plastic events occur within the ACC in response to trace fear learning, and whether GluN2B subunits are required remains unknown. Here we show that the ACC is necessary for trace fear learning, and shows a rapid 20% upregulation of membrane AMPA receptor GluA1 subunits that is evident immediately after conditioning. Inhibition of NMDA receptor GluN2B subunits during training prevented the upregulation, and disrupted trace fear memory retrieval 48 h later. Furthermore, intra-ACC injections of the CP-AMPAR channel antagonist, 1-naphthylacetyl spermine (NASPM) immediately following trace fear conditioning blocked 24 h fear memory retrieval. Accordingly, whole cell patch clamp recordings from c-fos positive and c-fos negative neurons within the ACC in response to trace fear learning revealed an increased sensitivity to NASPM in recently activated neurons that was reversed by reconsolidation update extinction. Our results suggest that trace fear learning is mediated through rapid GluN2B dependent trafficking of CP-AMPARs, and present in vivo evidence that CP-AMPAR activity within the ACC immediately after conditioning is necessary for subsequent memory consolidation processes.

Whiplash injury (WHI) is characterised by a forced neck flexion/extension, which frequently occurs after motor vehicle collisions. Previous studies characterising differences in brain metabolite concentrations and correlations with neuropathic pain (NP) components with chronic whiplash-associated disorders (WAD) have been demonstrated in affective pain-processing areas such as the anterior cingulate cortex (ACC). However, the detection of a difference in metabolite concentrations within these cortical areas with chronic WAD pain has been elusive. In this study, single-voxel magnetic resonance spectroscopy (MRS), following the latest MRSinMRS consensus group guidelines, was performed in the anterior cingulate cortex (ACC), left dorsolateral prefrontal cortex (DLPFC), and occipital cortex (OCC) to quantify differences in metabolite concentrations in individuals with chronic WAD with or without neuropathic pain (NP) components. Healthy individuals (n = 29) and participants with chronic WAD (n = 29) were screened with the Douleur Neuropathique 4 Questionnaire (DN4) and divided into groups without (WAD-noNP, n = 15) or with NP components (WAD-NP, n = 14). Metabolites were quantified with LCModel following a single session in a 3 T MRI scanner within the ACC, DLPFC, and OCC. Participants with WAD-NP presented moderate pain intensity and interference compared with the WAD-noNP group. Single-voxel MRS analysis demonstrated a higher glutamate concentration in the ACC and lower total choline (tCho) in the DLPFC in the WAD-NP versus WAD-noNP group, with no intergroup metabolite difference detected in the OCC. Best fit and stepwise multiple regression revealed that the normalised ACC glutamate/total creatine (tCr) (p = 0.01), DLPFC n-acetyl-aspartate (NAA)/tCr (p = 0.001), and DLPFC tCho/tCr levels (p = 0.02) predicted NP components in the WAD-NP group (ACC r 2 = 0.26, α = 0.81; DLPFC r 2 = 0.62, α = 0.98). The normalised Glu/tCr concentration was higher in the healthy than the WAD-noNP group within the ACC (p < 0.05), but not in the DLPFC or OCC. Neither sex nor age affected key normalised metabolite concentrations related to WAD-NP components when compared to the WAD-noNP group. This study demonstrates that elevated glutamate concentrations within the ACC are related to chronic WAD-NP components, while higher NAA and lower tCho metabolite levels suggest a role for increased neuronal-glial signalling and cell membrane dysfunction in individuals with chronic WAD-NP components.

The mechanisms by which aging leads to alterations in brain structure and cognitive deficits are unclear. Α deficient cholinergic system has been implicated as one of the main factors that could confer a heightened vulnerability to the aging process, and mice lacking high-affinity nicotinic receptors (β2(-/-)) have been proposed as an animal model of accelerated cognitive aging. To date, however, age-related changes in neuronal microanatomy have not been studied in these mice. In the present study, we examine the neuronal structure of yellow fluorescent protein (YFP(+)) layer V neurons in 2 cytoarchitectonically distinct cortical regions in wild-type (WT) and β2(-/-) animals. We find that (1) substantial morphological differences exist between YFP(+) cells of the anterior cingulate cortex (ACC) and primary visual cortex (V1), in both genotypes; (2) in WT animals, ACC cells are more susceptible to aging compared with cells in V1; and (3) β2 deletion is associated with a regionally and temporally specific increase in vulnerability to aging. ACC cells exhibit a prematurely aged phenotype already at 4-6 months, whereas V1 cells are spared in adulthood but strongly affected in old animals. Collectively, our data reveal region-specific synergistic effects of aging and genotype and suggest distinct vulnerabilities in V1 and ACC neurons.

The anterior cingulate cortex (ACC) responds to noxious and innocuous sensory inputs, and integrates them to coordinate appropriate behavioral reactions. However, the role of the projections of ACC neurons to subcortical areas and their influence on sensory processing are not fully investigated. Here, we identified that ACC neurons projecting to the contralateral claustrum (ACC→contraCLA) preferentially respond to contralateral mechanical sensory stimulation. These sensory responses were enhanced during attending behavior. Optogenetic activation of ACC→contraCLA neurons silenced pyramidal neurons in the contralateral ACC by recruiting local circuit fast-spiking interneuron activation via an excitatory relay in the CLA. This circuit activation suppressed withdrawal behavior to mechanical stimuli ipsilateral to the ACC→contraCLA neurons. Chemogenetic silencing showed that the cross-hemispheric circuit has an important role in the suppression of contralateral nociceptive behavior during sensory-driven attending behavior. Our findings identify a cross-hemispheric cortical-subcortical-cortical arc allowing the brain to give attentional priority to competing innocuous and noxious inputs.