Prenatal tetrahydrocannabinol and cannabidiol exposure produce sex-specific pathophysiological phenotypes in the adolescent prefrontal cortex and hippocampus.

Clinical and preclinical evidence has demonstrated an increased risk for neuropsychiatric disorders following prenatal cannabinoid exposure. However, given the phytochemical complexity of cannabis, there is a need to understand how specific components of cannabis may contribute to these neurodevelopmental risks later in life. To investigate this, a rat model of prenatal cannabinoid exposure was utilized to examine the impacts of specific cannabis constituents (Δ9-tetrahydrocannabinol [THC]; cannabidiol [CBD]) alone and in combination on future neuropsychiatric liability in male and female offspring. Prenatal THC and CBD exposure were associated with low birth weight. At adolescence, offspring displayed sex-specific behavioural changes in anxiety, temporal order and social cognition, and sensorimotor gating. These phenotypes were associated with sex and treatment-specific neuronal and gene transcriptional alterations in the prefrontal cortex, and ventral hippocampus, regions where the endocannabinoid system is implicated in affective and cognitive development. Electrophysiology and RT-qPCR analysis in these regions implicated dysregulation of the endocannabinoid system and balance of excitatory and inhibitory signalling in the developmental consequences of prenatal cannabinoids. These findings reveal critical insights into how specific cannabinoids can differentially impact the developing fetal brains of males and females to enhance subsequent neuropsychiatric risk.

Serotonergic input from the dorsal raphe nucleus shapes learning-associated odor responses in the olfactory bulb.

AIM: Neural activity in the olfactory bulb (OB) can represent odor information during different brain and behavioral states. For example, the odor responses of mitral/tufted (M/T) cells in the OB change during learning of odor-discrimination tasks and, at the network level, beta power increases and the high gamma (HG) power decreases during odor presentation in such tasks. However, the neural mechanisms underlying these observations remain poorly understood. Here, we investigate whether serotonergic modulation from the dorsal raphe nucleus (DRN) to the OB is involved in shaping activity during the learning process in a go/no-go task in mice. METHODS: Fiber photometry was used to record the population activity of DRN serotonergic neurons during a go/no-go task. In vivo electrophysiology was used to record neural activity (single units and local field potentials) in the OB during the go/no-go task. Real-time place preference (RTPP) and intracranial light administration in a specific subarea (iClass) tests were used to assess the ability of mice to encoding reward information. RESULTS: Odor-evoked population activity in serotonergic neurons in the DRN was shaped during the learning process in a go/no-go task. In the OB, neural activity from oscillations to single cells showed complex, learning-associated changes and ability to encode information during an odor discrimination task. However, these properties were not observed after ablation of DRN serotonergic neurons. CONCLUSION: The activity of neural networks and single cells in the OB, and their ability to encode information about odor value, are shaped by serotonergic projections from the DRN.

Decoding state-dependent cortical-cerebellar cellular functional connectivity in the mouse brain.

The cortex and cerebellum form multi-synaptic reciprocal connections. We investigate the functional connectivity between single spiking cerebellar neurons and the population activity of the mouse dorsal cortex using mesoscale imaging. Cortical representations of individual cerebellar neurons vary significantly across different brain states but are drawn from a common set of cortical networks. These cortical-cerebellar connectivity features are observed in mossy fibers and Purkinje cells as well as neurons in different cerebellar lobules, albeit with variations across cell types and regions. Complex spikes of Purkinje cells preferably associate with the sensorimotor cortex, whereas simple spikes display more diverse cortical connectivity patterns. The spontaneous functional connectivity patterns align with cerebellar neurons' functional responses to external stimuli in a modality-specific manner. The tuning properties of subsets of cerebellar neurons differ between anesthesia and awake states, mirrored by state-dependent changes in their long-range functional connectivity patterns with mesoscale cortical activity.

Perturbing cortical networks: in vivo electrophysiological consequences of pan-neuronal chemogenetic manipulations using deschloroclozapine.

Introduction: Chemogenetic techniques, specifically the use of Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), have become invaluable tools in neuroscience research. Yet, the understanding of how Gq- and Gicoupled DREADDs alter local field potential (LFP) oscillations in vivo remains incomplete. Methods: This study investigates the in vivo electrophysiological effects of DREADD actuation by deschloroclozapine, on spontaneous firing rate and LFP oscillations recorded from the anterior cingulate cortex in lightly anesthetized male rats. Results: Unexpectedly, in response to the administration of deschloroclozapine, we observed inhibitory effects with pan-neuronal hM3D(Gq) stimulation, and excitatory effects with pan-neuronal hM4D(Gi) stimulation in a significant portion of neurons. These results emphasize the need to account for indirect perturbation effects at the local neuronal network level in vivo, particularly when not all neurons express the chemogenetic receptors uniformly. In the current study, for instance, the majority of cells that were transduced with both hM3D(Gq) and hM4D(Gi) were GABAergic. Moreover, we found that panneuronal cortical chemogenetic modulation can profoundly alter oscillatory neuronal activity, presenting a potential research tool or therapeutic strategy in several neuropsychiatric models and diseases. Discussion: These findings help to optimize the use of chemogenetic techniques in neuroscience research and open new possibilities for novel therapeutic strategies.

Zona incerta modulation of the inferior olive and the pontine nuclei.

The zona incerta (ZI) is a subthalamic structure that has been implicated in locomotion, fear, and anxiety. Recently interest has grown in its therapeutic efficacy in deep brain stimulation in movement disorders. This efficacy might be due to the ZI's functional projections to the other brain regions. Notwithstanding some evidence of anatomical connections between the ZI and the inferior olive (IO) and the pontine nuclei (PN), how the ZI modulates the neuronal activity in these regions remains to be determined. We first tested this by monitoring responses of single neurons in the PN and IO to optogenetic activation of channelrhodopsin-expressing ZI axons in wild-type mice, using an in vivo awake preparation. Stimulation of short, single pulses and trains of stimuli at 20 Hz elicited rapid responses in the majority of recorded cells in the PN and IO. Furthermore, the excitatory response of PN neurons scaled with the strength of ZI activation. Next, we used in vitro electrophysiology to study synaptic transmission at ZI-IO synapses. Optogenetic activation of ZI axons evoked a strong excitatory postsynaptic response in IO neurons, which remained robust with repeated stimulation at 20 Hz. Overall, our results demonstrate a functional connection within ZI-PN and ZI-IO pathways.

Peripheral direct current reduces naturally evoked nociceptive activity at the spinal cord in rodent models of pain.

Objective.Electrical neuromodulation is an established non-pharmacological treatment for chronic pain. However, existing devices using pulsatile stimulation typically inhibit pain pathways indirectly and are not suitable for all types of chronic pain. Direct current (DC) stimulation is a recently developed technology which affects small-diameter fibres more strongly than pulsatile stimulation. Since nociceptors are predominantly small-diameter Aδand C fibres, we investigated if this property could be applied to preferentially reduce nociceptive signalling.Approach.We applied a DC waveform to the sciatic nerve in rats of both sexes and recorded multi-unit spinal activity evoked at the hindpaw using various natural stimuli corresponding to different sensory modalities rather than broad-spectrum electrical stimulus. To determine if DC neuromodulation is effective across different types of chronic pain, tests were performed in models of neuropathic and inflammatory pain.Main results.We found that in both pain models tested, DC application reduced responses evoked by noxious stimuli, as well as tactile-evoked responses which we suggest may be involved in allodynia. Different spinal activity of different modalities were reduced in naïve animals compared to the pain models, indicating that physiological changes such as those mediated by disease states could play a larger role than previously thought in determining neuromodulation outcomes.Significance.Our findings support the continued development of DC neuromodulation as a method for reduction of nociceptive signalling, and suggests that it may be effective at treating a broader range of aberrant pain conditions than existing devices.

Non-canonical adrenergic neuromodulation of motoneuron intrinsic excitability through ß-receptors in wild-type and ALS mice.

Altered neuronal excitability and synaptic inputs to motoneurons are part of the pathophysiology of Amyotrophic Lateral Sclerosis. The cAMP/PKA pathway regulates both of them but therapeutic interventions at this level are limited by the lack of knowledge about suitable pharmacological entry points. Here we used transcriptomics on microdissected and in situ motoneurons to reveal the modulation of PKA-coupled receptorome in SOD1(G93A) ALS mice, vs WT, demonstrating the dysregulation of multiple PKA-coupled GPCRs, in particular on vulnerable MNs, and the relative sparing of ß-adrenergic receptors. In vivo MN electrophysiology showed that ß2/ß3 agonists acutely increase excitability, in particular the input/output relationship, demonstrating a non-canonical adrenergic neuromodulation mediated by ß2/ß3 receptors both in WT and SOD1 mice. The excitability increase corresponds to the upregulation of immediate-early gene expression and dysregulation of ion channels transcriptome. However the ß2/ß3 neuromodulation is submitted to a strong homeostasis, since a ten days delivery of ß2/ß3 agonists results in an abolition of the excitability increase. The homeostatic response is largely caused by a substantial downregulation of PKA-coupled GPCRs in MNs from WT and SOD1 mice. Thus, ß-adrenergic receptors are physiologically involved in the regulation of MN excitability and transcriptomics, but, intriguingly, a strong homeostatic response is triggered upon chronic pharmacologic intervention.

Sleep- and sleep deprivation-related changes of vertex auditory evoked potentials during the estrus cycle in female rats.

The estrus cycle in female rodents has been shown to affect a variety of physiological functions. However, little is known about its presumably thorough effect on auditory processing during the sleep-wake cycle and sleep deprivation. Vertex auditory evoked potentials (vAEPs) were evoked by single click tone stimulation and recorded during different stages of the estrus cycle and sleep deprivation performed in metestrus and proestrus in female rats. vAEPs showed a strong sleep-dependency, with the largest amplitudes present during slow wave sleep while the smallest ones during wakefulness. Higher amplitudes and longer latencies were seen in the light phase during all vigilance stages. The largest amplitudes were found during proestrus (light phase) while the shortest latencies were seen during estrus (dark phase) compared to the 2nd day diestrus baseline. High-amplitude responses without latency changes were also seen during metestrus with increased homeostatic sleep drive. More intense and faster processing of auditory information during proestrus and estrus suggesting a more effective perception of relevant environmental cues presumably in preparation for sexual receptivity. A 4-h sleep deprivation resulted in more pronounced sleep recovery in metestrus compared to proestrus without difference in delta power replacement suggesting a better tolerance of sleep deprivation in proestrus. Sleep deprivation decreased neuronal excitability and responsiveness in a similar manner both during metestrus and proestrus, suggesting that the negative consequences of sleep deprivation on auditory processing may have a limited correlation with the estrus cycle stage.

Cognitive performance in aged rats is associated with differences in distinctive neuronal populations in the ventral tegmental area and altered synaptic plasticity in the hippocampus.

Introduction: Deterioration of cognitive functions is commonly associated with aging, although there is wide variation in the onset and manifestation. Albeit heterogeneity in age-related cognitive decline has been studied at the cellular and molecular level, there is poor evidence for electrophysiological correlates. The aim of the current study was to address the electrophysiological basis of heterogeneity of cognitive functions in cognitively Inferior and Superior old (19-20 months) rats in the ventral tegmental area (VTA) and the hippocampus, having Young (12 weeks) rats as a control. The midbrain VTA operates as a hub amidst affective and cognitive facets, processing sensory inputs related to motivated behaviours and hippocampal memory. Increasing evidence shows direct dopaminergic and non-dopaminergic input from the VTA to the hippocampus. Methods: Aged Superior and Inferior male rats were selected from a cohort of 88 animals based on their performance in a spatial learning and memory task. Using in vivo single-cell recording in the VTA, we examined the electrical activity of different neuronal populations (putative dopaminergic, glutamatergic and GABAergic neurons). In the same animals, basal synaptic transmission and synaptic plasticity were examined in hippocampal slices. Results: Electrophysiological recordings from the VTA and hippocampus showed alterations associated with aging per se, together with differences specifically linked to the cognitive status of aged animals. In particular, the bursting activity of dopamine neurons was lower, while the firing frequency of glutamatergic neurons was higher in VTA of Inferior old rats. The response to high-frequency stimulation in hippocampal slices also discriminated between Superior and Inferior aged animals. Discussion: This study provides new insight into electrophysiological information underlying compromised cerebral ageing. Further understanding of brain senescence, possibly related to neurocognitive decline, will help develop new strategies towards the preservation of a high quality of life.

Sleep and local field potential effect of the D2 receptor agonist bromocriptine during the estrus cycle and postpartum period in female rats.

BACKGROUND: Pituitary lactotrophs are under tonic dopaminergic inhibitory control and bromocriptine treatment blocks prolactin secretion. METHODS: Sleep and local field potential were addressed for 72 h after bromocriptine treatments applied during the different stages of the estrus cycle and for 24 h in the early- and middle postpartum period characterized by spontaneously different dynamics of prolactin release in female rats. RESULTS: Sleep changes showed strong dependency on the estrus cycle phase of the drug application. Strongest increase of wakefulness and reduction of slow wave sleep- and rapid eye movements sleep appeared during diestrus-proestrus and middle postpartum treatments. Stronger sleep-wake effects appeared in the dark phase in case of the estrus cycle treatments, but in the light phase in postpartum treatments. Slow wave sleep and REM sleep loss in case of estrus cycle treatments was not compensated at all and sleep loss seen in the first day post-injection was gained further later. In opposition, slow wave sleep loss in the light phase after bromocriptine injections showed compensation in the postpartum period treatments. Bromocriptine treatments resulted in a depression of local field potential delta power during slow wave sleep while an enhancement in beta and gamma power during wakefulness regardless of the treatment timing. CONCLUSIONS: These results can be explained by the interplay of dopamine D2 receptor agonism, lack of prolactin release and the spontaneous homeostatic sleep drive being altered in the different stages of the estrus cycle and the postpartum period.

Basolateral amygdala parvalbumin interneurons coordinate oscillations to drive reward behaviors.

The basolateral amygdala (BLA) mediates both fear and reward learning.1,2 Previous work has shown that parvalbumin (PV) interneurons in the BLA contribute to BLA oscillatory states integral to fear expression.3,4,5,6,7 However, despite it being critical to our understanding of reward behaviors, it is unknown whether BLA oscillatory states and PV interneurons similarly contribute to reward processing. Local field potentials in the BLA were collected as male and female mice consumed sucrose reward, where prominent changes in the beta band (15-30 Hz) emerged with reward experience. During consumption of one water bottle during a two-water-bottle choice test, rhythmic optogenetic stimulation of BLA PVs produced a robust bottle preference, showing that PVs can sufficiently drive reward seeking. Finally, to demonstrate that PV activity is necessary for reward value use, PVs were chemogenetically inhibited following outcome devaluation, rendering mice incapable of using updated reward representations to guide their behavior. Taken together, these experiments provide novel information about the physiological signatures of reward while highlighting BLA PV interneuron contributions to behaviors that are BLA dependent. This work builds upon established knowledge of PV involvement in fear expression and provides evidence that PV orchestration of unique BLA network states is involved in both learning types.

Evoked compound action potential (ECAP)-controlled closed-loop spinal cord stimulation in an experimental model of neuropathic pain in rats.

BACKGROUND: Preclinical models of spinal cord stimulation (SCS) are lacking objective measurements to inform translationally applicable SCS parameters. The evoked compound action potential (ECAP) represents a measure of dorsal column fiber activation. This measure approximates the onset of SCS-induced sensations in humans and provides effective analgesia when used with ECAP-controlled closed-loop (CL)-SCS systems. Therefore, ECAPs may provide an objective surrogate for SCS dose in preclinical models that may support better understanding of SCS mechanisms and further translations to the clinics. This study assessed, for the first time, the feasibility of recording ECAPs and applying ECAP-controlled CL-SCS in freely behaving rats subjected to an experimental model of neuropathic pain. METHODS: Adult male Sprague-Dawley rats (200-300 g) were subjected to spared nerve injury (SNI). A custom-made six-contact lead was implanted epidurally covering T11-L3, as confirmed by computed tomography or X-ray. A specially designed multi-channel system was used to record ECAPs and to apply ECAP-controlled CL-SCS for 30 min at 50 Hz 200 µs. The responses of dorsal column fibers to SCS were characterized and sensitivity towards mechanical and cold stimuli were assessed to determine analgesic effects from ECAP-controlled CL-SCS. Comparisons between SNI rats and their controls as well as between stimulation parameters were made using omnibus analysis of variance (ANOVA) tests and t-tests. RESULTS: The recorded ECAPs showed the characteristic triphasic morphology and the ECAP amplitude (mV) increased as higher currents (mA) were applied in both SNI animals and controls (SNI SCS-ON and sham SCS-ON). Importantly, the use of ECAP-based SCS dose, implemented in ECAP-controlled CL-SCS, significantly reduced mechanical and cold hypersensitivity in SNI SCS-ON animals through the constant and controlled activation of dorsal column fibers. An analysis of conduction velocities of the evoked signals confirmed the involvement of large, myelinated fibers. CONCLUSIONS: The use of ECAP-based SCS dose implemented in ECAP-controlled CL-SCS produced analgesia in animals subjected to an experimental model of neuropathic pain. This approach may offer a better method for translating SCS parameters between species that will improve understanding of the mechanisms of SCS action to further advance future clinical applications.

IKKß deletion from CNS macrophages increases neuronal excitability and accelerates the onset of EAE, while from peripheral macrophages reduces disease severity.

BACKGROUND: Multiple sclerosis (MS) is a neuroinflammatory demyelinating disease characterized by motor deficits and cognitive decline. Many immune aspects of the disease are understood through studies in the experimental autoimmune encephalomyelitis (EAE) model, including the contribution of the NF-κB transcription factor to neuroinflammation. However, the cell-specific roles of NF-κB to EAE and its cognitive comorbidities still needs further investigation. We have previously shown that the myeloid cell NF-κB plays a role in the healthy brain by exerting homeostatic regulation of neuronal excitability and synaptic plasticity and here we investigated its role in EAE. METHODS: We used constitutive MφIKKßΚΟ mice, in which depletion of IKKß, the main activating kinase of NF-κB, was global to CNS and peripheral macrophages, and ΜgΙΚΚßKO mice, in which depletion was inducible and specific to CNS macrophages by 28 days after tamoxifen administration. We subjected these mice to MOG35-55 induced EAE and cuprizone-induced demyelination. We measured pathology by immunohistochemistry, investigated molecular mechanisms by RNA sequencing analysis and studied neuronal functions by in vivo electrophysiology in awake animals. RESULTS: Global depletion of IKKß from myeloid cells in MφIKKßΚΟ mice accelerated the onset and significantly supressed chronic EAE. Knocking out IKKß only from CNS resident macrophages accelerated the onset and exacerbated chronic EAE, accompanied by earlier demyelination and immune cell infiltration but had no effect in cuprizone-induced demyelination. Peripheral T cell effector functions were not affected by myeloid cell deletion of IKKß, but CNS resident mechanisms, such as microglial activation and neuronal hyperexcitability were altered from early in EAE. Lastly, depletion of myeloid cell IKKß resulted in enhanced late long-term potentiation in EAE. CONCLUSIONS: IKKß-mediated activation of NF-κΒ in myeloid cells has opposing roles in EAE depending on the cell type and the disease stage. In CNS macrophages it is protective while in peripheral macrophages it is disease-promoting and acts mainly during chronic disease. Although clinically protective, CNS myeloid cell IKKß deletion dysregulates neuronal excitability and synaptic plasticity in EAE. These effects of IKKß on brain cognitive abilities deserve special consideration when therapeutic interventions that inhibit NF-κB are used in MS.

Nerve injury disrupts temporal processing in the spinal cord dorsal horn through alterations in PV+ interneurons.

How mechanical allodynia following nerve injury is encoded in patterns of neural activity in the spinal cord dorsal horn (DH) remains incompletely understood. We address this in mice using the spared nerve injury model of neuropathic pain and in vivo electrophysiological recordings. Surprisingly, despite dramatic behavioral over-reactivity to mechanical stimuli following nerve injury, an overall increase in sensitivity or reactivity of DH neurons is not observed. We do, however, observe a marked decrease in correlated neural firing patterns, including the synchrony of mechanical stimulus-evoked firing, across the DH. Alterations in DH temporal firing patterns are recapitulated by silencing DH parvalbumin+ (PV+) interneurons, previously implicated in mechanical allodynia, as are allodynic pain-like behaviors. These findings reveal decorrelated DH network activity, driven by alterations in PV+ interneurons, as a prominent feature of neuropathic pain and suggest restoration of proper temporal activity as a potential therapeutic strategy to treat chronic neuropathic pain.

Inhibition of fatty acid binding protein-5 in the basolateral amygdala induces anxiolytic effects and accelerates fear memory extinction.

RATIONALE: The endocannabinoid (eCB) system critically controls anxiety and fear-related behaviours. Anandamide (AEA), a prominent eCB ligand, is a hydrophobic lipid that requires chaperone proteins such as Fatty Acid Binding Proteins (FABPs) for intracellular transport. Intracellular AEA transport is necessary for degradation, so blocking FABP activity increases AEA neurotransmission. OBJECTIVE: To investigate the effects of a novel FABP5 inhibitor (SBFI-103) in the basolateral amygdala (BLA) on anxiety and fear memory. METHODS: We infused SBFI-103 (0.5 µg-5 µg) to the BLA of adult male Sprague Dawley rats and ran various anxiety and fear memory behavioural assays, neurophysiological recordings, and localized molecular signaling analyses. We also co-infused SBFI-103 with the AEA inhibitor, LEI-401 (3 µg and 10 µg) to investigate the potential role of AEA in these phenomena. RESULTS: Acute intra-BLA administration of SBFI-103 produced strong anxiolytic effects across multiple behavioural tests. Furthermore, animals exhibited acute and long-term accelerated associative fear memory extinction following intra-BLA FABP5 inhibition. In addition, BLA FABP5 inhibition induced strong modulatory effects on putative PFC pyramidal neurons along with significantly increased gamma oscillation power. Finally, we observed local BLA changes in the phosphorylation activity of various anxiety- and fear memory-related molecular biomarkers in the PI3K/Akt and MAPK/Erk signaling pathways. At all three levels of analyses, we found the functional effects of SBFI-103 depend on availability of the AEA ligand. CONCLUSIONS: These findings demonstrate a novel intra-BLA FABP5 signaling mechanism regulating anxiety and fear memory behaviours, neuronal activity states, local anxiety-related molecular pathways, and functional AEA modulation.

Hemodynamic responses in the rat hippocampus are simultaneously controlled by at least two independently acting neurovascular coupling mechanisms.

We combined electrical perforant pathway stimulation with electrophysiological and fMRI recordings in the hippocampus to investigate the effects of neuronal afterdischarges (nAD) on subsequent fMRI BOLD signals in the presence of isoflurane and medetomidine. These two drugs already alter basal hemodynamics in the hippocampus, with isoflurane being mildly vasodilatory and medetomidine being mildly vasoconstrictive. The perforant pathway was stimulated once for 8 seconds with either continuous 20 Hz pulses (continuous stimulation) or 8 bursts of 20 high-frequency pulses (burst stimulation). Burst stimulation in the presence of medetomidine elicited long-lasting nAD that coincided with a brief positive BOLD response and a subsequent long-lasting decrease in BOLD signals. Under isoflurane, this stimulation elicited only short-lasting nAD and only a short-lasting decline in BOLD signals. In contrast, continuous stimulation under isoflurane and medetomidine caused a similar duration of nAD. Under isoflurane, this caused only a sharp and prolonged decline in BOLD signals, whereas under medetomidine, again, only a brief positive BOLD response was elicited, followed by a shorter and moderate decline in BOLD signals. Our results suggest that nAD simultaneously activate different neurovascular coupling mechanisms that then independently alter local hemodynamics in the hippocampus, resulting in an even more complex neurovascular coupling mechanism.

Impact of volume and expression time in an AAV-delivered channelrhodopsin.

Optogenetics has revolutionised neuroscience research, but at the same time has brought a plethora of new variables to consider when designing an experiment with AAV-based targeted gene delivery. Some concerns have been raised regarding the impact of AAV injection volume and expression time in relation to longitudinal experimental designs. In this study, we investigated the efficiency of optically evoked post-synaptic responses in connection to two variables: the volume of the injected virus and the expression time of the virus. For this purpose, we expressed the blue-shifted ChR2, oChIEF, employing a widely used AAV vector delivery strategy. We found that the volume of the injected virus has a minimal impact on the efficiency of optically-evoked postsynaptic population responses. The expression time, on the other hand, has a pronounced effect, with a gradual reduction in the population responses beyond 4 weeks of expression. We strongly advise to monitor time-dependent expression profiles when planning or conducting long-term experiments that depend on successful and stable channelrhodopsin expression.

Towards a central origin of nociceptive hypersensitivity in adult rats after a neonatal maternal separation.

Early life adversities influence a nervous system still in development with long-term consequences for later life. These include nociceptive circuit alterations critical to shape an adaptive pain response to protect the organism from potential damage. Adult rats with a history of neonatal maternal separation (NMS) display visceral and somatic nociceptive hypersensitivity and inefficient analgesic responses to stress. In this study, we have characterized the consequences of NMS on wide dynamic range neurons (WDR) in the spinal cord of anaesthetized adult rats during the nociceptive processing of hot and cold noxious information. We found that WDR neurons of NMS rats display an excessive coding of mechanical and thermal information applied at the rat's hindpaws. This nicely explains the hypernociceptive behaviours seen after noxious mechanical, cold and hot peripheral stimulation. A peripheral change in the expression of molecular transducers for these stimuli (i.e., TRPV1, TRPM8 and TRPA1) does not seem to account for this general hyperexcitability. Instead, a decreased chloride-mediated inhibitory tone on WDR neurons may play a role as indicated by the abnormal elevation of the type 1 Na-K-Cl cotransporter transcripts. Altogether, we propose that long-term consequences of NMS are associated with reduced spinal cord inhibition favouring the expression of pain hypersensitivity. We cannot exclude that this phenomenon is also present at supraspinal sites, as other NMS-associated symptoms include excessive anxiety and impaired sociability.

Electrophysiological Recordings from Identified Cell Types in the Olfactory Cortex of Awake Mice.

Neural circuits consist of a myriad of distinct cell types, each with specific intrinsic properties and patterns of synaptic connectivity, which transform neural input and convey this information to downstream targets. Understanding how different features of an odor stimulus are encoded and relayed to their appropriate targets will require selective identification and manipulation of these different elements of the circuit. Here, we describe methods to obtain dense, extracellular electrophysiological recordings of odor-evoked activity in olfactory (piriform) cortex of awake, head-fixed mice, and optogenetic tools and procedures to identify genetically defined cell types within this circuit.

Dual Modulator of ASIC Channels and GABAA Receptors from Thyme Alters Fear-Related Hippocampal Activity.

Acid-sensing ion channels (ASICs) are proton-gated ion channels that mediate nociception in the peripheral nervous system and contribute to fear and learning in the central nervous system. Sevanol was reported previously as a naturally-occurring ASIC inhibitor from thyme with favorable analgesic and anti-inflammatory activity. Using electrophysiological methods, we found that in the high micromolar range, the compound effectively inhibited homomeric ASIC1a and, in sub- and low-micromolar ranges, positively modulated the currents of α1ß2γ2 GABAA receptors. Next, we tested the compound in anxiety-related behavior models using a targeted delivery into the hippocampus with parallel electroencephalographic measurements. In the open field, 6 µM sevanol reduced both locomotor and θ-rhythmic activity similar to GABA, suggesting a primary action on the GABAergic system. At 300 µM, sevanol markedly suppressed passive avoidance behavior, implying alterations in conditioned fear memory. The observed effects could be linked to distinct mechanisms involving GABAAR and ASIC1a. These results elaborate the preclinical profile of sevanol as a candidate for drug development and support the role of ASIC channels in fear-related functions of the hippocampus.