Loss of mGlu5 receptors in somatostatin-expressing neurons alters negative emotional states.

Subtype 5 metabotropic glutamate receptors (mGlu5) are known to play an important role in regulating cognitive, social and valence systems. However, it remains largely unknown at which circuits and neuronal types mGlu5 act to influence these behavioral domains. Altered tissue- or cell-specific expression or function of mGlu5 has been proposed to contribute to the exacerbation of neuropsychiatric disorders. Here, we examined how these receptors regulate the activity of somatostatin-expressing (SST+) neurons, as well as their influence on behavior and brain rhythmic activity. Loss of mGlu5 in SST+ neurons elicited excitatory synaptic dysfunction in a region and sex-specific manner together with a range of emotional imbalances including diminished social novelty preference, reduced anxiety-like behavior and decreased freezing during retrieval of fear memories. In addition, the absence of mGlu5 in SST+ neurons during fear processing impaired theta frequency oscillatory activity in the medial prefrontal cortex and ventral hippocampus. These findings reveal a critical role of mGlu5 in controlling SST+ neurons excitability necessary for regulating negative emotional states.

Brainstem system of hippocampal theta induction: The role of the ventral tegmental area.

This article summarizes the results of studies concerning the influence of the ventral tegmental area (VTA) on the hippocampal theta rhythm. Temporary VTA inactivation resulted in transient loss of the hippocampal theta. Permanent destruction of the VTA caused a long-lasting depression of the power of the theta and it also had some influence on the frequency of the rhythm. Activation of glutamate (GLU) receptors or decrease of GABAergic tonus in the VTA led to enhancement of dopamine release and increased hippocampal theta power. High time and frequency cross-correlation was detected for the theta band between the VTA and hippocampus during paradoxical sleep and active waking. Thus, the VTA may belong to the broad network involved in theta rhythm regulation. This article also presents a model of brainstem-VTA-hippocampal interactions in the induction of the hippocampal theta rhythm. The projections from the VTA which enhance theta rhythm are incorporated into the main theta generation pathway, in which the septum acts as the central node. The neuronal activity that may be responsible for the ability of the VTA to regulate theta probably derives from the structures associated with rapid eye movement (sleep) (REM) sleep or with sensorimotor activity (i.e., mainly from the pedunculopontine and laterodorsal tegmental nuclei and also from the raphe).

Discriminating rapid eye movement sleep from wakefulness by analyzing high frequencies from single-channel EEG recordings in mice.

Rapid eye movement sleep (REMS) is characterized by the appearance of fast, desynchronized rhythms in the cortical electroencephalogram (EEG), similar to wakefulness. The low electromyogram (EMG) amplitude during REMS distinguishes it from wakefulness; therefore, recording EMG signal seems to be imperative for discriminating between the two states. The present study evaluated the high frequency components of the EEG signal from mice (80-500 Hz) to support REMS detection during sleep scoring without an EMG signal and found a strong positive correlation between waking and the average power of 80-120 Hz, 120-200 Hz, 200-350 Hz and 350-500 Hz. A highly negative correlation was observed with REMS. Furthermore, our machine learning approach demonstrated that simple EEG time-series features are enough to discriminate REMS from wakefulness with sensitivity of roughly 98 percent and specificity of around 92 percent. Interestingly, assessing only the higher frequency bands (200-350 Hz as well as 350-500 Hz) gives significantly greater predictive power than assessing only the lower end of the EEG frequency spectrum. This paper proposes an approach that can detect subtle changes in REMS reliably, and future unsupervised sleep-scoring approaches could greatly benefit from it.

Localization and Registration of 2D Histological Mouse Brain Images in 3D Atlas Space.

To accurately explore the anatomical organization of neural circuits in the brain, it is crucial to map the experimental brain data onto a standardized system of coordinates. Studying 2D histological mouse brain slices remains the standard procedure in many laboratories. Mapping these 2D brain slices is challenging; due to deformations, artifacts, and tilted angles introduced during the standard preparation and slicing process. In addition, analysis of experimental mouse brain slices can be highly dependent on the level of expertise of the human operator. Here we propose a computational tool for Accurate Mouse Brain Image Analysis (AMBIA), to map 2D mouse brain slices on the 3D brain model with minimal human intervention. AMBIA has a modular design that comprises a localization module and a registration module. The localization module is a deep learning-based pipeline that localizes a single 2D slice in the 3D Allen Brain Atlas and generates a corresponding atlas plane. The registration module is built upon the Ardent python package that performs deformable 2D registration between the brain slice to its corresponding atlas. By comparing AMBIA's performance in localization and registration to human ratings, we demonstrate that it performs at a human expert level. AMBIA provides an intuitive and highly efficient way for accurate registration of experimental 2D mouse brain images to 3D digital mouse brain atlas. Our tool provides a graphical user interface and it is designed to be used by researchers with minimal programming knowledge.

The role of subicular VIP-expressing interneurons on seizure dynamics in the intrahippocampal kainic acid model of temporal lobe epilepsy.

The subiculum, a key output region of the hippocampus, is increasingly recognized as playing a crucial role in seizure initiation and spread. The subiculum consists of glutamatergic pyramidal cells, which show alterations in intrinsic excitability in the course of epilepsy, and multiple types of GABAergic interneurons, which exhibit varying characteristics in epilepsy. In this study, we aimed to assess the role of the vasoactive intestinal peptide interneurons (VIP-INs) of the ventral subiculum in the pathophysiology of temporal lobe epilepsy. We observed that an anatomically restricted inhibition of VIP-INs of the ventral subiculum was sufficient to reduce seizures in the intrahippocampal kainic acid model of epilepsy, changing the circadian rhythm of seizures, emphasizing the critical role of this small cell population in modulating TLE. As we expected, permanent unilateral or bilateral silencing of VIP-INs of the ventral subiculum in non-epileptic animals did not induce seizures or epileptiform activity. Interestingly, transient activation of VIP-INs of the ventral subiculum was enough to increase the frequency of seizures in the acute seizure model. Our results offer new perspectives on the crucial involvement of VIP-INs of the ventral subiculum in the pathophysiology of TLE. Given the observed predominant disinhibitory role of the VIP-INs input in subicular microcircuits, modifications of this input could be considered in the development of therapeutic strategies to improve seizure control.

Control of Theta Oscillatory Activity Underlying Fear Expression by mGlu5 Receptors.

Metabotropic glutamate 5 receptors (mGlu5) are thought to play an important role in mediating emotional information processing. In particular, negative allosteric modulators (NAMs) of mGlu5 have received a lot of attention as potential novel treatments for several neuropsychiatric diseases, including anxiety-related disorders. The aim of this study was to assess the influence of pre- and post-training mGlu5 inactivation in cued fear conditioned mice on neuronal oscillatory activity during fear retrieval. For this study we used the recently developed mGlu5 NAM Alloswicth-1 administered systemically. Injection of Alloswicth-1 before, but not after, fear conditioning resulted in a significant decrease in freezing upon fear retrieval. Mice injected with Alloswicth-1 pre-training were also implanted with recording microelectrodes into both the medial prefrontal cortex (mPFC) and ventral hippocampus (vHPC). The recordings revealed a reduction in theta rhythmic activity (4-12 Hz) in both the mPFC and vHPC during fear retrieval. These results indicate that inhibition of mGlu5 signaling alters local oscillatory activity in principal components of the fear brain network underlying a reduced response to a predicted threat.

Proximal perimeter encoding in the rat rostral thalamus.

Perimeters are an important part of the environment, delimiting its geometry. Here, we investigated how perimeters (vertical walls; vertical drops) affect neuronal responses in the rostral thalamus (the anteromedial and parataenial nuclei in particular). We found neurons whose firing patterns reflected the presence of walls and drops, irrespective of arena shape. Their firing patterns were stable across multiple sleep-wake cycles and were independent of ambient lighting conditions. Thus, rostral thalamic nuclei may participate in spatial representation by encoding the perimeters of environments.

Modulation of hippocampal theta rhythm by the opioid system of the pedunculopontine tegmental nucleus.

The pedunculopontine tegmental nucleus (PPN) belongs to the brainstem system which synchronizes hippocampal activity. Theta relevant intra-PPN circuitry involves its cholinergic, GABA-ergic and glutamatergic neurons and Substance P as neuromodulator. Evidence that PPN opioid elements also modulate the hippocampal theta is provided here. In urethane-anesthetized rats a unilateral microinjection of morphine (MF) (1.5 and 5 microg) increased the maximal peak power of tail pinch-induced theta. The higher dose also increased the corresponding frequency. When the theta was evoked by intra-PPN injection of carbachol (10 microg), the addition of MF (5 microg) prolonged theta latency and shortened the duration of the theta. These effects of MF were blocked by naloxone (5 microg). The results obtained suggest that the PPN opioid system can enhance or suppress the hippocampal theta depending on the actual level of PPN activation.

Hippocampal theta rhythm after local administration of procaine or amphetamine into the ventral tegmental area in fear conditioned rats.

The ventral tegmental area (VTA) is thought to be an important component in the mesocorticolimbic system involved in the regulation of theta rhythm in the hippocampus. In this study we investigate the effect of pharmacological inactivation (local procaine infusion) or activation (local amphetamine infusion) of the VTA on theta rhythm parameters during task specific behavior in fear conditioned, freely moving rats. Animals were implanted with bilateral recording electrodes into the dorsal hippocampus (CA1) and bilateral injection cannulas into the VTA. Behavioral activities and hippocampal local field potentials (LFP) were recorded throughout the experiment, in pre- and post-injection conditions. We found that intra-VTA injection of procaine temporarily suppressed fear conditioned avoidance response (escape from the foot-shock arena) and also influenced hippocampal theta rhythm parameters during immobility linked with arousal and/or attention. Procaine infusion decreased the signal power (Pmax) of theta rhythm during immobility behavior, in comparison to the control group (water infusion), whereas administration of amphetamine had no effect on the behavior and hippocampal LFP. Our results indicate that temporal inactivation of neuronal activity in the VTA affects hippocampal theta rhythm linked with attentional immobility and suppresses avoidance response in fear conditioned animals.

Theta activity in local field potential of the ventral tegmental area in sleeping and waking rats.

Hippocampal theta rhythm appears in two vigilance states: active waking and paradoxical sleep. The ventral tegmental area (VTA) is active in sleep and waking and is connected to the hippocampus. We assessed the relationship between local field potential (LFP) of the VTA and sleep-waking stages in freely moving rats. Electrical activity of the VTA was divided into: quiet waking (W), waking with theta (WT), slow wave sleep (SWS) and paradoxical sleep (PS), depending on the hippocampal signal and the animal's behavior. We analyzed total power in the VTA signal and we also extracted peak power (Pmax) and corresponding frequency (Fmax) in theta and delta bands from both the VTA and hippocampal recording. In the VTA the 6-9 Hz band had the highest power during PS, and the ratio of the 6-9 to 3-6 Hz power was highest during both PS and WT, which accentuated Pmax of this particular theta sub-band. During W, a very slight increase (or plateau) in signal power was seen in theta range. Pmax and Fmax of theta were higher in PS than in both WT and W, and these parameters did not differ between W and WT. During WT and PS, Fmax in the 6-9 Hz band was greatly correlated between the VTA and hippocampus signal. We also detected high cross-correlation in power spectra between the hippocampus and the VTA (for delta and theta, during WT and PS). The results suggest that the VTA may belong to the broad network involved in theta rhythm induction.

NMDA-glutamatergic activation of the ventral tegmental area induces hippocampal theta rhythm in anesthetized rats.

Glutamate afferents reaching the ventral tegmental area (VTA) affect dopamine (DA) cells in this structure probably mainly via NMDA receptors. VTA appears to be one of the structures involved in regulation of hippocampal theta rhythm, and this work aimed at assessing the role of glutamatergic activation of the VTA in the theta regulation. Male Wistar rats (n=17) were divided into groups, each receiving intra-VTA microinjection (0.5 µl) of either solvent (water), glutamatergic NMDA agonist (0.2 µg) or antagonist (MK-801, 3.0 µg). Changes in local field potential were assessed on the basis of peak power (Pmax) and corresponding peak frequency (Fmax) for the delta (0.5-3 Hz) and theta (3-6 Hz) bands. NMDA microinjection evoked long-lasting hippocampal theta. The rhythm appeared with a latency of ca. 12 min post-injection and lasted for over 30 min; Pmax in this band was significantly increased for 50 min, while simultaneously Pmax in the delta band remained lower than in control conditions. Theta Fmax and delta Fmax were increased in almost entire post-injection period (by 0.3-0.5 Hz and 0.3-0.7 Hz, respectively). MK-801 depressed the sensory-evoked theta: tail pinch could not induce theta for 30 min after the injection; Pmax significantly decreased in the theta band and at the same time it increased in the delta band. Theta Fmax decreased 10 and 20 min post injection (by 0.4-0.5 Hz) and delta Fmax decreased in almost entire post injection period (by 0.3-0.7 Hz). NMDA injection generates theta rhythm probably through stimulation of dopaminergic activity within the VTA.

Dopaminergic transmission in the midbrain ventral tegmental area in the induction of hippocampal theta rhythm.

Hippocampal rhythmic slow activity (RSA, theta) is regulated by many brainstem structures, including the midbrain ventral tegmental area (VTA). This work aimed at assessing the role of the dopaminergic (DA) transmission of the VTA in this regulation. Male Wistar rats (n=35) in urethane anaesthesia received an intra-VTA microinjection of either flupenthixol (FLU; doses of 5.0, 2.5, 1.25 and 0.625 µg) or amphetamine (AMPH; 2.5 and 5.0 µg) following control solvent microinjection. Peak power (Pmax) and corresponding peak frequency (Fmax) for delta and theta bands were extracted from EEG recording. Flupenthixol at a dose of 1.25 µg evoked long-lasting theta, continuing for 32.0 min on average, with a mean latency of 7.1 min. Other doses of FLU caused an increase of Pmax theta and reduction of Pmax delta without generating visually recognizable, regular theta rhythm. 5 µg of AMPH evoked theta continuing for 24.4 min on average, with a mean latency of 9.7 min. The lower dose was much less effective, with its outcome resembling the one after the less active FLU doses. During pharmacologically induced theta rhythm, both after FLU and AMPH, brief episodes of asynchronous activity appeared periodically, and they were more frequent and longer in AMPH groups. AMPH may act locally on multiple sites, inhibiting DA cells in somatodendritic region but also increasing dopamine release in target structures, and this, depending on AMPH dose, can lead to induction of theta rhythm. Locally administered DA antagonist on the other hand, when used at a proper dose, can produce theta most likely by the mechanism of inhibiting autoreceptors.

Hippocampal theta rhythm induced by rostral pontine nucleus stimulation in the conditions of pedunculopontine tegmental nucleus inactivation.

Theta rhythm in rat hippocampus occurs during cortical activation in different forms of waking as well as during paradoxical phase of sleep. The multi-level regulatory system of theta, based mainly on cholinergic transmission, includes structures from the forebrain to the medulla. Among them the most important are two reticular nuclei: the pedunculopontine tegmental nucleus (PPN) and rostral pontine tegmental nucleus (RPO). Functional relations between these two nuclei are still unidentified. It is known that cholinergic stimulation of these nuclei with carbachol leads to induction of theta in the hippocampus. Electrical stimulation has the same effect but only when applied to the RPO. In our experiments, performed on urethanized rats, each of these two methods was applied to the RPO with the PPN being inactivated in the contralateral hemisphere. We found that inactivation of the PPN does not suppress theta induced with carbachol microinjection into the RPO, but completely blocks theta induction with electrical stimulation of the RPO. The results suggest the important role of the PPN in theta rhythm generation from brainstem level, depending on the method of theta rhythm induction, i.e. cholinergic or electric stimulation of the RPO.

NMDA receptor antagonist-enhanced high frequency oscillations: are they generated broadly or regionally specific?

Systemic administration of NMDA receptor antagonists, used to model schizophrenia, increase the power of high-frequency oscillations (130-180Hz, HFO) in a variety of neuroanatomical and functionally distinct brain regions. However, it is unclear whether HFO are independently and locally generated or instead spread from a distant source. To address this issue, we used local infusion of tetrodotoxin (TTX) to distinct brain areas to determine how accurately HFO recorded after injection of NMDAR antagonists reflect the activity actually generated at the electrode tip. Changes in power were evaluated in local field potentials (LFPs) recorded from the nucleus accumbens (NAc), prefrontal cortex and caudate and in electrocorticograms (ECoGs) from visual and frontal areas. HFO recorded in frontal and visual cortices (ECoGs) or in the prefrontal cortex, caudate (LFPs) co-varied in power and frequency with observed changes in the NAc. TTX infusion to the NAc immediately and profoundly reduced the power of accumbal HFO which correlated with changes in HFO recorded in distant cortical sites. In contrast, TTX infusion to the prefrontal cortex did not change HFO power recorded locally, although gamma power was reduced. A very similar result was found after TTX infusion to the caudate. These findings raise the possibility that the NAc is an important neural generator. Our data also support existing studies challenging the idea that high frequencies recorded in LFPs are necessarily generated at the recording site.

The effect of dopamine receptor blockade in the rodent nucleus accumbens on local field potential oscillations and motor activity in response to ketamine.

Altered functioning of the nucleus accumbens (NAc) has been implicated in the psychotomimetic actions of NMDA receptor (NMDAR) antagonists and the pathophysiology of schizophrenia. We have shown previously that NMDAR antagonists enhance the power of high-frequency oscillations (HFO) in the NAc in a dose-dependent manner, as well as increase locomotor activity. Systemic administration of NMDAR antagonists is known to increase the release of dopamine in the NAc and dopamine antagonists can reduce ketamine-induced hyperactivity. In this study, we examined the effect of 0.5 µl intra-NAc infusion of 3.2 µg SCH23390 (D1 antagonist), 10 µg raclopride (D2 antagonist) and saline on ketamine-induced changes in motor and oscillatory activity. We found that local blockade of D1 receptors attenuated ketamine-induced increases in motor activity and blockade of D2 receptors produced a much weaker effect, with respect to saline-infused control groups. In contrast, none of the antagonists, infused separately or together, significantly modified the power or dominant frequency of ketamine-induced increases in HFO, but changes in delta and theta frequency bands were observed. Together, these findings suggest, that, in contrast to delta and theta frequency bands, the generation of ketamine enhanced-HFO in the NAc is not causally related to locomotor activation and occurs largely independently of local changes in dopamine receptor activation.

Hippocampal theta rhythm after serotonergic activation of the pedunculopontine tegmental nucleus in anesthetized rats.

The pedunculopontine tegmental nucleus (PPN), as a part of reticular formation activating system, is thought to be involved in the sleep/wake cycle regulation, and plays an important role in the generation and regulation of hippocampal rhythmical slow activity. The activity of PPN can be modulated by serotonergic system, mainly through multiple projections from raphe nuclei, which can influence PPN neurons through different classes of 5-HT receptors. In the present study, the effect of intra-PPN injection of two serotonin agonists: 8-OH-DPAT and 5-CT, on hippocampal formation EEG activity was examined in urethane-anesthetized rats. The study found that the microinjections induced prolonged spontaneous theta rhythm in both hippocampi with a short latency. The results obtained suggest that local inhibition of presumably cholinergic neurons in the PPN acts as a trigger for hippocampal theta activity.