Chronic chemogenetic stimulation of the anterior olfactory nucleus reduces newborn neuron survival in the adult mouse olfactory bulb.

During adult rodent life, newborn neurons are added to the olfactory bulb (OB) in a tightly controlled manner. Upon arrival in the OB, input synapses from the local bulbar network and the higher olfactory cortex precede the formation of functional output synapses, indicating a possible role for these regions in newborn neuron survival. An interplay between the environment and the piriform cortex in the regulation of newborn neuron survival has been suggested. However, the specific network and the neuronal cell types responsible for this effect have not been elucidated. Furthermore, the role of the other olfactory cortical areas in this process is not known. Here we demonstrate that pyramidal neurons in the mouse anterior olfactory nucleus, the first cortical area for odor processing, have a key role in the survival of newborn neurons. Using DREADD (Designer Receptors Exclusively Activated by Designer Drugs) technology, we applied chronic stimulation to the anterior olfactory nucleus and observed a decrease in newborn neurons in the OB through induction of apoptosis. These findings provide further insight into the network regulating neuronal survival in adult neurogenesis and strengthen the importance of the surrounding network for sustained integration of new neurons.

FxRIamide regulates the oscillatory activity in the olfactory center of the terrestrial slug Limax.

The terrestrial slug Limax acquires odor-aversion memory. The procerebrum is the secondary olfactory center in the brain of Limax, and functions as the locus of the memory formation and storage. The change in the local field potential oscillation in the procerebrum reflects the information processing of the learned odor. However, it is not fully understood what factors, intrinsic or extrinsic in the procerebrum, alter the oscillatory activity and how it is regulated. In the present study, we found that FxRIamide (Phe-x-Arg-Ile-NH2), which was previously identified as a myomodulatory peptide in the gastropod Fusinus ferrugineus, downregulates the oscillatory frequency of the local field potential oscillation in the procerebrum of Limax. FxRIamide peptides were encoded by two distinct transcripts, which exhibit partially overlapping expression patterns in the brain. Immunohistochemical staining revealed a scattered distribution of FxRIamide-expressing neurons in the cell mass layer of the procerebrum, in addition to the ramified innervation of FxRIamidergic neurons in the neuropile layers. Down-regulation of the oscillatory frequency of the local field potential was explained by the inhibitory effects of FxRIamide on the bursting neurons, which are the kernels of the local field potential oscillation in the procerebrum. Our study revealed the previously unidentified role of FxRIamide peptides in the network of interneurons of Limax, and these peptides may play a role in the mnemonic functions of the procerebrum.

Lisdexamfetamine Alters BOLD-fMRI Activations Induced by Odor Cues in Impulsive Children.

INTRODUCTION: Lisdexamfetamine (LDX) is a drug used to treat ADHD/impulsive patients. Impulsivity is known to affect inhibitory, emotional and cognitive function. On the other hand, smell and odor processing are known to be affected by neurological disorders, as they are modulators of addictive and impulsive behaviors specifically. We hypothesize that, after LDX ingestion, inhibitory pathways of the brain would change, and complementary behavioral regulation mechanisms would appear to regulate decision-making and impulsivity. METHODS: 20 children were studied in an aleatory crossover study. Imaging of BOLD-fMRI activity, elicited by olfactory stimulation in impulsive children, was performed after either LDX or placebo ingestion. RESULTS: Findings showed that all subjects who underwent odor stimulation presented activations of similar intensities in the olfactory centers of the brain. This contrasted with inhibitory regions of the brain such as the cingulate cortex and frontal lobe regions, which demonstrated changed activity patterns and intensities. While some differences between the placebo and medicated states were found in motor areas, precuneus, cuneus, calcarine, supramarginal, cerebellum and posterior cingulate cortex, the main changes were found in frontal, temporal and parietal cortices. When comparing olfactory cues separately, pleasant food smells like chocolate seemed not to present large differences between the medicated and placebo scenarios, when compared to non-food-related smells. CONCLUSION: It was demonstrated that LDX, first, altered the inhibitory pathways of the brain, secondly it increased activity in several brain regions which were not activated by smell in drug-naïve patients, and thirdly, it facilitated a complementary behavioral regulation mechanism, run by the cerebellum, which regulated decision-making and impulsivity in motor and frontal structures.

Association between olfactory function and inhibition of emotional competing distractors in major depressive disorder.

We aimed to investigate the changes of olfaction of major depressive disorder (MDD) before and after medical treatment, and to preliminarily scrutinize the association between the olfactory function and the severity of depressive symptoms, response inhibition, and emotional responding. Forty-eight medicine-naïve MDD patients plus 33 healthy controls (HC) matched on gender, ages, and level of education, were recruited in the test group. The Chinese Smell Identification Test (CSIT), Self-reported Olfactory Scale (SROS), 17-item Hamilton Depression Rating Scale (HAMD-17), Hamilton Anxiety Rating Scale (HAMA), and mean reaction time/accuracy rate (ΔMRT) of emotional Stroop test were measured. The patients were assessed before the treatment (baseline) and 3 months after the treatment (follow-up). The data at the baseline level were measured then associated using multiple linear regression stepwise analysis. The MDD patients had lower scores of the CSIT and SROS and longer ΔMRT at baseline level compared to HC while the ΔMRT of MDD patients remained longer after 3-month treatment (p's < 0.05). At the baseline level, the regression equation including age and ΔMRT of negative word-color congruent (NEG-C), was finally observed as follows: y(CSIT) = 10.676-0.063 × 1-0.002 × 2, [x1 = the age(y), x2 = the NEG-C (ms)]. The olfactory function of MDD appears to be correlated negatively with the age and the ΔMRT of negative stimuli before treatment. After the remission of MDD, the olfactory dysfunction was improved, which might be regarded as a responding phenotype of brain function of MDD rather than the emotional responding.

Coding of odors in the anterior olfactory nucleus.

Odorant molecules stimulate olfactory receptor neurons, and axons of these neurons project into the main olfactory bulb where they synapse onto mitral and tufted cells. These project to the primary olfactory cortex including the anterior olfactory nucleus (AON), the piriform cortex, amygdala, and the entorhinal cortex. The properties of mitral cells have been investigated extensively, but how odor information is processed in subsequent brain regions is less well known. In the present study, we recorded the electrical activity of AON neurons in anesthetized rats. Most AON cells fired in bursts of 2-10 spikes separated by very short intervals (<20 ms), in a period linked to the respiratory rhythm. Simultaneous recordings from adjacent neurons revealed that the rhythms of adjacent cells, while locked to the same underlying rhythm, showed marked differences in phase. We studied the responses of AON cells to brief high-frequency stimulation of the lateral olfactory tract, mimicking brief activation of mitral cells by odor. In different cells, such stimuli evoked transient or sustained bursts during stimulation or, more commonly, post-stimulation bursts after inhibition during stimulation. This suggests that, in AON cells, phase shifts occur as a result of post-inhibitory rebound firing, following inhibition by mitral cell input, and we discuss how this supports processing of odor information in the olfactory pathway. Cells were tested for their responsiveness to a social odor (the bedding of a strange male) among other simple and complex odors tested. In total, 11 cells responded strongly and repeatedly to bedding odor, and these responses were diverse, including excitation (transient or sustained), inhibition, and activation after odor presentation, indicating that AON neurons respond not only to the type of complex odor but also to temporal features of odor application.

Metabotropic Glutamate Receptor 5 and 8 Modulate the Ameliorative Effect of Ultramicronized Palmitoylethanolamide on Cognitive Decline Associated with Neuropathic Pain.

This study investigated whether metabotropic glutamate receptor (mGluR) 5 and 8 are involved in the effect of ultramicronizedpalmitoylethanolamide (um-PEA) on the cognitive behavior and long term potentiation (LTP) at entorhinal cortex (LEC)-dentate gyrus (DG) pathway in mice rendered neuropathic by the spare nerve injury (SNI). SNI reduced discriminative memory and LTP. Um-PEA treatment started after the development of neuropathic pain had no effects in sham mice, whereas it restored cognitive behavior and LTP in SNI mice. 2-Methyl-6-(phenylethynyl) pyridine (MPEP), a selective mGluR5 antagonist, improved cognition in SNI mice and produced a chemical long term depression of the field excitatory postsynaptic potentials (fEPSPs) in sham and SNI mice. After theta burst stimulation (TBS) MPEP restored LTP in SNI mice. In combination with PEA, MPEP antagonized the PEA effect on discriminative memory and decreased LTP in SNI mice. The (RS)-4-(1-amino-1-carboxyethyl)phthalic acid (MDCPG), a selective mGluR8 antagonist, did not affect discriminative memory, but it induced a chemical LTP and prevented the enhancement of fEPSPs after TBS in SNI mice which were treated or not treated with PEA. The effect of PEA on LTP and cognitive behavior was modulated by mGluR5 and mGluR8. In particular in the SNI conditions, the mGluR5 blockade facilitated memory and LTP, but prevented the beneficial effects of PEA on discriminative memory while the mGluR8 blockade, which was ineffective in itself, prevented the favorable action of the PEA on LTP. Thus, although their opposite roles (excitatory/inhibitory of the two receptor subtypes on the glutamatergic system), they appeared to be required for the neuroprotective effect of PEA in conditions of neuropathic pain.

Precise Synaptic Balance in the Zebrafish Homolog of Olfactory Cortex.

Neuronal computations critically depend on the connectivity rules that govern the convergence of excitatory and inhibitory synaptic signals onto individual neurons. To examine the functional synaptic organization of a distributed memory network, we performed voltage clamp recordings in telencephalic area Dp of adult zebrafish, the homolog of olfactory cortex. In neurons of posterior Dp, odor stimulation evoked large, recurrent excitatory and inhibitory inputs that established a transient state of high conductance and synaptic balance. Excitation and inhibition in individual neurons were co-tuned to different odors and correlated on slow and fast timescales. This precise synaptic balance implies specific connectivity among Dp neurons, despite the absence of an obvious topography. Precise synaptic balance stabilizes activity patterns in different directions of coding space and in time while preserving high bandwidth. The coordinated connectivity of excitatory and inhibitory subnetworks in Dp therefore supports fast recurrent memory operations.

Hippocampal projections to the anterior olfactory nucleus differentially convey spatiotemporal information during episodic odour memory.

The hippocampus is essential for representing spatiotemporal context and establishing its association with the sensory details of daily life to form episodic memories. The olfactory cortex in particular shares exclusive anatomical connections with the hippocampus as a result of their common evolutionary history. Here we selectively inhibit hippocampal projections to the anterior olfactory nucleus (AON) during behavioural tests of contextually cued odour recall. We find that spatial odour memory and temporal odour memory are independently impaired following inhibition of distinct, topographically organized hippocampal-AON pathways. Our results not only reveal a longstanding unknown function for the AON but offer new mechanistic insights regarding the representation of odours in episodic memory.

CHARACTERISTICS OF GAMMA OSCILLATIONS INDUCED BY KAINATE PRESSURE EJECTION ON CA1 HIPPOCAMPUS OF MICE BRAIN SLICES IN SUBMERGED CHAMBERS.

Aim - mostly, gamma oscillations are studied in interface-type chambers. The purpose of the presented investigation is to describe the characteristics of gamma oscillations induced in submerged chambers by kainite pressure ejection. Horizontal combined entorhynal-hippocampal slices 300-350 µm were prepared from young mice (P18-28). Gamma oscillations were induced by 1 mM kainite pressure ejection at the boundary of stratum radiatum and lacunosum-moleculare of area CA1. Field potential recordings were registered from the vicinity of kainite application. Induced CA1 local field potential (LFP) oscillations were brief (7.55±3.77 sec.) and had heterogeneous nature; they could be divided into three epochs: well developed initial part of oscillation, middle part with reduced gamma power and last part of the rhythm with sporadic immergence of sparse (3 to 5) gamma cycles. Generally, initial parts of oscillations had higher amplitude and frequency than the middle part of it. Induction of consecutive gamma oscillations did not depend on the duration of the time intervals between oscillations. Their amplitude was affected by the order of induction but not by time intervals between oscillations. Neither the frequency was affected by the order of induced activities in the same slice. However, comparatively lower frequency oscillations were recorded after long time intervals between gamma activities. Induction of CA1 gamma oscillations in submerged conditions will offer significant experimental advantage, like using patch-clamp techniques to study the mechanism of this activity.

Mutation in HFE gene decreases manganese accumulation and oxidative stress in the brain after olfactory manganese exposure.

Increased accumulation of manganese (Mn) in the brain is significantly associated with neurobehavioral deficits and impaired brain function. Airborne Mn has a high systemic bioavailability and can be directly taken up into the brain, making it highly neurotoxic. While Mn transport is in part mediated by several iron transporters, the expression of these transporters is altered by the iron regulatory gene, HFE. Mutations in the HFE gene are the major cause of the iron overload disorder, hereditary hemochromatosis, one of the prevalent genetic diseases in humans. However, whether or not HFE mutation modifies Mn-induced neurotoxicity has not been evaluated. Therefore, our goal was to define the role of HFE mutation in Mn deposition in the brain and the resultant neurotoxic effects after olfactory Mn exposure. Mice carrying the H67D HFE mutation, which is homologous to the H63D mutation in humans, and their control, wild-type mice, were intranasally instilled with MnCl2 with different doses (0, 0.2, 1.0 and 5.0 mg kg(-1)) daily for 3 days. Mn levels in the blood, liver and brain were determined using inductively-coupled plasma mass spectrometry (ICP-MS). H67D mutant mice showed significantly lower Mn levels in the blood, liver, and most brain regions, especially in the striatum, while mice fed an iron-overload diet did not. Moreover, mRNA expression of ferroportin, an essential exporter of iron and Mn, was up-regulated in the striatum. In addition, the levels of isoprostane, a marker of lipid peroxidation, were increased in the striatum after Mn exposure in wild-type mice, but were unchanged in H67D mice. Together, our results suggest that the H67D mutation provides decreased susceptibility to Mn accumulation in the brain and neurotoxicity induced by inhaled Mn.

Mystixin-7 mini-peptide protects ionotropic glutamatergic mechanisms against oxygen-glucose deprivation in vitro.

The aim of the present study was to explore the neuroprotective effects of the mystixin-7 mini-peptide (MTX, a synthetic corticotropin-releasing-factor-like, 7-amino-acid peptide) on an in vitro oxygen glucose deprivation model (OGD, 10min). The study used a technique of on-line monitoring of changes in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) and N-methyl-d-aspartic acid receptor (NMDAR)-mediated field excitatory postsynaptic potentials (fEPSPs) in the olfactory cortex slices in the OGD model. OGD resulted in an irreversible blockade of both AMPAR and NMDAR activity. Pretreatment of slices by MTX and their subsequent exposure to OGD resulted in decreased activity of these postsynaptic mechanisms (AMPARs, 71%; NMDARs, 68% as compared to baseline), but they were not blocked altogether. The degree protection of activity of both AMPARs and NMDARs had dose-dependent manner, with a maximal effect at 100mg/mL. These protective effects were retained after the removal of MTX from the bathing medium. To evaluate the protective efficacy of MTX on NMDARs, the slices were pretreated by MTX and exposed to OGD and then treated with l-glutamate (1mM). NMDARs' response to application of l-glutamate was minimal at higher concentrations of MTX and maximal at lower concentrations. These findings indicate that the molecules of MTX interact with a certain amount of NMDARs, and thereby protect them from the OGD. Pretreatment of slices with MTX contributed to the protection of network activity against OGD and promoted the development of the learning process in the form of long-term potentiation. To specify the protective effects of MTX, it was denatured by trypsin. The proteolytic cleavage of MTX resulted to a significant decrease in the activity of both AMPARs and NMDARs against OGD as compared with that of the native peptide. Together, these findings provide further insight into the protective potential of the MTX mini-peptide. We believe that the data presented can be the basis for the development of therapeutics MTX-based medications for the treatment of the ischemic stroke.

Exercise-mimetic AICAR transiently benefits brain function.

Exercise enhances learning and memory in animals and humans. The role of peripheral factors that may trigger the beneficial effects of running on brain function has been sparsely examined. In particular, it is unknown whether AMP-kinase (AMPK) activation in muscle can predict enhancement of brain plasticity. Here we compare the effects of running and administration of AMPK agonist 5-Aminoimidazole-4-carboxamide 1-ß-D-ribofuranoside (AICAR, 500 mg/kg), for 3, 7 or 14 days in one-month-old male C57BL/6J mice, on muscle AMPK signaling. At the time-points where we observed equivalent running- and AICAR-induced muscle pAMPK levels (7 and 14 days), cell proliferation, synaptic plasticity and gene expression, as well as markers of oxidative stress and inflammation in the dentate gyrus (DG) of the hippocampus and lateral entorhinal cortex (LEC) were evaluated. At the 7-day time-point, both regimens increased new DG cell number and brain-derived neurotrophic factor (BDNF) protein levels. Furthermore, microarray analysis of DG and LEC tissue showed a remarkable overlap between running and AICAR in the regulation of neuronal, mitochondrial and metabolism related gene classes. Interestingly, while similar outcomes for both treatments were stable over time in muscle, in the brain an inversion occurred at fourteen days. The compound no longer increased DG cell proliferation or neurotrophin levels, and upregulated expression of apoptotic genes and inflammatory cytokine interleukin-1ß. Thus, an exercise mimetic that produces changes in muscle consistent with those of exercise does not have the same sustainable positive effects on the brain, indicating that only running consistently benefits brain function.

Top-down inputs from the olfactory cortex in the postprandial period promote elimination of granule cells in the olfactory bulb.

Elimination of granule cells (GCs) in the olfactory bulb (OB) is not a continual event but is promoted during a short time window in the postprandial period, typically with postprandial sleep. However, the neuronal mechanisms for the enhanced GC elimination during the postprandial period are not understood. Here, we addressed the question of whether top-down inputs of centrifugal axons from the olfactory cortex (OC) during the postprandial period are involved in the enhanced GC elimination in the OB. Electrical stimulation of centrifugal axons from the OC of anesthetized mice increased GC apoptosis. Furthermore, pharmacological suppression of top-down inputs from the OC to the OB during the postprandial period of freely behaving mice by γ-aminobutyric acid (GABA)A receptor agonist injection in the OC significantly decreased GC apoptosis. Remarkable apoptotic GC elimination in the sensory-deprived OB was also suppressed by pharmacological blockade of top-down inputs. These results indicate that top-down inputs from the OC to the OB during the postprandial period are the crucial signal promoting GC elimination, and suggest that the life and death decision of GCs in the OB is determined by the interplay between bottom-up sensory inputs from the external world and top-down inputs from the OC.