Appetite-regulating hormones modulate odor perception and odor-evoked activity in hypothalamus and olfactory cortices.

Odors guide food seeking, and food intake modulates olfactory function. This interaction is mediated by appetite-regulating hormones like ghrelin, insulin, and leptin, which alter activity in the rodent olfactory bulb, but their effects on downstream olfactory cortices have not yet been established in humans. The olfactory tract connects the olfactory bulb to the cortex through 3 main striae, terminating in the piriform cortex (PirC), amygdala (AMY), olfactory tubercule (OT), and anterior olfactory nucleus (AON). Here, we test the hypothesis that appetite-regulating hormones modulate olfactory processing in the endpoints of the olfactory tract and the hypothalamus. We collected odor-evoked functional magnetic resonance imaging (fMRI) responses and plasma levels of ghrelin, insulin, and leptin from human subjects (n = 25) after a standardized meal. We found that a hormonal composite measure, capturing variance relating positively to insulin and negatively to ghrelin, correlated inversely with odor intensity ratings and fMRI responses to odorized vs. clean air in the hypothalamus, OT, and AON. No significant correlations were found with activity in PirC or AMY, the endpoints of the lateral stria. Exploratory whole-brain analyses revealed significant correlations near the diagonal band of Broca and parahippocampal gyrus. These results demonstrate that high (low) blood plasma concentrations of insulin (ghrelin) decrease perceived odor intensity and odor-evoked activity in the cortical targets of the medial and intermediate striae of the olfactory tract, as well as the hypothalamus. These findings expand our understanding of the cortical mechanisms by which metabolic hormones in humans modulate olfactory processing after a meal.

Polyherbal Formulation Enhancing Cerebral Slow Waves in Sleeping Rats.

Polyherbal medicines are composed of multiple herbs and have traditionally been used in East Asian countries for the remedy of physiological symptoms. Although the effects of polyherbal formulations have been investigated at the molecular and behavioral levels, less is known about whether and how medicinal herbs affect the central nervous system in terms of neurophysiology. We introduced a novel blended herbal formulation that consisted of 35% linden, 21% mulberry, 20% lavandin, 20% butterfly pea, and 4% tulsi. After intraperitoneal administration of this formulation or saline, we simultaneously recorded epidural electrocorticograms (ECoGs) from the olfactory bulb (OB), primary somatosensory cortex (S1), and primary motor cortex (M1), along with electromyograms (EMGs) and electrocardiograms (ECGs), of rats exploring an open field arena. Using the EMGs and OB ECoGs, we segmented the behavioral states of rats into active awake, quiet awake, and sleeping states. Compared to saline, herbal medicine significantly shortened the total sleep time. Moreover, we converted the ECoG signal into a frequency domain using a fast Fourier transform (FFT) and calculated the powers at various ECoG oscillation frequencies. In the sleeping state, a slow component (0.5-3 Hz) of S1 ECoGs was significantly enhanced following the administration of the formulation, which suggests a region- and frequency-specific modulation of extracellular field oscillations by the polyherbal medicine.

Representation of Olfactory Information in Organized Active Neural Ensembles in the Hypothalamus.

The internal representation of sensory information via coherent activation of specific pathways in the nervous system is key to appropriate behavioral responses. Little is known about how chemical stimuli that elicit instinctive behaviors lead to organized patterns of activity in the hypothalamus. Here, we study how a wide range of chemosignals form a discernible map of olfactory information in the ventromedial nucleus of the hypothalamus (VMH) and show that different stimuli entail distinct active neural ensembles. Importantly, we demonstrate that this map depends on functional inputs from the vomeronasal organ. We present evidence that the spatial locations of active VMH ensembles are correlated with activation of distinct vomeronasal receptors and that disjunct VMH ensembles exhibit differential projection patterns. Moreover, active ensembles with distinct spatial locations are not necessarily associated with different behavior categories, such as defensive or social, calling for a revision of the currently accepted model of VMH organization.

Sex differences in main olfactory system pathways involved in psychosexual function.

We summarize literature from animal and human studies assessing sex differences in the ability of the main olfactory system to detect and process sex-specific olfactory signals ("pheromones") that control the expression of psychosexual functions in males and females. A case is made in non primate mammals for an obligatory role of pheromonal signaling via the main olfactory system (in addition to the vomeronasal-accessory olfactory system) in mate recognition and sexual arousal, with male-specific as well as female-specific pheromones subserving these functions in the opposite sex. Although the case for an obligatory role of pheromones in mate recognition and mating among old world primates, including humans, is weaker, we review the current literature assessing the role of putative human pheromones (eg, AND, EST, "copulin"), detected by the main olfactory system, in promoting mate choice and mating in men and women. Based on animal studies, we hypothesize that sexually dimorphic effects of putative human pheromones are mediated via main olfactory inputs to the medial amygdala which, in turn, transmits olfactory information to sites in the hypothalamus that regulate reproduction.

Evaluation of human electroencephalogram change for sensory effects of fragrance.

BACKGROUND: The stabilizing effect of lavender and the arousal effect of peppermint essential oils are acknowledged and used widely in aromatherapy and the cosmetics industry. However, no evaluation method confirms the effects of essential oils through quantitative and objective electroencephalogram (EEG) results; instead, only a psychological and subjective method exists. Therefore, this study aims to create a new emotional cosmetic evaluation paradigm using EEG values. Moreover, it enables quantitative interpretation of the results in addition to the subjective survey outcomes. METHODS: For this study, 12 healthy female Korean participants were recruited and three fragrances were used. The EEG results were collected for 3 minutes (1 minute each before, during, and after inhalation of every fragrance). RESULTS: The quantitative EEG outcomes indicate changes in the participant's brainwaves before and after inhalation. Significant changes in the EEG were observed. Based on the results, the effects of fragrances were confirmed to be stabilizing for lavender, and arousing for peppermint and coffee aroma. Furthermore, the subjective questionnaire results indicate similar tendency as that of the quantitative EEG results. CONCLUSION: In addition to psychological and subjective assessments, our emotional evaluation method can verify the cosmetic fragrance effects through quantitative and objective results.

Induction of smell through transethmoid electrical stimulation of the olfactory bulb.

BACKGROUND: Anosmia has an estimated prevalence of 5% of the general population. Outside of inflammatory causes, therapeutic options are limited despite research advances. Bypassing peripheral neuronal damage through central stimulation is a potential therapeutic option that has shown success in other sensory systems, most notably with hearing. We performed a pilot study to determine the feasibility of inducing smell through artificial electrical stimulation of the olfactory bulbs in humans. METHODS: Subjects with a history of sinus surgery, including total ethmoidectomy, with intact ability to smell were enrolled. The ability to smell was confirmed with a 40-item smell identification test. Awake subjects underwent nasal endoscopy and either a monopolar or bipolar electrode was positioned at 3 areas along the lateral lamella of the cribriform plate within the ethmoid sinus cavity. A graded stimulation current of 1-20 mA at 3.17 Hz was administered while cortical evoked potential (CEP) recordings were collected. Subjective responses of perceived smell along with reports of discomfort were recorded. Subjects with artificially induced smell underwent repeat stimulation after medically induced anosmia. RESULTS: Five subjects (age, 43-72 years) were enrolled. Three subjects reported smell perception smell with electrical stimulation. This was reproducible after inducing anosmia, but CEP recordings could not provide objective support. All subjects tolerated the study with minimal discomfort. CONCLUSION: This is the first report of induced smell through transethmoid electrical stimulation of the olfactory bulb. These results provide a proof of concept for efforts in development of an olfactory implant system.

Learning-Dependent and -Independent Enhancement of Mitral/Tufted Cell Glomerular Odor Responses Following Olfactory Fear Conditioning in Awake Mice.

Associative fear learning produces fear toward the conditioned stimulus (CS) and often generalization, the expansion of fear from the CS to similar, unlearned stimuli. However, how fear learning affects early sensory processing of learned and unlearned stimuli in relation to behavioral fear responses to these stimuli remains unclear. We subjected male and female mice expressing the fluorescent calcium indicator GCaMP3 in olfactory bulb mitral and tufted cells to a classical olfactory fear conditioning paradigm. We then used awake, in vivo calcium imaging to quantify learning-induced changes in glomerular odor responses, which constitute the first site of olfactory processing in the brain. The results demonstrate that odor-shock pairing nonspecifically enhances glomerular odor representations in a learning-dependent manner and increases representational similarity between the CS and nonconditioned odors, potentially priming the system toward generalization of learned fear. Additionally, CS-specific glomerular enhancements remain even when associative learning is blocked, suggesting two separate mechanisms lead to enhanced glomerular responses following odor-shock pairings.SIGNIFICANCE STATEMENT In the olfactory bulb (OB), odors are uniquely coded in a spatial map that represents odor identity, making the OB a unique model system for investigating how learned fear alters sensory processing. Classical fear conditioning causes fear of the conditioned stimulus (CS) and of neutral stimuli, known as generalization. Combining fear conditioning with fluorescent calcium imaging of OB glomeruli, we found enhanced glomerular responses of the CS as well as neutral stimuli in awake mice, which mirrors fear generalization. We report that CS and neutral stimuli enhancements are, respectively, learning-independent and learning-dependent. Together, these results reveal distinct mechanisms leading to enhanced OB processing of fear-inducing stimuli and provide important implications for altered sensory processing in fear generalization.

Identification of an insect-produced olfactory cue that primes plant defenses.

It is increasingly clear that plants perceive and respond to olfactory cues. Yet, knowledge about the specificity and sensitivity of such perception remains limited. We previously documented priming of anti-herbivore defenses in tall goldenrod plants (Solidago altissima) by volatile emissions from a specialist herbivore, the goldenrod gall fly (Eurosta solidaginis). Here, we explore the specific chemical cues mediating this interaction. We report that E,S-conophthorin, the most abundant component of the emission of male flies, elicits a priming response equivalent to that observed for the overall blend. Furthermore, while the strength of priming is dose dependent, plants respond even to very low concentrations of E,S-conophthorin relative to typical fly emissions. Evaluation of other blend components yields results consistent with the hypothesis that priming in this interaction is mediated by a single compound. These findings provide insights into the perceptual capabilities underlying plant defense priming in response to olfactory cues.Plants are able to prime anti-herbivore defenses in response to olfactory cues of insect pests. Here, Helms et al. identify the insect pheromone E,S-conophthorin produced by the goldenrod gall fly as the specific chemical component that elicits this priming response in goldenrod plants.

Defective signaling through plexin-A1 compromises the development of the peripheral olfactory system and neuroendocrine reproductive axis in mice.

The olfacto-genital syndrome (Kallmann syndrome) associates congenital hypogonadism due to gonadotropin-releasing hormone (GnRH) deficiency and anosmia. This is a genetically heterogeneous developmental disease with various modes of transmission, including oligogenic inheritance. Previous reports have involved defective cell signaling by semaphorin-3A in the disease pathogenesis. Here, we report that the embryonic phenotype of Plxna1-/- mutant mice lacking plexin-A1 (a major receptor of class 3 semaphorins), though not fully penetrant, resembles that of Kallmann syndrome fetuses. Pathohistological analysis indeed showed a strongly abnormal development of the peripheral olfactory system and defective embryonic migration of the neuroendocrine GnRH cells to the hypothalamic brain region in some of the mutant mice, which resulted in reduced fertility in adult males. We thus screened 250 patients for the presence of mutations in PLXNA1, and identified different nonsynonymous mutations (p.V349L, p.V437L, p.R528W, p.H684Y, p.G720E, p.R740H, p.R813H, p.R840Q, p.A854T, p.R897H, p.L1464V, p.K1618T, p.C1744F), all at heterozygous state, in 15 patients. Most of these mutations are predicted to affect plexin-A1 stability or signaling activity based on predictive algorithms and a structural model of the protein. Moreover, in vitro experiments allowed us to show the existence of deleterious effects of eight mutations (including a transcript splicing defect), none of which are expected to result in a complete loss of protein synthesis, targeting, or signaling activity, though. Our findings indicate that signaling insufficiency through plexin-A1 can contribute to the pathogenesis of Kallmann syndrome, and further substantiate the oligogenic pattern of inheritance in this developmental disorder.

Afferent projections to the different medial amygdala subdivisions: a retrograde tracing study in the mouse.

The medial amygdaloid nucleus (Me) is a key node in the socio-sexual brain, composed of anterior (MeA), posteroventral (MePV) and posterodorsal (MePD) subdivisions. These subdivisions have been suggested to play a different role in reproductive and defensive behaviours. In the present work we analyse the afferents of the three Me subdivisions using restricted injections of fluorogold in female outbred CD1 mice. The results reveal that the MeA, MePV and MePD share a common pattern of afferents, with some differences in the density of retrograde labelling in several nuclei. Common afferents to Me subdivisions include: the accessory olfactory bulbs, piriform cortex and endopiriform nucleus, chemosensory amygdala (receiving direct inputs from the olfactory bulbs), posterior part of the medial bed nucleus of the stria terminalis (BSTM), CA1 in the ventral hippocampus and posterior intralaminar thalamus. Minor projections originate from the basolateral amygdala and amygdalo-hippocampal area, septum, ventral striatum, several allocortical and periallocortical areas, claustrum, several hypothalamic structures, raphe and parabrachial complex. MeA and MePV share minor inputs from the frontal cortex (medial orbital, prelimbic, infralimbic and dorsal peduncular cortices), but differ in the lack of main olfactory projections to the MePV. By contrast, the MePD receives preferential projections from the rostral accessory olfactory bulb, the posteromedial BSTM and the ventral premammillary nucleus. In summary, the common pattern of afferents to the Me subdivisions and their interconnections suggest that they play cooperative instead of differential roles in the various behaviours (e.g., sociosexual, defensive) in which the Me has been shown to be involved.

Functional differentiation of cholinergic and noradrenergic modulation in a biophysical model of olfactory bulb granule cells.

Olfactory bulb granule cells are modulated by both acetylcholine (ACh) and norepinephrine (NE), but the effects of these neuromodulators have not been clearly distinguished. We used detailed biophysical simulations of granule cells, both alone and embedded in a microcircuit with mitral cells, to measure and distinguish the effects of ACh and NE on cellular and microcircuit function. Cholinergic and noradrenergic modulatory effects on granule cells were based on data obtained from slice experiments; specifically, ACh reduced the conductance densities of the potassium M current and the calcium-dependent potassium current, whereas NE nonmonotonically regulated the conductance density of an ohmic potassium current. We report that the effects of ACh and NE on granule cell physiology are distinct and functionally complementary to one another. ACh strongly regulates granule cell firing rates and afterpotentials, whereas NE bidirectionally regulates subthreshold membrane potentials. When combined, NE can regulate the ACh-induced expression of afterdepolarizing potentials and persistent firing. In a microcircuit simulation developed to investigate the effects of granule cell neuromodulation on mitral cell firing properties, ACh increased spike synchronization among mitral cells, whereas NE modulated the signal-to-noise ratio. Coapplication of ACh and NE both functionally improved the signal-to-noise ratio and enhanced spike synchronization among mitral cells. In summary, our computational results support distinct and complementary roles for ACh and NE in modulating olfactory bulb circuitry and suggest that NE may play a role in the regulation of cholinergic function.

Innate Predator Odor Aversion Driven by Parallel Olfactory Subsystems that Converge in the Ventromedial Hypothalamus.

The existence of innate predator aversion evoked by predator-derived chemostimuli called kairomones offers a strong selective advantage for potential prey animals. However, it is unclear how chemically diverse kairomones can elicit similar avoidance behaviors. Using a combination of behavioral analyses and single-cell Ca(2+) imaging in wild-type and gene-targeted mice, we show that innate predator-evoked avoidance is driven by parallel, non-redundant processing of volatile and nonvolatile kairomones through the activation of multiple olfactory subsystems including the Grueneberg ganglion, the vomeronasal organ, and chemosensory neurons within the main olfactory epithelium. Perturbation of chemosensory responses in specific subsystems through disruption of genes encoding key sensory transduction proteins (Cnga3, Gnao1) or by surgical axotomy abolished avoidance behaviors and/or cellular Ca(2+) responses to different predator odors. Stimulation of these different subsystems resulted in the activation of widely distributed target regions in the olfactory bulb, as assessed by c-Fos expression. However, in each case, this c-Fos increase was observed within the same subnuclei of the medial amygdala and ventromedial hypothalamus, regions implicated in fear, anxiety, and defensive behaviors. Thus, the mammalian olfactory system has evolved multiple, parallel mechanisms for kairomone detection that converge in the brain to facilitate a common behavioral response. Our findings provide significant insights into the genetic substrates and circuit logic of predator-driven innate aversion and may serve as a valuable model for studying instinctive fear and human emotional and panic disorders.

Thunbergia laurifolia extract ameliorates cognitive and emotional deficits in olfactorectomized mice.

CONTEXT: Thunbergia laurifolia Lindl. (Acanthaceae) is a Thai medicinal plant used for the detoxification of poison which is likely to be beneficial for the treatment of cognitive deficits including Alzheimer's disease. OBJECTIVE: To elucidate the effects of Thunbergia laurifolia leaf extract (TLL) on cognitive dysfunction and depression-like behavior in olfactory bulbectomized mice (OBX). MATERIALS AND METHODS: OBX mice were treated daily with TLL at the dose of 250 and 500 mg/kg, tacrine, and imipramine, on the day after 10 d of OBX operation. The effects of TLL on cognitive and depression-like behavior of the animals were analyzed. After completing behavioral experiments, the expression levels of cholinergic marker genes encoding ChAT and muscarinic M1 receptor were quantitatively analyzed. RESULTS: TLL and tacrine reduced OBX-induced cognitive deficits in the object recognition test (ORT) with the time spent for the novel object two times longer than that of the familiar object. Moreover, TLL at the dose of 500 mg/kg and imipramine ameliorated depression-like behavior in the tail suspension test (TST) by reducing the duration of immobility from 25.18% to 3.16% and from 25.18% to 6.48%, respectively. TLL at the dose of 250 and 500 mg/kg reversed the OBX-induced down-regulation of ChAT mRNA expression in the hippocampus from 0.12 to 0.17 and 0.24, respectively, while the down-regulation of mRNA expression of muscarinic M1 receptor was also reversed by TLL from 0.23 to 0.38 and 0.48, respectively. CONCLUSIONS: TLL ameliorates non-spatial short-term memory deficits in OBX mice, and has the potential to exhibit an antidepressant-like action.

Greater excitability and firing irregularity of tufted cells underlies distinct afferent-evoked activity of olfactory bulb mitral and tufted cells.

Mitral and tufted cells, the two classes of principal neurons in the mammalian main olfactory bulb, exhibit morphological differences but remain widely viewed as functionally equivalent. Results from several recent studies, however, suggest that these two cell classes may encode complementary olfactory information in their distinct patterns of afferent-evoked activity. To understand how these differences in activity arise, we have performed the first systematic comparison of synaptic and intrinsic properties between mitral and tufted cells. Consistent with previous studies, we found that tufted cells fire with higher probability and rates and shorter latencies than mitral cells in response to physiological afferent stimulation. This stronger response of tufted cells could be partially attributed to synaptic differences, as tufted cells received stronger afferent-evoked excitation than mitral cells. However, differences in intrinsic excitability also contributed to the differences between mitral and tufted cell activity. Compared to mitral cells, tufted cells exhibited twofold greater excitability and peak instantaneous firing rates. These differences in excitability probably arise from differential expression of voltage-gated potassium currents, as tufted cells exhibited faster action potential repolarization and afterhyperpolarizations than mitral cells. Surprisingly, mitral and tufted cells also showed firing mode differences. While both cell classes exhibited regular firing and irregular stuttering of action potential clusters, tufted cells demonstrated a greater propensity to stutter than mitral cells. Collectively, stronger afferent-evoked excitation, greater intrinsic excitability and more irregular firing in tufted cells can combine to drive distinct responses of mitral and tufted cells to afferent-evoked input.

Fish oil improves anxiety-like, depressive-like and cognitive behaviors in olfactory bulbectomised rats.

Depression is increasingly present in the population, and its pathophysiology and treatment have been investigated with several animal models, including olfactory bulbectomy (Obx). Fish oil (FO) supplementation during the prenatal and postnatal periods decreases depression-like and anxiety-like behaviors. The present study evaluated the effect of FO supplementation on Obx-induced depressive-like behavior and cognitive impairment. Female rats received supplementation with FO during habituation, mating, gestation, and lactation, and their pups were subjected to Obx in adulthood; after the recovery period, the adult offspring were subjected to behavioral tests, and the hippocampal levels of brain-derived neurotrophic factor (BDNF), serotonin (5-HT) and the metabolite 5-hydroxyindoleacetic (5-HIAA) were determined. Obx led to increased anxiety-like and depressive-like behaviors, and impairment in the object location task. All behavioral changes were reversed by FO supplementation. Obx caused reductions in the levels of hippocampal BDNF and 5-HT, whereas FO supplementation restored these levels to normal values. In control rats, FO increased the hippocampal level of 5-HT and reduced that of 5-HIAA, indicating low 5-HT metabolism in this brain region. The present results indicate that FO supplementation during critical periods of brain development attenuated anxiety-like and depressive-like behaviors and cognitive dysfunction induced by Obx. These results may be explained by increased levels of hippocampal BDNF and 5-HT, two major regulators of neuronal survival and long-term plasticity in this brain structure.

Portal glucose influences the sensory, cortical and reward systems in rats.

The detection of glucose in the hepatoportal area is a simple but crucial peripheral cue initiating a nervous signal that ultimately leads to a wide array of metabolic and behavioural responses, such as decreased food intake, tighter control of glucose homeostasis, or appearance of food preference. This signal has been suggested to mediate the effects of high-protein diets, as opposed to high-fat/high-sucrose diets. Nevertheless, the central targets of the signal originating from the hepatoportal area remain largely undocumented. Using immunohistochemistry on the brain of male rats, we show here that portal glucose increases c-Fos expression in the brainstem, in the hypothalamus (in particular in neurons expressing pro-opiomelanocortin) and also in olfactory and other limbic and cortical areas, including those functionally implicated in reward (Experiment 1). In similar postabsorptive conditions, a high-protein diet induced similar effects in the hypothalamus and the granular cells of the main olfactory bulb, whereas the high-fat/high-sucrose diet actually reduced the basal expression of c-Fos in cortical layers. Both diets also decreased the number of neurons expressing c-Fos in the amygdala and gustatory areas (Experiment 2). Altogether, these findings suggest that the peripheral signal primed by portal glucose sensing may influence behavioural adaptation such as food preference via a network including the olfactory pathway, central amygdala, nucleus accumbens and orbitofrontal cortex, in addition to satiety and metabolic effects primarily implicating the hypothalamic response.

Bacopa monnieri ameliorates memory deficits in olfactory bulbectomized mice: possible involvement of glutamatergic and cholinergic systems.

This study investigated the effects of alcoholic extract of Bacopa monnieri (L.) Wettst. (BM) on cognitive deficits using olfactory bulbectomized (OBX) mice and the underlying molecular mechanisms of its action. OBX mice were treated daily with BM (50 mg/kg, p.o.) or a reference drug, tacrine (2.5 mg/kg, i.p.), 1 week before and continuously 3 days after OBX. Cognitive performance of the animals was analyzed by the novel object recognition test, modified Y maze test, and fear conditioning test. Brain tissues of OBX animals were used for neurochemical and immunohistochemical studies. OBX impaired non-spatial short-term memory, spatial working memory, and long-term fair memory. BM administration ameliorated these memory disturbances. The effect of BM on short-term memory deficits was abolished by a muscarinic receptor antagonist, scopolamine. OBX downregulated phosphorylation of synaptic plasticity-related signaling proteins: NR1 subunit of N-methyl-D-aspartate receptor, glutamate receptor 1 (GluR1), and calmodulin-dependent kinase II but not cyclic AMP-responsive element binding protein (CREB), and reduced brain-derived neurotrophic factor (BDNF) mRNA in the hippocampus. OBX also reduced choline acetyltransferase in the hippocampus and cholinergic neurons in the medial septum, and enlarged the size of lateral ventricle. BM administration reversed these OBX-induced neurochemical and histological alterations, except the decrease of GluR1 phosphorylation, and enhanced CREB phosphorylation. Moreover, BM treatment inhibited ex vivo activity of acetylcholinesterase in the brain. These results indicate that BM treatment ameliorates OBX-induced cognition dysfunction via a mechanism involving enhancement of synaptic plasticity-related signaling and BDNF transcription and protection of cholinergic systems from OBX-induced neuronal damage.

Potential protective effect of biphasic electrical stimulation against growth factor-deprived apoptosis on olfactory bulb neural progenitor cells through the brain-derived neurotrophic factor-phosphatidylinositol 3'-kinase/Akt pathway.

Stem cell therapy may provide a therapeutic method for the replacement and regeneration of damaged neurons of the central nervous system. However, neural stem cells (NSCs) and neural precursor cells (NPCs) are especially vulnerable after transplantation due to a lack of sufficient growth factors at the transplant site. Electrical stimulation (ES) has recently been found to participate in the regulation of cell proliferation, growth, differentiation, and migration, but its underlying anti-apoptotic effects remain unclear. This study investigated the protective effects of biphasic electrical stimulation (BES) on olfactory bulb NPCs against growth factor-deprived apoptosis, examining the survival and apoptotic features of the cells. Differentiation was assessed by neuronal and glial markers. Brain-derived neurotrophic factor-phosphatidylinositol 3'-kinase (BDNF)-PI3K/Akt pathway activation was determined by enzyme-linked immunosorbent assay and Western blot. The chemical inhibitor wortmannin was used to inhibit the PI3K/Akt pathway. BES exerts a protective effect against growth factor-deprived apoptosis in the NPCs. BES enhanced cell survival and decreased the apoptotic/necrotic rate. Expression of phosphorylated Akt and BDNF secretion increased with BES for 12 h. Furthermore, the protective effects of BES were inhibited by blocking PI3K/AKT signalling. These results suggest that BES prevents growth factor-deprived apoptosis through the BDNF-PI3K/Akt signalling. This work strengthens the opinion that BES may be used as an auxiliary strategy for improving cell survival and preventing cell apoptosis in stem cell-based transplantation therapy.

A two-layer biophysical model of cholinergic neuromodulation in olfactory bulb.

Cholinergic inputs from the basal forebrain regulate multiple olfactory bulb (OB) functions, including odor discrimination, perceptual learning, and short-term memory. Previous studies have shown that nicotinic cholinergic receptor activation sharpens mitral cell chemoreceptive fields, likely via intraglomerular circuitry. Muscarinic cholinergic activation is less well understood, though muscarinic receptors are implicated in olfactory learning and in the regulation of synchronized oscillatory dynamics in hippocampus and cortex. To understand the mechanisms underlying cholinergic neuromodulation in OB, we developed a biophysical model of the OB neuronal network including both glomerular layer and external plexiform layer (EPL) computations and incorporating both nicotinic and muscarinic neuromodulatory effects. Our simulations show how nicotinic activation within glomerular circuits sharpens mitral cell chemoreceptive fields, even in the absence of EPL circuitry, but does not facilitate intrinsic oscillations or spike synchronization. In contrast, muscarinic receptor activation increases mitral cell spike synchronization and field oscillatory power by potentiating granule cell excitability and lateral inhibitory interactions within the EPL, but it has little effect on mitral cell firing rates and hence does not sharpen olfactory representations under a rate metric. These results are consistent with the theory that EPL interactions regulate the timing, rather than the existence, of mitral cell action potentials and perform their computations with respect to a spike timing-based metric. This general model suggests that the roles of nicotinic and muscarinic receptors in olfactory bulb are both distinct and complementary to one another, together regulating the effects of ascending cholinergic inputs on olfactory bulb transformations.

Objective assessment of olfactory function using functional magnetic resonance imaging.

OBJECTIVE: To show the results of a device that generates automated olfactory stimuli suitable for functional magnetic resonance imaging (fMRI) experiments. MATERIAL AND METHODS: Ten normal volunteers, 5 women and 5 men, were studied. The system allows the programming of several sequences, providing the capability to synchronise the onset of odour presentation with acquisition by a trigger signal of the MRI scanner. The olfactometer is a device that allows selection of the odour, the event paradigm, the time of stimuli and the odour concentration. The paradigm used during fMRI scanning consisted of 15-s blocks. The odorant event took 2s with butanol, mint and coffee. RESULTS: We observed olfactory activity in the olfactory bulb, entorhinal cortex (4%), amygdala (2.5%) and temporo-parietal cortex, especially in the areas related to emotional integration. CONCLUSIONS: The device has demonstrated its effectiveness in stimulating olfactory areas and its capacity to adapt to fMRI equipment.