Neuronal Activity In Response Research Articles

REM sleep promotes experience-dependent dendritic spine elimination in the mouse cortex

In many parts of the nervous system, experience-dependent refinement of neuronal circuits predominantly involves synapse elimination. The role of sleep in this process remains unknown. We investigated the role of sleep in experience-dependent dendritic spine elimination of layer 5 pyramidal neurons in the visual (V1) and frontal association cortex (FrA) of 1-month-old mice. We found that monocular deprivation (MD) or auditory-cued fear conditioning (FC) caused rapid spine elimination in V1 or FrA, respectively. MD- or FC-induced spine elimination was significantly reduced after total sleep or REM sleep deprivation. Total sleep or REM sleep deprivation also prevented MD- and FC-induced reduction of neuronal activity in response to visual or conditioned auditory stimuli. Furthermore, dendritic calcium spikes increased substantially during REM sleep, and the blockade of these calcium spikes prevented MD- and FC-induced spine elimination. These findings reveal an important role of REM sleep in experience-dependent synapse elimination and neuronal activity reduction.

Tongue Posture, Tongue Movements, Swallowing, and Cerebral Areas Activation: A Functional Magnetic Resonance Imaging Study

The aim of this study was to pinpoint the cerebral regions implicated during swallowing by comparing the brain activation areas associated with two different volitional movements: tongue protrusion and tongue elevation. Twenty-four healthy subjects (11—males 22 ± 2.9 y; 13—females 23 ± 4.1 y; were examined through functional magnetic resonance imaging (fMRI) while performing two different swallowing tasks: with tongue protrusion and with tongue elevation. The study was carried out with the help of fMRI imaging which assesses brain signals caused by changes in neuronal activity in response to sensory, motor or cognitive tasks. The precentral gyrus and the cerebellum were activated during both swallowing tasks while the postcentral gyrus, thalamus, and superior parietal lobule could be identified as large activation foci only during the protrusion task. During protrusion tasks, increased activations were also seen in the left-middle and medial frontal gyrus, right thalamus, inferior parietal lobule, and the superior temporal gyrus (15,592-voxels; Z-score 5.49 ± 0.90). Tongue elevation activated a large volume of cortex portions within the left sub-gyral cortex and minor activations in both right and left inferior parietal lobules, right postcentral gyrus, lentiform nucleus, subcortical structures, the anterior cingulate, and left insular cortex (3601-voxels; Z-score 5.23 ± 0.52). However, the overall activation during swallowing tasks with tongue elevation, was significantly less than swallowing tasks with tongue protrusion. These results suggest that tongue protrusion (on inferior incisors) during swallowing activates a widely distributed network of cortical and subcortical areas than tongue elevation (on incisor papilla), suggesting a less economic and physiologically more complex movement. These neuromuscular patterns of the tongue confirm the different purpose of elevation and protrusion during swallowing and might help professionals manage malocclusions and orofacial myofunctional disorders.

Layers II/III of Prefrontal Cortex in Df(h22q11)/+ Mouse Model of the 22q11.2 Deletion Display Loss of Parvalbumin Interneurons and Modulation of Neuronal Morphology and Excitability.

The 22q11.2 deletion has been identified as a risk factor for multiple neurodevelopmental disorders. Behavioral and cognitive impairments are common among carriers of the 22q11.2 deletion. Parvalbumin expressing (PV+) interneurons provide perisomatic inhibition of excitatory neuronal circuits through GABAA receptors, and a deficit of PV+ inhibitory circuits may underlie a multitude of the behavioral and functional deficits in the 22q11.2 deletion syndrome. We investigated putative deficits of PV+ inhibitory circuits and the associated molecular, morphological, and functional alterations in the prefrontal cortex (PFC) of the Df(h22q11)/+ mouse model of the 22q11.2 hemizygous deletion. We detected a significant decrease in the number of PV+ interneurons in layers II/III of PFC in Df(h22q11)/+ mice together with a reduction in the mRNA and protein levels of GABAA (α3), a PV+ putative postsynaptic receptor subunit. Pyramidal neurons from the same layers further experienced morphological reorganizations of spines and dendrites. Accordingly, a decrease in the levels of the postsynaptic density protein 95 (PSD95) and a higher neuronal activity in response to the GABAA antagonist bicuculline were measured in these layers in PFC of Df(h22q11)/+ mice compared with their wild-type littermates. Our study shows that a hemizygotic deletion of the 22q11.2 locus leads to deficit in the GABAergic control of network activity and involves molecular and morphological changes in both the inhibitory and excitatory synapses of parvalbumin interneurons and pyramidal neurons specifically in layers II/III PFC.

Social Behavioral Deficits with Loss of Neurofibromin Emerge from Peripheral Chemosensory Neuron Dysfunction

Neurofibromatosis type 1 (NF1) is a neurodevelopmental disorder associated with social and communicative disabilities. The cellular and circuit mechanisms by which loss of neurofibromin 1 (Nf1) results in social deficits are unknown. Here, we identify social behavioral dysregulation with Nf1 loss in Drosophila. These deficits map to primary dysfunction of a group of peripheral sensory neurons. Nf1 regulation of Ras signaling in adult ppk23+ chemosensory cells is required for normal social behaviors in flies. Loss of Nf1 attenuates ppk23+ neuronal activity in response to pheromones, and circuit-specific manipulation of Nf1 expression or neuronal activity in ppk23+ neurons rescues social deficits. This disrupted sensory processing gives rise to persistent changes in behavior beyond the social interaction, indicating a sustained effect of an acute sensory misperception. Together our data identify a specific circuit mechanism through which Nf1 regulates social behaviors and suggest social deficits in NF1 arise from propagation of sensory misinformation.

Sexual experience with a known male modulates c-Fos expression in response to mating and male pheromone exposure in female mice

Sexually naïve female mice are not sexually receptive in their first mating opportunity. Four to five sexual encounters are needed to display high sexual receptivity as assessed by the lordosis reflex. The neuronal changes induced by sexual experience are not well understood. In this study, we evaluated if repeated sexual stimulation with the same male was associated with an increase in the neuronal activity evaluated by c-Fos expression in brain structures associated with the control of sexual behavior such as the accessory olfactory bulb (AOB), ventromedial hypothalamus (VMH), and the medial preoptic area (MPOA). Ovariectomized female mice were randomly distributed into three groups: sexually naïve (SN), with no prior sexual stimulation; sexually inexperienced (SI), with one prior mating session; and sexually experienced (SE), with six prior mating sessions. Females were primed with estradiol benzoate and progesterone once a week for 7 weeks. Neuronal activation in response to mating or soiled bedding was evaluated in the 7th week. Each group was subdivided into three subgroups: clean (exposure to clean bedding), male bedding (exposure to sawdust soiled with secretions from a male), or mating. Each female mated with her assigned male; in the exposure subgroup, soiled bedding was obtained from the male with whom she mated.Neuronal activity data showed that SE females had a higher c-Fos response in the VMH when they mated in comparison to females exposed to clean bedding. SI females that mated had a decrease c-Fos expression in the glomerular cell layer of the AOB, compared to females exposed to male bedding. The mitral cell layer showed a higher c-Fos response in SI females that mated in comparison to those exposed to male bedding. Comparisons between groups presented with the same stimulus indicate that SI females exposed to male bedding showed a decrease in c-Fos response in the mitral cell layer in comparison to SE and SN females. Correlation analysis demonstrated that the lordosis quotient from the last mating test correlated positively with the number of c-Fos-positive cells in the mitral cell layer in SE and SI groups. A similar correlation was found in the MPOA in SI females. Prior mating in female mice is required to increase sexual receptivity. Changes in the neuronal activity in the AOB and VMH may be involved in the neuronal plasticity induced by repeated sexual stimulation.

Integration of energy homeostasis and stress by parvocellular neurons in rat hypothalamic paraventricular nucleus.

Central regulation of energy homeostasis and stress are believed to be reciprocally regulated, i.e. excessive food intake suppresses, while prolonged hunger exacerbates, stress responses in vivo. This relationship may be mediated by neuroendocrine parvocellular corticotropin-releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus that receive both stress- and feeding-related input. We find that hunger strongly and selectively potentiates, while re-feeding suppresses, a cellular analogue of a stress response induced by acute glucopenia in CRH neurons in rat hypothalamic slices. Neuronal activation in response to glucopenia was mediated synaptically, via the relative enhancement of glutamate over GABA input. These results illustrate how acute stress responses may be initiated in vivo and show that it is reciprocally integrated with energy balance via local hypothalamic mechanisms acting at the level of CRH neurons and their afferent terminals. Increased food intake is a common response to help cope with stress, implying the existence of a previously postulated but imperfectly understood, inverse relationship between the regulation of feeding and stress. We have identified components of the neural circuitry that can integrate these homeostatic responses. Prior fasting (∼24h) potentiates, and re-feeding suppresses, excitatory responses to acute glucopenia in about half of the corticotropin releasing hormone (CRH)-expressing, putatively neurosecretory, stress-related neurons in the paraventricular nucleus of the hypothalamus studied. Glucoprivation stress ex vivo resulted from a preferential relative increase in excitatory (glutamatergic) over inhibitory (GABAergic) inputs. Putative preautonomic cells were less sensitive to fasting, and showed a predominant inhibition to acute glucopenia. We conclude that hunger may sensitize hypothalamic stress responses by acting via local mechanisms, at the level of CRH neurons and their presynaptic inputs. Those mechanisms involve neither presynaptic ATP-sensitive potassium channels nor postsynaptic ATP levels.

Effects of salt loading on the organisation of microtubules in rat magnocellular vasopressin neurones.

Magnocellular vasopressin (VP) neurones are activated by increases in blood osmolality, leading to the secretion of VP into the circulation to promote water retention in the kidney, thus constituting a key mechanism for the regulation of body fluid homeostasis. However, chronic high salt intake can lead to excessive activation of VP neurones and increased circulating levels of VP, contributing to an elevation in blood pressure. Multiple extrinsic factors, such as synaptic inputs and glial cells, modulate the activity of VP neurones. Moreover, magnocellular neurones are intrinsically osmosensitive, and are activated by hypertonicity in the absence of neighbouring cells or synaptic contacts. Hypertonicity triggers cell shrinking, leading to the activation of VP neurones. This cell-autonomous activation is mediated by a scaffold of dense somatic microtubules, uniquely present in VP magnocellular neurones. Treating isolated magnocellular neurones with drugs modulating microtubule stability modifies the sensitivity of neuronal activation in response to acute hypertonic stimuli. However, whether the microtubule network is altered in conditions associated with enhanced neuronal activation and increased VP release, such as chronic high salt intake, remains unknown. We examined the organisation of microtubules in VP neurones of the supraoptic and paraventricular hypothalamic nuclei (SON and PVN, respectively) of rats subjected to salt-loading (drinking 2% NaCl for 7days). Using super-resolution imaging, we found that the density of microtubules in magnocellular VP neurones from the SON and PVN was significantly increased, whereas the density and organisation of microtubules remain unchanged in other hypothalamic neurones, as well as in neurones from other brain areas (e.g., hippocampus, cortex). We propose that the increase in microtubule density in magnocellular VP neurones in salt-loading promotes their enhanced activation, possibly contributing to elevated blood pressure in this condition.

Laminar Organization of FM Direction Selectivity in the Primary Auditory Cortex of the Free-Tailed Bat.

We studied the columnar and layer-specific response properties of neurons in the primary auditory cortex (A1) of six (four females, two males) anesthetized free-tailed bats, Tadarida brasiliensis, in response to pure tones and down and upward frequency modulated (FM; 50 kHz bandwidth) sweeps. In addition, we calculated current source density (CSD) to test whether lateral intracortical projections facilitate neuronal activation in response to FM echoes containing spectrally distant frequencies from the excitatory frequency response area (FRA). Auditory responses to a set of stimuli changing in frequency and level were recorded along 64 penetrations in the left A1 of six free-tailed bats. FRA shapes were consistent across the cortical depth within a column and there were no obvious differences in tuning properties. Generally, response latencies were shorter (<10 ms) for cortical depths between 500 and 600 μm, which might correspond to thalamocortical input layers IIIb–IV. Most units showed a stronger response to downward FM sweeps, and direction selectivity did not vary across cortical depth. CSD profiles calculated in response to the CF showed a current sink located at depths between 500 and 600 μm. Frequencies lower than the frequency range eliciting a spike response failed to evoke any visible current sink. Frequencies higher than the frequency range producing a spike response evoked layer IV sinks at longer latencies that increased with spectral distance. These data support the hypothesis that a progressive downward relay of spectral information spreads along the tonotopic axis of A1 via lateral connections, contributing to the neural processing of FM down sweeps used in biosonar.

Inhibition of nociceptive dural input to the trigeminocervical complex through oxytocinergic transmission

Migraine is a complex brain disorder that involves abnormal activation of the trigeminocervical complex (TCC). Since an increase of oxytocin concentration has been found in cerebrospinal fluid in migrainous patients and intranasal oxytocin seems to relieve migrainous pain, some studies suggest that the hypothalamic neuropeptide oxytocin may play a role in migraine pathophysiology. However, it remains unknown whether oxytocin can interact with the trigeminovascular system at TCC level. The present study was designed to test the above hypothesis in a well-established electrophysiological model of migraine. Using anesthetized rats, we evaluated the effect of oxytocin on TCC neuronal activity in response to dural nociceptive trigeminovascular activation. We found that spinal oxytocin significantly reduced TCC neuronal firing evoked by meningeal electrical stimulation. Furthermore, pretreatment with L-368,899 (a selective oxytocin receptor antagonist, OTR) abolished the oxytocin-induced inhibition of trigeminovascular neuronal responses. This study provides the first direct evidence that oxytocin, probably by OTR activation at TCC level inhibited dural nociceptive-evoked action potential in this complex. Thus, targeting OTR at TCC could represent a new avenue to treat migraine.

Compressive Sensing Inference of Neuronal Network Connectivity in Balanced Neuronal Dynamics.

Determining the structure of a network is of central importance to understanding its function in both neuroscience and applied mathematics. However, recovering the structural connectivity of neuronal networks remains a fundamental challenge both theoretically and experimentally. While neuronal networks operate in certain dynamical regimes, which may influence their connectivity reconstruction, there is widespread experimental evidence of a balanced neuronal operating state in which strong excitatory and inhibitory inputs are dynamically adjusted such that neuronal voltages primarily remain near resting potential. Utilizing the dynamics of model neurons in such a balanced regime in conjunction with the ubiquitous sparse connectivity structure of neuronal networks, we develop a compressive sensing theoretical framework for efficiently reconstructing network connections by measuring individual neuronal activity in response to a relatively small ensemble of random stimuli injected over a short time scale. By tuning the network dynamical regime, we determine that the highest fidelity reconstructions are achievable in the balanced state. We hypothesize the balanced dynamics observed in vivo may therefore be a result of evolutionary selection for optimal information encoding and expect the methodology developed to be generalizable for alternative model networks as well as experimental paradigms.

Neuronal activation in orbitofrontal cortex subregions: Cfos expression following cue-induced reinstatement of cocaine-seeking behavior.

Cocaine-use disorders are characterized by repeated relapse to drug-seeking and drug-taking behavior following periods of abstinence. Former drug users display increased activation of the orbitofrontal cortex (OFC) in response to drug-related cues, and similar phenomena are also observed in rodent models of drug relapse. The lateral, but not medial, OFC functionally contributes to the maintenance of cue-drug associations; however, less is known about the role of the ventral OFC in this process. To examine the pattern of neuronal activation in OFC subregions in response to drug-associated cues, rats were trained to respond on a lever for a cocaine infusion paired with a complex cue (2-hr sessions, minimum 10 days). Cocaine self-administration was followed by extinction training, in which lever responses resulted in no consequences (2-hr sessions, minimum 7 days). During a 1-hr reinstatement test, drug-seeking behavior (i.e., responses on the drug-paired lever) was examined in the presence or absence of contingent drug-paired cues (Cue TEST vs. Ext TEST, respectively). Rats were overdosed with a ketamine + xylazine cocktail 30-min post session, and transcardially perfused with 4% paraformaldehyde. Cfos protein expression was utilized to measure potential changes in neural activation between the reinstatement test groups. An increase in the number of Cfos-Immunoreactive cells was observed in the ventral and lateral subregions of the OFC in the Cue TEST group. The present findings provide evidence that the ventral and lateral regions of the rat OFC display similar patterns of neuronal activation in response to cocaine-paired cues. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Pathogenic Tau Impairs Axon Initial Segment Plasticity and Excitability Homeostasis

Dysregulation of neuronal excitability underlies the pathogenesis of tauopathies, including frontotemporal dementia (FTD) with tau inclusions. A majority of FTD-causing tau mutations are located in the microtubule-binding domain, but how these mutations alter neuronal excitability is largely unknown. Here, using CRISPR/Cas9-based gene editing in human pluripotent stem cell (iPSC)-derived neurons and isogenic controls, we show that the FTD-causing V337M tau mutation impairs activity-dependent plasticity of the cytoskeleton in the axon initial segment (AIS). Extracellular recordings by multi-electrode arrays (MEAs) revealed that the V337M tau mutation in human neurons leads to an abnormal increase in neuronal activity in response to chronic depolarization. Stochastic optical reconstruction microscopy of human neurons with this mutation showed that AIS plasticity is impaired by the abnormal accumulation of end-binding protein 3 (EB3) in the AIS submembrane region. These findings expand our understanding of how FTD-causing tau mutations dysregulate components of the neuronal cytoskeleton, leading to network dysfunction.

Genetic Suppression of mTOR Rescues Synaptic and Social Behavioral Abnormalities in a Mouse Model of Pten Haploinsufficiency.

Heterozygous mutations in PTEN, which encodes a negative regulator of the mTOR and β-catenin signaling pathways, cause macrocephaly/autism syndrome. However, the neurobiological substrates of the core symptoms of this syndrome are poorly understood. Here, we investigate the relationship between cerebral cortical overgrowth and social behavior deficits in conditional Pten heterozygous female mice (Pten cHet) using Emx1-Cre, which is expressed in cortical pyramidal neurons and a subset of glia. We found that conditional heterozygous mutation of Ctnnb1 (encoding β-catenin) suppresses Pten cHet cortical overgrowth, but not social behavioral deficits, whereas conditional heterozygous mutation of Mtor suppresses social behavioral deficits, but not cortical overgrowth. Neuronal activity in response to social cues and excitatory synapse markers are elevated in the medial prefrontal cortex (mPFC) of Pten cHet mice, and heterozygous mutation in Mtor, but not Ctnnb1, rescues these phenotypes. These findings indicate that macroscale cerebral cortical overgrowth and social behavioral phenotypes caused by Pten haploinsufficiency can be dissociated based on responsiveness to genetic suppression of Ctnnb1 or Mtor. Furthermore, neuronal connectivity appears to be one potential substrate for mTOR-mediated suppression of social behavioral deficits in Pten haploinsufficient mice. Autism Res 2019, 12: 1463-1471. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: A subgroup of individuals with autism display overgrowth of the head and the brain during development. Using a mouse model of an autism risk gene, Pten, that displays both brain overgrowth and social behavioral deficits, we show here that that these two symptoms can be dissociated. Reversal of social behavioral deficits in this model is associated with rescue of abnormal synaptic markers and neuronal activity.

Defining the Ensemble‐Specific Activity Signatures Controlling Cocaine Reinforcement

While significant effort has been made to understand the neural basis of addiction, it remains unclear exactly how the brain controls motivated behavior and how drugs of abuse alter these neural systems to control drug taking and seeking. The goal of this study was to understand how cocaine and associated stimuli are encoded in the brain and how neuronal activation in response to cocaine drives drug seeking. In a given brain region, only a small percentage of cells are activated in response to a stimulus – this activated group of neurons is termed an “ensemble”. Here we defined the role of cocaine‐activated ensembles in the nucleus accumbens (NAc) – a brain region central to reward encoding – in driving motivated behaviors. Using transgenic animals that allowed for the expression of optical tools within ensembles, we were able to record from, identify, and manipulate ensembles that are selectively activated by cocaine. Opsins were expressed in cocaine‐ or saline‐activated neuronal ensembles within the NAc. A fiberoptic was placed above the region and animals performed operant conditioning tasks, where a nosepoke triggered a laser pulse that would reactivate or inhibit cocaine‐activated ensembles to determine their role in motivated behaviors. Mice were highly motivated to optically reactivate ensembles associated with the first cocaine experience, highlighted by their high rates of responding for reactivation. Repeated cocaine injections in these animals did not change the reinforcing efficacy of ensemble activation, suggesting that the increases in motivated behavior that occur following repeated cocaine exposure may be due to the recruitment of a novel ensemble. Indeed, via immunohistochemistry, we find minimal overlap between the neurons activated by the first cocaine experience and the tenth. Using a similar approach as described above, we expressed GCaMP6f, a genetically encoded calcium indicator, within each ensemble, allowing for the recording of ensembles over time during ongoing behavior. We show, for the first time, that temporally specific activation of the neurons activated by the first cocaine experience are critical mediators of reinforcement behavior. We also show that repeated cocaine exposure recruits a new population of neurons to guide behavior and hypothesize that this neural ensemble control of behavior may be a critical mediator of the transition to addiction.Support or Funding InformationFunding was provided by startup funds from Vanderbilt University School of Medicine Department of Pharmacology (E.S.C), as well as from the National Institutes of Health (NIH). Funds from the National Institute of Drug Abuse (NIDA) DA042111(E.S.C), National Insitute of Mental Health (NIMH) MH064913 (K.C.T), the Brain and Behavior Research Foundation (to E.S.C), Whitehall Foundation (to E.S.C), Edward J Mallinckrodt Jr. Foundation (to E.S.C) also supported this work.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Fos activation patterns related to acute ethanol and conditioned taste aversion in adolescent and adult rats.

Studies in rats have revealed marked age differences in sensitivity to the aversive properties of ethanol, with a developmental insensitivity to ethanol aversion that is most pronounced during pre- and early adolescence, declining thereafter to reach the enhanced aversive sensitivity of adults. The adolescent brain undergoes significant transitions throughout adolescence, including in regions linked with drug reward and aversion; however, it is unknown how ontogenetic changes within this reward/aversion circuitry contribute to developmental differences in aversive sensitivity. The current study examined early adolescent (postnatal day [P]28-30) and adult (P72-74) Sprague-Dawley male rats for conditioned taste aversion (CTA) after doses of 0, 1.0, or 2.5g/kg ethanol, and patterns of neuronal activation in response to ethanol using Fos-like immunohistochemistry (Fos+) to uncover regions where age differences in activation are associated with ethanol aversion. An adolescent-specific ethanol-induced increase in Fos+ staining was seen within the nucleus accumbens shell and core. An age difference was also noted within the Edinger-Westphal nucleus (EW) following administration of the lower dose of ethanol, with 1g/kg ethanol producing CTA in adults but not in adolescents and inducing a greater EW Fos response in adults than adolescents. Regression analysis revealed that greater numbers of Fos+ neurons within the EW and insula (Ins) were related to lower consumption of the conditioned stimulus (CS) on test day (reflecting greater CTA). Some regionally specific age differences in Fos+ were noted under baseline conditions, with adolescents displaying fewer Fos+ neurons than adults within the prelimbic (PrL) cortex, but more than adults in the bed nucleus of the stria terminalis (BNST). In the BNST (but not PrL), ethanol-induced increases in Fos-immunoreactivity (IR) were evident at both ages. Increased ethanol-induced activity within critical appetitive brain regions (NAc core and shell) supports a role for greater reward-related activation during adolescence, possibly along with attenuated responsiveness to ethanol in EW and Ins in the age-typical resistance of adolescents to the aversive properties of ethanol.

Learning-induced sensory plasticity of mouse olfactory epithelium

Traditionally, studies of the neurobiology of learning and memory focus on the circuitry that interfaces between sensory inputs and behavioral outputs, such as the amygdala and cerebellum. However, evidence is accumulating that some forms of learning can in fact drive stimulus­specifc changes very early in sensory systems, including not only primary sensory cortices but also precortical structures and even the peripheral sensory organs themselves. In this study, we investigated the effect of olfactory associative training on the functional activity of olfactory epithelium neurons in response to an indifferent stimulus (orange oil). It was found that such a peripheral structure of the olfactory system of adult mice as the olfactory epithelium (OE) demonstrates experience­dependent plasticity. In our experiment, associative learning led to changes in the patterns of OE cell activation in response to orange oil in comparison with the control group and animals that were given odor without reinforcement. To interpret the results obtained, we compared the distribution of MRI contrast across the zones of OE in response to a conditioned odor in trained animals and in control animals that were given orange oil at three concentrations: original (used for conditioning), 4­fold higher and 4­fold lower. Since the OE activation patterns obtained coincided in the group of trained animals and controls, which were stimulated with orange oil at the 4­fold higher concentration, it can be concluded that associative conditioning increased the sensitivity of the OE to the conditioned stimulus. The observed increase in OE response to orange oil may be the result of neurogenesis, i. e. the maturation of new olfactory neurons responsive to this stimulus, or the consequence of an increase in individual sensitivity of each OE neuron. Based on data of MRI contrast accumulation in mouse OE, the sensory plasticity way in learning­induced increase in sensitivity of OE to conditioned stimulus is more possible. Thus, the sensory plasticity of the OE plays a signifcant role in the formation of the neuronal response to the provision of an initially indifferent odor and is part of the adaptive responses to the environmental changing.

Pheromone-Induced Odor Associative Fear Learning in Rats

Alarm pheromones alert conspecifics to the presence of danger. Can pheromone communication aid in learning specific cues? Such facilitation has an evident evolutionary advantage. We use two associative learning paradigms to test this hypothesis. The first is stressed cage mate-induced conditioning. One pair-housed adult rat received 4 pairings of terpinene + shock over 30 min. Ten minutes after return to the home cage, its companion rat was removed and exposed to terpinene. Single-housed controls were exposed to either terpinene or shock only. Companion rats showed terpinene-specific freezing, which was prevented by β-adrenoceptor blockade. Using Arc to index neuronal activation in response to terpinene re-exposure, stressed cage-mate induced associative learning was measured. Companion rats showed increased neuronal activity in the accessory olfactory bulb, while terpinene + shock-conditioned rats showed increased activity in the main olfactory bulb. Both groups had enhanced activity in the anterior basolateral amygdala and central amygdala. To test involvement of pheromone mediation, in the 2nd paradigm, we paired terpinene with soiled bedding from odor + shock rats or a rat alarm pheromone. Both conditioning increased rats’ freezing to terpinene. Blocking NMDA receptors in the basolateral amygdala prevented odor-specific learning suggesting shock and pheromone-paired pathways converge in the amygdala. An alarm pheromone thus enables cue-specific learning as well as signalling danger.

Brain Sub/Region-Specific Effects of Olanzapine on c-Fos Expression of Chronically Socially Isolated Rats

Olanzapine (Olz) is an atypical antipsychotic used to treat depression, anxiety and schizophrenia, which can be caused by chronic psychosocial stress. c-Fos protein expression has been used as an indirect marker of neuronal activity in response to various forms of stress or pharmacological treatments. We examined the effects of a 3-week treatment of Olz (7.5 mg/kg/day) on c-Fos protein expression in stress-relevant brain sub/regions, its relationship with isolation-induced behavioral changes, and potential sites of Olz action on control and male rats exposed to 6 weeks of chronic social isolation (CSIS), an animal model of depression. Olz treatment reversed depression- and anxiety-like behaviors induced by CSIS and suppressed a CSIS-induced increase in the number of c-Fos-positive cells in subregions of the dorsal hippocampus, ventral (v) DG, retrosplenial cortex, and medial prefrontal cortex. In contrast, no change in c-Fos expression was seen in the CA3v, amygdala and thalamic, hypothalamic or striatal subregions in Olz-treated CSIS rats, suggesting different brain sub/regions’ susceptibility to Olz. An increased number of c-Fos-positive cells in the CA1v, amygdala and thalamic, hypothalamic and striatal subregions in controls as well as in the CA1v and subregion of the hypothalamus and nucleus accumbens in Olz-treated CSIS rats was found. Results suggest the activation of brain sub/regions following CSIS that may be involved in depressive and anxiety-like behaviors. Olz treatment showed region-specific effects on neuronal activation. Our data contribute to a better understanding of the mechanisms underlying the CSIS response and potential brain targets of Olz in socially isolated rats.

TPH2 Deficiency Influences Neuroplastic Mechanisms and Alters the Response to an Acute Stress in a Sex Specific Manner.

Dysregulations of the central serotoninergic system have been implicated in several psychopathologies, characterized by different susceptibility between males and females. We took advantage of tryptophan hydroxylase 2 (TPH2) deficient rats, lacking serotonin specifically in the brain, to investigate whether a vulnerable genotype can be associated with alterations of neuronal plasticity from the early stage of maturation of the brain until adulthood. We found a significant increase, in both gene and protein expression, of the neurotrophin brain-derived neurotrophic factor (BDNF), in the prefrontal cortex (PFC) of adult TPH2-deficient (TPH2−/−) male and female rats in comparison to wild type (TPH2+/+) counterparts. Interestingly, a development-specific pattern was observed during early postnatal life: whereas the increase in Bdnf expression, mainly driven by the modulation of Bdnf isoform IV was clearly visible after weaning at postnatal day (pnd) 30 in both sexes of TPH2−/− in comparison to TPH2+/+ rats, at early stages (pnd1 and pnd10) Bdnf expression levels did not differ between the genotypes, or even were downregulated in male TPH2−/− animals at pnd10. Moreover, to establish if hyposerotonergia may influence the response to a challenging situation, we exposed adult rats to an acute stress. Although the pattern of corticosterone release was similar between the genotypes, neuronal activation in response to stress, quantified by the expression of the immediate early genes activity regulated cytoskeleton associated protein (Arc) and Fos Proto-Oncogene (cFos), was blunted in both sexes of animals lacking brain serotonin. Interestingly, although upregulation of Bdnf mRNA levels after stress was observed in both genotypes, it was less pronounced in TPH2−/− in comparison to TPH2+/+ rats. In summary, our results demonstrated that serotonin deficiency affects neuroplastic mechanisms following a specific temporal pattern and influences the response to an acute stress.

Hypothalamic AgRP neurons and the regulation of appetite and body weight: A review

The maintenance of energy balance is essential for the survival of animals. The hypothalamus in the brain plays a central role in this process through the integration of neural, nutritional and hormonal signals. Multiple and distributed neuronal populations in the hypothalamus form complex circuits to regulate appetite and body weight. Located in the arcuate nucleus of hypothalamus, agouti-related peptide (AgRP)-expressing cells are known as the hunger-promoting neurons. Over the past three decades, extensive studies have been performed to understand the role of AgRP neurons in energy balance control. AgRP neurons are both necessary and sufficient to orchestrate feeding behavior. The AgRP neuron activity adapts to and thereby is regulated by the nutritional status in the body. Furthermore, we now know that this alternation is driven by various circulating hormones, such as Leptin and Ghrelin, as well as synaptic inputs from upstream neurons. Neurotransmitters (e.g. glutamate and GABA) play a vital role in the regulation of AgRP neuron activity. The excitatory glutamatergic input is required in fasting-related activation of AgRP neurons, whereas the inhibitory GABAergic inputs is crucial in the rapid reduction of AgRP neuron activity in response to food-related cues, and thus, to terminate a meal. In addition to these molecules, signaling molecules and pathways in AgRP neurons, such as receptors, ion channels, kinases (e.g. IKKβ), endoplasmic reticulum stress (ER stress) and mitochondrial dynamic, are critically involved in the control of its activity. Moreover, AgRP neurons release neuropeptides AgRP and NPY, as well as neurotransmitter GABA to regulate neuronal activity. Both AgRP and NPY potently promote appetite. Although NPY is widely expressed in the central nervous system, it is mainly co-expressed with AgRP in the arcuate nucleus of hypothalamus. The appetite-promoting effect of NPY is mediated by Y1 and Y5 receptors, while AgRP exert its orexigenic effect mainly by antagonizing the central melanocortin system. Surprisingly, ablation of AgRP neurons in neonates has little effect on body weight, whereas these neurons are essential for the maintenance of appetite in adult mice. Moreover, accumulating evidences indicate that GABA released by AgRP neurons is required to retain animals appetite. At the circuit level, AgRP neurons project to both intra- and extra-hypothalamic regions to regulate energy balance. For example, in arcuate nucleus, AgRP neurons innervate and inhibit POMC neurons via the inhibitory GABAergic synapses. Conversely, POMC neurons release β-endorphin, a μ-opioid receptor agonist, to inhibit the activity of AgRP neurons. In summary, AgRP neurons play a crucial role in the regulation of appetite and energy balance. Targeting hypothalamic AgRP neurons might be a relevant approach to treat common obesity.