C-fos expression in the rat brain following lithium chloride-induced illness

Hypothalamic and brainstem glucose-dependent insulinotropic polypeptide receptor neurons employ distinct mechanisms to affect feeding

Central glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) signaling is critical in GIP-based therapeutics' ability to lower body weight, but pathways leveraged by GIPR pharmacology in the brain remain incompletely understood. We explored the role of Gipr neurons in the hypothalamus and dorsal vagal complex (DVC) - brain regions critical to the control of energy balance. Hypothalamic Gipr expression was not necessary for the synergistic effect of GIPR/GLP-1R coagonism on body weight. While chemogenetic stimulation of both hypothalamic and DVC Gipr neurons suppressed food intake, activation of DVC Gipr neurons reduced ambulatory activity and induced conditioned taste avoidance, while there was no effect of a short-acting GIPR agonist (GIPRA). Within the DVC, Gipr neurons of the nucleus tractus solitarius (NTS), but not the area postrema (AP), projected to distal brain regions and were transcriptomically distinct. Peripherally dosed fluorescent GIPRAs revealed that access was restricted to circumventricular organs in the CNS. These data demonstrate that Gipr neurons in the hypothalamus, AP, and NTS differ in their connectivity, transcriptomic profile, peripheral accessibility, and appetite-controlling mechanisms. These results highlight the heterogeneity of the central GIPR signaling axis and suggest that studies into the effects of GIP pharmacology on feeding behavior should consider the interplay of multiple regulatory pathways.

Chemogenetic inhibition of the bed nucleus of the stria terminalis suppresses the intake of a preferable and learned aversive sweet taste solution in male mice

Conditioned taste aversion (CTA) is established by pairing a taste solution as a conditioned stimulus (CS) with visceral malaise as an unconditioned stimulus (US). CTA decreases the taste palatability of a CS. The bed nucleus of the stria terminalis (BNST) receives taste inputs from the brainstem. However, the involvement of the BNST in CTA remains unclear. Thus, this study examined the effects of chemogenetic inhibition of the BNST neurons on CS intake after CTA acquisition. An adeno-associated virus was microinjected into the BNST of male C57/BL6 mice to induce the inhibitory designer receptor hM4Di. The mice received a pairing of 0.2% saccharin solution (CS) with 0.3 M lithium chloride (2% BW, intraperitoneal). After conditioning, the administration of clozapine-N-oxide (CNO, 1 mg/kg) significantly enhanced the suppression of CS intake on the retrieval of CTA compared with its intake following saline administration (p < 0.01). We further assessed the effect of BNST neuron inhibition on the intake of water and taste solutions (saccharin, sucralose, sodium chloride, monosodium glutamate, quinine hydrochloride, and citric acid) using naïve (not learned CTA) mice. CNO administration significantly decreased the intake of saccharin and sucralose (p < 0.05). Our results indicate that BNST neurons mediate sweet taste and regulate sweet intake, regardless of whether sweets should be ingested or rejected. BNST neurons may be inhibited in the retrieval of CTA, thereby suppressing CS intake.

Behavior and Fos activation reveal that male and female rats differentially assess affective valence during CTA learning and expression

Females are more affected by psychiatric illnesses including eating disorders, depression, and post-traumatic stress disorder than males. However, the neural mechanisms mediating these sex differences are poorly understood. Animal models can be useful in exploring such neural mechanisms. Conditioned taste aversion (CTA) is a behavioral task that assesses how animals process the competition between associated reinforcing and aversive stimuli in subsequent task performance, a process critical to healthy behavior in many domains. The purpose of the present study was to identify sex differences in this behavior and associated neural responses. We hypothesized that females would value the rewarding stimulus (Boost®) relative to the aversive stimulus (LiCl) more than males in performing CTA. We evaluated behavior (Boost® intake, LiCl-induced behaviors, ultrasonic vocalizations (USVs), CTA performance) and Fos activation in relevant brain regions after the acute stimuli [acute Boost® (AB), acute LiCl (AL)] and the context-only task control (COT), Boost® only task (BOT) and Boost®-LiCl task (BLT). Acutely, females drank more Boost® than males but showed similar aversive behaviors after LiCl. Females and males performed CTA similarly. Both sexes produced 55 kHz USVs anticipating BOT and inhibited these calls in the BLT. However, more females emitted both 22 kHz and 55 kHz USVs in the BLT than males: the latter correlated with less CTA. Estrous cycle stage also influenced 55 kHz USVs. Fos responses were similar in males and females after AB or AL. Females engaged the gustatory cortex and ventral tegmental area (VTA) more than males during the BOT and males engaged the amygdala more than females in both the BOT and BLT. Network analysis of correlated Fos responses across brain regions identified two unique networks characterizing the BOT and BLT, in both of which the VTA played a central role. In situ hybridization with RNAscope identified a population of D1-receptor expressing cells in the CeA that responded to Boost® and D2 receptor-expressing cells that responded to LiCl. The present study suggests that males and females differentially process the affective valence of a stimulus to produce the same goal-directed behavior.

Semaglutide lowers body weight in rodents via distributed neural pathways

Semaglutide, a glucagon-like peptide 1 (GLP-1) analog, induces weight loss, lowers glucose levels, and reduces cardiovascular risk in patients with diabetes. Mechanistic preclinical studies suggest weight loss is mediated through GLP-1 receptors (GLP-1Rs) in the brain. The findings presented here show that semaglutide modulated food preference, reduced food intake, and caused weight loss without decreasing energy expenditure. Semaglutide directly accessed the brainstem, septal nucleus, and hypothalamus but did not cross the blood-brain barrier; it interacted with the brain through the circumventricular organs and several select sites adjacent to the ventricles. Semaglutide induced central c-Fos activation in 10 brain areas, including hindbrain areas directly targeted by semaglutide, and secondary areas without direct GLP-1R interaction, such as the lateral parabrachial nucleus. Automated analysis of semaglutide access, c-Fos activity, GLP-1R distribution, and brain connectivity revealed that activation may involve meal termination controlled by neurons in the lateral parabrachial nucleus. Transcriptomic analysis of microdissected brain areas from semaglutide-treated rats showed upregulation of prolactin-releasing hormone and tyrosine hydroxylase in the area postrema. We suggest semaglutide lowers body weight by direct interaction with diverse GLP-1R populations and by directly and indirectly affecting the activity of neural pathways involved in food intake, reward, and energy expenditure.

Artificial taste avoidance memory induced by coactivation of NMDA and β-adrenergic receptors in the amygdala

The association between a taste and gastric malaise allows animals to avoid the ingestion of potentially toxic food. This association has been termed conditioned taste aversion (CTA) and relies on the activity of key brain structures such as the amygdala and the insular cortex. The establishment of this gustatory-avoidance memory is related to glutamatergic and noradrenergic activity within the amygdala during two crucial events: gastric malaise (unconditioned stimulus, US) and the post-acquisition spontaneous activity related to the association of both stimuli. To understand the functional implications of these neurochemical changes on avoidance memory formation, we assessed the effects of pharmacological stimulation of β-adrenergic and glutamatergic NMDA receptors through the administration of a mixture of L-homocysteic acid and isoproterenol into the amygdala after saccharin exposure on specific times to emulate the US and post-acquisition local signals that would be occurring naturally under CTA training. Our results show that activation of NMDA and β-adrenergic receptors generated a long-term avoidance response to saccharin, like a naturally induced rejection with LiCl. Moreover, the behavioral outcome was accompanied by changes in glutamate, norepinephrine and dopamine levels within the insular cortex, analogous to those displayed during memory retrieval of taste aversion memory. Therefore, we suggest that taste avoidance memory can be induced artificially through the emulation of specific amygdalar neurochemical signals, promoting changes in the amygdala-insular cortex circuit enabling memory establishment.

NMDA receptor and nitric oxide synthase activity in the central amygdala is involved in the acquisition and consolidation of conditioned odor aversion

Rats readily learn to avoid a tasteless odorized solution if they experience visceral malaise after consuming it. This phenomenon is referred to as conditioned odor aversion (COA). Several studies have shown that COA depends on the functional integrity of the amygdala, with most studies focusing on the basolateral nucleus. On the other hand, the role of the central amygdala (CeA) which is known to be involved in the consolidation of conditioned taste aversion (CTA) remains to be established. To address this issue, we evaluated the effect of inhibiting NMDA receptor activity in this structure on COA memory formation. Intra-CeA infusions of non-competitive NMDA receptor inhibitor MK-801 prevented memory formation both when administered before and up to 15 min after COA conditioning, while no effect of this drug was observed when given before long-term memory test. We next evaluated the role of one of the main downstream effectors of brain NMDA receptor signaling, nitric oxide synthase (NOS), known to play a key role in a wide variety learning tasks including some types of olfactory conditioning. Similar results were obtained with inhibition of either NOS or neuron-specific NOS; which proved to be required both during and after COA training, though for a shorter time span than NMDA receptors. Also, neither isoform showed to be required to memory retrieval. These results suggest that the US signaling during acquisition and the initial consolidation step of COA depends on glutamate-NO system activation in the CeA.

The Functional and Neurobiological Properties of Bad Taste

The gustatory system serves as a critical line of defense against ingesting harmful substances. Technological advances have fostered the characterization of peripheral receptors and have created opportunities for more selective manipulations of the nervous system, yet the neurobiological mechanisms underlying taste-based avoidance and aversion remain poorly understood. One conceptual obstacle stems from a lack of recognition that taste signals subserve several behavioral and physiological functions which likely engage partially segregated neural circuits. Moreover, although the gustatory system evolved to respond expediently to broad classes of biologically relevant chemicals, innate repertoires are often not in register with the actual consequences of a food. The mammalian brain exhibits tremendous flexibility; responses to taste can be modified in a specific manner according to bodily needs and the learned consequences of ingestion. Therefore, experimental strategies that distinguish between the functional properties of various taste-guided behaviors and link them to specific neural circuits need to be applied. Given the close relationship between the gustatory and visceroceptive systems, a full reckoning of the neural architecture of bad taste requires an understanding of how these respective sensory signals are integrated in the brain.

The role of the gustatory cortex in incidental experience-evoked enhancement of later taste learning

The strength of learned associations between pairs of stimuli is affected by multiple factors, the most extensively studied of which is prior experience with the stimuli themselves. In contrast, little data is available regarding how experience with "incidental" stimuli (independent of any conditioning situation) impacts later learning. This lack of research is striking given the importance of incidental experience to survival. We have recently begun to fill this void using conditioned taste aversion (CTA), wherein an animal learns to avoid a taste that has been associated with malaise. We previously demonstrated that incidental exposure to salty and sour tastes (taste preexposure-TPE) enhances aversions learned later to sucrose. Here, we investigate the neurobiology underlying this phenomenon. First, we use immediate early gene (c-Fos) expression to identify gustatory cortex (GC) as a site at which TPE specifically increases the neural activation caused by taste-malaise pairing (i.e., TPE did not change c-Fos induced by either stimulus in isolation). Next, we use site-specific infection with the optical silencer Archaerhodopsin-T to show that GC inactivation during TPE inhibits the expected enhancements of both learning and CTA-related c-Fos expression, a full day later. Thus, we conclude that GC is almost certainly a vital part of the circuit that integrates incidental experience into later associative learning.

Bilateral lesions in a specific subregion of posterior insular cortex impair conditioned taste aversion expression in rats

The gustatory cortex (GC) is widely regarded for its integral role in the acquisition and retention of conditioned taste aversions (CTAs) in rodents, but large lesions in this area do not always result in CTA impairment. Recently, using a new lesion mapping system, we found that severe CTA expression deficits were associated with damage to a critical zone that included the posterior half of GC in addition to the insular cortex (IC) that is just dorsal and caudal to this region (visceral cortex). Lesions in anterior GC were without effect. Here, neurotoxic bilateral lesions were placed in the anterior half of this critical damage zone, at the confluence of the posterior GC and the anterior visceral cortex (termed IC2 ), the posterior half of this critical damage zone that contains just VC (termed IC3), or both of these subregions (IC2 + IC3). Then, pre- and postsurgically acquired CTAs (to 0.1 M NaCl and 0.1 M sucrose, respectively) were assessed postsurgically in 15-minute one-bottle and 96-hour two-bottle tests. Li-injected rats with histologically confirmed bilateral lesions in IC2 exhibited the most severe CTA deficits, whereas those with bilateral lesions in IC3 were relatively normal, exhibiting transient disruptions in the one-bottle sessions. Groupwise lesion maps showed that CTA-impaired rats had more extensive damage to IC2 than did unimpaired rats. Some individual differences in CTA expression among rats with similar lesion profiles were observed, suggesting idiosyncrasies in the topographic representation of information in the IC. Nevertheless, this study implicates IC2 as the critical zone of the IC for normal CTA expression.

Parabrachial calcitonin gene-related peptide neurons mediate conditioned taste aversion

Conditioned taste aversion (CTA) is a phenomenon in which an individual forms an association between a novel tastant and toxin-induced gastrointestinal malaise. Previous studies showed that the parabrachial nucleus (PBN) contains neurons that are necessary for the acquisition of CTA, but the specific neuronal populations involved are unknown. Previously, we identified calcitonin gene-related peptide (CGRP)-expressing neurons in the external lateral subdivision of the PBN (PBel) as being sufficient to suppress appetite and necessary for the anorexigenic effects of appetite-suppressing substances including lithium chloride (LiCl), a compound often used to induce CTA. Here, we test the hypothesis that PBel CGRP neurons are sufficient and necessary for CTA acquisition in mice. We show that optogenetic activation of these neurons is sufficient to induce CTA in the absence of anorexigenic substances, whereas genetically induced silencing of these neurons attenuates acquisition of CTA upon exposure to LiCl. Together, these results demonstrate that PBel CGRP neurons mediate a gastrointestinal distress signal required to establish CTA.

Correlation Between Activation of the Prelimbic Cortex, Basolateral Amygdala, and Agranular Insular Cortex During Taste Memory Formation

Conditioned taste aversion (CTA) is a well-established learning paradigm, whereby animals associate tastes with subsequent visceral illness. The prelimbic cortex (PL) has been shown to be involved in the association of events separated by time. However, the nature of PL activity and its functional network in the whole brain during CTA learning remain unknown. Here, using awake functional magnetic resonance imaging and fiber tracking, we analyzed functional brain connectivity during the association of tastes and visceral illness. The blood oxygen level-dependent (BOLD) signal significantly increased in the PL after tastant and lithium chloride (LiCl) infusions. The BOLD signal in the PL significantly correlated with those in the amygdala and agranular insular cortex (IC), which we found were also structurally connected to the PL by fiber tracking. To precisely examine these data, we then performed double immunofluorescence with a neuronal activity marker (c-Fos) and an inhibitory neuron marker (GAD67) combined with a fluorescent retrograde tracer in the PL. During CTA learning, we found an increase in the activity of excitatory neurons in the basolateral amygdala (BLA) or agranular IC that project to the PL. Taken together, these findings clearly identify a role of synchronized PL, agranular IC, and BLA activity in CTA learning.

Brainstem origins of glutamatergic innervation of the rat hypothalamic paraventricular nucleus

Multiple lines of evidence document a role for glutamatergic input to the hypothalamic paraventricular nucleus (PVH) in stress-induced activation of the hypothalamic-pituitary-adrenocortical (HPA) axis. However, the neuroanatomical origins of the glutamatergic input have yet to be definitively determined. We have previously shown that vesicular glutamate transporter 2 (VGLUT2) is the predominant VGLUT isoform expressed in the basal forebrain and brainstem, including PVH-projecting regions, and that the PVH is preferentially innervated by VGLUT2-immunoreactive terminals/boutons. The present study employed a dual-labeling approach, combining immunolabeling for a retrograde tract tracer, Fluoro-Gold (FG), with in situ hybridization for VGLUT2 mRNA, to map the brainstem and caudal forebrain distribution of glutamatergic PVH-projecting neurons. The present report presents evidence for substantial dual labeling in the periaqueductal gray, caudal portions of the zona incerta and subparafascicular nucleus, and the lateral parabrachial nucleus. The current data also suggest that relatively few PVH-projecting neurons in ascending raphe nuclei, nucleus of the solitary tract, or ventrolateral medulla are VGLUT2 positive. The data reveal multiple brainstem origins of glutamatergic input to PVH that are positioned to play a role in transducing a diverse range of stressful stimuli.

Neural substrates of fear conditioning, extinction, and spontaneous recovery in passive avoidance learning: a c-fos study in rats

Extinguishing fear conditioning and preventing the return of fear are the goal in the treatment of anxiety disorders. However, the neural substrates that mediate fear conditioning, extinction, and spontaneous recovery (i.e., the return of fear) remain uncertain. We utilized the aversive passive avoidance learning paradigm and Fos-like immunoreactivity to elucidate this issue. Exception for naïve rats that did not receive any treatment served as the control group, the other rats were subjected to three sessions of context/footshock (0.5 mA, 2s) pairings followed by 12 extinction sessions (context-no footshock). After the last extinction test, these rats were assigned to one of three groups reflecting the number of resting days before the test session (context-no footshock): Day 8, Day 9, and Day 10 groups. Only the Day 10 group exhibited spontaneous recovery during the test session. Fos-like immunoreactivity associated with fear conditioning was seen in the amygdala and cingulate cortex area 1 (Cg1). The extinction of fear was seen to be related to Cg1, cingulate cortex area 2 (Cg2), piriform cortex (Pir), and entorhinal cortex (Ect). Spontaneous recovery was seen to be related to amygdala, Pir, and Ect. The present findings indicate that the brain substrates of fear acquisition, extinction and spontaneous recovery have different ensembles of brain activations. These differences suggest that different brain targets may be considered for fear extinction and for avoiding the return of fear in anxiety disorders.

Common brain activations for painful and non-painful aversive stimuli

BACKGROUND

Identification of potentially harmful stimuli is necessary for the well-being and self-preservation of all organisms. However, the neural substrates involved in the processing of aversive stimuli are not well understood. For instance, painful and non-painful aversive stimuli are largely thought to activate different neural networks. However, it is presently unclear whether there is a common aversion-related network of brain regions responsible for the basic processing of aversive stimuli. To help clarify this issue, this report used a cross-species translational approach in humans (i.e. meta-analysis) and rodents (i.e. systematic review of functional neuroanatomy).

RESULTS

Animal and human data combined to show a core aversion-related network, consisting of similar cortical (i.e. MCC, PCC, AI, DMPFC, RTG, SMA, VLOFC; see results section or abbreviation section for full names) and subcortical (i.e. Amyg, BNST, DS, Hab, Hipp/Parahipp, Hyp, NAc, NTS, PAG, PBN, raphe, septal nuclei, Thal, LC, midbrain) regions. In addition, a number of regions appeared to be more involved in pain-related (e.g. sensory cortex) or non-pain-related (e.g. amygdala) aversive processing.

CONCLUSIONS

This investigation suggests that aversive processing, at the most basic level, relies on similar neural substrates, and that differential responses may be due, in part, to the recruitment of additional structures as well as the spatio-temporal dynamic activity of the network. This network perspective may provide a clearer understanding of why components of this circuit appear dysfunctional in some psychiatric and pain-related disorders.

Taste neophobia and c-Fos expression in the rat brain

Taste neophobia refers to a reduction in consumption of a novel taste relative to when it is familiar. To gain more understanding of the neural basis of this phenomenon, the current study examined whether a novel taste (0.5% saccharin) supports a different pattern of c-Fos expression than the same taste when it is familiar. Results revealed that the taste of the novel saccharin solution evoked more Fos immunoreactivity than the familiar taste of saccharin in the basolateral region of the amygdala, central nucleus of the amygdala, gustatory portion of the thalamus, and the gustatory insular cortex. No such differential expression was found in the other examined areas, including the bed nucleus of stria terminalis,medial amygdala, and medial parabrachial nucleus. The present results are discussed with respect to a forebrain taste neophobia system.

Similar neural activity during fear and disgust in the rat basolateral amygdala

Much research has focused on how the amygdala processes individual affects, yet little is known about how multiple types of positive and negative affects are encoded relative to one another at the single-cell level. In particular, it is unclear whether different negative affects, such as fear and disgust, are encoded more similarly than negative and positive affects, such as fear and pleasure. Here we test the hypothesis that the basolateral nucleus of the amygdala (BLA), a region known to be important for learned fear and other affects, encodes affective valence by comparing neuronal activity in the BLA during a conditioned fear stimulus (fear CS) with activity during intraoral delivery of an aversive fluid that induces a disgust response and a rewarding fluid that induces a hedonic response. Consistent with the hypothesis, neuronal activity during the fear CS and aversive fluid infusion, but not during the fear CS and rewarding fluid infusion, was more similar than expected by chance. We also found that the greater similarity in activity during the fear- and disgust-eliciting stimuli was specific to a subpopulation of cells and a limited window of time. Our results suggest that a subpopulation of BLA neurons encodes affective valence during learned fear, and furthermore, within this subpopulation, different negative affects are encoded more similarly than negative and positive affects in a time-specific manner.

Identifying a network of brain regions involved in aversion-related processing: a cross-species translational investigation

The ability to detect and respond appropriately to aversive stimuli is essential for all organisms, from fruit flies to humans. This suggests the existence of a core neural network which mediates aversion-related processing. Human imaging studies on aversion have highlighted the involvement of various cortical regions, such as the prefrontal cortex, while animal studies have focused largely on subcortical regions like the periaqueductal gray and hypothalamus. However, whether and how these regions form a core neural network of aversion remains unclear. To help determine this, a translational cross-species investigation in humans (i.e., meta-analysis) and other animals (i.e., systematic review of functional neuroanatomy) was performed. Our results highlighted the recruitment of the anterior cingulate cortex, the anterior insula, and the amygdala as well as other subcortical (e.g., thalamus, midbrain) and cortical (e.g., orbitofrontal) regions in both animals and humans. Importantly, involvement of these regions remained independent of sensory modality. This study provides evidence for a core neural network mediating aversion in both animals and humans. This not only contributes to our understanding of the trans-species neural correlates of aversion but may also carry important implications for psychiatric disorders where abnormal aversive behavior can often be observed.

Ontogenetic differences in sensitivity to LiCl- and amphetamine-induced taste avoidance in preweanling rats

When amphetamine is associated with a tastant conditioned stimulus, rats learn to avoid the taste even when employing doses that promote conditioned place preference. One hypothesis raised to account for this effect proposes that taste avoidance induced by amphetamine may be motivated by fear. A sensitive period has been identified in the rat (until postnatal day 10) in which infants learn conditioned appetitive effects to stimuli to which aversions are conditioned after this period. Exogenous administration of corticosterone within this period reverses this effect, generating aversive conditioning. In the present study, we tested conditioning of aversions to amphetamine or LiCl, within and after the sensitive period (Experiments 1 and 2). A third experiment evaluated unconditioned rejection of an aversive quinine solution within the sensitive period. Finally, we tested whether corticosterone administration before conditioning modulates amphetamine-induced taste avoidance. After the sensitive period, infant rats rejected the solution paired with amphetamine or LiCl after 2 conditioning trials, but within the sensitive period, aversions were conditioned only by LiCl and after 4 conditioning trials. Amphetamine-induced taste avoidance was not observed even when corticosterone was administered before conditioning. Additionally, during the sensitive period, a low LiCl dose promoted conditioned taste preference. According to Experiment 3, parameters employed in this study were suitable to yield rejection of aversive solutions within the sensitive period. These results suggest that during the sensitive period, there is a notable resistance to the acquisition of taste avoidance induced by amphetamine. The present experimental framework may represent a useful tool for studying mechanisms underlying taste avoidance and aversion effects.

A genetic network model of cellular responses to lithium treatment and cocaine abuse in bipolar disorder

Background

Lithium is an effective treatment for Bipolar Disorder (BD) and significantly reduces suicide risk, though the molecular basis of lithium's effectiveness is not well understood. We seek to improve our understanding of this effectiveness by posing hypotheses based on new experimental data as well as published data, testing these hypotheses in silico, and posing new hypotheses for validation in future studies. We initially hypothesized a gene-by-environment interaction where lithium, acting as an environmental influence, impacts signal transduction pathways leading to differential expression of genes important in the etiology of BD mania.

Results

Using microarray and rt-QPCR assays, we identified candidate genes that are differentially expressed with lithium treatment. We used a systems biology approach to identify interactions among these candidate genes and develop a network of genes that interact with the differentially expressed candidates. Notably, we also identified cocaine as having a potential influence on the network, consistent with the observed high rate of comorbidity for BD and cocaine abuse. The resulting network represents a novel hypothesis on how multiple genetic influences on bipolar disorder are impacted by both lithium treatment and cocaine use. Testing this network for association with BD and related phenotypes, we find that it is significantly over-represented for genes that participate in signal transduction, consistent with our hypothesized-gene-by environment interaction. In addition, it models related pharmacogenomic, psychiatric, and chemical dependence phenotypes.

Conclusions

We offer a network model of gene-by-environment interaction associated with lithium's effectiveness in treating BD mania, as well as the observed high rate of comorbidity of BD and cocaine abuse. We identified drug targets within this network that represent immediate candidates for therapeutic drug testing. Posing novel hypotheses for validation in future work, we prioritized SNPs near genes in the network based on functional annotation. We also developed a "concept signature" for the genes in the network and identified additional candidate genes that may influence the system because they are significantly associated with the signature.

c-Fos expression is elevated in GABAergic interneurons of the gustatory cortex following novel taste learning

Long-term sensory memories are considered to be stored in the relevant cortical region subserving the given modality. We and others have recently identified a series of molecular alterations in the gustatory cortex (GC) of the rat at different time intervals following novel taste learning. Some of these correlative modifications were also necessary for taste memory acquisition and/or consolidation. However, very little is known about the localization of these molecular modifications within the GC or about the functional activation of the GC hours after novel taste learning. Here, we hypothesize that inhibitory interneurons are activated in the GC on a scale of hours following learning and used c-Fos expression and confocal microscopy with different markers to test this hypothesis. We found that GABAergic interneurons are activated in the GC in correlation with novel taste learning. The activation was evident in the deep but not superficial layers of the dysgranular insular cortex. These results suggest that the GABAergic machinery in the deep layers of the GC participates in the processing of taste information hours after learning, and provide evidence for the involvement of a local cortical circuit not only during acquisition of new information but also during off-line processing and consolidation of taste information.

Identification of flap structure-specific endonuclease 1 as a factor involved in long-term memory formation of aversive learning

We previously proposed that DNA recombination/repair processes play a role in memory formation. Here, we examined the possible role of the fen-1 gene, encoding a flap structure-specific endonuclease, in memory consolidation of conditioned taste aversion (CTA). Quantitative real-time PCR showed that amygdalar fen-1 mRNA induction was associated to the central processing of the illness experience related to CTA and to CTA itself, but not to the central processing resulting from the presentation of a novel flavor. CTA also increased expression of the Fen-1 protein in the amygdala, but not the insular cortex. In addition, double immunofluorescence analyses showed that amygdalar Fen-1 expression is mostly localized within neurons. Importantly, functional studies demonstrated that amygdalar antisense knockdown of fen-1 expression impaired consolidation, but not short-term memory, of CTA. Overall, these studies define the fen-1 endonuclease as a new DNA recombination/repair factor involved in the formation of long-term memories.

Cadmium exposure induces expression of the HOXB8 gene in COS-7 cells

Cadmium (Cd) is a serious toxic metal, which is classified as a possible human carcinogen. We assessed the effects of Cd on the expression levels of homeobox genes, which are associated with carcinogenesis. Among 6 homeobox genes examined in this study, only HOXB8 exhibited increased mRNA expression in COS-7 cells treated with 10 microM CdCl(2). Semiquantitative reverse transcription-polymerase chain reaction analysis revealed that the HOXB8 mRNA level was increased by a maximum of 5.4-fold after 6h of Cd exposure. The levels of HOXA7, A9, C4, C9 and C10 mRNAs decreased from 0.1 to 0.3-fold. Silencing of HOXB8 mRNA expression using a siRNA increased HOXC9 and C10 mRNA expression levels by 6.6- and 1.9-fold, respectively. These results suggest that HOXB8 upregulation is associated with suppression of HOXC9 and C10, and that decreased expression of HOXC9 and C10 after Cd exposure is partly due to HOXB8 induction. In conclusion, Cd disrupts the HOX network. Comprehensive analyses of all the HOX gene expression levels in the presence of Cd may afford clues toward understanding Cd-induced carcinogenesis and teratogenesis.

Internal body state influences topographical plasticity of sensory representations in the rat gustatory cortex

Primary sensory cortices are remarkably organized in spatial maps according to specific sensory features of the stimuli. These cortical maps can undergo plastic rearrangements after changes in afferent ("bottom-up") sensory inputs such as peripheral lesions or passive sensory experience. However, much less is known about the influence of "top-down" factors on cortical plasticity. Here, we studied the effect of a visceral malaise on taste representations in the gustatory cortex (GC). Using in vivo optical imaging, we showed that inducing conditioned taste aversion (CTA) to a sweet and pleasant stimulus induced plastic rearrangement of its cortical representation, becoming more similar to a bitter and unpleasant taste representation. Using a behavior task, we showed that changes in hedonic perception are directly related to the maps plasticity in the GC. Indeed imaging the animals after CTA extinction indicated that sweet and bitter representations were dissimilar. In conclusion, we showed that an internal state of malaise induces plastic reshaping in the GC associated to behavioral shift of the stimulus hedonic value. We propose that the GC not only encodes taste modality, intensity, and memory but extends its integrative properties to process also the stimulus hedonic value.

Differential effects of neurotoxin-induced lesions of the basolateral amygdala and central nucleus of the amygdala on lithium-induced conditioned disgust reactions and conditioned taste avoidance

When rats are intraorally exposed to saccharin solution that has previously been paired with lithium chloride (LiCl), they display Pavlovian conditioned disgust reactions. When exposed to LiCl-paired saccharin solution by bottle, they display suppressed instrumental approach to the bottle resulting in suppressed consumption. The present experiments demonstrated that while neither neurotoxin-induced lesions of the basolateral amygdala (BLA) nor the central nucleus of the amygdala (CeA) attenuated the display of Pavlovian conditioned disgust reactions, lesions of the BLA (but not the CeA) attenuated instrumental conditioned avoidance of the taste. The results are discussed in light of current models of the role of the amygdala in aversive learning.