Inactivation Of Basolateral Amygdala Research Articles

Overexpression of EphB2 in the basolateral amygdala is crucial for inducing visceral pain sensitization in rats subjected to water avoidance stress.

Basolateral amygdala (BLA), as a center for stress responses and emotional regulation, is involved in visceral hypersensitivity of irritable bowel syndrome (IBS) induced by stress. In the present study, we aimed to investigate the role of EphB2 receptor (EphB2) in BLA and explore the underlying mechanisms in this process. Visceral hypersensitivity was induced by water avoidance stress (WAS). Elevated plus maze test, forced swimming test, and sucrose preference test were applied to assess anxiety- and depression-like behaviors. Ibotenic acid or lentivirus was used to inactivate BLA in either the induction or maintenance stage of visceral hypersensitivity. The expression of protein was determined by quantitative PCR, immunofluorescence, and western blot. EphB2 expression was increased in BLA in WAS rats. Inactivation of BLA or downregulation of EphB2 in BLA failed to induce visceral hypersensitivity as well as anxiety-like behaviors. However, during the maintenance stage of visceral pain, visceral hypersensitivity was only partially relieved but anxiety-like behaviors were abolished by inactivation of BLA or downregulation of EphB2 in BLA. Chronic WAS increased the expression of EphB2, N-methyl-D-aspartate receptors (NMDARs), and postsynaptic density protein (PSD95) in BLA. Downregulation of EphB2 in BLA reduced NMDARs and PSD95 expression in WAS rats. However, activation of NMDARs after the knockdown of EphB2 expression still triggered visceral hypersensitivity and anxiety-like behaviors. Taken together, the results suggest that EphB2 in BLA plays an essential role in inducing visceral hypersensitivity. In the maintenance stage, the involvement of EphB2 is crucial but not sufficient. The increase in EphB2 induced by WAS may enhance synaptic plasticity in BLA through upregulating NMDARs, which results in IBS-like symptoms. These findings may give insight into the treatment of IBS and related psychological distress.

Role of Amygdala-Infralimbic Cortex Circuitry in Glucocorticoid-induced Facilitation of Auditory Fear Memory Extinction.

The basolateral amygdala (BLA) and infralimbic area (IL) of the medial prefrontal cortex (mPFC) are two interconnected brain structures that mediate both fear memory expression and extinction. Besides the well-known role of the BLA in the acquisition and expression of fear memory, projections from IL to BLA inhibit fear expression and have a critical role in fear extinction. However, the details of IL-BLA interaction have remained unclear. Here, we investigated the role of functional reciprocal interactions between BLA and IL in mediating fear memory extinction. Using lidocaine (LID), male rats underwent unilateral or bilateral inactivation of the BLA and then unilateral intra-IL infusion of corticosterone (CORT) prior to extinction training of the auditory fear conditioning paradigm. Freezing behavior was reported as an index for conditioned fear. Infusions were performed before the extinction training, allowing us to examine the effects on fear expression and further extinction memory. Experiments 1-3 investigated the effects of left or right infusion of CORT into IL and LID unilaterally into BLA on fear memory extinction. Intra-IL infusion of CORT in the right hemisphere reduced freezing behavior when administrated before the extinction training. Auditory fear memory extinction was impaired by asymmetric inactivation of BLA and CORT infusion in the right IL; however, the same effect was not observed with symmetric inactivation of BLA. IL-BLA neural circuit may provide additional evidence for the contribution of this circuit to auditory fear extinction. This study demonstrates dissociable roles for right or left BLA in subserving the auditory fear extinction. Our finding also raises the possibility that left BLA-IL circuitry may mediate auditory fear memory extinction via underlying mechanisms. However, further research is required in this area. Corticosterone infusion in the right (but not the left) infralimbic area facilitates auditory fear memory extinction.Corticosterone infusion in the right infralimbic area following symmetric basolateral amygdala inactivation has no effect on auditory fear memory extinction.Asymmetric basolateral amygdala inactivation prior to corticosterone infusion into the right infralimbic area impairs auditory fear memory extinction. Previous studies have established that glucocorticoids, which are released in stressful conditions, enhance fear memory extinction. In this study, we found that corticosterone infusion into the right infralimbic area, but not the left one, facilitates auditory fear memory extinction. The effect of corticosterone infusion in the infralimbic area was not blocked by the intra-basolateral amygdala injections of lidocaine when administrated in the ipsilateral hemisphere. However, asymmetric basolateral amygdala inactivation and corticosterone infusion into the right infralimbic area impairs auditory fear memory extinction.

Effects of electrical stimulation and temporary inactivation of basolateral amygdala on morphine-induced conditioned place preference in rats

In the present study, to evaluate the role of the basolateral amygdala (BLA) in morphine addiction, the BLA was stimulated electrically, or inactivated temporarily using lidocaine. The electrical stimulation (ES) was delivered to BLA with low or high intensities (LI or HI: 25 or 150 µA, respectively), and five minutes before morphine administration with effective or ineffective doses, lidocaine was microinjected into the BLA. Using a 5-day conditioned place preference (CPP) paradigm, the dependence on morphine was evaluated. The results showed that LI-ES of BLA induced CPP in both the acquisition and expression phases, in the control and the ineffective dose of morphine groups. HI-ES had no effect on CPP acquisition but induced aversion in the expression, with both effective and ineffective doses of morphine. Inactivation of BLA using lidocaine, inhibited morphine-induced CPP in both acquisition and expression phases. The results of the present study indicate the prominent role of BLA in morphine addiction and dependence. Considering the contradictory results of different intensities of ES, it can be inferred that there are different neural circuits in this area of the brain, in relation to the reward responses.

Developmental Shifts in Amygdala Activity during a High Social Drive State.

Amygdala abnormalities characterize several psychiatric disorders with prominent social deficits and often emerge during adolescence. The basolateral amygdala (BLA) bidirectionally modulates social behavior and has increased sensitivity during adolescence. We tested how an environmentally-driven social state is regulated by the BLA in adults and adolescent male rats. We found that a high social drive state caused by brief social isolation increases age-specific social behaviors and increased BLA neuronal activity. Chemogenetic inactivation of BLA decreased the effect of high social drive on social engagement. High social drive preferentially enhanced BLA activity during social engagement; however, the effect of social opportunity on BLA activity was greater during adolescence. While this identifies a substrate underlying age differences in social drive, we then determined that high social drive increased BLA NMDA GluN2B expression and sensitivity to antagonism increased with age. Further, the effect of a high social drive state on BLA activity during social engagement was diminished by GluN2B blockade in an age-dependent manner. These results demonstrate the necessity of the BLA for environmentally driven social behavior, its sensitivity to social opportunity, and uncover a maturing role for BLA and its GluN2B receptors in social engagement.SIGNIFICANCE STATEMENT Social engagement during adolescence is a key component of healthy development. Social drive provides the impetus for social engagement and abnormalities underlie social symptoms of depression and anxiety. While adolescence is characterized by transitions in social drive and social environment sensitivity, little is known about the neural basis for these changes. We found that amygdala activity is uniquely sensitive to social environment during adolescence compared with adulthood, and is required for expression of heightened social drive. In addition, the neural substrates shift toward NMDA dependence in adulthood. These results are the first to demonstrate a unique neural signature of higher social drive and begin to uncover the underlying factors that heighten social engagement during adolescence.

Contributions of prelimbic cortex, dorsal and ventral hippocampus, and basolateral amygdala to fear return induced by elevated platform stress in rats

Fear relapse is a major challenge in the treatment of stress-related mental disorders. Most investigations have focused on fear return induced by stimuli associated with the initial fear learning, while little attention has been paid to fear return evoked after exposure to an unconditioned stressor. This study explored the neural mechanisms of fear return induced by elevated platform (EP) stressor in Sprague-Dawley rats initially subjected to auditory fear conditioning. The contributions of the prelimbic cortex (PL), dorsal hippocampus (DH), ventral hippocampus (VH), and basolateral amygdala (BLA) were examined by targeted bilateral intracerebral injection of the GABAA agonist muscimol after elevated platform (EP) stressor. Muscimol-induced inactivation of PL or BLA significantly impaired the return of conditioning fear, while inactivation of the DH or VH had no effect. These results suggest that fear return induced by non-associative stressor may depend on the PL and BLA but not on the hippocampus.

Basolateral Amygdala to Nucleus Accumbens Communication Differentially Mediates Devaluation Sensitivity of Sign- and Goal-Tracking Rats.

Rats rely on communication between the basolateral amygdala (BLA) and nucleus accumbens (NAc) to express lever directed approach in a Pavlovian lever autoshaping (PLA) task that distinguishes sign- and goal-tracking rats. During PLA, sign-tracking rats preferentially approach an insertable lever cue, while goal-tracking rats approach a foodcup where rewards are delivered. While sign-tracking rats inflexibly respond to cues even after the associated reward is devalued, goal-tracking rats flexibly reduce responding to cues during outcome devaluation. Here, we sought to determine whether BLA–NAc communication, which is necessary for sign, but not goal-tracking, drives a rigid appetitive approach of sign-tracking rats that are insensitive to manipulations of outcome value. Using a contralateral chemogenetic inactivation design, we injected contralateral BLA and NAc core with inhibitory DREADD (hm4Di-mCherry) or control (mCherry) constructs. To determine sign- and goal-tracking groups, we trained rats in five PLA sessions in which brief lever insertion predicts food pellet delivery. We sated rats on training pellets (devalued condition) or chow (valued condition) before systemic clozapine injections (0.1 mg/kg) to inactivate BLA and contralateral NAc during two outcome devaluation probe tests, in which we measured lever and foodcup approach. Contralateral BLA–NAc chemogenetic inactivation promoted a flexible lever approach in sign-tracking rats but disrupted the flexible foodcup approach in goal-tracking rats. Consistent with a prior BLA–NAc disconnection lesion study, we find contralateral chemogenetic inactivation of BLA and NAc core reduces lever, but not the foodcup approach in PLA. Together these findings suggest rigid appetitive associative encoding in BLA–NAc of sign-tracking rats hinders the expression of flexible behavior when outcome value changes.

Remediation of chronic immobilization stress-induced negative affective behaviors and altered metabolism of monoamines in the prefrontal cortex by inactivation of basolateral amygdala

Exposure to chronic stress precipitates depression and anxiety. Stress-induced responses are differentially regulated by the prefrontal cortex (PFC) and basolateral amygdala (BLA). For instance, repeated stress leads to hypertrophy of BLA, resulting in the emergence of affective symptoms. Chronic stress-induced changes in the metabolism of monoamines are central in the manifestation of affective symptoms. Interestingly, BLA via its reciprocal connections modulates prefrontal cortical monoaminergic responses to acute stress. However, the effects of BLA inactivation on chronic stress-induced affective behaviors and monoaminergic changes in the PFC are relatively unknown. Thus, we hypothesized that inactivation of BLA might prevent chronic immobilization stress (CIS)-induced depressive-, anxiety-like behaviors, and associated monoaminergic alterations in the prelimbic (PrL) and anterior cingulate cortex (ACC) subregions of PFC. We used two different BLA silencing strategies, namely ibotenic acid lesion and reversible temporary inactivation using lidocaine. We found that CIS precipitates depressive- and anxiety-like behaviors. Further, CIS-induced negative affective behaviors were associated with decreased levels of 5-HT, DA, and NE, and increased 5-HIAA/5-HT, DOPAC + HVA/DA, and MHPG/NE ratio in the PrL and ACC, suggesting enhanced metabolism. Interestingly, BLA lesion prior to CIS blocked the emergence of depressive- and anxiety-like behaviors. Moreover, the lesion of BLA prior to CIS was sufficient to prevent alterations in levels of monoamines and their metabolites in the PrL and ACC. Thereafter, we evaluated whether the effects of BLA lesion could be mirrored by temporary inactivation of BLA, specifically during stress. Remarkably, temporary inactivation of BLA during stress recapitulated the effects of lesion. Our results have implications for understanding the role of BLA in chronic stress-induced metabolic alterations in prefrontal cortical monoaminergic systems, and associated mood and anxiety disorders. The current study supports the hypothesis that combating amygdalar hyperactivity might be a viable strategy for the management of stress and associated affective disorders.

Basolateral amygdalar inactivation blocks chronic stress-induced lamina-specific reduction in prefrontal cortex volume and associated anxiety-like behavior

Chronic exposure to stress causes cognitive deficits, anxiety and depression. Earlier studies have suggested that the prefrontal cortex (PFC) and basolateral amygdala (BLA) can differentially modulate the stress-induced alterations either by their action on HPA axis or via direct reciprocal connections between them. The PFC dysfunction and BLA hypertrophy following stress are known to cause anxiety and affective symptoms. Recent studies indicate that inactivation of BLA projections to PFC remarkably decreases anxiety. However, the effect of BLA inactivation on stress-induced anxiety and associated volume loss in prelimbic (PrL) and anterior cingulate (ACC) subregions of PFC is not known. Accordingly, we evaluated the effect of BLA lesion or inactivation during chronic immobilization stress (CIS) on an approach-avoidance task and associated volume loss in the PFC. The stressed rats showed a significant volumetric reduction in layer I and II of the PrL and ACC. Interestingly, BLA lesion prior to stress prevented the volume loss in PrL and ACC. Further, BLA lesion blocked the anxiety-like behavior in stressed rats. However, in the absence of stress, BLA lesion increased the number of shocks as compared to controls. As BLA lesion produced an anticonflict effect, we performed temporary inactivation of BLA specifically during stress. Similar to BLA lesion, lidocaine-induced inactivation prevented the stress-induced volume loss and anxiety-like behavior. We demonstrate that inactivation of BLA during stress prevents CIS-induced anxiety and associated structural correlates in the PFC. The present study extends the hypothesis of amygdalar silencing as a possible management strategy for stress and associated disorders.

Inactivation of Basolateral Amygdala Prevents Stress-Induced Astroglial Loss in the Prefrontal Cortex.

Repeated stress causes cognitive decline and decreases the expression of glial fibrillary acidic protein (GFAP)+ astroglial cells in the prefrontal cortex (PFC). The stress-induced alterations in astroglial density and morphology might significantly contribute to cognitive impairments. Apart from PFC, a key region involved in modulation of repercussions of stress is basolateral amygdala (BLA), which undergoes hypertrophy following chronic immobilization stress (CIS) and has intense reciprocal connections to the PFC. Interestingly, inactivation of BLA precludes stress-induced learning deficits. However, the modulatory role of BLA on CIS-induced alterations in GFAP+ astroglial density and associated learning deficits are presently unknown. Accordingly, we present two sets of experiments evaluating the effects of BLA inactivation either permanently or temporarily on CIS-induced changes in learning and astroglial expression in the PFC. CIS causes impairment in novel object recognition memory and astroglial loss in the PFC. In experiment I, we permanently inactivated the BLA by ibotenate lesion prior to CIS and observed a significant improvement in learning. Surprisingly, BLA lesion also prevented the stress-induced astroglial loss in the PFC. Furthermore, in the experiment II, we analyzed whether the effects of permanent inactivation could be mirrored by the temporary blockage of BLA specifically during stress. Interestingly, temporary inactivation of BLA mimics the effects of lesion. There was a notable prevention of learning impairment and astroglial loss in the PFC following BLA inactivation during stress. The present study emphasizes that stress-induced astroglial loss might contribute to cognitive deficits and modulation of BLA activity might be a viable strategy for management of stress-related PFC dysfunctions.

Prevention of chronic immobilization stress-induced enhanced expression of glucocorticoid receptors in the prefrontal cortex by inactivation of basolateral amygdala

Repeated exposure to stress precipitates anxiety, depression and cognitive deficits. Stress-induced activation of the hypothalamus–pituitary–adrenal (HPA) axis is modulated by the prefrontal cortex (PFC) and basolateral amygdala (BLA). It is well established that BLA positively regulates the HPA axis and undergoes hypertrophy following chronic immobilization stress (CIS). However, it is not known whether inactivation of the BLA can modulate the stress-induced changes in the expression of glucocorticoid receptors (GRs) in the PFC. To address this, we stereologically estimated GR+ cell densities in the prelimbic (PrL) and anterior cingulate cortex (ACC). Following ibotenate lesioning of the BLA, rats were subjected to CIS and GR+ cell densities were assessed. CIS increases the GR+ cell densities in PrL and ACC. BLA lesion prior to CIS abolished the CIS-induced increase in GR+ cell densities in both regions. In the second part of experiments, we evaluated whether selective inactivation of BLA during CIS would mimic the effects of BLA lesion. Interestingly, the BLA inactivation specifically during CIS prevented the increase in GR+ cell densities in the PrL and ACC. The findings of our study suggest that BLA regulates the stress-induced increase in prefrontal GR expression, which might be crucial in the emergence of affective and cognitive symptoms following stress. We speculate that modulation of BLA during stress might prevent HPA axis dysfunctions and GR resistance in stress-related disorders, and could assist in the development of novel therapeutic strategies to treat stress and associated disorders like depression. Further, molecular studies are warranted for the understanding of stress-induced GR resistance and its prevention via BLA inactivation.

Disconnection of basolateral amygdala and insular cortex disrupts conditioned approach in Pavlovian lever autoshaping

Previously established individual differences in appetitive approach and devaluation sensitivity observed in goal- and sign-trackers may be attributed to differences in the acquisition, modification, or use of associative information in basolateral amygdala (BLA) pathways. Here, we sought to determine the extent to which communication of associative information between BLA and anterior portions of insular cortex (IC) supports ongoing Pavlovian conditioned approach behaviors in sign- and goal-tracking rats, in the absence of manipulations to outcome value. We hypothesized that the BLA mediates goal-, but not sign- tracking approach through interactions with the IC, a brain region involved in supporting flexible behavior. We first trained rats in Pavlovian lever autoshaping to determine their sign- or goal-tracking tendency. During alternating test sessions, we gave unilateral intracranial injections of vehicle or a cocktail of gamma-aminobutyric acid (GABA) receptor agonists, baclofen and muscimol, unilaterally into the BLA and contralaterally or ipsilaterally into the IC prior to reinforced lever autoshaping sessions. Consistent with our hypothesis we found that contralateral inactivation of BLA and IC increased the latency to approach the food cup and decreased the number of food cup contacts in goal-trackers. While contralateral inactivation of BLA and IC did not affect the total number of lever contacts in sign-trackers, this manipulation increased the latency to approach the lever. Ipsilateral inactivation of BLA and IC did not impact approach behaviors in Pavlovian lever autoshaping. These findings, contrary to our hypothesis, suggest that communication between BLA and IC maintains a representation of initially learned appetitive associations that commonly support the initiation of Pavlovian conditioned approach behavior regardless of whether it is directed at the cue or the location of reward delivery.

Inactivation of basolateral amygdala prevents chronic immobilization stress-induced memory impairment and associated changes in corticosterone levels

Chronic stress causes detrimental effects on various forms of learning and memory. The basolateral amygdala (BLA) not only plays a crucial role in mediating certain forms of memory, but also in the modulation of the effects of stress. Chronic immobilization stress (CIS) results in hypertrophy of the BLA, which is believed to be one of the underlying causes for stress’ effects on learning. Thus, it is plausible that preventing the effects of CIS on amygdala would preclude its deleterious cognitive effects. Accordingly, in the first part, we evaluated the effect of excitotoxic lesion of the BLA on chronic stress-induced hippocampal-dependent spatial learning using a partially baited radial arm maze task. The BLA was ablated bilaterally using ibotenic acid prior to CIS. Chronically stressed rats showed impairment in spatial learning with decreased percentage correct choice and increased reference memory errors. Excitotoxic lesion of the BLA prevented the impairment in spatial learning and reference memory. In the retention test, lesion of the BLA was able to rescue the chronic stress-induced impairment. Interestingly, stress-induced enhanced plasma corticosterone levels were partially prevented by the lesion of BLA. These results motivated us to evaluate if the same effects can be observed with temporary inactivation of BLA, only during stress. We found that chronic stress-induced spatial learning deficits were also prevented by temporary inactivation of the BLA. Additionally, temporary inactivation of BLA partially precluded the stress-induced increase in plasma corticosterone levels. Thus, inactivation of BLA precludes stress-induced spatial learning deficits, and enhanced plasma corticosterone levels. It is speculated that BLA inactivation-induced reduction in corticosterone levels during stress, might be crucial in restoring spatial learning impairments. Our study provides evidence that amygdalar modulation during stress might be beneficial for strategic management of stress-related cognitive deficits.

Individual Differences in Animal Stress Models: Considering Resilience, Vulnerability, and the Amygdala in Mediating the Effects of Stress and Conditioned Fear on Sleep.

To examine the REM sleep response to stress and fearful memories as a potential marker of stress resilience and vulnerability and to assess the role of the basolateral amygdala (BLA) in mediating the effects of fear memory on sleep. Outbred Wistar rats were surgically implanted with electrodes for recording EEG and EMG and with bilateral guide cannulae directed at the BLA. Data loggers were placed intraperitoneally to record core body temperature. After recovery from surgery, the rats received shock training (ST: 20 footshocks, 0.8 mA, 0.5-s duration, 60-s interstimulus interval) and afterwards received microinjections of the GABAA agonist muscimol (MUS; 1.0 μM) to inactivate BLA or microinjections of vehicle (VEH) alone. Subsequently, the rats were separated into 4 groups (VEH-vulnerable (VEH-Vul; n = 14), VEH-resilient (VEH-Res; n = 13), MUS-vulnerable (MUS-Vul; n = 8), and MUS-resilient (MUS-Res; n = 11) based on whether or not REM was decreased, compared to baseline, during the first 4 h following ST. We then compared sleep, freezing, and the stress response (stress-induced hyperthermia, SIH) across groups to determine the effects of ST and fearful context re-exposure alone (CTX). REM was significantly reduced on the ST day in both VEH-Vul and MUS-Vul rats; however, post-ST MUS blocked the reduction in REM on the CTX day in the MUS-Vul group. The VEH-Res and MUS-Res rats showed similar levels of REM on both ST and CTX days. The effects of post-ST inactivation of BLA on freezing and SIH were minimal. Outbred Wistar rats can show significant individual differences in the effects of stress on REM that are mediated by BLA. These differences in REM can be independent of behavioral fear and the peripheral stress response, and may be an important biomarker of stress resilience and vulnerability.

Basolateral amygdala and ventral hippocampus in stress-induced amplification of nicotine self-administration during reacquisition in rat.

Cigarette smoking remains the leading cause of preventable morbidity and mortality in the USA, although only 3-5 % of quitters are successful for 6-12 months. Stress during abstinence increases the likelihood of relapse to smoking. We recently reported that repeated stress during abstinence from operant nicotine self-administration (SA) amplifies the reacquisition of nicotine SA and affects the diurnal intake of nicotine in rats. Herein, we sought to identify brain regions critical for the expression of stress-enhanced nicotine SA during reacquisition. Rats acquired nicotine SA (FR5) with virtually unlimited drug access (23 h/day). During abstinence (8 day), 30 min of restraint stress was applied on days 1, 3, 5, and 7. Beginning day 8, nicotine SA was reacquired over 5 days, and basolateral amygdala (BLA) was inactivated bilaterally or disconnected from nucleus accumbens core (NAcc). Similarly, ventral hippocampus (vHP) was inactivated or disconnected from BLA. Bilateral inactivation (muscimol + baclofen) of BLA or disconnection from NAcc abolished the stress-enhanced reacquisition of nicotine SA without affecting basal levels of nicotine SA. Similarly, bilateral inactivation of vHP or disconnection of vHP and BLA also abolished stress-enhanced reacquisition of nicotine SA. BLA, vHP, and functional interactions between BLA-NAcc and vHP-BLA are required for expression of stress-enhanced nicotine SA during reacquisition. However, without stress, these functional interactions are not necessary for reexpression of nicotine SA during reacquisition. Therefore, BLA, vHP, and these regional interactions specifically mediate the effects of repeated stress on the reacquisition of nicotine SA behavior.

The central amygdala nucleus is critical for incubation of methamphetamine craving.

Cue-induced methamphetamine seeking progressively increases after withdrawal but mechanisms underlying this 'incubation of methamphetamine craving' are unknown. Here we studied the role of central amygdala (CeA), ventral medial prefrontal cortex (vmPFC), and orbitofrontal cortex (OFC), brain regions implicated in incubation of cocaine and heroin craving, in incubation of methamphetamine craving. We also assessed the role of basolateral amygdala (BLA) and dorsal medial prefrontal cortex (dmPFC). We trained rats to self-administer methamphetamine (10 days; 9 h/day, 0.1 mg/kg/infusion) and tested them for cue-induced methamphetamine seeking under extinction conditions during early (2 days) or late (4-5 weeks) withdrawal. We first confirmed that 'incubation of methamphetamine craving' occurs under our experimental conditions. Next, we assessed the effect of reversible inactivation of CeA or BLA by GABAA+GABAB receptor agonists (muscimol+baclofen, 0.03+0.3 nmol) on cue-induced methamphetamine seeking during early and late withdrawal. We also assessed the effect of muscimol+baclofen reversible inactivation of vmPFC, dmPFC, and OFC on 'incubated' cue-induced methamphetamine seeking during late withdrawal. Lever presses in the cue-induced methamphetamine extinction tests were higher during late withdrawal than during early withdrawal (incubation of methamphetamine craving). Muscimol+baclofen injections into CeA but not BLA decreased cue-induced methamphetamine seeking during late but not early withdrawal. Muscimol+baclofen injections into dmPFC, vmPFC, or OFC during late withdrawal had no effect on incubated cue-induced methamphetamine seeking. Together with previous studies, results indicate that the CeA has a critical role in incubation of both drug and non-drug reward craving and demonstrate an unexpected dissociation in mechanisms of incubation of methamphetamine vs cocaine craving.

Dissociable contributions of anterior cingulate cortex and basolateral amygdala on a rodent cost/benefit decision-making task of cognitive effort.

Personal success often requires the choice to expend greater effort for larger rewards, and deficits in such effortful decision making accompany a number of illnesses including depression, schizophrenia, and attention-deficit/hyperactivity disorder. Animal models have implicated brain regions such as the basolateral amygdala (BLA) and anterior cingulate cortex (ACC) in physical effort-based choice, but disentangling the unique contributions of these two regions has proven difficult, and effort demands in industrialized society are predominantly cognitive in nature. Here we utilize the rodent cognitive effort task (rCET), a modification of the five-choice serial reaction-time task, wherein animals can choose to expend greater visuospatial attention to obtain larger sucrose rewards. Temporary inactivation (via baclofen-muscimol) of BLA and ACC showed dissociable effects: BLA inactivation caused hard-working rats to 'slack off' and 'slacker' rats to work harder, whereas ACC inactivation caused all animals to reduce willingness to expend mental effort. Furthermore, BLA inactivation increased the time needed to make choices, whereas ACC inactivation increased motor impulsivity. These data illuminate unique contributions of BLA and ACC to effort-based decision making, and imply overlapping yet distinct circuitry for cognitive vs physical effort. Our understanding of effortful decision making may therefore require expanding our models beyond purely physical costs.

Gating of Fear in Prelimbic Cortex by Hippocampal and Amygdala Inputs

The prefrontal cortex (PFC) regulates emotional responses, but it is unclear how PFC integrates diverse inputs to select the appropriate response. We therefore evaluated the contribution of basolateral amygdala (BLA) and ventral hippocampus (vHPC) inputs to fear signaling in the prelimbic (PL) cortex, a PFC region critical for the expression of conditioned fear. In conditioned rats trained to press for food, BLA inactivation decreased the activity of projection cells in PL, and reduced PL conditioned tone responses. In contrast, vHPC inactivation decreased activity of interneurons in PL and increased PL conditioned tone responses. Consistent with hippocampal gating of fear after extinction, vHPC inactivation increased fear and PL pyramidal activity in extinguished, but not in conditioned, rats. These results suggest a prefrontal circuit whereby hippocampus gates amygdala-based fear. Thus, deficient hippocampal inhibition of PFC may underlie emotional disorders, especially in light of reduced hippocampal volume observed in depression and PTSD.

Transient inactivation of basolateral amygdala during selective satiation disrupts reinforcer devaluation in rats.

Basolateral amygdala (BLA) function is critical for flexible, goal-directed behavior, including performance on reinforcer devaluation tasks. Here we tested, in rats, the hypothesis that BLA is critical for conditioned reinforcer devaluation during the period when the primary reinforcer (food) is being devalued (by feeding it to satiety), but not thereafter for guiding behavioral choices. We used a spatially independent task that used two visual cues, each predicting one of two foods. An instrumental action (lever press) was required for reinforcer delivery. After training, rats received BLA or sham lesions, or cannulae implanted in BLA. Under control conditions (sham lesions, saline infusions), devaluation of one food significantly decreased responding to the cue associated with that food, when both cues were presented simultaneously during extinction. BLA lesions impaired this devaluation effect. Transient inactivation of BLA by microinfusion of the γ-aminobutyric acid receptor type A agonist muscimol resulted in an impairment only when BLA was inactivated during satiation. When muscimol was infused after satiation and therefore, BLA was inactivated only during the choice test, rats showed no impairment. Thus, BLA is necessary for registering or updating cues to reflect updated reinforcer values, but not for guiding choices once the value has been updated. Our results are the first to describe the contribution of rat BLA to specific components of reinforcer devaluation and are the first to show impairment in reinforcer devaluation following transient inactivation in the rat.

Inactivation of Basolateral Amygdala Specifically Eliminates Palatability-Related Information in Cortical Sensory Responses

Evidence indirectly implicates the amygdala as the primary processor of emotional information used by cortex to drive appropriate behavioral responses to stimuli. Taste provides an ideal system with which to test this hypothesis directly, as neurons in both basolateral amygdala (BLA) and gustatory cortex (GC)-anatomically interconnected nodes of the gustatory system-code the emotional valence of taste stimuli (i.e., palatability), in firing rate responses that progress similarly through "epochs." The fact that palatability-related firing appears one epoch earlier in BLA than GC is broadly consistent with the hypothesis that such information may propagate from the former to the latter. Here, we provide evidence supporting this hypothesis, assaying taste responses in small GC single-neuron ensembles before, during, and after temporarily inactivating BLA in awake rats. BLA inactivation (BLAx) changed responses in 98% of taste-responsive GC neurons, altering the entirety of every taste response in many neurons. Most changes involved reductions in firing rate, but regardless of the direction of change, the effect of BLAx was epoch-specific: while firing rates were changed, the taste specificity of responses remained stable; information about taste palatability, however, which normally resides in the "Late" epoch, was reduced in magnitude across the entire GC sample and outright eliminated in most neurons. Only in the specific minority of neurons for which BLAx enhanced responses did palatability specificity survive undiminished. Our data therefore provide direct evidence that BLA is a necessary component of GC gustatory processing, and that cortical palatability processing in particular is, in part, a function of BLA activity.

Accumbens shell AMPA receptors mediate expression of extinguished reward seeking through interactions with basolateral amygdala

Extinction is the reduction in drug seeking when the contingency between drug seeking behavior and the delivery of drug reward is broken. Here, we investigated a role for the nucleus accumbens shell (AcbSh). Rats were trained to respond for 4% (v/v) alcoholic beer in one context (Context A) followed by extinction in a second context (Context B). Rats were subsequently tested in the training context, A (ABA), or the extinction context, B (ABB). Pre-test injections of the glutamate AMPA receptor antagonist, NBQX (1 µg) into AcbSh had no effect on renewal of alcoholic beer seeking when rats were returned to the training context (ABA). However, NBQX increased responding when rats were tested in the extinction context (ABB). In a second experiment, rats received training, extinction, and test in the same context. Pre-test injections of NBQX (0, 0.3, and 1 µg) into the AcbSh dose-dependently attenuated expression of extinction. We also found that NBQX in the AcbSh had no effect on initial acquisition of extinction or the motivation to respond for reward as measured by break point on a progressive ratio schedule. Finally, we show that pharmacological disconnection of a basolateral amygdala (BLA) → AcbSh pathway via NBQX in AcbSh combined with reversible inactivation of the contralateral BLA attenuates expression of extinction. Together, these results suggest that AcbSh AMPA receptors mediate expression of extinguished reward seeking through glutamatergic inputs from the BLA.