Differential roles of nucleus reuniens and perirhinal cortex in Pavlovian trace fear conditioning in rats.

The nucleus reuniens (RE) and the perirhinal cortex (PRC) are two major relay stations that interconnect the hippocampus (HPC) and the medial prefrontal cortex (mPFC). Previous studies have shown that both the RE and the PRC are involved in the acquisition of trace fear conditioning. However, the respective contribution of the two regions is unclear. In this study, we used pharmacological approach to compare their roles. Our data suggested that inactivation of the RE or the PRC during conditioning partially impaired, whereas inactivation of both areas totally abolished, the encoding of trace fear. We next examined whether the impaired encoding of trace fear under RE inactivation can be rescued with enhanced cholinergic tone in the PRC, and vice versa. Against our hypothesis, regardless of whether the RE was on-line or not, animals failed to encode trace fear when further engaging cholinergic activities in the PRC. Conversely, depending on PRC activation level during conditioning, further recruiting cholinergic activities in the RE led to a down-shift of fear response during retrieval. Our results revealed that the RE and the PRC were necessary for the encoding of trace fear. Moreover, there was differential importance of cholinergic modulation during the process.

Inactivation of medial or lateral orbitofrontal cortex during fear extinction did not interfere with fear renewal.

Hyperactive orbitofrontal cortical activation is commonly seen in patients of obsessive-compulsive disorder (OCD). Previous studies from our laboratory showed that for rats with aberrant activation of the orbitofrontal cortex (OFC) during the extinction phase, they were unable to use contexts as the reference for proper retrieval of fear memory during renewal test. This result supported the phenomenon that many OCD patients show poor regulation of fear-related behavior. Since there are robust anatomical connections of the OFC with the fear-circuit, we aim to further examine whether the OFC is actively engaged in fear regulation under normal circumstances. In this study, the lateral or medial OFC was inactivated during the extinction phase using the ABA fear renewal procedure. We found that these animals showed intact fear renewal during retrieval test with their freezing levels equivalent to the control rats, revealing that the OFC did not have decisive roles in extinction acquisition. Together with our previous study, we suggest that the OFC only interferes with fear regulation when it becomes pathophysiologically hyperactive.

Analysis of collateral projections from the lateral orbitofrontal cortex to nucleus accumbens and basolateral amygdala in rats.

The orbitofrontal cortex (OFC) is an important brain area for executive functions. The OFC projects to both the nucleus accumbens (NAc) and the basolateral nucleus of the amygdala (BLA). These two pathways share some similar behavioral functions, but their anatomical and physiological properties have not been compared before. In this study, we first explored the connection of the lateral OFC (lOFC) to NAc core (NAcc) and/or BLA, especially the collateral projections (experiments 1 and 2) with rats. In experiment 1, fluorophore-conjugated retrograde tracers were locally infused into the NAcc and the BLA to sample neurons in the lOFC. Our results revealed that along the anterior-posterior axis of the lOFC, more NAcc- and/or BLA-projecting neurons were distributed toward the posterior end, but the average percentage of collateral projecting neurons at the four sampled lOFC levels remained fairly stable. In experiment 2, antidromic single units in the lOFC responsive to the NAcc and/or the BLA stimulation were identified in anesthetized rats. However, we found that collateral projections from the lOFC to NAcc and BLA were sparse. We next studied the physiological characteristics of these two pathways (experiment 3). In this experiment, orthodromic single units in the NAcc or the BLA responsive to the lOFC stimulation were located in anesthetized rats. Our results showed no difference in the evoked thresholds or the intensity-response probability curves between the two. Together, our results showed that these two pathways were similar in projecting neuron distribution and physiological characteristics.NEW & NOTEWORTHY Using the double retrograde tracing and electrophysiological approach, we reported that among the sampled NAcc- or the BLA-projecting lOFC neurons, the percentage of collateral projections were fairly stable (about 20%-25%) along the lOFC anterior-posterior axis. Furthermore, among the neurons sampled in the NAcc and the BLA, there was no difference in physiological characteristics in response to lOFC stimulation between the two pathways.

Functional Reuniens and Rhomboid Nuclei Are Required for Proper Acquisition and Expression of Cued and Contextual Fear in Trace Fear Conditioning.

BACKGROUND: The reuniens (Re) and rhomboid (Rh) nuclei (ReRh) of the midline thalamus interconnect the hippocampus and the medial prefrontal cortex. The hippocampus and medial prefrontal cortex are both involved in the acquisition of trace fear conditioning, in which a conditioned stimulus (tone) and an aversive unconditioned stimulus (footshock) are paired but separated in time with a trace interval. Earlier, we demonstrated that ReRh inactivation during trace conditioning impaired the acquisition of cued fear. In contrast, ReRh inactivation during both conditioning and test resulted in heightened fear to tones during retrieval. Because there was a generalized contextual fear on top of heightened fear to tones in the latter experiment, here we aimed to examine the specific importance of the functional ReRh in cued fear and contextual fear through introducing prolonged contextual exposure. METHODS: The ReRh were pharmacologically inactivated with muscimol (or saline as controls) before each experimental session. RESULTS: We showed that although ReRh inactivation before trace fear conditioning impaired the acquisition of cued fear, the animals still acquired a certain level of fear to the tones. However, without the functional ReRh throughout the entire behavioral sessions, these animals showed heightened contextual fear that did not decline much with the passage of time, which generalized to the other context, and fear to tones reoccurred when the tones were presented. CONCLUSIONS: Our results suggested that functional ReRh are important for proper acquisition and expression of fear to context and tones acquired under trace procedure.

Activation of medial orbitofrontal cortex abolishes fear extinction and interferes with fear expression in rats.

Pavlovian fear conditioning and extinction procedures have long been used to study the regulation of learned fear. The amygdala is vital for the association of cues and fear expression, whereas the medial prefrontal cortex (mPFC) is critical for fear regulation after extinction. The medial orbitofrontal cortex (mOFC) has an extensive connection with the fear circuit. In human studies, emotional regulation disorders, such as obsessive-compulsive disorder and post-traumatic stress disorder, are often linked to an abnormality in the orbitofrontal cortex (OFC). Therefore, in a series of experiments, we examined whether abnormal mOFC activities interfere with the regulation of learned fear. The mOFC of rats was pharmacologically activated with N-methyl-D-aspartate (NMDA) during the acquisition, early consolidation, or retrieval phase of fear extinction. Under mOFC activation, there was a general initial suppression of the fear response followed by the development of nonspecific fear expression. Moreover, pre-extinction activation of the mOFC abolished extinction acquisition, causing an up-shift in the fear response during the retrieval test. Nonetheless, immediate post-extinction activation of the mOFC did not interfere with extinction consolidation. Overall, our results suggested that mOFC activation abolished fear extinction acquisition and interfered with fear expression.

Property changes of caseinate in response to its dityrosine formation induced by horseradish peroxidase, glucose oxidase and d-glucose.

BACKGROUND: A ternary system containing horseradish peroxidase (HRP), glucose oxidase and d-glucose using one- or two-step treatment was evidently able to cross-link proteins via dityrosine formation and thus was assessed for its possible impact on several properties of a protein ingredient caseinate. RESULTS: HRP, glucose oxidase and d-glucose were used at 200 U, 6 U and 0.05 mmol g-1 protein to treat caseinate by one- and two-step methods, producing two cross-linked caseinates named CLCN-I and CLCN-II, respectively. In response to the conducted cross-linking, both CLCN-I and CLCN-II gained slightly reduced dispersibility at pH 5-10, enlarged hydrodynamic radius (particle size distribution, 266.37 and 258.33 versus 226.67 nm) and negative zeta-potential (-26.60 and -22.27 versus -14.30 mV) in dispersions, increased water-binding (3.70 and 3.09 versus 2.68 kg kg-1 protein), decreased oil-binding (1.75 and 2.74 versus 2.87 kg kg-1 protein) and emulsifying activity (76.2 and 82.3 versus 94.3 m2 g-1 protein), increased emulsion stability (84.3% and 82.5% versus 78.6%), and enhanced thermal stability with lower mass loss (58.5% and 59.6% versus 64.3%) or higher decomposition temperatures (331.2 °C and 328.7 °C versus 327.6 °C) upon heating at 105-450 °C. In addition, CLCN-I and CLCN-II had decreased gelling temperatures and shortened gelling times when forming acid-induced gels, and the gels were endowed with increased values in four textural indices and finer microstructure. Moreover, CLCN-I with a higher cross-linking extent showed greater property changes than CLCN-II. CONCLUSION: This ternary system could be used in caseinate cross-linking to improve properties such as aggregation, emulsification, gelation and thermal stability. © 2020 Society of Chemical Industry.

Inhibitory Modulation of Orbitofrontal Cortex on Medial Prefrontal Cortex-Amygdala Information Flow.

The amygdala receives cortical inputs from the medial prefrontal cortex (mPFC) and orbitofrontal cortex (OFC) that are believed to affect emotional control and cue-outcome contingencies, respectively. Although mPFC impact on the amygdala has been studied, how the OFC modulates mPFC-amygdala information flow, specifically the infralimbic (IL) division of mPFC, is largely unknown. In this study, combined in vivo extracellular single-unit recordings and pharmacological manipulations were used in anesthetized rats to examine how OFC modulates amygdala neurons responsive to mPFC activation. Compared with basal condition, pharmacological (N-Methyl-D-aspartate) or electrical activation of the OFC exerted an inhibitory modulation of the mPFC-amygdala pathway, which was reversed with intra-amygdala blockade of GABAergic receptors with combined GABAA and GABAB antagonists (bicuculline and saclofen). Moreover, potentiation of the OFC-related pathways resulted in a loss of OFC control over the mPFC-amygdala pathway. These results show that the OFC potently inhibits mPFC drive of the amygdala in a GABA-dependent manner; but with extended OFC pathway activation this modulation is lost. Our results provide a circuit-level basis for this interaction at the level of the amygdala, which would be critical in understanding the normal and pathophysiological control of emotion and contingency associations regulating behavior.

Pharmacological activation of the lateral orbitofrontal cortex on regulation of learned fear and extinction.

Obsessive-compulsive disorder (OCD) is usually accompanied with hyperactivity of the orbitofrontal cortex (OFC). OCD patients have anxiety issues, and there is high comorbidity of OCD and post-traumatic stress disorder (PTSD). One of the leading factors of PTSD is the failure of fear extinction. In this study, we examined whether hyperactivity of the OFC interfered with extinction processes. The lateral OFC (lOFC) was pharmacologically activated with N-methyl-d-aspartate (NMDA) in behaving rats during encoding, consolidation, and retrieval, of Pavlovian fear extinction. We found that when we brought the lOFC on-line before extinction training or retrieval test, there was a general initial suppression of fear expression regardless behavioral history, which was followed by development of nonspecific fear response. Moreover, pre-extinction activation of the lOFC impaired the encoding of extinction demonstrated by a general up-shift of fear levels during retrieval test compared to controls. We also found that regardless of whether the lOFC was activated or not, immediate post-extinction manipulation interfered extinction consolidation in general. To conclude, activation of the lOFC altered expression of learned fear and negatively impaired extinction outcome. Our results provided a new angle to study the etiology of comorbid OCD and PTSD.

Inhibitory modulation of medial prefrontal cortical activation on lateral orbitofrontal cortex-amygdala information flow.

KEY POINTS: The basolateral complex of the amygdala (BLA) receives input from the lateral orbitofrontal cortex (lOFC) for cue-outcome contingencies and the medial prefrontal cortex (mPFC) for emotion control. Here we examined how the mPFC modulates lOFC-BLA information flow. We found that the majority of BLA neurons responsive to lOFC stimulation were also responsive to mPFC stimulation. Activation of the mPFC exerted an inhibitory modulation of the lOFC-BLA pathway, which was reversed with intra-amygdala blockade of GABAergic receptors. mPFC tetanus potentiated the lOFC-BLA pathway, but did not alter its inhibitory modulatory gating. These results show that the mPFC potently inhibits lOFC drive of the BLA in a GABA-dependent manner, which is informative in understanding the normal and potential pathophysiological state of emotion and contingency associations in regulating behaviour. ABSTRACT: Several neocortical projections converge onto the basolateral complex of the amygdala (BLA), including the lateral orbitofrontal cortex (lOFC) and the medial prefrontal cortex (mPFC). Lateral orbitofrontal input to the BLA is important for cue-outcome contingencies, while medial prefrontal input is essential for emotion control. In this study, we examined how the mPFC, specifically the infralimbic division of the mPFC, modulates lOFC-BLA information flow, using combined in vivo extracellular single-unit recordings and pharmacological manipulations in anaesthetized rats. We found that the majority (over 95%) of BLA neurons that responded to lOFC stimulation also responded to mPFC stimulation. Compared to basal condition, pharmacological (N-methyl-d-aspartate) or electrical activation of the mPFC exerted an inhibitory modulation of the lOFC-BLA pathway, which was reversed with intra-amygdala blockade of GABAergic receptors with combined GABAA and GABAB antagonists (bicuculline and saclofen). Moreover, mPFC tetanus potentiated the lOFC-BLA pathway, but mPFC tetanus or low-frequency stimulation did not alter its inhibitory modulatory gating on the lOFC-BLA pathway. These results show that the mPFC potently inhibits lOFC drive of BLA neurons in a GABA-dependent manner. Our result is informative in understanding the normal and potential pathophysiological state of emotion and contingency associations regulating behaviour.

Lateral Orbitofrontal Cortical Modulation on the Medial Prefrontal Cortex-Amygdala Pathway: Differential Regulation of Intra-Amygdala GABAA and GABAB Receptors.

Background: The basolateral complex of the amygdala receives inputs from neocortical areas, including the medial prefrontal cortex and lateral orbitofrontal cortex. Earlier studies have shown that lateral orbitofrontal cortex activation exerts an inhibitory gating on medial prefrontal cortex-amygdala information flow. Here we examined the individual role of GABAA and GABAB receptors in this process. Methods: In vivo extracellular single-unit recordings were done in anesthetized rats. We searched amygdala neurons that fire in response to medial prefrontal cortex activation, tested lateral orbitofrontal cortex gating at different delays (lateral orbitofrontal cortex-medial prefrontal cortex delays: 25, 50, 100, 250, 500, and 1000 milliseconds), and examined differential contribution of GABAA and GABAB receptors with iontophoresis. Results: Relative to baseline, lateral orbitofrontal cortex stimulation exerted an inhibitory modulatory gating on the medial prefrontal cortex-amygdala pathway and was effective up to a long delay of 500 ms (long-delay latencies at 100, 250, and 500 milliseconds). Moreover, blockade of intra-amygdala GABAA receptors with bicuculline abolished the lateral orbitofrontal cortex inhibitory gating at both short- (25 milliseconds) and long-delay (100 milliseconds) intervals, while blockade of GABAB receptors with saclofen reversed the inhibitory gating at long delay (100 milliseconds) only. Among the majority of the neurons examined (8 of 9), inactivation of either GABAA or GABAB receptors during baseline did not change evoked probability per se, suggesting that local feed-forward inhibitory mechanism is pathway specific. Conclusions: Our results suggest that the effect of lateral orbitofrontal cortex inhibitory modulatory gating was effective up to 500 milliseconds and that intra-amygdala GABAA and GABAB receptors differentially modulate the short- and long-delay lateral orbitofrontal cortex inhibitory gating on the medial prefrontal cortex-amygdala pathway.

Dopaminergic Modulation of Lateral Amygdala Neuronal Activity: Differential D1 and D2 Receptor Effects on Thalamic and Cortical Afferent Inputs.

BACKGROUND: In auditory fear conditioning, the lateral nucleus of the amygdala (LA) integrates a conditioned stimulus (CS) from the auditory thalamus (MGN) and the auditory association cortex (Te3) with an aversive unconditioned stimulus. The thalamic input provides a basic version of the CS, while the cortical input provides a processed representation of the stimulus. Dopamine (DA) is released in the LA under heightened arousal during the presentation of the CS. METHODS: In this study we examined how D1 or D2 receptor activation affects LA afferent-driven neuronal firing using in vivo extracellular single-unit recordings with local micro-iontophoretic drug application in anesthetized rats. LA neurons that were responsive (~50%) to electrical stimulation in either the MGN or the Te3 were tested by iontophoresis of either the D1 agonist, SKF38393, or the D2 agonist, quinpirole. RESULTS: We found that most of the LA projection neurons exhibited either facilitatory or attenuating effects (changes in evoked probability >15% relative to baseline) on afferent input by activation of D1 or D2 receptors. In general, it required significantly higher stimulation current to evoke ~50% baseline responses to the cortical input. Activation of the D1 receptor showed no difference in modulation between the thalamic or cortical pathways. On the other hand, activation of the D2 receptor had a stronger inhibitory modulation of the cortical pathway, but a stronger excitatory modulation of the thalamic pathway. CONCLUSIONS: Our results suggest that there is a shift in balance favoring the thalamic pathway in response to DA acting via the D2 receptor.

Amygdala ß-noradrenergic receptors modulate delayed downregulation of dopamine activity following restraint.

Stress, which involves a heightened arousal and excitability, triggers important adaptive responses to maintain homeostasis and prepare a response. In the current studies, we administered a psychological stressor of 2 h acute restraint on rats, and found that 24 h after the cessation of the restraint session, there was a significant decrease in ventral tegmental area dopaminergic (DA) neuron population activity and a significant attenuation in amphetamine-induced locomotor activity. Systemic or intra-basolateral nuclei of the amygdala administration of the ß-noradrenergic receptor antagonist, propranolol, reversed the decrease, suggesting that the delayed attenuation of DA neuron firing following a stressor depends on a noradrenaline-mediated mechanism. This alteration in DA activity may adaptively prepare the individual to avoid the stressor, or in the extreme, may be a factor that contributes to pathological changes in behavior or physiological responses.

Anatomical analyses of collateral prefrontal cortex projections to the basolateral amygdala and the nucleus accumbens core in rats.

The basolateral amygdala (BLA) and the nucleus accumbens core (NAcc) share some similar behavioral functions, such as associative learning, Pavlovian to instrumental transfer, and choice behavior. However, their prefrontal anatomical inputs have not been well characterized before, especially the collateral projections. In this study, we analyzed the distribution and collateralization of projections to the BLA and the NAcc from the prefrontal cortices (PFC), including the prelimbic (PL) and the infralimbic (IL) divisions of the medial prefrontal cortex (mPFC) and the subregions of the orbitofrontal cortex (OFC), such as the medial OFC (MO), the lateral OFC (LO), and the ventral OFC (VO). Double retrograde tracing approach was used, in which Cholera toxin subunit B conjugated with the Alexa Fluor 488 (CTB-AF488) or Alexa Fluor 594 (CTB-AF594) were unilaterally injected into the BLA and the NAcc, respectively, in male Long-Evans rats (n = 6). Among the sampled neurons, prefrontal projection to the BLA or the NAcc is more robust on the ipsilateral side, and more robust from the PL, the IL, and the MO compared to from the LO and the VO. The majority of the projections from the PFC to the BLA and/or the NAcc are confined in deep layer. In addition, for each of the prefrontal areas, about 15-25% BLA-projecting neurons send collateral projections to the NAcc, and vice versa. In conclusion, our data suggested that prefrontal control over the BLA and the NAcc is not entirely independent. The functional importance of the collateral projections awaits further examination.

Pharmacological activation of the amygdala, but not single prolonged footshock-induced acute stress, interferes with cue-induced motivation toward food rewards in rats.

In the face of threats, animals adapt their behaviors to cope with the situation. Under such circumstances, irrelevant behaviors are usually suppressed. In this study, we examined whether food-seeking motivation would decrease under activation of the amygdala, an important nucleus in the regulation of stress response in the central nervous system, or after a physical acute stress session. In Experiment 1, we pharmacologically activated the basolateral nucleus (BLA) or the central nucleus of the amygdala (CeA) before a cue-induced reinstatement test in rats. Our results showed that activation of the BLA or the CeA abolished cue-induced motivation toward food rewards, while locomotor activity and free food intake were not affected. In Experiments 2 and 3, we further assessed anxiety and despair levels, as well as cue-induced reinstatement, after a single prolonged footshock-induced acute stress in rats. Behaviorally, acute stress did not affect anxiety level, despair level, or cue-induced motivation toward food rewards. Physiologically, there was no difference in cellular activities of the amygdala immediately after acute stress. To conclude, our results suggested that pharmacological activation of the amygdala decreased cue-induced motivation toward food reward. However, physiological acute stress did not immediately interfere with the negative emotions, motivation, or amygdala activities of the animals.

Activation of the basolateral or the central amygdala dampened the incentive motivation for food reward on high fixed-ratio schedules.

The amygdala plays crucial roles in emotional processing, motivated behaviors, and stress responses. It receives sensory information and modulates fear- and anxiety-related behaviors. Neuronal activations are induced in the basolateral complex of the amygdala (BLA) and the central nucleus of the amygdala (CeA) when exposing to acute stress, leading to increased alertness and proper behavioral adaptation. Previous studies have shown that animals displayed a decrease in appetitive motivated behaviors under stress conditions. However, whether the hyperactive amygdala is responsible for the decrease in appetitive motivated behaviors remains unknown. In this study, we aimed to examine the role of BLA or CeA activation in effort-based motivated behavior. We pharmacologically activated the BLA or the CeA with N-methyl-D-aspartate (NMDA) before the lever-pressing for food reward test on different fixed-ratio (FR) schedules (FR1, FR16, or FR32) in male Long-Evans rats. Our data showed that activation of either the BLA or the CeA with NMDA (0.05 µg in 0.5 µl per site) decreased the lever-pressing behavior on higher FR schedules of FR16 and FR32, but not on the FR1 test. Importantly, locomotor activity and free-feeding food intake were intact under amygdala activation, suggesting that the decrease in lever-pressing behavior was not due to motor disablement or decreased appetite. These results suggested that activation of the BLA or the CeA negatively impaired the effort-based motivated behavior that the animals were less willing to work for food reward.

Medial prefrontal cortex activation facilitates re-extinction of fear in rats.

It has been suggested that reduced infralimbic (IL) cortical activity contributes to impairments of fear extinction. We therefore explored whether pharmacological activation of the IL would facilitate extinction under conditions it normally fails (i.e., immediate extinction). Rats received auditory fear conditioning 1 h before extinction training. Immediately prior to extinction, rats received microinfusions into the IL of the GABA(A) receptor antagonist, picrotoxin, or the NMDA receptor partial agonist, D-cycloserine. Although neither drug facilitated extinction, they both facilitated the subsequent re-extinction of fear when animals were trained in a drug-free state, suggesting that activating the IL primes behavioral extinction.

Aberrant orbitofrontal cortical activation interferes with encoding of Pavlovian fear conditioning.

Obsessive-compulsive disorder (OCD) patients were usually found with the hyper-activation of the orbitofrontal cortex (OFC) and a deficit in fear extinction learning. The OFC can be subdivided into the lateral OFC (lOFC) and the medial OFC (mOFC). Previous studies have suggested that both subregions are involved in the modulation of negative emotions. However, how aberrant activation of the OFC interacts with the encoding of Pavlovian fear remains unknown. In this study, the lOFC or the mOFC was pharmacologically activated or inactivated before the fear conditioning on Day 1, followed by a context test on Day 2 and a tone test on Day 3 in male Long-Evans rats. We found that for the animals that underwent fear conditioning under aberrant activation of either the lOFC or the mOFC, they showed normal within-session fear expression. However, the acquisition/consolidation of contextual fear was impaired under mOFC activation, while the acquisition/consolidation of cued fear was impaired under either the lOFC or the mOFC activation, in that these animals showed lower freezing compared to controls during the retrieval test. On the other hand, for the animals that underwent fear conditioning under inactivation of either the lOFC or the mOFC, they showed normal within-session fear expression, as well as intact encoding of both the contextual and cued fear. Together, our results suggested that the OFC was not actively engaged in the acquisition of Pavlovian fear conditioning, but aberrant activation of the OFC impaired fear learning.

Analysis of lateral orbitofrontal cortex activation on acquisition of fear extinction and neuronal activities in fear circuit.

Inappropriate fear expression and failure of fear extinction are commonly seen in patients with post-traumatic stress disorder (PTSD) and obsessive-compulsive disorder (OCD). Among the patients, aberrant and asymmetric activation of the lateral orbitofrontal cortex (lOFC) is reported in some clinical cases. In this study, we aimed to examine the role of lOFC activation in extinction acquisition and explore the potential functional lateralization of lOFC on extinction. We bilaterally or unilaterally activated the lOFC with N-methyl-D-aspartate (NMDA) before fear extinction acquisition in rats. Our data suggested that both left and bilateral lOFC activation interfered with the in-session expression of conditioned fear, whereas activation of the right lOFC did not. In addition, pre-extinction unilateral or bilateral activation of the lOFC, regardless of the side, impaired the acquisition of fear extinction. We also quantified the neuronal activities during the late phase of extinction with immunohistochemical approach. Our data showed that activation of the lOFC increased the neuronal activities on the injection side(s) in the medial prefrontal cortex (mPFC), the lateral amygdala (LA), the basolateral amygdala (BLA; preferentially the non-GABAergic neurons), and the medial intercalated cells (mITC; preferentially the right side). To conclude, aberrant activation of the lOFC during extinction disturbed the excitatory/inhibitory balance of neuronal activities in fear-related brain regions, which interfered with the expression of conditioned fear and impaired the acquisition of fear extinction.

Medial or lateral orbitofrontal cortex activation during fear extinction differentially regulates fear renewal.

Some anxiety-related disorders, such as panic disorder, specific phobia, post-traumatic stress disorder (PTSD), and obsessive-compulsive disorder (OCD), develop because of the poor regulation and inappropriate expression of fear-related behavior at the wrong place and wrong time. In clinical settings, exposure therapy, which consists of repeated presentation of trauma-related stimuli without real threats in the therapeutic context, is commonly used to treat these disorders. However, 30-50 % of patients suffer from the recurrence of anxiety symptoms after they leave the therapeutic context. This behavioral phenomenon is called renewal. In this study, ABA Pavlovian fear renewal paradigm was used to assess the role of the aberrant orbitofrontal cortex (OFC) activation, a symptom of OCD patients, on fear regulation in laboratory settings. The rats were fear conditioned in one context (context A), extinguished to the tones in another context (context B), and then tested in either context A or B. During extinction, rats were subjected to lateral or medial OFC activation. We found that rats that underwent extinction with either lateral or medial OFC activation were unable to use the context to determine whether it was a safe or dangerous context during renewal test. Interestingly, the rats with lateral OFC activation during extinction showed generally high fear, whereas the rats with medial OFC activation during extinction showed generally low fear. In conclusion, our results suggested that aberrant activation of specifically the lateral OFC may have a negative impact during exposure therapy treatments and results in their poor regulation of fear-related behavior.

Early extinction after fear conditioning yields a context-independent and short-term suppression of conditional freezing in rats.

Extinction of Pavlovian fear conditioning in rats is a useful model for therapeutic interventions in humans with anxiety disorders. Recently, we found that delivering extinction trials soon (15 min) after fear conditioning yields a short-term suppression of fear, but little long-term extinction. Here, we explored the possible mechanisms underlying this deficit by assessing the suppression of fear to a CS immediately after extinction training (Experiment 1) and the context specificity of fear after both immediate and delayed extinction training (Experiment 2). We also examined the time course of the immediate extinction deficit (Experiment 3). Our results indicate that immediate extinction produces a short-lived and context-independent suppression of conditional freezing. Deficits in long-term extinction were apparent even when the extinction trials were given up to 6 h after conditioning. Moreover, this deficit was not due to different retention intervals that might have influenced the degree of spontaneous recovery after immediate and delayed extinction (Experiment 4). These results suggest that fear suppression under immediate extinction may be due to a short-term, context-independent habituation process, rather than extinction per se. Long-term extinction memory only develops when extinction training occurs at least six hours after conditioning.