Divergent projections of the prelimbic cortex bidirectionally regulate active avoidance.
ABSTRACT: The prefrontal cortex (PFC) integrates incoming information to guide our actions. When motivation for food-seeking competes with avoidance of danger, the PFC likely plays a role in selecting the optimal choice. In platform-mediated active avoidance, rats avoid a tone-signaled footshock by stepping onto a nearby platform, delaying access to sucrose pellets. This avoidance requires prelimbic (PL) PFC, basolateral amygdala (BLA), and ventral striatum (VS). We previously showed that inhibitory tone responses of PL neurons correlate with avoidability of shock (Diehl et al., 2018). Here, we optogenetically modulated PL terminals in VS and BLA to identify PL outputs regulating avoidance. Photoactivating PL-VS projections reduced avoidance, whereas photoactivating PL-BLA projections increased avoidance. Moreover, photosilencing PL-BLA or BLA-VS projections reduced avoidance, suggesting that VS receives opposing inputs from PL and BLA. Bidirectional modulation of avoidance by PL projections to VS and BLA enables the animal to make appropriate decisions when faced with competing drives.
Project description:Much is known about the neural circuits of conditioned fear and its relevance to understanding anxiety disorders, but less is known about other anxiety-related behaviors such as active avoidance. Using a tone-signaled, platform-mediated avoidance task, we observed that pharmacological inactivation of the prelimbic prefrontal cortex (PL) delayed avoidance. Surprisingly, optogenetic silencing of PL glutamatergic neurons did not delay avoidance. Consistent with this, inhibitory but not excitatory responses of rostral PL neurons were associated with avoidance training. To test the importance of these inhibitory responses, we optogenetically stimulated PL neurons to counteract the tone-elicited reduction in firing rate. Photoactivation of rostral (but not caudal) PL neurons at 4 Hz impaired avoidance. These findings suggest that inhibitory responses of rostral PL neurons signal the avoidability of a potential threat and underscore the importance of designing behavioral optogenetic studies based on neuronal firing responses.
Project description: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.
Project description:The prefrontal cortex and amygdala are anatomical substrates linked to both social information and emotional valence processing, but it is not known whether sub-circuits in the medial prefrontal cortex (mPFC) that project to the basolateral amygdala (BLA) are recruited and functionally contribute to social approach-avoidance behavior. Using retrograde labeling of mPFC projections to the BLA, we find that BLA-projecting neurons in the infralimbic cortex (IL) are preferentially activated in response to a social cue as compared with BLA-projecting neurons in the prelimbic cortex (PL). Chemogenetic interrogation of these sub-circuits shows that activation of PL-BLA or inhibition of IL-BLA circuits impairs social behavior. Sustained closed-loop optogenetic activation of PL-BLA circuitry induces social impairment, corresponding to a negative emotional state as revealed by real-time place preference behavioral avoidance. Reactivation of foot shock-responsive PL-BLA circuitry impairs social behavior. Altogether, these data suggest a circuit-level mechanism by which valence-encoding mPFC-BLA sub-circuits shape social approach-avoidance behavior.
Project description:Associative learning can enable environmental cues to signal food and stimulate feeding, independent of physiological hunger. Two forebrain regions necessary in cue driven feeding, the basolateral area of the amygdala and the medial prefrontal cortex, communicate via extensive, topographically organized connections. The basolateral nucleus (BLA) sends extensive projections to the prelimbic cortex (PL), and our aim here was to determine if this pathway was selectively recruited during cue-food associative learning. The anterior and posterior basolateral nuclei are recruited during different phases of cue-food learning, and thus we examined whether distinct pathways that originate in these nuclei and project to the PL are differently recruited during early and late stages of learning. To accomplish this we used neuroanatomical tract tracing combined with the detection of Fos induction. To identify projecting neurons within the BLA, prior to training, rats received a retrograde tracer, Fluoro-Gold (FG) into the PL. Rats were given either one or ten sessions of tone-food presentations (Paired group) or tone-only presentations (Control group). The Paired group learned the tone-food association quickly and robustly and had greater Fos induction within the anterior and posterior BLA during early and late learning compared to the Control group. Notably, the Paired group had more double-labeled neurons (FG + Fos) during late training compared to the Control group, specifically in the anterior BLA. This demonstrates selective recruitment of the anterior BLA-PL pathway by late cue-food learning. These findings indicate plasticity and specificity in the BLA-PL pathways across cue-food associative learning.
Project description:The prefrontal cortex (PFC) regulates emotional behavior via top-down control of the basolateral amygdala (BLA). However, the influence of PFC inputs on the different projection pathways within the BLA remains largely unexplored. Here, we combine whole-cell recordings and optogenetics to study these cell-type specific connections in mouse BLA. We characterize PFC inputs onto three distinct populations of BLA neurons that project to the PFC, ventral hippocampus, or nucleus accumbens. We find that PFC-evoked synaptic responses are strongest at amygdala-cortical and amygdala-hippocampal neurons and much weaker at amygdala-striatal neurons. We assess the mechanisms for this targeting and conclude that it reflects fewer connections onto amygdala-striatal neurons. Given the similar intrinsic properties of these cells, this connectivity allows the PFC to preferentially activate amygdala-cortical and amygdala-hippocampal neurons. Together, our findings reveal how PFC inputs to the BLA selectively drive feedback projections to the PFC and feedforward projections to the hippocampus.
Project description:Many forms of behavior require selective amplification of neuronal representations of relevant environmental signals. Emotional learning enhances sensory responses in the sensory cortex, yet the underlying circuits remain poorly understood. We identify a pathway between the basolateral amygdala (BLA), an emotional learning center in the mouse brain, and the inhibitory reticular nucleus of the thalamus (TRN). Optogenetic activation of BLA suppressed spontaneous, but not tone-evoked, activity in the auditory cortex (AC), amplifying tone-evoked responses. Viral tracing identified BLA projections terminating at TRN. Optogenetic activation of amygdala-TRN projections further amplified tone-evoked responses in the auditory thalamus and cortex. The results are explained by a computational model of the thalamocortical circuitry, in which activation of TRN by BLA primes thalamocortical neurons to relay relevant sensory input. This circuit mechanism shines a neural spotlight on behaviorally relevant signals and provides a potential target for the treatment of neuropsychological disorders.
Project description:Chronic social isolation stress during adolescence induces susceptibility for neuropsychiatric disorders. Here we show that 5-week post-weaning isolation stress induces sex-specific behavioral abnormalities and neuronal activity changes in the prefrontal cortex (PFC), basal lateral amygdala (BLA), and ventral tegmental area (VTA). Chemogenetic manipulation, optogenetic recording, and in vivo calcium imaging identify that the PFC to BLA pathway is causally linked to heightened aggression in stressed males, and the PFC to VTA pathway is causally linked to social withdrawal in stressed females. Isolation stress induces genome-wide transcriptional alterations in a region-specific manner. Particularly, the upregulated genes in BLA of stressed males are under the control of activated transcription factor CREB, and CREB inhibition in BLA normalizes gene expression and reverses aggressive behaviors. On the other hand, neuropeptide Hcrt (Hypocretin/Orexin) is among the top-ranking downregulated genes in VTA of stressed females, and Orexin-A treatment rescues social withdrawal. These results have revealed molecular mechanisms and potential therapeutic targets for stress-related mental illness. Overall design: Male control BLA (3 replicates) vs male stress BLA (3 replicates), female control VTA (3 replicates) vs female stress VTA (3 replicates)
Project description:Brain-derived neurotrophic factor (BDNF) is critical for establishing activity-related neural plasticity. There is increasing interest in the mechanisms of active avoidance and its extinction, but little is known about the role of BDNF in these processes. Using the platform-mediated avoidance task combined with local infusions of an antibody against BDNF, we show that blocking BDNF in either prelimbic (PL) or infralimbic (IL) medial prefrontal cortex during extinction training impairs subsequent recall of extinction of avoidance, differing from extinction of conditioned freezing. By combining retrograde tracers with BDNF immunohistochemistry, we show that extinction of avoidance increases BDNF expression in ventral hippocampal (vHPC) neurons, but not amygdala neurons, projecting to PL and IL. Using the CRISPR/Cas9 system, we further show that reducing BDNF production in vHPC neurons impairs recall of avoidance extinction. Thus, the vHPC may mediate behavioral flexibility in avoidance by driving extinction-related plasticity via BDNFergic projections to both PL and IL. These findings add to the growing body of knowledge implicating the hippocampal-prefrontal pathway in anxiety-related disorders and extinction-based therapies.
Project description:Orchestrating appropriate behavioral responses in the face of competing signals that predict either rewards or threats in the environment is crucial for survival. The basolateral nucleus of the amygdala (BLA) and prelimbic (PL) medial prefrontal cortex have been implicated in reward-seeking and fear-related responses, but how information flows between these reciprocally connected structures to coordinate behavior is unknown. We recorded neuronal activity from the BLA and PL while rats performed a task wherein competing shock- and sucrose-predictive cues were simultaneously presented. The correlated firing primarily displayed a BLA?PL directionality during the shock-associated cue. Furthermore, BLA neurons optogenetically identified as projecting to PL more accurately predicted behavioral responses during competition than unidentified BLA neurons. Finally photostimulation of the BLA?PL projection increased freezing, whereas both chemogenetic and optogenetic inhibition reduced freezing. Therefore, the BLA?PL circuit is critical in governing the selection of behavioral responses in the face of competing signals.
Project description:Ensembles of principal neurons in the basolateral amygdala (BLA) generate the initial engrams for fear memories, while projections from the BLA to the medial prefrontal cortex (mPFC) are essential for the encoding, transfer and storage of remote fear memories. We tested the effects of chronic pain on remote fear memories in mice. Male mice underwent classic fear conditioning by pairing a single tone (conditional stimulus, CS) with a single electric foot shock (unconditional stimulus, US). Sciatic nerve constriction was used to induce neuropathic pain at various time points before or after the fear conditioning. The mice with sciatic nerve cuffs implanted 48 h after the fear conditioning showed an increased freezing response to CS when compared to mice without cuffs or when compared to mice in which the nerve cuffing was performed 48 h before the fear conditioning. The enhancing effect of pain on consolidated fear memory was further tested and mice in which the nerve cuffing was performed 14 days after the fear conditioning also showed an increased fear response when tested 56 days later. We used immunostaining to detect morphological changes in the BLA that could suggest a mechanism for the observed increase in fear response. We found an increased number of calbindin/parvalbumin positive neurons in the BLA and increased perisomatic density of GAD65 on projection neurons that connect BLA to mPFC in mice with nerve cuffs. Despite the strong increase of c-Fos expression in BLA and mPFC that was induced by fear recall, neither the BLA to mPFC nor the mPFC to BLA projection neurons were activated in mice with nerve cuffs. Furthermore, non-injured mice had an increased fear response when BLA to mPFC projections were inhibited by a chemogenetic method. In conclusion, this study provides evidence that persistent pain has a significant impact on consolidated fear memories. Very likely the underlying mechanism for this phenomenon is increased inhibitory input onto the BLA to mPFC projection neurons, possibly from neurons with induced parvalbumin expression. Conceivably, the increased fear response to consolidated fear memory is a harbinger for the later development of anxiety and depression symptoms associated with chronic pain.