Glucocorticoids interact with the noradrenergic arousal system in the nucleus accumbens shell to enhance memory consolidation of both appetitive and aversive taste learning

Duration of aversive memory in zebrafish after a single shock

Studies on memory consolidation and reconsolidation, memory loss, and the associated biochemical mechanisms have garnered interest in the past decades due to knowledge of memory performance-affecting factors such as stress, emotions, sleep, age, several neurological diseases, drugs, and chemical pollutants. Memory research has been using animal models, with increased interest in the zebrafish model. This freshwater fish species shows a wide range of behaviors relevant to memory research such as social behavior, aggression, and predator avoidance; however, few studies have investigated the duration of long-term memory. Hence, we designed an experiment to test memory duration by exposing zebrafish to avoidance conditioning using electroshock as the aversive stimulus. Zebrafish were trained to avoid the black side of a black-and-white tank and subsequently tested for aversive memory at 24 h, 48 h, 72 h, 96 h, 168 h, and 240 h. At the 72 h-interval, another zebrafish group was trained and exposed to MK-801(NMDAr antagonist) and then tested. The fish retained memories of the task and avoided the black side of the tank for up to 7 days. At 10 days post-training, the animals could no longer retrieve the aversive memory. Zebrafish treated with MK-801 did not retrieve memory. Knowledge of memory and of long-term memory duration is crucial for optimizing the zebrafish model for use in research investigating cognitive impairments such as memory loss and its ramifications. Additionally, identifying a long-term aversive memory lasting up to 7 days in zebrafish enables further research into the neuronal changes underlying this persistence. Such in-depth investigation could bring valuable insights into memory mechanisms and facilitate targeted interventions for memory-related conditions.

Drawbacks to Strengthening Neural Salience Encoding: A Link Between Cortisol and Risky Drinking

Emotionally salient experiences are encoded and remembered more strongly, an effect that can be amplified by hormones like cortisol. Such memories can in turn profoundly influence later behavior. However, little is known about the link between amplified salience encoding and subsequent behavior. This pathway may be particularly important for risky alcohol drinking, which has been linked to sensitized salience responses, memory, and cortisol. To test this possibility, we integrated pharmacology using a double-blind cross-over design with fMRI, cognitive, and motivation assays across a range of healthy male and female social drinkers. As anticipated, cortisol enhanced memory for salient alcohol-related events; critically, this bias was in turn associated with later alcohol motivation. Increased alcohol motivation was particularly pronounced in more susceptible risky drinkers, for whom cortisol enhanced brain salience responses to alcohol. These sensitized salience responses predicted both memory biases and alcohol motivation. Together, these findings reveal maladaptive consequences of enhanced salience encoding.

Viscerosensory signalling to the nucleus accumbens via the solitary tract nucleus

The nucleus of the solitary tract (NTS) receives direct viscerosensory vagal afferent input that drives autonomic reflexes, neuroendocrine function and modulates behaviour. A subpopulation of NTS neurons project to the nucleus accumbens (NAc); however, the function of this NTS-NAc pathway remains unknown. A combination of neuroanatomical tracing, slice electrophysiology and fibre photometry was used in mice and/or rats to determine how NTS-NAc neurons fit within the viscerosensory network. NTS-NAc projection neurons are predominantly located in the medial and caudal portions of the NTS with 54 ± 7% (mice) and 65 ± 3% (rat) being TH-positive, representing the A2 NTS cell group. In horizontal brainstem slices, solitary tract (ST) stimulation evoked excitatory post-synaptic currents (EPSCs) in NTS-NAc projection neurons. The majority (75%) received low-jitter, zero-failure EPSCs characteristic of monosynaptic ST afferent input that identifies them as second order to primary sensory neurons. We then examined whether NTS-NAc neurons respond to cholecystokinin (CCK, 20 μg/kg ip) in vivo in both mice and rats. Surprisingly, there was no difference in the number of activated NTS-NAc cells between CCK and saline-treated mice. In rats, just 6% of NTS-NAc cells were recruited by CCK. As NTS TH neurons are the primary source for NAc noradrenaline, we measured noradrenaline release in the NAc and showed that NAc noradrenaline levels declined in response to cue-induced reward retrieval but not foot shock. Combined, these findings suggest that high-fidelity afferent information from viscerosensory afferents reaches the NAc. These signals are likely unrelated to CCK-sensitive vagal afferents but could interact with other sensory and higher order inputs to modulate learned appetitive behaviours.

Orexins/Hypocretins: Gatekeepers of Social Interaction and Motivation

Ever since the discovery of the brain's orexin/hypocretin system, most research was directed toward unveiling its contribution to the normal functioning of individuals. The investigation of reward-seeking behaviors then gained a lot of attention once the distribution of orexinergic neurons was revealed. Here, we discuss findings on the involvement of orexins in social interaction, a natural reward type. While some studies have succeeded in defining the relationship between orexin and social interaction, the controversy regarding its nature (direct or inverse relation) raises questions about what aspects have been overlooked until now. Upon examining the literature, we identified a research gap concerning conditions influencing the impact of orexins on social behavior expression. In this review, we introduce a number of factors (e.g., stress, orexin's source) that must be considered while studying the role of orexins in social interaction. Furthermore, we refer to published research to investigate the stage at which orexins affect social interaction and we highlight the nucleus accumbens (NAc) shell's role in social interaction and other rewarding behaviors. Finally, the underlying orexin molecular pathway influencing social motivation in particular illnesses is proposed. We conclude that orexin's impact on social interaction is multifactorial and depends on specific conditions available at a time.

Stress-related cellular pathophysiology as a crosstalk risk factor for neurocognitive and psychiatric disorders

In this narrative review, we examine biological processes linking psychological stress and cognition, with a focus on how psychological stress can activate multiple neurobiological mechanisms that drive cognitive decline and behavioral change. First, we describe the general neurobiology of the stress response to define neurocognitive stress reactivity. Second, we review aspects of epigenetic regulation, synaptic transmission, sex hormones, photoperiodic plasticity, and psychoneuroimmunological processes that can contribute to cognitive decline and neuropsychiatric conditions. Third, we explain mechanistic processes linking the stress response and neuropathology. Fourth, we discuss molecular nuances such as an interplay between kinases and proteins, as well as differential role of sex hormones, that can increase vulnerability to cognitive and emotional dysregulation following stress. Finally, we explicate several testable hypotheses for stress, neurocognitive, and neuropsychiatric research. Together, this work highlights how stress processes alter neurophysiology on multiple levels to increase individuals' risk for neurocognitive and psychiatric disorders, and points toward novel therapeutic targets for mitigating these effects. The resulting models can thus advance dementia and mental health research, and translational neuroscience, with an eye toward clinical application in cognitive and behavioral neurology, and psychiatry.

Neurofunctional underpinnings of individual differences in visual episodic memory performance

Episodic memory, the ability to consciously recollect information and its context, varies substantially among individuals. While prior fMRI studies have identified certain brain regions linked to successful memory encoding at a group level, their role in explaining individual memory differences remains largely unexplored. Here, we analyze fMRI data of 1,498 adults participating in a picture encoding task in a single MRI scanner. We find that individual differences in responsivity of the hippocampus, orbitofrontal cortex, and posterior cingulate cortex account for individual variability in episodic memory performance. While these regions also emerge in our group-level analysis, other regions, predominantly within the lateral occipital cortex, are related to successful memory encoding but not to individual memory variation. Furthermore, our network-based approach reveals a link between the responsivity of nine functional connectivity networks and individual memory variability. Our work provides insights into the neurofunctional correlates of individual differences in visual episodic memory performance.

Elevated corticosterone after fear learning impairs remote auditory memory retrieval and alters brain network connectivity

Glucocorticoids are potent memory modulators that can modify behavior in an adaptive or maladaptive manner. Elevated glucocorticoid levels after learning promote memory consolidation at recent time points, but their effects on remote time points are not well established. Here we set out to assess whether corticosterone (CORT) given after learning modifies remote fear memory. To that end, mice were exposed to a mild auditory fear conditioning paradigm followed by a single 2 mg/kg CORT injection, and after 28 d, auditory memory was assessed. Neuronal activation was investigated using immunohistochemistry for the immediate early gene c-Fos, and coactivation of brain regions was determined using a correlation matrix analysis. CORT-treated mice displayed significantly less remote auditory memory retrieval. While the net activity of studied brain regions was similar compared with the control condition, CORT-induced remote memory impairment was associated with altered correlated activity between brain regions. Specifically, connectivity of the lateral amygdala with the basal amygdala and the dorsal dentate gyrus was significantly reduced in CORT-treated mice, suggesting disrupted network connectivity that may underlie diminished remote memory retrieval. Elucidating the pathways underlying these effects could help provide mechanistic insight into the effects of stress on memory and possibly provide therapeutic targets for psychopathology.

Benzophenone-3 causes oxidative stress in the brain and impairs aversive memory in adult zebrafish

Oxybenzone (BP-3) is an ultraviolet (UV) filter widely used in industries that is directly or indirectly released into the aquatic environment. However, little is known about its effects on brain performance. Here, we investigated whether BP-3 exposure affects the redox imbalance in zebrafish and how they respond to a task that requires memory of an aversive situation. Fish were exposed to BP-3 10 and 50 μg L-1 for 15 days and then tested using an associative learning protocol with electric shock as a stimulus. Brains were extracted for reactive oxygen species (ROS) measurement and qPCR analysis of antioxidant enzyme genes. ROS production increased for exposed animals, and catalase (cat) and superoxide dismutase 2 (sod 2) were upregulated. Furthermore, learning and memory were reduced in zebrafish exposed to BP-3. These results suggested that BP-3 may lead to a redox status imbalance, causing impaired cognition and reinforcing the need to replace the toxic UV filters with filters that minimize environmental effects.

Stress effects on the top-down control of visuospatial attention: Evidence from cue-dependent alpha oscillations

Stress is assumed to inhibit the top-down control of attention and to facilitate bottom-up processing. Evidence from human experiments, however, remains scarce. Previous studies have addressed how stress affects the interplay of bottom-up and top-down mechanisms of attention. A key open question is in how far such effects can actually be attributed to a stress-induced modulation of top-down attention control. We sought to isolate top-down from bottom-up effects by assessing stress effects on anticipatory changes in alpha oscillations that precede stimulus processing. Participants performed in a cued target detection task in which a cue prompted them to covertly shift their attention to left or right screen positions, 20 min after being exposed to the bilateral feet cold pressor test or a warm water control procedure. The stressor led to a substantial increase in cortisol, peaking 20 min post stressor, along with rises in heart rate, blood pressure, and subjective ratings of stress and arousal. As expected, cued attention deployment led to higher alpha power over posterior electrodes contralateral versus ipsilateral to the attended hemifield during the cue-target interval. Importantly, this purely endogenous effect was potentiated by stress, however, significant differences were restricted to the middle of the cue-target interval and thus temporally separated from the appearance of the target. These results indicate that stress does not impair top-down attentional control per se but may introduce a qualitative change modulating the way attention is deployed to meet action goals.

Corticosterone Levels and Glucocorticoid Receptor Gene Expression in High Drinking in the Dark Mice and Their Heterogeneous Stock (HS/NPT) Founder Line

The High Drinking in the Dark (HDID-1) line of mice has been selectively bred for achieving high blood alcohol levels (BALs) in the Drinking in the Dark task, a model of binge-like drinking. Recently, we determined that glucocorticoid receptor (GR) antagonism with either mifepristone or CORT113176 (a selective GR antagonist) reduced binge-like ethanol intake in the HDID-1 mice, but not in their founder line, HS/NPT. Here, we examined whether the selection process may have altered glucocorticoid functioning by measuring (1) plasma corticosterone levels and (2) expression of the genes encoding GR (Nr3c1) and two of its chaperone proteins FKBP51 and FKBP52 (Fkbp5 and Fkbp4) in the brains (nucleus accumbens, NAc) of HDID-1 and HS/NPT mice. We observed no genotype differences in baseline circulating corticosterone levels. However, HDID-1 mice exhibited a greater stimulated peak corticosterone response to an IP injection (of either ethanol or saline) relative to their founder line. We further observed reduced basal expression of Fkbp4 and Nr3c1 in the NAc of HDID-1 mice relative to HS/NPT mice. Finally, HDID-1 mice exhibited reduced Fkbp5 expression in the NAc relative to HS/NPT mice following an injection of 2 g/kg ethanol. Together, these data suggest that selective breeding for high BALs may have altered stress signaling in the HDID-1 mice, which may contribute to the observed selective efficacy of GR antagonism in reducing binge-like ethanol intake in HDID-1, but not HS/NPT mice. These data have important implications for the role that stress signaling plays in the genetic risk for binge drinking.

Extended amygdala, conditioned withdrawal and memory consolidation

Opioid withdrawal can be associated to environmental cues through classical conditioning. Exposure to these cues can precipitate a state of conditioned withdrawal in abstinent subjects, and there are suggestions that conditioned withdrawal can perpetuate the addiction cycle in part by promoting the storage of memories. This review discusses evidence supporting the hypothesis that conditioned withdrawal facilitates memory consolidation by activating a neurocircuitry that involves the extended amygdala. Specifically, the central amygdala, the bed nucleus of the stria terminalis, and the nucleus accumbens shell interact functionally during withdrawal, mediate expression of conditioned responses, and are implicated in memory consolidation. From this perspective, the extended amygdala could be a neural pathway by which drug-seeking behaviour performed during a state of conditioned withdrawal is more likely to become habitual and persistent.

Amphetamine Modulation of Long-Term Object Recognition Memory in Rats: Influence of Stress

Amphetamine is a potent psychostimulant that increases brain monoamine levels. Extensive evidence demonstrated that norepinephrine is crucially involved in the regulation of memory consolidation for stressful experiences. Here, we investigated amphetamine effects on the consolidation of long-term recognition memory in rats exposed to different intensities of forced swim stress immediately after training. Furthermore, we evaluated whether such effects are dependent on the activation of the peripheral adrenergic system. To this aim, male adult Sprague Dawley rats were subjected to an object recognition task and intraperitoneally administered soon after training with amphetamine (0.5 or 1 mg/kg), or its corresponding vehicle. Rats were thereafter exposed to a mild (1 min, 25 ± 1°C) or strong (5 min, 19 ± 1°C) forced swim stress procedure. Recognition memory retention was assessed 24-h after training. Our findings showed that amphetamine enhances the consolidation of memory in rats subjected to mild stress condition, while it impairs long-term memory performance in rats exposed to strong stress. These dichotomic effects is dependent on stress-induced activation of the peripheral adrenergic response.

Accumbens and amygdala in taste recognition memory: The role of d1 dopamine receptors

The attenuation of taste neophobia (AN) is a good model for studying the structural and neurochemical mechanisms of the emotional component of memory because taste recognition memory exhibits the unique feature of being necessarily linked to hedonic properties. Whilst novel tastes elicit cautious neophobic responses, taste exposures which are not followed by aversive consequences attenuate neophobia as the taste becomes safe and palatable. Given the involvement of the nucleus accumbens in reward and of the amygdala in emotional memories, we applied c-Fos immunohistochemistry as an index of neural activity in Wistar rats that were exposed to a vinegar solution for one, two or six days. An inverse pattern of accumbens nucleus vs amygdala activity was found on the second exposure day on which AN occurred. The number of c-Fos positive cells in the nucleus accumbens shell increased whilst the number of c-Fos positive cells in the basolateral amygdala decreased. Further analyses revealed a positive correlation between AN and the number of c-Fos positive cells in the accumbens shell but a negative correlation in the basolateral amygdala. Furthermore the accumbens-amygdala interplay relevant for AN seems to be mediated by dopamine D1 receptors (D1DR). The injection of SCH23390 (D1DR antagonist) in both the accumbens shell and the basolateral amygdala on the second taste exposure resulted in selectively impaired AN but had opposite long term effects. This finding supports the relevance of a dopaminergic network mediated by D1DRs in the nucleus accumbens shell and basolateral amygdala which is critical for adding the emotional component during the formation of taste memory.

Targeting the Glucocorticoid Receptor Reduces Binge-Like Drinking in High Drinking in the Dark (HDID-1) Mice

BACKGROUND

Chronic alcohol exposure can alter glucocorticoid receptor (GR) function in some brain areas that promotes escalated and compulsive-like alcohol intake. GR antagonism can prevent dependence-induced escalation in drinking, but very little is known about the role of GR in regulating high-risk nondependent alcohol intake. Here, we investigate the role of GR in regulating binge-like drinking and aversive responses to alcohol in the High Drinking in the Dark (HDID-1) mice, which have been selectively bred for high blood ethanol (EtOH) concentrations (BECs) in the Drinking in the Dark (DID) test, and in their founder line, the HS/NPT.

METHODS

In separate experiments, male and female HDID-1 mice were administered one of several compounds that inhibited GR or its negative regulator, FKBP51 (mifepristone [12.5, 25, 50, 100 mg/kg], CORT113176 [20, 40, 80 mg/kg], and SAFit2 [10, 20, 40 mg/kg]) during a 2-day DID task. EtOH consumption and BECs were measured. EtOH conditioned taste and place aversion (CTA and CPA, respectively) were measured in separate HDID-1 mice after mifepristone administration to assess GR's role in regulating the conditioned aversive effects of EtOH. Lastly, HS/NPT mice were administered CORT113176 during DID to assess whether dissimilar effects from those of HDID-1 would be observed, which could suggest that selective breeding had altered sensitivity to the effects of GR antagonism on binge-like drinking.

RESULTS

GR antagonism (with both mifepristone and CORT113176) selectively reduced binge-like EtOH intake and BECs in the HDID-1 mice, while inhibition of FKBP51 did not alter intake or BECs. In contrast, GR antagonism had no effect on EtOH intake or BECs in the HS/NPT mice. Although HDID-1 mice exhibit attenuated EtOH CTA, mifepristone administration did not enhance the aversive effects of EtOH in either a CTA or CPA task.

CONCLUSION

These data suggest that the selection process increased sensitivity to GR antagonism on EtOH intake in the HDID-1 mice, and support a role for the GR as a genetic risk factor for high-risk alcohol intake.

Enhancing memory with stress: Progress, challenges, and opportunities

Stress can strongly influence what we learn and remember, including by making memories stronger. Experiments probing stress effects on hippocampus-dependent memory in rodents have revealed modulatory factors and physiological mechanisms by which acute stress can enhance long-term memory. However, extending these findings and mechanisms to understand when stress will enhance declarative memory in humans faces important challenges. This review synthesizes human and rodent studies of stress and memory, examining translational gaps related to measurements of declarative memory and stress responses in humans. Human studies diverge from rodent research by assessing declarative memories that may not depend on the hippocampus and by measuring peripheral rather than central stress responses. This highlights opportunities for future research across species, including assessing stress effects on hippocampal-dependent memory processes in humans and relating peripheral stress responses to stress effects on the function of memory-related brain regions in rodents. Together, these investigations will facilitate the translation of stress effects on memory function from rodents to humans and inform interventions that can harness the positive effects of stress on long-term memory.

Presynaptic α2-adrenoceptor modulates glutamatergic synaptic transmission in rat nucleus accumbens in vitro

The nucleus accumbens (NAc), integrating information from the prefrontal cortex and limbic structures, plays a critical role in reward and emotion regulation. Previous studies have reported that the NAc shell receives direct noradrenergic projections, and activation of α₂-adrenoceptor (α₂-AR) in the NAc shell decreases the fear or anxiety level of rats. However, the underlying mechanism is still little known. Intriguingly, glutamatergic neurotransmission in the NAc shell is closely related to reward and emotion. Here, using brain slice preparations and whole-cell patch clamp recordings, we examined the effect of activation of α₂-AR on glutamatergic neurotransmission in the NAc shell. Perfusing slice with α₂-AR selective agonist clonidine (CLON) reduced the evoked excitatory postsynaptic currents (EPSCs) on the NAc shell neurons. This inhibitory effect on AMPA-mediated glutamatergic EPSCs was blocked by the α₂-AR selective antagonist yohimbine (YOH). Notably, CLON reduced the frequency but not the amplitude of miniature EPSCs. Furthermore, CLON decreased the first EPSC amplitude but increased the paired-pulse facilitation on the NAc shell neurons, and it did not affect postsynaptic AMPA/NMDA ratio, revealing a presynaptic mechanism of α₂-AR-mediated inhibition on glutamatergic transmission. In addition, the modulation on glutamatergic transmission by α₂-AR was independent of presynaptic NMDA receptor. These results suggest that noradrenergic afferent inputs may suppress glutamatergic synaptic transmission via presynaptic α₂-AR in the NAc shell, and actively participate in rewarding and emotional processes via the NAc.

Emotional Modulation of Learning and Memory: Pharmacological Implications

Memory consolidation involves the process by which newly acquired information becomes stored in a long-lasting fashion. Evidence acquired over the past several decades, especially from studies using post-training drug administration, indicates that emotional arousal during the consolidation period influences and enhances the strength of the memory and that multiple different chemical signaling systems participate in this process. The mechanisms underlying the emotional influences on memory involve the release of stress hormones and activation of the basolateral amygdala, which work together to modulate memory consolidation. Moreover, work suggests that this amygdala-based memory modulation occurs with numerous types of learning and involves interactions with many different brain regions to alter consolidation. Additionally, studies suggest that emotional arousal and amygdala activity in particular influence synaptic plasticity and associated proteins in downstream brain regions. This review considers the historical understanding for memory modulation and cellular consolidation processes and examines several research areas currently using this foundational knowledge to develop therapeutic treatments.

NMDA and dopamine D1 receptors within NAc-shell regulate IEG proteins expression in reward circuit during cocaine memory reconsolidation

Reactivation of consolidated memory initiates a memory reconsolidation process, during which the reactivated memory is susceptible to strengthening, weakening or updating. Therefore, effective interference with the memory reconsolidation process is expected to be an important treatment for drug addiction. The nucleus accumbens (NAc) has been well recognized as a pathway component that can prevent drug relapse, although the mechanism underlying this function is poorly understood. We aimed to clarify the regulatory role of the NAc in the cocaine memory reconsolidation process, by examining the effect of applying different pharmacological interventions to the NAc on Zif 268 and Fos B expression in the entire reward circuit after cocaine memory reactivation. Through the cocaine-induced conditioned place preference (CPP) model, immunohistochemical and immunofluorescence staining for Zif 268 and Fos B were used to explore the functional activated brain nuclei after cocaine memory reactivation. Our results showed that the expression of Zif 268 and Fos B was commonly increased in the medial prefrontal cortex (mPFC), the infralimbic cortex (IL), the NAc-core, the NAc-shell, the hippocampus (CA1, CA2, and CA3 subregions), the amygdala, the ventral tegmental area (VTA), and the supramammillary nucleus (SuM) following memory reconsolidation, and Zif 268/Fos B co-expression was commonly observed (for Zif 268: 51-68%; for Fos B: 52-66%). Further, bilateral NAc-shell infusion of MK 801 and SCH 23390, but not raclopride or propranolol, prior to addictive memory reconsolidation, decreased Zif 268 and Fos B expression in the entire reward circuit, except for the amygdala, and effectively disturbed subsequent CPP-related behavior. In summary, N-methyl-d-aspartate (NMDA) and dopamine D1 receptors, but not dopamine D2 or β adrenergic receptors, within the NAc-shell, may regulate Zif 268 and Fos B expression in most brain nuclei of the reward circuit after cocaine memory reactivation. These findings indicated that the NAc played a key role in regulating addictive memory reconsolidation by influencing the function of the entire addictive memory network.

Peripheral and central effects of circulating catecholamines

Physical challenges, emotional arousal, increased physical activity, or changes in the environment can evoke stress, requiring altered activity of visceral organs, glands, and smooth muscles. These alterations are necessary for the organism to function appropriately under these abnormal conditions and to restore homeostasis. These changes in activity comprise the "fight-or-flight" response and must occur rapidly or the organism may not survive. The rapid responses are mediated primarily via the catecholamines, epinephrine, and norepinephrine, secreted from the adrenal medulla. The catecholamine neurohormones interact with adrenergic receptors present on cell membranes of all visceral organs and smooth muscles, leading to activation of signaling pathways and consequent alterations in organ function and smooth muscle tone. During the "fight-or-flight response," the rise in circulating epinephrine and norepinephrine from the adrenal medulla and norepinephrine secreted from sympathetic nerve terminals cause increased blood pressure and cardiac output, relaxation of bronchial, intestinal and many other smooth muscles, mydriasis, and metabolic changes that increase levels of blood glucose and free fatty acids. Circulating catecholamines can also alter memory via effects on afferent sensory nerves impacting central nervous system function. While these rapid responses may be necessary for survival, sustained elevation of circulating catecholamines for prolonged periods of time can also produce pathological conditions, such as cardiac hypertrophy and heart failure, hypertension, and posttraumatic stress disorder. In this review, we discuss the present knowledge of the effects of circulating catecholamines on peripheral organs and tissues, as well as on memory in the brain.

Glucocorticoid receptor antagonism disrupts the reconsolidation of social reward-related memories in rats

Reconsolidation is the process whereby consolidated memories are destabilized upon retrieval and restabilized to persist for later use. Although the neurobiology of the reconsolidation of both appetitive and aversive memories has been intensively investigated, reconsolidation of memories of physiologically relevant social rewards has received little attention. Social play, the most characteristic social behaviour displayed by young mammals, is highly rewarding, illustrated by the fact that it can induce conditioned place preference (CPP). Here, we investigated the role of signalling mechanisms implicated in memory processes, including reconsolidation, namely glucocorticoid, mineralocorticoid, NMDA glutamatergic and CB1 cannabinoid receptors, in the reconsolidation of social play-induced CPP in rats. Systemic treatment with the glucocorticoid receptor antagonist mifepristone before, but not immediately after, retrieval disrupted the reconsolidation of social play-induced CPP. Mifepristone did not affect social play-induced CPP in the absence of memory retrieval. Treatment with the NMDA receptor antagonist MK-801 modestly affected the reconsolidation of social play-induced CPP. However, the reconsolidation of social play-induced CPP was not affected by treatment with the mineralocorticoid and CB1 cannabinoid receptor antagonists spironolactone and rimonabant, respectively. We conclude that glucocorticoid neurotransmission mediates the reconsolidation of social reward-related memories in rats. These data indicate that the neural mechanisms of the reconsolidation of social reward-related memories only partially overlap with those underlying the reconsolidation of other reward-related memories.

Corticosterone and propranolol's role on taste recognition memory

Taste recognition is a robust procedure to study learning and memory processes, as well as the different stages involved in them, i.e. encoding, storage and recall. Considerable evidence indicates that adrenal hormones and the noradrenergic system play an important role in aversive and appetitive memory formation in rats and humans. The present experiments were designed to characterize the effects of immediate post training corticosterone (Experiment 1) and propranolol administration (Experiment 2 and 3) on taste recognition memory. Administration of a high dose of corticosterone (5mg/kg, sc) impairs consolidation of taste memory, but the low and moderate doses (1 and 3mg/kg, sc) didn't affect it. On the other hand, immediate post-training administration of propranolol (1 and 2mg/kg, ip) impaired taste recognition memory. These effects were time-dependent since no effects were seen when drug administration was delayed 3h after training. These findings support the importance of stress hormones and noradrenergic system on the modulation of taste memory consolidation.

Glucocorticoids interact with noradrenergic activation at encoding to enhance long-term memory for emotional material in women

Evidence from the animal literature suggests that post-training glucocorticoids (GCs) interact with noradrenergic activation at acquisition to enhance memory consolidation for emotional stimuli. While there is evidence that GCs enhance memory for emotional material in humans, the extent to which this depends on noradrenergic activation at encoding has not been explored. In this study, 20-mg hydrocortisone was administered to healthy young women (18-35 yrs old) in a double-blind fashion 10 min prior to viewing a series of emotional and neutral images. Saliva samples were taken at baseline, 10 min after drug or placebo administration, immediately after viewing the images, 10, 20, and 30 min after viewing the images. Participants returned 1 week later for a surprise recall test. Results suggest that, hydrocortisone administration resulted in emotional memory enhancement only in participants who displayed an increase in endogenous noradrenergic activation, measured via salivary alpha-amylase at encoding. These results support findings in the animal literature, and suggest that GC-induced memory enhancement relies on noradrenergic activation at encoding in women.

Positive emotional arousal increases duration of memory traces: different role of dopamine D1 receptor and β-adrenoceptor activation

We investigated the effects of post-training administration of dopamine D1 receptor antagonist SCH 23390 and β-adrenergic receptor antagonist Propranolol on memory retention of an object sampled in a state of positive emotional arousal. Saline-treated mice trained and tested under high emotional/motivational arousal (High) showed discrimination of a novel object both 24 and 96 h post-training. Instead, mice trained and tested under low motivational arousal (Low) were unable to discriminate the novel object 96 h post-training. Both a high (2 mg/kg) and a low (1 mg/kg) dose of Propranolol reduced object discrimination in High mice tested 24 h post-training, whereas neither dose was effective in Low mice. A high dose of SCH 23390 (0.025 mg/kg) reduced discrimination of the novel object in High mice tested both 24 and 96 h post-training, whereas a low dose of the D1 antagonist (0.01 mg/kg) reduced discrimination in High mice tested 96 h post-training and abolished discrimination in Low mice tested 24h after training.

Neurobiological mechanisms underlying relapse to cocaine use: contributions of CRF and noradrenergic systems and regulation by glucocorticoids

Considering its pervasive and uncontrollable influence in drug addicts, understanding the neurobiological processes through which stress contributes to drug use is a critical goal for addiction researchers and will likely be important for the development of effective medications aimed at relapse prevention. In this paper, we review work from our laboratory and others focused on determining the neurobiological mechanisms that underlie and contribute to stress-induced relapse of cocaine use with an emphasis on the actions of corticotropin-releasing factor in the ventral tegmental area (VTA) and a key pathway from the bed nucleus of the stria terminalis to the VTA that is regulated by norepinephrine and beta adrenergic receptors. Additionally, we discuss work suggesting that the influence of stress in cocaine addiction changes and intensifies with repeated cocaine use in an intake-dependent manner and examine the potential role of glucocorticoid hormones in the underlying drug-induced neuroadaptations. It is our hope that research in this area will inform clinical practice and medication development aimed at minimizing the contribution of stress to the addiction cycle, thereby improving treatment outcomes and reducing the societal costs of addiction.

Involvements of stress hormones in the restraint-induced conditioned place preference

The conditioned place preference (CPP) paradigm is widely used when examining the reinforcing effects of drugs. Some previous studies have shown that an acute stressor, such as restraint could also induce CPP. Although the modulating effects of stress hormones on various forms of learning are well known, the finding that a stressor has a potentially direct role in the reinforcement mechanism is novel. This study focused on the function of stress hormones in restraint-induced CPP in Wistar rats administered agonist or antagonist of 2 critical stress hormones prior to conditioning. Results showed that peripheral applications of corticosterone (CORT, 1, 3, 5, and 10 mg/kg, subcutaneously) failed to induce CPP. Furthermore, a glucocorticoid (GC) antagonist (mifepristone, 10, 40, or 100 mg/kg, sc) failed to block the restraint-induced CPP. Intracerebroventricular injection of a selective corticotropin-releasing factor receptor 1 (CRFR1) antagonist antalarmin (1 μg/5 μl), on the contrary, completely blocked the restraint-induced CPP. We concluded that CRFR1 plays an essential role in the neural mechanism of restraint-induced CPP. Negative feedback of CORT from peripheral sources may not be involved in this phenomenon.

Region-specific role of Rac in nucleus accumbens core and basolateral amygdala in consolidation and reconsolidation of cocaine-associated cue memory in rats

RATIONALE AND OBJECTIVES

Drug reinforcement and the reinstatement of drug seeking are associated with the pathological processing of drug-associated cue memories that can be disrupted by manipulating memory consolidation and reconsolidation. Ras-related C3 botulinum toxin substrate (Rac) is involved in memory processing by regulating actin dynamics and neural structure plasticity. The nucleus accumbens (NAc) and amygdala have been implicated in the consolidation and reconsolidation of emotional memories. Therefore, we hypothesized that Rac in the NAc and amygdala plays a role in the consolidation and reconsolidation of cocaine-associated cue memory.

METHODS

Conditioned place preference (CPP) and microinjection of Rac inhibitor NSC23766 were used to determine the role of Rac in the NAc and amygdala in the consolidation and reconsolidation of cocaine-associated cue memory in rats.

RESULTS

Microinjections of NSC23766 into the NAc core but not shell, basolateral (BLA), or central amygdala (CeA) after each cocaine-conditioning session inhibited the consolidation of cocaine-induced CPP. A microinjection of NSC23766 into the BLA but not CeA, NAc core, or NAc shell immediately after memory reactivation induced by exposure to a previously cocaine-paired context disrupted the reconsolidation of cocaine-induced CPP. The effect of memory disruption on cocaine reconsolidation was specific to reactivated memory, persisted at least 2 weeks, and was not reinstated by a cocaine-priming injection.

CONCLUSIONS

Our findings indicate that Rac in the NAc core and BLA are required for the consolidation and reconsolidation of cocaine-associated cue memory, respectively.

Making memories matter

This article reviews some of the neuroendocrine bases by which emotional events regulate brain mechanisms of learning and memory. In laboratory rodents, there is extensive evidence that epinephrine influences memory processing through an inverted-U relationship, at which moderate levels enhance and high levels impair memory. These effects are, in large part, mediated by increases in blood glucose levels subsequent to epinephrine release, which then provide support for the brain processes engaged by learning and memory. These brain processes include augmentation of neurotransmitter release and of energy metabolism, the latter apparently including a key role for astrocytic glycogen. In addition to up- and down-regulation of learning and memory in general, physiological concomitants of emotion and arousal can also switch the neural system that controls learning at a particular time, at once improving some attributes of learning and impairing others in a manner that results in a change in the strategy used to solve a problem.