Enhanced CRFR1-Dependent Regulation of a Ventral Tegmental Area to Prelimbic Cortex Projection Establishes Susceptibility to Stress-Induced Cocaine Seeking.

The ability of stress to trigger cocaine seeking in humans and rodents is variable and is determined by the amount and pattern of prior drug use. This study examined the role of a corticotropin releasing factor (CRF)-regulated dopaminergic projection from the ventral tegmental area (VTA) to the prelimbic cortex in shock-induced cocaine seeking and its recruitment under self-administration conditions that establish relapse vulnerability. Male rats with a history of daily long-access (LgA; 14 × 6 h/d) but not short-access (ShA; 14 × 2 h/d) self-administration showed robust shock-induced cocaine seeking. This was associated with a heightened shock-induced prelimbic cortex Fos response and activation of cholera toxin b retro-labeled VTA neurons that project to the prelimbic cortex. Chemogenetic inhibition of this pathway using a dual virus intersectional hM4Di DREADD (designer receptor exclusively activated by designer drug) based approach prevented shock-induced cocaine seeking. Both shock-induced reinstatement and the prelimbic cortex Fos response were prevented by bilateral intra-VTA injections of the CRF receptor 1 (CRFR1) antagonist, antalarmin. Moreover, pharmacological disconnection of the CRF-regulated dopaminergic projection to the prelimbic cortex by injection of antalarmin into the VTA in one hemisphere and the D1 receptor antagonist, SCH23390, into the prelimbic cortex of the contralateral hemisphere prevented shock-induced cocaine seeking. Finally, LgA, but not ShA, cocaine self-administration resulted in increased VTA CRFR1 mRNA levels as measured using in situ hybridization. Altogether, these findings suggest that excessive cocaine use may establish susceptibility to stress-induced relapse by recruiting CRF regulation of a stressor-responsive mesocortical dopaminergic pathway.SIGNIFICANCE STATEMENT Understanding the neural pathways and mechanisms through which stress triggers relapse to cocaine use is critical for the development of more effective treatment approaches. Prior work has demonstrated a critical role for the neuropeptide corticotropin releasing factor (CRF) in stress-induced cocaine seeking. Here we provide evidence that stress-induced reinstatement in a rat model of relapse is mediated by a CRF-regulated dopaminergic projection from the ventral tegmental area (VTA) that activates dopamine D1 receptors in the prelimbic cortex. Moreover, we report that this pathway may be recruited as a result of daily cocaine self-administration under conditions of extended drug access/heightened drug intake, likely as a result of increased CRFR1 expression in the VTA, thereby promoting susceptibility to stress-induced cocaine seeking.

Corticotropin-releasing hormone-binding protein and stress: from invertebrates to humans.

Corticotropin-releasing hormone (CRH) is a key regulator of the stress response. This peptide controls the hypothalamic-pituitary-adrenal (HPA) axis as well as a variety of behavioral and autonomic stress responses via the two CRH receptors, CRH-R1 and CRH-R2. The CRH system also includes an evolutionarily conserved CRH-binding protein (CRH-BP), a secreted glycoprotein that binds CRH with subnanomolar affinity to modulate CRH receptor activity. In this review, we discuss the current literature on CRH-BP and stress across multiple species, from insects to humans. We describe the regulation of CRH-BP in response to stress, as well as genetic mouse models that have been utilized to elucidate the in vivo role(s) of CRH-BP in modulating the stress response. Finally, the role of CRH-BP in the human stress response is examined, including single nucleotide polymorphisms in the human CRHBP gene that are associated with stress-related affective disorders and addiction. Lay summary The stress response is controlled by corticotropin-releasing hormone (CRH), acting via CRH receptors. However, the CRH system also includes a unique CRH-binding protein (CRH-BP) that binds CRH with an affinity greater than the CRH receptors. In this review, we discuss the role of this highly conserved CRH-BP in regulation of the CRH-mediated stress response from invertebrates to humans.

Brain CRF-binding protein modulates aspects of maternal behavior under stressful conditions and supports a hypo-anxious state in lactating rats.

Reduced corticotropin-releasing factor (CRF) receptor activation in the postpartum period is essential for adequate maternal behavior. One of the factors contributing to this hypo-activity might be the CRF-binding protein (CRF-BP), which likely reduces the availability of free extracellular CRF/urocortin 1. Here, we investigated behavioral effects of acute CRF-BP inhibition using 5µg of CRF(6-33) administered either centrally or locally within different parts of the bed nucleus of the stria terminalis (BNST) in lactating rats. Additionally, we assessed CRF-BP expression in the BNST comparing virgin and lactating rats. Central CRF-BP inhibition increased maternal aggression during maternal defense but did not affect maternal care or anxiety-related behavior. CRF-BP inhibition in the medial-posterior BNST had no effect on maternal care under non-stress conditions but impaired the reinstatement of maternal care following stressor exposure. Furthermore, maternal aggression, particularly threat behavior, and anxiety-related behavior were elevated by CRF-BP inhibition in the medial-posterior BNST. In the anterior-dorsal BNST, CRF-BP inhibition increased only non-maternal behaviors following stress. Finally, CRF-BP expression was higher in the anterior compared to the posterior BNST but was not different between virgin and lactating rats in either region. Our study demonstrates a key role of the CRF-BP, particularly within the BNST, in modulating CRF's impact on maternal behavior. The CRF-BP is important for the reinstatement of maternal care after stress, for modulating threat behavior during an aggressive encounter and for maintaining a hypo-anxious state during lactation. Thus, the CRF-BP likely contributes to the postpartum-associated down-regulation of the CRF system in a brain region-dependent manner.

Binge Drinking Decreases Corticotropin-Releasing Factor-Binding Protein Expression in the Medial Prefrontal Cortex of Mice.

BACKGROUND: Dysregulation of the corticotropin-releasing factor (CRF) system has been observed in rodent models of binge drinking, with a large focus on CRF receptor 1 (CRF-R1). The role of CRF-binding protein (CRF-BP), a key regulator of CRF activity, in binge drinking is less well understood. In humans, single-nucleotide polymorphisms in CRHBP are associated with alcohol use disorder and stress-induced alcohol craving, suggesting a role for CRF-BP in vulnerability to alcohol addiction. METHODS: The role and regulation of CRF-BP in binge drinking were examined in mice exposed to the drinking in the dark (DID) paradigm. Using in situ hybridization, the regulation of CRF-BP, CRF-R1, and CRF mRNA expression was determined in the stress and reward systems of C57BL/6J mice after repeated cycles of DID. To determine the functional role of CRF-BP in binge drinking, CRF-BP knockout (CRF-BP KO) mice were exposed to 6 cycles of DID, during which alcohol consumption was measured and compared to wild-type mice. RESULTS: CRF-BP mRNA expression was significantly decreased in the prelimbic (PL) and infralimbic medial prefrontal cortex (mPFC) of C57BL/6J mice after 3 cycles and in the PL mPFC after 6 cycles of DID. No significant changes in CRF or CRF-R1 mRNA levels were observed in mPFC, ventral tegmental area, bed nucleus of the stria terminalis, or amygdala after 3 cycles of DID. CRF-BP KO mice do not show significant alterations in drinking compared to wild-type mice across 6 cycles of DID. CONCLUSIONS: These results reveal that repeated cycles of binge drinking alter CRF-BP mRNA expression in the mPFC, a region responsible for executive function and regulation of emotion and behavior, including responses to stress. We observed a persistent decrease in CRF-BP mRNA expression in the mPFC after 3 and 6 DID cycles, which may allow for increased CRF signaling at CRF-R1 and contribute to excessive binge-like ethanol consumption.

Impact of inflammasomes on the ocular surface.

PURPOSE OF REVIEW: The ocular surface is prone to inflammation due to exposure to environmental irritants and pathogens. Inflammasomes are intracellular, multiprotein complexes that communicate potentially dangerous signals to the immune system. The identification of inflammasomes in various inflammatory ocular surface conditions can aid in the development of therapeutics to treat these chronic inflammatory conditions. RECENT FINDINGS: Several inflammasomes have been associated with ocular surface disorders including dry eye disease, keratitis, and allergies. Mechanisms for activation of these inflammasomes with regards to specific disorders have been explored in models to aid in the development of targeted treatments. SUMMARY: Research efforts continue to characterize the types of inflammasomes and activators of these in inflammatory ocular surface conditions. Various therapies targeting specific inflammasome types or pyroptosis are being tested preclinically to assess effects on decreasing the associated chronic inflammation.

Conversion of short-term to long-term memory in the novel object recognition paradigm.

It is well-known that stress can significantly impact learning; however, whether this effect facilitates or impairs the resultant memory depends on the characteristics of the stressor. Investigation of these dynamics can be confounded by the role of the stressor in motivating performance in a task. Positing a cohesive model of the effect of stress on learning and memory necessitates elucidating the consequences of stressful stimuli independently from task-specific functions. Therefore, the goal of this study was to examine the effect of manipulating a task-independent stressor (elevated light level) on short-term and long-term memory in the novel object recognition paradigm. Short-term memory was elicited in both low light and high light conditions, but long-term memory specifically required high light conditions during the acquisition phase (familiarization trial) and was independent of the light level during retrieval (test trial). Additionally, long-term memory appeared to be independent of stress-mediated glucocorticoid release, as both low and high light produced similar levels of plasma corticosterone, which further did not correlate with subsequent memory performance. Finally, both short-term and long-term memory showed no savings between repeated experiments suggesting that this novel object recognition paradigm may be useful for longitudinal studies, particularly when investigating treatments to stabilize or enhance weak memories in neurodegenerative diseases or during age-related cognitive decline.

Long-term alcohol consumption alters dorsal striatal dopamine release and regulation by D2 dopamine receptors in rhesus macaques.

The dorsal striatum (DS) is implicated in behavioral and neural processes including action control and reinforcement. Alcohol alters these processes in rodents, and it is believed that the development of alcohol use disorder involves changes in DS dopamine signaling. In nonhuman primates, the DS can be divided into caudate and putamen subregions. As part of a collaborative effort examining the effects of long-term alcohol self-administration in rhesus macaques, we examined DS dopamine signaling using fast-scan cyclic voltammetry. We found that chronic alcohol self-administration resulted in several dopamine system adaptations. Most notably, dopamine release was altered in a sex- and region-dependent manner. Following long-term alcohol consumption, male macaques, regardless of abstinence status, had reduced dopamine release in putamen, while only male macaques in abstinence had reduced dopamine release in caudate. In contrast, female macaques had enhanced dopamine release in the caudate, but not putamen. Dopamine uptake was also enhanced in females, but not males (regardless of abstinence state). We also found that dopamine D2/3 autoreceptor function was reduced in male, but not female, alcohol drinkers relative to control groups. Finally, we found that blockade of nicotinic acetylcholine receptors inhibited evoked dopamine release in nonhuman primates. Altogether, our findings demonstrate that long-term alcohol consumption can sex-dependently alter dopamine release, as well as its feedback control mechanisms in both DS subregions.

Pituitary CRH-binding protein and stress in female mice.

The CRH-binding protein (CRH-BP) binds CRH with very high affinity and inhibits CRH-mediated ACTH release from anterior pituitary cells in vitro, suggesting that the CRH-BP functions as a negative regulator of CRH activity. Our previous studies have demonstrated sexually dimorphic expression of CRH-BP in the murine pituitary. Basal CRH-BP expression is higher in the female pituitary, where CRH-BP mRNA is detected in multiple anterior pituitary cell types. In this study, we examined stress-induced changes in CRH-BP mRNA and protein expression in mouse pituitary and assessed the in vivo role of CRH-BP in modulating the stress response. Pituitary CRH-BP mRNA was greater than 200-fold more abundant in females than males, and restraint stress increased pituitary CRH-BP mRNA by 11.8-fold in females and 3.2-fold in males as assessed by qRT-PCR. In females, restraint stress increased CRH-BP mRNA levels not only in POMC-expressing cells, but also in PRL-expressing cells. The increase in female pituitary CRH-BP mRNA following stress resulted in significant increases in CRH-BP protein 4-6h after a 30-minute restraint stress as detected by [(125)I]-CRH:CRH-BP cross-linking analyses. Based on this temporal profile, the physiological role of CRH-BP was assessed using a stressor of longer duration. In lipopolysaccharide (LPS) stress studies, female CRH-BP-deficient mice showed elevated levels of stress-induced corticosterone release as compared to wild-type littermates. These studies demonstrate a role for the pituitary CRH-BP in attenuating the HPA response to stress in female mice.