Probes for INS

Hypothalamic-pituitary-adrenal (HPA) axis dynamics are disrupted by opioids and may be involved in substance abuse; this persists during withdrawal and abstinence and is associated with co-morbid sleep disruption leading to vulnerability to relapse. We hypothesized that chronic sleep restriction (SR) alters the HPA axis diurnal rhythm and the sexually dimorphic response to acute stressor during opioid abstinence. We developed a rat model to evaluate the effect of persistent sleep loss during opioid abstinence on HPA axis dynamics in male and female rats. Plasma ACTH and corticosterone were measured diurnally and in response to acute restraint stress in rats Before (control) compared to During subsequent opioid abstinence without or with SR. Abstinence, regardless of sleep state, led to an increase in plasma ACTH and corticosterone in the morning in males. There was a tendency for higher PM plasma ACTH during abstinence in SR males (p = 0.076). ACTH and corticosterone responses to restraint were reduced in male SR rats whereas there was a failure to achieve the post-restraint nadir in female SR rats. There was no effect of the treatments or interventions on adrenal weight normalized to body weight. SR resulted in a dramatic increase in hypothalamic PVN AVP mRNA and plasma copeptin in male but not female rats. This corresponded to the attenuation of the HPA axis stress response in SR males during opioid abstinence. We have identified a potentially unique, sexually dimorphic role for magnocellular vasopressin in the control of the HPA axis during opioid abstinence and sleep restriction.

Despite the higher prevalence of post-traumatic stress disorder (PTSD) in women, the majority of preclinical research has been conducted utilizing male subjects. We have found that male rats exposed to the predator scent 2,4,5-trimethyl-3-thiazoline (TMT) show heterogenous long-term anxiety-like behavior and conditioned fear to the TMT environment. Stress-Resilient males exhibit increased mGlu5 mRNA expression in the basolateral amygdala (BLA) and prefrontal cortex (PFC). Here we sought to determine whether the same behavioral and genetic responses would be observed in female rats exposed to TMT. Female Sprague-Dawley rats were exposed to TMT for ten minutes, while Controls were exposed to an unscented environment. Anxiety and anhedonia were assessed 7-14 days later with elevated plus maze (EPM), acoustic startle response, light-dark box, and sucrose preference test (SPT). TMT-exposed females spent less time in the EPM open arms, exhibited greater startle amplitude, and reduced sucrose intake compared to Controls. Median split analyses conducted on EPM and SPT data yielded stress-Susceptible and -Resilient phenotypes that displayed behavior in the light-dark box consistent with EPM and SPT behavior. Susceptible females displayed greater BLA mGlu5 mRNA expression than Resilient and Control rats and did not show conditioned fear, in contrast to previous results in males. Resilient females displayed greater mGlu5 mRNA expression in the nucleus accumbens. These data indicate that the predator scent stress model of PTSD produces distinct stress-Susceptible and Resilient phenotypes in female rats that are associated with changes in mGlu5 mRNA expression in several brain regions.

Fear-associated memories and behavior are often expressed in contexts/environments distinctively different from those in which they are created. This generalization process contributes to psychological disorders, particularly PTSD. Stress-related neurocircuits in the basolateral amygdala (BLA) receive inputs from hypothalamic orexin (Orx) neurons, which mediate neuronal activity by targeting orexin 1 (Orx1R) and orexin 2 (Orx2R) receptors via opposing functions. In BLA, inhibition of Orx1R or activation of Orx2R ameliorate stress responsiveness and behavior. We discovered that most Orx1R+ cells also express CamKIIα, while a majority of Orx2R+ cells are colocalized with GAD67. Further, Orx1R gene Hcrtr1 expression was positively correlated, and Orx2R gene Hcrtr2 expression was negatively correlated, with freezing in a phenotype-dependent fashion (Escape vs Stay) in the Stress Alternatives Model (SAM). The SAM consists of 4-days of social interaction between test mice and novel larger aggressors. Exits positioned at opposite ends of the SAM oval arena provide opportunities to actively avoid aggression. By Day 2, mice commit to behavioral phenotypes: Escape or Stay. Pharmacologically manipulating Orx receptor activity in the BLA, before Day 3 of the SAM, was followed with standard tests of anxiety: Open Field (OF) and Elevated Plus Maze (EPM). In Stay mice, freezing in response to social conflict and locomotion during SAM interaction (not home cage locomotion) were generalized to OF, and blocked by intra-BLA Orx1R antagonism, but not Orx2R antagonism. Moreover, patterns of social avoidance for Escape and Stay mice were recapitulated in OF, with generalization mediated by Orx1R and Orx2R antagonism, plus Orx2R stimulation.

Chronic stress represents a major contributor for the development of mental illness. This study aimed to investigate how animals exposed to chronic mild stress (CMS) responded to an acute stress (AS), as a vulnerability's challenge, and to establish the potential effects of the antipsychotic drug lurasidone on such mechanisms. Adult male Wistar rats were exposed or not (controls) to a CMS paradigm for 7 weeks. Starting from the end of week 2, animals were randomized to receive vehicle or lurasidone for 5 weeks. Sucrose intake was used to measure anhedonia. At the end, half of the animals were exposed to an acute stress before sacrifice. Exposure to CMS produced a significant reduction in sucrose consumption, whereas lurasidone progressively normalized such alteration. We found that exposure to AS produced an upregulation of Brain derived neurotrophic factor (Bdnf) in the prefrontal cortex of controls animals. This response was impaired in CMS rats and restored by lurasidone treatment. While in control animals, AS-induced increase of Bdnf mRNA levels was specific for Parvalbumin cells, CMS rats treated with lurasidone show a significant upregulation of Bdnf in pyramidal cells. Furthermore, when investigating the activation of different brain regions, CMS rats showed an impairment in the global response to the acute stressor, that was largely restored by lurasidone treatment. Our results suggest that lurasidone treatment in CMS rats may regulate specific circuits and mechanisms, which will ultimately contribute to boost resilience under stressful challenges.