Temporally graded, context-specific retrograde amnesia and its alleviation by context preexposure: effects of postconditioning exposures to morphine in the rat

Early pharmacological interventions for universal prevention of post-traumatic stress disorder (PTSD)

BACKGROUND

Post-traumatic stress disorder (PTSD) is a severe and debilitating condition. Several pharmacological interventions have been proposed with the aim to prevent or mitigate it. These interventions should balance efficacy and tolerability, given that not all individuals exposed to a traumatic event will develop PTSD. There are different possible approaches to preventing PTSD; universal prevention is aimed at individuals at risk of developing PTSD on the basis of having been exposed to a traumatic event, irrespective of whether they are showing signs of psychological difficulties.

OBJECTIVES

To assess the efficacy and acceptability of pharmacological interventions for universal prevention of PTSD in adults exposed to a traumatic event.

SEARCH METHODS

We searched the Cochrane Common Mental Disorders Controlled Trial Register (CCMDCTR), CENTRAL, MEDLINE, Embase, two other databases and two trials registers (November 2020). We checked the reference lists of all included studies and relevant systematic reviews. The search was last updated on 13 November 2020.

SELECTION CRITERIA

We included randomised clinical trials on adults exposed to any kind of traumatic event. We considered comparisons of any medication with placebo or with another medication. We excluded trials that investigated medications as an augmentation to psychotherapy.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodological procedures. In a random-effects model, we analysed dichotomous data as risk ratios (RR) and number needed to treat for an additional beneficial/harmful outcome (NNTB/NNTH). We analysed continuous data as mean differences (MD) or standardised mean differences (SMD).

MAIN RESULTS

We included 13 studies which considered eight interventions (hydrocortisone, propranolol, dexamethasone, omega-3 fatty acids, gabapentin, paroxetine, PulmoCare enteral formula, Oxepa enteral formula and 5-hydroxytryptophan) and involved 2023 participants, with a single trial contributing 1244 participants. Eight studies enrolled participants from emergency departments or trauma centres or similar settings. Participants were exposed to a range of both intentional and unintentional traumatic events. Five studies considered participants in the context of intensive care units with traumatic events consisting of severe physical illness. Our concerns about risk of bias in the included studies were mostly due to high attrition and possible selective reporting. We could meta-analyse data for two comparisons: hydrocortisone versus placebo, but limited to secondary outcomes; and propranolol versus placebo. No study compared hydrocortisone to placebo at the primary endpoint of three months after the traumatic event. The evidence on whether propranolol was more effective in reducing the severity of PTSD symptoms compared to placebo at three months after the traumatic event is inconclusive, because of serious risk of bias amongst the included studies, serious inconsistency amongst the studies' results, and very serious imprecision of the estimate of effect (SMD -0.51, 95% confidence interval (CI) -1.61 to 0.59; I² = 83%; 3 studies, 86 participants; very low-certainty evidence). No study provided data on dropout rates due to side effects at three months post-traumatic event. The evidence on whether propranolol was more effective than placebo in reducing the probability of experiencing PTSD at three months after the traumatic event is inconclusive, because of serious risk of bias amongst the included studies, and very serious imprecision of the estimate of effect (RR 0.77, 95% CI 0.31 to 1.92; 3 studies, 88 participants; very low-certainty evidence). No study assessed functional disability or quality of life.  Only one study compared gabapentin to placebo at the primary endpoint of three months after the traumatic event, with inconclusive evidence in terms of both PTSD severity and probability of experiencing PTSD, because of imprecision of the effect estimate, serious risk of bias and serious imprecision (very low-certainty evidence). We found no data on dropout rates due to side effects, functional disability or quality of life. For the remaining comparisons, the available data are inconclusive or missing in terms of PTSD severity reduction and dropout rates due to adverse events. No study assessed functional disability.

AUTHORS' CONCLUSIONS

This review provides uncertain evidence only regarding the use of hydrocortisone, propranolol, dexamethasone, omega-3 fatty acids, gabapentin, paroxetine, PulmoCare formula, Oxepa formula, or 5-hydroxytryptophan as universal PTSD prevention strategies. Future research might benefit from larger samples, better reporting of side effects and inclusion of quality of life and functioning measures.

The relationship between early administration of morphine or nitrous oxide gas and PTSD symptom development

BACKGROUND

Posttraumatic Stress Disorder (PTSD) is a debilitating mental health disorder. Certain drugs, such as morphine and nitrous oxide gas (N₂O), are administered to individuals who just experienced a traumatic event (e.g., soldiers, injured civilians). It is therefore crucial to understand if they incidentally affect PTSD symptom development. Furthermore, such observations could pave the way for the development of pharmacological prevention strategies of PTSD.

METHODS

In this prospective population-based cohort study (n = 2,070), we examined the relationship between morphine or N₂O administration during childbirth, and subsequent childbirth-related PTSD symptoms at eight weeks postpartum. Pain during labour, prior PTSD symptoms, and birth medical severity were included as covariates in the analyses.

RESULTS

In women who developed PTSD symptoms, N₂O administration during childbirth predicted reduced PTSD symptom severity (p < .001, small to medium effect size). A similar tendency was observed for morphine, but was not significant (p < .065, null to small effect size). Both drugs predicted increased PTSD symptoms when combined with severe pain during labour.

LIMITATIONS

This study was observational, thus drug administration was not randomised. Additionally, PTSD symptoms were self-reported.

CONCLUSIONS

Peritraumatic N₂O administration may reduce subsequent PTSD symptom severity and thus be a potential avenue for PTSD secondary prevention. This might also be the case for morphine. However, the role of severe peritraumatic pain in context of drug administration deserves further investigation.

Posttraumatic Stress in Children After Injury: The Role of Acute Pain and Opioid Medication Use

OBJECTIVES

After injury, many children experience posttraumatic stress symptoms (PTSS) that negatively impact recovery. Acute pain and PTSS share neurobiological pathways, and acute dosage of morphine has been linked to reduced PTSS in naturalistic studies. However, the complex interactions between pain, morphine and other opioid use, and PTSS have yet to be investigated in robust pediatric samples.This prospective, longitudinal study examined relationships between acute pain, opioid medications, and PTSS after pediatric injury.

METHODS

Ninety-six children aged 8 to 13 years (mean = 10.60, SD = 1.71), hospitalized for unintentional injury, completed assessments at baseline (T1) and 12 weeks (T2) later. Pain ratings and opioid administration data were obtained via chart review.

RESULTS

Structural equation modeling revealed that worst pain endorsed during hospitalization was positively associated with concurrent and later PTSS when controlling for evidence-based risk factors (ie, age, sex, prior trauma history, traumatic appraisals of injury event, heart rate). Neither opioid medications overall nor morphine specifically (milligram/kilogram/day) administered during hospitalization mediated the relationship between pain and T2 PTSS.

CONCLUSIONS

Pain during hospitalization may increase susceptibility for persistent PTSS above and beyond the influence of other empirical risk factors. Findings suggest that pain assessment may be a useful addition to pediatric PTSS screening tools and highlight the need for additional research on pharmacological secondary prevention approaches. Given that inadequate pain control and persistent PTSS each hinder recovery and long-term functioning, better understanding of interactions between acute pain and PTSS after injury is essential for improving screening, prevention, and early intervention efforts.

Time-dependent protective effects of morphine against behavioral and morphological deficits in an animal model of posttraumatic stress disorder

Post-traumatic stress disorder (PTSD) arises after an individual has experienced a major traumatic event. Recent evidence suggests that acute morphine treatment may serve as a strategy to reduce PTSD development. In the present study, we investigated the time-dependent effects of morphine on behavioral and morphological deficits induced by the single prolonged stress (SPS), an experimental model of PTSD, in adult male rats. The rats were exposed to SPS (restraint for 2 h, forced swimming for 20 min, and ether anesthesia), and kept undistributed for 11 days. Morphine was injected immediately, 6, 12 and 24 h after SPS. Anxiety profile was evaluated using the elevated plus maze11 days after SPS. Then, animals were conditioned in a fear conditioning task and extinction training was performed on days 1, 2, 3, 4 and 11 after fear conditioning which followed by morphological assessments in the medial prefrontal cortex (mPFC). SPS rats showed increased anxiety levels and impaired contextual fear extinction retention. SPS also decreased dendritic length in the infra-limbic (IL) and dendritic spines in the IL and pre-limbic (PL) regions of the mPFC. Conversely, morphine treatment 6, 12 and 24 h but not immediately after SPS significantly improved anxiety-like behaviors, fear extinction, increased dendritic length, and spines in the mPFC. Morphine-induced much stronger response when injected 24 h after the SPS, and this effect was blocked by naloxone. Our findings show that morphine within a restricted time window selectively reversed the SPS-induced deficits in anxiety profile, fear extinction, and dendritic morphology in the mPFC. Finally, these findings suggest that the time point of morphine injection following a traumatic event is an important determinant of the full therapeutic effect of morphine against PTSD.

Prevention of Post-Traumatic Stress Disorder After Trauma: Current Evidence and Future Directions

Post-traumatic stress disorder (PTSD) is a frequent, tenacious, and disabling consequence of traumatic events. The disorder's identifiable onset and early symptoms provide opportunities for early detection and prevention. Empirical findings and theoretical models have outlined specific risk factors and pathogenic processes leading to PTSD. Controlled studies have shown that theory-driven preventive interventions, such as cognitive behavioral therapy (CBT), or stress hormone-targeted pharmacological interventions, are efficacious in selected samples of survivors. However, the effectiveness of early clinical interventions remains unknown, and results obtained in aggregates (large groups) overlook individual heterogeneity in PTSD pathogenesis. We review current evidence of PTSD prevention and outline the need to improve the disorder's early detection and intervention in individual-specific paths to chronic PTSD.

Morphine administration during low ovarian hormone stage results in transient over expression of fear memories in females

Acute exposure to morphine after a traumatic event reduces trauma related symptoms in humans and conditioned fear expression in male rats. We aimed to determine whether acute administration of morphine alters consolidation of fear learning and extinction. Male and female rats in proestrus and metaestrus (high and low ovarian hormones respectively) underwent fear conditioning and received saline or morphine (2.5 mg/kg s.c.). The next day they underwent extinction. Results showed increased freezing during extinction only in the morphine metaestrus group while morphine did not affect males or proestrus females. Recall of extinction was similar on all groups. On a second experiment, a subset of rats conditioned during metaestrus was administered morphine prior to extinction producing no effects. We then measured mu opioid receptor (MOR) expression in the amygdala and periaqueductal gray (PAG) at the end of extinction (day 2). In males and proestrus females, morphine caused an increase in MOR in the amygdala but no in the PAG. In metaestrus females, morphine did not change MOR expression in either structure. These data suggests that ovarian hormones may interact with MORs in the amygdala to transiently alter memory consolidation. Morphine given after trauma to females with low ovarian hormones might increase the recall of fear responses, making recovery harder.

Effect of morphine on the persistence of long-term memory in rats

RATIONALE

Current evidence suggests that pharmacological manipulation around 12 h after training alters the persistence of long-term memory. However, no study has addressed whether opioids modulate the persistence of fear. The current study examined whether morphine alters the persistence of the memory of contextual fear conditioning.

METHODS

Male adult Wistar rats were injected with saline (NaCl 0.9 %, intraperitoneally (i.p.)) or morphine (3 and/or 10 mg/kg, i.p.) 6, 9, 12, or 24 h post-training and tested 2 or 7 days after training, when freezing responses were assessed. The involvement of state dependence and opioid receptors in the effect of morphine was investigated by respectively injecting naloxone (1 mg/kg, i.p.) 30 min before morphine, and morphine (10 mg/kg, i.p.) 30 min before testing.

RESULTS

Morphine (10 mg/kg, i.p., 12 h post-training) did not alter freezing to context in animals tested 2 days after training but impaired freezing to context when testing was carried out 7 or 14 days after training. Morphine (10 mg/kg, i.p.) administration 6, 9, or 24 h post-training did not alter freezing measured 2 or 7 days after training. Pre-test morphine improved recall but did not alter the deleterious effect of 12 h post-training morphine. The deleterious effect of morphine was prevented by naloxone, indicating that opioid receptors are involved in this effect.

CONCLUSIONS

Our findings indicate an inhibitory role for opioid receptors in memory persistence. This is relevant from both the experimental and clinical point of views, since it may have implications for the prevention of post-traumatic stress disorder (PTSD).

The role of early pharmacotherapy in the development of posttraumatic stress disorder symptoms after traumatic injury: an observational cohort study in consecutive patients

OBJECTIVE

Pharmacological intervention during traumatic memory consolidation has been suggested to prevent posttraumatic stress disorder (PTSD). The aim of this study was to examine the association between prescription of early pharmacotherapy and the risk of developing PTSD symptoms following traumatic injury.

METHOD

The use of opiate analgesics, beta-adrenergic blockers, corticosteroids and benzodiazepines within 48 h postinjury was documented based on hospital charts for 629 Level 1 trauma center patients. PTSD symptoms were assessed using structured clinical interviews. Primary outcome was 6-week PTSD symptoms. Secondary outcomes were PTSD diagnoses at 6 weeks and during 1 year posttrauma.

RESULTS

Linear regression analyses showed that opiate administration within 48 h was negatively associated with PTSD symptoms at 6 weeks (β=-0.14, P=.009) after controlling for demographic and injury-related characteristics and concurrent pharmacotherapy. Fewer patients with opiates had a PTSD diagnosis at 6 weeks (P=.047) and during 1 year posttrauma (P=.013) than patients with none of the specified pharmacotherapies. Low prescription frequency of beta-blockers (3.8%), corticosteroids (2.2%) and benzodiazepines (7.8%) precluded further examination of their role in the development of PTSD symptoms because of limited statistical power.

CONCLUSIONS

This study suggests a possible beneficial influence of opiate administration within 48 h posttrauma on the development of PTSD symptoms. Future studies may evaluate the effectiveness of inhospital opiate analgesics compared to placebo in preventing PTSD and may focus on the mechanisms underlying the effect of opiates in preventing PTSD.

Pharmacological secondary prevention of PTSD in youth: challenges and opportunities for advancement

Child and adolescent posttraumatic stress disorder (PTSD) is associated with an increased risk for a number of deleterious mental and physical health outcomes that if untreated may persist throughout the life course. Efficacious interventions applied soon after trauma exposure have the potential to reduce or prevent the development of PTSD symptoms and their associated impact on behavior and physical health. We review extant research related to treatment-modifiable peritraumatic predictors of pediatric PTSD, which have informed an emerging field of pharmacologic secondary prevention (i.e., occurring shortly following trauma exposure) of PTSD. Challenges and opportunities for early posttrauma PTSD prevention are described. Finally, we offer new models for biologically informed integration of pharmacologic and psychosocial secondary prevention intervention strategies for children and adolescents.

Post-conditioning experience with acute or chronic inflammatory pain reduces contextual fear conditioning in the rat

There is evidence that pain can impact cognitive function in people. The present study evaluated whether Pavlovian fear conditioning in rats would be reduced if conditioning were followed by persistent inflammatory pain induced by a subcutaneous injection of dilute formalin or complete Freund's adjuvant (CFA) on the dorsal lumbar surface of the back. Formalin-induced pain specifically impaired contextual fear conditioning but not auditory cue conditioning (Experiment 1A). Moreover, formalin pain only impaired contextual fear conditioning if it was initiated within 1h of conditioning and did not have a significant effect if initiated 2, 8 or 32 h after (Experiments 1A and 1B). Experiment 2 showed that formalin pain initiated after a session of context pre-exposure reduced the ability of that pre-exposure to facilitate contextual fear when the rat was limited to a brief exposure to the context during conditioning. Similar impairments in context- but not CS-fear conditioning were also observed if the rats received an immediate post-conditioning injection with CFA (Experiment 3). Finally, we confirmed that formalin and CFA injected s.c. on the back induced pain-indicative behaviours, hyperalgesia and allodynia with a similar timecourse to intraplantar injections (Experiment 4). These results suggest that persistent pain impairs learning in a hippocampus-dependent task, and may disrupt processes that encode experiences into long-term memory.

Opioid receptors regulate retrieval of infant fear memories: effects of naloxone on infantile amnesia

The authors examined the role of the endogenous opioid system in infantile amnesia for contextual fear conditioning. Rats that were 18 days of age received an aversive footshock in a novel context. Rats displayed conditioned fear when tested 1 min after training but not 24 hr after training. Systemic injection of the opioid receptor antagonist naloxone prior to test, but not immediately after training, alleviated infantile amnesia. Naloxone also alleviated infantile amnesia when injected prior to test 7 days after training. These effects of naloxone were due to actions on central rather than peripheral opioid receptors and were not due to any tendency of the drug to produce fear or freezing. These results show that central opioid receptors regulate retrieval of fear memories in infant rats.

A study of the protective function of acute morphine administration on subsequent posttraumatic stress disorder

BACKGROUND

To index the extent to which acute administration of morphine is protective against development of posttraumatic stress disorder (PTSD).

METHODS

Consecutive patients admitted to hospital after traumatic injury (n=155) were assessed for current psychiatric disorder, pain, and morphine dose in the initial week after injury and were reassessed for PTSD and other psychiatric disorders 3 months later (n=120).

RESULTS

Seventeen patients (14%) met criteria for PTSD at 3 months. Patients who met criteria for PTSD received significantly less morphine than those who did not develop PTSD; there was no difference in morphine levels in those who did and did not develop major depressive episode or another anxiety disorder. Hierarchical regression analysis indicated that PTSD severity at 3 months was significantly predicted by acute pain, mild traumatic brain injury, and elevated morphine dose in the initial 48 hours after trauma, after controlling for injury severity, gender, age, and type of injury.

CONCLUSIONS

Acute administration of morphine may limit fear conditioning in the aftermath of traumatic injury and may serve as a secondary prevention strategy to reduce PTSD development.

The effect of the mu-opioid receptor antagonist naloxone on extinction of conditioned fear in the developing rat

Several recent studies report that neurotransmitters that are critically involved in extinction in adult rats are not important for extinction in young rats. Specifically, pretest injection of the gamma-aminobutryic acid (GABA) receptor inverse agonist FG7142 has no effect on extinction in postnatal day (P)17 rats, although it reverses extinction in P24 rats as reported by Kim and Richardson in an earlier paper. Further, pre-extinction injection of the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 has no effect on extinction in P17 rats, whereas it impairs long-term extinction in P24 rats as per Langton and colleagues in an earlier work. These findings indicate that extinction in P17 rats is qualitatively different from extinction in older rats. The present study examines the involvement of the endogenous opioid system in extinction in the developing rat using systemic injections of the mu-opioid receptor antagonist naloxone. Experiment 1 showed that injection of naloxone before extinction training disrupted the acquisition of extinction in both P17 and P24 rats. This effect was dependent on central rather than peripheral mu-opioid receptors (Experiment 2), and neither pre-test nor post-extinction injection of naloxone had effects on extinction (Experiments 3 and 4). Taken together, these findings indicate that opioid neurotransmission, in contrast to GABA and NMDA activity, is critical for extinction acquisition across development.

The effect of the NMDA receptor antagonist MK-801 on the acquisition and extinction of learned fear in the developing rat

Recent findings reveal qualitative developmental differences in extinction of learned fear. The present study explored potential developmental differences in the role of NMDA in acquisition and extinction. Rats were injected with MK-801 prior to fear conditioning or extinction training. Acquisition was found to be NMDA dependent in both age groups, whereas extinction was found to be NMDA dependent in 23-day-old rats, but NMDA independent in 16-day-old rats. These results illustrate another fundamental developmental difference in extinction as well as a dissociation in the role of NMDA in the acquisition and extinction of fear early in development.

Endogenous opiates and behavior: 2003

This paper is the 26th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2003 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Understanding contextual fear conditioning: insights from a two-process model

Contextual fear conditioning is an important behavioral paradigm for studying the neurobiology of learning and memory and the mnemonic function of the hippocampus. We suggest that research in this domain can profit by a better theoretical understanding of the processes that contribute to this phenomenon. To facilitate this understanding, we describe a theory which assumes that physical elements of a conditioning context represented in the brain as either (a) a set of independent features or (b) features bound into a conjunctive representation by the hippocampus which supports pattern completion. Conditioning produced by shocking a rat in a particular context, in principle, can be produced by strengthening connections between the feature representations and/or the conjunctive representation and basolateral region of the amygdala. We illustrate how this theory clarifies some of the complexities associated with the existing literature and how it can be used to guide future empirical work. We also argue that the mechanisms (conjunctive representations and pattern completion) that mediate the contribution the hippocampus makes to contextual fear conditioning are the same ones that enable the hippocampus to support declarative memory in humans.