Reversal of morphine conditioned behavior by an anti-dopaminergic post-trial drug treatment during re-consolidation

Opioid-environment interaction: Contrasting effects of morphine administered in a novel versus familiar environment on acute and repeated morphine induced behavioral effects and on acute morphine ERK activation in reward associated brain areas

We report that environmental context can have a major impact on morphine locomotor behavior and ERK effects. We manipulated environmental context in terms of an environmental novelty/ familiarity dimension and measured morphine behavioral effects in both acute and chronic morphine treatment protocols. Wistar rats (n=7 per group) were injected with morphine 10 mg/kg or vehicle (s.c.), and immediately placed into an arena for 5 min, and locomotor activity was measured after one or 5 days. The morphine treatments were initiated either when the environment was novel or began after the rats had been familiarized with the arena by being given 5 daily nondrug tests in the arena. The results showed that acute and chronic morphine effects were strongly modified by whether the environment was novel or familiar. Acute morphine administered in a novel environment increased ERK activity more substantially in several brain areas, particularly in reward-associated areas such as the VTA in comparison to when morphine was given in a familiar environment. Repeated morphine treatments initiated in a novel environment induced a strong locomotor sensitization, whereas repeated morphine treatments initiated in a familiar environment did not induce a locomotor stimulant effect but rather a drug discriminative stimulus dis-habituation effect. The marked differential effects of environmental novelty/familiarity and ongoing dopamine activity on acute and chronic morphine treatments may be of potential clinical relevance for opioid drug addiction.

Developmental Outcomes after Opioid Exposure in the Fetus and Neonate

The overall prevalence of opiate use has been increasing, currently affecting approximately 0.6% of the global population and resulting in a significant proportion of infants being born with prenatal opioid exposure. Animal and human models of prenatal opioid exposure demonstrate detrimental effects on brain anatomy as well as neurodevelopment. Less is known about the neurologic sequelae of postnatal opioid exposure in hospitalized infants. In this review, we summarize our current understanding of the impact of prenatal and postnatal opioid exposure on the brain and on neurodevelopment outcomes. We also identify resources and management strategies that may help mitigate neurodevelopmental delays and deficits associated with opioid exposure in this vulnerable population.

Treating neuropathic pain and comorbid affective disorders: Preclinical and clinical evidence

INTRODUCTION

Neuropathic pain (NP) significantly impacts quality of life and often coexists with affective disorders such as anxiety and depression. Addressing both NP and its psychiatric manifestations requires a comprehensive understanding of therapeutic options. This study aimed to review the main pharmacological and non-pharmacological treatments for NP and comorbid affective disorders to describe their mechanisms of action and how they are commonly used in clinical practice.

METHODS

A review was conducted across five electronic databases, focusing on pharmacological and non-pharmacological treatments for NP and its associated affective disorders. The following combination of MeSH and title/abstract keywords were used: "neuropathic pain," "affective disorders," "depression," "anxiety," "treatment," and "therapy." Both animal and human studies were included to discuss the underlying therapeutic mechanisms of these interventions.

RESULTS

Pharmacological interventions, including antidepressants, anticonvulsants, and opioids, modulate neural synaptic transmission to alleviate NP. Topical agents, such as capsaicin, lidocaine patches, and botulinum toxin A, offer localized relief by desensitizing pain pathways. Some of these drugs, especially antidepressants, also treat comorbid affective disorders. Non-pharmacological techniques, including repetitive transcranial magnetic stimulation, transcranial direct current stimulation, and photobiomodulation therapy, modulate cortical activity and have shown promise for NP and mood disorders.

CONCLUSIONS

The interconnection between NP and comorbid affective disorders necessitates holistic therapeutic strategies. Some pharmacological treatments can be used for both conditions, and non-pharmacological interventions have emerged as promising complementary approaches. Future research should explore novel molecular pathways to enhance treatment options for these interrelated conditions.

A partial habituation method to test for anterograde and retrograde amnestic treatment effects: Evidence that antagonism of the NMDA receptor can induce anterograde but not retrograde amnestic effects

BACKGROUND

A progressive decrease in spontaneous locomotion with repeated exposure to a novel environment has been assessed using both within and between-session measures. While both are well-established and reliable measurements, neither are useful alone as methods to concurrently assess treatment effects on acquisition and retention of habituation.

NEW METHOD

We report a behavioral method that measures habituation by combining the within and between measurements of locomotion. We used a 30 min session divided into 6 five min blocks. In the first novel environment session activity was maximal in the first 5 min block but was reduced to a low level by the sixth block, indicative of within-session habituation. Using 8 daily sessions, we showed that this terminal block low level of activity progressed incrementally to the first block to achieve complete habituation.

RESULTS/COMPARISON WITH EXISTING METHODS

Within-session activity across sessions was used to identify different stages of between session habituation. It was then possible to assess drug treatment effects from partial to complete habituation, so that treatment effects on retention of the previously acquired partial habituation, expressed as a reversion to an earlier within session habituation pattern (retrograde amnesia assessment), as well as the effects on new learning by the failure in subsequent sessions to acquire complete between-session habituation (anterograde amnesia assessment).

CONCLUSIONS

The use of spontaneous motor activity to assess learning and memory effects provides the opportunity to assess direct treatment effects on behavior and motor activity in contrast to many learning and memory models.

Ibuprofen for acute postoperative pain in children

BACKGROUND

Children often require pain management following surgery to avoid suffering. Effective pain management has consequences for healing time and quality of life. Ibuprofen, a frequently used non-steroidal anti-inflammatory drug (NSAID) administered to children, is used to treat pain and inflammation in the postoperative period.

OBJECTIVES

1) To assess the efficacy and safety of ibuprofen (any dose) for acute postoperative pain management in children compared with placebo or other active comparators. 2) To compare ibuprofen administered at different doses, routes (e.g. oral, intravenous, etc.), or strategies (e.g. as needed versus as scheduled).

SEARCH METHODS

We used standard Cochrane search methods. We searched CENTRAL, MEDLINE, Embase, CINAHL and trials registries in August 2023.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) in children aged 17 years and younger, treated for acute postoperative or postprocedural pain, that compared ibuprofen to placebo or any active comparator. We included RCTs that compared different administration routes, doses of ibuprofen and schedules.

DATA COLLECTION AND ANALYSIS

We adhered to standard Cochrane methods for data collection and analysis. Our primary outcomes were pain relief reported by the child, pain intensity reported by the child, adverse events, and serious adverse events. We present results using risk ratios (RR) and standardised mean differences (SMD), with the associated confidence intervals (CI). We used GRADE to assess the certainty of the evidence.

MAIN RESULTS

We included 43 RCTs that enroled 4265 children (3935 children included in this review). We rated the overall risk of bias at the study level as high or unclear for 37 studies that had one or several unclear or high risk of bias judgements across the domains. We judged six studies as having a low risk of bias across all domains. Ibuprofen versus placebo (35 RCTs) No studies reported pain relief reported by the child or a third party, or serious adverse events. Ibuprofen probably reduces child-reported pain intensity less than two hours postintervention compared to placebo (SMD -1.12, 95% CI -1.39 to -0.86; 3 studies, 259 children; moderate-certainty evidence). Ibuprofen may reduce child-reported pain intensity, two hours to less than 24 hours postintervention (SMD -1.01, 95% CI -1.24 to -0.78; 5 studies, 345 children; low-certainty evidence). Ibuprofen may result in little to no difference in adverse events compared to placebo (RR 0.79, 95% CI 0.51 to 1.23; 5 studies, 384 children; low-certainty evidence). Ibuprofen versus paracetamol (21 RCTs) No studies reported pain relief reported by the child or a third party, or serious adverse events. Ibuprofen likely reduces child-reported pain intensity less than two hours postintervention compared to paracetamol (SMD -0.42, 95% CI -0.82 to -0.02; 2 studies, 100 children; moderate-certainty evidence). Ibuprofen may slightly reduce child-reported pain intensity two hours to 24 hours postintervention (SMD -0.21, 95% CI -0.40 to -0.02; 6 studies, 422 children; low-certainty evidence). Ibuprofen may result in little to no difference in adverse events (0 events in each group; 1 study, 44 children; low-certainty evidence). Ibuprofen versus morphine (1 RCT) No studies reported pain relief or pain intensity reported by the child or a third party, or serious adverse events. Ibuprofen likely results in a reduction in adverse events compared to morphine (RR 0.58, 95% CI 0.40 to 0.83; risk difference (RD) -0.25, 95% CI -0.40 to -0.09; number needed to treat for an additional beneficial outcome (NNTB) 4; 1 study, 154 children; moderate-certainty evidence). Ibuprofen versus ketorolac (1 RCT) No studies reported pain relief or pain intensity reported by the child, or serious adverse events. Ibuprofen may result in a reduction in adverse events compared to ketorolac (RR 0.51, 95% CI 0.27 to 0.96; RD -0.29, 95% CI -0.53 to -0.04; NNTB 4; 1 study, 59 children; low-certainty evidence).

AUTHORS' CONCLUSIONS

Despite identifying 43 RCTs, we remain uncertain about the effect of ibuprofen compared to placebo or active comparators for some critical outcomes and in the comparisons between different doses, schedules and routes for ibuprofen administration. This is largely due to poor reporting on important outcomes such as serious adverse events, and poor study conduct or reporting that reduced our confidence in the results, along with small underpowered studies. Compared to placebo, ibuprofen likely results in pain reduction less than two hours postintervention, however, the efficacy might be lower at two hours to 24 hours. Compared to paracetamol, ibuprofen likely results in pain reduction up to 24 hours postintervention. We could not explore if there was a different effect in different kinds of surgeries or procedures. Ibuprofen likely results in a reduction in adverse events compared to morphine, and in little to no difference in bleeding when compared to paracetamol. We remain mostly uncertain about the safety of ibuprofen compared to other drugs.

The hippocampal FTO-BDNF-TrkB pathway is required for novel object recognition memory reconsolidation in mice

Memory reconsolidation refers to the process by which the consolidated memory was restored after reactivation (RA). Memory trace becomes labile after reactivation and inhibition of memory reconsolidation may disrupt or update the original memory trace, which provided a new strategy for the treatment of several psychiatric diseases, such as drug addiction and post-traumatic stress disorder. Fat mass and obesity-associated gene (FTO) is a novel demethylase of N6-methyladenosine (m6A) and it has been intensively involved in learning and memory. However, the role of FTO in memory reconsolidation has not been determined. In the present study, the function of FTO in memory reconsolidation was investigated in the novel object recognition (NOR) model in mice. The results showed that RA of NOR memory increased hippocampal FTO expression in a time-dependent manner, while FTO inhibitor meclofenamic acid (MA) injected immediately, but not 6 h after RA disrupted NOR memory reconsolidation. MA downregulated BDNF expression during NOR memory reconsolidation in the hippocampus, while the TrkB agonist 7,8-Dihydroxyflavone (7,8-DHF) reversed the disruptive effects of MA on NOR memory reconsolidation. Furthermore, overexpression of FTO increased BDNF expression via decreasing mRNA m6A in HT22 cells. Taken together, these results indicate that FTO may up-regulate the BDNF-TrkB pathway to promote NOR memory reconsolidation through m6A modification.

Pharmacological interventions for the management of pain and discomfort during lumbar puncture in newborn infants

BACKGROUND

Lumbar puncture (LP) is a common invasive procedure, most frequently performed to diagnose infection. Physicians perform LP in newborn infants with the help of an assistant using a strict aseptic technique; it is important to monitor the infant during all the steps of the procedure. Without adequate analgesia, LP can cause considerable pain and discomfort. As newborns have increased sensitivity to pain, it is crucial to adequately manage the procedural pain of LP in this population.

OBJECTIVES

To assess the benefits and harms, including pain, discomfort, and success rate, of any pharmacological intervention during lumbar puncture in newborn infants, compared to placebo, no intervention, non-pharmacological interventions, or other pharmacological interventions.

SEARCH METHODS

We searched CENTRAL, PubMed, Embase, and three trial registries in December 2022. We also screened the reference lists of included studies and related systematic reviews for studies not identified by the database searches.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) and quasi-RCTs comparing drugs used for pain management, sedation, or both, during LP. We considered the following drugs suitable for inclusion. • Topical anesthetics (e.g. eutectic mixture of local anesthetics [EMLA], lidocaine) • Opioids (e.g. morphine, fentanyl) • Alpha-2 agonists (e.g. clonidine, dexmedetomidine) • N-Methyl-D-aspartate (NMDA) receptor antagonists (e.g. ketamine) • Other analgesics (e.g. paracetamol) • Sedatives (e.g. benzodiazepines such as midazolam) DATA COLLECTION AND ANALYSIS: We used standard Cochrane methods. We used the fixed-effect model with risk ratio (RR) for dichotomous data and mean difference (MD) or standardized mean difference (SMD) for continuous data, with their 95% confidence intervals (CIs). Our main outcomes were successful LP on first attempt, total number of LP attempts, episodes of bradycardia, pain assessed with validated scales, episodes of desaturation, number of episodes of apnea, and number of infants with one or more episodes of apnea. We used the GRADE approach to evaluate the certainty of the evidence.

MAIN RESULTS

We included three studies (two RCTs and one quasi-RCT) that enrolled 206 newborns. One study included only term infants. All studies assessed topical treatment versus placebo or no intervention. The topical anesthetics were lidocaine 4%, lidocaine 1%, and EMLA. We identified no completed studies on opioids, non-steroidal anti-inflammatory drugs, alpha-2 agonists, NMDA receptor antagonists, other analgesics, sedatives, or head-to-head comparisons (drug A versus drug B). Based on very low-certainty evidence from one quasi-RCT of 100 LPs in 76 infants, we are unsure if topical anesthetics (lidocaine), compared to no anesthesia, has an effect on the following outcomes. • Successful LP on first attempt (first-attempts success in 48% of LPs in the lidocaine group and 42% of LPs in the control group) • Number of attempts per LP (mean 1.9 attempts, [standard error of the mean 0.2] in the lidocaine group, and mean 2.1 attempts [standard error of the mean 2.1] in the control group) • Episodes of bradycardia (0% of LPs in the lidocaine group and 4% of LPs in the control group) • Episodes of desaturation (0% of LPs in the lidocaine group and 8% of LPs in the control group) • Occurrence of apnea (RR 3.24, 95% CI 0.14 to 77.79; risk difference [RD] 0.02, 95% CI -0.03 to 0.08). Topical anesthetics compared to placebo may reduce pain assessed with the Neonatal Facial Coding System (NFCS) score (SMD -1.00 standard deviation (SD), 95% CI -1.47 to -0.53; I² = 98%; 2 RCTs, 112 infants; low-certainty evidence). No studies in this comparison reported total number of episodes of apnea. We identified three ongoing studies, which will assess the effects of EMLA, lidocaine, and fentanyl. Three studies are awaiting classification.

AUTHORS' CONCLUSIONS

The evidence is very uncertain about the effect of topical anesthetics (lidocaine) compared to no anesthesia on successful lumbar puncture on first attempt, the number of attempts per lumbar puncture, episodes of bradycardia, episodes of desaturation, and occurrence of apnea. Compared to placebo, topical anesthetics (lidocaine or EMLA) may reduce pain assessed with the NFCS score. One ongoing study will assess the effects of systemic treatment.

Morphine and dopamine: Low dose apomorphine can prevent both the induction and expression of morphine locomotor sensitization and conditioning

The disinhibition of dopamine neurons in the VTA by morphine is considered an important contributor to the reward potency of morphine. In this report, three experiments were conducted in which a low dose of apomorphine (0.05mg/kg) was used as a pretreatment to reduce dopamine activity. Locomotor hyperactivity was used as the behavioral response to morphine (10.0mg/kg). In the first experiment, five treatments with morphine induced the development of locomotor and conditioned hyperactivity that were prevented by apomorphine given 10min prior to morphine. Apomorphine before either vehicle or morphine induced equivalent reductions in locomotion. In the second experiment, the apomorphine pretreatment was initiated after induction of a conditioned hyperactivity and the apomorphine prevented the expression of the conditioning. To assess the effects of the apomorphine on VTA and the nucleus accumbens, ERK measurements were carried out after the induction of locomotor and conditioned hyperactivity. Increased ERK activation was found and these effects were prevented by the apomorphine in both experiments. A third experiment was conducted to assess the effects of acute morphine on ERK before locomotor stimulation was induced by morphine. Acute morphine did not increase locomotion, but a robust ERK response was produced indicating that the morphine induced ERK activation was not secondary to locomotor stimulation. The ERK activation was again prevented by the apomorphine pretreatment. We suggest that contiguity between the ongoing behavioral activity and the morphine activation of the dopamine reward system incentivizes and potentiates the ongoing behavior generating equivalent behavioral sensitization and conditioned effects.

Changes in incidence and mortality trend due to COVID-19 in southern Iran, from 2020 to 2021: based on Cochran-Armitage trend test

Background

In 2020, COVID-19 spread rapidly in Iran and other parts of the world. Some of the epidemiological aspects of this disease remain unknown; therefore, the present study was designed with the aim of determining the trend of incidence and mortality of COVID-19 from February 2020 to July 2021 in southern Iran.

Methods

The present study was a cross-sectional analytical study that included all people who had COVID-19 in the period from February 2020 to July 2021 and whose information had been registered in the Infectious Diseases Center of Larestan city and MCMC unit. The study area included the cities of Larestan, Evaz, and Khonj, located in the south of Fars province in southern Iran.

Results

Since the emergence of COVID-19 until July 2021, a total of 23,246 new cases of infection were reported in the southern region of Fars province. The average age of patients was 39.90±18.30 years and the range of ages varied from 1 to 103 years. The results of the Cochran-Armitage trend test showed that the trend of the disease in 2020 was completely upward. The first positive case of COVID-19 was recorded on February 27, 2020. The incidence curve in 2021 is sinusoidal, but in general, the results of the Cochran-Armitage trend test showed that the incidence of the disease increased significantly (P-trend < 0.001). Most cases were reported in July, April, and the end of March.

Conclusion

In general, the incidence rate of COVID-19 has varied sinusoidally from 2020 to mid-2021. Although the incidence of the disease increased, the number of deaths has fallen. It seems that the increase in the number of diagnostic tests and the implementation of the national COVID-19 immunization program have been effective in changing the trend of the disease.

Pharmacological interventions for the management of pain and discomfort during lumbar puncture in newborn infants

This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

To assess the benefits and harms, including pain, discomfort, and success rate, of any pharmacological intervention during lumbar puncture in newborn infants, compared to placebo, no intervention, non‐pharmacological interventions, or other pharmacological interventions.

Context evoked morphine conditioned effects can be equivalent to morphine induced drug effects in terms of behavioral response and ERK activation in reward associated subcortical brain structures

Conditioned drug cues can evoke brief drug-like responses. In this report we show that using brief test sessions, contextual cues can induce conditioned hyperlocomotion and ERK responses equivalent to morphine induced responses. To assess acute unconditioned effects, rats that received morphine (MOR-1) or vehicle (VEH-1), were immediately placed onto an arena for a 5-min locomotion recording session after which ERK was measured in the ventral tegmental area (VTA) and nucleus accumbens (NAc). There were no differences in locomotion between the groups. However, the MOR-1 group had strong ERK activation in VTA and NAc. To assess MOR-conditioned effects, a chronic phase was carried out according to a Pavlovian conditioning protocol. There were two MOR paired groups (MORP), one MOR unpaired (MOR-UP) group and two VEH groups. The treatments were administered over 5 daily five minute test sessions. The final conditioning test was on day 6, in which one of the MOR-P groups and one of the VEH groups received VEH (MOR-P/VEH-6 and VEH/VEH-6, respectively). The other MOR-P group and VEH group received MOR (MOR-P/MOR; VEH/MOR-6, respectively). The MOR-UP group received VEH (MOR-UP/VEH-6). Rats received the treatments immediately prior to a 5-min arena test, and after the session ERK was measured. No morphine induced locomotor stimulation was observed on day 1 but on days 2 to 5, hyperlocomotion in both MOR-P groups occurred. On test day 6, the MOR-P/VEH-6 and the MOR-P/MOR-6 groups had comparable locomotor stimulant responses and similar ERK activity in the VTA and NAc. The MOR-UP group did not differ from the VEH group. We suggest that ERK activation evoked by acute morphine served as a Pavlovian unconditioned stimulus to enable the contextual cues to acquire morphine conditioned stimulus properties and increase the incentive value of the contextual cues.

Biochemical and Proteomic Characterization, and Pharmacological Insights of Indian Red Scorpion Venom Toxins

The Indian red scorpion (Mesobuthus tamulus) is one of the world's deadliest scorpions, with stings representing a life-threatening medical emergency. This species is distributed throughout the Indian sub-continent, including eastern Pakistan, eastern Nepal, and Sri Lanka. In India, Indian red scorpions are broadly distributed in western Maharashtra, Saurashtra, Kerala, Andhra Pradesh, Tamil Nadu, and Karnataka; however, fatal envenomations have been recorded primarily in the Konkan region of Maharashtra. The Indian red scorpion venom proteome comprises 110 proteins belonging to 13 venom protein families. The significant pharmacological activity is predominantly caused by the low molecular mass non-enzymatic Na+ and K+ ion channel toxins. Other minor toxins comprise 15.6% of the total venom proteome. Indian red scorpion stings induce the release of catecholamine, which leads to pathophysiological abnormalities in the victim. A strong correlation has been observed between venom proteome composition and local (swelling, redness, heat, and regional lymph node involvement) and systemic (tachycardia, mydriasis, hyperglycemia, hypertension, toxic myocarditis, cardiac failure, and pulmonary edema) manifestations. Immediate administration of antivenom is the preferred treatment for Indian red scorpion stings. However, scorpion-specific antivenoms have exhibited poor immunorecognition and neutralization of the low molecular mass toxins. The proteomic analysis also suggests that Indian red scorpion venom is a rich source of pharmacologically active molecules that may be envisaged as drug prototypes. The following review summarizes the progress made towards understanding the venom proteome of the Indian red scorpion and addresses the current understanding of the pathophysiology associated with its sting.

Morphine reward effects and morphine behavioral sensitization: The adventitious association of morphine activation of brain reward effects with ongoing spontaneous activity

The development of sensitization is one of the hallmarks of addictive drugs such as morphine. We administered morphine (10 mg/kg; MOR) to induce locomotor sensitization and ERK activation in the VTA and NAc. In the first experiment, four groups of rats received five daily 30 min sessions in an open-field, and locomotion was measured. For the first four sessions, one group received MOR pre-test (MOR-P); a second group received vehicle pre-test (MOR-UP) and MOR 30 min post-test; the remaining 2 groups received vehicle (VEH) pre-test. On the fifth session, the MOR-P, MOR-UP, and one VEH group received MOR pre-test and the remaining VEH group received VEH. Sensitization emerged in the first 5 min and progressed over to the second and third 5 min blocks only in the MOR-P group. For the second experiment, 4 groups received MOR and 4 groups VEH, and were then returned to their home cage and after 5, 15, 30 or 60 min post-injection, were euthanized for ERK measurements in VTA and NAc. ERK activation increased and peaked at 5 min post injection in the MOR group and then declined to VEH levels by 30 min. Another two groups received either MOR or VEH immediately before a 5 min arena test and ERK was measured immediately post-test. MOR had no effect on locomotion but increased ERK in the VTA and NAc. The peak ERK activation in VTA reflected activation of reward systems by morphine that reinforced locomotor behavior and with repeated treatments, induced a sensitization effect.

Genomics approaches to synthesize plant-based biomolecules for therapeutic applications to combat SARS-CoV-2

COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is devastative to the humankind for which neither vaccines nor precise therapeutic molecules for treatment are identified. The search for new drugs and repurposing of existing drugs are being performed; however, at the same time, research on plants to identify novel therapeutic compounds or testing the existing ones is progressing at a slower phase. In this context, genomics and biotechnology offer various tools and strategies to manipulate plants for producing those complex biopharmaceutical products. This review enumerates the scope for research on plant-based molecules for their potential application in treating SARS-CoV-2 infection. Strategies to edit gene and genome, overexpression and silencing approaches, and molecular breeding for producing target biomolecules in the plant system are discussed in detail. Altogether, the present review provides a roadmap for expediting research on using plants as a novel source of active biomolecules having therapeutic applications.

Morphine administered post-trial induces potent morphine conditioned effects if the context is novel but not if the context is familiar

Morphine administered shortly after exposure to a novel environment induces potent locomotor stimulant conditioning. Environmental novelty is important as pre-exposure (PE) to a stimulus can attenuate the capacity to acquire conditioned stimulus (CS). Here, the importance of environmental novelty for the efficacy of an open-field to become a CS for elicitation of a morphine conditioned response was assessed by comparing the effects of morphine administered post-trial following a 5 min exposure to a novel environment versus a PE environment. Four groups of rats (2 vehicle and 2 morphine groups) were used. Two groups received ten daily 5 min non-drug PEs to an open-field arena and the other two groups were not pre-exposed to the environment. Subsequently, all groups received post-trial injections of either vehicle or morphine immediately after each of five daily 5 min sessions in the open-field. Importantly, on the first day of testing prior to the first post-test morphine administration, the locomotor activity of the novel and PE groups was not different. Over the 5 post-trial morphine treatments, the activity of the PE morphine group, the PE vehicle and the novel environment vehicle groups did not change and were equivalent. In contrast, in the novel environment morphine group, a conditioned hyper-activity response increased with repeated post-trial morphine treatments. For the morphine group it is suggested that the novel environment initiated a post-trial stimulus trace that occurred in temporal contiguity with the post-trial drug response and enabled the trace to become a CS for the morphine unconditioned response. In contrast, PE induced a latent inhibition effect in the PE morphine group, thus the post-trial CS trace was insufficient to become associated to the morphine response and no conditioning occurred. In addition to conventional drug induced Pavlovian delay conditioning, the findings are suggestive of drug induced Pavlovian trace conditioning.