Ketamine exacerbates cortical neuroapoptosis under hyperoxic conditions by upregulating expression of the N-methyl-D-aspartate receptor subunit NR1 in the developing rat brain

Mechanistic advances of hyperoxia-induced immature brain injury

The impact of hyperoxia-induced brain injury in preterm infants is being increasingly investigated. However, the parameters and protocols used to study this condition in animal models lack consistency. Research is further hampered by the fact that hyperoxia exerts both direct and indirect effects on oligodendrocytes and neurons, with the precise underlying mechanisms remaining unclear. In this article, we aim to provide a comprehensive overview of the conditions used to induce hyperoxia in animal models of immature brain injury. We discuss what is known regarding the mechanisms underlying hyperoxia-induced immature brain injury, focusing on the effects on oligodendrocytes and neurons, and briefly describe therapies that may counteract the effects of hyperoxia. We also identify further studies required to fully elucidate the effects of hyperoxia on the immature brain as well as discuss the leading therapeutic options.

Use of Both Fluoro-Jade B and Hematoxylin and Eosin to Detect Cell Death in the Juvenile Rat Brain Exposed to NMDA-Receptor Antagonists or GABA-Receptor Agonists in Safety Assessment

Administration of pediatric anesthetics with N-methyl D-aspartate (NMDA)-receptor antagonist and/or γ-aminobutyric acid (GABA) agonist activities may result in neuronal degeneration and/or neuronal cell death in neonatal rats. Evaluating pediatric drug candidates for this potential neurotoxicity is often part of overall preclinical new drug development strategy. This specialized assessment may require dosing neonatal rats at postnatal day 7 at the peak of the brain growth spurt and evaluating brain tissue 24 to 48 hours following dosing. The need to identify methods to aid in the accurate and reproducible detection of lesions associated with this type of neurotoxic profile is paramount for meeting the changing needs of neuropathology assessment and addressing emerging challenges in the neuroscience field. We document the use of Fluoro-Jade B (FJB) staining, to be used in conjunction with standard hematoxylin and eosin staining, to detect acute neurodegeneration and neuronal cell death that can be caused by some NMDA-receptor antagonists and/or GABA agonists in the neonatal rat brain. The FJB staining is simple, specific, and sensitive and can be performed on brain specimens from the same cohort of animals utilized for standard neurotoxicity assessment, thus satisfying animal welfare recommendations with no effect on achievement of scientific and regulatory goals.

The protective effect of olanzapine on ketamine induced cognitive deficit and increased NR1 expression in rat model of schizophrenia

BACKGROUND

Impaired cognitive flexibility is the core manifestation of schizophrenia (SZ). Previous literature raised a claim against the effect of atypical antipsychotic drugs (AAD) on cognitive and executive functions whose cause needs further investigation. Attention set-shifting task (ASST) tests the prefrontal cortex's (PFC) executive and flexibility functions.

GOALS

To examine Olanzapine (OLZ) effect on ASST, expression of N-methyl-D-aspartate receptor 1 (NMDR-NR1) in prefrontal cortex (PFC), and metabolic comorbidity in ketamine (KET) model of SZ.

METHODS

Sixty-two male rats were divided into three groups: 8 for ASST and 30 for open field, ELISA and immunohistochemistry sub-chronic study, and 24 for regular serological and histopathological examination. Rats treated with V: vehicle; K: KET and KO: OLZ plus KET.

RESULTS

KET caused significant increase in time, trials, and errors to reach criterion. OLZ co-administration reversed effects of KET in ASST with no reduction of locomotor activity. OLZ normalized KET-induced rise of NR1 expression and protected against KET-induced degenerative changes in hippocampus and PFC. Significant increase in serum liver enzymes, total bilirubin, and lipids with chronic compared to sub-chronic OLZ administration. In contrast, insignificant difference between sub-chronic OLZ and vehicle was found.

CONCLUSIONS

Current study demonstrated the efficacy of OLZ to reverse KET-induced cognitive deficits in ASST with neither reduction in NR1 expression in PFC nor metabolic malfunction in the sub-chronic study. It also showed the protective effect of OLZ on KET induced neuronal degeneration and necrosis. We suggest that chronic OLZ treatment-induced-metabolic malfunction might be the cause of time-dependent cognitive deterioration.

Premedication practices for less invasive surfactant administration - results from a nationwide cohort study

BACKGROUND AND AIMS

There are no established premedication schemes for less invasive surfactant administration (LISA) in neonatal RDS. The aim was to describe "real-world" practices and to assess the safety of premedication and its impact on the technical ease of the LISA procedure.

METHODS

Data from the prospective LISA cohort study conducted in 31 tertiary neonatal units were evaluated for premedication practices. Infants who received analgesics and/or sedatives before LISA and those receiving non-pharmacological sedation with sublingual 30% glucose were compared versus nonpremedicated neonates, acting as a reference. Safety of premedication was assessed with the rate of adverse events during LISA, changes in oxygenation status, the need for rescue intubation, and mechanical ventilation in the first 24 h of life. Ease of conducting LISA was an efficacy endpoint.

RESULTS

Of 500 enrolled newborns, 102 (20.4%) received premedication for LISA; 88 infants were given analgesics/sedatives and 14 sublingual glucose. Pharmacological sedation was most often performed with ketamine (51/88; 57.9%), midazolam (16/88; 18.2%) and propofol (8/88; 1.6%). Compared to non-premedication, the use of analgesics/sedatives was associated with a significant increase in the rate of apnea (9.1 vs 2.6%; p = 0.009) and a significantly higher decrease in SpO₂/FiO₂ (-55 ± 62 vs -32 ± 50; p < 0.001). However, the rates of rescue intubation and the need for early mechanical ventilation were not significantly different. Sedation with glucose did not affect the frequency of adverse events. LISA procedures had a similar level of ease regardless of the premedication used and were rated as easy or very easy in 69% of non-premedicated infants, 65.9% of the analgesics/sedatives group and 78.5% of the glucose group (p = ns).

CONCLUSION

Analgesics/sedatives prior to LISA increased the rate of apnea and decreased blood oxygenation but did not lead to tracheal intubation and early mechanical ventilation. Trials addressing the impact on LISA-related stress are necessary to determine the ultimate usefulness of premedication.

Potential mechanisms for phencyclidine/ketamine-induced brain structural alterations and behavioral consequences

Evidence of structural abnormalities in the nervous system of recreational drug [e.g., phencyclidine (PCP) or ketamine] users and/or preclinical animal research models suggests interference with the activity of multiple neurotransmitters, particularly glutamate neurotransmission. The damage to the central nervous system (CNS) may include neuronal loss, synaptic changes, disturbed neural network formation and reduced projections to subcortical fields. Notably, the reduced projections may considerably compromise the establishment of the subcortical areas, such as the nucleus accumbens located in the basal forebrain. With its abundant dopaminergic innervation, the nucleus accumbens is believed to be directly associated with addictive behaviors and mental disorders. This review seeks to delineate the relationship between PCP/ketamine-induced loss of cortical neurons and the reduced level of polysialic acid neural cell adhesion molecule (PSA-NCAM) in the striatum, and the likely changes in striatal synaptogenesis during development. The basic mechanism of how PSA-NCAM cell surface expression may be regulated will also be discussed, as well as the hypothesis that PSA-NCAM activity is critical to the regulation of synaptic protein expression. Overall, the present review will address the general hypothesis that damage/interruption of cortico-striatal communication and subcortical synaptogenesis could underlie the erratic/sensitization or addictive states produced by chronic or prolonged PCP/ketamine usage.

N-methyl-D-aspartate receptor subunit 1 regulates neurogenesis in the hippocampal dentate gyrus of schizophrenia-like mice

N-methyl-D-aspartate receptor hypofunction is the basis of pathophysiology in schizophrenia. Blocking the N-methyl-D-aspartate receptor impairs learning and memory abilities and induces pathological changes in the brain. Previous studies have paid little attention to the role of the N-methyl-D-aspartate receptor subunit 1 (NR1) in neurogenesis in the hippocampus of schizophrenia. A mouse model of schizophrenia was established by intraperitoneal injection of 0.6 mg/kg MK-801, once a day, for 14 days. In N-methyl-D-aspartate-treated mice, N-methyl-D-aspartate was administered by intracerebroventricular injection in schizophrenia mice on day 15. The number of NR1-, Ki67- or BrdU-immunoreactive cells in the dentate gyrus was measured by immunofluorescence staining. Our data showed the number of NR1-immunoreactive cells increased along with the decreasing numbers of BrdU- and Ki67-immunoreactive cells in the schizophrenia groups compared with the control group. N-methyl-D-aspartate could reverse the above changes. These results indicated that NR1 can regulate neurogenesis in the hippocampal dentate gyrus of schizophrenia mice, supporting NR1 as a promising therapeutic target in the treatment of schizophrenia. This study was approved by the Experimental Animal Ethics Committee of the Ningxia Medical University, China (approval No. 2014-014) on March 6, 2014.