Effects on adult cognitive function after neonatal exposure to clinically relevant doses of ionising radiation and ketamine in mice.

BACKGROUND: Radiological methods for screening, diagnostics and therapy are frequently used in healthcare. In infants and children, anaesthesia/sedation is often used in these situations to relieve the patients' perception of stress or pain. Both ionising radiation (IR) and ketamine have been shown to induce developmental neurotoxic effects and this study aimed to identify the combined effects of these in a murine model. METHODS: Male mice were exposed to a single dose of ketamine (7.5 mg kg-1 body weight) s.c. on postnatal day 10. One hour after ketamine exposure, mice were whole body irradiated with 50-200 mGy gamma radiation (137Cs). Behavioural observations were performed at 2, 4 and 5 months of age. At 6 months of age, cerebral cortex and hippocampus tissue were analysed for neuroprotein levels. RESULTS: Animals co-exposed to IR and ketamine displayed significant (P≤0.01) lack of habituation in the spontaneous behaviour test, when compared with controls and single agent exposed mice. In the Morris Water Maze test, co-exposed animals showed significant (P≤0.05) impaired learning and memory capacity in both the spatial acquisition task and the relearning test compared with controls and single agent exposed mice. Furthermore, in co-exposed mice a significantly (P≤0.05) elevated level of tau protein in cerebral cortex was observed. Single agent exposure did not cause any significant effects on the investigated endpoints. CONCLUSION: Co-exposure to IR and ketamine can aggravate developmental neurotoxic effects at doses where the single agent exposure does not impact on the measured variables. These findings show that estimation of risk after paediatric low-dose IR exposure, based upon radiation dose alone, may underestimate the consequences for this vulnerable population.

Etomidate exposure in early infant mice (P10) does not induce apoptosis or affect behaviour.

BACKGROUND: Numerous animal studies have shown that all commonly used intravenous anaesthetic drugs and volatile agents may cause neuronal apoptosis following exposure in early life. Most studies have focussed on detecting increased apoptosis but their methods are not always readily transferrable to humans. The lipid formulation of etomidate represents an alternative to the currently established intravenous anaesthetic agents but there is no animal or human data on apoptosis or long-term behavioural changes. The aim of our study was to investigate the effects of etomidate on cerebral neuronal apoptosis and long-term behavioural effects using an established mouse model that represents the clinically relevant period of anaesthesia during early infancy in humans. METHODS: Six groups of 10 day old mice (P10) were injected with either etomidate 0.3, 3 or 10 mg/kg, propofol 60 mg/kg, ketamine 50 mg/kg or placebo only. Apoptosis in the cerebral cortex and hippocampus was assessed 24 h after treatment (activated caspase-3). Late behavioural effects were tested at 2 months of age (spontaneous activity in a new environment). RESULTS: No evidence was found of differences in activated caspase 3-concentrations among the study groups. Significant late behavioural changes were only observed in the ketamine group. CONCLUSION: A single dose of etomidate in early infant mice at P10 did not produce evidence of cerebral apoptosis or impaired adult motor behaviour.

Clonidine abolishes the adverse effects on apoptosis and behaviour after neonatal ketamine exposure in mice.

BACKGROUND: An increasing amount of both experimental and epidemiological data indicates that neonatal anaesthesia causes disruption of normal brain development in rodents and primates, as manifested by acute increased apoptosis and long-lasting altered behaviour and learning. It is necessary to seek strategies that avoid the possible adverse effects after anaesthesia. Our purpose is to show that increased apoptosis and behavioural alterations after ketamine exposure during this period may be prevented by clonidine, a compound already used by paediatric anaesthetists for sedation. METHODS: To investigate the protective properties of clonidine pre-treatment, five groups of 10-day-old mice were injected with either ketamine 50 mg/kg, clonidine 40 µg/kg, ketamine 50 mg/kg 30 min after 10 µg/kg clonidine, ketamine 50 mg/kg 30 min after 40 µg/kg clonidine or saline (control). Apoptosis was measured 24 h after treatment using Flouro-Jade staining. Spontaneous activity in a novel environment was tested at an age of 55 days. RESULTS: Pre-treatment with 40 µg/kg clonidine, but not 10 µg/kg clonidine, 30 min before ketamine exposure abolished ketamine-induced apoptosis and the behavioural changes observed in the young adult mice. The mice exposed to clonidine alone showed no differences from the saline-treated (control) mice. CONCLUSION: The administration of clonidine eliminated the adverse effects of ketamine in this mouse model, suggesting a possible strategy for protection. Alone, clonidine did not cause any adverse effects in these tests.

Neonatal exposure to deca-brominated diphenyl ether (PBDE 209) causes dose-response changes in spontaneous behaviour and cholinergic susceptibility in adult mice.

Polybrominated diphenyl ethers (PBDEs), used as additive flame-retardants, are increasing in the environment and are present in human mother's milk, newborns and toddlers. We reported earlier that several PBDEs, highly brominated PBDEs, caused developmental neurotoxic effects in mice, manifested as persistent aberrations in spontaneous behaviour, habituation capability, learning and memory, and changes in the cholinergic system. The present study was undertaken to explore the dose-response effects of PBDE 209 on spontaneous behaviour, habituation and its effects on the murine cholinergic system. Neonatal male NMRI mice were given 1.4, 2.3, 14 or 21micromol PBDE 209/kg body weight, when 3 days old. The agent was administered as a single oral dose via a metal gastric tube. Spontaneous behaviour and response to the cholinergic agonist nicotine were observed in adult mice at 2 and 4 months of age. Mice were also observed for anxiety-like behaviour in an elevated plus-maze. Adult mice, 2 and 4 months old, showed a dose-response related change in spontaneous behaviour, viz. were hyperactive and showed reduced or lack of habituation, effects that worsen with age. At the adult age of 4 months the susceptibility of the cholinergic system was also affected in a dose-response related manner, viz. reduced and/or hypoactive response to nicotine. This shows that PBDE 209 can be as potent as the lower brominated PBDEs in causing developmental neurotoxic defects.

A brominated flame retardant, 2,2',4,4',5-pentabromodiphenyl ether: uptake, retention, and induction of neurobehavioral alterations in mice during a critical phase of neonatal brain development.

Polybrominated diphenyl ethers (PBDEs) are used in large quantities as flame retardant additives. In a recent study, we have seen that neonatal exposure to some brominated flame retardants can cause permanent aberrations in spontaneous motor behavior that seem to worsen with age. In view of an increasing amount of PBDEs in mother's milk and in the environment, the present study was undertaken to investigate whether there is a critical and limited phase, during neonatal life, for induction of persistent neurotoxic effects of 2,2',4,4',5-pentaBDE (PBDE 99). Neonatal NMRI male mice were exposed on day 3, 10, or 19 to 8 mg 2,2',4,4',5-pentaBDE/kg body weight. Uptake and retention of 2,2',4,4',5-penta[(14)C]BDE were studied in the mouse brain after exposure to 1.5 M becquerel (Bq) 2,2',4,4',5-penta[(14)C]BDE /kg body weight (bw) on postnatal day 3, 10, or 19. Spontaneous motor behavior was observed in 4-month-old mice. Mice exposed to 2,2',4,4',5-pentaBDE on day 3 or 10 showed significantly impaired spontaneous motor behavior, whereas no effect was seen in mice exposed on day 19. Neonatal mice exposed to 2,2',4,4',5-penta[(14)C]BDE 99 on postnatal day 3, 10, or 19 were sacrificed 24 h or 7 days posttreatment. The amount of radioactivity, given as per mille ( per thousand) of total amount administered, was between 3.7 and 5.1 per thousand in the three different age categories at 24 h after administration. Seven days after the administration, 2,2',4,4',5-penta[(14)C]BDE or its metabolites could still be detected in the brain. The amount of radioactivity in the brain was not higher in mice exposed on day 3 or 10 when compared to exposure on day 19. Thus, the behavioral disturbances observed in adult mice following neonatal exposure to 2,2',4,4',5-pentaBDE are induced during a defined critical period of neonatal brain development.

The developing cholinergic system as target for environmental toxicants, nicotine and polychlorinated biphenyls (PCBs): implications for neurotoxicological processes in mice.

During neonatal life, offspring can be affected by toxic agents either by transfer via mother's milk or by direct exposure. In many mammalian species the perinatal period is characterized by a rapid development of the brain - "the brain growth spurt" (BGS). This period in the development of the mammalian brain is associated with numerous biochemical changes that transform the feto-neonatal brain into that of the mature adult. In rodents, the cholinergic transmitter system undergoes a rapid development during the neonatal period, a time when spontaneous motor behaviour also reaches peak activity. We have observed that low-dose exposure to environmental toxicants such as nicotine, polychlorinated biphenyls (PCBs) and polybrominated diphenylethers (PBDE, flame retardants) during the "BGS" can lead to irreversible changes in adult brain function in the mouse. The induction of persistent effects on behaviour and cholinergic nicotinic receptors in the adult animal appears to be limited to a short period during neonatal development. Furthermore, the neurotoxic effects were shown to develop over time, indicating a time-response/time-dependent effect. This indicates that environmental toxicants, such as nicotine, PCBs and probably PBDEs, might be involved in the slow, implacable induction of neurodegenerative disorders and/or interfere with normal aging processes.