Striatal perfusion of indomethacin attenuates dopamine increase in immature rat brain exposed to anoxia: an in vivo microdialysis study

Current Therapies for Neonatal Hypoxic-Ischaemic and Infection-Sensitised Hypoxic-Ischaemic Brain Damage

Neonatal hypoxic-ischaemic brain damage is a leading cause of child mortality and morbidity, including cerebral palsy, epilepsy, and cognitive disabilities. The majority of neonatal hypoxic-ischaemic cases arise as a result of impaired cerebral perfusion to the foetus attributed to uterine, placental, or umbilical cord compromise prior to or during delivery. Bacterial infection is a factor contributing to the damage and is recorded in more than half of preterm births. Exposure to infection exacerbates neuronal hypoxic-ischaemic damage thus leading to a phenomenon called infection-sensitised hypoxic-ischaemic brain injury. Models of neonatal hypoxia-ischaemia (HI) have been developed in different animals. Both human and animal studies show that the developmental stage and the severity of the HI insult affect the selective regional vulnerability of the brain to damage, as well as the subsequent clinical manifestations. Therapeutic hypothermia (TH) is the only clinically approved treatment for neonatal HI. However, the number of HI infants needed to treat with TH for one to be saved from death or disability at age of 18-22 months, is approximately 6-7, which highlights the need for additional or alternative treatments to replace TH or increase its efficiency. In this review we discuss the mechanisms of HI injury to the immature brain and the new experimental treatments studied for neonatal HI and infection-sensitised neonatal HI.

Effect of perinatal asphyxia and carbamazepine treatment on cortical dopamine and DOPAC levels

Background

One of the most important manifestations of perinatal asphyxia is the occurrence of seizures, which are treated with antiepileptic drugs, such as carbamazepine. These early seizures, combined with pharmacological treatments, may influence the development of dopaminergic neurotransmission in the frontal cortex. This study aimed to determine the extracellular levels of dopamine and its main metabolite DOPAC in 30-day-old rats that had been asphyxiated for 45 min in a low (8%) oxygen chamber at a perinatal age and treated with daily doses of carbamazepine. Quantifications were performed using microdialysis coupled to a high-performance liquid chromatography (HPLC) system in basal conditions and following the use of the chemical stimulus.

Results

Significant decreases in basal and stimulated extracellular dopamine and DOPAC content were observed in the frontal cortex of the asphyxiated group, and these decreases were partially recovered in the animals administered daily doses of carbamazepine. Greater basal dopamine concentrations were also observed as an independent effect of carbamazepine.

Conclusions

Perinatal asphyxia plus carbamazepine affects extracellular levels of dopamine and DOPAC in the frontal cortex and stimulated the release of dopamine, which provides evidence for the altered availability of dopamine in cortical brain areas during brain development.

Contributions of microdialysis to new alternative therapeutics for hepatic encephalopathy

Hepatic encephalopathy (HE) is a common complication of cirrhosis, of largely reversible impairment of brain function occurring in patients with acute or chronic liver failure or when the liver is bypassed by portosystemic shunts. The mechanisms causing this brain dysfunction are still largely unclear. The need to avoid complications caused by late diagnosis has attracted interest to understand the mechanisms underlying neuronal damage in order to find markers that will allow timely diagnosis and to propose new therapeutic alternatives to improve the care of patients. One of the experimental approaches to study HE is microdialysis; this technique allows evaluation of different chemical substances in several organs through the recollection of samples in specific places by semi-permeable membranes. In this review we will discuss the contributions of microdialysis in the understanding of the physiological alterations in human hepatic encephalopathy and experimental models and the studies to find novel alternative therapies for this disease.

Thromboxane receptor activation enhances striatal dopamine release, leading to suppression of GABAergic transmission and enhanced sugar intake

The extracellular dopamine level is regulated not only by synaptic inputs to dopamine neurons but also by local mechanisms surrounding dopaminergic terminals. However, much remains to be investigated for the latter mechanism. Thromboxane A(2) is one of the cyclooxygenase products derived from arachidonic acid, and acts on its cognate G protein-coupled receptor [thromboxane receptor (TP)]. We show here that TP in the striatum locally facilitates dopamine overflow. Intrastriatal injection of a TP agonist increased extracellular dopamine levels in the striatum as measured by in vivo microdialysis. TP stimulation also augmented electrically evoked dopamine overflow from striatal slices. Conversely, TP deficiency reduced dopamine overflow evoked by N-methyl-d-aspartic acid (NMDA) and acetylcholine in striatal slices. TP immunostaining showed that TP is enriched in vascular endothelial cells. Pharmacological blockade of nitric oxide (NO) synthesis and genetic deletion of endothelial NO synthase (eNOS) suppressed NMDA/acetylcholine-induced dopamine overflow. This involvement of NO was abolished in TP-deficient slices, suggesting a role for eNOS-derived NO synthesis in TP-mediated dopamine overflow. As a functional consequence of TP-mediated dopamine increase, a TP agonist suppressed GABAergic inhibitory postsynaptic currents in medium spiny neurons through a D2-like receptor-dependent mechanism. Finally, TP is involved in sucrose intake, a dopamine-dependent motivational behavior. These data suggest that TP stimulation in the striatum locally facilitates dopamine overflow evoked by synaptic inputs via NO synthesis in endothelial cells.

The effects of indomethacin on caspases, glutathione level and lipid peroxidation in the newborn rats with hypoxic-ischemic cerebral injury

Activation of phospholipase A(2), degradation of membrane phospholipids resulting in tissue accumulation of arachidonic acid, and the activation of cyclooxygenase that leads to the formation of prostaglandin and free radicals may occur after hypoxic-ischemic damage. The aim of this study was to investigate the effects of indomethacin, a nonselective cyclooxygenase inhibitor, on caspase activity, glutathione levels and lipid peroxidation in newborn rats with hypoxic-ischemic encephalopathy. The effects of indomethacin were evaluated by measuring caspase-3 and caspase-8 activities and glutathione levels. Lipid peroxidation was evaluated by measuring concentrations of malondialdehyde in rat brains. Seven-day-old rat pups with the Levine-Rice model of hypoxic-ischemic cerebral injury were randomly divided into three study groups. In the indomethacin-treated group, rats were administered three doses of indomethacin, at a dose of 2 mg/kg every 12 h. Sham and the hypoxic-ischemic group of rats were given physiologic saline. The sham group underwent all surgical procedures except for arterial ligation. After 72 hours, the rats were decapitated and brain tissues were evaluated. Caspase-3 and caspase-8 activities and glutathione and malondialdehyde levels were evaluated in all groups. There was an obvious decrease in caspase-3 and caspase-8 activities and depleted glutathione levels were reversed in the indomethacin-treated group compared to the hypoxic-ischemia group (p<0.001). As indomethacin was unable to prevent lipid peroxidation, malondialdehyde concentrations increased to ischemia-induced levels. In conclusion, indomethacin administration after hypoxic-ischemic encephalopathy injury has a neuroprotective effect since it inhibits caspase activity and reverses the depletion of glutathione. However, it also aggravates lipid peroxidation-induced ischemia.

Evidence for thermoregulation by dopamine D1 and D2 receptors in the anteroventral preoptic region during normoxia and hypoxia

Hypoxia causes a regulated decrease in body temperature (Tb), a response that has been called anapyrexia. Stimulation of dopamine receptors in the central nervous system (CNS) reduces Tb in rats, and dopamine D1 and D2 receptors seem to be involved in this response. Thus, we predicted that injection of SCH 23390 and haloperidol, D1 and partly D2 receptor antagonists, respectively, into the anteroventral preoptic region (AVPO, the thermointegrative region of the CNS) would lessen the hypoxia-induced anapyrexia. We measured Tb of conscious Wistar rats before and after injection of SCH 23390 (50 and 100 ng/100 nl) or haloperidol (50 e 500 ng/100 nl) or their respective vehicles (saline and DMSO 5%) into the AVPO followed by 30 min of hypoxia (7% O2). Vehicles and the lower doses of SCH 23390 and haloperidol had no effect on Tb during normoxia or hypoxia. The higher doses of SCH 23390 and haloperidol attenuated (P<0.05) the drop in Tb elicited by hypoxia. However, this higher haloperidol dose also increased Tb during normoxia. The present data is consistent with the notion that dopamine is an important thermoregulatory neurotransmitter in a way that D2 receptors are mainly involved with maintenance of Tb in euthermia, while D1 receptors are activated to induce hypoxic anapyrexia in the AVPO.