Oxygen-induced modifications of benzodiazepine receptors and D2 dopamine receptors in the rat under hyperoxia

Dopamine, Neurochemical Processes, and Oxygen Toxicity at Pressure

All mammals, including man, exposed to breathing gas mixtures at high pressures exhibit central nervous system disturbances, which differ according to the gas used. With the use of compressed air, the increased oxygen partial pressure induces hyperoxic disturbances that consist of epileptic seizures that occur, on average, after 30 min exposure to 2.8 ATA in man or to 5 ATA in rats. Increased oxygen partial pressure induces reactive oxygen species and reactive nitrogen species production that could be related to neurotransmitter changes reported for the preepileptic phase or at pressures that produce epileptic seizures. In rats, oxygen pressures lower than 5 ATA induce a decrease of dopamine release in the stratum that could be due to disturbances of neurotransmitter regulatory processes that are different from those implicated for hyperbaric oxygen-induced epileptic seizures. © 2016 American Physiological Society. Compr Physiol 6:1339-1344, 2016.

Alteration of striatal dopamine levels under various partial pressure of oxygen in pre-convulsive and convulsive phases in freely-moving rats

The purpose of this study was to investigate the change in the striatal dopamine (DA) level in freely-moving rat exposed to different partial pressure of oxygen (from 1 to 5 ATA). Some works have suggested that DA release by the substantia nigra pars compacta (SNc) neurons in the striatum could be disturbed by hyperbaric oxygen (HBO) exposure, altering therefore the basal ganglia activity. Such changes could result in a change in glutamatergic and GABAergic control of the dopaminergic neurons into the SNc. Such alterations could provide more information about the oxygen-induced seizures observed at 5 ATA in rat. DA-sensitive electrodes were implanted into the striatum under general anesthesia. After 1 week rest, awaked rats were exposed to oxygen-nitrogen mixture at a partial pressure of oxygen of 1, 2, 3, 4 and 5 ATA. DA level was monitored continuously (every 3 min) by in vivo voltammetry before and during HBO exposure. HBO induced a decrease in DA level in relationship to the increase in partial pressure of oxygen from 1 ATA to 4 ATA (-15 % at 1 ATA, -30 % at 2 ATA, -40 % at 3 ATA, -45 % at 4 ATA), without signs of oxygen toxicity. At 5 ATA, DA level strongly decreases (-75 %) before seizure which occurred after 27 min ± 7 HBO exposure. After the epileptic seizure the decrease in DA level disappeared. These changes and the biphasic effect of HBO were discussed in function of HBO action on neurochemical regulations of the nigro striatal pathway.

Oxygen as a therapy for reducing nicotine withdrawal symptoms

Nicotine addiction leads to withdrawal symptoms in many persons who quit smoking. In addition to craving, the most commonly experienced symptoms are: depression; difficulty sleeping; irritability, frustration, or anger; anxiety; difficulty concentrating; restlessness; decreased heart rate; and increased appetite or weight gain. The severity of withdrawal symptoms are variable, and often lead to relapse. By altering the course of withdrawal symptoms it is possible to improve the chances of the quit attempt and reduce the risk of relapse. There is strong evidence that dopamine is the primary neurotransmitter in the reward pathway in addiction. The use of nicotine replacement therapies and Zyban (sustained release bupropion hydrochloride), both of which are suspected of exploiting dopamine's role in addiction, enhance the likelihood of long-term smoking cessation. Anecdotal reports of oxygen's capacity to reduce both the desire for nicotine and withdrawal symptoms suggest that this may be a therapeutic possibility for those who do not experience success with more traditional cessation approaches. Oxygen may have a favorable effect on nicotine withdrawal, as it appears to alter the balance of central neurotransmitters such as dopamine.

Blood oxygen partial pressure affects plasma prolactin concentration in humans

Responses of plasma prolactin (PRL) concentration to acute and repeated changes in blood oxygen partial pressure (PO2a) at rest were investigated in two studies (A; B), with special reference to possible effects mediated via serotonin (5-HT) synthesis. In A, nine male subjects inhaled for 105 min gas containing different oxygen fractions for 6 days. Gas concentrations consisted of 14% (A14), 21 % (A21), 40% (A40), 60% (A60) and 80% (A80) O2 mixed with N2 as well as 100% O2 (A100). Venous and capillary blood samples were drawn before and every 15 min during gas inhalation for analysis of plasma PRL and PO2a. In B, two groups of subjects (B I; B II) were exposed to 30 min day(-1) of gas inhalation over 14 consecutive days. Gas concentration consisted for B I of 14% O2/86% N2 and for B II of 100% O2. During pre- and post-examination a baseline blood sample was drawn, followed by a neuroendocrine test of serotonergic function using a partial 5-HT1A receptor agonist (60 mg of buspirone hydrochloride). In A, each increase of inhaled oxygen fraction also resulted in higher blood POb2a. In A14, A21 and A40, plasma PRL concentrations did not change from basal level. Increases in plasma PRL concentration were found in A60 after 30 min as well as in A80 and A100 after 15 min. A higher blood PO2a induced a higher plasma PRL secretion but also an earlier decline from peak plasma PRL value despite continued inhalation of the respective oxygen concentration. During post-examination in B, basal plasma PRL concentrations were increased in B I and decreased in B II. Plasma PRL response to stimulation challenge was not affected by treatments. Thus, chronic adaptations of basal plasma PRL concentrations to decreased/increased blood PO2a were not related to up/down-regulation, respectively, of central serotonergic receptor function.

Differential effects of in vitro peroxidation on peripheral- and central-type benzodiazepine receptors. Protection by diverse antioxidants

The influence of various concentrations of ferrous iron and ascorbate on in vitro peroxidation and drug binding of diverse membrane preparations (cerebral cortex and liver) was studied. Peroxidation was not simply dose-related to ascorbate and ferrous iron, but a complex relationship between iron and ascorbate when added in association was established. Under our conditions 0.01 mM Fe2+ and 0.5 mM ascorbate was the most peroxidative combination for cerebral and liver membranes. Under the same conditions, cerebral membranes were more peroxidated than liver membranes. Considering the consequences of drug binding, peripheral-type benzodiazepine receptors (PBRs) of liver were more affected by peroxidative events than central-type benzodiazepine receptors (CBRs) of the cerebral cortex. The degree of binding disturbance was generally inversely correlated to the degree of peroxidation and this was more significant for liver PBRs than for cerebral CBRs. The liver membrane model was retained for testing in vitro protection by diverse putative antioxidants. Under our conditions desferrioxamine, ethylene diamine tetra acetate (EDTA), trolox, and rutin were good protective antioxidants, whereas phenyl-butyl-nitrone (PBN) and tocopherol were not effective.

Amino acids and ammonia in the cerebral cortex, the corpus striatum and the brain stem of the mouse prior to the onset and after a seizure induced by hyperbaric oxygen

The contents of amino acids (AA) and ammonia (NH3) were measured in corpus striatum, brain stem and cerebral cortex of two strains of mice exposed to hyperbaric oxygen (HBO). Mice of the HBO-sensitive strain (CD1) were exposed to 600 kPa O2 for 24 min versus 90 min for mice of the normal C57 strain, so that 50% of the mice in both strains developed a generalized convulsion. In the cortex of exposed but unconvulsed (EXUN) C57 mice, the contents of taurine, glutamine and NH3 increased while that of GABA decreased when compared to control mice. In the CD1 mice, NH3 content was increased while that of Asp decreased. After a convulsion, NH3 was increased in both strains, the AA contents returned to normal in C57 but Asp remained low in CD1 mice. Somewhat similar changes occurred in the striatum except that NH3 levels were less affected while GABA ones were significantly decreased in the CD1 mice exposed to HBO, whether convulsed or not. In the EXUN brain stem, Asp and Glu contents decreased. These decreases were greater in C57 on a percentage basis than in CD1 mice. GABA content was decreased in the C57 strain. After a convulsion, Asp and Glu levels remained low and NH3 accumulated in CD1 whereas in C57 only the Glu level was decreased. The cortical and striatal changes may indicate a lesser GABA supply in C57 strain and some Asp release in CD1 strain. In the brain stem of both strains, Asp and Glu release is possible in addition to GABA in C57 strain.(ABSTRACT TRUNCATED AT 250 WORDS)