Brain dopamine and mild hypoxia

Transcription

1 Brain dopamine and mild hypoxia Denoroy L, Orset C, Parrot S, Berod A, Sauvinet V, Cottet-Emard JM, Pequignot JM. Université Claude Bernard, Lyon, France

2 Striatum vulnerable to hypoxia ischemia necrotic and apoptotic neuronal death Mild (tolerable) hypoxaemic hypoxia no neuronal loss alterations in behavior : locomotion changes in neurotransmission?

3 Striatum Glutamate GABA, Enkephalin Substance P Acetylcholine NPY VIP Serotonin Dopamine

4 To in vivo determine extracellular dopamine and metabolites in the striatum of awake rats during acute hypoxia (1%O 2-9%N 2, 1 hour)

5 Microdialysis 1-4 mm Microdialysis probe capillary artificial CSF (1 µl/min) sample stainless steel tubing membrane monitoring of the extracellular concentrations of neurotransmitters in situ administration of drugs by reverse dialysis detection of several neurotransmitters (depending on the analytical techniques) 225 µm

6 acsf (1.5 µl/min.) Microdialysis probe Dental cement guide cortex Membrane ø = 225µm L = 3 mm striatum

7 Analysis of microdialysates Capillary electrophoresis with laser-induced fluorescence detection (Naphtalene-2,3-dicarboxyaldehyde/NaCN derivatization) Dopamine High performance liquid chromatography with electrochemical detection 3,4 dihydroxyphenylacetic acid (DOPAC) Homovanillic acid (HVA)

8 Rats 28 gr day1 Protocol day7 day15 Recovery Habituation implantation of guide microdialysis 1%O 2 Implantation of microdialysis probe Overnight stabilisation Normoxia Hypoxia Normoxia h 1h15 2h15 3h15 Collection of 15 min microdialysates

9 Why in vivo studies in awake animals? Anaesthesia + Hypoxia +/- Release of neurotransmitters - carotid chemoreceptors Adaptation response

10 1% O 2 9% N 2 Air pump Microdialysate collection acsf perfusion Th. Plethysmographic chamber Reference chamber Temperature controlled system pressure transducer Data analysis

11 F R (cycle/min) V T (ml) Effect of 1% O 2 hypoxia on ventilation normoxia hypoxia (5 th min) hypoxia (15 th min) normoxia hypoxia (5 th min) hypoxia (15 th min) Ve (ml/min) normoxia hypoxia (5 th min) hypoxia (15 th min)

12 Effect of mild hypoxaemic hypoxia on extracellular dopamine 25 control hypoxic % of basal concentration % O

13 Effect of mild hypoxaemic hypoxia on extracellular DOPAC 14 hypoxic 12 control % of basal concentration % O

14 Effects of mild hypoxia in the striatum of awake rats dopamine DOPAC, HVA No changes in glutamate and aspartate

15 Tyrosine TH DOPA AP-5 MK-81 DOPAC NMDA D2 MAO DA DA Nomifensine DA DA Ca 2+ Na + Tetrodotoxin DA DA Ca 2+ D1

16 Effect of nomifensine on hypoxia-induced induced increase in dopamine % of basal concentration hypoxic control hypoxic control % O 2 1 μm nomifensine

17 Origin of 1% O 2 hypoxia-induced induced increase in dopamine Nomifensine : Inhibits dopamine increase when applied prior to hypoxia Fails to alter dopamine increase when applied after the beginning of hypoxia Hypoxia-induced increase in dopamine : Onset : dependent on dopamine transporters Maintenance : not linked to dopamine transporters

18 25 Effect of tetrodotoxin on hypoxia-induced induced increase in dopamine 25 TTX TTX 2 2 % of basal concentration % of basal concentration % O 2 5 μm tetrodotoxin

19 Origin of 1% O 2 hypoxia-induced induced increase in dopamine Tetrodotoxin : Inhibits dopamine increase when applied prior to hypoxia after the beginning of hypoxia Hypoxia-induced increase in dopamine : Onset and maintenance need voltage-dependent Na+ channels

20 Origin of 1% O 2 hypoxia-induced induced increase in dopamine Modulation by glutamate receptors of the N-methyl-D-aspartate type? Effects of NMDA receptors antagonists on hypoxia-induced dopamine increase

21 Effect of MK-81 on hypoxia-induced induced increase in dopamine % of basal concentration hypoxic control hypoxic control % O 2 5 μm MK 81

22 Origin of hypoxia-induced induced increase in dopamine Onset : dependent on voltagegated Na + channels dependent on dopamine transporters inhibited by NMDA receptors Maintenance : dependent on voltagegated Na + channels not linked to dopamine transporters independent of NMDA receptors control hypoxic 1% O

23 Hypoxia-induced induced increase in striatal dopamine depends on voltage-gated gated Na+ channels Enhanced activity in nigro-striatal dopaminergic pathway? Study of c-fos gene expression Immunohistochemistry of Fos protein

24 Nucleus tractus solitarii Hypoxia Substantia nigra Normoxia Hypoxia Normoxia

25 Acknowledgements INSERM U512 S. Parrot C. Orset V. Sauvinet A. Berod UA-6451 J.M. Cottet-Emard CNRS UMR 5123 J.M. Pequignot Y. Dalmaz Support Université Claude Bernard Lyon I CNRS INSERM Région Rhône-Alpes

26 A 22 2 % of basal concentration B % of basal concentration Nomifensine C % of basal concentration Nomifensine D 25 2 TTX E 25 2 TTX % of basal concentration % of basal concentration Fig. 2. Effect of hypoxia (1% oxygen during 1 h ; top black bar) on dopamine concentrations in microdialysates from striatum of freely-moving rats (A). The normoxic group (n=5) is represented by the vertical white bars and the hypoxic group (n=8) by the vertical black bars. Nomifensine (1 µm) was perfused (crossed bar) just before (B) (normoxic n=6 ; hypoxic n=5) or 14 minutes after the beginning of the hypoxic period (C) (normoxic n=6 ; hypoxic n=6). TTX (5µM) was perfused (hatched bar) just before (D) (normoxic n=6 ; hypoxic n=5) or 14 minutes after the beginning of the hypoxic period (E) (normoxic n=6 ; hypoxic n=7). Data are expressed as percentages (mean ± SEM) of the baseline values preceding hypoxia and drug administration. p<.5 vs. control animals (ANOVA and post-hoc Student s t test).

27 Origin of 1% O 2 hypoxia-induced induced decreases in DOPAC and HVA Unaffected by nomifensine and MK-81 May be linked to a fall in dopamine synthesis