In Vivo Voltammetry and Microdialysis Monitoring of Monoamine Metabolism in the Rat Brainstem Neurons

Abstract

Two “in vivo” techniques allow the monitoring of extracellular levels of monoamines and related compounds in selected rat brainstem regions : voltammetry and microdialysis. “In vivo” voltammetry has a high regional selectivity : for example, we have been able to perform a subregional study and to show that the increase in extracellular DOPAC induced by 30 min-hypotension was twice as larg in the rostral as in the caudal rat locus coeruleus. The spatial resolution, as expressed by x1/₂ (see text), is 4 times better for voltammetry (50 μm) than for microdialysis (190 μm). Another advantage of voltammetry is its excellent time resolution. However, microdialysis has a much better biochemical specificity than voltammetry. Furthermore it allows some enzymatic activities, such as tyrosine hydroxylase, to be measured almost continuously in catecholaminergic brain nuclei. From a functional point of view, the results of our experiments (α₂ ligand administration, arterial hypotension or stress) illustrate the respective interest and complementarity of these two “in vivo” techniques. Their current developments will lead to a better temporal and biochemical resolution combined with an increase in the number of substances analyzed “in vivo”, including peptides and nitric oxide.

Key Words:

• brain slice
• carbon fiber microelectrode
• catecholamine neurons
• DOPAC
• HPLC
• intracerebral microdialysis
• in vivo voltammetry
• locus coeruleus
• medulla oblongata
• tyrosine hydroxylase