Korean J Physiol Pharmacol.  2002 Feb;6(1):9-14.

Characterization of Norepinephrine Release in Rat Posterior Hypothalamus Using in vivo Brain Microdialysis

• Sung KW
• Kim SY
• Kim ON
• Lee SB

Abstract

In the present study, we used the microdialysis technique combined with high performance liquid chromatography (HPLC) and electrochemical detection to measure the extracellular levels of norepinephrine (NE) in the posterior hypothalamus in vivo, and to examine the effects of various drugs, affecting central noradrenergic transmission, on the extracellular concentration of NE in the posterior hypothalamus. Microdialysis probes were implanted stereotaxically into the posterior hypothalamus (coordinates: posterior 4.3 mm, lateral 0.5 mm, ventral 8 mm, relative to bregma and the brain surface, respectively) of rats, and dialysate collection began 2 hr after the implantation. The baseline level of monoamines in the dialysates were determined to be: NE 0.17 +/- 0.01, 3,4-dihydroxyphenylacetic acid (DOPAC) 0.94 +/- 0.07, homovanillic acid (HVA) 0.57 +/- 0.05 pmol/sample (n=8). When the posterior hypothalamus was perfused with 90 mM potassium, maximum 555% increase of NE output was observed. Concomitantly, this treatment significantly decreased the output of DOPAC and HVA by 35% and 28%, respectively. Local application of imipramine (50microM) enhanced the level of NE in the posterior hypothalamus (maximum 200%) compared to preperfusion control values. But, DOPAC and HVA outputs remained unchanged. Pargyline, an irreversible monoamine oxidase inhibitor, i.p. administered at a dose of 75 mg/kg, increased NE output (maximum 165%), while decreased DOPAC and HVA outputs (maximum 13 and 12%, respectively). These results indicate that NE in dialysate from the rat posterior hypothalamus were neuronal origin, and that manipulations which profoundly affected the levels of extracellular neurotransmitter had also effects on metabolite levels.

Keyword

Hypothalamus; Microdialysis; Norcpinephrine; Rat

MeSH Terms

3,4-Dihydroxyphenylacetic Acid
Animals
Brain*
Chromatography, Liquid
Dialysis Solutions
Homovanillic Acid
Hypothalamus
Hypothalamus, Posterior*
Imipramine
Microdialysis*
Monoamine Oxidase Inhibitors
Neurons
Neurotransmitter Agents
Norepinephrine*
Pargyline
Potassium
Rats*
3,4-Dihydroxyphenylacetic Acid
Dialysis Solutions
Homovanillic Acid
Imipramine
Monoamine Oxidase Inhibitors
Neurotransmitter Agents
Norepinephrine
Pargyline
Potassium