Korean J Physiol Pharmacol.  1997 Apr;1(2):135-142.

The influence of N-6-cyclopentyladenosine and magnesium on norepinephrine release in the rat hippocampus

• Park YB
• Park SD
• Choi BK

Abstract

As it has been reported that the depolarization-induced norepinephrine (NE) release is modulated by activation of presynaptic A-1-adenosine heteroreceptor and various lines of evidence indicate that A-2-adenosine receptor also presents in hippocampus, and that the adenosine effect is magnesium dependent, the present study was undertaken to delineate the role of adenosine receptors in the modulation of hippocampal NE release. Slices from the rat hippocampus were equilibrated with (3H)-NE and the release of the labelled product, (3H)-NE, was evoked by electrical stimulation (3 Hz, 5 V cm-1, 2 ms, rectangular pulses), and the influence of various agents on the evoked tritium outflow was investigated. N-6-cyclopentyladenosine (CPA), in concentrations ranging from 0.1 to 10 micrometer, decreased the (3H)-NE release in a dose-dependent manner without changing the basal rate of release, and these effects were significantly inhibited by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 2 micrometer) treatment. When the magnesium concentration was reduced to 0.4 mM or completely removed, the evoked NE release increased along with decreased basal rate of release. In contrast, increasing the magnesium concentrations to 2.4 and 4 mM, decreased the evoked NE release. The CPA effects on evoked NE release were reduced by magnesium removal, but potentiated by 2.4 mM magnesium in the medium. 5-(N-cyclopropyl)-carboxamodiadenosine (CPCA, 1 & 10 micrometer), an A-2-agonist, decreased the evoked tritium outflow, and this effect was also abolished by DPCPX pretreatment. CGS, a powerful A-2-agonist, did not affect the evoked NE release. However, the effects of CPCA and CGS on evoked NE release were significantly increased by pretreatment of DPCPX in the magnesium-free medium. These results indicate that inhibitory effect of A-1-adenosine receptor on NE release is magnesium-dependent, and A-2-receptor may be present in the rat hippocampus.

Keyword

N6-cyclopentyladenosin; Magnesium; Norepinephrine

MeSH Terms

Adenosine
Animals
Electric Stimulation
Hippocampus*
Magnesium*
Norepinephrine*
Rats*
Receptors, Purinergic P1
Tritium
Adenosine
Magnesium
Norepinephrine
Receptors, Purinergic P1
Tritium