ISSN:
1432-1912
Keywords:
Periaqueductal gray slices
;
[3H]Noradrenaline release
;
[3H]Dopamine release
;
[3H]5-Hydroxytryptamine release
;
Rat
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The periaqueductal gray is a brain region of considerable interest. It is innervated by monoamine-containing neurons as well as by a variety of peptidergic fiber systems, and it participates in the regulation of various functions. Virtually nothing is known about monoamine release in the periaqueductal gray and its receptor-mediated modulation. We therefore studied the release of radioactivity from periaqueductal gray slices preloaded with tritriated monoamines, using an in vitro superfusion method. The release of radioactivity from superfused periaqueductal gray slices after preloading of the tissue with [3H]noradrenaline increased upon electrical stimulation in a frequency-dependent manner. The stimulus-evoked release of radioactivity was Ca2+-dependent. Clonidine reduced and yohimbine enhanced the release. The inhibition curve for the effect of clonidine was shifted to the right in the presence of 10−6 M yohimbine. While phenylephrine, isoprenaline, SK&F 38393, quinpirole, carbachol, [Arg8]vasopressin, α-MSH and ACTH-(1-24), at a concentration of 10−6 M, did not influence the electrically evoked release of radioactivity, [Leu5]enkephalin reduced it. The selective μ-opioid receptor agonists [d-Ala2,NMePhe4,Gly-ol5]enkephalin and [d-Arg2,Lys4]-dermorphin-(1–4)-amide reduced the release of radioactivity, whereas the selective δ opioid receptor agonist [d-Pen2,d-Pen5]enkephalin and the selective K opioid receptor agonist U-69593 had no effect. In the presence of naloxone, which by itself had no effect on the release of radioactivity, the effect of [d-Arg2,Lys4]dermorphin-(1–4)-amide was abolished. These results show that the release of noradrenaline from periaqueductal gray slices is via a Ca2+-dependent. exocytotic process, and that it is modulated through α2-adrenoceptors as well as via μ-opioid receptors. Though the overflow of radioactivity from slices preloaded with [3H]dopamine in the presence of desipramine was measurable, there are reasons to assume that we are dealing here with the release of tritiated catecholamines from a population of nerve endings consisting of noradrenergic and dopaminergic terminals. The release of radioactivity from periaqueductal gray slices preloaded with [3H]5-hydroxytryptamine upon elevation of the K+ concentration in the superfusion medium was much more pronounced than that induced by electrical stimulation. The K+-evoked release of radioactivity was almost completely abolished in the absence of Cat2+; showing that the release is via a Ca2+-dependent process. 5-Hydrotryptamine reduced the K+-evoked release of radioactivity in a concentration-dependent manner.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00184290
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