Effects of amantadine on uptake and release of dopamine by a particulate fraction of rat basal ganglia

Abstract

Amantadine, in vitro, produced dose-dependent blockade of dopamine uptake into a synaptosome-rich particulate fraction of an homogenate of the basal ganglia of rats. A concentration of 3.6 x 1 0 -6~ was required to inhibit uptake by 50%. Diethazine was less potent in blocking dopamine uptake, the equiactive concentration being 8.0 x lO-'j~. Amantadine and (+)-amphetamine in concentrations in excess of 1 0 -5~ caused the release of small quantities of added dopamine from the particulate fraction.The findings of Vernier, Harmon & others (1969) and of Heimans, Rand & Fennessy (1 972) suggest that amantadine potentiates the peripheral pharmacological effects of dopamine by blocking uptake of amines in a variety of adrenergically innervated preparations. We have investigated the effect of amantadine on dopamine uptake and release by the particulate fraction of an homogenate obtained from basal ganglia, the presumed site of pathology in Parkinson's disease (Hornykiewicz, 1963). METHODS Preparation of homogenate from rat basal gangliaThe preparation was modified from that described by Horn, Coyle & Snyder (1971). Rats, 200-300 g, were stunned and decapitated and the basal ganglia, consisting of corpus striatum, caudate and putamen were rapidly dissected and removed to ice, according to Glowinski & Iverson (1966). The tissue was weighed (100-125 mg) and homogenized in 4 ml of 0 . 2 5~ sucrose at 0" before centrifuging for 10 min at 100 g in an M.S.E. refrigerated centrifuge. The supernatant fluid was then carefully decanted from the pellet of tissue debris which was discarded. The resulting fluid containing particulate fraction was gently stirred to produce a homogeneous suspension. Dopamine uptake by the synaptosome-containing homogenateAn aliquot of the homogenate (0.1 ml) was transferred to a 20 ml vial containing 3.9 ml of modified Krebs-Henseleit solution of the following composition: NaCI, 118 mM; KCI, 4.7 mM; NaHCO,, 25 mM; MgSO,, 0.45 m~; KH,P04, 1.03 mM; CaCI,, 1.25 m~; D-(+)-glucose, 11.1 mM; together with nialamide 1.25 x 1 0 -5~ and ascorbic acid, 0.2 mg/ml. Disodium EDTA, 0.1 mg/ml, and various concentrations of amantadine or diethazine were added to this solution. The solution was kept at 37" and continuously aerated with a stream of 5 % carbon dioxide in oxygen. The preparation was incubated for 5 min, 5 to 40 p1 of 30 mM dopamine (side-chain l,WH; specific activity 1.3 Ci/mmol) was added and incubation continued for 5 min.

Some actions of amantadine on peripheral tissues

“…There is evidence consonant with the suggestion that amantadine blocks the uptake of dopamine and other amines in the periphery and it is likely therefore that amantadine could block the uptake of dopamine centrally. Furthermore, it has been shown that amantadine blocks the uptake of dopamine by synaptosomes prepared from rat basal ganglia (Heimans, Rand & Fennessy, 1972).…”

The production of an alternative laboratory model of the Parkinson syndrome using a new benzylimidoylurea derivative LON 954

“…The failure of amantadine to modify LON 954 tremor would appear to support the findings of various authors (Baldessarini et al, 1972;Fletcher and Redfern, 1970;Symchowicz et al, 1973) that increased synthesis and release of dopamine (Scatton et al, 1970;Farnebo et al, 1971), inhibition of dopamine uptake (Heimans et al, 1972) and/or a direct action on dopamine receptors (Papeschi, 1974) are not the primary mechanisms by which amantadine exerts its antiParkinson effects.…”

The Pharmacology of Rauwolfia Alkaloids

“…The rigidity and changes in ac-motoneurone and y-fibre activity in rats produced by reserpine are also abolished by amantadine (JURNA et al, 1972): this agent acts by inhibiting dopamine uptake into synaptosomes from rat basal ganglia (HEIMANS et al, 1972), and would thereby facilitate dopaminergic transmission.…”