[3H]Tyramine binding: A comparison with neuronal [3H]-dopamine uptake and [3H]mazindol binding processes

Abstract

[3H]Spiperone [( 3H]SPI) binding sites in rat or bovine striata have been solubilized using CHAPS or digitonin detergents. Solubilized sites retained the binding characteristics of those in native membrane preparations. The same solubilized material, however, did not bind [3H]tyramine [( 3H]PTA), thus indicating that [3H]PTA binding sites and DA receptors are different chemico-physical entities. In membrane preparations or crude synaptosomes obtained from the c.striatum of neonatally-rendered hypothyroid rats, when central DA-pathways are impaired, both [3H]PTA binding and [3H]DA uptake processes were markedly decreased, with no effect on [3H]mazindol [( 3H]MAZ) binding, compared to euthyroids. Reserpine, a well-known inhibitor of DA-uptake into a variety of secretory vesicles, and a potent in vivo and in vitro inhibitor of [3H]PTA binding, did not affect the [3H]MAZ binding process. This further supported the suggestion that while [3H]PTA binding sites are almost totally associated with the vesicular transporter for DA, [3H]MAZ does label a site involved in the DA-translocation across the neuronal membrane. The latter process seems to be rather insensitive to thyroid hypofunction, when however the intracellular storage of DA might be consistently impaired. In conclusion, PTA might be well exploited as a marker of the DA vesicular transporter through its molecular characterization, whenever possible.

Trace Amines Depress GABAB Response in Dopaminergic Neurons by Inhibiting G-βγ-Gated Inwardly Rectifying Potassium Channels

“…Although the IC 50 value for the reducing effects of trace amines is greater than the nanomolar range usually found in the brain (Berry, 2004), it could be possible that under particular metabolic conditions or pharmacological treatments (e.g., monoamine oxidase inhibition), the synaptic activity of GABA B receptors is regulated by TAs. Therefore, saturable, high-affinity binding sites for [p-3 H]tyramine (Ungar et al, 1977;Vaccari, 1986;Vaccari and Gessa, 1989) and ␤-[…”

Trace Amines Cause More than One Effect on Dopaminergic Neurons

“…Therefore, the reduction of the GABA B IPSP might be principally due to the activation of G protein-coupled trace amine receptors that are stimulated by TYR and -PEA. Accordingly, saturable, high affinity binding sites for p-[3H]tyramine (Ungar, et al, 1977, Vaccari, 1986, Vaccari and Gessa, 1989 and -[3H]PEA (Nguyen and Juorio, 1989) have been reported in the nigrostriatal system. Although the IC50 for the reducing effects of trace amines is above the nanomolar range usually found in the brain (Berry, 2004), it could be possible that, under particular metabolic conditions or pharmacological treatments (e.g.…”

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“…2.5 fold higher than those of ptyramine itself (Table 1). The failure of cocaine, a recognized blocker of the neuronal uptake of catecholamines, to inhibit [3H]-tyramine binding further supports the purported attachment of tyramine at the vesicular transport system for dopamine (Vaccari, 1986;Vaccari & Gessa, 1989), thus implying that intraneuronal MPP+ may label a vesicular site in dopaminergic regions of the brain. Of course, MPP+ may reach additional intraneuronal targets, as inferred from Hill coefficients different from unity.…”

“…There has previously been no evidence that synaptic vesicles are a target for intraneuronal MPP +, though this might be expected, in view of the purported similarity of catecholamine neurones and adrenomedullary chromaffin cells where, in fact, MPP+ is extensively transported and stored (Daniels & Reinhard, 1988). Tyramine has been shown to associate mostly in the rat striatum with a reserpine-sensitive site putatively involved with the vesicular transport of dopamine (Vaccari, 1986;Vaccari & Gessa, 1989). Both tyramine and MPP+ infused into the caudate nucleus via microdialysis procedures cause a massive release of dopamine from nigrostriatal terminals (Rollema et al, 1988;Fairbrother et al, 1990).…”