Visualization of Antipsychotic Drug Binding to Living Mesolimbic Neurons Reveals D2 Receptor, Acidotropic, and Lipophilic Components

Abstract

To examine the binding of antipsychotic drugs to living neurons, we applied fluoroprobe derivatives of the D2 antagonist spiperone to mesolimbic system neurons in postnatal culture . We found that rhodamine-N-(p-aminophenethyl)spiperone (rhodamine-NAPS) stereospecifically labeled the plasma membranes of 38 6% of ventral tegmental area neurons, 22 ± 7% of which were dopaminergic, and 50 ± 6% of medium-sized putatively GABAergic nucleus accumbens neurons, with a time constant of -8 min . In contrast, the BODIPY derivative of NAPS rapidly labeled intracellular sites in all neurons in a punctate pattern, consistent with acidotropic uptake . Native antipsychotics also show acidotropic uptake, which we visualized by their displacement of the fluorescent weak base vital dye acridine orange from acidic intracellular compartments . We found that acidotropic uptake correlated best with the partition coefficients of the drugs. With a time constant of 23 min, rhodamine-NAPS labeled all neurons in a pattern suggestive of lipophilic solvation . Thus, initially rhodamine-NAPS makes possible visualization of D2 receptors on living neurons ; however, acidotropic uptake and lipophilic solvation obscure receptor labeling and may account for time-dependent factors in the action of antipsychotic drugs, as well as affect their use as radioreceptor ligands.The therapeutic efficacy of antipsychotic drugs correlates with their affinity for D2-like dopamine (DA) receptors (Javitch and Kaufmann, 1991), but also with their brain-to-serum ratios , suggesting that the physiochemical properties of the drugs play a critical role in their action . Indeed, receptor binding is far more rapid than therapeutic action, indicating that factors beyond receptor binding contribute importantly to antipsychotic drug action . It is striking that most antipsychotic drugs are detectable in rat brain for days to weeks following a single administration, far longer than their receptor affinity would dic-

Imaging Synaptic Neurotransmission with in Vivo Binding Competition Techniques: A Critical Review

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“…Challenges that increase synaptic DA decrease the BP of these ra diotracers, and vice versa. The amphetamine-induced re ductions of [ " C]raclopride BP and r ' 23 I]IBZM BP have been especially well validated as a measure of amphet amine-induced DA release: the amphetamine effect is mediated by DA release, since it is blunted by co- Values reproduced from Rayport and Sulzer (1995). treatments that are expected to block amphetamine induced DA depletion (AMPT, reserpine, GBR 12909).…”

Antagonism of Dopamine Receptor 2 Long Affects Cannabinoid Receptor 1 Signaling in a Cell Culture Model of Striatal Medium Spiny Projection Neurons

“…Conversely, sulpiride displays a lower affinity and a much faster dissociation rate, which would produce rapidly reversible antagonism (Kapur and Seeman, 2001). In addition, highly lipophilic antagonists, such as haloperidol, can accumulate in cell membranes and can reach receptors in membrane folds more easily than hydrophilic D 2 antagonists, such as sulpiride (Rayport and Sulzer, 1995;Sahlholm et al, 2016). Therefore, lipophilic D 2 antagonists with slow dissociation rates, such as haloperidol, have higher E Max for Ga s -dependent CREB activation.…”

Clozapine, atypical antipsychotics, and the benefits of fast-off D2 dopamine receptor antagonism

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