Autoradiographic mapping of dopamine‐D₂/D₃ receptor stimulated [³⁵S]GTPγS binding in the human brain

Abstract

Agonist stimulated [35S]guanosine 5'-gamma-thiotriphosphate ([35S]GTPgammaS) binding autoradiography was established for the examination of dopamine-D2/D2 receptors in human brain sections. The distribution of G proteins activated by dopamine-D2/D3 receptors was studied in whole hemisphere cryosections. Dopamine stimulated [35S]GTPgammaS binding in brain regions with high densities of dopamine D2-like receptors, i.e. putamen (23 +/- 2%, mean +/- SEM,% stimulation over basal binding), caudate (20 +/- 0%) and substantia nigra (22 +/- 2%), but also in regions with lower receptor densities such as amygdala (17 +/- 8%), hippocampus (16 +/- 6%), anterior cingulate (13 +/- 3%), and thalamus (12 +/- 2%). Dopamine stimulated [35S]GTPgammaS binding to significantly higher levels in the dorsal than in the ventral part of the striatum. Dopamine caused low or very low stimulation in all cortical areas. Raclopride, a selective D2/D3 receptor antagonist, potently inhibited dopamine stimulated [35S]GTPgammaS binding, whereas R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH23390), a selective D1 antagonist, did not block the [35S]GTPgammaS binding response stimulated by dopamine. Hence, the stimulatory effect of dopamine was primarily mediated by D2/D3 receptors. Quinpirole stimulated [35S]GTPgammaS binding in the same regions as dopamine. The maximal level of stimulation induced by dopamine and quinpirole was not significantly different. The present study demonstrates that agonist stimulated [35S]GTPgammaS binding autoradiography could be a suitable technique for the examination of dopamine-D2/D3 receptors in the human brain. This functional assay could provide useful new information about dopamine receptor/G protein coupling in the postmortem human brain, and reveal possible disease related alterations of the interaction between D2/D3 receptors and G proteins.

Characterization of dopamine D2 receptor coupling to G proteins in postmortem brain of subjects with schizophrenia

“…In postmortem human brain tissue, previous autoradiographic mapping of [ 35 S]GTPγS binding response to single concentrations of dopamine or selective D1R and D2R agonists demonstrated an anatomical distribution of the functional activation with the highest effects (24% approximately) in dorsal caudate [34]. Present findings in the same brain area indicated a D2R pharmacological profile that agrees with previous data in rodents.…”

“…This may have led to antagonism over other GPCRs, especially when dopamine was used as agonist. It should also be recognized that maximal stimulatory effects observed herein are lower than those reported in rodents [35,37], although similar to values in human caudate sections [34]. Efficacy of agonist-stimulated [ 35 S]GTPγS binding is very sensitive to experimental conditions and mainly depends on GDP and NaCl concentrations employed [17,19,[35][36][37].…”

“…Afterwards, the potential dysfunction of D2R coupling to G proteins in caudate of schizophrenia subjects was assessed. Caudate head was selected due to the important activation by D2R agonist [34] and the D2R density alterations in basal ganglia previously described in schizophrenia [1,6,7]. The dorsolateral prefrontal cortex was explored, because it constitutes a critical area in schizophrenia where D1R show higher expression than D2R [5].…”

Parkin Expression Profile in Dopamine D3 Receptor Knock-Out Mice Brains

“…DRD3 is a presynaptic auto-receptor present in dopaminergic neurons and well distributed in various brain regions [23]. This receptor is involved in the control of basal DA levels and increases neurotransmitter reuptake in the striatum [14].…”

Hypothetical membrane mechanisms in essential tremor

“…Some ET patients have the gly9 susceptibility variant of the DRD3 gene [ 40 , 41 ]. DRD3 receptor is expressed in the thalamus and substantia nigra where limb-movement related neurons are present [ 42 ]. Two of the possible effects of this mutation could be directly related to the regulation of membrane excitability.…”