Binding Characteristics of a Potent AMPA Receptor Antagonist [³H]Ro 48‐8587 in Rat Brain

Abstract

The distribution and abundance of specific binding sites (=95% of total) in sections of rat CNS, revealed by quantitative receptor radioautography and image analysis, indicated a very discrete localization. Highest binding values were observed in cortical layers (binding in layers 1 and 2> binding in layers 3-6), hippocampal formation, striatum, dorsal septum, reticular thalamic nucleus, cerebellar molecular layer, and spinal cord dorsal horn. At 1 nM, the values for specific binding were highest in the cortical layers 1 and 2 and lowest in the brainstem (=2.6 and 0.4 pmol/mg of protein, respectively). Ro 48-8587 is a potent and selective AMPA receptor antagonist with improved binding characteristics (higher affinity, selectivity, and specific binding) compared with those previously reported. Key Words: a-Amino-3-hydroxy-5-methylisoxazole-4-propionate-9-lmidazol-1 -yl-8-nitro-2,3, 5,6-tetrahydro- High-affinity a-aniino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors are ligand-gated cation channels for L-glutalnate, the major excitatory transmitter in the mammalian CNS. Their activation mediates fast transmission at glutamatergic synapses. The receptors, heterooligomeric proteins composed of the subunits G1uR1 -4 with flip and flop forms (Hollmann and Heinemann, 1994;Bettler and Mulle, 1995;Barnard, 1997), play key roles in CNS physiology and pathology. AMPA receptor subunits G1uR1 -4 are differentially regulated during ontogeny, and in adult rat brain they have only partially overlapping distributions (Keinanen et al

Differential Effects of Two Chronic Diazepam Treatment Regimes on Withdrawal Anxiety and AMPA Receptor Characteristics

“…Levels of both AMPA subunit mRNAs are low in the thalamic regions; however, in the amygdala, GluR1 and GluR2 mRNAs are highly expressed in all nuclei (Figure 2d and f). This is consistent with previous ISH studies and also with studies examining [ 3 H]AMPA binding (Monaghan et al, 1984;Rainbow et al, 1984;Olsen et al, 1987;Nielsen et al, 1988) and [ 3 H]Ro48 8587 binding (Mutel et al, 1998) to the AMPA receptor in rat brain. of the AMPA receptor was found in the AI (Figure 4a) in rats treated chronically with 5 mg/kg i.p.…”

“…The pattern of [ 3 H]Ro48 8587 binding was found to be heterogeneous in rat brain and comparable to that found by Mutel et al (1998) using the same radioligand, with the highest density of binding being apparent in hippocampus, outer layers of the cortex, striatum, reticular nucleus of the thalamus, and amygdaloid nuclei. Intermediate levels of binding were observed in other thalamic nuclei and in the mammillary body (Figure 2a and b).…”

“…Secondly, although changes in subunit expression may result in altered functionality of the AMPA receptor, this would not necessarily be reflected as altered AMPA binding since the ligand employed does not appear to distinguish between these subunits. This is based on evidence that the patterns of distribution of the subunit proteins and binding of [ 3 H]Ro48 8587 in rat brain overlap (Mutel et al, 1998), thus indicating that the radioligand does not preferentially bind to any one of the subunits.…”

“…This radioligand has been demonstrated to be more selective for the AMPA receptor than the best previously available quinoxalinedione antagonists (NBQX, CNQX, and YM 90K), with reported selectivity factors of B160-and 41000-fold for AMPA vs kainate and NMDA receptors, respectively (Mutel et al, 1998).…”

Asymmetric Synthesis and Receptor Pharmacology of the Group II mGlu Receptor Ligand (1S,2R,3R,5R,6S)‐2‐Amino‐3‐hydroxy‐bicyclo[3.1.0]hexane‐2,6‐dicarboxylic Acid—HYDIA

“…[29] Figure 7. Effect of (+)-9 HYDIA on (+)-4 LY354740-induced decrease of Horizontal Activity in mice.…”