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Metabotropic glutamate receptor (mGluR) subtypes (mGluR1 to mGluR8) act as important pre- and postsynaptic regulators of neurotransmission in the CNS. These receptors consist of two domains, an extracellular region containing the orthosteric agonist site and a transmembrane heptahelical domain involved in G protein activation and recognition of several recently synthesized pharmacological modulators. The presynaptic receptor mGluR7 shows the highest evolutionary conservation within the family, but no selective pharmacological tool was known. Here we characterize an mGluR7-selective agonist, N,N'-dibenzhydrylethane-1,2-diamine dihydrochloride (AMN082), which directly activates receptor signaling via an allosteric site in the transmembrane domain. At transfected mammalian cells expressing mGluR7, AMN082 potently inhibits cAMP accumulation and stimulates GTP[gamma]S binding (E[C.sub.50]-values, 64-290 nM) with agonist efficacies comparable with those of L-2-amino-4-phosphonobutyrate (L-A[P.sub.4]) and superior to those of L-glutamate. AMN082 ([less than or equal to]10 [micro]M) failed to show appreciable activating or inhibitory effects at other mGluR subtypes and selected ionotropic GluRs. Chimeric receptor studies position the binding site of AMN082 in the transmembrane region of mGluR7, and we demonstrate that this allosteric agonist has little, if any, effect on the potency of orthosteric ligands. Here we provide evidence for full agonist activity mediated by the heptahelical domain of family 3 G protein-coupled receptors (which have mGluR-like structure) that may lead to drug development opportunities. Further, AMN082 is orally active, penetrates the blood-brain barrier, and elevates the plasma stress hormones corticosterone and corticotropin in an mGluR7-dependent fashion. Therefore, AMN082 is a valuable tool for unraveling the role of mGluR7 in stress-related CNS disorders. G protein | mGluR

Radioligand binding studies were performed in membranes of rabbit whole brain and striatum using the novel iodinated radioligand for 5-hydroxytryptamine 5-HT and 5-HT sites, Serotonin-5-O-Carboxymethyl-Glycyl[I]Tyrosinamide ([I]GTI). [I]GTI labelled a finite number of high affinity sites in rabbit brain membranes, B = 191 +- 47 fmol/mg protein, pK (-log mol/1) = 8.50 +- 0.13, n = 5. The pharmacological profile of [I]GTI binding was fully comparable to that reported previously in human and other brain preparations known to possess 5-HT sites (using either [H]5-HT or [I]GTI) and displayed a characteristic rank order of affinity: 5-carboxamidotryptamine > 5-HT = dihydroergotamine _> ergotamine ≥_ sumatriptan >_ CGS 12066 >- metergoline > yohimbine >_ methysergide > ICYP > 8-OH-DPAT >_ CP 93129 > (-)pindolol > ketanserin > isamoltane > mesulergine > corynanthine > buspirone > MDL 72222. Autoradiographic studies were performed on rabbit brain slices using [H]5-HT in the presence of 100 nmol/1 8-OH-DPAT and mesulergine (in order to mask 5-HT and 5-HT binding sites) and [I]CYP (iodocyanopindolol) in the presence of β µmol/I isoprenaline and 100 nmol/l 8-OH-DPAT (in order to mask β adrenoceptor and 5-HT binding sites). There was no detectable specific binding of [I]CYP through the brain, thus excluding the presence of 5-HT sites in rabbit brain. By contrast, [H]5-HT labelled a high density of sites in globus pallidus, substantia nigra and superior colliculus. Other regions displaying labelling include the striatum, the dentate gyrus of the hippocampus and the periaqueductal grey matter. This pattern of distribution is compatible with that reported for 5-HT sites in other species. The present data strongly suggest that rabbit brain has recognition sites with the pharmacological profile and distribution characteristic of the 5-HT recognition site. These findings are in agreement with results obtained by Limberger et al. (1991), suggesting the terminal 5-HT autoreceptor of the rabbit brain to belong to the 5-HT subtype. Except for limited species variations (see Bruinvels et al. 1992), the pharmacology of these sites does not justify an addition to the existing nomenclature ('5-HT'), in contrast to what has been proposed by Xiong and Nelson (1989). The rabbit represents another laboratory species in which 5-HT receptor mediated effects could be studied. [ABSTRACT FROM AUTHOR]

Abstract: A novel series of agonists at the benzodiazepine binding site of the GABAA receptor was prepared by functionalizing a known template. Adding substituents to the pyrazolone-oxygen of CGS-9896 led to a number of compounds with selectivities for either α2- or α1-containing GABAA receptor subtypes offering an entry into indications such as anxiety and insomnia. In this communication, structure–activity relationship and efforts to increase in vitro stabilities are discussed. [Copyright &y& Elsevier]