M1 and m2 muscarinic receptor subtypes regulate antidepressant-like effects of the rapidly acting antidepressant scopolamine

Scopolamine produces rapid and significant symptom improvement in patients with depression, and most notably in patients who do not respond to current antidepressant treatments. Scopolamine is a nonselective muscarinic acetylcholine receptor antagonist, and it is not known which one or more of the five receptor subtypes in the muscarinic family are mediating these therapeutic effects. We used the mouse forced-swim test, an antidepressant detecting assay, in wild-type and transgenic mice in which each muscarinic receptor subtype had been genetically deleted to define the relevant receptor subtypes. Only the M1 and M2 knockout (KO) mice had a blunted response to scopolamine in the forced-swim assay. In contrast, the effects of the tricyclic antidepressant imipramine were not significantly altered by gene deletion of any of the five muscarinic receptors. The muscarinic antagonists biperiden, pirenzepine, and VU0255035 (N-[3-oxo-3-[4-(4-pyridinyl)-1-piper azinyl]propyl]-2,1,3-benzothiadiazole-4-sulfonamide) with selectivity for M1 over M2 receptors also demonstrated activity in the forced-swim test, which was attenuated in M1 but not M2 receptor KO mice. An antagonist with selectivity of M2 over M1 receptors (SCH226206 [(2-amino-3-methyl-phenyl)-[4-[4-[[4-(3 chlorophenyl)sulfonylphenyl]methyl]-1-piperidyl]-1-piperidyl]methanone]) was also active in the forced-swim assay, and the effects were deleted in M2 (-/-) mice. Brain exposure and locomotor activity in the KO mice demonstrated that these behavioral effects of scopolamine are pharmacodynamic in nature. These data establish muscarinic M1 and M2 receptors as sufficient to generate behavioral effects consistent with an antidepressant phenotype and therefore as potential targets in the antidepressant effects of scopolamine.

Identification of a high-affinity binding site involved in the transport of endocannabinoids

Phytocannabinoids, such as the principal bioactive component of marijuana, delta9-tetrahydrocannabinol, have been used for thousands of years for medical and recreational purposes. delta9-Tetrahydrocannabinol and endogenous cannabinoids (e.g., anandamide) initiate their agonist properties by stimulating the cannabinoid family of G protein-coupled receptors (CB1 and CB2). The biosynthesis and physiology of anandamide is well understood, but its mechanism of uptake (resulting in signal termination by fatty acid amide hydrolase) has been elusive. Mounting evidence points to the existence of a specific anandamide transport protein; however, no direct evidence for this protein has been provided. Here, we use a potent, competitive small molecule inhibitor of anandamide uptake (LY2318912, IC50 7.27 +/- 0.510 nM) to identify a high-affinity, saturable anandamide transporter binding site (LY2318912; K(d) = 7.62 +/- 1.18 nM, B(max) = 31.6 +/- 1.80 fmol/mg protein) that is distinct from fatty acid amide hydrolase. Systemic administration of the inhibitor into rodents elevates anandamide levels 5-fold in the brain and demonstrates efficacy in the formalin paw-licking model of persistent pain with no obvious adverse effects on motor function. Identification of the anandamide transporter binding site resolves a missing mechanistic link in endocannabinoid signaling, and in vivo results suggest that endocannabinoid transporter antagonists may provide a strategy for positive modulation of cannabinoid receptors.

Neuropeptide Y receptor subtypes in the basolateral nucleus of the amygdala modulate anxiogenic responses in rats

The behavioral effects induced by intra-amygdala stimulation of the neuropeptide Y (NPY) Y(2) and the NPY Y(5) receptor subtypes were assessed in the social interaction (SI) test. Microinjections of NPY(3-36), an NPY Y(2) preferring agonist, into the basolateral nucleus of the amygdala (BLA) produced bi-directional dose-response curve. At low doses NPY(3-36) has an anxiogenic effect while at higher doses it produced an anxiolytic effect. Pretreatment with the NPY Y(5) receptor antagonist Novartis 1(1 nmol), an analog of CGP71683A synthesized by Eli Lilly and Company, IN, blocked the anxiolytic effects of NPY(3-36) (80 pmol), while pretreatment with BIBO 3304 (200 pmol), a Y(1) antagonist, had no effect, suggesting that the Y(5), but not the Y(1) receptor was involved in the anxiolytic behavior produced following intra-amygdalar NPY(3-36) administration. In addition, the Y(5) antagonist had no behavioral effect when given alone at 1.0 nmol. These findings support the hypothesis that amygdalar Y(2) receptors may play a role in mediating anxiogenic effects, while Y(5) receptors may be involved in the anxiolytic behaviors of NPY.

Characterization of neuropeptide Y Y1-like and Y2-like receptor subtypes in the mouse brain

To characterize receptor subtypes in the mouse, we performed autoradiographic localization and pharmacological characterization studies using the selective radiolabeled agonists, [(125)I]-Leu(31), Pro(34)-PYY and [(125)I]-PYY 3-36. The pharmacology of [(125)I]-Leu(31), Pro(34)-PYY and [(125)I]-PYY 3-36 binding to mouse brain homogenates were consistent with Y1-like and Y2-like receptors, respectively. Using receptor autoradiography, high Y1-like binding was observed in the islands of Calleja and dentate gyrus. [(125)I]-PYY 3-36 binding was highest in the hippocampus, lateral septum, stria terminalis of the thalamus, and compacta and lateralis of the substantia nigra. In addition, there are differences in receptor distribution in mouse brain compared to other species that may translate into different functional roles for the NPY receptors within each species.

Pharmacological characterization of (125)I-1229U91 binding to Y1 and Y4 neuropeptide Y/Peptide YY receptors

1229U91 (GW1229 or GR231118) [lle,Glu,Pro,Dpr,Tyr, Arg,Leu,Arg, Tyr-NH(2))2 cyclic (2,4'),(2'4)-diamide] has been reported by several research groups to be a potent antagonist at the Y1 neuropeptide Y (NPY) receptor subtype. However, 1229U91 also displaces (125)I-peptide YY (PYY) with high affinity from the Y4 subtype. Previously, we reported that 1229U91 had full agonist properties for the Y4 receptor. To characterize the pharmacological properties of 1229U91 directly, we had it radioiodinated with the chloromine-T method. (125)I-1229U91 bound to cell lines expressing the human Y1 and Y4 receptors with high affinity. The K(d) and B(max) for (125)I-1229U91 binding to Y1 were 14.9 pM and 1458 fmol/mg protein, respectively. The Y4 receptor bound (125)I-1229U91 with a K(d) of 12.5 pM and a B(max) of 1442 fmol/mg protein. When competing (125)I-1229U91 binding from Y1 and Y4 receptors, a similar rank order of potency was observed: 1229U91 > [Leu(31),Pro(34)]-NPY >/= [Leu(31),Pro(34)]-PYY > PYY >/= NPY > NPY(2-36) > PYY(3-36). Pancreatic polypeptide (PP) potently displaced (125)I-1229U91 from the Y4 receptor, but displayed little affinity for Y1. In autoradiographic studies with rat brain sections, (125)I-1229U91 bound with a distribution similar to that reported for the Y1 receptor when localized with (125)I-[Leu(31),Pro(34)]-PYY. Brain regions exhibiting binding sites for (125)I-PP were not detected with this radioligand. Those include the interpeduncular nucleus and the periventricular nucleus of the hypothalamus. Furthermore, (125)I-labeled rat PP was not displaced from these areas with 10 nM 1229U91. Thus, (125)I-1229U91 is a high affinity Y1 and Y4 radioligand and binds with a distribution in the rat brain consistent with the localization of the Y1 receptor.

Role of corticotropin-releasing factor and urocortin within the basolateral amygdala of rats in anxiety and panic responses

The amygdala is a critical temporal lobe structure involved in the expression of anxiety and stress responses. The basolateral nucleus (BLA) of the amygdala in particular, may play a key role in anxiety. Furthermore, corticotropin-releasing factor (CRF), a 41 amino acid peptide, has been strongly implicated in the regulation of stress and anxiety responses. Centrally administered CRF has been shown to increase the anxiety-like behaviors of rodents in several animal models. A recently cloned related peptide, Urocortin (Ucn), appears to have similar affinity for the CRF1 receptor, but higher affinity at the CRF2 receptor. When microinjected into the BLA, we found Ucn was substantially more potent than CRF in producing anxiogenic-like behavior as assessed in the social interaction test. Furthermore, repetitive administration of subthreshold doses of Ucn and CRF resulted in 'priming'. Once primed, these animals exhibited behavioral and cardiovascular responses to intravenous sodium lactate, a panicogenic agent in susceptible human patients. These results suggest central CRF and Ucn play a role in generating anxiety which may be similar to that seen in pathological conditions such as panic disorder.

Structure-activity relationship of a series of diaminoalkyl substituted benzimidazole as neuropeptide Y Y1 receptor antagonists

A series of benzimidazoles (4) was synthesized and evaluated in vitro as potent and selective NPY Y1 receptor antagonists. Substitution of the piperidine nitrogen of 4 with appropriate R groups resulted in compounds with more than 80-fold higher affinity at the Y receptor compared to the parent compound 5 (R = H). The most potent benzimidazole in this series was 21 (Ki = 0.052 nM).

Structure-activity relationships of a series of benzothiophene-derived NPY Y1 antagonists: optimization of the C-2 side chain

A series of benzo[b]thiophene-derived NPY-1 receptor antagonists is described. Systematic modification of the C-2 substituent afforded a 1000-fold range in Y1 receptor affinity. Appropriate substitution at the ortho and para positions of the C-2 phenyl ether produced a synergistic effect on Y1 binding affinity, which led to the discovery of the most active ligands, 12t (K(i) = 15 nM), 12u (K(i) = 11 nM), and 12v (K(i) = 13 nM).

Characterization of the neuropeptide Y5 receptor in the human hypothalamus: a lack of correlation between Y5 mRNA levels and binding sites

Neuropeptide Y (NPY) is a 36-amino-acid peptide that appears to play a central role in the control of feeding behavior. Recently, a cDNA encoding a novel NPY receptor subtype (Y5) was cloned from the rat and human hypothalamus, and shown to have a pharmacology consistent with NPY-induced feeding. We have subsequently cloned this cDNA from human hypothalamus and stably expressed it in CHO cells. Consistent with earlier reports, hY5 has a high affinity for NPY, [Leu31, Pro34]NPY, and NPY(3-36), but low affinity for larger C-terminal deletions of NPY and BIBP3226. High levels of hY5 mRNA were found in the human testis, brain, spleen and pancreas, with lower levels in several other tissues. In the human brain, hY5 mRNA levels were typically higher than hY2, but lower in comparison to hY1 receptor mRNA. To quantify the relative amounts of hY1, hY2 and hY5 mRNA in the human hypothalamus, we employed competitive RT-PCR. Interestingly, the relative amount of hY5 mRNA was substantially higher than either hY1 or hY2. However, pharmacological characterization of NPY binding sites in human hypothalamus membranes revealed predominantly the hY2 subtype. These data establish that while hY5 mRNA levels are very high in the human hypothalamus, conventional radioligand binding techniques do not detect hY5-like binding site. Whether hY5-like binding sites exist in the other human tissues that express hY5 mRNA (and what function hY5 has in those tissues) awaits future investigation.

Synthesis and evaluation of a series of novel 2-[(4-chlorophenoxy)methyl]benzimidazoles as selective neuropeptide Y Y1 receptor antagonists

A series of novel benzimidazoles (BI) derived from the indole 2 was synthesized and evaluated as selective neuropeptide Y (NPY) Y1 receptor antagonists with the aim of developing antiobesity drugs. In our SAR approach, the (4-chlorophenoxy)methyl group at C-2 was kept constant and a series of BIs substituted with various piperidinylalkyl groups at N-1 was synthesized to identify the optimal spacing and orientation of the piperidine ring nitrogen relative to the benzimidazole. The 3-(3-piperidinyl)propyl in 33 was found to maximize affinity for the Y1 receptor. Because of the critical importance of Arg33 and Arg35 of NPY binding to the Y1 receptor, the incorporation of an additional aminoalkyl functionality to the structure of 33 was explored. Methyl substitution was used to probe where substitution on the aromatic ring was best tolerated. In this fashion, the C-4 was chosen for the substitution of the second aminoalkyl functionality. Synthesis of such compounds with a phenoxy tether using the 4-hydroxybenzimidazole 11 was pursued because of their relative ease of synthesis. Functionalization of the hydroxy group of 45 with a series of piperidinylalkyl groups provided the dibasic benzimidazoles 55-62. Among them, BI 56 demonstrated a Ki of 0.0017 microM, which was 400-fold more potent than 33. To evaluate if there was a stereoselective effect on affinity for these BIs, the four constituent stereoisomers (69-72) of the BI 60 were prepared using the S- and R-isomers of bromide 17. Antagonist activity of these BIs was confirmed by measuring the ability of selected compounds to reverse NPY-induced forskolin-stimulated cyclic AMP. The high selectivity of several BI antagonists for the Y1 versus Y2, Y4, and Y5 receptors was also shown.

Structure-activity relationships of a series of 1-substituted-4-methylbenzimidazole neuropeptide Y-1 receptor antagonists

The characterization of a novel series of NPY-1 receptor antagonists derived from the 4-methylbenzimidazole 4 is described. Appropriate substitution on the piperidyl nitrogen of 4 led to systematic increases in Y-1 receptor affinity, to approximately 50-fold, and to the discovery of the importance of a second basic substituent.

The neuropeptide Y Y1 antagonist, 1229U91, a potent agonist for the human pancreatic polypeptide-preferring (NPY Y4) receptor

Recently, a novel high-affinity peptide antagonist, 1229U91, was published as a selective neuropeptide Y Y1 antagonist. The selectivity of 1229U91 was evaluated in the human NPY Y1 receptor containing cell line, SK-N-MC, and cells containing the cloned human NPY Y2, the pancreatic polypeptide-preferring (NPY Y4), and the NPY Y5 receptors. 1229U91 potently displaced [125I]-peptide YY (PYY) binding to human NPY Y1 receptors (IC50 = 0.245+/-0.004 nM, n = 4). but displayed little affinity for the human NPY Y2 and Y5 receptors (IC50 > 1000 nM). Interestingly, 1229U91 displaced [125I]-PYY with even greater affinity at the human NPY Y4 receptor (IC50 = 0.081+/-0.009 nM, n = 4). Using a cyclic AMP accumulation assay, 1229U91 blocked NPY inhibition of forskolin-induced adenylate cyclase activity in NPY Y1 receptor containing SK-N-MC cells. In the human NPY Y4 receptor expressing cell line, 1229U91 did not block pancreatic polypeptide (PP) inhibition of forskolin stimulated adenylate cyclase. However, in the absence of PP, 1229U91 was able to inhibit forskolin stimulated cyclic AMP accumulation (IC50 = 7.16+/-2.8 nM, n = 4). We conclude that 1229U91 binds non-selectively with high affinity to both human NPY Y1 and Y4 receptors. Furthermore, 1229U91 displays antagonist activity at the NPY Y1 receptor, while having agonist activity at the NPY Y4 receptor.

Increased expression of peripheral benzodiazepine receptors in the facial nucleus following motor neuron axotomy

Peripheral benzodiazepine receptors (PBRs) are expressed in a variety of tissues but are normally found at low levels in the brain. Following various types of nerve injury, a reactive gliosis results that exhibits a high expression of this receptor. To further characterize the expression of PBRs following neuronal injury, we evaluated PBR expression in the facial nucleus following facial nerve axotomy (FNA). Injury to a peripheral nerve results in a complex series of metabolic and morphological changes around the injured neuron. Transections of the facial nerve results in a rapid activation of both astrocytes and microglia around axotomized motor neurons. FNA resulted in an increase in the staining for both astrocytes (glial fibrillary acidic protein) and activated microglia (OX42). There was also a reduction in synaptic contacts with the motor nucleus as evidenced by reduced staining for the synaptic marker, synaptophysin. In sections labeled with [3H]-PK11195, the subsequent autoradiograms displayed marked increases in the labeling for PBRs. This increase was observed at 5, 7 and 10 days after nerve transection. The increase was primarily in the level of expression (Bmax), with no change in the affinity of the ligand (Kd). The increase in PBR expression after FNA supports the hypothesis that PBRs can be used as a sensitive marker for CNS injury.

Identification of multiple neuropeptide Y receptor subtypes in the human frontal cortex

Recently, we found abundant mRNA and binding sites for neuropeptide Y Y1-like receptors in the human cerebral cortex. However, an earlier study using indirect labeling methods failed to detect substantial neuropeptide Y1-like receptor binding in numerous areas of the human brain, including the cerebral cortex. To resolve the disparity in these findings, we characterized the neuropeptide Y receptor subtypes labeled with [125I]peptide YY in homogenates of human frontal cortex. Competition experiments using 100 pM [125I]peptide YY binding to human frontal cortex homogenates indicated predominantly neuropeptide Y Y2 receptors are labeled with this concentration of ligand. However, saturation analysis of [125I]peptide YY binding to frontal cortex membranes resulted in isotherms best characterized by a two-site fit. Binding of [125I]peptide YY to the high affinity (Kd = 40 pM) binding site was prevented using a 100 nM concentration of the neuropeptide Y Y2 receptor agonist peptide YY-(3-36). By masking the higher affinity site, we found a low affinity [125I]peptide YY binding site (Kd = 1.4 nM) exhibiting a pharmacology consistent with a neuropeptide Y Y1-like receptor. It appears that neuropeptide Y Y2 receptors are the predominant subtype labeled with low concentrations of[125I]peptide YY and that the neuropeptide Y Y1 receptor is a low affinity [125I]peptide YY binding site in the human frontal cortex.

Analysis of NPY receptor subtypes in the human frontal cortex reveals abundant Y1 mRNA and binding sites

Receptors for neuropeptide Y (NPY) are widely distributed throughout the mammalian brain. Using indirect labeling methods, the human brain was reported to contain predominantly the Y2 receptor subtype, whereas the rat brain contains a mixture of Y1 and Y2 receptor subtypes. To more accurately assess NPY receptors in the human brain, we used type Y1- and Y2-selective radioligands [125I] [Leu31,Pro34]PYY and [125I]PPY (3-36), respectively, to examine NPY receptors in the human frontal cortex. Contrary to an earlier report, abundant Y1 binding sites were found in homogenates of human frontal cortex. Moreover, saturation analysis showed similar densities of both Y1 (Kd = 433 +/- 36 pM, Bmax = 313 +/- 15 fmol/mg protein) and Y2 (Kd = 444 +/- 39 pM, Bmax = 458 +/- 22 fmol/mg protein) receptor subtypes in the human frontal cortex. Subsequently, Northern blot analysis revealed abundant expression of Y1 mRNA, with very low levels of Y2 mRNA, in cerebral cortex and in other areas of the human brain. These findings were confirmed by competitive RT-PCR in the human frontal cortex. Therefore, it appears that Y1 binding sites and mRNA are expressed abundantly in the human frontal cortex and, earlier findings, suggest that the human brain contains a mixture of Y1 and Y2 receptor subtypes.

[125I]Leu31, Pro34-PYY is a high affinity radioligand for rat PP1/Y4 and Y1 receptors: evidence for heterogeneity in pancreatic polypeptide receptors

Cloned receptors for the PP-fold peptides are subdivided into Y1, Y2, PP1/Y4, Y5 and Y6. NPY and PYY have similar affinity for Y1, Y2, Y5 and Y6 receptors while PP has highest affinity for PP1. Pro34-substituted analogs of NPY and PYY have selectivity for Y1 and Y1-like receptors over Y2 receptors. In the present study, we found the putative Y1-selective radioligand, [125I]Leu31, Pro34-PYY, also binds with high affinity to the rat PP1 receptor in cell lines expressing the receptor. However, in rat brain sections, [125I]Leu31, Pro34-PYY does not appear to bind to the interpeduncular nucleus, a brain region containing a high density of [125I]-bPP binding sites. Therefore, it appears there is additional heterogeneity in receptors recognizing PP.

The neuropeptide Y Y1 receptor selective radioligand, [125I][Leu31,Pro34]peptide YY, is also a high affinity radioligand for human pancreatic polypeptide 1 receptors

A number of receptors for the pancreatic polypeptide-fold peptides are proposed based on findings from pharmacology and molecular biology studies. Neuropeptide Y and peptide YY have similar affinity for neuropeptide Y Y1 and neuropeptide Y Y2 while pancreatic polypeptide has highest affinity for pancreatic polypeptide 1. Pro34-substituted analogs of neuropeptide Y and peptide YY have selectivity for neuropeptide Y Y1 over neuropeptide Y Y2 receptors. In the present study, we found that one such 'neuropeptide Y Y1-selective' radioligand, [125I][Leu31,Pro34]peptide YY, also binds with high affinity to the pancreatic polypeptide 1 receptor. Therefore, caution needs to be exercised when using Pro34-analogs to define the neuropeptide Y Y1 receptor in vivo and using tissue preparations.

Pharmacological characterization of neuropeptide Y-(2-36) binding to neuropeptide Y Y1 and Y2 receptors

Neuropeptide Y-(2-36) has been reported by several research groups to be a more potent orexigenic agent than intact neuropeptide Y. Therefore, it has been proposed that a novel 'Y1 variant' may modulate ingestive behavior. To define the receptor subtype involved in neuropeptide Y-stimulated feeding behavior, we evaluated the binding properties of neuropeptide Y-(2-36) and [125I]neuropeptide Y-(2-36) in established neuropeptide Y1 and Y2 containing cell lines and tissues. Neuropeptide Y-(2-36) displaced [125I]peptide YY binding to SK-N-MC cells (neuropeptide Y Y1 receptors) with a Ki of 3.69 nmol and SK-N-BE(2) cells (neuropeptide Y Y2 receptors) with a Ki of 3.08 nmol. Neuropeptide Y-(2-36) also displaced [125I]peptide YY binding to rat cerebral cortex, hippocampus and olfactory bulb with similar affinities. To examine the brain distribution of [125I]peptide YY, [125I]neuropeptide Y and [125I]neuropeptide Y-(2-36), adjacent sections were labeled and the binding sites detected by autoradiography. A similar distribution of binding was observed for each radioligand in all regions examined. Therefore, neuropeptide Y-(2-36) binds non-selectively to neuropeptide Y Y1 and neuropeptide Y Y2 receptors, but with lower affinity than neuropeptide Y and peptide YY. The increased potency and selectivity seen with neuropeptide Y-(2-36) in feeding studies cannot be explained on the basis of a unique in vitro pharmacology.

Characterization of the peptide binding requirements for the cloned human pancreatic polypeptide-preferring receptor

Traditionally, neuropeptide Y (NPY) receptors have been divided into Y1 and Y2 subtypes based on peptide pharmacology and synaptic localization. Other receptor subtypes have been proposed based on preferences for NPY, peptide YY (PYY), or pancreatic polypeptide (PP). Recently, we discovered a novel human member of this receptor family exhibiting high affinity for PP and PYY. In the current study, we expressed a DNA clone encoding this human PP-preferring receptor [hPP1 (or Y4)] in Chinese hamster ovary cells and performed a peptide structure-activity study. [125I]pPYY bound to homogenates of hPP1-Chinese hamster ovary cells with a Kd of 0.064 +/- 0.006 nM and a Bmax of 244 +/- 12 fmol/mg protein. Human PP inhibited binding with a Ki of 0.023 nM, whereas human PYY (Ki = 0.31 nM) and human NPY Ki = 12 nM) were significantly less potent. Rat, porcine, and bovine PP inhibited binding with similar affinities to human PP, whereas avian PP was substantially less potent (Ki = 1 nM). Deletion of the first four amino acids reduced the affinity of bovine PP to 1 nM. Carboxyl-terminal fragments of NPY and PYY also had reduced potency compared with the native peptides. In addition, deletion of Tyr36-amide produced a substantial reduction in affinity. Pro34-substituted NPY and PYY had modestly increased affinity compared with the native peptides, although Gln34-bPP had similar affinity compared with bovine PP. The carboxyl-terminally derived Y1 antagonist 1229U91 was a very potent (Ki = 0.042 nM) inhibitor of binding to hPP1. Thus, the carboxyl-terminal region of PP seems to be the most important part of the peptide for high affinity binding to hPP1. A few key residues (amino acids 2 and 3) in the amino-terminal region of PP contribute to the high affinity of the native peptide. Thus, features required for peptide recognition by the hPP1 receptor seem to be distinct from the Y1 and Y2 receptor.

The cloned rat pancreatic polypeptide receptor exhibits profound differences to the orthologous receptor

Pancreatic polypeptide (PP) is produced in the islets of Langerhans and released in response to meals. It belongs to a family of peptides that also includes neuropeptide Y and peptide YY. In the present communication, we describe a rat receptor with high affinity for PP, therefore named PP1. Clones for the PP1 receptor were obtained by PCR using sequence information for the neuropeptide Y receptor Y1 from several species. The PP1 receptor has 46% overall amino acid sequence identity to the rat Y1 receptor and 56% identity in the transmembrane regions. The PP1 receptor displays a pharmacological profile that is distinct from previously described neuropeptide Y-family receptors. In competition with iodinated bovine PP, it binds rat PP with an affinity (K(i)) of 0.017 nM, while the affinities for peptide YY and neuropeptide Y are substantially lower with K(i) values of 162 and 192 nM, respectively. In stably transfected CHO cells, the PP1 receptor inhibits forskolin-stimulated cAMP synthesis. Northern blot hybridizations to a panel of mRNAs detected transcripts in testis and lung. A faint band was seen in colon and total brain. In contrast, the human receptor is expressed primarily in colon and small intestine. Whereas rat and human PP1 bind PP with the same affinity, the rat receptor has much lower affinity than its human ortholog for peptide YY and neuropeptide Y. Interestingly, the amino acid sequence identity between rat and human PP1 is only 75%. Thus, the sequence, the tissue distribution, and the binding profile of the PP1 receptor differ considerably between rat and human.

[3H]LY303870, a novel nonpeptide radioligand for the NK-1 receptor

We synthesized a potent and selective antagonist radioligand for the neurokinin (NK)-1 receptor and characterized its binding to guinea pig striatal membranes. (R)-N-[2-[Acetyl[3H3][(2-methoxyphenyl)-methyl]amino]- 1-(1H-indol-3-ylmethyl) ethyl][1,4'-bipiperidine]- 1'-acetamide ([3H]LY303870) binds to a single class of sites with an equilibrium KD of 0.22 nM and a Bmax of 723 fmol/mg of protein. Unlabeled LY303870 potently inhibited the binding with an IC50 of 0.56 nM, whereas the less active (S)-enantiomer (LY306155) was substantially less potent. The nonpeptide NK-1 antagonists (+/-)-CP96,345 and (+/-)-RP 67580 had IC50 values of 0.74 and 49 nM, respectively. Substance P (SP) was also a potent inhibitor with with an IC50 of 3.1 nM. The inhibition by SP could be separated into two components: a high-affinity component with a Ki of 0.53 nM and a lower-affinity component with a Ki of 155 nM. Addition of 100 microM guanylyl 5'-imidodiphosphate [Gpp(NH)p] in the incubation increased the relative amount of the low-affinity agonist state of the receptor. Consistent with the antagonist properties of LY303870, the dissociation rate of [3H]-LY303870 was not changed by the presence of 100 microM Gpp(NH)p. The distribution of [3H]LY303870 binding sites in the guinea pig brain closely matched the distribution of NK-1 receptors labeled by [3H]SP. Therefore, [3H]LY303870 is a potent and selective antagonist radioligand for NK-1 receptors in guinea pig brain. In addition, regulation of NK-1 agonist affinity by guanine nucleotides is similar to that seen for monoaminergic receptors.

Expression cloning of a human brain neuropeptide Y Y2 receptor

The 36-amino acid peptide, neuropeptide Y (NPY), is a member of a peptide family that includes the endocrine peptides, peptide YY (PYY), and pancreatic polypeptide (PP). NPY receptors have been broadly subdivided into postsynaptic Y1 receptors and presynaptic Y2 receptors based on the preference of Pro34-substituted analogues for the Y1 receptors and carboxyl-terminal fragments for the Y2. A Y1 receptor has been cloned, and this receptor appears to mediate several effects of NPY, including vasoconstriction and anxiolysis in animal models. We report the cloning of a human brain Y2 receptor from a human brain library. Pools of clones were transiently expressed in COS-1 cells, and 125I-PYY binding pools were identified by autoradiography. After a single positive pool was detected in the original screening, a single clone was isolated by four rounds of sequential enrichment. The clone encoded a 381-amino acid protein of the heptahelix (seven TM) type. Amino acid identity of this receptor with the Y1 receptor was 31% overall with 40% identity in the TM regions. Comparison with the human PP1 receptor indicated 33% overall amino acid identity with 42% identity in the TM regions. Pharmacologically, the receptor exhibited high affinity for NPY, PYY, and carboxyl-terminal fragments of NPY and PYY. In addition, Pro34-substituted analogues had very low affinity. With the use of Northern blot analysis, high levels of Y2 mRNA were detected in a variety of brain regions with little expression in peripheral tissues. Thus, the receptor protein has the pharmacological properties and distribution of the human Y2 receptor.

Cloning of a human receptor of the NPY receptor family with high affinity for pancreatic polypeptide and peptide YY

Neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) are structurally related peptides found in all higher vertebrates. NPY is expressed exclusively in neurons, whereas PYY and PP are produced primarily in gut endocrine cells. Several receptor subtypes have been identified pharmacologically, but only the NPY/PYY receptor of subtype Y1 has been cloned. This is a heptahelix receptor that couples to G proteins. We utilized Y1 sequence information from several species to clone a novel human receptor with 43% amino acid sequence identity to human Y1 and 53% identity in the transmembrane regions. The novel receptor displays a pharmacological profile that distinguishes it from all previously described NPY family receptors. It binds PP with an affinity (Ki) of 13.8 pM, PYY with 1.44 nM, and NPY with 9.9 nM. Because these data may identify the receptor as primarily a PP receptor, we have named it PP1. In stably transfected Chinese hamster ovary cells the PP1 receptor inhibits forskolin-stimulated cAMP synthesis. Northern hybridization detected mRNA in colon, small intestine, pancreas, and prostate. As all three peptides are present in the gut through either endocrine release or innervation, all three peptides may be physiological ligands to the novel NPY family receptor PP1.

Peripheral benzodiazepine receptors are colocalized with activated microglia following transient global forebrain ischemia in the rat

In mammalian brain the expression of peripheral benzodiazepine receptors (PBRs) can be markedly induced following different types of neuronal injury. PBRs are believed to be expressed on non-neuronal cells in the brain, yet the specific cell type that expresses these receptors following CNS insult has not been defined. In the present study, we investigated the effects of transient global forebrain ischemia on PBRs by autoradiographic localization of 3H-PK11195 binding. The distribution of PBRs was compared to glial fibrillary acidic protein (GFAP) as a marker for astrocytes and OX42 as a marker for microglia. Five to 6 d following four-vessel occlusion (4-VO), an increase in PBRs was seen in the CA1 region of all 15 brains examined. In brains from rats subjected to 4-VO, microglia were selectively activated in stratum pyramidale of the CA1 layer. In contrast, astrocytes appeared to be activated in multiple hippocampal cell layers including stratum radiatum and stratum oriens. Activated astrocytes were also found in regions that did not exhibit increased 3H-PK11195 binding. In some brains, selected regions of secondary lesion, specifically necrotic thalamic nuclei and the isocortex were found to be strongly immunoreactive for OX42 but lacked GFAP immunoreactive cells. In adjacent sections, these same regions displayed high densities of 3H-PK1195 binding. These observations lend further support to the application of 3H-PK11195 binding as a marker of neuronal injury in the brain. Furthermore, the data strongly suggest that activated microglia rather than astrocytes express PBRs following ischemic insults.

Comparison of (R)-[3H]tomoxetine and (R/S)-[3H]nisoxetine binding in rat brain

(R)-[3H]Tomoxetine is a radioligand that binds to the norepinephrine (NE) uptake site with high affinity but also binds to a second, lower-affinity site. The goal of the present study was to identify the nature of this low-affinity site by comparing the binding properties of (R)-[3H]tomoxetine with those of (R/S)-[3H]nisoxetine, a highly selective ligand for the NE uptake site. In homogenate binding studies, both radioligands bound to the NE uptake site with high affinity, whereas (R)-[3H]tomoxetine also bound to a second, lower-affinity site. The autoradiographic distribution of binding sites for both radioligands is consistent with the known distribution of NE-containing neurons. However, low levels of (R)-[3H]tomoxetine binding were seen in the caudate-putamen, globus pallidus, olfactory tubercle, and zona reticulata of the substantia nigra, where (R/S)-[3H]nisoxetine binding was almost absent. In homogenates of the caudate-putamen, the NE uptake inhibitors desipramine and (R)-nisoxetine and the serotonin (5-HT) uptake inhibitor citalopram produced biphasic displacement curves. Autoradiographic studies using 10 nM (R)-nisoxetine to mask the binding of (R)-[3H]tomoxetine to the NE uptake site produced autoradiograms that were similar to those produced by [3H]citalopram. Therefore, (R)-[3H]tomoxetine binds to the NE uptake site with high affinity and the 5-HT uptake site with somewhat lower affinity.

(R)-thionisoxetine, a potent and selective inhibitor of central and peripheral norepinephrine uptake

Inhibitors of neuronal norepinephrine (NE) uptake are useful for the treatment of a variety of diseases including depression and urinary incontinence. In the present study, we synthesized and evaluated a novel analog of the potent and selective NE uptake inhibitor, nisoxetine. Thionisoxetine more potently inhibited the uptake of [3H]-NE into hypothalamic synaptosomes and [3H]-nisoxetine binding to the NE transporter than (R)-nisoxetine. The (R) enantiomer of this compound was significantly more potent than the (S) enantiomer, having a Ki of 0.20 nM in [3H]-nisoxetine binding. The (R) enantiomer was approximately 70-fold more potent in inhibiting [3H]-NE uptake when compared to [3H]-5HT uptake. In rats, (R)-thionisoxetine prevented hypothalamic NE depletion by 6-hydroxydopamine with an ED50 of 0.21 mg/kg. Depletion of NE in peripheral nerves was accomplished by the administration of metaraminol to rats. In this paradigm, (R)-thionisoxetine prevented the depletion of heart NE with an ED50 of 3.4 mg/kg and urethral NE with an ED50 of 1.2 mg/kg. Thus, (R)-thionisoxetine is a potent and selective inhibitor of NE uptake in both central and peripheral tissues.

Novel halogenated analogs of tomoxetine that are potent and selective inhibitors of norepinephrine uptake in brain

Halogenated analogs of the potent norepinephrine (NE) uptake inhibitor, tomoxetine, were synthesized and their affinities for the serotonin (5HT) and NE uptake sites evaluated. One of the most potent was the 2-iodo substituted analog (289306) that inhibited [3H]tomoxetine binding to rat cerebral cortex with a Ki of 0.37 nM. The compound also inhibited the uptake of [3H]NE into rat hypothalamic synaptosomes with a Ki of 3.5 nM. This analog was significantly less potent at the 5HT uptake site, as exhibited by a Ki of 25 nM in the inhibition of [3H]paroxetine binding and a Ki of 121 nM in [3H]5HT uptake. The resolved (R) enantiomer (303926) was 10 times more potent as a [3H]NE uptake inhibitor and 29 times more potent as an inhibitor of [3H]tomoxetine binding than the (S) enantiomer (303884). Administration of 289306 to rats prior to an i.c.v. injection of 6-hydroxydopamine prevented the depletion of hypothalamic NE and Epi with ED50 values of 0.28 and 0.47 mg/kg, respectively. Thus, 289306 was a potent inhibitor of NE uptake in vitro and in vivo. In addition, these compounds provide structures for potential ligands for the study of NE uptake sites by autoradiography, PET or SPECT imaging.

Synthesis and evaluation of [125I]-(S)-iodozacopride, a high affinity radioligand for 5HT3 receptors

We have developed a high specific activity radioiodinated ligand for the biochemical evaluation and autoradiographic localization of 5HT3 receptors in the brain. [125I]-(S)-iodozacopride was synthesized by radioiodination of deschloro-(S)-zacopride using chloramine-T, and the product was purified by HPLC. The equilibrium kinetics and pharmacology of the binding of this radioligand were studied in homogenates of rat cerebral cortex, while the distribution of binding was examined by quantitative autoradiography. [125I]-(S)-iodozacopride bound to a single, saturable, specific binding site (Kd = 192 +/- 9 pM, Bmax = 1.2 +/- 0.2 fmol/mg protein). The binding had the pharmacological properties of a 5HT3 receptor, being potently inhibited by a variety of 5HT3 agonists and antagonists including (S)-zacopride (Ki = 0.032 nM), Quipazine (Ki = 0.45 nM), LY278584 (Ki = 0.5 nM), (1-m-chlorophenyl)-biguanide (Ki = 0.6 nM) and ICS 205-930 (Ki = 1.0 nM). Autoradiographic studies were undertaken by incubating sections with 400 pM [125I]-(S)-iodozacopride and exposing them to film for 3-7 days to obtain suitable autoradiograms. Specific binding of [125I]-(S)-iodozacopride was found at various amounts in a variety of brain regions. The highest levels of binding were found in the brainstem, principally the nucleus of the solitary tract with somewhat lower levels in the area postrema, substantia gelatinosa of the trigeminal nucleus and dorsal motor nucleus of the vagus. In the rat forebrain, moderate levels of specific binding were found in the glomerular layer of the olfactory bulb, anterior olfactory nucleus and various subnuclei of the amygdala. Lower levels of binding were seen in the superficial laminae of the parietal cerebral cortex and diffusely distributed throughout the hippocampal formation. In conclusion, [125I]-(S)-iodozacopride binds to a receptor site with the pharmacological properties and distribution that is consistent with the 5HT3 receptor. [125I]-(S)-iodozacopride represents a significant improvement in autoradiographic studies of the 5HT3 receptor by reducing the required exposure time for producing autoradiograms from the 3-6 months required for [3H]-labeled ligands to 3-7 days.

[Leu31-Pro34] neuropeptide Y identifies a subtype of 125I-labeled peptide YY binding sites in the rat brain

Subtypes of the neuropeptide Y (NPY) receptor in the rat brain were identified by the use of the selective Y-1 analog, [Leu34-Pro34] NPY. In rat brain homogenate binding studies, [Leu31-Pro34] NPY was found to produce a partial inhibition of 100 pM 125I-labeled peptide YY (PYY) binding with a plateau at 50-1000 nM [Leu31-Pro34] NPY resulting in a 70% inhibition of binding. The C-terminal fragment NPY 13-36, a putative Y-2 agonist, exhibited very little selectivity in rat brain homogenates. Scatchard analysis of 125I-labeled PYY binding to rat brain homogenate yielded biphasic plots with Kd values of 40 and 610 pM. Inclusion of 100 nM [Leu31-Pro34] NPY was found to eliminate the low affinity component of 125I-labeled PYY binding leaving a single, high affinity binding site with a Kd of 68 pM. In autoradiographic studies, displacement curves indicated that [Leu31-Pro34] NPY completely inhibited binding in the cerebral cortex with little effect on the binding in the hypothalamus. On the other hand NPY 13-36 inhibited binding in the hypothalamus at low concentrations but required higher concentrations to inhibit binding in the cerebral cortex. Other brain regions such as the hippocampus, appeared to contain both subtypes. Subsequent to these studies, a quantitative autoradiographic map was conducted using 50-100 pM 125I-labeled PYY in the presence and absence of [Leu31-Pro34] NPY which produced a selective displacement of binding in certain distinct brain regions. These areas included the cerebral cortex, certain thalamic nuclei and brainstem while ligand binding was retained in other brain regions including the zona lateralis of the substantia nigra, lateral septum, nucleus of the solitary tract and the hippocampus. Numerous brain regions appeared to contain both receptor subtypes. Therefore, the Y-1 and Y-2 receptor subtypes exhibited a somewhat distinct distribution in the brain. In addition, 125I-labeled PYY appears to label the Y-2 receptor with relatively higher affinity when compared to the Y-1 receptor.

Angiotensin II receptor subtypes in rat brain: dithiothreitol inhibits ligand binding to AII-1 and enhances binding to AII-2

Angiotensin II (AII) receptor subtypes have been proposed on the basis of the selectivity of non-peptide AII antagonists. In the present study, the sulfhydryl reducing agent dithiothreitol (DTT) was found to reduce binding to the AII-1 receptor while enhancing binding at the AII-2 site. The neuroanatomical distribution of these effects were consistent with the distribution of AII-1 and AII-2 receptors, respectively. These data indicate that AII receptor subtypes in the brain can be differentiated by both biochemical and pharmacological means.

Autoradiographic localization of subtypes of angiotensin II antagonist binding in the rat brain

The non-peptide angiotensin II receptor compounds DuP 753 and WL 19 were utilized to detect subtypes of [125I]Sar1-Ile8-angiotensin II binding to angiotensin II receptors in the rat brain. In rat forebrain homogenates, DuP 753 and WL 19 produced a partial displacement of [125I]Sar1-Ile8-angiotensin II binding with DuP 753 displacing approximately 65% of the binding and WL 19 displacing approximately 35% of the binding. Using the techniques of quantitative receptor autoradiography, a distinct regional distribution of the subtypes of angiotensin II antagonist bind was detected. The angiotensin II-1 binding site (the receptor subtype preferentially displaced by DuP 753) appeared to predominate in the dipsogenic, cardiovascular and endocrine areas, including the subfornical organ, paraventricular and periventricular nuclei of the hypothalamus, anterior pituitary, dorsal motor nucleus of the vagus, nucleus of the solitary tract and the area postrema. Additional areas that contained predominantly the angiotensin II-1 receptor subtype were the ventral hippocampus, substantia gelatinosa of the trigeminal nucleus, nucleus of the lateral olfactory tract, piriform cortex and median preoptic nucleus. The angiotensin II-2 binding site (displaced by WL 19) was the predominant subtype in the thalamus, inferior olive, lateral septum, subthalamic nucleus, locus coeruleus, medial geniculate and medial amygdala. Several areas of the brain appeared to contain both receptor subtypes, including the superior and inferior colliculi, and the olfactory bulb. The angiotensin II-1 binding site was concentrated in areas of the brain involved in mediating angiotensin II effects on drinking, endocrine status and blood pressure. Localization of angiotensin II-2 sites in the thalamus and areas of the brain which process sensory information suggests a novel modulatory role for angiotensin II at this receptor subtype. These results indicate that DuP 753 and WL 19 are highly selective for angiotensin II binding site subtypes in the brain and that, in general these subtypes are compartmentalized in distinct brain regions. The non-peptide compounds used in these studies should provide excellent tools to discern the functional role of angiotensin II receptor subtypes in the brain.

Perinatal expression of type I IGF receptors in porcine small intestine

The gastrointestinal tract of the pig undergoes enhanced growth as well as morphological and functional differentiation during the perinatal period. Concurrently, porcine neonates ingest physiologically significant amounts of insulin-like growth factor-I (IGF-I) via colostrum and milk. The objectives of this study were to examine newborn pig small intestine for the presence of high affinity, IGF-I receptors and to evaluate the possible contributions of maternally derived and locally produced IGF-I to receptor-mediated postnatal growth of intestine. The specific binding of 125I-IGF-I to membranes prepared from scraped intestinal mucosa was time, temperature, and pH dependent; optimal conditions were 48 h, 4 C, and a pH of 7.8, respectively. Several pure peptides were evaluated for competition with 125I-IGF-I in binding to intestinal membrane sites. The relative order of competition was IGF-I greater than insulin-like growth factor-II (IGF-II) greater than insulin, whereas bombesin and epidermal growth factor were noncompetitive. Chemical cross-linking of 125I-IGF-I to binding sites, followed by denaturing SDS-PAGE and autoradiography, demonstrated labeled protein complexes of Mrs 135,000 and 260,000. Both autoradiographic bands were diminished when excess unlabeled IGF-I or IGF-II was included in the binding step. Insulin at higher concentrations also slightly inhibited labeling of both membrane proteins. Membranes prepared from intestinal mucosa of piglets at days 0 (less than 2-h old, colostrum-deprived), 3, 5, and 21 postnatal were evaluated for developmental variations in specific binding of 125I-IGF-I. Binding was highest at birth, declined (-43%) by day 3, remained low at day 5, and increased by day 21. Receptor affinity was relatively invariant whereas receptor number (per mg membrane protein) was variable. Intestine wt increased disproportionately to body wt between days 0 to 3, postnatal. Radioimmunoassay of extracts of the corresponding intestinal mucosa revealed a significant increase in content of IGF-I by day 3 (P = 0.05), whereas RNA dot-blot hybridization demonstrated low and unchanging IGF-I mRNA abundance in intestine. The quantitative variations in IGF-I protein content and IGF receptor numbers temporally coincide with intestinal villous growth, cessation of intestinal transport of macromolecules (closure), and onset of maturation of intestinal function.

Fibroblast mitogens in swine milk include an epidermal growth factor-related peptide

Mammary secretions obtained from lactating sows can support in vitro growth of mammalian cells when added to Dulbecco's Modified Eagle Medium. In order to identify the growth factors present within, sow milk was fractionated and fractions having mitogenic activity were identified by their ability to stimulate DNA synthesis in density-arrested, quiescent (murine) AKR-2B fibroblasts. A prominent mitogenic activity (peak III) was observed in the 3,000-5,000 Mr range. This activity was partially purified by (1) preparative Sephadex G-200 chromatography, (2) gel-filtration in Sephadex G-50 columns and (3) DEAE-cellulose anion exchange chromatography. The last step resolved peak III activity into at least two distinct components. One component was highly-purified by use of reverse-phase high-performance liquid chromatography (RP-HPLC). This activity was identified as an epidermal growth factor (EGF)-related peptide based on its inactivation by polyclonal antibody (IgG fraction) specific for murine EGF (mEGF) and proteolytic agents. The other component is unrelated to EGF. Using cloned mEGF cDNA as a probe, the presence of EGF-related mRNA in lactating mammary tissues and newborn pig small intestine was also demonstrated. These factors may contribute to the preferential growth of gastrointestinal tissues in neonatal pigs.