Indole-2-carboxylates, novel antagonists of the N-methyl-D-aspartate (NMDA)-associated glycine recognition sites: in vivo characterization.

Recent in vitro receptor binding studies have indicated that indole-2-carboxylates with halogen substitutions at the position 5 or 6 are potent competitive antagonists of the NMDA (N-methyl-D-aspartate)-associated strychnine-insensitive glycine receptor (Gray N. M., Dappen M. S., Cheng B. K., Cordi A. A., Biesterfeldt J. P., Hood W. F. and Monahan J. B. (1992) J. med. Chem. 34: 1283-1292; Hood W. F., Gray N. M., Dappen M. S., Watson G. B., Compton R. P., Cordi A. A., Larthorn T. H. and Monahan J. B. (1992) J. Pharmac. exp. Ther. 262: 654-660). In the present investigation, a series of indole-2-carboxylates and two putative antagonists of glycine receptor HA-966 (3-amino-l-hydroxypyrrolidin-2-one) and 7-chlorokynurenic acid were examined for their effects on cGMP responses, mediated by the NMDA receptor complex, in vivo. Both SC-49648 (6-chloro-2-carboxyindole-3-acetic acid, intracerebellar injection, i.c.b.) and HA-966 (i.c.b. or intraperitoneal, i.p.) antagonized increases in levels of cyclic GMP in the cerebellum of the mouse, induced by the intracerebellar administration of NMDA and D-serine, agonists of the NMDA and the NMDA-associated glycine recognition sites, respectively. The drugs SC-49648 and 7-chlorokynurenic acid (i.p.) did not affect cGMP responses, suggesting poor bioavailability in brain. Following direct intracerebellar injection, SC-49648 was eliminated with a half-life of 12 min from the brain. Following intraperitoneal administration, SC-50132, the 3-ethylester analog of SC-49648, was eliminated from the brain with a half-life of 35 min and was found to be metabolized to SC-49648, in vivo. Some lipophilic analogs of SC-49648, designed as its prodrugs, were minimally active as glycine antagonists, in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of 3-carboxy-5-phosphono-1,2,3,4-tetrahydroisoquinoline (SC-48981), a potent competitive N-methy-D-aspartate (NMDA) receptor antagonist, in vitro and in vivo.

(+/-)-3-Carboxy-5-phosphono-1,2,3,4-tetrahydroisoquinoline (SC-48981), a conformationally restricted analog of the potent competitive N-methyl-D-aspartate (NMDA) antagonist, 2-amino-5-phosphonopentanoate (AP-5), potently inhibited the binding of [3H]glutamate to the N-methyl-D-aspartate (NMDA) receptors with a Ki of 1.6 mcM, but with minimal affinity for kaininate and quisqualate receptors (Ki greater than 50 mcM), in vitro. Consistent with its ability to antagonize the NMDA receptor, SC-48981 decreased the binding of [3H]glycine and [3H]TCP [1-(2-thienyl)cyclohexylpiperidine] to the NMDA-associated glycine and phencyclidine (PCP) recognition sites, in vitro. SC-48981 attenuated levels of basal cGMP and harmaline-induced increases in levels of cGMP in the mouse cerebellum, in vivo, in a competitive manner, with ED50 values of 5.5 and 8.7 mg/kg, i.p. Direct intracerebellar injection of SC-48981 (0.5 microgram) attenuated increases in levels of cGMP induced by central injection of the NMDA-associated glycine receptor agonist, D-serine and by NMDA itself. Parenteral administration of SC-48981 (25 mg/kg, s.c.) decreased basal levels of cGMP for up to 3 h. These results indicate that SC-48981 represents a novel bioavailable competitive NMDA antagonist with a long duration of action.

Actions of D-cycloserine at the N-methyl-D-aspartate-associated glycine receptor site in vivo.

The antibiotic, D-cycloserine has been shown to be a partial agonist at the N-methyl-D-aspartate (NMDA)-coupled, strychnine-insensitive glycine receptor by in vitro receptor binding. This partial agonism was further investigated in an in vivo system, by monitoring changes in levels of cyclic guanosine-monophosphate (cGMP), a well characterized second messenger response, mediated by the NMDA receptor complex, in the cerebellum of the mouse. Parenteral injections of D-cycloserine produced a biphasic dose-response curve which suggested partial agonism. In support of this contention, when intracerebellar injections were made together with D-serine, a glycine agonist, D-cycloserine attenuated the N-methyl-D-aspartate receptor-mediated increase in levels of cGMP. Likewise, systemic administration of D-cycloserine attenuated increases in cGMP induced by pentylenetetrazol. These data are relevant to the study of N-methyl-D-aspartate-mediated neurotransmission, since D-cycloserine is a parenterally bioavailable compound, with both agonist and depressant properties at the N-methyl-D-aspartate-associated glycine receptor.

Effects of sigma ligands on mouse cerebellar cyclic guanosine monophosphate (cGMP) levels in vivo: further evidence for a functional modulation of N-methyl-D-aspartate (NMDA) receptor complex-mediated events by sigma ligands.

In the present investigation, the effects of sigma ligands [WY-47384 [8-fluoro-2,3,4,5-tetrahydro-2[3-(3-pyridinyl)propyl)1H- pyrido(4,3b)indole], (+)-pentazocine, (+)-SFK 10,047 (N-allylnormetazocine), mafoprazine, opipramol, dextromethorphan, dextrorphan, (+)-3-PPP [3-(3-hydroxyphenyl)-N-propylpiperidine], (-)-butaclamol, DTG [1,3-di(2-tolyl)guanidine], rimcazole, ifenprodil and BMY-14802 [alpha-(fluorophenyl)-4-(5-fluoropyrimidinyl)-1-piperazine butanol]] on harmaline-, pentylenetetrazol (PTZ)-, methamphetamine (MA)- and D-serine-induced increases in mouse cerebellar levels of cGMP were determined. Ifenprodil, BMY-14802, dextromethorphan, dextrorphan, (+)-SKF 10,047, opipramol and mafoprazine reversed harmaline-, PTZ-, MA- and D-serine-induced increases in levels of cGMP. Rimcazole reversed only the harmaline-induced response. WY-47384 reversed harmaline-, MA-, D-serine-, but not PTZ- or quisqualate-induced increases in levels of cGMP. (+)-Pentazocine attenuated harmaline- and D-serine-, but not PTZ- and MA-induced cGMP responses. Haloperidol did not affect harmaline- and D-serine-induced cGMP responses. (+)-3-PPP and (-)-butaclamol did not affect any of the responses studied. Furthermore, (+)-3-PPP-induced increases in levels of cGMP were reversed by the competitive N-methyl-D-aspartate (NMDA) antagonist, CPP]3-(2-carboxypiperazin-4-yl)propyl- 1-phosphonic acid, the non-competitive NMDA antagonist, (+)-MK-801 (dizocilipine maleate), the NMDA-associated glycine receptor antagonist, HA-966 (3-amino-1-hydroxypyrrolidin-2-one), the partial glycine agonist, DCS (D-cycloserine) as well as by the sigma ligands, ifenprodil, WY-47384, (+)-pentazocine, (+)-SKF 10,047, dextromethorphan and dextrorphan but not by rimcazole.(ABSTRACT TRUNCATED AT 250 WORDS)

(+) 3-[3-hydroxyphenyl-N-(1-propyl) piperidine] selectively differentiates effects of sigma ligands on neurochemical pathways modulated by sigma receptors: evidence for subtypes, in vivo.

The effects of sigma ligands, (+)3PPP 3-[3-hydroxyphenyl-N(1-propyl) piperidine] and (-)butaclamol, were evaluated in vivo on the metabolism of dopamine (DA) and in the striatum release of adrenocorticotrophic hormone (ACTH) and prolactin in the rat and changes in levels of cyclic guanosine monophosphate (cGMP) in the cerebellum of the mouse and compared with the effects of (+)NANM (N-allyl-normetazocine, SKF 10,047) and (+)pentazocine. Both (+)3PPP and (-) butaclamol decreased the release of prolactin and did not affect the metabolism of DA. N-Allyl-normetazocine and (+)pentazocine increased release of prolactin and have been shown previously to increase the metabolism of DA. All four ligands increased release of ACTH; however, only the increases caused by (+)NANM and (+)pentazocine were reversed by pretreatment with CPP, a N-methyl-D-aspartate (NMDA) receptor antagonist. (+)Pentazocine and (+)NANM inhibited the NMDA receptor-mediated changes in levels of cGMP in the cerebellum of the mouse, while (+)3PPP and (-)butaclamol did not attenuate the response to NMDA. In addition to further confirming a functional interaction between sigma receptors and NMDA receptors, these studies divide the observed effects of putative sigma ligands into two groups, characterized by benzomorphan compounds and non-benzomorphan compounds, suggesting the possibility of subtypes at sigma receptor in vivo.

Polyamines modulate events mediated by the N-methyl-D-aspartate (NMDA) receptor complex through an ifenprodil-insensitive pathway: in vivo measurements of cyclic GMP in the cerebellum.

In the present investigation, the effects of polyamines, spermidine and spermine on events mediated by the N-methyl-D-aspartate (NMDA) receptor complex were examined. Spermine and spermidine did not alter basal levels of cyclic GMP (cGMP) in the cerebellum of the mouse, over a wide range of concentrations. However, exogenously added spermine, spermidine, D- and L-ornithine and putrescine attenuated the increases in cGMP seen after the administration of D-serine, an agonist of the NMDA receptor-associated glycine recognition sites. Spermine and/or spermidine also antagonized harmaline-, methamphetamine- and pentylenetetrazol-induced increases in the levels of cGMP. Spermidine also potentiated (+)-MK-801 (dizocilipine)-induced attenuation of basal levels of cGMP. Intracerebroventricular administration of ifenprodil, a suggested polyamine antagonist, did not antagonize spermine- and spermidine-induced attenuation of the response to D-serine. These data suggest that exogenously added polyamines attenuate events mediated by the NMDA receptor complex, in an ifenprodil-insensitive manner.

Clozapine attenuates N-methyl-D-aspartate receptor complex-mediated responses in vivo: tentative evidence for a functional modulation by a noradrenergic mechanism.

Recent studies revealed a role for dopamine and noradrenaline in the etiology of ischemia-induced neuronal cell death. In the present investigation, the modulation by clozapine, an atypical antipsychotic agent that interacts with adrenergic receptors, of N-methyl-D-aspartate (NMDA) receptor complex-mediated events were studied by examining its effects on levels of cGMP in the cerebellum. Clozapine decreased basal levels of cGMP in the cerebellum and antagonized harmaline-, methamphetamine-, pentylenetetrazol- and D-serine-induced increases in levels of cGMP with ED50 values of 3.9, 2.36, 2.13 and 2.1 mg/kg (i.p.). However, clozapine (1.25-25 mg/kg) did not attenuate the quisqualate-induced increases in levels of cGMP, indicating a specific modulation of events modulated by the NMDA receptor complex. Antagonists of dopamine (D2), serotonin (5-HT)-5-HT1, 5-HT2 and 5-HT3 [haloperidol, propranolol, ritanserin, ICS 205-930 [(3-tropanyl-indole-3-carboxylate methiodide)] respectively], did not reverse the response to harmaline. However, WB-4101 [(2,6-dimethoxy-phenoxyethyl)aminomethyl-1,4-benzodioxane HCl], and alpha 1-adrenergic antagonist, reversed harmaline-, D-serine-, PTZ- and MA-induced increases in levels of cGMP, indicating an adrenergic modulation of the events mediated by the NMDA receptor complex. Intracerebellar and intracerebroventricular administration of clozapine and intracerebellar administration of WB-4101 reversed the D-serine-induced response, indicating a central locus of action. These results indicated that clozapine modulates levels of cGMP predominantly through its interactions with central adrenergic receptors.

N-methyl-D-aspartate treatment increases circulating adrenocorticotropin and luteinizing hormone in the rat.

Excitatory amino acids have been known to increase pituitary secretion of LH in vivo and are probably involved in the neuroendocrine regulation of the hypothalamic-pituitary-gonadal axis. We have found that systemic administration of the excitatory amino acid agonist N-methyl-D-aspartate (NMDA) evokes a transient and profound increase in circulating levels of ACTH as well. Treatment of adult male Long-Evans rats with NMDA (30 mg/kg, sc) maximally increased plasma ACTH and immunoreactive beta-endorphin from 7-15 min after injection, and levels of both remained significantly elevated until 60 min into the time course. Corresponding increases in corticosterone were observed 15 and 30 min after treatment, while LH, similar to other pituitary hormones, was increased from 7-30 min after NMDA. Stimulation of the pituitary-adrenal and pituitary-gonadal neuroendocrine axes by NMDA was monitored in subsequent studies by plasma ACTH and LH, respectively; both were increased in a dose-related manner after the administration of 3-60 mg/kg NMDA, although stimulation of ACTH (800%) was more pronounced than that of LH (200%). The increases in ACTH and LH due to NMDA were inhibited by pretreatment with the competitive NMDA antagonist (+/-)3-(2-carboxypiperazin-4- yl)propyl-1-phosphonic acid, CPP (6 and 10 mg/kg, ip, for 21 min); by contrast, dexamethasone pretreatment (50 micrograms/kg, ip, for 4 h) blocked only the NMDA-evoked increase in circulating ACTH. These findings indicate that an NMDA receptor mechanism might be involved in the acute activation of the hypothalamic-pituitary-adrenal axis in the rat.

Neurochemical interactions of competitive N-methyl-D-aspartate antagonists with dopaminergic neurotransmission and the cerebellar cyclic GMP system: functional evidence for a phasic glutamatergic control of the nigrostriatal dopaminergic pathway.

Direct intrastriatal injection of N-methyl-D-aspartate (NMDA; 100 micrograms/rat) increased striatal dopamine (DA) release in vivo. However, parenteral administration of (+/-)-3-(2-carboxypiperizin-4-yl)propyl-1-phosphonic acid (CPP) and cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS-19755) did not alter DA metabolism and release in several brain regions in the rat and mouse. Intracerebroventricular administration of the competitive NMDA antagonists CPP, CGS-19755, 2-amino-5-phosphonopentanoate, and 2-amino-7-phosphonoheptanoate did not alter rat striatal DA metabolism and release but profoundly reduced cerebellar cyclic GMP (cGMP) levels in the same animals. CPP and CGS-19755 decreased basal cerebellar cGMP levels in the mouse with ED50 values of 6 and 1 mg/kg, i.p., respectively. CPP antagonized the harmaline-induced increases in cGMP levels with an ED50 value of 5.0 mg/kg, i.p. CPP (25 mg/kg, i.p.) also decreased basal cGMP levels in mouse cerebellum for up to 3 h, a result suggesting brain bioavailability and a long duration of NMDA receptor antagonism in vivo. These contrasting patterns suggest that NMDA receptors exert a tonic excitatory tone on the guanine nucleotide signal transduction pathway in the cerebellum while exerting a phasic control over nigrostriatal dopaminergic neurotransmission. These results also indicate that competitive NMDA antagonists, unlike phencyclidine receptor agonists, may not mediate biochemical and behavioral effects via dopaminergic mechanisms.

Contrasting neurochemical interactions of tiletamine, a potent phencyclidine (PCP) receptor ligand, with the N-methyl-D-aspartate-coupled and -uncoupled PCP recognition sites.

Neurochemical interactions of tiletamine, a potent phencyclidine (PCP) receptor ligand, with the N-methyl-D-aspartate (NMDA)-coupled and -uncoupled PCP recognition sites were examined. Tiletamine potently displaced the binding of [3H]1-(2-thienyl)cyclohexylpiperidine with an IC50 of 79 nM without affecting sigma-, glycine, glutamate, kainate, quisqualate, or dopamine (DA) receptors. Like other PCP ligands acting via the NMDA-coupled PCP recognition sites, tiletamine decreased basal, harmaline-, and D-serine-mediated increases in cyclic cGMP levels and induced stereotypy and ataxia. Tiletamine was nearly five times more potent than PCP at inhibiting the binding of 3-hydroxy[3H]PCP to its high-affinity NMDA-uncoupled PCP recognition sites. However, following parenteral administration, dizocilpine maleate (MK-801), ketamine, PCP, dexoxadrol, and 1-(2-thienyl)cyclohexylpiperidine HCl, but not tiletamine, increased rat pyriform cortical DA metabolism and/or release, a response modulated by the NMDA-uncoupled PCP recognition sites. Pretreatment with tiletamine did not attenuate the MK-801-induced increases in rat pyriform cortical DA metabolism, a result suggesting that tiletamine is not a partial agonist of the NMDA-uncoupled PCP recognition sites in this region. However, following intracerebroventricular administration (100-500 micrograms/rat), tiletamine increased pyriform cortical DA metabolism with a bell-shaped dose-response curve. These data indicate a differential interaction of tiletamine with the NMDA-coupled and -uncoupled PCP recognition sites. The paradoxical effects of tiletamine suggest that tiletamine might activate receptor(s) or neuronal pathways of unknown pharmacology.

Immune modifying effects of misoprostol and natural prostaglandins.

The synthetic prostaglandin misoprostol was found to enhance the immunosuppressive effects of cyclosporine A in vitro on human peripheral lymphocytes and mouse spleen cells, by synergizing with the latter drug, although on its own misoprostol was not potent as an immunosuppressive. These results suggest the possibility of exploiting the use of synthetic prostaglandins as adjunctive therapy in preventing clinical transplant rejection.

Neurochemical characterization of dopaminergic effects of opipramol, a potent sigma receptor ligand, in vivo.

Opipramol, a tricyclic antidepressant drug, potently interacted with sigma recognition sites labelled by [3H](+)-3-hydroxyphenyl)N-(1-propyl)piperidine [( 3H](+)-3-PPP) with a Ki value of 50 +/- 8 nM and with minimal affinity for phencyclidine receptors (Ki greater than 30,000 nM). Opipramol potently increased the metabolism of dopamine in the striatum, olfactory tubercle and pyriform cortex of the rat and increased the release of dopamine from the striatum of the mouse, as measured by increases in the levels of 3-methoxytyramine in vivo. Opipramol increased plasma prolactin in the rat, only at a dose as large as 50 mg/kg dose. Irreversible inactivation of dopamine receptors by EEDQ (N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline) did not affect the opipramol-induced increases in levels of dihydroxyphenylacetic acid (DOPAC) in the striatum of the rat, indicating a predominant role of activation of sigma receptors in the dopaminergic effects of opipramol. However, pretreatment with the putative sigma ligand, rimcazole, markedly potentiated the ability of opipramol to increase the metabolism of release of DA in the striatum of the mouse in vivo. These results suggest that rimcazole and opipramol interact at two distinct receptors, the pharmacological significance of which is yet to be elucidated.

Opipramol, a potent sigma ligand, is an anti-ischemic agent: neurochemical evidence for an interaction with the N-methyl-D-aspartate receptor complex in vivo by cerebellar cGMP measurements.

Opipramol, a potent sigma ligand and a tricyclic antidepressant compound, provided significant neuronal protection (P less than 0.0001) against ischemia-induced neuronal cell loss in the hippocampus in Mongolian gerbils, at a dose of 50 mg/kg (30 min pretreatment). However, opipramol did not offer protection when given 60 min after the ischemic insult. Opipramol decreased basal levels of cGMP in the cerebellum of the mouse and harmaline-induced increases in levels of cGMP, with approximate ED50 values of 4 and 27 mg/kg. Opipramol antagonized methamphetamine- and pentylenetetrazol-induced increases in levels of cGMP. Parenteral administration of opipramol also antagonized the increases in levels of cGMP in the cerebellum of the mouse after the local administration of D-serine, an agonist at the N-methyl-D-aspartate (NMDA)-associated, strychnine-insensitive glycine receptor. These results indicate that opipramol attenuates responses mediated through the NMDA receptor complex. These results further support the functional modulation of the NMDA receptor complex by sigma ligands and provide a neurochemical correlate for the observed anti-ischemic properties of opipramol.

6,7-Dinitroquinoxaline-2,3-dione and 6-nitro,7-cyanoquinoxaline-2,3-dione antagonize responses mediated by N-methyl-D-aspartate and NMDA-associated glycine recognition sites in vivo: measurements of cerebellar cyclic-GMP.

Direct intracerebellar administration of quisqualate resulted in marked increases in levels of cGMP in the cerebellum of the mouse, with a Hill number of 2.0. Quinoxalinediones, DNQX (6,7-dinitroquinoxaline-2,3-dione) and CNQX (6-nitro,7-cyanoquinoxaline-2,3-dione) attenuated the quisqualate-induced response. 6,7-Dinitroquinoxaline-2,3-dione also attenuated the D-serine-induced increases in levels of cGMP in a competitive manner. Intracerebellar injection of DNQX also antagonized the response to parenterally-administered harmaline. Similar results were also obtained with CNQX. These results indicate that these quinoxalinediones can attenuate the responses, mediated through the NMDA-associated glycine recognition sites, as well as the NMDA receptor complex. However, the glycine antagonist HA-966 (3-amino-1-hydroxypyrrolidone-2), at doses which completely reversed the increases induced by D-serine, failed to alter the response to quisqualate, indicating a lack of effect of glycine antagonists on quisqualate-mediated synaptic events. These results further support the interaction of the quinoxalinediones, DNQX and CNQX, with the NMDA receptor complex as established in receptor binding and electrophysiological studies.

Glycine, glycinamide and D-serine act as positive modulators of signal transduction at the N-methyl-D-aspartate (NMDA) receptor in vivo: differential effects on mouse cerebellar cyclic guanosine monophosphate levels.

Direct intracerebellar (icb) administration of glycine, glycinamide and D-serine produced time- and dose-dependent changes in mouse cerebellar cGMP levels, indicating a modulation of ongoing neuronal activity through the NMDA receptor complex. Intracerebroventricular administration of glycinamide also produced a time-dependent change in cGMP levels, indicating a central mechanism of action. The icb dose-response data indicated a unimolecular interaction for these compounds. D-serine-, glycine-, and glycinamide-mediated increases in cGMP levels were reversed by the competitive NMDA antagonist, CPP and the NMDA-associated glycine receptor antagonist, HA-966, indicating mediation via the NMDA receptor complex. Glycine and D-serine were less effective than glycinamide at increasing cerebellar cGMP levels. In contrast, L- and D-serinamide did not affect cGMP levels. These results indicate that glycine receptor is not saturated under physiological conditions and also suggest possible existence of multiple glycine pools.

Sigma receptors modulate both A9 and A10 dopaminergic neurons in the rat brain: functional interaction with NMDA receptors.

The sigma receptor ligands, (+)-pentazocine and (+)-SKF 10,047, were found to increase dopamine metabolism (DOPAC, HVA) and release (3-MT) in both the striatum and olfactory tubercle of the rat, in a dose-dependent manner, after central as well as peripheral administration. The effect of (+)-SKF 10,047 was stereospecific. The increase in dopamine metabolism was not blocked by naloxone pretreatment, excluding an action via opioid receptors. More interestingly, this modulation was blocked by pretreatment with the NMDA receptor antagonist, CPP. Neither sigma ligand exhibited any affinity for D1 or D2 dopamine receptors or for NMDA, PCP or NMDA-associated glycine receptors. Sigma receptors thus appear to modulate dopaminergic function in both A9 and A10 projections. This modulation appears to involve a functional interaction with NMDA receptors or an NMDA-utilizing synapse downstream to neurons modulated by sigma receptors.

Inhibition of climbing and mossy fiber, and basket and stellate cell inputs to mouse cerebellar Purkinje cells by novel anti-ischemic agents, ifenprodil and BMY-14802.

Cerebellar cyclic guanosine monophosphate (cGMP) levels reflect the ongoing neuronal activity mediated by the N-methyl-D-aspartate (NMDA) receptor complex. Due to the putative role of the NMDA receptor complex in the etiology of ischemic neuronal injury, the effects of two novel anti-ischemic agents, ifenprodil and BMY-14802, were examined on cGMP responses mediated by harmaline, methamphetamine (MA), and pentylenetetrazol (PTZ), agents which modulate the Purkinje cell activity by three distinct pharmacological mechanisms. Similar to the competitive NMDA antagonist, CPP [(+/-)-3-carboxypiperazin-4-yl)propyl-1-phosphonic acid], ifenprodil and BMY-14802 reversed the harmaline-, MA- and PTZ-induced cGMP levels. Unlike CPP, ifenprodil was nearly 3-times less potent at reversing the harmaline-induced increases in cGMP levels than at reversing MA-and PTZ-induced increases in cGMP levels. These results suggest a differential modulation of basket and stellate, and mossy fiber activity by ifenprodil.

The polyamines, spermine and spermidine, negatively modulate N-methyl-d-aspartate (NMDA) and quisqualate receptor mediated responses in vivo : Cerebellar cyclic GMP measurements.

The effects of the polyamines, spermine and spermidine on basal and d-serine-, harmaline- and quisqualate-induced cyclic GMP (cGMP) were measured in mouse cerebellum. Spermine and spermidine at 200 ?g/mouse, intracerebellar injection (icb), did not alter basal cGMP levels. d-Serine (200 ?g/mouse, icb) and quisqualic acid (5 ?g/mouse, icb) caused 5- and 15-fold increases in cGMP. These increases were significantly reversed by co-injected spermine and spermidine (200 ?g/mouse, icb). Furthermore, direct intracerebellar spermidine (200 ?g) completely reversed harmaline (100 mg/kg, sc) induced increases in cGMP. These data indicate that the polyamines, spermine and spermidine attenuate responses mediated through the N-methyl-D-aspartate (NMDA), NMDA-associated glycine receptor and quisqualate receptors. These results provide an in vivo neurochemical evidence for polyamine modulation of excitatory amino acid receptors. Due to their putative abilities to increase mitochondrial uptake of [Ca(+2)], spermine and spermidine are likely to modulate the responses of several excitatory amino acid agonists. The polyamines spermine and spermidine are widely distributed in neural and non-neural tissues and have been shown to play a key role in cell differentiation and growth (Kremzner et al ., 1970; Harik and Snyder, 1974; Raina and Janne, 1975; Seiler, 1981; Pegg and McCann, 1982). Extensive studies have indicated an important role of the polyamines, spermine and spermidine, in the regulation of intracellular [Ca(+2)] levels (Nicchitta and Williamson, 1984; Iqbal and Koenig, 1985; Jensen Lynch and Baudrey, 1987; 1989 a, b). The precise regulation of intracellular [Ca(+2)] levels and maintenance of [Ca(+2)] gradients across the cell membranes are essential in cell survival as prolonged and excessive exposure to calcium can result in neuronal injury and death (Farber, 1981; Rasmussen and Barnett, 1984). The excitatory amino acid glutamate is known to interact with three subclasses of receptors, N-methyl-D-aspartate (NMDA), quisqualate and kainate (Cotman and Iversen, 1987). The role of excitatory amino acids in the etiology of ischemic neuronal death is also well established (Cotman and Iversen, 1987). Although the precise mechanisms of ischemic injury are unknown, excessive release of glutamate and/or other endogenous excitatory amino acid(s) which result(s) in massive influx of [Ca(+2)] into neurons (Garthwhite et al ., 1986; Choi et al ., 1987) is considered in important event. Due to the pivotal role played by polyamines in the regulation of intracellular [Ca(+2)] levels, it is likely that polyamines may have an important role in the pathophysiology of ischemic injury. Recent in vitro evidence suggests that the NMDA receptor complex has recognition sites for the polyamines, spermine and spermidine, besides the putative sites for glycine, phencyclidine (PCP), and divalent ions such as [Mg(+2)] and [Zn(+2)] (Ransom and Stec, 1988). Recently, ifenprodil, a novel NMDA receptor antagonist, was shown to interact with the polyamines (Reynolds and Miller, 1989) which may explain its unique pharmacological profile. However, the precise functional interactions of polyamines with NMDA and other excitatory amino acids are unknown at this time. The present investigation was aimed at elucidating the in vivo functional interrelationships between polyamines and the excitatory amino acids in general, and with the NMDA receptor complex in particular, by examining the effects of spermine and spermidine on mouse cerebellar cGMP levels, a well characterized excitatory amino acid receptor-mediated second messenger response (Wood et al ., 1982; 1987; 1989; Rao et al ., 1989).

Phencyclidine-like effects of tetrahydroisoquinolines and related compounds.

A series of 1,2,3,4-tetrahydroisoquinolines, tetrahydrothieno[2,3-c]pyridines, and related compounds were evaluated for their ability to inhibit binding of [3H]-1-[1-(2-thienyl)piperidine and [3H]-N-allylnormetazocine to phencyclidine (PCP) and sigma receptors, respectively. A representative series of compounds was evaluated in behavioral assays to determine the ability of the compounds to induce PCP-like stereotyped behavior and ataxia. All of the compounds caused stereotyped behavior and ataxia, indicating their agonist actions at the PCP site.

Synthesis, configuration, and evaluation of two conformationally restrained analogues of phencyclidine.

Brown oxidation of cis-bicyclo[3.1.0]hexan-3-ol afforded bicyclo[3.1.0]hexan-3-one in 98% yield. Treatment of this ketone with either phenyllithium or phenylamagnesium bromide in ether at room temperature followed by solvolysis of the resulting alcohol in a mixture of trifluoroacetic acid, sodium azide, and chloroform gave a mixture of cis- and trans-3-azido-3-phenylbicyclo[3.1.0]hexanes. LAH reduction of this crude mixture of azides afforded a 1:3.5 mixture of cis- and trans-3-phenyl-3-bicyclo[3.1.0]hexylamine, respectively, in 51% overall yield from the alcohol. Separation of the mixture of amines by column chromatography followed by cyclization of each by heating at 60 degrees C in DMF solution with 1 equiv of 1,5-dibromopentane furnished the two conformationally restrained analogues of phencyclidine (PCP), cis- and trans-3-phenyl-3-piperidinylbicyclo[3.1.0]hexane (1 and 2, respectively), in high yield. Configurations were assigned on the basis of an X-ray crystallographic analysis of the cis isomer (1). Bond lengths and angles are similar to those found in PCP and its derivatives. Binding to PCP receptors and sigma sites as well as behavioral effects of 1 and 2 in rats was determined relative to PCP. In displacement of specifically bound [3H]TCP (1-[1-(2-thienyl)cyclohexyl]piperidine) from PCP receptors, 1 and 2 were nearly equipotent and about one-seventh as potent as PCP. These compounds were about one-fifth as potent as PCP in displacing [3H]-(+)-SKF 10,047 from its binding site. Calculation of the ED50 values of 1 and 2 for stereotyped behavior and ataxia indicated that they were about equipotent, and 2-3-fold less active than PCP.