A novel benzodiazepine inverse agonist, S-8510, as a cognitive enhancer.

1. Pharmacological actions of a novel benzodiazepine receptor ligand, S-8510 (2-(3-isoxazolyl)-3,6,7,9-tetrahydroimidazo[4,5-d]pyrano+ ++[4,3-b] pyridine monophosphate monohydrate), were examined in in vitro and in vivo studies. 2. S-8510 was characterized as a partial inverse agonist with a modest GABA ratio and low efficacy. 3. S-8510 ameliorated memory impairment induced by cholinergic deficit in the water maze paradigm of Wistar rats. 4. S-8510 augmented LTP of the Schaffer collateral/commissural fiber-CA1 synapses in the hippocampal slice preparations of SD rat. 5. S-8510 increased the extracellular levels of acetylcholine and noradrenaline in the hippocampus of Wistar rat. 6. S-8510 selectively potentiated pentylenetetrazol-induced convulsion without affecting minimal electroconvulsive shock- or strychnine-induced convulsion in ddY mice. 7. S-8510 failed to induce any sign of anxiety in the Wistar rat pro-conflict test. 8. S-8510 showed antidepressant-like pharmacological actions in ddY mice. 9. These results suggest that S-8510 can be used as a therapeutic drug for senile dementia, including Alzheimer's disease with little risk for inducing anxiety or convulsion.

Synthesis and structure--activity relationships of fused imidazopyridines: a new series of benzodiazepine receptor ligands.

2-Arylimidazo[4,5-c]quinolines and analogous fused imidazopyridines were synthesized and evaluated as benzodiazepine receptor ligands. Affinity to the receptors was greatly affected by the bulkiness of the aryl group at the 2-position, compared to the pyrazoloquinolines such as CGS-9896. Derivatives with an isoxazole moiety at the 2-position showed high binding affinity and in vivo activity. In the imidazo[4,5-c]quinoline series, substitution at the 6-position decreased or abolished activity. Most derivatives with an unsubstituted isoxazolyl group showed antagonist or inverse agonist activity except for the 7-halo analogues, which exhibited agonist activity. On the other hand, 5-methylisoxazol-3-yl or 3-methylisoxazol-5-yl derivatives generally exhibited agonist activity. A similar substitution effect on the isoxazole moiety was observed in the imidazopyridines fused with a nonaromatic ring. From the detailed pharmacological evaluation, S-8510, 2-(3-isoxazolyl)-3,6,7,9-tetrahydroimidazo[4,5-d]pyrano++ +[4,3-b]pyridine monophosphate, possessing weak inverse agonist activity was selected as a therapeutic candidate for the treatment of some symptoms of senile dementia.

Behavioral and electroencephalographic properties of duloxetine (LY248686), a reuptake inhibitor of norepinephrine and serotonin, in mice and rats.

Duloxetine is a dual inhibitor of norepinephrine and serotonin reuptake. Duloxetine (3.13-50 mg/kg p.o.) significantly prevented tetrabenazine (1 and 50 mg/kg s.c.)-induced ptosis in mice and rats. Moreover, duloxetine (1.56-12.5 mg/kg p.o.) also inhibited reserpine (1 mg/kg s.c.)-induced hypothermia in mice. When duloxetine (12.5-100 mg/kg p.o.) and 5-hydroxytryptophan (80 and 100 mg/kg i.p.), a precursor of serotonin, were administered simultaneously to mice and rats, head movement behavior and tremor were observed. In addition, duloxetine (25-100 mg/kg p.o.) significantly attenuated immobility in forced swimming in mice, as equally effective as commonly used antidepressant drugs. Duloxetine (12.5-25 mg/kg p.o.) significantly decreased rapid eye movement sleep and slow-wave deep sleep and increased the awake period, as shown in the rat EEG. However, duloxetine (25-200 mg/kg p.o.) did not affect salivation and lacrimation induced by oxotremorine (1 mg/kg s.c.), a cholinergic agonist, whereas it (25-50 mg/kg) reduced the oxotremorine-induced tremor in part. These results indicated that duloxetine produced behavioral and electroencephalographic responses resulting from the inhibition of norepinephrine and serotonin reuptake in vivo, and that it had a weak anticholinergic action. Therefore, duloxetine may be clinically useful as an antidepressant.

Pharmacological studies on a new dihydrothienopyridine calcium antagonist, S-312-d. 5th communication: anticonvulsant effects in mice.

S-312, S-312-d, but not S-312-l, L-type calcium channel antagonists, showed anticonvulsant effects on the audiogenic tonic convulsions in DBA/2 mice; and their ED50 values were 18.4 (12.8-27.1) mg/kg, p.o. and 15.0 (10.2-23.7) mg/kg, p.o., respectively, while that of flunarizine was 34.0 (26.0-44.8) mg/kg, p.o. Although moderate anticonvulsant effects of S-312-d in higher doses were observed against the clonic convulsions induced by pentylenetetrazole (85 mg/kg, s.c.) or bemegride (40 mg/kg, s.c.), no effects were observed in convulsions induced by N-methyl-D-aspartate, picrotoxin, or electroshock in Slc:ddY mice. S-312-d may be useful in the therapy of certain types of human epilepsy.

Inhibitory effect of CCK-8 and ceruletide on glutamate-induced rises in intracellular free calcium concentrations in rat neuron cultures.

To study the mechanism by which cholecystokinin octapeptide (CCK-8) and its potent analogue, ceruletide, prevent glutamate-induced neuronal cell death in rat neuron cultures, we examined the effect of both peptides on glutamate-induced increases in the intracellular free calcium concentrations ([Ca2+]i), which are known to be a crucial trigger of the neurodegeneration induced by glutamate. CCK-8 itself did not alter [Ca2+]i in rat neuron cultures. Glutamate increased [Ca2+]i in neuron cultures rapidly and markedly. CCK-8 and ceruletide significantly suppressed the increases in [Ca2+]i induced by glutamate. The maximum inhibitory effects of CCK-8 and ceruletide at 10(-6) M reached 43 and 46% of the response to glutamate, respectively. Gastrin-I and CCK-4 also significantly attenuated the increases in [Ca2+]i induced by glutamate. The inhibitory effect of CCK-8 was completely blocked by the selective antagonist for CCK-B receptors, (+)L-365,260, but not by (-)L-364,718, which is a selective antagonist for CCK-A receptors. CCK-8 significantly suppressed [Ca2+]i response to kainate and high concentrations of extracellular K+, but not to N-methyl-D-aspartate. With cultured astrocytes, CCK-8 did not inhibit the increment of [Ca2+]i induced by glutamate. These findings clearly demonstrated that CCK-8 and ceruletide inhibit glutamate-induced increases in [Ca2+]i in neuron cultures through CCK-B receptors, suggesting that CCK-8 may participate in the central actions of glutamate.

Ischemia-induced irreversible deficit of memory function in gerbils.

Ischemia for 5 min temporarily increased locomotor activity in gerbils after 1 and 3 days. Temporary increases were also noted within 7 and 5 days after 20-min ischemia and repeated ischemia (three 2-min ischemia at 1-h intervals), respectively. In a passive avoidance task, gerbils were trained 2 or 14 days before the occlusion and then tested 1 day after it. Shortened step-through latency was observed in the retention test 3 days after 5-min ischemia, but not after 15 days (reversible deficit). In contrast, following 20-min ischemia, the step-through latency was significantly lower after 3 days and also after 15 days (irreversible deficit). Working memory was also tested with gerbils trained for an 8-arm radial maze task. A significantly higher working error was observed 1 day after 5-min ischemia but not after 5 days (reversible deficit). However, ischemia for 20-min and repeated ischemia led to markedly increase working error 1 day after the occlusion, with significant increases even after 14 and 28 days (irreversible deficit). In addition, while 5-min ischemia occurred the neuronal death in the hippocampal CA1 subfield, 20-min ischemia produced it not only in the CA1 subfield but also in the CA2-4 subfield and dorsal striatum. These results indicated that 5-min ischemia led to a reversible memory deficit, while 20-min and repeated ischemia produced an irreversible deficit.

Systemic administration of a cholecystokinin analogue, ceruletide, protects against ischemia-induced neurodegeneration in gerbils.

The neuroprotective action of a cholecystokinin octapeptide analogue, ceruletide, was evaluated in models of cerebral ischemia using Mongolian gerbils. Ceruletide significantly suppressed the hyperactivity and amnesia induced by ischemia when injected s.c. 30 min before 5-min occlusion of the bilateral common carotid arteries at room temperature or immediately after their reperfusion. Ceruletide also reduced behavioral changes in ischemic gerbils whose body temperature was maintained at 37 degrees C during the 3-min occlusion. In these groups, delayed neuronal cell death in the hippocampal CA1 area following ischemia was markedly attenuated by s.c. administration of ceruletide. On the other hand, ceruletide could not inhibit the behavioral changes or the neurodegeneration induced in the hippocampal CA1 area by 5-min occlusion at 37 degrees C. These findings indicate that peripheral injection of ceruletide produces a neuroprotective action against moderate cerebral ischemia, which is the first evidence suggesting the efficacy of ceruletide in neurodegenerative diseases.

Protective effect of CCK-8 and ceruletide on glutamate-induced neuronal cell death in rat neuron cultures: possible involvement of CCK-B receptors.

Cholecystokinin octapeptide (CCK-8), ceruletide (CLT) and gastrin-I, which were added simultaneously with glutamate to rat neuron cultures, significantly suppressed the neuronal cell death induced by glutamate which can be observed from the efflux of lactate dehydroxylase into the culture medium. However, gastrin-I (1-13) had no effect on the response to glutamate. The inhibitory effect of CLT on glutamate-induced neuronal cell death could be completely blocked by a selective antagonist for CCK-B receptors, (+)L-365,260. These findings clearly indicate that CCK-8, CLT and gastrin-I exhibit a protective effect against glutamate-induced neurotoxicity via the CCK-B receptor.

Inhibitory effect of ceruletide on haloperidol-induced catalepsy in rats.

Ceruletide (CLT: 160 micrograms/kg, SC) produced a relatively long-lasting inhibition of haloperidol (HPD: 2 mg/kg, PO) catalepsy in rats. Neither bilateral vagotomies nor hypophysectomy abolished the anticataleptic effect of CLT. However, (-)-L-364,718 and proglumide blocked the effect of CLT. CLT (160 micrograms/kg) significantly inhibited HPD (2 mg/kg)-induced increase in dopamine (DA) release from the rat striatum. This effect of CLT was also antagonized by proglumide. These results suggest that CLT (160 micrograms/kg) primarily acts on cholecystokinin-A receptor in the brain, exerts some modulatory influence on HPD binding to striatal DA receptors via unknown neural pathways and, consequently, inhibits HPD catalepsy.

Thienylpyrazoloquinolines with high affinity to benzodiazepine receptors: continuous shift from inverse agonist to agonist properties depending on the size of the alkyl substituent.

2-(5-Alkylthien-3-yl)-(1),2-(4-alkylthien-2-yl)-(2), and 2-(5-alkylthien-2-yl)-2,5-dihydro-3H-pyrazolo[4,3-c]quinolines (3) were prepared in four steps starting from ethyl 4-chloroquinoline-3-carboxylate (4) and hydrazinothiophene-carboxylates 5, 8, and 9. All the assayed compounds possessed high affinities for benzodiazepine receptors (Ki = 0.3-2.6 nM). The activities of agonists and inverse agonists were assessed on the basis of inhibition or facilitation of pentylenetetrazole-induced convulsions, respectively. Introduction of alkyl groups of different sizes into the unsubstituted inverse agonistic compounds results in a corresponding shift in the activity from an inverse agonist to an antagonist to an agonist. The susceptibility of such a shift increases in the order of 1 less than 2 less than 3. This tendency may be explained by slight differences in the geometry of the alkyl substituents among the three series.

Thienylpyrazoloquinolines: potent agonists and inverse agonists to benzodiazepine receptors.

Synthesis and structure-activity relationships of a series of 2-(thien-3-yl)- and 2-(thien-2-yl)-2,5-dihydro-3H-pyrazolo[4,3-c]quinolin-3-ones are reported. A number of the compounds possessed 1 order of magnitude higher affinity for the receptors than diazepam. Planarity was one of the structural requirements for binding to benzodiazepine receptors. The activities of agonists and inverse agonists were assessed on the basis of inhibition or facilitation of the pentylenetetrazole-induced convulsions, respectively. Thien-3-yl compounds exhibited inverse agonist activity whereas thien-2-yl analogues with a 5'-alkyl group showed agonist activity. Substitution on the quinoline moiety did not enhance in vivo activity. The most potent compounds were the 5-methylthien-3-yl derivative 6a as an inverse agonist and the 5-methylthien-2-yl compound 13a as an agonist.

Activation of brain function by S-135, a benzodiazepine receptor inverse agonist.

1. S-135, 2-(5-methylthien-3-yl)-2,5-dihydro-3H-pyrazolo[4,3-c]quinoline-3- one, bind binds to benzodiazepine receptors with a high affinity and shows pharmacological actions opposite to those of conventional benzodiazepine drugs. 2. S-135 induced no convulsion in mice by itself, but selectively potentiated the effect of subconvulsive dose of pentylenetetrazole. 3. S-135 potentiated rat crossed extensor reflex and Ro 15-1788 completely antagonized this potentiation. 4. S-135 antagonized pentobarbital-induced anesthesia, tetrabenazine-induced ptosis and reserpine-induced hypoactivity and shortened immobilization time in the despair test in mice, indicating that this compound possesses antidepressive properties. 5. S-135 antagonized amnesia in mice and rats in passive avoidance tasks. 6. Glucose utilization in brain areas relating to memory and arousal functions was enhanced following S-135 treatment. 7. These results indicate that S-135 can be a useful drug for activating depressed brain function.

Inhibitory effect of centrally administered atrial natriuretic polypeptide on the brain dopaminergic system in rats.

The effects of intracerebroventricular injection of atrial natriuretic polypeptide (ANP) and angiotensin II (AII) on the concentration of dopamine, noradrenaline, serotonin and their primary metabolites in the rat brain were studied using high performance liquid chromatography with electrochemical detection. ANP (2 and 5 micrograms) decreased the level of dopamine and its metabolite in the septum and hypothalamus. In contrast, AII (100 ng) increased their levels in these brain regions. The simultaneous administration of ANP (5 micrograms) with AII (100 ng) resulted in a marked reduction of the AII-induced increase of dopamine and its metabolite. No significant changes were observed in the concentrations of noradrenaline and serotonin throughout the brain. These results suggest that the central action of ANP is mediated in part via the dopaminergic system.

Possible involvement of central atrial natriuretic polypeptide in regulation of hypothalamo-pituitary-adrenal axis in conscious rats.

The effects of intracerebroventricular (i.c.v.) administration of angiotensin II (AII) and atrial natriuretic polypeptide (ANP) on the plasma corticosterone level were studied in conscious, unrestrained rats. Although i.c.v. injection of ANP had no apparent effect on the basal plasma corticosterone level, it attenuated the plasma corticosterone increase induced by centrally injected AII dose-dependently. These results suggest that ANP in the brain is involved in the regulation of the hypothalamo-pituitary-adrenal axis.

Leumorphin is a potent inhibitor of vasopressin secretion.

The effects of intracerebroventricular (i.c.v.) injection of leumorphin on the vasopressin secretion induced by angiotensin II or dehydration were studied in conscious unrestrained rats. The vasopressin secretion induced by angiotensin II (100 pmol) was significantly inhibited by the simultaneous injection of leumorphin (6 pmol-600 pmol) in a dose-dependent manner. In 72-hour water-deprived rats, the i.c.v. injection of leumorphin (60 pmol or 600 pmol) significantly suppressed the vasopressin secretion dose-dependently. These results suggest that leumorphin is involved in the regulation of the vasopressin secretion.

1-Azacycloalkyl-1,4-benzodiazepin-2-ones with antianxiety-antidepressant actions.

A series of 1-azacycloalkyl-1,4-benzodiazepin-2-ones were synthesized from 1-azacycloalkyl-2-benzoylanilines and corresponding imines and then evaluated for their central nervous system activities. Pharmacological data showed that some of these compounds have potent antidepressant properties, as assessed by their antagonism of tetrabenzine (TBZ) induced ptosis and their inhibition of [3H]norepinephrine uptake into rat brain synaptosomes, as well as their moderate antianxiety properties of preventing of pentylenetetrazol (PTZ) convulsion, suppressing conflict behavior, and displacing potential for [3H]diazepam binding. Introduction of a halogen substituent at position 7 of the 1,4-benzodiazepine ring lengthened the anti-PTZ effects, although the peak effect was slightly reduced and clearly enhanced the anti-PTZ and anticonflict properties. Introduction of Cl to the ortho position of the phenyl ring at position 5 greatly reduced the antidepressant properties. The secondary amine function of the azacyclic ring at position 1 was essential for the production of the antidepressant properties. Of these new series, 7-fluoro-5-(2-fluorophenyl)-1,3-dihydro-1-(4-piperidinyl)-2H-1,4-benzodi azepin-2 -one has the potential to become a useful antidepressant drug with a moderate antianxiety property.

Synthesis and neuroleptic activity of N-[(1-ethyl-2-pyrrolidinyl)methyl]-2-methoxy-5-sulfonamidobenzamide s.

A series of some novel N-[(1-ethyl-2-pyrrolidinyl)methyl]benzamides involving replacement of the sulfamoyl group in sulpiride with a sulfonamido group was synthesized and tested for dopamine receptor blockade. In comparison with sulpiride, several compounds were considerably more potent than sulpiride as dopamine receptor blockers. The structure-activity relationships are discussed.

[Pharmacological studies of a new sleep-inducer, 1H-1,2,4-triazolyl benzophenone derivatives (450191-S) (I). Behavioral analysis].

The behavioral effects of 450191-S and its metabolites were investigated in mice, rats, cats and rhesus monkeys, and they were compared with those of related benzodiazepines (BDZ) such as diazepam and nitrazepam. Oral administration of 450191-S consistently caused sedation without excitability in mice and rats, and it was only 1/2 to 1/266 as potent as the BDZ in producing motor incoordination as assessed by traction, rotarod performance and inclined screen tests in mice, induced much less ataxia in cats and monkeys, and inhibited respiration in anesthetized cats. The locomotor activities of mice and rats measured by Animex and the open field test were not affected by 450191-S, but rearing and preening decreased with 450191-S as with the BDZ. 450191-S was equipotent with nitrazepam and 2 to 6 times more potent than diazepam and estazolam in potentiating chlorprothixene-induced hypnosis and thiopental-Na-induced anesthesia. These effects were not different with successive 14-day administration of 450191-S. Anti-pentylenetetrazol, picrotoxin and bicuculline convulsions of 450191-S had the same potency as nitrazepam, but caused much less anti-electroshock convulsion than the BDZ. 450191-S had potent antianxiety activity as observed by anti-aggressive and anti-conflict activities and had almost the same effect as diazepam on operant behavior. The metabolites M-1, M-2, M-A and M-3 showed approximately the same potency as 450191-S in inducing anesthetic potentiation and antianxiety activity, but they were much more potent in causing disturbance of the somatic functions. These results indicate that 450191-S possesses inhibitory effects on the central nervous system, including a potent sleep-inducing effect, and is characterized by markedly weak muscle relaxant activity and motor incoordination.

Pharmacological properties of 2-[4-(2-thiazolyloxy)-phenyl]-propionic acid (480156-S), a new non-steroidal antiinflammatory agent.

In terms of antiinflammatory activity in acute and chronic animal models, 2-[4-(2-thiazolyloxy)-phenyl]-propionic acid (480156-S) was more active than ibuprofen but inferior to indomethacin. The analgesic activities of 480156-S measured by the writhing method and the Randall & Selitto method were comparable or superior to those of indomethacin, diclofenac-Na and ketoprofen. 480156-S also had strong antagonistic action against bradykinin, markedly inhibiting all bradykinin-induced edema and pain reactions (tail licking in mice and flexor reflex of rabbit hind limb). On scald-induced pain in which bradykinin is greatly involved, 480156-S had an obviously stronger analgesic effect than any of the reference drugs. As for its effects on prostaglandin (PG), 480156-S weakly inhibited arachidonic acid-induced edema and pain reactions but also inhibited PGE2 synthesis of bovine vesicular gland microsomes.