Effects of 5-HT1A agonists and 5-HT2 antagonists on haloperidol-induced dyskinesias in squirrel monkeys: no evidence for reciprocal 5-HT-dopamine interaction.

Dyskinetic movements and dystonic postures may be induced by neuroleptics in monkeys that have undergone previous neuroleptic treatment, and these motor abnormalities constitute a primate model of drug-induced extrapyramidal symptomatology. In view of previous suggestions that brain serotonergic systems may tonically inhibit dopamine neurons, the effects of several new and selective 5-HT2 receptor antagonists and 5-HT1A receptor agonists were investigated in this model. Setoperone, a dopamine D2 receptor antagonist with extremely potent 5-HT2 antagonism, caused dyskinetic movements. Although ritanserin is a potent 5-HT2 antagonist with very weak dopamine antagonist properties, this drug did not antagonize dyskinesias but induced them when administered at a high dose (30 mg/kg). Buspirone induced dyskinesias and blocked apomorphine-induced climbing, supporting prior reports that it has dopamine antagonist effects. Gepirone, a 5-HT1A agonist with less marked dopamine antagonist properties, induced dyskinesias in only one of six monkeys at 30 mg/kg and did not block haloperidol-induced dyskinesias. 8-OH-DPAT partly attenuated haloperidol-induced dyskinesias, an effect possibly attributable to its weak dopamine agonist properties. Tonic inhibition of brain extrapyramidal dopamine systems by serotonin systems does not appear to characterize neuroleptic-related dyskinesias in squirrel monkeys.

Leukocyte stimulation of intimal lesion formation is inhibited by treatment with diclofenac sodium and dexamethasone.

This investigation tested the effect of anti-inflammatory agents acting at different levels of the arachidonic acid cascade on leukocyte migration into the vessel wall. An animal model of vasculitis was used in which leukocytes stimulate migration of smooth muscle cells from the media into the intima resulting in formation of intimal lesions. In this model, an endotoxin-soaked thread is implanted in the adventitia along the ventral side of the rat femoral artery. At 2 days, subendothelial and medial leukocyte accumulation occurs exclusively in the ventral half of the vessel. At 14 days, intimal lesions composed primarily of smooth muscle cells are localized to the ventral half of the vessel. Treatment with neither the lipoxygenase inhibitor L-651,392 nor the dual cyclooxygenase and lipoxygenase inhibitor BW755C affected leukocyte migration into the vessel wall or subsequent lesion formation. Treatment with the cyclooxygenase inhibitor diclofenac sodium greatly reduced both leukocyte accumulation and lesion formation, whereas leukocyte migration and lesion formation were nearly totally inhibited by treatment with dexamethasone. Thus, it has been demonstrated that although leukocyte accumulation in the vessel wall stimulates intimal lesion formation, pharmacologic inhibition of leukocyte accumulation prevents lesion formation.

Behavioral tolerance and sensitization to CGS 19755, a competitive N-methyl-D-aspartate receptor antagonist.

Competitive N-methyl-D-aspartate (NMDA) receptor antagonists, including CGS 19755, have the ability to antagonize NMDA-induced convulsions, to cause ataxia and, at high doses, to increase spontaneous locomotor activity. It was of interest to determine whether or not repeated treatment with CGS 19755 would induce tolerance to some or all of these effects. CGS 19755 was administered to mice twice daily for 14 days at 54 mg/kg i.p. per injection. One day after the last repeated injection, mice were challenged with vehicle or one of several doses of CGS 19755 (10, 30, 54 and 100 mg/kg) and were tested for evidence of motor impairment (using righting reflex and traction tests), for spontaneous locomotor activity and for the threshold dose of NMDA required to induce convulsions. When challenged with CGS 19755, mice that had previously received only vehicle showed reduced motor activity in response to doses of 54 and 100 mg/kg. In contrast, mice that had received the repeated treatment regimen of CGS 19755 increased motor activity in response to challenge doses of 30 and 54 mg/kg. These effects resembled those reported previously by some investigators for phencyclidine. However, repeated treatment with CGS 19755 induced only slight tolerance to the ability of this drug to cause ataxia. In mice treated repeatedly with CGS 19755, the threshold dose of NMDA to induce convulsions did not differ significantly from that in mice treated repeatedly with vehicle, indicating no demonstrable tolerance to the apparent anticonvulsant effects of CGS 19755 over this time period.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine neurochemical profile of atypical antipsychotics resembles that of D-1 antagonists.

The release and metabolism of dopamine in the mouse caudate-putamen were determined after the oral administration of antipsychotic drugs at doses equal to or sixfold greater than the ED50 dose for their inhibition of apomorphine-induced climbing. Dopamine release was equated with concentrations of 3-methoxytyramine (3-MT) and metabolism was equated with concentrations of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels. Like the D-1 antagonists SCH 23390 and SKF 83566, most antipsychotic agents with an atypical preclinical profile suggestive of low extrapyramidal symptomatology (CGS 10746B, flumezapine, CL 77328, rimcazole, clozapine, RMI 81582, and fluperlapine) never increased dopamine release and produced variable increases in dopamine metabolism. Other atypical antipsychotics (thioridazine, mesoridazine, melperone) increased dopamine release at only one dose tested but increased dopamine metabolism at most doses. Antipsychotic agents associated with extrapyramidal side effects (setoperone, perlapine, haloperidol, chlorpromazine, and metoclopramide) increased dopamine release and metabolism at almost every dose tested. Thus, atypical antipsychotics increase the metabolism but not release of dopamine at behaviorally effective doses. The resemblance of these minimal effects on dopamine release to those obtained with D-1 antagonists that also have an atypical preclinical profile suggests that a mechanism related to D-1 receptor antagonism may contribute to the action of atypical antipsychotics.

Motor activity changes following cerebral ischemia in gerbils are correlated with the degree of neuronal degeneration in hippocampus.

Cerebral ischemia was induced in Mongolian gerbils by bilateral occlusion of the carotid arteries. Subsequent histological assessment revealed neuronal degeneration in the CA1 area of the hippocampus. A functional behavioral change was reflected in an elevation of motor activity compared with sham-operated animals. The degree of hippocampal damage was positively correlated with the increase in motor activity. It is concluded that alterations in both measures result from the interruption of blood flow to the brain but may be brought about by different mechanisms.

The N-methyl-D-aspartate antagonists CGS 19755 and CPP reduce ischemic brain damage in gerbils.

N-Methyl-D-aspartate (NMDA) antagonists reduce ischemic brain damage and associated hypermotility. Two potent, selective and competitive NMDA antagonists, cis-4-(phosphonomethyl)-2-piperidine-carboxylic acid (CGS 19755) and 4-(3-phosphonopropyl)-2-piperazine-carboxylic acid (CPP), were characterized in the gerbil ischemia model with respect to dose-response and time course effects. Both drugs were effective in reducing ischemia-induced hippocampal brain damage as well as hypermotility. In this model, CGS 19755 was more potent than CPP, and had protective effects when given after longer delays between ischemia and drug administration.

The novel N-methyl-D-aspartate (NMDA) antagonist CGS 19755 prevents ischemia-induced reductions of adenosine A1, NMDA, and PCP receptors in gerbil brain.

Transient brain ischemia results in a selective destruction of cell bodies within the hippocampus and cortex. This cellular destruction appears to be mediated through a release of endogenous exictatory amino acids following the ischemic episode, since the neurotoxic effects of ischemia can be attenuated by compounds that have antagonist activity at N-methyl-D-aspartate (NMDA) receptors. In the present study, the protective effects of a novel NMDA receptor antagonist, CGS 19755, were further evaluated by using quantitative autoradiography to characterize adenosine A1, NMDA, PCP, and benzodiazepine receptors in ischemic gerbil brain. Bilateral carotid artery occlusion (20 minutes) resulted in marked decreases (30-60%) in adenosine A1, NMDA, and PCP, but not benzodiazepine, receptors in gerbil forebrain. Postischemic treatment with CGS 19755 was found to completely block the ischemia-induced decreases in brain adenosine and NMDA receptors. [3H]TCP binding in ischemic gerbil brain was also elevated by CGS 19755 treatment; significant differences remained, however, between the CGS 19755-treated and control gerbils. These results indicate that transient brain ischemia produces significant and selective alterations in gerbil forebrain receptor systems. The observed decreases in radioligand binding are probably reflective of an ischemia-induced destruction of forebrain structures. However, there is some evidence that transient ischemia can also cause long-term changes in the affinity of some receptor systems. The postischemic efficacy of CGS 19755 appears to be due to its ability to block the neurotoxic effects of transient ischemia.

Lack of tolerance or withdrawal effects in mice after chronic administration of the non-sedating anxiolytic, CGS 9896.

CGS 9896, a non-sedating anxiolytic, was compared to diazepam with respect to the development of tolerance and withdrawal. Both compounds were administered daily to mice at various doses (3, 10 or 30 mg/kg) for periods of up to 4 weeks. Measures of sedation/muscle relaxation, motor activity and anticonvulsant effects were then assessed. When administered acutely, CGS 9896 increased motor activity, had no effect on traction reflex, and elevated the threshold for PTZ-induced convulsions. After chronic administration of CGS 9896, no changes in these parameters were observed compared to the effects seen after acute treatment. Acute administration of diazepam reduced motor activity, impaired traction reflex and increased PTZ-induced convulsion threshold. Tolerance developed to the effects of diazepam in all three measures. Following a four week dosing period with 30 mg/kg of either CGS 9896 or diazepam, the drugs were withdrawn and similar behavioral measures obtained at various withdrawal intervals up to 15 days. In separate groups of mice, precipitated withdrawal was also assessed by the administration of the benzodiazepine agonist, CGS 8216. No effects were observed after any period of withdrawal from CGS 9896. By contrast, withdrawal from diazepam resulted in significant alterations of motor activity and convulsion threshold. These results indicate that CGS 9896 is likely to be free of undesirable tolerance and withdrawal effects typically associated with the benzodiazepines.