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M S Eison

Publications and source records attributed to M S Eison.

36 records · Page 2Linked to original sources

Use of animal models: toward anxioselective drugs.

The debilitating psychopathology of anxiety neurosis is particularly amenable to relief by pharmacotherapy. While currently available drugs successfully alleviate the distressing symptoms suffered by anxious patients, they also carry potential liabilities which must be considered in their use. Through the use of predictive animal models, researchers hope to elucidate a set of structure-activity relationships through which anxiolytic, and most particularly anxioselective compounds can be rationally designed. Such models should predict side-effect potential as well as efficacy, so that unwanted ancillary effects of potential anxiolytics can be eliminated by appropriate structural modifications. The state of the art in preclinical testing for anxiolytic potential will be discussed with particular emphasis on the need to design test systems capable of detecting anxiolytic activity in diverse, nontraditional chemical series. The contribution of such methodology to the discovery and development of one anxioselective, non-benzodiazepine anxiolytic, buspirone, will be discussed.

Animals↗

Neuropharmacology of buspirone.

Buspirone is a clinically effective anxiolytic with a unique structure and pharmacology which distinguishes it from the benzodiazepines. It has been termed anxioselective because it lacks anticonvulsant, sedative, or muscle-relaxant properties. Preclinical evidence suggests it lacks potential for abuse or physical dependence and interacts minimally with CNS depressants such as alcohol. Rather than working through traditional benzodiazepine mechanisms, buspirone affects diverse aspects of the brain's neurochemical circuitry. For example, it exerts potent influences on the nigrostriatal and mesolimbic dopamine systems, the dorsal raphe serotonergic system, and the locus coeruleus noradrenergic system. Although without direct receptor interaction, potentiation of cholinergically mediated behavior and involvement with GABAergic neurotransmission have also been demonstrated.

Animals↗

Determination of functionally-relevant serum levels of MJ 13859-1 in the dog: relationship to blockade of amphetamine stereotypy.

The ability of drugs to block dopamine-agonist induced stereotypy in animals has proven to be a reliable in vivo predictor of antipsychotic efficacy in man. Assessment of a drug's potency at displacing [3H]spiperone from rat striatal membranes is an in vitro test which also has predictive validity for antipsychotic actions. Methods are described for assessing stereotyped behavior in the dog, and for measuring the ability of serum samples taken from treated animals at behaviorally interesting time points, to displace [3H]spiperone from washed synaptic membranes of rat striata. In these studies, oral administration of the potential antipsychotic agent MJ 13859-1 blocked amphetamine-induced stereotyped behavior in the dog for 6 hours. This behavioral effect was accompanied by sustained serum levels of [3H]spiperone displacing moieties derived from MJ 13859-1.

Amphetamine↗

Two routes of continuous amphetamine administration induce different behavioral and neurochemical effects in the rat.

Continuous amphetamine administration has proven to be a useful pharmacological tool. The two systems popularly used for the continuous administration of amphetamine differ in their release characteristics; output of drug from passive diffusion silicone-tubing implants gradually declines over several days, while that osmotically driven, active pumps remain more stable over time. A matched-dose comparison of the behavioral and neurochemical effects of both systems was performed in which silicone pellets and pumps were filled with appropriate concentrations of drug so as to release equal total quantities over the test period of 5 days. Rat behavior and brain catecholamine levels were affected in quantitatively and qualitatively different ways. The interesting constellation of behavioral and neurochemical changes associated with the use of silicone-tubing systems for the continuous administration of amphetamine may not be confounded by its declining output, but rather caused by it.

Amphetamines↗

Buspirone: an anxioselective alternative for the management of anxiety disorders.

Buspirone HCl (Buspar) is a novel anxiolytic agent unrelated to the benzodiazepines or other psychotherapeutic agents. Animal studies support an anxioselective profile, i.e. relief of anxiety without sedation, muscle relaxation or anticonvulsant activity. Double-blind clinical studies show buspirone to be effective in the treatment of anxiety and anxiety in the presence of depression. The effects of buspirone on psychomotor function, physical dependence and abuse potential tests are similar to those seen with placebo treatments. Mechanism of action studies indicate activity in a variety of neuronal systems.

Aggression↗

Continuous amphetamine intoxication: an animal model of the acute psychotic episode.

When amphetamines are administered to humans every few hours for several days, either during the 'speed runs' of addicts or in controlled laboratory settings, the psychosis which reliably results is similar to paranoid schizophrenia in a number of important aspects. This unique regimen of drug intake, which involves the continuous presence of stimulants over a prolonged period of time, can be simulated in animals using subcutaneously implanted slow-release silicone pellets containing d-amphetamine base. Monkeys and rats implanted with these pellets develop stages of behavioural alterations which are somewhat similar in sequence to those observed in humans who have received frequent doses of amphetamine. An initial period of hyperactivity and exploratory behaviour is followed by the gradual development of motor stereotypies which become virtually incessant. A period of relative inactivity then appears which is followed, at 4-5 days after pellet implantation, by a late stage. This final stage is characterized by 'wet-dog' shakes, parasitotic-like grooming episodes, and a variety of other forms of hallucinatory-like behaviour. At about the same time there are distinctive and partially irreversible alterations in dopaminergic innervations of the caudate nucleus, but not in mesolimbic dopamine innervation of the nucleus accumbens or in several other neurotransmitter systems. Continuous amphetamine administration may reproduce some aspects of the prolonged excitation which accompanies an acute psychotic episode and may be a fruitful model for the clarification of the dopamine theory of schizophrenia.

Animals↗

The behavioural effects of a novel substance P analogue following infusion into the ventral tegmental area or substantia nigra of rat brain.

The behavioural response following infusion of a novel, stable substance P (SP) analogue, DiMe-C7, into the ventral tegmental area (VTA) of rats was characterized and contrasted with the response to an equal dose of the parent compound SP. DiMe-C7 produced a longer-lasting behavioural stimulation than SP as evidenced in several behaviours, including locomotor activity, wet dog shakes, rearing and grooming. DiMe-C7-induced locomotor activity and rearing were potentiated by concurrent peripheral administration of D-amphetamine and blocked by pretreatment with haloperidol. Such responses to DiMe-C7 may thus be dependent upon dopaminergic activity. When given immediately following VTA infusion of DiMe-C7, morphine decreased, while naloxone had no effect upon most behavioural measures. The effect of methysergide on DiMe-C7 or SP into the substantia nigra reticulata produced a pattern of responses similar to nature to those produced by VTA infusion but different with respect to time course. These findings suggest that DiMe-C7 is a metabolically stable analogue of substance P which manifests prolonged actions on behaviour when centrally administered. Further, a role for central dopaminergic mechanisms is implicated in DiMe-C7-induced behavioural action.

Animals↗

Dopamine and antianxiety activity.

Clinical trials have indicated that buspirone (Buspar) is effective in the treatment of anxiety with efficacy and dosage comparable to diazepam. Until recently it has been thought that antianxiety drugs must alter benzodiazepine receptor binding in vitro. However, buspirone lacks any structural similarity to te benzodiazepines and does not interact with the benzodiazepine/gamma-aminobutyric acid (GABA) axis. Specifically, buspirone neither stimulates nor inhibits [3H]benzodiazepine binding, does not affect the influence o GABA or halide anions on benzodiazepine binding, and does not interfere with GABA binding or uptake. Behavioral testing has revealed that buspirone does not produce muscle weakness, does not control seizures, does not potentiate the impairment of psychophysiological function or lethality produced by administration of CNS depressants, does not produce sedation/hypnosis and does not appear to possess any abuse potential or liability for physical dependence. Thus, buspirone has been termed an anxioselective agent. Buspirone appears to only interact with the dopaminergic system with reasonable potency and exhibits properties of both a dopamine agonist and a dopamine antagonist. This suggests that dopamine is implicated in the etiology and expression of anxiety. A discussion of this implication is presented with a review of the clinical efficacy of nonbenzodiazepine drugs, especially dopamine agonists and dopamine antagonists, in the management of anxiety. In addition, neuropharmacological studies which have investigated the role of dopamine in animal models of anxiety are considered. Finally, the multiplicity of dopamine receptors and their regional localization in the brain are considered in the formulation of an hypothesis which features a role for the dopaminergic agents in the pharmacotherapy of anxiety.

Animals↗

Alterations in the stages of continuous amphetamine intoxication produced by lesions of locus coeruleus and substantia nigra.

1. Slow-release silicone pellets containing d-amphetamine base were implanted subcutaneously in rats 20 days following radio-frequency lesions of the locus coeruleus (LC), substantia nigra (SN), or control operations. 2. LC-lesioned rats exhibited enhanced motor stereotypies soon after implantation, while SN-lesioned animals showed increased locomotion but decreased stereotypy and anorexia. 3. The later behavioral stages of continuous amphetamine intoxication were attenuated in both lesioned groups as controls then entered the most intense stereotypy, showed the greatest withdrawal to the burrows, and maximally exhibited the increase in socially disruptive behaviors which appear following four days of constant amphetamine intoxication. 4. The integrity of both dopaminergic and noradrenergic systems was necessary for the full expression of the late stages of this animal model of amphetamine psychosis.

Amphetamine↗

Pharmacology and neurochemistry of buspirone.

Biochemically, buspirone is unlike the benzodiazepines in that it neither stimulates nor inhibits 3H-benzodiazepine binding, does not affect the influence of GABA or halide anion on 3H-benzodiazepine binding, and does not interfere with GABA binding or uptake. Buspirone lacks anticonvulsant activity, interacts minimally with CNS depressants, and does not cause muscle relaxation. Its tranquilizing activity is characterized by the ability to (1) tame aggressive rhesus monkeys, (2) block conditioned avoidance responding in the rat, (3) inhibit shock-induced fighting in the mouse, and (4) attenuate shock-induced suppression of drinking in the rat. In vitro binding experiments indicate that buspirone lacks significant activity at several binding sites. It appears to interact only with the dopaminergic system and possesses properties that are similar to both dopamine agonists and dopamine antagonists.

Aggression↗

The regional distribution of d-amphetamine and local glucose utilization in rat brain during continuous amphetamine administration.

The distribution of radioactivity following administration of either [3H]d-ampetamine or [3H]2-deoxy-d-glucose was examined by scintillation counting of 22 microdissected brain regions from rats pretreated with either acute or continuous amphetamine, or continuously administered labeled d-amphetamine. Animals continuously administered drug were sacrificed in behaviorally distinct stages of the continuous amphetamine syndrome, a potential animal model of amphetamine psychosis. Both isotopes were heterogeneously distributed within brain, and their distributions were differentially affected by acute or continuous amphetamine regimens. While the distribution of either isotope in naive rats was characterized by greatest concentrations of counts in rostral rather than caudal regions, and grey-matter rather than white-matter structures, continuous amphetamine administration resulted in progressively increased retention of amphetamine by mesolimbic but not nigrostriatal brain regions; this was accompanied by locally enhanced levels of glucose utilization. This effect was predominantly localized in the nucleus accumbens, which exhibited the greatest retention of amphetamine and greatest relative increase in glucose utilization of any region studied during that stage of the continuous amphetamine syndrome thought to best model amphetamine psychosis. Alterations in amphetamine distribution and local levels of neural activity may reflect a change in the principal locus of control of amphetamine effects within brain as animals progress through the stages of the continuous amphetamine syndrome.

Amphetamine↗

The regional distribution of amphetamine in rat brain is altered by dosage and by prior exposure to the drug.

Rats were sacrificed 30 min after an i.p. injection of tritium-labeled d-amphetamine and the regional distribution of radioactivity was determined in 22 discreet brain regions. Amphetamine accumulation was greatest in rostral brain areas such as cortex ad forebrain and least in brainstem and white matter. Sensory regions (occipital cortex and thalamus) retained more label than did nonsensory regions (entorhinal cortex and hypothalamus). The regional distribution of d-amphetamine in drug naive animals was altered by variations in carrier dosage with heightened drug accumulation in occipital cortex and thalamus at a 1.5 mg/kg carrier dose and enhanced accumulation in the hippocampus and amygdala with a 5.0 mg/kg carrier dose. Increased amphetamine retention by dopamine-rich regions, such as the caudate, was observed in rats to which 28 daily injections of the drug had been administered previously. Thus, the regional distribution of d-amphetamine in rat brain is altered by variations in carrier dosage and previous drug experience.

Animals↗

Long-term changes in dopaminergic innervation of caudate nucleus after continuous amphetamine administration.

Silicone pellets containing d-amphetamine base were implanted subcutaneously in rats. These pellets release amphetamine continuously for at least 10 days. Several days after implantation, swollen dopamine axons concomitant with large decreases in tyrosine hydroxylase activity were observed in the caudate nucleus. Decreased tyrosine hydroxylase activity was still present 110 days after pellet removal in the caudate but not in several other brain regions, nor in the caudate of rats injected with an equivalent amount of amphetamine in daily injections. This implies that continuous amphetamine administration has a selective neurotoxic effect on dopamine terminals in the caudate.

Animals↗

Stages of constant amphetamine intoxication: delayed appearance of abnormal social behaviors in rat colonies.

Rats in colonies were observed for 7 days after half of them were implanted with slow-release silicone pellets containing d-amphetamine base. The drug-implanted animals were initially hyperactive and exploratory, but this gradually evolved over the next 24 h into motor stereotypies of an increasingly more circumscribed nature. On the 4th day after amphetamine implantation they transiently withdrew to the burrows area; thereafter they were characterized by heightened startle responses and increased social behaviors such as fighting and fleeing. During the last phase some of the drug-implanted animals tended to focus their fighting behaviors on one other drug-implanted animal. This late phase of constant amphetamine intoxication in rats has a number of similarities to amphetamine psychosis in humans, and can serve as a useful animal model for the study of its biochemical correlates.

Animals↗

A slow-release silicone pellet for chronic amphetamine administration.

A slow release amphetamine pellet consisting of a silicone capsule containing d-amphetamine base in polyethylene glycol is described. When implanted s.c. in rats this pellet produces brain levels initially comparable to an i.p. dose of 2 mg/kg of d-amphetamine sulfate; these levels gradually fall but appreciable amphetamine remains present in the brain for over 10 days. Rats implanted with these pellets exhibit sustained motor stereotypies and constant hyperactivity in stabilimeters for 2-3 days. Four days after implantation activity declines to near control levels even though amphetamine is still present in the brain. During this later stage rats show exaggerated startle responses and resist handling. This pellet is a unique tool for the study of the behavioral and physiological effects of prolonged amphetamine intoxication.

Amphetamine↗

Opposed effects of locus coeruleus and substantia nigra lesions on social behavior in rat colonies.

Rats were observed in enriched colony environments following radio-frequency lesions of the locus coeruleus (LC), zona compacta of substantia nigra (SN, or control operations. LC-lesioned animals were initially inactive, stayed in the burrows, and fell when climbing ropes and ramps. SN-lesioned rats were opposite to LC animals in many ways. They were hyperactive, had minimal motor disturbances, and were hyperaggressive. SN animals self-isolated and were not social-groomers, whereas LC rats socially-groomed and mounted other animals more than controls. These results provide evidence that the dopaminergic nigrostriatal pathway and the noradrenergic fibers innervating the cerebral cortex and limbic forebrain exert opposed effects upon behavior.

Aggression↗