Carbamazepine normalizes the altered behavioral and neurochemical response to stress in benzodiazepine-withdrawn rats

Rats chronically treated with diazepam (2 mg/kg per day, i.p.) for 21 days were tested 96 h after the last injection in both the forced swim test (inescapable stress) and in an active avoidance test (escapable stress). The influence of carbamazepine (7.5 mg/kg, i.p.) administered 25 min prior to each behavioral task was investigated. Withdrawn animals showed a reduced time spent in immobility in the forced swim test and an enhanced latency to escape in the active avoidance test. Both behavioral effects were normalized by a single carbamazepine administration. An additional experiment was performed to investigate the effect of a forced swim experience on cortical chloride uptake following GABA (γ-aminobutyric acid) stimulation 96 h after diazepam withdrawal, and the influence of a single administration of carbamazepine on these effects. An increased chloride uptake was observed in vehicle-treated rats but not in diazepam-withdrawn animals following the swimming experience. Carbamazepine pretreatment enhanced chloride uptake after diazepam withdrawal but did not modify chloride flux in stressed or unstressed vehicle-treated rats. These results support the hypothesis that diazepam withdrawal affects the ability to develop adaptive responses to stress and that carbamazepine can normalize such an alteration.     

Correlation of neurochemical and behavioral effects of triethyl lead chloride in rats

Adult male Fischer-344 rats were dosed sc with 1 or 2.5 mg/kg of triethyl lead chloride (TEL) for 5 consecutive days. One week after the last dose, TEL-exposed rats had decreased Met-enkephalin in the hypothalamus, septum, and frontal cortex, while substance P was decreased in the hippocampus and frontal cortex. Dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) in the caudate nucleus were not altered by TEL nor were serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the caudate nucleus, hypothalamus, hippocampus, or frontal cortex. In a second experiment, rats were dosed with 1.75 mg/kg sc for 5 days. Subsequent assay of brain tissue indicated that TEL decreased met-enkephalin levels in the septum of rats one and seven days after cessation of dosing; effects on substance P were not observed. TEL-induced decreases in Met-enkephalin in the septum were temporally associated with increased hot plate latencies. One day after cessation of dosing with TEL, concentration of 5-HIAA in the caudate nucleus, hippocampus, frontal cortex, and brain stem, and 5-HT in the hippocampus and brain stem were increased. Biogenic amine concentrations were not affected in any other region or at any other time postdosing. A third experiment indicated that TEL-induced analgesia could be attenuated by 10 mg/kg chlordiazepoxide or 10 mg/kg of naloxone. The present results suggest that TEL-induced analgesia may be due to alterations in emotionality or reactivity to noxious stimuli, which may be associated with the alteration in delta opiate mechanism in the limbic system, such as the change of septal enkephalin neuronal activities.     

The relationship between the locomotor response to a novel environment and behavioral disinhibition in rats

Behavioral disinhibition, a component of impulsivity, has been associated with cocaine abuse and dependence. To examine the relationship between behavioral disinhibition and vulnerability to cocaine use disorders, we employed the high responder (HR)/low responder (LR) rodent model, in which rats that exhibit high levels of activity in response to a novel environment are more sensitive to the effects of psychostimulants. In Experiment 1, performance under a differential reinforcement of low-rate (DRL) schedule was used as a measure of behavioral disinhibition in HR and LR rats. The HR rats displayed more behavioral disinhibition relative to LR rats on the DRL 20- and 35-s schedules. In Experiment 2, rats were divided into groups with high disinhibition (HD) and low disinhibition (LD) based on DRL 20-s performance, then challenged with cocaine. Rats characterized as HD and LD had similar DRL 20-s performance to rats characterized as HR and LR (Experiment 1), respectively, but did not differ in their response to cocaine. The results of this study suggest that the HR phenotype may also be characterized by greater behavioral disinhibition, and that the DRL task is a suitable animal model to investigate the role of behavioral disinhibition in vulnerability to the behavioral effects of cocaine.     

Feeding conditions differentially affect the neurochemical and behavioral effects of dopaminergic drugs in male rats

The high co-morbidity of eating disorders and substance abuse suggests that nutritional status can impact vulnerability to drug abuse. These studies used rats to examine the effects of food restriction on dopamine clearance in striatum and on the behavioral effects of amphetamine (locomotion, conditioned place preference), the dopamine receptor agonist quinpirole (yawning), and the dopamine receptor antagonist raclopride (catalepsy). Amphetamine increased locomotion and produced conditioned place preference. Food restriction reduced dopamine clearance, which was restored by repeated treatment with amphetamine or by free feeding. Food restriction also decreased sensitivity to quinpirole-induced yawning and raclopride-induced catalepsy; normal sensitivity to both drugs was restored by free feeding. The same amphetamine treatment that normalized dopamine clearance, failed to restore normal sensitivity to quinpirole or raclopride, suggesting that in food-restricted rats the activity of dopamine transporters and dopamine receptors is differentially affected by pathways that are stimulated by amphetamine. These studies show that modest changes in nutritional status markedly alter dopamine neurotransmission and the behavioral effects of direct-acting dopamine receptor drugs (agonist and antagonist). These results underscore the potential importance of nutritional status (e.g., glucose and insulin) in modulating dopamine neurotransmission and in so doing they begin to establish a neurochemical link between the high co-morbidity of eating disorders and drug abuse.     

Tolerance to the behavioral and neurochemical effects of haloperidol and morphine in rats chronically treated with morphine or haloperidol

Summary The acute administration of morphine sulfate (79 moles/kg) or haloperidol (6.65 moles/kg) produced catalepsy and concomitant increase in striatal dopamine turnover in rats. The animals made dependent on morphine by 52 morphine injections (maintenance dose of 1056 moles/kg/day, given in four daily doses) and then tested during 3 days of withdrawal from morphine, showed tolerance to the cataleptic and the neurochemical effects of morphine as well as those of haloperidol. That tolerance was not seen after 14 days of withdrawal from morphine. The animals chronically treated with haloperidol for 12 days (maintenance dose of 53.2 moles/kg/day, given in two daily doses) and then tested 72 h after last haloperidol injection, did not show tolerance to the cataleptic or the neurochemical effect of haloperidol or morphine. These results suggest that dopaminergic systems underlying motor coordination and regulation of the neurotransmitter synthesis are among those susceptible to narcotic action and to the process of tolerance development during aarcotic dependence.     

Reactivity to amphetamine in perinatally undernourished rats: behavioral and neurochemical correlates

Adult rats deprived at perinatal age and then rehabilitated on balanced chow were treated with a multiple amphetamine (AMPH) schedule (2 mg/kg/48 hr) and submitted, on days of injections, to an open-field test. Throughout 11 sessions, deprived rats showed a progressive increase of locomotor activity as compared with controls. Stereotyped activity evaluated during the AMPH treatment did not differ between control and deprived animals. No differences were detected in basal values of the dopaminergic function measured in naive control and deprived animals. By the end of the multiple AMPH treatment, a reduction of striatal DA and DOPAC levels together with a lower apparent DA turnover rate was detected in deprived animals. Besides, DA receptor binding was significantly increased in striatum from deprived rats as compared with controls. These results demonstrate that a repeated AMPH treatment, that was unable to alter the normal behavior of control rats, produced in early undernourished animals a progressive sensitization to AMPH effects, in addition to significant changes in the striatal dopaminergic function.     

Gender impacts behavioral and neurochemical adaptations in ethanol-dependent rats

Previous investigations have found gender differences in the effects of chronic ethanol exposure on ethanol withdrawal behaviors as well as GABA(A) receptor gene expression. The present investigation extended these studies with additional behavioral and neurochemical measures of ethanol dependence and withdrawal. No significant gender differences in the elevated plus-maze assessment of ethanol withdrawal anxiety behaviors were found. However, the neuroactive steroid, 3alpha,5alpha-THP, increased exploratory behavior in ethanol withdrawn female, but not male, rats. GABA(A) receptor binding assays showed potent competition of [35S]TBPS binding by 3alpha,5alpha-THP. Control females displayed a decreased affinity for 3alpha,5alpha-THP compared to control males, as evidenced by a nearly 30% increase in the IC50 value. There was no significant effect of ethanol withdrawal on 3alpha,5alpha-THP modulation of [35S]TBPS binding. However, gender differences were observed in the effects of chronic ethanol exposure on GABA(A) receptor subunit peptide levels in the hypothalamus. Female rats had a significant increase in peptide levels for the alpha2 and alpha3 but not alpha4 subunit, whereas male rats displayed a significant increase in alpha4 and alpha3 but not alpha2 subunits compared to pair-fed control levels. Chronic ethanol-induced alterations in gene expression in the hypothalamus did not coincide with previous findings in the cerebral cortex. In particular, male rats showed an increase in alpha1 subunit peptide levels in the hypothalamus, whereas significant decreases in this subunit have been observed in the cerebral cortex. Both female and male rats showed significant increases in the alpha3 subunit in the hypothalamus but not the cerebral cortex. Taken together, these studies provide additional support for gender-selective effects of chronic ethanol-elicited adaptations at the molecular level.     

Neurochemical, pharmacokinetic, and behavioral effects of the novel selective serotonin reuptake inhibitor BMS-505130

BMS-505130 is a potent and selective serotonin transport inhibitor; K(i) for binding to the serotonin transporter = 0.18 nM (K(i) values for binding to the norepinephrine and dopamine transporters = 4.6 and 2.1 microM, respectively). In platelet serotonin uptake studies BMS-505130 (5 mg/kg, p.o.) produced a robust inhibition of serotonin uptake. In microdialysis studies oral dosing with BMS-505130 produced a dose-dependent increase in cortical serotonin levels that reached a maximal effect of 200% above baseline at a dose of 1 mg/kg, p.o.; the peak serotonin response was transient in nature. Following oral administration, peak plasma concentrations of BMS-505130 reached Tmax at 1.6 +/- 0.7 h and then declined to concentrations <10% of Cmax within the following 6 h; plasma half-life following i.v. dosing was 0.46 +/- 0.02 h. Parallel microdialysis and pharmacokinetic studies revealed that changes in serotonin levels in the cortex mirrored changes in the brain concentration of BMS-505130. In a behavioral assay known to be sensitive to selective serotonin reuptake inhibitors (SSRIs), mouse tail suspension, BMS-505130 produced a robust response after either oral or intraperitoneal dosing. BMS-505130 exhibits a pharmacological, neurochemical and behavioral profile consistent with a potent SSRI. Moreover, BMS-505130's short half-life may be advantageous for the treatment of premature ejaculation where an acute effect to delay ejaculation followed by a relatively rapid fall in SSRI plasma concentrations might be desirable.     

Prolonged exposure of rats to intravenous methamphetamine: behavioral and neurochemical characterization

The translational value of preclinical models of methamphetamine abuse depends in large part on the degree to which the drug regimens used in animals produce methamphetamine exposure patterns similar to those experienced by human methamphetamine abusers. To approximate one common form of methamphetamine abuse, we studied the effects of a schedule of intravenous methamphetamine administration in rats which included 2 weeks of progressively more frequent drug injections (0.125 mg/kg/injection) followed by 40 maintenance days during which animals received 40 daily injections (at 15-min intervals), with the dose gradually increasing (0.125–0.25 mg/kg per injection) every 5–10 days. This treatment produced an emerging behavioral profile characterized by gradually more continuous periods of activation consisting of progressively more intense, focused stereotypy interrupted by episodic bursts of locomotion. We also assessed markers of dopamine neurotransmission (dopamine transporter, vesicular monoamine transporter, and dopamine D1 and D2 receptors) at 15 min and (including dopamine levels) at 6 and 30 days following cessation of methamphetamine treatment. All dopamine components measured in caudate–putamen were significantly reduced at 15 min and 6 days after the final methamphetamine injection. Dopamine D1 and D2 receptors fully recovered after 30 days of drug abstinence, whereas dopamine and the dopamine transporter exhibited significant but incomplete recovery by this time point. In contrast, only the vesicular monoamine transporter exhibited no evidence of recovery over the 30-day withdrawal period. These data are discussed in terms of damage to dopamine terminals and compensatory adjustments in mechanisms maintaining functional dopaminergic transmission.     

Prenatal cocaine exposure alters behavioral and neurochemical sensitization to amphetamine in adult rats

This study examined the neurochemical correlates of amphetamine (AMPH)-induced behavioral effects in prenatally saline (PSAL)-exposed or cocaine (PCOC)-exposed male rats. Pregnant Long-Evans rats received saline or saline containing cocaine hydrochloride (20 mg/kg s.c., b.i.d.) from gestational days 15-21. Animals were left with their biological mothers. Adult offspring were exposed to daily saline or AMPH (0.5, 1.5, or 5 mg/kg, i.p.) injections for 7 days. Behaviors were recorded in an open field during the first hour post-injection. PCOC rats did not exhibit behavioral anomalies during habituation to injection-stress or placement in the open field. PCOC rats displayed significant alterations in stereotyped responses to acute or intermittent exposure to various doses of AMPH. Within 48 h of the final testing day, striatal tissue was obtained from these animals and electrically-evoked [3H]acetylcholine (ACh) release was measured from striatal slices. Superfusion of tissue slices with various concentrations of AMPH (1-1000 nM) produced dose-dependent inhibition of ACh release in both PSAL and PCOC rats repeatedly injected with saline as adults. However, AMPH-induced inhibition of ACh release was decreased in PCOC rats repeatedly injected with AMPH as adults. At 5 mg/kg AMPH, PCOC rats exhibited increased mortality compared to PSAL rats. These data suggest that PCOC exposure produces long-lasting alterations in nigrostriatal transmission and behaviors mediated by this system.     

Comparative analysis of the behavioral, neurochemical and autonomotropic effects of mebikar and diazepam

It has been shown that the tranquilizers, diazepam (a 1,4-benzodiazepine derivative) and mebicar (a derivative of bicyclic bisureas) produce one-line inhibition of the production of the conditioned reflex of active avoidance in rats and of their "open-field" motor activity. Both the drugs change the balance of neuroactive amino acids in the animals' brain. However they produce different changes: diazepam increases the content of asparaginic and glutamic acids, while mebicar raises that of gamma-butyric acid. No interrelationship was found between psychotropic and vegetotropic effects of the tranquilizers.     

Differential neurochemical and behavioral adaptation to cocaine after response contingent and noncontingent exposure in the rat

Rationale In naive rats, passive administration of drugs of abuse preferentially increases extracellular dopamine (DA) in the nucleus accumbens (NAc) shell as compared to the core. Repeated exposure to the same drugs results in behavioral and biochemical sensitization characterized by stereotyped activity and reduction of the shell/core DA response ratio. Objectives The aim of this work is to study the neurochemical and behavioral effects of response-contingent vs response-noncontingent drug administration in rats, who were bilaterally implanted with chronic intracerebral guide cannulae and trained to self-administer cocaine by nose poking in daily 1-h sessions for 3 weeks (5 days/week). Nose poking in the active hole by master rats resulted in intravenous injection of cocaine (0.25 mg/kg) in master rats and in rats yoked to them. Dialysate DA was monitored before, during, and for 30 min after cocaine availability on alternate days by inserting the probe into the NAc shell and core. Stereotyped and non-stereotyped behavior was recorded during the sessions. Results In master rats, dialysate DA increased preferentially in the NAc shell during cocaine self-administration throughout the 3 weeks of cocaine exposure. In yoked rats, DA increased preferentially in the shell but to a lesser extent than in master rats. With continued exposure to cocaine, the shell/core ratio of DA changes decreased progressively and, on the third week, was reversed so that DA increased more in the core than in the shell. Yoked rats showed a progressive and faster increase in stereotyped behaviors than master rats. Conclusions Response-noncontingent cocaine administration is particularly prone, compared to response-contingent administration, to induce behavioral and biochemical sensitization.     

Simultaneous analyses of the neurochemical and behavioral effects of the norepinephrine reuptake inhibitor reboxetine in a rat model of antidepressant action

Abstract Rationale. The forced swimming test (FST) is a rodent behavioral assay widely used to predict clinical efficacy of putative antidepressants. Few studies have examined the effects of the FST on neurotransmitter levels and how antidepressant drug treatment may alter neurotransmitter levels and behavior simultaneously during the performance of a stressful task. Objectives. The present study examined the role of norepinephrine in mediating active behaviors in the FST after treatment with reboxetine, a selective norepinephrine reuptake inhibitor. Methods. High-pressure liquid chromatography was used to analyze microdialysis samples collected from awake, freely moving rats before, during and after exposure to the FST. Reboxetine (10 mg/kg) was given three times over a 24-h period prior to the test swim. Behavioral responses, including immobility, swimming and climbing, were counted during the 5-min test on day 1 and day 2. Results. The first exposure to swim stress elicited a 65% increase in extracellular norepinephrine (NE). A second exposure on day 2 elicited a 52% increase of NE and a behavioral profile characterized by increased immobility and a reduction of active behaviors. A subchronic course (three injections over 24 h) of treatment with reboxetine between the two swim exposures resulted in antidepressant-like activity, i.e., decreased immobility and increased climbing behavior on day 2. A significantly greater increase in extracellular NE (112%) was observed in the group of animals that received reboxetine injections. Conclusions. Treatment with reboxetine in a schedule commonly used in the FST resulted in a potentiated noradrenergic response to the swim challenge concomitant with behavioral alterations consistent with antidepressant-like activity. Electronic Publication     

Correlation of behavioral and neurochemical effects of d- and l-amphetamines

In an attempt to correlate the behavioral and neurochemical effects of d- and l-amphetamines, the time courses of the effects of the two isomers (1 mg/kg; base, i.p.) were studied on spontaneous motor activity (SMA) and stereotyped behavior (ST) as well as on the concentrations of norepinephrine (NE), dopamine (DA), and serotonin (5-HT) in discrete brain areas, such as the caudate nucleus (CN), pons-medulla (PM), and diencephalonmidbrain (DM) in rats. In addition, the dose-response relationship for d-isomer (0.5–2 mg/kg, i.p.) and l-isomer (1–4 mg/kg, i.p.) was also studied on SMA and ST. SMA increased with the dose up to 1.5 mg/kg for d-isomer and up to 3 mg/kg for l-isomer and then decreased, whereas ST increased with the dose for both the isomers. At 1 mg/kg dose, SMA reached its peak during the fourth postdrug 20–minute period for both d- and l-isomers, whereas ST reached its peak during third to fifth 20-minute periods for d-isomer and during the third period for the l-isomer. The d-isomer significantly increased the DA levels in the CN and DM at 30 minutes postdrug, which reached their maximum at 60 minutes, whereas NE levels in the PM had no significant change at 30 minutes, but were significantly reduced in the DM at 30 minutes and in both PM and DM at 60 minutes postdrug; 5-HT levels in the PM and DM showed no significant change. Compared to d-amphetamine, the l-isomer at 30 and 60 minutes postdrug caused more or less similar changes in the NE levels in the DM and PM, whereas it produced less increase in the DA levels in the CN and DM and significant decrease in 5-HT levels in the DM and PM. It appears that the difference in the behavioral effects induced by the two isomers of amphetamine may be due to the difference in their effects on dopaminergic and serotonergic systems.     

Persisting behavioral and neurochemical deficits in rats following lesions of the basal forebrain

The effects of excitotoxic lesions of the nucleus basalis magnocellularis on cortical cholinergic activity and passive avoidance performance were examined in rats at 6, 14, 84 and 180 days after lesioning. Lesioned rats showed significant impairment of passive avoidance retention at every time point tested, with no evidence of behavioral recovery compared to unoperated and sham-lesioned (i.e., vehicle-injected) control rats. Cortical choline acetyltransferase (CAT) activity was reduced relative to controls at all time points examined, with the greatest reduction (i.e., 28%) occurring at approximately 14 days after lesioning. The levels of CAT activity at 180 postlesioning remained reduced compared to control animal levels, but less so than at 14 days after lesioning, indicating partial recovery. No changes in cholinergic muscarinic binding were observed at any time following lesioning. The results indicate that the behavioral and neurochemical effects of NbM lesions persist for at least 6 months following lesioning, but that partial, gradual recovery of cholinergic activity occurs.     

A comparison of the neurochemical and behavioral effects of clenbuterol and desipramine

Because both long-term adrenoceptor agonist administration and antidepressant treatment in animals down-regulate CNS beta-adrenoceptors and attenuate brain adenylate cyclase activity, beta-adrenoceptor agonists may also possess antidepressant properties. We compared the effects of the centrally acting beta-adrenoceptor agonist clenbuterol (5, 10 and 35 mg/kg per day), and the combination of propranolol (5 mg/kg per day) and clenbuterol (10 mg/kg per day), with desipramine (15 mg/kg per day) on forced swim test performance and on cortical beta-adrenoceptors in rats following 7 days of drug administration. Desipramine (15 mg/kg per day), and clenbuterol (10 and 35 mg/kg per day, but not 5 mg/kg per day) both significantly reduced immobility in the forced swim test. Frontal cortex beta-adrenoceptors were significantly down-regulated after desipramine and all 3 doses of clenbuterol. The co-administration of propranolol (5 mg/kg per day) blocked both the reduction in immobility and down-regulation of cortical beta-receptors induced by clenbuterol (10 mg/kg per day). Propranolol (5 mg/kg per day) alone up-regulated frontal cortex beta-adrenoceptors, but had no significant effect on swimming performance. These data suggest that the physiological consequences of beta-adrenoceptor down-regulation are important in the mechanism of action of antidepressants. The results also suggest that clenbuterol may be useful in the treatment of depression.     

The effects of FK506, a specific calcineurin inhibitor, on methamphetamine-induced behavioral change and its sensitization in rats

RATIONALE: FK506 inhibits calcineurin activity, resulting in the inhibition of calcium-dependent intracellular processes. Recent studies have suggested that intracellular calcium is likely to be involved in methamphetamine (MAP)-induced locomotor activity and stereotyped behavior, and in the development of sensitization to MAP. OBJECTIVES: We investigated the effects of FK506 on MAP-induced behavioral changes and the development of sensitization in rats. METHODS: In experiment 1, animals were administered IP 2 mg/kg FK506 or vehicle followed 10 min later by MAP (1, 2, 4 and 8 mg/kg, IP). Another set of animals were administered FK506 (0.1, 2, 5 and 10 mg/kg) followed by 2 mg/kg MAP. Locomotor activity and stereotyped behavior were assessed. In experiment 2, animals received repeated IP injections of 2 mg/kg MAP pretreated with 2 mg/kg FK506 or vehicle for 5 consecutive days. One week later, rats were challenged with 1 mg/kg MAP. RESULTS: Pretreatment with 2 mg/kg FK506 caused a rightward shift of the inverted U-shaped response curve of the locomotor activity induced by 1-8 mg/kg MAP. The same pretreatment significantly attenuated augmentation of the MAP-induced stereotyped behavior. FK506 at doses of 0.1-10 mg/kg dose-dependently inhibited the behavioral response induced by 2 mg/kg MAP. Coadministration of 2 mg/kg FK506 with 2 mg/kg MAP for 5 consecutive days resulted in significant suppression of the behavioral response to challenge with 1 mg/kg MAP. CONCLUSIONS: These results suggest that calcineurin plays an important role in MAP-induced behavioral changes and sensitization, especially the latter.     

Behavioural and neurochemical effects of medetomidine, a novel veterinary sedative

The effects of the novel veterinary sedative, medetomidine, were studied in rats. In addition to a dose-dependent sedation, which at high doses (greater than 100 micrograms/kg) included loss of the righting reflex and hypothermia, there was a concurrent decrease in the turnover rate of biogenic amines in the brain. Noradrenaline turnover was dose dependently decreased as judged by (i) the decrease in the brain concentration of its metabolite, MHPG-SO4, (ii) a decrease in the ability of alpha-methyl-p-tyrosine methyl ester to deplete brain noradrenaline stores and (iii) a dose-dependent decrease in the level of unconjugated MHPG in the CSF of freely moving rats. Brain dopamine turnover was also inhibited at higher doses as judged by the alpha-methyl-p-tyrosine method and by a decrease in the concentration of HVA in the rat brain 4 h after medetomidine. Serotonin turnover as estimated by the ratio of biogenic amine to its metabolite was also significantly depressed. These changes in brain biogenic amine turnover were inhibited by prior or simultaneous administration of alpha 2-adrenoceptor antagonists, either yohimbine or the more specific, novel alpha 2-antagonist, atipamezole.     

Tolerance to the behavioral effects of scopolamine in rats

Summary Two behavioural indices for psychotomimetic activity have been used to elucidate the probable role of methoxy group configuration in the mescaline molecule. The first method using a shuttle box CAR has been reported previously in this series. The second is based on the Sidman Avoidance schedule and utilizes the Bovet-Gatti profiles. Our results indicate that only two analogues of mescaline are active-the 2,3,4,5 and 2,3,4,5,6 compounds. This indicates that the 3,4,5 configuration is necessary and that adding extra methoxy groups increases activity. The great activity of the penta methoxy compound may be due to the fact that this compound substituted in the 2 and 6 positions cannot be metabolized by mescaline oxidase. The significance of these results is discussed.