5-Hydroxytryptamine involvement in the locomotor activity suppressant effects of amphetamine in the mouse

Cell-Type Specific Deletion of CB2 Cannabinoid Receptors in Dopamine Neurons Induced Hyperactivity Phenotype: Possible Relevance to Attention-Deficit Hyperactivity Disorder

DAT-Cnr2 mice are conditional knockout (cKO) animals that do not express cannabinoid CB2 receptors (CB2R), in midbrain dopamine neurons. The hyperactivity phenotype of DAT-Cnr2 cKO mice were paradoxically reduced by low dose of amphetamine. Here, we report on the locomotor activity analysis in male and female adolescent (PND 30 ± 2) mice in basal conditions and in response to different doses of amphetamine, using the Open Field (OF), Elevated Plus-Maze (EPM) tests and the Novel Object Recognition (NOR) task as a putative model of attention deficit hyperactivity disorder (ADHD). Results showed that both male and female adolescent DAT-Cnr2 mice displayed significant increases in distance traveled in the OF test compared with WT mice. However, 2 mg/kg dose of amphetamine reduced the distance traveled by the DAT-Cnr2 but was increased in the WT mice. In the EPM test of anxiety-like behavioral responses, DAT-Cnr2 spent more time in the open arms of the maze than the WT mice, suggesting a reduction in anxiety-like response. DAT-Cnr2 mice showed significant increase in the number of unprotected head dips in the maze test and in the cliff avoidance reaction (CAR) test demonstrating impulsivity and risky behavior. DAT-Cnr2 mice also exhibited deficient response in the delay decision making (DDM), with impulsive choice. Both DAT-Cnr2 and WT were able to recognize the new object in the NOR task, but the exploration by the DAT-Cnr2 was less than that of the WT mice. Following the administration of 2 mg/kg of amphetamine, the similarities and differential performances of the DAT-Cnr2 and WT mice in the EPM test and NOR task was probably due to increase in attention. Microglia activation detected by Cd11b immunolabelling was enhanced in the hippocampus in DAT-Cnr2 cKO than in WT mice, implicating neuro-immune modulatory effects of CB2R. The results demonstrates that DAT-Cnr2 cKO mice with cell-type specific deletion of CB2R in midbrain dopaminergic neurons may represent a possible model for studying the neurobiological basis of ADHD.

A methamphetamine vaccine attenuates methamphetamine-induced disruptions in thermoregulation and activity in rats

BACKGROUND

There are no approved pharmacotherapies for d-methamphetamine (METH) addiction and existing therapies have limited efficacy. Advances in using immunotherapeutic approaches for cocaine and nicotine addiction have stimulated interest in creating a similar approach for METH addiction. This study investigated whether active vaccination against METH could potentially attenuate responses to METH in vivo.

METHODS

Male Sprague Dawley rats (n = 32) received a four-boost series with one of three candidate anti-METH vaccines (MH2[R], MH6, and MH7) or a control keyhole limpet hemocyanin conjugate vaccine. Effects of METH on rectal temperature and wheel activity at 27°C ambient temperature were determined. The most efficacious vaccine, MH6, was then contrasted with keyhole limpet hemocyanin conjugate vaccine in a subsequent experiment (n = 16), wherein radiotelemetry determined home cage locomotor activity and body temperature at 23°C ambient temperature.

RESULTS

The MH6 vaccine produced high antibody titers with nanomolar affinity for METH and sequestered METH in the periphery of rats. In experiment 1, the thermoregulatory and psychomotor responses produced by METH at 27°C were blocked in the MH6 group. In experiment 2, METH-induced decreases in body temperature and locomotor activity at 23°C were also attenuated in the MH6 group. A pharmacokinetic study in experiment 2 showed that MH6-vaccinated rats had higher METH serum concentrations, yet lower brain METH concentrations, than control rats, and METH concentrations correlated with individual antibody titer.

CONCLUSIONS

These data demonstrate that active immunopharmacotherapy provides functional protection against physiological and behavioral disruptions induced by METH.

Changes in ambient temperature differentially alter the thermoregulatory, cardiac and locomotor stimulant effects of 4-methylmethcathinone (mephedrone)

BACKGROUND

The substituted cathinone compound known as mephedrone (4-methylmethcathinone; 4-MMC) has become popular with recreational users of psychomotor-stimulant compounds. Only recently have the first preclinical studies provided information about this drug in the scientific literature; nevertheless, media reports have led to drug control actions in the UK and across several US states. Rodent studies indicate that 4-MMC exhibits neuropharmacological similarity to 3,4-methylenedioxymethamphetamine (MDMA) and prompt investigation of the thermoregulatory, cardiac and locomotor effects of 4-MMC. This study focuses on the role of ambient temperature, which has been shown to shift the effects of MDMA from hyperthermic to hypothermic.

METHODS

Male Sprague-Dawley rats were monitored after subcutaneous administration of 4-MMC (1.0-5.6 mg/kg) using an implantable radiotelemetry system under conditions of low (20 °C) and high (30 °C) ambient temperature.

RESULTS

A pharmacokinetic study found a T(max) of 0.25 h and a C(max) of 1206 ng/ml after 5.6 mg/kg 4-MMC. A dose-dependent reduction of body temperature was produced by 4-MMC at 20 °C but there was no temperature change at 30 °C. Increased locomotor activity was observed after 4-MMC administration under both ambient temperatures, however, significantly more activity was observed at 30 °C. Heart rate was slowed by 1.0 and 5.6 mg/kg 4-MMC at 20°C, and was slower in the 30 °C vs. 20 °C condition across all treatments.

CONCLUSION

These results show that the cathinone analog 4-MMC exhibits in vivo thermoregulatory properties that are distinct from those produced by MDMA.

Contrasting effects of d-methamphetamine, 3,4-methylenedioxymethamphetamine, 3,4-methylenedioxypyrovalerone, and 4-methylmethcathinone on wheel activity in rats

BACKGROUND

Reports from U.S., U.K. and European drug policy entities, and ongoing media accounts, show increasing recreational use of 4-methylmethcathinone (4-MMC, mephedrone) and 3,4-methylenedioxypyrovalerone (MDPV). Severe sympathomimetic symptoms, hallucinations, psychoses, and even deaths have been reported, yet little scientific information is available on the effects of these compounds in laboratory models. Available studies on the neurochemistry of these drugs show that 4-MMC and MDPV enhance DA neurotransmission, while 4-MMC additionally enhances 5-HT neurotransmission--a pattern much like that reported for methamphetamine versus 3,4-methylenedioxymethamphetamine (MDMA). As is the case for designer amphetamines, these neurochemical distinctions may predict differential potential for repetitive versus episodic abuse and distinct lasting toxicities.

METHODS

This study determined relative locomotor stimulant effects of 4-MMC (1-10 mg/kg, s.c.) and MDPV (0.5-5.6 mg/kg, s.c.), in comparison with d-methamphetamine (MA; 0.5-5.6 mg/kg, s.c.) and MDMA (1-7.5 mg/kg, s.c.) on a measure of locomotor activity--voluntary wheel running--in male Wistar rats (N=8).

RESULTS

Compared to counts of wheel rotations after saline, a biphasic change in the pattern of counts was observed after injections of MA and MDPV, with relatively higher counts following lower doses and lower counts following the highest dose. However, monophasic, dose-dependent reductions in counts were observed in response to injections of MDMA and 4-MMC.

CONCLUSION

Thus, voluntary wheel running yielded the same categorical distinctions for these drugs as did prior experiments testing the effects of these drugs on monoaminergic neurotransmission. These data indicate that MDPV produces prototypical locomotor stimulant effects whereas 4-MMC is more similar to the entactogen MDMA.

Influences of activity wheel access on the body temperature response to MDMA and methamphetamine

Recreational ingestion of the drug 3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") can result in pathologically elevated body temperature and even death in humans. Such incidents are relatively rare which makes it difficult to identify the relative contributions of specific environmental and situational factors. Although animal models have been used to explore several aspects of MDMA-induced hyperthermia and it is regularly hypothesized that prolonged physical activity (e.g., dancing) in the nightclub environment increases risk, this has never been tested directly. In this study the rectal temperature of male Wistar rats was monitored after challenge with doses of MDMA and methamphetamine (MA), another drug frequently ingested in the rave/nightclub environment, either with or without access to an activity wheel. Results showed that wheel activity did not modify the hyperthermia produced by 10.0mg/kg MDMA. However, individual correlations were observed in which wheel activity levels after a locomotor stimulant dose of MDMA were positively related to body temperature change and lethal outcome. A modest increase in the maximum body temperature observed after 5.6mg/kg MA was caused by wheel access but this was mostly attributable to a drop in temperature relative to vehicle treatment in the absence of wheel activity. These results suggest that nightclub dancing in the human Ecstasy consumer may not be a significant factor in medical emergencies.

Pharmacological models of ADHD

For more than 50 years, heavy metal exposure during pre- or post-natal ontogeny has been known to produce long-lived hyperactivity in rodents. Global brain injury produced by neonatal hypoxia also produced hyperactivity, as did (mainly) hippocampal injury produced by ontogenetic exposure to X-rays, and (mainly) cerebellar injury produced by the ontogenetic treatments with the antimitotic agent methylazoxymethanol or with polychlorinated biphenyls (PCBs). More recently, ontogenetic exposure to nicotine has been implicated in childhood hyperactivity. Because attention deficits most often accompany the hyperactivity, all of the above treatments have been used as models of attention deficit hyperactivity disorder (ADHD). However, the causation of childhood hyperactivity remains unknown. Neonatal 6-OHDA-induced dopaminergic denervation of rodent forebrain also produces hyperactivity - and this model, or variations of it, remain the most widely-used animal model of ADHD. In all models, amphetamine (AMPH) and methylphenidate (MPH), standard treatments of childhood ADHD, typically attenuate the hyperactivity and/or attention deficit. On the basis of genetic models and the noted animal models, monoaminergic phenotypes appear to most-closely attend the behavioral dysfunctions, notably dopaminergic, noradrenergic and serotoninergic systems in forebrain (basal ganglia, nucleus accumbens, prefrontal cortex). This paper describes the various pharmacological models of ADHD and attempts to ascribe a neuronal phenotype with specific brain regions that may be associated with ADHD.

Amphetamine-induced chorea in attention deficit-hyperactivity disorder

Attention deficit-hyperactivity disorder (ADHD) is treated frequently with stimulants in both children and adults. While tics are occasional complications of stimulant therapy, chorea is reported rarely. We describe an adult ADHD patient who developed chorea upon dose escalation of mixed amphetamine salts, which resolved on discontinuation of the drug.

Serotoninergics attenuate hyperlocomotor activity in rats. Potential new therapeutic strategy for hyperactivity

Hyperactivity is thought to be associated with an alteration of dopamine (DA) neurochemistry in brain. This conventional view became solidified on the basis of observed hyperactivity in DA-lesioned animals and effectiveness of the dopaminomimetics such amphetamine (AMP) in abating hyperactivity in humans and in animal models of hyperactivity. However, because AMP releases serotonin (5-HT) as well as DA, we investigated the potential role of 5-HT in an animal model of hyperactivity. We found that a greater intensity of hyperactivity was produced in rats when both DA and 5-HT neurons were damaged at appropriate times in ontogeny. Therefore, previously we proposed this as an animal model of attention deficit hyperactivity disorder (ADHD) - induced by destruction of dopaminergic neurons with 6-hydroxydopamine (6-OHDA) (neonatally) and serotoninergic neurons with 5,7-dihydroxytryptamine (5,7-DHT) (in adulthood). In this model effects similar to that of AMP (attenuation of hyperlocomotion) were produced by m-chlorophenylpiperazine (m-CPP) but not by 1-phenylbiguanide (1-PG), respective 5-HT2 and 5-HT3 agonists. The effect of m-CPP was shown to be replicated by desipramine, and was largely attenuated by the 5-HT2 antagonist mianserin. These findings implicate 5-HT neurochemistry as potentially important therapeutic targets for treating human hyperactivity and possibly childhood ADHD.

Effects of melatonin injection on running-wheel activity and body temperature differ by the time of day

Melatonin, which is released from the pineal gland, influences many physiological events concerned with circadian rhythm. Body temperature levels and rhythmicity are tightly coupled with locomotor activity. To understand the functions of melatonin, we determined the effects of melatonin injection on locomotor activity measured by running-wheel activity and body temperature in rats. The rats were kept under a 12-h light and 12-h dark lighting condition, with the light on at zeitgeber time 0 (ZT 0, correspond to 7:00 JST). Melatonin injection, between ZT 3 and ZT 5 (light period) and between ZT 15 and ZT 17 (dark period), attenuated the wheel-running activity in a dose-dependent manner (10 microg to 1 mg/100 g body weight [bw]). A significant attenuation of activity by melatonin was recognized when injected at ZT 8, ZT 14 and ZT 20. After the injection of melatonin, the animal's body temperature was elevated at ZT 2 and ZT 8 (during light), while it fell at ZT 14 and ZT 20 (during darkness). We propose a plausible explanation underlying the observed changes in body temperature during the light and dark periods accompanying the suppression of activity induced by melatonin.

Neurobehavioral and pregnancy effects of prenatal zidovudine exposure in Sprague-Dawley rats: preliminary findings

In 1994, the Public Health Service made prenatal zidovudine (ZDV, AZT) the standard of care to prevent mother-to-child transmission of HIV. The current study was undertaken to determine if prenatal exposure to ZDV has an impact on pregnancy outcomes, birth anomalies, or offspring behavior in an animal model using Sprague-Dawley (SD) rats. Thirty-one virgin female SD rats were mated and randomly assigned to receive either ZDV at 150 mg/kg/day or vehicle via gastric intubation for 22 days starting on gestation day (G) 1. On G 22, teratologic examination of 12 litters showed no gross structural malformations. There were no significant differences between the groups for maternal food and water consumption or maternal weight gain across pregnancy. However, ZDV treatment significantly reduced litter size and increased birth weights for both male and female pups. One developmental milestone, pinna detachment, occurred significantly earlier in the ZDV-exposed male pups compared to the vehicle-intubated male controls. On day 21-22 of life, pups in each litter were injected with one of four doses of amphetamine and were observed for behavioral activity in a photobeam-based activity monitor for 1 h. Overall amphetamine increased activity and decreased thigmotaxis or wall-hugging behavior. ZDV treatment increased the locomotor response to amphetamine in females only and dampened the action of amphetamine to decrease thigmotaxis in both genders. Further studies are warranted to determine the threshold dose at which these changes occur, the duration of the effects, as well as the neurochemical system(s) responsible for the altered amphetamine responses.

Preweaning cocaine administration alters the adult response to quipazine: comparison with fluoxetine

This study investigated whether exposure to cocaine during the preweaning period affects the behavioral response to administration of a challenge dose of quipazine, a relatively nonselective serotonin (5-HT) mixed agonist/antagonist, in adulthood. To determine whether selective inhibition of the 5-HT transporter during the preweaning period would produce a cocaine-like pattern of effects, another group of rats was given fluoxetine, a highly selective and potent inhibitor of the 5-HT transporter, and was tested along with the cocaine-treated rats. Male and female rats received 25 mg/kg cocaine HCl (82.5 mumol/kg), 25 mg/kg fluoxetine HCl (72.3 mumol/kg), or vehicle subcutaneous (s.c.) during postnatal days 11-20. Both treatments reduced weight gain during the injection period only. At 60 days of age, subjects were administered a single dose of quipazine (0, 0.4, or 1.0 mg/kg, s.c.) and placed in the Accuscan activity monitor for 1 h of behavioral recording. Overall, distance traveled, vertical activity, and time in the center of the chamber decreased during the initial time blocks of the session and vertical activity decreased with increasing doses of quipazine. Females in general showed greater overall activity levels than males as well as greater responsivity to quipazine. Preweaning cocaine exposure produced different effects in males and females. In males, cocaine enhanced the response to quipazine for vertical activity whereas it had no effect on quipazine-induced alterations on the other two behaviors. On the other hand, cocaine-treated females showed dampened dose-related quipazine responses across all behavioral measures. Fluoxetine administration produced a dampening of the quipazine effect for vertical activity and distance traveled in males and females. Therefore, these data indicate that cocaine administration during the preweaning period of development produced an increase in the effect of a serotonergic drug to alter vertical activity in males and a global dampening of the behavioral responses to that same drug in females. Preweaning fluoxetine treatment produced effects that resembled those produced by cocaine in females, a dampening of serotonergic responsivity, along with an overall decrease in locomotor activity. Because the majority of effects are seen during the initial portion of the behavioral session, a time of heightened activity in response to a novel environment, the data suggest that inhibition of the 5-HT transporter during the preweaning period alters serotonergic influences over novelty-induced activity but that brief periods of inhibition or other actions of cocaine, such as those at the catecholamine transporters, prevent this from happening, particularly in males.

Pathophysiology and management of the serotonin syndrome

OBJECTIVE

To review the symptoms, pathophysiology, and treatment of the serotonin syndrome (SS).

DATA SOURCES

A MEDLINE search (1957-1995) of the English-language literature pertaining to the SS was performed. Additional literature was obtained from reference lists of pertinent articles identified through the search.

STUDY SELECTION AND DATA EXTRACTION

All articles were considered for possible inclusion in the review. Pertinent information, as judged by the authors, was selected for discussion.

DATA SYNTHESIS

The SS, an occasionally fatal disorder, is characterized by symptoms such as mental status changes, seizures, myoclonus, and blood dyscrasias. Both the central and peripheral serotonergic systems and several serotonin receptor types are involved in the symptomatology of the SS. The pathogenesis of SS may be due to endogenous as well as iatrogenic deficits in peripheral serotonin metabolism, a stimulus for release of serotonin, and interactions with other neurotransmitter systems. Lorazepam, serotonin-blockers, and nitroglycerin have been used successfully to treat SS.

CONCLUSIONS

The SS is increasingly recognized and reported in the literature. Clinical and basic science research have increased our understanding of the pathophysiology, conditions, and agents that may predispose to the development of the syndrome. Newer treatment strategies are discussed.

Modification of acoustic startle reactivity by cocaine administration during the postnatal period: comparison with a specific serotonin reuptake inhibitor

This study investigated whether exposure to cocaine during postnatal period affects the acoustic startle response (ASR) following administration of the serotonin (5-HT) agonists, 8-OH-DPAT and mCPP, in adulthood. To test the hypothesis that alterations in reactivity may be due to cocaine's effects at the 5-HT carrier, another group of rats was given fluoxetine, a specific 5-HT uptake inhibitor, during the same postnatal period and tested along with the cocaine-treated rats. Male and female rats received 25 mg/kg/day cocaine HCl, fluoxetine HCl, or vehicle SC during postnatal days 11-20. At 75 days of age, subjects were ASR tested for 30 min on 2 consecutive days. On the first test day, there was a significant effect of treatment and gender with post hoc analysis indicating that, overall, the males were more reactive than the females and that the fluoxetine-treated males showed a pattern of reactivity resembling sensitization. On the second test day, subjects received a dose of the 5-HT1A agonist 8-OH-DPAT, the 5-HT1B/2C agonist, mCPP, or saline prior to being placed in the startle chamber. Cocaine-exposed males showed an enhanced response to 8-OH-DPAT and a reduction in the depression produced by mCPP administration compared to their response to saline. Fluoxetine exposed males showed a significant increase in startle response following saline administration compared to the rats receiving vehicle during the postnatal period and 8-OH-DPAT produced an insignificant enhancement of that startle response. mCPP reduced startle in fluoxetine-treated males as it did in the postnatal vehicle-treated controls. In females, the postnatal cocaine and fluoxetine treatments did not alter the response to 8-OH-DPAT or mCPP compared to females receiving vehicle during the postnatal period. Together these data indicate that, in males, whereas postnatal cocaine alters the development of the 5-HT system as evidenced by an altered startle response to 5-HT agonists, cocaine does not produce the same alteration as that produced by the administration of a specific 5-HT uptake inhibitor during the same period of development.

Long-continuous observation of the effects of methamphetamine on wheel-running and drinking in mice

1. Effects of methamphetamine (MAP) on wheel-running and drinking in mice, housed under 12-hr light-dark schedule (light period; 06:00-18:00), were investigated through long-continuous observation. 2. MAP (1, 2 and 4 mg/kg, s.c.) acutely increased the wheel-running and drinking for 2-4 hr in a dose-dependent manner after the administration at 11:00, midpoint of light period. 3. MAP administered at 11:00 sub-acutely suppressed the spontaneous increment during dark period (18:00-06:00) in both the behaviors. 4. Many factors, such as the time-of-day and interval of the administration as well as the dose administered, affected the behavioral suppression induced by MAP. 5. In addition to these findings, the wheel-running and drinking during the light period increased even on the days without MAP administration. 6. These results suggest that MAP have not only acute stimulant and sub-acute depressant effects, but also long-lasting effects.

Proposed animal model of attention deficit hyperactivity disorder

Dopamine (DA) neurons are implicated in the hyperlocomotion of neonatal 6-hydroxydopamine (6-OHDA)-lesioned rats, an animal model of attention deficit hyperactivity disorder (ADHD). Because serotonin (5-HT) neurons mediate some DA agonist effects, we investigated the possible role of 5-HT neurons on locomotor activity. Rats were treated at 3 days after birth with vehicle or 6-OHDA (134 micrograms ICV; desipramine pretreatment, 20 mg/kg IP, 1 h), and at 10 weeks with vehicle or 5,7-dihydroxytryptamine (5,7-DHT; 75 micrograms ICV; pretreatment with desipramine and pargyline, 75 mg/kg IP, 30 min), to destroy DA and/or 5-HT fibers. Intense spontaneous hyperlocomotor activity was produced in rats lesioned with both 6-OHDA and 5,7-DHT. Locomotor time in this group was 550 +/- 17 s in a 600 s session, vs. 127 +/- 13 s in the 6-OHDA group and < 75 s in 5,7-DHT and intact control groups (p < 0.001). Oral activity dose-effect curves established that 5,7-DHT attenuated DA D1 receptor supersensitivity and further sensitized 5-HT2c receptors. Acute treatment with dextroamphetamine (0.25 mg/kg SC) reduced locomotor time in 6-OHDA + 5,7-DHT-lesioned rats to 76 +/- 37 s (p < 0.001). Striatal DA was reduced by 99% and 5-HT was reduced by 30% (vs. 6-OHDA group). Because combined 6-OHDA (to neonates) and 5,7-DHT (to adults) lesions produce intense hyperlocomotion that is attenuated by amphetamine, we propose this as a new animal model of ADHD. The findings suggest that hyperactivity in ADHD may be due to injury or impairment of both DA and 5-HT neurons.

No triazolam-induced expression of Fos protein in raphe nuclei of the male Syrian hamster

While the visual projections to the suprachiasmatic nuclei (SCN) play a role in mediating the effects of light on circadian rhythms, the functional significance of the serotonergic projection from the raphe nuclei (RN) to the SCN is uncertain. Because previous results indicated that RN would appear to be a likely site for triazolam (Tz)-induced phase shifts, we used the expression of Fos-protein as a marker of Tz-induced neuronal activation. Immunocytochemistry was used to visualize the presence of Fos-like protein. Tz-induced Fos-labeled nuclei were found in superior colliculi, Edinger-Westphal nuclei (EW) and dorsal tegmental nuclei (DTg), but not in the RN. The SCN showed only occasionally labeled nuclei in all experimental groups, whereas there was no Tz-induced Fos-immunoreactivity in the intergeniculate leaflet (IGL). The present data not necessarily exclude the implication of the RN in the phase shifting effect of Tz. The phase shift could still be accomplished using a different set of immediate early genes (IEG), or without an IEG response. Alternatively, as will be discussed, other pathways could mediate the phase shifting effect of Tz.

Cross-familiarisation conditioned taste aversion procedure as a method to reveal stimulus resemblance between drugs: studies on the 5-HT1A agonist 8-OHDPAT

In the present study a cross-familiarisation conditioned taste aversion (CTA) paradigm was utilized to reveal stimulus resemblance between the selective 5-HT1A agonist 8-OHDPAT and a variety of serotonergic and non-serotonergic drugs. In male mice, a 0.22 mg/kg dose of 8-OHDPAT was used as the reference compound inducing CTA. Dose-dependent effects of pre-exposure to 24 different test drugs on the magnitude of the 8-OHDPAT-induced CTA were tested as a measure for stimulus similarity between these test drugs and 8-OH-DPAT (the reference compound). Pre-exposure to 8-OH-DPAT itself, ipsapirone, buspirone, RU 24969, sertraline, d-amphetamine, LSD, metergoline and idazoxan effectively prevented the development of CTA induced by 8-OHDPAT. Pre-exposure to apomorphine, diazepam, SCH 23390, LiCl, spiperone, DOI, spiroxatrine, umespirone, pindolol, mCPP, haloperidol, MK 212, clonidine, quipazine and also 5-MeODMT was not effective in completely abolishing the CTA produced by 8-OHDPAT. It is concluded from these results that the relatively simple and fast cross-familiarisation taste aversion method is a suitable paradigm to study similarities in stimulus properties of different drugs.

Behavioral concomitants of regional changes in the brain's biogenic amines after apomorphine and amphetamine

Behavioral and neurochemical changes were analyzed in rats after systemical injections of the dopamine receptor agonist apomorphine (0.5 mg/kg) or the indirect agonist amphetamine (1.0 mg/kg). As expected, amphetamine led to an increase in locomotion, whereas apomorphine resulted in decreases in locomotion, rearings, and grooming. The analysis of biogenic amines in tissue samples showed that amphetamine decreased 3,4-dihydroxy-phenylacetic acid (DOPAC) levels and DOPAC/dopamine ratios in the neostriatum, and resulted in a lower 5-hydroxyindole-3-acetic acid (5-HIAA)/5-hydroxytryptamine (5-HT) ratio in the ventral mesencephalon. Apomorphine decreased the dopamine metabolites [DOPAC, homovanillic acid (HVA), 3-methoxy-tyramine (3-MT)] and their respective metabolite/transmitter ratios and increased dopamine levels in the neostriatum. Similar decreases in dopamine metabolites or their ratios were found in the ventral mesencephalon, septum, and frontoparietal cortex but not the thalamus. In addition to its effects on dopamine, apomorphine decreased norepinephrine in the ventral neostriatum and 5-HT and 5-HIAA in the cortex. Correlations between behavioral activity and neurochemical metabolism (using the metabolite-transmitter ratios for the latter) revealed relationships between locomotion and serotonergic activity in the thalamus of animals treated with amphetamine. Evidence for a relationship between locomotion or rearings and dopaminergic activity was found in all six brain areas analyzed. Here, the pattern of correlation was dependent on the kind of treatment and the behavioral and neurochemical measures. These results support earlier findings on the neurochemical effects of apomorphine and amphetamine in the neostriatum and ventral mesencephalon, and add new evidence for an action on the septal area, thalamus, and frontoparietal cortex.

Cocaine treatment in neonatal rats affects the adult behavioral response to amphetamine

This study investigated whether exposure to cocaine during critical periods of brain development alters the motor stimulating effects of amphetamine given in adulthood. Female rats received 50 mg/kg/day cocaine HCl SC or vehicle during either postnatal days 1-10 or 11-20. At 60-65 days of age, activity counts were collected over a 15-min baseline period. Subjects then received one of 3 doses (0, 0.1, 0.25 mg/kg) of d-amphetamine sulfate SC followed by a 90-min period of activity monitoring. Adult activity in 1-10-day cocaine-treated rats was different from vehicle-treated rats in response to 0.1 mg/kg amphetamine only. Adult activity in 11-20-day cocaine-treated rats was different from vehicle-treated rats in response to 0.25 mg/kg only. The observed differences represented an increase and decrease in activity, respectively. These alterations in amphetamine response may be related to the observed alterations in D-1 receptor concentrations as well as the altered rates of brain glucose metabolism we have observed in adult rats neonatally exposed to cocaine.

Social isolation increases the stimulatory effect of ethanol on locomotor activity

The stimulatory effects of low alcohol doses are of great interest because of their role in human drinking and their possible relation to reinforcement from alcohol. The preferred animal model for studying them is the mouse. The effects of various doses of ethanol on locomotor activity were now studied in both group-housed mice and in mice socially isolated for 36-44 weeks. The housing situation was found to have a strong influence: a large stimulatory effect was observed in isolated mice but little effect was seen in group-housed animals. The results suggest that socially isolated mice are more sensitive to the stimulatory effect of ethanol on locomotor activity.

Reverse tolerance to amphetamine evokes reverse tolerance to 5-hydroxytryptophan

Repeated intermittent administration of amphetamine in mice caused reverse tolerance to 5-hydroxy-L-tryptophan (5-HTP)-induced head twitch, as well as to amphetamine-induced stereotypy. The repeated administration of 5-HTP alone also resulted in reverse tolerance in the head-twitch test. Daily pretreatment with haloperidol prior to amphetamine administration blocked the development of both reverse tolerance to amphetamine and to 5-HTP, whereas daily pretreatment with cyproheptadine prior to amphetamine blocked only the reverse tolerance to 5-HTP. On the other hand, 5-HTP-induced reverse tolerance was blocked by daily pretreatment with cyproheptadine, but not with haloperidol. There appears to be no difference in the persistence of the reverse tolerance to 5-HTP, whether induced by amphetamine or by 5-HTP; in both instances, the persistence does not correlate with the persistence of reverse tolerance to amphetamine. The data suggest that the reverse tolerance to amphetamine and the associated reverse tolerance to 5-HTP are independent events, both of which are mediated by dopaminergic mechanisms.

Prenatal amphetamine effects on behavior: possible mediation by brain monoamines

The present analysis indicates that the literature is currently too limited to draw anything but very tentative conclusions about whether amphetamine during pregnancy is detrimental to the offspring. However, exposure to very high doses of the drug appears to be teratogenic; and studies in which animals were exposed to lower doses of either amphetamine or methamphetamine throughout pregnancy indicate that this class of drugs can have long-term neurochemical and behavioral consequences for rodent offspring. The commonly reported behavioral effects include abnormal responding on aversively motivated tasks, and heightened motor activity which might be associated with slower habituation. Neurochemical studies have focused on various aspects of the monoamine neurotransmitter systems and suggest that prenatal amphetamine exposure can increase the synthesis and turnover of DA and NE and reduce the number of adrenergic receptors in adult offspring. In addition, concentrations of NE appear to be reduced at birth suggesting prenatal depletion and are sometimes found to be altered at later times. Although these studies are provocative, the absence of pair-fed controls and cross-fostering prevent ruling out the possible confounding effects of undernutrition and altered maternal care. In addition to the above limited empirical support, the effects of amphetamines on adult brain provide a logical rationale for anticipating that prenatal exposure to the drug could be detrimental. This rationale is essentially that amphetamine can have long-term effects of monoaminergic systems in the brains of adults, including neural degeneration; and, since the drug can cross the placenta, it should also have long-lasting consequences for the developing fetus. It is proposed that the later stages of gestation might be particularly sensitive to the long-term behavioral effects of amphetamine. Although there are no systematic studies on critical periods for the effects of prenatal amphetamine exposure, several reports indicate that exposure restricted to GD 12-15 has little effect. Since amphetamine predominantly affects the neuron terminals and terminals develop later than GD 15, it is proposed that amphetamine exposure later in gestation, after the monoaminergic systems are more mature, will have a greater effect. The rationale for the long-term behavioral effects of prenatal amphetamine is based on studies indicating that 1) rapidly developing systems are very sensitive to insult from external agents; 2) the monoaminergic systems and pituitary-adrenal organization are developing rapidly during the later gestation and early neonatal periods; 3) amphetamine influences each of these systems in adults and the monoamine systems in fetuses; and, 4) alterations in the systems cause predictable behavioral changes.(ABSTRACT TRUNCATED AT 400 WORDS)