The 5-HT(1A) antagonist WAY 100635 can block the low-dose locomotor stimulant effects of cocaine

Fos expression in response to dopamine D3-preferring phenylpiperazine drugs given with and without cocaine

WC 44 and WC 10 are phenylpiperazines with low (23 fold) to moderate (42 fold) selectivity for dopamine D3 receptors (D3Rs) over D2Rs, respectively. WC 44 is a full D3R agonist in the forskolin-stimulated adenylyl cyclase (AC) assay, whereas WC 10 has little efficacy. In contrast to their opposite effects in the AC assay, these drugs often produce similar behavioral effects, suggesting that the AC assay does not predict the efficacy of these drugs in vivo. Here, we examined whether Fos protein expression induced by these drugs would be more consistent with their behavioral effects in vivo. Rats received either vehicle, WC 10 (5.6 mg/kg, i.p.), WC 44 (10.0 mg/kg, i.p), cocaine (10.0 mg/kg, i.p.), or cocaine with WC 10 (5.6 mg/kg, i.p.) or with WC 44 (10.0 mg/kg, i.p). Locomotion was monitored for 90 min and the brains were harvested for immunohistochemistry. Both WC 10 and WC 44 decreased spontaneous and cocaine-induced locomotion. Both compounds also increased Fos expression relative to saline in the dorsal striatum and nucleus accumbens core and shell, and relative to cocaine alone in the nucleus accumbens shell. The findings suggest that even though these compounds have different efficacy in the AC bioassy, they produce similar brain activation and attenuation of cocaine hyperlocomotion. Together with our previous research demonstrating that these compounds down-shift the cocaine self-administration dose-effect function, the findings support the idea that D3R-selective compounds may be useful for cocaine dependence medications development.

Serotonin and psychostimulant addiction: Focus on 5-HT1A-receptors

Serotonin(1A)-receptors (5-HT(1A)-Rs) are important components of the 5-HT system in the brain. As somatodendritic autoreceptors they control the activity of 5-HT neurons, and, as postsynaptic receptors, the activity in terminal areas. Cocaine (COC), amphetamine (AMPH), methamphetamine (METH) and 3,4-methylenedioxymethamphetamine ("Ecstasy", MDMA) are psychostimulant drugs that can lead to addiction-related behavior in humans and in animals. At the neurochemical level, these psychostimulant drugs interact with monoamine transporters and increase extracellular 5-HT, dopamine and noradrenalin activity in the brain. The increase in 5-HT, which, in addition to dopamine, is a core mechanism of action for drug addiction, hyperactivates 5-HT(1A)-Rs. Here, we first review the role of the various 5-HT(1A)-R populations in spontaneous behavior to provide a background to elucidate the contribution of the 5-HT(1A)-Rs to the organization of psychostimulant-induced addiction behavior. The progress achieved in this field shows the fundamental contribution of brain 5-HT(1A)-Rs to virtually all behaviors associated with psychostimulant addiction. Importantly, the contribution of pre- and postsynaptic 5-HT(1A)-Rs can be dissociated and frequently act in opposite directions. We conclude that 5-HT(1A)-autoreceptors mainly facilitate psychostimulant addiction-related behaviors by a limitation of the 5-HT response in terminal areas. Postsynaptic 5-HT(1A)-Rs, in contrast, predominantly inhibit the expression of various addiction-related behaviors directly. In addition, they may also influence the local 5-HT response by feedback mechanisms. The reviewed findings do not only show a crucial role of 5-HT(1A)-Rs in the control of brain 5-HT activity and spontaneous behavior, but also their complex role in the regulation of the psychostimulant-induced 5-HT response and subsequent addiction-related behaviors.

Modification of cocaine-induced behavioral and neurochemical effects by serotonin1A receptor agonist/antagonist in mice

Administration of cocaine causes a locomotor stimulant effect and increases extracellular levels of serotonin (5-HT) and dopamine (DA) in the brains of rodents. Previous studies show that 5-HT1A receptor agonist and antagonist modify the cocaine-induced behavioral and neurochemical effects in the rats. However, the role of the 5-HT system on the effects of cocaine has not been studied in the prefrontal cortex. The present study examined in ddY-strain male mice the effects of the 5-HT1A receptor agonist osemozotan and the receptor antagonist WAY100635 on cocaine-induced locomotor stimulant effect and increases in extracellular levels of 5-HT and DA in the prefrontal cortex. The cocaine-induced locomotor stimulant effect was attenuated by osemozotan and enhanced by WAY100635. The cocaine-induced increase in extracellular levels of 5-HT was attenuated by osemozotan, and enhanced by WAY100635. The cocaine-induced increase in extracellular levels of DA was enhanced by osemozotan, but not affected by WAY100635. These results suggest that the prefrontal 5-HT system plays a pivotal role in the locomotor stimulant effect of cocaine in mice.

Pharmacological inhibition of DA- and 5-HT activity blocks spontaneous and cocaine-activated behavior: reversal by chronic cocaine treatment

Recently it was shown that the combined pretreatment with low autoreceptor preferring dose levels of apomorphine (0.05 mg/kg) and 8-OHDPAT (0.05 mg/kg), which decrease dopaminergic and serotonergic activity, induces a profound behavioral inhibition and also blocks the stimulant effects of cocaine. In two experiments, we report that the acute blockade of spontaneous and cocaine locomotor stimulant effects by pretreatment with 8-OHDPAT (0.05 mg/kg) plus apomorphine (0.05 mg/kg) is dose-dependently (0.0 2.5, 5.0, and 10.0 mg/kg cocaine) reversed with repeated cocaine treatments. Using a paired vs. unpaired Pavlovian conditioning protocol, we found that this reversal by cocaine (10 mg/kg) of the inhibition by the combined 8-OHDPAT plus apomorphine pretreatment occurred for the paired but not the unpaired cocaine treatment. The findings suggest that this reversal of behavioral inhibition is mediated by the transformation of the drug cues generated by 8-OHDPAT and apomorphine into cocaine-conditioned stimuli which can activate behavior.

The 5-HT1A receptor and behavioral stimulation in the rat: effects of 8-OHDPAT on spontaneous and cocaine-induced behavior

RATIONALE

The contribution of the 5-HT(1A) somato-dendritic autoreceptor populations to spontaneous and cocaine-induced locomotion is unclear.

OBJECTIVES

To use a low dose range of +/-8-hydroxy-2-(di- n-propylamino)tetralin (8-OHDPAT) to preferentially stimulate 5-HT(1A) autoreceptors and a medium 8-OHDPAT dose range to stimulate both 5-HT(1A) autoreceptors and postsynaptic receptors as pretreatments prior to either saline or cocaine.

METHODS

In experiment 1, either a medium dose of 8-OHDPAT (0.4 mg/kg) or a low dose (0.05 mg/kg) was given as pretreatments 20 min before five separate 20-min open-field tests. In experiment 2, the pretreatments were changed to a low dose range of 8-OHDPAT (0.01-0.05 mg/kg), with or without WAY 100635 (0.01-0.05 mg/kg). In experiment 3, the 8-OHDPAT pretreatments (0.01, 0.025 or 0.05 mg/kg) were administered 20 min prior to saline or cocaine (10 mg/kg) tests. In experiment 4, a medium dose range (0.2-0.3 mg/kg) was given 20 min prior to saline or cocaine (10 mg/kg) tests.

RESULTS

Experiment 1 showed that 8-OHDPAT (0.4 mg/kg) tended to increase locomotor activity but that pretreatment with 0.05 mg/kg severely suppressed locomotor activity. In experiment 2, 8-OHDPAT in the low dose range inhibited locomotor activity and this effect was reversed by co-administration of WAY 100635. Experiment 3 showed that the low-dose 8-OHDPAT pretreatment reduced locomotor activity in saline but not cocaine tests. In experiment 4, 8-OHDPAT in the medium dose range enhanced locomotor activity in cocaine tests.

CONCLUSIONS

It is suggested that the facilitatory effect of 8-OHDPAT on cocaine-induced locomotor stimulation is mediated by inhibition of 5-HT(1A) somato-dendritic autoreceptors.

Dopaminergic and serotonergic autoreceptor stimulation effects are equivalent and additive in the suppression of spontaneous and cocaine induced locomotor activity

We used the D(2) receptor agonist, apomorphine (APO) and the 5-HT(1A) receptor agonist, 8-OHDPAT (8OH) in a low dose range to stimulate autoreceptors and in this way assess the separate and combined effects of reduced DA and 5-HT activity upon spontaneous and cocaine induced locomotor behavior. Two separate experiments were conducted. In the first experiment, separate groups of rats (N=10) were tested with either saline, 8OH, APO or 8OH plus APO (0.01, 0.025, 0.05 mg/kg). At 0.05 mg/kg, 8OH and APO induced similar dose related decreases (up to approximately 50%) in locomotor activity. The combined 8OH plus APO treatment induced dose-related decreases in locomotion (approximately 90%). At the 0.05 mg/kg dose level, the drug treatments given separately blocked cocaine induced increases in activity and the 8OH and APO inhibitory effects were again additive. In the second experiment, separate groups (N=10) received saline, 0.05 mg/kg APO, 0.05 mg/kg 8OH or 0.05 mg/kg APO plus 0.05 mg/kg 8OH. As in the first experiment, the 8OH and APO given separately reduced locomotor activity by approximately 50% and when given together, locomotor activity was virtually eliminated (reduced 80-90%). When the combined APO/8OH group also received the 5-HT(1A) antagonist, WAY 100635 (0.05 mg/kg), the effect on activity was equivalent to 0.05 mg/kg APO alone. Ex vivo neurochemical measurement of dopamine (DA) and serotonin (5-HT) metabolism confirmed that the APO decreased DA turnover, 8OH decreased 5-HT turnover and the combined treatment reduced both the DA and 5-HT turnover. Thus, for both spontaneous and cocaine induced locomotor behavior, the low dose 8OH and APO treatments suppressed locomotor activity and these effects were additive. These findings indicate that DA and 5-HT systems contribute separately to motoric activation. These results suggest that it is important to consider both DA and 5-HT contributions to disorders of motoric impoverishment such as Parkinson's disease as well as to hyperkinetic states such as those induced by stimulant drugs.

Nucleus accumbens serotonin1A receptors control cocaine-induced hyperactivity but not local serotonin increase: an in vivo microdialysis study

The nucleus accumbens (Nac) is an important structure for cocaine-induced hyperactivity and receives a dense serotonergic (5-HT) innervation. Previous studies showed that a systemic activation of 5-HT(1A) receptors potentiates cocaine-induced hyperlocomotion, but attenuates the cocaine-induced 5-HT increase in the Nac. In order to address the role of Nac 5-HT(1A) receptors in the control of cocaine-induced and spontaneous behavioural activity and local 5-HT release, we used in vivo microdialysis in freely moving rats. The 5-HT(1A)-receptor agonist, 8-OH-DPAT (0, 1 and 10 microM), was applied locally into the Nac by reverse dialysis followed by a cocaine (10 mg/kg) or saline i.p. injection. The Nac 5-HT(1A)-receptor activation potentiated cocaine-induced hyperlocomotion, but attenuated rearing behaviour dose-dependently. Parallel to that, the cocaine-induced increase in Nac 5-HT dialysate level was unaffected, as were the decreases in 5-HIAA and DOPAC dialysate levels after cocaine. In saline treated rats, the local application of 8-OH-DPAT into the Nac affected neither spontaneous behavioural activity nor 5-HT, 5-HIAA or DOPAC dialysate levels in the Nac. These data suggest that Nac 5-HT(1A) receptors exert a bi-directional control of cocaine-induced hyperactivity, while not affecting spontaneous behaviour. Furthermore, accumbal 5-HT(1A) receptors do not appear to be directly involved in the acute effects of cocaine on 5-HT, 5-HIAA or DOPAC levels in the Nac.

Serotonin1A-receptor agonism attenuates the cocaine-induced increase in serotonin levels in the hippocampus and nucleus accumbens but potentiates hyperlocomotion: an in vivo microdialysis study

The hippocampus and the nucleus accumbens (Nac) are important structures for the modulation of spontaneous locomotor activity. Both structures receive a serotonergic (5-HT) innervation. We have previously reported that the 5-HT(1A)-receptor antagonist WAY 100635 blocked cocaine-induced hyperactivity, while potentiating cocaine-induced 5-HT increases in the hippocampus and the Nac. In order to further investigate the relationship between extracellular 5-HT concentration and cocaine-induced behaviour, we used in vivo microdialysis to measure the effects of the 5-HT(1A)-receptor agonist 8-OH-DPAT on cocaine-induced changes in the extracellular 5-HT concentration in the hippocampus and the Nac and on behavioural activity. Following a pilot pretest in which we determined the lowest effective dose of 8-OH-DPAT for potentiating cocaine-induced hyperlocomotion, four groups of rats were given one of the following drug treatments: 8-OH-DPAT (0.2 mg/kg) and cocaine (10 mg/kg), saline and cocaine (10 mg/kg), 8-OH-DPAT (0.2 mg/kg) and saline, or saline and saline. The injections were administered i.p. and spaced 30 min apart. We found that the 5-HT(1A)-receptor agonist 8-OH-DPAT attenuated the cocaine-induced increases in 5-HT in the hippocampus and the Nac, but potentiated cocaine-induced hyperlocomotion. 5-HT metabolite measurements revealed a complex role for the 5-HT(1A)-receptor in the broad spectrum of cocaine's neurochemical effects. Altogether, these observations support an important role of the 5-HT(1A)-receptor in the hippocampus and Nac in the modulation of cocaine stimulant effects.

The selective serotonin(1A)-receptor antagonist WAY 100635 blocks behavioral stimulating effects of cocaine but not ventral striatal dopamine increase

An increase in the extracellular dopamine (DA) concentration is generally accepted as an important neurochemical mediator of the behavioral effects of cocaine. Cocaine induced increases in serotonergic (5-HT) activity also appears to be involved in these effects. Here we describe the effects of the 5-HT(1A)-receptor antagonist WAY 100635 on the behavioral and neurochemical effects of cocaine. In-vivo microdialysis was used in behaving rats to measure extracellular concentration of DA in the nucleus accumbens (Nac). Four groups of animals received one of the following drug combinations: WAY 100635 (0.4 mg/kg) and cocaine (10 mg/kg), saline and cocaine (10 mg/kg), WAY 100635 (0.4 mg/kg) and saline, or saline and saline. The injections were administered i.p. and spaced 20 min apart. The pretreatment with WAY 100635 significantly attenuated the locomotor stimulant effects of cocaine without altering the DA overflow in the Nac. WAY 100635 itself did not modify locomotion or the extracellular DA concentration in the Nac. These results indicate that (1) the 5-HT(1A)-receptor is an important component in the mediation of cocaine locomotor stimulant effects, and (2) an increase in the extracellular DA concentration in the Nac might be a necessary but is not a sufficient condition for the locomotor stimulant effects of cocaine.

Cocaine increases serotonergic activity in the hippocampus and nucleus accumbens in vivo: 5-HT1a-receptor antagonism blocks behavioral but potentiates serotonergic activation

The hippocampus is an important mediator of learning and reinforcement, but its role in cocaine effects has received little attention. Neuronal activity in the hippocampus and the nucleus accumbens (Nac) depend on serotonergic (5-HT) transmission. Here we describe for the first time a cocaine-induced increase in 5-HT concentration in the hippocampus and the Nac parallel to behavioral activation. In addition, pretreatment with the 5-HT(1A)-receptor antagonist WAY 100635 blocked the behavioral activation after cocaine while potentiating the 5-HT increase in the hippocampus and the Nac. In vivo microdialysis was used in behaving rats to measure extracellular concentration of 5-HT in the hippocampus and the Nac. Four groups of animals received one of the following drug combinations: WAY 100635 (0.4 mg/kg) and cocaine (10 mg/kg), saline and cocaine (10 mg/kg), WAY 100635 (0.4 mg/kg) and saline, or saline and saline. The injections were administered i.p. and spaced 30 min apart. It was found that 1.) cocaine, at a dose that activates behavior, increases 5-HT levels in the hippocampus and in the Nac, and 2.) 5-HT(1A)-receptor antagonism can cause a dissociation of the hippocampal and Nac 5-HT activity from behavioral activation after cocaine. These results are discussed within the framework of the hippocampal-accumbens projection and its contribution to behavioral activity. They suggest that the hippocampus may have a role in mediating the behavioral and neurochemical effects of cocaine.

5-HT1A agonist/antagonist modification of cocaine stimulant effects: implications for cocaine mechanisms

The 5-HT1A receptor site has been demonstrated to be an important pharmacological target in the modulation of unconditioned behavioral effects induced by cocaine. In this study, separate groups of rats (n=7) received a series of the 5-HT1A agonist treatments, 8-OHDPAT (0.2,0.4 mg/kg) in combination with saline or cocaine (10 mg/kg). Using a crossover design, the treatments were subsequently switched to the 5-HT1A antagonist, WAY 100635 (0.4,0.8 mg/kg) and then, switched back again to 8-OHDPAT (0.2,0.4 mg/kg). When the 8-OHDPAT was given in combination with cocaine, locomotion was substantially enhanced but when the treatment was switched to WAY 100635, the cocaine induced locomotion was suppressed. Neither the 8-OHDPAT or WAY 100635 given with saline affected locomotion as compared to saline treated animals. These findings indicated a reciprocal facilitatory/inhibitory influence of 5-HT1A agonists/antagonists upon cocaine induced locomotion. The 8-OHDPAT treatments, however, did not enhance all cocaine behavioral responses. Initially, 8-OHDPAT suppressed cocaine induced rearing and central zone entry, but with repeated treatments, these response suppression effects subsided. As a consequence, the facilitative influence of 8-OHDPAT upon cocaine induced locomotion could not be attributed to response redistribution effects. While WAY 100635 markedly reduced cocaine induced locomotion and rearing to nearly saline response levels, the same WAY 100635 treatments did not modify locomotor stimulant effects induced by caffeine (10 mg/kg). In that caffeine stimulant effects are not directly linked to serotonergic mechanisms, the absence of an influence of WAY 100635 upon caffeine induced locomotor stimulation lent further support to the proposition that the 5-HT1A receptor site contributes to locomotor behavior in situations where the serotonergic system is pharmacologically activated by drugs such as cocaine. These findings point to a potential role for 5-HT1A antagonists in treatment of cocaine abuse.

Developmental effects of prenatal cocaine exposure on 5-HT1A receptors in male and female rat offspring

Prenatal cocaine exposure results in behavioral abnormalities throughout development in rats, but little is known regarding the biological mechanisms underlying these abnormalities. Pregnant rats received subcutaneous twice-daily injections (1 ml/kg) of normal saline or 15 mg/kg of cocaine hydrochloride throughout gestation (gestation days 1-20). Following delivery, pups were placed with untreated surrogates. Male and female pups were killed on postnatal days 30, 60 or 120 for assessment of 5-HT(1A) receptor development in the forebrain, diencephalon, midbrain and pons using radiolabel immunocytochemistry. Findings revealed gender and age differences in developmental regulation of 5-HT(1A) receptors, indicating that male rats are more susceptible to long-term consequences of prenatal cocaine exposure in comparison to females. This study also demonstrates gender-specific development of serotonin (5-HT(1A)) receptors across postnatal ages, demonstrating a fundamentally different pattern of development of 5-HT(1A) receptors between males and females.

Effects of kappa-opioid receptor agonists on long-term cocaine use and dopamine neurotransmission

kappa-Opioid receptor agonists have been suggested as treatments for cocaine addiction based on studies showing that they block cocaine-related behaviors. To determine the effects of kappa-opioid receptor agonists on long-term behavioral effects associated with cocaine and the neurochemical bases underlying these effects, rats were treated with the selective kappa-opioid receptor agonist U-69593 ((+)(5alpha,7alpha,8beta)-N-methyl-N-[7-(1-pyrrolidinyl)-1 oxaspiro[4.5]dec-8-yl]-benzeneacetamide) alone or in combination with cocaine and locomotor activity was measured daily. In addition, dopamine transporter and dopamine receptor densities were measured using autoradiographic techniques, and tyrosine hydroxylase was measured using immunoautoradiographic techniques. Treatment with U-69593 with or without cocaine decreased locomotor activity. When challenged with cocaine after a 5-day treatment period, the effects of cocaine were markedly reduced in rats initially treated with U-69593 compared to vehicle. When U-69593 was administered five times with 3-day intervals, it alone had no effect on locomotor activity but still reduced activity associated with a cocaine injection. After five daily injections, U-69593 decreased dopamine transporter and dopamine D(2) receptor densities and increased tyrosine hydroxylase levels. These changes were not seen after the 3-day interval regimen, even though cocaine-induced activity was greatly reduced. These findings show that the effects associated with daily U-69593 treatment are attenuated if the drug is administered with a greater interval, while maintaining a blockade of cocaine-induced activity. In addition, U-69593 can block cocaine-induced locomotor effects without major perturbation of the dopamine system.